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7021 (7021-T6, AlZn5.5Mg1.5) Aluminum

7021 aluminum is a 7000-series aluminum alloy: the main alloying addition is zinc and it is formulated for primary forming into wrought products. Cited properties are appropriate for the T6 temper. To achieve this temper, the metal is solution heat-treated and artificially aged until it meets standard mechanical property requirements. 7021 is the Aluminum Association (AA) designation for this material. In European standards, it will be given as EN AW-7021. Additionally, the EN chemical designation is AlZn5,5Mg1,5. And the UNS number is A97021.

It originally received its standard designation in 1976.

The graph bars on the material properties cards below compare 7021 aluminum to: 7000-series alloys (top), all aluminum alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Elastic (Young's, Tensile) Modulus

69 GPa 10 x 106 psi

Elongation at Break

9.4 %

Fatigue Strength

150 MPa 22 x 103 psi

Poisson's Ratio

0.32

Shear Modulus

26 GPa 3.8 x 106 psi

Shear Strength

270 MPa 40 x 103 psi

Tensile Strength: Ultimate (UTS)

460 MPa 67 x 103 psi

Tensile Strength: Yield (Proof)

390 MPa 57 x 103 psi

Thermal Properties

Latent Heat of Fusion

380 J/g

Maximum Temperature: Mechanical

200 °C 380 °F

Melting Completion (Liquidus)

630 °C 1170 °F

Melting Onset (Solidus)

510 °C 940 °F

Specific Heat Capacity

870 J/kg-K 0.21 BTU/lb-°F

Thermal Conductivity

150 W/m-K 87 BTU/h-ft-°F

Thermal Expansion

24 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

38 % IACS

Electrical Conductivity: Equal Weight (Specific)

120 % IACS

Otherwise Unclassified Properties

Base Metal Price

9.5 % relative

Density

2.9 g/cm3 180 lb/ft3

Embodied Carbon

8.3 kg CO2/kg material

Embodied Energy

150 MJ/kg 65 x 103 BTU/lb

Embodied Water

1140 L/kg 140 gal/lb

Common Calculations

Resilience: Ultimate (Unit Rupture Work)

41 MJ/m3

Resilience: Unit (Modulus of Resilience)

1110 kJ/m3

Stiffness to Weight: Axial

13 points

Stiffness to Weight: Bending

47 points

Strength to Weight: Axial

44 points

Strength to Weight: Bending

45 points

Thermal Diffusivity

59 mm2/s

Thermal Shock Resistance

20 points

Alloy Composition

Among wrought aluminum alloys, the composition of 7021 aluminum is notable for containing a comparatively high amount of zinc (Zn) and including zirconium (Zr). Zinc is used to achieve significant increases in strength, at the cost of increased susceptibility to stress corrosion cracking. Among other things, this limits weldability. Zirconium is used to increase an alloy's recrystallization temperature, which increases the temperature at which the alloy can be used without permanent loss of mechanical properties.

Aluminum (Al)Al 90.7 to 93.7
Zinc (Zn)Zn 5.0 to 6.0
Magnesium (Mg)Mg 1.2 to 1.8
Iron (Fe)Fe 0 to 0.4
Zirconium (Zr)Zr 0.080 to 0.18
Silicon (Si)Si 0 to 0.25
Copper (Cu)Cu 0 to 0.25
Manganese (Mn)Mn 0 to 0.1
Titanium (Ti)Ti 0 to 0.1
Chromium (Cr)Cr 0 to 0.050
Residualsres. 0 to 0.15

All values are % weight. Ranges represent what is permitted under applicable standards.

Followup Questions

Similar Alloys

Further Reading

Handbook of Aluminum vol. 2: Alloy Production and Materials Manufacturing, George Totten and D. Scott MacKenzie (editors), 2003

Aluminum: Properties and Physical Metallurgy, John E. Hatch (editor), 1984

EN 755-2: Aluminium and aluminium alloys. Extruded rod/bar, tube and profiles. Mechanical properties

EN 485-2: Aluminium and aluminium alloys. Sheet, strip and plate. Mechanical properties

ASM Specialty Handbook: Aluminum and Aluminum Alloys, J. R. Davis (editor), 1993

ISO 6361-2: Wrought aluminium and aluminium alloys - Sheets, strips and plates - Part 2: Mechanical properties

EN 573-3: Aluminium and aluminium alloys. Chemical composition and form of wrought products. Chemical composition and form of products