Nickel Aluminium Bronze Alloy

Bronze alloys of copper and aluminium are known as aluminium bronze and, with the addition of other alloying elements, provide a range of properties that benefit several industries. The group of Nickel–Aluminium Bronze Alloys is the most frequently used. They have been adjusted over time to optimise performance and can offer a combination of characteristics that presents a cost-effective alternative to other alloy systems. Final applications include landing gear bushings and bearings for all commercial aircraft globally, sea water pumps and valves, marine and merchant ship propellers, spark-free tools in the oil and gas sector and cladding in architecture.

Nickel–Aluminium Bronzes are available in both cast and wrought forms and exhibit a combination of properties, including:

- Demonstrated wear and abrasion resistance
- High strength with a density approximately 10% lower than steel
- Non-sparking behaviour
- Low magnetic permeability (<1,03 µ for selected types)
- High corrosion resistance
- Adequate stress corrosion properties
- Acceptable low temperature performance
- High resistance against cavitation
- Damping capacity double that of steel
- High resistance to biofouling
- A protective oxide layer on the surface that is capable of self-repair.

Specifications for Nickel–Aluminium Bronze Alloys

In general, Nickel–Aluminium Bronzes can be categorised into alloys containing 6–13% aluminium and up to 7% iron and 7% nickel. The most common alloys typically contain 3–6% of these two elements. Manganese is added up to approximately 1.5% as a deoxidiser and strengthening element.

Applications for Nickel–Aluminium Bronze Alloys

Aerospace

The primary application for nickel–aluminium bronze in aerospace is found in landing gear bearings for the global fleet of commercial aircraft. The alloys are selected for their bearing performance relative to steel, their corrosion resistance during saline de-icing operations on runways in winter and their mechanical properties. Relevant specifications include AMS 4640, AMS 4880, AMS 4881, AMS 4590, BS2 B 23, NFL14-702, NFL14-705 and NFL14-706. In addition, aircraft manufacturers and major suppliers have their own specifications, for example, Airbus ASN-A 3406, ASN-A 3315, ASN-A6127A and Rolls Royce MSR 8503.

Architecture

Aluminium bronzes are employed in a range of architectural applications. Their ability to form a protective oxide layer in oxygen-rich environments permits their use in both inland and marine atmospheres. Nickel–aluminium bronze produces a golden oxide and offers additional advantages based on its measured properties. The Parliament building in London, Portcullis House, incorporates 450 tonnes of nickel–aluminium bronze in the window frames, cladding and roof (artificially darkened). The structure has a design life of 120 years and is engineered to withstand bomb impacts.

Maritime

A considerable market exists for nickel–aluminium bronze in maritime applications, particularly for submarine fleets. Key applications include sea water piping and valve systems, armament handling equipment, flexible couplings, sonar devices, sea water external hatches, hydraulic valves and bearings, fasteners and sealing flanges, low-noise propellers, drive systems and periscope assemblies. In these applications, the alloys are used for their corrosion resistance, non-sparking properties, wear resistance, high strength and notch impact performance. They also demonstrate a damping capacity double that of steel, which is important for silent operation in submarines. For armament handling systems, non-sparking and wear resistance characteristics are essential. Certain variants, with reduced iron and nickel contents, achieve a magnetic permeability of less than 1,03 µ.

Nickel–aluminium bronze is one of the principal alloys used for ship propellers on merchant and cruise ships. Its high cavitation resistance, together with its cost advantages and ease of repair following damage, renders it a preferred material for this application. Hub components for controllable pitch propellers are also manufactured from nickel–aluminium bronze. The alloy exhibits anti-galling characteristics when in contact with itself, which is important for the rotation of propeller blades in cylindrical openings. It is further used in winch gearboxes on offshore yachts, where deposit protection, high strength and corrosion resistance against salt mist are required.

Offshore Oil/Gas and Petrochemicals

In the offshore oil and gas industry, nickel–aluminium bronze is used in a variety of applications. The alloy is employed in piping, valves and pumps within sea water pump systems, particularly in fire-fighting installations. It is compatible with copper–nickel piping systems and is used for associated pumps and valves. It is also applied in sea water pump systems to re-inject water into wells.

Actuator valves represent an important application in both onshore pipelines and subsea oil transport. In onshore contexts, pipelines may be located in remote or inhospitable areas. Actuator valves are critical for pipeline safety and for preventing oil leaks into the environment. The valves must operate under extreme temperature conditions, ranging from −50°C in very cold conditions (for example, in Arctic regions) to +50°C during high summer temperatures in desert regions of the Near East. They are required to resist sand ingress and must function after extended periods of inactivity. Consequently, many designs employ nickel–aluminium bronze because of its corrosion resistance and bearing properties. The alloy forms the main component that seals the valves within the piping system. In offshore applications, actuator valves are installed on drilling platforms where access is limited and activation must occur via radio signals.

Desalination and Water Condenser Systems

This sector is an important market for nickel–aluminium bronze. The alloy is used in pumps, valves, water boxes, impellers, condenser tube plates and housings. It is suitable for use at elevated temperatures up to approximately 325°C in high-pressure condenser systems. The material may be used for pumping sea water at a recommended speed of 4.3 m/sec, which exceeds the limits tolerated by 90–10 and 70–30 copper–nickel alloys. Although aluminium bronzes do not resist biofouling to the same degree as copper–nickel alloys, they still offer significant resistance to marine growth.