Effect of Complex Modification on Microstructure and Mechanical Properties of Hypoeutectic Al–Si

Hypoeutectic Al–Si alloy was modified by Al–5Ti and Al–3P alloys. The microstructure, fracture morphology, and mechanical properties of the alloys were characterized using optical microscopy, scanning electron microscopy, and a universal electronic testing machine. The results show that there was more primary α-Al phase in the Al–7Si alloy modified with 0.5 wt.% Al–5Ti and Al–3P compared to that modified with 0.5 wt.% Al–5Ti alone. With increased Al–3P, the area fraction of α-Al phase in the complex modified Al–7Si alloy decreased. For 0.1 wt.% Al–3P, eutectic silicon appeared as short rods or flakes, distributed uniformly in the Al–7Si alloy. Compared with hypoeutectic Al–Si alloy modified with 0.5 wt.% Al–5Ti, the relative amount of α-Al phase decreased and the amount of eutectic microstructure increased in the complex modified alloy with increased Si content. The complex modified Al–7Si alloy exhibited 10% higher tensile strength, 21% higher elongation, and presented ductile fracture.