Influence of Active Recovery and Initial Microstructures on Metadynamic Recrystallization of 5083 Aluminum Alloy

To study metadynamic recrystallization, hot compression tests were conducted using Thermecmastor-Z thermomechanical simulator equipped with an automatic water-cooling system, which can shorten the delay time between the compression and cooling processes. The widely used offset yield stress method is no longer applicable to calculate the recrystallized fraction from the obtained stress–strain curve when the initial microstructure is as-extruded, because deformation in the two passes actually starts at different microstructures. A modified method to compensate for microstructural changes using the Hall–Petch relationship is thus proposed. Electron backscatter diffraction (EBSD) characterization and microhardness tests were carried out to get microstructural and mechanical properties for further understanding metadynamic recrystallization. During the interpass time, the external stress caused by the fixed anvil shows a non-negligible effect on the static softening behavior. It accelerates static recovery, but retards metadynamic recrystallization. As-extruded initial microstructure leads to a more recrystallized but less homogeneous microstructure and a smaller decrease in yield stress, showing good potential to maintain strength. Interestingly, unless the temperature or strain rate is sufficiently high, a certain incubation time, although as short as approximately 1 s, is still required for metadynamic recrystallization. In addition, not only the previously dynamic recrystallized grains, but also the recovery-enhanced subgrains, together act as potential nuclei for the subsequent metadynamic recrystallization.