溫度對冷軋5083鋁-鎂-錳合金最佳超塑性之影響及其變形活化能之探究

Abstract

Common superplastic deformation is conducted at high temperature and low strain rate, in which the performance in various metals is satisfying. However, conditions such as high temperature and low strain rate are not economically efficient, as to extend further applications for superplastic deformation technique in manufacturing processes. Therefore, this experiment aimed at the commercial 5083 (Al-Mg-Mn) alloy, which is cheap and a possible material to be applied in quantitative manufacture by superplastic forming. The objective is to investigate the effects of no-recrystallization before superplastic deformation and rapid heating have on the grain structure and optimum superplasticity, under various deformation temperatures and strain rates. The experimental results reveal that, by the method of no-recrystallization before deformation and rapid heating, the specimen has equiaxed grains under 10 μm in size before deformation, and the elongation rate under various testing temperatures and strain rates meets the industrial requirement. The optimum elongation rate was 600% at 500°C for 1x10-3 s-1. The microstructure and cavity distribution at different testing temperature were analyzed. It was found that at 500°C, the tendency of change in aspect ratio and of grain growth were moderate, and only at 500°C would the cavities on the rolling face be unobvious and tiny. The analyses also reveal that the activation energies of deformation are not exactly the same at each test temperature. The activation energy are 90 kJ/mole in the temperature range of 450-500°C, and 128 kJ/mole in the temperature range of 500-550°C. This shows that 5083 aluminum alloy is temperature sensitive and also helped to explain the difference in elongation rate under different testing temperatures.