Study on Constructing Indoor Accelerated Simulation Methods for Steel with Galvalume Coating Exposed to Marine Atmosphere

To investigate the corrosion behavior and mechanism of steel with galvalume coating (Zn–55%Al–1.6%Si) in marine atmospheric environments, an indoor accelerated corrosion test method was constructed. Both marine atmospheric exposure tests and spectrum-based accelerated corrosion tests were carried out to compare the corrosion kinetics, corrosion products, and electrochemical behavior. A corrosion prediction model was established using the weight-loss method. Surface morphologies were observed by scanning electron microscopy (SEM), the compositions of corrosion products were identified by X-ray diffraction (XRD), and electrochemical tests were conducted to elucidate the time-dependent electrochemical characteristics. The results showed that after two years of natural exposure and 16 cycles of accelerated testing, the specimens exhibited mainly uniform corrosion of the galvalume coating without significant localized corrosion. The corrosion products were primarily composed of ZnO, Zn5(OH)6(CO3)2, Zn5(OH)8Cl2·H2O, and Al2O3. The corrosion potential increased while the corrosion current density decreased with prolonged testing, indicating that the corrosion product film effectively inhibited corrosion and enhanced protection. By integrating the corrosion kinetics, product composition, and electrochemical mechanism from both outdoor and indoor tests, the constructed spectrum-based accelerated test method demonstrated good correlation with actual marine atmospheric corrosion processes, providing a reliable approach for evaluating the corrosion resistance and service life of steel with galvalume coating in marine environments.