Achieving defect-free repair in ZM6 magnesium alloy through cold metal transfer welding combined with preheating

The application of Cold Metal Transfer (CMT) welding technology for defect repair in cast magnesium alloys presents substantial research significance. Nevertheless, research in this field is still in its nascent stage, requiring further systematic investigation. This study investigates the effects of preheating temperature, wire feeding speed, and heat treatment on the microstructure and mechanical properties of CMT-repaired ZM6 magnesium alloy castings. The repair zone consists of fine equiaxed α-Mg grains with Mg₁₂(Nd,Zn) phases precipitated at grain boundaries. The tensile strength increases with the increase of preheating temperature but decreases with the increase of wire feeding speed. However, the elongation after fracture decreases with the increase of both preheating temperature and wire feeding speed. Optimal properties are achieved at 400 °C preheating and 5.5 m/min wire feeding speed, yielding tensile strength of 184.52 MPa and elongation of 8.6%—improvements of 17.68% and 88.18% over the base metal, respectively. Post-weld heat treatment increases grain size and tensile strength but reduces ductility. The heat-affected zone (HAZ), where grain boundary precipitates undergo partial melting due to arc heating, is identified as the weakest region. This study develops a high-strength cold metal transfer (CMT) repair welding process and elucidating the mechanism by which CMT repair welding parameters influence the tensile strength of the repaired joints. The mechanical properties and repair welding efficiency of the developed CMT repair welding are significantly higher than those of traditional manual tungsten inert gas (TIG) repair welding.