The short answer
Use 2024-T3 where the part carries cyclic tension and stays roughly flat — skins, webs, doublers, splices. Use 6061-T6 where the part has to be formed, welded or machined, and the load is moderate — brackets, ribs with tight flanges, fittings, non-primary structure.
The deciding factor is usually not strength. It is that 6061-T6 bends to about a third of the radius 2024-T3 needs, and that 6061 can be welded while 2024 effectively cannot.
Side by side
Only figures that appear in the primary sources. Where a row would need a number the FAA documents do not publish, the row says so rather than borrowing one.
| Property | 2024-T3 | 6061-T6 | Source |
|---|---|---|---|
| Bend radius, 0.016" | 1½t – 3t | 0 – 1t | AC Table 4-6 |
| Bend radius, 0.032" | 2t – 4t | ½t – 1½t | AC Table 4-6 |
| Bend radius, 0.064" | 3t – 5t | 1t – 2t | AC Table 4-6 |
| Bend radius, 0.128" | 4t – 6t | 1½t – 3t | AC Table 4-6 |
| Brinell hardness | 120 (T4 figure) | 95 | AC Table 4-5 |
| Allowable tensile stress, bare | 70,000 psi | not listed | AC Table 4-9 note d |
| Ultimate tensile / yield | not in either source | not in either source | see MMPDS |
| Corrosion resistance bare | Poor — usually bought Alclad | Good | AMT Handbook |
| Weldable | No, in practice | Yes | AMT Handbook |
The bend radius rows are the whole argument. At every thickness in the table, 6061-T6 takes roughly a third to a half the radius 2024-T3 needs.
When to choose 2024-T3
Skins and anything under cyclic tension. 2024 in T3 tolerates repeated loading better, and an airframe's problem is thousands of moderate cycles, not one large load.
When the drawing says so. Which, for primary structure on a certified aircraft, it will.
When the part is essentially flat — a doubler, a splice plate, a web — so the poor formability never comes up.
Expect to buy it Alclad, and remember the clad sheet carries a lower allowable stress: 55,000 psi against 70,000 for bare in the AC's own splice calculations.
When to choose 6061-T6
When it has to bend. This is the main reason. A rib flange or a bracket with a tight radius that cracks in 2024-T3 forms without complaint in 6061-T6.
When it has to be welded. 6061 welds; 2024 essentially does not, and attempting it destroys the heat-affected zone.
When it has to be machined from bar or plate — fittings, spacers, brackets.
When corrosion exposure is high and cladding is not an option. Bare 6061 holds up where bare 2024 does not.
When it does not matter
More often than the internet suggests. On a non-structural bracket, a fairing rib, an interior panel or a shim, either alloy will do the job and availability decides.
It also does not matter when you have no choice: if approved data names the alloy, the comparison is academic. The point of knowing the difference is understanding why the drawing chose what it chose, not overriding it.
And it does not matter if the part is going to be formed annealed and heat treated afterwards — at that point you are choosing a process, not a temper.
Questions people actually ask
Is 2024-T3 stronger than 6061-T6?
In the properties that matter for airframe skins, yes — and it is markedly more fatigue-tolerant, which is usually the real reason it is specified. We are not quoting ultimate or yield figures here because neither FAA source publishes them for these alloys; MMPDS is where those live.
Can I substitute 6061-T6 for 2024-T3?
Not on your own judgement in structural work. It is a material substitution and belongs to approved data. 6061-T6 is weaker and less fatigue-tolerant; where a drawing calls for 2024-T3 it generally has a reason.
Why does everyone use Alclad 2024 instead of bare?
Because bare 2024 corrodes readily — the copper that provides the strength also hurts corrosion resistance. Cladding is a sacrificial layer of near-pure aluminum on both faces. The cost is structural: the AC's splice tables use 55,000 psi for clad against 70,000 psi for bare.
Which one can I weld?
6061. 2024 is not practically weldable for structural purposes; it is a riveted alloy.
My 6061-T6 bracket cracked when I bent it. Was it the wrong alloy?
Probably not the alloy. Check the radius against Table 4-6 for your actual thickness, and check the bend direction relative to the grain — bending along the rolling direction cracks at radii the chart permits. 6061-T6 is forgiving, not immune.
Sources
- FAA AC 43.13-1B CHG 1, Tables 4-5, 4-6, 4-9 and 4-10 — every numeric row in the comparison table above.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1 — alloy characteristics, cladding, weldability and general application.
- MMPDS (formerly MIL-HDBK-5) — design allowables. Deliberately not reproduced here: a substantiation cites MMPDS, not a website.