The Electrical Conductivity of Wrought Copper and Copper Alloys

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Introduction to the Electrical Conductivity of Copper and Copper Alloys

The key properties of copper and copper alloys, which determine their applications, include electrical conductivity, thermal conductivity, corrosion resistance, machinability, fatigue resistance, malleability, formability, and strength. In addition, copper's attractive color, nonmagnetic nature, and ease of finishing (through plating or lacquering) make it a versatile material. Copper is also easily welded, brazed, and soldered, adding to its utility in various industries.

Key Properties of Copper and Copper Alloys

When improving certain properties, especially strength, without compromising other important characteristics, alloying often provides the solution. Common commercial materials such as brass, bronze, copper-nickel alloys, and special bronzes are designed to enhance these properties while maintaining copper's fundamental benefits.

The electrical conductivity of copper is its most significant property, particularly in electrical applications. Copper's high conductivity is combined with its resistance to corrosion and its ease of formability. Even with very high conductivity, a material that is difficult to draw or fabricate easily or is prone to corrosion would be unsuitable for the electrical industry.

Impact of Alloying on Copper's Conductivity and Strength

Electrolytic tough pitch copper (ETP) is the preferred material for current-carrying components, with conductivity of 101% IACS (International Annealed Copper Standard) in the soft temper and a tensile strength of 220 MPa. In spring-rolled temper, the conductivity drops to 97%, but the tensile strength rises to 345 to 380 MPa. When exposed to temperatures above 200°C, ETP copper softens, reducing tensile strength to 240-300 MPa.

Silver-bearing copper alloys, such as silver-bearing tough pitch copper, resist softening up to around 340°C, making them suitable for highly stressed components like turbo generator windings and high-speed commutators.

Applications of Copper and Copper Alloys in Electrical Systems

Copper alloys are indispensable in the electrical industry due to their excellent conductivity and other beneficial properties, such as machinability and corrosion resistance. Electrolytic tough pitch copper is preferred for conductors, while chromium copper and beryllium copper are used in applications requiring higher tensile strength. These alloys are essential for electrical systems, from power transmission cables to electronic components.

Common Copper Alloys and Their Electrical Conductivity

Table 1 provides the nominal compositions of various wrought copper materials, including electrolytic tough pitch copper (ETP), phosphorized copper, oxygen-free copper, and several others. The corresponding electrical conductivity of these alloys is shown in Table 2, highlighting how alloying affects the material's performance in electrical applications.

Table 1. Nominal composition of Wrought Copper Materials

Alloy	Composition
Coppers
Electrolytic tough pitch (ETP)	99.90 Cu - 0.04 O
Phosphorized. high residual phosphorus (DHP)	99.90 Cu - 0.02 P
Phosphorized, low residual phosphorus (DLP)	99.90 Cu - 0.005 P
Lake	Cu - 8 oz/t Ag
Silver-bearing (10-15)	Cu - 10 to 15 oz/t Ag
Sliver-bearing (25-30)	Cu - 25 to 30 oz/t Ag
Oxygen-free (OF) (no residual deoxidants)	99.92 Cu (min)
Free-cutting	99Cu - 1 Pb
Free-cutting	99.5 Cu - 0.5 Te
Free-cutting	99.4 Cu - 0.6 Se
Chromium copper (heat treatable)	Cu+Cr and Ag or Zn
Cadmium copper	99 Cu - 1 Cd
Tellurium-nickel copper (heat treatable)	98.4 Cu - 1.1 Ni - 0.5 Te
Beryllium copper (heat treatable)	Cu - 2 Be - 0.25 Co or 0.35 Ni
Plain Brasses
Gliding %	95 Cu - 5 Zn
Commercial bronze 90%	90 Cu - 10 Zn
Red brass 85%	85 Cu - 15 Zn
Low brass 80%	80 Cu - 20 Zn
Cartridge brass 70%	70 Cu - 30 Zn
Yellow brass 65%	65 Cu - 35 Zn
Muntz metal	60 Cu - 40 Zn
Free-Cutting Brasses
Leaded commercial bronze (rod)	89 Cu - 9.25 Zn - 1.75 Pb
Leaded brass strip (B121-3)	65 Cu - 34 Zn - 1 Pb
Leaded brass strip (B121-5)	65 Cu - 33 Zn - 2 Pb
Leaded brass tube (B135-3)	66 Cu - 33.5 Zn - 0.5 Pb
Leaded brass tube (B135-4)	66 Cu - 32.4 Zn - 1.6 Pb
Medium-leaded brass rod	64.5 Cu - 34.5 Zn - 1 Pb
High-leaded brass rod	62.5 Cu - 35.75 Zn - 1.75 Pb
Free-cutting brass rod (B16)	61.5 Cu - 35.5 Zn - 3 Pb
Forging brass	60 Cu - 38 Zn - 2 Pb
Architectural bronze	57 Cu - 40 Zn - 3 Pb
Miscellaneous Brasses
Admiralty (inhibited)	71 Cu - 28 Zn -1 Sn
Naval brass	60 Cu - 39.25 Zn - 0.75 Sn
Leaded naval brass	60 Cu - 37.5 Zn - 1.75 Pb - 0.75 Sn
Aluminum brass (inhibited)	76 Cu - 22 Zn - 2 Al
Manganese brass	70 Cu - 28.7 Zn - 1.3 Mn
Manganese bronze rod A (B138)	58.5 Cu - 39 Zn - 1.4 Fe - 1 Sn - 0.1 Mn
Manganese bronze rod B (B138)	65.5 Cu - 23.3 Zn - 4.5 Al - 3.7 Mn - 3 Fe
Phosphor Bronzes
Grade A	95 Cu - 5 Sn
Grade B (rod, B139, alloy B1)	94 Cu - 5 Sn - 1 Pb
Grade C	92 Cu - 8 Sn
Grade D	90 Cu - 10 Sn
Grade E	98.75 Cu - 1.25 Sn
444 bronze rod (B139, alloy B2)	88 Cu - 4 Zn - 4 Sn - 4 Pb
Miscellaneous Bronzes
Silicon bronze A	Cu - 3 Si - 1 Mn
Silicon bronze B	Cu - 1.75 Si - 0.3 Mn
Aluminum bronze, 5%	95Cu - 5 Al
Aluminum bronze, 7%	91 Cu - 7 Al - 2 Fe
Aluminum bronze, 10%	Cu - 9.5 Al
Aluminum-silicon bronze	91 Cu - 7 Al - 2 Si
Nickel-Containing Alloys
Cupro-nickel, 10%	88.5 Cu - 10 Ni - 1.5 Fe
Cupro-nickel, 30%	69.5 Cu - 30 Ni - 0.5 Fe
Nickel silver A	65 Cu - 17 Zn - 18 Ni
Nickel silver B	55 Cu - 27 Zn - 18 Ni
Leaded nickel silver rod (B151)	62 Cu - 19 Zn - 18 N - 1 Pb

Table 2. Comparative Electrical Conductivity of Wrought Copper Materials

Alloy	% IACS
Coppers
Electrolytic (ETP)	101
Silver-bearing, 8 oz/t	101
Silver-bearing, 10 to 15 oz/t	101
Silver-bearing, 25 to 30 oz/t	101
Oxygen-free (OF)	101
Phosphorized (DLP)	97 to 100
Free-cutting (S, Te or Pb)	90 to 98
Chromium coppers	80 to 90
Phosphorized (DHP)	80 to 90
Cadmium copper (1%)	80 to 90
Tellurium-nickel copper	50
Copper Alloys
Brasses	25 to 50
Phosphor bronze E	25 to 50
Naval brass	25 to 50
Admiralty	25 to 50
Phosphor bronze A, C, D	10 to 20
Aluminum bronze, 5%	10 to 20
Silicon bronze B	10 to 20
Beryllium copper	10 to 20
Cupro-nickel, 30%	5 to 15
Nickel silver	5 to 15
Aluminum bronze (over 5% Al)	5 to 15
Silicon bronze A	5 to 15

Conclusion

The selection of copper or its alloys depends on the required balance between electrical conductivity, mechanical strength, and other physical properties. By understanding the conductive properties and alloy compositions, manufacturers can select the optimal material for specific applications in industries like telecommunications, power generation, and electronics.