Aluminum 2219: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 2219 is a member of the 2xxx series of aluminum-copper alloys specifically engineered for high-strength, heat-treatable applications. Its primary alloying element is copper (Cu ≈ 5.8–6.8 wt%), with controlled additions of manganese, titanium and trace elements to refine grain structure and improve mechanical performance. The strengthening mechanism for 2219 is precipitation hardening (heat-treatable): solution heat treatment followed by quenching and artificial or natural aging produce fine Al2Cu (θ′/θ) precipitates that raise yield and tensile strength substantially.

Key traits of 2219 include high specific strength, good fracture toughness particularly at cryogenic temperatures, and relatively good weldability for a Cu-bearing alloy when appropriate filler metals are used. Corrosion resistance is moderate; the alloy is more susceptible to localized attack than many Mg-bearing 5xxx series alloys but can be protected with coatings, claddings or corrosion allowances. Formability is fair in annealed condition and becomes limited in peak-aged tempers; machining and fabrication are typical of high-strength aluminum alloys used in structural applications.

Industries that commonly use 2219 are aerospace (fuel tanks, cryogenic tanks, primary structure), cryogenics, missile and space hardware, and specialized pressure vessels. Designers choose 2219 over other alloys when a combination of high strength, weldability and toughness at low temperatures is required and when the superior specific stiffness-to-weight of Al-Cu systems is advantageous compared with alternative materials.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed; maximum ductility and formability
T3	Moderate	Moderate	Good	Good	Solution heat-treated, cold worked, naturally aged
T6	High	Low-Moderate	Limited	Moderate	Solution treated, artificially aged to peak strength
T8	High	Low-Moderate	Limited	Moderate	Solution treated, cold worked, artificially aged
T87	High	Low-Moderate	Limited	Moderate	Solution treated, stress-relieved by stretching, artificially aged; common aerospace temper
T351	Moderate-High	Moderate	Fair	Good	Solution treated, stress-relieved by stretching, naturally aged

Temper has a first-order effect on both strength and ductility in 2219 because the Cu-rich precipitates formed during aging control yield and ultimate strength. Annealed (O) stock is used for forming and drawing, while T6/T87 variants are selected for structural parts requiring maximum strength and controlled residual stresses.

Different tempers also influence weldability and HAZ response; aged conditions will experience localized softening in the HAZ while O and naturally aged tempers display more uniform properties after welding. Selection of temper must balance forming operations, required proof strength, and anticipated welding or joining sequence.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.20	Impurity control; high Si reduces toughness
Fe	≤ 0.30	Common impurity; can form intermetallics that reduce ductility
Mn	0.2–0.4	Grain structure control and strength
Mg	≤ 0.10	Low; not a primary strengthening element in 2219
Cu	5.8–6.8	Principal strengthening element (Al2Cu precipitates)
Zn	≤ 0.25	Minor; limited solid solution strengthening
Cr	≤ 0.10	Trace; can influence recrystallization
Ti	0.02–0.10	Grain refiner for castings and wrought products
Others	Balance Al, trace elements ≤0.05 each	Includes V, Zr traces depending on mill practice

Copper is the dominant alloying species and determines the heat-treatable nature of 2219; its precipitation when aged is responsible for the alloy's strength. Manganese and trace titanium act primarily as microstructure controllers that limit grain growth during thermal cycles, improving toughness and fatigue resistance. Controlled limits of silicon and iron minimize hard intermetallics that would embrittle the material and impair fatigue performance.

Mechanical Properties

2219 exhibits a strong dependence of tensile properties on temper and thickness; the alloy achieves high tensile and yield strengths in peak-aged tempers but loses ductility compared with the annealed state. In T6/T87 conditions the alloy typically displays high yield strength and UTS suitable for primary structural members, while annealed material is used where forming or impact toughness is prioritized. Fatigue behavior is contingent on surface finish, residual stress, and local hardness; fine-grained, well-processed 2219 offers acceptable fatigue life for aerospace detail parts.

Hardness correlates with aging condition: O condition has low Brinell or Rockwell hardness, while T6/T87 conditions raise hardness considerably due to dense θ′ precipitate populations. Thickness effects are notable: thick plates and extrusions require longer solution-treatment times to homogenize and to dissolve Cu-rich phases, and cooling rate during quench can vary properties across section thickness. For welded structures, HAZ softening is often the limiting factor for local strength and must be considered in design and post-weld treatments.

Fracture toughness of 2219 is generally better than many other high-strength Al-Cu alloys, which helps in cryogenic applications and tanks subjected to cyclic loading; toughness advantages stem from controlled chemistry and thermo-mechanical processing that avoid coarse intermetallics.

Property	O/Annealed	Key Temper (e.g., T6/T87)	Notes
Tensile Strength (UTS)	~200–260 MPa	~380–440 MPa	Values vary with thickness and heat treatment; aerospace sheets often near upper end of range
Yield Strength	~70–130 MPa	~300–350 MPa	Yield in peak-aged tempers suitable for primary structure
Elongation	~20–30%	~8–16%	Ductility drops significantly with peak aging
Hardness (HB)	~30–55 HB	~80–115 HB	Hardness scales with aging response and precipitate density

Physical Properties

Property	Value	Notes
Density	2.84 g/cm³	Typical for Al-Cu wrought alloys; good specific strength
Melting Range	Solidus ≈ 500–515 °C; Liquidus ≈ 635–655 °C	Alloying depresses solidus from pure Al and broadens melting range
Thermal Conductivity	~120–140 W/m·K	Lower than pure Al due to Cu content; still high compared with steels
Electrical Conductivity	~28–34 % IACS	Reduced relative to purer Al and Mg-rich alloys
Specific Heat	~0.89–0.92 J/g·K	Typical aluminum alloy specific heat near room temperature
Thermal Expansion	~23–24 ×10^-6 /K	Typical coefficient for wrought aluminum alloys

The physical properties reflect the compromise between added copper for mechanical strengthening and the retained advantages of aluminum for density and conductivity. Thermal conductivity and electrical conductivity are reduced relative to pure aluminum but remain favorable for heat-sinking and structural thermal designs compared with ferrous metals. The thermal expansion coefficient is similar to other aluminum alloys, so mismatch with composites or steels must be addressed in multi-material assemblies.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.4 mm	Good uniformity in thin gauge	O, T3, T351, T87	Aerospace sheet often supplied in T87 for skin and structural panels
Plate	6 mm – 150+ mm	Strength varies with section; thicker plates require extended heat treatment	O, T6, T87	Thick sections need long solution treatments and controlled quenching
Extrusion	Profiles up to large cross-sections	Mechanical anisotropy possible; similar peak strengths after heat treat	O, T3, T6	Extrusion die design must consider limited hot-temperature strength degradation
Tube	Thin-walled to thick-walled	Good for pressure and cryogenic applications	O, T6, T87	Welded and seamless tubes used in cryotanks and feedlines
Bar/Rod	Ø few mm – 200 mm	Homogeneous properties if properly heat-treated	O, T6	Common for machined structural fittings and fasteners

Processing differences across forms center on heat flow, quench rates, and residual stresses. Sheets and thin-walled extrusions achieve more uniform properties after quench and aging, while plates and large extrusions must be processed with long soak times and specialized quench techniques to avoid segregation and hardness gradients. Application choices reflect these process constraints: thin-gauge components are preferred where high uniform strength and fatigue life are critical, whereas thick parts may require extra inspection and post-heat-treatment processing.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2219	USA	Primary designation under Aluminium Association standards
EN AW	2219 (EN AW-AlCu)	Europe	Equivalent chemistry is marketed under same numeric family but tolerances may differ
JIS	A2219	Japan	JIS variants follow similar nominal chemistry with regional specification differences
GB/T	2219	China	GB/T grade exists with comparable composition; processing allowances and testing can vary

Although the numeric “2219” is used across several standards, subtle differences in allowable impurity levels, product form testing, and certification practices exist between regions. European and Japanese specifications may include different acceptance criteria for mechanical properties, heat-treatment response and non-destructive testing for aerospace qualification. When procuring critical components, engineers should verify the producing mill's certified composition, temper condition and process history rather than relying solely on grade name.

Corrosion Resistance

In atmospheric environments 2219 has moderate general corrosion resistance provided appropriate surface treatments are applied. The copper content makes the alloy more prone to localized corrosion (pitting and intergranular attack) than Mg-rich 5xxx series alloys, so protective coatings, cladding or cathodic protection are common in marine or corrosive-service designs.

Marine behavior requires care: unprotected 2219 in chloride-rich environments will develop localized corrosion more readily than 5xxx or 6xxx alloys. Proper design to avoid crevices, selection of compatible fasteners, and post-fabrication finishes (anodizing, cladding or conversion coatings) mitigate lifetime risks in seawater exposure. Stress corrosion cracking is a concern for high-strength Al-Cu alloys; 2219 can experience SCC in tensile and corrosive environments, especially when residual tensile stresses are present near yield strength.

Galvanic interactions with more noble materials (stainless steel, copper alloys) can accelerate localized attack of 2219 if electrical contact is present and an electrolyte exists. Compared with 6xxx (Al-Mg-Si) alloys, 2219 trades corrosion resilience for higher strength and cryogenic toughness, demanding more aggressive corrosion control strategies in hostile environments.

Fabrication Properties

Weldability

2219 is among the more weldable of the Al-Cu family when practiced with appropriate filler alloys such as AA2319 (Al-6Cu) designed to match chemistry and minimize hot cracking. Fusion welding (GTAW/TIG, GMAW/MIG) is commonly used for sheet, plate and assembly of tanks and vessels; weld procedure control is critical to limit porosity and control distortion. The HAZ in peak-aged tempers will experience softening due to precipitate dissolution and coarsening; post-weld artificial aging or selection of temper T87/T351 can mitigate residual property loss.

Machinability

2219 machines reasonably well for a high-strength aluminum alloy, with machinability indices typically below those of more free-machining aluminum alloys but acceptable with carbide tooling and rigid setups. Good chip control, positive rake angles and moderate feeds minimize built-up edge and work hardening at the tool interface. Coolant use extends tool life and controls temperatures to avoid smearing and galling during high‑ratio machining operations.

Formability

Formability is excellent in the annealed (O) condition and degrades in peak-aged tempers where ductility is limited; deep draws and complex bends should be performed in O or T3 conditions. Typical minimum bend radii depend on thickness and temper but for sheet metal applications, an inside radius equal to 1–2× thickness in O condition is common practice; more conservative radii are used for T6/T87 tempers. Cold working after heat treatment is possible for small deformation adjustments, but significant forming operations should occur prior to final artificial aging to avoid cracking.

Heat Treatment Behavior

2219 is a classic heat-treatable Al-Cu alloy where solution treatment, quenching and aging control the precipitation state and therefore strength. Typical solution treatment temperatures are in the range of 510–535 °C with sufficient soak times to dissolve copper-rich phases and homogenize composition through thin sections; quenching must be rapid to retain Cu in solid solution. Artificial aging schedules (e.g., 160–190 °C for several hours) produce the fine θ′ precipitates responsible for peak strength in T6 and related tempers; variations in time-temperature profiles yield T8, T87 and other aerospace-oriented tempers tuned for stress-relief and dimensional stability.

Temper transitions are important: overstretching, uncontrolled natural aging or slow quench rates lead to coarse precipitates that reduce yield strength and toughness. Post-weld heat treatment is rarely feasible for large assemblies, so designers apply temper selection and local heat-control strategies to manage HAZ softening. For annealing or softening, elevated temperature exposure above 300 °C for extended periods will overage and soften the alloy as precipitates coarsen.

High-Temperature Performance

At elevated temperatures, 2219 exhibits progressive loss of yield and tensile strength as θ′ precipitates dissolve or coarsen; significant reductions are seen above roughly 150–200 °C depending on exposure time. For sustained service, designers usually limit operating temperatures well below typical artificial aging temperatures to preserve mechanical properties and avoid overaging. Oxidation is limited by the formation of a protective Al2O3 film, but high-temperature corrosion in aggressive atmospheres (sulfidizing or chloride-bearing) can be a concern and may require protective claddings or coatings.

The heat-affected zone adjacent to welds is particularly sensitive under thermal exposure, where softening and grain growth can reduce local allowable stresses; applications subject to cyclic thermal excursion need careful qualification and may require post-fabrication stabilization treatments to control property drift.

Applications

Industry	Example Component	Why 2219 Is Used
Aerospace	Cryogenic fuel tanks, pressure vessels, fuselage fittings	Excellent strength-to-weight, fracture toughness at low temperature, weldability with matched fillers
Marine / Cryogenics	LNG and cryogenic storage tanks, piping	Good low-temperature performance and weldability for sealed pressure systems
Defense / Space	Missile motor casings, launch vehicle tanks	High specific strength and reliability under cyclic and thermal loads
Industrials / Machinery	High-strength structural frames, tooling fixtures	Strength and machinability for critical, weight-sensitive components
Electronics	Precision housings and heat spreaders	Reasonable thermal conductivity and machinability for medium-duty thermal components

2219 continues to be specified when the design prioritizes a high-strength, weldable alloy with proven cryogenic and fatigue performance. Its combination of toughness, weldability (with suitable filler), and predictable precipitation response make it a mainstay in aerospace pressure-containing hardware and niche industrial applications.

Selection Insights

Use 2219 when high strength combined with weldability and good fracture toughness—especially at low temperatures—is more important than maximum corrosion resistance or electrical conductivity. Choose annealed (O) for forming steps and convert to T6/T87 where structural strength and resistance to tensile deformation are primary requirements.

Compared with commercially pure aluminum (e.g., 1100), 2219 sacrifices electrical and thermal conductivity and formability for much higher strength and fracture toughness, making it unsuitable where electrical performance or extensive cold forming are the primary drivers. Compared with common work-hardened alloys (e.g., 3003, 5052), 2219 offers substantially higher strength but typically lower corrosion resistance and modestly poorer formability; select 2219 when structural strength outweighs the need for superior environmental resistance.

Compared with common heat-treatable alloys (e.g., 6061/6063), 2219 may provide better fracture toughness and cryogenic performance even if peak-age strengths are comparable or slightly lower; it is chosen when aluminum-copper alloy characteristics (particularly toughness and weldability with Al-Cu fillers) better match the service environment than Al-Mg-Si alloys.

Closing Summary

Alloy 2219 remains a highly relevant engineering aluminum due to its heat-treatable, Cu-strengthened matrix that delivers a favorable combination of high specific strength, weldability with matched fillers and superior toughness at low temperatures. For aerospace, cryogenic and pressure-containing structural applications where those attributes outweigh modest corrosion and conductivity trade-offs, 2219 continues to be a material of choice and a robust option for demanding service conditions.