Classification and properties of copper and copper alloys
Copper and copper alloys are one of the major categories of commercial metals. They offer a wide range of properties, including excellent electrical and thermal conductivity, excellent corrosion resistance, good strength and fatigue resistance, and appearance. They can be easily machined, brazed and welded.
Selection of copper and copper alloys
The main selection criteria for copper and copper alloys include:
Electrical conductivity: Copper is the most conductive of the engineering metals. Silver or other elements can be added to increase strength, resistance to softening, or other properties without significant loss of conductivity.
Thermal Conductivity: This property is similar to electrical conductivity. Copper alloys are useful for this property, where good corrosion resistance compensates for the increased conductivity loss of alloying.
Color and Appearance: Many copper alloys have unique colors that may change as the object weathers. For most alloys, it is easy to prepare and maintain surfaces to a high standard even under adverse corrosion conditions. Many alloys are used in decorative applications, either in their native form or after metal plating. These alloys come in specific colors, ranging from salmon pink for copper, through yellows, golds and greens, to deep bronze in weathered conditions. Exposure to the atmosphere produces a green or bronze finish, and pre-alloys are available on some product forms.
Ease of fabrication: Most alloys can be easily cast, hot or cold formed, machined, joined, etc. These alloys are often the standard against which other metals are compared.
Alloy Properties
Many alloys are solid solution strengthened but are based on the copper crystal structure and have good ductility. Most alloys can be further strengthened by cold working, thereby increasing tensile and fatigue strength while maintaining useful ductility. Some alloys can be dispersion strengthened and some can be age hardened to very high strength levels.
different types of metal alloys
Copper is essentially commercially pure copper, which is usually very soft and ductile, with a total impurity content of up to around 0.7%. These materials are used for their electrical and thermal conductivity, corrosion resistance, appearance and color, and ease of processing. They have the highest electrical conductivity of any engineering metal and are very ductile, easy to braze, and often welding. Typical applications include electrical wiring and fittings, bus bars, heat exchangers, roofs, wall cladding, water pipes, air pipes and process equipment.
High copper alloys contain small amounts of various alloying elements such as beryllium, chromium, zirconium, tin, silver, sulfur or iron. These elements change one or more fundamental properties of copper, such as strength, creep resistance, workability, or solderability. Most uses are similar to those given above for copper, but the application conditions are more extreme.
Brass is a copper-zinc alloy containing up to 45% zinc, with the possible addition of small amounts of lead to improve workability and tin for strength. Copper-zinc alloys are single-phase and contain up to about 37% zinc in forged conditions. Single-phase alloys have excellent ductility and are typically used in the cold-worked condition for better strength. Alloys containing more than about 37% zinc are duplex alloys and have greater strength than single-phase alloys but limited ductility at room temperature. Duplex brass is usually cast or heat-finished. Typical uses of brass are construction, drawn and rotating containers and components, radiator cores and tanks, electrical terminals, plugs and light fittings, locks, door handles, nameplates, plumbers' hardware, fasteners, cartridges, cylinders for pumps set.
Bronze is an alloy of copper and tin, plus at least one of phosphorus, aluminum, silicon, manganese and nickel. These alloys can achieve high strength and have good corrosion resistance. They are used in springs and fixtures, metal forming dies, bearings, bushings, terminals, contacts and connectors, construction accessories and features. The use of cast bronze for statues is well known.
Cupro-nickel is an alloy of copper and nickel, containing small amounts of iron and sometimes small amounts of other alloys such as chromium or tin. The alloy has excellent corrosion resistance in water and is widely used in seawater applications such as heat exchangers, condensers, pumps and piping systems, and ship hull sheathing.
Nickel silver contains 55 – 65% copper alloyed with nickel and zinc, and lead is sometimes added to improve workability. These alloys are named for their appearance, which is similar to sterling silver, although they do not contain silver. They are used in jewelry and nameplates and as bases for silver plates (EPNS), as springs, fasteners, coins, keys and camera parts.
