Magnesium AZ91D vs. Plastic UHMWPE

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

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Plastic UHMWPEBulk polymer (molded or machined)

Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	20MPasourcetypical, tensile stress at yield ISO 527, 50 mm/min
Ultimate tensile strength	230MPasourcetypical, ambient temperature	43MPasourcetypical, tensile stress at break ISO 527, 50 mm/min
Elongation at break	3%sourcetypical, ambient temperature	465%sourcetypical, nominal elongation at break ISO 527
Young's modulus (stiffness)	45GPasourcetypical	0.66GPasourcetypical, tensile modulus ISO 527, 1 mm/min
Density	1,810kg/m³sourcetypical	930kg/m³sourcetypical1.95x lighter
Strength to weight	82.9kN·m/kg3.85x higher	21.5kN·m/kg
Stiffness to weight	24.9MN·m/kg35x higher	0.71MN·m/kg
Poisson's ratio	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)	not sourced
Shear modulus	16.7GPa	not sourced
Bulk modulus	50GPa	not sourced
Speed of sound	4,986m/s	842m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	0.4W/m·Ksourcetypical, unfilled (narrative value, generic Celanese UHMWPE)
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	200µm/m·Ksourcetypical, 20 to 100 °C (generic Celanese UHMWPE)
100 mm part over a 50 °C swing	125µm growth8x less	1,000µm growth
Specific heat	1,050J/kg·Ksourcetypical	not sourced
Heats up and cools (diffusivity)	37.9mm²/s	not sourced
Thermal shock resistance	6,240W/m	not sourced
Melting point	470–595°Csourcemelting range	130–138°CsourceDSC 10 K/min
Max service temperature	not sourced	80°Csourcerecommended max constant operating temperature
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.	Celanese GUR 4120 (avg. molecular weight 4.7x10^6 g/mol), typical values on compression-molded specimens; CTE and thermal conductivity from Celanese's generic UHMWPE guide (grade not named)

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 UHMWPE?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 20 MPa for Plastic UHMWPE (7.5x).

Which is lighter, Magnesium AZ91D or Plastic UHMWPE?

Plastic UHMWPE is lighter: 930 kg/m³ against 1,810 kg/m³ for Magnesium AZ91D.

Which is stiffer, Magnesium AZ91D or Plastic UHMWPE?

Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 0.66 GPa for Plastic UHMWPE, so the same part in Magnesium AZ91D deflects less under the same load.

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

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, strong beam, strong panel or plate.

Part that must be	Magnesium AZ91D	Plastic UHMWPE
Stiff rod or tie (tension)	lighter	35x heavier
Stiff beam (bending)	lighter	4.24x heavier
Stiff panel or plate	lighter	2.1x heavier
Strong rod or tie	lighter	3.85x heavier
Strong beam	lighter	1.97x heavier
Strong panel or plate	lighter	41% 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 Plastic UHMWPE?

Magnesium AZ91D conducts heat better: 72 W/m·K against 0.4 W/m·K for Plastic UHMWPE.

Which expands less with temperature?

Magnesium AZ91D expands less: 25 µm/m·K against 200 µm/m·K for Plastic UHMWPE.

Among 72 materials

Stiffness against density

Strength against density