In this paper, Al x CoFe 1.9 Ni 2.1 (x = 0.5, 0.8, 1.0, 1.5) high entropy alloys are prepared by vacuum arc melting furnace. The effect of aluminum content on the microstructure and mechanical properties of Al x CoFe 1.9 Ni 2.1 high entropy alloys was studied. The microstructure of high entropy alloy was characterized by SEM, X-ray diffraction and EDS. The results show that with the increase of aluminum content, the microstructure varies from FCC to FCC+BCC structure and finally to single BCC structures. And when the aluminum content is 0.5, the microstructure exhibits slender dendritic structure, then turns to mixture of eutectic structure and FCC phase at x = 0.8 and x = 1.0. when x reaches 1.5, the microstructure changes into dendritic structure. With the increase of aluminum content, the yield strength increased from 172.3 MPa to 949.6 MPa, and the hardness increased from 127 HV to 479 HV, which significantly improved the strength and hardness of the alloy.

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