Copper Alloys The most common way to catalog copper and copper alloys is to divide them into six families: coppers, dilute-copper (or high-copper) alloys, brasses, bronzes, copper nickels, and nickel silvers. The first family, the coppers, is essentially commercially pure copper, which ordinarily is soft and ductile and contains less than about 0.7% total impurities. The dilute-copper alloys contain small amounts of various alloying elements, such as beryllium, cadmium, chromium, or iron, each having less than 8 at.% solid solubility; these elements modify one or more of the basic properties of copper. Each of the remaining families contains one of five major alloying elements as its primary alloying ingredient: Family Alloying elements Solid solubility, at.% (a) Brasses Zinc 37 Phosphor bronzes Tin 9 Aluminum bronzes Aluminum 19 Silicon bronzes Silicon 8 Copper-nickels, nickel silvers Nickel 100 (a ) At 20 °C (70 °F) A general classification for wrought and cast copper alloys is given in Table 9 . Table 9 Generic classification of copper alloys Generic name UNS numbers Composition Wrought alloys Coppers C10100- C15760 >99% Cu High-copper alloys C16200- C19600 >96% Cu Brasses C20500- C28580 Cu-Zn Leaded brasses C31200- C3890 Cu-Zn-Pb Tin brasses C40400- C49080 Cu-Zn-Sn-Pb Phosphor bronzes C50100- C52400 Cu-Sn-P Leaded phosphor bronzes C53200- C54800 Cu-Sn-Pb-P
Transcript
Copper Alloys
The most common way to catalog copper and copper alloys is to divide them into six families: coppers, dilute-copper (or high-copper) alloys, brasses, bronzes, copper nickels, and nickel silvers. The first family, the coppers, is essentially commercially pure copper, which ordinarily is soft and ductile and contains less than about 0.7% total impurities. The dilute-copper alloys contain small amounts of various alloying elements, such as beryllium, cadmium, chromium, or iron, each having less than 8 at.% solid solubility; these elements modify one or more of the basic properties of copper. Each of the remaining families contains one of five major alloying elements as its primary alloying ingredient:
Family Alloying elements Solid solubility,
at.%(a)
Brasses Zinc 37
Phosphor bronzes Tin 9
Aluminum bronzes Aluminum 19
Silicon bronzes Silicon 8
Copper-nickels, nickel silvers Nickel 100
(a) At 20 °C (70 °F)
A general classification for wrought and cast copper alloys is given in Table 9.
Table 9 Generic classification of copper alloys
Generic name UNS numbers Composition
Wrought alloys
Coppers C10100-C15760 >99% Cu
High-copper alloys C16200-C19600 >96% Cu
Brasses C20500-C28580 Cu-Zn
Leaded brasses C31200-C3890 Cu-Zn-Pb
Tin brasses C40400-C49080 Cu-Zn-Sn-Pb
Phosphor bronzes C50100-C52400 Cu-Sn-P
Leaded phosphor bronzes C53200-C54800 Cu-Sn-Pb-P
Copper-phosphorus and copper-silver-phosphorus alloys C55180-C55284 Cu-P-Ag
Aluminum bronzes C60600-C64400 Cu-Al-Ni-Fe-Si-Sn
Silicon bronzes C64700-C66100 Cu-Si-Sn
Other copper-zinc alloys C66400-C69900 . . .
Copper-nickels C7000-C79900 Cu-Ni-Fe
Nickel silvers C73200-C79900 Cu-Ni-Zn
Cast alloys
Coppers C80100-C81100 >99% Cu
High-copper alloys C81300-C82800 >94 Cu
Red and leaded red brasses C83300-C85800 Cu-Zn-Sn-Pb (75-89% Cu)
Yellow and leaded yellow brasses C85200-C85800 Cu-Zn-Sn-Pb (57-74% Cu)
Manganese bronzes and leaded manganese bronzes C86100-C86800 Cu-Zn-Mn-Fe-Pb
Solid-Solution Alloys. The most compatible alloying elements with copper are those that form solid-solution fields. These include all elements forming useful alloy families (see Table 9) plus manganese. Hardening in these systems is great enough to make useful objects without encountering brittleness associated with second phases or com pounds.
Cartridge brass is typical of this group. It consists of 30% Zn in copper and exhibits no phase except
an occasional small amount due to segregation; the phase normally disappears after the first anneal. Provided that there are no tramp elements such as iron, cold-working and grain growth relationships are easily reproduced in practice.
Modified Solid-Solution Alloys. The solid solution-strengthened alloys of copper are noted for their strength and formability. Because they are single phase and are not transformed by heating or cooling, their maximum strength is developed by cold working methods such as cold rolling or cold drawing. Formability is reduced in proportion to the amount of cold work applied.
Modifications of some solid-solution alloys were developed by adding elements that react to form dispersions of intermetallic particles. These dispersions have a grain-refining and strengthening effect. As a result, higher strengths can be produced with less cold working, resulting in better formability at higher strength levels. Because these modifications do not require large amounts of costly elements, the gains are reasonably economical.
Alloy C63800 (95Cu-2.8Al-1.8Si-0.4Co) is a high-strength alloy with a nominal annealed tensile strength of 570 MPa (82 ksi) and nominal tensile strengths of 660 to 900 MPa (96 to 130 ksi) for the standard-rolled tempers. Cobalt provides the dispersion of strengthening intermetallic particles.
Alloy C68800 (73.5Cu-22.7Zn-3.4Al-0.4Co) is a high-strength modified aluminum brass. Its bend formability parallel to the direction of rolling is outstanding relative to its strength. It owes some of its unique properties to a dispersion of intermetallic particles resulting from the presence of cobalt. Its strength range is essentially the same as that of alloy C63800.
Alloy C65400 (95.44Cu-3-Si-1.5Sn-0.06Cr) is a very high-strength alloy that has excellent stress-relaxation resistance at temperatures up to 105 °C (220 °F). Its nominal strength range in rolled tempers is 570 to 945 MPa (82 to 137 ksi). Electrical contact and connector springs are heat treated at 200 to 250 °C (390 to 480 °F) for 1 h to stabilize internal stresses and maximize stress-relaxation resistance.
Alloy C66-400 (86.5Cu-11.5Zn-1.5Fe-0.5Co) is a low-zinc brass modified by the addition of iron and cobalt. The dispersion of intermetallic particles resulting from these additions strengthens the alloy. At the same time, conductivity is only moderately reduced, and resistance to SCC is very high. A high-zinc brass of the same strength and conductivity would be subject to SCC unless plated for protection.
Other modified solid-solution-strengthened alloys are probably described in the literature of the brass mill industries. Those described above should serve as examples of this additional class of copper alloys, which is expanding through the development efforts of the producers of brass mill products throughout the world.
Age-Hardenable Alloys. Age hardening produces very high strengths but is limited to those few copper alloys in which the solubility of the alloying element decreases sharply with decreasing temperature. The beryllium-coppers can be considered typical of the age-hardenable copper alloys.
Wrought beryllium-coppers can be precipitation hardened to the highest strength levels attainable in copper-base alloys. There are two commercially significant alloy families employing two ranges of beryllium with additions of cobalt or nickel. The so-called red alloys contain beryllium at levels
ranging from approximately 0.2 to 0.7 wt%, with additions of nickel or cobalt totaling 1.4 to 2.7 wt%, depending on the alloy. Alloys C17500 and C17510 are examples of red alloys; these low-beryllium alloys achieve relatively high conductivity (for example, 50% IACS) and retain the pink luster of other low-alloy coppers. The red alloys achieve yield strengths ranging from about 170 to 550 MPa (25 to 80 ksi) with no heat treatment to greater than 895 MPa (130 ksi) after precipitation hardening, depending on degree of cold work.
The more highly beryllium-alloyed systems can contain from 1.6 to 2.0 wt% Be and about 0.25 wt% Co, for example, alloys C17000 and C17200. These alloys frequently are called the gold alloys because of the shiny luster imparted by the substantial amount of beryllium present ( 12 at.%). The gold alloys are the high-strength beryllium-coppers because they can attain yield strengths ranging from approximately 205 to 690 MPa (30 to 100 ksi) in the age-hardenable condition to above 1380 MPa (200 ksi) after aging. The conductivity of the gold alloys is lower than that of the red alloy family by virtue of the high beryllium content. However, conductivity ranging from about 20% to higher than 30% IACS is obtained in wrought products depending on the amount of cold work and the heat treatment schedule. For enhanced machinability in rod and wire, lead is added (as in alloy C17300). More detailed information on beryllium-containing copper alloys can be found in the article "Beryllium-Copper and Other Beryllium-Containing Alloys" in this Section.
Other age-hardenable alloys include C15000; C15100 (zirconium-copper); C18200, C18400, and C18500 (chromium-coppers); C19000 and C19100 (copper-nickel-phosphorus alloys); and C64700 and C70250 (copper-nickel-silicon alloys). Some age-hardening alloys have different desirable characteristics, such as high strength combined with better electrical conductivity than the beryllium-coppers.
Alloy C71900 (copper-nickel-tin) and other similar alloys can be hardened by spinodal decomposition. By combining cold working with hot working, these alloys can achieve high strengths that are equivalent to those of the hardenable beryllium-coppers. These alloys are unique in that their forming characteristics are isotropic and thus do not reflect the directionality normally associated with wrought alloys.
Other Alloys. Certain aluminum bronzes, most notably those containing more than about 9% Al, can be hardened by quenching from above a critical temperature. The hardening process is a martensitic-type process, similar to the martensitic hardening that occurs when iron-carbon alloys are quenched. Mechanical properties of aluminum bronzes can be varied somewhat by temper annealing after quenching or by using an interrupted quench instead of a standard quench. Aluminum bronzes alloyed with nickel or zinc use reversible martensitic transformations to provide shape memory effects (see the article "Shape Memory Alloys" in this Volume).
Insoluble Alloying Elements. Lead, tellurium, and selenium are added to copper and copper alloys to improve machinability. These elements, along with bismuth, make hot rolling and hot forming nearly impossible and severely limit the useful range of cold working. The high-zinc brasses avoid these
limitations, however, because they become fully phase at high temperature. The phase can dissolve lead, thus avoiding a liquid grain-boundary phase at hot forging or extrusion temperatures. Most free-cutting brass rod is made by extrusion. Alloy C37700, one of the leaded high-zinc brasses, is so readily hot forged that it is the standard alloy against which the forgeability of all copper alloys is measured.
Mechanical Working
High-purity copper is a very soft metal. It is softest in its undeformed single-crystal form and requires a shear stress of only 3.9 MPa (570 psi) on {111} crystal planes for slip. Annealed tough pitch copper is almost as soft as high-purity copper, but many of the copper alloys are much harder and stiffer, even in annealed tempers.
Copper is easily deformed cold. Once flow has been started, it takes little energy to continue, and thus extremely large changes in shape or reductions in section are possible in a single pass. The only limitation appears to be the ability to design and build the necessary tools. Very heavy reductions are possible, especially with continuous flow. Rolling reductions of more than 90% in one pass are used for rolling strip.
Copper and many of its alloys also respond well to sequential cold working. Tandem rolling and gang-die drawing are common. Some copper alloys work harden rapidly; therefore, the number of operations that can be performed before annealing to resoften the metal is limited.
Copper can be cold reduced almost limitlessly without annealing, but heavy deformation (more than about 80 to 90%) may induce preferred crystal orientation, or texturing. Textured metal has different properties in different directions, which is undesirable for some applications.
Both the cold-working and the hot-working characteristics of copper are described below. For more detailed information, see Forming and Forging, Volume 14 of ASM Handbook, formerly 9th Edition Metals Handbook.
Cold working increases both tensile strength and yield strength, but it has a more pronounced effect on the latter. For most coppers and copper alloys, the tensile strength of the hardest cold-worked temper is approximately twice the tensile strength of the annealed temper. For the same alloys, the yield strength of the hardest cold-worked temper can be as much as five to six times that of the annealed temper.
Hardness as a measure of temper is inaccurate: The relation between hardness and strength is different for different alloys. Usually, hardness and strength for a given alloy can be correlated only over a rather narrow range of conditions. Also, the rangeof correlation is often different for different methods of hardness determination.
Hot Working. Not all shaping is confined to cold deformation. Hot working is commonly used for alloys that remain ductile above the recrystallization temperature. Hot working permits more extensive changes in shape than cold working, and thus a single operation often can replace a sequence of forming and annealing operations. To avoid preferred orientation and textures, and to achieve processing economy, copper and many copper alloys are hot worked to nearly finished size. Hot working reduces the as-cast grain size from about 1 to 10 mm (0.04 to 0.4 in.) to about 0.1 mm (0.004 in.) or less and yields a soft texture-free structure suitable for cold finishing.
Some hot-working operations may produce strengths that exceed that of the annealed temper. However, property control by hot working is very difficult and is rarely attempted.
Alloy and Temper Designation Systems
Alloy Designations. In North America, the accepted designation for copper alloys is part of the Unified Numbering System (UNS). Under the UNS system, the identifiers of copper alloys take the form of five-digit codes preceded by the letter "C" (for copper). The five-digit codes are based on, and supersede, an older three-digit system administered by the Copper Development Association Inc. (CDA). The UNS designations for copper alloys are simply two-digit extensions of the CDA numbers. For example, the leaded brass (85Cu-5Sn-5Pb-5Zn, or 85-5-5-5), once known as CDA Alloy No. 836, became UNS C83600.
Table 2 summarizes the standard UNS designation system. As this table indicates, wrought alloys are assigned UNS numbers from C10000 through C79999; cast alloys are numbered from C80000 through C99999.
Table 2 Generic classification of copper alloys
Generic name UNS No. Composition
Wrought alloys
Coppers C10100-C15760 >99% Cu
High-copper alloys C16200-C19600 >96% Cu
Brasses C20500-C28580 Cu-Zn
Leaded brasses C31200-C38590 Cu-Zn-Pb
Tin brasses C40400-C49080 Cu-Zn-Sn-Pb
Phosphor bronzes C50100-C52400 Cu-Sn-P
Leaded phosphor bronzes C53200-C54800 Cu-Sn-Pb-P
Copper-phosphorus and copper-silver-phosphorus alloys C55180-C55284 Cu-P-Ag
Aluminum bronzes C60600-C64400 Cu-Al-Ni-Fe-Si-Sn
Silicon bronzes C64700-C66100 Cu-Si-Sn
Other copper-zinc alloys C66400-C69900 . . .
Copper-nickels C70000-C79900 Cu-Ni-Fe
Nickel silvers C73200-C79900 Cu-Ni-Zn
Cast alloys
Coppers C80100-C81100 >99% Cu
High-copper alloys C81300-C82800 >94% Cu
Red and leaded red brasses C83300-C85800 Cu-Zn-Sn-Pb (75-89% Cu)
Yellow and leaded yellow brasses C85200-C85800 Cu-Zn-Sn-Pb (57-74% Cu)
Manganese bronzes and leaded manganese bronzes C86100-C86800 Cu-Zn-Mn-Fe-Pb
Tin bronzes and leaded tin bronzes C90200-C94500 Cu-Sn-Zn-Pb
Nickel-tin bronzes C94700-C94900 Cu-Ni-Sn-Zn-Pb
Aluminum bronzes C95200-C95810 Cu-Al-Fe-Ni
Copper-nickels C96200-C96800 Cu-Ni-Fe
Nickel silvers C97300-C97800 Cu-Ni-Zn-Pb-Sn
Leaded coppers C98200-C98800 Cu-Pb
Special alloys C99300-C99750 . . .
Temper Designations. Copper alloys are also described by their tempers, which are terms that define metallurgical condition, heat treatment, and/or casting method. The temper designations for wrought copper and copper alloys were traditionally specified on the basis of cold reduction imparted by rolling or drawing. This scheme related the nominal temper designations to the amount of reduction stated in Brown & Sharpe (B & S) gage numbers for rolled sheet and drawn wire. Heat-treatable alloys and product forms such as rod, tube, extrusions, and castings were not readily described by this system. To remedy this situation, ASTM B 601, "Standard Practice for Temper Designations for Copper and
Copper Alloys--Wrought and Cast," was developed. This standard established an alphanumeric code that can be assigned to each of the standard descriptive temper designations (Table 3).
Table 3 ASTM B 601 temper designation codes for copper and copper alloys
Temper designation Temper name or material condition
(a) Cold-worked tempers to meet standard requirements based on cold rolling or cold drawing.(b) Cold-worked tempers to meet standard requirements based on temper names applicable to specific products.(c) Tempers produced by controlled amounts of cold work followed by a thermal treatment to produce order
strengthening.(d) Annealed to meet specific mechanical property requirements.(e) Annealed to meet prescribed nominal average grain size.(f) Tempers of fully finished tubing that has been drawn or annealed to produce specified mechanical properties or that
has been annealed to produce a prescribed nominal average grain size are commonly identified by the appropriate H, O, or OS temper designation.
International Alloy Designations. A common designation system used within the International Organization for Standardization (ISO) is a compositional system described in ISO 1190 Part 1, based on the element symbols and the descending order of magnitude of alloying elements. For example, a leaded brass containing 60% Cu and 2%Pb is designated CuZn38Pb2. Because this system is unwieldy when used to describe complex alloys, a European numbering system has been formulated by the ComitéEuropéen de Normalisation (CEN). CEN/TC 132 describes a six-digit alpha-numerical system. The first letter, "C," indicates a copper alloy. A second letter was introduced to indicate the material state (i.e., W for a wrought material, C for castings, and M for master alloys). Three numbers are then used to identify the material, and a final third letter is used to identify the classification of individual copper material groups and to enlarge the capacity of the designation system. Table 4 shows the
preferred number ranges and letters allocated by the CEN numbering system to the different copper alloy groups. Table 5 cross references some ISO and CEN designations.
Table 4 CEN European numbering system for copper and copper alloys, showing the preferred number ranges and letters allocated to the different material groups
Material groups
Numberranges
availablefor positions3, 4, and 5
Finalletter,
designatingmaterial
group
Number rangeallocated tomaterialspreferredby CEN
Copper 001-999 A 001-049A
001-999 B 050-099B
Miscellaneous copper alloys 001-999 C 100-149C
001-999 D 150-199D
001-999 E 200-249E
001-999 F 250-299F
Copper-aluminum alloys 001-999 G 300-349G
Copper-nickel alloys 001-999 H 350-399H
Copper-nickel-zinc alloys 001-999 J 400-449J
Copper-tin alloys 001-999 K 459-499K
Copper-zinc-alloys, binary 001-999 L 500-549L
001-999 M 550-599M
Copper-zinc-lead alloys 001-999 N 600-649N
001-999 P 650-699P
Copper-zinc alloys, complex 001-999 R 700-749R
750-799S
Copper material not standardized by CEN/TC 133 800-999 A-S(a) 800-999(a)
(a) Letter as appropriate for the material group
Table 5 Selected ISO copper and copper alloys cross referenced to CEN numbers
The purpose of adding alloying elements to copper is to optimize the strength, ductility (formability), and thermal stability, without inducing unacceptable loss in fabricability, electrical/thermal conductivity, or corrosion resistance. Copper alloys show excellent hot and cold ductility, although usually not to the same degree as the unalloyed parent metal. Even alloys with large amounts of solution-hardening elements--zinc, aluminum, tin, and silicon--that show rapid work hardening are readily commercially processed beyond 50% cold work before a softening anneal is required to permit additional processing. The amount of cold working and the annealing parameters must be balanced to control grain size and crystallographic texturing. These two parameters are controlled to provide annealed strip products at finish gage that have the formability needed in the severe forming and deep drawing commonly done in commercial production of copper, brass, and other copper alloy hardware Typical mechanical properties for these materials are given in Table 7.
Table 7 Properties of wrought copper and copper alloys
(a) F, flat products; R, rod; W, wire; T, tube; P, pipe; S, shapes.(b) Ranges are from softest to hardest commercial forms. The strength of the standard copper alloys depends on the
temper (annealed grain size or degree of cold work) and the section thickness of the mill product. Ranges cover standard tempers for each alloy.
(c) Based on 100% for C36000.(d) Values are for as-hot-rolled material.(e) Values are for as-extruded material.
Types
The pure copper alloys, also called the coppers (C10100 to C15900), are melted and cast in inert atmosphere from the highest-purity copper in order to maintain high-electrical conductivity(oxygen-free, or OF, copper, C10200). Copper is more commonly cast with a controlled oxygen content (0.04% O as in electrolytic tough pitch, or ETP, copper, C11000) to refine out impurity elements from solution by oxidation. Included in this group are the alloys that are deoxidized with small addition of various elements such as phosphorus (C12200, or Cu-0.03P) and the alloys that use minor amounts of alloy additions to greatly improve softening resistance, such as the silver-bearing copper alloys (C10500, Cu-0.034 min Ag) and the zirconium-bearing alloys (C15000 and C15100, Cu-0.1Zr).
High-copper alloys (C16000 to C19900) are designed to maintain high conductivity while using dispersions and precipitates to increase strength and soften resistance: iron dispersions in Cu-(1.0-2.5)Fe alloys (C19200, C19400), chromium precipitates in Cu-1Cr (C18200), and the coherent precipitates in the Cu-(0.3-2.0)Be-Co,Ni age-hardening alloys (C17200, C17410, and C17500).
Brass alloys are a rather large family of copper-zinc alloys. A significant number of these are binary copper-zinc alloys (C20500 to C28000), utilizing the extensive region of solid solution up to 35% Zn, offering excellent formability with good work-hardening strength at reasonable cost. (These alloys are commonly referred to as alpha brasses.)The alloys below 15% Zn have good corrosion and stress-corrosion resistance. Alloys above 15% Zn need a stress-relieving heat treatment to avoid stress corrosion and, under certain conditions, can be susceptible to dezincification. Alloys at the higher zinc levels of 35 to 40% Zn contain the body-centered cubic (bcc) beta phase, especially at elevated temperatures, making them hot extrudeable and forgeable (alloy C28000 with Cu-40Zn, for example). The beta alloys are also capable of being hot worked while containing additions of 1 to 4% Pb, or more recently bismuth, elements added to provide the dispersion of coarse particles that promote excellent machinability characteristics available with various commercial Cu-Zn-Pb alloys(C31200 to C38500). The tin brasses (C40400 to C49000) contain various tin additions from 0.3 to 3.0% to enhance corrosion resistance and strength in brass alloys. Besides improving corrosion-resistance properties in copper-zinc tube alloys, such as C44300 (Cu-30Zn-1Sn), the tin addition also provides for good combinations of strength, formability, and electrical conductivity required by various electrical connectors, such as C42500 (Cu-10Zn-2Sn). A set of miscellaneous copper-zinc alloys (C66400 to C69900) provide improved strength and corrosion resistance through solution hardening with aluminum, silicon, and manganese, as well as dispersion hardening with iron additions.
Bronze alloys consist of several families named for the principal solid-solution alloying element. The familiar tin bronzes (C50100 to C54400) comprise a set of good work-hardening, solid-solution alloys containing from nominally 0.8% Sn (C50100) to 10% Sn (C52400), usually with a small addition of phosphorus for deoxidation. These alloys provide an excellent combination of strength, formability, softening resistance, electrical conductivity, and corrosion resistance. The aluminum-bronze alloys contain 2 to 15% Al (C60800 to C64200), an element adding good-solid-solution strengthening and work hardening, as well as corrosion resistance. The aluminum-bronzes usually contain 1 to 5% Fe, providing elemental dispersions to promote dispersion strengthening and grain size control. The silicon-bronze alloys (C64700 to C66100) generally offer good strength through solution- and work-hardening characteristics, enhanced in some cases with a tin addition, as well as excellent resistance to stress corrosion and general corrosion.
Cupronickels are copper-nickel alloys (C70100 to C72900) that utilize the complete solid solubility that copper has for nickel to provide a range of single-phase alloys (C70600 with Cu-10Ni-1.5Fe, and C71500 with Cu-30Ni-0.8Fe, for example) that offer excellent corrosion resistance and strength. The family of copper-nickel alloys also includes various dispersion- and precipitation-hardening alloys due to the formation of hardening phases with third elements, such as Ni2Si in C70250 (Cu-3Ni-0.7Si-0.15Mg) and the spinodal hardening obtainable in the Cu-Ni-Sn alloys (C72700 with Cu-10Ni-8Sn, for example).
Copper-nickel-zinc alloys, also called nickel-silvers, are a family of solid-solution-strengthening and work-hardening alloys with various nickel-zinc levels in the Cu-(4-26)Ni-(3-30)Zn ternary alloy
system valued for their strength, formability, and corrosion and tarnish resistance, and for some applications, metallic white color.
Strengthening Mechanisms for Wrought Copper Alloys
Solution Hardening. Copper can be hardened by the various common methods without unduly impairing ductility or electrical conductivity. The metallurgy of copper alloys is suited for using, singly or in combination, the various common strengthening mechanisms:solid solution and work hardening, as well as dispersed particle and precipitation hardening. The commonly used solid-solution hardening elements are zinc, nickel, manganese, aluminum, tin, and silicon, listed in approximate order of increasing effectiveness. Commercial alloys represent the entire range of available solid-solution compositions of each element up to 35% Zn, and up to (and even beyond) 50%Ni, 50% Mn, 9% Al, 11% Sn, and 4% Si. The relative amount of solution strengthening obtained from each element or particular combination of elements is determined by the ability of the solute to interfere with dislocation motion and is reflected in the work-hardening rate starting with the annealed condition, as illustrated by the increase in tensile strength with cold work shown in Fig. 3.
Fig. 3 Tensile strength of single-phase copper alloys as affected by percentage reduction in thickness by rolling (temper). Curves of lesser slope indicate a low rate of work hardening and a higher capacity for redrawing. ETP, electrolytic tough pitch
Work hardening is the principal hardening mechanism applied to most copper alloys, the degree of which depends on the type and amount of alloying element and whether the alloying element remains in solid solution or forms a dispersoid or precipitate phase. Even those alloys that are commercially age hardenable are often provided in the mill hardened tempers; that is, they have been processed with cold work preceding and/or following an age-hardening heat treatment. For the leaner alloys (below 12%Zn, or 3% Al, for example), processing generates dislocations that develop into entanglements and into cells, with some narrow shear band formation beyond 65%cold reduction in thickness. After
90% cold work, the distinct "copper"or "metal" deformation crystallographic texture begins to develop. With the richer solid-solution alloys that lower the stacking-fault energy, planar slip is the dominant dislocation mechanism, with associated higher work hardening. Beyond 40% cold work in these richer alloys, stacking faults, shear banding, and deformation twinning become important deformation mechanisms that, beyond 90% cold work, lead to the "brass" or"alloy" type of crystallographic deformation texture and accompanying anisotropy of properties. Figure 4shows the variation in tensile properties with cold working of an annealed Cu-30Zn alloy (C26000). The degree of work hardening seen with cold working several selected single-phase copper alloys is illustrated by the cold-rolling curves in Fig. 3. Many copper alloys are used in wrought forms in a worked temper, chosen for the desired combination of work-hardened strength and formability, either for direct use in service or for subsequent component fabrication.
Fig. 4 The effect of cold rolling on the strength, hardness, and ductility of annealed copper alloy C26000 when it is cold rolled in varying amount up to 62% reduction in thickness.
Dispersion strengthening is used in copper alloys for hardening, controlling grain size, and providing softening resistance, as exemplified by iron particles in copper-iron alloys, C19200 or C19400, and in aluminum bronzes, C61300 or C63380. Cobalt silicide particles in alloy C63800 (Cu-2.8Al-1.8Si-0.4Co), for example, provide fine-grain control and dispersion hardening to give this alloy high strength with reasonably good formability. Alloy C63800 offers an annealed tensile strength of 570 MPa (82 ksi) and rolled temper tensile strengths of 660 to 900 MPa (96 to 130 ksi). Alloys offering exceptionally good thermal stability have been developed using powder metallurgy (P/M) techniques to incorporate dispersions of fine Al2O3 particles (3 to 12 nm in size) in a basic copper matrix, which is finish processed to rod, wire, or strip products. This family of alloys, C15715 to C15760, can resist softening up to and above 800 °C(1472 °F). More detailed information on oxide-dispersion-strengthened copper alloys is found in the article "Copper Powder Metallurgy Products" in this Section.
Precipitation Hardening. Age-hardening mechanisms are used in those few but important copper systems that offer a decreasing solubility for hardening phases. The beryllium-copper system offers a series of wrought and cast age-hardening alloys, UNS C17000 to C17530 and C82000 to C82800. The wrought alloys contain 0.2 to 2.0% Be and 0.3 to 2.7%Co (or up to 2.2% Ni). They are solution heat treated in the 760 to 955 °C(1400 to 1750 °F) range and age hardened to produce the beryllium-rich coherent precipitates when aged in the 260 to 565 °C (500 to 1050 °F)range, with the specific temperature being chosen for the particular alloy and desired property combination (Fig. 5). The precipitation sequence during aging consists of the formation of solute-rich G-P zones, followed in sequence by coherent platelets of the metastable intermediate phases ' and ''. Overaging is marked by the appearance of the B2 ordered equilibrium -BeCu phase as particles within grains and along grain boundaries, large enough to be seen in the light microscope. The cobalt and nickel additions form dispersoids of equilibrium (Cu, Co, or Ni)Be that restrict grain growth during solution annealing in the two-phase field at elevated temperatures (Fig. 5b). A cold-working step following solution annealing is often used to increase the age-hardening response. Alloy C17200 (Cu-1.8Be-0.4Co), for example, can be processed to reach high strength; that is, tensile strengths after solutionization (470 MPa, or 68 ksi), after cold rolling to the hard temper (755 MPa, or 110 ksi) and after aging (1415 MPa, or 205 ksi). While they are commercially available in the heat-treatable (solutionized) condition, the beryllium-copper alloys are commonly provided in the mill-hardened temper with the optimal strength/ductility/conductivity combination suitable for the application.
Fig. 5 Phase diagrams for beryllium-copper alloys. (a)Binary composition for high-strength alloys such as C17200. (b) Pseudobinary composition for C17510, a high-conductivity alloy
Other age-hardening copper alloys include the chromium coppers, which contain 0.4 to 1.2% Cr (C18100, C18200, and C18400); these alloys produce arrays of pure chromium precipitates and dispersoid particles when aged. The Cu-Ni-Si alloys, C64700 and C70250, age harden by precipitating the Ni2Si intermetallic phase. Compositions in the Cu-Ni-Sn system, C71900 and C72700, are hardenable by spinodal decomposition, a mechanism that provides high strength and good ductility through the formation of a periodic array of coherent, fcc solid-solution phases that require the electron microscope to be seen. Each of these alloys, including the beryllium-coppers can be thermomechanically processed to provide unique combinations of strength, formability, electrical conductivity, softening resistance, and stress-relaxation resistance.
Copper Casting Alloys
The copper casting alloys are generally similar to the wrought counterparts, but they do offer their own unique composition/property characteristics. For example, they do offer the opportunity to add lead to levels of 25% that could not be easily made by wrought techniques in order to provide compositions in which dispersions of lead particles are useful for preventing galling in bearing applications. The copper casting alloys are used for their corrosion resistance and their high-thermal and electrical conductivity. The most common alloys are the general-purpose Cu-5Sn-5Pb-5Zn alloy (C83600), used for valves and plumbing hardware, and C84400, widely used for cast plumbing system components. C83600 contains lead particles dispersed around the single-phase matrix and offers good machinability, with moderate levels of corrosion resistance, tensile strength (240 MPa, or 35 ksi), ductility, and conductivity (15% IACS).
While the Cu-Sn-PB-(and/or Zn) casting alloys have only moderate strength, the cast manganese and aluminum bronzes offer higher tensile strengths, 450 to 900 MPa (65 to 130 ksi). As with the wrought alloys, the cast aluminum-bronze alloys commonly contain an iron addition (0.8 to 5.0%) to provide iron-rich particles for grain refinement and added strength. In addition, at aluminum levels in the 9.5 to 10.5% range (or 8.0 to 9.5% Al with nickel or manganese additions) the alloys are heat treatable for added strength. Depending on the section thickness and cooling rate of the casting, as well as the alloy composition and heat treatments, the microstructures can be rather complex. The aluminum-bronzes can be annealed completely or partially in the field and quenched to form martensite with needles. Aging these alloys will temper the martensite by precipitation fine needles. One of the aluminum-bronze alloys, Cu-10.5Al-5Fe-5Ni, for example, is used for the combination of high
strength and good corrosion resistance. Through heat treatment, the intermetallic -phase, with a complex composition(iron, nickel, copper) aluminum and CsCl crystal structure, provides a strengthening component in any of the morphologies: as globular particles, fine precipitates, or as a component of cellular eutectoid colonies.
