Tailoring the Mechanical Properties of Al_0.4CrFe₂Ni₂ Medium-Entropy Alloy via Thermomechanical Processing

The microstructure and properties of a cobalt-free, cost-effective Al_0.4CrFe₂Ni₂ medium-entropy alloy (MEA) after multi-stage thermomechanical processing, including annealing, rolling over a wide temperature range from hot to cryogenic conditions, and subsequent precipitation strengthening, were investigated in the present study. The initially cast microstructure was effectively homogenized through hot rolling with an 80% thickness reduction followed by homogenization annealing, resulting in the formation of a single-phase supersaturated solid solution and enhanced stability of plastic deformation. Strengthening of the MEA was achieved by rolling under both ambient and cryogenic conditions, with the deformation process predominantly governed by shear band formation. However, rolling under cryogenic conditions led to a more pronounced localization of plastic deformation, promoting the formation of deformation nanotwins and resulting in significantly higher strengthening compared to ambient rolling, with the alloy reaching a yield strength of 1040 MPa and an ultimate tensile strength of 1235 MPa. Precipitation hardening was governed by the formation of B2-type (ordered body-centered cubic, BCC) precipitates, which preferentially nucleated along deformation bands, thereby effectively strengthening the alloy to a yield strength of 1420 MPa and an ultimate tensile strength of 1465 MPa. Our results demonstrate that the investigated MEA offers a wide range of tunable mechanical properties, which can be effectively tailored through appropriate combinations of thermomechanical processing routes.