The formation process of hot-dip galvanized layer is the process of forming iron-zinc alloy between the iron matrix and the pure zinc layer outside, and the iron-zinc alloy layer is formed on the surface of the workpiece during hot dip plating, so that the iron and pure zinc layer are well combined. The process of large coil galvanized wire can be simply described as: when the iron workpiece is immersed in the molten zinc liquid, the first zinc and α-iron (body-centered) solid melt is formed on the interface. This is a crystal formed by the matrix metal iron dissolved with zinc atoms in a solid state, and the two metal atoms are fused, and the gravitational attraction between the atoms is relatively small.
Therefore, when zinc reaches saturation in the solid melt, the two elements of zinc and iron atoms diffuse each other, the zinc atoms diffused into (or infiltrated into) the iron matrix migrate in the matrix lattice, and gradually form an alloy with iron, and the iron diffused into the molten zinc liquid forms an intermetallic compound FeZn13 with zinc, which sinks into the bottom of the hot galvanized pot, that is, zinc slag. When the workpiece is removed from the zinc leaching solution, the surface of the pure zinc layer is formed, which is a hexagonal crystal, and the iron content is not more than 0.003%.
Hot dip galvanizing, also known as hot dip galvanizing, is a method of dipping steel components into molten zinc liquid to obtain a metal coating. With the rapid development of high-voltage power transmission, transportation and communications, the protection requirements for steel parts are getting higher and higher, and the demand for hot-dip galvanizing is also increasing. Usually the thickness of the galvanizing layer is 5 to 15μm, and the large roll galvanizing wire layer is generally more than 35μm, or even up to 200μm. Hot dip galvanizing has good covering capacity, dense coating and no organic inclusion.
As we all know, the mechanism of resistance to atmospheric corrosion of zinc has mechanical protection and electrochemical protection, in the atmospheric corrosion conditions of zinc layer surface ZnO, Zn(OH)2 and basic zinc carbonate protective film, to a certain extent to slow the corrosion of zinc, this layer of protective film (also known as white rust) is damaged, and will form a new film.
When the zinc layer is seriously damaged, endangering the iron matrix, zinc will produce electrochemical protection on the matrix, the standard potential of zinc is -0.76V, and the standard potential of iron is -0.44V. When zinc and iron form microbatteries, zinc will be dissolved as the anode, and iron will be protected as the cathode. Obviously, the atmospheric corrosion resistance of hot-dip galvanizing is better than that of electrogalvanizing.
Post time: 11-12-23