A housing is usually asked to do more than hold something. It may carry a current to ground, pull heat away from a sensor, shield a circuit, hold a thread that is tightened a thousand times, and survive the environment it is mounted in. Copper, brass and aluminium answer those jobs in a different order, and the three are usually discussed as a price ladder when price is the last thing that should decide the question. What decides it is what the housing has to conduct, how much it is allowed to weigh, and whether it will be bolted to a different metal in a wet place. This comparison reads the three against those functions, then looks at what each one does under a deep drawing press, because a metal that wins on paper can still lose on the tool.
Copper vs brass vs aluminium housing: which metal fits which function?
Copper, brass and aluminium split the housing job three ways, and the deciding numbers are electrical conductivity in per cent IACS, thermal conductivity in W/m·K and density. Copper such as C11000 runs at about 100 per cent IACS and 390 W/m·K at a density of 8.96 g/cm³, so it is the choice when the housing is also the current path or the shield. Aluminium 1050A sits near 61 per cent IACS and 230 W/m·K at 2.70 g/cm³, roughly one-third of the density for about one-quarter of the conductivity, which is why it wins wherever weight and material cost dominate. Brass CuZn37 lands around 27 to 28 per cent IACS and 120 W/m·K at about 8.4 g/cm³, and it is chosen for what the other two do not offer: free-machining threads, stiffness and sound damping. The condition that overrides all three is the joint — aluminium must not sit wet against copper or brass.
What each metal is actually specified as
A housing drawing should name an alloy and a temper, never a colour. Copper in a drawn housing normally means electrolytic tough pitch copper C11000, or oxygen-free C10100 where the part is later brazed or annealed in a hydrogen atmosphere; both are around 99.9 per cent copper. Brass is a family rather than one material: CuZn37 and cartridge brass CuZn30 are the forming grades, while free-cutting brass is alloyed with 2 to 3.5 per cent lead and is bought for machined housings where the thread, not the drawn wall, is the critical feature. Aluminium is specified by grade and temper together, because the two are not separable: 1050A and 3003 give the easiest drawing, 5052 adds strength and corrosion resistance, and 6061 is normally machined rather than drawn unless it is supplied fully annealed. Ask for the temper by name, O or H14 or H32, because the same grade in two tempers behaves nothing alike under the press.
The three numbers that decide the housing
- Electrical conductivity: about 100 per cent IACS for C11000 copper, 61 per cent for 1050A aluminium, around 35 per cent for 5052 and 27 to 28 per cent for CuZn37 brass — against roughly 10 per cent IACS for DC04 mild steel and 2 to 3 per cent for 304 stainless. Where the housing carries current or bonds to earth through its own body, that gap is the whole decision, not a detail.
- Thermal conductivity: about 390 W/m·K for copper C11000, 230 W/m·K for 1050A, 190 W/m·K for 3003 and 167 W/m·K for 6061-T6 aluminium, and near 120 W/m·K for brass. Copper moves heat fastest in a fixed envelope; aluminium moves enough heat per kilogram, which is often the number a portable design really cares about.
- Density: 8.96 g/cm³ for copper, about 8.4 g/cm³ for brass and 2.70 g/cm³ for aluminium. The same aluminium housing weighs less than a third of the copper version, which changes mount loads, drop behaviour and freight cost as well as material price.
Conductivity per kilogram, not conductivity
The ranking moves once the comparison is put on a mass basis, which is how a portable or vehicle-mounted housing is normally judged. Aluminium carries roughly twice as much heat, and roughly twice as much current, per kilogram as copper does, because its density advantage is larger than its conductivity deficit; copper still wins on absolute conductivity inside a fixed envelope, where volume rather than mass is the constraint. Brass is behind both on every count, which is why a brass housing is specified for stiffness, damping and machinability rather than for any conductivity figure. If the requirement is written as a thermal resistance or a current-carrying target per unit mass, aluminium will usually win; if it is written as attenuation or resistance across a joint in a fixed space, copper will.
How copper, brass and aluminium behave under a deep drawing press
All three draw, and each one fails in a way that has to be designed around rather than discovered in the tryout.
- Copper: an annealed C11000 blank draws deeply and cleanly, but its recrystallised grain grows easily, so coarse-grain strip can orange-peel into a rough, dimpled surface that shows through ironing and cannot be polished out economically. Buy to a controlled grain size and keep the interstage anneal in the route.
- Brass CuZn37: cartridge brass was the original deep drawing material, so the formability is proven, but it work-hardens quickly and a tall cup normally needs an in-process anneal between stages. Free-cutting leaded brass is not a drawing grade — specify it only where the feature is machined.
- Aluminium: 1050A and 3003 draw to deep cups without difficulty, 5052 needs more generous radii and better lubrication, and 6061 is normally machined rather than drawn unless fully annealed. Springback is higher than in steel or brass, so punch radius and die clearance have to allow for it, and galling has to be controlled with the right lubricant.
- Wall thinning and conductivity: ironing raises strength in all three metals, but it also raises dislocation density and lowers conductivity, so a conductivity requirement belongs on the finished, annealed part with the test method named, not on the incoming strip.
Galvanic corrosion is the rule that overrides the numbers
Copper alloys sit near the top of the galvanic series and aluminium sits well below them, so a copper or brass housing in electrical contact with aluminium, with moisture or chloride present, drives the aluminium into corrosion: the aluminium becomes the anode and the joint fails long before the housing does. The practical answers are to break the electrical path with an insulating washer, sleeve or coating; to plate or coat the aluminium contact face; or to accept the couple only inside a dry, sealed enclosure where no electrolyte can bridge the joint. Brass or copper against stainless steel is a milder couple, but it is not a free one, and in chloride-bearing environments brass can also dezincify, leaving a copper-coloured surface that still looks intact and no longer has the strength it was specified for.
What actually drives the cost of the housing
Raw material is the first difference and the largest: per kilogram, aluminium is roughly one-quarter to one-third the price of copper, with brass in between and moving with both metals. That gap then widens or narrows in the finished part for three reasons. The first is forming and annealing effort, because brass usually needs an extra in-process anneal, copper needs a controlled grain and a clean lubricant film, and aluminium needs careful radius and lubricant control. The second is scrap and offal value, which is high for all three and partly offsets the price of the blank. The third, and often the decisive one, is secondary operations: where the housing needs a thread, a flat or a machined bore, free-cutting brass will often win the whole quotation despite costing more per kilogram, because it can be machined at rates the other two do not allow.
How to specify the material on a drawn housing drawing
- Name the alloy and the temper, not the colour: C11000 hard or annealed, CuZn37 half hard, 1050A H14, 5052 H32, 6061-T6. Add the sheet standard the certificate will be read against, so the mill certificate can be checked rather than admired.
- State the function the metal has to perform: a conductivity figure, a shielding requirement, a thermal path, a thread class or a corrosion class. A housing that only has to hold a thread does not need the conductivity of copper, and paying for it is a design error rather than a safety margin.
- Say whether the housing is part of a magnetic circuit. Copper, brass and aluminium are all non-magnetic, so none of them can serve as a flux path; if the housing sits in the magnetic circuit, the correct material is a soft magnetic steel, not one of these three.
- Draw the joint, not just the part: name the mating material, the coating and the washer, because the galvanic pair is decided at assembly level and cannot be fixed later by the housing supplier.
- Put any conductivity or thermal requirement after forming and anneal, with the test method and the measurement position, so it is verified on the finished part rather than on the strip that went into the press.
What Balford runs
Balford deep draws and irons housings up to 250 mm in diameter in Zhuji, Zhejiang, on presses from 25 t to 350 t, with the tooling designed and built in house, so the material choice, the draw schedule and the anneal position are one engineering decision rather than three purchase orders. We run copper and brass, 1050, 3003, 5052 and 6061 aluminium, DC01 and DC04 mild steel, and 304 and 316L stainless, and the feasibility review happens before the tool is cut. Two statements to keep the picture honest: we hold ISO 9001:2015 and our quality controls are aligned with the requirements of IATF 16949, but we do not claim IATF 16949 certification; and bulk heat treatment, including the interstage anneals these metals often need, is carried out by qualified external partners and is declared as outsourced, as is plating. Forming, machining, assembly and inspection of the part itself are done in our own plant.
Key point
Let the function pick the metal: copper where the housing is the current path or the shield and mass is not the constraint, aluminium where weight and material cost dominate and the joint can be kept dry, brass where the money is really being spent on machined threads and stiffness rather than on conductivity. Then check the secondary rules before the drawing is released — none of the three is magnetic, so a housing inside a magnetic circuit belongs in soft magnetic steel, and an aluminium housing that will be bolted wet against brass needs the joint insulated, not just drawn.
Frequently asked questions
Is aluminium better than copper for a housing?
For a portable or vehicle-mounted housing, usually yes: aluminium 1050A runs at roughly 61 per cent IACS and 230 W/m·K at about one-third of the density of copper, so it delivers about twice the conductivity per kilogram at a fraction of the material cost. Copper remains the better answer where the performance has to be obtained inside a fixed envelope, because per unit volume it conducts more than three times as much as aluminium, and where the housing is also the EMI shield and needs the lowest possible resistance across its joints.
Can copper and aluminium be used in the same assembly?
They can be, but only with the galvanic couple managed. Copper is strongly cathodic to aluminium, so wherever moisture or chloride is present the aluminium becomes the anode and corrodes, which is why the standard practice is to insulate the joint with a washer or sleeve, coat or plate the aluminium face, and keep the assembly dry. Inside a sealed indoor enclosure the couple is manageable; in a wet or marine assembly it should be designed out rather than tolerated, because the corrosion is driven by the potential difference and not by the quality of either part.
Why use brass instead of copper for a machined housing?
Because the cost of that housing is usually in the machining rather than in the metal. Free-cutting brass is the reference material on the machinability scale, so threads, flats and bores are cut quickly and cleanly, while pure copper is gummy and tends to tear unless it is alloyed or specially treated, and aluminium threads need more care and strip more easily. Brass also damps sound better than either of the other two, which is why it still dominates the acoustic housings where it has traditionally been used.
Does deep drawing change the conductivity of copper or aluminium?
Yes. Forming stores dislocations in the metal, which raises resistivity, so a drawn wall conducts slightly less than the annealed strip it was cut from, and ironing a wall down to a thinner section increases the effect. Intermediate and final anneals restore most of the loss. Where a conductivity figure is specified on the finished housing, it should be written on the drawing as a requirement on the finished, heat-treated part with the test method named, because a value taken from incoming material does not describe the part that ships.
Which of the three is best for a housing that must also shield EMI?
Copper gives the highest attenuation and the lowest joint resistance, which is why it is chosen for RF and microwave housings and for shielding cans. Aluminium shields well too, but it forms an insulating oxide, so the enclosure has to be treated first — a conductive conversion coating, plating, or a conductive gasket at every seam — before it behaves like a shield rather than a gap in one. Brass sits between the two and remains the traditional material for connector bodies and waveguides, where a stiff plated shell around a machined interface is what the application needs.