Corrosion Behavior of FexCrMnAlCu High-Entropy Alloy in 0.5 M H2SO4 Solution

Abstract

Fe_xCrMnAlCu (x = 0, 0.5, 1.0, 1.5, 2.0 wt%) high-entropy alloys (HEAs) were synthesized via vacuum arc melting to investigate the Fe-induced microstructural evolution and corrosion mechanisms in 0.5 M H₂SO₄ solution. The results demonstrate that increasing the Fe content progressively transforms the phase structure of the Fe_xCrMnAlCu HEAs from an initial BCC + BCC2(L2₁) configuration to an FCC + BCC structure. Microstructural analysis revealed that the dendritic regions primarily consist of Cr, Fe, Mn, and Al-enriched solid solutions, while the interdendritic regions comprise Cu and Al-enriched solid solutions. The addition of Fe promotes the formation of the FCC phase while simultaneously inhibiting the precipitation of the L2₁ phase. Immersion corrosion tests and electrochemical measurements indicate that the corrosion resistance of the Fe_xCrMnAlCu HEAs exhibits a graded degradation with increasing Fe content (Fe₀ > Fe_0.5 > Fe_1.0 > Fe_1.5 > Fe_2.0). The Fe₀ alloy demonstrated the optimal corrosion resistance, characterized by the highest corrosion potential and the lowest corrosion current density. This superior performance is attributed to its unique BCC + BCC2(L2₁) dual-phase structure and the formation of a stable, compact passive film during corrosion. In contrast, the Fe_0.5 alloy failed to develop a dense and stable passive film. Localized corrosion pits were observed on the dendritic regions of the Fe_1.0 alloy, while the Fe_1.5 and Fe₂.₀ alloys underwent severe selective dissolution of the dendritic phase. The deterioration in corrosion performance primarily stems from the synergistic effects of: (i) alterations in passive film characteristics induced by Fe addition, (ii) enhanced microgalvanic coupling resulting from the phase transition (BCC + L2₁ → FCC + BCC), and (iii) dilution of the critical corrosion-resistant element Cr, which significantly weakens the passivation capability of the dendritic regions.