Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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Sources3 documents: Kaiser Aluminum, Korth Kristalle, U.S. Department of Defense
Aluminum 6061-T6
6061-T6/T651, Kaiser Aluminum typical properties; Poisson from MIL-HDBK-5J
Silicon
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.
1
Alloy 6061 Sheet, Coil & Plate Technical DataKaiser Aluminumarchived copyAluminum 6061-T6 · Yield strength: typical, 0.2% offset, .500 in dia specimenAluminum 6061-T6 · Ultimate tensile strength: typicalAluminum 6061-T6 · Elongation at break: typical, in 4D, 0.500 in dia specimenAluminum 6061-T6 · Young's modulus (stiffness): typicalAluminum 6061-T6 · Density: nominalAluminum 6061-T6 · Thermal conductivity: typical, 20 °CAluminum 6061-T6 · Thermal expansion: typical, mean 20-100 °CAluminum 6061-T6 · Specific heat: typical, at 100 °CAluminum 6061-T6 · Melting point: solidus-liquidus
2
Si: SiliconKorth Kristallearchived copySilicon · Ultimate tensile strength: modulus of rupture (bending fracture stress); brittle, no yield pointSilicon · Flexural strength: modulus of ruptureSilicon · Young's modulus (stiffness): typical (single quoted value of an anisotropic crystal)Silicon · Density: typicalSilicon · Poisson's ratio: typicalSilicon · Thermal conductivity: typical at 313 K (40 °C)Silicon · Thermal expansion: typical at 300 KSilicon · Specific heat: typicalSilicon · Melting point: typicalSilicon · Max service temperature: producer's maximum application temperature (optical components)
3
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseAluminum 6061-T6 · Poisson's ratio: typical (handbook physical constant)
Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Mechanical
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).
Thermal
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.