Aluminum 7050-T7451 vs. Steel AISI 4340

Compare Aluminum 7050-T7451 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	469MPasourcetypical, longitudinal, 0.2% offset	1,035MPasourcetypical, transverse
Ultimate tensile strength	524MPasourcetypical, longitudinal	1,140MPasourcetypical, transverse
Elongation at break	11%sourcetypical, longitudinal	18%sourcetypical, transverse
Young's modulus (stiffness)	70.3GPasourcetypical	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	2,830kg/m³sourcenominal	7,840kg/m³sourcetypical
Strength to weight	166kN·m/kg26% higher	132kN·m/kg
Stiffness to weight	24.8MN·m/kg	25.5MN·m/kg3% higher
Poisson's ratio	0.33sourcetypical (handbook physical constant)	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	26.4GPa	75.7GPa2.87x stiffer in shear
Bulk modulus	68.9GPa	185GPa
Speed of sound	4,984m/s	5,049m/s
Thermal
Thermal conductivity	157W/m·Ksourcetypical, 20 °C	37.5W/m·Ksourcetypical
Thermal expansion	23.5µm/m·Ksourcetypical, mean 20-100 °C	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	118µm growth	56.5µm growth2.08x less
Specific heat	860J/kg·Ksourcetypical, at 100 °C	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	64.5mm²/s6.05x faster	10.7mm²/s
Thermal shock resistance	29,862W/m2.56x more resistant	11,678W/m
Melting point	524–635°Csourcemelting range	not sourced
Values for	7050-T7451 plate, Kaiser Aluminum sheet, coil & plate typical datasheet (longitudinal); Poisson from MIL-HDBK-5J	Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Is Aluminum 7050-T7451 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 469 MPa for Aluminum 7050-T7451 (2.21x).

Which is lighter, Aluminum 7050-T7451 or Steel AISI 4340?

Aluminum 7050-T7451 is lighter: 2,830 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Aluminum 7050-T7451 or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 70.3 GPa for Aluminum 7050-T7451, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Aluminum 7050-T7451 or Steel AISI 4340?

For the same stiffness or strength: Aluminum 7050-T7451 is lighter for a stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Steel AISI 4340 is lighter for a stiff rod or tie (tension).

Part that must be	Aluminum 7050-T7451	Steel AISI 4340
Stiff rod or tie (tension)	3% heavier	lighter
Stiff beam (bending)	lighter	1.64x heavier
Stiff panel or plate	lighter	1.96x heavier
Strong rod or tie	lighter	26% heavier
Strong beam	lighter	1.63x heavier
Strong panel or plate	lighter	1.86x heavier

For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).

Which conducts heat better, Aluminum 7050-T7451 or Steel AISI 4340?

Aluminum 7050-T7451 conducts heat better: 157 W/m·K against 37.5 W/m·K for Steel AISI 4340.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 23.5 µm/m·K for Aluminum 7050-T7451.

Among 59 materials

Stiffness against density

Strength against density