Alloys, tempers & product forms
Know what you are forming before you load the press. Wrong temper ruins parts; sanding through Alclad ruins corrosion protection.
Product forms
| Form | Typical use on 707-family work |
|---|---|
| Sheet | Skins, webs, light brackets, formed channels |
| Plate | Thick fittings, machined from solid, spar caps / fittings where plate stock is called |
| Extrusion | Stringers, longerons, some frame sections |
| Forging | High-load fittings, landing-gear related parts, complex fittings |
| Bar / rod | Machined pins, bushings blanks, small fittings |
| Honeycomb | Sandwich panels (core + skins) — handle and bond per process specs |
Alloys you will see
| Alloy | Role | Notes |
|---|---|---|
| 2024 | Skins, lower wing structure, many formed sheet parts | Workhorse aero sheet/plate. Often Alclad. Strong in T3/T4 family. |
| 7075 | Stringers, fittings, high-strength machined parts | Higher strength than 2024; stress-corrosion watch — T73 family often preferred for fittings. |
| 7178 | Legacy upper wing / high-strength applications (watch-out) | Historical high-strength alloy. Know it on drawings; treat carefully for SCC and availability. |
| 7079 | Legacy thick forgings / fittings (watch-out) | Older alloy with known issues in some thick sections. Flag on prints; follow engineering disposition. |
Watch-outs: 7178 & 7079
These show up on older 707-family drawings. Do not casually substitute. Engineering owns alloy swaps — shop owns forming the called temper correctly.
Tempers
| Temper | Meaning (shop view) |
|---|---|
| O | Annealed — softest; form freely, then heat treat to final temper |
| W | Solution heat-treated, unstable — form soon after quench; then age |
| T3 / T4 | Solution treated + cold work / naturally aged — common for 2024 sheet in service |
| T6 / T651 | Solution treated + artificially aged (651 = stress relieved) — high strength |
| T73 / T76 | Overaged for SCC resistance (esp. 7075 family fittings) |
Shop rule
Form in O or W. Fly in T3 / T6 / T73 (as called). Trying to stretch or brake hard T6 sheet is how you crack parts and scrap material.
Alclad
Many 2024 sheets carry a pure aluminum cladding for corrosion protection. Do not sand through it. Blend carefully; if cladding is gone, the part may need rework or scrap per engineering.