Aluminum 6061-T6 vs. Silicon

Compare Aluminum 6061-T6 vs. Silicon strength, stiffness, weight and thermal properties.

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SiliconGrown single crystal

Mechanical
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Yield strength	276MPasourcetypical, 0.2% offset, .500 in dia specimen	not given (tensile used)
Ultimate tensile strength	310MPasourcetypical	130MPasourcemodulus of rupture (bending fracture stress); brittle, no yield point
Flexural strength	not sourced	130MPasourcemodulus of rupture
Elongation at break	17%sourcetypical, in 4D, 0.500 in dia specimen	not sourced
Young's modulus (stiffness)	68.3GPasourcetypical	131GPasourcetypical (single quoted value of an anisotropic crystal)
Density	2,700kg/m³sourcenominal	2,329kg/m³sourcetypical
Strength to weight	102kN·m/kg1.83x higher	55.8kN·m/kg
Stiffness to weight	25.3MN·m/kg	56.2MN·m/kg2.22x higher
Poisson's ratio	0.33sourcetypical (handbook physical constant)	0.221sourcetypical
Shear modulus	25.7GPa	53.6GPa2.09x stiffer in shear
Bulk modulus	67GPa	78.3GPa
Speed of sound	5,030m/s	7,500m/s
Thermal
Thermal conductivity	167W/m·Ksourcetypical, 20 °C	163W/m·Ksourcetypical at 313 K (40 °C)
Thermal expansion	23.6µm/m·Ksourcetypical, mean 20-100 °C	2.62µm/m·Ksourcetypical at 300 K
100 mm part over a 50 °C swing	118µm growth	13.1µm growth9.01x less
Specific heat	896J/kg·Ksourcetypical, at 100 °C	732J/kg·Ksourcetypical
Heats up and cools (diffusivity)	69mm²/s	95.6mm²/s39% faster
Thermal shock resistance	19,159W/m	48,095W/m2.51x more resistant
Melting point	582–652°Csourcesolidus-liquidus	1,412°Csourcetypical
Max service temperature	not sourced	300°Csourceproducer's maximum application temperature (optical components)
Values for	6061-T6/T651, Kaiser Aluminum typical properties; 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 6061-T6 stronger than Silicon?

Aluminum 6061-T6 is stronger: its yield strength is 276 MPa against tensile strength 130 MPa for Silicon (2.12x).

Which is lighter, Aluminum 6061-T6 or Silicon?

Silicon is lighter: 2,329 kg/m³ against 2,700 kg/m³ for Aluminum 6061-T6.

Which is stiffer, Aluminum 6061-T6 or Silicon?

Silicon is stiffer: Young's modulus 131 GPa against 68.3 GPa for Aluminum 6061-T6, so the same part in Silicon deflects less under the same load.

Which is lighter for the same job, Aluminum 6061-T6 or Silicon?

For the same stiffness or strength: Aluminum 6061-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 6061-T6	Silicon
Stiff rod or tie (tension)	2.22x heavier	lighter
Stiff beam (bending)	1.61x heavier	lighter
Stiff panel or plate	44% heavier	lighter
Strong rod or tie	lighter	1.83x heavier
Strong beam	lighter	42% heavier
Strong panel or plate	lighter	26% 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 6061-T6 or Silicon?

Aluminum 6061-T6 conducts heat better: 167 W/m·K against 163 W/m·K for Silicon.

Which expands less with temperature?

Silicon expands less: 2.62 µm/m·K against 23.6 µm/m·K for Aluminum 6061-T6.

Among 72 materials

Stiffness against density

Strength against density