Aluminium Design and Construction John Dwight

4.2.1 Non-heat-treatable alloys
(a) 1xxx-series alloys
The materials in this series comprise commercially pure aluminium in
a range of purities. The third and fourth digits in the reference number
define the purity, by indicating the minimum percentage of aluminium
over and above 99.00. Thus ‘1050’ refers to a material having a purity
of at least 99.50%. Possible purities range from 99.00 to 99.99%.
Pure aluminium is weak, with a maximum possible tensile strength
of about 150 N/mm 2 . It is selected when corrosion resistance is critical,
as in chemical plant. The higher the purity the better the corrosion
resistance, but the lower the strength. In the O or F condition, pure
aluminium is relatively soft, and is used when high formability is needed.
The most ductile version is ‘super-purity’ (99.99% pure aluminium),
which is produced from lower purity metal by a further ‘zone-refining’
process.
(b) 3xxx-series alloys
The relatively low manganese content of these alloys, sometimes with
added magnesium, makes them half as strong again as pure aluminium,
while retaining a very high resistance to corrosion. Tensile strengths go
up to 200 N/mm2 or more. In construction, the main application (in the
fully-hard temper) is for profiled sheeting, as used in the cladding of
buildings and other structures. 3xxx-series strip is also employed for
making welded tube (irrigation pipe, for example).
(c) 4xxx-series alloys
These Al-Si alloys are omitted from Table 4.4 because they seldom appear
in the form of actual members. Their usage is for castings (Section 4.5),
and weld filler wire (Section 4.6.2). At one time architectural extrusions
were occasionally produced in material of this type, because of the
attractive dark finish that can be produced on it by natural anodizing.
(d) 5xxx-series alloys
These represent the major structural use of the non-heat-treatable alloys.
The magnesium content varies from 1 to 5%, often with manganese
added, providing a range of different strengths and ductilities to suit
different applications. Corrosion resistance is usually excellent, although
it is possible for the stronger versions to suffer abnormal forms of corrosion
when operating in hot environments.
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