Welding Characteristics of Galvanized Steel

Galvanized steel surface coated with a layer of zinc is generally low carbon steel, galvanized layer is generally 20um thick. At 419 ° C, the melting point of zinc is about 908 ° C. During welding, zinc is melted into the liquid that floats on the surface of the cell or the root of the weld. Zinc is more soluble in iron and the zinc corrosion solution will enter the weld metal along the grain boundaries, forming a "low melting point of liquid metal embrittlement." At the same time, brittle intermetallics of zinc and iron may form, and these brittle phases, Tensile stress cracks in the weld metal plasticity decreased. If the weld, fillet weld is the most easy to penetrate the crack. When welding galvanized steel, the zinc layer oxidizes, melts, evaporates and even volatilizes white smoke and steam at the bevel surface and edges at the arc heat, easily causing the weld pores.


Zinc oxide is formed as a result of oxidation and its melting point is about 1800 ° C or higher. If the parameters are small during the welding, zinc oxide dross will occur simultaneously. Because zinc is a deoxidizer. Generate FeO MnO or feo-mno-sio2 low-melting oxide slag. Second, due to the evaporation of zinc, a large amount of white smoke volatiles, stimulate the body, the impact of harm, therefore, the necessary welding galvanized layer is in the grinding process.


Galvanized steel and low carbon steel welding preparation is generally the same, you have to pay attention to be careful to deal with groove size and galvanized near. Infiltration, the size of the groove to be appropriate, generally 60 ~ 65 °, leaving a gap, generally 1.5 ~ 2.5mm; Zinc to reduce weld penetration, before welding, galvanized tank can be clear, and then welding the back layer. In the actual supervision, the use of centralized play slot, leaving blunt-edge technology for centralized control, two welding process, reducing the possibility of incomplete penetration.


When multi-layer welding the first layer of weld seam in order to evaporate evaporation of molten zinc layer to avoid welding, can greatly reduce the zinc liquid left in the weld. When the fillet weld is melted on the first layer of vaporized zinc coating, the evaporation and escape of the solder are done by first removing the front part of the electrode from 5 to 7 mm and melting the zinc layer, then continuing to return to its original position. And when cross-welding and vertical welding, such as welding slag, such as short J427 choice, the trend of weakening will be small; if the technology of round-trip conveyor belt, but also can be a defect-free welding quality.