Dynamic recrystallisation: A quantitative study on grain boundary characteristics and dependence on temperature and strain rate in an aluminium alloy

Dynamic recrystallisation (DRX) usually occurs during hot forming of metallic materials, significantly impacting the mechanical properties of the final parts. Although DRX has been studied for decades, the types of DRX that occurs in high stacking fault energy (SFE) materials like aluminium alloys are still controversial, and their dependence on both temperature and strain rate is surprisingly missing. To fill these gaps, in the present study, uniaxial compression tests on an aluminium alloy AA6061 were carried out at different temperatures from 250 to 475 °C and strain rates from 0.01 to 1 s-1. The grain orientation and misorientation before and after the hot deformation were quantitively characterised using high-resolution Electron Backscatter Diffraction (EBSD) with a misorientation resolution of 0.05°, enabling high-angle grain boundaries (HAGBs), low-angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs) to be accurately quantified and correlated against temperature and strain rate. Results reveal that both continuous dynamic recrystallisation (CDRX) and geometric dynamic recrystallisation (GDRX) occurred concurrently, resulting in the formation of discontinuous HAGBs and fine equiaxed grains, respectively. The misorientation angle distributions of the discontinuous HAGBs exhibit an opposite trend compared to those of the fine grains' HAGBs. Both temperature and strain rate significantly affect the density of HAGBs formed by DRX, but have little effect on their misorientation angle distributions. This study sheds light on the fundamental understanding of DRX and provides comprehensive experimental data for future modelling of DRX processes in high SFE materials.