Aluminum 2219 - AlCu6Mn - EN AW-2219

When and why was alloy 2219 developed?

Alloy 2219 (EN AW-2219, AlCu6Mn) is a precipitation-hardenable aluminum-copper alloy developed in the 1950s to provide excellent weldability and stable properties over a wide temperature range, from cryogenic conditions up to ≈ 300 °C. Its high toughness and very good SCC resistance in T8 explain its key role in welded tanks and pressurized structures (Saturn V, Space Shuttle external tank, Ariane 5, ISS modules). More recent Al-Li alloys (2195, 2050) gain advantage where weight is critical, but 2219 remains the benchmark when robustness and weldability prevail.

The aluminum alloy 2219 is a high-performance material in the wrought aluminum-copper family. It has several international designations: AA-2219 for the Aluminum Association, EN AW-2219 under the European standard EN 573 (chemical alias AlCu6Mn), and UNS A92219 in North America. In France it was formerly known as A-U6MT (AFNOR).

Development context (1950s)

In the mid-1950s, AA2219 was designed to maintain good mechanical properties up to ≈ 300 °C while remaining weldable. Compared with 2024 from the 1930s, it offered better hot strength and far superior weldability — the main weakness of 2024 — at the cost of slightly lower ambient strength. This Al-Cu alloy also shows excellent low-temperature performance, proven down to liquid hydrogen (−252 °C, typ.) without embrittlement.

First applications (1960s) and emblematic programs

From the early 1960s, 2219 was used for structural parts exposed to high temperatures (engines, nacelle elements, forgings). However, its use in aircraft remained more limited than 2024 or 7075 due to weight and corrosion concerns.

The Apollo program used 2219 panels and rings welded for the large Saturn V tanks. Concorde used 2618 for heated structure because creep resistance was critical and AA2219 performed less well in that respect. It was mainly weldability and thermal stability that made 2219 popular, together with Alcoa’s ability at that time to produce large homogeneous plates of consistent quality.

How did 2219 evolve versus Al-Li alloys?

In the space sector, the combination of weldability + thermal strength made 2219 a standard for cryogenic tanks and pressurized structures. For example, the Space Shuttle’s standard external tank used welded 2219 sub-assemblies. Likewise, Ariane 5 and pressurized modules (e.g., Columbus, Cupola) use 2219 for its stable performance over a wide thermal range.

Since the 1990s, lighter Al-Li alloys (e.g., 2195 then 2050) have partly replaced 2219 where weight is critical. NASA introduced AA2195 for the “super-light” external tank. However, 2219 remains a proven alloy for programs where weldability and robustness outweigh density.

How does the chemical composition define 2219 properties?

2219 belongs to the Al-Cu series. Its main element is copper (5.8–6.8 %). Manganese (Mn ≈ 0.3 %), vanadium (V ≈ 0.10 %), zirconium (Zr ≈ 0.17 %) and titanium (Ti ≈ 0.05 %) refine grain size and control recrystallization. Magnesium is nearly absent (≤ 0.02 %), a deliberate choice that greatly improves weldability by reducing hot-cracking risk.

Copper provides precipitation hardening (Al₂Cu) but lowers natural corrosion resistance. V, Zr and Ti refine microstructure and raise recrystallization temperature, stabilizing the HAZ during welding. The alloy is therefore hardenable by solution heat treatment and aging, with precipitate size/distribution adjusted by temper.

What are 2219 physical properties?

Density and conductivity

Density ≈ 2.84 g/cm³ (typ.), slightly higher than low-alloy Al due to Cu. Thermal conductivity ≈ 120 W·m⁻¹·K⁻¹ (typ.), helpful for dissipating heat. Electrical conductivity ≈ 30–40 % IACS.

Characteristic temperatures

Solidus ≈ 543 °C, liquidus ≈ 643 °C. Mean linear expansion coefficient ≈ 22×10⁻⁶/°C at 20 °C, ≈ 24×10⁻⁶/°C around 250 °C (typ.). It therefore exhibits significant thermal expansion that must be considered in designs facing wide ΔT.

What are the mechanical properties by temper?

AA2219 is precipitation-hardenable: solution heat treatment followed by natural or artificial aging. Typical tempers: O (annealed), T6 (artificially aged), T8/T87 (solution treated + cold-worked + aged), T851 (solution treated, stress-relieved, aged). Each temper defines the precipitate distribution and strength/ductility balance.

Typical strength levels

Product standards (e.g. EN 485-2 / ASTM B209) specify guaranteed minima by thickness and orientation.

Toughness and fatigue

Fracture toughness is high, delaying crack initiation/propagation under variable loading. Fatigue limit ≈ 90–130 MPa for ≈ 10⁷ cycles (depending on temper and surface). T8 often offers the best compromise for demanding service.

How to use alloy 2219?

Machinability and formability

2219 offers good machinability compared with other high-strength Al alloys since Cu promotes short chips and reduces tool sticking. In O temper, complex shapes are easily machined with reduced tool wear.

Cold formability is moderate: machining is preferred where possible. Annealing (O) before forming improves ductility for light bending or stamping. Rapid work-hardening limits severe forming without intermediate treatment.

Weldability, processes and effects

Unlike most Al-Cu alloys, 2219 is readily weldable by TIG/MIG. Additions of V/Zr/Ti reduce hot-cracking, allowing even heavy-section assemblies.

The FZ/HAZ becomes locally softened as precipitation hardening is partly lost during welding. Consequently Rp_0.2 in the weld approaches the O-temper range (≈ 100–170 MPa). Where possible, a restoration heat treatment (re-solution + aging) recovers properties; otherwise design must account for reduced strength around the joint.

Weld beads are more anodic and require protection (anodizing, paint, coatings) to prevent localized attack. A T8-type post-weld condition improves stress-corrosion resistance.

How does 2219 resist different types of corrosion?

Like other Cu-rich Al alloys, 2219 has lower general corrosion resistance than 5000 or 6000 series. Using Alclad cladding and/or surface treatments (anodizing, paints) is recommended for long-term durability, with the protection level adapted to the environment (marine, humidity, galvanic exposure).

In suitable tempers—especially T8—2219 shows excellent SCC resistance. In marine environments, unprotected alloy is prone to pitting and galvanic coupling and thus requires robust protection systems such as epoxy paints or coatings. With proper protection, durability under harsh conditions is well controlled.