Spatter and Porosity in Gas-Metal Arc Welding of Magnesium Alloys: Mechanisms and Elimination

Recently, there has been a rapid increase in the use of Mg alloys for weight reduction, in an effort to improve fuel economy in the automotive industry. A versatile process for welding Mg alloys is needed. Gas metal arc welding (GMAW), though widely used for welding Al alloys, is still not used much for Mg alloys. The present study focuses on 1) 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 2) gas porosity, which has hardly been studied in GMAW of Mg alloys. The widely used AZ31 Mg (similar to Mg-3Al-1Zn) sheets were welded with its recommended AZ61 Mg (similar to 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. The much more severe gas porosity in Mg GMAW than Al GMAW was explained. 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.