ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
Zamak 3 (ASTM B86 die cast), Nathan Trotter (zinc alloy producer) technical data sheet, typical values
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 Zinc Zamak 3?
Zinc Zamak 3 is stronger: its yield strength is 221 MPa against 150 MPa for Magnesium AZ91D (47%).
Which is lighter, Magnesium AZ91D or Zinc Zamak 3?
Magnesium AZ91D is lighter: 1,810 kg/m³ against 6,600 kg/m³ for Zinc Zamak 3.
Which is stiffer, Magnesium AZ91D or Zinc Zamak 3?
Zinc Zamak 3 is stiffer: Young's modulus 85.5 GPa against 45 GPa for Magnesium AZ91D, so the same part in Zinc Zamak 3 deflects less under the same load.
Which is lighter for the same job, Magnesium AZ91D or Zinc Zamak 3?
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
Zinc Zamak 3
Stiff rod or tie (tension)
lighter
1.92x heavier
Stiff beam (bending)
lighter
2.65x heavier
Stiff panel or plate
lighter
2.94x heavier
Strong rod or tie
lighter
2.47x heavier
Strong beam
lighter
2.82x heavier
Strong panel or plate
lighter
3x 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 Zinc Zamak 3?
Zinc Zamak 3 conducts heat better: 113 W/m·K against 72 W/m·K for Magnesium AZ91D.
Which expands less with temperature?
Magnesium AZ91D expands less: 25 µm/m·K against 27.4 µm/m·K for Zinc Zamak 3.