Mechanism and Elimination of Spatter and Porosity in Gas-Metal Arc Welding of Mg Alloys

The original objective of this study to make GMAW a versatile process for welding Mg alloys and reduce the Spatter, which can cause 50% or more loss of the filler metal and which has long hindered the use of GMAW for Mg alloys, and Gas porosity, which has hardly been studied in GMAW of Mg alloys. The widely used AZ31 Mg (~ Mg-3Al-1Zn) sheets were welded with its recommended AZ61 Mg (~ Mg-6Al-1Zn) welding wire. Spatter was very severe with conventional Mg GMAW as expected. The mechanism for spatter was established. In order to suppress spatter, the use of CSC-GMAW for welding Mg alloys was explored, which is an advanced GMAW process with controlled short circuiting (CSC).Spatter was eliminated and the reason explained. However, with either process severe gas porosity was encountered, much worse than that in Al GMAW. The porosity-formation mechanism was established. Porosity was eliminated either by cleaning the welding wire with sandpaper before welding or baking the welding wire before welding. Recommendations for preventing gas porosity in Mg GMAW based on the present study were made to both the manufacturers and users of Mg welding wires.