Abstract: In order to improve the stability of the barrier layer, MgAlSnZnCu series of lightweight high entropy alloys were prepared by electromagnetic induction heating method under the protection of a covering agent and argon gas. The as-cast microstructure, annealed microstructure and phases of the alloys were characterized and analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy spectrum analysis (EDS), and microhardness test was used to study its hardness. The results show that the microstructure of as-cast MgAlSnZnCu alloy is composed of (AlMgZnCu)-FCC phase and Mg₂Sn phase. The morphology of Mg₂Sn phase is 2-6 μm granular and irregular block. When the content of Mg decreases from 22% to 12%, the hardness of the alloy increases from 277 HV0.2 to 326 HV0.2, and the compressive strength increases from 223 MPa to 237 MPa. Needle-like and flake-like impurity phases appear in the microstructure after the decrease of Sn and Zn contents, and the dispersion of hardness values is large, after annealing at 450 ℃ for 6 h, the impurity phases in the microstructure tend to accumulate and grow obviously. The mechanical test results show that the annealing have little effect on compressive strength and hardness. The MgAlSnZnCu series alloys can maintain good thermal stability at 450 ℃.

Key words: lightweight high entropy alloys, diffusion annealling, microstructure, vickers hardness, compressive strength