Microstructure and Properties of ZM5 Alloy Repaired by Cold Welding

The repair of magnesium alloy castings is of great importance in terms of engineering and economic benefits. This study employs the cold welding technique to repair the ZM5 alloy, and the effects of current and preheating treatment on the microstructure and mechanical properties were investigated. The increase in current exacerbates the cracks, while the preheating treatment can effectively control them. However, the liquefaction cracks occur near the heat-affected zone after preheating at 300 °C. The microstructure of the repaired zone shows finer dendritic structure consisting of α-Mg and β-Mg₁₇Al₁₂ phases. After preheating treatment, the repaired zone shows the microhardness of 72 HV_0.1, higher than the non-preheating samples (65 HV_0.1), and the substrate (63 HV_0.1). The average tensile strength of the preheated samples is 110 MPa higher than the non-preheating samples, and reaching 88.7% of the substrate. The fracture mechanism for both the substrate and repaired samples was brittle failure.