Excellent low-frequency microwave absorption and corrosion resistance in FeCoNiMn0.9Cu0.1La0.02 high-entropy alloys via microstructural engineering

High-entropy alloys (HEAs) are pivotal in the advancement of high-efficiency microwave-absorbing materials. Owing to their tunable electromagnetic characteristics, superior mechanical properties, and remarkable corrosion resistance, HEAs are regarded as highly promising candidate materials for microwave absorption applications. However, HEAs still face key challenges in achieving both high-efficiency low-frequency absorption and enhanced corrosion resistance. Herein, excellent low-frequency absorption and high corrosion stability are achieved in FeCoNiMn 0.9 Cu 0.1 La 0.02 HEAs by microstructural engineering strategy implemented through a heat treatment method. The minimum reflection loss (RL min ) reaches −46.8 dB at 1.36 GHz, and an engineered effective absorption (RL min ≤ −5 dB) covers nearly the entire L band. The synergistic electromagnetic effects modulated by microstructure engineering enhance low-frequency impedance matching, leading to the high-efficiency microwave absorption performance. Remarkably, FeCoNiMn 0.9 Cu 0.1 La 0.02 HEAs retains superior low-frequency microwave absorption performance (RL min of −54.6 dB at 1.98 GHz) even after 360-hour corrosion in acidic saline solution, exhibiting excellent corrosion-resistant property. This is attributed to the protective role of the MnO layer formed during the annealing process. Its relatively high electrode potential reduces the adsorption capacity of Cl⁻ and COOH⁻ on the passive film, thereby slowing down the degradation of the passive film. Simultaneously, the MnO phase facilitates the development of a complete, dense, and stable corrosion product film on the alloy surface, which further enhances its corrosion resistance. This research provides insights into designing HEAs with low-frequency microwave absorption and excellent corrosion resistance. • The minimum reflection loss (RLmin) of the high-entropy alloy (HEA), annealed at 200°C for 2 hours, reaches -46.8 dB at 1.36 GHz, indicating excellent electromagnetic wave absorption in the L band. • Electrochemical testing of samples M, T200, and T600 showed that as annealing temperature increased, the corrosion current density (I corr ) of FeCoNiMn 0.9 Cu 0.1 La 0.02 decreased and the corrosion potential (E corr ) shifted positively, indicating improved corrosion resistance. • After being exposed to an acidic salt solution for 360 h, the RLmin of T600 remains at −54.6 dB at 1.98 GHz. This exceptional stability is primarily attributed to the formation of a corrosion-resistant MnO phase protective layer during the annealing process, which effectively inhibits further degradation.