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

在汽车/航空航天工业中，高强度铝合金经常被用来实现轻量化的结构概念。然而，在激光焊接过程中，这类合金非常容易形成热裂纹，这严重降低了接头的强度。先前的研究表明，零件在成形过程中塑性变形不均匀产生的附加应力对后续连接过程中中心线热裂纹的形成有重要影响。这些发现表明，激光焊接过程中热裂纹的形成可以通过在连接区产生特定的压缩残余应力来防止。根据前一个项目的结果，在后续项目中，将定量地规定防止热裂纹所需的残余压应力条件。为此，将确定在连接区产生定义的残余应力的合适的成形工艺。目的是开发局部产生压缩残余应力的成形方法，以防止在高强铝合金的激光焊接接合区中形成热裂纹。考虑到车身制造中的整个工艺链，这些成形方法应该能够对前一成形过程中已经进行的焊接工艺进行优化。跨工艺链优化方法的目的是一方面确保更高的整体工艺可靠性，另一方面确保高强度铝合金在实现轻量化设计概念时具有更大的自由度。

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.