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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]

• The effects of Sc, Y and Zr on the performances and microstructure evolution of Al-0.7Mg-0.6Si-0.2Ce alloys were studied. • An excellent combination of strength, elongation and electrical conductivity was achieved with the addition of Sc and Y. • The strengthening and electrical resistance mechanism of the studied alloys were revealed by statistical calculation. [Display omitted] In order to achieve the compatibility between excellent mechanical properties and good electrical conductivity of Al-Mg-Si alloys, detailed investigation was carried out to understand the microstructure evolution and their influences on performances of different Al-0.7Mg-0.6Si-0.2Ce-X (X Sc, Y and Zr) alloys prepared by casting, homogenization, hot extrusion, solution and aging treatments. Under aging state, Ce can form a large number of micron-sized AlCeSi and a few AlCeFeSi phase. The strength increased to 334 MPa as a result of decreased grain size and improved precipitation effect and the electrical conductivity increased up to 53.53%IACS because of lower solute Si atoms. The β" precipitates were coarsened and consequently the volume fracture was largely reduced due to the presence of Sc element, leading to the decreased strength of 311 MPa. The more solute Mg, Si and Sc atoms increased the degree of free electron scattering and the electrical conductivity decreased to 51.86%IACS. It is also found that Sc significantly enhanced the elongation of the alloy from 11.8% to 18.0%, which might be attributed to the formation of Al 3 Sc and (Al, Si) 3 Sc phases. The addition of Y raised the electrical conductivity of Al-Mg-Si-Ce alloy to 55.79%IACS by ameliorating the volume fraction and distribution of β" precipitates and decreasing the solute Si atoms. The co-addition of Sc and Y inherited the advantages of such two alloys. The ultimate tensile strength, elongation, electrical conductivity of Al-0.7Mg-0.6Si-0.2Ce-0.2Sc-0.1Y alloy processed by aging treatments is 336 MPa, 19.4% and 53.11%IACS, respectively. [ABSTRACT FROM AUTHOR]