Cast Copper-Base Alloys
Casting makes it possible to produce parts with shapes that cannot be
achieved easily by fabrication methods such as forming or machining.
Often it is more economical to produce a part as a casting than to
fabricate it by other means.
Copper alloy castings serve in applications that require superior
corrosion resistance, high thermal or electrical conductivity, good bearing
surface qualities, or other special properties.
All copper alloys can be successfully sand-cast, for this process
allows the greatest flexibility in casting size and shape and is the most
economical and widely used casting method, especially for limited production
quantities. Permanent mold casting is best suited for tin, silicon,
aluminum, and manganese bronzes, as well as yellow brasses. Most
copper alloys can be cast by the centrifugal process.
Brass die castings are made when great dimensional accuracy and/or a
better surface finish is desired. While inferior in properties to hotpressed
parts, die castings are adaptable to a wider range of designs, for
they can be made with intricate coring and with considerable variation
in section thickness.
The estimated market distribution of the dominant copper alloys by
end-use application is shown in Table 6.4.18. Chemical compositions
and selective mechanical and physical properties of the dominant alloys
used to produce sand castings are listed in Table 6.4.19.
Test results obtained on standard test bars (either attached to the casting
or separately poured) indicate the quality of the metal used but not
the specific properties of the casting itself because of variations of
thickness, soundness, and other factors. The ideal casting is one with a
fairly uniform metal section with ample fillets and a gradual transition
from thin to thick parts.
Properties and Processing of Copper Alloys
Mechanical Properties Cold working copper and copper alloys increases
both tensile and yield strengths, with the more pronounced increase
imparted to yield strength. For most alloys, tensile strength of the
hardest cold-worked temper is approximately twice the tensile strength
of the annealed temper, whereas the yield strength of the hardest coldworked
temper can be up to 5 to 6 times that of the annealed temper.
While hardness is a measure of temper, it is not an accurate one, because
the determination of hardness is dependent upon the alloy, its strength
level, and the method used to test for hardness.
All the brasses may be hot-worked irrespective of their lead content.
Even for alloys having less than 60 percent copper and containing the
beta phase in the microstructure, the process permits more extensive
changes in shape than cold working because of the plastic (ductile)
nature of the beta phase at elevated temperatures, even in the presence
of lead. Hence a single hot-working operation can often replace a sequence
of forming and annealing operations. Alloys for extrusion, forging,
or hot pressing contain the beta phase in varying amounts.
Extruded sections of many copper alloys are made in a wide variety of
shapes. In addition to architectural applications of extrusions, extrusion
is an important production process since many objects such as hinges,
pinions, brackets, and lock barrels can be extruded directly from bars.
While the copper-zinc alloys (brasses) may contain up to 40 percent
zinc, those with 30 to 35 percent zinc find the greatest application for
they exhibit high ductility and can be readily cold-worked. With decreasing
zinc content, the mechanical properties and corrosion resistance
of the alloys approach those of copper. The properties of these
alloys are listed in Table 6.4.20.
Heat Treating Figures 6.4.3 and 6.4.4 show the progressive effects
of cold rolling and annealing of alloy C26000 flat products. Cold rolling
clearly increases the hardness and the tensile and yield strengths while
concurrently decreasing the ductility.Annealing below a certain minimum temperature has practically no
effect, but when the temperature is in the recrystallization range, a rapid
decrease in strength and an increase in ductility occur. With a proper
anneal, the effects of cold working are almost entirely removed. Heating
beyond this point results in grain growth and comparatively little further
increase in ductility. Figures 6.4.5 and 6.4.6 show the variation of properties
of various brasses after annealing at the temperatures indicated.

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