Numerical simulation analysis of pore suppression behavior in vacuum laser lap welding of Ta10W alloy

In this paper, the vacuum laser welding method was used to weld Ta-10 W alloy in the form of lap joint. Aiming at the porosity defects inside the welded joint, it is found that there are more porosity defects inside the weld joint when welding under the atmosphere, and the porosity size can reach tens of microns. With the gradual decrease of environmental pressure, the porosity defect in the weld decreases significantly and the porosity pole is easy to appear at the lap joint surface. When the environmental pressure is 20 Pa, the longitudinal section of the weld joint has no obvious porosity defect. The laser welding process can be characterized by the welding temperature field and flow field, where the flow of the molten pool and the dynamic behavior of the keyhole are closely related to porosity defects. This paper presents a novel 3D numerical model that characterizes the keyhole dynamic and melt flow behaviors during laser welding of Ta-10 W alloy under vacuum. The model accounts for the influence of environmental pressure on the laser welding process by optimizing the boiling point of the Ta10W alloy and the recoil pressure of the evaporated metal vapor jet. The numerical simulation results show two distinct keyhole closure modes corresponding to three primary flow trends in the overlapping melt pool. The keyhole closure is primarily driven by the collapse of the front and rear keyhole walls during the welding process. Compared to the atmospheric environment, keyholes in the vacuum environment exhibit lower collapse frequency and amplitude, indicating greater keyhole stability that can effectively reduce the occurrence of keyhole closure and the primary source of pore formation.