In cold welding (CW), pressure is applied to the workpieces through dies or rolls.
Because of the plastic deformation involved, it is necessary that at least one (but
preferably both) of the mating parts be ductile. Prior to welding, the interface is
degreased, wire brushed, and wiped to remove oxide smudges. Cold welding can be
used to join small workpieces made of soft, ductile metals. Applications include wire
stock and electrical connections.
During the joining of two dissimilar metals that are mutually soluble, brittle
intermetallic compounds may form (Section 4.2.2); these will produce a weak and
brittle joint. An example occurs in the bonding of aluminum and steel, where a
brittle intermetallic compound is formed at the interface. The best bond strength is
obtained with two similar materials.
Roll Bonding. The pressure required for welding can be applied through a pair
of rolls (Fig. 31.1); this process is called roll bonding or roll welding (ROW).
Developed in the 1960s, roll bonding is used for manufacturing some U.S. coins (see
Example 31.1). The process can be carried out at elevated temperatures
(loot roll bonding). Surface preparation is important for interfacial
strength.