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. ©2008 The Japan Institute of Light Metals.