Effects of thermal treatment on precipitate shape and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Precipitation reactions in a Mg–8Gd–4Y–Nd–Zr alloy have been investigated using TEM, HREM, hardness measurements and tensile testing. Globular β′ precipitates, which were different from the typical plate-shaped β′ precipitates usually observed in Mg–Gd-based alloys, were detected in the 160 °C/192 h-aged sample. Instead of dissolution and then precipitating as plate-shaped β′ precipitates, the formed globular β′ precipitates grew up when further aged at 215 °C, which resulted in the decrease in strength comparing with that of the 215 °C single-stage aged samples. Two-stage ageing treatments on the alloy demonstrated that ageing 192 h at 150 °C plus 16 h at 215 °C made the ultimate strength and the yield strength improved 17 MPa and 13 MPa, respectively.

► We observed the globular β′ precipitates in Mg–8Gd–4Y–Nd–Zr alloy. ► We investigated the effect of globular precipitates on mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy. ► Pre-aged at 150 °C can improve the strength of the alloy.