Pore formation during laser beam welding of die-cast magnesium alloy AM60B - Mechanism and remedy

Weld metal porosity is a major concern during laser beam welding of magnesium alloys. This study seeks to identify both the mechanism of pore formation and a remedy for this problem during continuous-wave Nd:YAG laser beam Welding of die-cast magnesium alloy AM60B. Preexisting pores in the base metal coalesced and expanded during welding of this alloy and, as a result, large pores were commonly present in the weld metal. Unlike laser beam welding of aluminum alloys, the stability of the keyhole was not a major factor in pore formation during laser beam welding of alloy AM60B. The porosity in the fusion zone increased with the increase in heat input, i.e., increase in the laser power and decrease in the welding speed. It was found that well-controlled remelting of the fusion zone led to removal of gas bubbles and reduced porosity in the fusion zone.