Effects of cerium and phosphorus on microstructures and properties of hypereutectic Al-21% Si alloy

The influences of P and rare earth (RE) complex modifier on the microstructure and mechanical properties of hypereutectic Al-21% Si alloy were studied. The ingots were made by metal mold casting and the proportion of Ce+P ingredient was different. The result showed that the size of grains could be refined obviously by the Ce+P modifier and the effect of phosphorus was more intensive. The primary silicon crystal was refined, while the needle-like eutectic silicon was turned fibrous or short. The alloy mechanical properties had the best performance when 0.08% P and 0.6% Ce were added. The modification of primary silicon grains mainly depended on the heterogeneous nucleation mechanism, and the metamorphic mechanism of eutectic silicon was explained by adsorbing-twinning theory. The strengthening mechanism of experimental alloy was also discussed. The sigma(b), 20 degrees C increases from 236.2 to 287.6 MPa and sigma(b), 300 degrees C increases from 142.5 to 210 MPa.