Aluminium Design and Construction John Dwight

Where a range is given, as for the first three elements, this denotes the
minimum and maximum permitted content of an intended ingredient.
Where a single figure is given (as for the last four) this refers to an
impurity, which must not exceed the value quoted. This is the official
way of specifying such an alloy. In everyday parlance, it is more convenient
to talk in terms of the nominal composition, quoting the mean percentages
of the intended elements only. The above 6082 alloy would be described
as containing a nominal:
Si 1.0 Mn 0.7 Mg 0.9%
Aluminium alloys are grouped into seven alloy series, depending on their
main alloying ingredient(s) (Table 4.1). The first digit of an alloy number
indicates the series to which that alloy belongs, while the other three usually
have no particular significance. An alloy series may be referred to collectively
by putting xxx after the first digit, i.e. the ‘5xxx series’.
Sometimes a slightly modified version of an existing alloy is registered,
in which case an ‘A’ may be added to distinguish it from the original
(e.g. 5154 and 5154A).
The AA also carry an 8xxx series, used for compositions that do not easily
fit into any of the first seven. One such type of alloy, containing a substantial
amount of lithium, has raised interest in the aircraft industry because of its
significantly lower density compared to other aluminium alloys.
4.1.3 Work hardening
Non-heat-treatable alloys are strengthened by means of cold work applied
during manufacture, as in the cold reduction of sheet or drawn tube.
The reduction per pass, and any heating, are controlled to produce the
required combination of strength and ductility. For a given degree of
cold work, the resulting increase in the proof stress (yield) is relatively
much greater than the increase in tensile strength (UTS), as compared
with the annealed condition.
The condition (or temper) of work-hardened sheet and drawn tube can
be crudely expressed in terms of its hardness, the standard tempers being
Table 4.1 The seven alloy series
Note. NHT=non-heat-treatable, HT=heat-treatable
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