Pores in TIG Welding of Die Casting AZ91D Magnesium Alloy

The plates of die casting AZ91D magnesium alloy were autogenously welded by tungsten inert gas welding (TIG) processing. The effect of welding currents on porosity was investigated. The characteristic and formation mechanism of pores in different zones in the weld were also analyzed. The results indicate that pores are mainly present in the subsurface and near the fusion line in the weld. The area of convexity, melting and porosity all increase with the increasing welding currents. Pores in the subsurface are induced by hydrogen, which results mainly from the base metal. And pores in the center of weld, influenced by the fluid force and buoyancy, are not a serious problem. However, pores in the partially melted zone have few chances to float out of the molten pool, because of the effect of fluid force and the high viscosity of molten metal, which results in a great number of large pores in the partially melted zone.