Due to the presence of the zinc coating on its surface, galvanized square tube faces a series of unique process difficulties during the welding process, and also puts forward higher requirements for quality control.
First, the gasification of the zinc coating is a major difficulty. Under the action of high welding temperature, the zinc coating will quickly gasify and produce a large amount of zinc vapor. These zinc vapors will not only form white smoke around the weld, affecting the visibility of the welding operation, but also may cause defects such as pores in the weld. For example, in manual arc welding, if the welding parameters are not set properly, the zinc vapor cannot escape in time, and it is easy to be wrapped in the weld metal to form pores, which seriously reduces the density and strength of the weld.
Secondly, the embrittlement problem of the heat-affected zone of welding cannot be ignored. When welding galvanized square tube, the metal in the heat-affected zone will undergo changes in structure and properties due to heat, and the presence of zinc may accelerate this process, resulting in a decrease in the toughness of the heat-affected zone and easy cracking. Especially when using high-energy density welding methods such as laser welding, the heat-affected zone is relatively small but the temperature gradient is large, which is more prone to embrittlement.
Furthermore, it is difficult to ensure the formation and aesthetics of the weld. Due to the influence of the galvanized layer, the fluidity and surface tension of the molten pool will change during welding, making the weld prone to defects such as undercut and lack of fusion, affecting the appearance quality and connection strength of the weld.
In view of these difficulties, the key points of quality control are as follows:
First, the preparation work before welding. The galvanized layer of the galvanized square tube welding part must be thoroughly cleaned. Mechanical grinding or chemical cleaning can be used to remove the galvanized layer on the surface to reduce the amount of zinc vapor generated during welding.
Second, the reasonable selection of welding process parameters. According to the material, thickness and welding method of the galvanized square tube, accurately adjust the welding current, voltage, welding speed and other parameters. For example, in gas shielded welding, appropriately reducing the welding current and increasing the welding speed can help reduce the influence of zinc vapor on the weld and ensure the good formation of the weld.
Third, choose the appropriate welding material. Welding materials that match the galvanized square tube material and have good crack resistance should be selected, such as low-hydrogen welding rods or welding wires with a high nickel content, to improve the crack resistance and toughness of the weld.
Fourth, strengthen the protection during welding. Use appropriate gas protection methods, such as carbon dioxide or argon protection, to prevent impurities such as oxygen and nitrogen in the air from entering the molten pool, and further reduce the generation of weld defects.
Fifth, post-weld treatment. Clean and inspect the weld after welding, remove the welding slag and spatter on the surface, and use non-destructive testing methods such as X-ray flaw detection or ultrasonic flaw detection to check the internal quality of the weld to ensure that the weld has no defects such as pores and cracks.
Sixth, carry out necessary heat treatment. For some important welding structures or galvanized square tube welded parts with high performance requirements, appropriate heat treatment, such as annealing, can be carried out after welding to eliminate welding stress, improve the organization and performance of the heat-affected zone, and improve the overall quality of the welded joint.
Only by strictly controlling the above welding process difficulties and quality control points can we ensure the high-quality completion of galvanized square tube welding and enable it to play a reliable role in various engineering structures.
