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 336 MPa. It was observed that these Al–Si alloys fracture in a mixed mode with quasi-cleavage and ductile fracture morphology.