Research on the hot deformation behavior of Al-6.2Zn-0.70Mg-0.3Mn-0.17Zr alloy using processing map

The hot deformation behavior of Al-6.2Zn-0.70Mg-0.3Mn-0.17Zr alloy was studied using hot compression tests over deformation temperature range of 623-773 K and strain rate of 0.01-20 s−1. The flow stress behavior and microstructural evolution were observed during the hot deformation process. The results show the flow stresses and microstructure evolution are sensitive to deformation parameters. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 178.85 KJ/mol. The dynamic flow softening for the alloy is accounted for dynamic recovery and dynamic recrystallization. Under conditions of high ln Z values, only dynamic recovery occurred, and the main soften mechanism transformed from dynamic recovery to dynamic recrystallization at low ln Z values. With decreasing the value of ln Z parameter, the size of recrystallization grain becomes larger. According to the TEM evolution, it can easily observed that high densities of the fine and nano-scaled Al3Zr particles have precipitate in the aluminum matrix and grain boundary, which can effectively inhibit the dynamic recrystallization of experiment alloy. Based on dynamic material model and Prasad' instability criterion, the processing maps for the alloy are built at true strains of 0.3 and 0.5. The processing map at the strain of 0.5 exhibits the optimum processing conditions are in deformation temperature range from 703 K to 773 K and strain rate range from 0.03 s−1 to 0.32 s−1 with the maximum efficiency of 33%.