Why Aluminum Transfers Heat So Efficiently
Aluminum combines a thermal conductivity of roughly 235 W/m·K with a density of only 2.70 g/cm³, which is why it dominates heat sinks, radiator cores and thermal spreaders. Free electrons carry most of the energy while lattice vibrations, or phonons, handle the remainder, so heat spreads through a solid section instead of accumulating in one hot spot. Copper still conducts better at about 401 W/m·K, but it is more than three times heavier, so on a conductivity-to-mass basis aluminum normally wins inside an enclosure.
Commercially pure grades such as 1050, 1060 and 1100 give the highest conductivity. Alloying elements scatter electrons and pull the number down, so the values below are sizing guidance rather than a replacement for certified mill test data.
| Grade / temper | Thermal conductivity at 20 °C (W/m·K) | Typical thermal duty |
|---|---|---|
| 1060-O | 234 | Busbars, thermal spreaders, foil cores |
| 3003-H14 | 193 | Radiator fins, heat exchanger tubes |
| 6061-T6 | 167 | Structural heat sinks, cold plates |
| 5052-H32 | 138 | HVAC and marine housings |
| 5083-O | 117 | Cryogenic and pressure equipment |
Thermal Expansion: The Design Driver Nobody Can Ignore
The linear coefficient of thermal expansion of aluminum is about 23 × 10-6 per K, close to twice the 12 × 10-6 per K of structural steel. A 1 m aluminum part therefore grows roughly 0.023 mm for every 1 °C of temperature change, which is why expansion gaps, slotted bolt holes and compliant adhesive layers appear wherever the metal is used structurally. The coefficient belongs to the aluminum lattice rather than to the temper, so alloy choice barely shifts it, and verification follows ASTM E228 push-rod dilatometry.
Heat Exchangers, Fins and Microchannel Geometry
The conductivity-to-weight ratio of aluminum is roughly fifteen times that of carbon steel, which is why HVAC coils, automotive radiators and condensers are built from it. Fins of about 0.1 mm multiply surface area at negligible weight, and microchannel tubes raise transfer further by pushing refrigerant through many small parallel channels instead of a few large ones.
Foil and fin stock is supplied mainly in 1100, 1200, 3003, 8011 and 8006, with 8011 and 8006 used where higher fin strength is needed.
Clad brazing sheet carries a 4004 or 4045 alloy layer so a single furnace pass joins a complete radiator core.
Plate-fin cores suit air-cooled electronics and compressed-air dryers where compactness matters more than pressure rating.
Strength at High and Low Temperatures
Pure aluminum melts at about 660 °C, and that ceiling shapes every high-temperature decision. Yield strength falls steeply above roughly 150 °C, and continuous service above 400 °C causes grain-boundary diffusion that cooling cannot reverse, while a brief excursion to 300 °C costs about half of room-temperature strength only until the part returns to ambient. Strain-hardened 3003, 3004, 5052 and 5083 suit warm service, and at the cold end the metal gains ductility and notch toughness, which puts 5083, 5052 and 6061 in liquefied-gas tanks and cryogenic piping with expansion loops absorbing contraction.
Coatings, Joints and Practical Limitations
Anodizing, painting and powder coating all reduce surface conductivity because the oxide or polymer layer insulates, so thermal interface areas are masked before finishing. Where aluminum meets steel or copper in a wet and warm environment, galvanic corrosion controls the design and calls for insulated washers or a sacrificial coating. Aluminum also tolerates fewer high-strain thermal cycles than titanium or nickel-base alloys, so cycled joints need compliant geometry. Brazing with aluminum-silicon filler keeps joint temperature below the melting range of the parent metal, and friction stir welding limits the porosity of thick-section joints.
Frequently Asked Questions
Q: What is the thermal conductivity of aluminum?
Pure aluminum conducts about 235 W/m·K at room temperature, while common alloys such as 3003, 6061 and 5052 fall between roughly 120 and 195 W/m·K.
Q: Is copper a better thermal conductor than aluminum?
Copper conducts about 401 W/m·K against 235 W/m·K for aluminum, but aluminum weighs about a third as much, so its conductivity-to-weight ratio is usually the more useful figure.
Q: How much does aluminum expand when heated?
The linear coefficient is about 23 × 10-6 per K, so a 1 m aluminum bar grows roughly 0.023 mm per 1 °C and about 0.23 mm over a 10 °C rise.
Q: Can aluminum be used above 300 °C?
Short excursions are tolerable because strength lost on heating returns after cooling, but continuous service above 400 °C degrades grain boundaries permanently.
Q: Why are aluminum fins only about 0.1 mm thick?
Thin fins raise surface area per unit volume while keeping weight and material cost low, and conductivity is high enough that the fin stays nearly isothermal along its length.
