Characterization of hot deformation behavior and constitutive modeling of Al-Mg-Si-Mn-Cr alloy

To characterize the hot deformation behavior of commonly used aluminum alloy, a homogeneous Al-Mg-Si-Mn-Cr alloy was analyzed by thermal simulation test at deformation temperature range of 653-803K and strain rate range of 0.01-10s(-1). The flow stresses were predicted by modified Johnson-Cook model, modified Zerilli-Armstrong model and strain-compensated Arrhenius model. The results show that the three models are able to predict the flow behavior of the alloy. Strain-compensated Arrhenius model has the best simulation ability in predicting flow stresses, while the modified Johnson-Cook model has lower prediction accuracy and the modified Zerilli-Armstrong model has poorer predictive ability at low strain rates. Microstructure evolution shows that subgrain boundaries form at original grain boundaries at first, moving toward to the center of the deformed grains. The dislocation density decreases, while the number and the size of subgrains increase with the decreasing Zener-Hollomon (Z) parameter. Both dynamic recovery (DRV) and dynamic recrystallization take place in hot deformation process. DRV is considered to be the primary dynamic softening mechanism throughout the entire hot deformation range. Continuous dynamic recrystallization and discontinuous dynamic recrystallization operate concurrently at low strain rates and high temperatures. The relationship of subgrain size and predicted flow stress is presented. Moreover, activation volume is introduced to reveal the thermal activation mechanism during hot deformation.