Heißrissvermeidung beim Schweißen von Aluminiumlegierungen mit einem Scheibenlaser

Due to the high beam quality of modern disk lasers slim and deep welds can be produced, which results in coarse columnar grain structures in the weld. Such kind of structures has a high hot cracking susceptibility. Therefore, the aim of this study is to increase the weld-ability of laser welds of aluminum alloys by grain refinement. In order realize grain re-finement, the weld grain structure was investigated depending on Ti/B-contents and weld parameters. Based on this investigation, the influence of grain refinement on hot crack susceptibility was studied via DELTA test. In order to understand the mechanism of hot cracking prevention by grain refinement, an analytical model was developed which de-scribes the influences of the grain structure and solidification parameters on the three main factors, which are the duration of the mush zone, the capillary pressure as well as the permeability of the dendritic network in the melt pool. The model reveals that the hot cracking susceptibility is determined by the combination of these three factors. With this model the hot cracking susceptibility can be quantitatively predicted depending on the grain structure. Thanks to this work, a knowledge base has been created for a controllable increase of weldability by grain refinement.