Aluminium, in its usable form, is a relatively new metal that is
produced using an electrolytic process. In its pure form it has only a
few limited uses, however, when it is alloyed it becomes an extremely
versatile and widely used material. Industrial sectors such as aviation,
medical, scientific and electronics all make use of the key properties
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
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
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
O the product is annealed, soft.
T4 solution heat treated and naturally aged to a substantially stable
T5 cooled from elevated temperature shaping process and artificially
H12 strain hardened to ¼ hard.
H14 strain hardened to ½ hard.
H16 strain hardened to ¾ hard.
H18 hard condition.