This chapter contains the engineering properties and related characteristics of wrought and cast aluminum alloys used in aircraft and missile structural applications.
General comments on engineering properties and the considerations relating to alloy selection are presented in this section. Mechanical and physical property data and characteristics pertinent to specific alloy groups or individual alloys are reported in Sections 3.2 through 3.9. Element properties are presented in Section 3.10.
Aluminum is a lightweight, corrosion-resistant structural material that can be strengthened through alloying and, dependent upon composition, further strengthened by heat treatment and/or cold working [Reference 3.1(a)]. Among its advantages for specific applications are: low density, high strength-to-weight ratio, good corrosion resistance, ease of fabrication and diversity of form.
Wrought and cast aluminum and aluminum alloys are identified by a four-digit numerical designation, the first digit of which indicates the alloy group as shown in Table 3.1. For structural wrought aluminum alloys the last two digits identify the aluminum alloy. The second digit indicates modifications of the original alloy or impurity limits. For cast aluminum and aluminum alloys the second and third digits identify the aluminum alloy or indicate the minimum aluminum percentage. The last digit, which is to the right of the decimal point, indicates the product form: XXX.0 indicates castings, and XXX.1 and XXX.2 indicate ingot.
| Alloy Group | Wrought Alloys — Major Alloying Elements | Alloy Group | Cast Alloys — Major Alloying Groups |
|---|---|---|---|
| 1XXX | 99.00 percent minimum aluminum | 1XX.0 | 99.00 percent minimum aluminum |
| 2XXX | Copper | 2XX.0 | Copper |
| 3XXX | Manganese | 3XX.0 | Silicon with added copper and/or magnesium |
| 4XXX | Silicon | 4XX.0 | Silicon |
| 5XXX | Magnesium | 5XX.0 | Magnesium |
| 6XXX | Magnesium and Silicon | 6XX.0 | Unused Series |
| 7XXX | Zinc | 7XX.0 | Zinc |
| 8XXX | Other Elements | 8XX.0 | Tin |
| 9XXX | Unused Series | 9XX.0 | Other Elements |
The layout of this chapter is in accordance with this four-digit number system for both wrought and cast alloys [Reference 3.1(b)]. Table 3.1.1 is the aluminum alloy index that illustrates both the general section layout as well as details of those specific aluminum alloys presently contained in this chapter. The wrought alloys are in Sections 3.2 through 3.7, whereas the cast alloys are in Sections 3.8 and 3.9.
| Section | Alloy Designation | Section | Alloy Designation |
|---|---|---|---|
| 3.2 | 2000 series wrought alloys | 3.6.2 | 6061 |
| 3.2.1 | 2014 | 3.6.3 | 6151 |
| 3.2.2 | 2017 | 3.7 | 7000 series wrought alloys |
| 3.2.3 | 2024 | 3.7.1 | 7010 |
| 3.2.4 | 2025 | 3.7.2 | 7040 |
| 3.2.5 | 2026 | 3.7.3 | 7049/7149 |
| 3.2.6 | 2090 | 3.7.4 | 7050 |
| 3.2.7 | 2124 | 3.7.5 | 7055 |
| 3.2.8 | 2219 | 3.7.6 | 7075 |
| 3.2.9 | 2297 | 3.7.7 | 7150 |
| 3.2.10 | 2424 | 3.7.8 | 7175 |
| 3.2.11 | 2519 | 3.7.9 | 7249 |
| 3.2.12 | 2524 | 3.7.10 | 7475 |
| 3.2.13 | 2618 | 3.8 | 200.0 series cast alloys |
| 3.3 | 3000 series wrought alloys | 3.8.1 | A201.0 |
| 3.4 | 4000 series wrought alloys | 3.9 | 300.0 series cast alloys |
| 3.5 | 5000 series wrought alloys | 3.9.1 | 354.0 |
| 3.5.1 | 5052 | 3.9.2 | 355.0 |
| 3.5.2 | 5083 | 3.9.3 | C355.0 |
| 3.5.3 | 5086 | 3.9.4 | 356.0 |
| 3.5.4 | 5454 | 3.9.5 | A356.0 |
| 3.5.5 | 5456 | 3.9.6 | A357.0 |
| 3.6 | 6000 series wrought alloys | 3.9.7 | D357.0 |
| 3.6.1 | 6013 | 3.9.8 | 359.0 |
The properties of the aluminum alloys are determined by the alloy content and method of fabrication. Some alloys are strengthened principally by cold work, while others are strengthened principally by solution heat treatment and precipitation hardening [Reference 3.1(a)]. The temper designations, shown in Table 3.1.2, are indicative of the type of strengthening mechanism employed.
Among the properties presented herein, some, such as the room-temperature tensile, compressive, shear and bearing properties, are either specified minimum properties or derived minimum properties related directly to the specified minimum properties, and may be directly useful in design. Data on the effect of temperature on properties are presented so that percentages may be applied directly to the room-temperature minimum properties. Other properties, such as the stress-strain curve, fatigue and fracture toughness data, and modulus of elasticity values, are presented as average or typical values, which may be used in assessing the usefulness of the material for certain applications.
| Temper | Description |
|---|---|
| F | As fabricated. Applies to products of shaping processes in which no special control over thermal conditions or strain-hardening is employed. For wrought products, there are no mechanical property limits. |
| O | Annealed. Applies to wrought products annealed to obtain the lowest strength temper, and to cast products annealed to improve ductility and dimensional stability. |
| H | Strain-hardened (wrought products only). Applies to products strengthened by strain-hardening, with or without supplementary thermal treatment. Always followed by two or more digits: H1 = strain-hardened only; H2 = strain-hardened and partially annealed; H3 = strain-hardened and stabilized. The following digit (1–9) indicates the degree of strain-hardening (8 ≈ full hard). |
| W | Solution heat-treated. An unstable temper applicable only to alloys that spontaneously age at room temperature after solution heat treatment; specific only when the period of natural aging is stated (e.g., W – ½ hr). |
| T | Thermally treated to produce stable tempers other than F, O, or H, with or without supplementary strain-hardening. Always followed by one or more digits (T1–T10, see below). |
| T1 – T10 | T1: cooled from an elevated-temperature shaping process and naturally aged. T2: same, plus cold worked. T3: solution heat-treated, cold worked, and naturally aged. T4: solution heat-treated and naturally aged. T5: cooled from an elevated-temperature shaping process and artificially aged. T6: solution heat-treated and artificially aged. T7: solution heat-treated and overaged/stabilized. T8: solution heat-treated, cold worked, and artificially aged. T9: solution heat-treated, artificially aged, and cold worked. T10: cooled from an elevated-temperature shaping process, cold worked, and artificially aged. |
| T_51, T_510, T_511, T_52, T_54 | Stress-relieved variants of the T tempers — by stretching (T51/T510/T511), by compressing (T52), or by restriking cold in the finish die (T54). |
| T42, T62 | Solution heat-treated from annealed or F temper (rather than as-produced) and naturally aged (T42) or artificially aged (T62). |
| P (suffix) | Denotes H, T, or O temper variations privately negotiated between manufacturer and purchaser rather than registered with the Aluminum Association. |
| Solution heat treatment (footnote e) is achieved by heating cast or wrought products to a suitable temperature, holding long enough for constituents to enter solid solution, and cooling rapidly enough to hold the constituents in solution. Full temper-registration footnotes are in MIL-HDBK-5J Table 3.1.2. |
3.1.2.1.1 Strength (Tension, Compression, Shear, Bearing) — The design strength properties at room temperature are listed at the beginning of the section covering the properties of an alloy. The effect of temperature on these properties is indicated in figures which follow the tables.
The A- and B-basis values for tensile properties for the direction associated with the specification requirements are based upon a statistical analysis of production quality control data obtained from specimens tested in accordance with procurement specification requirements. For sheet and plate of heat-treatable alloys, the specified minimum values are for the long-transverse (LT) direction, while for sheet and plate of non-heat-treatable alloys and for rolled, drawn, or extruded products, the specified minimum values are for the longitudinal (L) direction. For forgings, the specified minimum values are stated for at least two directions. The design tensile properties in other directions, and the compression, shear, and bearing properties, are "derived" properties, based upon relationships developed by tests of at least ten lots of material applied to the established A-, B-, or S-basis properties.
Tensile and compressive strengths are given for the longitudinal, long-transverse, and short-transverse directions wherever data are available. Short-transverse strengths may be relatively low, and transverse properties should not be assumed to apply to the short-transverse direction unless so stated. Where the direction in which the material will be used is not known, the lesser of the applicable longitudinal or transverse properties should be used.
Bearing strengths are given without reference to direction and may be assumed to be about the same in all directions, with the exception of plate, die forging, and hand forging, where a reduction factor is used for edgewise bearing load in thick bare and clad plate of 2000 and 7000 series alloys (Table 3.1.2.1.1). Bearing data reported from tests made in accordance with ASTM E 238 require clean pins and specimens; designers should consider a reduction factor when applying these values to structural analyses.
Remaining subsections of 3.1.2 (elastic modulus, ductility, fatigue, fracture toughness, temperature effects, corrosion resistance) and Section 3.1.3 Manufacturing Considerations pending further digitization from MIL-HDBK-5J, pp. 3-7–3-25.