Copper and its alloys are some of the most versatile materials available to the engineer. Their combination of strength, conductivity, corrosion resistance, machinability and ductility can be suited to a wide range of end uses by using variations in composition and manufacturing methods.
The main copper alloys include brasses (copper/zinc alloys), bronzes (copper/tin alloys) including leaded bronzes and phosphor bronzes, aluminium bronzes (copper/aluminium alloys), copper nickel alloys and nickel silvers (copper/nickel/zinc alloys).
Copper and copper alloys are available in both cast and wrought forms. They can also be fastened mechanically using rivets and screws, soldered (as in electrical connections), brazed and welded (excepting high lead content alloys). These materials also lend themselves to being recycled. Recycling accounts for around 40% of the world’s consumption of copper.
Electrolytic Tough Pitch and High Conductivity Copper
This is one of the most readily available of the high conductivity grades 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. These are the materials generally used for electrical applications.
Tough pitch coppers are not easily brazed or welded because they 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 deoxidised coppers have been developed for applications requiring welding.
Phosphorous Deoxidised Copper
C106 or Cu-DHP is the material normally used for the manufacture of copper tubes as it can be readily welded or brazed. The phosphorous acts as a deoxidant removing the copper oxide which would otherwise react with hydrogen (there is only a slight reduction in conductivity). 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. It does however creep readily.
Oxygen Free Coppers
C103 or Cu-OF and CU110 or 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.
Contains from 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.
Contains from 0.3 to 1.4% chromium. It is hardenable by heat treatment and has good conductivity with good high temperature strength.
Containing from 0.4 to 1.9% beryllium, it is heat treatable to very high strength levels with good conductivity. A number of commercial alloys exist, some with additions also of cobalt and nickel. 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.
• 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 to the food.
• Copper is the only widely used commercial metal that has a colour 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
Due to its excellent electrical conductivity, electrolytic tough pitch high copper is the primary material used in power transmission and automotive spark plug electrodes. It is very efficient leading to high current densities and low losses. The material is available in a wide range of forms, including wrought, drawn wire, rod, hollow rod, profiles, sheet, strip, plate and forgings.
Examples of applications include electrical wiring, cables, busbars, high strength, high conductivity wires and sections, overheads lines, contact wires, resistance-welding electrodes, terminals, high conductivity items for use at raised temperatures
The high thermal conductivity of copper has made it a preferred choice for heat exchangers, such as in refrigeration tubing.
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.
Arc Melting Crucibles
Primary Author: Dr. Agnes Segal
Abstracted from Materials Information Service, “Using copper and copper alloys” , edited by Justin Furness
For further details on the Materials Information Service or this publication visit The Institute of Materials