Hot Dip Galvanization
- May 02, 2018 -
Hot dip galvanization is also known as hot dip galvanization, which is a method of obtaining metal coating in molten zinc solution of steel components.In recent years, with the rapid development of high-voltage power transmission, transportation and communication, the protection requirements of steel parts are becoming higher and higher, and the demand for hot galvanizing is increasing.
Generally, the thickness of the electrogalvanizing layer is 5 ~ 15 mu m, while the hot galvanizing layer is usually above 35 mu m, and even up to 200 mu m.Hot galvanizing coating is good, the coating is dense, no organic matter inclusions.As is known to all, the mechanism of resistance to atmospheric corrosion of zinc have mechanical and electrochemical protection, under the condition of atmospheric corrosion of zinc layer surface of ZnO, zinc (OH) 2 and alkali carbonate zinc coating, to a certain extent reduce the corrosion of zinc, this layer of protective film (also called white rust) is damaged and will form a new film.Destroyed when the zinc layer, endanger the iron matrix, the zinc electrochemical protection on the substrate, the standard potential of zinc - 0.76 V, iron the standard potential of 0.44 V, zinc and iron to form the micro battery zinc as the anode is dissolved, iron are protected as the cathode.It is obvious that the anti - atmospheric corrosion ability of hot - galvanizing metal iron is better than that of electrogalvanizing.
Galvanized layer formation process is the most out of pure iron substrate and formed between the zinc layer of iron, zinc alloy, the process of workpiece surface formed in hot dip plating of iron - zinc alloy layer, and makes good combination between iron and pure zinc layer, the process can be simply described as follows: when the blacksmith a immersed in molten zinc liquid, zinc first formed in the interface and alpha (heart) solid solution.This is a matrix of metallic iron dissolved in a solid state with zinc atoms forming a crystal, the two metal atoms are fused together, the atom is less attractive.So when zinc in solid solution after reaching saturation, two kinds of zinc iron atom diffusion, spread to (or called infiltration) iron matrix of zinc atom in the lattice matrix migration, gradually formed and iron alloy, and spread to molten zinc liquid iron and zinc in the formation of intermetallic compounds FeZn13, sank into the hot dip galvanized pot is zinc slag.When the workpiece is removed from the zinc-impregnated liquid, it forms a pure zinc layer, which is a hexagon crystal.Its iron content is not greater than 0.003%.