Formation mechanism and conditions of fine primary silicon being uniformly distributed on single αAl matrix in Al-Si alloys

Abstract

In this study, solidification microstructure of fine primary silicon being uniformly distributed on single αAl matrix was obtained when adding Cu–9 wt%P alloy to an Al–10 wt%Si alloy melt or an Al–20 wt%Si alloy melt, stirring at 200 r/min for 12 min and cooling at the cooling rate of 16.3 K·s−1. The change law of silicon phase size with cooling rate and modified treatment parameters was determined by examining the solidification microstructures. It was found that ultrafine AlP was easily swallowed by primary silicon when the cooling rate was slow. The formation mechanism of superfine AlP particles, the growth process of αAl phase around primary silicon and the disappearance process of eutectic silicon were researched under intense stirring of the melt during the Cu–9 wt%P alloy modification. Moreover, the conditions under which fine primary silicon was uniformly distributed in single αAl matrix in hypereutectic Al-Si alloy were put forwarded. Finally, the formation mechanism of the solidification microstructure without eutectic Si in hypereutectic Al-Si alloy was analyzed.