News

The presence of zinc layer brings certain difficulties to the welding of galvanized steel, mainly including increased sensitivity to welding cracks and pores, zinc evaporation and smoke, oxide slag inclusion, and melting and damage of galvanized layer. Among them, welding cracks, porosity, and slag inclusion are the main problems.
weldability
(1) Crack
During the welding process, molten zinc floats on the surface of the molten pool or is located at the root of the weld seam. Due to the much lower melting point of zinc compared to iron, iron in the molten pool crystallizes first, and liquid zinc infiltrates along the grain boundaries of the steel, resulting in weaker intergranular bonding. Moreover, brittle intermetallic compounds Fe3Zn10 and FeZn10 are easily formed between zinc and iron, further reducing the plasticity of the weld metal. Therefore, under the action of welding residual stress, it is easy to crack along the grain boundary and form cracks.
Factors affecting crack sensitivity: ① Thickness of zinc layer: Galvanized steel has a thinner zinc layer and lower crack sensitivity, while hot-dip galvanized steel has a thicker zinc layer and higher crack sensitivity. ② Workpiece thickness: The thicker the thickness, the greater the welding constraint stress and the greater the crack sensitivity. ③ Groove gap: The larger the gap, the greater the crack sensitivity. ④ Welding method: When welding with manual arc welding, the crack sensitivity is low, while when welding with CO2 gas shielded welding, the crack sensitivity is higher.
Methods to prevent cracks: ① Before welding, make a V-shaped, Y-shaped, or X-shaped groove at the welding point of the galvanized sheet. Use methods such as oxyacetylene or sandblasting to remove the galvanized layer near the groove, while controlling the gap not to be too large, usually around 1.5mm. ② Select welding materials with low Si content. Gas shielded welding should use welding wire with low Si content, while manual welding should use titanium and titanium calcium welding rods.

(2) Stomata
The zinc layer near the groove undergoes oxidation (forming ZnO) and evaporation under the action of arc heat, and emits white smoke and vapor, which easily causes porosity in the weld seam. The higher the welding current, the more severe the evaporation of zinc and the greater the sensitivity of porosity. When welding with titanium and titanium calcium welding rods, it is not easy to produce pores within a medium current range. When using cellulose and low hydrogen welding rods for welding, porosity is prone to occur under both low and high currents. In addition, the angle of the welding rod should be controlled within the range of 30 °~70 ° as much as possible.
(3) Evaporation of Zinc and Smoke Dust
When welding galvanized steel plates with arc welding, the zinc layer near the molten pool oxidizes into ZnO and evaporates under the action of arc heat, forming a large amount of smoke and dust. The main component of this smoke is ZnO, which has a significant stimulating effect on the respiratory organs of workers. Therefore, good ventilation measures must be taken during welding. Under the same welding specifications, the amount of smoke generated during welding with titanium oxide type electrodes is lower, while the amount of smoke generated during welding with low hydrogen type electrodes is higher.
(4) Oxide slag inclusion

When the welding current is low, the ZnO formed during the heating process is not easy to escape, which can easily cause ZnO slag inclusion. ZnO is relatively stable, with a melting point of 1800 ℃. The large block shaped ZnO slag has a very adverse effect on the plasticity of the weld seam. When using titanium oxide type welding rods, ZnO is finely and uniformly distributed, and has little effect on plasticity and tensile strength. When using cellulose or hydrogen type welding rods, the ZnO in the weld seam is relatively large and abundant, resulting in poor weld performance.