Enhancing the long-term marine atmospheric corrosion performance of structural steel via an advanced tin thermal diffusion process

In this study, 45 steel was taken as the research object, and a tin-iron alloy layer was prepared on its surface via a thermal diffusion tinning process. Combined with a series of characterization methods, the microstructure and element distribution of the thermal diffusion layer were systematically analyzed. Additionally, through cyclic immersion tests, electrochemical measurements, and outdoor exposure tests in marine atmosphere, the effects of thermal diffusion temperature and tin content in the diffusion agent on the structure and corrosion resistance of the thermal diffusion layer were systematically investigated. The results show that thermal diffusion tinning can form an alloy layer dominated by FeSn2 on the surface of 45 steel. Moreover, the higher the thermal diffusion temperature and the greater the tin content in the diffusion agent, the larger the thickness (up to 15 μm) and the better the compactness of the alloy layer. The corrosion resistance of the tinned steel is significantly better than that of 45 steel, and it is further improved with the increase of thermal diffusion temperature, tin content, and extension of thermal diffusion time. Among them, the tinned steel prepared under the thermal diffusion process of 80%-280°C-4h exhibits a corrosion current density of 4.027 μA · cm -2 , which is only 1/400 of that of 45 steel (12.095 μA · cm -2 ), and demonstrates the latest corrosion initiation and slowest development rate in marine atmospheric exposure. The key factors contributing to the improved corrosion resistance are the stable structure of FeSn 2 intermetallic compounds in the thermal diffusion layer, the physical barrier effect of the dense alloy layer, and the protective rust layer formed during the corrosion process.