What are Copper Alloys – Definition

What are Copper Alloys Definition

Copper alloys are alloys based on copper, in which the main alloying elements are Zn, Sn, Si, Al, Ni. Copper and copper-based alloys including brasses (Cu-Zn) and bronzes (Cu-Sn) are widely used in different industrial and societal applications.

High purity copper is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a reddish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement. High purity copper has the ultimate strength of approximately 210 MPa, and yield strength of 33 Mpa, which limits its usability in industrial applications. But similarly as for other alloys , copper may be strengthened. The main strengthening mechanism is alloying in Cu-based alloys.

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.

Properties of Copper

Copper is a soft, tough, ductile and malleable material. These properties make copper extremely suitable for tube forming, wire drawing, spinning and deep drawing. The other key properties exhibited by copper and its alloys include:

Excellent thermal conductivity. Copper has a 60% higher thermal conductivity rating than aluminium, so it is better able to reduce thermal hot spots in electrical wiring systems. The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized.
Excellent electrical conductivity. 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. However, aluminium is usually used in overhead high-voltage power lines because it has about half the weight and lower cost of a comparable resistance copper cable. At a given temperature, the thermal and electrical conductivities of metals are proportional, but raising the temperature increases the thermal conductivity while decreasing the electrical conductivity. This behavior is quantified in the Wiedemann–Franz law.
Good corrosion resistance. Copper does not react with water, but it does slowly react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion (passivation). Copper nickel alloys, aluminium brass, and aluminium demonstrate superior resistance to saltwater corrosion.
Good biofouling resistance
Good machinability. Machining of copper is possible, although alloys are preferred for good machinability in creating intricate parts.
Retention of mechanical and electrical properties at cryogenic temperatures
Diamagnetic

Uses of Copper and Copper Alloys

Historically, alloying copper with another metal, for example tin to make bronze, was first practiced about 4000 years after the discovery of copper smelting, and about 2000 years after “natural bronze” had come into general use. An ancient civilization is defined to be in the Bronze Age either by producing bronze by smelting its own copper and alloying with tin, arsenic, or other metals. The major applications of copper are electrical wire (60%), roofing and plumbing (20%), and industrial machinery (15%). Copper is used mostly as a pure metal, but when greater hardness is required, it is put into such alloys as brass and bronze (5% of total use). Copper and copper-based alloys including brasses (Cu-Zn) and bronzes (Cu-Sn) are widely used in different industrial and societal applications. Some of the common uses for brass alloys include costume jewelry, locks, hinges, gears, bearings, ammunition casings, automotive radiators, musical instruments, electronic packaging, and coins. Bronze, or bronze-like alloys and mixtures, were used for coins over a longer period. is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings, and is particularly common in the bearings of small electric motors. Brass and bronze are common engineering materials in modern architecture and primarily used for roofing and facade cladding due to their visual appearance.

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.

Copper and Waste Management

Currently, the preferred option for final disposal of high-level radioactive waste is a deep geological repository (DGR), which is an underground emplacement in stable geological formations. Crystalline rock (granite, welded tuff and basalt), salt and clay are the most suitable formations for geological disposal. The once-through cycle considers the spent nuclear fuel to be high-level waste (HLW) and, consequently, it is directly disposed of in a storage facility without being put through to any chemical processes, where it will be safely stored for millions of years until its radiotoxicity reaches natural uranium levels or another safe reference level.

One of possible options is to encapsulate this spent fuel in copper (CuOFP alloy – oxygen-free phosphorus-containing copper) capsules and deposit these cannisters in a layer of bentonite clay, in a circular hole, eight meters deep and with a diameter of two meters, drilled in a cave 500 metres down into crystalline rock. The deposits of native (pure) copper in the world have proven that the copper used in the final disposal container can remain unchanged inside the bedrock for extremely long periods, if the geochemical conditions are appropriate (low levels of groundwater flow). The findings of ancient copper tools, many thousands of years old, also demonstrate the long-term corrosion resistance of copper, making it a credible container material for long-term radioactive waste storage.

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 to gold to silver 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.

For example, UNS C26000 cartridge brass alloy (70/30) is from the yellow brass series, which has the highest ductility. Cartridge brasses are mostly cold formed and they can also be easily machined, which is necessary in making cartridge cases. It can be used for radiator cores and tanks, flashlight shells, lamp fixtures, fasteners, locks, hinges, ammunition components or plumbing accessories.

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.

Historically, alloying copper with another metal, for example tin to make bronze, was first practiced about 4000 years after the discovery of copper smelting, and about 2000 years after “natural bronze” had come into general use. An ancient civilization is defined to be in the Bronze Age either by producing bronze by smelting its own copper and alloying with tin, arsenic, or other metals. Bronze, or bronze-like alloys and mixtures, were used for coins over a longer period. is still widely used today for springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings, and is particularly common in the bearings of small electric motors. Brass and bronze are common engineering materials in modern architecture and primarily used for roofing and facade cladding due to their visual appearance.

Properties of Copper Alloys

Material properties are intensive properties, that means they are independent of the amount of mass and may vary from place to place within the system at any moment. The basis of materials science involves studying the structure of materials, and relating them to their properties (mechanical, electrical etc.). Once a materials scientist knows about this structure-property correlation, they can then go on to study the relative performance of a material in a given application. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and the way in which it has been processed into its final form.

Mechanical Properties of Copper Alloys

Materials are frequently chosen for various applications because they have desirable combinations of mechanical characteristics. For structural applications, material properties are crucial and engineers must take them into account.

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.

Hardness of Copper Alloys

Vickers hardness of electrolytic-tough pitch (ETP) copper depends greatly on the temper of the material, but it is between 50 – 150 HV.
Brinell hardness of carthridge brass – UNS C26000 is approximately 100 MPa.
Brinell hardness of aluminium bronze – UNS C95400 is approximately 170 MPa. The hardness of aluminum bronzes increases with aluminum (and other alloy) content as well as with stresses caused through cold working.
Brinell hardness of tin bronze – UNS C90500 – gun metal is approximately 75 BHN.
Rockwell hardness of copper beryllium – UNS C17200 is approximately 82 HRB.
Brinell hardness of cupronickel – UNS C70600 is approximately HB 100.
Rockwell hardness of nickel silver – UNS C75700 is approximately 45 HRB.

Rockwell hardness test is one of the most common indentation hardness tests, that has been developed for hardness testing. In contrast to Brinell test, the Rockwell tester measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). The minor load establishes the zero position. The major load is applied, then removed while still maintaining the minor load. The difference between depth of penetration before and after application of the major load is used to calculate the Rockwell hardness number. That is, the penetration depth and hardness are inversely proportional. The chief advantage of Rockwell hardness is its ability to display hardness values directly. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale.

The Rockwell C test is performed with a Brale penetrator (120°diamond cone) and a major load of 150kg.