Aluminum 7021-O vs 7021-T4
Aluminum · 7021 temper comparison
7021-O and 7021-T4 are two conditions of the same aluminum grade, 7021: O (annealed) versus T4 (solution heat treated and naturally aged). The chemistry is identical, so every difference below comes from the condition. 7021-T4 is the stronger of the two: yield strength 215 MPa (31.2 ksi) against 115 MPa (16.7 ksi) for 7021-O, about 87% more; tensile strength follows at 345 MPa (50 ksi) vs 230 MPa (33.4 ksi). In exchange, 7021-O is the more ductile: elongation 20% versus 18% for 7021-T4, and 7021-T4 is harder (95 HB vs 60 HB). 7021-O runs hotter in service (120°C vs 100°C continuous) and 7021-O conducts heat better (170 W/m·K vs 130 W/m·K). On the shop floor, 7021-T4 machines more easily (52 vs 40 out of 100).
7021-OChoose it when the part is bent, formed or impact-loaded, or when the part sees heat.
7021-T4Choose it when strength drives the design, or when the part is machined in volume.
7021-O vs 7021-T4: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all aluminum grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all aluminum grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Shear Strength
Fatigue Strength (Endurance Limit)
Hardness, Brinell
Same in both: Elastic (Young's) Modulus 70 GPa10.2 Msi · Shear Modulus 26.5 GPa3.8 Msi · Bulk Modulus 75 GPa10.9 Msi · Poisson's Ratio 0.33 · Compressive Strength 375 MPa54.4 ksi · Fracture Toughness (K_IC) 30 MPa·√m27.3 ksi·√in · Hardness, Vickers 135 HV
Physical
Density and transition temperatures.
Same in both: Density 2.78 g/cm³0.1 lb/in³ · Melting Point (Solidus) 600°C1,112 °F · Liquidus Temperature 645°C1,193 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Max Service Temperature (continuous)
Same in both: Specific Heat Capacity 880 J/kg·K0.21 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 23.4 µm/m·K13 µin/in·°F · Latent Heat of Fusion 390 J/g168 BTU/lb · Min Service Temperature -196°C-321 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Same in both: Electrical Resistivity 5.2×10⁻⁸ Ω·m2.05 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.85 V
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Formability (cold)
Same in both: Machinability Rating (AISI 1212 = 100 %) 70% · Weldability 70 / 100 · Brazeability / Solderability 20 / 100 · Polishability 60 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 200 MJ/kg85,985 BTU/lb · Embodied Carbon (primary production) 12.5 kg CO₂/kg · Embodied Water 1,200 L/kg144 gal/lb · Typical Recycled Content 25%
Strength versus weight
Yield strength against density for every aluminum grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
7021-O vs 7021-T4 — frequently asked
Is 7021-T4 stronger than 7021-O?
Yes. 7021-T4 has a typical yield strength of 215 MPa (31.2 ksi) against 115 MPa (16.7 ksi) for 7021-O — about 87% more. Tensile strength is 345 MPa (50 ksi) vs 230 MPa (33.4 ksi).
Which condition does FabDigit quote by default, O or T4?
Specify the condition in the material field or the drawing note; FabDigit prices the quote for the state you call out.
Which is easier to machine, 7021-O or 7021-T4?
7021-T4, by a small margin. Both rate fair for machinability — 52/100 against 40/100 for 7021-O.
Ready to make it?
Upload a CAD file and FabDigit prices the part in 7021-O and 7021-T4 side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.