Effect of in situ γ-Al2O3 particles on the microstructure of hypereutectic Al-20%Si alloy

In the present study, the effect of in situ γ-Al2O3 particles on the morphology and size of the primary and eutectic Si phases in hypereutectic Al-20%Si alloy has been investigated. Microstructural analyses demonstrates that in situ γ-Al2O3 particles significantly refined primary Si crystals from coarse polygonal and star-like shape to fine blocky shape with smooth edges and corners. The eutectic Si structure was modified from the coarse acicular structure to fine flake-like morphology that is intermediate between acicular and coral-like fibrous structure. In addition, the modification mechanism of in situ γ-Al2O3 particles on Al-20%Si alloy was also discussed.