Effect of Cyclic Deep Cryogenic Treatment on Corrosion Resistance of 7075 Alloy

The cyclic deep cryogenic treatment was proposed to improve both the hardness and corrosion resistance of the high strength 7075 aluminum alloy. The effect of different CDCT times on the exfoliation corrosion and intergranular corrosion of the alloys were observed by scanning electron microscope. The corrosion behaviors of the alloys were monitored by electrochemical techniques. The hardness of the alloy was measured by Vickers hardness tester. Furthermore, the microstructures of the alloys were examined by transmission electron microscope. The results show that the corrosion resistance and hardness are strongly affected by the precipitate state. The discontinuous grain boundary precipitates and the wide precipitate free zones will enhance the corrosion resistance. The fine precipitates distributed evenly in the matrix can increase the hardness. After the CDCT, the corrosion resistance is remarkably improved without sacrificing the hardness. The best combination of the hardness and corrosion resistance is exhibited for the alloy treated with the CDCT twice.