Aluminium bronze is a type of bronze in which aluminium is the main alloying metal added to copper, in contrast to standard bronze (copper and tin) or brass (copper and zinc). A variety of aluminium bronzes of differing compositions have found industrial use, with most ranging from 5% to 11% aluminium by weight, the remaining mass being copper; other alloying agents such as iron, nickel, manganese, and silicon are also sometimes added to aluminium bronzes.
The following table lists the most common standard aluminium bronze wrought alloy compositions, by ISO 428 designations. The percentages show the proportional composition of the alloy by weight. Copper is the remainder by weight and is not listed:
|CuAl5||4.0–6.5%||0.5% max.||0.8% max.||0.5% max.||0.5% max.||0.4% max.|
|CuAl8||7.0–9.0%||0.5% max.||0.8% max.||0.5% max.||0.5% max.|
|CuAl8Fe3||6.5–8.5%||1.5–3.5%||1.0% max.||0.8% max.||0.5% max.|
|CuAl9Mn2||8.0–10.0%||1.5% max.||0.8% max.||1.5–3.0%||0.5% max.|
|CuAl10Fe3||8.5–11.0%||2.0–4.0%||1.0% max.||2.0% max.||0.5% max.|
|CuAl10Fe5Ni5||8.5–11.5%||2.0–6.0%||4.0–6.0%||2.0% max.||0.5% max.|
Aluminium bronzes are most valued for their higher strength and corrosion resistance as compared to other bronze alloys. These alloys are tarnish-resistant and show low rates of corrosion in atmospheric conditions, low oxidation rates at high temperatures, and low reactivity with sulfurous compounds and other exhaust products of combustion. They are also resistant to corrosion in sea water. Aluminium bronzes' resistance to corrosion results from the aluminium in the alloys, which reacts with atmospheric oxygen to form a thin, tough surface layer of alumina (aluminium oxide) which acts as a barrier to corrosion of the copper-rich alloy. The addition of tin can improve corrosion resistance.
Another notable property of aluminium bronzes are their biostatic effects. The copper component of the alloy prevents colonization by marine organisms including algae, lichens, barnacles, and mussels, and therefore can be preferable to stainless steel or other non-cupric alloys in applications where such colonization would be unwanted.
Aluminium bronzes tend to have a golden color.
Aluminium bronzes are most commonly used in applications where their resistance to corrosion makes them preferable to other engineering materials. These applications include plain bearings and landing gear components on aircraft, guitar strings, valve components, engine components (especially for seagoing ships), underwater fastenings in naval architecture, and ship propellers. Aluminium bronze is also used to fulfil the ATEX directive for Zones 1, 2, 21, and 22. The attractive gold-toned coloration of aluminium bronzes has also led to their use in jewellery.
Aluminium bronzes are in the highest demand from the following industries and areas:
Aluminium bronze is used to replace gold for the casting of dental crowns. The alloys used are chemically inert and have the appearance of gold.
Alloys similar to aluminium bronze are used in making coins, for example the 20, 200 and 500 Italian Lire, 10 Philippine peso coin on the inner ring, the one and two dollar coins of Australian and New Zealand currency produced by the Royal Australian Mint, some Mexican coins and the Nordic gold used for some euro coins. The Canadian 2 dollar coin, produced by the Royal Canadian Mint and circulated since 1996, is a bi-metallic piece with an outer ring of nickel-plated steel and an inner circle of Aluminium bronze composed of 92% copper, 6% Aluminium, and 2% nickel (also known as Bronzital).