Influence of aging treatment on corrosion behavior of Al-Zn-Mg-Zr alloy with Sc element

The influences of aging treatment on corrosion behavior of Al-Zn-Mg alloy with Sc element were investigated by means of constant temperature immersion corrosion method, electrochemical polarization curves measure, slow strain rate test(SSRT), scanning electron microscopy and transmission electron microscopy. The experimental results show that natural aging has worst exfoliation corrosion(EXCO) and intercrystalline corrosion resistance, with the corrosion susceptibility order from low to high under different aging conditions as follows: T73 temper, T6 temper, under aging,natural aging. The same trend of corrosion behavior with aging treatment is demonstrated by electrochemical polarization curves. T73 temper has low susceptibility of stress corrosion cracking(SCC) compared with T6 temper at the same strain rate. Meanwhile, the alloy is more susceptible to SCC at 1.33×10 6s 1than at 6.67×10 6s 1at the same aging temper.The corrosion susceptibility of Al-Zn-Mg alloy with Sc element is related to the sizes and distribution of precipitated phase(MgZn2) and precipitate free zone(PFZ) at grain boundaries. Under T6 temper, due to the continuous chain distribution of precipitated phase at grain boundary, the corrosion susceptibility of the alloy is high. On the contrary, with the equilibrium phases discontinuous and PFZ widening, T73 temper can decrease corrosion susceptibility of the alloy.