The Metallurgy of Copper Wire

Introduction
Copper is the preferred and predominant choice in the electrical industry because of its
high conductivity, both electrical and thermal. In order to obtain the required
properties, unalloyed high purity copper is almost always used. This article discusses
the rationale for this choice and it pays particular attention to the underlying
metallurgical principles. It is intended to serve as a technical discussion of pertinent
developments spanning the past several decades in the copper wire industry.
Conductor Requirements
Considerable progress has been made in recent years to explain the electronic nature
of the noble metals, i.e., copper, silver, and gold. These elements exhibit high
conductivity because their conduction electrons show relatively little resistance to
movement under an electric field. Copper in particular is an excellent conductor
because outermost electrons have a large mean free path (about 100 atomic
spacings) between collisions. The electrical resistivity is inversely related to this mean
free path.
Several electrically conductive metals are lighter than copper, but since they would
require larger cross-sections to carry the same current, are unacceptable if limited
space is a major requirement (e.g., in small electron motors). Consequently, aluminum
is used mainly when excessive weight could become a problem. Copper possesses
the best characteristics from commercial applications, in as much as silver must be
dismissed because of its prohibitively high cost.
Applications
Copper is one of the few metals that finds most widespread use in the pure form, rather
than as an alloy. There are approximately four dozen different wrought alloys that
contain a minimum copper content of 99.3 weight percent (and therefore designated as
“coppers”), albeit only a handful are used industrially as electrical conductors. The
most widely used of these dilute alloys is known as electrolytic tough pitch (ETP)
copper, which consists of extremely high purity metal that has been alloyed with
oxygen in the range of 100 to 650 ppm. ETP copper is not recommended for use in
hydrogen environments due to its susceptibility to hydrogen embrittlement when
exposed to those temperatures. Under these environmental environments, either
oxygen-free electronic (OFE) grades of copper should be used. Silver bearing copper