DE102014004656A1 - Component, in particular structural component for a motor vehicle and method for producing a component - Google Patents

Abstract

The invention relates to a component, in particular a structural component for a motor vehicle, comprising a base body (12) formed of a heat-transformable steel, which is provided with a coating (14) at least in a partial area, comprising a first layer (16) and at least one at least zinc comprising second layer (18) arranged in register with said first layer (16), said first layer (16) disposed between said base body (12) and said second layer (18) and formed as a liquid metal embrittlement and diffusion barrier layer.

Description

The invention relates to a component, in particular a structural component for a motor vehicle according to the preamble of patent claim 1 and a method for producing a component according to the preamble of patent claim 7.

Such a component and such a method are for example from US 2012/0118437 A1 to be known as known. The component has a basic body formed from a hot-forming steel. The main body is provided with a coating at least in a partial area. The main body is thus a steel substrate which is coated. The coating has a first layer and at least one second layer. The first layer and the second layer are disposed in mutual overlay, the second layer comprising at least zinc (Zn).

The main body is, for example, a thermoformable sheet metal, wherein the base body is formed, for example, of boron steel. As part of a hot forming of the base body is exposed together with the coating high temperatures. Usually, a coating having at least two layers is also referred to as a "coating system". Two coating systems for hot-forming steel sheets are known from the general state of the art: a first of these coating systems is a hot-dip galvanizing, the second coating system being a fire-aluminizing. This means that the steel of the body is either hot-dip galvanized or fire-aluminized. Such hot-dip galvanized or hot-dip aluminized steels are used, for example, in mass production of press-hardened structural components, in particular for motor vehicles. Hot-dip galvanized steels offer good corrosion resistance due to the reduced electrochemical stress compared to the steel substrate (cathodic corrosion protection). As a result, the following phenomena are problematic in this type of coating: during hot forming liquid metal embrittlement occurs at high temperatures. Liquid zinc diffuses into grain boundaries of the steel substrate and causes cracking in the substrate. This phenomenon can be avoided by a two-stage transformation. Here, a conventional transformation takes place at room temperature. Subsequently, a press hardening takes place with a low degree of deformation. In this case, there is an evaporation of the zinc coating, which means a loss of corrosion protection material. Furthermore, an oxidation of the zinc coating takes place. As a consequence, these components are cleaned or blasted after the forming process, for example, to allow painting. The diffusion phenomena of iron into the coating, due to the processing temperatures during hot working, cause an increase in the iron content on the surface and a reduction in cathodic protection. As a result, red rust occurs on the component surface.

Hot-dip aluminized steels have good forming properties in single-stage press-hardening without liquid-metal embrittlement and cracking in the steel substrate. Such a coating results in stable corrosion products and cleaning of the hot formed product is not required. However, the following phenomenon is problematic in this type of coating: a fire aluminizing does not provide a galvanic protective effect. In other words, the component can not be protected from corrosion by the principle of the sacrificial anode. The diffusion phenomena of iron into the coating, due to the process temperatures during hot working, cause an increase of the iron content on the surface. As a result, red rust occurs on the component surface.

Object of the present invention is therefore to provide a component and a method of the type mentioned, in which the problems mentioned can be avoided.

This object is achieved by a component having the features of claim 1 and by a method having the features of claim 7. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the remaining claims.

In order to provide a component with a coating system in which the problems mentioned above can be avoided, it is provided according to the invention that the first layer is arranged between the main body, that is to say the steel substrate and the second layer, and is formed as a liquid metal embrittlement and diffusion barrier layer. In other words, the first layer, which is preferably applied directly to the steel substrate and arranged between the steel substrate and the second layer, acts as a barrier layer against liquid metal embrittlement.

In addition, the liquid metal embrittlement can be reduced or kept to a minimum by the high melting point of zinc cobalt (ZnCo) and zinc manganese (ZnMn) or zinc alloys of the second layer. In addition, a reduction in the diffusion of iron into the zinc layer or into the zinc-alloyed layer (second layer) can be reduced by the first layer, so that the occurrence of red rust can be avoided. Furthermore For example, the second layer formed as a zinc layer or zinc-alloyed layer offers cathodic protection against corrosion. Furthermore, stable corrosion products can be realized with a reduced dissolution rate by the alloy of zinc.

It has proved to be advantageous if the second layer is formed from ZnCo (zinc-cobalt) or ZnMn (zinc-manganese). In the coating system, moreover, the zinc evaporation can be reduced by the increased melting point in the alloy of zinc.

An advantageous embodiment is characterized in that the coating has at least one, in overlap with the first layer and the second layer disposed third layer, which is formed as oxidation or evaporation barrier layer or as passivation of the second layer. It is preferably provided that the first layer and the second layer between the main body and the third layer are arranged. The third layer can thus act as a cover layer, which is preferably applied directly to the second layer. By this applied cover layer, the zinc evaporation and the zinc oxidation can be reduced.

The steel substrate, that is, the main body is preferably formed of a hardenable steel or a deep-drawing steel, which may be, for example, a boron steel or manganese-boron steel and microalloyed steels.

The coating system, that is to say the coating, can be produced, for example, by a PVD method (Physical Vapor Deposition), a CVD (Chemical Vapor Deposition) method, a dipping method, a slurry method, galvanic or electrolytic processes as well as by thermal spraying.

As coating materials, in particular the first and the third layer, for example, at least one oxide, nitride, sulfide, carbide, hydrate, silicate, chromate, molybdate, tungsten, vanadate, titanate, borate , Carbonate, chloride or phosphate compound of a base metal are used. Here, the use of alkaline earth metals, alkali metals, semimetals and transition metals is also conceivable.

It has been found that particularly advantageous properties of the layers, in particular the first and the third layer, can be realized if materials from the following group are used: zinc, manganese, magnesium, cobalt, aluminum, chromium (III ), Molybdenum, titanium, tungsten, vanadium, boric oxide and zinc chromates, zinc molybdate, zinc tungstate, zinc vanadate, zinc titanate, zinc borate.

In addition, it has been found that metal phosphates of metallic salt of phosphoric or diphosphoric acid with metals from the following group are particularly suitable as coating material, in particular for the first and third layers: Cu, Mo, Fe, Mn, Sb, Zn, Ti, Ni. Co, V, Mg, Bi, Be, Al, B, Ce, Ba, Sr, Na, K, Ge, Ga, Ca, Cr, In, Sn.

In order to realize a high thermal stability, it is advantageous if the applied materials of the first and of the third layers have a melting point of at least 600 degrees Celsius in order to avoid the oxidation and the evaporation of lower layers and to reduce the liquid metal embrittlement.

Moreover, it has been found to be particularly advantageous if the first layer and / or the third layer are formed as a ceramic layer or coating. In particular, it is advantageous to form the first and / or the third layer as a ceramic coating with materials from the following group: MgAl ₂ O ₄ , TiAlN, TiAlO, CoO, SiO ₂ , Al ₂ O ₃ , MgO ₂ , MnO ₂ , Mn ₂ O ₃ , CaO, Fe ₂ O ₃ , ZnO, SnO ₂ , TiO ₂ , ZfO ₂ , Cr ₂ O ₃ .

Thanks to the high melting point, these ceramic coatings have very good properties for the diffusion barrier of zinc in the substrate as well as of iron in the coating.

The invention is based on the idea or the knowledge that in hot-formed components, in particular in press-hardened components, in particular two oxidation phenomena can occur. A first of these oxidation phenomena is effected, for example, on the vehicle by loading the component through an aqueous environment with salts. The second oxidation phenomenon can occur during component production itself. The second oxidation phenomenon is caused, for example, by an oxidizing environment during the heating phase of the press-hardening.

In order to avoid the first oxidation phenomenon, for example, anticorrosion layers can be used as the sacrificial anode. A sacrificial anode has a lower electrochemical potential compared to exterior alloys. For example, to avoid the second oxidation phenomenon, an additional cover layer (third layer) may be used. This cover layer has a barrier to oxidation of the underlying layers (second layer and first layer) and suppresses the Evaporation. The liquid metal embrittlement and the diffusion of iron into the coating are avoided by the use of an alloyed or ceramic layer in the form of the first layer with an increased melting point. For this purpose, it is preferably provided that the first layer is applied directly to the steel substrate, that is, the steel substrate touched.

Conventionally, anti-corrosion coating systems for steel sheets have been chosen to be as inexpensive as possible. For cold-formed sheets, this may be justified. In hot forming, however, the cost, especially the material cost, plays a minor role, since the process of hot working is in itself so costly that additional costs for producing the coating are negligible. Therefore, when selecting coating systems for hot stamped sheet metal, the main objective is to achieve the best possible corrosion protection, even if the associated coating system is costly in terms of application and / or material costs. This goal can be realized in the component according to the invention.

In particular, the use of a ZnMn layer or a ZnCo layer, in particular as a second layer, a particularly high corrosion protection effect can be achieved because ZnMn and ZnCo form stable corrosion products with a low dissolution rate after the formation of ZnCo and ZnMn intermetallic phases.

The invention also includes a method in which it is provided according to the invention that the first layer is arranged between the base body and the second layer and is formed as a liquid metal embrittlement and diffusion barrier layer in time prior to hot working. This means that the base body is hot-formed together with the coating, in particular press-hardened. Advantageous embodiments of the component according to the invention are to be regarded as advantageous embodiments of the method according to the invention and vice versa.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings;

These show in:

1 a schematic sectional view of a component according to a first embodiment, wherein a formed of a steel body of the component is provided with a coating comprising two layers; and

2 1, a schematic sectional view through the component according to a second embodiment, the coating having three layers.

In the figures, the same or functionally identical elements are provided with the same reference numerals.

1 shows in a schematic sectional view with a whole 10 designated component. The component is, for example, a structural component for a motor vehicle, in particular a passenger car. In particular, it may be in the component 10 to trade a body component of the motor vehicle. The component 10 has a basic body 12 on, which is formed of a heat-formable steel. As part of the production of the component 10 is formed for example as a steel sheet body 12 hot-formed, in particular press-hardened.

Out 1 is recognizable that the component 10 also a coating 14 having, with which the basic body 12 is coated. In other words, the main body 12 with the coating 14 Mistake. Preferably, the coating 14 before hot forming (press hardening) of the base body 12 Applied to this, so that's the coating 14 together with the main body 12 is thermoformed. The main body 12 is thus a steel substrate, which with the coating 14 provided, that is coated.

The coating 14 is formed as a coating system and has a first layer 16 and a second layer 18 on. The layers 16 and 18 are arranged in mutual overlap. The second layer 18 has at least zinc (Zn). This means that the second layer 18 of zinc (Zn), in particular of substantially pure zinc. By this is meant, for example, that the second layer 18 greater than 99 weight percent (wt.%) zinc. The second layer 18 may alternatively be formed from a zinc alloy (Zn alloy). It is preferably provided that the second layer 18 ZnCo or ZnMn, that is ZnCo (zinc-cobalt) or ZnMn (zinc-manganese) is formed. By using ZnMn or ZnCo a particularly high corrosion protection effect can be achieved.

The first shift 16 is in the coating system between the body 12 and the second layer 18 arranged and formed as liquid metal embrittlement and diffusion barrier layer.

The first shift 16 is directly on the steel substrate (basic body 12 ), thus touching the steel substrate and covers it at least in a partial area. The second layer 18 is right on the first layer 16 applied and covers the first layer 16 at least in one subarea. The first shift 16 is an intermediate layer which acts as a barrier against liquid metal embrittlement. In addition, the first layer works 16 as a barrier against diffusion of iron into the Zn having second layer 18 , As a result, the emergence of red rust in particular during hot forming of the body 12 with the coating 14 be avoided.

1 shows the component 10 according to a first embodiment. According to the first embodiment, the coating comprises 14 the two layers 16 and 18 , 2 shows the component 10 according to a second embodiment. The second embodiment differs from the first embodiment in that the coating 14 not just the first layer 16 and the second layer 18 but also a third layer 20 wherein the third layer 20 directly on the second layer 18 is applied and this covers at least a portion. Thus, the layers are 16 and 18 between the main body 12 and the third layer 20 arranged. The third layer 20 is a capping layer which acts as an oxidation or vapor barrier layer or as a passivation of the second layer 18 is trained. Through the on the second layer 18 applied cover layer in the form of the third layer 20 For example, zinc evaporation and zinc oxidation, at least during hot working, can at least be reduced. In addition, there is a reduction in the adhesion of liquid materials from the lower layers to the press tools for press hardening.

The coating 14 represents a two- or three-stage coating system, which allows the realization of particularly advantageous mechanical properties and at the same time the realization of a very good corrosion protection of hot-formed, in particular press-hardened, components.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2012/0118437 A1 [0002]

Claims (7)

Component, in particular structural component for a motor vehicle, with a base body formed from a hot-forming steel ( 12 ), which at least in a partial area with a coating ( 14 ), which is a first layer ( 16 ) and at least one at least zinc and in overlap with the first layer ( 16 ), second layer ( 18 ), characterized in that the first layer ( 16 ) between the main body ( 12 ) and the second layer ( 18 ) and formed as a liquid metal embrittlement and diffusion barrier layer. Component according to claim 1, characterized in that the coating ( 14 ) at least one in overlap with the first layer ( 16 ) and the second layer ( 18 ), third layer ( 20 ), which as oxidation or evaporation barrier layer or as passivation of the second layer ( 18 ) is trained. Component according to claim 2, characterized in that the first layer ( 16 ) and the second layer ( 18 ) between the main body ( 12 ) and the third layer ( 20 ) are arranged. Component according to one of the preceding claims, characterized in that the first layer ( 16 ) and the third layer ( 20 ) at least one oxide, nitride, sulfide, carbide, hydrate, silicate, chromate, molybdate, tungsten, vanadate, titanate, borate, carbonate, chloride or phosphate compound of a non-noble Have metal. Component according to one of the preceding claims, characterized in that the first layer ( 16 ) and the third layer ( 20 ) at least one metal phosphate of metallic salt of phosphoric or diphosphoric acid with metals from the following group: Cu, Mo, Fe, Mn, Sb, Zn, Ti, Ni, Co, V, Mg, Bi, Be, Al, B, Ce, Ba, Sr, Na, K, Ge, Ga, Ca, Cr, In, Sn. Component according to one of the preceding claims, characterized in that the first layer ( 16 ) and the third layer ( 20 ) as a ceramic coating with a material from the following group: MgAl2O4, TiAlN, TiAlO, CoO, SiO2, Al2O3, MgO2, MnO2, Mn2O3, CaO, Fe2O3, ZnO, SfO2, TiO2, ZrO2, Cr2O3 are formed. Method for producing a component ( 10 ), in which a basic body formed from a heat-transformable steel ( 12 ) at least in a partial area with a coating ( 14 ), which is a first layer ( 16 ) and at least one at least zinc and in overlap with the first layer ( 16 ), second layer ( 18 ) and then together with the coating ( 14 ) is thermoformed, characterized in that the first layer ( 16 ) between the main body ( 12 ) and the second layer ( 18 ) and formed as a liquid metal embrittlement and diffusion barrier layer prior to hot working.

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