T6
Solution heat-treated (or press-quenched with water), then artificially aged to peak strength. The standard temper for beams sized by strength.
High-strength crash extrusion
7021 T6 Automotive Aluminium Profile
7021 is one of the strongest extrusion alloys in the weldable Al-Zn-Mg group, with typical T6 yield strength near 390 MPa. Vehicle makers use it where a beam must be lighter than a 7003 or 6082 design can achieve, such as bumper beams, sill reinforcements and battery-protection members. Metline supplies 7021-T6 profiles to drawing, with full certification, worldwide.
- Alloy
- 7021 (AlZn5.5Mg1.5)
- Temper
- T6 (also T5, T7x)
- Typical yield (T6)
- about 390 MPa
- Standards
- EN 755-2 · ASTM B221 · GB/T 33910
What is 7021 aluminium and why use it in vehicles?
7021 carries about 5.5 % zinc and 1.5 % magnesium, roughly 7 % in total. That is near the practical upper limit for an alloy that is still extruded into automotive hollows, and it is why 7021 sits above 7003 and 7005 on strength while remaining far easier to process than copper-rich aerospace 7075.
Zirconium (0.08 – 0.18 %) is the only grain-control addition; chromium and manganese are kept very low. Zirconium holds a fibrous, unrecrystallised structure in the extruded section, which improves toughness and reduces sensitivity to stress corrosion and to quench rate. Copper is restricted to 0.25 % maximum.
The price of the higher alloy content is lower extrusion speed, a narrower process window and a higher need for SCC control. In practice, 7021 is chosen for parts where the weight saving justifies that care: a 7021 bumper beam can be made thinner than a 7003 beam with the same bending capacity, saving material across a high-volume vehicle programme.
7021 chemical composition (wt %)
Limits as registered for EN AW-7021 in EN 573-3 and in the Aluminum Association listing. The certificate for each cast reports the actual analysis.
| Element | Minimum | Maximum | Role |
|---|---|---|---|
| Zinc (Zn) | 5.0 | 6.0 | Main strengthening element |
| Magnesium (Mg) | 1.2 | 1.8 | Strengthening with Zn |
| Zirconium (Zr) | 0.08 | 0.18 | Fibrous grain structure, SCC resistance |
| Copper (Cu) | — | 0.25 | Limited for weldability |
| Iron (Fe) | — | 0.40 | Impurity |
| Silicon (Si) | — | 0.25 | Impurity |
| Manganese (Mn) | — | 0.10 | |
| Titanium (Ti) | — | 0.10 | Grain refiner |
| Chromium (Cr) | — | 0.05 | |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder |
Mechanical properties of 7021-T6 profiles
Yield strength is always lower than tensile strength; any table that shows a 7021 yield above its tensile value contains an error. Order to the minimums in your specification and check them on the certificate.
| Temper / basis | Tensile strength | Yield strength (0.2 %) | Elongation |
|---|---|---|---|
| T6, minimum tensile commonly specified (sections up to 20 mm) | 410 MPa | per specification table | about 8 – 10 % |
| T6, typical | about 460 MPa | about 390 MPa | about 9 % |
Physical properties (typical)
- Density
- about 2.78 g/cm³
- Modulus of elasticity
- about 69 – 70 GPa
- Thermal conductivity
- about 150 W/m·K
- Coefficient of thermal expansion
- about 23.5 µm/m·°C
- Melting range
- about 510 – 630 °C
Typical values from published alloy data; guaranteed values depend on the standard, section thickness and temper.
7021 tempers
T5
Press-quenched and aged; possible on thinner sections when the quench at the press is fast enough.
Over-aged (T7x)
A second ageing step beyond peak lowers strength somewhat but improves stress-corrosion and exfoliation resistance and crash ductility. Many OEM specifications for 7xxx crash parts call for this type of practice.
7021 standards and supply range
| System | Designation | Typical standard |
|---|---|---|
| European (EN) | EN AW-7021 / AlZn5.5Mg1.5 | EN 755-2, EN 573-3 |
| Aluminum Association | 7021 | ASTM B221 (where agreed) |
| China (GB) | 7021 | GB/T 3190, GB/T 33910 |
| Section | Typical range |
|---|---|
| Wall thickness | About 0.5 – 20 mm depending on section |
| Width | About 20 – 300 mm |
| Shapes | Multi-cell bumper beams, square, rectangular and round tube, angles, custom hollows |
| Length | To vehicle programme drawing |
7021 T6 profile supply range
- Section types
- Open profiles (angle, channel, T, hat), single- and multi-cell hollows, round, square and rectangular tube, solid bar
- Circumscribing circle
- Typically up to about 250 – 300 mm for 7xxx; larger sections reviewed case by case
- Wall thickness
- From about 1.5 – 2 mm for hollows, depending on section complexity
- Length
- Mill lengths of 3 – 7 m, or cut to exact length, bent, punched or machined on request
- Surface
- Mill finish, anodised, e-coated, powder coated or prepared for chrome or paint
- Documents
- EN 10204 3.1 certificate, dimensional report, PPAP-style records on request
Extrusion dies are made to your drawing. Send the section with critical dimensions and tolerances.
Welding, forming and corrosion control
Welding
Weldable by MIG and TIG with 5xxx filler (ER5356, ER5183), but the higher zinc and magnesium make it more prone to hot cracking than 7003 or 7005. Many crash structures in 7021 are therefore joined mechanically, by self-piercing rivets, flow-drill screws or bolts, rather than welded.
Stress corrosion
Like all Al-Zn-Mg alloys, 7021 can crack under sustained tensile stress in damp or salty service if the temper, residual stress and grain structure are wrong. Specify a controlled ageing practice, avoid cold forming after ageing, keep assembly stresses low, and ask for SCC test data (for example ASTM G47 alternate immersion) on critical parts.
Forming and bending
Stretch bending and rotary-draw bending are best done in the freshly quenched (W) or T4 condition, then aged to T5 or T6. Bending in the fully aged condition needs generous radii and raises residual stress.
Machining
Machines more cleanly than 6xxx alloys in the aged condition, with short chips and a good finish using sharp carbide tools and flood coolant.
Surface finishing
Accepts anodising, e-coating and powder coating. Zinc-rich alloys anodise with a slight yellow-grey tint, so check colour needs for visible parts. Coatings also add a barrier against galvanic and stress corrosion.
Joining to steel
Isolate 7021 from steel, carbon fibre and copper with sealants, coatings or insulating washers, and use coated fasteners, to avoid galvanic corrosion in wet road environments.
Surface damage
Scratches and dents act as stress raisers and corrosion sites on a highly stressed beam. Protect profiles in handling and transport and coat cut edges where specified.
Automotive applications of 7021
| Component | Reason for 7021 | Joining |
|---|---|---|
| Front and rear bumper beams | Highest strength in the weldable Al-Zn-Mg group; thinner walls | Bolted or riveted to crash boxes |
| Sill and rocker reinforcements | Side-impact resistance with low mass | Riveted or bonded |
| Door intrusion beams | Bending strength in a compact section | Mechanical fasteners |
| Battery-pack side members | Protection of cells in side impact | Bolted or welded (with care) |
7021 is a structural extrusion alloy. Doors, bonnets and other outer panels use 5xxx and 6xxx sheet, and wheels and brake callipers are cast or forged from other alloys. 7021 sheet is also used for consumer-electronics housings; see our 7021 sheet guide.
7021 compared with 7003, 7129 and 6082
| Property | 7021-T6 | 7003-T5 | 7129-T6 | 6082-T6 |
|---|---|---|---|---|
| Typical yield strength | about 390 MPa | about 300 MPa | about 390 MPa | about 260 – 310 MPa |
| Extrudability | Fair | Good | Fair | Very good |
| Weldability | Fair | Good | Fair | Good |
| SCC care needed | High | Moderate | High | Low |
How to order 7021 automotive profiles
- SpecifyAlloy and temper (7021-T6 or an over-aged practice), section drawing, length, quantity and machining.
- Confirm the standardEN 755-2, GB/T 33910 or your OEM material specification, including SCC and crash requirements.
- QuoteWe confirm availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP) for your plant or port.
- Process and inspectProfiles are extruded, quenched, aged, cut and inspected, with tensile tests per lot and SCC tests where specified.
- Document and shipEach lot ships with an EN 10204 3.1 mill test certificate and packing list, in seaworthy export packing by sea or air; third-party inspection on request.
References and standards
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- EN 573-3 – Aluminium and aluminium alloys: chemical composition and form of wrought products
- EN 755-2 – Extruded rod/bar, tube and profiles: mechanical properties
- ASTM G47 – Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX Aluminum Alloy Products
- GB/T 33910 – Aluminium and aluminium alloy extruded profiles for motor vehicles
- IATF 16949 – Quality management system requirements for automotive production and relevant service parts organisations
7021 automotive aluminium (aluminum) profiles: FAQ
How strong is 7021-T6?
Typical values are about 460 MPa tensile and 390 MPa yield, with about 9 % elongation. Minimum tensile strength commonly specified for sections up to 20 mm is about 410 MPa.
Can 7021 be welded?
Yes, with 5xxx filler wire, but it is more prone to hot cracking than 7003 or 7005. Many crash parts in 7021 are riveted, screwed or bolted instead.
What is the difference between 7021 and 7003?
7021 contains more magnesium (1.2 – 1.8 % against 0.5 – 1.0 %), which raises strength by roughly a quarter but makes extrusion slower and stress-corrosion control more demanding.
Is 7021 used for car wheels or brake callipers?
Not normally. Wheels are cast (A356) or forged (6061, 6082), and callipers are cast or forged. 7021 is used for extruded beams and reinforcements.
What surface treatments suit 7021 profiles?
E-coating, powder coating and anodising. Coatings also act as a barrier against galvanic and stress corrosion.
Designing a lighter crash beam?
Send your 7021 section and volumes. We will reply with feasibility, certification and a delivered price.
