Effects of morphology and I-Mg3Zn6Y second-phase distribution on hot-compressive-deformation behavior of Mg-Zn-Y-Zr alloy under a strain rate of 1.0 s-1

The current study used compression testing at 523 and 573 K and a strain rate of 1.0 s(-1) to evaluate the deformation microstructure evolution and mechanism of high-pressure-solidified Mg(96.17)Zn(3.15)Y(0.50)Zr(0.18)alloy showing particle- or short-fiber-like divorced I-Mg3Zn6Y second-phases. When the high-pressure-solidified alloy was deformed at 523 K, four twin patterns were activated during the initial deformation. The proportions of contraction twins (CTs) and secondary twins (STs) were significantly higher in the high-pressure-solidified alloy than in the as-cast alloy deformed under the same conditions. After 10% deformation, the flow stress in the high-pressure-solidified alloy reached the near-peak stress (233 MPa), which was much higher than that in the as-cast alloy. The high-pressure-solidified alloy showed a higher storage energy than the as-cast alloy in the initial deformation. During continuous deformation, DRXed grains preferentially nucleated around the particle- or short-fiber-like divorced I-Mg3Zn6Y. More CTs and STs sprouted and grew and were then broken apart and shredded, providing more potential nucleation sites for DRXed grains. Moreover, the twin boundaries were converted into normal HABs, which also afforded more potential nucleation sites for DRXed grains. When the high-pressure-solidified alloy was deformed at 573 K, the twinning pattern was dominated by ETs. During continuous deformation, the ET boundaries were converted into either LABs or regular HABs, which became an effective nucleation substrate for DRXed grains. The number of high-density LABs continually increased around I-Mg3Zn6Y and interwove with the fragmented twin boundaries, thereby providing more potential nucleation sites for DRXed grains. Therefore, the high-pressure-solidified alloy showed a higher degree of DRX (94%) than the conventional as-cast alloy when deformed 60% at 573 K.