The demand for hot-dip galvanizing is also increasing

1. Hot-dip galvanizing, also called hot-dip galvanizing, is a method of immersing steel components in molten zinc to obtain a metal coating. In recent years, with the rapid development of high-voltage power transmission and transformation, transportation, communications and other industries, the protection requirements for steel parts have become higher and higher, and the demand for hot-dip galvanizing has also continued to increase.

2. Protection performance of hot-dip galvanized layer

The thickness of the electro-galvanized layer is generally 5-15μm, while the hot-dip galvanized layer is generally above 35μm, even as high as 200μm. The hot-dip galvanizing has good coverage, dense coating and no organic inclusions. As we all know, the anti-atmospheric corrosion mechanism of zinc includes mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, there are protective films of ZnO, Zn(OH) 2 and basic zinc carbonate on the surface of the zinc layer, which slow down the corrosion of zinc to a certain extent. The protective film (also called white rust) is damaged and a new film is formed. When the zinc layer is severely damaged and the iron matrix is threatened, zinc will electrochemically protect the matrix. The standard potential of zinc is -0.76V, and the standard potential of iron is -0.44V. When zinc and iron form a microbattery, zinc is dissolved as an anode. It is protected as a cathode. Obviously, hot-dip galvanizing has better atmospheric corrosion resistance than electro-galvanizing.

3. Formation process of hot-dip galvanized layer

The formation process of the hot-dip galvanized layer is a process of forming an iron-zinc alloy between the iron matrix and the outermost pure zinc layer. During hot-dip plating, an iron-zinc alloy layer is formed on the surface of the workpiece, making the iron and pure zinc layer very close. A good combination, this process can be simply described as: when the iron is immersed in the molten zinc, a solid solution of zinc and alpha iron (body core) is first formed at the interface. This is a crystal formed by dissolving zinc atoms in the base metal iron in a solid state. Two metal atoms fuse together, and the attraction between the atoms is relatively small. Therefore, when zinc reaches saturation in the solid solution, the two element atoms of zinc and iron diffuse each other, and the zinc atoms that have diffused (or penetrated) into the iron matrix migrate in the matrix lattice, and gradually form alloys with iron. The iron and zinc diffused to form an intermetallic compound FeZn13, which sinks into the bottom of the hot-dip galvanizing pot, called zinc dross. When the workpiece is taken out of the zinc immersion solution, a pure zinc layer is formed on the surface, which is a hexagonal crystal. The iron content does not exceed 0.003%.