Microstructure Evolution of Mg–4.3Zn–0.7Y–0.6Zr Alloy during Solution Heat Treatment

Abstract

The microstructure evolution in a Mg–4.3Zn–0.7Y–0.6Zr (mass%) alloy was investigated during solution heat treatment from 300 to 500°C for 12 h. In the as-cast and solution-treated at 300°C for 12 h states, the microstructures are consisting of I-phase and α-Mg. After solution treated at 400°C for 12 h, besides I-phase and α-Mg, some long strip precipitates-which are determined as Zn₂Zr phase-, also appear in the microstructure. In the solution-treated sample at 500°C for 12 h, small amounts of Zn₂Zr and Mg_0.97Zn_0.03 phases have been found. With the increase of heat treatment temperature, the phase constituents for different states are: α-Mg + I-phase (as-cast) → α-Mg + I-phase (300°C for 12 h) → α-Mg + I-phase + W-phase + Zn₂Zr (400°C for 12 h) → α-Mg + Zn₂Zr + Mg_0.97Zn_0.03 (500°C for 12 h).