Correlations among stress corrosion cracking, grain-boundary microchemistry, and Zn content in high Zn-containing Al-Zn-Mg-Cu alloys
The correlations among the corrosion behaviour, grain-boundary microchemistry, and Zn content in Al-Zn-Mg-Cu alloys were studied using stress corrosion cracking (SCC) and intergranular corrosion (IGC) tests, combined with scanning electron microscopy (SEM) and high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) microstructural examinations. The results showed that the tensile strength enhancement of high Zn-containing Al-Zn-Mg-Cu alloys was mainly attributed to the high density nano-scale matrix precipitates. The SCC plateau velocity for the alloy with 11.0 wt.％ Zn was about an order of magnitude greater than that of the alloy with 7.9 wt.％ Zn, which was mainly associated with Zn enrichment in grain boundary precipitates and wide precipitates-free zones. The SCC mechanisms of different Zn-containing alloys were discussed based on fracture features, grain-boundary microchemistry, and electrochemical properties.
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