Influence of Yb and Al-Ti-B Complex Modification on Microstructure and Performance of Hypereutectic Al-Si Casting Alloys

The microstructure evolution and mechanical properties of hypereutectic Al-20Si alloy containing rare earth Yb and Al-5Ti-1B refiner were investigated. The microstructures of the samples were characterized by optical microscopy, scanning electron microscopy, and electron probe microanalysis. Microstructural analysis demonstrates that the primary Si is significantly refined from a coarse polygonal, platelet-like or star-like shape into a fine blocky shape; the eutectic Si structure is modified from a coarse platelet-like/needle-like structure into fine particles or a fibrous structure; and the coarse alpha-Al dendrites are refined into fine equiaxed dendrites after addition mass fraction of 0.5% Yb and 0.3% Al-5Ti-1B complex. However, the primary and eutectic Si phases become coarser when the content of Al-5Ti-1B refiner reaches 0.4%. The mechanical properties of the Al-20Si alloy with different modifiers and different modifier concentrations were investigated by the tensile test. The results show that after combined addition of 0.5% Yb and 0.3% Al-5Ti-B the ultimate tensile strength and elongation of the prepared sample increase by 83.7% and 92.1%, respectively.