Mechanistic insights and kinetics of continuous and geometric dynamic recrystallisation in hot deformed aluminium alloy

Dynamic recrystallisation (DRX) is a significant restoration mechanism in the hot deformation of materials with high stacking fault energy (SFE), such as aluminium alloys. Both continuous DRX (CDRX) and geometric DRX (GDRX) have been observed concurrently during hot deformation of aluminium alloys. However, the kinetics of these DRX mechanisms during hot deformation remain considerably controversial in the literature, leading to the development of distinct constitutive models for CDRX and GDRX. To address this knowledge gap, the present study conducted hot compression tests on an aluminium alloy (AA6061) at varying strain levels up to 1.5. Crystallographic orientation and misorientation were characterised over a large area of the deformed samples using high-resolution electron backscatter diffraction (HR-EBSD) with a misorientation resolution of 0.05°. A quantitative analysis was then performed on the characteristics of high-angle grain boundaries (HAGBs), low-angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs). The results indicate that CDRX initiates in the early stages of deformation and reaches saturation as deformation progresses. This saturation of CDRX is attributed to a reduction in GNDs and LAGBs. GDRX occurs slightly before CDRX saturation, then accelerates as deformation continues, ultimately becoming the dominant mechanism at higher strain levels. In addition, hot deformation results in formation of Σ3 (60° <111>) twin boundaries (TBs), initially in the original HAGBs and subsequently in new HAGBs produced through GDRX. In contrast, these TBs are not observed in the new HAGBs generated through CDRX. This research provides significant insights into the kinetics of CDRX and GDRX in high SFE materials, supporting the development of predictive models for these DRX mechanisms.