modifications or impurity limits. The last two digits
T5 Artificially aged only
identify the particular alloy or indicate the aluminum
T6 Solution heat treated, then artificially
purity.
aged
In the 1xxx group for 99.00 percent minimum
T7 Solution heat treated, then stabilized
aluminum, the last two digits show the minimum
aluminum percentage to the right of the decimal point.
T8 Solution heat treated, cold worked,
The second digit shows modifications in impurity
then artificially aged
limits. If the second digit in the designation is zero,
there is no special control on individual impurities. If
T9 Solution heat treated, artificially
the second digit is 1 through 9, it shows some special
aged, then cold worked
control of one or more individual impurities. As an
T10 Artificially aged, then cold worked
example, 1030 indicates a 99.30 percent minimum
aluminum without special control on individual
Note that some temper designations apply only to
impurities. Designations 1130, 1230, 1330, and so
wrought products and others to cast products; but
on, indicate the same purity with special control of
most apply to both. A second digit may appear to the
one or more individual impurities.
right of the mechanical treatment. This second digit
Designations 2 through 8 are aluminum alloys. In
indicates the degree of hardening; 2 is 1/4 hard, 4 is
the 2xxx through 8xxx alloy groups, the second digit
1/2 hard, 6 is 3/4 hard, and 8 is full hard. For
indicates any alloy modification. The last two of the
example, the alloy 5456-H32 is an aluminum/
four digits identify the different alloys in the group.
magnesium alloy, strain hardened, then stabilized, and
In addition to the four-digit alloy designation, a
1/4 hard.
letter or letter/number is included as a temper
designation. This designation follows the four-digit
Standard Marking of Metals
alloy number and is separated from it by a dash. As
an example, 2024-T6 is an aluminum-copper alloy
solution. The T6 designation shows the metal is heat
Metals used by the Navy are usually marked by
treated, then artificially aged; T6 is the temper
the producer with the continuous identification
designation. The following list contains the
marking system. We'll explain the system in the
aluminum alloy temper designations and their
following paragraphs. Do not depend only on the
meanings:
markings to be sure you are using the correct metal.
F
Fabricated
Often, the markings will be worn off or cut off and
you are left with a piece of metal you are not sure
O Annealed recrystallized (wrought only)
about. Additional systems, such as separate storage
H Strain hardened (wrought only)
areas or racks for different types of metal or etching
on the metal with an electric etcher could save you
H1, plus one or more digits, strain hardened
time later.
only
H2, plus one or more digits, strain hardened,
The continuous identification marking system,
then partially annealed
which is described in Federal Standards, is a means
for positive identification of metal products even after
H3, plus one or more digits, strain hardened,
some portions have been used. In this system, the
then stabilized
markings are actually "printed" on the metal with a
W Solution heat treated, unstable temper
heavy ink that is almost like a paint, and they appear
T Treated to produce stable tempers other
at intervals of not more than 3 feet. So, if you cut off
than F, O, or H
a piece of bar stock, the remaining portions will still
carry the proper identification. Some metals, such as
T2 Annealed (cast only)
small tubing, coils of wire, and small bar stock cannot
T3 Solution heat treated, then cold worked
be marked readily by this method. On these items,
tags with the marking information are fastened to the
T4 Solution heat treated and naturally
aged to a substantially stable condition
metal.
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