Effects of yttrium addition on microstructural stability and elevated-temperature mechanical properties of a cast Mg–Zn alloy

Abstract

The effects of adding 2 wt% Yttrium (Y) element on the thermal stability, microstructural evolution, and mechanical properties of an Mg–4Zn alloy were examined. The as-cast microstructure of Mg–4Zn included α-Mg matrix and Mg7Zn3 intermetallic phase. Because of the low-thermal stability that is typical of this phase, there was a significant decrease in the strength of the Mg–4Zn alloy with an increase in the temperature. Addition of Y led to simultaneous refinement of the microstructure and improvement in both shear strength and microstructural stability of Mg–4Zn at high temperature. This was manifested by the retention of the initial fine microstructure and strength of the Y-containing material after a prolonged annealing at 370 °C. The decrease in the volume fraction of the unstable Mg7Zn3, and formation of the thermally stable Mg3Zn3Y2 intermetallic particles hindered the grain growth during annealing treatment, resulting in improved stability and strength at both ambient and elevated temperatures. Such behavior was in contrast to what was observed in the base material, showing substantial strength drop due to the excessive grain growth as a result of dissolved Mg7Zn3 particles at high temperature.