Magnesium AZ91D vs. Nickel Inconel 718

Compare Magnesium AZ91D vs. Nickel Inconel 718 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	1,207MPasourcetypical, 1.0 in. hot-rolled bar, 0.2% offset
Ultimate tensile strength	230MPasourcetypical, ambient temperature	1,389MPasourcetypical, 1.0 in. bar
Elongation at break	3%sourcetypical, ambient temperature	20%sourcetypical, 1.0 in. bar
Young's modulus (stiffness)	45GPasourcetypical	200GPasourcetypical, 21 °C, annealed + aged
Density	1,810kg/m³sourcetypical	8,221kg/m³sourcenominal, annealed and aged
Strength to weight	82.9kN·m/kg	147kN·m/kg1.77x higher
Stiffness to weight	24.9MN·m/kg2% higher	24.3MN·m/kg
Poisson's ratio	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)	0.294sourcetypical, 21 °C, annealed + aged
Shear modulus	16.7GPa	77.3GPa4.64x stiffer in shear
Bulk modulus	50GPa	162GPa
Speed of sound	4,986m/s	4,932m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	11.4W/m·Ksourcetypical, 21 °C, annealed + aged (calculated from resistivity per footnote a)
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	13.2µm/m·Ksourcetypical, mean 21-93 °C, annealed + aged
100 mm part over a 50 °C swing	125µm growth	66µm growth1.89x less
Specific heat	1,050J/kg·Ksourcetypical	435J/kg·Ksourcetypical, 21 °C
Heats up and cools (diffusivity)	37.9mm²/s11.9x faster	3.19mm²/s
Thermal shock resistance	6,240W/m1.7x more resistant	3,680W/m
Melting point	470–595°Csourcemelting range	1,260–1,336°Csourcemelting range
Max service temperature	not sourced	704°Csourceupper use temperature stated by producer
Values for	ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.	INCONEL alloy 718, standard grade, 1750 °F/1 hr anneal + 1325 °F/8 hr F.C. to 1150 °F aged; Special Metals bulletin SMC-045 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 Nickel Inconel 718?

Nickel Inconel 718 is stronger: its yield strength is 1,207 MPa against 150 MPa for Magnesium AZ91D (8.05x).

Which is lighter, Magnesium AZ91D or Nickel Inconel 718?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 8,221 kg/m³ for Nickel Inconel 718.

Which is stiffer, Magnesium AZ91D or Nickel Inconel 718?

Nickel Inconel 718 is stiffer: Young's modulus 200 GPa against 45 GPa for Magnesium AZ91D, so the same part in Nickel Inconel 718 deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Nickel Inconel 718?

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 beam, strong panel or plate; Nickel Inconel 718 is lighter for a strong rod or tie.

Part that must be	Magnesium AZ91D	Nickel Inconel 718
Stiff rod or tie (tension)	lighter	2% heavier
Stiff beam (bending)	lighter	2.15x heavier
Stiff panel or plate	lighter	2.76x heavier
Strong rod or tie	1.77x heavier	lighter
Strong beam	lighter	13% heavier
Strong panel or plate	lighter	1.6x 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 Nickel Inconel 718?

Magnesium AZ91D conducts heat better: 72 W/m·K against 11.4 W/m·K for Nickel Inconel 718.

Which expands less with temperature?

Nickel Inconel 718 expands less: 13.2 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density