Effects of Si content and Ca modification on microstructure and thermal expansion property of Mg–Si alloys

Abstract

The effect of Si content on the coefficient of thermal expansion (CTE) of Mg-xSi (x = 1, 2, 3, 4 wt%) alloys and the influence of Ca addition of Mg–4Si-yCa (y = 0.2, 0.4, 0.6, 0.8, 1.0 wt%) alloys have been studied. The results show that with the increase of Si content, the CTE of Mg–Si alloys decrease sharply, which is decreased by 30.8%, from 26 × 10−6/K of pure Mg to 17.98 × 10−6/K of Mg–4Si alloy at room temperature. When appropriate amount of Ca is added, the morphology of Mg2Si in Mg–4Si alloy can be effectively modified, but excessive addition of Ca about 1 wt% can result in over-modification. When 0.2 wt% Ca is added, the CTE of Mg–4Si alloy is increased compared with no Ca addition. After this, along with the increase of Ca content, the CTE of the alloy is decreased.