Aluminium 6061 is the default heat sink material for machined prototypes, 6063 for extrusions, and copper only when footprint or heat flux leaves no alternative — that is the short answer, and it holds because conductivity is only one of four properties that decide the outcome. SkillsProto machines heat sinks in all three materials (plus hybrid bonded constructions), so this guide compares them on the numbers that actually drive a design: conductivity, density, machinability and cost behaviour, ending in a decision table you can apply directly to a thermal design review.
The conductivity numbers
All values below are typical room-temperature figures for the common tempers; alloy datasheets vary slightly by source and heat-treatment condition.
| Material | Thermal conductivity (W/m·K) | Density (g/cm³) | Specific heat (J/kg·K) | Typical form | Notes |
|---|---|---|---|---|---|
| Copper C1100 (ETP) | ~401 | 8.96 | 385 | Machined baseplates,embedded pedestals | 3.3× the conductivity of 6061, 3.3× the weight |
| Aluminium 6063-T5 | ~209 | 2.70 | 900 | Extrusions | The standard extrusion alloy; better conductivity than 6061 |
| Aluminium 6060-T5 | ~200 | 2.70 | 900 | Extrusions (EU common) | Close cousin of 6063 |
| Aluminium 1060/1050 | ~229–237 | 2.70 | 900 | Extrusions, bonded fins | Near-pure aluminium; soft, poor strength |
| Aluminium 6061-T6 | ~167 | 2.70 | 896 | Machined billet, plate | Best all-round machinable alloy |
| Die-cast ADC12 (A383) | ~96 | 2.74 | ~960 | Die-cast housings/sinks | Cast microstructure costs ~half the conductivity |
| Zinc Zamak 5 | ~109 | 6.70 | 420 | Die-cast small sinks | Heavy; used for shielding/EMI + modest cooling |
Two reading rules for the table:
1. Alloys of the same base metal vary far less than process choices. The step from 6061 to 6063 is ~25%; the step from machining to die casting costs ~50%. A badly chosen process hurts more than a badly chosen alloy.
2. Conductivity is not the whole resistance chain. Total thermal resistance = conduction (material) + convection (geometry + airflow) + interface (TIM + flatness). Below roughly 50 W heat loads with decent airflow, geometry and interface quality dominate; above that, or in natural convection, spreading resistance makes material choice decisive.
Aluminium 6061 — the machined default
6061-T6 is what SkillsProto machines heat sinks from by default. Its conductivity (~167 W/m·K) is 30–40% below 6063, but it is available as thick plate and billet in every market, machines cleanly (fin walls hold 1 mm without chatter in most setups), anodizes well, and carries the structural load when the sink is also the bracket. For prototype and low-volume machined sinks — MOQ 1 piece at SkillsProto — it is the pragmatic answer, and thermal simulations almost always confirm the conductivity delta to 6063 is recoverable with 10–15% more fin area.
Aluminium 6063 — the extrusion standard
6063-T5 exists for extrusion: it pushes through narrow die gaps cleanly and its ~209 W/m·K conductivity is the best of the structural extrusion alloys. If your heat sink is a straight-fin profile going into volume production, 6063 via extrusion is unbeatable per kilogram. Its weaknesses show up in machining (gummier chips, worse surface finish on thin fins) and in strength-critical integrated designs — it is a profile alloy, not a chassis alloy.
Copper — when physics overrules accounting
Copper's ~401 W/m·K is why every high-flux application — laser diodes, RF power amplifiers, IGBT modules, GPU vapor-chamber bases — ends up with copper somewhere. It also weighs 3.3× more per unit volume and costs several times more per kilogram, so the standard pattern is copper where the flux is, aluminium where it isn't: a copper baseplate or pedestal spreading heat into an aluminium fin field, joined by press-fit, brazing or soldering. Fully-copper sinks make sense when the footprint is fixed by the enclosure and every millimetre of spreading resistance counts. SkillsProto machines both and delivers hybrid constructions with the joint specified for thermal, not just mechanical, performance.
Die-cast and the conductivity tax
Die-cast ADC12/Zamak sinks appear in high-volume consumer products because the process net-shapes complex housings with mounting features in one shot. The metallurgical price is a coarse, porous microstructure at roughly half of 6061's conductivity, plus wall-thickness and draft constraints. For industrial and professional equipment, die casting wins on integration, not on thermal metrics — and its 15–25 day mold lead time plus 500-piece minimum (SkillsProto's die-cast starting volume) keeps it out of prototype territory entirely.
Decision table
| Your situation | Material + process | Why |
|---|---|---|
| Prototype, custom geometry, 1–100 pcs | 6061-T6, CNC machined | No tooling, 3–7 days, conductivity adequate |
| Pilot run of a future extruded design | 6061 machined first, extrude in volume later | Design risk retired before paying a die |
| Straight-fin profile, 1,000+ pcs | 6063-T5, extruded | Best cost per watt at volume |
| Footprint-limited, high heat flux | Copper base/pedestal + aluminium fins | Spreading resistance dominates |
| One-piece enclosure + cooling, 500+ pcs | ADC12 die cast | Integration beats conductivity |
| Weight-critical (aerospace, portable) | 6061 machined, optimized fin field | kg/W wins, not W/m·K |
How SkillsProto helps
Every SkillsProto quote includes free DFM review, and for heat sink enquiries the review covers material selection and fin geometry against your airflow and footprint assumptions, with a mechanical engineer verifying every finding — quoted within 24 hours. Parts are produced in ISO 9001 facilities, with FAI reports and material certifications on request, shipped DDP via DHL/FedEx/UPS in 3–5 days to the UK, EU and North America, MOQ 1 piece across all services.
Frequently Asked Questions
Which aluminium is best for a heat sink?
For extrusions, 6063-T5 (≈209 W/m·K) is the standard. For machined heat sinks, 6061-T6 (≈167 W/m·K) — the conductivity gap is small and recoverable with slightly more fin area, while 6061 is far easier to machine from billet. SkillsProto defaults to 6061 for machined parts and will flag in DFM if copper or a hybrid is worth the premium.
How much better is copper than aluminium for heat sinks?
About 2.4× the conductivity of 6061 (401 vs 167 W/m·K) at 3.3× the weight and a multiple of the cost. In practice copper earns its place at the heat source — baseplates and pedestals — rather than across the whole fin field.
Does heat treatment affect thermal conductivity?
Yes, modestly. The T6 temper of 6061 costs roughly 10–15 W/m·K versus annealed or near-pure grades; alloying elements (Mg, Si, Cu) — not heat treatment alone — are the main driver. That is why near-pure 1060 conducts better but is too soft for structural or precision-machined features.
Is die-cast aluminium good for heat sinks?
It is acceptable, not good: ADC12 delivers ~96 W/m·K, roughly half of 6061, due to cast microstructure and silicon content. Die casting is chosen for one-piece integration at 500+ piece volumes, not for thermal efficiency. SkillsProto offers die casting from 500 pieces with a 15–25 day mold lead time.
Related capabilities
Related guides
Have parts to quote?
Upload your files — DFM-checked quotation within 24 hours.