Aluminium Design and Construction John Dwight

Figure 4.11 Minimum stress-strain curves for a selection of aluminium materials, based on
a thickness of 6 mm, generally for flat material. The 6063 curve is for 6 mm thick extruded
profile.
(low n). Much of aluminium construction is in materials that are either
fully heat-treated, or else in a heavily work-hardened condition. These
typically have a low ultimate/proof ratio (below 1.2) and hence a stressstrain
curve with a fairly abrupt knee. A higher value for f u /f o ,
corresponding to a more rounded curve, would be exhibited by material
in the T4 or annealed condition.
Figure 4.11 gives curves constructed by the above method for a selection
of aluminium materials.
Mazzolani discusses the use of more precise mathematical expressions
for representing the stress-strain relation [26].
4.5 CASTING ALLOYS
Compared to forgings, castings are generally less ductile and weaker,
although tensile strengths up to 300 N/mm2 are possible. They are cheaper
than forgings. The design of aluminium castings is beyond the scope of
this book, but below we give some limited data on certain alloys.
4.5.1 Numbering system
The unified system for specifying cast material, now adopted in Europe,
is described in BSEN.1706. For a given material it uses a two-part reference,
such as AC.51400-F or AC.42000-T6, in which the first part refers to the
alloy, and the second part to the condition. In Britain, the new European
alloy numbers for castings supersede the old ‘LM’ system, although the
actual compositions are broadly the same.
Copyright 1999 by Taylor & Francis Group. All Rights Reserved.