Copper, Brass & Bronze
C110/C101, brass 360, bronze and beryllium copper: conductivity, machinability, cost
Copper alloys are selected for electrical conductivity (C101/C110), machinability (C360 free-machining brass) and bearing/wear duty (bronzes). Pure copper is an outstanding conductor but gummy to machine; brasses machine beautifully and dominate plumbing and terminals; aluminum bronze and phosphor bronze serve heavy wear. Beryllium copper adds spring and strength at premium cost.
1. Alloy families
Pure copper C110 (ETP) conducts ~101% IACS and is standard for busbars, terminals and heatsinks; C101 (OFHC) adds purity for vacuum and electronics. Copper anneals easily, so machined parts are typically supplied in half-hard or hard temper for dimensional stability.
Brasses (copper-zinc): C360 free-cutting brass (UTS ≈400 MPa) machines like butter — the default for high-volume turned fittings; C260 cartridge brass for stamping and springs; C230 red brass for plumbing. Bronzes: C510 phosphor bronze (springs, bearings), C954 aluminum bronze (heavy wear, UTS ≈550 MPa+), C932 bearing bronze.
2. Machining and finishing
Free-cutting brass C360 gives excellent finish, tight tolerances (±0.05 mm routine) and long tool life; pure copper C110 is gummy — sharp tools, controlled feeds and plenty of coolant. Copper work-hardens; avoid fine chips jamming in automated machines.
Finishes: electroplating (tin, nickel, silver, gold on copper/brass), clear lacquer to prevent tarnishing, polishing to mirror, and passivation for copper. Beryllium copper can be heat-treated to 38–42 HRC for springs and tooling.
3. Applications
Electrical: busbars, contacts, heat sinks (copper conducts ~60% better than aluminum per volume but weighs 3.3× more). Plumbing: brass fittings and valves. Marine: silicon bronze and aluminum bronze for propellers and bearings. Tooling: beryllium copper for spark-safe tools and molds that need fast heat extraction.
Cost: copper ≈3–4× steel per kilogram and heavy (density 8.9 g/cm³); beryllium copper costs significantly more. Specify material condition (temper) because annealed parts distort during machining.
4. Selection guidance
Choose C110/C101 for conductivity, C360 for machined fittings and terminals, C260 for stampings, C510 for springs, C954 for wear. Avoid brass in food/acid contact without verification (dezincification), and avoid beryllium copper where an alternative metal works — it needs special handling in grinding (beryllium dust).
For quoting, copper alloys are priced by weight with a machining multiplier; tight tolerances and fine finishes are economical on brass but costly on pure copper.
Quick reference
| Alloy | UTS MPa | Density g/cm³ | Conductivity %IACS | Best for |
|---|---|---|---|---|
| C110 ETP copper | 220–270 | 8.89 | 101 | Busbars, heatsinks, terminals |
| C101 OFHC | 220–270 | 8.94 | 101 | Vacuum, electronics |
| C360 brass | 400 | 8.53 | 28 | Machined fittings, terminals |
| C510 phosphor bronze | 440–560 | 8.78 | 15 | Springs, contacts |
| C954 aluminum bronze | 550–650 | 7.45 | 13 | Heavy wear, bearings |
| C17200 BeCu | 1240 (HT) | 8.25 | 22 | Springs, spark-safe tooling |
Sources & references
- ASTM B187 — Copper bar
- ASTM B16 — Free-cutting brass
- ASTM B139 — Phosphor bronze
- C17200 per ASTM B194
- Xometry Learning Center — Copper & Brass Guide (public engineering reference)