Oxidation and Hot Corrosion of Al–Si Diffusion-Coated AISI 304 Stainless Steel Exposed to Na₂SO₄–NaCl–V₂O₅ Molten Salts

A silicon-modified aluminide diffusion coating was developed on AISI 304 stainless steel via a powder-based Al–Si process and vacuum heat treatment at 1050 °C. Oxidation behavior was evaluated in air at 1100 °C for 100 h, and hot corrosion performance was investigated electrochemically in a molten Na₂SO₄–NaCl–V₂O₅ salt mixture at 750 °C. Uncoated AISI 304 exhibited rapid oxidation kinetics with thick, cracked Fe₂O₃/Fe₃O₄ scales and high mass gain. In contrast, the Al-Si diffusion-coated steel showed an order-of-magnitude lower weight gain, associated with the formation of a dense, continuous Al₂O₃-rich scale. Electrochemical measurements revealed a 1.5-fold reduction in corrosion current density for the coated sample, indicating suppressed anodic dissolution in the molten salt. The improved performance is attributed primarily to the protective Al₂O₃ scale; direct evidence of a synergistic role of silicon was not observed. The results demonstrate that Al-Si diffusion coatings offer a cost-effective solution for extending the high-temperature durability of austenitic stainless steels in aggressive molten-salt environments.