Characterization and modeling of continuous dynamic recrystallization (CDRX): Application to 2139 aluminum alloy

Abstract

Controlling microstructure is a key factor in hot metal forming as it affects the performance of metallic materials. In high stacking-fault-energy materials, including aluminum alloys, continuous dynamic recrystallization (CDRX) drives microstructural evolution. In this study, hot compression tests were conducted on the AA2139 alloy across a wide range of thermomechanical conditions to (i) characterize the CDRX mechanism and (ii) generate experimental data for model calibration. Microstructural investigations were conducted to examine the development of grain and subgrain structures, and the evolution of disorientation distributions. Evidence of CDRX was observed through the formation of low-angle grain boundaries (LAGBs), their progressive increase in disorientation, and their transformation into high-angle grain boundaries (HAGBs), both in grain interiors and near original grain boundaries. Increasing strain promoted the progressive disorientation of LAGBs. Strain rate and temperature strongly influenced subgrain size, LAGB density, and dynamic recovery. Based on these results, a physically based CDRX model was developed by extending the work of Gourdet and Montheillet. The proposed improvements introduce the contribution of LAGB energy and disorientation angle to the subgrain-rotation law, a crystallite-size-dependent rate of LAGB creation through a refined physical description of the parameter $\alpha$, and the incorporation of self-heating effects during deformation. Together, these developments significantly enhance the physical consistency of the model. The overall experimental trends were reproduced, including the decrease in crystallite size and the increase in LAGB density at higher strain rates and lower temperatures, as well as the higher mean LAGB disorientation angle observed at lower strain rates. In addition, the model captures the macroscopic flow stress under various thermomechanical conditions.