Aluminium bronze

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Aluminium bronze with 20% Aluminium, V=50:1
Aluminium bronze with 20% Aluminium, V=50:1

Aluminium bronze is a type of bronze in which aluminium is the main alloying metal added to copper. 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.

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[edit] Compositions

Following is a list of common standard aluminium bronze wrought alloy compositions, by ISO 428 designations (proportional composition by weight; copper is the remainder by weight and is not listed):

Alloy Aluminium Iron Nickel Manganese Zinc Arsenic
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
CuAl10Fe5Ni15 8.5% - 11.5% 2.0% - 6.0% 4.0% - 6.0% 2.0% max 0.5% max

[edit] Material properties

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 rests in the aluminium component of 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.

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.

[edit] Applications

Aluminium bronzes are most commonly used in applications where their resistance to corrosion makes them preferable to other engineering materials. These applications include bearing brushes and landing gear components on aircraft, engine components (especially for sea-going ships), underwater fastenings in naval architecture, and ship propellers. The attractive gold-toned coloration of aluminium bronzes has also led to their use in jewelry.

Aluminium bronzes are in the highest demand from the following industries and areas:

Aluminium bronze can be welded using the MIG welding technique with an aluminium bronze core and pure argon gas.

Alloys similar to Aluminium bronze are used in making coins, for example the $1 and $2 Australian coins produced by the Royal Australian Mint and the Nordic gold used for some Euro coins.

[edit] References