Nanostructured phases, mechanical properties, exfoliation and intergranular corrosion behaviours of 7075 Al–Zn–Mg–Cu alloy–Effect of one-stage and two-stage aging processes

Abstract

The control of the aging conditions for the aluminium alloys has been considered as an effective strategy to improve the properties of the alloy, especially in enhancement of the corrosion resistance. In this study, a detailed investigation of the effect of one-stage (T6) and two-stage (T76x) aging temper on mechanical properties, exfoliation and intergranular corrosion behaviours of 7075 Al–Zn–Mg–Cu alloy was implemented. Microstructures of the aged alloys were observed by optical microscopy and scanning electron microscopy (SEM), exfoliation and intergranular corrosion behaviours were investigated according to ASTM G34-2001 and ASTM G110-1992, respectively; the mechanical properties of the aged alloys were determined followed the standard methods. The microstructures of the sample aged with the T6 temper showed the finer particle size of precipitates than that of obtained from T76x tempers. Additionally, while the T6-aged sample revealed no appearance of the Precipitate Free Zones (PFZ), the PFZ with 40–50 nm in width was observed in the alloys treated with T76x tempers. The mechanical properties of the sample aged with T76x temper were negligibly reduced comparing to that of obtained with T6 temper, however, the exfoliation and intergranular corrosion behaviours were significantly improved by using two-stage aging conditions. The mechanism in enhancement of the corrosion resistance of the alloys treated with T76x temper over T6 temper was also discussed.