Processing modes in laser beam oscillating welding of Al-6Cu alloy

The laser-materials interaction is crucial for laser material processing. In this paper, the laser beam oscillating welding (LBOW) was used to weld 2219 Al-6Cu alloy sheets. The effects of the welding parameters on the processing modes were studied. The differences of weld geometry, internal defects, and microstructure between different modes were investigated, and the laser-material interaction process in different modes was discussed. The results indicated that the LBOW process could be classified into three modes: 1) keyhole mode, 2) transition mode, and 3) conduction mode. In the keyhole mode, the oscillating keyhole pushed the molten pool to flow in a vortex, which improved the stability of the welding process. As the oscillating speed increased, the laser absorption rate decreased. When the laser energy absorbed by the liquid metal was not sufficient to form a keyhole, the keyhole mode transited to the transition mode. In the transition mode, the laser irradiated into the vapor depression without multiple reflections. There was almost no porosity generated in the laser weld. When the laser absorption rate was further reduced, the transition mode changed to the conduction mode. In the conduction mode, the material evaporation hardly occurred. Only a few metals on the surface melted.