Effects of laser oscillation on metal mixing, microstructure, and mechanical property of Aluminum–Copper welds

Laser welding of dissimilar metals is important in many industrial applications. However, as dissimilar metals get mixed during the melting process, intermetallic compounds are often formed in the welds which can significantly undermine the electrical and mechanical properties of the welds. This poses a critical challenge to the widespread utilization of this welding technique. Compared with conventional line-scan laser welding, oscillating laser welding offers additional processing parameters to control the welding process. Although some work has been reported on oscillating laser welding of dissimilar metals, a mechanistic understanding of this process was still missing. The research objective of this work was to reveal the physical mechanisms and evaluate their relative significance to the fluid flow, metal mixing, and microstructure evolution in the molten pool in oscillating laser welding of dissimilar metals. A combination of experiments and simulations was leveraged to achieve the objective. Four fluid flows have been found to determine the metal mixing in the molten pool, and their dependences on the laser oscillating parameters were discussed. In addition, the thermo-solutal conditions of the molten pool solidification were quantified as functions of the laser oscillating parameters, and the effects of the thermo-solutal conditions on the final weld microstructures were analyzed.