Monday, 25 May 2020 09:09

Technical Profile: Aluminium Bronze

Singapore 5 cent coin
Singapore, Aluminium
bronze 5 cent coin

The Bronze Age is the archaeological period, between the 4th and the 2nd millennium BC, in which bronze was the hardest metal in widespread use. The discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible.

Bronze is an alloy of copper with other metals, such as tin, lead, aluminium, manganese, nickel or zinc, making it harder than copper alone and imparting other useful properties such as stiffness, ductility, or machinability.

Aluminium bronzes have found industrial use where the corrosion resistance is particularly important, with most alloys ranging from 5% to 11% aluminium content. These applications include valves, pumps, engine components for ships, underwater fastenings in naval architecture and ship propellers.

The peculiar corrosion resistance of Aluminium bronzes comes from the aluminium in the alloys, which reacts with atmospheric oxygen to form a thin and tough surface layer of aluminium oxide. The aluminium oxide acts as a barrier to corrosion and can heal rapidly if damaged.

Aluminium bronze alloys have good resistance to erosion and wear, as well as good corrosion fatigue properties.

Major constituents of seawater
Source: NASA Aquarius

Marine environments are highly corrosive since they contain high concentration of salts (mainly sodium chloride), dissolved oxygen and carbon dioxide. Seawater can vary significantly in its corrosivity, which can vary widely due to location, temperature and biological activity.

The alloy performance may be seriously affected when the seawater is under stagnant or polluted conditions, where corrosive species such as ammonia, sulphide compounds and/or sulphate reducing bacteria (SRB) are generated.

Level of resistance graph
Source: Oldfield and Masters, 1996

Aluminium-bronze alloys are a cost-effective solution in marine environments when compared with conventional austenitic stainless steels such as CF8M. Aluminium-bronze alloys resist marine fouling, show limited pitting corrosion in stagnant water and offer good cavitation and erosion protection when the flow rates are limited to 18 m/s.

Zetco Valves has an extensive range of valves in a variety of configurations, produced by ISO 9001 certified manufacturers. Aluminium bronze is also available, upon request, for marine, mining and heavy industrial applications.

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