In the United States, a thin galvanized test piece with a film thickness of 0.03mm has been tested, and the results have found that the average life expectancy in rural areas, coastal areas and industrial areas is about 3:2:1, which means that in the polluted air, the galvanized layer has the highest life expectancy. Corrosion is prone to occur because the exhaust gas emitted by factories in industrial areas contains many oxides of sulfur (SOx) and oxides of nitrogen (NOx) that will damage the zinc coating. In coastal areas, the presence of a large number of salt crystals and liquid particles (chlorides) in the atmosphere will cause metal corrosion, and the relative humidity of the atmosphere also significantly affects the corrosion rate.
The Institute of Materials Protection, University of Science and Technology Beijing has also conducted atmospheric exposure corrosion tests of galvanized coatings in different parts of the mainland. The test period was one year. The results found that the highest corrosion rate was in the atmosphere with the highest content of SO2, chloride (sea salt particles) and Areas with the highest relative humidity. Among them, atmospheric relative humidity is considered to be the main factor causing corrosion, while atmospheric pollutants, especially SO2 and chloride, are the main factors promoting corrosion.
In the process of production, storage and transportation of galvanized screws, the galvanized layer of the galvanized screw may be whitened, darkened, blackened, etc., mainly due to the corrosion of the galvanized layer in contact with corrosive media and moisture, oxygen, and carbon dioxide in the atmosphere. the result of.
