The main ore of aluminium is bauxite, which contains aluminium oxide Al ₂ O₃. The aluminium oxide is melted and used as the electrolyte for aluminium extraction. There are various alloys available to use in extrusion, from pure aluminium which is relatively soft, through to hardenable alloys. The most appropriate alloy needs to be chosen according to the end use of the profile and the finishing requirements.
By far the most widely used is the 6000 series which has magnesium and silicon as its alloying elements. This series can be aged (precipitation hardened) to temper. The ageing process is carried out in special ‘ovens’ over several hours at 180⁰C +/-5.
The following considerations need to be made:
1) Strength requirements
2) Surface finish
3) Suitability for decorative anodising
4) Corrosion resistance
The strongest alloy in the series is 6082 alloy, which has high tensile strength and impact toughness but is not normally suited to decorative anodising. This alloy may be used in road transport applications, or anywhere where supporting strength is needed.
6063 is the most common alloy, having both mid strength and good surface finish properties. This alloy is suitable for a wide range of end uses such as building, exhibition, a point of sale displays and signage, to name but a few.
For a higher tensile strength (but still retaining good surface finish properties), then 6005A would be a good choice. For applications requiring a highly decorative, mirror-like finish 6463 alloys may be considered. 6463 is a particularly good brightening alloy and may be used, for example, for shower screen applications.
The extrusion can be polished, chemically brightened and anodised silver/gold.
Did you know that most of the world’s bauxite comes from Australia? Other bauxite producers include China, Brazil and India.
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