Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
Try it on a partA sample part to run stress or thermal on, free in your browser
Sources3 documents: Kaiser Aluminum, Korth Kristalle, U.S. Department of Defense
Aluminum
6061-T6/T651, Kaiser Aluminum typical properties (sheet, coil & plate datasheet); 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 · Yield strength: typical, 0.2% offset, .500 in dia specimenAluminum · Ultimate tensile strength: typicalAluminum · Elongation at break: typical, in 4D, 0.500 in dia specimenAluminum · Young's modulus (stiffness): typicalAluminum · Density: nominalAluminum · Thermal conductivity: typical, 20 °CAluminum · Thermal expansion: typical, mean 20-100 °CAluminum · Specific heat: typical, at 100 °CAluminum · 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 · 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 stronger than Silicon?
Aluminum is stronger: its yield strength is 276 MPa against tensile strength 130 MPa for Silicon (2.12x).
Which is lighter, Aluminum or Silicon?
Silicon is lighter: 2,329 kg/m³ against 2,700 kg/m³ for Aluminum.
Which is stiffer, Aluminum or Silicon?
Silicon is stiffer: Young's modulus 131 GPa against 68.3 GPa for Aluminum, so the same part in Silicon deflects less under the same load.
Which is lighter for the same job, Aluminum or Silicon?
For the same stiffness or strength: Aluminum 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
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 or Silicon?
Aluminum 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.