Aluminium

Aluminium is a silvery white reactive metal which is usually covered in oxide. The oxide makes it inert to acids, but it is attacked by alkali. It is extracted from Bauxite by electrolysis of the oxide dissolved in molten sodium hexafluoroaluminate. The metal has good thermal properties and is malleable and ductile. During the 19th century aluminium was the most expensive metal and some jewellery was made from it.


Abundance

The most common metallic element in the earth’s crust at 82000 ppm.

Alloys

Aluminum containing specified quantities of alloying elements added to obtain the necessary mechanical and physical properties. There are a number of grades of aluminium designed for specific applications.

Bauxite

An ore of aluminum consisting of moderately pure hydrated alumina. Symbol Al2O32H2O

Bright Dip

For high-purity aluminium an acid/copper solution is used. The pieces are dipped in order to obtain a clean, bright surface. The reaction is entirely chemical with no external source of electrical current.

Discovered

The element was known in prehistoric times. In 1825 Hans Christian Oersted isolated impure aluminium. The pure metal was first isolated by Friedrich Wohler in 1827.

Grades

There are a number of different grades that have some significantly different properties and machining qualities. Aluminium also forms a number of different alloys.

Joining

Brazing – You can braze aluminium with zinc/aluminium alloys – one commercially available brazing rod is Durafix. Issue is this is more of a filler than a structural join.

TIG Welding – The best way to join aluminium parts structurally.

Machining

parting tool used to machine cooling fins in aluminium

Parting Aluminium on the lathe can be tricky, so some simple rules to make this easier.

Image shows a parting tool being used to machine deep cooling fins into the cylinder barrel of a small engine. Lightweight and thermal conductivity make this a perfect material selection.

Oxides

Alminium Oxide (Al2O3) – the most widely used oxide ceramic, either in pure form or as raw material to be mixed with other oxides.

Temper

The heat treatment and coding as applied to aluminium.

FAs fabricated
HStrain hardened by cold working with or without thermal treatment
H1XStrain hardened without cold working
H2XStrain hardened with partial annealed
H3XStrain hardened and stabilized with low temperature heating
HX2ź Hard
HX4˝ Hard
HX6ž Hard
HX8Full Hard
HX9Extra Hard
OAnnealed (Full Soft) or T0
T1Cooled from hot working and naturally aged (at room temperature)
T2Cooled from hot working, cold worked and naturally aged
T3Solution heat treated, cold worked and naturally aged
T4Solution heat treated and naturally aged
T5Cooled from hot working and artificially aged (at elevated temperatures)
T6Solution heat treated and artificially aged
T7Solution heat treated and stabilized
T8Solution heat treated, cold worked and artificially aged
T9Solution heat treated, artificially aged and cold worked
Aluminium Temper Codes

Use

The alloys are widely used for various applications including aircraft assemblies and engine parts.

bentley rotary engine

Pistons – W.O. Bentley experimented with aluminium pistons in 1913, he designed new alloys to add strength and to stop the aluminium from melting at high temperatures, finally settling on a formula of 88% aluminium and 12% copper.

The Bentley BR1 rotary engine designed by W. O. Bentley as an improvement on the Clerget 9C. It first ran as a prototype in 1916 and had aluminium cylinders, cast iron liners, aluminium pistons and dual ignition.

References

  1. Aluminium World – the aluminium industry aims to promote a wider understanding of its activities and demonstrate both its responsibility in producing the metal and the potential benefits to be realised through their use in sustainable applications and through recycling.

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