| The stress-corrosion cracking (SCC) mechanism of Al-Zn-Mg alloy has been studied in terms of the relationship between pre-exposure embrittlement (PEE) and SCC. PEE and SCC susceptibilities were measured as a function of ageing state, pre-exposure time and applied potential by means of the slow strain rate method. The specimen pre-exposed to water vapour-saturated air, followed by reheat treatment (re-solutionized in vacuum and aged in dry air) showed a pronounced increase in fracture energy as compared to the pre-exposed specimen. This suggests that PEE is caused by reversible embrittlement, i.e., by hydrogen embrittlement. The similar trends in SCC susceptibility were obtained with respect to ageing state as well as to applied potential. This implies that the SCC mechanism remains unchanged regardless of ageing state and applied potential. When pre-exposure time was large enough than 120 h, the susceptibility to PEE and fracture surface of PEE were very similar to those associated with SCC. On the basis of experimental results, it is believed that SCC as well as PEE is caused by hydrogen embrittlement |
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