Nickel Aluminium Bronze ?

While aluminium bronze (without the nickel) is used, the most popular alloy, certainly for valve applications is the duplex alloy of around 8% - 11% of aluminium with the addition of iron and nickel to give higher strength and correctly known as nickel-aluminium bronze. Unfortunately, this is often and confusingly abbreviated to aluminium bronze. In order to simplify matters, only NAB will be considered here. Alloys are available in both cast and wrought form. A summary of the main cast alloys is:

American ASTM B148 UNS C95800

Nominal Cu bal 9Al 4.5Ni 4Fe 1.2Mn

    UNS C95500 Nominal Cu bal 11Al 4Ni 4Fe
European EN 1982 CC333G Nominal Cu bal 10Al 5Ni 5Fe

Mention must also be made of the still popular (although the standard is obsolete) BS1400 AB2 and the British Navy specification DEF STAN 02-747 and the equivalent wrought specification DEF STAN 02-833. These alloys are all similar with detail differences hinging on the introduction of manganese and the balance between iron and nickel.

NAB alloys are considered as high strength. As engineers know, high strength is not everything and ductility is a significant factor. In this instance the trade-off is between C95500 with 6% elongation and a minimum tensile strength of 620 MPa and C95800 with 15% and 585 MPa respectively

An overview of general properties of the material is that it is weldable, castable and has an outstanding corrosion resistance due to a tough oxide film. Shock and wear resistance is also excellent (variants of the material can be used as bearings) and it is also non-sparking and has a low relative magnetic permeability (for near-zero relative magnetic permeability combined with excellent corrosion properties, aluminium-silicon bronze can be used). The conductivity, both electrical and thermal, is also very good. Additionally NAB retains its strength and ductility at low temperatures and is suitable for cryogenic service

Considering properties in isolation is all very well, but it is only when comparisons with “rival” materials are made that performance can be properly evaluated. The mechanical and corrosion properties will therefore be discussed comparatively in the next sections.

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