Optimizing the electromagnetic properties of the FeCoNiAlCrx high entropy alloy powders by composition adjustment and annealing treatment

High entropy alloy powders are promising candidates for new microwave absorbents due to its advantages in corrosion resistance, heat resistance and soft magnetic properties. In this work, flake-shaped FeCoNiAlCrx (x = 0.1, 0.3, 0.5, 0.7, and 0.9, in molar ratios) alloy powders are prepared by mechanical alloying, and then annealed at 500 °C. The experimental results show that the milled and annealed FeCoNiAlCrx powders contain similar FCC and BCC phase structure. The addition of Cr element results in more flattened powder particles and more polarization sites, which enhances the surface polarization and ultimately increases the real and imaginary parts of complex permittivity (ε′ and ε″). The real and imaginary parts of complex permeability (μ′ and μ″) decrease first and then increase as the proportion of Cr increases. The minimum reflection loss (RLmin) is improved and moves to the low frequency region (11.20 GHz to 8.23 GHz) as the proportion of Cr increases. After annealing, the enhanced saturation magnetization (Ms) increased μr, and the improvement of crystallinity also increased εr. For FeCoNiAlCr0.9 samples, annealing treatment directly improves the minimum reflection loss from −26.88 dB (8.23 GHz) to −47.55 dB (7.375 GHz), suggesting the positive effects of annealing treatment on reflection loss. All the above findings provide experimental and theoretical basis for FeCoNiAlCrx high entropy alloy powders as absorbing material.