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ALUMINUM ALLOY DESIGNATIONS
The aluminum industry uses a four-digit index system
for the designation of its wrought aluminum alloys.
As outlined below, the first digit indicates the
alloy group according to the major alloying elements.
1xxx Series
In this group. minimum aluminum content is 99%. and
there is no major alloying element.
The second digit indicates modifications in impurity
limits. If the second digit is zero, there is no special control on
individual impurities. Digits 1 through 9, which are assigned
consecutively as needed, indicate special control of one or more
individual impurities.
The last two digits indicate specific minimum
aluminum content. Although the absolute minimum aluminum content in this
group is 99% the minimum for certain grades is higher than 99%, and the
last two digits represent the hundredths of a per cent over 99.
Thus, 1030 would indicate 99.30% minimum aluminum.
without special control on individual impurities. The designations 1130,
1230, 1330, etc.. indicate the same purity with special control on one
or more impurities. Likewise. 1100 indicates minimum aluminum content of
99.00% with individual impurity control.
2xxx through 9xxx Series
The major alloying elements are indicated by the
first digit, as follows:
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesium and silicon
7xxx Zinc
8xxx Other element
9xxx Unused series
The second digit indicates alloy modification. If the
second digit is zero. it indicates the original alloy: digits 1 through
9, which are assigned consecutively, indicate alloy modifications. The
last two digits have no special significance, serving only to identify
the different alloys in the group.
Experimental Alloys
Experimental alloys are designated according to the
four digit system, but they are prefixed by the letter X. The prefix is
dropped when the alloy becomes standard. During development, and before
they are designated as experimental, new alloys are identified by serial
numbers assigned by their originators. Use of the serial number is
discontinued when the X number is assigned.
ALUMINUM TEMPER DESIGNATIONS
Temper designations of wrought aluminum alloys
consist of suffixes to the numeric alloy designations. For example, in
3003-H14, 3003 denotes the alloy and “H14” denotes the temper, or
degree of hardness. The temper designation also reveals the method by
which the hardness was obtained. Temper designations differ between non
heat-treatable alloys and heat-treatable alloys. and their meanings are
given below:
Non Heat-Treatable Alloys
The letter “H” is always followed by 2 or 3
digits. The first digit indicates the particular method used to obtain
the temper. as follows:
— Hl means strain hardened only.
— H2 means strain hardened, then partially
annealed.
— H3 means strain hardened, then stabilized.
The temper is indicated by the second digit as
follows:
2 1/4 hard
4 I/2 hard
6 3/4 hard
8 full hard
9 extra hard
Added digits indicate modification of standard
practice.
Heat-Treatable Alloys
-F As fabricated
-O Annealed
-T Heat treated
The letter “T” is always followed by one or more
digits. These digits indicate the method used to produce the stable
tempers, as follows:
-T3 Solution heat treated, then cold worked.
-T351 Solution heat treated, stress-relieved
stretched, then cold worked.
-T36 Solution heat treated, then cold worked
(controlled).
-T4 Solution heat treated, then naturally aged.
-T451 Solution heat treated, then stress relieved
stretched.
-T5 Artificially aged only.
-T6 Solution heat treated, then artificially aged.
-T61 Solution heat treated (boiling water quench),
then artificially aged.
-T651 Solution heat treated, stress-relieved
stretched, then artificially aged (precipitation heat treatment).
-T652 Solution heat treated, stress relieved by
compression. then artificially aged.
-T7 Solution heat treated, then stabilized.
-T8 Solution heat treated, cold worked, then
artificially aged.
-T81 Solution heat treated, cold worked (controlled),
then artificially aged.
-T851 Solution heat treated, cold worked,
stress-relieved stretched, then artificially aged.
-T9 Solution heat treated, artificially aged, then
cold worked.
-T10 Artificially aged, then cold worked.
Added digits indicate modification of standard
practice.
COMPARISON OF MODERN & OLD SYSTEMS OF ALUMINUM
ALLOY DESIGNATION
Although the old system of aluminum identification
has been obsolete for many years, stock with the old markings is still
occasionally found. The following comparison is presented as an aid in
identifying such materials in terms of the modern system.
In the old system, alloy composition was indicated by
a one- or two-digit number followed by the letter “S” to indicate
that it was a wrought alloy, i.e., an alloy that could be shaped by
rolling, drawing or forging. Any variation in the basic composition was
indicated by a letter preceding the numerical alloy designation. For
example, A17S was a modification of the basic alloy 17S. In modern
terminology these two alloys are designated 2117S and 2017S,
respectively. Temper was designated by a second letter: “O” for soft
(annealed), “H”for strain hardness of non heat-treatable alloys, and
“T”for hardness of heat-treatable alloys. Degree of hardness of non
heat-treatable alloys was indicated by a fraction preceding the letter
“H”. For example, 3S1/4H would be quarter-hard 3S alloy.
The following Table gives examples of the old and
modern designations of some common aluminum alloys.
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