What the primary sources do give
| Property | Value | Source |
|---|---|---|
| Allowable tensile stress, bare 2024-T3 sheet | 70,000 psi | AC 43.13-1B, Table 4-9 engineering note d |
| Allowable tensile stress, Alclad 2024-T3 sheet | 55,000 psi | AC 43.13-1B, Table 4-10 engineering note d |
| Minimum bend radius, 0.032" sheet | 2t – 4t | AC 43.13-1B, Table 4-6 |
| Minimum bend radius, 0.064" sheet | 3t – 5t | AC 43.13-1B, Table 4-6 |
| Brinell hardness (2024-T4) | 120 | AC 43.13-1B, Table 4-5 |
The hardness figure is for T4, not T3 — Table 4-5 does not list T3, and we are not going to present one temper's number as another's. Both stress figures are the values the AC used to calculate its own splice tables, which is a specific context, not a general-purpose allowable.
The number that decides most jobs: 70,000 vs 55,000
That 15,000 psi gap between bare and Alclad is the most useful thing on this page, and it is rarely quantified anywhere.
Alclad 2024-T3 is 2024-T3 sheet with a thin layer of nearly pure aluminum rolled onto both faces. The cladding corrodes sacrificially and protects the core, which is why it exists — 2024 on its own has poor corrosion resistance because of the copper that gives it its strength.
The cladding is soft. It contributes almost nothing structurally, but it counts in the sheet thickness you measure. So a 0.032" clad sheet has less than 0.032" of load-carrying 2024 in it, and the AC's own splice calculations reflect that with a lower allowable stress — roughly 21% lower.
The practical consequence: you cannot substitute clad for bare, or bare for clad, without it being a design change. They are different structural materials that share an alloy number.
Forming it
2024-T3 is the least forgiving of the common airframe alloys. Table 4-6 wants 2t-4t at 0.032" and 3t-5t at 0.064" — where 6061-T6 does the same thicknesses at ½t-1½t and 1t-2t.
Two escape routes exist and both are in the AC's footnotes to that table. Clad sheet tolerates slightly smaller radii than bare, unquantified. And immediately after quenching, 2024 can be formed over appreciably smaller radii — the basis of the form-then-age sequence for parts that will not bend in T3.
Neither is a licence to bend tight on stock sheet. If the part will not form, the answer is a different alloy, an annealed blank, or a different part.
Grain direction is the usual culprit when 2024-T3 cracks at a radius the chart permits. Bend across the grain.
Where it is used, and why it is used despite all this
Skins, and most of the structure behind them. It is the default for anything that carries tension and sees cyclic load: fuselage skins, wing skins, spar webs, doublers, splice plates.
The reason it survives its own handling difficulties is fatigue behaviour. 2024 in T3 tolerates repeated loading better than the higher-strength 7075 alloys, and an airframe's problem is not usually one big load — it is a great many small ones over decades.
Where formability matters more than fatigue, or the part is a bracket rather than a skin, 6061-T6 is usually the better answer.
Substitutions and equivalents
Bare ↔ Alclad: not interchangeable. See above — different allowable stress, different corrosion behaviour.
2024-T3 ↔ 2024-T42: different tempers, different properties. Not a shop-floor swap.
2024-T3 ↔ 7075-T6: 7075 is stronger and less fatigue-tolerant, and bends worse still. A substitution decision against approved data, never a convenience.
2024-T3 ↔ 6061-T6: only where the drawing permits. 6061 forms far better and is weaker.
In every case: material substitution in a structural repair is approved-data territory. This page tells you what the differences are, not that you may act on them.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4 — Tables 4-5, 4-6, 4-9, 4-10 — hardness, recommended bend radii, and the allowable tensile stresses used in the splice tables for bare and Alclad 2024-T3.
- MMPDS (formerly MIL-HDBK-5) — the actual home of design allowables for aluminum alloys. AC 43.13-1B points at it explicitly and so do we — it is what a repair substantiation cites, not a website.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1 — alloy designation and temper system, cladding, and forming practice.