Copper Welding differs from steel and other non-ferrous metals in properties & color. It is having high density compared to steel.
Copper is one of the precious metals, is easy to shape, tough, and is characterized in particular by its good conductivity of heat and electricity. Preferred methods for copper welding are the Gas welding, MIG, and TIG welding processes.
Copper is mixed with other elements to produce Copper alloys such as Brass and Bronze.
Bronze is an alloy of copper with tin, aluminum, manganese, and iron while brass is an alloy of copper and zinc.
- Brass: Copper + Zinc,
- Bronze: Copper + Tin.
The main alloying element of bronze is tin. Bronzes are also aluminum, cadmium. An alloy of copper with nickel-cupronickel, an alloy with nickel and zinc-nickel silver.
Cupronickel and bronze are resistant to the active effects of water and, therefore, are used mainly by the marine industry.
Read more: Brass Welding Guide.
Weldability of Copper
Copper and its alloys can be welded using arc welding, although the degree of weldability is lower compared to steel. The challenges in welding copper and its alloys can be attributed to several factors.
- Firstly, due to its high thermal conductivity, there is a tendency for inadequate fusion.
- Secondly, the high thermal expansion of copper can cause distortion and cracking.
- Thirdly, the low melting point of copper can result in slag inclusions in stick welding (SMAW) since the melting temperature of the slag can be higher than that of the weld metal.
- Fourthly, the coarse crystal grains in the weld metal can negatively impact its mechanical properties.
- Finally, the addition of certain elements, such as Pb, Sn, Bi, and P, can cause cracking and embrittlement, while Zn vapors can result in insufficient fusion.
Copper Weldability Issues
Copper, like all non-ferrous metals, tends to absorb atmospheric gases during the welding process. This can affect the weld due to the creation of welding porosity.
Two other factors that play a major role in welding copper are the thermal conductivity and thermal expansion of the material. In the case of copper:
- The thermal conductivity at room temperature 6 times and at a temperature of 1000 degrees Celsius 15 times higher, - The thermal expansion is 1.4 times greater and - The shrinkage during solidification is about twice as large.
compared to mild steel. The high thermal conductivity means that a large part of the welding heat introduced is dissipated into the base material. As a result, this heat is no longer available to melt the base material.
During copper welding, following can be the main weldability concerns:
- Increased oxidization when heated to a molten state.
- High sensitivity to the adverse effects of hydrogen.
- The tendency of increased distortion and embrittlement of welded products due to heating in the heat treatment zone.
- Influence of impurities that lead to cracking and embrittlement of the welding seam.
Before starting work, the seams are carefully cleaned of contamination and oxidation. In order for copper welding to be successful, it is necessary to protect the bath from the effects of oxygen.
To do this, it is recommended to use an electrode wire, which must be alloyed with aluminum, and phosphorus. In some cases, it is required to preheat copper before welding.
Copper Stick Welding (SMAW)
To weld copper and its alloys, matching filler metals of ERCu and ECu can be used with the TIG, MIG, and Stick Welding.
However, for applications where high electrical or thermal conductivity is not necessary, copper alloy type filler metals like ERCuSi-A, ERCuSn-A, ECuSi, ECuSn-A, and ECuSn-C can be utilized.
These copper alloy filler metals have lower heat conductivity than copper type filler metals, resulting in better fusion at lower preheating temperatures.
Nonetheless, silicon- and phosphor-bronze weld metals have higher electrical resistivity than copper base metal.
TIG & MIG Copper Welding
TIG and MIG produce better fusion and penetration than SMAW because they have higher heat concentration.
Argon gas is commonly used for shielding in TIG & MIG, while helium gas can reduce the minimum preheating temperature.
Generally, TIG is more suitable for thin metals up to 6 mm, while MIG is more appropriate for thicker metals over 6 mm.
Due to the high thermal conductivity of copper, preheating is necessary to achieve complete fusion and sufficient joint penetration.
Gas welding of copper
Basically, copper can be welded very well using Gas welding. However, depending on the application and for pipe thicknesses of up to 3 mm, processes such as brazing copper tubes are more likely to be used.
In gas welding (gas-oxygen flame), the copper workpiece must be evenly preheated to 400°F to 1000°F (200°C to 500°C). This is due to high thermal conductivity of the copper.
Due to the rapidly developing passive layer, a corresponding flux must be used when joining two copper workpieces. The fluxes are usually applied to the seam joints and to the welding rods.
Gas Welding wire for copper
Copper and copper alloy welding wires and rods are classified in AWS A5.7 specification. The most commonly used Copper gas welding wire rods are:
- ERCu (Pure copper),
- ERCuSi-A (Silicon bronze),
- ERCuSn-A (Phosphor bronze),
- ERCuSn-C (Phosphor bronze),
- ERCuNi (Copper-nickel),
- ERCuAl-A1 (Aluminum bronze),
- ERCuAl-A2 (Aluminum bronze),
- ERCuAl-A3 (Aluminum bronze),
- ERCuNiAl (Nickel-aluminum bronze),
- ERCuMnNiAl (Manganese-nickel aluminum bronze).
The chemical compositions of these above welding wires are given in the below table.
TIG Welding of Copper and its Alloys
Read more: How to weld Aluminum Bronze.
Copper and its alloys can be welded with TIG welding. Pure argon gas shielding is required for weld pool protection.
Below are the types of Copper TIG Welding wires.
- ERCu: For welding Pure copper,
- ERCuSi-A: For welding Silicon bronze,
- ERCuSn-A: For welding Phosphor bronze,
- ERCuSn-C: For welding Phosphor bronze,
- ERCuNi: For welding Copper-nickel,
- ERCuAl-A1: For welding Aluminum bronze,
- ERCuAl-A2: For welding Aluminum bronze,
- ERCuAl-A3: For welding Aluminum bronze,
- ERCuNiAl: For welding Nickel-aluminum bronze,
- ERCuMnNiAl: For welding Manganese-nickel aluminum bronze.
Welding Preheat for Copper Welding
Apply a welding preheat temperature of 400°F to 1000°F (200°C to 500°C) when welding using ERCu filler wire. ERCu can be used with TIG and MIG Welding both.
No welding preheat is required for welding with ERCuSi. However, control on interpass temperature is required. Keep interpass temperature below 150°F (65°C) to avoid hot cracking issue.
For welding aluminum bronze, preheating is generally not required.
Copper welding with steel
Welding copper with steel is difficult, but it is possible. The only thing that you need to pay attention to is the different melting point of metals.
Therefore, when making weld preparation, it is necessary to keep steel root face bigger than copper to ensure good fusion.
If the welding is done with stick welding electrodes, the welding is carried out on direct polarity direct current (DCEP).
Welding steel (Mild steel, carbon steel or stainless steel) to copper can be carried out using ECuNi or ECuAl-A2 stick welding rod.
Similarly, TIG welding steel (Mild steel, carbon steel or stainless steel) to copper can be carried out using ERCuNi or ERCuAl-A2 TIG filler rod.