Aluminum 6063-T6 vs. Magnesium AZ91D

Compare Aluminum 6063-T6 vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	215MPasourcetypical, T6, 0.0625 in specimen	150MPasourcetypical, 0.2% tensile yield, ambient temperature
Ultimate tensile strength	240MPasourcetypical, T6	230MPasourcetypical, ambient temperature
Elongation at break	12%sourcetypical, T6, in 4D	3%sourcetypical, ambient temperature
Young's modulus (stiffness)	69GPasourcetypical1.53x stiffer	45GPasourcetypical
Density	2,700kg/m³sourcenominal, 20 °C	1,810kg/m³sourcetypical
Strength to weight	79.6kN·m/kg	82.9kN·m/kg4% higher
Stiffness to weight	25.6MN·m/kg3% 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	5,055m/s	4,986m/s
Thermal
Thermal conductivity	201W/m·Ksourcetypical, T6, 20 °C	72W/m·Ksourcetypical
Thermal expansion	23.4µm/m·Ksourcetypical, mean 20-100 °C	25µm/m·Ksourcetypical, temperature range not stated
100 mm part over a 50 °C swing	117µm growth7% less	125µm growth
Specific heat	901J/kg·Ksourcetypical, 20 °C (Hydro EN AW-6063)	1,050J/kg·Ksourcetypical
Heats up and cools (diffusivity)	82.6mm²/s2.18x faster	37.9mm²/s
Thermal shock resistance	not sourced	6,240W/m
Melting point	615–655°Csourcemelting range	470–595°Csourcemelting range
Values for	6063-T6 extruded tube, Kaiser Aluminum Tube & Pipe Alloy 6063 Technical Data (Rev. 05/06), typical properties; specific heat from Hydro EN AW-6063 extruded-products datasheet (Rev.4, 03/2023).	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 6063-T6 stronger than Magnesium AZ91D?

Aluminum 6063-T6 is stronger: its yield strength is 215 MPa against 150 MPa for Magnesium AZ91D (43%).

Which is lighter, Aluminum 6063-T6 or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,700 kg/m³ for Aluminum 6063-T6.

Which is stiffer, Aluminum 6063-T6 or Magnesium AZ91D?

Aluminum 6063-T6 is stiffer: Young's modulus 69 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum 6063-T6 deflects less under the same load.

Which is lighter for the same job, Aluminum 6063-T6 or Magnesium AZ91D?

For the same stiffness or strength: Aluminum 6063-T6 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 6063-T6	Magnesium AZ91D
Stiff rod or tie (tension)	lighter	3% heavier
Stiff beam (bending)	20% heavier	lighter
Stiff panel or plate	29% heavier	lighter
Strong rod or tie	4% heavier	lighter
Strong beam	17% heavier	lighter
Strong panel or plate	25% 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 6063-T6 or Magnesium AZ91D?

Aluminum 6063-T6 conducts heat better: 201 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Aluminum 6063-T6 expands less: 23.4 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density