Effect of Y addition on microstructure and corrosion behavior of extruded Mg–Zn–Nd–Zr alloy

In this study, the effect of Y addition (0, 0.5, 1 and 2 wt%) on microstructure and corrosion properties of Mg–6Zn–0.5Zr–1Nd (wt%) alloy was investigated. The alloys were produced by low-pressure die casting method and extruded at 300 °C and 400 °C after homogenization treatment at 400 °C for 24 h. The results showed that the as-cast microstructure of the alloy with no Y addition consisted of α-Mg, Mg–Zn binary and Mg–Zn–Nd ternary phases. With increasing Y additions, the average grain size showed a substantial decrease and two kinds of ternary Mg–Zn–Y ternary phases, designated as I-phase (Mg3Zn6Y) and W-phase (Mg3Zn3Y2) were formed. Homogenization treatment resulted in a partial dissolution of second phase particles. Extrusion process gave rise to a remarkable grain refinement due to the DRX mechanism. The extruded alloys with no Y addition exhibited poor corrosion resistance due to the strong micro galvanic coupling effect. Y additions up to 1 wt% improved the corrosion resistance due to the formation of finer grains, fine and uniform distribution of second phase particles and more stable oxide film.