Hot-dip galvanizing, also called hot-dip galvanizing, is a method of obtaining a metallic coating by immersing steel components in molten zinc. With the rapid development of high-voltage power transmission, transportation, and communications in recent years, the requirements for protection of iron and steel parts have become higher and higher, and the demand for hot-dip galvanizing has also increased.
Protective properties of hot-dip galvanized layer
Usually the thickness of the galvanized layer is 5-15um, while the hot-dip galvanized layer is generally above 65um, even as high as 100um. Hot-dip galvanizing has good covering ability, dense plating and no organic inclusions. As we all know, the mechanism of zinc’s resistance to atmospheric corrosion includes mechanical protection and electrochemical protection. Under the condition of atmospheric corrosion, there are protective films of Zn0, Zn (OH) 2 and basic zinc carbonate on the surface of zinc layer, which can slow down the corrosion of zinc to a certain extent. If the protective film (also called white rust) is damaged, a new layer will be formed.
When the zinc layer is severely damaged and the iron matrix is endangered, zinc generates electrochemical protection for the matrix. The standard potential of zinc is -0.76V, the standard potential of iron is -0.44V. When zinc and iron form a microbattery, zinc is dissolved as an anode, and iron is dissolved. Protected as a cathode. Obviously, the hot-dip galvanizing ability of the base metal iron is better than that of electro-galvanizing.
Formation process of hot-dip galvanized layer
The process of hot-dip galvanizing layer formation is the process of forming an iron-zinc alloy between the iron substrate and the outermost pure zinc layer. The surface of the workpiece is formed with an iron-zinc alloy layer during hot dip plating, which makes the iron and pure zinc layer very Good combination, the process can be simply described as follows: when an iron workpiece is immersed in molten zinc liquid, zinc and a iron (body-centered) solid solution are first formed on the interface. This is a crystal formed by dissolving zinc atoms in the solid state of the base metal iron. The two metal atoms are fused and the attraction between the atoms is relatively small.
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