Corrosion Behavior of Zinc Aluminum Magnesium Coating After 24 Months of Exposure to Sunlight in Shenyang Industrial Atmospheric Environment

Zn–Al–Mg coating is based on zinc plating, adding a small amount of Al and Mg elements to form a complex corrosion resistance structure to achieve high corrosion resistance. However, the development of period of Zn–Al–Mg coating is short, and further research is required to determine its suitability for different environments. Thus, the corrosion behavior of Zn–Al–Mg coated steel exposed to the atmosphere for 24 months in Shenyang was studied by means of weight loss, morphology observation, composition, energy spectrum analysis, and electrochemical analysis. The results show that the corrosion rate of Zn–Al–Mg coating decreases first and then increases with the extension of time, and the average annual corrosion rate of Zn–Al–Mg coating in the second year is higher than that in the first year. The corrosion process is different between the skyward and field-ward sides. After exposure for 12 and 24 months, the corrosion rate of the skyward side was lower than that of field-ward side, and the corrosion rate difference between the two sides after exposure for 24 months was smaller than that after exposure for 12 months. The densified corrosion product Zn4(SO4)(OH)6·4H2O can effectively reduce the corrosion rate of skyward side. Corrosion pits and cracks are easy to form on the field-ward side, which accelerates the corrosion process of field-ward side, thus increasing the overall average annual corrosion rate of the sample.