Study on the molten pool behavior and porosity formation mechanism in dual-beam laser welding of aluminum alloy

Based on the mechanism of dynamic coupling between molten pool and keyhole, a three-dimensional (3D) transient model for the dual-beam laser welding of aluminum alloy is established by considering the surface tension, Marangoni force, and recoil pressure. The morphology of the molten pool, porosity formation process, and the heat transfer mechanism during the process of laser welding under different parameters are analyzed. A double rotating 3D Gaussian heat source is used to represent the laser beam, and the volume of fluid method is used to track the gas-liquid free surface, and the gas-liquid interface force is transformed by the continuous surface force model. The results show that in the process of dual-beam welding, the interaction between the two keyholes enhances the fluid flow perpendicular to the spot line, and the shape of weld pool surface changes from elliptical to circular. Furthermore, welding speed and spot spacing have a significant effect on the shape of the molten pool. Furthermore, it is observed that dual-beam welding can improve the stability of the keyhole and reduce the maximum oscillation amplitude and the number of keyhole breakups. At a specific spot spacing, a unique process of separation and fusion is discovered in addition to the common stages of growth, maintenance, breakup, and shrinkage of the keyhole. The simulation results are in good agreement with the existing experimental results. Overall, this paper provides useful insights into the dynamics of the molten pool in dual-beam welding and reveals the molten pool behavior and porosity formation mechanism.