Why does galvanized sheet rust

Why does galvanized sheet rust 

1.Definition Galvanized steel plate is to prevent the surface of the steel plate from being corroded and prolong its service life, a layer of metal zinc is coated on the surface of the steel plate, and this galvanized thin steel plate is called galvanized sheet. 

2. Classification and use According to the production and processing methods, it can be divided into the following categories: 

(1) hot-dip galvanized steel plate. A thin steel plate is immersed in a molten zinc bath so that a layer of zinc adheres to its surface. At present, it is mainly produced by continuous galvanizing process, that is, the coiled steel plate is continuously immersed in the plating tank with zinc melted to make galvanized steel plate;

 (2) Alloyed galvanized steel sheet. This steel plate is also made by the hot-dip method, but immediately after it is slotted, it is heated to about 500°C to form an alloy film of zinc and iron. This galvanized sheet has good coating adhesion and weldability; 

(3) Electro-galvanized steel plate. The electroplating method is used to manufacture this galvanized steel sheet, which has good machinability. However, the coating is thinner, and the corrosion resistance is not as good as that of hot-dip galvanized sheet; 

(4) Single-sided galvanized steel sheet and double-sided differential galvanized steel sheet. Single-sided galvanized steel sheet, i.e. a product that is galvanized on only one side. In welding, painting, anti-rust treatment, processing, etc., it has better adaptability than double-sided galvanized sheet. In order to overcome the shortcomings of uncoated zinc on one side, there is another galvanized sheet coated with a thin layer of zinc on the other side, that is, double-sided differential galvanized sheet; 

(5) Alloy and composite galvanized steel plate. It is a steel plate made of zinc and other metals such as lead, zinc alloys and even composite plating. 

This kind of steel plate has both very good anti-rust properties and good coating properties. In addition to the above five types, there are also color galvanized steel sheets, printed and coated galvanized steel sheets, PVC laminated galvanized steel sheets, etc. But at present, the commonly used is still hot-dip galvanized sheet.