2124-T851
Solution heat-treated, stretched 1.5 – 3 % and artificially aged. The main aerospace temper: high yield strength, improved stress-corrosion resistance and best dimensional stability for heavy machining.
Thick-section aerospace plate
2124 Aluminium Plate (T351, T851)
2124 is a high-purity version of 2024 made for thick aerospace plate: lower iron and silicon give it better fracture toughness and through-thickness ductility in sections from about 25 mm to 150 mm. Metline supplies 2124-T851 and T351 plate and cut blocks, ultrasonically tested and certified to AMS 4101 and ASTM B209, to customers worldwide.
- Alloy
- 2124 (high-purity 2024)
- Tempers
- T851, T351, O
- Thickness
- typically 25 – 150 mm
- Standards
- AMS 4101 · ASTM B209
What is 2124 aluminium plate?
2124 has the same copper, magnesium and manganese content as 2024 but much tighter limits on iron (0.30 % maximum instead of 0.50 %) and silicon (0.20 % instead of 0.50 %). Those impurities form coarse, brittle intermetallic particles; reducing them makes thick plate tougher, more ductile in the short-transverse direction and more consistent through the section.
The alloy was developed for aircraft parts machined from thick plate, such as wing spars and ribs, bulkheads, fuselage frames and landing-gear support structure, where 2024 plate in heavy gauges would show low through-thickness elongation and fracture toughness. It is normally supplied in the T851 temper (stretched and artificially aged), which gives high yield strength, good resistance to stress-corrosion cracking and stable properties at moderately elevated temperatures.
Because 2124 is made specifically for critical aerospace use, its purchase specifications normally include guaranteed minimum fracture toughness, ultrasonic inspection of the full plate and full lot traceability. For non-critical machined parts, 2024-T351 or 2024-T851 is usually more economical.
2124 chemical composition (wt %)
Registered Aluminum Association limits for 2124, shown alongside 2024 so the difference is clear. The certificate for every lot reports the actual analysis.
| Element | 2124 | 2024 | Effect of the tighter 2124 limit |
|---|---|---|---|
| Silicon (Si) | ≤ 0.20 | ≤ 0.50 | Fewer Mg2Si and Si-bearing particles |
| Iron (Fe) | ≤ 0.30 | ≤ 0.50 | Fewer coarse Al-Cu-Fe-Mn constituents, which start cracks |
| Copper (Cu) | 3.8 – 4.9 | 3.8 – 4.9 | Same strengthening base |
| Manganese (Mn) | 0.30 – 0.9 | 0.30 – 0.9 | |
| Magnesium (Mg) | 1.2 – 1.8 | 1.2 – 1.8 | |
| Chromium (Cr) | ≤ 0.10 | ≤ 0.10 | |
| Zinc (Zn) | ≤ 0.25 | ≤ 0.25 | |
| Titanium (Ti) | ≤ 0.15 | ≤ 0.15 | |
| Others, each / total | 0.05 / 0.15 | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | Remainder |
Mechanical properties of 2124 plate
Thick plate properties depend strongly on thickness and test direction. The longitudinal (L) direction is strongest; the short-transverse (ST) direction, through the thickness, is weakest and matters most for parts loaded across the plate. The table gives representative specified minimums for 2124-T851 in the longitudinal direction and typical values for comparison.
| Condition | Tensile strength | Yield strength (0.2 %) | Elongation |
|---|---|---|---|
| T851, 25 – 50 mm, specified minimum (L) | 455 MPa / 66 ksi | 395 MPa / 57 ksi | 5 % |
| T851, 127 – 152 mm, specified minimum (L) | 434 MPa / 63 ksi | 372 MPa / 54 ksi | 4 % |
| T851, typical (L) | about 480 MPa / 70 ksi | about 440 MPa / 64 ksi | 6 – 9 % |
| T351, typical (L) | about 470 MPa / 68 ksi | about 325 MPa / 47 ksi | 15 – 19 % |
Minimums summarised from the ASTM B209 tables for 2124-T851; AMS 4101 adds requirements for other directions, fracture toughness and ultrasonic quality. Use the specification and mill certificate for design and acceptance.
Physical properties (typical)
- Density
- 2.78 g/cm³ (0.100 lb/in³)
- Modulus of elasticity
- about 73 GPa
- Thermal conductivity
- about 150 W/m·K (T851)
- Electrical conductivity
- about 38 – 39 % IACS (T851)
- Coefficient of thermal expansion
- about 22.9 µm/m·°C (20 – 100 °C)
- Melting range
- about 502 – 638 °C
2124-T851, T351 and O compared
2124-T351
Solution heat-treated, stretched and naturally aged. Lower yield strength but higher elongation and toughness; chosen where damage tolerance outweighs yield strength, or where the part will be aged later.
2124-O
Annealed plate for forming or for heat treatment by the user. Rarely ordered in thick gauges.
The artificial ageing step that turns T351 into T851 raises yield strength by roughly a third and changes the precipitate structure along grain boundaries, which is what improves resistance to stress-corrosion cracking. The cost is lower elongation and somewhat lower toughness than T351, so specifications choose the temper part by part.
Why low iron and silicon matter in thick plate
In a thin sheet, coarse constituent particles are small and well broken up by rolling, and they have little effect on toughness. In a 100 mm plate, the centre receives much less deformation and cools more slowly during quenching, so particles remain larger and properties through the thickness are lower. Cracks prefer to run along bands of these particles.
Cutting iron and silicon reduces the volume of constituent particles. The practical effects, reported in aerospace data since 2124 was introduced, are higher plane-strain fracture toughness (KIC), better short-transverse elongation and more uniform fatigue performance in thick sections. That is why many aircraft programmes call for 2124-T851 where 2024-T851 would otherwise be used in heavy gauges.
- Better resistance to fast fracture from a flaw or fatigue crack
- More reliable through-thickness properties for lugs and fittings loaded across the plate
- Lower risk of rejection at ultrasonic inspection due to inclusions
The same principle explains other "high-purity" aerospace variants such as 7475 (from 7075) and 2524 (from 2024 sheet).
2124 specifications and designations
| System | Designation | Standard |
|---|---|---|
| Aerospace (SAE) | 2124-T851 plate | AMS 4101 |
| Aerospace (SAE, ex-federal) | 2124 plate | AMS-QQ-A-250/29 |
| ASTM | 2124-T851 / T351 | ASTM B209 (B209M) |
| UNS | A92124 | — |
| European (EN) | EN AW-2124 | EN 573-3; EN aerospace (EN 2000/4000 series) standards |
| Ultrasonic inspection | — | AMS-STD-2154 (formerly MIL-STD-2154), class per drawing |
Aerospace specifications are revised regularly; give the revision on your purchase order. Customer-specific material specifications (for example from airframe makers) can be quoted against on request.
2124 plate sizes and weights
Supply range
- Thickness
- Typically 25 – 150 mm (1 – 6 in) in T851; thinner and thicker gauges on mill order
- Width × length
- Full mill plates or saw-cut pieces; common cut sizes 305 × 305 mm (12 × 12 in) up to 610 × 1220 mm (24 × 48 in)
- Cut blocks
- Saw-cut to near-net size for machining, with orientation (L, LT, ST) marked
- Inspection
- Ultrasonic testing, dimensional check, conductivity and hardness check where specified
- Documents
- EN 10204 3.1 certificate with chemistry, tensile results and heat-treatment lot
2124 weighs 2.78 kg per m² per millimetre of thickness. Imperial gauges are common for aerospace plate:
| Thickness | kg per m² | 305 × 305 mm piece (kg) | 610 × 1220 mm piece (kg) |
|---|---|---|---|
| 1 in (25.4 mm) | 70.6 | 6.57 | 52.5 |
| 1.5 in (38.1 mm) | 105.9 | 9.85 | 78.8 |
| 2 in (50.8 mm) | 141.2 | 13.14 | 105.1 |
| 2.5 in (63.5 mm) | 176.5 | 16.42 | 131.4 |
| 3 in (76.2 mm) | 211.8 | 19.71 | 157.6 |
| 4 in (101.6 mm) | 282.4 | 26.27 | 210.2 |
| 5 in (127 mm) | 353.1 | 32.84 | 262.7 |
| 6 in (152.4 mm) | 423.7 | 39.41 | 315.3 |
Inspection and certification of 2124 plate
Thick aerospace plate is accepted on more than tensile results. Typical requirements on a 2124 order are listed below; tell us which apply to your programme.
- Chemistry: cast analysis confirming the low Fe and Si limits
- Tensile tests: L, LT and, for thicker plate, ST directions at the locations defined in the specification
- Fracture toughness: KIC testing to ASTM E399 where the specification guarantees minimum values
- Ultrasonic inspection: to AMS-STD-2154, commonly class A or AA for critical parts
- Electrical conductivity and hardness: as a check on correct heat treatment
- Traceability: every piece marked with alloy, temper, lot and plate number, carried through cutting
Machining and processing thick 2124 plate
Machining
Machines well with carbide tooling at high speeds. Because up to 90 % of a plate may be removed, rough both sides symmetrically and finish in stages to keep residual-stress distortion to a minimum.
Orientation
Lay out parts so primary loads run in the L or LT direction. Keep lugs and attachment holes away from the plate mid-thickness when ST loading is high.
Joining
Not fusion welded. Parts are bolted or riveted into assemblies.
Protection
Finish with anodising (sulphuric or boric-sulphuric acid), conversion coating and primer as specified for the aircraft programme.
2124 compared with 2024 and 7050 plate
| Property | 2024-T851 | 2124-T851 | 7050-T7451 |
|---|---|---|---|
| Typical tensile strength | about 480 MPa | about 480 MPa | about 510 – 525 MPa |
| Typical yield strength | about 445 MPa | about 440 MPa | about 455 – 470 MPa |
| Thick-plate toughness | Moderate | Higher | High |
| Stress-corrosion resistance | Good (T851) | Good (T851) | Very good (T74 family) |
| Strength at 100 – 150 °C | Good | Good | Falls faster than 2xxx |
| Typical use | General thick machined parts | Critical thick aerospace parts | Thick wing and fuselage structure |
7050-T7451 has largely taken over many thick-plate airframe applications because of its higher strength and toughness, but 2xxx alloys like 2124 keep an advantage where parts run warm, for example near engines or in supersonic aircraft structure, and where existing designs are qualified on 2124.
Common mistakes when buying 2124 plate
- Not stating the revisionAMS 4101 and customer specifications change over time. Quote the revision on the order so the certificate matches the drawing.
- Ignoring orientationA cut block without L, LT and ST marks cannot be laid out correctly. Ask for orientation to be transferred to every piece.
- Assuming 2024 data appliesDesign allowables for 2124 come from its own specification and handbook data; do not mix 2024 and 2124 values in stress calculations.
- Skipping ultrasonic classThick plate for rotating or primary structure normally needs class A or AA. Specify it at enquiry, because it affects which plates qualify.
- Over-specifyingFor thin plate or non-critical fixtures, 2024-T351 or T851 performs the same job at lower cost and with shorter supply times.
Applications of 2124 plate
- Wing spars, ribs and bulkheads machined from thick plate
- Fuselage frames, longerons and landing-gear support structure
- Engine pylons and structure exposed to moderately elevated temperature
- Military aircraft and missile structure
- High-performance tooling and test fixtures where certified toughness is required
In each case the reason is the same: the part is machined from a thick section, carries high cyclic or static load, and must tolerate a flaw without sudden fracture. Where only one of those conditions applies, a more common grade is usually the better buy, and our team can help you compare the options before you order.
How to order 2124 plate
- SpecifyAlloy and temper (2124-T851 or T351), thickness, cut sizes and grain orientation, quantity, specification and revision (AMS 4101, ASTM B209 or a customer specification), ultrasonic class and any toughness requirement.
- QuoteWe confirm availability, tolerances, certification, packing and delivery terms (EXW, FOB, CIF or DAP) for your destination.
- ProcessPlates are saw-cut to size with orientation and traceability marks transferred to every piece, then inspected and packed with corner protection.
- DocumentEach delivery carries a mill test certificate to EN 10204 3.1 with the cast analysis and mechanical results for the lot; third-party inspection can be arranged on request.
- ShipSheets are interleaved or film-protected, packed on pallets or in seaworthy wooden cases, and shipped by sea or air to your port or door.
References and standards
- SAE AMS 4101 – Aluminum Alloy Plate, 2124-T851
- ASTM B209 – Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
- SAE AMS-STD-2154 – Inspection, Ultrasonic, Wrought Metals
- ASTM E399 – Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits for Wrought Aluminum (Teal Sheets)
- ASM Handbook, Volume 2 – Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
2124 aluminium plate: frequently asked questions
What is the difference between 2124 and 2024?
The alloying elements are the same, but 2124 limits iron to 0.30 % and silicon to 0.20 %. Fewer coarse particles give thick 2124 plate higher fracture toughness and better through-thickness ductility than 2024.
Why is 2124 usually supplied in T851?
T851 combines high yield strength with better stress-corrosion resistance and dimensional stability than naturally aged T351, which suits heavily machined aerospace parts.
What thickness is 2124 plate made in?
It is aimed at thick sections, usually about 25 – 150 mm (1 – 6 in). Thinner plate is normally ordered in 2024 because the toughness benefit is small.
Can 2124 replace 2024 on a drawing?
Technically 2124 meets or exceeds 2024 properties, but in aerospace a substitution must be approved by the design authority. For non-aerospace work it is usually acceptable.
Is 2124 plate weldable?
No, not by conventional fusion welding. It is machined and mechanically fastened.
Do you supply small cut pieces of 2124-T851?
Yes. We saw-cut pieces from full plates to your sizes, mark orientation and lot on each piece and supply a 3.1 certificate.
Need 2124-T851 plate or cut blocks?
Send thickness, sizes, quantity, specification and ultrasonic class. We will reply with availability, certification and price.
