Topological aspects in the microstructural evolution of AA6082 during hot plastic deformation

During thermomechanical processing of AA6082, the continuous dynamic recrystallization phenomenon is the restoration mechanism following dynamic recovery at high temperatures. This work proposes a microstructure model to describe the evolution of dislocation densities, misorientation distributions, fractions of high and low angle grain boundaries, and grain and subgrain sizes during hot deformation. The microstructure evolution is coupled with constitutive equations to predict the flow stresses depending on the strain, strain rate, and temperature. The flow curves, obtained by compression tests and the microstructure characterization done with SEM-EBSD analysis of non-deformed and deformed samples, are used to refine and validate the physical-based model. The topology of the grains before deformation is considered by assuming a mean ellipsoidal shape of the grains. Therefore, the influence of the deformation direction for an initially elongated grain structure can be predicted. The deformation in the normal direction leads to faster evolution of the microstructure than in the rolling direction. The hot compression changes the initial fibre texture to Brass and Goss type for compression in normal and rolling directions, respectively. Due to progressive crystal rotation, the changes in texture and the progressive formation of new low-angle grain boundaries evidence continuous dynamic recrystallization.