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When a Part Is Worth Making in Copper Instead of Aluminum

September 21, 2026

Copper and aluminum both show up in electrical and thermal parts, and the choice between them is usually made on habit rather than on numbers. Here is the comparison that matters when you are about to send a drawing.

The four numbers

Property	Copper (C110)	Aluminum
Electrical conductivity	About 100 percent IACS	About 61 percent IACS for conductor grade, about 43 percent for 6061
Thermal conductivity	Roughly 390 W per metre per kelvin	Roughly 170 to 230 W per metre per kelvin depending on alloy
Density	About 8.9 g per cubic centimetre	About 2.7 g per cubic centimetre
Machinability	Rated near 20 against free-cutting brass	Far higher, breaks its chip cleanly

Add a fifth, unquantified but real: copper costs several times more per kilogram than aluminum, and the gap moves with the market.

The conductor trade, done properly

The common mistake is comparing equal volumes. The honest comparison is equal performance.

To carry the same current as a copper conductor, an aluminum one needs roughly 1.6 times the cross section. At that size it is bulkier, and it still weighs roughly half as much, because copper is more than three times denser.

So the real trade is:

Copper wins on space. Same current in a smaller cross section. This is why copper dominates inside enclosures, switchgear and anywhere the conductor has to fit through something.

Aluminum wins on weight and cost. This is why it dominates in overhead transmission, long runs and large structures where the space is available.

The thermal trade

Copper conducts heat roughly twice as well as most aluminum alloys. That matters when heat has to move through a small cross section from a concentrated source: the base of a heat sink under a power module, a heat spreader, a cold plate wall.

It matters much less when the limiting factor is getting heat from the fins into the air. In a large convection limited sink, the fin material makes far less difference than fin area and airflow, and a bigger aluminum sink often beats a smaller copper one for less money and less mass.

A common answer is a hybrid: a copper base or embedded copper slug to spread the concentrated heat, with an aluminum fin structure to dump it. You pay for copper only where it is doing work. See how to design a machined copper heat sink.

The machining trade, which is bigger than people expect

This is the part that gets left out of material comparisons.

Aluminum breaks its chip. Copper does not. That single difference shows up as longer cycle times, more chip management, hand deburring and a worse surface if the shop gets its tooling wrong. Everything in why copper is difficult to machine is a cost that aluminum simply does not carry.

So the price gap between a copper part and an aluminum part is wider than the material price ratio alone. On a feature heavy part it can be much wider.

If you have decided you need copper but the part is full of threads and small features, consider a free-machining copper grade before you consider aluminum. It recovers most of the machining gap while keeping above 90 percent IACS. See C101, C110 and tellurium copper compared.

Joining and corrosion

Aluminum forms a tough oxide immediately, which is good for corrosion and bad for electrical contact, so aluminum joints need preparation and often plating.

Where copper and aluminum touch with any moisture present, the aluminum corrodes preferentially. Real assemblies handle this with plated contact surfaces, bimetallic transition washers or lugs, or by keeping the joint sealed and dry. It is a solved problem, but it is not one to leave to chance.

Aluminum also creeps more than copper under sustained bolt pressure, which is why aluminum joints often use spring washers to maintain contact force over time.

A decision list

Choose copper when:

• The conductor has to fit a tight cross section
• Heat has to move through a small area from a concentrated source
• The joint must be as low resistance and as stable as possible
• The part goes into vacuum, hydrogen brazing or RF service
• It is an EDM electrode or a welding electrode

Choose aluminum when:

• Weight matters and space is available
• The part is large and convection limited rather than conduction limited
• Cost is the binding constraint and performance has headroom
• The part is feature heavy and the conductivity requirement is modest

Consider both when a small copper element inside a larger aluminum part gets you the performance for a fraction of the price.

If you are still unsure

Write the requirement rather than the material. Put the current, the thermal load or the resistance target on the drawing and say the material is open. A shop that machines both will tell you which one meets it for less, and that answer is worth more than any table.

Frequently asked questions

Keep reading

• C18150 vs C18200: Which Chromium Copper to Put on the Drawing
• C14700 Sulfur Copper: What It Gains Over C110 and Where It Stops