| Summary: | The effect of annealing temperature on the microstructure, phase constituents and mechanical properties of Al<sub>0.5</sub>CoCrFeMo<sub>x</sub>Ni high-entropy complex alloys has been investigated at a fixed annealing time (10 h). The 600 °C-annealing has no obvious effect on their microstructures, while the annealing at 800⁻1200 °C enhances the precipitation of (Al,Ni)-rich ordered BCC phase or/and (Cr,Mo)-rich σ phase, and thereby greatly affects the microstructure and mechanical properties of the alloys. All the annealed Al<sub>0.5</sub>CoCrFeNi alloys are composed of FCC and (Al,Ni)-rich ordered BCC phases; the phase constituent of the Al<sub>0.5</sub>CoCrFeMo<sub>0.1</sub>Ni alloy changes from FCC + BCC (600 °C) to FCC + BCC + σ (800 °C) and then to FCC + BCC (1100 °C); the phase constituents of the Al<sub>0.5</sub>CoCrFeMo<sub>0.2</sub>Ni and Al<sub>0.5</sub>CoCrFeMo<sub>0.3</sub>Ni alloys change from FCC + BCC + σ to FCC + BCC with the annealing temperature rising from 600 to 1200 °C; while all the annealed Al<sub>0.5</sub>CoCrFeMo<sub>0.4</sub>Ni and Al<sub>0.5</sub>CoCrFeMo<sub>0.5</sub>Ni alloys consist of FCC, BCC and σ phases. The phase constituents of most of the alloys investigated are in good agreement with the calculated results from Thermo-Calc program. The alloys annealed at 800 °C under current investigation conditionshave relative fine precipitations and microstructure, and thereby higher hardness and yield stress.
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