| The stress corrosion cracking (SCC) of AA 7075 in an aqueous 3.5 wt.% 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^(-1) for peakaged specimens and 65.8 kJ mole^(-1) for overaged specimens. Time to failure due to SCC, t_f, increased with decreasing potential until -966 mV_(SHE) and then decreased. Stress corrosion crack propagation rate was found to be 0.85-1.05×10^(-5) ㎜ sec^(-1) (24.6-30.4 ㎃ ㎝^(-2)) at the open circuit potential, -566mV_(SHE), and 1.2-1.5×10^(-4) ㎜ sec^(-1) (347.7-434.6 ㎃ ㎝^(-2)) at the anodic overvoltage of ＋200mV. Time to failure, t_f, increased as ageing time increased at the open circuit potential. The similar ageing time dependence of failure time was also observed at the applied anodic potential of ＋200mV. It is suggested on the basis of observations of SCC fracture surfaces and SCC activation energy, and results of t_f variations with applied potential that SCC is caused by hydrogen embrittlement. The results of ageing stage dependence of t_f indicate that SCC behaviour is mainly controlled by matrix precipitate. |
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