Aluminum 7075-T6 vs. Silicon

Compare Aluminum 7075-T6 vs. Silicon strength, stiffness, weight and thermal properties.

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SiliconGrown single crystal

Mechanical
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Yield strength	503MPasourcetypical, 0.2% offset, .500 in dia specimen	not given (tensile used)
Ultimate tensile strength	572MPasourcetypical	130MPasourcemodulus of rupture (bending fracture stress); brittle, no yield point
Flexural strength	not sourced	130MPasourcemodulus of rupture
Elongation at break	11%sourcetypical, in 4D	not sourced
Young's modulus (stiffness)	71GPasourcetypical	131GPasourcetypical (single quoted value of an anisotropic crystal)
Density	2,800kg/m³sourcenominal	2,329kg/m³sourcetypical
Strength to weight	180kN·m/kg3.22x higher	55.8kN·m/kg
Stiffness to weight	25.4MN·m/kg	56.2MN·m/kg2.22x higher
Poisson's ratio	0.33sourcetypical (handbook physical constant)	0.221sourcetypical
Shear modulus	26.7GPa	53.6GPa2.01x stiffer in shear
Bulk modulus	69.6GPa	78.3GPa
Speed of sound	5,036m/s	7,500m/s
Thermal
Thermal conductivity	130W/m·Ksourcetypical, 20 °C, T651	163W/m·Ksourcetypical at 313 K (40 °C)
Thermal expansion	23.4µm/m·Ksourcetypical, mean 20-100 °C	2.62µm/m·Ksourcetypical at 300 K
100 mm part over a 50 °C swing	117µm growth	13.1µm growth8.93x less
Specific heat	960J/kg·Ksourcetypical, at 100 °C	732J/kg·Ksourcetypical
Heats up and cools (diffusivity)	48.4mm²/s	95.6mm²/s1.98x faster
Thermal shock resistance	26,370W/m	48,095W/m1.82x more resistant
Melting point	532–635°Csourcemelting range	1,412°Csourcetypical
Max service temperature	not sourced	300°Csourceproducer's maximum application temperature (optical components)
Values for	7075-T6/T651, Kaiser Aluminum rod & bar (mechanical) and sheet/coil/plate (physical) typical datasheets; Poisson from MIL-HDBK-5J	Synthetic single-crystal silicon (cubic, diamond structure), Korth Kristalle (crystal grower) material data; Korth usually supplies Floating Zone (FZ) material, Czochralski (Cz) also offered. Silicon is elastically anisotropic; the producer quotes one modulus and the solver is isotropic.

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 7075-T6 stronger than Silicon?

Aluminum 7075-T6 is stronger: its yield strength is 503 MPa against tensile strength 130 MPa for Silicon (3.87x).

Which is lighter, Aluminum 7075-T6 or Silicon?

Silicon is lighter: 2,329 kg/m³ against 2,800 kg/m³ for Aluminum 7075-T6.

Which is stiffer, Aluminum 7075-T6 or Silicon?

Silicon is stiffer: Young's modulus 131 GPa against 71 GPa for Aluminum 7075-T6, so the same part in Silicon deflects less under the same load.

Which is lighter for the same job, Aluminum 7075-T6 or Silicon?

For the same stiffness or strength: Aluminum 7075-T6 is lighter for a strong rod or tie, strong beam, strong panel or plate; Silicon is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate.

Part that must be	Aluminum 7075-T6	Silicon
Stiff rod or tie (tension)	2.22x heavier	lighter
Stiff beam (bending)	1.63x heavier	lighter
Stiff panel or plate	47% heavier	lighter
Strong rod or tie	lighter	3.22x heavier
Strong beam	lighter	2.05x heavier
Strong panel or plate	lighter	1.64x 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 7075-T6 or Silicon?

Silicon conducts heat better: 163 W/m·K against 130 W/m·K for Aluminum 7075-T6.

Which expands less with temperature?

Silicon expands less: 2.62 µm/m·K against 23.4 µm/m·K for Aluminum 7075-T6.

Among 72 materials

Stiffness against density

Strength against density