This article aims to improve the corrosion resistance of 304 stainless steel in high-temperature chloride molten salts, clarify the application effect and corrosion inhibition mechanism of aluminum powder as a corrosion inhibitor, and provide a practical reference for the material protection of solar thermal storage molten salt systems.

The high-temperature electrochemical corrosion behavior of 304 stainless steel was investigated in a ternary chloride molten salt (NaCl-KCl-MgCl₂) at 700 ℃ with the addition of aluminum powder at mass fractions of 0, 1%, 2%, and 5% respectively. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion kinetics and interfacial characteristics. The surface and cross-sectional morphologies, elemental distribution, and phase composition of corrosion products were analyzed using scanning electron microscopy combined with energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD).

The addition of aluminum powder significantly suppressed the corrosion of 304 stainless steel. With 5% aluminum powder addition, the corrosion current density decreased from 299.98 mA/cm² (without addition) to 31.673 mA/cm², representing a reduction of 89.4%. The polarization resistance increased markedly from 0.348 Ω (without aluminum) to 2.974 Ω (with 5% aluminum), indicating enhanced resistance to corrosion reactions. Electrochemical impedance spectroscopy (EIS) analysis revealed that the addition of aluminum altered the corrosion control mechanism from diffusion-controlled (without aluminum) to a dual-layer synergistic protection system at higher aluminum contents. After 100 h of corrosion，the thickness of the internal diffusion layer was significantly reduced from 150 μm (without aluminum) to 36 μm (with 5% aluminum powder addition). XRD and SEM/EDS analysis showed that at aluminum additions of 2% and 5%，a continuous and dense Al₂O₃ layer formed on the surface，while aluminum diffused inward to form an aluminum-rich layer and intermetallic AlNi₃ phase within the alloy subsurface. This dual-layer structure effectively suppressed the outward diffusion of Cr and Fe，thereby mitigating corrosion.

The corrosion inhibition mechanism of aluminum powder involves a synergistic protective process. Aluminum preferentially reacts with oxidizing impurities (e.g., moisture and oxygen) in the molten salt, forming a stable Al₂O₃ film on the alloy surface. Simultaneously, a portion of aluminum diffuses inward, creating an aluminum-rich layer and precipitating AlNi₃ phases, which together act as an internal diffusion barrier. This combined surface film and internal diffusion barrier system effectively blocks the outward migration of Cr and Fe, substantially reducing the corrosion rate. The results demonstrate that adding aluminum powder to chloride molten salts is a simple and effective strategy to enhance the corrosion resistance of 304 stainless steel. Future work should focus on the evaluation of the long-term durability and erosion resistance of this protective system under dynamic flow conditions, to facilitate its practical applications in concentrating solar power systems.