2009 Volume 50 Issue 4 Pages 711-718
Compression tests were conducted at the temperature of 573 K with the true strain rates of 0.1 s−1 on Mg-9Al-1Zn-1Ca and Mg-9Al-1Zn (in mass%) alloys, and the dynamic recrystallization behaviors were examined. Superplastic deformation of the alloys at 573 K after the hot compression was also investigated. When the homogenized Mg-9Al-1Zn-1Ca alloy specimens were deformed to the true compressive strain of 1.6, a fully recrystallized microstructure with the grain size of approximately 5 μm was obtained. However, unrecrystallized regions were observed locally in the hot-compressed as-cast Mg-9Al-1Zn-1Ca and homogenized Mg-9Al-1Zn alloys, which is induced by initial microstructural heterogeneity. The superplastic deformation at 573 K of hot-compressed Mg-9Al-1Zn-1Ca was negligibly impaired by the second phase particles below the strain rates of 10−2 s−1 because the stress concentration due to the particles can be relaxed by diffusion. Microstructural observations of the hot-compressed Mg-9Al-1Zn alloy deformed to fracture suggested the detrimental effect of the unrecrystallized regions on the superplasticity.