The important alloys of copper and tin from an industrial point of view are the bronzes comprised within certain limits of tin content. As in the case of the brasses, the addition of tin to cooper results in the formation of a series of solid solutions. The constitutional diagram of copper-tin alloys is very complex, but that part of it which deals with alloys of industrial importance is reproduced in Fig. 1.

Figure 1. Constitutional Diagram of the Copper-Tin Alloys

The addition of tin to copper results in the formation of a series of solid solutions which, in accordance with usual practice, are referred to in order of diminishing copper content as the α, β, γ, etc., constituents. The diagram may be summarized as follows:

Percentage composition		Constituent just below the freezing point	Constituent after slow cooling to 400°C
Copper	Tin
100 to 87	0 to 13	α	α
87 to 86	13 to 14	α + β	α
86 to 78	14 to 22	α + β	α + δ
78 to 74	22 to 26	β–>(α + β)	α + δ

Further changes on cooling from 400°C to room temperature are so sluggish that they only occur in conditions very far removed from actual practice.

The α solution is the softest of the constituents; it may be rolled or stamped cold, but it hardens under this treatment much more rapidly decreases than α-brass.

The β and a constituents do not exist in the alloy slowly cooled to room temperature: this is due to successive changes occurring at 586°C and 520°C whereby β is resolved into α +γ and γ into α + δ.

The δ constituent has the crystal structure of γ-brass. It has a narrow range of composition corresponding approximately to the formula Cu_3lSn₈ and, like all intermetallic compounds, is extremely hard and brittle. The δ -> (α + ε) change at 350°C does not occur in commercial practice, though alloys richer in tin may contain the a constituent, which corresponds to Cu₃Sn, and the η solid solution, which approximates to the composition CuSn.

95:5 Copper-Tin Alloy

On cooling from the liquid condition, the solid solution which first forms contains only about 2 percent of tin. Thus the cast metal has a cored structure and the coring is very marked because of the long range between liquidus and solidus; but it may be eliminated by diffusion on cooling more slowly or by annealing.

Any absorption of oxygen occurring during manufacture results in the presence of SnO₂ in the alloy, tending to make it brittle. A deoxidizer such as zinc is therefore frequently added. The addition of zinc, as in coinage bronze, causes no change in the microscopical appearance of the homogeneous α constituent. The zinc, however, exerts its deoxidizing effect in the liquid, and slight hardening effect on the solid solution. The structure of a bronze coin shows marked deformation of the crystals. On annealing, recrystallization takes place with subsequent crystal growth. Twinning is a characteristic feature of the cold-worked and annealed alloy.

90:10 Copper-Tin Alloy

This is typical gun-metal, most varieties of which, however, contain a deoxidizer, frequently zinc (e.g. Admiralty gun-metal, copper 88%, tin 10%, zinc 2%). The structure of the cast material depends on the rate of cooling, both through the range of solidification and below.

On account of the wide solidification range of the alloy and the slow rate of tin diffusion, the apparent solubility limit of the α solution is well below that shown in the diagram. The cast structure is always definitely dendritic and if coring is pronounced, some β solution may be formed at 798°C This interdendritic β, on cooling, gives rise to the hard δ constituent. On the other hand, after slow cooling or prolonged annealing, the homogeneous α constituent may be produced. A chill-cast gun-metal will therefore be very different in structure and properties from one which has been annealed.

85:15 Copper-Tin Alloy

This chemical composition is typical for a number of bronzes used as bearing metals, most of which, however, contain a little zinc as a deoxidizer. It is also the approximate composition of bell metal.

Immediately after solidification the alloy consists of the α and β constituents. If rapidly cooled, these are preserved. If slowly cooled, the β (or γ) is completely broken down below 520°C into a complex α + δ. The α + β structure is being replaced by α + (α + δ) complex in the slowly cooled alloy. This accounts for the fact that sand castings of this alloy are much harder than chill castings. It also provides the basis of heat treatment method, applied in the one case to bells and in the other to bearing metals.

The copper alloys may be endowed with a wide range of properties by varying their composition and the mechanical and heat treatment to which they are subjected. For this reason they probably rank next to steel in importance to the engineer.

The important alloys of copper and zinc from an industrial point of view are the brasses comprised within certain limits of zinc content. That portion of the constitutional diagram which refers to these alloys is given in the Figure 1.

Figure 1. Constitutional Diagram of the Copper-Zinc Alloys

The addition of zinc to copper results in the formation of a series of solid solutions which, in accordance with usual practice, are referred to in order of diminishing copper content as the a, b, g, etc., constituents. The diagram may be summarized as follows:

Percentage composition		Constituent just below the freezing point	Constituent after slow cooling to 400°C
Copper	Zinc
100 to 67.5	0 to 32.5	a	a
67.5 to 63	32.5 to 37	a + b	a
63 to 61	37 to 39	b	a
61 to 55.5	39 to 45.5	b	a + b`
55.5 to 50	45.5 to 50	b	b`
50 to 43.5	50 to 56.5	b	b` + g
43.5 to 41	56.5 to 59	b + g	b` + g

Further changes in composition of the a and b` phases below 400°C are only observed after prolonged annealing.

There is a certain connection between the properties and the microstructure which may be expressed in general terms.

The tensile strength increases with increase in zinc content, rises somewhat abruptly with the appearance of b, and reaches a maximum at a composition corresponding roughly to equal parts of a and b. It falls off rapidly at the appearance of the g constituent.

Elongation rises to a maximum and begins to fall again before the composition reaches the limit of the a solution. It falls considerably as the amount of b increases, and is very small in the presence of g.

The a constituent shows the greatest resistance to shock. This is diminished by the presence of b, and the alloy becomes extremely brittle when g is present.

Hardness is greatly increased by the presence of b and still further when g appears.

Alloys containing a phase only are specially suitable for cold working, and may be hot- or cold rolled. Those containing a and b will suffer very little deformation without rupture in the cold rolling and may only be hot rolled. The b constituent may also be forged, rolled or hot extruded, but alloys containing g should invariably be avoided for any mechanical treatment.

Designation system of brasses

The brasses of industrial importance are often designated by their copper and zinc content.

C 23000 - Red Brass (85 Cu, 15 Zn)

This alloy is used for ornaments and for cheap jewellery which is to be gilded: it withstands cold-work, cupping, etc. On account of the range of solidification, the cast material has a dendritic structure.

If cooled very slowly or annealed, diffusion takes place, yielding polyhedral grains of uniform composition. The process of diffusion is assisted by mechanical deformation of the grains by hot- or cold work followed by annealing. The changes which occur in rolling and annealing are similar to those described for 70:30 brass.

C 26000 - Cartridge Brass (70 Cu: 30 Zn)

This alloy, which is used widely for tubes, sheets and wires, also shows a dendritic structure of the a solid solution when chill fast. The b constituent does not begin to appear in the cast structure until the zinc exceeds 32% except in the presence of an additional element like aluminum or tin.

After annealing, the alloy consists of homogeneous solid solution, and it is specially suitable for cold-working. To withstand this treatment, especially drawing, it is necessary that the brass should be perfectly sound and free from impurities.

Since high grade 70:30 brass is usually made from the purest copper and zinc available without admixture of any but the cleanest scrap, these impurities are chiefly inclusions of dross (oxides or silicates) or charcoal. Such inclusions, if present, frequently lead to failure of the material during manufacture or in use. They become entrapped in the solidifying metal, either by splashing or by rapid solidification in moulds of small cross section.

It is a frequent procedure in casting brass to draw it into rod to employ very long moulds of very small cross section, in order to minimize subsequent mechanical treatment. Ingots made in such moulds are most liable to contain inclusions and to show piping to a great depth, resulting in central unsoundness over a considerable length of the ingot. To ensure soundness it is necessary to cast in a mould such that the cross section is large enough to give relatively slow cooling. The mould and stream of molten metal should be so arranged as to avoid splashing; the dimensions of the mould and speed of pouring should be such as to result in the ingot solidifying from bottom upwards.

The effect of cold-work on the microstructure is to break down the crystal grains by plastic deformation, and so crush them into confused debris. Annealing after cold-work results in recrystalization and subsequent crystal growth.

C 28000 - Muntz Metal (60 Cu: 40 Zn)

The molten metal begins to freeze at about 905°C, and dendrites of the b solution are formed. With sufficiently slow cooling through the range of solidification the alloy consists of homogeneous b constituent when just solid, but, on cooling, this solution retains less copper and at 770°C the a constituent separates from the homogeneous b and increases in amount as the temperature falls. The structure on reaching atmospheric temperature is therefore a mixture of a and b, the relative proportions of which may be controlled to some extent by the rate of cooling.

For example, a thin section of 60:40 brass quenched from 800°C consists of homogeneous b. With a larger section it is impossible to suppress completely the separation of a, but a specimen rapidly cooled from this temperature always contains more b than a specimen more slowly cooled. These microstructural characteristics are accompanied by changes in mechanical properties which can be deduced from the known hardness and brittleness of the b constituent and the softness and ductility of the a constituent.

Hot-rolled 60:40 brass, the rolling of which has been stopped above 700°C, shows a uniform structure in longitudinal and transverse directions. After the separation, the a and b constituents are each elongated in the direction of rolling, giving the normal structure of rolled 60:40 brass. The lower temperature of finishing, the smaller will be the grain size. If, however, rolling is continued much below 600°C, recrystalization does not keep pace with the deformation and the metal is cold-worked.

Brazing solder (50 Cu: 50 Zn)

This alloy, if cooled sufficiently slowly through the range of solidification, consists of homogeneous b solution, which, however, may decompose on cooling if the copper content is less than 50%. At atmospheric temperature the b solution will retain a maximum of just 50% of zinc if no impurities are present, but any content of zinc over 50% causes the separation of the g constituent, which increases in amount as the temperature falls. Its presence renders the alloy extremely hard and brittle.

Pure copper is extremely difficult to cast as well as being prone to surface cracking, porosity problems, and to the formation of internal cavities. The casting characteristics of copper can be improved by the addition of small amounts of elements including beryllium, silicon, nickel, tin, zinc, chromium and silver.

Copper alloys in cast form (designated in UNS numbering system as C80000 to C99999) are specified when factors such as tensile and compressive strength, wear qualities when subjected to metal-to-metal contact, machinability, thermal and electrical conductivity, appearance, and corrosion resistance are considerations for maximizing product performance. Cast copper alloys are used for applications such as bearings, bushings, gears, fittings, valve bodies, and miscellaneous components for the chemical processing industry. These alloys are poured into many types of castings such as sand, shell, investment, permanent mold, chemical sand, centrifugal, and die casting.

The copper-base casting alloy family can be subdivided into three groups according to solidification (freezing range). Unlike pure metals, alloys solidify over a range of temperatures. Solidification begins when the temperature drops below the liquidus; it is completed when the temperature reaches the solidus. The liquidus is the temperature at which the metal begins to freeze, and the solidus is the temperature at which the metal is completely frozen.

Group I alloys

Group I alloys are alloys that have a narrow freezing range (about 50^oC), that is, a range of 50^oC between the liquidus and solidus temperature. Group I alloys includes: copper (UNS No. C81100), chromium copper (C81500), yellow brass (C85200, C85400, C85700, C85800, C87900), manganese bronze (C86200, C86300, C86400, C86500, C86700, C86800), aluminum bronze (C95200, C95300, C95400, C95410, C95500, C95600, C95700, C95800) nickel bronze (C97300, C97600, C97800), white brass (C99700, C99750).

Pure Copper and Chromium Copper. Commercially pure copper and high copper alloys are very difficult to melt and are very susceptible to gassing. In the case of chromium copper, oxidation loss of chromium during melting is a problem. Copper and chromium copper should be melted under a floating flux cover to prevent both oxidation and the pickup of hydrogen from moisture in the atmosphere. In the case of copper, crushed graphite should cover the melt. With chromium copper, the cover should be a proprietary flux made for this alloy. When the molten metal reaches 1260^oC, either calcium boride or lithium should be plunged into the molten bath to deoxidize the melt. The metal should then be poured without removing the floating cover.

Yellow Brasses. These alloys flare, or lose zinc, due to vaporization at temperatures relatively close to the melting point. For this reason, aluminum is added to increase fluidity and keep zinc vaporization to a minimum. The proper amount of aluminum to be retained in the brass is 0.15 to 0.35%. Above this amount, shrinkage takes place during freezing, and the use of risers becomes necessary. After the addition of aluminum, the melting of yellow brass is very simple, and no fluxing is necessary. Zinc should be added before pouring to compensate the zinc lost in melting.

Manganese Bronzes. These alloys are carefully compounded yellow brasses with measured quantities of iron, manganese, and aluminum. The metal should be melted and heated to the flare temperature or to the point at which zinc oxide vapor can be detected. At this point, the metal should be removed from the furnace and poured. No fluxing is required with these alloys. The only addition required with these alloys is zinc. The amount required is that which is eeded to bring the zinc content back to the original analysis. This varies from very little, if any, when an all-ingot heat is being poured, to several percent if the heat contains a high percentage of remelt.

Aluminum Bronzes. These alloys must be melted carefully under an oxidizing atmosphere and heated to the proper furnace temperature. If needed, degasifiers can be stirred into the melt as the furnace is being tapped. By pouring a blind sprue before tapping and examining the metal after freezing, it is possible to tell whether it shrank or exuded gas. If the sample purged or overflowed the blind sprue during solidification, degassing is necessary. Degasifiers remove hydrogen and oxygen. Also available are fluxes that convert the molten bath. These are in powder form and are usually fluorides. They aid in the elimination of oxides, which normally form on top of the melt during melting and superheating.

Nickel Bronzes. These alloys, also known as nickel silver, are difficult to melt. They gas readily if not melted properly because the presence of nickel increases the hydrogen solubility. Then, too, the higher pouring temperatures aggravate hydrogen pickup. These alloys must be melted under an oxidizing atmosphere and quickly superheated to the proper furnace temperature to allow for temperature losses during fluxing and handling. Proprietary fluxes are available and should be stirred into the melt after tapping the furnace. These fluxes contain manganese, calcium, silicon, magnesium, and phosphorus and do an excellent job in removing hydrogen and oxygen.

White Manganese Bronze. There are two alloys in this family; both of them are copper-zinc alloys containing a large amount of manganese and, in one case, nickel. They are manganese bronze type alloys; they are simple to melt, and can be poured at low temperatures because they are very fluid. They should not be overheated, as this serves no purpose. If the alloys are unduly superheated, zinc is vaporized and the chemistry of the alloy is changed. Normally, no fluxes are used with these alloys.

Group II alloys

Group II alloys are those that have an intermediate freezing range, that is, a freezing range of 50 to 110^oC between the liquidus and the solidus. Group II alloys are: beryllium copper (C81400, C82000, C82200, C82400, C82500, C82600, C82800), silicon brass (C87500), silicon bronze (C87300, C87600, C87610, C87800), copper-nickel (C96200, C96400).

Beryllium Coppers. These alloys are very toxic and dangerous if beryllium fumes are not captured and exhausted by proper ventilating equipment. They should be melted quickly under a slightly oxidizing atmosphere to minimize beryllium losses. They can be melted and poured successfully at relatively low temperatures. They are very fluid and pour well.

Silicon Bronzes and Brasses. The alloys known as silicon bronzes, UNS alloys C87300, C87600, and 87610, are relatively easy to melt and should be poured at the proper pouring temperatures. If overheated, they can pick up hydrogen. While degassing is seldom required, if necessary, one of the proprietary degasifiers used with aluminum bronze can be successfully used. Normally no cover fluxes are used here. The silicon brasses (UNS alloys C87500 and C87800) have excellent fluidity and can be poured slightly above their freezing range. Nothing is gained by excessive heating, and in some cases, heats can be gassed if this occurs. Here again, no cover fluxes are required.

Copper-Nickel Alloys. These alloys (90Cu-10Ni, UNS C96200 and 70Cu-30Ni, UNS C96400) must be melted carefully because the presence of nickel in high percentages raises not only the melting point but also the susceptibility to hydrogen pickup. In virtually all foundries, these alloys are melted in coreless electric induction furnaces, because the melting rate is much faster than it is with a fuel-fired furnace. When ingot is melted in this manner, the metal should be quickly heated to a temperature slightly above the pouring temperature and deoxidized either by the use of one of the proprietary degasifiers used with nickel bronzes or, better yet, by plunging 0.1% Mg stick to the bottom of the ladle. The purpose of this is to remove all the oxygen to prevent any possibility of steam-reaction porosity from occurring. Normally there is little need to use cover fluxes if the gates and risers are cleaned by shot blasting prior to melting.

Group III alloys

Group III alloys have a wide freezing range. These alloys have a freezing range of well over 110^oC, even up to 170^oC. Group III alloys are: leaded red brass (C83450, C83600, C83800), leaded semi-red brasses (C8400, C84800), tin bronze (C90300, C90500, C90700, C91100, C91300), leaded tin bronze (C92200, C92300, C92600, C92700), high-leaded tin bronze (C92900, C93200, C93400, C93500, C93700, C93800, C94300).

These alloys, namely leaded red and semi-red brasses, tin and leaded tin bronzes, and high-leaded tin bronzes, are treated the same in regard to melting and fluxing and thus can be discussed together. Because of the long freezing ranges involved, it has been found that chilling, or the creation of a steep thermal gradient, is far better than using only feeders or risers. Chills and risers should be used in conjunction with each other for these alloys. For this reason, the best pouring temperature is the lowest one that will pour the molds without having misruns or cold shuts. In a well-operated foundry, each pattern should have a pouring temperature, which is maintained by use of an immersion pyrometer.

Fluxing. In regard to fluxing, these alloys should be melted from charges comprised of ingot and clean, sand free gates and risers. The melting should be done quickly in a slightly oxidizing atmosphere. When handled at the proper furnace temperature and cooled to the proper pouring temperature, the crucible is removed or the metal is tapped into a ladle. At this point, a deoxidizer (15% phosphor copper) is added. The phosphorus is a reducing agent (deoxidizer). This product must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. This residual level of phosphorus must be closely controlled by chemical analysis to a range between 0.010 and 0.020% P. If more is present, internal porosity may occur and cause leakage if castings are machined and pressure tested.

In addition to phosphor copper, pure zinc should be added at the point at which skimming and temperature testing take place prior to pouring. This replaces the zinc lost by vaporization during melting and superheating. With these alloys, cover fluxes are seldom used. In some foundries in which combustion cannot be properly controlled, oxidizing fluxes are added during melting, followed by final deoxidation by phosphor copper.

Beryllium additions, up to about 2 wt%, produce dramatic effects in several base metals. In copper and nickel, this alloying addition promotes strengthening through precipitation hardening. In aluminum alloys, a small addition improves oxidation resistance, castability and workability. Other advantages are produced in magnesium, gold, zinc, and other base metals.

The most widely used beryllium-containing alloys by far are the wrought beryllium-coppers. They rank high among copper alloys in attainable strength while retaining useful levels of electrical and thermal conductivity. Applications for these alloys include:

• Electronic components, where the strength, formability, and favorable elastic modulus of these alloys make them well suited for use as electronic connector contacts
• Electrical equipment, where their fatigue strength, conductivity, and stress relaxation resistance lead to their use as switch and relay blades
• Control hearings, where anti-galling features are important
• Housings for magnetic sensing devices, where low magnetic susceptibility is critical
• Resistance welding systems, where hot hardness and conductivity are important in structural and consumable welding components.

Commercial copper-beryllium alloys are classified as high-copper alloys. Wrought produce fall in the nominal range 0.2 to 2.00 wt% Be, 0.2 to 2.7 wt% Co (or up to 2.2 wt% Ni), with the balance consisting essentially of copper. Casting alloys are somewhat richer, with up to 2.85 wt% Be. Within this compositional band, two distinct classes of commercial materials have been developed, the high-strength alloys and the high-conductivity alloys.

The wrought high-strength alloys (C 17000 and C 17200) contain 1.60 to 2.00 wt% Be and nominal 0.25 wt% Co. A free-machining version of C 17200 which is modified with a small lead addition and available only as rod and wire, is designated C 17300. The traditional wrought high-conductivity alloys (C l7500 and C 17510) contain 0.2 to 0.7 wt% Be and nominal 2.5 wt% Co (or 2 wt% Ni). The leanest and most recently developed high-conductivity alloy is C 17410, which contains somewhat less than 0.4 wt% Be and 0.6 wt% Co.

The high-strength casting alloys (C 82400, C 82500, C 82600, and C 82800) contain 1.60 to 2.85 wt% Be, nominal 0.5 wt% Co, and a small silicon addition. Grain refinement in these foundry products is achieved by a minor titanium addition to the casting ingot or by increased cobalt content (up to a nominal content of 1 wt% Co) as in C 82510. The high-conductivity casting alloys (C 82000, C 82100 and C 82200) contain up to 0.8 wt% Be.

Copper-beryllium alloys are available in all common commercial mill forms, including strip, wire, rod, bar, tube, plate, casting ingot, and cast billet. Free-machining copper-beryllium is offered as rod.

Copper-beryllium alloys respond readily to conventional forming, plating, and joining processes. Depending on mill form and condition (temper), the wrought materials can be stamped, cold formed by a variety of conventional processes, or machined. Cast billet can be hot forged, extruded, or machined, and castings can be produced by a variety of foundry techniques.

Finished components can be conventionally plated with tin, nickel, semiprecious metals, or precious metals. Alternatively, strip can be clad or inlayed with other metals. Surfaces can also be modified by various techniques to enhance performance or appearance. Beryllium-copper alloys are solderable with standard fluxes and, if care is taken to preserve the properties achieved by heat treatment can be joined by nominal brazing and many fusion welding processes.

Heat Treatment

Solution annealing is performed by heating the alloy to a temperature slightly below the solidus to dissolve a maximum amount of beryllium, then rapidly quenching the material to room temperature to retain the beryllium in a supersaturated solid solution. Users of copper-beryllium alloys are seldom required to perform solution annealing, this operation is almost always done by the supplier.

Typical annealing temperature ranges are 760 to 800^oC for the high-strength alloys and 900 to 955^oC (1650 to 1750^oF) for the high-conductivity alloys. Temperatures below the minimum can result in incomplete recrystallization. Too low a temperature can also result in the dissolution of an insufficient amount of beryllium for satisfactory age hardening. Annealing at temperatures above the maximum can cause excessive grain growth or induce incipient melting.

Age hardening involves reheating the solution-annealed material to a temperature below the equilibrium solvus for a time sufficient to nucleate and grow the beryllium-rich precipitates responsible for hardening. For the high-strength alloys, age hardening is typically performed at temperatures of 260 to 400^oC for 0.1 to 4h. The high-conductivity alloys are age hardened at 425 to 565^oC for 0.5 to 8h.

Within limits, cold working the alloy between solution annealing and age hardening increases both the rate and the magnitude of the age-hardening response in wrought products. As cold work increases to about a 40% reduction in area, the maximum peak-age hardness increases. Further cold work beyond this point is nonproductive and results in decreased hardness alter age hardening and diminished ductility in the unaged condition. Commercial alloys intended for user age hardening are therefore limited to a maximum of about 37% cold work in strip (H temper). For wire, the maximum amount of cold work is commonly somewhat greater.

High-Strength Wrought Alloys. When age hardened at 315 to 335^oC strength increases to a plateau in about 3h for annealed material, or about 2h for cold-worked material and remains essentially constant thereafter. At lower age-hardening temperatures, longer aging times are required to reach an aging response plateau.

High-Conductivity Wrought Alloys. Aging at 450 to 480^oC for 2 to 3h is commonly recommended. Overaging is less pronounced than in the high-strength alloys and can be employed to advantage because the appreciable cobalt or nickel content of these alloys increases the thermal stability of the age-hardening precipitates.

Underage, Peak-Age, and Overage Treatments. Material that has been aged for an insufficient amount of time to attain the maximum possible hardness at a particular temperature is said to be underaged. Material aged at time-temperature combinations resulting in maximum attainable hardness is said to be peak aged.

Mechanical Properties

Wrought products are supplied in a range of both heat-treatable and mill-hardened conditions. The heat-treatable conditions include the solution-annealed temper (commercial designation A, or ASTM designation TB00) and a range of annealed and cold-worked tempers (1/4 H through H, or TD01 through TD04) that must be age hardened by the user after forming. Increasing cold work, within limits, increases the strength obtained during age hardening.

Heat-treatable tempers are the softest and generally most ductile materials in the as-shipped condition, and they can be formed into components of varying complexity depending upon the level of cold work. Age hardening these heat-treatable tempers develops strength levels that range higher than those in any other copper-base alloys. After age hardening by the user, the solution-annealed material is redesignated AT, or TF00, and the annealed and cold-worked tempers are redesignated 1/4 HT through HT, or TH01 through TH04.

Mill-hardened tempers, designated AM through XHMS, or TM00 through TM08, receive proprietary cold-working and age-hardening treatments from the supplier prior to shipment, and they do not require heat treatment by the user after forming. Mill-hardened tempers exhibit intermediate-to-high strength and good-to-moderate ductility; these property levels satisfy many component fabrication requirements.

Strip. Wrought high-strength copper-beryllium alloy C 17200 strip attains ultimate tensile strengths as high as 1520 MPa in the peak-age-hardened HT (TH04) condition; the corresponding electrical conductivity is on the order of 20% IACS. Because of its slightly lower beryllium content, alloy C 17000 achieves maximum age-hardened strengths slightly lower than those of C 17200. Mill-hardened C 17200 strip is supplied in a range of tempers that have ultimate tensile strengths from 680 to 1320 MPa.

Ductility varies inversely with strength. It decreases with increasing cold work in the heat-treatable tempers and with increasing strength in the mill-hardened tempers. Beryllium-copper C 17500 and C 17510 strip can be age hardened to tensile strengths up to 940 MPa and electrical conductivities in excess of 45% IACS. Mill-hardened tempers of these high-conductivity alloys span the tensile strength range of 510 to 1040 MPa and include one specially processed temper with a minimum electrical conductivity of 60% IACS.

Other Wrought Products. Plate, bar, wire, rod and tube also are available in the solution-annealed temper, the annealed and cold-worked heat-treatable temper, and the mill-hardened temper. Strength and ductility combinations in wire are similar to those of corresponding alloys in strip form. Age-hardened strengths of plate, bar, and tube products range somewhat lower than those of strip or wire and, to a minor degree, vary inversely with section thickness. In addition to these traditional heavy-section product properties unique property combinations often can be developed by proprietary mill-hardening treatments in response to the changing requirements of emerging applications.

Forgings and hot-finished extruded products are available in the solution-annealed temper and the annealed and age-hardened temper. Cold work is not imparted prior to age hardening.

Cast Products. Regarding typical mechanical properties, four conditions exist for castings:

• As-cast (C temper or ASTM M01 through M07: the ASTM temper designation depends upon the casting practice, such as sand, permanent mold, investment, continuous casting and so on)
• As-cast plus age hardened (CT temper, no ASTM designation)
• As-cast plus solution annealed (A temper, or ASTM TB00)
• As-cast plus solution annealed and age hardened (AT temper, or ASTM TF00).

The solution-annealing temperature range for the high-strength casting alloys C 82400 through C 82800 is 760 to 790^oC, these alloys are age hardened at 340^oC. The high-conductivity casting alloys C 82000 and C 82200 are annealed at 870 to 900^oC and age hardened at 480^oC. Annealing times of 1h per inch of casting section thickness are recommended, with a minimum soak of 3h for the high-strength alloys to ensure maximum property uniformity. An age-hardening time of 3h is recommended for the temperatures indicated.

Maximum strength is obtained from the casting alloys in the AT (TF00) temper. These alloys reach strength levels slightly lower than those of the corresponding wrought AT temper copper-beryllium. The CT temper produces strengths slightly lower than those of the AT temper: however, the lower strength is offset by reduced processing costs. In addition, CT temper components experience less shrinkage and age-hardening distortion than the AT temper castings.

The slower solidification and cooling rates associated with sand or ceramic molds or heavy sections can result in lower CT temper strength. Castings in the solution-annealed and age-hardened (AT) temper are less susceptible to the effects of a slow cooling rate or variable section size. Water quenching of annealed temper castings with a large cast grain size may cause cracking. Slowing the cooling rate during quenching is recommended in such cases; however, this will reduce the AT temper aging response of the materials.

COPPER and its alloys constitute one of the major groups of commercial metals. They are widely used because of their excellent electrical and thermal conductivity, outstanding resistance to corrosion, and ease of fabrication, together with good strength and fatigue resistance. They are generally nonmagnetic.

They can be readily brazed, and many coppers and copper alloys can be welded by various gas, arc and resistance methods. For decorative parts, standard alloys having specific colors are readily available. Copper alloys can be polished and buffed to almost any desired texture and luster. They can be plated, coated with organic substances or chemically colored to further extend the variety of available finishes.

Pure copper is used extensively for cables and wires, electrical contacts, and a wide variety of other parts that are required to pass electrical current. Coppers and certain brasses, bronzes and cupronickels are used extensively for automobile radiators, heat exchangers, home heating systems, panels for absorbing solar energy and various other applications requiring rapid conduction of heat across or along a metal section. Because of their outstanding ability to resist corrosion, coppers, brasses, some bronzes, and cupronickels are used for pipes, valves and fittings in systems carrying potable water, process water or other aqueous fluids.

In all classes of copper alloys, certain alloy compositions for wrought products have counterparts among the cast alloys, which enables the designer to make an initial alloy selection before deciding on the manufacturing process.

Most wrought alloys are available in various cold worked conditions, which have room temperature strengths and fatigue resistances that depend on the amount of cold work more than on alloy content. Typical applications of cold worked conditions (cold worked tempers) include springs, fasteners, hardware, small gears, and cams. Certain types of parts - most notably plumbing fittings and valves - are produced by hot forging simply because no other fabrication process can produce the required shapes and properties as economically.

Copper alloys containing 1 to 6% Pb are free machining grades, and are used widely for machined parts especially those produced in screw machines.

Copper and its alloys are relatively good conductors of electricity and heat. In fact, copper is used for these purposes more often than any other metal. Alloying invariably decreases electrical conductivity and, to a lesser extent, thermal conductivity. For this reason, coppers and high copper alloys are preferred over copper alloys containing more than a few percent total alloy content when high electrical or thermal conductivity is required for the application. The amount of reduction due to alloying does not depend on conductivity or any other bulk property of the alloying element, but only on the effect that the particular foreign atoms have on the copper lattice.

Electrical coppers

Commercially pure copper is represented by UNS numbers C10100 to C13000. The various coppers within this group have different degrees of purity, and therefore different metal characteristics. Fire refined tough pitch copper C12500 is made by deoxidizing anode copper until the oxygen content has been lowered to the optimum value of 0.02 to 0.04%.

Electrolytic tough pitch copper C11000 is made from cathode copper - that is, copper that has been refined electrolytically. C11000 is the most common of all the electrical coppers. It has high electrical conductivity, in excess of 100% IACS. It has the same oxygen content as C 12500, but differs in sulfur content and in over-all purity. C11000 has less than 50 ppm total metallic impurities (including sulfur).

Oxygen-free coppers C10100 and C10200 are made by induction melting prime-quality cathode copper under nonoxidizing conditions produced by a granulated graphite bath covering and a protective reducing atmosphere that is low in hydrogen.

If resistance to softening at slightly elevated temperature is required, C11100 is often specified. This copper contains a small amount of cadmium, which raises the temperature at which recovery and recrystallization occurs.

High purity copper is a very soft metal. It is softest in its undeformed, single-crystal form, requiring a shear stress of only 3.9 MPa . 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.

Cold working increases both tensile strength and yield strength, but the effect is more pronounced 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 may be as much as five to six times that of the annealed temper.

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, so that a single operation can replace a sequence of forming and annealing operations.

Annealing. Work-hardened metal can be returned to a soft state by heating, or annealing. During annealing, deformed and highly stressed crystals are transformed into unstressed crystals by recovery, recrystallization and grain growth. In severely deformed metal, recrystallization occurs at lower temperatures than in lightly deformed metal. Also, the grains are smaller and more uniform in size when severely deformed metal is recrystallized. Grain size can be controlled by proper selection of cold working and annealing practices.

Anneal-resistant coppers. Addition of small amounts of elements such as silver and cadmium to deoxidized copper increase resistance to softening at times and temperatures encountered in soldering operations such as those used to join components of automobile and truck radiators. The thermal and electrical conductivity of copper are relatively unaffected by small amounts of either silver or cadmium. Room temperature mechanical properties also are unchanged. C111000, C14300 and C16200 (cadmium-bearing coppers) work harden at higher rates than either C11400 or C11000.

Copper Alloys

The most common way to catalog copper and its alloys is to divide them into six families: coppers, dilute 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 that modify one or more of the basic properties of copper.

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 (Zn, Sn, Al, Si…). Hardening in these systems is great enough to make useful objects without encountering brittleness associated with second phases or compounds.

Cartridge brass is typical of this group, consisting of 30% Zn in copper and exhibiting no beta phase except an occasional small amount due to segregation, which normally disappears after the first anneal. Provided that there are no elements such as Fe, cold working and grain growth relation ships are easily reproduced in practice.

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. Other age-hardenable alloys include C15000 (zirconium copper); C18200, C18400 and C18500 (chromium coppers); C19000 and C19100 (copper nickel phosphorus alloys); and C64700 (copper nickel silicon alloy).

By combining cold working with heat treatment, higher strengths can be obtained than can be achieved by either cold working or age hardening alone. Beryllium copper illustrates well the effects of heat treatment and cold working: in the soft, solution treated condition, the tensile strength is about 500 MPa, solution treated and aged, about 1000 MPa, and solution treated, cold worked and aged, about 1400 MPa.

Some age-hardening alloys have different desirable characteristics, such as high strength combined with better electrical conductivity than the beryllium coppers.

Insoluble Alloying Elements. Lead, tellurium and selenium are added to copper and its alloys to improve machinability. They, along with bismuth, make hot rolling and hot forming nearly impossible and severely limit the useful range of cold working.

An exception here are the high-zinc brasses, which become fully beta phase at high temperature. The beta 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 beta extrusion. C37700, one of the leading high-zinc brasses, is so readily hot forged that it is the standard alloy against which the forgeability of all copper alloys is judged.

Deoxidixers Li, Na, Be, Mg, B, Al, C, Si and P can be used to deoxidize copper. Ca, Mn and Zn can sometimes be considered deoxidizers, although they normally fulfill different roles.

The first requirement of a deoxidizer is that it have an affinity for oxygen in molten copper. Probably the second most important requirement is that it be relatively inexpensive compared to copper and any other additions. Thus, although zinc normally functions as a solid-solution strengthener, it is sometimes added in small amounts to function as a deoxidizer, because it has high affinity for oxygen and is relatively low in cost. In tin bronze, phosphorus has traditionally been the deoxidizer, hence the name "phosphor bronzes" for these alloys. Silicon instead of phosphorus is the deoxidizer for chromium coppers because phosphorus severely reduces electrical conductivity. Most deoxidizers contribute to hardness and other qualities, which often makes classification as a deoxidizer indistinct.