Coupling Discharge Between Keyhole Plasma and Arc Plasma in Laser-Arc Welding of Mg Alloy

This paper describes investigations on the coupling discharge process between laser keyhole plasma and arc plasma during laser-arc welding. The characteristics of single arc plasma and hybrid arc plasma in different locations were comparably estimated by spectral diagnosing. Together with the plasma behavior observation, the particle exchanges between laser keyhole plasma and arc plasma were analyzed. During laser-arc welding, the keyhole plasma acts as an excellent connector between arc plasma and workpiece, resulting in a concentration of electron flows. Coupling discharge leads to the difference in the local thermodynamic equilibrium (LTE) state along the column of the hybrid arc plasma. The keyhole part of the hybrid arc plasma possesses the smallest deviation from absolute LTE state, which benefits the transfer from electric energy to heat during welding.