Effect of Al on Corrosion Resistance of Bridge Steel in Humid and Warm Industrial-Marine Atmosphere

The effect of Al on the corrosion resistance of bridge steel in simulated industrial-marine atmosphere was investigated by wet/dry alternate immersion corrosion testing, mass loss testing, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical testing. The results indicate that the corrosion process of the experimental steel shows a good agreement with the power function, and the growth trend of the rust layer is mainly inward. Al has the advantages in strengthening ferrite microstructure, inhibiting the crystallization of corrosion products, and promoting the formation of a dense protective film made of fine-grained oxide, which can help to improve the weather resistance of the steel. However, in the humid and warm industry-marine atmosphere, acids could be generated by the reaction between SO2 and H2O, leading to the corrosion of the rust layer and steel substrate. Besides, compared with iron oxides, the Al-containing oxides are easier to react with acids and result in more rust nests and cracks forming in the rust layer. With the increase of corrosion time, the number of cracks increases, and the volume of rust nests becomes bigger, the structure of the rust layer is thus continuously being damaged. By the late stage of corrosion, the infiltration of corrosive particles is accelerated by the formation of the cracks perpendicular to the steel substrate, leading to the increase of corrosion rate and the decline of corrosion resistance of the steel.