Stress corrosion behavior and microstructure analysis of Al-Zn-Mg-Cu alloys friction stir welded joints under different aging conditions

The friction stir welding joints of Al-Zn-Mg-Cu alloy were prepared, then their stress corrosion evolution during slow strain rate tensile testing was studied by in-situ electrochemical impedance spectroscopy. Slow stress corrosion process can be divided into three stages according to the corrosion trend, the corresponding charge-transfer resistance also shows three evolutionary patterns. Grain boundary precipitates in thermal machine affected zone (TMAZ) of the pre-weld RRA treatment are more discrete and coarser, and have a higher Cu content than those of pre-weld double-stage aging treatment TMAZ, which reducing the potential difference with the surrounding substrate and exhibiting higher stress corrosion resistance.