Page 43 - Welding of Aluminium and its Alloys

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Material standards, designations and alloys

3.1 Designation criteria
Aluminium alloys may be divided into two broad classes, cast and wrought
products.These two classes can be further subdivided into families of alloys
based on chemical composition and finally on temper designation. Temper
designations are used to identify the condition of the alloy, in other words
the amount of cold work the alloy has undergone or its heat treatment con-
dition. There are a number of schemes available for identification of the
alloy and its condition. In this book the numeric method adopted by the
European Committee for Standardisation (CEN) will be used as standard.
This system uses four digits to identify the wrought alloys and five digits
to identify the cast alloys, and is broadly the same as the ISO and US nu-
merical methods of identification where a four digit number identifies the
unique alloy composition. This is in agreement with the recommendation
made in the early 1970s for an International Designation System issued by
the Aluminum Association in the USA. The chemical composition limits
specified in the CEN specifications are identical with those registered with
the Aluminum Association for the equivalent alloys. This should simplify
the sourcing of alloys and remove the confusion that can surround the iden-
tification of specific grades. One perennial problem for the welding engi-
neer is the use of superseded specification designations to identify alloy
compositions. As an aid to identification a table of comparative specifica-
tion designations is included as Appendices C and D.

3.2 Alloying elements

The principal alloying elements are copper, silicon, manganese, magnesium,
lithium and zinc. Elements such as nickel, chromium, titanium, zirconium
and scandium may be added in small amounts to achieve specific proper-
ties. Other elements may also be present in small amounts as unwanted
impurities. These elements, known as tramp or residual elements, have no

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