Nickel aluminium bronze is aluminium bronze with 4% or more nickel, and that single addition changes the metallurgy decisively. In a plain aluminium bronze above about 9.4% aluminium, slow cooling forms brittle gamma-2 that corrodes preferentially and causes dealuminification. Nickel suppresses that reaction outright, replacing gamma-2 with dispersed iron- and nickel-rich kappa phases that add strength and wear resistance without the corrosion penalty. The result is the benchmark copper alloy for seawater: resistant to high-velocity flow, cavitation, crevice attack and biofouling, tough down to cryogenic temperatures, non-sparking and non-magnetic. C95800 casts more ship propellers than any other alloy; C63000 is ASTM F468 Cu 630, the strongest certified copper-alloy bolting material there is, at 690–896 MPa. Watch the iron-shall-not-exceed-nickel rule — on C63200 and C95800 it is an explicit acceptance criterion.
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Nickel is the whole point of this family, and what it does is chemical rather than simply strengthening. A plain aluminium bronze above about 9.4% aluminium carries a beta phase at temperature, and on slow cooling through roughly 565 °C that beta decomposes to alpha plus gamma-2 (γ₂, Cu₉Al₄) — a hard, brittle intermetallic that corrodes preferentially and is the direct cause of dealuminification. Adding 4% nickel or more suppresses that eutectoid decomposition outright. What forms instead is a family of iron- and nickel-rich kappa (κ) phases, conventionally κI to κIV: dispersed, relatively noble intermetallics that raise strength, hardness and wear resistance without setting up the galvanic couple that destroys a gamma-2-bearing alloy in seawater. That substitution — kappa in place of gamma-2 — is why nickel aluminium bronze, and not plain aluminium bronze, is the standard material for ship propellers, seawater pumps, valves and offshore hardware.
The iron-to-nickel rule follows directly, and it is written into the specifications. Both C63200 and C95800 carry the explicit requirement that the iron content shall not exceed the nickel content. Iron and nickel are both kappa formers, but an excess of iron over nickel leaves too little nickel in solution to do the eutectoid-suppressing job, and the corrosion resistance falls away. A heat that meets every individual element range and still has Fe > Ni is non-conforming. It is the single most commonly overlooked acceptance criterion on this family — check it on the certificate, not just the element ranges.
The heat-treated condition is not a detail, and the two cast grades behave differently. C95500 is quench hardenable: solution treat at 871–913 °C for one hour, water quench, then temper anneal at 621–663 °C — the TQ50 condition, which lifts the sand-cast minimum from 621 to 758 MPa and Brinell from 190 to 200, typical values reaching 827 MPa and 230 HB. C95800 is not: CDA register a stress relief at 316 °C and no solution treatment, and publish no TQ50 properties. Where C95800 needs a temper anneal — after welding, or on heavy naval sections — the requirement comes from MIL-B-24480 or the purchaser's specification, not from the C95400 or C95500 cycle. C63020 is different again: AMS 4590 specifies it as martensitic, solution heat treated and tempered extrusions.
What the alloy buys you in service, and where it stops. It handles conditions no other copper alloy manages together: high-velocity and turbulent seawater without impingement attack; cavitation at propeller tips and pump inlets, where it outperforms stainless steels on erosion rate; crevice and pitting conditions that would attack austenitic stainless; and long-term biofouling resistance from the copper matrix. It is non-sparking and essentially non-magnetic, holds toughness at cryogenic temperature with no ductile-to-brittle transition, and keeps strength hot better than brasses or tin bronzes. The limits: oxidising acids, notably nitric, attack it; stagnant sulphide-polluted seawater is its worst case, and a layup in a polluted harbour can do more damage than years at speed; ammonia and amines can still crack it under stress; and it is cathodic to steel, so steel fasteners in a nickel aluminium bronze component will be attacked — match or isolate.
C63000 is the strongest certified copper-alloy bolting material in the ASTM nonferrous fastener standards. ASTM F468 and F467 list it as Cu 630, marking F 468H, at 690–896 MPa (100–130 ksi) tensile with 345 MPa minimum yield, 85–100 HRB, in all diameters. Set that against Cu 613 at 552–758 MPa, Cu 614 at 517–758 MPa and Cu 464 naval brass at 345 MPa with 103 MPa yield. A Cu 630 bolt is in the strength class of a carbon steel structural bolt while being non-sparking, non-magnetic and better in seawater than any of them. The trade is ductility — F468 requires only 5% minimum elongation for Cu 630 against 30% for Cu 613 and Cu 614, so where a joint must yield and redistribute load, the lower-aluminium grades remain the better answer.
Nickel aluminium bronze is tougher and more work hardening than plain aluminium bronze, and the kappa phases that give it its wear resistance also abrade tooling. CDA machinability ratings here are low throughout: 30 for the wrought grades C63000 and C63200, 50 for the cast C95500, and only 20 for C95800 — the propeller alloy is the hardest of the group to cut. No leaded nickel aluminium bronze exists, because lead and aluminium together make the alloy hot short. What works is rigid setups and heavy, continuous cuts, because the alloy work hardens the moment a tool rubs or dwells; positive rake on a keen, well-supported edge; low surface speed with generous feed, never the reverse; carbide as standard, with ceramic or CBN on the harder heat-treated conditions; and flood coolant throughout. Where a part is to be both heat treated and machined, rough machine, heat treat, then finish — the quench will move the part.
All composition and machinability data from the Copper Development Association alloy records. Aluminium, nickel and iron figures are read directly from the individual grade pages. Machinability is on the CDA scale where C36000 free-cutting brass = 100.
| Grade | Designation | Form | Aluminium % | Nickel % | Iron % | Structure | Machinability | Chosen For |
|---|---|---|---|---|---|---|---|---|
| C63000 | Nickel Aluminium Bronze | Wrought | 9.0–11.0 | 4.0–5.5 | 2.0–4.0 | Alpha + kappa | 30 | ASTM F468 Cu 630 — strongest certified Cu bolting |
| C63020 | Martensitic NAB, AMS 4590 | Wrought | 10.0–11.0 | 4.2–6.0 | 4.0–5.5 | Alpha + kappa | — | Solution treated and tempered; bearings and valve balls |
| C63200 | Weldable Nickel Aluminium Bronze | Wrought | 8.7–9.5 | 4.0–4.8 | 3.5–4.3 | Alpha + kappa | 30 | Excellent weldability; 20–25% elongation |
| C95400 | Cast Aluminium Bronze | Cast | 10.0–11.5 | 1.5 max | 3.0–5.0 | Cast alpha-beta | 60 | Not a nickel aluminium bronze — see the aluminium bronze hub |
| C95500 | Cast NAB, High Strength | Cast | 10.0–11.5 | 3.0–5.5 | 3.0–5.0 | Cast alpha + kappa | 50 | Strongest here — 758 MPa min at TQ50 |
| C95800 | Cast NAB, Propeller Alloy | Cast | 8.5–9.5 | 4.0–5.0 | 3.5–4.5 | Cast alpha + kappa | 20 | The standard propeller alloy; MIL-B-24480 |
Read the nickel column first — it is what makes these alloys what they are. At 4% and above, nickel suppresses the gamma-2 eutectoid and replaces it with kappa phases, which is why every grade here outperforms a plain aluminium bronze of similar strength in seawater. On the wrought side, C63000 is the high-strength general-purpose grade and the ASTM F468 Cu 630 fastener alloy; C63200 trades strength for 20–25% elongation and Excellent weldability and is the grade for welded seawater fabrications; and C63020 is the martensitic AMS 4590 extrusion alloy — though CDA register composition and specifications only, with no mechanical, physical or thermal data, and we have not substituted figures from its neighbours. On the cast side, C95500 is quench hardenable to 758 MPa minimum and C95800 is the standard propeller alloy — lower strength, far more ductile, covered by MIL-B-24480, and not quench hardened. C95400 is listed here for completeness but is not a nickel aluminium bronze: CDA class it as a plain copper-aluminium-iron casting alloy with nickel only as a 1.5% maximum limit, so it is documented on the aluminium bronze hub and that row links there rather than duplicating the page. Finally, note the Fe ≤ Ni requirement on C63200 and C95800.
We are committed to delivering zero-defect nickel aluminium bronze fasteners, components and castings. All products undergo rigorous testing including PMI (Positive Material Identification), chemical analysis with aluminium, nickel, iron and manganese certified explicitly — and the iron-to-nickel comparison stated on the certificate, because on C63200 and C95800 a heat that meets every individual element range can still be non-conforming — heat-treatment certification to the specified cycle, mechanical and hardness verification against the condition and section supplied, microstructural examination for gamma-2 and kappa phase distribution, dimensional inspection and full traceability with EN 10204 3.1 certification.
Exotic Alloy exports nickel aluminium bronze rod, bar, extrusions, plate, tube, forgings, castings, fasteners and machined components to shipbuilding, naval, offshore, subsea, desalination, seawater pump and valve clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.