발간논문

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Vol.30, No.2, 224 ~ 230, 1992
Title
Superplastic Behavior of 7475 Al Alloy
신동혁Dong H . Shin, 주연준Yeon J . Joo, 하종신Jong S . Ha, 맹선재Sun C . Maeng
Abstract
The superplastic properties of fine-grained 7475 Al alloy were investigated at 516℃ over the strain-rate range of 2.8 × 10^(-4)s : to 1.7 × 10^(-2)s^(-1). A significant improvement in superplastic elongation was achieved by adopting two-stage strain-rate deformation compared to a usual single strain-rate test. The initially higher strain-rate deformation in the first stage caused rapid microstructural changes including the conversion of subboundaries to high angle grain boundaries, The optimum stain-rate in the first stage was found to be 8.3 × 10^(-3)s^(-1). The specimens tested at lower strain-rates, revealed the dispersoid-free zones(DFZs) near grain boundaries normal to the stress axis. When a higher strain-rate was applied to the specimens with DFZs, the grain refining was not observed. This absence of grain refining was due to the concentration of plastic deformation in the weak DFZs.
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