Take C65100 silicon bronze — a workhorse in marine fasteners and electrical connectors — and push the silicon content from roughly 1% to about 3%. Add manganese. The result is C65500, sometimes called high silicon bronze, and it behaves differently in the machine shop: it is stronger, tougher, more resistant to stress corrosion cracking, and noticeably harder on tooling than its low-silicon sibling. If you are designing clevis pins, turnbuckle bodies, pump shafts, valve stems, or chemical-process hardware and the part needs to resist flowing seawater, dilute sulfuric acid, or high-pressure steam — and you want a single alloy that is weldable, formable, and will not suffer dezincification — C65500 is worth evaluating before jumping directly to duplex stainless or nickel alloy.
Grade Designation, Standards, and What “High Silicon” Actually Means
C65500 is the UNS number for a wrought copper-silicon-manganese alloy. Its closest EN designation is CuSi3Mn1 (CW116C in EN 1652); the ISO parallel is CuSi3Mn. In older trade nomenclature it has been called “Everdur 1015” (a former trademark). It is commonly referred to as high silicon bronze to distinguish it from C65100 (CuSi1 / low silicon bronze).
The governing ASTM specifications for C65500 are:
- ASTM B96 — Standard Specification for Copper-Silicon Alloy Plate, Sheet, Strip, and Rolled Bar for General Purposes and Pressure Vessels
- ASTM B98 — Standard Specification for Copper-Silicon Alloy Rod, Bar, and Shapes
- ASTM B283 — Standard Specification for Copper and Copper-Alloy Die Forgings (Hot-Pressed)
These standards define different mechanical property requirements for different product forms and tempers, so quoting “the” tensile strength of C65500 without specifying form and temper is misleading. We keep that distinction clear.
Chemical Composition per ASTM B96/B98
| Element | Content (weight %) | Role in the Alloy |
|---|---|---|
| Copper (Cu) + named elements | ≥ 99.8 min (remainder) | Base metal — provides electrical conductivity and corrosion resistance |
| Silicon (Si) | 2.8–3.8 | Primary strengthener; forms a protective SiO₂-rich surface film |
| Manganese (Mn) | 0.50–1.30 | Secondary strengthener; improves hot workability and counters impurity embrittlement |
| Iron (Fe) | ≤ 0.80 | Grain refiner in small amounts; excess promotes brittle Fe-Si intermetallics |
| Zinc (Zn) | ≤ 1.50 | Residual — too much shifts the alloy toward brass-type dezincification behavior |
| Nickel (Ni) | ≤ 0.60 | Incidental |
| Lead (Pb) | ≤ 0.05 | Kept low because lead harms hot workability and weld quality |
Source: ASTM B96 / ASTM B98, composition limits for C65500.
The silicon range is roughly three times that of C65100 (Si 0.8–2.0%). The extra silicon shifts solid-solution strengthening upward and alters the oxide chemistry — which matters for both corrosion performance and welding behavior.
How Temper Affects Mechanical Properties
C65500 is not heat-treatable by precipitation hardening; its strength comes from cold work (strain hardening) and the solid-solution effect of silicon and manganese.
| Temper | Product Form | Tensile (MPa, min) | Yield — 0.5% Ext. (MPa, min) | Elongation in 50 mm (%, min) |
|---|---|---|---|---|
| O61 (annealed) | Rod/Bar | 345 | 140 | 35 |
| H01 (quarter-hard) | Rod/Bar | 380 | 170 | 25 |
| H02 (half-hard) | Rod/Bar | 450 | 205 | 18 |
| H04 (hard) | Rod/Bar | 550 | 310 | 10 |
| O61 (annealed) | Sheet/Strip | 345 | 140 | 35 |
| H02 (half-hard) | Sheet/Strip | 450 | 310 | 12 |
| H04 (hard) | Sheet/Strip | 550 | 415 | 6 |
Source: ASTM B98-22 and ASTM B96-22, minimum values for C65500; actual mill test certificates may report higher values.
In the H04 (hard) temper, C65500 rod reaches approximately 550 MPa tensile strength — comparable to annealed 304 stainless steel (minimum 515 MPa per ASTM A276) but at a fraction of the machining difficulty.
Physical Properties at Room Temperature
| Property | Value | Unit |
|---|---|---|
| Density | 8.53 | g/cm³ |
| Electrical conductivity | ~6.5–7.0 (11–12% IACS) | MS/m (%IACS) |
| Thermal conductivity | ~36 | W/(m·K) at 20°C |
| Modulus of elasticity (tension) | ~105 | GPa |
| Melting range | ~971–1026 | °C |
| CTE (20–300°C) | ~18.0 × 10⁻⁶ | /K |
Source: Copper Development Association (CDA) data for C65500, annealed condition unless otherwise noted.
The electrical conductivity at 11–12% IACS is significantly lower than C65100 (~17% IACS) because the higher silicon content disrupts the copper lattice. If your application needs both high conductivity and corrosion resistance, C65100 is typically a better fit. If strength and stress-corrosion resistance matter more, C65500 takes the lead.
Corrosion Behavior: Where It Excels
- Seawater and marine atmosphere: Long service record in marine hardware. The SiO₂-rich passive film provides good resistance to flowing seawater. C65500 does not suffer dezincification — unlike admiralty brass (C44300) or Muntz metal (C28000). Crevice corrosion is possible under stagnant conditions but uncommon in well-designed parts.
- Dilute sulfuric acid and industrial atmospheres: High silicon bronze handles dilute H₂SO₄ and sulfur-bearing industrial atmospheres better than most brasses and many aluminum bronzes.
- Organic acids, fresh water, and steam: Good resistance; widely used in chemical plant hardware and steam fittings.
- Stress corrosion cracking (SCC): The manganese addition improves SCC resistance in ammoniacal environments compared to low-silicon bronze. This matters if your part is exposed to cleaning agents, fertilizers, or ammonia-containing atmospheres.
- Not recommended for: Strongly oxidizing acids (nitric, chromic). Sulfide environments where cupronickel (C70600, C71500) would be a better choice.
CNC Machining C65500: Tougher Than It Looks
Machinability and Chip Behavior
C65500 has a machinability index of approximately 30 (relative to C36000 free-cutting brass = 100). The alloy contains no lead or free-machining additions, so expect long, stringy, tough chips — especially in the annealed temper. Half-hard (H02) and hard (H04) tempers produce more manageable chips because the cold-worked structure is less ductile.
Tooling and Geometry
- Insert grade: Uncoated or PVD-TiN coated carbide, sharp positive-rake geometry (ISO K10–K20, or C2–C3 in the old US system). HSS is usable for low-volume work but tool life drops quickly.
- Rake angle: 10–18° positive back rake for turning; 8–12° positive radial rake for milling. Positive geometry reduces built-up edge tendency.
- Clearance angle: 8–12° — slightly higher than typical steel parameters.
- Edge prep: Sharp (honed, not heavily chamfered). A heavy T-land will push material rather than cut it, causing work hardening and dimension drift.
Starting-Point Cutting Parameters
The values below are suggested starting points for rigid CNC equipment with flood coolant. Machine stiffness, workholding, tool holder quality, coolant delivery, and part geometry all affect outcomes. Validate with a test cut.
| Operation | Speed (m/min) | Feed (mm/rev) | DOC (mm) | Tooling |
|---|---|---|---|---|
| Rough turning | 80–140 | 0.15–0.35 | 1.5–4.0 | Carbide, positive rake, TiN |
| Finish turning | 100–160 | 0.05–0.15 | 0.2–0.8 | Carbide, sharp edge, polished flank |
| Rough milling | 60–110 | 0.08–0.20/tooth | 0.5–2.5 radial | Solid carbide, 2–3 flute |
| Finish milling | 80–130 | 0.05–0.12/tooth | 0.2–0.5 radial | Solid carbide, polished flute |
| Drilling (HSS) | 25–45 | 0.08–0.20 | — | HSS, 118°, polished flutes |
| Drilling (carbide) | 60–90 | 0.10–0.25 | — | Solid carbide, TiN coated |
Coolant, Workholding, and Finish
- Flood coolant (soluble oil emulsion at 5–8%) is recommended primarily for chip evacuation and thermal stability, not for lubrication — copper alloys generate less cutting heat than steels.
- Long stringy chips can wrap around the tool or workpiece. Use chip breakers, peck drilling cycles, and high-pressure through-tool coolant.
- Annealed C65500 is ductile enough to indent under hard jaw clamping. Use soft jaws or machined fixtures that distribute the clamping load.
- With sharp tools and a stable setup, Ra 0.8–1.6 µm is achievable in turning; Ra 1.6–3.2 µm in milling. Actual results depend on machine, fixture, and part geometry — not solely on the material grade.
Welding and Joining: A Genuine Strength
C65500 is one of the most weldable copper alloys:
- GTAW (TIG): Preferred. ERCuSi-A (AWS A5.7) filler, DCEN, argon shielding. Preheat to 50–150°C for sections over 3 mm. The silicon in filler and base metal acts as a deoxidizer, producing clean weld pools with minimal porosity.
- GMAW (MIG): Feasible with ERCuSi-A wire and argon shielding. Spray transfer for sections over 6 mm.
- Brazing and soldering: Excellent with silver brazing alloys (BAg series per AWS A5.8) after removing the SiO₂ surface film.
- Post-weld stress relief: 475–540°C for critical service where SCC risk exists.
Alternatives: When C65500 Is and Is Not the Right Call
| Alloy | Key Difference vs C65500 |
|---|---|
| C65100 (low-Si bronze) | Better conductivity (~17% vs ~11% IACS). Lower strength in equivalent tempers. Less SCC resistance. Choose C65100 if conductivity is the priority. |
| C46400 (naval brass) | Contains zinc (~39%) and is susceptible to dezincification in stagnant water. C65500 avoids this failure mode entirely. |
| C63000 (Ni-Al bronze) | Much higher strength and hardness. Better in high-velocity seawater and cavitation. Harder to machine. Choose C63000 for propellers and wear parts; C65500 for general hardware. |
| 316 stainless | Higher strength and temperature capability. Much harder to machine — C65500 cuts at roughly 3–4× the speed. No chloride SCC risk in C65500 (a known failure mode for 316 above ~60°C). |
What to Put on Your RFQ or Drawing
When requesting a quote for C65500 CNC machined parts, include:
- Material callout: “UNS C65500 per ASTM B98” or “CuSi3Mn1 (CW116C) per EN 12165,” including temper (e.g., H02 half-hard).
- Product form: Rod, bar, plate, or forging — different ASTM specs apply (B98 vs B96 vs B283).
- Quantity and delivery condition: Are prototypes acceptable in annealed temper with production in H02?
- Critical tolerances: C65500 has a higher CTE than steel (~18 × 10⁻⁶/K vs ~12 × 10⁻⁶/K). If the part assembles with steel at a different temperature, state the inspection temperature.
- Surface finish: Ra target and lay direction if critical.
- Welding after machining: If the part will be welded into an assembly, specify the process and filler metal.
- Certification: Mill test certificate per EN 10204 3.1, or certificate of conformance?
For a firm quotation, send your drawing, material specification with temper, target quantity, and required surface finish. We will evaluate part geometry against available stock forms, recommend a machining approach, and return a detailed proposal.
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