Microstructural evolution and aging behavior of Mg–4.5Y–2.5Nd–1.0Gd–0.5Zr alloys with different Zn additions

Abstract

Microstructures and mechanical properties of Mg–4.5Y–2.5Nd–1.0Gd–0.5Zr–xZn (x = 0, 0.5, 1.0, and 1.5; wt%) alloys under as-cast and peak-aged states were investigated in this work. The results indicate that the intermetallic phase components are closely dependent on Zn content. Under as-cast state, the dominant eutectic phase is Mg5RE in the alloys with 0 wt% and 0.5 wt% Zn additions while Mg5RE, 18R- and 14H-LPSO (long period stacking ordered) phases in the alloys with 1.0 wt% and 1.5 wt% Zn additions. After solution and peak-aging, the highest strength and hardness were obtained on the alloy with 0.5 wt% Zn addition. Transmission electron microscopy (TEM) characterizations revealed that there are denser and finer precipitates on basal (β′) and prismatic (γ″) planes, respectively. Therefore, the excellent mechanical performance of the alloy with 0.5 wt% Zn addition is mainly due to precipitation strengthening and grain boundary strengthening.