The stress corrosion cracking (SCC) of AA7075 in an aqueous 3.5wt.% NaCl solution acidified with HCl to PH=1 was studied under constant load as a function of the applied potential, ageing stage and temperature. Activation energy due to SCC was found to be 57 kJ/mole for peakaged specimens and 68.5 kJ/mole for overaged specimens. The time to failure due to SCC, $t_f$, increased with decreasing potential until $-966mV_{SHE}$ and then decreased. Crack propagation rate was found to be $0.85-1.05\times10^{-5}mm/sec(24.6-30.4mA/cm^2)$ at the open circuit potential, $-566mV_{SHE}$, and $1.2-1.5\times10^{-4}mm/sec (347.7-474.6 mA/cm^2)$ at anodic overvoltage of +200mV. $t_f$ increased as ageing time increased at the open circuit potential. The same ageing time dependence of failure time was also observed at the applied anodic potential of +200mV. It is suggested on the basis of observation of SCC fracture surfaces, SCC activation energy and the results of $t_f$ variations with applied potential that SCC is caused by hydrogen subrittlement. The results of ageing stage dependence of $t_f$ indicate that SCC behaviour is mainly controlled by matrix precipitate.
