The effect of microstructure evolution on the elevated temperature mechanical properties in Mg-Sn-Ca system

Abstract

The effect of microstructural evolution on the creep properties in Mg-Sn-Ca system has been investigated. As-cast microstructure of Mg-Sn-Ca alloy consists of two or three phases depending on the Ca/Sn ratio, i.e. Mg2Sn, CaMgSn and Mg2Ca phases. Ternary CaMgSn phase has two types of morphology by its pseudo hyper-eutectic reaction with α-Mg; coarse rod-like primary or feather-like eutectic phase. Primary solidified CaMgSn phase exhibit negative effect on the tensile properties in spite of its high thermal stability up to 500°C. According to the creep test results, apparent stress exponent value (n = 7) indicates climb controlled creep mechanism by core diffusion above 150°C. Activation energy of Mg-5Sn-2Ca alloy (74 kJ/mol) is close to grain boundary diffusion for pure magnesium, 92 kJ/mol. Creep resistance is remarkably improved with the presence of Mg2Ca phase. © 2008 The Japan Institute of Metals.