Electrochemical study of Al–Zn–Mg–Cu alloy during deep cryogenic process

Abstract

AbstractAl–Zn–Mg–Cu alloy was treated by deep cryogenic treatment combined with T6 treatment to obtain excellent properties. The hardness of the alloy was measured by a Vickers hardness tester. The corrosion behaviors of the alloy were monitored by electrochemical techniques and scanning electron microscopy. Furthermore, the microstructures of the alloy were examined by transmission electron microscope. The results show that after deep cryogenic treatment, the hardness and corrosion resistance of the alloy will be optimized, and the corrosion resistance and hardness will be strongly affected by the precipitate state. When the distance between grain boundary precipitates becomes larger and discontinuous, the corrosion resistance will be significantly improved. When the amount of matrix precipitates is large, the fine dispersion distribution can well increase the hardness. The best combination of the hardness and corrosion resistance is exhibited for the alloy treated at −196°C for 10 h with aging treatment at 120°C for 16 h, the hardness, the intergranular corrosion depth, the current density, and the corrosion rate are 189.6 HV, 31.8 μm, 0.0019 mA/cm2, and 0.0022 mm/a, respectively.