Study on corrosion behavior and mechanism of Q235 steel in tropical marine atmosphere based on real-time electrochemical monitoring

This study systematically investigates the corrosion behavior of Q235 steel in the tropical marine atmosphere of Sanya through a two-year field exposure test integrated with real-time atmospheric corrosion monitoring (ACM) technology. The corrosion mechanisms were elucidated by corrosion kinetics analysis, characterization of corrosion products using scanning electron microscopy (SEM), 3-dimensional laser scanning confocal microscope (3D-LSCM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The corrosion kinetics follow a power-law model ( D = 6.9 t 0.4 ), indicating the formation of a protective rust layer. The average corrosion rate decreased over time due to the formation of a dense, adherent rust layer composed of γ-FeOOH, α-FeOOH, Fe 3 O 4 , and Fe 2 O 3 . The early-stage formation of α-FeOOH was crucial for enhancing the protectiveness of the rust layer, as confirmed by the increase in R f + R ct observed in the EIS analysis. Localized corrosion intensified with exposure time, with the maximum pit depth reaching 89.868 μm after two years of exposure. The cumulative electric charge ( Q ACM-instant ), obtained by integrating the instantaneous corrosion current ( I ACM-instant ) measured by the ACM sensor, exhibited a strong correlation with the trend of measured corrosion depth. Analysis of ACM sensor data revealed that the corrosion current closely followed changes in relative humidity, indicating that wet-dry cycles play a driving role in the corrosion process. This study deepens the understanding of the corrosion mechanisms of Q235 steel in tropical marine atmospheres from a dynamic perspective, offering valuable data and theoretical insights for marine engineering materials and corrosion protection technologies.