1. Weldability Characteristics of Pure Copper
The weldability of pure copper is mainly restricted by the following physical and chemical properties:
High thermal conductivity: Pure copper has extremely fast heat conduction, which makes it easy to lose a lot of heat during welding, resulting in difficulty in forming molten pools, incomplete fusion, incomplete penetration and low welding efficiency.
High coefficient of linear expansion: It expands greatly when heated and shrinks strongly when cooled, which easily causes large welding deformation and residual stress, and even leads to welding cracks.
Tendency to produce porosity: Hydrogen and oxygen dissolved in copper will precipitate in the form of pores during solidification, and hydrogen pores are the most common defect in copper welding.
Insoluble oxide film: Copper oxide (Cu₂O) is formed on the surface at high temperature, which has a high melting point and is difficult to remove. It will reduce the plasticity and toughness of the weld and easily cause grain boundary embrittlement.
Low strength at high temperature: Pure copper softens obviously at high temperature, and the weld and heat-affected zone are prone to collapse and thermal cracking.
Therefore, pure copper cannot be welded by simple open-fire operation. It needs preheating, strong protection and appropriate heat input to obtain qualified joints.
2. Suitable Welding Methods for Pure Copper
According to the thickness of pure copper parts, structure, production efficiency and service requirements, the following welding methods are commonly used:
2.1 TIG Welding (Tungsten Inert Gas Welding)
TIG welding is the most widely used and most reliable welding method for pure copper, especially suitable for thin plates, precision parts and small structures.
Advantages: The arc is stable, the heat is concentrated, the weld formation is beautiful, the splash is small, and the weld is pure.
Protection: Usually argon (Ar) is used as shielding gas to effectively isolate air and prevent oxidation and porosity.
Application: Suitable for pure copper sheets, pipes, electrical components, heat exchangers, etc.
Key points: Proper preheating is required for medium-thick plates; AC or DC positive connection can be selected according to thickness.
2.2 MIG/MAG Welding (Gas Metal Arc Welding)
MIG welding is suitable for medium and thick pure copper workpieces with high welding efficiency.
Advantages: High deposition efficiency, deep penetration, suitable for long welds and mass production.
Welding wire: Generally use pure copper welding wire or silicon bronze welding wire to improve fluidity and crack resistance.
Protection: 100% argon or argon-helium mixture is used to enhance protection and heat concentration.
Application: Used in large copper structural parts, thick copper plates, electrical busbars, etc.
2.3 Plasma Arc Welding
Plasma arc welding has greater energy density and penetration ability than TIG welding.
Advantages: It can realize single-side welding and double-side forming for copper plates of a certain thickness, with small deformation and high joint strength.
Application: Suitable for medium-thickness pure copper structural parts requiring high quality and high efficiency.
2.4 Brazing
Brazing is suitable for thin-walled parts, small parts and dissimilar metal connections involving pure copper.
Features: Low welding temperature, no melting of base metal, small deformation, suitable for complex components.
Brazing filler metals: Phosphorus copper brazing filler metal, silver copper brazing filler metal, etc.
Application: Copper pipe connections, electrical contacts, heat exchanger cores, copper and steel, copper and aluminum dissimilar connection.
2.5 Electron Beam Welding and Laser Welding
These are high-energy beam welding methods with high precision and low deformation.
Advantages: Deep penetration, narrow heat-affected zone, small welding deformation, suitable for high-precision and high-performance pure copper components.
Application: Used in aerospace, high-end electronics, precision instruments and other fields.
3. Conclusion
In summary, pure copper is a difficult-to-weld material with poor weldability under conventional conditions, but qualified welded joints can be obtained through reasonable process selection and strict parameter control. Among many welding methods, TIG welding is the most versatile and commonly used for pure copper, MIG welding is suitable for medium-thick plates and high-efficiency occasions, brazing is suitable for thin parts and dissimilar connections, and laser or electron beam welding is used for high-precision occasions.
