Page 46 - Welding of Aluminium and its Alloys

38 The welding of aluminium and its alloys

Master alloys, which will not concern the shop-floor welding engineer,
are identified with the prefix ‘AM’ followed by the number ‘9’, the second
and third figures are the atomic number of the main alloying element,
e.g. 14 for silicon, 29 for copper, the last two digits being chronological
and issued in the order of registration of the alloy. For example, an
aluminium–silicon master alloy could carry the designation AM 91404,
identifying the alloy as being the fourth Al-Si alloy to be registered.

3.3.2 Temper designations

The mechanical properties of the alloys are affected not only by their
chemical composition but also by their condition, e.g. annealed, cold
worked, precipitation hardened. It is obviously important that this condi-
tion is clearly and unequivocally identified for both the designer and the
welding engineer. To do this CEN has developed a system of suffixes that
identify the amount of strain hardening the alloy has undergone or its heat
treatment condition. There are five basic designations identified by a single
letter which may be followed by one or more numbers to identify the
precise condition.
The basic designations are as follows:
• F – as fabricated. This applies to wrought products where there is no
control of the amount of strain hardening or the thermal treatments.
There are no mechanical properties specified for this condition.
• O – annealed. This is for products that are annealed to produce the
lowest strength. There may be a suffix to indicate the specific heat
treatment.
• H – strain hardened (cold worked). The letter ‘H’ is always followed by
at least two digits to identify the amount of cold work and any heat
treatments that have been carried out to achieve the required mechani-
cal properties.
• W – solution heat treated. This is applied to alloys which precipitation
harden at room temperature (natural ageing) after a solution heat treat-
ment. It is followed by a time indicating the natural ageing period, e.g.
W 1h.
• T – thermally treated.This identifies the alloys that are aged to produce
a stable condition. The ‘T’ is always followed by one or more numbers
to identify the specific heat treatment.

The first digit after ‘H’ identifies the basic condition:
• H1 – strain hardened only.
• H2 – strain hardened and partially annealed. This applies to the alloys
that are hardened more than is required and that are then annealed at