Key facts
| Property | Value | Source |
|---|---|---|
| Brinell hardness, 7075-T6 | 135 (500 kg load, 10 mm ball) | AC 43.13-1B CHG 1, Table 4-5 |
| Sheet tensile stress behind the AN-3 bolt count in a splice | 70,000 psi | AC 43.13-1B CHG 1, Table 4-9 engineering note d (table title lists bare 7075-T6 sheet) |
| Welding | Do not weld — severe cracking | AC 43.13-1B CHG 1, par. 4-89d |
The 70,000 psi figure is the value the AC used to calculate its own splice table. It is a specific context, not a general-purpose allowable, and it is shared with the other alloys in the table title.
Bend radii, 7075 (AC 43.13-1B Table 4-6)
| Alloy and temper | 0.016" | 0.032" | 0.064" | 0.128" | 0.182" | 0.258" |
|---|---|---|---|---|---|---|
| 7075-O | 0 | 0 – 1t | 0 – 1t | ½t – 1½t | 1t – 2t | 1½t – 3t |
| 7075-T6 | 2t – 4t | 3t – 5t | 4t – 6t | 5t – 7t | 5t – 7t | 6t – 10t |
Recommended radii for 90-degree bends, sheet thickness t. “0” means no radius required. Alclad sheet may be bent over slightly smaller radii than the uncoated alloy (Table 4-6 footnote 1).
Design allowables — 7075-T6/T62 bare sheet
0.040–0.125 in thick. MIL-HDBK-5J Table 3.7.6.0(b1). A and B bases in ksi unless a unit is shown.
| Property | A basis | B basis | Unit |
|---|---|---|---|
| Ftu, L | 78 | 80 | ksi |
| Ftu, LT | 78 | 80 | ksi |
| Fty, L | 70 | 72 | ksi |
| Fty, LT | 68 | 70 | ksi |
| Fcy, L | 69 | 71 | ksi |
| Fcy, LT | 72 | 74 | ksi |
| Fsu | 47 | 48 | ksi |
| Fbru, e/D = 1.5 | 121 | 124 | ksi |
| Property | A basis | B basis | Unit |
|---|---|---|---|
| Fbru, e/D = 2.0 | 156 | 160 | ksi |
| Fbry, e/D = 1.5 | 102 | 105 | ksi |
| Fbry, e/D = 2.0 | 119 | 122 | ksi |
| Elongation, LT (S-basis) | 8 | — | % |
| E | 10.3 | 10.3 | 10³ ksi |
| Ec | 10.5 | 10.5 | 10³ ksi |
| G | 3.9 | 3.9 | 10³ ksi |
| Density | 0.101 | 0.101 | lb/in³ |
Form: sheet; temper: T6 and T62; specification: AMS 4045 and AMS-QQ-A-250/12; thickness 0.040–0.125 in. Bearing values are dry-pin values (MIL-HDBK-5J Section 1.4.7.1). The handbook prints E, Ec, G and density once across both bases, and the elongation in the A column with the B cell blank. Source: MIL-HDBK-5J (31 Jan 2003), Table 3.7.6.0(b1), p. 3-371. MIL-HDBK-5J (2003) is superseded by MMPDS; check current MMPDS before design use. Density 0.101 lb/in³ is about 2.80 g/cm³ (converted); the sheet weight calculator uses the same figure.
Where it is used
The AC says 7075 is most often used in machined fittings such as wing-spar attachments, landing-gear attachments and other structural parts. The AMT Handbook says it is generally used in tension applications where fatigue is not critical.
Forms: the title of AC Table 4-9 lists 7075-T6 as bare and clad sheet, and as plate, bar, rod, tube and extrusions.
Compared with 2024: higher strength, lower fracture toughness (AMT Handbook, p. 4-31). See 2024-T3.
Temper and heat treatment
T6 is solution heat-treated and artificially aged. T651 adds stress relief by stretching, 1 to 3 percent permanent set (AC 43.13-1B Table 4-4).
The AMT Handbook names the alternatives to T6: T7351 has excellent stress corrosion resistance and better fracture toughness than T6, and T76 is often used to improve resistance to exfoliation corrosion (p. 4-31).
Structural aluminum parts are heat-treated to the manufacturer's instruction, and riveted parts are heat-treated before riveting, to avoid warping and corrosion (AC par. 4-54).
Corrosion and forming
Corrosion. The AMT Handbook says the T6 temper should be avoided in corrosive environments (p. 4-31). The AC adds that 7075 is more susceptible to inter-granular corrosion if improperly heat-treated and then exposed (par. 6-16), and shows 7075-T6 attacked next to a steel fastener (Figure 6-9). Exfoliation is the advanced form of that attack (par. 6-18).
Forming. The AC warns that cold straightening or forming of 7075-T6 can cause cracking, so limit it to minor cold straightening (par. 4-58b). It also notes greater notch sensitivity: avoid notches, small radii, machine marks, nicks, scratches and rapid changes of section.
Repairs to aluminum members use the same material or a suitable material of higher strength (par. 4-58b).
Questions people actually ask
Can I weld 7075-T6?
No. The AC lists 2024 and 7075 as aluminum alloys that must not be welded, because the heat causes severe cracking (par. 4-89d).
Why is it not used for skins?
The AMT Handbook gives it lower fracture toughness than 2024 and recommends it for tension applications where fatigue is not critical (p. 4-31). Fatigue is what matters on a skin.
Limits — when NOT to use this
- Not a source of design allowables. Strength, elongation, shear, bearing and modulus come from MMPDS with their basis and thickness range. The structural repair manual governs a repair.
- Not for forming. Cold straightening or forming of 7075-T6 can cause cracking (AC par. 4-58b). If a part must be bent tight, that is a design question, not a shop one.
- Not a drop-in for 2024-T3. Different fatigue and fracture behaviour. Material substitution in a structural repair is approved-data territory.
- No welding. Weld repair of 7075 is not allowed (AC par. 4-89d).
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4 — Tables 4-4, 4-5, 4-6, 4-9; pars. 4-54, 4-58, 4-89; Chapter 6 — pars. 6-16, 6-18, Figure 6-9 — hardness, bend radii, temper definitions, splice-table stress, repair, welding and corrosion statements.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4, pp. 4-30 to 4-31 — 7075 properties, tempers and corrosion behaviour.
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures — density, and the home of the design allowables (Chapter 3, aluminum). Cancelled; replaced by MMPDS.
- MIL-HDBK-5J (31 Jan 2003), Table 3.7.6.0(b1), p. 3-371 — 7075-T6/T62 sheet, 0.040–0.125 in: Ftu, Fty, Fcy, Fsu, Fbru, Fbry, elongation, E, Ec, G and density.
- MMPDS (formerly MIL-HDBK-5) — the current home of design allowables with A, B and S basis. Cancelled MIL-HDBK-5J was superseded by it. A repair substantiation cites MMPDS or the SRM, not a website.