Papers by Author: B.H. Lee

Abstract: The influence of initial texture on the formation of primary twin system of AZ31 Magnesium rolled plate was investigated in this work. Uniaxial compression tests were carried out on samples cut along the rolling direction (RD) and normal direction (ND) of rolled AZ31 Mg plate at various temperatures (RT, 150, 200, 250, 300, 350, 400, 450°C) with the fixed strain rate (0.01s-1). The results showed that the primary twinning system of AZ31 Mg alloy (c-axis extension twin) occurred actively in the RD compression specimens, which promoted homogeneous deformation as compared to the ND compression specimens. The effect of temperature on the formation of deformation twins was also investigated, and slip/twin transition temperature was found to be 250°C.

Abstract: In this study, optimum processing conditions for strip-cast AZ31 Mg alloy was investigated on the basis of processing map and microstructural analysis. To obtain the processing map, isothermal compression tests were carried out to a strain of 0.5 at temperatures of 200 ∼ 400°C with the strain rates of 0.01 ∼ 10s-1. It was found that maximum efficiency indicating the optimum processing condition occurred at 300°C and 10s-1. The possible deformation mechanisms operating at high temperature was also discussed.

Abstract: High temperature deformation behavior of AZ31 Mg alloy was investigated in this study on the basis of a processing map (e » 0.6). To construct a processing map, compression tests were carried out at various temperatures and strain rates. Two regions of high deformation efficiency (h) were identified as: (1) a dynamic recrystalization (DRX) domain at 250°C and 1/s and (2) a superplasticity domain at 450°C and 10-4/s. The average grain size observed in the DRX region was considerably smaller (2.9µm) than in any other region. In the superplastic condition, tensile elongation to failure approached to 1040%. At the high Z regions, flow softening occurred resulting from the dynamic recrystallization but below 1010 of Z value, flow hardening occurred due to the grain growth. Possible deformation mechanisms operating at high temperature were discussed in relation to the activation energy. A two-stage deformation method was found to be effective in enhancing the superplasticity of AZ31 Mg alloy.