Influence of grain-boundary pre-precipitation and corrosion characteristics of inter-granular phases on corrosion behaviors of an Al–Zn–Mg–Cu alloy

► Grain boundary pre-precipitation enhances distribution discontinuity of the precipitates. ► Increase of Cu content of grain-boundary precipitates. ► Potentials differences among inter-granular phases obviously decrease after pre-precipitation. In this paper the influence of high-temperature pre-precipitation treatment on corrosion behaviors of 7055 aluminum alloy is investigated. High-temperature pre-precipitation treatment enhances the discontinuing distribution of the coarse precipitates along the grain boundary, and increases the Cu content of grain-boundary precipitates, which obviously improves stress corrosion resistance, suppresses the serve fracture of sub-grain boundary under the stress corrosion and reduces inter-granular corrosion (IGC) susceptibility with the same strength and ductility. The electrochemical corrosion results of inter-granular phases indicate that the Cu-rich, discrete and coarse grain-boundary precipitates and the decreasing potential difference among inter-granular phases in the grain boundary are responsible for the enhancement of corrosion resistance of 7055 alloy.