Aluminum 2424: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Aluminum 2424 is a wrought, heat-treatable alloy that belongs to the 2xxx series of aluminum–copper–magnesium alloys. It is closely related to the well-known 2024 family and is formulated for increased strength and improved fracture toughness by modest adjustments to copper, magnesium and manganese levels and tighter control of iron and silicon impurities.

The dominant alloying elements are copper (primary strengthening agent), magnesium (forms Guinier–Preston zones and Mg2Si-like precipitates that contribute to age hardening) and manganese (grain structure control and dispersoid formation). Strengthening is achieved primarily through precipitation hardening following solution treatment and artificial aging, with a secondary contribution from strain hardening in certain tempers.

Key traits include high specific strength and good fatigue resistance when appropriately treated and surface finished, moderate formability in softened tempers, limited intrinsic corrosion resistance versus 5xxx/6xxx alloys, and moderate weldability when using proper procedures and filler metals. Typical industries include aerospace (structures and fittings), defense (airframe components), motorsports and specialty industrial sectors where high strength-to-weight and fatigue performance are required.

Engineers select 2424 over other alloys when the design prioritizes high fracture toughness and fatigue performance in a heat-treatable alloy, or when a close balance of high static strength and damage tolerance is required. It is chosen instead of higher-strength 7xxx alloys when improved corrosion performance, toughness, and weldability are important, and instead of 6xxx/5xxx alloys when higher peak strength is required.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility and formability
T3	Medium-High	Moderate	Good	Limited	Cold worked and naturally aged; good fatigue properties
T4	Medium	Moderate-High	Good	Limited	Solution heat-treated and naturally aged
T6	High	Low-Moderate	Limited	Challenging	Solution heat-treated and artificially aged for peak strength
T8 / T851	High	Low-Moderate	Limited	Challenging	Solution treated, cold worked, and artificially aged / stabilized for improved fracture toughness
T351	Medium-High	Moderate	Good	Limited	Stress-relieved by stretching after solution heat treatment

Tempering dramatically alters 2424 properties by changing the distribution, size and coherence of Cu- and Mg-containing precipitates. Soft tempers (O, T4) maximize ductility and formability, while aged tempers (T6, T8) provide the highest yield and ultimate strength at the expense of elongation and bendability.

Heat-treatment and cold-work sequences also influence residual stress, susceptibility to stress-corrosion cracking, and machinability; stabilized tempers (e.g., T851) are used when dimensional stability and resistance to further aging are required.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.50	Controlled low Si to minimize brittle intermetallics and improve toughness
Fe	≤ 0.50	Kept low to reduce coarse Fe-rich intermetallics that impair ductility
Mn	0.3–1.2	Grain structure control, dispersoid formation, improves toughness
Mg	1.2–1.9	Contributes to precipitation hardening with Cu and to solid solution strengthening
Cu	3.8–5.0	Primary strengthening element forming Al2Cu and other precipitates
Zn	≤ 0.25	Minor, usually residual; kept low to avoid deleterious precipitates
Cr	≤ 0.10	Trace levels to control grain structure and recrystallization in some heats
Ti	≤ 0.15	Refining agent when added in trace amounts during ingot production
Others (each)	≤ 0.05	Balance of alloying and residual elements; Al remainder

The composition is centered on copper and magnesium to enable classical Al–Cu–Mg age-hardening reactions that form GP zones and metastable precipitates (θ′ and S-phase), which are the microstructural origin of strength in 2424. Manganese and small additions of titanium or chromium act as grain refiners and dispersoid formers, improving toughness and reducing susceptibility to recrystallization during thermal cycles.

Mechanical Properties

Tensile behavior of 2424 is characterized by a high ultimate tensile strength and a proportional increase in yield strength when aged to T6/T8 tempers. The alloy exhibits a distinct yield plateau in some heat-treatment conditions and a relatively linear elastic region up to yield; post-yield strain-hardening rates are influenced by prior cold work and precipitate distribution. Elongation to failure decreases with increasing temper strength; annealed material is substantially more ductile than T6 or T8 tempers.

Hardness correlates well with temper and aging condition; T6/T8 tempers produce peak hardness values associated with coherent/semi-coherent precipitates, while solutionized or annealed conditions show much lower hardness. Fatigue performance is a strong point for 2424 when processed and surface-treated correctly: shot peening, peening-induced compressive surface stresses, and removal or suppression of surface defects can significantly raise fatigue crack-initiation thresholds. Thickness and product form influence mechanical outcomes substantially — thicker sections can cool more slowly after solution treatment, producing coarser precipitate distributions and slightly lower strength and toughness compared to thin-gauge sheet.

Property	O/Annealed	Key Temper (T6 / T851 typical)	Notes
Tensile Strength (UTS)	~240–300 MPa	~450–510 MPa	Values are typical ranges; specific values depend on exact chemistry, thickness and aging cycle
Yield Strength (0.2% offset)	~100–160 MPa	~320–420 MPa	Yield increases markedly with artificial aging and cold-work prior to aging
Elongation	~18–30%	~6–14%	Ductility drops in peak-aged tempers; elongation depends on gauge and heat treatment
Hardness (HB)	~40–60 HB	~120–150 HB	Hardness correlates with precipitate volume fraction and coherence

Physical Properties

Property	Value	Notes
Density	2.78 g/cm³	Typical for Al–Cu–Mg wrought alloys; higher than pure aluminum due to Cu content
Melting Range	~500–640 °C	Alloy solidus–liquidus span; full melting near pure Al melting point but influenced by alloying phases
Thermal Conductivity	~120–150 W/m·K	Reduced relative to pure Al due to alloying; still good for many thermal management applications
Electrical Conductivity	~28–40 % IACS	Dependent on temper; higher conductivity in annealed states
Specific Heat	~0.90 J/g·K	Typical for aluminum alloys in ambient temperature range
Thermal Expansion	~23–24 µm/m·K	Similar to other aluminum alloys; design for thermal strain is necessary in mixed-metal assemblies

The physical property set places 2424 as a high-strength aluminum with thermal and electrical conductivities lower than pure aluminum but still adequate for many structural and thermal-management roles. Density is slightly elevated by copper, which affects mass-sensitive designs and needs to be accounted for in weight-critical applications. Thermal expansion is similar to most aluminum alloys and can lead to differential thermal strain when used with steels or composites.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.4–6.4 mm	Thin gauges reach peak strength after aging; good surface finish	O, T3, T4, T6, T8	Common for aerospace skins, fittings; often clad for corrosion protection
Plate	6.4–50 mm+	Thickness reduces attainable strength and requires longer solution times	O, T6, T851	Heavy sections used for structural members and bulkheads; quench sensitivity is important
Extrusion	Profile-dependent	Limited compared to 6xxx alloys, but possible for certain profiles	T4, T6	More difficult to extrude; control of homogenization important
Tube	Wall/OD variable	Similar behavior to sheet/plate depending on wall thickness	O, T6	Used for structural tubing where high strength is needed
Bar/Rod	Ø few mm to 100+ mm	Forging/extrusion required for large sections	O, T6	Forged components for fittings and high-load fasteners

Processing route (rolling vs forging vs extrusion) and section thickness change microstructure, quench rate, and precipitation kinetics significantly. Sheet and thin-gage forms achieve more consistent high-strength tempers because of faster quench rates, whereas thick plate requires process adjustments (longer solution times, controlled quench fixtures) to avoid soft central sections and to ensure uniform mechanical properties.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2424	USA	Primary North American designation used in aerospace applications
EN AW	2xxx series (varies)	Europe	Exact EN cross-reference may be to a 2xxx-series alloy with similar Cu–Mg balance
JIS	A2xxx (varies)	Japan	Local designations exist; cross-reference must be confirmed by chemistry and properties
GB/T	2A24	China	Common Chinese wrought designator uses a “2Axx” style number that approximates AA 2424

Cross-references between standards are approximate and must be validated by chemical composition and mechanical property requirements for critical applications. Differences in allowable impurity levels, certification practices, and temper definitions mean that designers should always verify material certificates and, when available, use direct standard-to-standard equivalence charts or perform mechanical testing for qualification.

Corrosion Resistance

Atmospheric corrosion resistance for 2424 is moderate and inferior to 5xxx and 6xxx series alloys due to its higher copper content, which promotes localized corrosion (pitting) in aggressive environments. In common atmospheric service, 2424 performs adequately if painted, anodized, or clad (Alclad) with a purer aluminum layer for sacrificial protection; the cladding approach is common in aerospace to combine surface corrosion protection with core high strength.

In marine or chloride-rich environments 2424 is susceptible to accelerated pitting and intergranular attack, particularly in peak-aged tempers; protective measures such as cladding, coatings, cathodic protection or selection of alternate alloys (5xxx) are frequently required. Tensile stresses and corrosive species together can provoke stress-corrosion cracking (SCC) in 2xxx-series alloys; stabilized tempers and avoidance of sustained tensile stress in aggressive environments reduce SCC risk.

Galvanic interactions require careful design when 2424 is mated to more noble metals (e.g., stainless steels, copper alloys) because copper-containing aluminum alloys tend to be relatively cathodic in seawater; insulating interfaces, coatings, or sacrificial anodes mitigate galvanic corrosion. Compared with 6xxx (Al–Mg–Si) and 5xxx (Al–Mg) families, 2424 trades corrosion resistance for higher strength and fatigue performance, and thus is more commonly used with surface protection schemes in corrosive service.

Fabrication Properties

Weldability

Welding of 2424 is challenging relative to 5xxx/6xxx series alloys because of hot-cracking susceptibility and loss of strength in the heat-affected zone (HAZ). Fusion welding (TIG/MIG/GMAW) typically requires specialized Al–Cu filler alloys (such as 2319) and pre- and post-weld thermal control; filler selection aims to minimize cracking and provide compatible mechanical properties. Resistance welding and mechanical fastening are common alternatives where full structural joints are required; if welding is used, post-weld solution treatment and aging may be necessary but are often impractical for large assemblies.

Machinability

2424 machines reasonably well in certain tempers because its higher strength and work-hardening rate enable predictable chip formation; however, peak-aged conditions can produce higher tool wear. Machinability index is often rated moderate; carbide tooling with positive rake angles and adequate coolant is recommended. Typical practice uses slower speeds and heavier feeds than for pure aluminum to control built-up edge and to maintain dimensional accuracy on interrupted cuts.

Formability

Formability is best in O, T4 and some T3 tempers where ductility and bendability are high; minimum bend radii are larger in T6/T8 tempers due to limited elongation and higher springback. Cold forming is feasible for sheet under controlled conditions with jigs and draw dies tuned to avoid cracking at bend radii and at holes. Warm forming or using softer tempers followed by localized heat treatment can expand formability for complex shapes.

Heat Treatment Behavior

Solution treatment for 2424 is performed at temperatures typically in the range of about 495–520 °C to dissolve Cu- and Mg-containing phases into a supersaturated solid solution. Proper solutionizing requires full penetration of the section and avoidance of incipient melting of low-melting constituents; quench rate after solutioning must be rapid enough to retain solute in supersaturation, especially for thicker sections.

Artificial aging (T6) usually occurs at temperatures in the 160–190 °C range for several hours, producing coherent metastable precipitates (θ′ and S′) that provide peak strength; variations in time–temperature produce tradeoffs between peak strength and fracture toughness. T temper designations such as T8 and T851 incorporate pre-aging cold work and stabilization steps to tailor fatigue and SCC resistance while maintaining elevated strength.

If a non-heat-treatable processing route is used, strength can be increased by strain hardening (H tempers) where cold work imparts higher yield and tensile strength; annealing (O) returns ductility by coarsening precipitates and dissolving strain hardening. Re-aging and stabilization procedures are used in assemblies to control long-term property evolution during service.

High-Temperature Performance

Service temperatures for 2424 are limited compared with steels and some high-temperature aluminum alloys; long-term elevated-temperature exposure above about 120–150 °C will progressively reduce yield and tensile strength as precipitates coarsen and dissolve. Short-term exposure to higher temperatures (up to ~200 °C) can be tolerated but will affect fatigue life and dimensional stability.

Oxidation in air is minimal in the temperature range typical for structural applications because of the protective aluminum oxide film, but high-temperature scaling and intergranular oxidation can occur in extended service at elevated temperatures. HAZ softening around welds and thermal treatments must be considered for components exposed to cyclic thermal loading.

Applications

Industry	Example Component	Why 2424 Is Used
Aerospace	Fittings, wing ribs, control surfaces	High strength-to-weight, good fatigue performance, ability to be clad for corrosion protection
Marine	Structural members (protected), trim pieces	High fatigue strength in protected or coated conditions; used where strength outweighs corrosion drawbacks
Automotive / Motorsport	Suspension links, chassis components	High specific strength, toughness and fatigue resistance for performance applications
Electronics	Structural supports, moderate heat spreaders	Reasonable thermal conductivity combined with structural capability
Defense	Armature fittings, mountings	Damage tolerance and high load capability in mission-critical parts

2424 is used where a balance of high static strength, damage tolerance and fatigue life are required and where surface protection can be provided to mitigate corrosion. The alloy is often applied in aerospace and high-performance vehicles where weight savings are critical but toughness cannot be sacrificed.

Selection Insights

Choose 2424 when the design requires higher specific strength and superior fatigue/fracture properties compared with common work-hardened alloys, and when the application can accommodate cladding, coatings or design measures to control corrosion. The alloy is particularly compelling for aerospace fittings, structural components and high-performance chassis parts where heat-treatable strength and toughness are priorities.

Compared with commercially pure aluminum (1100), 2424 trades much higher strength and fatigue resistance for reduced electrical and thermal conductivity and reduced formability in peak tempers. Compared with work-hardened alloys such as 3003 or 5052, 2424 offers substantially higher static strength but typically lower corrosion resistance, so protective coatings or cladding are often required. Compared with common heat-treatable alloys such as 6061, 2424 provides higher peak strength and better fatigue/fracture toughness in many conditions, and is chosen when those properties outweigh the benefits of 6061's superior weldability and corrosion resistance.

Closing Summary

Aluminum 2424 remains a relevant high-strength, heat-treatable choice for demanding structural and fatigue-critical applications where the balance of strength, toughness and service life is more important than intrinsic corrosion resistance. With appropriate temper selection, surface protection and fabrication controls, 2424 delivers a compelling combination of mechanical performance for aerospace, motorsport and specialty industrial uses.