Dynamic behavior of keyhole and molten pool under different oscillation paths for galvanized steel laser welding

This study investigated the dynamic behavior of a keyhole and molten pool under circular and zig-zag oscillating paths for laser welding on galvanized steel. A large variation in the length of the keyhole and a bulge in the molten pool resulted in more spatters in the case of a circular oscillating path, whereas a little spatter was observed in the case of a zig-zag oscillating path because of the relatively stable keyhole and molten pool observed by a high-speed camera. Numerical simulation results showed that zinc vapor entered the keyhole with a velocity of 93 m/s because of a large amount of zinc evaporation in the first half of the circular oscillating path, leading to a rapid increase in the keyhole size. In this case, the fluid near the rear wall of the keyhole accelerated to 1.7 m/s and gushed out of the molten pool in a spatter. In the zig-zag oscillating path, the zinc vapor continually entered the keyhole at a lower velocity, leading to a relatively stable keyhole. In this case, the maximum liquid velocity of the molten pool was 0.9 m/s, not reached the critical spattering velocity (1.36 m/s), thus no spatter occurred. These numerical results sufficiently explain the dynamic behavior of a keyhole and molten pool induced by zinc vapor, and an effective spatter suppression method is proposed.