Corrosion behavior and inhibition methods of Fe-Cr-Ni alloys in MgCl₂-KCl thermal energy storage cycles with solid-liquid phase transition

Binary chloride salts, specifically MgCl₂-KCl, are viable high-temperature phase-change materials for thermal energy storage, enabling repeated melting and solidification cycles for heat storage and release. This research investigates the corrosion characteristics of Fe-Cr-Ni alloy (Inconel 625) during the high-temperature charging and discharging cycles (melting-solidification) of MgCl₂-KCl and explores potential corrosion control strategies. Experimental findings reveal that the corrosion progression of Inconel 625 occurs in several stages. After 21 days of corrosion, a dense oxide protective layer consisting of Mg, Cr, and O forms on the alloy’s surface. Although this layer effectively prevents molten salt diffusion into the internal alloy, some Cl₂ still penetrates. Increasing the Mg content (0.02 wt% to 2.0 wt%) reduced the corrosion rate of Inconel 625 from 197.25 μm·year⁻¹ to 27.47 μm·year⁻¹. Cross-sectional analysis confirmed that Mg addition promoted the oxide layer transition from MgCr₂O₄ to MgO, significantly controlled the dissolution and diffusion of Cr, thereby enhancing the protective layer’s compactness. In conclusion, the addition of Mg enhances the corrosion resistance of Fe-Cr-Ni alloy in MgCl₂-KCl thermal energy storage applications, offering an effective corrosion protection strategy for nickel-based alloys in such environments.