Some effects of alloy composition on stress corrosion cracking in Al–Zn–Mg–Cu alloys. (September 2015) - Knight, S.P.
Highlights: A copper content of ∼0.6 wt% may be overaged when the quench-rate is not too rapid. Crack arrest markings spacings could be related to the hydrogen diffusivity. XPS showed that the oxide of AA7075 was slightly more hydrated than on AA7079. Abstract: Stress corrosion cracking (SCC) of two lower-copper Al–Zn–Mg–Cu alloys, AA7079 and AA7022 (0.6–0.9 wt% Cu), and a higher-copper 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. X-ray photoelectron spectroscopy showed that the oxide formed in ambient conditions (e.g. ∼50% RH) was more hydrated on the AA7075-T651 than AA7079-T651.