Search

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]

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm2, respectively. [ABSTRACT FROM AUTHOR]

The effects of trace Sc and Y on the corrosion behaviors of cold-drawn Al-0.2Ce alloys were revealed by scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Electron Probe Micro-analyzer (EPMA), and electrochemical measurements. The results showed that the Al 3 Sc particles not only enable the increase of subgrain boundaries in the modified alloy after cold drawing but also improve the morphology and size of the Al 13 Fe 3 Ce phase. SKPFM analysis showed that the enrichment of Y around the Al 13 Fe 3 Ce phase in the modified alloy can decrease its electrochemical inertness and thus reduce the micro-galvanic corrosion susceptibility of the alloy. The results of the electrochemical analysis showed that the individual and composite addition of Sc and Y can improve the corrosion resistance of the cold-drawn Al-0.2Ce alloy. The corrosion potential and current of Al-0.2Ce-0.2Sc alloy are −0.892 V and 0.91 μA·cm−2, while the corrosion potential and current of Al-0.2Ce-0.1Y alloy are −0.918 V and 1.08 μA·cm−2, respectively. It is obvious that Sc element improves the corrosion resistance of Al-0.2Ce alloy more effectively than Y element. The corrosion depth of Al-0.2Ce-0.2Sc-0.1Y alloy was the smallest tested by immersion under the same conditions, and its corrosion potential and corrosion current were −0.842 V and 0.79 μA·cm−2, respectively, corresponding to the best corrosion resistance. The formal mechanism of pitting corrosion in the alloys is also discussed. [Display omitted] • Effect of Sc on microstructure and corrosion of Al-0.2Ce alloy was revealed. • The enrichment of Y atoms around Al 13 Fe 3 Ce can reduce the potential difference. • The corrosion behaviors of pitting corrosion induced by Al 13 Fe 3 Ce was discussed. • The equivalent circuit of the studied alloys was identified. [ABSTRACT FROM AUTHOR]