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Characteristics of galvanized steel welding
Galvanized steel is generally low carbon steel plated with zinc, the zinc coating is generally 20um thick. At 419 ° C, the boiling point of about 908 ° C melting point of zinc. In welding, the melted liquid zinc bath floating on the surface or in the root of the weld location. Zinc has a greater solubility in iron, zinc etching liquid will go into the weld metal along the grain boundaries, low-melting zinc to form a “liquid metal embrittlement.” Meanwhile, zinc and iron brittle intermetallic compounds can be formed, these brittle phases so that the weld metal plastic lower under tensile stress and cracks. If the fillet weld, especially the fillet weld T-joints most prone to penetrate the cracks. When welding galvanized steel, zinc layer and the surface of the groove at the edge of the arc under the action of heat, oxidation, melting, evaporation as well as volatile white smoke and steam, can easily cause weld porosity. ZnO due to oxidation and the formation of its high melting point of about 1800 ° C or more, if small parameter in the welding process, will cause the ZnO slag, at the same time. Since Zn become deoxidizer. Produces FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Second, due to the evaporation of zinc, volatile lot of white smoke, to stimulate the human body, harmful effects, therefore, must be welded zinc coating at the polished off.
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