Designations for Aluminum Alloy Groups

Table 1-2.—Designations for Aluminum Alloy Groups In the 2xxx through 8xxx groups, the second digit indicates alloy modifications. If the second digit in the designation is zero, it indicates the original alloy, while numbers 1 through 9, assigned consecutively, indicate alloy modifications. The last two of the four digits have no special significance, but serve only to identify the different alloys in the group. The temper designation follows the alloy designation and shows the actual condition of the metal. It is always separated from the alloy designation by a dash. The letter F following the alloy designation indicates the “as fabricated condition, in which no effort has been made to control the mechanical properties of the metal, The letter O indicates dead soft, or annealed, condition. The letter W indicates solution heat treated. Solution heat treatment consists of heating the metal to a high temperature followed by a rapid quench in cold water, This in an unstable temper, applicable only to those alloys that spontaneously age at room temperature, Alloy 7075 may be ordered in the W condition. The letter H indicates strain hardened, cold-worked, hand-drawn, or rolled. Additional digits are added to the H to indicate the degree of strain hardening. Alloys in this group cannot be strengthened by heat treatment, hence the term nonheat-treatable. The letter T indicates fully heat treated. Digits are added to the T to indicate certain variations in treatment. Greater strength is obtainable in the heat-treatable alloys. They are often used in aircraft in preference to the nonheat-treatable alloys. Heat-treatable alloys commonly used in aircraft construction (in order of increasing strength) are 6061, 6062, 6063, 2017, 2024, 2014,7075, and 7178. Alloys 6061, 6062, and 6063 are sometimes used for oxygen and hydraulic lines and in some applications as extrusions and sheet metal. Alloy 2017 is used for rivets, stressed-skin covering, and other structural members. Alloy 2024 is used for airfoil covering and fittings. It may be used wherever 2017 is specified, since it is stronger. Alloy 2014 is used for extruded shapes and forgings. This alloy is similar to 2017 and 2024 in that it contains a high percentage of copper. It is used where more strength is required than that obtainable from 2017 or 2024. Alloy 7178 is used where highest strength is necessary, Alloy 7178 contains a small amount of chromium as a stabilizing agent, as does alloy 7075. Nonheat-treatable alloys used in aircraft construction are 1100, 3003, and 5052. These alloys do not respond to any heat treatment other than a softening, annealing effect. They may be hardened only by cold- working. Alloy 1100 is used where strength is not an important factor, but where weight, economy, and corrosion resistance are desirable. This alloy is used for 1-31