Aluminium Bronze
Fasteners
Manufacturer India
Aluminium Bronze — Why ≥760 MPa, Seawater, Non-Sparking, Non-Magnetic in One Alloy
Aluminium bronze (Cu-Al-Ni, Cu-Al-Ni-Fe) is the highest-strength copper alloy used as engineering fasteners — approximately twice the yield strength of silicon bronze C65500 (≥517 MPa UTS) and competitive with SS 316L in ultimate tensile strength, while maintaining all the marine corrosion resistance and non-sparking properties of the copper alloy family. The aluminium content (9–11%) forms a tenacious aluminium oxide (Al₂O₃) surface film that provides the corrosion protection — similar in principle to stainless steel’s Cr₂O₃ passive film but specifically resistant to seawater, alkaline solutions, and many acids where stainless steels fail.
The three unique engineering advantages that combine in no other readily available alloy: (1) High strength ≥760 MPa — sufficient for structural seawater applications where silicon bronze’s lower strength is inadequate, but without the extreme cost of Monel K500 (≥1000 MPa) or Inconel 625; (2) Seawater immune — the Al₂O₃ film is stable in seawater, chlorides, and many acids where SS 316L pits and 304 fails; (3) Non-sparking and non-magnetic — essential for use in explosive atmospheres (fuel tanks, munitions handling, oil platform areas) and MRI/magnetic field environments where ferromagnetic fasteners are prohibited.
Aluminium bronze is the standard fastener material for marine propulsion systems (propeller shaft bolting, rudder bearing bolts, propeller blade studs), subsea and offshore structural connections where both strength and seawater resistance must be maintained simultaneously, naval vessel weapons and propulsion hardware where non-magnetic properties are mandatory, and oil and gas platform firewater systems where the fastener must be non-sparking and seawater-resistant in the same application.
C63000 · C63200 · C95400 — Wrought and Cast Grade Profiles
C63000 is the primary wrought grade for machined fasteners. C63200 adds more Fe for enhanced seawater performance. C95400 is the cast-alloy equivalent for large cast nuts and flanged components. All three available from Akbar Fasteners.
C63000
C63200
C95400
Why Aluminium Bronze — Four Simultaneous Requirements
≥760 MPa — Highest Strength Copper Alloy
C63000 delivers ≥760 MPa UTS — approximately twice silicon bronze (≥517 MPa) and comparable to SS 316L (≥485 MPa) and SS 304 (≥515 MPa). For marine structural bolts in propeller shaft connections, rudder systems, and subsea structural connections where silicon bronze’s strength is inadequate, aluminium bronze provides the strength margin without leaving the copper alloy family’s corrosion and non-magnetic characteristics. Only Monel K500 (≥1000 MPa) exceeds it in the marine non-ferrous category, at significantly higher cost.
Seawater Immune — Al₂O₃ Passive Film
The 9–11% aluminium forms a tenacious aluminium oxide (Al₂O₃) passive film — chemically similar in protection mechanism to stainless steel’s chromia film but stable in seawater, chloride-containing environments, and many acids where austenitic stainless steels suffer pitting and crevice corrosion. The additional nickel and iron in C63000 and C63200 promote a more stable and adherent protective film, and provide partial biofouling resistance through Cu²⁺ ion release from the copper matrix. For continuous seawater immersion, aluminium bronze outlasts SS 316L in stagnant and low-flow seawater conditions where chloride pitting initiates.
Non-Sparking — ATEX and Hazardous Areas
Aluminium bronze generates no ignition sparks when struck — making it the correct specification for oil platform drilling deck fasteners, fuel tank covers, munitions handling equipment, grain elevator structural bolts, and all ATEX Zone 0/Zone 1 applications where a single spark from a ferrous fastener could cause a catastrophic ignition event. Unlike stainless steel, which can generate sparks under impact, copper alloys are classified as inherently non-sparking materials and are the standard specification for explosion-risk environments where both non-sparking and structural strength must be met simultaneously.
Non-Magnetic — Naval and MRI
Aluminium bronze is fully non-magnetic — essential for naval vessel applications where the ship’s magnetic signature must be minimised for mine avoidance and magnetic anomaly detection (MAD). Propulsion bolts, shaft couplings, and structural fasteners on naval vessels are specified as non-magnetic to avoid distorting the vessel’s magnetic field. MRI installation hardware, scientific instrument foundations, and all applications where the magnetic permeability of ferrous fasteners would interfere with measurement or detection systems also benefit from aluminium bronze’s non-magnetic property combined with its high structural strength.
Aluminium Bronze Fastener Types & Standards
C63000 is the primary stocking grade — the standard for machined aluminium bronze fasteners. C63200 for enhanced seawater applications. M4–M48 range with larger sizes on request for offshore structural bolting.
Stud Bolts
Fully threaded and equal-end stud bolts in C63000 and C63200 for marine pipeline flanges, propulsion system flanges, and offshore structural flanged connections. M8–M48, lengths to 600mm. Non-sparking, non-magnetic, seawater-resistant. Chemical analysis per ASTM B150 dispatched as standard. Used in ASME B16.5 flanges on seawater systems where both non-sparking and strength are required.
Hex Bolts
Full thread and partial thread hex bolts in C63000 and C63200. M4–M48. Marine propeller blade hex bolts, propeller shaft coupling hex bolts, rudder stock hex bolts, FPSO mooring equipment, offshore structural hex bolts, ATEX-rated equipment hex bolts (non-sparking), and naval vessel propulsion structural hex bolts where non-magnetic certification is required.
Hex Nuts
Standard hex and heavy hex nuts in C63000 and C63200. M4–M48. Matched from same ASTM B150 certified bar as stud bolts and hex bolts for single-alloy assembly. For marine propulsion and offshore structural assemblies where the nut thread interface must maintain the same corrosion immunity, non-sparking, and non-magnetic properties as the stud bolt.
Washers
Plain flat washers in C63000 aluminium bronze. M4–M48. For complete matched-alloy aluminium bronze fastener assemblies — stud bolt, nut, and washer from same ASTM B150 certified bar. The nut bearing face washer interface is the most common crevice corrosion site in seawater flange connections; matched-alloy aluminium bronze washers eliminate bimetallic corrosion at this interface.
Socket Cap Screws
Hex socket cap screws in C63000. M4–M24. Marine instrument housing screws, oil platform confined-access non-sparking screws, naval vessel interior structural screws requiring non-magnetic certification, and all applications where a high-strength (≥760 MPa), non-sparking, non-magnetic socket head fastener is required in a corrosive or hazardous marine environment.
Custom Al-Bronze
Non-standard dimensions, tapered shanks, special thread forms, and drawing-specific configurations in C63000 and C63200. For propulsion OEM-specific fastener profiles, marine machinery custom bolts, and defence/naval drawing-specific fastener configurations requiring non-magnetic certification documentation. Contact sales@akbarfasteners.in with application, drawing, and certificate requirement.
Aluminium Bronze vs Other Marine Fastener Alloys
Aluminium bronze occupies the strength and corrosion resistance zone between silicon bronze and Monel K500. This matrix identifies when C63000 is the correct and cost-effective choice for marine and offshore applications.
| Criterion | Al-Bronze C63000 This Page | Silicon Bronze C65500 | Monel K500 | SS 316L |
|---|---|---|---|---|
| MECHANICAL STRENGTH | ||||
| Min UTS | ≥760 MPa | ≥517 MPa | ≥1000 MPa | ≥485 MPa |
| Min Yield Strength | ≥410 MPa | ≥207 MPa | ≥690 MPa | ≥170 MPa |
| Density | 7.6–7.8 g/cm³ | 8.52 g/cm³ | 8.44 g/cm³ | 7.99 g/cm³ |
| MARINE / SEAWATER SERVICE | ||||
| Seawater immunity | ✔ Excellent | ✔ Excellent | ✔ Excellent | Pitting risk |
| Biofouling resistance | Good (Cu²⁺) | Good (Cu²⁺) | None | None |
| Below-waterline structural | ✔ High-load | Moderate load only | ✔ Very high load | Pitting risk |
| SPECIAL PROPERTIES | ||||
| Non-sparking (ATEX) | ✔ Yes | ✔ Yes | ✔ Yes | Can spark |
| Non-magnetic | ✔ Yes | ✔ Yes | ✔ Yes | ✔ Yes |
| COST POSITION | ||||
| Relative cost vs 316L | 2.5–4× 316L | 1.8–2.5× | 7–10× | Baseline 1× |
For extreme-strength seawater: Monel K500 (≥1000 MPa) · For below-waterline boat hull: Silicon Bronze C65500
Aluminium Bronze Application Areas
Marine propulsion, offshore structural, naval vessels, ATEX hazardous areas, subsea infrastructure, and MRI/non-magnetic installations — wherever high strength plus non-sparking plus non-magnetic plus seawater resistance must all be met simultaneously.
Marine Propulsion
rudder stock studs
Offshore / FPSO
seawater structural bolts
Naval Vessels
mine-safe propulsion hardware
ATEX Hazardous Areas
fuel tank cover fasteners
Pumps & Valves
valve stem connections
Subsea
ROV-operated connections
MRI & Medical
MRI room structural bolts
Desalination / Water
seawater intake structural
Aluminium Bronze Standards Coverage
Same ISO 9001:2015 quality system as our full copper alloy and exotic alloy ranges. PMI confirms Al%, Ni%, and Fe% — the three critical elements distinguishing C63000 from lower-grade aluminium bronzes.
Complete Documentation Package
ASTM B150 Traceable
Conformance
C63000 Confirmed
Tensile · Hardness
Lloyd’s · DNV · BV
Related Marine Fastener Alloys
Al-Bronze for ≥760 MPa strength + seawater + non-sparking. Monel K500 for ≥1000 MPa extreme strength. Silicon bronze for lower-load below-waterline. Cu-Ni 90/10 for Cu-Ni piping system compatibility.
Monel K500 Fasteners
When aluminium bronze’s ≥760 MPa is insufficient — Monel K500 (age-hardened, ≥1000 MPa UTS) provides the highest-strength seawater fastener in commercial engineering. For extreme-load propeller shaft bolts, subsea wellhead structural, and high-pressure seawater injection where Al-Bronze strength margin is borderline.
View K500 →Silicon Bronze C65500
When Al-Bronze strength (≥760 MPa) exceeds what the application requires and cost reduction is the priority — silicon bronze C65500 (≥517 MPa, ~40% lower cost per kg than C63000) is the correct lower-strength copper alloy for boat hull bolting, keel connection, and moderate-load marine structural connections below the waterline.
View Si-Bronze →Cu-Ni 90/10 Fasteners
For seawater piping systems where galvanic compatibility with Cu-Ni piping and tubing is required — Cu-Ni 90/10 provides system alloy matching, biofouling resistance, and seawater immunity at lower strength (≥276 MPa) than aluminium bronze. For Cu-Ni heat exchanger and pipeline flange bolts, not structural high-load applications.
View Cu-Ni →Super Duplex 2507
When stainless steel is mandatory rather than copper alloy — Super Duplex 2507 (PRE≈43) provides the highest seawater pitting resistance of any standard stainless steel with higher strength than Al-Bronze (≥795 MPa UTS). For stainless-specified offshore structural seawater applications where magnetic properties are acceptable.
View SS Range →Need Aluminium
Bronze Fasteners?
Grade (C63000 / C63200) · product form · size · classification society · documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
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