The formation process of hot dip galvanized layer is between the iron matrix and the outside of the pure zinc layer, the formation of iron-zinc alloy process, the workpiece surface in hot dip plating when the formation of iron-zinc alloy layer, so that the iron and pure zinc layer is well combined. The process of large roll 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 the solid state. The two metal atoms are fused with each other, and the 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 with each other, and the zinc atoms diffused into (or infiltrated into) the iron matrix migrate in the lattice of the matrix and gradually form an alloy with iron, while the iron diffused into the molten zinc liquid forms an intermetallic compound FeZn13 with zinc and sinks into the bottom of the hot-dip 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 hexagonal crystal, and its iron content is not more than 0.003%.
Hot dip galvanizing, also known as hot dip galvanizing, is a method of obtaining a metal covering layer by immersing a steel member into a molten zinc solution. With the rapid development of high-voltage power transmission, transportation and communication, the protection requirements for steel parts are becoming higher and higher, and the demand for hot-dip galvanizing is also increasing. Usually the thickness of electrogalvanized layer is 5 ~ 15μm, and the large roll galvanized wire layer is generally more than 35μm, or even up to 200μm. Hot dip galvanized coating ability is good, dense coating, no organic inclusions.
As we all know, the mechanism of resistance to atmospheric corrosion of zinc includes mechanical protection and electrochemical protection. Under the condition of atmospheric corrosion, there are ZnO, Zn(OH)2 and basic zinc carbonate protective film on the surface of zinc layer, which to a certain extent slows the corrosion of zinc. When this protective film (also known as white rust) is damaged, a new film will be formed.
When the zinc layer is seriously damaged and endangers the iron matrix, the 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, the zinc will be dissolved as the anode, and the iron will be protected as the cathode. Obviously, the atmospheric corrosion resistance of hot dip galvanizing is better than that of electric galvanizing.
Post time: 20-04-23