Welding characteristics of galvanized steel

Galvanized steel is generally coated with a layer of zinc on the low carbon steel, and the galvanized layer is generally 20um thick. Zinc has a melting point of 419°C and a boiling point of around 908°C. In welding, zinc melts into a liquid and floats on the surface of the molten pool or at the root of the weld.

Zinc has greater solid solubility in iron, zinc liquid will deeply etch the weld metal along the grain boundary, and low melting point zinc forms "liquid metal embrittlement". At the same time, zinc and iron can form brittle compounds between metals, these brittle phases reduce the plasticity of the weld metal, and produce cracks under the action of tensile stress.

Weld fillet welds, especially T-joint fillet welds are the most prone to penetrating cracks.

When galvanized steel is welded, the zinc layer on the surface and edge of the groove will be oxidized, melted, evaporated, and even white smoke and steam will be volatilized under the action of arc heat, which is likely to cause weld porosity.

The melting point of ZnO formed by oxidation is relatively high, above 1800°C. If the parameter is too small during welding, it will cause ZnO slag inclusion. Due to the evaporation of zinc, a large amount of white smoke is volatilized, which has a stimulating and harmful effect on the human body. Therefore, the galvanized layer at the weld must be polished away.