Aluminium

The basics
In its pure form, the metal is easily worked and possesses a high level of corrosion resistance, but its low strength reduces the number of applications for which it is suitable. When alloyed, however, aluminium becomes an extremely versatile and widely used material.

The alloying elements used are dependant on the finished article required. Additions of copper, iron, zinc, nickel, tin, lead, magnesium and silicon are all used to improve its attributes. Improved strength, corrosion resistance, ductility, workability, weldability and machinability are all possible.

As with all “pure” metals, the unalloyed product still contains some impurities, and the “commercially pure” product is normally in the region of 99.00% pure. In this form it is produced widely in rolled sheet for a variety of uses. In strip and foil forms it is also has variety of uses including food wrapping and roofing. In bar form it is often used as bus-bar for electrical purposes as its conductivity in this pure state is high.

Types of alloys
There are two main types of alloyed aluminium; wrought and cast. Wrought alloys (rolled, extruded or forged) are strengthened either by work–hardening or by heat treatment, with different alloying elements being added to achieve the required strength. Cast alloys are usually very different in their composition to their wrought counterparts, as suitable composition is required for the production of effective casting materials.

The wrought alloys are also divided into two groups: heat-treatable and non heat-treatable alloys. Heat-treatable alloys are produced in the main for their strength and durability while the non heat-treatable alloys for their ductility, weldability and corrosion resistance.

Alloy Specifications
All alloys are given a specification number and a combination of letters and numbers that are placed after this specification number to indicate the strengthening process undergone by the metal. For example, the alloy specification 6082 often carries the definition T6 – this indicates that it is solution treated and artificially aged (also known as “fully heat treated”), while alloy 2011 often carries the T3 definition, indicating it has been solution heat treated, cold worked and naturally aged to a substantially stable condition.

Other common designations are:
F as manufactured, with no heat treatment and without regard to work hardening.
O the product is annealed, soft.
T4 solution heat treated and naturally aged to a substantially stable condition.
T5 cooled from elevated temperature shaping process and artificially aged.
H12 strain hardened to ¼ hard.
H14 strain hardened to ½ hard.
H16 strain hardened to ¾ hard.
H18 hard condition.

Alloy selection