Galvanized steel is generally placed with zinc at low carbon steel, and the galvanized layer is generally 20um thick. The melting point of zinc is 419 ° C, and the boiling point is about 908 ° C. During the welding, zinc melted into liquid floating on the surface of the molten tank or on the root of the weld. Zinc has a large solid solution in the iron. Zinc liquids will deeply etch the welded metal along the crystal boundary, and low melting point zinc forms a "liquid metal crisp".
At the same time, zinc and iron can form a metal crispy compound. These brittleness phase reduces the plasticity of the welded metal and cracks under tensile stress.
If the welding angle weld, especially the corner welding of the T -shaped joint, the most likely to produce penetrating cracks. During the welding of galvanized steel, the zinc layer on the surface and edges of the ramp is under the action of arc thermal fever, which produces oxidation, melting, evaporation, and volatilization of white smoke and steam, which can easily cause welded air holes.
The ZNO formed by oxidation has a high melting point, about 1800 ° C. If the parameters are small during the welding process, the ZnO residue will be caused, and at the same time. Since Zn becomes a deoxyer. Generate Feo-Mno or Feo-Mno-SIO2 low melting point oxide slag. Secondly, due to the evaporation of zinc, a large amount of white smoke and dust evaporate have a stimulating and damage effect on the human body. Therefore, the galvanized layer of the welding area must be polished.
