What Is 2024 Aluminum?
2024 is a 2000-series aluminum alloy with copper as its primary alloying element (3.8–4.9% Cu, plus 1.2–1.8% Mg and 0.3–0.9% Mn). It gains strength through precipitation hardening — a controlled heat treatment cycle that forms sub-microscopic copper clusters in the aluminum lattice — rather than through cold working. The result is one of the strongest aluminum alloys available in wrought form, with a tensile strength competitive with mild steel at roughly one-third the density.
That copper content is also why 2024 corrodes more readily than 5xxx or 6xxx alloys. In practice, the material is almost always supplied as alclad sheet (pure aluminum metallurgically bonded to the surface) or protected by anodizing or paint. It is this strength-to-weight profile that makes 2024 the default choice for airframes and high-performance machinery — and exactly why the temper you choose, especially for formed parts, matters more than the alloy itself.
Understanding the T4 Temper
The full designation “T4” describes a two-step thermal treatment applied after the alloy is cast, worked to its final shape (sheet, plate, bar, or tube), and solution heat-treated.
- Solution heat treatment. The alloy is heated to approximately 493°C (920°F) to dissolve copper-rich precipitates into a uniform solid solution. At this temperature, the copper atoms are fully dispersed throughout the aluminum matrix. The material is then rapidly quenched — usually in cold water — to trap the copper in a supersaturated solid solution. If the alloy cooled slowly, the copper would precipitate as coarse, weakly bonded particles; the rapid quench prevents this.
- Natural aging. The quenched material is held at room temperature for several days. During this period, copper atoms diffuse short distances through the aluminum lattice and cluster on {100} planes, forming coherent zones known as Guinier-Preston (GP) zones. These zones strain the surrounding lattice and impede dislocation movement, which is the mechanism that increases strength. The aging process reaches near-peak strength after about 4–5 days and continues slowly for months, though the practical design properties stabilize within the first week.
The outcome is a temper that combines high tensile strength (~470 MPa UTS) with the highest ductility of the commonly specified 2024 tempers — typically 19–20% elongation in 50 mm. That ductility is the direct consequence of what T4 does not include: there is no cold-work step and no stress-relief stretch. The material retains the full formability of the freshly quenched condition while still reaching full aged strength.
How T4 Differs from T3
T3 is the closest temper to T4. Both are solution heat-treated and naturally aged. The difference is a single processing step: T3 receives a controlled cold-work reduction (typically 1–3%) after quenching and before natural aging. That cold work adds strain hardening — more dislocations in the lattice — which slightly increases tensile and yield strength but reduces ductility and formability.
For a part that will be formed, bent, or stretch-formed after heat treatment, T4 is the more practical choice. The absence of cold work means the material deforms more uniformly and tolerates tighter bend radii before cracking. For a part that will be used as-rolled or as-drawn without further forming, T3’s marginal strength advantage may be preferable. The 2024-T3 guide covers the cold-work route in more detail.
2024-T4 Mechanical Properties
| Majetek | Hodnota | Poznámky |
|---|---|---|
| Hustota | 2,78 g/cm³ | Typical for 2xxx-series |
| Mez pevnosti v tahu | 470 MPa (68 ksi) | Longitudinal, room temperature |
| Tensile Yield Strength (0.2% offset) | 324 MPa (47 ksi) | Governs most structural design calculations |
| Prodloužení při přetržení | ~19–20% | In 50 mm gauge; highest among 2024 tempers |
| Modul pružnosti | 73.1 GPa (10,600 ksi) | Approximately one-third of steel |
| Fatigue Strength (5×10⁸ cycles) | ~140 MPa (20 ksi) | Smooth specimen, R = −1 |
| Smyková pevnost | 285 MPa (41 ksi) | Relevant for fastener and rivet joint design |
| Tvrdost podle Brinella | 120 HB | 500 kg load, 10 mm ball |
| Elektrická vodivost | 30% IACS | Low for aluminum — specify for strength, not current carrying |
The yield strength of 324 MPa is the number that governs most structural designs. What distinguishes T4 from the other 2024 tempers is not the yield value — T351 reaches the same 325 MPa — but the elongation. At ~20%, T4 retains roughly 30–40% more ductility than T351 (~12–15%) and nearly double the ductility of T6 (~8–10%). That difference shows up directly in formability: a T4 sheet can be bent to a tighter radius or stretch-formed further before cracking than the same alloy in T3, T351, or T6.
Where 2024-T4 Is Used
The combination of high strength, fatigue resistance, and superior ductility makes T4 the standard temper for formed aerospace sheet and for applications where the material must be shaped after heat treatment.
Letecké a kosmické konstrukce
The primary application domain. Wing skins, fuselage panels, and structural covers are often formed from 2024-T4 sheet in the alclad condition. The forming operations — brake bending, stretch forming, or roll forming — take advantage of T4’s high elongation to achieve complex contours without cracking. Once formed, the part retains the full aged strength of the temper.
Wing lower skins and fuselage skins experience tension-dominated fatigue cycles during each flight. 2024-T4 provides the fatigue endurance needed for long service lives while keeping weight at approximately one-third of an equivalent steel design. The alclad layer protects against the corrosion that would otherwise limit the bare alloy’s service life in humid or salt-laden environments.
For machined structural components — bulkheads, fittings, brackets — T351 is typically preferred over T4 because the stress-relief stretch prevents machining distortion. T4’s role is specifically in formed sheet and light plate where forming capability matters more than machining stability. For a broader alloy-to-alloy comparison, the 2024 vs 7075 analysis covers when each alloy family fits.
Other High-Stress Applications
- Motorsport and performance vehicles. Body panels, suspension components, and structural brackets formed from 2024-T4 sheet appear in racing and high-performance applications where weight savings matter and the material must be shaped to complex geometries.
- Precision tooling and fixtures. Assembly jigs and inspection fixtures that require a combination of formability (to match contoured parts) and stiffness benefit from T4 sheet in moderate gauges.
- Military and defense. Structural housings, access panels, and formed covers where the strength-to-weight ratio and forming capability are both required.
T4 vs Other 2024 Tempers — How to Choose
2024 is available in several tempers, each optimized for a different manufacturing route. The table below maps the main options against typical selection criteria.
| Temperament | Treatment | UTS (MPa) | Mez kluzu (MPa) | Prodloužení | Nejlepší pro | Avoid when |
|---|---|---|---|---|---|---|
| T4 | Solution + natural age | 470 | 324 | ~20% | Formed sheet and light plate needing maximum ductility | Thick-section machining (no stress relief) |
| T3 | Solution + cold work + natural age | 483 | 345 | ~18% | Thin sheet requiring peak strength with moderate forming | Deep forming or tight bend radii |
| T351 | Solution + stretch + natural age | 470 | 325 | ~12–15% | Thick-section machined parts, fatigue-critical structures | Forming operations (lower ductility) |
| T6 | Solution + artificial age | 483 | 393 | ~8–10% | Maximum static strength applications | Fatigue-critical structures (lower fracture toughness) |
| T3511 | Same as T351, for extrusions | 425 | 310 | ~10% | Extruded bars, shapes, and tubes | Flat sheet or plate (T4 or T351 is the product-form equivalent) |
When T4 Is the Right Call
- The part will be formed, bent, or stretch-formed after heat treatment. T4’s ~20% elongation and absence of cold-work residual stress from deformation give it the widest forming window of any 2024 temper. Bend radii of 1.5t to 3t are practical for 90° bends in moderate gauges.
- The application prioritizes ductility and crack resistance over absolute yield strength. T4 reaches the same yield as T351 (324–325 MPa) while retaining significantly more elongation, which matters for parts that experience impact or must tolerate minor deformation without fracturing.
When Another Temper Fits Better
- The part will be heavily machined from thick plate. T4 has no stress-relief step, so residual quenching stresses remain in the material. Asymmetric material removal — deep pockets, one-sided milling — will release those stresses and cause the part to warp. 2024-T351 is the standard choice for machined structural components.
- Maximum static strength is the priority. T6’s artificial aging cycle pushes yield to 393 MPa — roughly 20% above T4 — but at the cost of ductility and fracture toughness. For purely static load applications without fatigue concerns, the 2024-T6 guide covers the trade-off.
- Thin sheet requiring peak strength. T3’s cold-work step adds a modest strength increment that can be useful in thin-gauge sheet where every kilownewton matters. The trade-off is reduced formability.
Working with 2024-T4 — What You Need to Know
Machining. 2024-T4 machines well with sharp carbide tooling at high spindle speeds and moderate feeds. The material produces short, clean chips and holds a good surface finish. However, because T4 retains residual quenching stresses, heavy material removal from one side of a plate or sheet can cause dimensional movement. For precision-machined parts from thick stock, switch to T351. For sheet-level operations — trimming, drilling, light milling — T4 is stable enough.
Welding. Fusion welding of 2024-T4 is not recommended. The alloy is susceptible to hot cracking in the weld zone, and the heat-affected zone (HAZ) loses the strengthening effect of the precipitation treatment, reverting to near-annealed properties adjacent to the weld. Practical joining methods are riveting, bolting, adhesive bonding, or friction stir welding. Friction stir welding preserves more base-metal strength because the peak temperature stays below the solution-treatment threshold, but it requires specialized equipment and process qualification.
Corrosion protection. Bare 2024-T4 will corrode in service — faster than 5xxx or 6xxx alloys and significantly faster in saltwater or humid environments. Three protection strategies cover most applications:
- Alclad. A thin layer of commercially pure aluminum (typically 1230 or 1100 alloy) is roll-bonded to both surfaces. The cladding acts as a sacrificial anode, protecting the core. Alclad 2024-T4 is standard for aerospace sheet.
- Anodizing. Sulfuric acid anodizing (MIL-A-8625 Type II) builds a controlled oxide layer that improves corrosion resistance and paint adhesion. Hard anodizing (Type III) is possible but may reduce fatigue life if not properly sealed.
- Chemical conversion coating and paint. Chromate conversion coating (Alodine) followed by epoxy primer and polyurethane topcoat is the standard protection system for machined 2024 parts.
Formability. T4 offers the best formability of the standard 2024 tempers. In the freshly quenched condition (before natural aging completes), it can be formed with even greater freedom. Once fully aged, bend radii of 1.5t to 3t for 90° bends in moderate gauges are practical. For complex shapes requiring severe deformation, forming should be completed before the material reaches full aged strength — typically within a few hours of quenching.
Pros and Limitations at a Glance
| Faktor | Výhoda | Omezení |
|---|---|---|
| Poměr pevnosti k hmotnosti | Competitive with mild steel at one-third the density | Yield strength lower than 7075-T6 or 2024-T6 |
| Fatigue | Excellent fatigue life in tension-dominated cycles | Notched fatigue sensitivity requires careful detail design |
| Tvarovatelnost | Highest ductility among 2024 tempers (~20% elongation) | Forming window narrows once natural aging completes |
| Machining stability | Good chip control and surface finish in sheet-level operations | No stress relief — heavy machining of thick stock causes warpage |
| Odolnost proti korozi | Acceptable with alclad or protective coating | Bare alloy not suitable for unprotected service |
| Svařitelnost | Friction stir weldable | Not fusion-weldable — hot cracking and HAZ strength loss |
| Dostupnost | Standard aerospace mill product in sheet and light plate | Thick plate typically specified as T351, not T4 |
Závěr
2024-T4 occupies a specific position in the aluminum temper spectrum: it delivers the full strength and fatigue resistance of the 2024 alloy family while retaining the highest ductility of any standard 2024 temper. That combination makes it the default choice for formed aerospace sheet and any application where the material must be shaped after heat treatment. The trade-off is equally clear — T4 has no stress-relief step, so it is not the right temper for heavily machined thick-section components, and like all 2024 variants it requires corrosion protection in service.
Linsy Aluminum supplies 2024 hliníková slitina in sheet, plate, bar, tube, and wire forms across the T3, T4, T351, and T851 tempers. Factory-direct supply with MTC documentation on every order and SGS test reports available on request means the material arrives with full traceability — no broker gaps, no unknown mill sources. Low-MOQ custom production supports non-stock dimensions with a typical lead time of 10–60 days.
Contact Linsy Aluminum today to discuss your 2024-T4 requirements and request a quote.
ČASTO KLADENÉ DOTAZY
What is the difference between 2024-T4 and 2024-T3?
Both tempers are solution heat-treated and naturally aged. T3 adds a controlled cold-work reduction (1–3%) after quenching, which slightly increases strength but reduces ductility. T4 skips the cold work, giving it roughly 20% elongation versus T3’s ~18%. Choose T4 for formed parts that need maximum formability; choose T3 for thin sheet where the marginal strength gain matters more than forming capability.
Can 2024-T351 be anodized?
Yes. Sulfuric acid anodizing (Type II per MIL-A-8625) is the most common specification. The resulting oxide layer improves corrosion resistance and provides a base for paint adhesion. Hard anodizing (Type III) is also possible but may reduce fatigue life if not properly controlled — the brittle oxide layer can act as a crack initiation site under cyclic loading. Specify sealed anodizing for fatigue-critical parts.
Can 2024-T4 be welded?
No — not by fusion welding. 2024 is susceptible to hot cracking in the weld zone, and the heat-affected zone reverts to near-annealed properties, losing the precipitation-hardened strength. Riveting, bolting, and adhesive bonding are the standard joining methods. Friction stir welding is a viable alternative for thick-section butt joints because it stays below the solution-treatment temperature, but it requires specialized equipment and process qualification.
What is the typical lead time for 2024-T351 plate?
Standard mill lead times for 2024-T351 plate range from 4 to 12 weeks depending on thickness and quantity. Aerospace-grade material with full mill certifications typically sits at the longer end. Working with a supplier that holds inventory of common gauges can reduce effective lead time significantly. Always confirm whether the quoted lead time includes the stretching and natural aging cycle — some shorter quotes exclude the full aging period and deliver material that will continue to strengthen after receipt.
How does 2024-T4 compare to 2024-T351 for machining?
T351 is the better choice for machined components. T351 includes a stress-relief stretch (1–3% elongation after quenching) that redistributes residual quenching stresses throughout the cross-section. T4 has no stress relief, so residual stresses remain. When you machine away material from one side of a T4 plate, those stresses release unevenly and the part warps. For sheet-level operations — trimming, drilling, light milling — T4 is stable. For deep-pocket milling or asymmetric material removal from thick stock, switch to T351.
Can 2024-T4 be used in marine environments?
Not without continuous protective treatment. Bare 2024 corrodes rapidly in saltwater exposure — faster than 5xxx-series marine alloys like 5083 or 5052. Alclad 2024-T4 with a full paint system can survive in above-deck or sheltered marine environments, but it requires regular maintenance. For immersed or splash-zone marine applications, choose a 5xxx or 6xxx alloy instead. 2024-T4 has no place in hull or deck structure.
What is the typical lead time for 2024-T4 sheet?
Standard mill lead times for 2024-T4 sheet range from 4 to 12 weeks depending on gauge, width, and quantity. Aerospace-grade alclad material with full mill certifications typically sits at the longer end. Working with a supplier that holds inventory of common gauges can reduce effective lead time significantly. Always confirm whether the quoted lead time includes the natural aging period — some shorter quotes deliver material that has not yet reached full aged strength.
