CU · copper alloy
Chromium Copper C18200 (UNS C18200)
Copper with chromium for strength: roughly 80% of the conductivity of pure copper and about twice the strength, and it machines better than C110 because it is harder.
Quoting this material
- Typical lead time
- 12–20 working days
- Condition
- Solution treated and aged, or cold worked and aged
- Achievable finish
- Ra 1.6 µm typical · Ra 0.8 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
Copper with chromium for strength: roughly 80% of the conductivity of pure copper and about twice the strength, and it machines better than C110 because it is harder.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength (aged) | 380–550 | MPa |
| Yield strength (aged) | 300–480 | MPa |
| Elongation (aged) | 15–20 | % |
| Hardness (aged) | 65–90 | HRB |
| Thermal conductivity | 324 | W/m·K |
| Modulus of elasticity | 130 | GPa |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Solution treated and aged, or cold worked and aged
Heat treatment
Age hardenable: solution treat, machine, then age at 450–480 °C. The aged condition is what delivers the strength with the conductivity retained - an unusual combination that a solid-solution alloy cannot provide.
Achievable surface finish
Ra 1.6 µm
Ra 0.8 µm
Finishes like copper but with better chip control because of the higher hardness.
Tooling and cutting parameters
Cutting speed
- 150–300 m/min (carbide)
Feed
- 0.10–0.30 mm/rev turning · 0.08–0.20 mm/tooth milling
Tooling
- Sharp uncoated or lightly coated carbide, high positive rake
Coolant
- Flood
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Resistance welding electrodes
- Electrical contacts and switchgear
- High-current connectors
- Mould cores needing fast cooling
- Circuit breaker components
DFM notes for this grade
- Ageing after machining gives the strength - a part machined from the solution-treated stock and never aged will not meet the drawing, and it will be soft
- It is bought for the conductivity-with-strength combination: for pure conductivity, C110 is cheaper; for pure strength, a bronze or a steel
- The chromium is only a fraction of a percent and it still doubles the strength - do not expect it to behave like an alloy steel
Questions buyers ask
- Why is chrome copper used for welding electrodes?
- Because a spot-welding electrode has to carry a lot of current and also resist being crushed and heat-softened. Pure copper conducts better but mushrooms under the load; chrome copper keeps its shape at about 80% of the conductivity, which is the right trade for a production electrode.
- Does ageing affect the conductivity?
- The age is what gives the strength; the conductivity stays high because the chromium comes out of solution into fine particles rather than staying dissolved. That combination is the reason the alloy exists.
Grades we would quote instead
C11000 ETP Copper
6/10Pure copper: gummy, prone to built-up edge and famous for long stringy chips.
C17200 Beryllium Copper
5/10Machines like a hard brass in the annealed state and like a tool steel after ageing.
C26000 Cartridge Brass
8/10The 70/30 brass: excellent cold-forming and good machining, though without the lead it does not break a chip as cleanly as C360.