Heat treatment of Mg-Zn-Gd and Mg-Zn-Dy alloys for enhanced wear and corrosion properties

In this study, the effect of heat-treatment on the microstructure, wear, and corrosion behavior of Mg-1Zn-2Gd-0.4Zr (wt. %) and Mg-1Zn-2Dy-0.4Zr (wt. %) alloys were studied. The alloys were solution treated at 500 ℃ for 12 h, followed by ageing for 12 h at 225 ℃ (T6). The microstructural analysis revealed significant amount of secondary phase precipitation after heat treatment in both alloys, which resulted in 20 to 25% increase in the hardness. Wear tests performed between 200 and 400 ℃, at different loading conditions (10 N, 20 N), revealed improved wear resistance in Mg-Zn-Gd alloy samples compared to Mg-Zn-Dy alloy. Further improvement in the wear resistance was also observed after heat treatment. Delamination, abrasion, and oxidation were found to be dominant wear mechanisms in these alloys. Immersion corrosion tests carried out in 3.5 wt. % NaCl solution demonstrated that the heat treatment can significantly improves the corrosion resistance. This is primarily due to the changes in microstructure, i.e., uniform distribution of secondary phases after heat treatment.Among the two alloys, Mg-Zn-Gd alloy in heat-treated condition was found to exhibit relatively lower corrosion rate than the Mg-Zn-Dy alloy in both as-cast and heat-treated conditions.