Effect of Mg and Zn Contents on the Microstructures and Mechanical Properties of Al–Si–Cu–Mg Alloys

In this work, we report the effect of Mg and Zn additions on the microstructure and mechanical properties of Al–11Si–2Cu–0.4Zn (group M) and Al–11Si–2Cu–0.1Mg (group Z) alloys. The microstructures and fracture surfaces of these Al–Si–Cu–Mg–Zn alloys were examined by optical microscopy and SEM. The highest quality index values of 362.6 and 427.8 MPa were observed in the M1 (Mg = 0.1 wt%, Zn = 0.4 wt%) and Z1 (Zn = 0.03 wt%, Mg = 0.1 wt%) alloys in the heat-treated conditions, respectively. It has been observed that the addition of Zn from 1.5 to 3.11 wt% did not affect the mechanical properties of the Zn group alloys. However, an increase in Mg from 0.98 to 2.5 wt% resulted in a decrease in the strength and elongation of the Mg group alloys. The addition of 0.4 wt% Zn decreases drastically the ultimate tensile strength of the Al–11Si–2Cu–0.1Mg–0.4Zn alloy. It was observed that these alloys fracture in a mixed mode with quasi-cleavage and ductile fracture morphology.