Study on Eutectic Microstructure and Modification Mechanism of Al-Si Alloys

Abstract

Sb is an effective additive to modify eutectic Si of Al-Si alloys and the modification mechanism has not yet been studied very clearly. In this paper, computer aided cooling curve thermal analysis and microstructure assessment were carried out to investigate the modification effects of Sb on Al7SiMg alloy. The results show that the Sb addition amount of 0.1~0.25% has improvement effect on eutectic Si morphology, which can be further confirmed from the thermal analysis results. The addition of Sb decreases the eutectic growth temperature by 5 °C to 7.8 °C, indicating an undercooling effect resulted from Sb modification. Compared to that of short rods, a better eutectic Si morphology of nearly granular particles can be obtained in a faster cooling rate. The length of silicon has been gradually shortened as holding time increased to 2.5 h from 0.5 h, which means a long period modification effect of Sb in Al-Si alloys. Owing to undercooling resulted from Sb addition in Al-Si alloys, the refinement structure of eutectic silicon can be achieved.