EFFECT OF ZIRCONIUM ON HIGH TEMPERATURE TENSILE PROPERTIES OF PRECIPITATION-HARDENED MG-ND-ZN CASTING ALLOY

Influences of Zr addition on microstructure and tensile properties at ambient and elevated temperatures have been investigated for precipitation-hardened Mg-3%Nd-0.6%Zn and Mg-3%Nd-0.6%Zn-0.2%Zr casting alloys. By the addition of Zr, the average grain size of α-(Mg) phase decreases remarkably. In T6-treated state, the Mg-3%Nd-0.6%Zn-0.2%Zr alloy shows higher YS, UTS and elongation at RT, 150°C and 200°C, compared to those of the Zr-free alloy. Better creep resistance is observed in the Zr-containing alloy at 175°C/120MPa condition, while its creep resistance becomes inferior to that of the Zr-free alloy at 215°C/80MPa and 250°C/40MPa conditions. The discrepancy between tensile and creep properties is discussed in relation to microstructural evolution.