Non Ferrous

Non Ferrous Copper Alloys

Copper conducts electricity at a rate 97% that of silver, and is the standard for electrical conductivity. Copper provides a diverse range of properties: good thermal and electrical conductivity, corrosion resistance, ease of forming, ease of joining, and color. In addition, however, copper and its alloys have relatively low strength-to-weight ratios and low strengths at elevated temperatures. Some copper alloys are also susceptible to stress-corrosion cracking unless they are stress relieved.

Copper and its alloys — the brasses and bronzes — are available in rod, plate, strip, sheet, tube shapes, forgings, wire, and castings. These metals are grouped according to composition into several general categories: coppers, high-copper alloys, brasses, leaded brasses, bronzes, aluminum bronzes, silicon bronzes, copper nickels, and nickel silvers.

Copper-based alloys form adherent films that are relatively impervious to corrosion and that protect the base metal from further attack. Certain alloy systems darken rapidly from brown to black in air. Under most outdoor conditions, however, copper surfaces develop a blue-green patina. Lacquer coatings can be applied to retain the original alloy color. An acrylic coating with benzotriazole as an additive lasts several years under most outdoor, abrasion-free conditions.

Although they work harden, copper and its alloys can be hot or cold worked. Ductility can be restored by annealing or heating incident to welding or brazing operations. For applications requiring maximum electrical conductivity, the most widely used copper is C11000, “tough pitch,” which contains approximately 0.03% oxygen and a minimum of 99.0% copper. In addition to high electrical conductivity, oxygen-free grades C10100 and C10200 provide immunity to embrittlement at high temperature. The addition of phosphorus produces grade C12200 — the standard water-tube copper.

High-copper alloys contain small amounts of alloying elements that improve strength with some loss in electrical conductivity. In amounts of 1%, for example, cadmium increases strength by 50%, with a loss in conductivity to 85%. Small amounts of cadmium raise the softening temperature in alloy C11600, which is used widely for printed circuits. Tellurium or sulfur, present in small amounts in Grades C14500 and C14700, has been shown to increase machinability.

Copper alloys do not have a sharply defined yield point, so yield strength is reported either as 0.5% extension under load, or as 0.2% offset. On the most common basis (0.5% extension), yield strength of annealed material is approximately one-third the tensile strength. As the material is cold worked or hardened, it becomes less ductile, and yield strength approaches tensile strength.