Cold welding (CW) process is a type of Solid-State Welding process and as the name suggests, cold welding (CW) is performed without the addition of heat. An external pressure is applied to the two parts being joined, resulting in substantial plastic deformation.
Accordingly, a fundamental requirement of CW is that at least one of the materials being joined is ductile and does not display significant work hardening.
As such, commercially pure aluminium and some of its alloys are well suited to cold welding. Cold welding can be conducted in both butt and lap configurations.
In the butt mode, the metal expelled from the joint during welding has to be removed mechanically. The plastic deformation occurring in the butt mode breaks up the oxides on the surface and these are also expelled with the flash. Thus, pre-cleaning of the faying surfaces is not as critical for butt joints.
But in lap joints, surface cleaning is crucial, usually degreasing followed by wire brushing is carried out. It is also important that there is little delay between the cleaning and performing the cold welding process.
While cold welding does not produce a Heat affected zone, it does produce a Mechanically Affected Zone (MAZ) at the bond region, where the material has been subjected to strain hardening as a result of the imposed plastic deformation.
Aluminium alloys of the 2xxx and 7xxx series, which cannot be fusion welded due to their tendency for hot cracking, can be successfully cold welded in the butt configuration. Butt and mitre joints can be made in most aluminium alloy wire, rod, tubing and simple extruded shapes. An upset distance of approximately 1.5 times the material thickness is required for butt joints in soft annealed alloys; higher strength alloys require greater upset distance, about 4–5 times the material thickness.
Welds in lap joints require a thickness reduction of about 70% at the weld location.