Galvanized steel can be welded by manual arc welding, gas metal arc welding, argon arc welding, resistance welding and other methods.
⑴Manual arc welding.
1) Preparation before welding.
In order to reduce welding smoke and prevent the occurrence of welding cracks and pores, in addition to making appropriate grooves, the zinc layer near the grooves should also be removed before welding. Removal methods can be flame baking or sand blasting. The groove gap should be controlled within 1.5~2mm as much as possible. When the thickness of the workpiece is large, it can be relaxed to 2.5~3mm.
2) Selection of welding rods.
The principle of selecting welding rods is that the mechanical properties of the weld metal should be as close as possible to the base metal, and the silicon content in the deposited metal of the welding rod should be controlled below 0.2%.
The joint strength obtained when welding with ilmenite type electrodes, titanium oxide type electrodes, cellulose type electrodes, calcium titanium type electrodes and low hydrogen type electrodes can all reach satisfactory indicators. However, welds welded with low hydrogen electrodes and cellulose electrodes are prone to slag inclusions and pores, so they are generally not used.
For low carbon steel galvanized steel sheets, J421/J422 or J423 electrodes should be preferred. For galvanized steel plates with strength levels above 500MPa, welding rods of E5001, E5003 and other models can be used. For galvanized steel plates with a strength above 600MPa, welding rods such as E6013, E5503 and E5513 should be used.
When welding, try to use a short arc and do not let the arc swing to prevent the expansion of the melted area of the galvanized layer, ensure the corrosion resistance of the workpiece and reduce the amount of smoke.
⑵ Gas metal arc welding.
CO2 gas shielded welding or Ar+CO2, Ar+O2 and other mixed gas shielded welding can be used for welding. The shielding gas has a significant impact on the Zn content in the weld. When pure CO2 or CO2+O2 is used, the Zn content in the weld is higher. When Ar+CO2 or Ar+O2 is used, the Zn content in the weld is relatively high. Low. The current has little effect on the Zn content in the weld. As the welding current increases, the Zn content in the weld decreases slightly.
When gas shielded welding is used to weld galvanized steel, the welding fume is much larger than that of manual arc welding, so special attention should be paid to exhaust. The factors that affect the amount and composition of smoke are mainly electric current and protective gas. The greater the current, or the greater the CO2 or O2 content in the protective gas, the greater the welding smoke, and the ZnO content in the smoke also increases. The maximum ZnO content can reach about 70%.
Under the same welding specifications, the penetration depth of galvanized steel is greater than that of non-galvanized steel. T-shaped joints, lap joints and downward vertical welding are more sensitive to welding porosity. The greater the welding speed, the easier it is to produce porosity. For galvanized alloy steel, the impact of welding speed is particularly obvious. When welding in multiple passes, the porosity sensitivity of subsequent passes is greater than that of the previous pass.
The composition of the shielding gas does not have a great impact on the mechanical properties of the joint. Pure CO2 is generally used for welding.
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