Specification :  Designation of Aluminium

Aluminium is most commonly alloyed with copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. Following Table describes the system for wrought alloys. Cast alloys have similar designations and use a five digit system.

For unalloyed wrought aluminium alloys designated 1XXX, the last two digits represent the purity of the metal. They are the equivalent to the last two digits after the decimal point when aluminium purity is expressed to the nearest 0.01 percent. The second digit indicates modifications in impurity limits. If the second digit is zero, it indicates unalloyed aluminim having natural impurity limits and 1 through 9, indicate individual impurities or alloying elements. For the 2XXX to 8XXX groups, the last two digits identify different aluminium alloys in the group. The second digit indicates alloy modifications. A second digit of zero indicates the original alloy and integers 1 to 9 indicate consecutive alloy modifications.

Heat Treatment

A range of heat treatments can be applied to aluminium alloys.

·  Homogenisation – the removal of segregation by heating after casting.

·  Annealing – used after cold working to soften work-hardening alloys (1XXX, 3XXX and 5XXX).

·  Precipitation or age hardening (alloys 2XXX, 6XXX and 7XXX).

·  Solution heat treatment before ageing of precipitation hardening alloys.

·  After heat treatment a suffix is added to the designation numbers.

        The suffix F means “as fabricated”.

         O means “annealed wrought products”.

         T means that it has been “heat treated”.

         W means the material has been solution heat treated.

         H refers to non heat treatable alloys that are “cold worked” or “strain hardened”.

           The non-heat treatable alloys are those in the 3XXX, 4XXX and 5XXX groups.

Work Hardening

The non-heat treatable alloys can have their properties adjusted by cold working. Cold rolling is a typical example.

These adjusted properties depend upon the degree of cold work and whether working is followed by any annealing or stabilising thermal treatment.

Nomenclature to describe these treatments uses a letter, O, F or H followed by one or more numbers. As outlined in Table 3, the first number refers to the worked condition and the second number the degree of tempering.

Temper codes for plate