2024 Aluminum
Also: AA2024, UNS A92024, AlCu4Mg1, 2024-T3, 2024-T351, 2024-T4, 2024-T851, Alclad 2024, Al 2024, aircraft aluminum
2024 is the aircraft aluminum: strong, with the best fatigue and crack tolerance of the common alloys, but corrodes bare and cannot be welded. Values for T3.
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At a glance
| Density | 2.78 g/cm³ (0.1 lb/in³) |
|---|---|
| Tensile strength | 483 MPa (70 ksi) |
| Yield strength | 345 MPa (50 ksi) |
| Hardness | 120 HB |
| Elongation | 18% (sheet); 12-19% (plate T351) |
| Modulus of elasticity | 73.1 GPa (10.6 Msi) |
| Thermal | Melts at 502-638 °C (935-1180 °F); thermal conductivity ~121 W/m·K (T3, T4); T81/T851 for service to about 150-175 °C (300-350 °F) |
| Composition | Al, 3.8-4.9% Cu, 1.2-1.8% Mg, 0.3-0.9% Mn, up to 0.5% Fe, up to 0.5% Si |
Typical values, T3 temper (sheet) / T351 (plate and bar): solution treated, cold worked, naturally aged. Alclad 2024-T3 sheet is about 448 MPa (65 ksi) tensile and 310 MPa (45 ksi) yield. Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- The copper makes it hard enough to break chips and hold a good finish; comparable to 7075 and better than 6061. T351 plate is stress-relieved and stays flat under heavy one-sided machining.
- WeldabilityPoor
- Fusion welding hot-cracks and wrecks the temper; 2024 is not TIG or MIG welded in structural work. Resistance spot welding and friction stir welding are used in production; job shops rivet, bolt or bond it.
- FormabilityFair
- T3 sheet bends at about 3-5x thickness inside radius and cracks tighter. Aircraft practice is to form in the O temper or within an hour or two of quenching (the W condition), then let it age naturally to T4.
- Corrosion resistancePoor
- The lowest of the common alloys: bare 2024 pits and exfoliates outdoors and in salt air. Specify Alclad sheet, anodize plus seal, or chem film plus primer for any service exposure.
2024 is a copper-magnesium (2xxx series) alloy that has been the aircraft skin and structure alloy since the 1930s. It is not the strongest aluminum (7075 is about 20% stronger) but it has better fatigue strength, slower crack growth and higher fracture toughness, which is why tension-loaded fuselage skins, lower wing skins and fatigue-critical fittings are 2024 and compression-loaded parts are 7075.
The T3 temper (solution treated, cold worked and naturally aged) is the usual sheet temper; T351 is the stress-relieved plate and bar equivalent; T4 is naturally aged without cold work. Alclad 2024 sheet carries a thin layer of nearly pure aluminum on each face that protects the copper-rich core from corrosion at a cost of about 5-10% in strength, and is the norm for exterior skins. T81 and T851 are artificially aged for service at higher temperatures.
Bare 2024 has the poorest corrosion resistance of the common alloys and pits and exfoliates in wet or salty air, so it is always anodized, chem-filmed or primed for service. It hot-cracks when fusion welded, machines well, and bends only in the O temper or freshly quenched. Outside aircraft it shows up in machined parts that need fatigue strength, such as truck wheels, screw machine products, and precision fixtures.
Heat treatment
Precipitation hardening. Solution treat at about 495 °C (920 °F), water quench, then age naturally at room temperature for about four days to reach T4; T3 adds cold work (rolling or stretching) between quench and aging, and T351 is stretched for stress relief. Artificial aging at about 190 °C (375 °F) for 12 hours gives T81/T851 for elevated-temperature service. Annealing (O) is about 415 °C (775 °F) with a slow cool. Forming is done in O or in the freshly quenched W condition, which can be held for hours by refrigerating the blanks.
Tempers and conditions
- O (annealed)
- T3 (sheet)
- T351 (stress-relieved plate and bar)
- T4
- T81 / T851 (artificially aged)
- T3511 (extrusions)
Stock forms
- Sheet (bare and Alclad)
- Plate (T351)
- Round, square and hex bar (T351)
- Extruded bar and profiles (T3511)
- Seamless tube
- Rivet wire
Relative cost
Tier 3 of 5. About 1.5-2x the price of 6061 per pound, similar to 7075, with fewer stocked sizes outside aerospace distributors. Alclad sheet costs a little more than bare.
Typical applications
- Aircraft fuselage and lower wing skins (Alclad sheet)
- Aircraft ribs, frames, fittings and fasteners
- Fatigue-critical machined structural parts
- Truck and trailer wheels
- Screw machine products that need strength
- Precision fixtures, gauges and tooling plates
- Motorsport and bicycle components
Process compatibility
How 2024 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | GoodGood | Chips break well and finishes are fine, similar to 7075; use T351 plate and bar for heavy machining so the part stays flat. |
| Screw Machining | GoodGood | A traditional screw machine alloy in T351 bar: hard enough for short chips and close tolerances. |
| Welding | Not recommendedNot recommended | Hot cracking and a heat-affected zone that loses most of the T3 strength; not fusion welded in structural work. Rivet, bolt, bond or use 6061. Can 2024 aluminum be welded? |
| Sheet Metal Fabrication | GoodGood | The aircraft sheet alloy: routed, drilled, riveted and formed, but bends are made in the O or W condition, not in T3. |
| Press Brake Forming | FairFair | T3 needs about 3-5x thickness inside radius; tight flanges are formed in O or freshly quenched and then aged. |
| Waterjet Cutting | ExcellentExcellent | No heat-affected zone, so it is the preferred way to blank fatigue-critical 2024 plate and sheet. |
| Laser Cutting | FairFair | Cuts sheet, but the edge is heat-affected and slightly cracked; aircraft parts are routed or waterjet cut instead. |
| Anodizing | GoodGood | Type II takes, with a duller, more yellow-grey tone than 6061 because of the copper; sulfuric or chromic (Type I) anodize plus seal is the usual aircraft finish. Can 2024 aluminum be anodized? |
| Hardcoat Anodizing | FairFair | Type III builds thinner and softer on 2024 than on 6061 and burns more easily; specify it only where wear resistance is essential and expect a thickness limit. |
| Chem Film (Chromate Conversion Coating) | ExcellentExcellent | MIL-DTL-5541 chromate is the standard aircraft corrosion barrier and primer base on 2024, bare or Alclad. |
| Forging | FairFair | Forgeable, but 2014 and 7075 are the usual 2xxx/7xxx forging alloys; 2024 forgings are uncommon. |
| Shot Peening | GoodGood | Routine on fatigue-critical 2024 parts (AMS 2430); peen after machining and before finishing. |
| Metal 3D Printing | PoorPoor | High-copper 2xxx alloys hot-crack in laser powder bed fusion; printed aluminum is AlSi10Mg. Machine 2024 instead. |
Compare 2024
Design and sourcing tips
- Specify the temper and the clad: "2024-T3 Alclad" for exterior sheet, "2024-T351" for plate and bar that will be machined, "2024-T851" for service above about 100 °C (210 °F).
- Never leave 2024 bare in service: call out chem film plus primer, or anodize plus seal, and keep the finish spec (MIL-DTL-5541, MIL-A-8625) on the drawing.
- Do not weld it; design riveted, bolted or bonded joints, or make welded parts from 6061.
- Choose 2024 over 7075 when fatigue life and crack tolerance matter more than peak strength; choose 7075 for stiffness-critical, compression-loaded parts.
- Form flanges in the O temper or within a couple of hours of quenching, then age; do not ask a shop to bend T3 sheet on a tight radius.
- Order to AMS 4037 or AMS 4041 with the mill cert when the part is for aircraft; commercial "2024" plate may not carry the traceability the customer expects.
Frequently asked questions
- What is the difference between 2024 and 7075 aluminum?
- 7075 is stronger (572 vs 483 MPa tensile) and is used where strength and stiffness govern. 2024 has better fatigue strength, slower crack growth and higher fracture toughness, so it is used for tension-loaded and fatigue-critical structure such as fuselage skins. Both machine well, neither welds, and both need protection from corrosion; 2024 needs it more.
- What does Alclad 2024 mean?
- Alclad sheet has a thin layer of high-purity aluminum (about 2.5-5% of the thickness per side) bonded to each face of the 2024 core. The cladding corrodes sacrificially and protects the copper-rich core, at a cost of about 5-10% in strength. It is the standard for aircraft exterior skins and is specified under AMS 4041 or AMS-QQ-A-250/5.
- Can 2024 aluminum be welded?
- Not by TIG or MIG for anything structural. The copper content makes it hot-crack during solidification and the heat-affected zone loses most of its strength. Aircraft assemblies in 2024 are riveted or bonded; resistance spot welding and friction stir welding are used in some production. For a welded part, use 6061 or 5052.
- Does 2024 aluminum corrode?
- Yes, more readily than any other common alloy. The copper-rich phases set up local galvanic cells, so bare 2024 pits in humid air and exfoliates in salt exposure. Alclad sheet, anodizing, chem film and primer are specified as a matter of course, and drawings that leave 2024 bare are a mistake.
- What is the difference between 2024-T3 and 2024-T4?
- Both are solution treated and naturally aged to about the same strength. T3 has cold work applied after quenching (the sheet is rolled or the plate stretched), which raises the yield slightly and, for T351, relieves residual stress so plate stays flat when machined. T4 has no cold work and is the usual temper for tube, some bar and parts formed after quenching.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B209 and B211 (mechanical property minimums by temper)
- AMS 4037, AMS 4041 and AMS 4120
- Aluminum Association, Aluminum Standards and Data
- MMPDS (MIL-HDBK-5) design allowables
