Aluminium Design and Construction John Dwight

will be only slightly above that for O. With plate, it is often considerably
higher, but not reliably so.
Often material ostensibly in the O condition gets very slightly cold
worked after annealing, as might occur in a straightening or flattening
operation. Such material is officially referred to as being in the H111,
rather than the O condition. However, the quoted properties are not
usually any different, and the use of the designation O for all such
material is unlikely to cause confusion.
4.1.5 Relation between temper and tensile strength
For work-hardened sheet material, there is a fairly consistent relation
between temper designation (H-number) and minimum tensile strength
(fu ), as laid down in BSEN.515.
The fully-hard temper (H18, H28 or H38), referred to as Hx8, is
described as the ‘hardest temper normally produced’, and for any given
alloy it is defined in terms of a specific amount by which fu exceeds the
value fuo for the same alloy in the annealed (O) condition. The intermediate
tempers are then defined by taking equal steps in fu between the two
extreme conditions (O and Hx8). The resulting value for fu is effectively
given by the following expression (plotted in Figure 4.1):
f u =Pf uo +Q (4.1)
in which the coefficients P and Q are a function of the temper (Table 4.3).
This expression is based on the BSEN.515 rules and is valid for any
composition having an annealed tensile strength greater than about 90 N/
mm 2 (i.e. excluding pure aluminium). In practice the actual material standard
Figure 4.1 Relation between temper and minimum tensile strength (f u ) for work-hardened
materials. f uo =minimum tensile strength in the O condition.
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