Strain hardening and microstructure evolution in ECAP-processed ultrafine-grained metals: a comparative study of copper, aluminum, and magnesium alloys

This study presents a comparative analysis of texture evolution, deformation mechanisms, and dislocation density evolution in pure copper, Al-1100 alloy, and Mg AZ31 alloy subjected to equal-channel angular pressing (ECAP). For that purpose, a unique grain fragmentation model combining continuum dislocation dynamics with Taylor-Lin crystal plasticity is presented. Copper and aluminum alloys, with their face-centered cubic (FCC) crystal structures, exhibit similar micromechanical processes during grain fragmentation. The post-ECAP textures for both materials align with ideal orientations, indicating a rotation of grains around the center of the flow direction. On the other hand, the magnesium AZ31 alloy, with its hexagonal close-packed (HCP) crystal structure, displays a rolling-like texture. Al-1100 showed high dislocation multiplication rate favored by dislocation glide, while Mg AZ31 displayed slower dislocation density evolution at 200 °C which can be associated with dynamic recrystallization and twinning low activity. Indeed, driven by elevated temperatures, dynamic recrystallization could form new grains, resulting in a gradual increase in dislocation density. Furthermore, the comparison of average grain size reduction rates aligns with the dislocation density findings, with aluminum alloys experiencing significant grain fragmentation and Mg AZ31 alloy undergoing the slowest rate of grain fragmentation. The employed continuum dislocation dynamics (CDD) coupled with a crystal plasticity modeling approach enables the prediction of material responses, offering a powerful tool for understanding and optimizing deformation behavior. Further research opportunities lie in exploring additional factors and refining the understanding of deformation behavior in FCC and HCP materials, as well as expanding the applicability of the modeling approach to other materials and processing techniques.