Comparative study on successive and simultaneous double-sided laser beam welding of AA6056/AA6156 aluminum alloy T-joints for aircraft fuselage panels

Double-sided laser beam welding—successive and simultaneous—is a promising method for joining the skin-stringer T-joints in the aircraft industry, because higher production efficiency and lower airframe weight can be achieved. In this work, a comparative study on the microstructure, mechanical properties, and porosity defects of the successive and simultaneous double-sided laser beam-welded AA6056-AA6156 aluminum alloy T-joints was conducted. The results indicate that there are no significant differences in the microstructure near the fusion line in the two cases, but the microstructure characteristics are markedly different at the centre of the fusion zone. The micro-hardness of the simultaneous weld fusion zone is lower than that of the successive weld unaffected fusion zone but higher than that of the successive weld reheat region. Lower head tensile strength and higher hoop tensile strength are obtained for the successively welded specimens. For the two T-joints, the failure propagates along the fusion layer upon tensile loading, but their final fracture positions are distinctly different. The radiographs of the optimized successively and simultaneously welded T-joints show that many porosity defects exist in the successively welded T-joints, whereas there are very few and even no porosity defects exist in the simultaneously welded T-joints.