Reduction of hot crack formation in laser beam welding of high strength aluminum alloys with local creation of residual stresses by forming

• Applicants: Professor Dr. Thomas Graf; Professor Dr.-Ing. Mathias Liewald
• Subject Area: Joining and Separation Technology ; Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 389369540

High-strength aluminum alloys are often used to implement lightweight construction concepts in the automotive/aerospace industry. In connection with laser beam welding processes, however, such alloys are highly susceptible to the formation of hot cracks, which severely reduce the strength of joints. The previous project showed that additional stresses caused by inhomogeneous plastic deformations during the forming process of the parts significantly influence the formation of centerline hot-cracks in the subsequent joining process. These findings imply that the formation of hot cracks during laser beam welding can be prevented by the specific creation of compressive residual stresses in the area of the joining zone. Based on the results of the preceding project, in the follow-up project the conditions of compressive residual stresses required for the prevention of hot cracks are to be specified quantitatively. For this suitable forming processes for the creation of defined residual stresses in joining zones will be identified.The aim is to develop forming methods for the local generation of compressive residual stresses that prevent the formation of hot cracks in laser-welded joining zones of high-strength aluminum alloys. Taking into account the entire process chain in car body manufacturing, these forming methods should enable the optimization of the welding process already during the preceding forming process. The cross-process-chain optimization approach is intended to ensure higher overall process reliability on the one hand and greater degrees of freedom in the implementation of lightweight design concepts with high-strength aluminum alloys on the other hand.

• DFG Programme: Research Grants