Magnesium AZ91D vs. Plastic Nylon PA66

Compare Magnesium AZ91D vs. Plastic Nylon PA66 strength, stiffness, weight and thermal properties.

Change either side

Plastic Nylon PA66Bulk polymer (molded or machined)

Mechanical
Try it on a partA bracket to run stress or thermal on, free in your browser	Open in LessCAD	Open in LessCAD
Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	85MPasourcetypical, dry
Ultimate tensile strength	230MPasourcetypical, ambient temperature	not sourced
Elongation at break	3%sourcetypical, ambient temperature	30%sourcenominal strain at break, dry
Young's modulus (stiffness)	45GPasourcetypical	3GPasourcetypical, dry
Density	1,810kg/m³sourcetypical	1,130kg/m³sourcetypical1.6x lighter
Strength to weight	82.9kN·m/kg10% higher	75.2kN·m/kg
Stiffness to weight	24.9MN·m/kg9.36x higher	2.65MN·m/kg
Poisson's ratio	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)	0.4sourcebase material: unfilled polyamide (PA), conditioned, maker design-guide family value (Covestro Table 3-1)
Shear modulus	16.7GPa15.6x stiffer in shear	1.07GPa
Bulk modulus	50GPa	5GPa
Speed of sound	4,986m/s	1,629m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical218x more heat through a fin	0.33W/m·Ksourcetypical
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	98µm/m·Ksourcelongitudinal, 23-55 °C
100 mm part over a 50 °C swing	125µm growth3.92x less	490µm growth
Specific heat	1,050J/kg·Ksourcetypical	1,700J/kg·Ksourcetypical
Heats up and cools (diffusivity)	37.9mm²/s221x faster	0.172mm²/s
Thermal shock resistance	6,240W/m109x more resistant	57.2W/m
Melting point	470–595°Csourcemelting range	260°CsourceDSC
Max service temperature	not sourced	101°CsourceIEC 60216 temperature index, 20000 h
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.	BASF Ultramid A3K (PA66, unreinforced injection-moulding grade), Product Information 02/2026, dry values (ISO methods)

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 Plastic Nylon PA66?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 85 MPa for Plastic Nylon PA66 (1.76x).

Which is lighter, Magnesium AZ91D or Plastic Nylon PA66?

Plastic Nylon PA66 is lighter: 1,130 kg/m³ against 1,810 kg/m³ for Magnesium AZ91D.

Which is stiffer, Magnesium AZ91D or Plastic Nylon PA66?

Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 3 GPa for Plastic Nylon PA66, so the same part in Magnesium AZ91D deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Plastic Nylon PA66?

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 rod or tie; Plastic Nylon PA66 is lighter for a strong beam, strong panel or plate.

Part that must be	Magnesium AZ91D	Plastic Nylon PA66
Stiff rod or tie (tension)	lighter	9.36x heavier
Stiff beam (bending)	lighter	2.42x heavier
Stiff panel or plate	lighter	1.54x heavier
Strong rod or tie	lighter	10% heavier
Strong beam	10% heavier	lighter
Strong panel or plate	21% 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, Magnesium AZ91D or Plastic Nylon PA66?

Magnesium AZ91D conducts heat better: 72 W/m·K against 0.33 W/m·K for Plastic Nylon PA66.

Which expands less with temperature?

Magnesium AZ91D expands less: 25 µm/m·K against 98 µm/m·K for Plastic Nylon PA66.

Among 72 materials

Stiffness against density

Strength against density