This study elucidates how Cu content affects the microstructure and mechanical properties of Al–14.5Si–0.5Mg alloy, by adding 4.65wt.% and 0.52wt.% Cu. Different Fe-bearing phases were found in the two alloys. The acicular β-Al 5 FeSi was found only in the high-Cu alloy. In the low-Cu alloy, Al 8 Mg 3 FeSi 6 was the Fe-bearing phase. Tensile testing indicated that the low-Cu alloy containing Al 8 Mg 3 FeSi 6 had higher UTS and elongation than the high-Cu alloy containing the acicular β-Al 5 FeSi. It is believed that the presence of the acicular β-Al 5 FeSi in the high-Cu alloy increased the number of crack initiators and brittleness of the alloy. Increasing Cu content in the Al–14.5Si–0.5Mg alloy also promoted solution hardening and precipitation hardening under as-quenched and aging conditions, respectively. The hardness of the high-Cu alloy therefore exceeded that of low-Cu alloy.