Aluminum 7021 · temper
Aluminum 7021-O
Properties of the O condition, compared with the other 7021 tempers.
Choose for deep drawing, severe bending or tube forming before a full solution-treat and age cycle.
What is 7021-O?
7021-O is 7021 in the O temper — choose for deep drawing, severe bending or tube forming before a full solution-treat and age cycle. 7021-O has a yield strength of 115 MPa (16.7 ksi) and a tensile strength of 230 MPa (33.4 ksi) — weaker than 79% of aluminum grades. Elongation at break is 20% and the elastic modulus is 70 GPa (10.2 Msi). 7021-O has a density of 2.78 g/cm³ (0.1 lb/in³), heavier than 74% of aluminum grades. It melts at 600°C (1,112 °F).
Advantages
- Ductile — tolerates forming and impact — 20%, better than 89% of aluminum grades
- Forms and bends easily — 70/100, better than 83% of aluminum grades
- Conducts heat well — 170 W/m·K (98.2 BTU/hr·ft·°F), better than 82% of aluminum grades
- Tough — resists crack growth — 30 MPa·√m (27.3 ksi·√in), better than 76% of aluminum grades
Limitations
- Difficult to machine — 40/100, worse than 80% of aluminum grades
- Low strength — 115 MPa (16.7 ksi), worse than 79% of aluminum grades
- Limited service temperature — 120°C (248 °F), worse than 79% of aluminum grades
7021-O properties
Typical room-temperature values for 7021-O — 10 properties are specific to this condition; the rest are grade-level values shared by every 7021 temper. Each bar shows where the value sits among the aluminum grades in FabDigit's library — further right is higher.
Physical3
7021-O has a density of 2.78 g/cm³ (0.1 lb/in³), heavier than 74% of aluminum grades. It melts at 600°C (1,112 °F).
Mechanical13
7021-O has a yield strength of 115 MPa (16.7 ksi) and a tensile strength of 230 MPa (33.4 ksi) — weaker than 79% of aluminum grades. Elongation at break is 20% and the elastic modulus is 70 GPa (10.2 Msi).
Thermal6
7021-O is rated for continuous service to 120°C (248 °F). It conducts heat at 170 W/m·K (98.2 BTU/hr·ft·°F), better than 82% of aluminum grades. Thermal expansion is 23.4 µm/m·K (13 µin/in·°F).
Electrical3
7021-O conducts electricity at 40 % IACS, better than 72% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), worse than 56% of aluminum grades.
Sustainability4
Producing a kilogram of 7021-O takes about 200 MJ of energy and emits 12.5 kg of CO₂ — less than 60% of aluminum grades. Typical recycled content is 25%.
Manufacturability7
7021-O's machinability is fair (40/100, worse than 80% of aluminum grades); weldability very good (70/100); formability very good (70/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 7021 tempers and conditions
7021 is also supplied in 5 other conditions. The full side-by-side table is on the 7021 overview.
- T6Default stocked condition: maximum strength for frames, tubes and structural extrusions where SCC exposure is moderate.370 MPa yield · 125 HB
- T651Use for machined plate or bar parts that must stay flat/straight after heavy metal removal.365 MPa yield · 125 HB
- T5Press-quenched extrusions aged without a separate solution treatment — cheaper and dimensionally stable, slightly below T6 strength.330 MPa yield · 115 HB
- T76Pick when chloride exposure or sustained stress makes stress-corrosion cracking the governing risk, accepting ~10 % lower strength than T6.330 MPa yield · 115 HB
- T4Intermediate strength with useful ductility; used when parts must still be bent or formed and will be artificially aged (or left to self-age) afterwards.215 MPa yield · 95 HB
- OChoose for deep drawing, severe bending or tube forming before a full solution-treat and age cycle.115 MPa yield · 60 HB
Working with 7021-O
Is 7021 easy to machine?
Machines well in T5/T6 with sharp carbide tooling, high speed and flood or MQL lubrication; chips are short and finish is good, but avoid heavy heat build-up that locally over-ages the surface.
Can 7021 be welded?
One of the more weldable 7xxx alloys — MIG/TIG with 5183/5356 filler; the HAZ naturally re-ages back toward parent strength, but keep heat input low and avoid welding in highly stressed peak-aged sections to limit SCC risk.
Can 7021 be formed, bent or molded?
Form in O or T4; T6/T651 tolerate only large-radius bends and require generous springback allowance — press-quench extrusion or hot forming for complex shapes.
What surface finishes work on 7021?
Responds well to clear and hard anodising and to chromate-free conversion coatings for painting; decorative colour anodising can be slightly grey/uneven, and shot peening plus paint is common on frames for SCC protection.
7021 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Zn | 5 – 6 | 5.5 |
| Mg | 1.2 – 1.8 | 1.5 |
| Zrgrain-structure control, replaces Cr | 0.08 – 0.18 | 0.12 |
| Si | ≤ 0.25 | — |
| Fe | ≤ 0.4 | — |
| Cukept low for weldability | ≤ 0.25 | — |
| Mn | ≤ 0.1 | — |
| Cr | ≤ 0.05 | — |
| Ti | ≤ 0.1 | — |
| Others (each)total 0.15 max | ≤ 0.05 | — |
| Al | balance | — |
7021-O — frequently asked
What is 7021-O used for?
7021-O is typically used for bicycle frame tubes and extrusions, motorcycle frame members, automotive bumper beams, ski poles, welded sports equipment tubing and defence hardware and fittings. In short: weldable extrusion.
What is the yield strength of 7021-O?
7021-O has a typical yield strength of 115 MPa (16.7 ksi) and a tensile strength of 230 MPa (33.4 ksi) — weaker than 79% of aluminum grades. Strength varies by condition: see the 6 listed tempers.
Is 7021-O easy to machine?
Not especially — machinability is rated fair (40/100, worse than 80% of aluminum grades). Machines well in T5/T6 with sharp carbide tooling, high speed and flood or MQL lubrication; chips are short and finish is good, but avoid heavy heat build-up that locally over-ages the surface.
Can 7021-O be welded?
Yes — weldability is rated very good (70/100). One of the more weldable 7xxx alloys — MIG/TIG with 5183/5356 filler; the HAZ naturally re-ages back toward parent strength, but keep heat input low and avoid welding in highly stressed peak-aged sections to limit SCC risk.
What surface finishes work on 7021-O?
Responds well to clear and hard anodising and to chromate-free conversion coatings for painting; decorative colour anodising can be slightly grey/uneven, and shot peening plus paint is common on frames for SCC protection.
Can 7021-O be formed, bent or molded?
Form in O or T4; T6/T651 tolerate only large-radius bends and require generous springback allowance — press-quench extrusion or hot forming for complex shapes.
What is the maximum service temperature of 7021-O?
7021-O is rated for continuous use to about 120°C (248 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 7021-O?
Yes — 7021-O is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- EN 573-3 Aluminium and aluminium alloys — chemical composition — CEN (2019)
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum (Teal Sheets) — The Aluminum Association (2018)
- EN 755-2 Aluminium alloy extruded rod/bar, tube and profiles — mechanical properties — CEN (2016)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys — ASM International (1990)
- ASM Handbook Vol. 13B — Corrosion: Materials — ASM International (2005)
- Al-Zn-Mg extrusion alloy datasheets (7020/7021/7022 class) — Constellium / Alcoa (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.