Electrical conductivity of metals
The electrical conductivity of metals is a fundamental property that determines their ability to conduct electric current. Silver possesses the highest conductivity of all elements at 63 × 10⁶ S/m at room temperature, followed by copper with 59.6 × 10⁶ S/m in the pure state and 58.0 × 10⁶ S/m in the annealed state. The International Annealed Copper Standard (IACS) establishes as a reference 100% conductivity for commercially pure annealed copper, equivalent to 58.0 MS/m at 20 °C.
| Property | Typical value |
|---|---|
| Conductivity of annealed copper (IACS) | 100% IACS = 58.0 MS/m |
| Conductivity of silver | 63.0 MS/m (104.9% IACS) |
| Conductivity of gold | 45.2 MS/m (71.7% IACS) |
| Conductivity of aluminum | 37.7 MS/m (59.8% IACS) |
| IACS reference temperature | 20 °C |
Chemical composition of electrolytic tough pitch copper (Cu-ETP / C101)
Section titled “Chemical composition of electrolytic tough pitch copper (Cu-ETP / C101)”Copper alloy C101, also designated HC (high conductivity) or Cu-ETP, contains a minimum of copper with controlled total impurities not exceeding 0.10%. This high purity guarantees maximum performance in electrical and thermal applications.
| Element | Content (% by weight) |
|---|---|
| Copper (Cu) | Balance (min. 99.90%) |
| Other elements (total) | 0.0 – 0.10 |
Mechanical properties by temper
Section titled “Mechanical properties by temper”The mechanical properties of high conductivity copper vary significantly according to the degree of cold work applied. Annealed material exhibits a tensile strength of 200 MPa with excellent ductility, while fully strain-hardened material reaches 360 MPa with elongations reduced to 5%.
| Temper | Tensile strength (MPa) | Yield strength (MPa) | Elongation A50 (%) | Vickers hardness (HV) |
|---|---|---|---|---|
| Annealed | 200 | 50 | 50 | 40 |
| Half hard | 280 | 200 | 20 | 80 |
| Hard | 360 | 340 | 5 | 110 |
Physical and thermal properties
Section titled “Physical and thermal properties”C101 copper exhibits a melting point of 1083 °C and a density of 8.92 g/cm³. Its modulus of elasticity of 117 GPa and coefficient of thermal expansion of 16.9 × 10⁻⁶/K make it suitable for components subjected to thermal cycles. Thermal conductivity reaches 391.1 W/m·K, the highest among commercial metals after silver.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density | 8.92 g/cm³ | 0.322 lb/in³ |
| Melting point | 1083 °C | 1981 °F |
| Modulus of elasticity | 117 GPa | 16 970 ksi |
| Electrical resistivity | 0.171 × 10⁻⁶ Ω·m | 1.71 μΩ·cm |
| Thermal conductivity | 391.1 W/m·K | 226 BTU·ft/(h·ft²·°F) |
| Coefficient of thermal expansion | 16.9 × 10⁻⁶/K | 9.4 × 10⁻⁶/°F |
Electrical conductivity in common metals
Section titled “Electrical conductivity in common metals”The electrical conductivity of metals is measured in siemens per meter and is often expressed as a percentage IACS. Silver is the metal with the highest absolute electrical conductivity, reaching 63.0 × 10⁶ S/m, equivalent to 104.9% IACS. Annealed copper constitutes the base reference with 58.0 × 10⁶ S/m. Metals such as aluminum offer a lighter alternative with 37.7 × 10⁶ S/m, although with approximately 60% of the conductivity of copper.
| Metal | Electrical conductivity (S/m) | Relative conductivity to silver (%) | Conductivity (% IACS) |
|---|---|---|---|
| Silver | 63.0 × 10⁶ | 100.0 | 104.9 |
| Copper (annealed) | 58.0 × 10⁶ | 94.6 | 100.0 |
| Copper (pure) | 59.6 × 10⁶ | 97.3 | 102.8 |
| Gold | 45.2 × 10⁶ | 71.7 | 75.4 |
| Aluminum | 37.7 × 10⁶ | 59.8 | 63.0 |
| Tungsten | 18.9 × 10⁶ | 30.0 | 31.6 |
| Zinc | 16.6 × 10⁶ | 26.3 | 27.8 |
| Nickel | 14.3 × 10⁶ | 22.6 | 23.9 |
| Iron | 9.93 × 10⁶ | 15.8 | 16.6 |
| Titanium | 13.7% relative to silver | 13.7 | 14.0 |
| Tin | 9.17 × 10⁶ | 14.6 | 15.3 |
| Lead | 8.4% relative to silver | 8.4 | 8.8 |
| Platinum | 9.66 × 10⁶ | 15.3 | 16.1 |
| Steel (typical) | 12.0% relative to silver | 12.0 | 12.0 |
IACS Reference Standard
Section titled “IACS Reference Standard”The International Annealed Copper Standard was established in 1914 by the United States Department of Commerce. The standard defines a reference conductivity value based on empirical measurements carried out around 1913 on copper samples from 14 refiners and wire manufacturers. The average resistance determined was 0.15292 Ω for copper wires with a mass of 1 gram, uniform cross section, and length of 1 meter at 20 °C. The International Electrotechnical Commission adopted a German modification that set the standard value at 58.0 × 10⁶ S/m at 20 °C. Currently, IACS is used universally as a comparative property to specify the conductivity of other metals and alloys, expressed as a percentage IACS. It is particularly relevant in the quality control of heat treatments in aluminum alloys, where specific conductivity values verify the correct execution of processes such as T73 in alloy 7075, which must present between 38.0% and 43.0% IACS to ensure resistance to stress corrosion cracking.
Factors affecting electrical conductivity in metals
Section titled “Factors affecting electrical conductivity in metals”Alloying elements and impurities constitute the most determining factor in the reduction of electrical conductivity. Small additions of phosphorus, iron, or arsenic in copper can drastically decrease the IACS percentage. Cold work introduces dislocations that reduce conductivity, although in pure copper the effect is moderate. Temperature has an inversely proportional effect: the higher the temperature, the greater the thermal agitation of the crystal lattice and the lower the conductivity. Annealing heat treatments restore the crystal structure and maximize conductivity. The presence of secondary phases, precipitates, or non-conductive inclusions reduces the effective conduction cross-section. Dissolved oxygen in copper forms Cu₂O particles that affect conductivity, especially in applications requiring vacuum or reducing atmospheres.
Applications by industry
Section titled “Applications by industry”The selection of conductive metals depends on the required balance between electrical conductivity, mechanical properties, corrosion resistance, and cost. High conductivity copper dominates general electrical applications, while other metals find specific niches where their complementary properties justify the lower conductivity.
| Industry | Main metal | Specific application | Conductivity requirement |
|---|---|---|---|
| Electrical and electronics | Copper C101 | Electrical conductors, busbars, windings | 100% IACS nominal |
| Automotive | Copper C101 | Wiring harnesses, electronic components | High conductivity + ductility |
| Power transmission | Aluminum | Overhead transmission cables | 59.8% IACS with lower weight |
| High reliability electronics | Silver | Electrical contacts, switches | Maximum conductivity (104.9% IACS) |
| Precision electronics | Gold | Connectors, non-oxidizing contacts | 71.7% IACS + corrosion resistance |
| Home appliances | Copper C101 | Cold formed components | High conductivity + formability |
| General engineering | Copper C101 | Electrical and thermal components | 100% IACS |
Advantages and limitations of conductive metals
Section titled “Advantages and limitations of conductive metals”High conductivity copper offers the best balance between electrical conductivity, thermal conductivity, ductility, and cost for most applications. Its corrosion resistance is good or excellent in most atmospheres, including marine and industrial environments, although it suffers corrosion from oxidizing acids, halogens, sulfides, and solutions containing ammonium ions. Silver provides maximum conductivity but its cost limits its use to critical applications. Aluminum reduces weight by approximately 70% relative to copper, although it requires a larger cross-section to match the current-carrying capacity. Gold is irreplaceable in high-reliability contacts where oxidation resistance is paramount. The main limitations of copper include its incompatibility with reducing atmospheres at high temperature and its tendency to hydrogen embrittlement cracking.
Supplementary manufacturing technical data
Section titled “Supplementary manufacturing technical data”Copper C101 can be cold worked with excellent ductility in the annealed state and work-hardens relatively slowly. The annealing temperature ranges between 370 °C and 650 °C, followed by rapid cooling. Hot working is performed without difficulty. Soldering is rated as excellent, brazing and butt welding as good, while gas-shielded arc welding receives an acceptable rating. Other welding processes are not recommended. The machinability of copper C101 is rated with index 20, taking brass 360 FC with index 100 as reference. It is typically supplied in the form of flat bar, round bar, and half-hard sheet.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”Which metal has the highest electrical conductivity?
Section titled “Which metal has the highest electrical conductivity?”Silver is the metal with the highest electrical conductivity, reaching 63.0 × 10⁶ S/m, which represents 104.9% IACS and surpasses annealed copper by approximately 5 percentage points of relative conductivity.
What does the IACS percentage mean in metal conductivity?
Section titled “What does the IACS percentage mean in metal conductivity?”The IACS percentage expresses the electrical conductivity of a material as a percentage of the international annealed copper standard. A value of 100% IACS equals a conductivity of 58.0 MS/m at 20 °C, which corresponds to commercially pure copper in the annealed state according to the standard established in 1914.
Why is aluminum used in transmission cables if it conducts less than copper?
Section titled “Why is aluminum used in transmission cables if it conducts less than copper?”Aluminum has a conductivity of 37.7 MS/m, equivalent to 59.8% IACS, but its density is approximately 3 times lower than that of copper. This conductivity-to-weight ratio makes it more efficient for overhead transmission lines where the self-weight of the conductor is a critical design factor.
How does temperature affect the electrical conductivity of metals?
Section titled “How does temperature affect the electrical conductivity of metals?”The increase in temperature increases the thermal agitation of atoms in the crystal lattice, which hinders the flow of electrons and reduces conductivity. The standard IACS measurement is referenced at 20 °C, and variations can be significant in high-temperature applications.
Which impurities most affect the conductivity of copper?
Section titled “Which impurities most affect the conductivity of copper?”Small amounts of phosphorus, iron, arsenic, and other elements drastically reduce the conductivity of copper. C101 copper for electrical applications keeps total impurities below 0.10% to guarantee the nominal 100% IACS conductivity.
Which metals offer a balance between conductivity and corrosion resistance?
Section titled “Which metals offer a balance between conductivity and corrosion resistance?”Gold offers 71.7% IACS with total immunity to atmospheric oxidation, while platinum provides 16.1% IACS with excellent chemical resistance. Copper offers 100% IACS with good corrosion resistance in most environments, although it is vulnerable to sulfides and ammonia solutions.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=2850
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/conductors-d_1381.html