Brass vs bronze vs copper: strength, conductivity, corrosion

At a glance

Which is stronger: brass C36000, bronze C95400 or copper?

Aluminium bronze C95400 has the highest specified tensile strength of the alloys, but the strengths are on different bases. Free-cutting brass C36000 round rod carries a specified tensile minimum from 330 MPa annealed to 480 MPa hard (H02 bar is 395 MPa). Cast Aluminium bronze C95400 is specified from 515 MPa for sand castings up to 655 MPa for heat-treated continuous cast.

On yield, compare like with like. Sand-cast bronze (205 MPa) sits above annealed brass (130 MPa), and heat-treated continuous-cast bronze (310 MPa) sits above hard brass (240 MPa). All are minimums in different forms, so real parts usually do better.

Soft Copper (Cu) has a yield strength of 69 MPa and a tensile strength of 179 to 262 MPa. In the H08 temper the copper profile notes a nominal 359 MPa yield for strip, not a minimum; the tensile strength and conductivity at that temper are not in our data. Monel 400 annealed is a range of 172 MPa to 345 MPa in a composite table that is not for specification, and Nickel annealed rod and bar are a nominal range up to 210 MPa. We do not claim any one of these out-yields the others.

Hard-temper brass rod is specified at only 4 % elongation minimum, against 15 % annealed, so a strong brass part has little room to bend. Stiffness differs too: the elastic modulus is 117 GPa for copper, 107 GPa for bronze, 179 to 180 GPa for Monel and 205 GPa for nickel. Brass has no usable modulus in its profile.

Which conducts best: copper, brass C36000 or bronze C95400?

Copper conducts best by a wide margin, and free-cutting brass C36000 conducts better than aluminium bronze C95400. Copper (Cu) has 391 W/(m·K), which is 3.4 times the value for Free-cutting brass C36000 and 6.7 times the value for Aluminium bronze C95400. Nickel (Nickel 200) is 70.3 W/(m·K), above bronze, and Monel 400 is last at 22 W/(m·K).

Electrical conduction follows the same order, but the units differ. Soft copper is 58 MS/m, which the profile gives as 100 %IACS. Brass C36000 is 26 %IACS and bronze C95400 is 13 %IACS.

Monel needs care. Its manufacturer datasheet gives an electrical resistivity of 0.511 µΩ·m (about 51 µΩ·cm). Converted to %IACS, that is roughly a tenth of the 34 % IACS in its profile, which is an encyclopedia entry and looks like a decimal slip. We use the datasheet value and rank Monel last.

The copper point is the soft temper, so it does not rank copper's strength. Ask for %IACS at the delivered temper.

Which is heavier: copper, brass C36000 or bronze C95400?

Copper is heavier than brass C36000, and brass is heavier than bronze C95400. Copper (Cu) has a density of 8.9 to 8.96 g/cm³, Free-cutting brass C36000 is 8.5 g/cm³ and Aluminium bronze C95400 is 7.45 g/cm³, so copper is 1.2 times the density of the bronze. Monel 400 at 8.8 to 8.83 g/cm³ and Nickel at 8.89 to 8.91 g/cm³ are close to copper.

How do their melting points compare?

Monel 400 and Nickel melt well above copper, and bronze melts below it. Copper (Cu) is listed at 1,083 to 1,085 °C from two sources, Monel 400 at 1,300 to 1,350 °C and Nickel at 1,455 °C as the element. Aluminium bronze C95400 melts between 1,027 °C and 1,038 °C.

Free-cutting brass C36000 is listed with a solidus of 954 °C and a liquidus of 1,049 °C from one supplier sheet. That liquidus looks high for a leaded brass of this composition (general engineering knowledge, not in our data), so we do not rank brass on melting point until a second source confirms it.

Which machines best?

Free-cutting brass C36000 is rated 100 and bronze C95400 is rated 60 on supplier indexes, so brass is indicated as easier to cut, but treat the comparison as indicative only. The brass scale defines C36000 as 100, and the profile says its two-phase structure breaks chips and the lead lubricates the cut. The bronze sheet does not name its reference alloy.

The copper profile has no machinability entry. For Monel 400, our profile cites an encyclopedia saying it work-hardens quickly and needs slow speeds and low feed rates.

Which resists corrosion best, and where do nickel and Monel fit?

Our data cannot rank brass C36000 and bronze C95400 directly. Free-cutting brass C36000 can dezincify (brass with more than 15 % zinc loses zinc, and C36000 has about 35 % zinc) and can crack in ammonia or amines under tensile stress; its profile rates both as moderate with no depth or rate. Aluminium bronze C95400 can lose aluminium in crevices, under deposits or with galvanic coupling, and can pit in sulphide-polluted seawater. We score those two failure risks moderate, our judgement from a source that calls this attack 'not usually of great significance'. Its pitting rating is 'unknown'.

By environment, our reading of the profiles is as follows. In chloride, hot or soft water, brass carries a sourced dezincification warning, while bronze C95400 has no measured rate; the 'low' for seawater is a generic statement about non-ferrous alloys. With ammonia or amines, brass is the weak choice; the 'low' cracking rating for bronze comes from a source about aluminium bronzes in general, not C95400, so it is one qualitative source. For seawater, nickel-aluminium bronzes are usually preferred over C95400 (general engineering knowledge, not in our data). Copper (Cu) tarnishes to cuprous oxide, then to chloride and sulphide products, in rural air, rated low.

Monel 400 is a nickel-copper alloy with at least 63.0 percent nickel plus cobalt and 28.0 to 34.0 percent copper. Its profile reports very low corrosion rates in flowing seawater, but stagnant seawater can cause crevice and pitting corrosion, and brass has no seawater rating to compare. It shows exceptional resistance to hydrofluoric acid up to the boiling point; stress-relieve it, because aerated hydrofluoric acid vapour can crack stressed Monel (general engineering knowledge, not in our data). Caustic at high temperature and stress can crack it, and steel in contact in salt water is attacked, so insulate them.

Nickel is Nickel 200, 99.0 % min nickel plus cobalt. It corrodes very slowly in air: 0.0002 mm/a at a rural site against 0.0056 mm/a at a heavy industrial site. Nickel silver and cupronickel are not in our data.

Terms used

Yield strength

the stress at which a metal starts to deform for good. Below it the part springs back.

%IACS

electrical conductivity as a percentage of annealed pure copper, which is set at 100 %. Higher is a better conductor.

Temper

the hardness state of a metal after rolling, drawing or heat treatment. Tempers are coded (for example O60, H02, H04), and strength and ductility differ a lot between them.

Solidus and liquidus

the temperature where an alloy starts to melt and the temperature where it is fully liquid.

Dezincification

corrosion of brass in which zinc leaches out and leaves a weak, porous copper layer behind.

Dealuminification

the aluminium bronze version of dezincification: aluminium is lost from the alloy and a weak copper residue is left.

Season cracking

stress corrosion cracking of brass. Residual stress from forming plus an ammonia or amine atmosphere makes the metal crack.

What to check before you order

1. Name the grade and standard: UNS C36000 (the profile prints ASTM B16 on its specifications line), C95400 to ASTM B505 (continuous cast) or B148 (sand cast), and C10200 for oxygen-free copper.
2. Name the temper code, not just soft or hard (brass O60, H02 or H04; copper H08 if you want the 359 MPa figure; bronze as cast or C95400HT), and ask for minimum strength and %IACS for that temper.
3. For brass, ask for the lead content and whether the part will touch drinking water. The profile notes a 0.25 % lead limit for lead-free plumbing brass in California, and C36000 is far above it.
4. For brass in service, ask about ammonia or amines, stress relief after cold work, and chloride-rich, hot or soft water.
5. For aluminium bronze, ask for the casting method and for evidence on dealuminification. Bunting's warning for its C95400 bars names nickel and lead, so ask for a composition certificate. Oxyacetylene welding is not recommended.

What do we not know yet?

• No price or availability data for any of these grades, which is often the deciding factor between brass, bronze and copper.
• Only two alloy grades are profiled: free-cutting leaded brass C36000 and aluminium bronze C95400. Tin bronzes, phosphor bronze, nickel-aluminium bronzes, other brasses (including lead-free), cupronickel and nickel silver are not covered, so this is not a comparison of the whole families.
• Corrosion data for brass, bronze and Monel are qualitative. No seawater corrosion rate for bronze C95400 or Monel 400, no seawater rating for brass C36000 and no dezincification depth were found. The brass melting range comes from a single supplier sheet and needs a second source.
• Machinability is a supplier index for brass and bronze on different scales; copper and Monel have no rating. Wear, galling and fatigue data are not recorded.
• Electrical data are not on a common footing: copper is in MS/m, brass and bronze in %IACS, and copper has no resistivity entry. The Monel profile carries a 34 % IACS encyclopedia entry that does not fit its own datasheet resistivity, so that entry needs correcting.
• Strength is not like-for-like (minimums against typical values, rod against casting against strip). The H08 copper yield of 359 MPa is only a profile note, and its tensile strength and conductivity at that temper are not recorded.

Questions people ask