Hot dip galvanizing, also known as hot dip galvanizing, is a method for steel members to be immersed in molten zinc liquid to obtain a metal covering layer. In recent years, with the rapid development of high-voltage power transmission, transportation and communication, the protection requirements for steel parts are getting higher and higher, and the demand for hot-dip galvanizing is also increasing. The thickness of the general galvanizing layer is 5 to 15μm, and the hot dip galvanizing layer is generally above 35μm, and even up to 200μm. Hot dip galvanized coating can be good, fine coating, no organic doping.
As we all know, the mechanism of zinc resistance to atmospheric corrosion has mechanical maintenance and electrochemical maintenance, in the atmospheric corrosion conditions of zinc layer surface ZnO, Zn(OH)2 and basic zinc carbonate maintenance film, to a certain extent to slow the corrosion of zinc, this layer of maintenance film (also known as white rust) is damaged and will form a new film. When the zinc layer is seriously damaged and endangers the iron matrix, the zinc performs electrochemical maintenance on the matrix, the gauge potential of zinc is -0.76V, and the gauge potential of iron is -0.44V. When zinc and iron form a microbattery, zinc is dissolved as the anode, and iron is maintained as the cathode.
Obviously, the atmospheric corrosion resistance of hot-dip galvanizing to matrix metal iron is better than that of electric galvanizing. Hot dip galvanized layer composition process is between the iron matrix and the outside pure zinc layer, the process of forming iron-zinc alloy, the workpiece surface in the hot dip plating to form an iron-zinc alloy layer, so that the iron and pure zinc layer is well combined, the process can be briefly described as: when the iron workpiece is immersed in the molten zinc liquid, the first zinc and α iron (body-centered) solid melt on the interface.
This is a crystal composed of zinc atoms dissolved in the matrix metal iron 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 full in the solid melt, the two elements of zinc and iron atoms are dispersed to each other, and the zinc atoms dispersed into (or into) the iron matrix migrate in the matrix lattice, and gradually form an alloy with iron.
The iron dispersed into the molten zinc liquid forms the intermetallic compound FeZn13 with zinc, which sinks into the bottom of the hot galvanized pot and is the zinc slag. When the workpiece is removed from the zinc leaching solution, the surface constitutes a pure zinc layer, which is a hexagonal crystal. Its iron content is not greater than 0.003%.
Post time: 22-11-23