Welding characteristics of galvanized steel sheet
Galvanized steel is usually galvanized low carbon steel, zinc coating is generally 20 um thick. The boiling point of zinc at 419 C is about 908 C. During welding, the molten liquid zinc bath floats on the surface or root of the welding position. Zinc has great solubility in iron. Zinc etching solution will enter the weld metal along the grain boundary, and low melting point zinc will form "liquid metal embrittlement". At the same time, brittle intermetallic compounds of zinc and iron can be formed. These brittle phases reduce the tensile stress and crack of weld metal plastics. If fillet welds, especially T-joints of fillet welds, are most likely to penetrate cracks. When galvanized steel sheet is welded, the groove surface of zinc layer and arc edge is easily caused by heat, oxidation, melting, evaporation, volatile white smoke and steam. The high melting point of zinc oxide is about 1800 C due to oxidation. If the welding parameters are small, the zinc oxide slag will be produced. At the same time, the zinc oxide slag will be produced. Because zinc becomes a deoxidizer. Production of FeO-MnO or FeO-MnO-SiO2 low melting point slag. Secondly, due to the evaporation of zinc, volatilization of a large amount of white smoke, stimulating the human body, harmful effects, therefore, zinc coating must be welded at the polishing place.


Welding process control
The preparation work before welding is generally the same as that of low carbon steel. It should be noted that the groove size and the nearby zinc coating should be carefully handled. For penetration, the groove size should be appropriate, generally 60-65 degrees, leaving some space, generally 1.5-2.5 mm. In order to reduce the penetration of the weld, zinc can be plated in the groove before welding and then welded a layer. In practice, monitoring, centralized grooving, leaving blunt edge technology for centralized control, two welding processes, reduce the possibility of incomplete penetration.


Galvanized pipe electrode should be based on the choice of substrate material, usually considering the ease of use of low carbon steel, J422 is more common.
Welding technology: When welding the first layer of multi-layer weld, try to make it melt and evaporate the zinc layer, evaporate and separate from the weld, which can greatly reduce the liquid zinc remaining in the weld. When fillet weld is welded, as far as possible, the galvanized layer is melted and evaporated in the first layer, evaporated and separated from the weld. This method first removes about 5-7 mm from the end of the electrode. At this time, the zinc layer melts down and goes back to the original position of the welding. Thirdly, when horizontal welding and vertical welding, such as welding slag, such as short J427, undercut is often the smallest; if stripping technology is used, flawless welding quality can be achieved.