The electrical conductivity of pure aluminum is approximately 3.5 × 107 S/m (Siemens per meter) at 20°C, which is about 61% that of copper. Compared to common conductors like copper and silver, aluminum is a good conductor due to the free movement of its valence electrons.
This article introduces the conductivity of aluminum, its influencing factors, and its comparison with other metals.
What Is the Electrical Conductivity of Aluminum?
The standard electrical conductivity of pure aluminum is approximately
36–38 MS/m at 20°C.
Electrical conductivity is inversely related to electrical resistivity, expressed as:
σ = 1 / ρ
where σ is the electrical conductivity (S/m) and ρ is the electrical resistivity (Ω·m).
Temperature affects conductivity: as temperature rises, atomic vibrations increase, scattering electrons and reducing conductivity.
Conversely, lower temperatures generally improve conductivity.
| Temperature (°C) | Electrical Conductivity (MS/m) |
|---|---|
| 0 | 40.0 |
| 20 | 37.7 |
| 100 | 34.0 |
| 200 | 30.0 |
| 300 | 26.5 |
Factors Affecting Aluminum’s Electrical Conductivity
Purity and Alloying Elements: High-purity aluminum exhibits maximum conductivity. Alloying with Mg, Si, Cu, or Zn reduces conductivity slightly while improving mechanical properties.
Temperature Effects: Conductivity decreases as temperature rises due to increased electron scattering.
Mechanical Processing: Cold working, extrusion, or rolling can introduce lattice defects that slightly reduce conductivity.
Oxidation and Surface Quality: Aluminum naturally forms a thin oxide layer. While thin, this layer can influence contact resistance in connections and interfaces.
Comparison with Other Conductive Metals
Aluminum’s conductivity is lower than copper or silver, but it is much lighter, providing advantages in weight-sensitive applications.
| Material | Electrical Conductivity (MS/m) | Density (g/cm³) | Notes |
|---|---|---|---|
| Aluminum | 36–38 | 2.70 | Lightweight alternative to copper |
| Copper | 58 | 8.96 | High conductivity, heavier |
| Silver | 63 | 10.49 | Highest conductivity, costly |
| Gold | 45 | 19.32 | High corrosion resistance, expensive |
| Iron | 10 | 7.85 | Low conductivity, structural use |
Electrical Conductivity of Aluminum Alloys
While pure aluminum offers high electrical conductivity (around 36–38 MS/m at 20 °C), most engineering applications use aluminum alloys that balance conductivity with mechanical strength, corrosion resistance, and processability.
Alloying elements such as magnesium (Mg), silicon (Si), copper (Cu), and zinc (Zn) improve strength but reduce conductivity due to lattice distortion and increased electron scattering.
In general, the higher the alloy content, the lower the electrical conductivity.
For example, high-strength alloys like 7075-T6 have only about 30–40 % of the conductivity of pure aluminum, while structural alloys like 6061-T6 and 6063-T5 retain moderate conductivity levels suitable for both electrical and thermal transfer components.
| Alloy | Temper | Electrical Conductivity (MS/m) | % IACS* | Remarks |
|---|---|---|---|---|
| Pure Aluminum (1100) | Annealed | 36–38 | ~61% | High conductivity, low strength |
| 6061-T6 | Heat-treated | 23–25 | ~40% | Balanced strength and conductivity |
| 6063-T5 | Extruded | 27–30 | ~47% | Common in architectural and heat sink profiles |
| 7075-T6 | High-strength | 17–19 | ~30% | Used in aerospace structures |
| 1350 | EC Grade | 35–37 | ~60% | Used for electrical conductors and bus bars |
*IACS = International Annealed Copper Standard (100% IACS = 58.0 MS/m)
Aluminum in Electrical Applications
Overhead power lines and busbars
Electric motor and transformer windings
Printed circuit boards (PCB) and heat sinks
Advantages: lightweight, cost-effective
Limitations: lower conductivity than copper, requiring larger cross-sections for the same current
How to Measure Aluminum’s Electrical Conductivity
Four-point probe method: Measures voltage drop along a sample with known current to avoid contact resistance errors.
Voltage-current (V-I) method: Simple method for bulk conductors.
ASTM / ISO standards: Provide testing guidelines for consistency and comparability.
Considerations: Temperature control, surface oxidation, and connection quality.
Enhancing Aluminum’s Conductivity
Using high-purity aluminum materials
Heat treatment such as annealing or T5/T6 processes
Minimizing impurities and oxide formation
Selecting special electrical-grade aluminum alloys designed for maximum conductivity
Electrical Conductivity of Aluminum Alloys
Aluminum alloys have slightly lower conductivity than pure aluminum due to alloying elements. Typical values are:
| Alloy | Condition | Electrical Conductivity (% IACS) | Notes |
|---|---|---|---|
| 1050 | Annealed | 61–62% | Commercially pure aluminum |
| 1100 | Annealed | 57–58% | Good corrosion resistance |
| 6061-T6 | Heat-treated | 40–42% | Balanced mechanical strength and conductivity |
| 6063-T5 | Extruded | 45–47% | Architectural applications |
| 7075-T6 | High-strength | 33–35% | Low conductivity, high strength |
Summary
Aluminum provides an effective balance of weight, cost, and electrical conductivity. Its conductivity is influenced by purity, alloying, temperature, and mechanical processing.
High-purity aluminum and select alloys can be optimized for electrical applications, while understanding limitations relative to copper is essential in design.
Proper measurement and heat treatment can further enhance conductivity for critical engineering applications.
FAQs
Q1. What is the electrical conductivity of pure aluminum?
The typical electrical conductivity of pure aluminum is about 3.5 × 10⁷ S/m at 20 °C.
Q2. How does temperature affect aluminum conductivity?
As temperature increases, atomic vibrations scatter electrons more, reducing conductivity. Lower temperatures generally improve conductivity.
Q3. Is aluminum a good conductor compared to copper?
Yes, aluminum is a good conductor, though its conductivity (~3.5 × 10⁷ S/m) is roughly 60% that of copper. It is lighter and cost‑effective for large-scale applications.
Q4. How can aluminum’s conductivity be improved?
Conductivity can be improved by using high‑purity aluminum, minimizing mechanical deformation, reducing surface oxidation, and selecting alloys/heat treatments optimized for conductivity.
Q5. Which standard methods are used to measure aluminum conductivity?
Common methods include the four‑point probe technique, voltage-current measurements, and ASTM/ISO standardized procedures for material property testing.
References
ASM Handbook, Volume 2: Nonferrous Alloys and Special-Purpose Materials
MatWeb Material Property Database – Aluminum
NIST Chemistry WebBook – Aluminum Thermodynamic and Electrical Data
Aluminum Association – Electrical Conductivity Data
