What defects are prone to occur during high-precision brass strip welding and what are the preventive measures?
Release Time : 2025-12-15
High-precision brass strip, being a copper-zinc alloy, is prone to welding defects due to the low boiling point of zinc (only 907℃). Zinc evaporates easily at high temperatures, leading to a series of defects, with porosity being one of the most common. Because brass has high thermal conductivity, the weld pool solidifies quickly, resulting in insufficient time for gas to rise. Furthermore, the zinc oxide fumes produced by zinc evaporation can block gas escape channels, ultimately forming porosity in the weld. Preventing porosity hinges on pre-weld cleaning to thoroughly remove oil, oxides, and moisture from the weldment surface. Adding deoxidizing elements such as silicon, aluminum, and titanium enhances the deoxidizing capacity of the weld pool, and appropriate heating during welding slows the cooling rate, prolonging gas escape time.
Cracking is another major concern in high-precision brass strip welding. Brass exhibits hot brittleness in the 200-600℃ temperature range and during the melting stage, and has a high coefficient of linear expansion, easily generating significant internal stress during welding, leading to weld cracking. In addition, changes in weld metal composition caused by zinc evaporation can form low-melting-point eutectics, further exacerbating the cracking tendency. To prevent cracking, the content of harmful elements such as oxygen, lead, bismuth, and sulfur in welding materials must be strictly controlled. Adding alloying elements such as manganese, silicon, and phosphorus to the welding wire enhances deoxidation capacity, and selecting welding wires that achieve a duplex microstructure refines the grain size. In terms of welding process, measures such as using concentrated heat sources, preheating before welding, selecting a reasonable welding sequence, and slow cooling after welding should be taken to reduce stress.
Zinc evaporation and oxidation are core challenges in high-precision brass strip welding. Zinc evaporation not only reduces the zinc content of the weld, leading to decreased corrosion resistance and mechanical properties, but also forms white zinc oxide fumes, hindering operation and posing health hazards. To reduce zinc evaporation, welding wires containing elements such as silicon, tin, and iron (e.g., wire 221, wire 222) can be used during gas welding. These elements can form a dense oxide film on the surface of the molten pool, hindering further zinc evaporation and oxidation. During argon arc welding, AC power is more effective than DC positive polarity in reducing zinc evaporation, and a larger nozzle orifice diameter and argon gas flow rate are required to enhance the protective effect. During operation, the residence time of the electric arc on the base material should be minimized. Arc ignition should be achieved by "short-circuiting" with filler wire to reduce direct heating of the base material.
Degraded joint performance is a direct consequence of welding defects. Due to alloy element evaporation, the intrusion of harmful impurities, and coarse grains in the heat-affected zone, the strength, plasticity, conductivity, and corrosion resistance of the welded joint are often lower than those of the base material. To improve joint performance, welding materials with a composition matching the base material should be selected, welding process parameters (such as welding current, speed, and preheating temperature) should be strictly controlled, and stress should be eliminated through post-weld annealing. For weldments in contact with corrosive media such as seawater and ammonia, annealing is particularly critical, typically requiring heating to 300-400℃ to prevent stress corrosion cracking.
Welding deformation is also a concern in high-precision brass strip welding. Brass has a higher coefficient of linear expansion and solidification shrinkage than steel, making it prone to significant deformation during welding, affecting dimensional accuracy. To control deformation, rigid fixing, reverse deformation, or segmented back-welding methods can be used, while optimizing the welding sequence to distribute heat input. For thick and large weldments, preheating to 150-250℃ before welding can reduce the temperature gradient and decrease the tendency for deformation.
The operating environment also significantly impacts weld quality. Welding areas should have adequate ventilation to promptly remove zinc oxide fumes generated by zinc evaporation, protecting welders' health. Furthermore, the placement of the weldment should be appropriate to avoid uneven performance caused by localized overheating. For example, thick weldments can be padded with insulating materials (such as asbestos boards) to slow heat loss.
Process parameter optimization is key to improving the quality of high-precision brass strip welding. Whether gas welding, manual arc welding, or argon arc welding, parameters must be precisely adjusted according to the thickness, material, and welding position of the weldment. For example, the nozzle power should be slightly higher for gas welding than for carbon steel, and the welding speed should be as fast as possible; for argon arc welding, the wire diameter, tungsten electrode diameter, and argon flow rate must be matched to form a stable molten pool. Through repeated experimentation and parameter optimization, defects can be significantly reduced, achieving high-quality welding.