Microstructural evolution and mechanical behavior of resistance spot welded CoCrFeMnNi high-entropy alloy: Experimental and simulation insights

Abstract

This study investigates resistance spot welding of CoCrFeMnNi high-entropy alloy (HEA) sheets, which has not been previously reported to the best of the authors' knowledge. Defect-free welds of adequate nugget diameter were achieved, exhibiting columnar dendrites in the fusion zone (FZ) and equiaxed grains in the base metal and heat affected zone (HAZ), while retaining a single-phase face-centred cubic structure. Coupled electro-thermomechanical simulations captured nugget growth and residual stress evolution across the weld zones, explaining the localized increase in geometrically necessary dislocation density and the corresponding ∼40% rise in hardness in the HAZ. A partially melted zone near the fusion boundary, was attributed to the alloy's low thermal conductivity and wide freezing range (∼162 K), which facilitated localized liquation. Lap-shear testing showed a desirable pull-out mode of failure, with fractography and electron backscattered diffraction analyses revealing ductile fracture features and deformation-induced mechanical twinning near the fracture line. Scheil's solidification predictions matched the observed Mn and Ni segregation in the FZ. Contributions from solid solution, Hall-Petch, and Taylor hardening were quantified, with the HAZ showing the highest predicted yield strength. Overall, these findings can pave the way for the deployment of HEAs in demanding automotive applications.