Stress corrosion cracking (SCC) of two lowercopper AlZnMgCu alloys, AA7079 and AA7022 (0.60.9 wt% Cu), and a highercopper AA7075 (1.5 wt% Cu) alloy are reported. In aqueous chloride, copper content of grain boundary precipitates is believed to be controlling, whereas in moist air it appears that the hydrogen diffusivity could be evident from the rate of crack growth between crack arrest markings. In moist air, the rate of hydrogen entry may control crack growth rates. Xray photoelectron spectroscopy showed that the oxide formed in ambient conditions (e.g. ~50% RH) was more hydrated on the AA7075T651 than AA7079T651.