Achieving exceptional high strain rate superplasticity in an Al0.5CoCrFeNiCu high entropy alloy via multiple grain refinement mechanism

An ultrafine-grained Al 0.5 CoCrFeNiCu HEA sheet with an average grain size of 1.2μm was produced by thermo-mechanical processing. The alloy exhibited remarkable HSRS, achieving an elongation of 1120 % at 1050 °C and 0.02 s -1 . During HSRS deformation, the alloy exhibited a high strain rate sensitivity (m-value), thereby maintaining homogeneous deformation. Microstructural evolution analysis revealed that grain boundary sliding was facilitated by the maintenance of a fine-grained structure, enabled by distinct grain refinement mechanisms operating at different stages. These involved continuous dynamic recrystallization in the initial stage and twin-induced grain refinement in the middle-to-later stages. Although their formation mechanisms differ, both contribute synergistically to grain refinement. This work shows a significant achievement in HSRS of HEA.