The deformation behavior and processing maps in the isothermal compression of 7A09 aluminum alloy

Isothermal compression tests of 7A09 aluminum alloy were carried out on a Gleeble-1500 simulator at the deformation temperatures ranging from 633 K to 733 K, the strain rates ranging from 0.01 s(-1) to 10.0 s(-1), and the height reductions ranging from 40% to 85%. Several modeling approaches, including the flow stress-strain curves, the kinetic analysis, the constitutive model and the processing maps, are used to characterize the deformation behavior in the isothermal compression of 7A09 aluminum alloy in this paper. The experimental results show that the flow stress in the isothermal compression of 7A09 alloy is significantly sensitive to the strain, the strain rate and the deformation temperature. The flow stress decreases with the increasing of deformation temperature due to the dissolution of intermetallic precipitates into Al matrix and the occurrence of selective DRX at higher deformation temperatures. And, it increases noticeably with the increasing of strain rate because of the increase in the rate of dislocation generation. The apparent activation energy for deformation (Q) in the isothermal compression of 7A09 aluminum alloy varies slightly with the strain. The Q-values are about from 136.61 kJ mol(-1) to 143.31 kJ mol(-1) which is close to that self diffusion in pure aluminum. The constitutive model in the isothermal compression of 7A09 aluminum alloy is developed using the Zener-Hollomon parameter in the exponent-type equation. The maximum relative error and minimum relative error between the calculated and the experimental flow stress are 6.67% and 0.07%, respectively. Finally, the processing maps at different strains with microstructural examination are established in the isothermal compression of 7A09 aluminum alloy. It is concluded that the effect of strain on the processing maps is significant. The peak efficiency of power dissipation at a strain of 0.7 is about 0.34 occurring at a deformation temperature of 713K and strain rate of 0.01 s(-1), which is correspondent to an optimal deformation condition of 7A09 aluminum alloy. (C) 2011 Elsevier B.V. All rights reserved.