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Mechanical property and corrosion resistance are essential performances in ultra-high strength Al-Zn-Mg-Cu alloys for the aerospace and weapon industries. In this study, the pre-strain and aging treatments were used to enhance such performances of the spray formed ultra-high strength Al-Zn-Mg-Cu alloy. After 2% pre-strain with peak aging (PA) and retrogression and re-aging (RRA) treatments, the ultimate tensile strength, yield strength, and elongation can reach to 774 MPa, 735 MPa, 10.7% and 774 MPa, 747 MPa, 9.4%, respectively. The coarser precipitates of the samples with 4% pre-strain can lead to the slight lower strength compared with the samples with 2% pre-strain. The proper combination of pre-strain and aging treatments can also effectively enhance the stress corrosion resistance of the studied alloy by the following reasons. First, the higher strain concentration degree and dislocation density introduced by pre-strain treatments have high internal energy and provide more stored energy for the growth of the passive film. Second, the spacing of grain boundary precipitates under double aging (DA) and RRA states is larger than that under PA state. The width of uniform precipitation free zone (PFZ) with 2% pre-strain is larger than that with 4% pre-strain. Third, after pre-strain treatments, the cracks perpendicular to the deformation direction can be produced in Al 7 Cu 2 Fe phase, which further breaks up such particles. According to the results of Kelvin probe microscopy, the Al 7 Cu 2 Fe phase with smaller dimension can obtain the lower difference of potential to Al matrix. • The strength and corrosion resistance of the alloy were enhanced by pre-strain. • The pre-strain produced cracks in Al 7 Cu 2 Fe particles and further broke up them. • The pre-strain improved the strain concentration degree and dislocation density. • The effect of precipitation free zone and precipitate is better under 2% strain. • The improvement mechanism of pre-strain treatment was revealed. [ABSTRACT FROM AUTHOR]

The precipitation behaviour, mechanical properties and corrosion performance of an Al-Zn-Mg-Sc-Zr alloy under one-stage aging (T6), two-stage aging (T74) and retrogression and re-aging (RRA) treatment were mainly investigated. For the RRA treatment, with increasing temperature and duration of retrogression, the grain interior precipitates (GIPs) gradually grew and changed from GP zones + η′ phases to η′ phases + η phases. In addition, the discontinuity of coarsened grain boundary precipitates (GBPs) significantly increased, and the width of precipitate free zones (PFZs) became broader. Consequently, progressive decrease in strength and hardness, and improved corrosion resistance of the alloy can be observed. Compared to conventional T6 and T74 treatments, a good balance of mechanical properties (168.5 HV for hardness, 547 MPa for ultimate tensile strength) and corrosion resistance can be obtained with retrogression treatment at 160 °C for 30 min. Moreover, research on the localized corrosion of the Al-Zn-Mg-Sc-Zr alloy showed that, at the initial stage of pitting corrosion, the Al matrix around the cathodic α-Al(Fe,Mn)Si particles was uniformly dissolved, leading to the detachment of the α-Al(Fe,Mn)Si particles from the matrix and the formation of pitting pits. • The strengthening and corrosion mechanisms of Al-Zn-Mg-Sc-Zr alloy under different aging conditions were studied. • A model for the process of pitting corrosion development is established. • The optimized RRA treatment for Al-Zn-Mg-Sc-Zr is obtained. [ABSTRACT FROM AUTHOR]