THERMAL ANALYSIS OF SOLIDIFYING SECONDARY PHASES IN THE EUTECTIC Al-Si ALLOY AND THE EFFECT OF Sr AND Fe

The effect of Fe and Sr on the evolution of the Fe intermetallic and eutectic phases in the Al-Si eutectic (Al-12.6 wt%Si) alloy was studied. Two different amounts of Sr (0.02 and 0.1 wt%) and three levels of Fe (0.5, 1 and 2 wt%) were introduced in the alloy; thermal analysis during solidification coupled with optical microscopy was carried out. It was observed, from the thermal data, that the nucleation temperature of the Fe intermetallic phase was not affected by the addition of Sr, but there is a significant variation in the heat balance during nucleation and growth of these phases during solidification. Additionally, the order of evolution of Al, Fe intermetallic phases and Si was significantly altered by the addition of Sr to the alloy. The analyses of the alloys showed that Fe intermetallic phase acted as nucleation sites for the Si phase while this was not the case in alloys with Sr addition. There is significant reduction in the size and alteration of the morphology of the Fe intermetallic phases when Sr was added to the alloy.