Effect of Zn addition on microstructure and mechanical properties of Mg-3Y-2Nd-0.5Zr alloy

Abstract

The effect of 0.5wt.% Zn addition on the microstructure and mechanical properties of Mg-3Y-2Nd-0.5Zr (WE32) alloy was investigated. The results indicate that WE32-0.5Zn alloy takes 48 h to reach peak hardness after solid solution treatment at 525 °C and aging at 200 °C, 10 h earlier than WE32 alloy, which implies an accelerated aging precipitation kinetics owing to the addition of 0.5wt.% Zn. A large quantity of fine-rod and rectangular block-like Zn-Zr precipitates in the α-Mg matrix are formed in the WE32-0.5Zn alloy, and numerous needle-like β1 phases are distributed at both ends of the Zn-Zr precipitates at peak-aged condition. In peak-aged condition, the ultimate tensile strength considerably increases from 263.2 MPa (WE32) to 309.6 MPa (WE32-0.5Zn), and the elongation dramatically increases from 4.3% (WE32) to 8.9% (WE32-0.5Zn). The β′ and β1 phases are the main precipitates of the WE32-0.5Zn alloy peak-aged at 200 °C. The β′ and β1 phases easily nucleate at the Zn-Zr precipitates, and the β1 phases are particularly likely to nucleate and grow at the interface between the two ends of the Zn-Zr precipitates, which accelerates aging precipitation kinetics and leads to a shorter time to achieve peak aging.