Key facts
Where to buy| Property | Value | Source |
|---|---|---|
| Density | 0.102 lb/in³ (2.83 g/cm³) | Teal Sheets |
| Allowables | None in Section 3.7 | MIL-HDBK-5J Table 3.1.1 |
| Named in | Comparison with 7050 T76 in stress corrosion | MIL-HDBK-5J 3.7.4.0 |
| Bend radius, 7178-O | See table below | FAA-H-8083-31B Chart 204 |
| Replacement | 7178-T6 and clad are in a substitution figure | FAA-H-8083-31B Figure 4-168 |
No strength value is given here because none of the sources used by this site prints one.
Reading the alloy and temper code
Composition limits, weight percent
| Element | Limit |
|---|---|
| Si | 0.40 |
| Fe | 0.50 |
| Cu | 1.6–2.4 |
| Mn | 0.30 |
| Mg | 2.4–3.1 |
| Cr | 0.18–0.28 |
| Zn | 6.3–7.3 |
| Ti | 0.20 |
| Al | Remainder |
A single number is a maximum. Other elements: 0.05 each, 0.15 total, except where the Teal Sheets say otherwise. Source: Aluminum Association Teal Sheets (Aug 2018).
Minimum bend radius, inches (AMT Handbook Chart 204)
| Alloy and temper | 0.020" | 0.032" | 0.040" | 0.063" | 0.125" | 0.190" |
|---|---|---|---|---|---|---|
| 7178-O, 2024-O, 5052-H34, 6061-T4, 7075-O | .03 | .03 | .06 | .09 | .25 | .38 |
Selected thicknesses from FAA-H-8083-31B Chart 204, p. 4-61. Chart 204 and AC Table 4-6 do not agree everywhere: where they differ, use the larger radius or the SRM.
Replacing it
AMT Handbook Figure 4-168 shows a material substitution table for one transport type, with factors that multiply the gauge when 7178-T6 or Clad 7178-T6 is replaced by another alloy. It is an example, and it sends the reader to the manufacturer for specific locations.
Limits on replacement in that figure include pressurized areas and part of the wing structure. Work only from the SRM for the aircraft.
MIL-HDBK-5J says the T76 temper of 7050 has better stress-corrosion resistance than the T6 tempers of 7075 and 7178 (3.7.4.0).
Questions people actually ask
Can I replace 7178 with 7075 of the same gauge?
Not by assumption. The Handbook's figure uses factors above 1 for this kind of swap. The SRM decides.
Limits — when NOT to use this
- Not a source of design allowables. Values are for reference. MMPDS and the SRM govern a repair.
- Not a substitution approval. A different alloy or temper needs approved data.
Where to buy
Distributors coming soon.
Sources
- FAA-H-8083-31B, AMT Handbook — Airframe, Volume 1, Chapter 4 — Chart 204, p. 4-61; Figure 4-168, p. 4-87.
- MIL-HDBK-5J (31 Jan 2003), Chapter 3 — Table 3.1.1; Section 3.7.4.0. Cancelled and superseded by MMPDS: check current MMPDS before design use.
- Aluminum Association, International Alloy Designations (Teal Sheets), rev. Aug 2018 — chemical composition limits and nominal densities.
- MMPDS (formerly MIL-HDBK-5) — the current home of design allowables. A repair substantiation cites MMPDS or the SRM, not a website.