ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
DuPont Delrin 100 acetal homopolymer, Table 2 'Typical Properties of Delrin Acetal Resins' (ASTM methods), Delrin Design Guide Module III hosted on delrin.com
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 Plastic POM/Acetal?
Magnesium AZ91D is stronger: its yield strength is 150 MPa against 69 MPa for Plastic POM/Acetal (2.17x).
Which is lighter, Magnesium AZ91D or Plastic POM/Acetal?
Plastic POM/Acetal is lighter: 1,420 kg/m³ against 1,810 kg/m³ for Magnesium AZ91D.
Which is stiffer, Magnesium AZ91D or Plastic POM/Acetal?
Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 2.8 GPa for Plastic POM/Acetal, so the same part in Magnesium AZ91D deflects less under the same load.
Which is lighter for the same job, Magnesium AZ91D or Plastic POM/Acetal?
For the same stiffness or strength: Magnesium AZ91D is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate.
Part that must be
Magnesium AZ91D
Plastic POM/Acetal
Stiff rod or tie (tension)
lighter
12.6x heavier
Stiff beam (bending)
lighter
3.15x heavier
Stiff panel or plate
lighter
1.98x heavier
Strong rod or tie
lighter
1.71x heavier
Strong beam
lighter
32% heavier
Strong panel or plate
lighter
16% 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 Plastic POM/Acetal?
Magnesium AZ91D conducts heat better: 72 W/m·K against 0.4 W/m·K for Plastic POM/Acetal.
Which expands less with temperature?
Magnesium AZ91D expands less: 25 µm/m·K against 122 µm/m·K for Plastic POM/Acetal.