Pressing and drawing
O and H24 sheet draws well; H14 is better for flat panels and shallow forms. Embossing for heat shields is routine and adds stiffness.
Automotive aluminium sheet
3A21 H14 / H24 Aluminium Sheet for Automotive Parts
3A21 is the Chinese GB designation for an aluminium-manganese alloy that is close to 3003, with slightly wider manganese limits and lower magnesium and zinc. In H14 and H24 tempers it gives a moderately strong, very formable and corrosion-resistant sheet for heat shields, tanks, air ducts, trim and other non-structural vehicle parts. Metline supplies 3A21 sheet and coil to GB/T 33227, ASTM B209 and EN 485 to buyers worldwide.
- Alloy
- 3A21 (Al-1.0-1.6Mn)
- Tempers
- O, H14, H24 (H18 on request)
- Thickness
- 0.3 – 3.5 mm
- Standards
- GB/T 33227 · GB/T 3880 · ASTM B209
What is 3A21 aluminium sheet?
3A21 (formerly LF21 in China, and the counterpart of the Russian AMts) is a non-heat-treatable aluminium-manganese alloy. Manganese in the range 1.0 – 1.6 % gives it about 20 % more strength than commercially pure aluminium while keeping excellent formability, weldability and corrosion resistance.
In vehicles, 3A21 is a workhorse for parts that need to be formed, joined and left in service for years without corrosion, but that do not carry crash or structural loads. Typical examples are heat shields over exhausts and turbochargers, fuel and fluid tanks for commercial vehicles, air and HVAC ducts, battery-pack covers and liners, wheel-arch and underbody shields, and interior trim backings.
It is worth being clear about what 3A21 is not used for. Modern aluminium outer panels (bonnets, doors, roofs) are made from bake-hardenable 6xxx alloys such as 6016 or 6014, and inner panels from high-magnesium 5xxx alloys such as 5182 or 5754, because those grades reach much higher strength and dent resistance. 3A21 cannot be hardened by heat treatment, so where older literature suggests it for bonnets or doors, a 6xxx or 5xxx body sheet is the right choice.
3A21 chemical composition (wt %)
Limits follow GB/T 3190. Each delivery carries a mill certificate with the measured analysis of the lot.
| Element | 3A21 (GB/T 3190) | 3003 (AA / EN AW-3003) | Comment |
|---|---|---|---|
| Silicon (Si) | ≤ 0.60 | ≤ 0.6 | Impurity |
| Iron (Fe) | ≤ 0.70 | ≤ 0.7 | Impurity |
| Copper (Cu) | ≤ 0.20 | 0.05 – 0.20 | 3003 requires a minimum copper content; 3A21 does not |
| Manganese (Mn) | 1.0 – 1.6 | 1.0 – 1.5 | Main alloying element |
| Magnesium (Mg) | ≤ 0.05 | — | |
| Zinc (Zn) | ≤ 0.10 | ≤ 0.10 | |
| Titanium (Ti) | ≤ 0.15 | — | Grain refiner |
| Others, each / total | 0.05 / 0.10 | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | Remainder |
Because 3A21 may contain no copper at all while 3003 needs at least 0.05 %, a 3A21 lot does not automatically satisfy a 3003 order, and vice versa. Where cross-certification matters, ask for the chemistry to be held inside both ranges.
Mechanical properties of 3A21 sheet by temper
Values are the ranges commonly applied to 3A21 sheet under GB/T 3880 and GB/T 33227. H14 is strain-hardened to half-hard; H24 reaches a similar strength by harder rolling followed by partial annealing, which leaves more ductility for forming.
| Temper | Thickness (mm) | Tensile strength Rm | Elongation A50 (min) | Typical use |
|---|---|---|---|---|
| O (annealed) | 0.3 – 3.5 | 100 – 150 MPa | about 20 % (thickness-dependent) | Deep drawing, spinning, complex shields |
| H14 | 0.8 – 4.5 | 145 – 215 MPa | 6 % or more (varies with thickness) | Flat and lightly formed panels, ducts |
| H24 | 0.8 – 4.5 | 145 MPa min | 6 % or more, typically higher than H14 | Pressed parts needing strength and formability |
| H18 (on request) | thin gauges | about 185 MPa min | low | Stiff flat covers and trim |
Yield strength is not always specified for 3A21 in GB tables; typical 0.2 % proof values are about 40 MPa in O and about 125 – 145 MPa in H14/H24. The certificate for each lot states the measured values.
Physical properties (approximate)
- Density
- 2.73 g/cm³
- Melting range
- about 640 – 655 °C
- Thermal conductivity
- about 160 – 180 W/m·K depending on temper
- Electrical conductivity
- about 40 – 50 % IACS
- Coefficient of thermal expansion
- about 23 µm/m·°C (20 – 100 °C)
- Modulus of elasticity
- about 69 GPa
3A21 standards and international equivalents
| System | Designation | Relationship to 3A21 |
|---|---|---|
| China (GB) | 3A21 (formerly LF21) | Chemistry to GB/T 3190; automotive sheet to GB/T 33227; general sheet to GB/T 3880 |
| Russia / CIS (GOST) | AMts (АМц), 1400 | Essentially the same alloy |
| Aluminum Association / ASTM | Nearest: 3003 | Sheet to ASTM B209; copper minimum differs |
| European (EN) | Nearest: EN AW-3003 (AlMn1Cu) | Sheet to EN 485; EN AW-3103 is the copper-free near match |
| Japan (JIS) | Nearest: A3003P | Sheet to JIS H4000 |
For a copper-free equivalent in the European system, EN AW-3103 (AlMn1) is often a closer chemical match than 3003. We confirm which designation will appear on the certificate before production.
3A21 automotive sheet sizes and surfaces
Typical supply range for 3A21 automotive sheet
- Tempers
- O, H14, H24; H18 and other H-tempers on request
- Thickness
- 0.3 – 3.5 mm
- Width
- About 800 – 2,400 mm for full-width panel stock; slit strip down to narrow widths for brackets and small pressings
- Form
- Cut sheets, blanks and coils (inner diameter 405, 505 or 605 mm)
- Surface texture
- Mill finish (MF) or electro-discharge textured (EDT) for better lubricant retention and paint appearance
- Pre-treatment
- Untreated, or titanium/zirconium conversion coating to improve adhesive bonding and paint adhesion
- Lubrication
- Dry, electrostatic oil (EO) or dry-film lubricant (prelube/hot-melt), with the coating weight agreed per order
- Order standards
- GB/T 33227, ASTM B209, EN 485 or JIS H4000, plus the customer's material specification
Widths, coil weights and surface combinations are confirmed against your press-line and blanking requirements at quotation.
3A21 weighs about 2.73 kg per square metre for each millimetre of thickness. Reference weights for common blank sizes:
| Thickness (mm) | kg per m² | 1250 × 2500 mm (kg) | 1500 × 3000 mm (kg) |
|---|---|---|---|
| 0.5 | 1.36 | 4.3 | 6.1 |
| 0.7 | 1.91 | 6.0 | 8.6 |
| 0.8 | 2.18 | 6.8 | 9.8 |
| 1 | 2.73 | 8.5 | 12.3 |
| 1.2 | 3.28 | 10.2 | 14.7 |
| 1.5 | 4.09 | 12.8 | 18.4 |
| 2 | 5.46 | 17.1 | 24.6 |
| 2.5 | 6.83 | 21.3 | 30.7 |
| 3 | 8.19 | 25.6 | 36.9 |
Additional requirements for automotive sheet
A body sheet is judged on more than tensile strength. Automotive sheet standards such as GB/T 33227 and the OEM material specifications that sit above them add forming, surface and processing requirements. The table summarises the points that are usually written into the purchase order.
| Requirement | What it controls | How it is specified |
|---|---|---|
| Hemming / flanging grade | Whether the edge can be folded flat (hemmed) around an inner panel without cracking | Grade agreed on the order; checked with flat-hem or bend tests |
| Paint-brush lines | Fine streaks that become visible after painting on outer panels | Grade agreed on the order for exposed parts |
| Forming limit (FLD) | The strain combinations the sheet can survive before necking | Forming limit curve supplied when the buyer requests it |
| Dent resistance | Resistance of finished panels to local denting | Test data supplied on request |
| High-strain-rate tensile data | Behaviour in crash simulation | Supplied on request for crash-relevant parts |
| Oil amount | Lubricant weight for pressing and corrosion protection in transit | g/m² per side, agreed on the order |
| Passivation / conversion film | Bonding and paint adhesion | Coating type and weight agreed on the order |
| Appearance | Scratches, roll marks, colour variation | Stricter for outer panels; minor marks that do not affect forming are acceptable on inner and structural parts |
Thickness, width and flatness tolerances
The body-panel thickness tolerances commonly applied to 0.7 – 1.5 mm automotive sheet are tighter than general-engineering tables, because thickness variation changes draw-die clearance and springback. Typical values:
| Thickness (mm) | Width 800 – 1,600 mm | Width > 1,600 – 1,800 mm | Width > 1,800 – 2,400 mm |
|---|---|---|---|
| 0.70 – 1.00 | ±0.03 mm | ±0.05 mm | ±0.08 mm |
| > 1.00 – 1.20 | ±0.04 mm | ±0.06 mm | ±0.09 mm |
| > 1.20 – 1.50 | ±0.05 mm | ±0.07 mm | ±0.10 mm |
Other dimensional limits (typical)
- Width of cut sheet
- Plus-only tolerance, from about +0.3 mm on narrow strip to +3 mm on wide sheet
- Length
- About +3 mm up to 2 m long, +5 mm over 2 m
- Flatness
- Maximum wave height of about 3 – 8 mm depending on width and thickness
- Squareness
- Diagonal difference limited in proportion to sheet width
Forming, joining and where 3A21 is used
Welding and brazing
TIG, MIG and resistance welding all work, with ER4043 or ER1100 filler. 3A21 also brazes easily, which suits fluid tanks and duct assemblies.
Corrosion
Very good resistance to road spray and atmosphere. Avoid direct contact with steel or copper without isolation to prevent galvanic attack.
- Heat shields: flat or embossed shields for exhausts, turbochargers and fuel lines
- Tanks: fuel, hydraulic oil, washer and air tanks, mainly on commercial vehicles
- Ducts and HVAC housings: air ducts, blower and heater boxes
- Battery packs: covers, liners and spacers where formability counts more than strength
- Underbody and wheel-arch shields: light protective covers
- Interior parts: trim backings, panel inserts and decorative surfaces
How to order 3A21 sheet
- SpecifyAlloy and temper (for example 3A21-H24), thickness, width, sheet length or coil ID and weight, surface and lubrication, quantity.
- Confirm the standardGB/T 33227 for automotive sheet or GB/T 3880 for general sheet; ASTM B209, EN 485 or JIS H4000 where a Western equivalent is ordered.
- QuoteWe confirm availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP) for your plant or port.
- Process and inspectCoils are slit or cut to length, oiled or film-protected as specified, and inspected for thickness, flatness and surface.
- Document and shipEach lot ships with an EN 10204 3.1 mill test certificate, lot traceability and a packing list, in seaworthy export packing. Third-party inspection can be arranged on request.
References and standards
- GB/T 3190-2020 – Chemical composition of wrought aluminium and aluminium alloys
- GB/T 33227-2016 – Aluminium and aluminium alloy sheet and strip for automobiles
- GB/T 3880.2 – Aluminium and aluminium alloy plates, sheets and strips for general engineering: mechanical properties
- ASTM B209 – Aluminum and Aluminum-Alloy Sheet and Plate
- EN 485-2 – Sheet, strip and plate: mechanical properties
3A21 aluminium (aluminum) sheet: frequently asked questions
Is 3A21 the same as 3003?
Very close but not identical. 3A21 allows 1.0 – 1.6 % manganese and no minimum copper; 3003 requires 0.05 – 0.20 % copper and 1.0 – 1.5 % manganese. Mechanical properties in the same temper are practically the same.
What is the difference between 3A21 H14 and H24?
Both are half-hard. H14 gets its strength from rolling alone; H24 is rolled harder and then partially annealed back to the same strength level, which leaves more elongation and better formability.
Can 3A21 be heat treated for higher strength?
No. It is non-heat-treatable. Strength comes only from manganese and cold work. If a part needs bake-hardening or high strength, use a 6xxx or 5xxx automotive sheet.
Is 3A21 suitable for car bonnets or doors?
Not for modern panels. Outer panels use bake-hardenable 6xxx sheet for dent resistance, and inner panels use 5182 or 5754. 3A21 suits heat shields, tanks, ducts and trim.
Does 3A21 weld well?
Yes. It welds by TIG, MIG and resistance methods and brazes easily, which is why it is common for tanks and ducting.
Do you export 3A21 sheet?
Yes. Metline ships 3A21 sheet and coil worldwide from Mumbai with EN 10204 3.1 certificates and seaworthy packing, on EXW, FOB, CIF or DAP terms.
Need 3A21 sheet for vehicle parts?
Send the temper, size, quantity and destination, and we will confirm availability, certification and a delivered price.
