Editorial Feature

Copper and Low Alloyed Coppers

Feb 7 2001

Image Credit: Flegere/Shutterstock.com

Copper and its alloys are some of the most versatile materials available to engineers. Their combination of strength, conductivity, corrosion resistance, machinability and ductility can be suited to a wide range of applications by using a variety of composition and manufacturing methods.

Types of Copper Alloys

The main copper alloys include brasses (copper/zinc alloys), bronzes (copper/tin alloys including leaded bronzes and phosphor bronzes), aluminum bronzes (copper/aluminum alloys), copper nickel alloys and nickel silvers (composed of copper/nickel/zinc alloys).

Copper and copper alloys are available in both cast and wrought forms. These materials can also be fastened mechanically using rivets and screws, soldered for electrical connections, brazed and welded, except when high lead content alloys are being used. These materials also lend themselves to being recycled. In fact, approximately 40% of the world’s copper demand is met from recycling.

Electrolytic Tough Pitch and High Conductivity Copper

As one of the most widely used grades of copper for electrical applications in the world, electrolytic tough pitch (ETP) copper is also one of the most readily available types of copper. It is designated C101 in British Standards and Cu-ETP in ISO and CEN standards. A higher purity grade made from Grade ‘A’ cathode copper is designated C100 or Cu-ETP1. ETP copper is most commonly used for electrical applications including electric power systems and electrical installations in homes, offices and industry, as well as numerous different types of electrical and electronic equipment.

Tough pitch coppers are not easily brazed or welded because they often suffer from embrittlement or ‘gassing’ when heated in a reducing atmosphere. This occurs because hydrogen reacts with the oxide in the metal to form steam and causes cracking. Oxygen free and deoxidized coppers have been developed for applications requiring welding.

Phosphorous Deoxidized Copper

C106 or Cu-DHP is the material normally used for the manufacturing of copper tubes, as it can be readily welded or brazed. The phosphorous acts as a deoxidant to remove copper oxide which would otherwise react with hydrogen. This grade of copper has deep drawing characteristics even better than tough pitch copper and it is readily available as tube, plate, sheet, strip, extrusions and forgings. Some of the most common applications of phosphorus deoxidized copper includes water heaters, air conditioning piping materials, construction purposes, electric refrigerators for water supplies and fuse caps.

Oxygen-Free Coppers

C103, otherwise known as Cu-OF, and CU110, also known as Cu-OFE, are produced by melting and casting the copper under a near vacuum atmosphere to give very low residual oxygen content. Such grades should be specified for applications where resistance to hydrogen embrittlement is required with no loss in conductivity. The grade C110 is designated for electronic purposes and is relatively expensive. The oxide film formed on its surface at high temperature is tightly adherent, making it suitable for vacuum tight glass to metal seals. It also has a very low content of volatiles, making it ideal for use in conditions requiring consistently high vacuum.

Low Alloyed Coppers

For applications where high conductivity is required but the mechanical properties of pure copper are inadequate, one of the low alloyed coppers can be specified. These generally contain less than 2% of an alloy addition. A selection of these alloys is detailed below.

Copper-Silver

This type of copper alloy typically contains 0.01 to 0.12% silver. This provides a progressive increase in creep strength and resistance to annealing in elevated temperature service without loss of conductivity. Another advantageous feature of copper-silver is its relatively high creep strength which is particularly useful when under strain at high temperatures. The addition of silver does not typically affect the electrical and thermal conductivity of this material.

Copper-Chromium

Copper-chromium alloys typically contain 0.3 to 1.4% chromium. This material can be further hardened by heat treatment and has good conductivity with good high temperature strength. Curing coper-chromium alloys can significantly improve its tensile strength and electrical conductivity.

Copper-Beryllium

Copper-beryllium alloys will typically contain 0.4 to 1.9% beryllium. These alloys are heat treatable to very high strength levels, all the while maintaining good conductivity. A number of commercial copper-beryllium alloys exist, some of which also incorporate cobalt and/or nickel additions to further improve the softening temperature of the material. Note that care must be taken when processing any alloys containing beryllium as the oxide, beryllia, is toxic.

Free Machining Coppers

Sulphur and tellurium are added to copper to give free machining properties.

Key Properties

Excellent heat conduction
Excellent electrical conduction
Good corrosion and biofouling resistance (although some alloys are prone to stress corrosion)
Good machinability
Extreme ductility and malleability in the annealed state enabling making it particularly suitable for tube forming, wire drawing, spinning and deep drawing
Mechanical and electrical properties are retained at cryogenic temperatures
Copper and copper alloys should be kept clear of foodstuffs as they impart an unpleasant taste on the food
Copper is the only widely used commercial metal that has a color other than metallic white
Most copper alloys can be joined by processes including brazing, welding or soldering
Copper and its alloys can be plated by electro-deposition using most metals commonly employed for this application
Copper is non-magnetic
Displays a high resistance to sparking

Applications

Electrical Conductors

Due to its excellent electrical conductivity, ETP copper is the primary material used in power transmission and automotive spark plug electrodes. Its high efficiency allows for high current densities and low losses to be achieved. This material is available in a wide range of forms, of which include wrought, drawn wire, rod, hollow rod, profiles, sheet, strip, plate and forgings.

Examples of electrical applications include wiring, cables, busbars, high strength, high conductivity wires and sections, overheads lines, contact wires, resistance-welding electrodes, terminals and high conductivity items for use at raised temperatures.

Heat Exchangers

The high thermal conductivity of copper has made it a preferred choice for heat exchangers, such as in refrigeration tubing. Copper is particularly useful for this application because of its intrinsic antimicrobial properties that reduce the growth of bacteria, mold and mildew, thereby improving system efficiency and eliminating the presence of foul odors.

Plumbing

Due to its ductility and malleability, copper tubing is commonly used in plumbing applications. The fact that it can be easily joined by brazing is also a benefit in this application. Copper pipes are also widely used for water supply lines and refrigerant lines in heating, cooling and air conditioning (HVAC) systems.

Arc Melting Crucibles

Some highly reactive metals are melted using an arc melting process. In such an instance, water-cooled copper crucibles are employed because of their high thermal conductivity, which alloys molten metal to freeze near the crucible wall before it has a chance to alloy with the copper.

Sources and Further Reading