Formation of Coarse Recrystallized Grains in 6016 Aluminum Alloy During Holding After Hot Deformation

Controlling the grain size of recrystallized grains during hot rolling is crucial in 6xxx aluminum alloys used in automotive applications to avoid the development of roughness on the surface of the formed sheet. The possible factors responsible for the development of coarse recrystallized grains are investigated in this paper. With this aim, hot compression tests followed by post-deformation holding in the testing furnace as well as by sequential annealing in the SEM chamber are performed and the evolution of the microstructure is characterized using EBSD. Grain overgrowth takes place in both types of experiments. The investigation shows that stored energy is the key factor behind the overgrowth of some recrystallized grains at the expense of others and that Smith–Zener pinning is unable to prevent this phenomenon because of the high driving pressure associated with stored energy. The anisotropic characteristics and behavior of coarse recrystallized grain boundaries are also studied. It comes out that the misorientation angle and axis are not sufficient to determine grain boundary migration rate.