AT10478U1 - COMPOSITE CASTING - Google Patents

Description

2 AT 010 478 U1

The invention relates to a method for producing a composite casting, wherein a melt of aluminum or magnesium or a base alloy of these metals is brought into contact and solidified with a solid body of aluminum or an aluminum-based alloy in a joining region.

Furthermore, the invention relates to a composite casting.

A current trend in automotive technology is the replacement of steel components with light metal components. By substituting heavy parts with lighter ones, a lower weight of motor vehicles should be achieved, which ultimately should also lead to reduced energy consumption in the operation of motor vehicles.

In the efforts to use the most lightweight components, it must not be forgotten that the steel parts substituting parts made of light metal should meet certain requirement profiles, for example, must have sufficient mechanical properties in order to be used as a substitute.

In this context, a main focus is on the production of light metal components in composite casting. Compound casting is a process in which two metallic materials, one of them solid, the other liquid, are brought into contact so that a diffusion resp. Reaction zone forms and a continuous metallic transition from one metal to another arises. The significance of composite castings made of light metals lies in particular in the fact that it is possible to optimally tune a component according to locally expected mechanical, thermal or other stress in its composition and its properties in certain areas. In other words, compound castings also allow a structured construction of components so that the most suitable material is located at each position.

In the manufacture of lightweight composite cast members, it is of interest to pair substrates of aluminum or an aluminum-based alloy with melts of aluminum, magnesium or a base alloy of one of these metals. However, there is the problem that bodies of aluminum or an aluminum-based alloy always carry on their surface due to the high affinity of aluminum for oxygen, at least a few nanometers thick layer of alumina. This aluminum oxide layer prevents wetting and a connection of the metallic melt or of the joining partner and results in that no continuous metallic bond is formed in the joining region.

As a result of the problem set out above, it often comes to forming an inhomogeneous joining zone with reduced strength and ductility, a poor thermal conductivity and unsatisfactory contact between the joining partners. The joining zone is virtually the weakest link in the chain and can be the starting point for a material failure in a component, for example a frame construction.

The invention now has for its object to provide a method of the type mentioned, which allows a production of a composite casting with improved joining zone.

Another object of the invention is to provide a composite casting having an improved joining zone.

The procedural object of the invention is achieved when a generic method comprises the steps of: a) optionally mechanical removal of alumina in the bond region of the solid body, b) treating the bond region of the solid with a zinc solution to obtain a zinc-containing layer, 3 AT C) depositing a further metallic layer on the zinc-containing layer, wherein the further metallic layer is formed from a metal or an alloy, which can or at least partially dissolve in the solid body and / or in the melt, without intermetallic Form phases that solidify below the melting or solidus temperatures of the solid 5 and the melt, d) contacting the solid body with melt in the joining region and solidification of the melt.

The advantages of a method according to the invention can be seen, in particular, in that an at least substantially defect-free joining zone is formed between the joining partners, that is to say the solid body and the solidifying melt. By the intended treatment of the joining region, that is the surface of the solid body which is to be brought into contact with the melt, with a preferably basic zinc solution, the adhering aluminum oxide is removed and instead of this a continuous zinc layer is formed. 15

As the inventors have realized, such a wet-chemically deposited zinc layer alone is not yet sufficient to ensure the desired bonding of the melt in each case, since upon heating of the solid prior to casting, the zinc can diffuse into the substrate or solid. In this case, the body made of aluminum or 20 an aluminum alloy is no longer protected and it forms again in the joining area, even before casting, alumina. According to the invention, it is therefore provided in a further step that a further metallic layer is deposited on the zinc layer. This layer is formed of a metal or alloy that can dissolve in the solid body and / or in the melt at least partially, without forming intermetallic phases 25, below the solidus temperatures of the solid and the melt solidify. On the one hand, diffusion is made possible by an edge solubility of the metal or the alloy, which supports the desired good binding. On the other hand, it is avoided that it finally comes to a solidification in the joining zone. The latter, due to concomitant reduction in volume, would lead to enormous stresses and, as experiments have shown, to cracks in the joining zone.

Suitable metals for the second metallic layer with respect to a mating partner will be readily apparent to one of ordinary skill in the art from well-known binary phase diagrams as exemplified by M. Hansen, McGraw-Hill, New York, 2nd Edition, 1958 or WG Moffatt, The Handbook of Binary Phase Diagrams, Schenec-Tady, New York, 1984).

In a final step, the solid body is contacted with melt in the joining region and the melt solidifies, wherein a substantially defect-free joining zone 40 is formed.

Optionally, a mechanical removal of aluminum oxide in the joining region of the solid body may be provided prior to deposition of the metallic layers. This is particularly recommended when a rolled part of aluminum 45 or an aluminum alloy is used as the substrate or body, since in this case a thickness of the aluminum oxide layer can be increased in comparison with a natural thickness in a non-rolled part. Also a chemical treatment, e.g. with caustic soda, can be provided in this regard. Thus, the zinc layer obtained by treating the joining region with, for example, a basic zinc solution is preferably formed within the scope of the invention with a thickness of 200 nanometers (nm) to 800 nm.

The thickness of the further metallic layer is preferably set to 1 micron (pm) to 30 pm, 55 preferably 3 pm to 20 pm. A thickness of 1 .mu.m, preferably 3 .mu.m, is sufficient to maintain a layer of sufficient thickness even when the solid is preheated and metal is diffused into the body. On the other hand, to ensure that a joining zone in the composite casting is as thin as possible, a maximum thickness of the further metallic layer can be limited to 30 μm, preferably 20 μm. 5

In order to form a continuous, homogeneous further metallic layer with a narrow size distribution of the deposited crystals, this is preferably deposited electrochemically. Alternatively, although associated with higher costs, deposition via the gas phase, e.g. by CVD, PVD or other coating methods. 10

If the solid substrate used or the body is cold-rolled, it proves useful to carry out the removal of aluminum oxide by grinding.

Further, in order to minimize the thermal stress on the solid body during the casting process, it may be advisable to contact the melt with the solid body at a melt temperature lower than a solidus temperature of the solid body becomes.

In a production of composite castings of aluminum or an aluminum alloy with a joining partner, which also consists of aluminum or an aluminum alloy, the further metallic layer is preferably formed from zinc or a zinc-based alloy.

With respect to a composite casting of aluminum or an aluminum alloy with magnesium or a magnesium-based alloy, it is advantageous if the further metallic layer consists of manganese or a manganese-based alloy, since manganese has sufficient surface solubility in magnesium but does not form low-melting intermetallic phases with magnesium ,

The further object of the invention is achieved by a composite casting which is produced by a method according to the invention.

A composite casting according to the invention is distinguished, above all, by an essentially defect-free joining zone, by means of which an excellent metallic bond is provided between the joining partners. Accordingly, composite castings according to the invention can be used in 35 heavy-duty vehicle components, for example frame structures, cylinder blocks or cylinder liners.

Other features, advantages and effects of the invention will become apparent from the context of the description and the following embodiments, with reference to which the inven-40 düng is shown even further.

Show it

I

Fig. 1: a schematic representation of a situation in which a coated body is brought into contact with a melt;

Fig. 2: A composite casting produced according to the invention;

3 shows a micrograph of a composite casting produced according to the invention in the region of a joining zone. so Example 1

A cold rolled aluminum alloy base sheet AIMg1 (1% by weight of magnesium, balance substantially aluminum) was worked with silicon carbide abrasive paper to reduce a thickness of the aluminum oxide film adhered to the sheet. Subsequently, the sheet was cleaned by exposing it to ultrasound AT010 478U1 at 55 ° C in a slightly basic solution. Thereafter, also for cleaning, the plate was pickled in a NaOH solution (pH> 13) at 55 ° C, whereupon the adhering film was removed with dilute HNO 3 solution.

Subsequent to the cleaning, the sheet was treated with a basic NaOH solution containing Zn (OH) 42 'or a zincate pickle known in the art, the remaining aluminum oxide layer dissolving and a continuous layer of zinc on the surface of the sheet Thickness of about 500 nm formed. Scanning electron micrographs showed that the thus deposited zinc layer was dense, which provided a desired oxidation protection.

Following the wet-chemical treatment, a further zinc layer was electrochemically deposited on the already existing zinc layer. A thickness of this further, second metallic layer was about 5 pm.

The thus treated sheet, with two zinc layers deposited thereon, was heated to about 200 ° C (higher temperatures, eg 600 ° C are possible) and then brought into contact with a melt whose composition of an aluminum base alloy AISi12 (12 weight percent silicon Balance essentially aluminum) and whose temperature was in the range of 650 ° C to 700 ° C. Thereafter, the resulting bond was allowed to solidify.

Fig. 1 shows an initial situation when contacting the coated sheet with a melt. In a first region 1, a substrate is present, which carries in a joining region, which carries a zinc layer 2 about 500 nm thick and a further zinc layer 3 deposited electrochemically thereon, about 5 μm thick. The zinc layers 2, 3 have a dual function: on the one hand, during the preparatory work, they reduce oxidation of the surface in the intended joining region, even at elevated temperatures. On the other hand, the zinc layers 2, 3 cause an excellent binding of the melt present in region 4 during solidification. This is demonstrated with reference to Fig. 2 which shows a composite casting made as described above. In a region A, the composite casting consists of the mentioned alloy AIMg-1, whereas in region B the composite casting consists of an alloy AISi12. Both areas are connected to each other via a common joint zone C, which joining zone C is formed substantially defect-free.

2 shows a light-microscopic photograph in the region of the joining zone C for the composite casting from FIG. 2. As can be seen, the joining zone C, which connects the regions A, B to one another, is free of cracks or other defects. Analytical investigations have shown that the zinc of the existing zinc layers 2, 3 (see FIG. 1) diffuses into the substrate or the solidifying melt during the production of the composite casting. These diffusion processes cause not only an excellent metallic binding of the solidifying melt, but in the end the zinc layers 2, 3 are hardly or not separately visible, unless a thickness of the zinc layer 3 is chosen to be too large (FIG. 3).

Other composite castings were prepared analogously, but with different compositions of aluminum melts, namely AISi7, AICu7 or AIZn7, also giving composite castings with excellently formed joining zones.

Example 2

A zinc layer having a thickness of 500 nm was applied to a cold rolled aluminum alloy sheet AIMg1 as described in Example 1. Subsequently, a layer of manganese was electrochemically deposited on the zinc layer, with a thickness of the second layer being 15 μm.

Claims (9)

6 AT 010 478 U1 The coated sheet was brought into contact with a magnesium melt having a temperature of 700 ° C. in the coated region, and the melt was then allowed to solidify. Similar to the embodiments according to Example 1, a substantially defect-free joining zone between the substrate made of an aluminum alloy and the cast magnesium part could again be obtained. In the context of the invention, a base alloy of a metal is understood to mean an alloy which consists predominantly of this metal. Claims 1. A method for producing a composite casting, wherein a melt of aluminum or magnesium or a base alloy of these metals is contacted and solidified with a solid body of aluminum or an aluminum-based alloy in a joining region, characterized in that the process comprises the following steps b) treating the joining region of the solid body with a zinc solution to obtain a zinc-containing layer, c) depositing another metallic layer on the zinc-containing layer, the further metallic Layer is formed of a metal or an alloy which can dissolve in the solid body and / or in the melt at least partially without forming intermetallic phases which solidify below the melting or solidus temperatures of the solid and the melt, d) Konta ktieren the solid body with melt in the joining area and solidification of the melt. 2. The method according to claim 1, characterized in that a thickness of the layer created in step b) is 200 nm to 800 nm. 3. The method according to any one of claims 1 or 2, characterized in that a thickness of the created in step c) further metallic layer 1 pm to 30 pm, preferably 3 pm to 20 pm. 4. The method according to any one of claims 1 to 3, characterized in that the further metallic layer is deposited electrochemically. 5. The method according to any one of claims 1 to 4, characterized in that the body is rolled and the removal of alumina is carried out by grinding. 6. The method according to any one of claims 1 to 5, characterized in that the melt with the solid body at a melt temperature, which is lower than a melting or. Solidus solid body temperature is brought into contact. 7. The method according to any one of claims 1 to 6, characterized in that the melt of aluminum or an aluminum alloy is formed and the deposited in step c) layer of zinc or a zinc-based alloy. 8. The method according to any one of claims 1 to 6, characterized in that the melt of magnesium or a magnesium-based alloy is formed and the deposited in step c) layer of manganese or a manganese based alloy. 9. composite casting obtainable according to one of claims 1 to 8. 7 7 AT 010 478 U1 Hiezu 1 sheet drawings