WO2019053181A1 - METHOD FOR FOAMING METAL WITH HEAT CONTACT - Google Patents

Abstract

The present invention relates to a process for producing a metal foam of at least a first metal containing the main component Mg, Al, Pb, Au, Zn, Ti or Fe in an amount of at least about 80% by weight, based on the amount of at least one first metal, comprising the steps of (I) providing a semifinished product comprising a foamable mixture comprising the at least one first metal and at least one propellant, (II) contacting at least a portion of the outer surface of the semifinished product with at least one heatable solid , and (III) heating the semifinished product via the at least one heatable solid body by solid contact heat conduction for foaming the foamable mixture by gas elimination from the at least one propellant to form the metal foam. Furthermore, the invention relates to a metal foam and a composite material obtainable by the method and a component comprising the metal foam and / or the composite material.

Description

 Process for foaming metal with thermal contact

The present invention relates to a process for producing a metal foam of at least a first metal comprising the main constituent Mg, Al, Pb, Au, Zn, Ti or Fe in an amount of at least about 80% by weight, based on the Amount of the at least one first metal, comprising the steps of (I) providing a semi-finished product comprising a foamable mixture comprising the at least one first metal and at least one propellant, (II) contacting at least a portion of the outer surface of the semifinished product with at least one heatable solid, and (III) heating the semifinished product via the at least one heatable solid by solid contact heat conduction for foaming the foamable mixture by gas elimination from the at least one propellant to form the metal foam. Furthermore, the invention relates to a metal foam and a composite material obtainable by the method and a component comprising the metal foam and / or the composite material.

Metal foams and composites comprising metal foams such as metal foam sandwiches have been known for years. The latter are of particular interest when the composite is a one-component system, ie when using a specific metal and its alloys, in particular aluminum and its alloys, and the connection between the core and cover layer is produced by means of a metallurgical bond. Corresponding methods for producing such metal foams and composites and components made therefrom are known from various publications. DE 44 26 627 C2 describes a process in which one or more metal powders are mixed with one or more propellant powders and the resulting powder mixture is compacted by means of axial hot pressing, hot isostatic pressing or rolling and in a subsequent operation with previously surface-treated metal sheets is assembled by roll-plating into a composite material. After reshaping of the resulting semi-finished product by, for example, pressing, deep-drawing or bending, the latter is heated in a final step to a temperature which is in the solidus-liquidus region of the metal powder. but is below the melting temperature of the outer layers. Since the blowing agent powder is chosen such that its gas separation takes place simultaneously in this temperature range, bubbles form within the viscous core layer, accompanied by a corresponding increase in volume. The subsequent cooling of the composite stabilizes the foamed core layer.

In a modification of the process known from DE 44 26 627 C2, in which the powder compact is already closed-pored, EP 1 000 690 A2 describes the production of such a composite material on the basis of a powder compact which was first produced open-pored and which did not become active until later Walzplattieren with the outer layers is closed pores. The remaining process steps are identical. By the original open porosity is to prevent that lead during storage of the powder compact possible gas splits of the propellant to geometry changes of the compact and thus to problems in the subsequent production of the composite with the outer layers. Furthermore, it is intended to facilitate the opening of the oxide layers forming during the storage of the compact in the production of the composite by the open porosity.

DE 41 24 591 C1 discloses a process for producing foamed composite materials, wherein the powder mixture is introduced into a hollow metal profile and then rolled together with it. The deformation of the resulting semi-finished product and the subsequent foaming carried out in the same manner as described in DE 44 26 627 C2.

EP 0 997 21 5 A2 discloses a process for the production of a metallic composite material consisting of solid metallic cover layers and a closed-pore, metallic core, which thereby combines the production of the core layer and the connection with the cover layers in one step, that the powder mixture is introduced into the nip between the two outer layers and thus compressed between them. Furthermore, it is proposed to add the powder in a protective gas atmosphere. so as to prevent the formation of oxide layers, which could adversely affect the required connection between the outer layers and powder mixture.

In a further, known from DE 197 53 658 AI process for producing such a composite material, the process steps of composite production between the core and cover layers on the one hand and the foaming on the other hand united by the fact that the core introduced in the form of a powder compact between the cover layers located in a mold is and connects only by the foaming process with these. Due to the compressive force applied by the core during foaming, the cover layers are at the same time subjected to a deformation corresponding to the shape enclosing them.

US 5,972,521 A discloses a method for producing a composite blank in which air and moisture are removed by evacuation from the powder. Subsequently, the evacuated air is replaced by a gas which is inert to the core material under elevated pressure, before the powder is compacted and connected to the cover layers. From EP 1 423 222 a process for producing a composite of cover layers and metal powder is known, in which the entire production process takes place under vacuum. In particular, the compaction of the powder bed and the subsequent rolling should take place under vacuum.

All of these known from the prior art method except that of EP 1 423 222 has in common that is enclosed by the production of the foamed core layer of air or inert gas in the compaction between the metal powder particles and compacted depending on the Kompaktierungsgrad. The resulting gas pressures, which increase even further during the temperature increase during the foaming process, lead to the formation of pores during heating even before reaching the temperature corresponding to the solidus-liquidus region of the metal powder material. In contrast to those aimed at by this method, by the outgassing of the propellant in the Solidus liquidus area of the metal powder taking place, closed, spherical pores, these are open, crack-shaped interconnected and irregularly shaped pores. While, for example, US Pat. No. 5,564,064 A1 discloses a process which specifically aims for such open porosity by expansion of enclosed gases below the melting temperature of the powder material, such pore formation is not desirable in the processes described above, since only the aspired closed, spherical pores allow optimal load transfer over the intact as possible, surrounding the pores cell walls, and thus contribute significantly to the strength of the core foams and thus the composite material.

DE 102 15 086 A1 discloses a method for producing foamable metal bodies by compacting and pre-compacting a semifinished product. The gas-splitting propellant is formed only after the compaction and pre-compression of the semi-finished product by hydrogenation of the mixture of metal-containing propellant pre-material and the at least one metal. The porous metal body is formed by heating the foamable metal body thus obtained to a temperature above the decomposition temperature of the blowing agent, and it is preferable that this takes place immediately after the production of the foamable metal body without intermediate cooling thereof. BR 10 201 2 023361 A2 discloses the production of a closed-cell metal foam, in which a semifinished product, which is a metal selected from the group consisting of Al, Zn, Mg, Ti, Fe, Cu and Ni, and a blowing agent, selected from the Group consisting of TiH ₂ , CaC0 ₃ , K ₂ C0 ₃ , MgH ₂ , ZrH ₂ , CaH ₂ , SrH ₂ and HfH ₂ and others, is foamed in a pre-heated to 780 ° C resistance furnace. WO 2007/014559 A1 discloses a process for the powder metallurgical production of metal foam in which a pressed semifinished product is used, which is heated in a pressure-tight sealable chamber to the melting or solidus temperature of the pulverulent metallic material, wherein after reaching the pressure in the chamber is reduced from an initial pressure to a final pressure, so that the semifinished product foams. DE 199 33 870 C1 discloses a method for producing a metal composite body using a foamable compact, wherein the compact or semifinished product is produced by compacting a mixture of at least one metal powder and at least one gas-releasing propellant powder. The

Pressling is then thermally treated together with a reinforcement in a foaming mold and thereby foamed. In US Pat. No. 6,391,250, a foamable semi-finished product obtained by powder metallurgy production processes and containing at least one functional structural element is foamed in a hollow mold under heating. US 2004/0081571 A1 relates to a process for producing foamable metal shavings which contain a mixture of a metal alloy powder with a foaming agent powder and which are foamed by heating to a temperature greater than the decomposition temperature of the foaming agent. EP 0 945 197 A1 discloses a method in which composite sheets or strips produced from clad rolled billets are formed from a blowing agent-containing aluminum alloy and then foamed under pressure and temperature increase to the ignition temperature of the blowing agent. From DE 199 08 867 Al a method for producing a composite body is known, in which a metal foam material is foamed by powder metallurgy under such heat supply to a first body part that the outer fabric layers melt on the connecting surfaces of a substrate body and thereby with the adjacent layers of fabric first body part are material metallurgically connected. The foaming processes known from the prior art suggest the heating of the respective precursor material (semifinished product) for foaming. Although certain heating sources, such as a resistance furnace, are proposed for this purpose, either no statement is made as to the exact type of heat transfer from the heat source to the semifinished product or the heat transfer takes place to a significant extent or finally indirectly via an air-filled gap between the heat source and semifinished product, ie without direct contact of the heat source and semifinished product, but via radiation with consequent heat losses. This has the disadvantage of a homogeneous transfer of the heat required for foaming, which does not occur uniformly over the entire surface, to the precursor material or semifinished product to be foamed. Different areas of the semifinished product are thus heated differently, which leads to reaching the foaming temperature and therefore to gas evolution from the propellant at different points of the semifinished product at respectively different times. This results in the normal foaming at the points at which the foaming temperature is reached, while at other points still no foaming takes place. Thus, in the areas between normal and non-foamy sites, voids, such as warps, bumps, bubbles, bulges, and voids are inevitably formed which do not correspond to the (intended) pores in the normally foamed areas. In particular, these imperfections in the intermediate areas result in unintentional and undesirable warping and deformation of the semifinished product as a whole, which makes it difficult or impossible to use the foamed products in components that are to be manufactured precisely, for example in motor vehicle or aircraft construction. Finally, many known foaming processes involve additional steps or tools, such as the making and using of (hollow) molds or the use of pressure chambers, and are therefore too expensive to carry out.

It is therefore an object of the present invention to provide an improved method for foaming metal which is suitable for overcoming the aforementioned disadvantages and thereby producing a virtually defect-free metal foam or composite comprising such a metal foam with as few process steps as possible.

Surprisingly, it has been found that foamable mixtures of metal and blowing agent, in particular in the form of semi-finished products, in close contact with at least one appropriately heated or heated solid by direct heat transfer in the Homogeneous foaming ways of solid contact heating, thereby forming a metal foam. When carrying out the metal foaming process according to the invention, defects, that is to say, for example, distortions, bulges, bubbles, bulges and cavities which do not correspond to the (intended) pores in the normally foamed regions, surprisingly do not occur. In particular, no (intermediate) areas with warping and bubbles are observed, so that warping and deformation of the semifinished product altogether is avoided. No protective gas is required; it may be according to the invention in ambient atmosphere or air atmosphere and ambient air pressure gearbei tet.

The present invention therefore provides:

 (1) a method of producing a metal foam of at least a first metal containing the main component Mg, Al, Pb, Au, Zn, Ti or Fe in an amount of at least about 80% by weight based on the amount of the at least one first Metal, comprising the steps

 (I) providing a semifinished product comprising a foamable mixture comprising the at least one first metal and at least one propellant,

(II) contacting at least a part of the outer surface of the semifinished product with at least one heatable solid, and

 (III) heating the semifinished product via the at least one heatable solid body by solid contact heat conduction for foaming the foamable mixture by gas elimination from the at least one propellant to form the metal foam;

 (2) a method according to embodiment (1), wherein

the semifinished product comprises at least a first region formed from the foamable mixture and at least one second region formed from the at least one second metal in the form of non-foamable solid material, such that a composite material may be formed with at least one first Area that made the metal foam of at least a first metal is formed, and at least a second region formed of at least one second metal in the form of non-foamable solid material;

 (3) a method according to embodiment (1) or (2), additionally comprising the step

(IV) preheating by heating the semifinished product from step (I) to a temperature which is about 50 ° C to 100 ° C below the foaming temperature, wherein the step (IV) before the step (II) and / or step (III ) is carried out;

 (4) a method according to any one of embodiments (1) to (3), additionally comprising the step

 (V) forming the semifinished product provided in step (I) into a molded part, wherein in step (III) and / or (IV) the heating of the resulting molded part takes place instead of the semifinished product;

 (5) A method according to any of the embodiments (1) to (4), comprising the step

 (VI) first metallurgical bonding of the powder particles of the foamable mixture with one another or with cover layers of a corresponding semifinished product after step (I)

 (6) A method according to any of the embodiments (1) to (5), comprising the step

 (VII) second metallurgical bonding, in particular of a foamable core obtained in step (VI), with the at least one, preferably two, outer layers of a corresponding semifinished product;

 (7) a metal foam obtainable by a method as defined in any of the embodiments (1), (3) or (4);

 (8) a composite material obtainable by a method as defined in any one of embodiments (2) to (4); and

 (9) A structural member comprising a metal foam as in Embodiment (5)

and / or a composite material as defined in embodiment (6). In the context of the invention, the term "about" or "substantially" is used with reference to values or ranges of values, or certain values result from the use of these terms (eg, the formulation "the outgassing temperature of A is approximately equal to the solidus temperature B "is to be understood as a certain temperature which results from the material B used by the person skilled in the art), this is to be understood as meaning that the person skilled in the art will regard as expertly usual in the given context. In particular, deviations of the specified values from +/- 10%, preferably from +/- 5%, more preferably from +/- 2%, particularly preferably from +/- 1%, of the terms "about" and "substantially" are included ,

The invention thus relates to a method for producing a metal foam or a metallic composite material containing a metal foam. The metal foam and the metal foam in the composite material according to the invention comprise or consist of at least one first metal, which forms voids in the form of pores, preferably in the form of closed pores containing a gas (gas inclusions) consisting of air, from the at least a propellant released gas or mixtures thereof may exist. Preference is exactly a first metal. The at least one first metal is foamed (foamed) with the aid of a blowing agent. In this case, the volume of the first metal increases as a result of pore formation or gas inclusions. For the foaming or foaming process, a mixture of the at least one first metal and the at least one blowing agent in the form of a foamable mixture is produced. This foamable mixture is preferably in the form or as part of a semi-finished product. The foamable mixture or the semi-finished product is brought into contact with at least one heatable solid for foaming (frothing) the at least one first metal or the foamable mixture. Heating the at least one solid leads to the release of a gas (gas separation) from the at least one blowing agent. The gas released here foams the at least one first metal by producing pores in the at least one first metal and thus the metal foam. The term "metal" herein means both a metal in its commercially pure form ("pure metal" such as pure magnesium, pure aluminum, pure iron, pure gold, etc.) and its alloys. In principle, all foamable (foamable) metals in pure form or as an alloy are suitable as the first metal. Metals in pure form (pure metals) contain the respective metal in an amount or with a content of at least 99 wt .-%, based on the respective metal. Suitable foamable metals are in particular magnesium (Mg), aluminum (Al), lead (Pb), gold (Au), zinc (Zn), titanium (Ti) or iron (Fe). The first metal may thus be magnesium (Mg), aluminum (Al), lead (Pb), gold (Au), zinc (Zn), titanium (Ti) or iron (Fe) in pure form, ie pure magnesium, pure aluminum, pure lead, Pure gold, pure zinc, pure titanium or pure iron, wherein a content of the respective metal of at least 99 wt .-%, based on the respective metal, is preferred. However, according to the invention, a metal in which magnesium (Mg), aluminum (Al), lead (Pb), gold (Au), zinc (Zn), titanium (Ti) or iron (Fe) in an amount is also suitable as the first metal of at least about 80% by weight (weight percent, weight%), based on the amount of the first metal, forms the major component. Therefore, alloys of the aforementioned metals are also used. Therefore, the term "metal" according to the invention in addition to the pure metal also includes metal alloys or alloys shortly. A suitable alloy of magnesium is, for example, AZ 31

(Mg96AI3Zn). Suitable alloys of aluminum are, for example, selected from the group consisting of

 higher strength aluminum alloys selected from the group consisting of aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), among the aluminum-zinc alloys (7000 series)

 AIZn4.5Mg (Alloy 7020) is preferred, and

higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C, preferably higher-strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C, comprising aluminum, magnesium and silicon. more preferably AISi6Cu7.5, AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), even more preferably Al Mg6Si6 and AIMg4 (± 1) Si8 (± 1), more preferably AIMg4 (± 1) Si8 (± 1) ,

The at least one first metal may be aluminum or pure aluminum (at least

99% by weight of aluminum), with aluminum being preferred in which the content of aluminum is from about 80% to about 90% by weight, more preferably about 83% by weight, based on the at least one first Metal, amounts. In addition, the at least one first metal may be a higher-strength aluminum alloy. The higher strength aluminum alloy may be selected from the group consisting of aluminum-magnesium silicon alloys (6000 series) and aluminum-zinc alloys (7000 series), of which AlZn4.5Mg (7020 alloy) is preferred among the aluminum-zinc alloys (series 7000) , The at least one first metal can therefore be in particular AIZn4.5Mg (alloy 7020). The at least one first metal may be a higher strength aluminum alloy having a melting point of about 500 ° C to about 580 ° C; preferred higher strength aluminum alloys are AISi6Cu7.5, AIMg6Si6 and AIMg4 (± 1) Si8 (± 1). The at least one first metal may also be a higher strength aluminum alloy having a melting point of about 500 ° C to about 580 ° C comprising aluminum, magnesium and silicon or composed solely of these chemical elements. Preferred higher strength aluminum alloys having a melting point of about 500 ° C to about 580 ° C comprising aluminum, magnesium and silicon are AIMg6Si6 and AIMg4 (± 1) Si8 (± 1), of which

AIMg4 (± 1) Si8 (± 1) is particularly preferred.

The terms "series" and "alloy" followed by a four digit number are common names for certain classes or series of aluminum alloys or a particular aluminum alloy known to those skilled in the art, as noted herein.

The indication (± 1) in the alloying formulas used herein means that the respective chemical element concerned may also have a mass percentage more or less than stated. In general, however, a correlation between two elements provided with such information in a formula, that is, if, for example, of the first element in the formula, which is provided with (± 1), a mass percent more present, then from the second element in the formula, which also with (± 1), one percent by mass less. The formula AIMg4 (± 1) Si8 (± 1) thus also includes the formulas AIMg5Si7 and AIMg3Si9. A suitable alloy of the lead is, for example, the lead-copper alloy with about 1% copper, ie PbCul or Pb-Cu. Suitable alloys of the gold are, for example, gold-titanium alloys with about 1% titanium, ie AuTil or AuTi. Suitable alloys of zinc are, for example, zinc-titanium alloys with about 1% to 3% titanium, ie for example ZnTil, ZnTi 2 or ZnTi 3. A suitable alloy of titanium is, for example, Ti-6Al-2Sn-4Zr-6Mo.

Suitable alloys of iron are mainly steel. According to the invention and according to DIN EN 10020: 2000-07, "steel" refers to a material whose mass fraction of iron is greater than that of any other element whose carbon content is generally less than 2% and which contains other elements. A limited number of chromium steels can contain more than 2% carbon, but 2% is the usual limit between steel and cast iron.

Semi-finished product according to the present invention is a foamable starting material, which after foaming a metal foam or a composite material comprising such a metal foam results. The semifinished product as a precursor for the metal foam comprises a foamable (foamable) mixture or has this exclusively. The foamable mixture comprises the metal to be foamed, ie the at least one first metal, at least one blowing agent and optionally at least one adjuvant. The foamable mixture or the entire semifinished product can be produced by powder metallurgy. Semi-finished products produced by powder metallurgy have the foamable mixture as compacted powder in the form of a compact or in such a compacted form that the mixture is rollable, for example as rollable ingots. The foamable mixture can also be used as a solid metal, which is a gas- miges propellant such as hydrogen gas has absorbed present. According to the invention, however, it is possible to use all semi-finished products which are known to the person skilled in the art and can be foamed to form a metal foam. These foamable semi-finished products must be able to expand correspondingly during foaming for the formation of the metal foam, which is naturally associated with an increase in volume of the semifinished product or the metal structure of the at least one first metal therein.

Composite material in the context of the present invention is a metallic material in which two structurally different materials, namely foamed metal (metal foam) and metal in the form of solid, non-foamable solid material are combined with each other and positively and / or materially connected to each other. The (final) material metallurgical connection between metal foam and solid metal takes place at their adjoining connecting surfaces by melting the same when foaming the foamable mixture with heat. However, the majority of the metallurgical connection between the foamable mixture and the solid material is already present in the semi-finished product. For example, by forming the foamable mixture or the core and the cover layers, oxide-free surfaces can be produced which result in the powder particles of the foamable mixture and the Solid solid material (the top layer (s)) join, ie There is a kind of welding instead.

The composite material according to the invention comprises a metal foam and metal in the form of non-foamable, solid solid material. For this purpose, the composite material comprises or has at least one first region, which is formed from the metal foam of the at least one first metal or comprises this metal foam, and at least one second region, which is formed from at least one second metal in the form of non-foamable solid material or this includes. Preferably, the at least one second region comprises or has exactly one second metal in the form of non-foamable solid material. The at least one second region can be used in particular as a solid, non-foamable metallic Layer, especially as a cover layer or cover layer, be formed on at least part of the surface of the at least one first region. On the surface of the first region, two second regions are preferably each applied as a layer, in particular cover layer or cover layer, in the form of non-foamable solid material, ie two solid layers. The two massive (deck) layers are preferably separated from one another by a zone of the first region in such a way that the first region could expand in foaming due to the associated increase in volume due to the formation of the metal foam in this zone. The composite material preferably has exactly one first area and exactly one second area. For certain applications, the composite preferably has exactly one first region and exactly two second regions. Particularly preferably, the composite material has exactly one first region and exactly two second regions, wherein each of the two second regions forms a layer on the first region. Most preferably, the two second regions or layers are separated by a zone in which the first region or the semifinished product could expand during the foaming.

The semifinished product as a precursor for the composite material or for the production of the composite material according to the present invention is a foamable starting material, which results after foaming the composite material. For this purpose, the semifinished product comprises or has at least one first region which is formed from or comprises the foamable mixture, and at least one second region which is formed from or comprises the at least one second metal in the form of non-foamable solid material. The at least one second region may in particular be formed as a solid, non-foamable metallic layer, in particular as cover layer or cover layer, on at least part of the surface of the at least one first region. On the surface of the first region, two second regions are preferably each applied as a layer, in particular cover layer or cover layer, in the form of non-foamable solid material, ie two solid layers. On the surface of the first region, two second regions are preferably each as a layer in the form of non-foamable solid material, so two massive Layers applied, which are separated by a zone of the first region such that the first region can expand during foaming due to the associated volume increase by the formation of the metal foam in this zone. The semifinished product for the composite material preferably has exactly one first region and exactly one second region. For certain applications, the semifinished product for the composite material preferably has exactly one first region and exactly two second regions. Particularly preferably, the semifinished product for the composite material has exactly one first region and exactly two second regions, wherein each of the two second regions forms a layer on the first region. Most preferably, the two second regions or layers are separated by a zone in which the first region or the semifinished product can expand during foaming. Particularly preferably, the semifinished product for forming a composite material is designed such that there are two outer layers of solid material, in particular aluminum or an aluminum alloy, and between these as the first region, the foamable mixture, in particular of an aluminum alloy, the lower a solidus temperature as the aluminum alloy of the two outer layers comprises. The foamable mixture is preferably already compressed to about 98% to 100% of the density of the corresponding solid material.

In a further embodiment of the method for producing a composite material, the semifinished product comprises at least one first region, which is formed from the foamable mixture, and at least one second region, which is formed from the at least one second metal in the form of non-foamable solid material, such that a composite may be formed having at least a first region formed of the metal foam of the at least one first metal and at least a second region formed of at least one second metal in the form of non-foamable bulk material.

In a further embodiment, in the composite material, the at least one first region as the foamed core and in the semi-finished product for producing this composite material at least one first area is designed as a foamable core. This core is covered in layers by the second region, ie in the form of at least one cover layer. In this case, sandwich-like structures, ie layered plate-shaped structures, layer structures or layered structures with planes of straight (non-curved) propagation direction are possible. Core and cover layer (s) then describe planes of straight (non-curved) propagation direction or are plate-shaped. But there are also spherical layer structures with curved layers or levels possible, such as in a layered solid rod or rod, a hose, a tube or a sausage. The spherical layer structure may be solid throughout with a solid rod-shaped core or with an innermost hollow core such that the foamable or foamed core has a tubular configuration.

Accordingly, according to the invention, the metal foams, composite materials and semifinished products can have any shape as long as a volume increase or volume expansion of the at least one first region with the foamable mixture is ensured in the semi-finished products. Thus, the semi-finished products can be plate-shaped, in particular in the form of semi-finished products with a foamable mixture between an upper and a lower cover layer as two second regions as solid material, as round or square bars and other, regularly or irregularly shaped body. In the case of the composite material, the semi-finished products may have a layered structure, but the at least one first and at least one second region may also be present in a different manner next to one another and connected to one another. In the case of a powder metallurgical production of the foamable mixture or the

Semi-finished is the foamable mixture at least at the beginning of the manufacturing process in the form of powder comprising powder particles before. The finished semifinished product may also contain the foamable mixture in powder form, but preferably the foamable mixture is present in the finished semifinished product in compacted form, for example as a compact. The Compaction of the powder leads to its solidification and may extend to a metallurgical connection of the powder particles with each other, ie the individual grains or particles of the powder (powder particles) by diffusion and formation of (first) intermetallic phases within the mixture partially or completely ver together - bound, instead of forming a loose powder. This (first) metallurgical bonding has the advantage of a more stable and more compact foamable first region or core, which forms almost no defects in the foam during foaming. The first metallurgical bonding also produces a stable rolling bar, ie the ductility of the semi-finished product, in particular by rolling, bending, deep drawing and / or hydroforming, is improved.

Furthermore, in the case of the preferred production of a composite material, by means of the first metallurgical bonding, the powder particles are partially joined to the at least one second region, in particular if present in the form of at least one layer, for example in the form of at least one cover layer or cover layer. Therefore, the method according to the invention may additionally comprise a step

 (VI) first metallurgical bonding of the powder particles of the foamable mixture with one another or with cover layers of a corresponding semifinished product after step 0)

include.

The term "first metallurgical bonding" is understood according to the invention as follows: bonding of the powder mixture and the cover layers by means of diffusion and formation of first intermetallic phases within the mixture. The first metallurgical bonding has the advantage of a more stable and compact foamable core, which forms almost no defects in the foam during foaming. The first metallurgical bonding produces a stable ingot. Furthermore, the powder particles are partially connected to the cover layers, in particular if, in the preferred embodiment, the lying invention comprises the semifinished aufschä to Bares material as the first area between two cover layers or cover plates as second regions of solid material.

The first metallurgical bonding in step (VI) can be carried out in particular by pre-compacting the foamable mixture, in particular together with at least one, preferably at least two outer layers or cover layers, using pressure in a range from about 0.05 MPa to about 1, 5MPa, preferably in a range of about 0.1 MPa to about 1.1 MPa, and more preferably in a range of 0.1 5 MPa to about 0.45 MPa, and at a temperature of the foamable mixture and container of about 400 ° C to about 490 ° C or from about 65% to about 90%, preferably from about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture or of the at least one first metal. The duration (holding period) may be from about 4 hours to about 48 hours, preferably from about 6 hours to about 32 hours, preferably to about 24 hours. In particular, the semifinished product can be heated to about 80% of the melting temperature of the foamable mixture and kept at this temperature for about 6 hours to about 32 hours, preferably up to about 24 hours. Preferably, the application of pressure is vertical to the first and second cover layers, wherein the first and second cover layers are arranged substantially plane-parallel to each other. The application of pressure can take place here by means of two plane-parallel tools, for example a table with a horizontal plate movable thereon, in a pressing process. The temperature of the foamable mixture or semifinished product during the first metallurgical bonding or pre-compression is preferably about 65% to about 90%, preferably about 70% to about 85%, in particular about 80% of the solidus temperature of the foamable mixture.

The first metallurgical bonding or precompression can take place by means of two plane-parallel tools in a pressing process. In this case, the precompression of the powder takes place at a pressure in a range from about 0.05 MPa to about 1.5 MPa, preferably in a range from about 0.1 MPa to about 1.1 MPa, and even more preferably in a in the range of about 0.15 MPa to about 0.45 MPa, and at a temperature in a range of about 400 ° C to about 490 ° C, preferably to about 470 ° C, more preferably to about 460 ° C, or about 65% to about 90%, preferably from about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture. Pre-compression of the powder preferably takes place at about 65% to about 90%, preferably about 70% to about 85%, in particular about 80%, of the solidus temperature of the foamable mixture. The pressing process may in particular take place when the semifinished product is in an air atmosphere at ambient air pressure. This saves the effort for a protective gas atmosphere or the application of vacuum and / or work under vacuum. By pre-compacting, which is preferably carried out by axial pressing, a stable ingot is produced. Furthermore, the powder particles are partially connected to the cover layers of the container.

Alternatively, the first metallurgical bonding in step (VI) can be carried out in particular by heating the foamable mixture, in particular together with at least one, preferably at least two outer layers or cover layers, to about 70% to about 90%, preferably about 75% to about 85%. , Preferably about 80%, the solidus temperature of the foamable mixture, wherein a widening of the semifinished product is largely prevented. Preferably, the temperature is in the range of about 450 ° C to about 495 ° C, more preferably in the range of about 455 ° C to about 465 ° C. The duration

(Holding time) is about 4 hours to about 48 hours, preferably about 6 hours to about 24 hours, more preferably about 24 hours to about 32 hours. In particular, the container may be heated to about 80% of the melting temperature of the foamable mixture and maintained at that temperature for about 6 hours to about 32 hours, more preferably to about 24 hours. This can be done especially at ambient air pressure. This saves the effort for a protective gas atmosphere or the application of vacuum and / or work under vacuum. The widening of the semifinished product can in this alternative embodiment by the skilled person known devices, such as by clamps, clamps, weights and / or a correspondingly dimensionally stable and rigid support frame, each or in Combining the semi-finished product to remain in its original form can be effectively prevented. The holding frame may also be a kind of shape, similar to a casting mold. Further, the expansion of the semifinished product by axial pressing, in particular by one or more presses, preferably perpendicular to the cover layers, which are fed before step (VI) of two or more sides of the semifinished product or along one or more axes of the semifinished, without to compress the semifinished product. The applied pressure is preferably in a range of about 0.15 MPa to about 0.6 MPa, more preferably in a range of about 0.2 MPa to about 0.4 MPa. The (premature) outgassing of the blowing agent in step (VI) is prevented by the precompression of the foamable mixture, either by the application of externally generated pressure or by the pressure created by the prevention of the expansion of the semifinished product in its interior.

The method according to the invention may additionally comprise a step

(VII) second metallurgical bonding, in particular a foamable core obtained in step (VI), comprising at least one, preferably two, outer layers of a corresponding semifinished product, preferably after carrying out step (VI). According to the invention, the term "second metallurgical bonding" is understood to mean the production of oxide-free surfaces by reshaping of the core and of the cover layers, which causes the powder particles and the cover layers to bond, i. There is a kind of welding instead. The second metallurgical bonding allows a simple method of bonding, since, for example, no individual welds must be attached and since a more stable connection results than can be achieved by adhesive, which would not survive unscathed the temperatures occurring during subsequent foaming. The second metallurgical bonding can also after

Step (I), it does not assume that the first metallurgical bonding after step (VI) was performed. However, this is advantageous because then highly uniform closed pores in the metal foam, in particular in the metal foam core of a sandwich Bundstoffstoffes with two outer layers and arranged therebetween metal foam core can be obtained.

The second metallurgical bonding can take place according to the invention by processes comprising diffusion and rolling, but also axial or hydrostatic pressing, wherein rolling is preferred, under the action of pressure on the semifinished product. In a rolling process, the pressure in the nip is preferably in a range of about 5000 to about 7000 tons, more preferably in a range of about 5600 to about 6500 tons. The temperature of the semifinished product is below the outgassing temperature of the at least one propellant, below the solidus temperature of the foamable core and below the solidus temperature of the at least one second metal from which the top layer is formed. Preferably, the temperature in the second metallurgical bonding is from about 400 ° C to about 520 ° C, preferably from about 440 ° C to about 510 ° C, even more preferably in a range from about 470 ° C to about 500 ° C, wherein the temperature must always be below the Ausgastempe- temperature of the at least one propellant so that there are no bubbles in the rolled material. In particular, the second metallurgical bonding may be carried out by hot-rolling the container at a temperature below the decomposition temperature of the blowing agent. Subsequently, a cold rolling process can follow, preferably to achieve sheet thicknesses below 9 mm.

By means of a rolling process or other techniques such as axial pressing or hydrostatic pressing, each in the specified temperature ranges, a second metallurgical compound of powder and cover layer is achieved and further the powder of the foamable mixture to about 90%, preferably to about 98%, to about 100 % of its nominal density compacted. The "nominal density" of the foamable mixture is the density the foamable mixture would have if it were not in powdered form but in a compact form as a solid solid material. Subsequently, the resulting, preferably at least three-layer semifinished product is made up and fed to the foaming process according to steps (II) and (III). The temperature of the semifinished product at the beginning of the respective process steps (VI) and / or (VII) can be from about 460.degree. C. to about 490.degree. This has the advantage that during the process steps (VI) and / or (VII) no cracks occur in the core and on the sides.

The powder of the at least one first metal consists of powder particles, which may have a particle size of about 2 μηι to about 250 μηι, preferably from about 10 μηι to about 150 μηι. These particle sizes have the advantage that a particularly homogeneous mixture, i. forms a particularly homogeneous foamable mixture, so that later occurring defects during foaming are avoided.

The foamable (foamable) mixture comprises at least a first metal and at least one blowing agent. Preferably, the foamable mixture comprises exactly one first metal and at least one blowing agent. For certain applications, the foamable mixture preferably comprises exactly one first metal and exactly two blowing agents. Particularly preferably, the foamable mixture comprises exactly one first metal and exactly one blowing agent. The foamable mixture may further comprise adjuvants. However, the foamable mixture preferably does not comprise an adjuvant, since with one or more auxiliaries the microstructure of the foamable mixture and foamable core is generally disturbed in such a way that the foamed (foamed) core obtained later from it contains defects such as inhomogeneities in the foam structure , too large pores or bubbles and / or open pores instead of closed pores. Particularly preferably, the foamable mixture contains only exactly one first metal, exactly one blowing agent, optionally one or more derivatives of the blowing agent and no further substances or auxiliaries. The foamable mixture may exclusively contain or consist of the aforementioned substances or constituents instead of just comprising them. One or more derivatives of the blowing agent are particularly suitable if the blowing agent is selected from the group of metal hydrides; In this case, the blowing agent as derivative (s) additionally comprise at least one oxide and / or oxihydride of the metal or metals of the metal hydride (s) used in each case. Such oxides and / or Oxihydride arise in a pretreatment of the propellant and its durability as well as its response during foaming, so improve the timing of the release of the propellant gas, so that the propellant used or the propellant not too early, but not too late release; too early or too late release of the propellant gas can produce oversized cavities and thus defects in the metal foam.

The inventive at least one propellant releases from a certain temperature, the Ausgastemperatur of the blowing agent, by means of degassing or gas separation, a propellant, which serves to foam the at least one first metal. When using a metal hydride as blowing agent is released as propellant hydrogen (H ₂ ). When using a metal carbonate as blowing agent carbon dioxide (C0 ₂ ) is released as a propellant gas.

The at least one blowing agent according to the invention is selected from the blowing agents known to the person skilled in the art for the respective first metal. Preferably exactly one propellant is used, but it is also possible to use mixtures of propellants, in particular mixtures of two different propellants. In particular, blowing agents which are selected from the group consisting of metal hydrides and metal carbonates are suitable for the metals explicitly mentioned herein. With regard to the choice of the blowing agent, it has surprisingly been found that the outgassing temperature of the at least one blowing agent should advantageously be equal to the solidus temperature of the at least one first metal or should be below the solidus temperature of the at least one first metal to later become a closed-cell foam free of defects and a good result in foaming the core. The outgassing temperature of the propellant should preferably be no more than about 90 ° C, more preferably no more than about 50 ° C below the solidus temperature of the at least one first metal. When producing a composite material and using at least one second metal, the outgassing temperature of the at least one propellant should also be less than the solidus temperature of the at least one second metal, since the at least one second metal does not enter its solidus area during foaming of the at least one first metal may, therefore, not begin to melt to prevent mixing with the at least one first metal, as explained elsewhere herein. The outflow temperature of the at least one propellant is therefore preferably below, more preferably at least about 5 ° C. below the solidus temperature of the at least one second metal. The blowing agent according to the invention is preferably selected as follows:

For Mg, Al, Pb, Au, Zn or Ti as a main constituent of the first metal, the at least one blowing agent is preferably selected from the group consisting of metal hydrides and metal carbonates, more preferably selected from

Metal hydrides of the group consisting of TiH ₂ , ZrH ₂ , HfH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ ; and

Carbonates of the second main group of the Periodic Table of the Elements (alkaline earth metals), ie in particular the group consisting of BeC0 ₃ , MgC0 ₃ , CaC0 ₃ , Sr-C0 ₃ and BaC0 ₃ .

For foaming Mg, Al, Pb, Au, Zn or Ti as the main constituent of the first metal, the at least one blowing agent is more preferably selected from the group consisting of TiH ₂ , ZrH ₂ , MgC0 ₃ and CaC0 ₃ . The propellant is in particular a metal hydride. The metal hydride is preferably selected from the group consisting of TiH ₂ , ZrH ₂ , HfH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ . The at least one metal hydride is more preferably selected from the group consisting of TiH ₂ , ZrH ₂ , HfH ₂ , LiBH ₄ and LiAlH ₄ , more preferably selected from the group consisting of TiH ₂ , ZrH ₂ , LiBH ₄ and LiAlH ₄ more preferably selected from the group consisting of TiH ₂ , LiBH ₄ and LiAlH ₄ . Preferably, the metal hydride is also selected from the group consisting of TiH ₂ , ZrH ₂ and HfH ₂ , more preferably consisting of TiH ₂ and ZrH ₂ . The metal hydride TiH ₂ is particularly preferred.

For certain applications, a combination of two metal hydrides selected from the group consisting of TiH ₂ , ZrH ₂ and HfH ₂ , preferably the combination of TiH ₂ and ZrH _{2 is} suitable. For certain applications, in particular a combination of two metal hydrides is suitable as a blowing agent, wherein each of the two groups

(a) TiH ₂ , ZrH ₂ and HfH ₂ ; and

(b) MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄

each one blowing agent is selected; preferred of these is the combination of TiH ₂ with a propellant selected from the group consisting of MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ ; particularly preferred is the combination of TiH ₂ with LiBH ₄ or LiAlH ₄ . Preferably, exactly one propellant is used according to the invention. If a metal hydride is used, it is particularly preferred to use precisely one metal hydride as blowing agent, more preferably TiH ₂ , ZrH ₂ , HfH ₂ , LiBH ₄ or LiAlH ₄ , even more preferably TiH ₂ , LiBH ₄ or LiAlH ₄ , particularly preferably TiH ₂ , The blowing agent is particularly an alkaline earth metal carbonate, ie in particular selected from the group consisting of MgC0 _3, Ca C0 _3, SRC0 ₃ and BAC0 _3, preferably selected from the group consisting of MgC0 _3, Ca C0 _3, SRC0 ₃ and BAC0 _3, more preferably selected from MgC0 _3, CaC0 ₃ and SRC0 ₃ of the group, particularly preferably selected from the group consisting of MgC0 ₃ and CaC0. ₃ For certain applications in the foaming of Mg, Al, Pb, Au, Zn or Ti as the main constituent of the first metal, in particular a combination of a metal hydride with a metal carbonate as blowing agent, wherein from each of the two groups

TiH ₂ , ZrH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ ; and

- MgC0 ₃ , CaC0 ₃ , SrC0 ₃ and BaC0 ₃ .

ever a propellant is selected. For iron as the main constituent of the at least one first metal and steel as at least one first metal, the at least one propellant is preferably selected from the group consisting of metal carbonates, more preferably selected from carbonates of the second main group of the Periodic Table of the Elements (alkaline earth metals), ie in particular the group consisting of MgC0 ₃ , CaC0 ₃ , SrC0 ₃ and BaC0 ₃ , even more preferably selected from the group consisting of MgC0 ₃ , CaC0 ₃ and SrC0 ₃ , more preferably selected from the group consisting of MgC0 ₃ and SrC0 ₃ . For the metal hydrides according to the invention, in particular as propellants, the outgassing temperature is in each case as follows (specification of the outgassing temperature in parentheses): TiH ₂ (about 480 ° C.), ZrH ₂ (about 640 ° C. to about 750 ° C.), HfH ₂ (approx 500 ° C to about 750 ° C), MgH ₂ (about 41 5 ° C), CaH ₂ (about 475 ° C), SrH ₂ (about 510 ° C), LiBH ₄ (about 100 ° C) and LiAlH ₄ ( about 250 ° C).

For the metal carbonates provided according to the invention, in particular as propellants, the outgassing temperature is in each case as follows (specification of the outgassing temperature in parentheses): MgC0 ₃ (about 600 ° C. to about 1300 ° C.), CaC0 ₃ (about 650 ° C. to about 700 ° C. ), SrCo ₃ (about 1 290 ° C) and BaC0 ₃ (about 1 360 ° C to about 1450 ° C).

According to the invention, the metal hydride may additionally comprise as blowing agent at least one oxide and / or oxihydride of the metal or of the metals of one or more of the metal hydrides used in each case. The oxides and / or oxihydrides are formed in the pretreatment of the metal hydride-containing propellant and improve its durability as well as its response during foaming, ie the timing of the release of the propellant gas. The improvement of the foaming response with respect to the timing of the release of the propellant gas is mainly a shift in the release of the propellant gas or the outgassing in the late direction to a too-fast outgassing and thus the formation of defects such as bubbles and holes instead ( closed) pores to avoid; this will become one achieved by said oxides and / or Oxihydride, on the other hand achieved in that the at least one blowing agent, especially in the case of using one or more metal hydrides, in the matrix of the semifinished product, after the metallic bonding within the first region and optionally after the metallic connection of the first region with the second region is under high pressure. In particular, the heat treatment in an oven, preferably at a temperature of 500 ° C., more preferably at a temperature in a range from about 450 ° C. to about 550 ° C., over a period of about 5 h, is suitable as a method for pretreating the propellant. preferably about 2h to 8h.

The oxide is in particular an oxide of the formula Ti _v O _w , where v is from about 1 to about 2 and w is from about 1 to about 2. The oxihydride is especially an oxihydride of the formula TiH _x O _y , where x is from about 1.82 to about 1.99 and y is from about 0.1 to about 0.3. In powder metallurgy production of the semifinished product, the oxide and / or oxihydride of the propellant may form a layer on the grains of the powder of the propellant; the thickness of this layer may be from about 10 nm to about 100 nm.

The amount of the blowing agent or the total amount of all blowing agents using at least two different blowing agents can be from about 0.1% by weight (wt .-%) to about 1, 9 wt .-%, preferably from about 0.3 wt. % to about 1, 9 wt .-%, each based on the total amount of the foamable mixture. The amount of the oxide and / or oxihydride may be from about 0.01% to about 30% by weight, based on the total amount of the at least one blowing agent. When producing a composite material and using at least one second metal, the at least one second metal may be arbitrarily selected, as long as it is suitable for the solid and permanent connection with the other material component, here the metal foam, which is typical in a composite material. Advantageously, the at least one first metal and the at least one second metal are not identical, ie both At least one of the alloy constituents, the mass or weight fraction of at least one alloying constituent and / or the nature (powder versus solid solid material), differ so that the solidus temperature of the at least one second metal is higher than the liquidus temperature of the at least one first metal. In particular, however, the solidus temperature of the at least one second metal is higher than the liquidus temperature of the foamable mixture.

Due to the nature of the at least one second metal as (solid, non-foamable) solid material compared to the at least one first metal as (compacted) powder, this usually has a different melting behavior than that, i. the same metal or metal alloy as a solid material begins to melt later in time at the same temperature due to a higher enthalpy of fusion than in the form of powder. However, solid material can only begin to melt at a somewhat higher temperature than when it is present as a (compacted) powder, especially if the latter is also mixed with a blowing agent, because this lowers the melting point of the mixture of metal powder and blowing agent the foamable mixture in total.

It is advantageous in the case of the composite material that the solidus temperature of the at least one second metal is higher than the liquidus temperature of the at least one first metal, in particular higher than the liquidus temperature of the foamable mixture. It is also advantageous if the at least one second metal begins to melt in time so much later (ie, sufficiently late) than the at least one first metal, so that the at least one second region made of the at least one second metal in solid, non-foamable form, which can be formed, for example, as a solid metallic cover layer, does not melt or start to melt during foaming of the foamable mixture. It has been found that otherwise, during the melting of the at least one layer during the foaming process, the latter is unintentionally deformed, in particular under the pressure of the gas released from the blowing agent. If the at least one second metal begins to melt on foaming of the at least one first metal, it mixes In this case, with the at least one first metal beyond the boundary layers and destroys the foam or does not allow its formation or even foamed itself, so that the foaming process is completely uncontrollable. The difference required between the solidus temperature of the at least one second metal and the liquidus temperature of the at least one first metal depends on the one hand on the (chemical) nature of the metals or metal alloys selected for the at least one first metal and the at least one second metal, on the other hand conditioned by their melting behavior. Advantageously, the at least one second metal has a solidus temperature that is at least about 5 ° C higher than the liquidus temperature of the foamable mixture. This higher solidus temperature and / or the temporally sufficiently early onset of melting of the at least one second metal can be realized according to the invention

 with the nature or chemical nature of the metals used as the main constituent; with the shape or nature of the at least one second metal (as a solid solid material compared to a powder form of the at least one first metal), ie a shape or texture which causes a higher solidus temperature and / or higher enthalpy of fusion (since metal melts earlier in powder form and one having lower solidus temperature than solid metal in the form of solid material); and / or - in that the at least one second metal has less alloying constituents than the at least one first metal and / or has (compared with) the at least one first metal at least one identical lower mass fraction alloying component in the alloy (ie, the mass fraction the alloy component which is identical in the at least one first and at least one second metal is lower or smaller in the at least one second metal than in the at least one first metal).

In the case that for both the at least one first region and the at least one second region the same metal as a main component with a content or in a Amount of at least about 80 wt .-% is used, the different melting, solidus and / or liquidus temperatures can be adjusted by different alloying additives in powder and solid material accordingly. Preferably, the solidus temperature of the at least one second metal is at least about 5 ° C higher than the liquidus temperature of the at least one first metal. Depending on the metal or metal alloy, the solidus temperature of the at least one second metal is more preferably at least about 6 ° C, more preferably at least about 7 ° C, even more preferably at least about 8 ° C, even more preferably at least about 9 ° C, even more preferably at least about 10 ° C, even more preferably at least about 1 1 ° C, even more preferably at least about 1 2 ° C, even more preferably at least about 1 3 ° C, still further preferably at least about 14 ° C, more preferably at least about 15 ° C, even more preferably at least about 1 6 ° C, even more preferably at least about 1 7 ° C, even more preferably at least about 18 ° C, even more preferably at least about 1 9 ° C and even more preferably at least about 20 ° C higher than the liquidus temperature of the at least one first metal. In any case, with the difference between the solidus temperature of the at least one second metal and the liquidus temperature of the at least one first metal, it must be ensured that the at least one second region, for example as the cover layer applied to the core, consisting of the at least one second metal does not exist during the foaming process so much softens or melts or melts that arise by the propellant gas formation and / or expansion unwanted bulges, bumps, cracks, holes and similar defects in at least a second area and / or the at least one second area with the at least one first area partially or completely fused or mixed. Typically, the solidus temperature of the at least one second metal should be at least about 5 ° C higher, preferably about 10 ° C higher and most preferably about 1 5 ° C higher than the liquidus temperature of the at least one first metal; in special cases, the solidus temperature of the at least one second metal is at least about 20 ° C higher than the liquidus temperature of the at least one first metal. In particular, it has surprisingly been found that a solidus temperature of the at least one second metal, which is about 15 ° C higher than the liquidus temperature of the at least one first metal usually a good compromise between the strength of the metal foam structure and the solid material on the one hand and the quality of Composite structure, so clear phase boundary between metal foam and solid material and no fusion of metal foam and solid material on the other hand, provides. Most preferably, the solidus temperature of the at least one second metal is higher than the liquidus temperature of the foamable mixture by the temperature stated above.

In a preferred embodiment, the at least one first and second metal are not identical. For this purpose, the at least one second metal has less alloy components than the at least one first metal; the at least one second metal, alternatively or additionally to the at least one first metal, comprises at least one identical lower mass fraction alloying component in the alloy; This makes it possible to achieve the higher solidus temperature of the second metal stated here relative to the liquidus temperature of the at least one first metal. According to the invention, the composite material and the semi-finished product for its production preferably contain exactly one second metal as solid (non-foamable) solid material.

Under solid material here massive metal that is not foamed, so has no pores, and is not present in powder form, understood. The metal can also be a metal alloy. The solid material according to this invention is not foamable (foamable), in contrast to the inventive foamable mixture. Preferably, the at least one second metal has the main component Mg (magnesium), Al (aluminum), Pb (lead), Au (gold), Zn (zinc), Ti (titanium), Fe (iron), or Pt (platinum) in one Amount of at least about 80 wt .-%, based on the amount of the at least one second metal on. For this purpose, by the way, the at least one second metal can be selected from those pure metals and alloys, as herein for the at least one first Metal defines. The at least one first metal and the at least one second metal preferably have the same main constituent Mg, Al, Pb, Au, Zn, Ti or Fe. If the at least one second metal has aluminum as the main constituent, it is in particular selected from the group consisting of

 - Pure aluminum and

 higher strength aluminum alloys selected from the group consisting of aluminum-magnesium alloys (5000 series), aluminum-magnesium-silicon alloys (6000 series) and aluminum-zinc alloys (7000 series). The at least one second metal may be aluminum or pure aluminum (at least

99% by weight of aluminum), with aluminum being preferred in which the content of aluminum is from about 85% to about 99% by weight, more preferably about 98% by weight, based on the at least one second Metal, amounts. In addition, the at least one second metal may be a higher strength aluminum alloy. The higher-strength aluminum alloy may be selected from the group consisting of aluminum-magnesium alloys (series 5000), aluminum-magnesium-silicon alloys (series 6000) and aluminum-zinc alloys (series 7000). The at least one second metal may in particular be an aluminum-magnesium alloy (series 5000). The at least one second metal may in particular be an aluminum-magnesium-silicon alloy (series 6000), preferably Al 6082 (Al Si 1 MgMn). Finally, the at least one second metal may in particular be an aluminum-zinc alloy (series 7000).

Suitable combinations of first and second metals include, but are not limited to, alloys having the following metals as a major constituent, i. in an amount of at least about 80 wt .-%, based on the respective first or second metal, wherein additionally by way of example, but not limited to suitable propellants are given:

Main component of the first propellant main component of the second Metal (alloy) metal (alloy)

Al TiH ₂ Al or Fe ¹

Zn MgH ₂ Al or Fe ¹

Pb ZrH ₂ Al or Fe ¹

Mg TiH ₂ Al or Fe ¹

Fe MgC0 ₃ Ti

Ti SrC0 ₃ Ti

Au SrC0 ₃ Pt or Ti

 In the case of iron (Fe) as a main component, steel may be used as the alloy.

The chronological order or sequence of the method steps according to the invention preferably corresponds to the numbering with Roman numbers as stated in embodiment (1), i. Preferably, first step (I), then step (II) and finally step (III). The steps (VI) and (VII) may preferably be carried out additionally and in this order, preferably cumulatively after step (I).

The heat input into the semifinished product during heating in step (III) and, if appropriate, preheating in step (IV) takes place according to the invention from the outside into the semifinished product, ie via the outer surface of the semifinished product or a part of the outer surface of the semifinished product. In step (III), the heat is introduced into the semifinished product when heated with at least one solid from the outside into the semifinished product, ie from at least one solid over the outer surface of the semifinished product or part of the outer surface of the semifinished product. Step (III) can be carried out simultaneously with step (II) if the contacting takes place with a solid already heated to a foaming temperature or higher / heated.

The heating in step (III) of the process is preferably carried out to a foaming temperature within the foamable mixture (a) at least as high as the outgassing temperature of the at least one blowing agent, and / or (b) at least as high as the solidus is the foamable mixture. The foaming temperature is a temperature at which the at least one first metal is in a foamable state and the blowing agent decomposes, thereby releasing a blowing gas which foams the at least one first metal. The at least one first metal is in a foamable state when it begins to melt (at its solidus temperature) or is partially or completely melted. The heat is supplied (fast) so that the rest of the at least one first metal is melted and foamable before the blowing agent has completely decomposed. In the case of the production of a composite material, the heating in step (III) is preferably carried out to a foaming temperature which is lower than the solidus temperature of the at least one second metal within the foamable mixture. This has the advantage that no mixing of the metals of the at least one first and second region can take place and the semifinished product during foaming, with the exception of the volume increase as a result of the foaming process, retains its original structure and does not warp. The foaming temperature in step (III) of the process according to the invention is the temperature at which the foamable mixture foams (foams up) and forms the metal foam. The foaming temperature should be equal to or higher than the outgassing temperature of the at least one propellant, at least as high as the solidus temperature of the at least one first metal (more precisely, taking into account a, albeit usually small, melting point depression by mixing with the at least one propellant and optionally one Auxiliaries: at least as high as the solidus temperature of the foamable mixture), and less than the solidus temperature of the at least one second metal in order to achieve the most homogeneous metal foam and preserve the character of the composite material, ie one for a superficial connection between Metal foam and metallic solid material to prevent merging of the two materials.

The process of the invention may additionally preheat step (IV) by heating the semifinished product of step (I) to a temperature of about 50 ° C to about 100 ° C below foaming temperature, step (IV) being performed prior to step (II) and / or step (III). Step (IV) preferably takes place before step (II), which in turn takes place before step (III). Step (IV) is preferably carried out after step (VI) and / or step (VII). This procedure has the advantage that the at least one heatable solid serving for foaming can be used more efficiently, ie at a higher throughput per unit time, because the at least one heatable solid still needs to be applied to or with this, for the foaming process necessary (residual) heat input into the semifinished product turns out to be less than if the semifinished product were to be heated from the ambient or room temperature, starting at the foaming temperature, to or with the at least one heatable solid. This makes it possible to preheat one or more simpler and less suitable for foaming of metal heating sources that do not inventive at least one heatable solid, such as electrical resistance ovens use.

The heating in step (III) of the method according to the invention can be carried out at a controlled heating rate to the time of sufficient for foaming the at least one first metal propellant gas development on the time of reaching a frothable state of the at least one first metal, such as its solidus temperature to vote. The heat should be supplied in such a way that a sufficiently strong propellant gas development for foaming the at least one first metal and any maximum propellant gas development is present when the at least one first metal has reached its foamable state, such as its solidus temperature. The heating in step (III) of the process preferably takes place for the metals and blowing agents provided according to the invention at a heating rate of about 0.5 K / s to about 10 K / s.

The contacting of the semifinished product in step (II) and / or the heat input via solid contact heat transfer into the foamable mixture or the semifinished product during heating in step (III) of the method according to the invention is preferably carried out with at least two Heatable solids, more preferably with at least two heatable solids on at least two different sides or surfaces of the semifinished product, more preferably with exactly two heatable solids, more preferably with exactly two heatable solids on exactly two different sides or surfaces of the semifinished product, particularly preferably with exactly two heatable solids on exactly two opposite sides or surfaces of the semifinished product, in particular on outer layers on both sides of the semifinished product. It should preferably the respective side or surface of the semifinished product are brought into contact with only one solid. For this purpose, each heatable solid should have a contact surface which is at least as large as the respective side or surface of the semifinished product, with which this is brought into contact. It is also possible, especially in the case of a particularly large semifinished product or one or more particularly large surfaces of a semifinished product, to use two or more solids on one side or surface of a semifinished product, in order to ensure a high homogeneity of the heat input. that the involved two or more solids on the affected side or surface of the semifinished product form a continuous, contiguous contact surface, which has no interruptions except a construction-related minimally small gap at the transition between two solids. Two or more solids on one side or surface of a semifinished product are also possible if these solids are arranged layered parallel to the contact surface. In the case of the production of a composite material, the contacting of the semifinished product in step (II) and / or the heat input via solid contact heat conduction into the according to steps (VI) and / or (VII) optionally precompressed or compressed foamable mixture or according to the Steps (VI) and / or (VII) optionally precompacted or compacted semifinished product when heated in step (III) of the method according to the invention as above, being selected as sides or surfaces of the semifinished especially or exclusively those which are part of the at least one second region are formed of at least a second metal in the form of non-foamable, solid solid material, in particular in the form of cover layers. Due to the abovementioned arrangements of semifinished product and at least two solids, the homogeneity of the heat input, since it takes place simultaneously from at least two sides, especially when these sides are opposite, is further improved, and thus the homogeneity of the metal foam formed is further improved. In particular, this reduces the formation of imperfections in the foam and, in the case of the composite material, also at the interfaces between the at least one first and at least one second region, ie between foam and non-foamable, solid solid material; This is especially true if the at least one second region in the composite material is formed as a layer or cover layer on the at least one first region. This is especially true when the composite material comprises exactly one first region and exactly two second regions, and each of the two second regions is formed as (cover) layer or cover layer on the exactly one first region, and is especially true if In these cases, the first region is formed as a core or core layer in the composite material, which is preferably formed as a sandwich.

In a further embodiment of the method, in step (II) a first surface of the semifinished product is brought into contact with a contact surface of a first heatable solid and optionally a second surface of the semifinished product is brought into contact with a contact surface of a second heatable solid.

For heat input is carried out according to the invention preferably, especially during step (III), the use of two heatable solids that form both parts of a tool or are inserted into such, so as the heat input not only via solid contact heat conduction, but also from or over two sides of the To carry out semi-finished products, and thus to further improve the homogeneity of the heat input. In this case, advantageously already in step (II) of the method, a first surface of the semifinished product is brought into contact with a contact surface of a first heatable solid and a second surface of the semifinished product with a contact surface of a second heatable solid. In this case, therefore, the semi-finished product in step (II) is placed in the tool, and that initially with the first surface of the semi-finished product placed on one of the two heatable solids (usually the lower and / or fixed solid) or its contact surface, while the second heatable solid or its contact surface is moved accordingly to the second surface of the semi-finished to the tool shut down; For this purpose, the second heatable solid body relative to the first heatable solid body can be arranged to be movable or rotatable. The two heatable solids can also be parts (upper and lower part) of a press or be inserted into such.

In any case, however, at least during the foaming process in step (III), at least one of the solids, usually the upper one must be able to shift or move relative to the other solid (s) to allow foaming and expansion of the metal foam. and advantageously, as described below, to exert a contact pressure. For this purpose, the solid bodies can be arranged (guided, that is to say with guide rails) so that they move or move relative to one another.

The first solid may have apertures distributed in the contact surface, such that by means of a vacuum device the semifinished product may be attached to the first solid for at least a limited period of time during step (II) and optionally at least for a limited period of time during heating in step (III) and / or or (IV) is aspirated and held.

The method according to the invention may additionally comprise the step

 (VIII) applying a release agent between the semifinished product and the first solid and optionally between the semifinished product and the second solid,

wherein step (VIII) is preferably carried out before the step (II) and optionally before the step (III). As a release agent, for example, graphite is suitable.

For a sufficiently high heat transfer to the semifinished product, in particular for better control of certain heating rates, especially when the heating rates are high, a corresponding high (specific) heat capacity and / or high thermal conductivity of the at least one heatable solid or of the material from which the at least one heatable solid body (mainly) consists or comprises. A high (specific) heat capacity and / or thermal conductivity of the at least one heatable solid thus surprisingly enables the formation of a particularly homogeneous metal foam, ie with a narrow size distribution of the pore sizes. In addition, the foaming process can be faster in this way. For this purpose, the at least one heatable solid body comprises or has a material

 (a) high specific heat capacity of from about 400 J / (kg · K) to about 800 J / (kg · K), and / or

 (b) high thermal conductivity ranging from about 30 W / (m · K) to about 400 W / (m · K).

In addition to increasing the specific heat capacity of the heatable solid but also the total heat capacity can be increased by the heatable solids consist of a corresponding amount of material, the heatable solids are thus carried out correspondingly heavy or high mass. In a particular embodiment of the invention

 (a) the high specific heat capacity material selected from the group consisting of steel, copper and graphite; and or

(b) the high thermal conductivity material selected from the group consisting of steel, copper and graphite.

In order to achieve a further improvement in the homogeneity of the heat transfer, the contact surface of the first solid body has at least the size of the first surface of the semifinished product and optionally the contact surface of the second solid body at least the size of the second surface of the semifinished product. The contact surface of the first solid body preferably has at least the size of the first surface of the semifinished product and the contact surface of the second solid body at least the size of the second surface of the semifinished product. The at least one heatable solid body can have any shape, as long as it allows a close contact (for solid contact heat conduction, ie without gaps) with the semifinished product. For this purpose, each heatable solid body should emulate the contour of the respective optionally curved surface of the semifinished product. In the case of flat semi-finished products or those whose at least one surface which is brought into contact with the at least one heatable solid forms a straight and no curved plane, correspondingly heatable solids with at least one straight (and not curved) plane are suitable as the contact surface. Thus, in another embodiment, the first and optionally the second solid body is formed as a plate.

In general, the first heatable solid body can be arranged essentially horizontally and below the first surface of the semifinished product and optionally the second heatable solid body can be arranged essentially horizontally and above the second surface of the semifinished product. For the formation of a metal foam with as homogeneous a pore distribution as homogeneous as possible heat transfer over the largest possible area in the semifinished product is required. For that it is favorable, if

 (i) the solid state contact thermal conduction occurs over about 90% to about 100% of the first area of the semifinished product and optionally over about 90% to about 100% of the second area of the semifinished product; and or

(ii) the solid state contact thermal conduction takes place substantially uniformly over approximately 90% to approximately 100% of the first surface of the semifinished product and optionally over approximately 90% to approximately 100% of the second surface of the semifinished product. The closer the contact of the at least one solid with the semifinished product, in particular in a design with at least one non-foamable solid material, preferably in the form of a first lower cover layer and even more preferably also with a second upper cover layer of solid material, the better the heat transfer in the way the solid-state contact heat conduction. Therefore, it is favorable if (i) the solid-body contact heat conduction through contact of the first, preferably lower, surface, in the case of the provision of a solid material with a surface of the semifinished product provided by a lower side thereof with the contact surface of the first, preferably upper, heatable solid and by contact of the second, preferably upper, surface, in the case of providence of a solid material with a surface of the semifinished product provided by an upper side thereof with the contact surface of the second, preferably upper, heatable solid, and

 (ii) by the mass of the second solid and / or by weighting of the second solid with additional mass and / or by the application of a first contact pressure on the second, in particular upper solid, more preferably only over a first contact pressure, a total thereof resulting second contact pressure is generated, with which the semifinished product is pressed against the contact surfaces of the first and second solids. On the first, but especially the second solid, so this is arranged above, ie above the first solid, usually a first or second contact pressure in the amount of about 0 MPa to about 0.05 MPa, preferably in a range of about 0.005 MPa to about 0.5 MPa, more preferably in a range of about 0.01 MPa to about 0.025 MPa.

In order to still allow the foaming despite exerting a contact pressure, the second contact pressure is preferably less than or equal to the gas pressure within the core, which results from the foaming (foaming) in step (III). Preferably, the second contact pressure with the gas pressure within the core, which results from the foaming in step (III), in a ratio of about 1: 5 to about 1: 1, preferably to about 1: 1, 1.

During the step (III), the second solid is preferably controlled in such a way that the second contact pressure remains substantially constant during the step (III), and preferably over the entire duration of the step (III), in particular until the end. foaming, in particular by consumption of at least one propellant. The second contact pressure, which is preferably generated only by the first contact pressure on the second, preferably upper, solid body, is preferably in a range of about 0.005 MPa to about 0.5 MPa, more preferably in a range of about 0.01 MPa to about 0.025 MPa. As a result, the conditions for the foaming are kept substantially constant, which has a positive effect on the homogeneity of the metal foam formed, in particular the homogeneity of the pore structure of the metal foam. It is also advantageously achieved a more uniform and thus firmer connection with cover layers, in particular an upper and a lower cover layer, when producing a composite material. Alternatively, however, the second solid may also be brought into contact with the upper side of the semifinished product only at the beginning of step (III) for a period of about 1 s to about 60 s.

In order to achieve a good mechanical strength, in particular good strength and / or torsional rigidity of the metal foam or composite material comprising a metal foam, the metal foam, also as a part or region of the composite material, formed closed-cell. The so-called closed, spherical pores allow optimal load transfer over the intact as possible, surrounding the pores cell walls, and thus contribute significantly to the strength of the metal foam and thus a composite material comprising a metal foam. A metal foam is closed-pore, if the individual gas volumes therein, in particular two adjoining gas volumes, by a separating solid phase (wall) are separated or at most by small production-related openings (cracks, holes) whose respective cross-section relative to the cross section of the two Gas volume separating solid phase (wall) is small, interconnected. According to the invention, the formation of a substantially closed-cell metal foam is preferably carried out, in particular in method step (III). The substantially closed-cell metal foam is characterized by the fact that the individual gas volumes can be produced at most by small supply-related openings (cracks, holes) are interconnected, but whose cross section is small in relation to the cross section of the solid phase separating the volumes.

The porosity of the formed metal foam, also the metal foam in a composite material, is from about 60% to about 92%, preferably from about 80% to about 92%, most preferably about 89.3%. The density of the unfoamed bulk material may be from about 90%, preferably from about 98%, to about 100% of the density of the raw / solid material. The density of the metal foam formed in step (III) may be from about 0.2 g / cm ³ to about 0.5 g / cm ³ for aluminum foam or, corresponding to the density of the unfoamed solid material, a porosity of about 60% to about Reach 92%.

The method according to the invention may additionally comprise the step

 (V) forming the semifinished product provided in step (I) into a molded part, wherein in step (III) and / or (IV) the heating of the resulting molded article takes place instead of the semifinished product.

The forming of the semifinished product can be carried out by methods known to the person skilled in the art. According to the invention, however, the forming is preferably carried out by a method selected from the group consisting of bending, deep drawing, hydroforming and hot pressing.

Finally, the present invention includes

 - A metal foam obtainable by a process

 a composite obtainable by a process

 - A component comprising a metal foam

- A component comprising a composite material

 - A component comprising a metal foam and a composite material

as disclosed herein. The term "component" refers to a component or manufacturing part which, for a particular purpose or specific use alone or together with other components, such as a device, a machine, a (water, air) vehicle, a building, furniture or another end product can be used. For this purpose, the component may have a specific, for example, for the interaction with other components necessary, approximately custom-fit, shaping. Such a shaping can advantageously already be carried out by the additional process step of reshaping described here (step (V)) on the non-foamed (ie foamable) semifinished product, which can be deformed more easily than the metal foam or composite material.

The invention will be further elucidated with reference to the accompanying drawings and figures, and the photos contained therein, from which further advantageous embodiments of the invention will be apparent, without, however, necessarily limiting the invention or individual features of the invention thereto. Rather, features described there can be combined with each other and with the features described above to form further embodiments of the invention.

Fig. 1 is a plan view of a non-uniform foamed metal foam sandwich which has been free-foamed (i.e., foamed without the upper stopper) in the hot mold, and therefore thermal contact with expansion has been lost;

FIGS. 2A and 2B) show a cross-section of a non-uniformly foamed metal foam sandwich as examples of a non-uniformly foamed metal foam sandwich (cracks in FIG. 2A, large pores in FIG. 2B) due to inhomogeneous temperature distribution due to free foaming (foaming without top Stop) in the hot tool; and

3 shows a plan view (top, FIG. 3A) and a cross-section (bottom, FIG. 3B) of a homogeneously expanded inside a heated tool with a hot pressure plate applied. Dated metal foam sandwiches. Homogeneous heat distribution between the pressure plate and the tool results in a uniform pore structure and expansion.

The invention will be explained in more detail with reference to the embodiments described below, without the invention or individual features of the invention being necessarily limited thereto.

Example 1 a

For the production of the foamable semi-finished product for the production of aluminum foam sandwich structures, the following process steps were used. First, a powder mixture (foamable mixture) was prepared. For this purpose, 0.4 to 1, 0 wt .-% TiH _{2 were} mixed in powder form (% by weight based on the total mass of the foamable mixture) with a powder of the aluminum alloy AISi8Mg4. Subsequently, this powder mixture was filled into an aluminum container of the alloy AI 6082 (Al Si 1 MgMn), in which two opposite walls formed the later cover layers or cover layers of the three-layered semifinished product, which foamed to a sandwich structure (composite material). Here, the aluminum alloy of the container was chosen so that it had a solidus temperature which was higher than the liquidus temperature of the powder mixture (foamable mixture). After the container was completely filled with the powder mixture, the powder mixture was dried. It was the

Powder heated to 300 ° C and the resulting moisture removed. Subsequently, the container was precompressed at a pressure of 0.2 MPa by means of two plane-parallel tools in a pressing process for about 28h for the first time. Here, the pre-compression of the powder was carried out at 400 ° C to 460 ° C. Pre-compaction produced a stable ingot. Furthermore, the powder particles were partially connected to the cover layers in the context of a first metallurgical compound. In the following second precompression rolling process, the vessel was hot rolled at a temperature of about 475 ° C and a nip pressure of about 6,000 t. Then followed by a cold rolling process to achieve sheet thicknesses below 9 mm. By means of the rolling process, a second metallurgical combination of powder and cover layer was achieved and further the powder was heated to about 98% to 100% of its nominal density compacted. Subsequently, the resulting three-layer sandwich semi-finished products were assembled and fed to the foaming process. The semifinished product produced in this way, consisting of two solid cover layers (solid material as a cover layer as two second regions of the semifinished product) and a foaming material as core as the first region, was placed between two heated, mutually movable steel plates which form the tool. The high (specific) heat capacity and the high thermal conductivity of the tool played an important role. Subsequently, the tool was closed, but not completely closed, so that the semifinished product could expand freely during the foaming process. About the thermal contact and the radiation from tool to semi-finished product that was brought to the foaming temperature. After exceeding the solidus temperature of the foamable core, the semifinished product began to expand. Due to the high mass, high (specific) heat capacity and high thermal conductivity of the tool, its temperature dropped only slightly and remained almost constant. However, the resulting foam quality and maximum expansion was only moderate (5- to 6-fold expansion), as the material of the semifinished product was rejected by the expansion, the thermal contact continued to decrease and the emitted radiation of the tool was insufficient to achieve an optimal result (see Figs. 1 and 2). The procedure was carried out accordingly also with a semi-finished product consisting only of a pressed foamable mixture without cover layers.

Example 1 b

The method of embodiment 1 a has been completely adopted. Instead of two heated steel plates moving against each other, two graphite plates were chosen. The heat input into the semifinished product increased in the ratio of the thermal conductivities of graphite to stainless steel and the foaming process was correspondingly accelerated. However, graphite had the disadvantage that it decomposed at the foaming temperatures in the long term in the air. Example 1 c

The method of embodiment 1 a has been completely adopted. Only two copper plates were chosen instead of two heated steel plates moving against each other. The heat input into the semifinished product increased in relation to the thermal conductivities of copper to stainless steel and the foaming process was correspondingly accelerated.

Example 2a So that the required homogeneous heat input into the foamable semifinished product was only achieved by direct thermal contact, a guided hot pressure plate made of steel was placed on the semifinished product between semifinished product and one of the two steel plates of the tool in the two-part heated tool. The method of embodiment 1 a, 1 b or 1 c was otherwise completely adopted. As a result of the constant self-weight of the printing plate, the semifinished product was kept in thermal contact throughout, as a result of which there was no formation of bubbles on the cover layers, as shown in FIG. 3A, and gave significantly better pore structures and more uniform foam expansion, as shown in FIG. 3B. The system controlled itself and needed no further control technology. The procedure was carried out accordingly also with a semi-finished product consisting only of a pressed foamable mixture without cover layers.

Example 2b

The method of embodiment 2a has been completely adopted. Instead of a guided hot steel pressure plate, a hot graphite pressure plate was used. The heat input into the semi-finished product increased in relation to the thermal conductivity of graphite to steel and the foaming process was correspondingly accelerated. However, graphite had the disadvantage that it decomposed at the foaming temperatures in the long term in the air. Example 2c

The method of embodiment 2a has been completely adopted. Instead of a guided hot steel pressure plate, a hot copper pressure plate was used. The heat input into the semi-finished product increased in the ratio of the thermal conductivities of copper to steel and the foaming process was accelerated accordingly.

Examples 3 to 9

The generally applicable methods according to Examples 1 a, 1 b, 1 c, 2 a, 2 b and 2 c have been correspondingly et al. with the following exemplary alloys and blowing agents, and under the conditions specified below.

Example 3

 The mold had a temperature of 550 ° C to 650 ° C and the foaming temperature was from 550 ° C to 650 ° C.

Example of alloy in the foaming propellant ¹ in the alloy of the top coats mixture foamable mixture

3.1 AISi8Mg4 TiH ₂ (1, 0 wt .-%) AI 6082

3.2 AISi8Mg4 TiH ₂ (0.5% by weight) AI 5754

3.3 AISi8Mg4 TiH ₂ (0.6% by weight) Al 5005

3.4 AISi8Mg4 TiH ₂ (0.6 wt%) Al 6016

3.5 AISi7 TiH ₂ (1.2% by weight) Al 3103

3.6 AISi6Cu7.5 TiH ₂ (0.8% by weight) Al 6060

3.7 AISi4Cu7.5 TiH ₂ (0.6 wt%) without overlays

3.8 AISi6Mg3 TiH ₂ (0.6 wt%) without overlays ¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture. The same procedure was carried out instead of TiH ₂ with the following blowing agents in the amounts indicated above: ZrH ₂ , HfH ₂ , MgH ₂ , CaH ₂ , SrH ₂ , LiBH ₄ and LiAlH ₄ and the combinations of TiH ₂ with LiBH ₄ and TiH ₂ with LiAIH ₄ .

Example 4

The mold had a temperature of 400 ° C to 500 ° C and the foaming temperature was from 380 ° C to 420 ° C.

¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture. The same procedure was carried out instead of MgH ₂ with TiH ₂ as blowing agent in the amounts indicated above.

Example 5

The mold had a temperature of 300 ° C to 400 ° C and the foaming temperature was from 310 ° C to 380 ° C.

Example of alloy in the foaming propellant ¹ in the alloy of the cover layers ble mix foamable mixture

5.1 PbCul ZrH ₂ (0.5% by weight) Al 6082

5.2 PbCul ZrH ₂ (0.6% by weight) Al 6082

5.3 PbCul ZrH ₂ (0.8% by weight) Al 6082

5.4 PbCul ZrH ₂ (1, 0 wt .-%) Al 6082

5.5 PbCul ZrH ₂ (1, 2 wt .-%) AI 6082

5.6 PbCul ZrH ₂ (0.8% by weight) without cover layers

5.7 PbZn5 ZrH ₂ (0.8% by weight) without cover layers

¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture. The same procedure was carried out instead of ZrH ₂ with TiH ₂ as blowing agent in the amounts indicated above. Example 6

The mold had a temperature of 550 ° C to 650 ° C and the foaming temperature was from 580 ° C to 630 ° C.

¹ The amount of the blowing agent in% by weight (% by weight) is based on the total amount of the foamable mixture. Example 7

The mold had a temperature of 1200 ° C to 1450 ° C and the foaming temperature was from 1 380 ° C to 1420 ° C.

¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture.

Example 8

The mold had a temperature of 1 300 ° C to 1 650 ° C and the foaming temperature was from 1500 ° C to 1680 ° C.

Example of alloy in the foaming propellant ¹ in the alloy of the top coats mixture foamable mixture

8.1 Ti-6Al-2Sn-4Zr-6Mo SrCo ₃ (0.5 wt%) Ti-5Al-2Sn-2Zr-4Mo-4Cr or Ti

8.2 Ti-6Al-2Sn-4Zr-6Mo SrC0 ₃ (0.6 wt%) Ti-5Al-2Sn-2Zr-4Mo-4Cr or Ti

8.3 Ti-6Al-2Sn-4Zr-6Mo SrC0 ₃ (0.8 wt%) Ti-5Al-2Sn-2Zr-4Mo-4Cr or Ti

8.4 Ti-6Al-2Sn-4Zr-6Mo SrCO ₃ (1, 0 wt%) Ti-5Al-2Sn-2Zr-4Mo-4Cr or Ti

8.5 Ti-6Al-2Sn-4Zr-6Mo SrC0 ₃ (1.2% by weight) Ti-5Al-2Sn-2Zr-4Mo-4Cr or Ti

8.6 Ti-6Al-2Sn-4Zr-6Mo SrCO ₃ (1, 0 wt .-%) without cover layers

8.7 Ti-5Al-2Sn-2Zr-4Mo-4Cr SrCO ₃ (1, 0 wt .-%) without cover layers

¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture.

Example 9

The tool had a temperature of 900 ° C to 1 1 50 ° C and the foaming temperature was from 980 ° C to 1 100 ° C.

¹ The amount of the blowing agent in% by weight (wt .-%) is based on the total amount of the foamable mixture.

Claims

claims 1 . A method of producing a metal foam of at least a first metal having the major component Mg, Al, Pb, Au, Zn, Ti or Fe in an amount of at least about 80% by weight, based on the amount of the at least one first metal, comprising the steps  (I) providing a semifinished product comprising a foamable mixture comprising the at least one first metal and at least one propellant, (II) contacting at least a part of the outer surface of the semifinished product with at least one heatable solid, and  (III) heating the semifinished product via the at least one heatable solid body by solid contact heat conduction for foaming the foamable mixture by gas separation from the at least one blowing agent to form the metal foam. 2. The method of claim 1, wherein the semifinished product comprises at least a first region, which is formed from the foamable mixture, and at least one second region, which is formed from at least one second metal in the form of non-foamable solid material, so that a composite material is formed with at least a first region which is formed from the metal foam of the at least one first metal, and at least a second region which is formed from the at least one second metal in the form of non-foamable solid material. 3. The process according to claim 2, wherein the at least one second metal comprises the main constituent Mg, Al, Pb, Au, Zn, Ti or Fe in an amount of at least about 80% by weight, based on the amount of the at least one second metal, having. 4. The method according to claim 3, wherein the at least one first metal and the at least one second metal have the same main constituent Mg, Al, Pb, Au, Zn, Ti or Fe. A method according to any one of claims 2 to 4, wherein the at least one second metal  (a) has a solidus temperature which is at least about 5 ° C higher than the liquidus temperature of the foamable mixture, and / or  (b) has less alloying constituents than the at least one first metal or at least one identical lower mass fraction alloy component in the alloy relative to the at least one first metal. The method of any one of claims 2 to 5, wherein the at least one second region is formed as a layer on at least a portion of the surface of the at least one first region. A method according to claim 6, wherein  (A) in the composite material, the at least one first region as a foamed core and  (B) in the semi-finished product, the at least one first region is designed as a foamable core. A method according to any one of claims 1 to 7, wherein the exhaust gas temperature of the at least one propellant  (a) is approximately equal to the solidus temperature of the at least one first metal, or (b) is below the solidus temperature of the at least one first metal, but not more than about 90 ° C below the solidus temperature of the at least one first metal. 9. The method according to any one of claims 2 to 8, wherein the exhaust temperature of the at least one blowing agent is below the solidus temperature of the at least one second metal. 10. The method according to any one of claims 1 to 9, wherein the at least one Propellant is selected from the group consisting of metal hydrides and metal carbonates. 1 1. A process according to any one of claims 1 to 10, wherein the heating in step (III) to a foaming temperature within the foamable mixture (a) is at least as high as the outgassing temperature of the at least one propellant, and / or  (b) is at least as high as the solidus temperature of the foamable mixture,  he follows. 1 2. The method according to any one of claims 2 to 1 1, wherein the heating in step (III) to a foaming temperature which is less than the solidus temperature of the at least one second metal within the foamable mixture. A method according to any one of claims 1 to 12, additionally comprising the step  (IV) preheating by heating the semifinished product from step (I) to a temperature which is about 50 ° C to 100 ° C below the foaming temperature, wherein the step (IV) before the step (II) and / or step (III ) is carried out. 14. A process according to any one of claims 1 to 13, wherein the heating in step (III) is at a heating rate of about 0.5 K / s to about 10 K / s. Method according to any of claims 1 to 14, wherein in step (II) a first surface of the semifinished product is brought into contact with a contact surface of a first heatable solid and optionally a second surface of the semifinished product is brought into contact with a contact surface of a second heatable solid. A method according to any one of claims 1 to 15, wherein  (A) the at least one heatable solid material comprises a material of high specific heat capacity in the amount of about 400 J / (kg · K) to about 800 J / (kg · K); and or  (B) the at least one heatable solid comprises a material of high thermal conductivity in the amount of about 30 W / (m · K) to about 400 W / (m · K). A method according to claim 1-6, wherein  (A) the material of high specific heat capacity is selected from the group consisting of steel, copper and graphite; and or  (b) the high thermal conductivity material is selected from the group consisting of steel, copper and graphite. A method according to any one of claims 1 to 1 7, wherein the contact surface of the first solid has at least the size of the first surface of the semifinished product and optionally the contact surface of the second solid at least the size of the second surface of the semifinished product. A method according to any one of claims 1-5 to 1 8, wherein  (A) the first and optionally the second solid body is formed as a plate;  and or  (b) the first solid body is arranged substantially horizontally and below the first surface of the semifinished product and optionally the second solid body is arranged substantially ho zontally and above the second surface of the semifinished product. A method according to any of claims 1-5 to 1 9, wherein  (i) the solid state contact thermal conduction occurs over about 90% to about 100% of the first area of the semifinished product and optionally over about 90% to about 100% of the second area of the semifinished product; and or  (ii) the solid state contact thermal conduction takes place substantially uniformly over approximately 90% to approximately 100% of the first surface of the semifinished product and optionally over approximately 90% to approximately 100% of the second surface of the semifinished product. A method according to any of claims 1-5, wherein  (i) the solid contact heat conduction takes place by contact of the first surface of the semifinished product with the contact surface of the first heatable solid and by contact of the second surface of the semifinished product with the contact surface of the second heatable solid, and  (ii) by the mass of the second solid and / or by weighting the second solid with additional mass and / or by the application of a first contact pressure on the second solid body resulting in a total resulting second contact pressure is generated with which the semifinished product against the contact surfaces of first and second solid is pressed. The method of claim 21, wherein the second contact pressure with the gas pressure within the core resulting from the foaming in step (III) is in a ratio of about 1: 5 to about 1: 1. A method according to claim 21 or 22, wherein the second solid is moved in a controlled manner during step (III) such that the second contact pressure remains substantially constant during step (III). A method according to any one of claims 1 to 23, wherein in step (III) the formation of a substantially closed-cell metal foam takes place. The method of any of claims 1 to 24, wherein the porosity of the metal foam formed in step (III) is from about 60% to about 92%. 26. A method according to any one of claims 1 to 25, additionally comprising the step  (V) forming the semifinished product provided in step (I) into a shaped part, wherein in step (III) and / or (IV) the heating of the resulting molded part takes place instead of the semifinished product. 27. A metal foam obtainable by a process as defined in any of claims 1, 8, 10, 11 and 13 to 26. A composite material obtainable by a process as defined in any one of claims 2 to 26. 29. A component comprising a metal foam as in claim 27 and / or a composite material as defined in claim 28.