2004 Superplastic Aluminium Sheet, Bare and Alclad

What makes 2004 different

Most aerospace alloys are chosen for strength or toughness. 2004 is chosen for formability: under the right conditions it stretches to several hundred per cent elongation without necking, so one sheet can be blown into a shape that would otherwise be a riveted assembly of many parts.

The alloy comes from the dilute Al-Cu-Zr family developed in the UK around 1970 and sold commercially as Supral. Zirconium forms very fine Al₃Zr particles that pin grain boundaries. The as-rolled sheet recrystallises dynamically during the early stage of hot deformation into grains of only a few micrometres, and that fine, stable grain is what allows grain-boundary sliding, the mechanism behind superplasticity.

In service, superplastically formed 2004 parts are used for secondary structure and complex non-structural items: ducts, fairings, access doors and inner panels, equipment boxes, cockpit and cabin parts, and parts for helicopters, missiles and spacecraft where reducing part count and fasteners is worth more than the highest strength.

2004 chemical composition (wt %)

Composition as given in the Aluminum Association registration and the AMS 4208 / 4209 titles (6.0Cu-0.40Zr). Check the current specification revision for exact limits.

AMS 4208 and AMS 4209

Both specifications are written for parts that need a high degree of formability (superplasticity) followed by response to heat treatment. Because they cover sheet under 6.35 mm, "2004 plate" in thick gauges is not a normal aerospace product. The F temper is deliberate: the sheet must arrive in its cold-worked, as-rolled state so that the fine grain develops during forming. Annealing it beforehand spoils the superplastic behaviour.

Alclad 2004 carries a thin, metallurgically bonded layer of more corrosion-resistant aluminium on each face, protecting the copper-rich core in the same way Alclad 2024 skins are protected.

Superplastic forming and heat treatment

1. HeatThe sheet is clamped over a heated die, typically at around 450 – 500 °C, the range where 2004 shows superplastic flow.
2. FormInert gas pressure is applied on one side, forcing the sheet into the die at a controlled, slow strain rate. Forming cycles take minutes rather than seconds.
3. Control thinningWall thickness varies with depth of draw; the pressure-time cycle and die design control how evenly the sheet thins.
4. Heat treatAfter forming, parts are solution heat-treated, quenched and aged to develop strength, following the user's process specification.
5. FinishTrim, inspect and protect; Alclad parts need only light surface treatment, bare parts need full corrosion protection.

Cavitation (small internal voids) can form during superplastic deformation of aluminium alloys. Back pressure during forming is a common way to suppress it; your forming specification should state how it is controlled and inspected.

2004 compared with other forming routes

Related pages

How to order 2004 sheet

1. SpecifyAlloy and temper, thickness, width and length, quantity and the governing specification with its revision (AMS 4208 bare or AMS 4209 Alclad).
2. ConfirmWe confirm the specification can be met, the tolerance class, test requirements and delivery terms (EXW, FOB, CIF or DAP).
3. InspectMaterial is checked for dimensions and surface condition; any extra tests named on the order are carried out or arranged.
4. DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry and mechanical results, traceable to the heat or lot number.
5. Pack and shipExport packing in sealed, moisture-protected cases or on pallets, shipped by sea or air to your port or door.

2004 superplastic aluminium (aluminum) sheet: FAQ