A380 aluminium high-pressure die-casting alloy, typical properties; Rheocast Company (aluminium die caster, Germantown WI) A380 alloy data page.
ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
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 Aluminum A380 stronger than Magnesium AZ91D?
Aluminum A380 is stronger: its yield strength is 160 MPa against 150 MPa for Magnesium AZ91D (7%).
Which is lighter, Aluminum A380 or Magnesium AZ91D?
Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,713 kg/m³ for Aluminum A380.
Which is stiffer, Aluminum A380 or Magnesium AZ91D?
Aluminum A380 is stiffer: Young's modulus 71 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum A380 deflects less under the same load.
Which is lighter for the same job, Aluminum A380 or Magnesium AZ91D?
For the same stiffness or strength: Aluminum A380 is lighter for a stiff rod or tie (tension); Magnesium AZ91D is lighter for a stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate.
Part that must be
Aluminum A380
Magnesium AZ91D
Stiff rod or tie (tension)
lighter
5% heavier
Stiff beam (bending)
19% heavier
lighter
Stiff panel or plate
29% heavier
lighter
Strong rod or tie
41% heavier
lighter
Strong beam
44% heavier
lighter
Strong panel or plate
45% heavier
lighter
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, Aluminum A380 or Magnesium AZ91D?
Aluminum A380 conducts heat better: 96.2 W/m·K against 72 W/m·K for Magnesium AZ91D.
Which expands less with temperature?
Aluminum A380 expands less: 21.8 µm/m·K against 25 µm/m·K for Magnesium AZ91D.