2024-T851 Aluminum: Properties, Temper, and How to Specify It

What Is 2024 Aluminum?

2024 is a 2000-series alloy with copper as its primary alloying element (3.8–4.9% Cu) and magnesium (1.2–1.8%) plus manganese (0.30–0.90%) as secondary strengtheners. It reaches high strength through precipitation hardening after solution heat treatment, which places it among the strongest wrought aluminum alloys.

That copper content also makes 2024 the least corrosion-resistant of the common aerospace alloys and generally unsuitable for fusion welding — bare sections are prone to intergranular and exfoliation corrosion and require cladding, anodizing, or paint for protection. It is this strength-to-weight profile, paired with reliable machinability, that makes 2024 the default choice for airframes and high-performance structural parts.

Understanding the T851 Temper

The “T851” designation describes a three-stage thermal-mechanical treatment applied to 2024 plate and comparable rolled or forged products:

1. Solution heat treatment. The plate is heated to roughly 493°C (920°F) to dissolve copper-rich precipitates into a uniform solid solution, then rapidly quenched.
2. Stress relief by stretching. Within a short window after quenching, the plate is stretched 1–3% of its length. This controlled plastic deformation relaxes the residual stresses locked in by the rapid quench.
3. Artificial aging. The stretched plate is heated to a lower temperature (around 190°C / 375°F) to precipitate the strengthening phase, raising strength to its peak.

The practical result is a 2024 plate that combines the alloy’s maximum static strength with low residual stress. The benefit appears during machining: a T851 plate stays flat and stable as material is removed, which is why it is favored for precision-machined fittings and blocks. For forgings, the equivalent compressive stress-relief temper is T852; the “1” suffix denotes stretch relief for plate and rolled product.

How T851 Differs from T351

T851 and T351 share the same solution heat treatment and stretch stress relief. The difference is the final step: T351 is naturally aged at room temperature, while T851 is artificially aged at elevated temperature. That single change pushes yield strength from roughly 325 MPa (T351) to about 450 MPa (T851) — the largest strength jump between any two 2024 tempers — but it cuts elongation from roughly 19% down to about 5%. T851 trades ductility for peak strength and machined stability.

2024-T851 Mechanical Properties

Eigendom	Waarde	Opmerking
Dichtheid	2,78 g/cm³	Typical for 2xxx-series
Uiteindelijke treksterkte	510 MPa (74 ksi)	Plate, room temperature
Tensile Yield Strength (0.2% offset)	450 MPa (65 ksi)	Peak among 2024 tempers
Rek bij breuk	~5%	Much lower than T351 (~19%)
Fatigue Strength (5×10⁸ cycles)	~120 MPa (17 ksi)	Smooth specimen, R = −1
Afschuifsterkte	300 MPa (43 ksi)	Relevant for fastener joints
Elasticiteitsmodulus	73 GPa (10.6×10³ ksi)	~One-third of steel
Thermische geleidbaarheid	121 W/m·K	Good heat dissipation
Thermische uitzettingscoëfficiënt	23 µm/m·K	-
Specifieke warmtecapaciteit	875 J/kg·K	-
Smeltbereik	502–638°C	Solidus to liquidus

The 450 MPa yield is the number that drives most T851 designs — it sits well above 6061-T6 (about 276 MPa) and roughly 40% above T351, letting engineers shrink cross-sections or add margin in compression-critical parts. The trade-off is ductility and corrosion, covered below.

Where 2024-T851 Is Used

The mix of peak strength, low residual stress, and post-machining dimensional stability makes T851 the temper of choice for thick 2024 plate that will be machined into high-load components.

Aerospace and Defense Structures

Wing spars and lower wing skins, fuselage frames, bulkheads, and structural fittings are often machined from 2024-T851 plate because the stress-relieved condition keeps large or asymmetric sections stable through milling. Landing-gear components, hydraulic valve bodies, and high-strength fasteners use the same temper where static strength and machined accuracy are non-negotiable. In these applications the plate is normally alclad or finish-protected, since bare 2024 does not survive aggressive environments unprotected.

Precision Tooling and High-Strength Blocks

Motorsport uprights, bell cranks, and structural brackets machined from T851 plate gain weight savings over steel without giving up stiffness. Precision jigs, inspection fixtures, and automation frames use T851 because it stays flat through temperature swings and repeated load cycles. Where the part is welded rather than fastened, 6061 is usually the better starting point — see the working notes below.

T851 vs Other 2024 Tempers — How to Choose

Temper	Treatment	UTS	YS	Geschikt voor	Avoid when
T851	Solution + stretch + artificial age (plate)	510 MPa (74 ksi)	450 MPa (65 ksi)	Max-strength machined plate, fittings	Welding, forming, saltwater
T3511	Solution + stretch + straighten (extrusion)	425 MPa (62 ksi)	310 MPa (45 ksi)	Machined extrusions, dimensional stability	Welding required, saltwater exposure
T3	Solution + cold work + natural age	483 MPa (70 ksi)	345 MPa (50 ksi)	Sheet skins, formed parts	Thick sections needing stability
T4	Solution + natural age	469 MPa (68 ksi)	324 MPa (47 ksi)	High-ductility parts	Corrosion-exposed without cladding
T351	Solution + stretch + natural age (plate)	470 MPa (68 ksi)	325 MPa (47 ksi)	Wing ribs, bulkheads, moderate forming	Peak strength needed

When T851 Is the Right Call

Two conditions point to T851: the part is a plate or forged block that will be machined, and it needs the highest possible static strength or machined stability. If both hold, the artificial-age treatment pays for itself in reduced scrap and rework on large, thin, or critically dimensioned sections.

When Another Temper Fits Better

When the geometry is an extruded bar, tube, or profile, T3511 delivers the same stress relief in the right product form. When moderate forming is required, T351 or T4 keeps enough ductility to bend or shape the part. When welding or saltwater service is part of the requirement, move off 2024 entirely — 6061 or a 5xxx alloy removes the corrosion and weldability limits at the cost of lower strength.

Working with 2024-T851 — What You Need to Know

Machining. 2024-T851 machines cleanly with good chip control and supports high cutting speeds, which is why it is a staple for precision CNC plate and screw-machine products. Tool wear stays manageable, but sharp tool geometry and consistent coolant flow keep surface finish tight on thin sections. Its low residual stress is the real advantage: parts stay flat through heavy material removal.

Welding and joining. Fusion welding is not recommended for 2024. The copper-rich composition makes the weld and heat-affected zone prone to hot cracking, and post-weld strength can fall well below the base material. For assemblies, use rivets, bolts, or adhesive bonding; if a welded structure is unavoidable, switch the design to 6061-T6 and accept the lower strength.

Corrosion protection. Bare 2024 has poor corrosion resistance and is vulnerable to intergranular and exfoliation attack, especially in chloride environments. Specify alclad (a metallurgically bonded pure-aluminum surface layer) for aircraft skins, or pair anodizing and paint for enclosed structures. In direct saltwater or marine immersion, 2024 is the wrong choice regardless of temper.

Formability. T851 is delivered as artificially aged plate at near-peak strength, so it is not intended for heavy cold forming after treatment — bending risks cracking because ductility is only about 5%. Form or shape the section before final aging where possible, or select T351/T4 if the design needs bends.

Pros and Limitations at a Glance

Afmeting	Voordeel	Beperking
Strength-to-weight	Highest static strength of wrought 2024	-
Machining stability	Stress-relieved plate, low distortion	-
Weerstand tegen vermoeiing	Strong for cyclic-load structures	Lower high-cycle endurance than T351
Corrosiebestendigheid	-	Poor; requires cladding or coating
Lasbaarheid	-	Fusion welding not recommended
Beschikbaarheid	Stock and custom plate available	Not a general sheet substitute
Kosten	-	Higher than 6061

Conclusie

2024-T851 brings the highest static strength and best machined stability of any 2024 temper to thick plate and forged blocks — but it gives up ductility, corrosion resistance, and weldability to get there. That trade-off is manageable only with the right protection and joining plan, and sourcing the correct plate with documentation is where projects stall.

Linsy Aluminum supplies 2024 aluminum in plate, bar, tube, profile, and wire forms — including T851 plate — with tight tolerances and tempers matched to your application. Stock standard sizes and low-MOQ custom production are typically delivered in 10–60 days, every order ships with an MTC, SGS test reports (including ultrasonic testing for thick plates) are available on request, and the plant holds ISO 9001, 14001, and 45001 certifications.

If your part needs 2024-T851’s peak strength and machining stability, send the drawing or specification to Linsy Aluminum for a stock check and quote on 2024-T851 aluminum plate.

Veelgestelde vragen

What is the difference between 2024-T851 and 2024-T351?

They share solution heat treatment and stretch stress relief, but T351 is naturally aged at room temperature while T851 is artificially aged. That one step raises yield strength from about 325 MPa (T351) to roughly 450 MPa (T851) and drops elongation from around 19% to about 5% — T851 trades ductility for peak strength.

Can 2024-T851 be welded?

No. Fusion welding is not recommended. The copper-rich alloy cracks in the weld and heat-affected zone and loses much of its strength. Use mechanical fastening or adhesive bonding, or choose 6061-T6 if welding is required.

Is 2024-T851 suitable for marine or saltwater use?

No. Bare 2024 has poor corrosion resistance and will pit or exfoliate in chloride environments. For saltwater or marine immersion, a 5xxx or 6xxx alloy is the safer choice; 2024 belongs in enclosed or well-coated structures.

What are the main advantages of 2024-T851?

Peak static strength among 2024 tempers (about 450 MPa yield), low residual stress that keeps large machined plates flat and stable, and good fatigue resistance for cyclic-load structures. It is the standard choice for machined high-strength aerospace plate.

How does 2024-T851 compare to 6061-T6?

T851 delivers roughly 40–60% higher yield strength and better machined stability, but it gives up corrosion resistance and weldability and costs more. 6061-T6 is the better pick when the part must be welded, see marine exposure, or stay low-cost; 2024-T851 wins when strength-to-weight and machined accuracy dominate.