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Project leader: Prof. Dr.-Ing. Volker Wesling; Prof. Dr. rer. nat. Harald Schmidt
Funding period: 11/2021 - 10/2024
Funding body: DFG
Researchers: Sascha Brechelt, M. Sc.; Jochen Junge, M. Sc.
The use of aluminum alloys in the production of vehicle bodies has great potential for reducing the overall vehicle mass. As a result, the specific fuel consumption and the exhaust emissions produced can be reduced and the effective range of BEV (Battery Electric Vehicle) can be further increased. However, the processing of aluminum alloys using resistance spot welding is subject to significantly accelerated thermal and metallurgical degradation of the electrode caps. While up to 6,000 welds are possible with steel materials before the quality limits are reached, only 1,200 welds are possible with zinc-coated steel materials and 50 welds with aluminum alloys. The causal diffusion-based mechanisms require frequent replacement or repair of the electrodes used, which reduces the cost efficiency of resistance spot welding. Within the DFG project, diffusion barrier layers in the µm range are to be developed by means of PVD (physical vapor deposition), which withstand the stresses occurring in the welding process and significantly reduce the degradation processes that occur.
The degradation process, which is the cause of premature failure of electrode caps, depends among other things on the level of electrical contact resistance and the local current density in the corresponding contact area. Targeted structuring of the electrode surfaces is intended to overcome the natural oxide layers of the aluminum substrates and achieve a homogeneous metallic contact. Together with the development of composite thin-film layers made of metallic and highly conductive ceramic components, effective diffusion barriers are also to be developed to protect the electrodes. The temperature-dependent properties of qualified coating systems are investigated in diffusion experiments. In addition, the coating systems produced are evaluated using electron microscopy and nanoindentation, and the coating adhesion strength achieved is assessed using scratch tests. The aim is to fully elucidate all mechanisms that contribute to the degradation process in the copper-aluminum material system. In addition, the measures developed to prevent degradation are to be tested on a laboratory and user scale.