The balance between work hardening and softening behaviors of Mg-xZn-1Gd-0.2Ca-0.1Zr alloys influenced by trace Zn addition

Abstract

In the present work, the effect of adding trace amounts of Zn element on the microstructure, mechanical properties, work hardening and softening behaviors of Mg-xZn-1Gd-0.2Ca-0.1Zr alloys (ZGX) (x = 1, 2, 3 wt%) were systematically investigated. With the decrease in Zn content, the static recrystallized rate of as-annealed ZGX alloys gradually increased and recrystallized grain size decreased. Besides, a decrease in Zn content inhibited the generation of large secondary phases but promoted the formation of finely dispersed secondary phases. The tensile tests of as-annealed ZGX alloys showed that the lower the Zn content, the greater the yield point elongation (YPE) and yield stress, mainly attributed to the hindrance of grain boundaries to dislocations. The work hardening rate of as-annealed ZGX alloy with high Zn content was higher than that of as-annealed ZGX alloy with low Zn content. At the same time, cyclic stress relaxation tests indicated that as-annealed ZGX alloy with high Zn content was easier to soften. The increase in Zn content broke the balance between work hardening and softening of as-annealed ZGX alloys, mainly reflected in the rapid reduction of stress for ZGX alloy with high Zn content during the loading process, which can be ascribed to the accumulated dislocations detached from the pinning of the grain boundary and the second phases. These results provided a reference for the follow-up study of the mechanical properties of Mg alloys.