Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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Sources3 documents: Kaiser Aluminum, Magnesium Elektron, U.S. Department of Defense
Aluminum
6061-T6/T651, Kaiser Aluminum typical properties (sheet, coil & plate datasheet); Poisson from MIL-HDBK-5J
Magnesium AZ91D
ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
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
Elektron Die Casting Alloys (Datasheet 475)Magnesium Elektronarchived copyMagnesium AZ91D · Yield strength: typical, 0.2% tensile yield, ambient temperatureMagnesium AZ91D · Ultimate tensile strength: typical, ambient temperatureMagnesium AZ91D · Elongation at break: typical, ambient temperatureMagnesium AZ91D · Young's modulus (stiffness): typicalMagnesium AZ91D · Density: typicalMagnesium AZ91D · Thermal conductivity: typicalMagnesium AZ91D · Thermal expansion: typical, temperature range not statedMagnesium AZ91D · Specific heat: typicalMagnesium AZ91D · Melting point: melting range
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)Magnesium AZ91D · Poisson's ratio: base material: AZ91C casting (MIL-HDBK-5J 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 Magnesium AZ91D?
Aluminum is stronger: its yield strength is 276 MPa against 150 MPa for Magnesium AZ91D (1.84x).
Which is lighter, Aluminum or Magnesium AZ91D?
Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,700 kg/m³ for Aluminum.
Which is stiffer, Aluminum or Magnesium AZ91D?
Aluminum is stiffer: Young's modulus 68.3 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum deflects less under the same load.
Which is lighter for the same job, Aluminum or Magnesium AZ91D?
For the same stiffness or strength: Aluminum is lighter for a stiff rod or tie (tension), strong rod or tie; Magnesium AZ91D is lighter for a stiff beam (bending), stiff panel or plate, strong panel or plate.
Part that must be
Aluminum
Magnesium AZ91D
Stiff rod or tie (tension)
lighter
2% heavier
Stiff beam (bending)
21% heavier
lighter
Stiff panel or plate
30% heavier
lighter
Strong rod or tie
lighter
23% heavier
Strong beam
about equal
about equal
Strong panel or plate
10% 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 is more ductile, Aluminum or Magnesium AZ91D?
Aluminum stretches further before it breaks: 17% elongation at break against 3% for Magnesium AZ91D.
Thermal
Which conducts heat better, Aluminum or Magnesium AZ91D?
Aluminum conducts heat better: 167 W/m·K against 72 W/m·K for Magnesium AZ91D.
Which expands less with temperature?
Aluminum expands less: 23.6 µm/m·K against 25 µm/m·K for Magnesium AZ91D.