Material
Copper Cu
Bought for conductivity first and corrosion behavior second. Nothing practical beats it for carrying current or heat except silver, and the alloy family covers everything from pure electrical copper to seawater-resistant nickel bronzes.
Overview
Copper is rarely a structural choice. It is specified because a design needs to move electricity or heat, because a bearing surface needs to be non-galling, or because a seawater component needs to resist biofouling. The alloy families diverge sharply: high conductivity coppers for busbar and windings, brasses for machined fittings and ammunition cases, bronzes and copper-nickels for marine service, and beryllium copper where high strength must coexist with conductivity and non-sparking behavior. In defense, copper alloys also carry a specific role no substitute matches, which is the driving band and cartridge case work in ammunition.
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Defense applications
Ammunition
Cartridge brass for cases and gilding metal for projectile jackets and rotating bands. These are high volume, tightly specified products with a small qualified supplier base and long-standing domestic sourcing expectations.
Cartridge cases, Projectile jackets, Rotating and driving bands, Primer cups
Naval seawater systems
Copper-nickel 90/10 and 70/30 resist seawater corrosion and biofouling simultaneously, which is why they persist in shipboard piping despite titanium's superior corrosion behavior.
Seawater piping, Condenser tubing, Heat exchangers, Hull sheathing
Electrical and electronic
Busbar, connectors, waveguide, motor and generator windings, and the lead frames and heat spreaders inside electronics. Beryllium copper covers connector springs that must conduct and flex indefinitely.
Busbar and grounding, Connector contacts, Waveguide, Motor windings, Heat spreaders
Alloys and grades
| Designation | Grade | Class | Notes | Typical forms |
|---|---|---|---|---|
| C11000 (Electrolytic Tough Pitch) | High conductivity copper | The standard commercial electrical copper. Highest practical conductivity, but the residual oxygen makes it susceptible to hydrogen embrittlement during brazing or welding. | Bar and Rod, Strip and Foil, Wire, Plate, Tube and Pipe | |
| C10100 (Oxygen-Free Electronic) | High conductivity copper | Oxygen-free high purity copper, used where brazing, high vacuum service or hydrogen exposure rules out tough pitch copper. | Bar and Rod, Plate, Strip and Foil, Tube and Pipe | |
| C26000 (Cartridge Brass, 70/30) | Alpha brass | The classic deep drawing brass, named for the application that defined it. Exceptional cold formability through many drawing operations. | Strip and Foil, Sheet, Tube and Pipe, Wire | |
| C21000 to C22000 (Gilding Metal) | Low zinc brass | High copper brass used for projectile jackets and rotating bands, where it must engrave into rifling without excessive bore wear. | Strip and Foil, Wire, Tube and Pipe | |
| C70600 (90/10 Copper-Nickel) | Copper-nickel | The standard shipboard seawater alloy, combining corrosion resistance with inherent biofouling resistance that titanium does not provide. | Tube and Pipe, Plate, Sheet, Bar and Rod | |
| C17200 (Beryllium Copper) | Precipitation hardening copper | Age hardens to strength approaching alloy steel while retaining useful conductivity, and is non-sparking and non-magnetic. Machining and grinding dust is a serious inhalation hazard. | Bar and Rod, Strip and Foil, Wire, Plate |
Properties
| Property | Value | Unit | Note |
|---|---|---|---|
| Density | 8.96 | g/cm3 | 0.324 lb/in3; heavier than steel |
| Melting point | 1085 | degrees C | 1984 degrees F for pure copper |
| Electrical conductivity | 100 | percent IACS | Copper is the reference standard; the scale is defined against it |
| Thermal conductivity | 390 to 400 | W/m-K | Roughly 20 times that of titanium alloys |
| Elastic modulus | 110 to 128 | GPa | |
| Tensile strength, C11000 annealed | 220 typical | MPa | 32 ksi; pure copper is soft |
| Tensile strength, beryllium copper aged | 1240 typical | MPa | 180 ksi; among the strongest copper alloys |
| Coefficient of thermal expansion | 16.5 | micrometre/m-K | |
| Antimicrobial behavior | Inherent | Copper surfaces are self-sanitizing, which also drives the antifouling behavior in seawater |
Advantages
- The reference standard for electrical conductivity at practical cost
- Thermal conductivity roughly twenty times that of titanium alloys
- Copper-nickel grades resist seawater corrosion and biofouling at the same time
- Non-sparking, which matters in ordnance and fuel handling environments
- Excellent formability, and brasses machine faster than almost any other metal
- Deep domestic recycling stream, since copper scrap holds most of its value
Limitations
- Heavier than steel, so it is almost never a weight-competitive structural choice
- Expensive relative to steel and aluminum, and priced on a volatile commodity market
- Pure copper is soft, so strength requires alloying that costs conductivity
- Susceptible to dezincification in brasses and stress corrosion cracking in ammonia environments
- Beryllium-containing alloys carry serious inhalation hazards during machining and grinding
- Galvanically noble, so it drives corrosion of steel and aluminum in contact
Governing specifications
| Designation | Body | Scope |
|---|---|---|
| ASTM B152 | ASTM International | Copper sheet, strip, plate and rolled bar |
| ASTM B36 | ASTM International | Brass plate, sheet, strip and rolled bar |
| ASTM B466 | ASTM International | Seamless copper-nickel pipe and tube |
| ASTM B194 | ASTM International | Copper-beryllium alloy plate, sheet, strip and rolled bar |
| MIL-T-16420 | U.S. Department of Defense | Copper-nickel tube, seamless, for naval service |
| ASTM B187 | ASTM International | Copper bar, bus bar, rod and shapes |