Effect of the precipitated phase of MgZn2 on surface nanocrystallization of Al-Zn-Mg alloy based on high-frequency impacting and rolling

Al-Zn-Mg alloy specimens before and after aging treatment were processed through high-frequency impacting and rolling. Grain refinement and work hardening were achieved in a certain depth from the top surface of specimen. Surface nanocrystallization mechanism was analyzed by TEM. The effect of precipitated phase of MgZn2 on grain refinement process was investigated in detail. The schematic illustration of grain refinement process of aging Al-Zn-Mg alloy was established. Results show that the role of precipitated phase is the crossing point of sub-grains boundaries and the obstacle of dislocation motion.