Aluminium Conductivity Thermal: Ranking the Best Heat Conductors

Aluminium’s thermal conductivity spans a wider range than most engineers expect. Pure aluminium conducts heat at 237 W/(m·K) — making it the third-best thermally conductive common metal after silver and copper. But aluminium alloys, which sacrifice some conductivity for strength and other properties, range from 96 W/(m·K) for high-copper aerospace alloys down to 237 W/(m·K) for commercially pure grades. Understanding where each aluminium alloy sits in the thermal conductivity ranking determines which grade is correct for any heat dissipation application.

This article ranks the best heat conductors across both pure metals and aluminium alloy families, explains what drives the differences within aluminium alloys, and provides the practical selection framework for engineers choosing between aluminium grades on the basis of thermal performance.

The Thermal Conductivity of Pure Aluminium

Pure aluminium (99.99% Al, also called super-purity or 1199 grade) has a thermal conductivity of 237 W/(m·K) at 25°C. This places it:

• Third among all pure metals, behind only silver (429 W/(m·K)) and copper (401 W/(m·K))
• Far above iron (80 W/(m·K)), titanium (22 W/(m·K)), and stainless steel (16 W/(m·K))
• Approximately 5× higher than titanium’s best alloys
• 15× higher than austenitic stainless steel (304)

The mechanism: aluminium’s thermal conductivity is primarily electronic (as with all metals). Free conduction electrons transport both heat and electrical current through the lattice. Anything that scatters electrons — alloying elements in solid solution, precipitate particles, grain boundaries, dislocations — reduces thermal conductivity. Pure aluminium has minimal scatterers; heavily alloyed grades have many.

Full Ranking: Aluminium Alloys and Competing Materials

Sources: ASM Handbook, Volume 2; CRC Handbook of Chemistry and Physics, 104th Edition; Smithells Metals Reference Book, 8th Edition.

The specific conductivity (k/ρ) column reveals why aluminium is the thermal management engineer’s material of choice: every aluminium alloy significantly outperforms copper, iron, and titanium on a per-unit-mass basis. Even the lowest-conductivity aluminium structural alloy (2024-T3, 121 W/(m·K)) has a specific conductivity of 43.5 W·m/kg — nearly identical to copper’s 44.8 W·m/kg at less than one-third the mass.

Why Alloying Reduces Aluminium’s Thermal Conductivity

The electron scattering mechanism

In pure aluminium, conduction electrons move relatively freely through the crystal lattice, carrying heat energy. When alloying elements are added:

Solid solution atoms: Dissolved atoms (Mg, Si, Cu, Zn, Mn) sitting in the aluminium crystal lattice distort the lattice locally, creating scattering centres for conduction electrons. The more alloy content in solid solution, the lower the conductivity.

Precipitate particles: When an alloy is heat-treated to form precipitation hardened tempers (T6, T8), alloying elements are removed from solid solution into coherent or semi-coherent precipitate particles. Precipitate particles scatter electrons less effectively than dissolved atoms — precipitation hardening improves conductivity relative to the solid-solution state (which is why 6061-T6 at 167 W/(m·K) is more conductive than 6061-T4 at 154 W/(m·K), as covered in the Al 6061 thermal conductivity article).

Grain boundaries: Smaller grain size means more grain boundaries per unit volume, each scattering electrons. Cold-worked tempers (H12, H14, H32) have more grain boundary scattering than annealed material — another reason annealed aluminium is more conductive than work-hardened alloys at equivalent composition.

What drives the alloy family differences

1xxx series (commercially pure aluminium, 99.0–99.99% Al): The lowest alloy content; highest conductivity in the aluminium family. 1100 alloy at 218–224 W/(m·K). Used for electrical conductor wire (EC grade, 1350) and heat exchanger fins where conductivity is the primary property.

3xxx series (Al-Mn): Manganese in solid solution reduces conductivity moderately (159–193 W/(m·K)). 3003 alloy (1.2% Mn) at 193 W/(m·K) is widely used for heat exchanger cores. Better formability than 1xxx with adequate conductivity for many thermal applications.

5xxx series (Al-Mg): Magnesium content of 2–5% significantly reduces conductivity (128–142 W/(m·K)). 5052 at 138 W/(m·K) is the main marine and general sheet metal alloy. Mg remains primarily in solid solution (5xxx alloys are not age-hardenable), producing consistently high electron scattering.

6xxx series (Al-Mg-Si): 6061 and 6063 are the dominant structural aluminium alloys. In T6 temper, Mg₂Si precipitation reduces solid solution content and improves conductivity relative to T4. 6061-T6 at 167 W/(m·K); 6063-T5 at 201 W/(m·K) (lower alloy content, less precipitate, higher conductivity — 6063 is the standard heat sink extrusion alloy in electronics).

7xxx series (Al-Zn-Mg-Cu): Zinc and copper alloying produces the highest-strength aluminium alloys and the lowest conductivity — 7075-T6 at 130 W/(m·K). The 7xxx series is not selected for thermal applications; it is used exclusively for maximum strength with thermal conductivity as a secondary consideration.

2xxx series (Al-Cu): Copper-bearing alloys. 2024-T3 at 121 W/(m·K) — the aerospace structural standard with mediocre conductivity. 2014-T6 at 154 W/(m·K) shows that varying temper conditions produce significant conductivity differences even within the same series.

Best Aluminium Grades for Thermal Applications

For maximum conductivity (heat sinks, electrical conductors):

1350 EC grade (electrical conductor): k = 228 W/(m·K). The standard for electrical transmission wire. Very soft; limited structural use. Available as wire, rod, and strip.

1100 alloy: k = 218–224 W/(m·K). The general-purpose high-conductivity aluminium. Good formability; low strength. Used for heat exchanger fins, sheet, and applications where conductivity plus formability matters more than strength.

6063-T5/T6: k = 201–210 W/(m·K). The standard heat sink extrusion alloy. Higher conductivity than 6061 due to lower alloy content (Mg 0.45–0.9%, Si 0.2–0.6% vs. 6061’s Mg 0.8–1.2%, Si 0.4–0.8%); excellent extrudability allowing fine-pitch, high-aspect-ratio fins; adequate structural strength for heat sink mounting. The first-choice alloy for extruded heat sinks in electronics.

For conductivity combined with structural strength:

6061-T6: k = 167 W/(m·K). The most versatile structural aluminium. 28% higher conductivity than 7075-T6 at adequate strength for most non-aerospace structural heat sink applications. Standard for machined heat sinks, thermal management enclosures, and laser-cut/bent cooling components.

6082-T6: k = 170 W/(m·K) (European equivalent of 6061, slightly higher Mn content). Widely used in European heat sink manufacture; essentially equivalent performance to 6061 for thermal applications.

When aluminium is not the right choice:

For maximum absolute heat removal where weight is not a constraint: copper (401 W/(m·K)) with its 2.4× conductivity advantage over 6061. Copper heat sinks are used for laser cooling, high-power radio frequency amplifiers, and any application where the conductivity advantage justifies the mass and cost premium.

For CTE-matched electronic packaging: AlSiC (aluminium-silicon carbide composite) at CTE 6–10 × 10⁻⁶ /°C and k = 170–200 W/(m·K) better matches silicon CTE (2.6 × 10⁻⁶ /°C) for power electronics where thermal cycling reliability is critical.

Temperature Dependence of Aluminium Thermal Conductivity

Aluminium’s thermal conductivity is not constant — it varies with temperature:

Source: ASM Handbook Vol. 2; NIST WebBook thermophysical data.

Key observations:

1. Aluminium conductivity increases at cryogenic temperatures — at −200°C, pure aluminium conducts over three times better than at room temperature. This makes aluminium alloys excellent cryogenic heat conductors.
2. Conductivity decreases modestly with increasing temperature, but the reduction is gradual — 6061 at 200°C (160 W/(m·K)) still has 96% of its room temperature conductivity.
3. For most practical thermal management applications (0–150°C operating range), the room temperature value is an adequate design figure; no significant correction is needed.

Learn more:

Exploring 6 Lightweight Metals: Top Choices for Aerospace and Automotive

Frequently Asked Questions About Aluminium Thermal Conductivity

Q: What is the thermal conductivity of aluminium?

Pure aluminium has a thermal conductivity of 237 W/(m·K) at 25°C — third among all pure metals, after silver (429 W/(m·K)) and copper (401 W/(m·K)). Aluminium alloys have lower conductivity: 6063-T5 (the standard heat sink extrusion alloy) at approximately 201–210 W/(m·K); 6061-T6 (the most common structural alloy) at 167 W/(m·K); 7075-T6 (highest-strength structural alloy) at 130 W/(m·K). The specific alloy and temper determine the actual conductivity value.

Q: Which aluminium alloy has the highest thermal conductivity?

Among commercially available structural aluminium alloys, 1100 alloy (commercially pure aluminium with 99% minimum Al) achieves 218–224 W/(m·K) — the closest to pure aluminium while still being produced and supplied as sheet, plate, and bar. Among heat sink-specific alloys, 6063-T5 (201–210 W/(m·K)) is the best choice because its combination of conductivity, extrudability (allowing fine fins), and structural adequacy makes it the dominant heat sink extrusion alloy worldwide.

Q: Is aluminium or copper better for thermal conductivity?

Copper is better in absolute terms: 401 W/(m·K) for copper vs. 237 W/(m·K) for pure aluminium (a 69% advantage). However, aluminium is better on a weight basis: at 2.4× higher thermal conductivity per unit mass (specific conductivity: Al = 87.8 W·m/kg; Cu = 44.8 W·m/kg), aluminium dissipates more heat per kilogram than copper. Copper heat sinks are appropriate when absolute heat flux is the constraint and mass is irrelevant; aluminium heat sinks are better when both heat dissipation and weight matter.

Q: How does alloying reduce aluminium thermal conductivity?

Alloying elements dissolved in the aluminium lattice (Mg, Si, Cu, Zn, Mn) create atomic-scale lattice distortions that scatter conduction electrons, reducing both thermal and electrical conductivity. The more alloying content in solid solution, the lower the conductivity. Precipitation heat treatments (T6, T8 tempers) remove alloying elements from solid solution into precipitate particles, reducing scattering and improving conductivity relative to the solution-treated state. This is why 6061-T6 at 167 W/(m·K) is more conductive than 6061-T4 at 154 W/(m·K).

Q: How does aluminium thermal conductivity compare to stainless steel?

Dramatically different: pure aluminium at 237 W/(m·K) is nearly 15× more conductive than 304 stainless steel at 16 W/(m·K). Even the lowest-conductivity structural aluminium alloy (2024-T3 at 121 W/(m·K)) is 7.6× more conductive than stainless. This difference explains why stainless steel components in electronics and lighting applications run much hotter than equivalent aluminium designs — the poor thermal conductivity traps heat in the stainless structure rather than dissipating it to ambient.

References

1. ASM Handbook, Volume 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials, 10th Edition. ASM International, Materials Park, OH, 1990. (Thermal conductivity data for the full range of aluminium alloys by series and temper: 1xxx through 7xxx series; temperature dependence of conductivity; comparison with copper, magnesium, and other competing thermal management materials.)
2. Haynes, W.M., ed., CRC Handbook of Chemistry and Physics, 104th Edition. CRC Press, Boca Raton, FL, 2024. (Pure metal thermal conductivity values: silver, copper, gold, aluminium, iron, titanium; thermal conductivity temperature dependence tables; the reference for all pure metal conductivity data in the ranking table.)
3. National Institute of Standards and Technology (NIST), NIST Standard Reference Database 69: NIST Chemistry WebBook, webbook.nist.gov. (Thermophysical properties of aluminium alloys including temperature-dependent thermal conductivity data; the standard government reference for property data cited in the temperature-dependence table.)
4. Gale, W.F. and Totemeier, T.C., eds., Smithells Metals Reference Book, 8th Edition. Elsevier Butterworth-Heinemann, Oxford, 2004. (Comprehensive alloy thermal property data including 1xxx, 3xxx, 5xxx, 6xxx, and 7xxx series aluminium alloys; beryllium, magnesium, zinc, and other competing lightweight thermal management materials — the secondary reference for alloy family thermal conductivity data in the ranking table.)

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Dr. Liu Che

Dr. Liu Che holds a Ph.D. in Engineering from Dalian University of Technology and completed postdoctoral research at the Mechanical Engineering Postdoctoral Fellowship of Harbin Institute of Technology. His research focuses on core algorithms for large-scale laser equipment integration, laser cladding remanufacturing, and real-time intelligent monitoring systems for processing. He possesses profound academic expertise in cutting-edge fields such as laser beam spatial shaping and the mechanism analysis of laser processing of special alloys. He has led numerous solutions to technical challenges in cutting and surface modification of high-hardness materials in the heavy machinery industry, demonstrating strong theoretical foundations and outstanding engineering implementation capabilities.

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