The Bottom Line on C61400 for CNC Machined Parts
If your part needs moderate strength, seawater corrosion resistance, and better machinability than nickel-aluminum bronzes—at lower material cost—C61400 aluminum bronze (UNS C61400, CuAl6Fe2) is the right starting point. It strikes a practical balance between the toughness of wrought aluminum bronze and the processability that keeps machining costs reasonable. The trade-off: lower strength and wear resistance than nickel-bearing grades like C63000, and a machinability rating of only about 30% of free-cutting brass. You choose C61400 when marine corrosion resistance matters more than ultimate mechanical properties, and when your shop can handle tough, continuous chips with proper tooling and coolant.
Grade Designation and Standards Landscape
C61400 is a wrought aluminum bronze in the UNS (Unified Numbering System) copper alloy classification, specified primarily under ASTM B150/B150M for rod and bar. It is also covered by ASME SB150 for pressure vessel applications and appears in several military and marine specifications including MIL-B-24480 for castings and AMS 4635 for specific product forms.
The European near-equivalent is CuAl6Fe2 per EN 12163 (wrought copper alloys for general purposes). In Chinese GB/T standards, the closest approximate grade is QAl7 under GB/T 4423, though the iron content differs — QAl7 carries 0.5–1.0% Fe versus C61400’s broader 1.5–3.5% Fe range. These are not drop-in substitutes; any substitution must be evaluated against the specific mechanical requirements and corrosion conditions in the drawing.
Chemical Composition Limits
The composition of C61400 per ASTM B150 defines a lean aluminum bronze with iron as the primary strengthening addition. No nickel, no significant zinc — this keeps the phase structure predominantly alpha, which simplifies hot working and improves ductility.
| Element | Content (wt%) | Role in Alloy |
|---|---|---|
| Copper (Cu) | Remainder (min 88.5%) | Matrix — corrosion resistance base |
| Aluminum (Al) | 6.0 – 8.0 | Primary solid-solution strengthener; forms protective Al₂O₃ surface film |
| Iron (Fe) | 1.5 – 3.5 | Grain refinement, strength through Fe-rich precipitates |
| Manganese (Mn) | ≤ 1.0 | Deoxidizer, improves hot workability |
| Zinc (Zn) | ≤ 0.20 | Residual — kept low to avoid dezincification |
| Lead (Pb) | ≤ 0.01 | Tramp element — negligible at this level |
| Other (total) | ≤ 0.50 | — |
Unlike C63000 (CuAl10Fe5Ni5) which carries 9.0–11.0% Al and 4.0–5.5% Ni, C61400’s lower aluminum content produces a simpler alpha-rich microstructure with fewer intermetallic phases. That translates directly to better hot formability, easier welding, and fewer hard spots during machining.
Mechanical Properties by Temper
C61400 is supplied in multiple tempers per ASTM B150. The properties you get depend sharply on the condition you order — don’t design around the annealed properties if your supplier ships hot-rolled stock.
| Temper | Condition | Tensile (MPa, min) | Yield 0.2% (MPa, min) | Elongation (%, min) | Hardness (HBW, approx.) |
|---|---|---|---|---|---|
| M20 | As Hot Rolled | 485 | 240 | 35 | ~140 |
| O61 | Annealed | 450 | 205 | 38 | ~130 |
| H04 | Hard (cold worked) | 550 | 345 | 22 | ~160 |
All values above are minimums per ASTM B150 for rod and bar forms at room temperature. Hardness values are approximate — ASTM B150 does not mandate hardness, but the ranges above are typical for each temper based on published producer data. For context, C63000 in comparable tempers runs 620–690 MPa tensile with hardness in the 180–210 HBW range — the nickel and higher aluminum make a measurable difference.
Physical Data for Thermal and Electrical Design
These values apply at room temperature (20°C) unless noted. They matter when designing parts that see thermal cycling or when calculating heat buildup during machining:
- Density: ~7.8 g/cm³ — slightly below pure copper (8.94) due to aluminum content
- Electrical conductivity: ~14% IACS — low for a copper alloy, reflecting the aluminum in solid solution
- Thermal conductivity: ~67 W/m·K at 20°C — about one-sixth of pure copper; heat does not dissipate as quickly during dry or light-coolant cuts
- Coefficient of thermal expansion: ~16.2 × 10⁻⁶/K (20–300°C) — close to stainless steels but lower than pure aluminum
- Melting range: ~1040–1070°C — narrow solidification range supports good weldability
- Modulus of elasticity: ~117 GPa — about half that of steel, expect more deflection under load
The relatively low thermal conductivity (for a copper alloy) is something to account for in machining: heat concentrates at the tool-workpiece interface rather than flowing into the chip and part. This makes effective flood coolant or high-pressure through-tool cooling more important than it would be for brass or pure copper.
Corrosion Behavior and Environmental Limits
Seawater and marine: This is C61400’s strongest suit. The aluminum content forms a tightly adherent Al₂O₃ surface film that resists pitting, crevice corrosion, and erosion-corrosion in flowing seawater. The alloy also exhibits low macro-biofouling tendency, reducing maintenance on marine heat exchanger components. Unlike some copper alloys, C61400 resists stress corrosion cracking in seawater service.
Industrial atmospheres: Good resistance to sulfur-bearing atmospheres and industrial fumes. The protective oxide film is self-healing in oxygenated environments.
Where it fails: Oxidizing acids (nitric acid in particular) attack C61400 aggressively. Strong alkaline solutions above pH ~10 can cause stress corrosion cracking. Environments containing ammonia, amines, or ammonium compounds pose a real risk of stress corrosion cracking — this is a common failure mode in copper alloys and must be flagged when reviewing service conditions. Chlorinated hydrocarbons can cause pitting at elevated temperatures.
CNC Machining: What to Expect on the Shop Floor
Machinability rating: approximately 30% relative to C36000 free-cutting brass (100%). For comparison, C63000 nickel-aluminum bronze rates around 20%. C61400 is one of the more machinable aluminum bronzes, but it is still a challenging material compared to brass or steel.
The chip control problem: C61400 produces long, tough, continuous chips — the kind that wrap around the tool or the workpiece if chip breakers aren’t doing their job. This is not a brittle chip material. You need positive rake geometry with well-designed chip breakers and aggressive enough feed rates to curl and break the chip mechanically. Light finishing passes at low feed can produce unbroken stringers.
Work hardening: The alloy work hardens under the cutting edge. If you take too shallow a depth of cut (below ~0.3 mm), the tool may rub rather than cut, hardening the surface and accelerating tool wear on subsequent passes. Maintain a minimum DOC above the work-hardened layer.
Tool wear mechanism: Aluminum in the alloy forms microscopic Al₂O₃ at the elevated temperatures in the cutting zone. This abrasive oxide contributes to flank wear. The low thermal conductivity concentrates heat at the tool tip, accelerating crater wear. AlTiN or TiAlN coatings help by forming an aluminum oxide barrier that resists both abrasive and thermal wear.
Starting Machining Parameters
The values below are conditional starting references only. Actual optimal parameters depend on your machine rigidity, tool holder type (hydraulic vs. shrink-fit vs. ER collet), tool geometry, coating, coolant delivery method, workpiece clamping stiffness, and the specific temper of your C61400 stock. Use these to establish a baseline, then adjust.
| Operation | Tool Type | Speed (m/min) | Feed | DOC (mm) | Coolant |
|---|---|---|---|---|---|
| Turning (rough) | Carbide CNMG, positive rake 8–12°, TiAlN coated | 120–180 | 0.15–0.25 mm/rev | 1.5–4.0 | Flood, 6–8% emulsion |
| Turning (finish) | Carbide VNMG or CCMT, TiAlN, sharp edge | 100–160 | 0.08–0.15 mm/rev | 0.3–1.0 | Flood + high pressure |
| Milling (rough) | Solid carbide, 3–4 flute, AlTiN, corner radius | 80–140 | 0.10–0.18 mm/tooth | Radial ≤ 40% D, axial 1.0–3.0 | Flood or MQL |
| Milling (finish) | Solid carbide, 4–5 flute, AlTiN, sharp | 60–110 | 0.05–0.12 mm/tooth | Radial 5–15% D, axial 0.2–0.8 | Flood |
| Drilling | Carbide drill, TiAlN, 140° point | 50–90 | 0.08–0.18 mm/rev | Peck cycle > 3×D | Through-coolant preferred |
| Tapping | Spiral flute HSS-Co tap | 8–15 | — | Thread depth per tap | Heavy cutting oil |
For small diameters (below 10 mm), reduce speeds by 20–30% to manage tool deflection and heat buildup. For large diameters (above 50 mm), you can push toward the upper end of the speed range if the machine has the torque to maintain consistent SFM.
Surface finish: Ra 0.8–3.2 μm is routinely achievable. Ra 0.4 μm is possible with optimized finishing parameters, sharp tooling, and rigid setup — but is not a guarantee without process validation on your specific geometry.
Where C61400 Is Used (and Why)
The alloy’s combination of seawater corrosion resistance, moderate strength, good hot workability, and absence of nickel makes it cost-effective for a specific set of applications:
- Marine propellers and impellers: Corrosion-fatigue resistance in seawater, easy to cast and machine to final contours
- Valve bodies and seats: Galling resistance plus corrosion resistance for seawater valves
- Pump casings and shafts: Erosion-corrosion resistance in high-velocity seawater
- Heat exchanger tube sheets and water boxes: Thermal conductivity adequate for heat transfer, plus corrosion immunity
- Offshore fasteners and bolts: Stress corrosion cracking resistance in marine atmosphere
- Wear plates and bearing cages: Moderate load — for high loads, C63000 or C95500 (cast) is the better choice
C61400 vs. Related Aluminum Bronzes
Comparing C61400 against the grades that designers often consider as alternatives:
| Property | C61400 | C63000 (Nickel-Al Bronze) | C61300 |
|---|---|---|---|
| Al content | 6.0–8.0% | 9.0–11.0% | 5.0–7.0% |
| Nickel | None | 4.0–5.5% | Max 0.15% |
| Tensile (M20, MPa) | 485 | 620–690 | 485–585 |
| Hardness (HBW, approx.) | 140 | 180–210 | 130–170 |
| Machinability | ~30% | ~20% | ~30% |
| Seawater corrosion | Excellent | Excellent | Very good |
| Cost indicator | Medium | High (Ni content) | Medium-low |
Choose C61400 over C63000 when: a) nickel content pushes the alloy cost too high for the application’s value, b) machining cycle time is a significant cost driver and C63000’s lower machinability hurts throughput, or c) the strength requirements are moderate and C63000’s extra 200 MPa of tensile strength is unnecessary overdesign. Choose C63000 when wear resistance, high-load bearing, or maximum erosion-corrosion resistance is the primary requirement.
A note on C61300: While C61300 and C61400 share the same CuAl6Fe2 designation in some references, their ASTM B150 composition ranges are different — C61300 allows up to 1.0% tin. Always specify the UNS number, not just the chemistry shorthand.
Welding and Joining Notes
C61400 welds well with GTAW (TIG) using ERCuAl-A2 filler wire, which closely matches the base metal chemistry. Preheat to 150–200°C for sections thicker than 25 mm to reduce thermal gradients. Post-weld stress relief is not typically required for non-pressure-boundary applications. Avoid oxyacetylene welding — the flame chemistry can introduce hydrogen embrittlement in aluminum bronzes.
Ready to Quote Your C61400 Part?
If you’re designing a component in C61400 or evaluating it against other aluminum bronzes, send us your package for a technical review and machining feasibility assessment. We need the following to give you an accurate response:
- 2D or 3D drawings with all critical dimensions and GD&T callouts
- Full material specification: UNS number, ASTM standard, and temper/condition required (M20, O61, H04, or other)
- Order quantity: prototype, small batch, or production volume
- Tolerance requirements: especially any features requiring better than ±0.025 mm
- Surface finish requirements: Ra target and any specific areas (sealing faces, bearing surfaces) requiring tighter control
- Any supplementary requirements: NDE, certification, traceability, or special packaging for marine shipment
If you need help deciding between C61400, C61300, C63000, or a cast aluminum bronze for your application, explore our copper alloy materials library, review our CNC turning capabilities, or browse marine and offshore application experience.
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