Enhanced high-temperature corrosion resistance of Al-Si coated steel via Cr thin-film deposition and alloy phase formation

Conventional Al-Si coated steels rely on Al₂O₃ passive films for corrosion and heat resistance; however, prolonged high-temperature exposure often results in Fe diffusion, intermetallic layer growth, and Fe₂O₃ formation, which compromise their protective capabilities. This study addresses these limitations by enhancing the high-temperature corrosion resistance of Al-Si coated steel through Cr thin-film deposition via physical vapor deposition followed by heat treatment. Specifically, a 300-nm Cr thin film was deposited on commercial Al-Si coated steel and heat treated at 600 °C, resulting in the formation of Al-Cr and Cr-Si alloy phases at the surface. Microstructural analyses demonstrated that the Cr layer and its alloy phases improved surface stability after thermal exposure, and strengthened adhesion between coating and substrate. The root mean square roughness (Rrms) for uncoated specimens increased markedly after exposure, whereas the Cr-coated and heat-treated specimens showed almost no increase. Adhesion was improved, as the peeling area in tape tests dropped from 91.5 % for Cr-only specimens to just 7.7 % after heat treatment. Thermogravimetric, electrochemical, and salt spray tests confirmed that ASC-600 specimens had the lowest oxidation weight gain and best corrosion resistance. TEM confirmed that dense Cr₂O₃ and α-Al₂O₃ films acted as barriers, highlighting the effectiveness of this approach for durable industrial coatings.