Why does white rust form on hot-dip galvanized surfaces?

　　White rust is the oxidation of zinc; the resulting oxide expands in volume and adheres to the coating surface, giving it a white powdery appearance, often accompanied by some light brownish spots. The swollen zinc oxide makes the coating appear severely damaged, though in reality only the surface has undergone slight corrosion. In dry environments, white rust will flake off, after which a dense protective layer re‑forms on the coating surface, without compromising its corrosion‑resistance performance.

　　White rust forms when a coating is exposed to rain and remains in a damp, poorly ventilated environment. It also appears conspicuously when the coated surface comes into contact with strong acids, strong alkalis, organic acids, or salts. During maritime transport, splashing seawater can likewise lead to the development of white rust.

　　In environments that allow for rapid drying, the coating will not develop white rust even after exposure to rain.

　　To prevent the formation of white rust, ensure that the storage environment is protected from rain and well-ventilated, keeping the area dry.