Steel Alloys and their Classification
Aluminum Alloys and their Classification: Aluminum alloys have been used in many applications where structural lightness and corrosion resistance are important. They are also extremely good conductors of electricity (third best after silver and copper, respectively), but have a high coefficient of thermal expansion that makes them unsuitable for high temperature applications (e.g., outer skin of high-speed aircraft, some engine components).
Aluminum Alloy Designations:
Aluminum alloys usually have a 4-digit designation. The first digit designates purity or alloy type. The second digit indicates modifications of the alloy. Only in 1xxx series the third and fourth digits indicate the purity. For example, 1050 indicates an aluminum with 99.50% purity. The third and fourth digits in the other series identify different alloys in the group and have no numerical importance.
1xxx - Aluminum (at least 99.0% pure). Characteristics: (a) very high corrosion resistance, (b) high electrical and thermal conductivity, (c) good formability, (d) low strength, and (e) not heat treatable.
2xxx - Aluminum-Copper alloy. Characteristics: (a) high strength-to-weight ratio, (b) low corrosion resistance, and (c) heat treatable.
2014-T6 Extrusions - thickness <= 0.499"(data from Ref. 2)
| Temperature (°F) | Exposure (hr) | e (%) | stu (ksi) | scy (ksi) | Ec (106 psi) | s0.7 (ksi) | s0.85 (ksi) | n |
| 75 | 2.0 | 7 | 60 | 53 | 10.7 | 53 | 50.3 | 18.5 |
| 300 | 2.0 | - | 51 | 42.5 | 10.2 | 41.5 | 40 | 24 |
| 450 | 2.0 | - | 28 | 21 | 9.2 | 20.5 | 19.5 | 25 |
| 600 | 2.0 | - | 10 | 8 | 7.4 | 5.5 | 4.5 | 5.4 |
2024-T3 Bare Sheet & Plate - thickness <= 0.25"(data from Ref. 2)
| Temperature (°F) |
Exposure (hr)
|
e (%) | stu (ksi) | scy (ksi) | Ec (106 psi) | s0.7 (ksi) | s0.85 (ksi) | n |
| 75 | 2.0 | 12 | 65 | 40 | 10.7 | 39 | 36 | 11.5 |
| 300 | 2.0 | - | 65 | 37 | 10.3 | 35.7 | 33.5 | 15 |
| 500 | 2.0 | - | 65 | 26 | 8.4 | 24.8 | 22.8 | 10.9 |
| 700 | 2.0 | - | 65 | 7.5 | 6.4 | 6.2 | 5.5 | 8.2 |
3xxx - Aluminum-Manganese alloy. Characteristics: (a) good formability, (b) moderate strength, and (c) not heat treatable.
4xxx - Aluminum-Silicon alloy. Characteristics: (a) lower melting point than normal, and (b) not heat treatable.
5xxx - Aluminum-Magnesium alloy. Characteristics: (a) good corrosion resistance, (b) easy to weld, (c) moderate to high strength, and (d) not heat treatable.
6xxx - Aluminum-Magnesium-Silicon alloy. Characteristics: (a) medium strength, (b) good formability, machinability and weldability, (c) corrosion resistant, (d) heat treatable.
6061-T6 Sheet, Heat Treated & Aged - thickness <= 0.25"(data from Ref. 2)
| Temperature (°F) | Exposure (hr) | e (%) | stu (ksi) | scy (ksi) | Ec (106 psi) | s0.7 (ksi) | s0.85 (ksi) | n |
| 75 | 0.5 | 10 | 42 | 35 | 10.1 | 35 | 34 | 31 |
| 300 | 0.5 | - | 42 | 29.5 | 9.5 | 29 | 28 | 26 |
| 450 | 0.5 | - | 42 | 20.5 | 8.5 | 19.3 | 17.7 | 10.9 |
| 600 | 0.5 | - | 42 | 7.5 | 7 | 6.6 | 6.2 | 15.2 |
7xxx - Aluminum-Zinc alloy. Characteristics: (a) moderate to very high strength, (b) heat treatable, and (c) prone to fatigue.
7075-T6 Bare Sheet & Plate - thickness <= 0.5"(data from Ref. 2)
| Temperature (°F) | Exposure (hr) | e (%) | stu (ksi) | scy (ksi) | Ec (106 psi) | s0.7 (ksi) | s0.85 (ksi) | n |
| 75 | 2.0 | 7 | 76 | 67 | 10.5 | 70 | 63 | 9.2 |
| 300 | 2.0 | - | 76 | 54 | 9.4 | 55.8 | 52.5 | 15.6 |
| 450 | 2.0 | - | 76 | 25.5 | 8.1 | 25.4 | 23.5 | 12.1 |
| 600 | 2.0 | - | 76 | 8 | 5.3 | 7.2 | 5.2 | 3.7 |
Aluminum-Lithium alloy (no numerical designation). Characteristics: (a) 10% lighter and 10% stiffer than other alumnium alloys, and (b) superior fatigue performance.
Aluminum-Iron-Molybdenum-Zirconium alloy (no numerical designation). Characteristics: high temperature tolerance, 600°F.
Heat Treatment:
The four digit designation of aluminum alloys is usually accompanied by any of the following four letters: F, O, W, and T. The extension F stands for as fabricated (forgings and castings prior to heat treatment), O for annealed, W for solution heat treated, and T for heat treated to stable temper conditions other than O or F. The following temper designations are commonly used:
T3 - solution heat treated,cold worked and naturally aged.
T4 - solution heat treated and naturally aged.
T6 - solution heat treated and artificially aged.
T7 - solution heat treated and overaged.
T8 - solution heat treated, cold worked and artificially aged.
In addition to these heat treatments, a heat treat condition number can have additional numerical information like T7xx, where the xx describes either a stress relieving treatment done to the alloy or the extent of aging.
Some examples of aluminum heat treatment and alloy designations:
2024 - T3 is an Aluminum-Copper alloy, fourth in the 2xxx series, which is solution heat treated, cold worked and naturally aged.
7075 - T7351 is an Aluminum-Zinc alloy that has been overaged and stress relieved by stretching [1].
For more information on material properties, go to www.matweb.com.
References:
[1] Niu, Michael C. Y., Airframe Structural Design,1988.
[2] Bruhn, E. F., Analysis and Design of Flight Vehicle Structures,1972.