Achieving the synergistic of strength and ductility in Mg-15Gd-1Zn-0.4Zr alloy with hierarchical structure

Currently, the hierarchical structure is one of the most effective means to enhance the strength and plasticity of metal materials, since the strain localization can be effectively delayed by the coordination of the unique microstructure. In this study, a hierarchical structure of Mg-15Gd-1Zn-0.4Zr (GZ151K) alloys containing grain, twin, and precipitation structural units was prepared by ultrasonic surface rolling process (USRP) and recrystallization annealing (RU). The results showed that the stress gradient generated by USRP formed a twin gradient structure, which will activate the twin-assisted precipitation (TAP) effect and twin-induced recrystallization (TIR) effect during RU. Then, the twin gradient structure transformed into a twin-precipitation gradient structure, and finally into a hierarchical structure with grain-twin-precipitation as the increasement of recrystallization degree. Besides, the dual gradient structure with twin and precipitation structural units had the highest strength and microhardness owing to the precipitation strengthening. However, the hierarchical structure with grain, twin, and precipitation structural units exhibited the most excellent combination of strength and plasticity under grain refinement and precipitation strengthening.