Effect of High Pressure Torsion on Stress Corrosion Resistance of Al-Zn-Mg-Cu-Zr Alloy

High pressure torsion (HPT) experiment and subsequent heat treatment were carried out on as -received Al-Zn-Mg-Cu-Zr alloy at 400 degrees C under the pressure of 1 GPa. Optical microscope, electrochemical workstation and slow strain rate tensile machine were used for microstructure observation, electrochemical corrosion and stress corrosion resistance test for the as -received and HPT processed samples. The results show that HPT processing can improve the tensile strength and stress corrosion resistance by modifying the size and distribution of grains and secondary phases. The secondary phases agglomerated at the grain boundary corrode continuously, which leads to obvious intergranular corrosion and weak stress corrosion resistance of the as -received alloy. After 0.5 turn of HPT processing, the fragmentation and content reduction of secondary phase reduce the corrosion sensitivity; at the same time, the planar slip decreases and homogeneous slip mode increases due to grain refinement, which synergetically results in a significant improvement of the stress corrosion resistance. The HPT processed sample with 2 turn has finer grains with uniform distribution, which leads to the further increases of homogeneous slip mode compared to that with 0.5 turn, but under the interaction of intense pitting and stress concentration, the resistance to stress corrosion slightly decreases.