Copper and copper alloys can be joined by welding, brazing, and soldering processes. Table C-6 summarizes the application of the most commonly used processes for major alloy classifications. The following information concerns some of the more important copper alloys and their weldability by various processes.

 

 

 

Copper Alloys, Weldability

Copper presents a unique welding problem because of its combined properties of (1) a relatively high melting temperature, 1083°C (1981″F), and (2) very high thermal conductivity. This means that a lot of energy is lost due to the very deep heat sink encountered by the arc. Fortunately, the problem is reduced by the alloys, because they can lower the thermal conductivity by as much as 70%, while simultaneously lowering the melting temperature by as much as 195°C (350°F). Heat losses due to high thermal conductivity can be reduced by controlling the preheat and interpass temperatures.

Arc Welding. Copper and most copper alloys can be joined by arc welding. Welding processes that use gas shielding are generally preferred, although shielded metal arc welding (SMAW) can be used for many non- critical applications.

Argon, helium, or mixtures of the two are used as shielding gases for gas tungsten arc welding (GTAW), plasma arc welding (PAW), and gas metal arc welding (GMAW). In general, argon is used when manually welding material that is either less than 3.2 mm (1/8 in.) thick, or has low thermal conductivity, or both. Helium or a mixture of 75% helium and 25% argon is

recommended for mechanized welding of thin sections and for manual welding of thicker sections or alloys having high thermal conductivity. Small additions of nitrogen or hydrogen to the argon shielding gas may be used to increase the effective heat input. The SMAW process can be used to weld a range of  thicknesses of copper alloys. Covered electrodes of  copper alloys for SMAW are available in standard  sizes ranging from 2.4 to 4.8 mm (3/32 to 3/16 in.).  Other sizes are available in certain electrode classifications. Submerged arc welding (SAW) has been used

for welding copper alloys, although the use of this process is not widespread.

Arc welding should be done in the flat position when practical. In positions other than flat, particularly in the overhead position, GTAW or SMAW is preferred. For the vertical and overhead positions with some copper alloys, GMAW with pulsed power and small diameter electrodes is also suitable. Higher thermal conductivity and thermal expansion of copper and

its alloys result in greater weld distortion than in comparable steel welds. The use of prehcar, fixtures, proper welding sequence, and tack welds can minimize distortion or warping.


Gas Tungsten Arc Welding.
The GTAW process can be used without filler metal to make square-butt joints on copper thinner than 3.2 mm (118 in.). Heavier sections, up to about 12 mm (1/2 in.), require the joints to be opened up and, therefore, filler metals are required. In many situations, the use of pulsed GMAW should be considered for thicknesses above 3.2 mm (1/8 in.).

With the exception of the oxidizable alloys, direct-current straight polarity (DCEN) is the preferred type of current for GTAW.

Although argon shielding can be used, helium-rich gases are more suitable because they produce more heat at the work surface for a given welding current. When oxides might form on the surface of the base metal, especially with beryllium copper, alternating current is a better choice because of the cleaning action produced during the DCEP half cycle. In this case, argon-rich gases must be used.

Available as filler metals are copper, phosphor-, aluminum-and silicon-bronzes and copper-nickel.  Filler metal specifications include: ANSUAWS A5.6, Specifications for Covered Copper and Copper Alloy Arc Welding Electrodes; A5.7, Specifications for Copper and Copper Alloy Bare Welding Rods and Electrodes; and A5.27, Specifcation for Copper and Copper Alloy Rods for Oxyfuel Gas Welding.

 

Gas Metal Arc Welding. The GMAW process is an excellent choice for welding thicknesses of copper and its alloys which are greater than 3.2 mm (1/8 in.). It offers the advantages of high energy concentration at the weld pool, a reasonable deposition rate, and ease of use. Single-V joints are used with thicknesses up to 12 mm (1/2 in.), while double-V joints are preferred

for thicker section sizes. Argon-rich gases are the rule. Helium in amounts up to 80% or 90% can be added to increase the heat input without affecting the desirable spray-arc transfer. Although very effective, the spray transfer is associated with a driving arc and fluid pool which preclude its use except in the flat or horizontal positions. The pulsed-spray mode allows welds to be made in all positions and also in thinner section sizes. A large range of alloy systems is available as filler

metals. (See ANSUAWS A5.7, Specifications for Copper and Copper Alloy Bare Welding Rods and Electrodes.)

Shielded Metal Arc Welding. Compared to the gas shielded methods, SMAW requires larger joint openings, higher welding currents, higher preheat and interpass temperatures, and more welder skill. In spite of the disadvantages, it still is being used by job shops which rely heavily on the process for welding other metals. Available as filler metals are copper; phosphor, aluminum and silicon bronzes, and copper-nickel. (See ANSUAWS A5.6, Specifications for Covered Copper and Copper Alloy Arc Welding Electrodes.)

 

Plasma Arc Welding. The PAW process offers some unique advantages for welding copper and its alloys. Most important is the electrical energy concentration which is produced. This allows higher welding speed and reduces the size of the heat-affected zone (HAZ). Also, the high velocity plasma protects the tungsten electrode from the fumes produced by volatile alloys such as zinc and tin. Because of the high speeds and narrow welds, it lends itself nicely to mechanization. Then filler metals are required, those used with the GTAW process are recommended. A precautionary note: The plasma arc process often uses hydrogen in the plasma gas to increase the energy concentration.  This must be avoided because the hydrogen can cause

embrittlement due to the formation of water vapor when it reduces the oxides of copper which can be found in copper alloys.

 

Submerged Arc Welding. The SAW process is typically used for making mechanized welds in thick sections.

References for information on copper include the

following:

ASTWSAE Publication DS-56/HS 1086, Metals and Alloys in the Unified Numbering System, 6th Edition, 1993. ASTM, Philadelphia, Pa., and Society of Automotive Engineers, Warrendale, Pa.
American Welding Society. Welding Handbook, 8th Edition, Vol. 3, Materials and Applications, Miami, Florida. 1996.

American Welding Society. ANSUAWS A5.6, Specification for Covered Copper and Copper Alloy Arc Welding Electrodes, Miami, Florida, Latest Edition.

For composition and properties, refer to Standards Handbook, Part 2-Alloy Data, Wrought Copper and Copper Alloy Mill Products; 8th Edition: Copper Development Association, Inc., New York. 1985.

For composition and properties, refer to Standards Handbook, Part 7-DatalSpecifications, Cast Copper and Copper Alloy Products: Copper Development Association, Inc., New York. 1970.

Manufacturers of copper alloy base metals, rods, fluxes and electrodes are an excellent source of information on material specification, recommended welding procedures, and safe handling for the particular metals and supplementary materials used in joining the copper alloys.

Safe Practices

In addition to safe practices required for the welding, brazing or soldering process used on copper, a good ventilation system must be provided when welding copper alloys. This is particularly important when welding beryllium copper, or when using a beryllium-copper welding rod. The dust, fumes and mist of beryllium compounds in virtually every form are highly toxic. Because no safe maximum concentration has been established, extreme precaution should be

taken to reduce dust, fumes and mist to zero. An effective high velocity ventilating system should be used regardless of the degree of contamination. The welding operator should also be protected with clothing, gloves and a breathing mask of the most improved type.

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