Copper Alloys

alloys based on copper. They were the first man-made alloys. Until about the mid-20th century, copper alloys were first among nonferrous alloys; aluminum alloys have since taken over the leading position.

With many elements, copper forms a wide range of substitutional solid solutions, in which the atoms of the added metal occupy the sites of copper atoms in the face-centered cubic lattice. In the solid state, copper dissolves up to 39 percent zinc, 15.8 percent tin, 9.4 percent aluminum, and an unlimited percentage of nickel. The formation of solid solutions based on copper increases its strength and electrical resistance and de-creases the temperature coefficient of electrical resistance. The corrosion resistance may increase significantly, and the plasticity remains sufficiently high. The addition of an alloying element in excess of the solubility limit leads to the formation of compounds,

particularly electron compounds, that are characterized by a definite electron concentration (the ratio of the total number of valence electrons to the number of atoms, which may be 3/2, 21/13, or 7/4). The formulas conventionally attributed to these compounds are CuZn, Cu₅Sn, Cu₃₁Sn₈, Cu₉Al₄, CuBe, and so on. Multicomponent copper alloys frequently contain complex metallic compounds whose composition has not been established, which are considerably harder than the copper-based solutions but are very brittle (the proportion of such compounds in the structure of two-phase and multiphase copper alloys is usually much smaller than the proportion of the solid solution based on copper).

Copper alloys are produced by melting copper with alloying elements or intermediate alloys (hardeners) containing the alloying elements. The addition of small quantities of phosphorus (a few tenths of a percent) is widely used for deoxidation (reduction of oxides).

A distinction is made between wrought and foundry copper alloys. Wrought copper alloys are poured into ingot molds or by the continuous method to give round or flat ingots, which then undergo hot or cold working, rolling, extrusion through dies, or drawing to produce sheets, bands, rods, profiles, tubing, and wire. Copper alloys are readily workable under pressure, and semifinished products manufactured by forming methods account for the bulk of their production. Foundry copper alloys have good casting properties; they are used to produce shaped articles, as well as decorative products and sculpture, by means of casting in sand or chill molds.

The mechanical properties of copper alloys vary within wide limits during cold working or annealing. Cold forming may be used to increase the hardness and the tensile strength of copper alloys by a factor of 1.5 to 3, with a simultaneous reduction in plasticity, and subsequent recrystallization annealing makes possible complete or partial restoration of the original forming properties, depending on the temperature and duration of the heat treatment. Softening annealing of copper alloys after cold working is performed at 600°-700°C. Most copper alloys do not undergo thermal treatment (quenching or aging) for strengthening, since such treatment is either impossible (if the alloy is single-phase at all temperatures) or the degree of such strengthening is very small. Alloying elements that form intermetallic compounds with copper or among themselves (for example, CuBe, NiBe, or Ni₃Al) are used to produce copper alloys that are capable of thermal hardening. The solubility of the intermetallic compounds in the copper-based solid solution decreases with decreasing temperature. Quenching of such alloys produces a supersaturated solid solution, from which disperse intermetallic compounds that strengthen the copper alloy separate during artificial aging.

Copper alloys are divided into brasses, bronzes, and cupronickels. In brasses, the principal additive is zinc; in bronzes the principal additive may be any element except zinc and nickel. The industrial brands of copper alloys produced in the USSR are designated by starting with the first letter of their names: L (latun’) for brass, Br (bronza) for bronze, and M (mednonikelevye splavy) for cupronickels. The alloying elements are designated by the letters A (aliuminii) for aluminum, N (nikeP) for nickel, O (olovo) for tin, Ts (tsink) for zinc, S (svinets) for lead, Zh (zhelezo) for iron, Mts (marganets) for manganese, K (kremnii) for silicon, F (fosfor) for phosphorus, and T (titan) for titanium. The brand symbol of a simple (binary) brass contains a number that corresponds to the average copper content. Thus, L90 brass contains 90 percent copper and 10 percent zinc. The brand symbol of a multicomponent brass contains numbers, the first of which indicates the average copper content and the following indicate the content of alloying elements. For example, LAN59-3-2 brass contains 59 percent Cu, 3 percent Al, and 2 percent Ni (the remainder is zinc). Letters and numbers in the symbols of various brands of bronzes and cupronickels indicate the percentages of the alloying elements. For example, Br AZhMts 10-3-1.5 bronze contains 10 percent Al, 3 percent Fe, and 1.5 percent Mn. The letter L at the end of a brand designation indicates that it is designed for shaped casting (for example, LK80-3L).

The composition, typical mechanical properties, and examples of uses of copper alloys are listed in Tables 1-3. All copper alloys are distinguished by high resistance to atmospheric corrosion. Oxygen at room temperature does not affect copper alloys; carbon dioxide does not react with them. Dry or moist uncontaminated vapor acts very weakly on bronzes. Hydrogen sulfide reacts vigorously at low moisture levels with copper alloys, particularly at high temperatures. Nitric and hydrochloric acids react vigorously with brass and tin bronzes; sulfuric acid reacts much more weakly with them.

Copper alloys are used as structural, spring, antifriction, and corrosion-resistant materials; as alloys with high electrical and thermal conductivity and with high electrical resistance and low thermal coefficient of electrical resistance; as alloys for thermocouples; for artistic casting; and for dishes. They are used in general machine building, in the construction of aircraft and motor-vehicles, in shipbuilding, in railroad transportation, in electrical engineering, and in instrument-making, as well as in the construction of water and steam equipment.