Effect of assembling clearance on welding characteristics of laser-MIG hybrid welding for aluminum alloy extrusions

Three-mm-thick 6106-T6 aluminum alloy extrusions were laser-MIG hybrid–welded with different assembling clearances. The effects of the assembling clearance on the weld formation, microstructure, and mechanical properties were investigated. When the assembling clearance was not larger than 0.7 mm, the optimum welding parameters were universal; the microstructure, microhardness distributions, tensile and fatigue properties were basically similar. To obtain well-formed weld formation, reducing the welding speed was more advantageous than increasing arc current when the assembling clearance enlarged. When the assembling clearances enlarged, the size of cellular dendrites increased and the width of columnar zone reduced; meanwhile, some cracks appeared near the fusion line. The lowest microhardness appeared closest to the fusion line in the heat-affected zone or existed away from the fusion line in the heat-affected zone when the assembling clearance was smaller or larger than 0.7 mm, and the lowest microhardness was reduced and the width of heat-affected zone increased as the assembling clearance enlarged. The average tensile strengths decreased when the assembling clearances enlarged. The tensile specimens fractured closest to the fusion line in the heat-affected zone or away from the fusion line in the heat-affected zone when the assembling clearances were smaller or larger than 0.7 mm, and the fracture features were changed from ductile to ductile-brittle–mixed failure mode. The median fatigue limit and safe fatigue limit were significantly decreased when the assembling clearance was larger than 0.7 mm, the fracture locations of fatigue specimens changed from in the weld zone to closest to the fusion line in the heat-affected zone, and the hot cracks that existed near the fusion line were the main reason.