Flow stress softening and deformation mechanism under competition of current density and strain rate in basket structured high-entropy alloy

Electrically assisted forming (EAF) is a reliable method of reducing the deformation resistance of metallic materials and enhancing their formability. In this study, the mechanical properties and microstructure of Al_0.5CoCrFeNi high-entropy alloy (HEA) under electrically assisted compression (EAC) were investigated. The results showed that the flow stress decreased with increasing current density in the EAC. Specifically, the flow curves exhibited S-shaped softening at a higher current density, which was dominated by the non-uniform distribution of the Joule heating temperature during EAC. When the flow stress was fixed at 500 MPa and 80 A·mm⁻², compressible deformation amounts of 63.7% were observed at a strain rate of 1 s⁻¹, indicating full compression of Al_0.5CoCrFeNi HEA at low-stress levels. Based on the microstructure, the flowability of Al_0.5CoCrFeNi HEA was improved during EAC, and the flow direction shifted from 45°to the horizontal direction. The current density, which influences the Joule heating temperature and strain rate, synergistically affects the stacking fault energy (SFE) and critical resolved shear stress (CRSS), which affect the tendency for twinning behavior. Thererfore, deformation nanoscale twins (DTs) were observed, indicating a shift in the deformation mechanisms from dislocation slip domination to a mixed pattern of dislocation slip and twinning. This study confirmed the deformability of Al_0.5CoCrFeNi HEA during EAC and provided an experimental foundation and theoretical support for the formation of HEAs. Graphic Abstract: (Figure presented.)