Magnesium AZ91D vs. Stainless Steel 303

Compare Magnesium AZ91D vs. Stainless Steel 303 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	275MPasourceOutokumpu typical (product P = hot rolled plate, transverse)
Ultimate tensile strength	230MPasourcetypical, ambient temperature	585MPasourceOutokumpu typical
Elongation at break	3%sourcetypical, ambient temperature	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	45GPasourcetypical	200GPasourceat RT (Table 12)
Density	1,810kg/m³sourcetypical	7,900kg/m³sourceat RT
Strength to weight	82.9kN·m/kg2.38x higher	34.8kN·m/kg
Stiffness to weight	24.9MN·m/kg	25.3MN·m/kg2% higher
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	5,032m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	15W/m·Ksourceat RT
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	125µm growth	80µm growth1.56x less
Specific heat	1,050J/kg·Ksourcetypical	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	37.9mm²/s9.98x faster	3.8mm²/s
Thermal shock resistance	6,240W/m6.92x more resistant	902W/m
Melting point	470–595°Csourcemelting range	not sourced
Max service temperature	not sourced	871°Csourcecontinuous, scaling limit
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.	1.4305 / UNS S30300, Outokumpu typical values (hot rolled, solution annealed) from 'Steel Grades, Properties and Global Standards'; max service from Carpenter CarTech 303 datasheet

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 303?

Stainless Steel 303 is stronger: its yield strength is 275 MPa against 150 MPa for Magnesium AZ91D (1.83x).

Which is lighter, Magnesium AZ91D or Stainless Steel 303?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, Magnesium AZ91D or Stainless Steel 303?

Stainless Steel 303 is stiffer: Young's modulus 200 GPa against 45 GPa for Magnesium AZ91D, so the same part in Stainless Steel 303 deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Stainless Steel 303?

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; Stainless Steel 303 is lighter for a stiff rod or tie (tension).

Part that must be	Magnesium AZ91D	Stainless Steel 303
Stiff rod or tie (tension)	2% heavier	lighter
Stiff beam (bending)	lighter	2.07x heavier
Stiff panel or plate	lighter	2.65x heavier
Strong rod or tie	lighter	2.38x heavier
Strong beam	lighter	2.91x heavier
Strong panel or plate	lighter	3.22x 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 303?

Magnesium AZ91D conducts heat better: 72 W/m·K against 15 W/m·K for Stainless Steel 303.

Which expands less with temperature?

Stainless Steel 303 expands less: 16 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density