Hot dip Galvanizing Process

Hot dip Galvanizing Process
1. Introduction

Hot-dip galvanizing, also known as hot-dip galvanizing, is a method in which steel members are immersed in molten zinc to obtain a metal coating. In recent years, with the rapid development of high-voltage transmission, transportation and communication, the requirements for steel parts are getting higher and higher, and the demand for hot-dip galvanizing is also increasing.

2. Hot-dip galvanized layer protection performance

Usually the thickness of the electroplated zinc layer is 5-15 μm, while the hot-dip galvanized layer is generally above 35 μm, even up to 200 μm. Hot-dip galvanizing coverage is good, the coating is dense, and there is no organic inclusions. It is well known that the mechanism of anti-atmospheric corrosion of zinc has mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, there are ZnO, Zn(OH)2 and basic zinc carbonate protective films on the surface of the zinc layer, which slows down the corrosion of zinc to some extent. A layer of protective film (also known as white rust) is destroyed and a new film layer is formed. When the zinc layer is seriously damaged and the iron matrix is endangered, zinc electrochemically protects 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. Protected as a cathode. It is obvious that hot-dip galvanizing is superior to electro-galvanizing in the resistance to atmospheric corrosion of the base metal iron.

3. Hot-dip galvanizing layer formation process

The hot-dip galvanizing layer formation process is a process of forming an iron-zinc alloy between the iron matrix and the outermost pure zinc layer, and the surface of the workpiece forms an iron-zinc alloy layer during hot dip plating, so that the iron and the pure zinc layer are very For a good combination, the process can be simply described as: when the iron workpiece is immersed in the molten zinc liquid, a zinc and an alpha iron (body center) solid solution are first formed at the interface. This is a crystal formed by the dissolution of zinc atoms in the solid state of the base metal iron. The fusion between the two metal atoms is relatively small. Therefore, when zinc is saturated in the solid solution, the two elements of zinc and iron diffuse into each other, and the zinc atoms diffused into (or infiltrated into) the iron matrix migrate in the matrix lattice, gradually forming an alloy with iron, and diffusing. The iron in the molten zinc solution forms an intermetallic compound FeZn13 with zinc and sinks into the bottom of the hot-dip galvanizing pot, which is zinc dross. When the workpiece is removed from the zinc immersion liquid, a pure zinc layer is formed on the surface, which is a hexagonal crystal. Its iron content is not more than 0.003%.

4. Hot-dip galvanizing process and related instructions

4.1 Process

Workpiece→degreasing→water washing→acid washing→water washing→immersion assisted plating solvent→drying preheating→hot galvanizing→finishing→cooling→passivation→rinsing→drying→testing