Copper alloys are alloys based on copper, in which the main alloying elements are Zn, Sn, Si, Al, Ni. Cu-based alloys constitute mostly substitutional solid solutions, for which solute or impurity atoms replace or substitute for the host atoms. Several features of the solute and solvent atoms determine the degree to which the former dissolves in the latter. These are expressed as the Hume–Rothery rules. There are as many as 400 different copper and copper alloy compositions loosely grouped into the categories: copper, high copper alloy, brasses, bronzes, copper nickels, copper–nickel–zinc (nickel silver), leaded copper, and special alloys. In addition, a limited number of copper alloys can be strengthened by heat treatment.; consequently, cold working and/or solid-solution alloying must be used to improve these mechanical properties.
Types of Copper Alloys
As was written, there are as many as 400 different copper and copper alloy compositions loosely grouped into the categories: copper, high copper alloy, brasses, bronzes, copper nickels, copper–nickel–zinc (nickel silver), leaded copper, and special alloys. In following points we summarize key properties of selected copper-based materials.
Electrolytic-tough pitch (ETP) copper. Electrolytic tough pitch copper, UNS C11000, is pure copper (with a maximum of 0.0355% of impurities) refined by electrolytic refining process and it is the most widely used grade of copper all over the world. ETP has a minimum conductivity rating of 100% IACS and is required to be 99.9% pure. It has 0.02% to 0.04% oxygen content (typical). Electrical wiring is the most important market for the copper industry. This includes structural power wiring, power distribution cable, appliance wire, communications cable, automotive wire and cable, and magnet wire. Roughly half of all copper mined is used for electrical wire and cable conductors. Pure copper has the best electrical and thermal conductivity of any commercial metal. The conductivity of copper is 97% that of silver. Due to its much lower cost and greater abundance, copper has traditionally been the standard material used for electricity transmission applications.- Brass. Brass is is the generic term for a range of copper-zinc alloys. Brass can be alloyed with zinc in different proportions, which results in a material of varying mechanical, corrosion and thermal properties. Increased amounts of zinc provide the material with improved strength and ductility. Brasses with a copper content greater than 63% are the most ductile of any copper alloy and are shaped by complex cold forming operations. Brass has higher malleability than bronze or zinc. The relatively low melting point of brass and its fluidity make it a relatively easy material to cast. Brass can range in surface color from red to yellow depending on the zinc content. Some of the common uses for brass alloys include costume jewelry, locks, hinges, gears, bearings, hose couplings, ammunition casings, automotive radiators, musical instruments, electronic packaging, and coins. Brass and bronze are common engineering materials in modern architecture and primarily used for roofing and facade cladding due to their visual appearance.
- Bronze. The bronzes are a family of copper-based alloys traditionally alloyed with tin, but can refer to alloys of copper and other elements (e.g. aluminum, silicon, and nickel). Bronzes are somewhat stronger than the brasses, yet they still have a high degree of corrosion resistance. Generally they are used when, in addition to corrosion resistance, good tensile properties are required. For example, beryllium copper attains the greatest strength (to 1,400 MPa) of any copper-based alloy.
- Copper-nickel Alloy. Cupronickels are copper-nickel alloys that contain typically from 60 to 90 percent of copper and nickel as the main alloying element. The two main alloys are 90/10 and 70/30. Other strengthening elements, such as manganese and iron, may be also contained. Cupronickels have excellent resistance to corrosion caused by sea water. Despite its high copper content, cupronickel is silver in colour. The addition of nickel to copper also improves strength and corrosion resistance, but good ductility is retained.
- Nickel Silver. Nickel silver, known also as German silver, nickel brass or alpacca, is a copper alloy with nickel and often zinc. For example, UNS C75700 nickel silver 65-12 copper alloy has good corrosion and tarnish-resistance, and high formability. Nickel silver is named due to its silvery appearance, but it contains no elemental silver unless plated.
Strength of Copper Alloys
In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. Strength of a material is its ability to withstand this applied load without failure or plastic deformation.
Ultimate Tensile Strength
Ultimate tensile strength of electrolytic-tough pitch (ETP) copper it is about 250 MPa.
Ultimate tensile strength of carthridge brass – UNS C26000 is about 315 MPa.
Ultimate tensile strength of aluminium bronze – UNS C95400 is about 550 MPa.
Ultimate tensile strength of tin bronze – UNS C90500 – gun metal is about 310 MPa.
Ultimate tensile strength of copper beryllium – UNS C17200 is about 1380 MPa.
Ultimate tensile strength of cupronickel – UNS C70600 is about 275 MPa.
Ultimate tensile strength of nickel silver – UNS C75700 is about 400 MPa.
The ultimate tensile strength is the maximum on the engineering stress-strain curve. This corresponds to the maximum stress that can be sustained by a structure in tension. Ultimate tensile strength is often shortened to “tensile strength” or even to “the ultimate.” If this stress is applied and maintained, fracture will result. Often, this value is significantly more than the yield stress (as much as 50 to 60 percent more than the yield for some types of metals). When a ductile material reaches its ultimate strength, it experiences necking where the cross-sectional area reduces locally. The stress-strain curve contains no higher stress than the ultimate strength. Even though deformations can continue to increase, the stress usually decreases after the ultimate strength has been achieved. It is an intensive property; therefore its value does not depend on the size of the test specimen. However, it is dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material. Ultimate tensile strengths vary from 50 MPa for an aluminum to as high as 3000 MPa for very high-strength steels.
Yield Strength
Proof strength of electrolytic-tough pitch (ETP) copper is between 60-300 MPa.
Yield strength of aluminium bronze – UNS C95400 is about 250 MPa.
Yield strength of tin bronze – UNS C90500 – gun metal is about 150 MPa.
Yield strength of copper beryllium – UNS C17200 is about 1100 MPa.
Yield strength of cupronickel – UNS C70600 is about 105 MPa.
Yield strength of nickel silver – UNS C75700 is about 170 MPa.
The yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point, the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible. Some steels and other materials exhibit a behaviour termed a yield point phenomenon. Yield strengths vary from 35 MPa for a low-strength aluminum to greater than 1400 MPa for very high-strength steels.
Young’s Modulus of Elasticity
Young’s modulus of elasticity of electrolytic-tough pitch (ETP) copper is about 120 GPa.
Young’s modulus of elasticity of carthridge brass – UNS C26000 is about 95 GPa.
Young’s modulus of elasticity of aluminium bronze – UNS C95400 is about 110 GPa.
Young’s modulus of elasticity of tin bronze – UNS C90500 – gun metal is about 103 GPa.
Young’s modulus of elasticity of copper beryllium – UNS C17200 is about 131 GPa.
Young’s modulus of elasticity of cupronickel – UNS C70600 is about 135 GPa.
Young’s modulus of elasticity of nickel silver – UNS C75700 is about 117 GPa.
The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests. Up to a limiting stress, a body will be able to recover its dimensions on removal of the load. The applied stresses cause the atoms in a crystal to move from their equilibrium position. All the atoms are displaced the same amount and still maintain their relative geometry. When the stresses are removed, all the atoms return to their original positions and no permanent deformation occurs. According to the Hooke’s law, the stress is proportional to the strain (in the elastic region), and the slope is Young’s modulus. Young’s modulus is equal to the longitudinal stress divided by the strain.
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