The Effects of Sc on the Microstructures of Hypereutectic Al-Si Alloys

Abstract

Sc has been known to be an very effective ppt-hardening element in Al and Al alloys and also to be effective in modification of eutectic Si in hypoeutectic Al-Si alloys. The modification mechanism of Sc is different from that of the traditional modifier Sr in Al-Si alloys. In the present study the effects of Sc on the primary and eutectic Si in hypereutectic Al-Si alloys were investigated with evaluating the microstructures with OM, EPMA and EBSD methods. The results represent that Sc has only a small effect on primary Si when added less than <TEX>$0.8wt\%$</TEX>. However, when Sc addition leading to the precipitation of metallic Sc within primary Si reaches <TEX>$1.6wt\%$</TEX>, very coarse primary Si occurs.