Constitutive Equation and Dynamic Softening Behavior of 7A55 Aluminum Alloy during Compression at Elevated Temperatures

摘要

Abstract The hot deformation behaviors of 7A55 aluminum alloy were investigated by compression tests at temperatures ranging from 270℃ to 450℃ and strain rate ranging from 0.1s~(-1) to 25s~(-1). Results show that the flow stress increased with increasing strain rate and decreasing temperature. A two-stage constitutive equation was established and the hot deformation activation energy was 140 kJ/mol. EBSD observations show that the fine and equiaxed grains with the misorientation angle above 15° nucleated at the initial grain boundaries under high temperature and low strain rate conditions. It is concluded that the softening mechanism of 7A55 aluminum alloy is dynamic recovery(DRV), together with a partial dynamic recrystallization(DRX). The nucleation mechanism of DRX could be explained by the strain induced grain boundary migration(SIBM). The DRX softening model was established based on the dislocation density theory finally.