The present invention provides an Al—Zn—Mg—Cu casting alloy that provides high strength for automotive and aerospace applications and optimized stress corrosion cracking resistance in highly corrosive and tensile environments. The inventive alloy composition includes about 3.5 wt. % to about 5.5 wt. % Zn; about 1.0 wt. % to about 3.0 wt. % Mg; about 0.5 wt. % to about 1.2 wt. % Cu; less than about 1.0 wt. % Si; less than about 0.30 wt. % Mn; less than about 0.30 wt. % Fe; and a balance of Al and incidental impurities.