4-1. General. Aluminum, magnesium, steel, and titanium alloys are explained in the following paragraphs.
4-2. Aluminum Alloys. Aluminum is combined with various percentages of such elements as chromium, copper,
magnesium, silicon, and zinc to form alloys. This combination results in a light, strong material. A protective coating,
known as Alclad, is applied to many aluminum alloys to give resistance to corrosion.
Identification. All wrought aluminum and aluminum alloys produced after 1 October, 1954, will be marked in
accordance with the new designation system. Procurement orders may continue to employ the old designation until such
time when material specifications are changed; therefore, materials will probably be received marked with either
designation. Material marked with either new or old designation will be utilized. Aluminum alloys are identified as
(1) Numbering. Wrought aluminum and aluminum alloys are designated by a four-digit index system. The first
digit of the designation serves to indicate alloy groups. The last two digits identify the aluminum alloy or indicate the
aluminum purity. The second digit indicates modifications of the original alloy or impurity limits.
(2) Designation for alloy groups. In the four-digit index system, the first digit indicates the alloy group as shown
in table 4-1. Thus, 1xxx indicates aluminum of 99 00 percent minimum and greater; 2xxx indicates an aluminum alloy in
which copper is the major alloying element; 3xxx, an aluminum alloy with manganese as the major alloying element, etc.
Although most aluminum alloys contain several alloying elements, only one group, 6xxx for alloys with magnesium and
silicon, designates more than one alloying element.
(3) Designation conversions. Aluminum alloy designation conversions are listed in table 4-2 and explained in
the following paragraphs.
(a) Aluminum. In the 1xxx group for aluminum of 99.00 percent minimum and greater, the last two of the
four digits in the designation indicate the minimum aluminum percentage. These digits are the same as the two digits to
the right of the decimal point in the minimum aluminum percentage when it is expressed to the nearest 0.01 percent.
The second digit in the designation indicates modifications in impurity limits. If the second digit in the designation is
zero, it indicates that there is no special control on individual impurities, while integers 1 through 9 which are assigned
consecutively as needed, indicate special control of one or more individual impurities. Thus, 1030 indicates 99.30
percent minimum aluminum without special control on individual impurities and 1130, 1230, 1330, etc., indicate the same
purity with special control on one or more impurities. Likewise, 1075, 1175,1275, etc., indicate 99 75 percent minimum
aluminum, and 1097, 1197, 1297, etc., indicate 99.97 percent.
(b) Aluminum alloys. In the 2xxx through 8xxx alloy groups, the last two of the four digits in the designation
have no special significance but serve only to identify the different alloys in the group. Generally, these digits are the
same as those formerly used to designate the same alloy. Thus, 2014 was formerly 14S, 3003 was 3S and 7075 was
75S For new alloys, these last two digits are assigned consecutively beginning with xx01. The second digit in alloy
designation indicates alloy modifications. If the second digit in the designation is zero, it indicates the original alloy;
integers 1 through 9, which are assigned consecutively, indicate alloy modifications. In the former system, letters were
used to designate alloy modification. These were assigned consecutively beginning with A. Thus, 17S is now 2017 and
A17S is 2117, 18S is 2018 and B18 is 2218.
(4) Experimental alloys. Experimental alloys are also designated in accordance with this system, but they are
indicated by the prefix 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.