Why Does Galvanized Sheet Rust?

Through long-term theoretical analysis, there may be two reasons for the rust of galvanized sheet: one is that the quality of galvanizing is unqualified, such as leaks, bubbles, etc. Such as acid rain, secondary humidity, etc. Third, improper storage methods. It will rust quickly if used in wet places. These three possibilities are obtained through theoretical analysis. Therefore, anti-rust work should be carried out on galvanized sheet.

The main reason for the rust of galvanized sheet is the surface galvanized layer. Zinc is chemically active and soluble in acids and bases. In a humid environment, zinc will undergo a chemical reaction to form an alkaline zinc carbonate film on the surface. When in contact with substances containing hydrogen sulfide, the corrosion resistance of zinc will be reduced, it will be easily corroded, the surface of the steel plate will be exposed, and it will eventually rust. The probability of rusting of electro-galvanized strip steel is relatively low. Due to the thicker galvanized layer, it is not easy to oxidize and rust the steel plate.

Galvanized sheet will not rust under normal environment. May rust due to improper storage, scratching and handling, water ingress and steam fumigation. Galvanized sheet rusts because zinc is usually corroded to protect other metals. Otherwise, the zinc plate is impure and contains impurities such as iron. Or the zinc coating is uneven, exposing the exterior metal and causing corrosion. Or inadvertently contact with other metals to form chemical corrosion. The galvanized sheet can guarantee that it will not rust for several years. This question depends on what environment, the thickness of the galvanized layer, different sources, etc.

Generally speaking, the corrosion of galvanized sheet is not that all the galvanized layers on the surface are corroded uniformly, but that the coating is corroded first under the condition of poor bonding between the coating and the substrate, resulting in severe localized corrosion and Use performance loss. From this point of view, the adhesion of the zinc coating, especially the overall adhesion, is more important than the thickness of the zinc coating. If the local adhesion of the galvanized layer is not good, even if the galvanized layer is thick, it will rust due to poor adhesion.

Galvanized steel coils need to be cut during use, and the interface after cutting will rust when used without treatment. After the plate is cut, anti-rust treatment must be carried out to reduce corrosion in subsequent use. When the galvanized coil plate is rusted, gently wipe it with water sandpaper to remove the surface rust, and then apply an anti-rust pen on the rusted part to dry the rusted part to prevent rust.