Elevated Temperature Creep and Tensile Performance of Extruded Mg-10Ce Alloy

Fitness-for-service testing on an extruded magnesium (Mg) alloy containing 10 wt.% cerium (Ce) has been conducted to understand how increased level of Ce affects the elevated temperature properties of Mg. Optical and scanning electron microscopy revealed a 39.4% area percentage of the Mg12Ce phase. The Mg12Ce intermetallic was formulated along the grain boundaries in semi-circular, asymmetrical and polyhedral morphologies. The Mg alloy was subjected to a room temperature (RT) and 200 °C tensile test and a 200 °C staircase creep test. At RT, the Mg-10Ce alloy exhibited an ultimate tensile strength (UTS), total elongation and toughness of 271 MPa, 0.95% and 1.6 MJ/m3, respectively. At 200 °C, the alloy exhibited a UTS, 0.2% yield strength, total elongation and toughness of 111 MPa, 103 MPa, 43 % and 39.8 MJ/m3, respectively. The alloy exhibits an increase in RT strength and 200°C toughness compared to conventional Mg alloys (i.e., AE44, WE43 etc.). The staircase creep experiment revealed steady-state creep rates of 1.88 x 10− 8, 3.40 × 10− 7  and 2.00 x 10− 6  s− 1 for applied loads of 22, 40 and 55 MPa, respectively. The stress exponent (4.88) calculated between 20 and 40 MPa indicated that power-law dislocation climb and activated cross-slip of the pyramidal planes (101¯1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10\overline{1}1$$\end{document}) are the two dominant creep mechanisms, which are typical for high temperature and low-stress applications. The stress exponent (5.57) calculated between 40 and 55 MPa indicated that power-law breakdown dislocation climb and activated cross-slip of the basal planes (0002) were the two dominant creep mechanisms. A stress exponent value above 5 indicated that the alloy was moved into the transitional phase of creep between high-temperature/low-load creep and high-temperature/high-load creep. The alloy’s strong basal (0002) texture and high volume fraction Mg12Ce intermetallic contributed to its poor creep performance.