Aluminum 2024: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

2024 is an aluminum-copper alloy in the 2xxx series, historically developed for high-strength structural applications. It uses copper as the primary alloying element and contains magnesium and manganese to refine microstructure and support precipitation hardening.

The material is a heat-treatable alloy that derives its strength by solution treating, quenching, and artificial aging to produce fine Al2Cu (θ′) precipitates. Strength levels are high compared with most other aluminum alloys, but this is balanced against moderate-to-poor general corrosion resistance and limited weldability without special procedures.

Key traits include high strength-to-weight ratio, good fatigue resistance when properly processed, reduced formability in strong tempers, and susceptibility to stress-corrosion cracking in some environments. Typical industries are aerospace, military, high-performance automotive, and other structural applications where stiffness and elevated strength are prioritized over forming ease.

Engineers choose 2024 when maximum structural strength and fracture/fatigue resistance are required in thin- to medium-gauge parts, and when the component can be protected by coatings or designed to avoid severely corrosive exposures. Its performance often outperforms alternative alloys where load-critical stiffness and fatigue life determine material selection.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for maximum ductility
H14	Medium	Low–Medium	Limited	Poor	Strain-hardened to a controlled degree, reduced ductility
T3	High	Medium	Limited	Poor	Solution heat-treated, cold worked and naturally aged
T4	High	Medium	Limited	Poor	Solution heat-treated and naturally aged (softens during forming)
T6	Very High	Low–Medium	Poor	Poor	Solution heat-treated and artificially aged for peak strength
T351	Very High	Low–Medium	Poor	Poor	Solution-treated, stress-relieved by stretching, then naturally aged
T651	Very High	Low–Medium	Poor	Poor	Solution-treated, stress-relieved by controlled stretching, artificially aged

Tempering strongly controls the trade-off between strength and ductility for 2024. Peak-aged tempers such as T6/T651 provide the highest tensile and yield strengths but reduce elongation and limit forming operations.

For fabrication, softer tempers (O or lightly cold-worked H-states) are used when forming and shaping are required and are subsequently solution-treated and aged if higher strength is later required. Temper selection also affects residual stress, fatigue behavior, and susceptibility to SCC (stress-corrosion cracking), so aerospace applications often use controlled tempers such as T351 and T651.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.5	Impurity element; high levels reduce corrosion resistance and toughness
Fe	≤ 0.5	Iron forms intermetallics that can lower ductility and toughness
Mn	0.30–0.90	Grain structure control; improves strength and fracture toughness
Mg	1.2–1.8	Contributes to precipitation hardening with Cu; improves strength
Cu	3.8–4.9	Principal strengthening element; increases strength and lowers corrosion resistance
Zn	≤ 0.25	Minor impurity; excessive Zn can reduce SCC resistance
Cr	0.04–0.35	Controls grain structure and recrystallization behavior
Ti	≤ 0.15	Grain refiner in cast/ingot processing
Others	≤ 0.15 each; balance Al	Introduced as trace elements; Al is the balance of the alloy

The alloy’s mechanical and corrosion characteristics are driven primarily by the Cu–Mg combination, which enables age-hardening via Al2Cu and related precipitates. Chromium and manganese are key microalloying additions that control grain structure, inhibit excessive recrystallization, and improve toughness and fatigue performance. Minor impurities such as Si and Fe are limited because they form brittle intermetallic particles that degrade formability and fracture behavior.

Mechanical Properties

Tensile behavior in 2024 is characterized by a high ultimate tensile strength and relatively high yield strength in peak-aged tempers. Yield and ultimate strengths are maximized in T6/T351 variants due to finely distributed precipitates. Elongation decreases as strength rises, with typical ductility adequate for many structural designs but limited for severe drawing or stretch forming.

Hardness correlates closely with temper; Brinell or Vickers hardness values double or more when moving from annealed to peak-aged conditions. Fatigue resistance in 2024 is generally superior to many other aluminum alloys at comparable static strengths, particularly when crack initiation sites are minimized by good surface finish and corrosion protection. Thickness affects mechanical response; thinner gauges are more easily hardened and show higher fatigue endurance, while thicker sections can be harder to solution-treat uniformly and may show reduced peak properties.

Property	O/Annealed	Key Temper (e.g., T351/T6)	Notes
Tensile Strength (MPa)	280–350	430–505	Peak-aged tempers reach upper range; values vary with product form and thickness
Yield Strength (0.2% offset, MPa)	125–200	300–390	Yield increases significantly after aging; saw-tooth variations possible across thickness
Elongation (%)	18–30	8–16	Ductility decreases with higher-strength tempers and thicker plates
Hardness (HB)	55–75	115–140	Hardness correlates with precipitate density and temper

Physical Properties

Property	Value	Notes
Density	2.78 g/cm³	Typical density for 2xxx-series Al alloys
Melting Range	Solidus ~500–515 °C; Liquidus ~640–650 °C	Typical melting interval for Al–Cu alloys; brazing/welding must account for hot-cracking
Thermal Conductivity	~120 W/m·K	Lower than pure Al due to alloying elements
Electrical Conductivity	~30–35 %IACS (≈18–20 MS/m)	Roughly one-third of pure aluminum conductivity
Specific Heat	~0.88 J/g·K (880 J/kg·K)	Temperature dependent; used for thermal design
Thermal Expansion	~23.2 μm/m·K (20–100 °C)	Similar to other aluminum alloys; important for thermal cycling design

2024's thermal and electrical conductivities are below those of pure aluminum, a consequence of copper and other solutes scattering electrons and phonons. The alloy's density and thermal expansion are typical for aluminum structural alloys, permitting lightweight designs but requiring consideration of differential expansion when joined to dissimilar materials.

The melting range and susceptibility to hot-cracking demand controlled thermal cycles during welding and brazing, and the relatively high thermal conductivity requires higher heat inputs for localized heating operations.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Uniform thin gauge response; good age-hardening	O, T3, T351, T6	Widely used for aerospace skins and fittings
Plate	>6.0 mm up to 150–250 mm	Harder to solution-treat uniformly; slower cooling affects properties	O, T351, T6	Thick sections require specialized solution-treatment facilities
Extrusion	Diameters up to 200 mm cross-sections	Precipitation hardening after aging; profile-dependent	O, T3, T6	Less common than 6061 extrusions, used for high-strength profiles
Tube	Thin- to medium-wall	Strength varies with wall thickness and temper	O, T3, T6	Used in structural tubing and aerospace hydraulic lines (with coatings)
Bar/Rod	Diameters up to 300 mm	Homogeneous in small cross-sections	O, T3, T6	Used for forgings and machined parts requiring high strength

Sheets and thin products respond rapidly to solution-treatment and quenching, enabling consistent peak properties and good fatigue performance. Plates and large extrusions pose quench challenges; they may not reach the same peak strength without special process controls, so design must allow for property scatter. The product form influences allowable tempers and the practicality of forming, welding, and machining operations in production.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2024	USA	ASTM/AA designation and common baseline for specifications
EN AW	2024	Europe	Often noted as AlCu4Mg1; chemical and temper standards per EN specifications
JIS	A2017 / A2024 (approx.)	Japan	Close equivalents exist but JIS alloys may differ slightly in Cu/Mg limits
GB/T	2A12	China	Typical Chinese equivalent for 2024-series alloys; temper designations similar

Equivalent designations exist across standards, but processing histories, allowable impurity limits, and temper definitions can differ by region and mill source. For aerospace or safety-critical parts, engineers should verify the exact standard specification and temper notation rather than relying on a nominal alloy number. Minor differences in impurity control and manufacturing practice can affect susceptibility to SCC, fatigue life, and machinability.

Corrosion Resistance

2024 exhibits moderate atmospheric corrosion resistance when compared to pure aluminum and magnesium-bearing alloys, but it is notably more sensitive than many Al-Mg (5xxx) or Al-Mg-Si (6xxx) alloys. The high copper content reduces natural passivity and increases general corrosion rates in cyclic wet-dry or chloride-rich atmospheres unless protective coatings or cladding are applied.

In marine or chloride-exposed environments, unclad 2024 is prone to localized corrosion and pitting unless protected. Aluminum–copper alloys also show higher susceptibility to stress-corrosion cracking (SCC) under sustained tensile loads in corrosive environments, particularly in peak-aged tempers. Design and maintenance strategies typically include controlled tempers, cladding with pure aluminum, or barrier coatings to mitigate SCC and pitting.

Galvanic interaction is a concern when 2024 is coupled with more noble metals such as stainless steel or copper; protective isolation or sacrificial anodes are commonly used. Compared to 5xxx alloys like 5052, 2024 trades corrosion resistance for strength and requires more robust environmental protection measures for long-term exposure.

Fabrication Properties

Weldability

Welding of 2024 is challenging in high-strength tempers because copper-rich precipitates promote hot-cracking and the weld region often softens due to dissolution of strengthening precipitates. Fusion welding (MIG/TIG) is typically avoided for critical structural parts; when welding is necessary, specialized filler metals (e.g., 2319 or matching Al-Cu fillers) and post-weld heat treatments are used. Resistance welding and mechanical fastening are common alternatives in aerospace applications.

Machinability

2024 is considered fairly machinable among high-strength aluminum alloys, with good chip control and high material removal rates in T3/T6 states compared with many steels. Carbide tooling with positive rake and proper coolant application is recommended to avoid built-up edge and secondary work-hardening. Typical machinability indices are high relative to steels but lower than free-machining aluminum alloys; speeds and feeds should be adjusted for temper and part rigidity.

Formability

Formability is best in the annealed O temper and deteriorates significantly with increasing strength. Bending and shallow drawing are possible in softer tempers with relatively small minimum bend radii (tight radii for thin sheet), while deep drawing and complex stretch forming are constrained in T6/T351 conditions. When complex shapes are required, forming in a softer temper followed by solution treatment and aging or by selecting more formable alloys is common practice.

Heat Treatment Behavior

2024 is a classical heat-treatable alloy that responds to solution treatment, quenching, and artificial aging. Solution treatment is typically performed at temperatures around 495–505 °C to put Cu and Mg into solid solution, followed by rapid quenching to retain a supersaturated matrix. Artificial aging (precipitation) follows at controlled temperatures (e.g., 160–190 °C) to achieve desired tempers such as T6 or T651.

Temper transitions are critical: over-aging reduces strength but can improve SCC resistance and toughness, while under-aging yields lower hardness and strength. For aircraft-grade components, precise control of soak times, quench rates, and aging cycles is used to achieve repeatable properties and to minimize residual stresses and distortion. Thick sections require tailored thermal cycles to avoid segregation and to ensure adequate precipitation throughout the cross-section.

High-Temperature Performance

2024 loses strength more rapidly with temperature than many more heat-resistant aluminum alloys; practical design limits are typically below 150 °C for sustained loading. Above 100–150 °C, precipitate coarsening leads to softening and reduced yield strength, making the alloy unsuitable for prolonged high-temperature structural use. Oxidation is not as severe as in some high-temperature alloys, but protective coatings are still advised for thermal cycling environments to limit surface degradation.

Heat-affected zones around welds suffer from overaging or precipitate dissolution, which reduces local strength and fatigue resistance. For components with transient elevated temperatures, design must account for reduced allowable stresses and possible accelerated corrosion mechanisms.

Applications

Industry	Example Component	Why 2024 Is Used
Aerospace	Fuselage and wing fittings, forgings, rivet-bearing structure	High strength-to-weight and excellent fatigue resistance
Marine	Structural components and fittings (coated or clad)	Strength and fatigue life for structural elements where corrosion control is applied
Automotive	High-performance structural brackets, suspension components	High static and fatigue strength for lightweight performance parts
Electronics	Frames and mechanical supports	Strength with moderate thermal conductivity for rigid lightweight structures

2024 remains a mainstay in aerospace applications where structural integrity and fatigue resistance are paramount and where protective finishing or cladding can be applied. Its combination of mechanical performance and availability in controlled tempers makes it attractive for mission-critical hardware in regulated industries.

Selection Insights

Choose 2024 when structural strength and fatigue resistance outweigh forming ease and environmental robustness. It is ideal for high-load thin structures where coatings, cladding, or design measures can mitigate corrosion and SCC risks.

Compared with commercially pure aluminum (e.g., 1100), 2024 trades off electrical and thermal conductivity and superior formability for substantially higher strength and better fatigue performance. Compared with work-hardened alloys such as 3003 or 5052, 2024 provides much higher static strength but requires more stringent corrosion protection and is less ductile. Compared with other heat-treatable alloys like 6061, 2024 typically offers higher fatigue strength and fracture toughness in many tempers, though 6061 can be easier to weld and has better general corrosion resistance; select 2024 when peak structural strength and fatigue life are the overriding criteria.

Closing Summary

2024 aluminum alloy remains a critical choice for high-strength, fatigue-critical applications where weight savings are essential and environmental protection can be implemented. Its heat-treatable nature and well-understood metallurgy deliver repeatable high performance in aerospace and other demanding industries, preserving relevance despite the availability of more corrosion-resistant or more readily weldable alternates.