Improved mechanical properties in cast Al-Si alloys by combined alloying of Fe and Cu

Al-Si eutectic alloys with the following composition (wt.%), 13.0 Si, 3.0-5.0 Cu, 0.3-0.8 Fe,<0.3 Ni,<0.15 Ti,<0.4 Mg and<0.6 Mn, were prepared by metal mold casting. The microstructure and fracture of these alloys were examined using SEM and TEM. It has been shown that Fe-rich and Cu-rich phases are solidified or precipitated in the form of a Chinese script or blocky α-Fe (Al₁₅(Fe, Mn)₃Si₂) and θ(Al₂Cu) at the grain boundaries of α-Al dendrites. The ultimate tensile strength (UTS) and elongation of the alloy with 3.0% Cu and 0.3% Fe reach 310 MPa and 3.2%, respectively. By increasing Cu content to 5.0% and Fe to 0.8%, the UTS of Al-Si alloy is further enhanced to 336MPa. It was observed that these Al-Si alloys fracture in a mixed mode with quasi-cleavage and ductile fracture morphology.