Numerical study on molten pool dynamics and solute distribution in laser deep penetration welding of steel and aluminum

Abstract

To shed new light on the molten pool behavior and transmission mechanism during the laser welding of dissimilar metals, a 3D transient numerical model was developed in this study. The fluid flow, heat transfer, keyhole evolution, and mass transport between two dissimilar metals were studied. The volume of fluid (VOF) method was used to track the free surface. The effects of recoil pressure and surface tension on the keyhole wall were mainly considered. The effects of convection, diffusion, and keyhole formation on the mass transfer were also considered. The relative importance of convection and conduction and the effects of various driving forces on the convection in the molten pool were analyzed in terms of dimensionless numbers. The results showed that the maximum temperature and liquid flow velocity of the molten pool slightly fluctuate at the peak value after the molten pool enters the quasi-steady state, and the stability of the keyhole depends on the dynamic balance between the recoil pressure and the surface tension. Because of the influence of the formation mechanism of the keyhole, the weld zone contained significant amounts of aluminum elements. The results also showed that the welding parameters significantly affect the transition layer thickness and element distribution, which is closely related to the weld quality. The numerical simulation results correspond well with the experimental results. This study provides new insights into the weld pool dynamics in the laser welding of dissimilar metals and can help guide the selection of the welding parameters.