Study on Annealed Microstructure and Mechanical Properties of Cold-Rolled FeCoCrNiMn High-Entropy Alloy

An equiatomic FeCoCrNiMn high-entropy alloy was processed by cold rolling followed by isothermal annealing at 900 °C for various durations. The microstructural evolution and mechanical properties of the alloy were systematically investigated as a function of annealing time. The results indicate that the alloy maintained a single-phase face-centered cubic (FCC) structure throughout the entire annealing process, with no secondary phases or precipitates detected. After annealing at 900 °C for 2 min, the recrystallized volume fraction reached approximately 80%, resulting in the formation of an ultrafine-grained microstructure. The corresponding Vickers hardness, yield strength, and total elongation were measured to be 249 HV, 616 MPa, and 32%, respectively, demonstrating a desirable combination of strength and ductility. The recrystallization process was essentially complete after 5 min of annealing. With further increases in annealing time, the grain size continued to coarsen, accompanied by a gradual decrease in hardness and strength and a progressive improvement in ductility, reflecting a typical strength–ductility trade-off.