Galvanized steel is generally in the low carbon steel outside a layer of zinc, galvanized layer is generally 20um thick. The melting point of zinc is at 419°C, and the boiling point is about 908°C. The zinc is used in the welding of galvanized steel. In welding, zinc melts into a liquid floating on the surface of the molten pool or in the root position of the weld. Zinc in iron has a large solid solubility, zinc liquid will be along the grain boundaries in-depth erosion of the weld metal, low melting point of zinc to form a “liquid metal embrittlement”.
At the same time, zinc and iron can form a brittle intermetallic compounds, these brittle phase to reduce the plasticity of the weld metal, under the action of tensile stress and cracks.
If welding fillet welds, especially T-joint fillet welds are most likely to produce penetration cracks. Galvanized steel welding, bevel surface and edge of the zinc layer, under the action of the arc heat, oxidation, melting, evaporation and volatile white soot and steam, very easy to cause weld porosity.
Due to oxidation and the formation of ZnO, its melting point is high, about 1800 ° C or more, if the parameters in the welding process is small, will cause ZnO slag, at the same time. As Zn becomes a deoxidizer. Produce FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Secondly, due to the evaporation of zinc, volatilization of a large number of white soot, irritating and injurious effects on the human body, therefore, it is necessary to grind the galvanized layer of the weld to dispose of it.
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