Welding copper and copper alloys

Features of welding copper and copper alloys


Copper is a metal that is capable of heat conduction, electric conductivity and good corrosion resistance. The density of copper is 8.93g / cm³. Melting temperature is 1083 degrees Celsius. Boiling temperature 2360 degrees Celsius.

On account of the large thermal conductivity, copper and copper alloys must use a large-capacity heat source to form a sealed tank.

Copper is easily oxidized to form CuO and CuO2. These oxides make copper welds brittle and  lead to create cracks during cooling. Therefore, welder must use and solder with deoxidizer: P, Si.
It is easy to overhead due to low melting point.

Brazing brass, zinc is prone to burn during welding process, which makes the metal components in welds change 


Technique of welding copper and copper alloy 

Copper welding technique


Based on the thickness of the materials, it devides into three main types: edge welding, bevel groove weld and non-bevel groove weld

Edge welding applies for the material that is less than 2mm thick.

No-bevel groove welding for materia  is less than 3mm thick

Bevel groove welding applied when the thickness exceeds 3mm. If the welding material is with the thickness of 3 to 10mm, beveled angle should be 45 degree. Moreover, objects are with thickness greater than 10mm, beveled edge ought to be 90 degree.

After the preparation is completed, clean up the weld edge carefully 

Welding flame capacity:

W = (190 ÷ 225) S (liter / hour)

If the object is preheated before welding, the flame output is:

W = (125 ÷ 150) S (liter / hour)

Copper welding can use two soldering irons: one for heating and one for welding. Flame capacity for each is 100 liters per hour with 1mm thickness 


Welding rod:

The welding rod diameter is calculated according to the formula:

Dqh = (0.5 ÷ 0.75) S (mm)

S: object thickness, mm

Welding flux

There are a variety of welding fluxes, such as: 

100% Na2B4O7

50% Na2B4O7 + 50% H3BO3

78% Na2B4O7 + 13% NaCl + 5% Na2CO3 + 4% H3BO3

Torch angle (α)

The welding torch with a surface angle is 90 degrees


After welding, welds should be forge welded on the surface. Depending on the thickness of the solder that can be hot forging or cold forging. A solder with a thickness of less than 5mm can be forged in cold state. Welded materials of high thickness must be welded at temperatures of 200 ÷ 300 degrees Celsius and do not weld at temperatures of 500 degrees Celsius.

Braze welding technique

Flame welding and flame welding capacity

Flame welding

Using oxidation flames to allow excess oxygen to oxidize zinc in the welding pool to form a ZnO film, which prevents the evaporation of zinc.

Flame capacity :

W = (100 ÷ 150) S (liter / hour)

Welding rod:

It is the best to use deoxygenated welding rods: Al, Si, Mn

Welding flux:

The welding flux used for braze is potassium.

Torch angle :

Welding torch with surface angle is (80 ÷ 90) degrees and welded to keep the distance from the tip of the flame to the welding surface (7 ÷ 10) mm.

Note: In order to improve the endurance of the weld, the weld should be forge welded on the surface. Depends on the copper content in the solder metal that can be forged in hot or cold state. Forged in hot state (700 degrees Celsius) when the welding material has copper content less than 60%. If the weld material has a copper content greater than 60%, it can be welded in cold state.

After forging, heat the solder at a temperature of (500 ÷ 700) C and cool slowly so that the weld is not brittle.

Technique of brass welding :


During welding, the elemental alloys in copper rods are susceptible to oxidation so that the brass rods are usually pitted and slagged.

For example: In the process of copper brass welding, welds are usually porous 

 because tin welding is easy to flamable. Copper brazing is easy to produce aluminum oxide (Al2O3) with a high melting point, which is difficult to exclude from the weld so that the weld is misted.


Welding flame and flame capacity

The flame used  is normal in welding 

The flame productivity in copper brass welding , you can choose according to ways below:

- No preheating:

W = (125 ÷ 175) S (liter / hour)

- Preheating

W = (100 ÷ 150) S (liter / hour)

In welding procedure, the flame tip is 7-10mm beyond from the welding surface.

Welding rod

Welding rod resembles the weld metal component.

Welding fluxes:

Welding fluxes should select based on the weld metal components

Aluminum brass welding should use welding fluxes containing the following ingredients:

45% KCL + 20% BaCl + 20% NaCl + 15% NaF

Nickel Bronze Copper welding use welding fluxes including components: Na2B4O7, H3BO3 and NaCl

Other types of brass should use Na2B4O7