Composite material and method for producing same - Patents.com

Abstract

The present invention relates to a composite material and a method for producing the composite material, the composite material comprising a carrier layer made of an aluminum wrought alloy and an outer solder layer made of an aluminum solder alloy, the solder layer having partially exposed silicon particles (1a) on a surface (O) thereof, the silicon particles forming a first proportion of the total area of ​​the surface (O) of the solder layer. To ensure stable flux-free soldering performance, the solder layer has a rolled surface (O), the aluminum solder alloy has at least 0.1% by weight of bismuth (Bi), the first proportion being greater than 2.5%.

Description

[Technical field]

[0001] The present invention relates to a method for producing a composite material, and more particularly to a plated sheet metal or strip, the composite material comprising a support layer made of a wrought aluminum alloy and an outer solder layer made of an aluminum solder alloy disposed on one or both of the planar surfaces of the support layer, the solder layer having silicon particles partially exposed on a surface thereof, the silicon particles constituting a first area percentage of the total area of ​​the surface of the solder layer. [Background technology]

[0002] For flux-free CAB soldering (controlled atmosphere soldering), EP 2844466 discloses a composite with a support or core layer made of AA3003 wrought aluminum alloy and a solder layer made of AlSi12 aluminum solder alloy, the solder layer having partially exposed silicon particles on the surface. To produce these silicon particles on the surface, the solder layer of the finished composite is alkaline pickled after cold rolling. However, this also roughens the rolled surface of the solder layer to a relatively high degree.

[0003] These relatively abrasive silicon particles on the surface combined with increased surface roughness can disadvantageously result in increased tool wear on the sheet metal working tools, e.g., stamping tools, that dimension the composite in preparation for soldering. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent No. 2844466 [Non-patent literature]

[0005] [Non-Patent Document 1] DIN EN ISO2813:2014 [Non-Patent Document 2] DIN ISO2533 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is therefore to modify a composite material of the type mentioned at the beginning so that, despite its flux-free solderability, it can be subjected to a less abrasive mechanical separation process. [Means for solving the problem]

[0007] The present invention achieves the object stated with respect to a composite material by means of the features of claim 1.

[0008] Since the aluminum matrix has a rolled surface, it is possible to ensure that the silicon particles partially exposed on the surface only protrude up to the reference plane formed by the surrounding aluminum matrix. This correspondingly reduces the abrasive action of the silicon particles on the cutting tool, more specifically because such a rolled surface may also be superior in terms of a correspondingly reduced characteristic value for roughness. However, the composite material according to the invention (e.g. in the form of a sheet metal or strip) may not only be superior to low-abrasive processing or additional processing using mechanical cutting methods, but also retains its flux-free solderability. This is realized by the fact that the solder layer has a rolled surface and the aluminum solder alloy contains at least 0.1% by weight of bismuth (Bi) and the first area fraction is greater than 2.5%. This provides a flux-free solder composite that is ready for soldering, similar to other composite materials that do not have flux-free solderability.

[0009] For the desired flux-free soldering, it may prove sufficient if the first area fraction is, for example, less than 25%. Despite the exposed silicon particles, tool wear can be kept to a minimum, and even more so if the first area fraction is less than 20%, or, for example, less than 12%.

[0010] Preferably, the first area ratio is in the range of 3-10%. More specifically, from the lower limit of 3%, the soldering process and thus the soldering result can already be significantly improved. Up to the upper limit of 10%, tool wear can be kept relatively low, minimizing the maintenance costs of the tools used to process the sheet metal or strip.

[0011] When the aluminum solder alloy contains up to 0.40% by weight of bismuth (Bi), the wettability between the molten solder material and the materials to be joined can be significantly improved. Furthermore, this allows the gap size to be slightly higher, which can, however, be quite significant for the resulting soldering results.

[0012] The low-wear tool processing of the composite material can be recognized, for example, from the fact that the rolled surface (O) of the solder layer has a gloss value according to DIN EN ISO2813:2014 of at least 50 GU, measured at an angle of 60° and transversely to the rolling direction. Preferably, the gloss value according to DIN EN ISO2813:2014 is greater than 60 GU. For example, a measuring device called "micro-TRI-gloss S" from BYK-Gardner GmbH can be used for this measurement.

[0013] The rolling surface may have silicon particles pressed into the aluminum matrix of the solder layer, which are fixed therein by the rolling process. These pressed silicon particles result in an increase in silicon on the surface of the solder layer, which in turn results in an improved melting ability during soldering. It is therefore possible to ensure flux-free solderability of the composite material even after forming with a relatively high degree of deformation, which makes the composite material suitable for general-purpose applications.

[0014] Tool wear during further processing of the sheet metal or strip can be further reduced if the aluminum matrix of the solder layer on the rolled surface shapes the reference profile of the roughness profile of the rolled surface and the silicon particles partially exposed on the rolled surface do not protrude from this reference profile.

[0015] Preferably, the silicon particles are located in depressions in the rolling surface, for example, the depressions at least partially, in particular completely, surround one or more silicon particles, thereby interrupting the flat course of the oxide layer over the surface of the aluminum matrix and facilitating its destruction during flux-free soldering, which makes the composite more accessible to the user during soldering, more particularly when soldering without flux.

[0016] Preferably, the aluminum solder alloy contains 6.8 to 13 weight percent silicon (Si), 0.1 to 0.40 weight percent bismuth (Bi), and 0.10 to 0.40 weight percent magnesium (Mg). Preferably, the aluminum solder alloy may contain 8.5 to 12 weight percent silicon (Si). Preferably, the aluminum solder alloy may contain 0.1 to 0.3 weight percent bismuth (Bi). Preferably, the aluminum solder alloy may contain 0.2 to 0.35 weight percent magnesium (Mg).

[0017] The aluminum solder alloys, individually or in combination, are optionally Zinc (Zn) up to 1.2% by weight, more specifically up to 0.3% by weight; up to 0.6% by weight, more specifically up to 0.5% by weight, of iron (Fe); Maximum 0.2% by weight of titanium (Ti), Manganese (Mn) up to 0.2% by weight, more specifically up to 0.1% by weight; Copper (Cu) up to 0.2% by weight, more specifically up to 0.1% by weight; Strontium (Sr) at a weight percent of up to 0.03%, more specifically up to 0.02%, tin (Sn) up to 0.2% by weight, more specifically up to 0.1% by weight; Antimony (Sb) up to 0.2% by weight, more specifically up to 0.1% by weight.

[0018] Aluminum solder alloys contain residual aluminum and unavoidable manufacturing related impurities up to 0.05% by weight each and up to 0.15% by weight in total.

[0019] Preferably, the ratio of weight percent of magnesium (Mg) to bismuth (Bi) in the aluminum solder alloy is less than or equal to 4. In particular, this can prevent unwanted deposition in the soldering furnace. The ratio is in the range of 0.5 to 2.7, which can have a particularly advantageous effect on the destruction of the aluminum oxide layer during soldering. More particularly, this range can also ensure sufficient fluidity of the solder.

[0020] Preferably, the wrought aluminum alloy contains 0-1.6 wt% manganese (Mn), 0-0.90 wt% copper (Cu), and 0.05-1.0 wt% silicon (Si). Preferably, the wrought aluminum alloy may contain 0.8-1.4 wt% manganese (Mn). Preferably, the wrought aluminum alloy may contain 0.05-0.6 wt% copper (Cu). Preferably, the wrought aluminum alloy may contain 0.05-0.6 wt% silicon (Si).

[0021] The aluminum solder alloys, individually or in combination, are optionally Iron (Fe) up to 0.60% by weight, more specifically up to 0.45% by weight; Magnesium (Mg) up to 0.8% by weight, more specifically up to 0.6% by weight; Zinc (Zn) up to 0.15% by weight, more specifically up to 0.10% by weight; It may contain up to 0.20% by weight of titanium (Ti).

[0022] Wrought aluminum alloys contain residual aluminum and unavoidable manufacturing-related impurities up to 0.05% by weight each and up to 0.15% by weight in total.

[0023] For example, to achieve the advantages of the present invention, the wrought aluminum alloy is of type EN AW-1xxx, EN AW-3xxx, EN AW-5xxx, or EN AW-6xxx.

[0024] The present invention achieves the object stated with respect to a method for producing a composite material by means of the features of claim 13.

[0025] It is known that the composite material can be reduced to its final thickness (end thickness) by cold rolling. This cold rolling of the sheet metal or strip (also called sheet metal strip or metal piece) can be used to generate a rolled surface on the solder layer. According to the invention, an increase in the first area fraction of silicon particles exposed on the surface of the solder layer is achieved when the composite material is subjected to cold rolling with at least one cold rolling pass and, prior to the cold rolling pass of the at least one cold rolling pass, the surface of the solder layer is subjected to a pickling treatment with an acid cleaner, more specifically an alkaline acid cleaner. This makes it possible to reproducibly generate a surface with silicon particles but with a low roughness.

[0026] For example, if the cold rolling process includes several cold rolling passes, the pickling treatment may be performed between two cold rolling passes of the cold rolling process.

[0027] When performed immediately prior to the final cold rolling pass of the cold rolling process, a relatively high first area percentage of silicon particles exposed on the surface of the solder layer can be achieved.

[0028] Preferably, the pickling treatment is carried out between two cold rolling passes of the cold rolling process and / or just before the last cold rolling pass of the cold rolling process, in order to make the process easier for the user.

[0029] Preferably, an acid cleaner is used having a pH value in the range of 11.0 to 14.0. An acid cleaner having a pH value in the range of 12 to 13.5 may prove sufficient for the desired first area ratio.

[0030] Preferably, the pickling duration may be in the range of 15 to 300 seconds to allow to expose a sufficiently large number of silicon particles on the surface, which particles are sufficiently strongly bonded to the aluminum matrix. Even a pickling duration in the range of 30 to 90 seconds may be sufficient.

[0031] When the pickling depth is in the range of, for example, 1 to 7 μm, a sufficiently large number of silicon particles can be exposed by removing the aluminum matrix around the silicon particles.

[0032] Preferably, the alkaline pickling agent contains a sodium hydroxide solution having a concentration in the range of 8-16% by weight to provide a sufficient pickling effect.

[0033] The composite material according to the invention produced by the method according to the invention may be suitable for flux-free thermal joining methods, more particularly for soldering, preferably under protective gas, more particularly also for joining methods at atmospheric pressure according to DIN ISO 2533 (1013.25 hPa).

[0034] By way of example, the subject matter of the invention is illustrated in greater detail in the figures. [Brief description of the drawings]

[0035] [Figure 1a] FIG. 2 shows a top view of a first composite material A without pickling treatment. [Figure 1b] FIG. 2 shows a top view of a second composite material B that has been subjected to pickling treatment after cold rolling. [Figure 1c] FIG. 13 shows a top view of the third composite C after pickling treatment before the final cold rolling pass. [Figure 1d] FIG. 13 shows a top view of the fourth composite D after pickling treatment before the final cold rolling pass. [Figure 1e] FIG. 13 shows a top view of the fifth composite E after pickling treatment before the final cold rolling pass. [Figure 1f] FIG. 13 shows a top view of the sixth composite material F after pickling treatment before the final cold rolling pass. [Figure 2a] FIG. 1b is a diagram of a first area fraction of exposed silicon particles of composite material A of FIG. [Figure 2b] FIG. 1b is a diagram of a first area fraction of exposed silicon particles of composite material B of FIG. [Figure 2c] FIG. 1c is a diagram of a first area fraction of exposed silicon particles of composite material C of FIG. [Figure 2d] FIG. 1d is a diagram of a first area fraction of exposed silicon particles of composite material D of FIG. [Figure 2e] FIG. 1c is a diagram of a first area fraction of exposed silicon particles of composite material E of FIG. 1e. [Figure 2f] FIG. 1f is a diagram of a first area fraction of exposed silicon particles of composite material F of FIG. [Figure 3a] FIG. 1c shows an enlarged top view of a silicon particle. [Figure 3b] 3 shows a cut view along line III-III in FIG. 3a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] 1a to 1f show secondary electron images of the surface of each composite measured with a Zeiss EVO 40 scanning electron microscope with an accelerating voltage of 15 kV and a working distance of 10.5 mm.

[0037] Figures 2a-f each represent a silicon mapping at a resolution of 512x384 pixels and consist of 25 individual images. From these figures 2a-f, the first area fraction of partially exposed silicon particles in the inverted images was evaluated using Olympus Stream phase analysis software, where a threshold value of 160 was used in Figures 2a-d and a threshold value of 210 was used in Figures 2e and 2f.

[0038] To demonstrate the effect achieved, strips (often also called sheet metal strips) are also considered for six composites A-F in the form of sheet metal, which materials were produced by roll cladding the flat surface of a support layer (often also called a core layer) with a solder layer on both sides. Composites A-F are solder materials. The material thickness after roll cladding is 1.5 mm (millimeters) for composite A, 0.5 mm for composites B and C, and 1.0 mm for composites D-F.

[0039] The support layers of composites A-F each comprise a wrought aluminum alloy, which also contains residual aluminum and unavoidable manufacturing related impurities, each up to 0.05 wt. % and collectively up to 0.15 wt. %.

[0040] [Table 1]

[0041] The solder layers of composites A to F each have an aluminum alloy, and also contain residual aluminum and unavoidable manufacturing-related impurities, each up to 0.05 wt % and collectively up to 0.15 wt %.

[0042] [Table 2]

[0043] Composite material A: Composite A has a support layer made of an aluminium alloy of type EN AW-3xxx and a solder layer according to table 1 corresponding to type EN AW-4xxx.

[0044] FIG. 1a shows a secondary electron image of the surface of composite material A measured with a Zeiss EVO 40 scanning electron microscope with an accelerating voltage of 15 kV and a working distance of 10.5 mm.

[0045] According to Fig. 1a, a small number of silicon particles 1a are exposed on the surface of the composite material A. In Fig. 1a, these appear as light grey circular areas surrounded by a black border. The silicon particles 1a are surrounded by an aluminium matrix 2. Some silicon particles 1b are evident through the surface but are not exposed on the surface.

[0046] 2a shows a first area fraction of partially exposed silicon particles 1a in composite material A. The first area fraction is 0.4%.

[0047] Composite material B: In comparison with composite A, after the last cold rolling pass in the cold rolling process of the composite to its final thickness, composite B was subjected to an alkaline pickling process with a sodium hydroxide solution having a concentration of 12 wt. % and a pH value of 12.9 for a duration of 75 s.

[0048] Figure 1b shows an image of the surface of Composite B. A large number of silicon particles 1a are exposed on the surface of Composite A, visible as light-coloured areas in Figure 1b.

[0049] 2b shows the first area fraction of exposed silicon particles 1a of composite material B. The first area fraction is 24.3%.

[0050] Composite material C (material according to the invention): In the case of composite material C according to the invention, in an exemplary embodiment just prior to the last cold rolling pass in the process of cold rolling the composite material to its final thickness, it has been subjected to an alkaline pickling effect on the surface of the solder layer as described for composite material B.

[0051] Figure 1c shows an image of the surface of composite C according to the invention. The number of silicon particles 1a exposed on the surface of composite C, visible in Figure 1c as light grey circular areas surrounded by a black border, is increased compared to that of composite A in Figure 1a. However, this number is significantly less compared to composite B.

[0052] 2c shows the first area fraction of the partially exposed silicon particles 1a of composite material C. The first area fraction is 7.2%.

[0053] Composite material D (material according to the invention): Similarly, composite material D according to the present invention has been subjected to an alkaline pickling effect on the surface of the solder layer in an exemplary embodiment just prior to the final cold rolling pass in the process of cold rolling the composite material to its final thickness.

[0054] Figure 1d shows an image of the surface of composite material D according to the invention. The number of silicon particles 1a exposed on the surface of composite material D, visible as light grey circular areas surrounded by a black border in Figure 1d, is increased compared to that of composite material A in Figure 1a, which is a similar material to composite material C.

[0055] 2d shows the first area fraction of partially exposed silicon particles 1a of composite material C. The first area fraction is 4.2%.

[0056] Composite material E (material according to the invention): Composite E is a solder material having a support layer of type 6xxx aluminum alloy and a solder layer of type 4xxx.

[0057] Similarly, Composite E has been subjected to an alkaline pickling effect on the surface of the solder layer in the exemplary embodiment just prior to the final cold rolling pass in the process of cold rolling the composite to its final thickness.

[0058] Figure 1e shows an image of the surface of composite E according to the present invention. The number of silicon particles 1a exposed on the surface of composite E, visible as light grey circular areas surrounded by a black border in Figure 1e, is increased compared to that of composite A in Figure 1a, similar to that of composites C and D, but significantly less than that of composite B.

[0059] 2e shows a first area fraction of partially exposed silicon particles 1a of composite material E. The first area fraction is 7%.

[0060] Composite material F (material according to the invention): The composite material F according to the invention is a solder material having a support layer made of an aluminium alloy of type 1xxx and a solder layer of type 4xxx.

[0061] Similarly, composite material F has been subjected to an alkaline pickling effect on the surface of the solder layer in the exemplary embodiment just prior to the final cold rolling pass in the process of cold rolling the composite material to its final thickness.

[0062] Figure 1f shows an image of the surface of composite F according to the invention. The number of silicon particles 1a exposed on the surface of composite F, visible as light grey circular areas surrounded by a black border in Figure 1f, is increased compared to that of composite A in Figure 1a, similar to that of composites C, D and E, but significantly less than that of composite B.

[0063] 2f shows a first area fraction of partially exposed silicon particles 1a of composite material F. The first area fraction is 8%.

[0064] The sheet metal parts were cut out from the composites A-F in the form of sheet metal using a mechanical cutting process, i.e. stamping. Furthermore, the composites A-F were soldered together using the flux-free CAB soldering method, i.e. by flux-free soldering with another aluminium material of type 3003 at atmospheric pressure (1013.25 hPa) according to DIN ISO 2533.

[0065] Composite materials A to F are characterized by the following properties:

[0066] [Table 3] Table 3: Measurement data

[0067] As is clear from Table 3, composite material A cannot be joined flux-free using the CAB soldering method.

[0068] Flux-free soldering is in fact possible for composite B, but this composite B has the disadvantageous features of a pickled surface and protruding silicon particles 1a and of high wear of the exposed surfaces of the cutting or forming tools used to set the dimensions or shape of composite B before joining. In particular, the additionally worked surface topography of the solder material has a considerable influence on the frictional conditions and, as a further consequence, also on the springback during forming. The result of high springback after forming is a considerable deterioration of the measurement tolerances and problems for soldering in terms of the minimum gap width. Also, a high surface roughness has a negative effect on the maximum deformability of the material, since the lubricant cannot be uniformly distributed in the contact zone of the rough surface. Wear of the exposed surface is mainly caused by wear of the cutting edge at the exposed Si particles of the solder layer, which, due to the pickling, protrude considerably from the surface of the aluminum matrix.

[0069] Furthermore, Composite B also exhibits a lower gloss of 25 GU compared to the other composites, the gloss measured transversely and at an angle of 60° to the rolling direction, again indicating the negative properties of the surface of Composite B.

[0070] Different surfaces can be seen in the composites C, D, E and F according to the invention. Here, no Si particles are visible protruding from the surface contour of the aluminium matrix, as can be seen in Fig. 1c to 1f. The silicon particles 1a are pressed into the aluminium matrix of the solder layer due to the rolling, i.e. cold rolling, and thus the reference profile O of the roughness profile of the rolled surface O of the solder layer. B As can be seen in Figure 3b, this reference profile O B is formed by the aluminum matrix 2 of the solder layer on the rolling surface. B is formed by the highest peak of the roughness profile of the aluminum matrix 2. For example, the maximum roughness depth R t or R max is plotted for clarity. Thus, the wear of the exposed surfaces against the tool is significantly reduced and an improvement in the dimensional accuracy of the formed parts is established, which is necessary for flux-free soldering.

[0071] Also, depressions 3 are visible at the surface O of the solder layer at the silicon particles 1a (see FIG. 1c), which at least partially surround the pressed silicon particles 1a. The depressions 3 are embodied elongated in the rolling direction, which can be seen, for example, by the eye-shaped boundary contour in FIG. 1c. The silicon particles 1a are located in these depressions 3.

[0072] These indented silicon particles, shown in Figures 1c-1f, also have little or no effect on the surface gloss. As a result, composites C, D, E, and F can be expected to have approximately the same gloss as composite A. This is also evident from Table 1. However, in direct comparison with composite B, composites C, D, E, and F each have a significantly higher gloss. This difference in gloss between unpickled composite A, pickled composite B without subsequent cold forming, and composites C, D, E, and F that are pickled before the final cold rolling step is clearly shown in Table 1. This is also quite evident in Figures 1a, 1b, and 1c-1f. These figures clearly show that the first area fraction of exposed silicon particles is significantly increased by pickling before the final cold rolling. This is in comparison to the material without pickling, where there are also indented silicon particles on the surface, but in much smaller numbers.

[0073] The pickling process destroys the aluminum matrix surrounding the silicon particles, leaving the silicon particles on the surface where they protrude from the matrix.

[0074] The pickling removal of the aluminum matrix depends in particular on the temperature, duration and concentration of the pickling solution and can be easily adjusted in this respect with great flexibility. The shaping of the material by cold rolling carried out after the pickling process causes the silicon particles protruding from the surface after pickling to be pushed into the surface (aluminum matrix) due to their higher strength compared to the aluminum matrix. This increases the number of silicon particles on the surface and enriches the surface of the solder material with silicon. This enrichment, which cannot be achieved by a rolling process without an additional pickling treatment, leads to an improvement in soldering with flux and an improvement in the use in the field of flux-free soldering with the same material's shaping behavior.

[0075] Thus, the flux-free solder composites C, D, E and F according to the invention can be used in low-wear mechanical cutting methods, e.g. stamping, and do not require special measures in the geometrical treatment prior to the joining process.

[0076] It should be noted that in general, the German expression "insbesondere" can be translated into English as "more particularly". Features beginning with "more particularly" are considered optional features, which can be omitted and thus, for example, do not limit the claims. Similarly, the German expression "vorzugsweise" is translated into English as "preferably".

Claims

1. 1. A composite material, more specifically a plated sheet metal or strip, with a support layer made of a wrought aluminum alloy and an external solder layer made of an aluminum solder alloy provided on one or both of the flat surfaces of the support layer, the solder layer having partially exposed silicon particles (1a) on a surface (O), the silicon particles (1a) constituting a first area fraction of the total area of ​​the surface (O) of the solder layer, the solder layer having a rolled surface (O), the aluminum solder alloy containing at least 0.1 wt. % bismuth (Bi), and the first area fraction being greater than 2.5%.

2. 2. The composite material of claim 1, wherein the first area fraction is less than 25%, and more specifically, less than 20% or less than 12%.

3. 3. The composite material according to claim 1, wherein the first area ratio is in the range of 3 to 10%.

4. 4. The composite material of claim 1, 2 or 3, wherein the aluminum solder alloy contains up to 0.40% by weight of bismuth (Bi).

5. 5. The composite material according to claim 1 , wherein the rolling surface (O) of the solder layer has a gloss according to DIN EN ISO 2813:2014 of at least 50 GU, preferably greater than 60 GU, measured at an angle of 60° and in a transverse direction to the rolling direction.

6. A composite material according to any one of the preceding claims, characterized in that the rolling surface (O) has the silicon particles (1a) pressed into the aluminium matrix of the solder layer.

7. The aluminum matrix of the solder layer on the rolled surface (O) is aligned with a reference profile (O Ｂ ) and the silicon particles (1a) partially exposed on the rolling surface (O) are formed according to this reference profile (O Ｂ 7. The composite material according to claim 1, wherein the first and second layers are not protruding from the first and second layers.

8. A composite material according to any one of the preceding claims, characterized in that the silicon particles (1a) are located in depressions (3) of the rolling surface (O).

9. The aluminum solder alloy is 6.8 to 13 wt. %, more specifically, 8.5 to 12 wt. % silicon (Si); 0.1 to 0.40 wt. %, more specifically, 0.1 to 0.3 wt. % bismuth (Bi); 0.10 to 0.40 wt. %, more specifically 0.2 to 0.35 wt. % magnesium (Mg); Optionally, individually or in combination: Zinc (Zn) up to 1.2% by weight, more specifically up to 0.3% by weight; max 0.6 wt.%, more specifically max 0.5 wt.% iron (Fe); Maximum 0.2% by weight of titanium (Ti); Manganese (Mn) up to 0.2% by weight, more specifically up to 0.1% by weight; Copper (Cu) up to 0.2% by weight, more specifically up to 0.1% by weight; Strontium (Sr) in a weight percent of up to 0.03%, more specifically up to 0.02%, 0.2% by weight or less, more specifically 0.1% by weight or less of tin (Sn); Antimony (Sb) up to 0.2% by weight, more specifically up to 0.1% by weight; A composite material according to any one of claims 1 to 8, characterised in that it also contains residual aluminium and unavoidable production-related impurities, each of which contains a maximum of 0.05% by weight and, in total, a maximum of 0.15% by weight.

10. The composite material according to any one of claims 1 to 9, characterized in that the ratio of weight percent of magnesium (Mg) to bismuth (Bi) of the aluminum solder alloy is less than or equal to 4, more specifically in the range of 0.5 to 2.

7.

11. The wrought aluminum solder alloy is 0 to 1.6 wt. %, more specifically 0.8 to 1.4 wt. % manganese (Mn); 0 to 0.90 wt. %, more specifically 0.05 to 0.6 wt. % copper (Cu); 0.05 to 1.0 wt. %, more specifically, 0.05 to 0.6 wt. % silicon (Si); Optionally, individually or in combination: Iron (Fe) up to 0.60% by weight, more specifically up to 0.45% by weight; Magnesium (Mg) up to 0.8% by weight, more specifically up to 0.6% by weight; Zinc (Zn) up to 0.15% by weight, more specifically up to 0.10% by weight; Contains up to 0.20% by weight of titanium (Ti); A composite material according to any one of claims 1 to 10, characterised in that it also contains residual aluminium and unavoidable production-related impurities, each of which contains a maximum of 0.05% by weight and, in total, a maximum of 0.15% by weight.

12. 12. A composite material according to any one of the preceding claims, characterized in that the wrought aluminium alloy is of type EN AW-1xxx, EN AW-3xxx, EN AW-5xxx or EN AW-6xxx.

13. 13. A method for producing a composite material according to any one of claims 1 to 12, wherein the composite material is subjected to cold rolling in at least one cold rolling pass, and prior to the cold rolling pass of said at least one cold rolling pass, the surface (O) of the solder layer is subjected to a pickling treatment with an acid cleaner, more particularly with an alkaline acid cleaner.

14. 14. The method according to claim 13, characterized in that the pickling treatment is carried out between two cold rolling passes of the cold rolling process and / or immediately before the last cold rolling pass of the cold rolling process.

15. 15. The method according to claim 13 or 14, characterized in that a pickling agent having a pH value in the range of 11.0 to 14.0, more particularly in the range of 12 to 13.5, is used and / or the pickling duration is in the range of 15 to 300 s, more particularly in the range of 30 to 90 s.

16. The method according to any one of claims 13 to 15, characterized in that the pickling depth is in the range of 1 to 7 μm.

17. A method according to any one of claims 13 to 16, characterized in that the alkaline pickling agent comprises a sodium hydroxide solution having a concentration in the range of 8 to 16% by weight.

18. Use of a composite material according to one of claims 1 to 12, more particularly produced with a method according to one of claims 13 to 17, for flux-free thermal joining methods, more particularly soldering, preferably under a protective gas, more particularly at atmospheric pressure.

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