<p>The hot corrosion behaviors of two FeNiCrAl alloys (3Al, 6Al) and 304 stainless steel in NaCl/KCl and NaCl/KCl/Na₂SO₄ mixed salts at 700&#xa0;°C were investigated and compared. The results show that in the NaCl/KCl molten salt, the corrosion mechanism is mainly dominated by “chlorine-activated corrosion”. The surface oxide layer on 304 stainless steel is prone to spalling due to its poor adhesion to the substrate. The oxide layer on the surface of 3Al alloy grows discontinuously with many defects and cannot effectively prevent the downward diffusion of corrosive media. In the NaCl/KCl/Na₂SO₄ molten salt, apart from “chloride active corrosion”, the 304 and 3Al alloys also form porous structures due to the continuous dissolution and re-precipitation of the oxide film caused by the “alkali-assisted melting” mechanism, <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\text{SO}}_{4}^{2-}\)</EquationSource> </InlineEquation>, S diffuses downward and undergoes “acidic dissolution” with metal elements and sulfidation, resulting in a large number of pores being enriched at the interface between the oxide film and the substrate. Moreover, the consumption of Cr near the grain boundaries during the corrosion process promotes intergranular corrosion. The 6Al alloy demonstrated the most outstanding resistance to hot corrosion in both molten salts, mainly due to the formation of a continuous and dense Al₂O₃ layer, which effectively prevents the mutual diffusion of atoms and suppresses the extensive formation of cation vacancies at the oxide film/matrix interface.</p>