Effect of Grain Size on Stress Corrosion Cracking Susceptibility of an Al-Zn-Mg Alloy

The stress corrosion cracking behaviors of two Al-Zn-Mg alloys with different grain sizes have been investigated using slow strain rate testing (SSRT)in 3.5% (mass fraction) NaCl solution at 50 ℃. The results indicate that the Al-Zn-Mg alloy with larger grain size has higher SCC susceptibility than the small-grain alloy. Statistical investigations by transmission electron microscopy (TEM) reveal that the area fraction of grain boundary (GB) precipitates on GB for the small-grain alloy is higher than that of larger grain alloy. This result implies that the area fraction of GB precipitates is the dominant mechanism for SCC of the Al-Zn-Mg alloy.