Mechanical Properties of Newly Developed Age Hardenable Mg-3.2 mol%Gd-0.5 mol%Zn Casting Alloy

Abstract

A new Mg-Gd-Zn-base cast alloy was developed for high strength casting products. Effects of Zn content on microstructures and tensile strength were investigated. Both Mg-3.2%Gd-0.5%Zn-0.2%Zr (in mol%, 0.5GZ) and Mg-3.2%Gd-0.75%Zn-0.2%Zr (0.75GZ) alloys showed remarkable age hardening by precipitation of β′ phase with bco structure as similar to Mg-Gd-Y-Zr alloy. The precipitates are finer and denser than those of Mg-Gd-Y-Zn-Zr alloy by Zn and a large amount of Gd addition. Mg₃Gd compound particles remained at grain boundaries after solution treatment. Long period stacking ordered (LPSO) phase did not form. It is considered that Mg₃Gd particles suppressed grain coarsening during the heat treatment, and provided fine grain structure of about 30 μm in diameter. Tensile strength of the T6-treated 0.5GZ alloy was 410 MPa at room temperature and the high strength was kept by 473 K.