O (annealed)
Maximum ductility for deep-drawn tank ends, spun domes, bellows-type parts and tube bending. The usual choice for welded tanks and pipe work.
Aerospace · Al-Mn sheet
3A21 Aerospace Aluminium Sheet & Plate
3A21 is an aluminium-manganese alloy, the GB counterpart of 3003 and the Russian AMts, used in aircraft and launch vehicles for welded tanks, fuel and oil lines, ducting and formed secondary panels. It is non-heat-treatable, so it is supplied in O, H14, H24, H18 and H112, not in T tempers. Metline supplies 3A21 sheet and plate with mill certificates, worldwide.
- Alloy
- 3A21 (Al-Mn, ≈ AMts / 3003)
- Tempers
- O, H14, H24, H18, H112
- Heat-treatable
- No: T tempers do not apply
- Standards
- GB/T 3190 · GB/T 3880
What 3A21 is used for in aerospace
3A21 is one of the older national designations that place a letter in the second position. It is a manganese-strengthened alloy often called "rust-proof aluminium", and it behaves almost exactly like 3003 and EN AW-3003.
Its value in aerospace is a combination of three things: it forms very easily, it welds without hot cracking, and it resists corrosion by fuels, oils, water and the atmosphere. Those properties made 3A21, and its Russian twin AMts, a standard material for welded fuel and oxidiser-system tanks, pipelines, ducting and formed panels in aircraft and launch vehicles designed to GB and GOST documentation. Many of those designs are still produced and maintained, so 3A21 continues to appear on drawings and purchase orders worldwide.
Strength is modest. Annealed 3A21 has a tensile strength of about 100 – 130 MPa, and half-hard H14 about 145 – 180 MPa. That is enough for tanks, lines and formed covers, but not for primary structure, which uses heat-treatable 2xxx and 7xxx alloys such as 2A12 (≈ 2024) and 7A04.
3A21 vs 3003 chemical composition (wt %)
| Element | 3A21 (GB/T 3190) | 3003 (AA / ASTM) |
|---|---|---|
| Silicon (Si) | ≤ 0.6 | ≤ 0.6 |
| Iron (Fe) | ≤ 0.7 | ≤ 0.7 |
| Copper (Cu) | ≤ 0.20 | 0.05 – 0.20 |
| Manganese (Mn) | 1.0 – 1.6 | 1.0 – 1.5 |
| Magnesium (Mg) | ≤ 0.05 | — |
| Zinc (Zn) | ≤ 0.10 | ≤ 0.10 |
| Titanium (Ti) | ≤ 0.15 | — |
| Others, each / total | 0.05 / 0.10 | 0.05 / 0.15 |
| Aluminium (Al) | Remainder | Remainder |
3A21 allows slightly more manganese and has no copper minimum. The two alloys are interchangeable in most non-critical uses, but an aerospace drawing that names 3A21 should be supplied as 3A21, certified to the GB document, unless the design authority approves 3003 in writing. Values are summarised from GB/T 3190 and the Aluminum Association registration; check the edition named on your order.
3A21 mechanical and physical properties
Typical values below are for guidance and match the ranges on our 3A21 sheet and plate page. GB/T 3880.2 sets the guaranteed limits by temper and thickness, and the certificate reports results against them.
| Temper | Condition | Tensile strength (typical) | Yield strength (typical) | Elongation (typical) |
|---|---|---|---|---|
| O | Annealed | 100 – 130 MPa | about 40 – 50 MPa | 20 – 30 % |
| H14 / H24 | Half hard (H24 partially annealed) | 145 – 180 MPa | about 125 – 150 MPa | 5 – 10 % |
| H18 | Full hard | 185 – 210 MPa | about 170 – 190 MPa | 2 – 4 % |
| H112 | As-rolled plate | 110 – 140 MPa | about 50 – 70 MPa | 15 – 20 % |
Physical properties (typical)
- Density
- 2.73 g/cm³
- Melting range
- about 643 – 654 °C
- Modulus of elasticity
- about 69 – 71 GPa
- Thermal conductivity
- about 160 – 190 W/m·K depending on temper
- Electrical resistivity
- about 0.034 – 0.043 Ω·mm²/m depending on temper
- Thermal expansion
- about 23 µm/m·°C (20 – 100 °C)
Fracture-toughness figures are not normally specified for a non-structural Al-Mn alloy, and we do not quote them.
3A21 tempers and what each is for
H14
Half hard. Holds shape in flat and lightly formed panels, covers and brackets; still bends well in thin gauges.
H24
Same strength band as H14 but reached by over-hardening and partial annealing, giving more elongation. Better when parts are bent after blanking.
H18
Full hard. Flat parts, fins and feedstock that will not be formed much.
H112
As-rolled plate above about 6 mm, for machined flanges, bosses and thick welded components.
Not available
T3, T4, T6 and other T tempers. If a drawing calls for them with 3A21, the drawing needs clarifying before material is ordered.
Standards and equivalent grades
| System | Designation | Document |
|---|---|---|
| China (GB) | 3A21 | GB/T 3190 (chemistry), GB/T 3880 (sheet and plate) |
| Russia / CIS | AMts (АМц) | GOST 4784 (chemistry); GOST 21631 (sheet) |
| Aluminum Association / ASTM | 3003 (near-equivalent) | ASTM B209 |
| Aerospace (SAE) | 3003-O / 3003-H14 (near-equivalent) | AMS 4006 / AMS 4008 |
| European | EN AW-3003 (near-equivalent) | EN 485, EN 573-3 |
| Tread plate | 3003 / 3A21 patterned plate | ASTM B632 (for 3003) |
Where a Western-designed programme needs a qualified alternative, AMS 4006 (3003-O) and AMS 4008 (3003-H14) are the closest aerospace documents. Where the drawing originates from a GB or GOST design office, the GB or GOST certificate is usually required as written.
Supply range and weights
3A21 supply range
- Sheet
- 0.5 – 6 mm in O, H14, H24 and H18
- Plate
- Above 6 mm, normally H112 or O
- Width
- Typically 1000 – 2000 mm; wider on request
- Length
- Standard sheets or cut to length and to blank drawings
- Surface
- Mill finish; film or paper interleaving on request
- Packing
- Export wooden cases or pallets, moisture-protected
Availability by size and temper is confirmed with each quotation.
| Thickness (mm) | kg/m² | 1000 × 2000 mm sheet (kg) | 1250 × 2500 mm sheet (kg) |
|---|---|---|---|
| 0.5 | 1.36 | 2.7 | 4.3 |
| 0.8 | 2.18 | 4.4 | 6.8 |
| 1 | 2.73 | 5.5 | 8.5 |
| 1.2 | 3.28 | 6.6 | 10.2 |
| 1.5 | 4.09 | 8.2 | 12.8 |
| 2 | 5.46 | 10.9 | 17.1 |
| 2.5 | 6.83 | 13.7 | 21.3 |
| 3 | 8.19 | 16.4 | 25.6 |
| 4 | 10.92 | 21.8 | 34.1 |
| 5 | 13.65 | 27.3 | 42.7 |
| 6 | 16.38 | 32.8 | 51.2 |
| 8 | 21.84 | 43.7 | 68.2 |
| 10 | 27.30 | 54.6 | 85.3 |
| 12 | 32.76 | 65.5 | 102.4 |
| 16 | 43.68 | 87.4 | 136.5 |
Welding, forming and finishing 3A21
Welding
Excellent by TIG and MIG, and historically by gas welding. Al-Mn or Al-Si fillers (for example ER4043) are usual. Tanks and lines are welded in O temper, so the weld zone loses little strength.
Forming
O temper draws, spins and flares without cracking. H14 bends to tight radii in thin sheet; use H24 when bending after cutting.
Brazing
Good brazeability, which suits heat-exchanger and cooling-plate work.
Machining
Soft and gummy in O; machine harder tempers with sharp, polished, high-rake tools.
Surface treatment
Accepts chemical conversion coatings, primer and paint; anodising gives a protective but slightly grey film.
Corrosion
Close to commercially pure aluminium; suitable for fuel, oil and water systems with correct isolation from copper and steel.
Typical 3A21 aerospace applications
- Tanks: welded fuel, oil, hydraulic-reservoir and water tanks; tank ends and domes spun or drawn from O sheet
- Lines and ducting: fuel, oil and air lines, ventilation and cooling ducts (with 3A21 tube from the same alloy family)
- Formed covers: fairings, access covers, closeouts and shrouds that carry no primary load
- Cooling hardware: heat-exchanger fins, cold plates and radiator parts
- Interiors: cabin panels, equipment housings and trays
- Ground equipment: fuel-bowser tanks, enclosures and covers
Wings, tail surfaces, flight-control parts and other primary structure are not 3A21 applications, whatever older marketing text may claim.
How to order 3A21 sheet and plate
- SpecifyAlloy and temper, thickness, size or blank drawing, quantity and the governing specification with its revision (GB/T 3880 with GB/T 3190 chemistry, GOST, or an approved 3003 document).
- ConfirmWe confirm the specification can be met, the tolerance class, test requirements and delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions and surface condition; any extra tests named on the order are carried out or arranged.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry and mechanical results, traceable to the cast or lot number.
- Pack and shipExport packing in sealed, moisture-protected cases or on pallets, shipped by sea or air to your port or door.
References and standards
- GB/T 3190 – Wrought aluminium and aluminium alloys: chemical composition
- GB/T 3880.1 / 3880.2 – Wrought aluminium and aluminium alloy plates, sheets and strips for general engineering
- GOST 4784 – Aluminium and wrought aluminium alloys: grades
- ASTM B209 – Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
3A21 aerospace aluminium (aluminum) sheet: buyer questions
Can 3A21 be supplied in T4 or T6 temper?
No. 3A21 is an Al-Mn alloy and is not heat-treatable, so T tempers do not apply. It is supplied in O, H14, H24, H18 or H112, with strength set by cold work.
Is 3A21 the same as 3003?
It is a close equivalent. 3A21 allows 1.0 – 1.6 % manganese and has no copper minimum, while 3003 requires 0.05 – 0.20 % copper. For aerospace parts, substitute only with the design authority's approval.
What is the Russian equivalent of 3A21?
AMts (АМц), covered by GOST 4784. Drawings from CIS design offices often use that designation.
Which temper should I use for welded tanks?
O temper is normal for tanks and lines: it forms easily and the weld zone loses little strength because the parent sheet is already annealed.
Is 3A21 strong enough for aircraft structure?
Not for primary structure. With 100 – 180 MPa tensile strength depending on temper, it suits tanks, lines, ducts and formed covers. Load-carrying parts use 2xxx or 7xxx alloys.
Do you supply 3A21 internationally?
Yes. Metline ships 3A21 sheet and plate from Mumbai to customers worldwide, with mill certificates and export packing.
Need 3A21 sheet or plate for a tank, line or panel?
Send the temper, thickness, size, quantity and standard. We will confirm availability and certification.
