(1) In the whole life cycle of galvanized sheet, the first corrosion is the oxidation of zinc coating on the surface, resulting in "white rust". After a long time, the "white rust" on the surface further reacts with carbon dioxide and other impurities in the humid air, forming "black spots". When the galvanized sheet has been used for a long time, and the galvanized layer is corroded seriously, the steel base loses the "sacrificial corrosion protection" function of zinc, and then it begins to oxidize, forming "red rust". Once the steel base begins to oxidize, the corrosion rate becomes very fast, "the galvanized sheet also ends its life.(2) In addition, there are two special corrosion conditions of galvanized sheet called "black transformation". One is that due to the influence of lead and other elements in the zinc coating after a period of use, the dull part of the zinc flower will turn black. The blackened zinc coating still has a protective effect on the steel base, but has a certain impact on the service life. This situation has been greatly improved after the lead was stopped and antimony was used to promote the formation of zinc flower. Another situation is that in the transportation of galvanized sheet, due to the small coiling tension, the looseness between the steel strip layers, the parts where the steel coil contacts the skid will rub against each other and produce oxidation. After the white oxide is rubbed off, the galvanized sheet surface will produce black spots, which will damage the passivation film, reduce the galvanized layer, greatly reduce the life of the galvanized sheet, and the appearance will also be affected.