Microstructural Evolution and Mechanical Properties of Al0.7CoCrFeNiCu High-Entropy Alloy During Annealing

The microstructure and mechanical properties of the Al0.7CoCrFeNiCu high-entropy alloy (HEA) were studied in both as-cast state and annealed state, and the results showed that the alloy was composed of FCC1, FCC2, and BCC phases. Cu-rich and Fe-Cr-rich precipitates were present within the BCC phase, while small amounts of needle-like precipitates were observed in both the FCC1 and the FCC2 phases. After annealing at 700 degrees C, the matrix phase composition of the alloy did not change significantly, but the volume fraction and size of the needle-like precipitates increased with the holding time. The hardness and yield strength first increased and then decreased with the extension of the holding time, reaching peak values at 48 h of holding time of 364 HV and 667 MPa, respectively. During annealing at 900 degrees C, the volume fraction of needle-like phases first increased and then decreased with prolonged holding time, while the precipitates underwent significant coarsening. The hardness and yield strength reached peak values at 1 h of holding time of 311 HV and 493 MPa, respectively. During the subsequent holding process, as the needle-like phase significantly coarsened, the mechanical properties of the alloy steadily declined, which led to the overall mechanical properties after annealing at 700 degrees C being superior to those after annealing at 900 degrees C.