Simulation of peripheral coarse grain structure during hot extrusion of AA7020 aluminum alloy

In this investigation, microstructural evolution during hot extrusion of AA7020 aluminum alloy has been simulated using multiscale physical models, finite element and Monte Carlo simulation. In addition to predicting the evolution of grain structure in different regions during and after hot extrusion, the framework was capable of indicating the origin of the nucleation of recrystallized grains, which is of fundamental importance for the understanding of the effects of various types of dynamic and static recrystallization events on the resultant microstructure after hot extrusion. To validate the framework, model predictions for peripheral coarse grain (PCG) structure was compared with experimental results. It was found that the operating mechanism of PCG formation depends mainly on the local deformation history. As a result of moderate deformation, the PCG structure was mostly composed of grains nucleated in the static mode after the extrudate left the die orifice and only a few grains in the PCG structure originated from dynamic recrystallization. Local large deformation could, however lead to a fully dynamically recrystallized grain structure and the PCG structure resulted from normal grain growth of dynamically recrystallized grains.