An aluminum casting alloy has 8.5-9.5 wt. % silicon, 0.5-2.0 wt. % copper (Cu), 0.27-0.53 wt. % magnesium (Mg), wherein the aluminum casting alloy includes copper and magnesium such that 4.7≦(Cu+10Mg)≦5.8, and other elements, the balance being aluminum. Selected elements may be added to the base composition to give resistance to degradation of tensile properties due to exposure to heat. The thermal treatment of the alloy is calculated based upon wt. % composition to solutionize unwanted phases having a negative impact on properties and may include a three level ramp-up and soak to a final temperature followed by cold water quenching and artificial aging.