Magnesium AZ91D vs. Plastic PBT GF30

Compare Magnesium AZ91D vs. Plastic PBT GF30 strength, stiffness, weight and thermal properties.

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Plastic PBT GF30Bulk polymer (molded or machined)

Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	not given (tensile used)
Ultimate tensile strength	230MPasourcetypical, ambient temperature	140MPasourcestress at break, 23 °C
Flexural strength	not sourced	210MPasourcetypical, 23 °C
Elongation at break	3%sourcetypical, ambient temperature	3%sourcestrain at break, 23 °C
Young's modulus (stiffness)	45GPasourcetypical	9.8GPasourcetypical, 23 °C
Density	1,810kg/m³sourcetypical	1,530kg/m³sourcetypical18% lighter
Strength to weight	82.9kN·m/kg	91.5kN·m/kg10% higher
Stiffness to weight	24.9MN·m/kg3.88x higher	6.41MN·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	2,531m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	0.27W/m·Ksourcetypical (DIN 52612-1)
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	25µm/m·Ksourcelongitudinal (flow), mean 23-55 °C
100 mm part over a 50 °C swing	125µm growth	125µm growth
Specific heat	1,050J/kg·Ksourcetypical	1,050J/kg·Ksourcetypical, 23 °C
Heats up and cools (diffusivity)	37.9mm²/s225x faster	0.168mm²/s
Thermal shock resistance	6,240W/m	not sourced
Melting point	470–595°Csourcemelting range	223°CsourceDSC (ISO 11357)
Max service temperature	not sourced	205°CsourceHDT 1.8 MPa
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 Ultradur B 4300 G6 (PBT, 30% glass fibre), injection moulding grade; product information sheet 09/2026, typical values for uncoloured product at 23 °C.

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 PBT GF30?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against tensile strength 140 MPa for Plastic PBT GF30 (7%).

Which is lighter, Magnesium AZ91D or Plastic PBT GF30?

Plastic PBT GF30 is lighter: 1,530 kg/m³ against 1,810 kg/m³ for Magnesium AZ91D.

Which is stiffer, Magnesium AZ91D or Plastic PBT GF30?

Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 9.8 GPa for Plastic PBT GF30, so the same part in Magnesium AZ91D deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Plastic PBT GF30?

For the same stiffness or strength: Magnesium AZ91D is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; Plastic PBT GF30 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Magnesium AZ91D	Plastic PBT GF30
Stiff rod or tie (tension)	lighter	3.88x heavier
Stiff beam (bending)	lighter	1.81x heavier
Stiff panel or plate	lighter	40% heavier
Strong rod or tie	10% heavier	lighter
Strong beam	13% heavier	lighter
Strong panel or plate	14% 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 PBT GF30?

Magnesium AZ91D conducts heat better: 72 W/m·K against 0.27 W/m·K for Plastic PBT GF30.

Which expands less with temperature?

Magnesium AZ91D expands less: 25 µm/m·K against 25 µm/m·K for Plastic PBT GF30.

Among 72 materials

Stiffness against density

Strength against density