Thermal Conductivity of Aluminum 6061: A Detailed Report

The thermal conductivity of aluminum 6061 is 167 W/(m·K) in the T6 temper at 25°C. This is the value you will find in the ASM Handbook and the Aluminum Association design data, and it is the correct value to use for heat transfer calculations involving 6061-T6 sheet, plate, extrusions, and machined components.

Thermal conductivity is the rate at which a material conducts heat — how quickly thermal energy flows through a unit thickness of the material per unit temperature difference. At 167 W/(m·K), aluminum 6061-T6 conducts heat approximately 4 times faster than stainless steel 304 (16.2 W/(m·K)), about 50% slower than pure aluminum (237 W/(m·K)), and roughly 10 times faster than titanium (7.2 W/(m·K)). Among common structural alloys, 6061 is an excellent thermal conductor — not as good as pure aluminum or copper (385 W/(m·K)), but far above steel in the same thermal application.

Thermal Conductivity of Aluminum 6061 in All Temperatures

Unlike Young’s modulus, which is the same across all 6061 tempers, thermal conductivity does vary with heat treatment. The T6 precipitation hardening process changes the distribution of Mg₂Si precipitates in the aluminum matrix, which affects the scattering of electron carriers responsible for heat conduction.

Source: ASM Handbook, Volume 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials, 10th Edition. ASM International, 1990.

Why T4 has lower conductivity than T6: In the T4 condition (naturally aged after quenching), a large fraction of the magnesium and silicon alloying elements remain in solid solution in the aluminum lattice. Dissolved solute atoms scatter conduction electrons, reducing thermal conductivity. The T6 artificial aging treatment causes Mg₂Si to precipitate as coherent particles, depleting the solid solution and thereby increasing electron mean free path — raising thermal conductivity from 154 to 167 W/(m·K).

Why annealed O condition has the highest conductivity: In the fully annealed condition, the alloy reaches its equilibrium microstructure with maximum Mg₂Si precipitation and minimum solid solution concentration. The very low electron scattering produces the highest thermal conductivity value: 180 W/(m·K).

The variation across tempers (154–180 W/(m·K)) is roughly 17% — significant enough to matter in thermal management design but small enough that “167 W/(m·K)” serves as an adequate single value for most engineering calculations on standard T6 or T651 material.

Converting the Thermal Conductivity Value: All Common Unit Systems

Conversion factors:

• W/(m·K) to BTU/(hr·ft·°F): multiply by 0.5779 → 167 × 0.5779 = 96.5 BTU/(hr·ft·°F)
• W/(m·K) to cal/(cm·s·°C): multiply by 0.002390 → 167 × 0.002390 = 0.399 cal/(cm·s·°C)

Why Aluminum 6061 Conducts Heat Well — The Physics

Electron carriers dominate metallic heat transport

In metals, heat is transported primarily by free (conduction) electrons — the same electrons responsible for electrical conductivity. This is why metals with high electrical conductivity generally also have high thermal conductivity: both properties reflect the density and mean free path of conduction electrons.

The Wiedemann-Franz law quantifies this relationship:

κ / σ = L₀ × T

Where:

• κ = thermal conductivity (W/m·K)
• σ = electrical conductivity (S/m)
• L₀ = Lorenz number = 2.44 × 10⁻⁸ W·Ω/K²
• T = absolute temperature (K)

For 6061-T6 at 25°C (298 K): σ ≈ 27.6 MS/m. Predicting thermal conductivity: κ = L₀ × σ × T = 2.44 × 10⁻⁸ × 27.6 × 10⁶ × 298 = 200 W/(m·K)

The prediction (200 W/(m·K)) is somewhat higher than the measured value (167 W/(m·K)) because the Wiedemann-Franz law assumes that electrons scatter only from phonons (lattice vibrations). In an alloy like 6061, electrons also scatter from the dissolved solute atoms and from grain boundaries, increasing electrical resistivity and reducing thermal conductivity below the pure-metal prediction.

Why is 6061 less conductive than pure aluminum?

Pure aluminum has a thermal conductivity of 237 W/(m·K) — about 42% higher than 6061-T6. The reduction is caused by the same electron scattering mechanisms that reduce electrical conductivity in alloys:

1. Solid solution scattering. Even in the T6 condition, some Mg and Si remain in solid solution. Each dissolved atom creates a local lattice distortion that scatters conduction electrons, reducing their mean free path. For the 6061 composition (0.8–1.2% Mg, 0.4–0.8% Si), the solid solution scattering penalty is approximately 40 W/(m·K) below pure aluminum.

2. Precipitate scattering. The Mg₂Si precipitates formed during T6 aging — the particles that give 6061 its strength — also scatter electrons at the particle-matrix interface. This contributes a modest additional reduction below the annealed condition.

3. Grain boundary scattering. Grain boundaries in polycrystalline aluminum scatter electrons that approach at certain angles. This effect is minor compared to solute and precipitate scattering in alloys, but it is present.

The net result: 6061-T6 has 167 W/(m·K) vs. pure aluminum’s 237 W/(m·K) — about 30% lower. The tradeoff is dramatic: 6061-T6 has a yield strength of 276 MPa vs. pure aluminum’s ≤35 MPa. The alloy pays a 30% thermal conductivity penalty and gains nearly 8× the yield strength.

Thermal Conductivity of 6061 vs. Temperature

Thermal conductivity changes with temperature. For 6061-T6:

Source: MIL-HDBK-5J; ASM Handbook Volume 2.

The temperature trend for 6061 is opposite to what many engineers expect: thermal conductivity increases with temperature over the normal engineering range (0–300°C). This is the opposite of pure metals like copper and gold, which decrease in conductivity with rising temperature.

The reason: in the T6 condition, some Mg and Si remain in solid solution even after aging. As the temperature rises, the equilibrium solubility of Mg₂Si in the aluminum lattice decreases, causing more Mg₂Si to precipitate out of solution. This reduces the solid solution scattering of electrons, actually improving conductivity even as phonon scattering from thermal vibrations increases.

Cryogenic behavior: At very low temperatures, phonon-phonon scattering nearly disappears, but impurity and defect scattering become dominant. The thermal conductivity of 6061 drops substantially below room temperature, to approximately 75 W/(m·K) at liquid nitrogen temperature. This is relevant for cryogenic piping supports, where the lower conductivity is actually advantageous (reducing heat influx from ambient to the cryogenic fluid).

Thermal Conductivity of 6061 vs. Other Engineering Materials

This comparison table positions 6061 in the thermal landscape relevant to fabricators and engineers:

The gap between aluminum 6061 and stainless steel is large enough to fundamentally change thermal design:

• A 6061 heat sink works approximately 10× faster than an equivalent stainless steel heat sink of the same geometry
• 6061 fins on a heat exchanger can be significantly thinner than stainless fins to achieve the same heat transfer rate
• 6061 enclosures dissipate electronic heat passively; stainless steel enclosures require additional cooling if the same heat load is present

The comparison with 7075-T6 and 2024-T3 is notable for fabricators: both of these higher-strength aluminum alloys have lower thermal conductivity than 6061, meaningfully. At 130 W/(m·K) and 121 W/(m·K), respectively, they are 22–28% lower than 6061-T6. For applications where both strength and thermal management matter — aerospace actuator housings, high-power electronics mounts, automotive brake components — 6061 often wins on the thermal side even when 7075 is structurally preferred.

Learn More:

K Value for Aluminum: Understanding Thermal Properties

Thermal Conductivity in 6061 Fabrication Contexts

Laser cutting aluminum 6061

Aluminum’s high thermal conductivity is the primary challenge in laser cutting. When the laser beam creates a melt pool at the focal point, heat conducts away from the kerf at a rate governed by the thermal conductivity — 167 W/(m·K) for 6061-T6. This rapid heat extraction works against the laser: the beam must deliver heat faster than conduction dissipates it to maintain the melt pool.

The consequence: cutting aluminum requires higher laser power density than cutting an equivalent thickness of stainless steel (16.2 W/(m·K)). A 3kW fiber laser cuts 4 mm stainless at a given speed; the same machine may require 4–6kW to cut 4 mm aluminum at equivalent quality because so much power is lost to conduction. The laser cutting aluminum guide covers the specific power and speed parameters.

High thermal conductivity also means the heat-affected zone (HAZ) in laser-cut 6061 is narrower than in stainless. Heat dissipates quickly, limiting the width of the zone where the T6 temper is disrupted. This is generally favorable for structural applications where maintaining the temper close to the cut edge matters.

Welding 6061 aluminum

High thermal conductivity accelerates heat loss from the weld pool during MIG (GMAW) and TIG (GTAW) welding. Aluminum welds require preheat (typically 93–150°C for 6061 plate above 6 mm) to compensate for the rapid heat extraction that would otherwise chill the weld pool prematurely. The combination of high thermal conductivity and low melting point makes aluminum welding sensitive to heat input rate — too slow and the weld pool chills before fusion; too fast and excessive heat spreads into the surrounding metal.

Heat sink and thermal management design

6061 aluminum is one of the most common heat sink materials in electronics, LED lighting, and power electronics. The combination of 167 W/(m·K) thermal conductivity with yield strength sufficient for structural fins, machinability for complex fin geometries, and anodizability for improved convective surface finish makes 6061 the standard material for extruded and machined heat sinks.

For maximum thermal performance, the annealed O condition (180 W/(m·K)) provides 8% higher conductivity than T6 — relevant for heat sink applications where strength is not critical and the additional conductivity is worth the slight reduction in structural integrity.

Frequently Asked Questions

Q: What is the thermal conductivity of 6061 aluminum?

167 W/(m·K) for 6061-T6 at 25°C — the standard reference value. In US customary units: 97 BTU/(hr·ft·°F). This applies to T6 and T651 tempers. The annealed O condition is slightly higher at 180 W/(m·K); T4 is lower at 154 W/(m·K).

Q: Does the T6 temper change thermal conductivity?

Yes, unlike Young’s modulus, thermal conductivity does vary with temper. 6061-O (annealed): 180 W/(m·K); 6061-T4: 154 W/(m·K); 6061-T6: 167 W/(m·K). The variation occurs because solid solution scattering of conduction electrons changes with the heat treatment state. T4 has more Mg and Si in solid solution (higher scattering, lower conductivity); O condition has maximum precipitation (minimum scattering, highest conductivity).

Q: How does 6061 thermal conductivity compare to stainless steel? 6061-T6 at 167 W/(m·K) is approximately 10× more thermally conductive than 304 stainless steel (16.2 W/(m·K)). This means a 6061 component of equivalent geometry dissipates heat roughly 10 times faster than a stainless steel component. For heat sink, cooling, and thermal management applications, this is the dominant material selection driver.

Q: Why is pure aluminum more thermally conductive than 6061?

Pure aluminum (1100-O) has a thermal conductivity of 237 W/(m·K) — 42% higher than 6061-T6. The reduction in 6061 comes from electron scattering by dissolved Mg and Si atoms and by Mg₂Si precipitate interfaces. The tradeoff is substantial: 6061-T6 has a yield strength 276 MPa vs. pure aluminum’s ≤35 MPa. For most structural applications, the conductivity penalty is acceptable relative to the strength gain.

Q: Does thermal conductivity increase or decrease with temperature in 6061?

It increases with temperature over the engineering range of 0–300°C, which is counterintuitive compared to pure metals. From 0°C to 300°C, 6061 thermal conductivity rises from approximately 158 to 194 W/(m·K). This occurs because rising temperature causes more Mg₂Si to precipitate from the solid solution, reducing electron scattering even as phonon scattering increases. Below room temperature (cryogenic range), conductivity drops sharply to approximately 75 W/(m·K) at −200°C.

Q: What is the thermal conductivity of 6061 aluminum in BTU/(hr·ft·°F)?

97 BTU/(hr·ft·°F) for 6061-T6 at 25°C. Conversion: 167 W/(m·K) × 0.5779 = 96.5, rounded to 97 BTU/(hr·ft·°F). This is the value used in US engineering calculations involving HVAC, process heat transfer, and industrial thermal analysis.

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 of 6061 by temper: O (180), T4 (154), T6 (167), T651 (167) W/(m·K); physical properties of 6000 series aluminum alloys; Wiedemann-Franz law discussion in aluminum thermal properties context.)
2. MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures, U.S. Department of Defense, 2003. (Temperature-dependent thermal conductivity curves for 6061-T6 from cryogenic to near-solidus temperatures; thermal properties as a function of temper and temperature; the aerospace design authority for aluminum thermal data.)
3. ASTM B209/B209M, Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate, ASTM International, current edition. (Material and temper classifications for 6061 sheet and plate; minimum mechanical property requirements; composition limits that govern alloying element concentrations affecting thermal conductivity.)
4. National Institute of Standards and Technology (NIST), NIST WebBook — Thermophysical Properties of Materials, available at webbook.nist.gov. (Reference thermal conductivity data for aluminum and aluminum alloys; Lorenz number and Wiedemann-Franz law constants used in the electron scattering analysis; comparison of thermal conductivity data for pure copper, silver, and aluminum cited in the comparative table.)

• Author
• Recent Posts

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.

Latest posts by Dr. Liu Che (see all)

• Laser Coating Removal Without Damaging the Substrate - September 30, 2026
• Laser Cleaning for Paint Adhesion: Improving Surface Energy - September 29, 2026
• Common Mistakes in Laser Rust Removal Applications - September 23, 2026