Aircraft skins
Fuselage, wing surfaces, vertical stabilizers, control surfaces. The cyclically loaded outer-shell of virtually every commercial airliner.
Aerospace aluminum · UNS A92024
Aluminum 2024-T3
The classic aerospace skin alloy. Aluminum-copper chemistry gives 2024-T3 outstanding fatigue resistance — that’s why it’s on virtually every commercial aircraft fuselage and wing. Strong, machinable, but corrosion-prone unless clad or finished.
UTS
470 MPa
Density
2.78 g/cc
Modulus
73.1 GPa
Mach.
80 /100
When to use
Pick 2024 when fatigue is the deciding factor.
2024-T3 sits between 6061 and 7075 in the aerospace aluminum hierarchy. Strength is between them (UTS 470 vs 310/572 MPa), but where 2024 wins is fatigue resistance — it’s the standard alloy for cyclically loaded aircraft skins. The 4-5% copper content gives it both the strength and the fatigue performance, and is also the reason it corrodes more readily than 6061.
For commercial aircraft skins, 2024 is almost always specified as "clad" or "Alclad" — sheet rolled with a thin pure-aluminum skin on each face for corrosion protection. Bare 2024 (no cladding) is the typical bar/plate stock for machined components.
Strengths
Why aircraft fly with it.
- Outstanding fatigueEndurance limit ~140 MPa at 5×10⁸ cycles — exceptional for aluminum. Standard for cyclically loaded airframe skins.
- Higher strength than 6061UTS 470 vs 310 MPa. Bridges the gap to 7075 with better damage tolerance.
- Machinability 80/100Cuts faster than 7075 and similar to 6061. Sharp tools, fast cycles.
- Excellent fracture toughnessHolds up to crack propagation — critical for skin/structure applications.
- Wide aerospace stockSheet, plate, bar in every aerospace size. Often available clad or bare.
- Heat-treatableT3 (cold worked + naturally aged), T351 (stretched + aged). T81/T62 for higher strength after solution treat.
Trade-offs
Where it loses.
- Poor corrosion resistanceThe copper that gives strength also kills corrosion behavior. Use Alclad sheet, anodize, or paint.
- Not weldableHigh copper makes it crack-sensitive in the HAZ. Use mechanical fasteners (rivets) — that’s how aircraft are assembled anyway.
- Stress corrosion susceptibilityTight bends or formed parts in T3 can crack from sustained stress + corrosion. T351 is preferred for thicker sections.
- Less strong than 7075UTS 470 vs 572 MPa. For the highest-strength aluminum applications, 7075 wins.
- Cost premium~20% more than 6061 by weight — justified for fatigue-critical work, not for general use.
- Bare vs cladClad sheet is standard for skins; bare for machined components. Don't mix them up on the drawing.
Specs
Mechanical, physical & chemical data.
Mechanical
Properties (T3 sheet)
| Ultimate tensile strength | 470 MPa (68 ksi) |
|---|---|
| Yield strength (0.2% offset) | 325 MPa (47 ksi) |
| Elongation at break | 18% |
| Modulus of elasticity | 73.1 GPa |
| Shear modulus | 28 GPa |
| Shear strength | 283 MPa |
| Hardness (T3) | 120 HB / ~75 HRB |
| Endurance limit 5 × 10⁸ cycles, R = -1 | 140 MPa |
Source: AA Aluminum Standards & Data; AMS 4037. T351 (plate, stress-relieved) values are essentially equivalent. T81 (artificially aged): UTS 485 MPa, YS 450 MPa.
Physical & thermal
At room temperature
| Density | 2.78 g/cc (0.100 lb/in³) |
|---|---|
| Melting range | 502 – 638 °C |
| Specific heat | 0.875 J/g·°C |
| Thermal conductivity | 121 W/m·K |
| CTE (20–100 °C) | 23.2 µm/m·°C |
| Electrical conductivity | 30% IACS |
| Magnetic | Non-magnetic |
Thermal conductivity ~75% of 6061 — the copper alloying drops it slightly. Still excellent.
Composition
Chemistry, weight %
| Copper (Cu) | 3.8 – 4.9 |
|---|---|
| Magnesium (Mg) | 1.2 – 1.8 |
| Manganese (Mn) | 0.30 – 0.90 |
| Iron (Fe) | 0.50 max |
| Silicon (Si) | 0.50 max |
| Zinc (Zn) | 0.25 max |
| Chromium (Cr) | 0.10 max |
| Titanium (Ti) | 0.15 max |
| Aluminum (Al) | balance (~93%) |
The 4-5% copper is the strength + fatigue driver. It's also the reason corrosion resistance is poor.
Specifications
Common purchase specs.
AMS 4037
Sheet, plate — bare T3 / T351
AMS 4041
Sheet — clad T3 (Alclad)
AMS 4120
Bar, rod, wire — T351 / T4
AMS 4192
Sheet, plate — 2024-T361
ASTM B209
Aluminum sheet, plate
ASTM B211
Bar, rod, wire — rolled
MIL-A-8625
Anodize spec (for corrosion finish)
AA 2024 / EN AW-2024
Aluminum Association / European
Machining
How we cut it.
2024 machines very similarly to 6061 — fast speeds, aggressive feeds, clean chip control. Slightly tougher chips than 6061 (the copper), so chip-breaker geometry helps.
Cutting speed
1,000–2,500 SFM with carbide. Slightly slower than 6061 due to chip toughness.
Feed rate
Aggressive constant feed. 2024 doesn't work-harden meaningfully.
Tooling
Polished or coated carbide. PCD for high-volume production.
Coolant
Flood with water-soluble. Some shops run dry with MQL.
Stress relief
T351 (stretched) for plate work — much more stable than T3 for thin-wall machining.
Anodize on bare
Bare 2024 should be anodized or chem-filmed before service to prevent corrosion.
Don't mix bare + clad
Bare and Alclad sheet have different surface chemistry — don't intermix in an assembly without thinking it through.
Threading
Standard taps work. Use thread inserts (Helicoil) in critical fastener locations for repeated assembly.
Applications
Where 2024 shows up.
Aircraft structural members
Stringers, spars, ribs, formers. Where fatigue resistance matters more than max strength (which would push you to 7075).
Gauges & precision plate
Inspection gauges, optical breadboards, thin-wall machined enclosures. T351 stress-relieved plate for stability.
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