Effects of a new dual-beam oscillating laser welding technique for aluminum alloy joints: Microstructure, properties, and formation mechanism

To optimize the welding process and joint performance of laser-welded aluminum alloys, a novel dual-beam oscillating laser welding technique was employed in this study. Specifically, by adjusting the power ratio of the composite beams and integrating the temperature field simulation, an intrinsic relationship was established among the composite beam process, microstructure, and joint performance. The results indicated that the primary laser beam ensured the welding efficiency and molten pool stability. The oscillation of the auxiliary laser achieved an orderly agitation within the molten pool, collectively refining the grains, destabilizing the grain growth, and establishing new orientations. Such a disruption led to the formation of fragmented fine grains with large grain misorientation angles and high geometrically necessary dislocation densities, as well as regulated temperature gradients in the central region and tiny equiaxed grains with dispersed orientations. Moreover, the power ratio between the primary and auxiliary beams was identified as a critical factor affecting the strength and ductility of the weld. A low power ratio induced keyhole instability, increased defects, and reduced joint performance, whereas a balanced power ratio refined the microstructure and enhanced the joint strength. With an optimal ratio of 950 W (primary) to 450 W (auxiliary), consistent penetration and stable internal oscillations were achieved, thereby improving the overall weld quality.