Laser-MIG hybrid welding of aluminium alloy extrusions for high-speed trains: effects of gap width on microstructure and properties

Abstract

6A01-T5 aluminum alloy extrusions with a thickness of 4.5 mm were welded by laser-MIG hybrid welding, and the effects of gap width on the microstructure and properties were studied in details. The results indicated that the priorities of the welding parameters on the tensile strength of joints were laser power, defocusing amount and arc current when the welding speed was constant. The gap tolerance of the optimal welding parameters could reach up to 1.1 mm. The morphology and size of the microstructures were similar when the gap width was no larger than 1.1 mm. The grain boundaries became obvious and even cracks appeared near the fusion line when the gap width increased to 1.5 mm. The microhardness distributions almost the same with the different gap widths: highest in the base materials zone, secondly in the heat-affected zone, then in the weld zone, and lowest near the fusion line. The microhardness values reduced in each zone except base materials when the gap width increased to 1.5 mm. The tensile strength reduced as the gap width increased, the specimens all fractured near the fusion line due to where had the lowest microhardness and the fracture showed ductile failure mode.