Aluminum 1100-O vs. Magnesium AZ91D

Compare Aluminum 1100-O vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	35MPasourcetypical, O, 0.0625 in specimen	150MPasourcetypical, 0.2% tensile yield, ambient temperature
Ultimate tensile strength	90MPasourcetypical, O	230MPasourcetypical, ambient temperature
Elongation at break	35%sourcetypical, O, in 4D	3%sourcetypical, ambient temperature
Young's modulus (stiffness)	69GPasourcetypical1.53x stiffer	45GPasourcetypical
Density	2,710kg/m³sourcenominal, 20 °C	1,810kg/m³sourcetypical
Strength to weight	12.9kN·m/kg	82.9kN·m/kg6.42x higher
Stiffness to weight	25.5MN·m/kg2% higher	24.9MN·m/kg
Poisson's ratio	not sourced	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)
Shear modulus	not sourced	16.7GPa
Bulk modulus	not sourced	50GPa
Speed of sound	5,046m/s	4,986m/s
Thermal
Thermal conductivity	222W/m·Ksourcetypical, O, 20 °C	72W/m·Ksourcetypical
Thermal expansion	23.6µm/m·Ksourcetypical, mean 20-100 °C	25µm/m·Ksourcetypical, temperature range not stated
100 mm part over a 50 °C swing	118µm growth6% less	125µm growth
Specific heat	901J/kg·Ksourcebase material: commercially pure aluminium EN AW-1050A (Hydro), 20 °C	1,050J/kg·Ksourcetypical
Heats up and cools (diffusivity)	90.9mm²/s2.4x faster	37.9mm²/s
Thermal shock resistance	not sourced	6,240W/m
Melting point	640–655°Csourcemelting range	470–595°Csourcemelting range
Values for	1100-O (annealed) commercially pure aluminium, Kaiser Aluminum Tube & Pipe Alloy 1100 Technical Data (Rev. 05/06), typical properties; specific heat from Hydro EN AW-1050A (99.5% Al) extruded-products datasheet (10/2018).	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 1100-O stronger than Magnesium AZ91D?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 35 MPa for Aluminum 1100-O (4.29x).

Which is lighter, Aluminum 1100-O or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,710 kg/m³ for Aluminum 1100-O.

Which is stiffer, Aluminum 1100-O or Magnesium AZ91D?

Aluminum 1100-O is stiffer: Young's modulus 69 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum 1100-O deflects less under the same load.

Which is lighter for the same job, Aluminum 1100-O or Magnesium AZ91D?

For the same stiffness or strength: Aluminum 1100-O 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 1100-O	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	6.42x heavier	lighter
Strong beam	3.95x heavier	lighter
Strong panel or plate	3.1x 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 1100-O or Magnesium AZ91D?

Aluminum 1100-O conducts heat better: 222 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Aluminum 1100-O expands less: 23.6 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density