Effect of two-stage strain-rate test on the superplastic behavior of an Al-Li-Cu-Mg-Zr alloy—Microstructural characterization

Abstract

The effect of two-stage strain rate tests on the mechanical behavior of a warm-rolled Al-Li-Cu-Mg-Zr alloy during superplastic deformation has been studied. The results showed that a two-stage strain rate test produces much higher elongation than that of single strain rate tests. The optimum deformation parameters correspond to the proper combination of strain rate hardening and strain hardening during the second stage of superplastic deformation. The paper examines the effect of two-stage strain rate tests on microstructural changes during superplastic deformation of an Al-Li-Cu-Mg-Zr alloy, and relates these changes to the superplasticity, as well as the effect of the first stage strain rate on the deformation-induced recrystallized grain size and the conversion rate from the subgrain structure to the high angle grain boundary structure. The results show that the higher first stage strain rate results in a faster deformation-induced recrystallization rate and a finer recrystallized grain size. The microstructure formed using the optimum first stage deformation parameters is characterized by stable fine recrystallized grains and less cavitation. Both a higher first stage strain rate and first stage strain may result in severe cavitation. The grain growth of the fine grains results in high strain hardening, necking resistance and great elongationsmore » during the second stage low strain rate deformation.« less