188 COPPER AND COPPER ALLOYS
ductility obviously decreases, and susceptibility to stress corrosion cracking may
increase in susceptible alloys and aggressive environments due to the presence
of residual stresses. Electrical conductivity of cold-worked alloys will be slightly
lower than that seen in annealed materials.
9 CASTINGS
Cast copper alloys are among the oldest fabricated materials. Ancient artisans
only had copper and crude tin bronzes to work with, but today’s designers con-
tinue to find new uses for cast copper alloys of all types. Cast copper alloys are
specified for their favorable mechanical properties, good friction and wear prop-
erties, high conductivity, excellent machinability and fabricability, biofouling
resistance, low manufactured cost, and attractive appearance. Mechanical prop-
erty data for cast copper alloys are listed in Table 7.
Casting is often chosen over other manufacturing methods because it offers
low cost. Copper alloys are not the lowest-cost raw materials, but they compete
successfully with other cast metals—especially stainless steels and nickel-base
alloys—because their predictable castability increases foundry yields, reducing
rejection rates and keeping overall foundry costs low. The alloys’ high mach-
inability reduces the cost of secondary operations and enables the use of high-
speed automatic machine tools that may not be suitable for other materials. Cast
copper alloys are fully recyclable at the end of their service life and their metal
value can eventually be recovered.
There are cast versions of many of the wrought alloys, and with certain minor
exceptions the properties of alloys in corresponding families, whether wrought
or cast, are also generally similar.
Temper designations for cast copper alloys are listed in Table 2. Most alloys
are used in the as-manufactured (as-cast) or cast-and-annealed condition, and a
few can be given postcasting heat treatments to enhance mechanical or other
properties.
9.1 Casting Methods
Selection of copper alloys for cast products should be based on the product’s
technical requirements. The casting’s size, shape, and complexity must also be
considered. The casting method can also influence alloy selection. In general,
copper metals can be cast using all conventional foundry methods: sand, per-
manent mold, continuous, centrifugal, investment, and plaster mold. Recent
advances in the pressure die-casting method, which until now has almost exclu-
sively been restricted to low-melting-point metals, will even enable this high-
rate process to be applied to copper.
The metallurgical characteristics of individual copper alloys and, sometimes,
entire alloy families make them more suitable for one or more casting methods
and less well suited to others. The subject is too complex to be covered ade-
quately here, but excellent relevant publications are available from the American
Foundrymen’s Society (AFS), the Non-Ferrous Founders Society (NFFS), and
CDA. Useful information can also be gained by discussing product requirements
with an experienced foundryman.
Briefly, the way an alloy solidifies largely determines its suitability to a given
process or a particular product configuration. Metals that freeze at a fixed tem-