300°Csourceproducer's maximum application temperature (optical components)
Values for
ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
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 Magnesium AZ91D stronger than Silicon?
Magnesium AZ91D is stronger: its yield strength is 150 MPa against tensile strength 130 MPa for Silicon (15%).
Which is lighter, Magnesium AZ91D or Silicon?
Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,329 kg/m³ for Silicon.
Which is stiffer, Magnesium AZ91D or Silicon?
Silicon is stiffer: Young's modulus 131 GPa against 45 GPa for Magnesium AZ91D, so the same part in Silicon deflects less under the same load.
Which is lighter for the same job, Magnesium AZ91D or Silicon?
For the same stiffness or strength: Magnesium AZ91D 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
Magnesium AZ91D
Silicon
Stiff rod or tie (tension)
2.26x heavier
lighter
Stiff beam (bending)
33% heavier
lighter
Stiff panel or plate
11% heavier
lighter
Strong rod or tie
lighter
48% heavier
Strong beam
lighter
42% heavier
Strong panel or plate
lighter
38% 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, Magnesium AZ91D or Silicon?
Silicon conducts heat better: 163 W/m·K against 72 W/m·K for Magnesium AZ91D.
Which expands less with temperature?
Silicon expands less: 2.62 µm/m·K against 25 µm/m·K for Magnesium AZ91D.