An equimolar AlCoCrFeNi high-entropy alloy (HEA) with trade-off properties between strength and ductility is prepared by hot extrusion for the first time. Compared with the HEAs prepared by casting and heat treatments, hot-extruded AlCoCrFeNi HEA not only contains uniform elements and phase distributions but also finer grains and microstructures. The average diameter of the homogeneous equal-axis fine grains is less than 5 µm. The compressive yield strength and ultimate compressive strength of the hot-extruded AlCoCrFeNi HEA reach 1450 and 3500 MPa respectively, while the compressive strain reach 42%. These excellent mechanical properties are attributed to the fine microstructure. In addition, the uniform dispersed network phase structures, ultrafine sub-grains, high density dislocations and blunted cracks in the deformed AlCoCrFeNi HEA are all the important factors affecting the strength and plasticity of the HEA. Hot-extruded AlCoCrFeNi HEA with excellent mechanical properties confirms a great prospect for the preparation of high-strength HEAs.

High-temperature heat treatments can improve the element distributions and phase structures of AlCoCrFeNi high entropy alloys (HEAs). However, the long-term isothermal annealing at high temperatures will make the grains grow crazily. In this study, the problem of grain growth caused by high-temperature annealing at 1200 °C was solved by heavily deformed AlCoCrFeNi HEAs. The ultrafine grains formed by dynamic recrystallization will grow firstly during the subsequent annealing process, which inhibits the increase in the larger grains in the hot-extruded AlCoCrFeNi HEAs. The effect of high-temperature annealing on hot-extruded AlCoCrFeNi HEAs was also explored simultaneously in detail. After annealing at 1200 ℃ for 2 h, the compressive strength and fracture strain of the AlCoCrFeNi HEA reached an astonishing result of 3750 MPa and 43%, respectively. The results are attributed to the skeleton-liked FCC structures deeply interspersed into the grains and more importantly, the fine annealed grains which still maintained an average diameter of 20 μm. Additionally, the new nano-precipitates did not expand wildly at high temperatures either. Research on heavily deformed AlCoCrFeNi HEAs isothermally annealed at 1200 °C provides an available idea for further improving the properties of these HEAs.

The mechanical properties of the AlCoCrFeNi high-entropy alloy (HEA) can be significantly enhanced by grain refinement. However, it is difficult to refine the grain size of AlCoCrFeNi HEA by solidification methods. In this study, fine-grained AlCoCrFeNi HEA was successfully prepared by heavy thermal mechanical processing. The AlCoCrFeNi HEA consists of FCC, B2, and BCC phases. The FCC phase is distributed on grain boundaries, while the B2 phase is embedded in the BCC matrix within the grains. The fine-grained AlCoCrFeNi HEA has enhanced strength and ductility compared with its coarse-grained counterpart. The enhanced strength–ductility synergy of the fine-grained AlCoCrFeNi HEA is attributed to three key factors: the fine-grained microstructure, the delayed initiation of cracks within the hard-to-deform grain matrix, and the impediment of crack propagation by the grain boundaries enriched with the FCC phase.