There is mainly four causes that explain why the welds might not be acceptable when welding with copper filler metal : the thermal conductivity, the welding position, the sensitivity to hot cracking and the tendency to make porosity.
To counter the thermal conductivity, it is important to use a procedure (preheating, heat input, protective gas) enable to transfer enough heat to the welding joint.
Molten copper is very fluid and has to be welded in the flat position. On fillet weld, it is possible to weld it in the horizontal position.
Copper is sensitive to hot cracking when it is cooling down to the solid state. This is mainly occurring with tin bronze, copper-nickel and alloys containing lead. You can improve your chance of success by buttering the face of the chamfer and by peening the weld bead while they are still hot.
Copper reacts easily with oxygen to form porosities, so it is important to ensure of the adequacy of the gas protection.
Here is some reminder on welding with copper alloys
- Weld in flat position whenever possible because of copper’s high fluidity
- Using a support plate will help keep the parts on for better penetration
- Good cleaning before and during welding will help to produce a quality weld
- If there is arc blow while welding dissimilar metals, increase the preheat temperature
- If the part is held in place by a vise or other metal device, preheating such devices will help maintain the temperature of the workpiece when preheating is required
- Heat losses during preheating can be prevented by using a non-flammable, insulating material such as Sodelfix and by placing the workpieces on insulating refractory material.
- When welding dissimilar metals, use the minimum welding currents recommended, whenever possible to minimize dilution
- To join cast iron to copper alloys with Sodel 661, use small diameter electrodes and make small, discontinuous beads.