Overlap joining of EN AW 7075 with laser beam welding in vacuum Fügen von EN AW 7075 im Überlappstoß mit dem Laserstrahlschweißen im Vakuum

Abstract

The integration of EN AW 7075 aluminium in Body in White structures is a promising way to achieve weight savings, which in turn can make a significant contribution to reducing CO₂-emissions. However, due to hot cracking susceptibility, conventional welding technologies offer limited possibilities to join the material. Therefore, laser beam welding in vacuum is introduced as a comparatively new joining technique. The investigations show, that it is possible to weld the EN AW 7075 alloy in an overlap joint configuration without pores or microcracks appearing in the weld seam. The weld seam has a very fine-grained structure, which presumably has a favourable effect on hot cracking mechanism. The prevention of cracking is likely due to the lower temperature gradient between the capillary wall and the fusion line caused by the low evaporation temperature due to the reduced pressure. The reduced temperature results in lower residual stresses, which presumably has a positive effect on the tendency to hot cracking. In addition, the fine-grained structures can absorb strain better than coarse grain structures, that usually occur in conventional laser beam welding.