Brass vs Copper: Properties, Machinability and Uses

Brass vs Copper at a Glance

Copper is a near-pure metal, usually 99.9% Cu, with about 101% IACS conductivity, 388 W/m·K thermal conductivity and excellent corrosion resistance. Brass is a copper-zinc alloy, typically 60-70% Cu, with roughly 28% IACS, higher strength and the highest machinability rating of any common metal. Choose copper for current, heat and sealing; brass for machined parts and wear surfaces.

They share a parent element, so purchasing buys them on one line, but they behave nothing alike on a lathe. Zinc content and the chip-breaking additions explain almost every difference: zinc pulls conductivity down, strength up, melting range down, and cutting speed up three to five times.

• Conductivity: 101% IACS for C11000, 28% for C36000, a 3.6x gap for the same cross section.
• Machinability: C36000 is the 100 benchmark; C11000 rates 65, C26000 about 30.
• Strength: annealed C11000 yields about 70 MPa, C36000 about 125 MPa.
• Melting: 1083 °C for copper, 885-905 °C for brass. That gap decides what you can braze without distortion.
• Weight and price: brass is 4.4% lighter and typically 70-85% of copper’s price per kilogram.

Telling them apart in the shop

Cut a fresh surface. Copper is red-orange, brass is yellow-gold and yellower with zinc. Copper is denser, so equal blanks weigh more, and soft enough for a file to bite. Copper weathers brown to green; brass tarnishes brown to olive and greens only in marine air.

Composition and Common Grades

Copper grades are defined by purity and deoxidation; brass grades by the copper-to-zinc ratio plus small additions of lead, tin, arsenic or silicon. Five cover most work: C10100 and C11000 copper, C26000 and C36000 brass, and C37700 forging brass, each traceable to a UNS number and an ASTM or EN product specification.

C10100 is oxygen-free electronic copper, 99.99% Cu with oxygen under 5 ppm, used for vacuum and RF hardware. C11000 is electrolytic tough pitch, 99.90% Cu with 0.02-0.05% oxygen as cuprous oxide. That oxygen is why C11000 cannot be welded or furnace-brazed in a reducing atmosphere above 400 °C: hydrogen reacts with the oxide and opens steam pockets at grain boundaries. C10100 avoids it at a premium; C12200 tube uses phosphorus instead, which brazes well but drops conductivity to about 85% IACS.

C26000 cartridge brass is 70% Cu, 30% Zn, the ductile choice for deep drawing. C36000 is 61.5% Cu, 35.5% Zn and 3.0% Pb; the lead is insoluble, sitting as particles that break the chip and lubricate the tool. C37700 is 59% Cu, 39% Zn, 2% Pb, for hot forging at 700-800 °C. Temper and composition data sit on the materials and alloy grades page.

Electrical and Thermal Conductivity

Copper sets the standard: 100% IACS means 58.00 MS/m, or 1.7241 µΩ·cm at 20 °C, defined by annealed tough pitch copper. C11000 and C10100 reach 101% IACS. Brass at 28% is 3.6 times more resistive, and that number governs busbar sizing, motor windings and heat spreaders.

Zinc in solid solution distorts the lattice and scatters electrons: 10% Zn drops the alloy to about 45% IACS, 30% Zn to 28%. Phosphorus is worse per atom, so 0.03% P in C12200 costs about 15 points.

Thermal conductivity follows: 388 W/m·K for C11000, about eight times carbon steel, 120 for C26000 and 115 for C36000. A copper heat sink spreads heat across its base instead of hot-spotting, while a brass bushing insulates the shaft. The same property complicates brazing a 6 mm copper fitting, which pulls heat out faster than a torch can put it in. It is also why a brass busbar of equal section carries only about 28% of the current at the same temperature rise, and why copper is specified whenever voltage drop or thermal margin is tight.

Density, Melting Range and Mechanical Properties

Brass is lighter, melts 200 °C lower and runs about 40% stronger than annealed copper. Copper wins on ductility and transport, and its modulus is higher at 117 GPa against 100 GPa, which matters when deflection sizes the part. Zinc strengthens brass; lead only breaks chips. Cold work can double strength, so temper matters as much as alloy.

Machinability Ratings and Cutting Data

Ratings use C36000 as the 100 benchmark, so 65 means copper removes metal at 65% of brass’s rate at equal tool life. C26000 rates about 30 because its chips never break, and C37700 about 90. That gap becomes cycle time on every screw machine part.

Lead particles in C36000 nucleate cracks so chips fracture short, lubricate the rake face and suppress built-up edge. Brass therefore turns dry with an air blast, and 0.8 µm Ra finishes come almost free.

Copper is soft and highly conductive, so heat runs into the part and the tool instead of leaving with the chip. It galls the edge, tears the finish and throws stringy chips that birdnest around the bar feeder. Use sharp polished tools, high positive rake, high-pressure coolant and feeds high enough to cut rather than rub. On copper, a 5-10° positive rake with polished flutes keeps the chip moving; on brass, a neutral to slightly positive rake avoids the rubbing that work-hardens the surface.

Treat these as carbide starting points. Tolerance work also needs a thermal check: copper grows 17.0 µm/m·°C, so a 200 mm part grows 3.4 µm per degree above 20 °C, and brass grows 4.1 µm. A part measured warm can read out of tolerance on a ±0.005 mm callout, which is why copper alloys are held and measured at 20 °C under the quality assurance and CMM inspection routine. Housings needing flats or cross holes move from CNC turning to CNC milling for the second op.

Corrosion, Patina and Tarnish

Copper resists corrosion better than brass almost everywhere. It grows a thin adherent cuprous oxide film that slows attack, then a stable green patina. Brass tarnishes faster, high-zinc alloys dezincify in stagnant chloride water, and stressed brass exposed to ammonia can crack.

The patina is a sequence. Indoors the surface darkens to brown and near-black oxide; outdoors sulfur compounds form brochantite, a green sulfate, and coastal air forms atacamite, a green chloride. The layer is protective and self-healing, and copper roofing lasts a century. Ammonia, oxidizing acids and wet chlorine still attack it.

Brass behavior splits by zinc content. Below 15% Zn it acts like copper; above that, zinc can leach out of stagnant chloride water and leave a porous copper sponge. The beta phase is the weak point, so duplex alpha-beta alloys like C37700 are more exposed than single-phase C26000. Arsenic, antimony or phosphorus inhibit leaching in DZR brasses, and C69300 resists it inherently. ISO 6509 tests dezincification, ASTM B858 covers ammonia stress corrosion, and a 250-300 °C stress relief anneal prevents season cracking.

Finishing differs too. Copper and brass cannot be anodized, because anodizing grows an oxide layer from an aluminum substrate, so the anodizing aluminum process applies to aluminum parts and not these alloys. Copper alloys get clear lacquer, nickel-chrome plating, or a deliberate patina.

Brazing, Soldering and Welding

Both metals are brazed far more often than welded. Copper brazes easily with self-fluxing copper-phosphorus filler or silver filler, and both accept lead-free solder. Brass is brazed or soldered and rarely fusion welded, because zinc boils at 907 °C, inside the brass melting range.

Copper pulls heat away at 388 W/m·K, so the torch must outrun the part. BCuP fillers flow at 700-800 °C and need no flux on copper-to-copper joints. AWS A5.8 silver filler covers copper-to-brass and brass-to-steel, and lead-free tin-antimony solders have replaced 50/50 tin-lead in potable water. Do not use copper-phosphorus filler on steel or nickel alloys, where phosphorus forms brittle phosphides; use silver filler there.

Where welding is unavoidable, grade matters. Oxygen in C11000 becomes steam at grain boundaries under a hydrogen-bearing arc, so C10100 or C10200 is correct for leak-tight work. GTAW with DCEN, ERCu filler, 200-500 °C preheat over 3 mm, and helium-rich shielding is standard.

Joining brass is harder. Zinc boils at 907 °C inside the 885-905 °C melting range, so fusion welding vaporizes it, giving porosity, a white zinc oxide plume and metal fume fever risk. Brass parts are brazed, soldered or joined mechanically, so design the joint for brazing.

Cost: Metal Price vs Finished Part Cost

Copper costs more per kilogram, but brass often costs less per finished part. C36000 is only about 62% copper, so mill rod typically lands at 70-85% of the copper price, and brass cuts three to five times faster. Metal price alone is a poor guide.

Run the arithmetic from a drawing. A C36000 fitting may cycle in 40 seconds where C11000 takes 2.5 to 3 minutes and needs a second deburr. Add tool life, coolant and scrap, and the metal saving disappears; brass turnings also segregate cleanly and hold scrap value. Prices move with the copper and zinc markets, so treat ratios as guidance, not quotes. Brass is also 4.4% lighter, which trims freight on high-volume shipments, while copper returns more at end of life because scrap buyers pay for its copper content.

Common Applications

Copper is specified where electrons or heat must move, or where a joint must outlast decades of weather. Brass is specified where a part must machine cheaply, resist wear, and look like metal. The application lists barely overlap, which is why the two alloys rarely compete head to head on a real bill of materials.

Copper: busbars and flexible connectors (C11000); terminals, lugs and contact fingers; heat sinks, cold plates and heat pipes; RF and vacuum hardware (C10100); EDM and welding electrodes; water and refrigeration tube (C12200); roofing; cupronickel marine hardware.

Brass: valve bodies, ball valves and pneumatic manifolds (C36000, C37700, C27450); lead-free faucet and water fittings; gears, worm wheels and bushings running against steel without galling; lock hardware, hinges and trim; terminal blocks at 28% IACS; cartridge cases (C26000); instruments and eyewear. Specify by function rather than habit: a brass terminal block asked to carry 200 A will overheat, and a copper lock housing costs more with no gain.

Lead-Free and RoHS Compliant Alternatives

RoHS caps lead at 0.1% in homogeneous materials, which rules out C36000 at 3% Pb unless an exemption applies. The copper alloy exemption for up to 4% lead has been winding down for most categories, with expiry dates that depend on the category, so EU-bound machined brass is now specified lead-free. US potable water rules are stricter on wetted surfaces.

C27450 caps lead at 0.09% with antimony or phosphorus additions that keep chips breaking; it is the closest drop-in for C36000. C69300 silicon brass, about 75% Cu, 21% Zn and 3% Si, is lead-free and dezincification resistant, stronger than C36000, with machinability around 90. C87850 silicon bronze covers cast potable-water parts. All appear in NSF/ANSI 61 listings for drinking water contact.

Expect process changes. Lead-free brasses are harder and more abrasive, so speeds drop 10-25%, feeds need re-tuning and tool life shortens. Chips run longer and hotter. Validate with first-article inspection plus a short production run, because failure shows up as tool wear over hundreds of pieces rather than a bad first cut.

Selection Guide for CNC Machining

Start from the requirement that cannot be compromised. If the part carries current or moves heat, copper wins. If it must machine to tight tolerance at low cost, brass wins. If both matter, split the assembly into a copper conductor and a brass body. On a 50-piece run, setup and inspection dominate, so alloy choice matters less than fixturing.

Six questions settle most jobs. Current or heat above a few tens of amps or a few watts: C11000 or C10100. Cycle time is the cost driver: C36000, or C27450 where lead is restricted. Hot forging: C37700; cold forming: C26000. Potable water: C27450, C69300 or C87850 with the NSF/ANSI 61 listing confirmed. Wet, stagnant, chloride-bearing service: a DZR grade, and no duplex alloys in thin walls. Welded joints: C10100 or C10200, with brass redesigned for brazing.

If weight rather than conductivity is the constraint, the 6061 vs 7075 aluminum breakdown covers strength-to-weight trade-offs for housings and brackets. YC Prime Precision machines C10100, C11000, C26000, C36000, C37700 and lead-free grades on 3-axis and 5-axis mills and live-tooling lathes to ±0.005 mm, with material certificates and inspection reports on request. Send a drawing and quantity to get an instant quote with cycle time and lead time attached.

FAQ

Is brass stronger than copper?

Yes, in comparable tempers. Annealed C36000 brass runs about 340 MPa tensile and 125 MPa yield, against 220-260 MPa tensile and 70 MPa yield for annealed C11000 copper. Cold work changes both, so compare temper as well as alloy before you specify.

Can brass be used for electrical conductors?

Only at low current. Brass runs about 28% IACS against 101% for copper, so it needs roughly 3.6 times the cross section for the same voltage drop and dissipates more heat. It is common in terminal blocks and small contacts where current is modest.

Which is better for potable water, copper or brass?

Copper tube such as C12200 is the default for supply lines because it resists corrosion and contains no lead. Brass serves valves and fittings but must be a lead-free grade such as C27450 or C69300 with an NSF/ANSI 61 listing, and dezincification resistance matters in soft or stagnant water.

Can you weld brass?

Fusion welding brass is impractical because zinc boils at 907 °C, within the alloy’s melting range, causing porosity, zinc fume and metal fume fever risk. Braze with silver filler or solder instead. Welding copper works with preheat, high heat input and oxygen-free grades such as C10100.

Which is cheaper per finished part?

Usually brass. Copper is often 20-40% more expensive per kilogram, and brass machines three to five times faster with better chip control and longer tool life. Copper wins only when its conductivity lets you delete another component from the assembly.

Is C36000 brass RoHS compliant?

Not on its own. At roughly 3% lead it exceeds the 0.1% RoHS limit and depended on the copper alloy exemption for up to 4% lead, which has been expiring for most product categories. For EU-bound products specify C27450 or C69300 and confirm exemption status with your compliance engineer.