Magnesium AZ91D vs. Stainless Steel 316

Compare Magnesium AZ91D vs. Stainless Steel 316 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	265MPasourcetypical (representative), annealed 1.0 mm sheet
Ultimate tensile strength	230MPasourcetypical, ambient temperature	583MPasourcetypical (representative), annealed 1.0 mm sheet
Elongation at break	3%sourcetypical, ambient temperature	61%sourcetypical (representative), annealed, in 2 in. (51 mm)
Young's modulus (stiffness)	45GPasourcetypical	200GPasourcetypical, in tension
Density	1,810kg/m³sourcetypical4.43x lighter	8,027kg/m³sourcetypical
Strength to weight	82.9kN·m/kg2.51x higher	33kN·m/kg
Stiffness to weight	24.9MN·m/kg	24.9MN·m/kg
Poisson's ratio	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)	0.3sourcedesign value (structural stainless steels)
Shear modulus	16.7GPa	76.9GPa4.62x stiffer in shear
Bulk modulus	50GPa	167GPa
Speed of sound	4,986m/s	4,992m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	14.6W/m·Ksource20–100 °C
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	16.5µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	125µm growth	82.5µm growth1.52x less
Specific heat	1,050J/kg·Ksourcetypical	450J/kg·Ksourceat 20 °C
Heats up and cools (diffusivity)	37.9mm²/s9.37x faster	4.04mm²/s
Thermal shock resistance	6,240W/m7.6x more resistant	821W/m
Melting point	470–595°Csourcemelting range	1,390–1,440°Csourcemelting range
Max service temperature	not sourced	871–899°Csourceoxidation (scaling) limit in air
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.	ATI 316 (UNS S31600), annealed 1.0 mm sheet, ATI technical data sheet (2012); Poisson's ratio from the Nickel Institute/SCI structural stainless design manual

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 Stainless Steel 316?

Stainless Steel 316 is stronger: its yield strength is 265 MPa against 150 MPa for Magnesium AZ91D (1.77x).

Which is lighter, Magnesium AZ91D or Stainless Steel 316?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 8,027 kg/m³ for Stainless Steel 316.

Which is stiffer, Magnesium AZ91D or Stainless Steel 316?

Stainless Steel 316 is stiffer: Young's modulus 200 GPa against 45 GPa for Magnesium AZ91D, so the same part in Stainless Steel 316 deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Stainless Steel 316?

For the same stiffness or strength: 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	Magnesium AZ91D	Stainless Steel 316
Stiff rod or tie (tension)	about equal	about equal
Stiff beam (bending)	lighter	2.1x heavier
Stiff panel or plate	lighter	2.7x heavier
Strong rod or tie	lighter	2.51x heavier
Strong beam	lighter	3.03x heavier
Strong panel or plate	lighter	3.34x 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 Stainless Steel 316?

Magnesium AZ91D conducts heat better: 72 W/m·K against 14.6 W/m·K for Stainless Steel 316.

Which expands less with temperature?

Stainless Steel 316 expands less: 16.5 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density