Parameter Optimization of Gas Tungsten-Arc Repair Welding Technique in Mg-6Gd-3Y-0.5Zr Alloy

The feasibility of gas tungsten-arc repair welding was studied in Mg-6Gd-3Y-0.5Zr alloy. The processing parameters were optimized by sequential experiments including comparative study to find proper filler material and the type of welding groove by butt welding, and the investigation of influence of preliminary heating, area of repair welding, post-weld heat treatment and thickness of welding plate on the mechanical properties of welded joints. In addition, the analysis of microstructure and tensile properties of Mg-6Gd-3Y-0.5Zr alloy was performed for comparison with welded joints. The results showed that the microstructure in as-cast condition was characterized by equiaxial -Mg and eutectic phase, including Mg-24(Gd,Y)(5) and Mg-5(Gd,Y) phase. The strength was improved greatly after T6 treatment, while the ductility was remarkably decreased. The filler material and the type of welding groove were chosen as Mg-6Gd-3Y-0.5Zr alloy and V-type, respectively. The optimal process parameters of repair welding consisted of preliminary heating, T6 treatment after welding, 4mm-thickness plates and welding area with the diameter of phi 15mm. The tensile strength of welded joints reached the maximum value up to 295MPa, equivalent to 99.7% of base material.