WO2005045080A1 - Aluminium alloy - Google Patents

Abstract

The invention relates to the production of an aluminium/manganese alloy, comprising good mechanical characteristics, as well as a good plasticity and corrosion resistance and which is particularly suitable as base material for cladded sheets in the production of heat exchangers. According to the invention, an aluminium alloy is used, with (in wt.%) 0.6 % to 1.5 % manganese, 0.05 % to 0.5 % scandium, 0.025 % to 0.25 % zirconium, 0.10 % to 0.90 % iron, up to 0.25 % chromium, up to 0.7 % silicon, up to 1.5 % magnesium, up to 1.5 % copper, up to 1.5 % zinc, up to 0.10 % titanium, the remainder being aluminium and unavoidable impurities from production. The invention further relates to the production of starting materials for components made from aluminum alloy, produced by welding, whereby a melt with a composition, corresponding to the above aluminum alloy is produced, said melt is cast to give a wide flat starting material and left to harden. Semi-finished products of high quality can be produced by said method.

Description

Alumimumlegierung

The invention relates to an aluminum alloy.

The invention further comprises a method for producing starting material for components made of an aluminum alloy that can be produced by soldering.

Aluminum-manganese alloys have been used for many years for components of heat exchangers or the like components which are used at temperatures of up to 400 ° C. These alloys, also known as "3000 alloys" in technical jargon, are characterized by good thermal conductivity and consistently high corrosion resistance.

As one of the wrought alloys, aluminum-manganese alloys continue to have good formability, and castings or primary materials made from such alloys can generally be easily formed into sheets, which in turn are processed into various objects such as heat exchangers.

In the course of processing sheets or parts thereof, for example in the manufacture of heat exchangers, it may be necessary to connect individual sheets or sheet metal parts to one another by soldering. In order to make this possible in a simple manner, aluminum-manganese alloy sheets can be plated on one or both sides with a layer which has a lower melting point than the aluminum-manganese alloy representing a base material.

Clad sheet metal parts can be placed in the area of the

Plating layers, subsequent melting of the plating layers and subsequent cooling of the sheet metal parts are bonded together. Since on the one hand mostly aluminum-silicon If alloys with a eutectic composition are used, i.e. alloys with a melting point of approx. 570 ° C and, on the other hand, melt aluminum-manganese alloys at temperatures above approx. 615 ° C, a material connection can be ensured at 600 "C without the base material melting ,

Due to the properties mentioned, such as good forming properties, high melting points and good corrosion resistance, even at use temperatures of, for example, 300.degree. C., the use of aluminum-manganese alloys for heat exchangers or the like at elevated temperatures has been established over the years.

However, it should be noted that these alloys have low strengths and that when parts made from these alloys are used, particularly when used at higher temperatures, they do not only depend on the

Corrosion resistance, but also significantly on the mechanical

Properties such as hardness and tensile strength as well as creep resistance are important.

Inadequate mechanical strength can cause parts to fail prematurely. In other words: an outstanding one

Corrosion resistance is of no use if a component is mechanical

Takes damage.

In a known aluminum-manganese alloy, there is a certain scope for increasing the strength by utilizing the knowledge that increasing the concentration of manganese up to 1.5% by weight is accompanied by an increase in the tensile strength (Rm). However, the tensile strength achieved is usually only about 100 MPa, even with 1.5% by weight of manganese. Even larger manganese contents are not considered to be expedient because coarse Al ₆ Mn crystals then form, which impair the formability. The tensile strength can be even lower if, as already explained, it is necessary to heat an aluminum-manganese alloy to a temperature of about 600 ° C. in the course of soldering. At such temperatures, the alloy softens and there is a decrease in tensile strength compared to the alloy before soldering. After a soldering process, tensile strength values of Rm ~ 50 MPa are common values for parts made of aluminum-manganese alloys.

Approaches have already been made to improve the mechanical properties of the aluminum-manganese alloys, which are valued for their good formability and corrosion resistance. Attempts have been made to make the aluminum-manganese alloys, which are in themselves not hardenable, hardenable by alloying certain elements.

For example, A. Gray et al. in "Development of roll-clad sheets for automotive brazing applications (Materials of the International Congress Aluminum Brazing, Düsseldorf, 10-12 ⁰¹ May 2000)" before alloying copper. This measure is intended to increase strength in aluminum-manganese alloys result, which can be attributed to solid solution strengthening and precipitation of ternary Al-Mn-Cu phases.

According to this approach, precipitation hardening can be achieved by soldering: Due to the high thermal conductivity of aluminum-manganese alloys, the base material quickly heats up to approx. 600 ° C and this temperature is sufficient to dissolve copper, which is why at one subsequent increased cooling or quenching of the soldered parts and subsequent aging, the aforementioned Al-Mn-Cu phases are eliminated. However, the tensile strengths Rm achieved with such an alloy after brazing are limited to 75 MPa. The object of the invention is to provide an aluminum-manganese alloy which, in addition to good formability and corrosion resistance, can be tempered to high mechanical parameters and which is particularly suitable for use as a base material in clad sheets for the production of heat exchangers.

This object is achieved by an aluminum alloy according to claim 1. Advantageous developments of the aluminum alloy according to the invention are the subject of claims 2 to 11.

The advantages achieved by the invention are to be seen in particular in the fact that, through a balanced alloy composition, sheets with high hardness, high yield strength and tensile strength as well as excellent creep resistance can be obtained. With regard to the use of components made of aluminum-manganese alloys at temperatures of up to 300 ° C., for example when operating a heat exchanger, it is to be seen as a particularly important advantage that sheets made from an alloy according to the invention have good mechanical properties even at high temperatures , in particular high tensile strength and low tendency to creep.

After heat treatment at 600 ° C, followed by aging, alloys according to the invention have high mechanical characteristics, which is why they are particularly suitable as base materials for clad sheets, which are used for the production of heat exchangers and which are hardened by means of a soldering process, optionally with subsequent hot aging become.

The individual effects of the elements in the aluminum alloy according to the invention and their interaction and their mutual influence can be explained as follows. Manganese (Mn): In the content range from 0.6% to 1.5% by weight, manganese contributes significantly to corrosion resistance and strength, whereby the contribution of manganese to strength can be seen in connection with a given iron content.

Manganese is generally not very soluble in equilibrium in α-aluminum, but remains in solution when a poured melt cools down rapidly. However, the presence of iron in the alloy according to the invention counteracts this oversaturation with the formation of strength-increasing AlβCMnFe) precipitates.

Preferred levels of manganese are in the range of 0.8% to 1.1% by weight because the best mechanical properties can be observed in these ranges.

Scandium (Sc): In an alloy according to the invention, scandium is mandatory in contents of 0.05% by weight to 0.5% by weight. Scandium works in several ways: First, when scandium and zircon are present, A Sc, AI ₃ Zr and possibly mixed phases form during hardening, which contribute significantly to the material strength. Secondly, scandium has a grain-refining effect and thus further increases the strength. Finally, the alloying of scandium can also shift the recrystallization temperature to significantly higher temperatures.

Zirconium (Zr): Zirconium mainly forms an increase in strength through the formation of zirconium-containing precipitates such as A ^ Zr0 and has a positive effect in this regard in a content range from 0.025% by weight to 0.25% by weight. It is particularly favorable if the weight ratio scandium to zircon is more than 2 and less than 4, preferably more than 2.6 and less than 3.4. With such a ratio, there is mainly the formation of Al ₃ (Srι _-x Zr _x ), since zircon - with the weight ratios mentioned - can be completely incorporated into the Al ₃ Sc crystal lattice. An AI ₃ (Srι.χZr _x ) phase is preferred in terms of elimination kinetics, because this phase tends to coagulate less in comparison with AI ₃ Sc or AI ₃ Zr and therefore favors a homogeneous microstructure.

Iron (Fe): In the alloy according to the invention, iron is mandatory and causes an excretion of Alβ (MnFe.) In the intended contents.

An upper limit of 0.90% by weight of iron results due to disadvantageous forming properties at higher contents. For example, undesired cracking can occur when rolling if the iron content is greater than 0.90% by weight.

With regard to both good mechanical properties and good formability, iron contents of 0.15% by weight to 0.7% by weight, preferably 0.25% by weight to 0.55% by weight, have proven successful.

Chromium (Cr):

Chromium contents of up to 0.25% by weight have a favorable effect on the strength of alloys according to the invention. At levels higher than 0.25% by weight, undesirable coarse intermetallic phases can form, which is why this chromium content represents an upper limit.

If the highest possible hardness is required, the chromium content should be at least 0.0125% by weight, it being particularly preferred if the weight ratio of zirconium to chromium is more than 0.5 and less than 2.5 and the weight ratio of scandium to zirconium is more than 2 and less than 4. According to current considerations and findings, fine precipitates of an AlmSc _n Zr _p Cr _q phase are formed in this case.

Silicon (Si): Silicon can cause fine Al (MnFe) Si phases to form in aluminum-manganese alloys, but at higher contents, in particular higher than 0.7% by weight, hot cracking is frequently observed in continuous casting. It is therefore preferred to set the silicon content to less than 0.3% by weight, particularly preferably to less than 0.1% by weight, of silicon.

Magnesium (Mg):

Magnesium has a strength-increasing effect in an alloy according to the invention and can be provided in contents of up to 1.5% by weight. With regard to a magnesium concentration in the material, it is preferred to provide magnesium at a content of at least 0.5% by weight, because then the amazing effect can be observed that the yield strength R _p o, _{2 is} higher at 150 ° C, i.e. in the range of typical use temperatures than at room temperature. A plausible explanation for this effect is given by the formation of Mg-containing precipitates at these temperatures. With regard to a maximum magnesium content, it is preferred to provide magnesium with a maximum of 1.05% by weight because the tensile strength decreases at higher contents.

Copper (Cu):

Copper can be present in contents of up to 1.5% by weight and can contribute to increasing the strength by forming ternary Al-Mn-Cu phases. For reasons of corrosion chemistry, however, it is preferred to limit the copper content to less than 0.15% by weight, preferably less than 0.10% by weight. Zinc (Zn):

Zinc levels of up to 1.5% by weight can be present without a significant influence on the mechanical properties. However, lower contents of less than 0.5%, preferably less than 0.10% zinc are preferred.

Titan (Ti):

In order to achieve the finest possible grain size or a small average grain size, titanium can be provided in an alloy according to the invention in a content of up to 0.10% by weight. It has proven to be advantageous to use titanium with contents of 0.01% by weight to 0.05% by weight: grain refinement effects are less pronounced below 0.01% by weight, and the grain refinement effect of titanium decreases above 0.05% by weight.

It has surprisingly been shown in extensive tests that particularly high mechanical characteristic values can be observed after hardening in an alloy according to the invention if plate-shaped castings or wide-flat primary material, including plate-shaped primary material with a ratio of width to thickness, is larger as the primary material for sheets is understood as 10 can be used.

On the basis of this knowledge, in a further aspect of the invention it is an object to specify a method for producing starting material for components made of an aluminum alloy that can be produced by soldering and with which high-quality semi-finished products can be provided.

This goal is achieved in that a melt is created from an aluminum alloy according to the invention in a method of the type mentioned at the outset, after which the melt is poured into a wide-flat starting material and allowed to solidify. The advantages achieved in terms of the process can be seen in particular in that, by casting an alloy according to the invention in wide-flat primary material, an advantageous cast structure with small size precipitates is achieved and the sheets produced from such panels or panel-shaped primary materials have excellent mechanical properties.

The preliminary material thus created can expediently be formed into a semi-finished product. The process is advantageously carried out in such a way that the primary material is formed by hot rolling and then cold rolling. In this way, the primary material can be processed in a simple manner into sheets with a small sheet thickness.

In the following, the invention is further explained using examples.

Exemplary alloys A, B, C and D with chemical compositions according to Table 1 are cast in 2 cm by 23 cm by 23 cm plates. Furthermore, round bolts with a diameter of 7 cm and a height of 17 cm are created from these alloys.

Table 1: Chemical composition of alloys A, B, C and D according to the invention (all data in percent by weight)

The cast plates and round bolts are then rolled at a temperature of 550 ° C to 580 ° C to a thickness of 1 cm.

Structural examinations on micrographs of the rolled plates and bolts each show a structure with homogeneously distributed precipitations for both primary materials. The average size of the excretions depends on the primary material from. When comparing the average size of excretions in plates and with that in bolts as primary material, it was found that the excretions in plates have an average size that is up to 10 times smaller.

Table 2 shows the hardness values determined on rolled plates before and after a heat treatment consisting of solution annealing at a temperature of 630 ° C. to 635 ° C. for 10 minutes, a subsequent quenching to room temperature and a subsequent heat aging at 300 ° C. for 300 minutes , It can be seen that alloy D has the greatest hardness in the hardened state (the hardness values in Table 2 and also below are Brinell hardnesses 2.5 / 62.5 / 16).

Table 2: Brinell hardness of sheets made from alloys according to the invention

As can be seen from a second investigation, the results of which can be seen in Table 3, high hardnesses can also be achieved with solution annealing at 600 ° C to 605 ° C, a subsequent quenching to room temperature with subsequent hot aging. The alloys according to the invention are therefore particularly suitable for use as the base material for plated sheets: solution annealing of sheets is not necessary because the required dissolving of alloying elements can take place as part of a soldering process. Table 3: Brinell hardness of sheets made from alloys according to the invention

Table 4 shows the yield strength (R _p o, ₂ ). the tensile strength (R _m ), the elongation at break (A5) and the constriction (Z) for tempered sheets of alloys A, B, C and D according to the invention are given in Table 1.

The values given in Table 4 correspond to test pieces which were made from sheet metal which had been annealed at 600 ° C. to 605 ° C. for 10 minutes, then quenched to room temperature and then aged at 300 ° C. for 300 minutes.

Table 4: Yield strength R _p o, ₂ , tensile strength R _m , elongation at break A ₅ and constriction Z for sheets annealed at 600-605 ° C (L ... values in the rolling direction, Q ... values in the transverse direction)

Table 4 shows, inter alia, that sheets made from the alloy according to the invention can have a high tensile strength of over 100 MPa even at 300 ° C.

In the case of sheets which were not made from plate-shaped but from bolt-shaped primary material, the same heat treatment was used in each case lower values of the yield strength R _p0 , 2, tensile strength Rm, elongation at break A ₅ and constriction Z were found.

For alloys A, creep tests on sheets made from plate-shaped or broad-flat primary material, which were subjected to a heat treatment comprising solution annealing at 600 ° C. for 10 minutes, subsequent quenching and hot aging at 300 ° C. , B, C and D after 200 hours of tensile stress of 100 MPa at 150 ° C elongation values ε of less than 0.3%, both lengthways and crossways to the rolling direction. Sheets made of alloys B, C and D showed particularly low elongation values ε of less than 0.15%.

It is understood by those skilled in the art that an alloy or sheet according to the invention can be subjected to the same alternative heat treatment method. It is thus possible to hot-roll broad-flat stock material in several passes at a temperature of over 200 ° C and then cold-roll it at ambient temperature, and finally to subject the sheets thus produced to soft annealing at 350 ° C for 90 minutes. Sheets made and treated accordingly from alloys B, C and D showed yield strength values R _p0 , ₂ of more than 280 MPa and tensile strength values R _m of more than 300 MPa.

Claims

claims 1. Aluminum alloy containing (in% by weight) 0.6% to 1.5% manganese 0.05% to 0.5% scandium 0.025% to 0.25% zircon 0.10% to 0.90% iron to 0.25% chromium to 0.7% silicon to 1.5% magnesium to 1.5% copper to 1.5% zinc to 0.10% titanium, the rest aluminum and production-related impurities. 2. Aluminum alloy according to claim 1, wherein the weight ratio of scandium to zircon is more than 2 and less than 4. 3. Aluminum alloy according to claim 1 or 2, wherein the weight ratio of scandium to zircon is more than 2.6 and less than 3.4. 4. Aluminum alloy according to one of claims 1 to 3, containing (in% by weight) 0.8% to 1.1% manganese. 5. Aluminum alloy according to one of claims 1 to 4, containing (in% by weight) 0.15% to 0.7%, preferably 0.25% to 0.55%, iron. 6. Aluminum alloy according to one of claims 1 to 5, containing (in% by weight) at least 0.0125% chromium. 7. Aluminum alloy according to one of claims 1 to 6, wherein the weight ratio of zirconium to chromium is more than 0.5 and less than 2.5. 8. Aluminum alloy according to one of claims 1 to 7, containing (in% by weight) less than 0.3%, preferably less than 0.1%, silicon. 9. Aluminum alloy according to one of claims 1 to 8, containing (in% by weight) 0.5% to 1.05% magnesium. 9. Aluminum alloy according to one of claims 1 to 8, containing (in% by weight) less than 0.15%, preferably less than 0.10%, copper. 10. Aluminum alloy according to one of claims 1 to 9, containing (in% by weight) less than 0.5%, preferably less than 0.10%, zinc. 11. Aluminum alloy according to one of claims 1 to 10, containing (in% by weight) 0.01% to 0.05% titanium. 12. Process for the production of primary material for solderable Components made of an aluminum alloy, characterized in that a melt with a composition corresponding to an aluminum alloy according to one of claims 1 to 11 is created, after which the melt is poured into a wide-flat material and allowed to solidify. 13. The method according to claim 12, characterized in that the wide-flat material is formed into a semi-finished product. 14. The method according to claim 14, characterized in that the forming of the wide-flat stock is carried out by hot rolling and / or subsequent cold rolling.