Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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Sources3 documents: Magnesium Elektron, BASF, U.S. Department of Defense
Magnesium AZ91D
ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.
Plastic PBT GF30
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.
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Elektron Die Casting Alloys (Datasheet 475)Magnesium Elektronarchived copyMagnesium AZ91D · Yield strength: typical, 0.2% tensile yield, ambient temperatureMagnesium AZ91D · Ultimate tensile strength: typical, ambient temperatureMagnesium AZ91D · Elongation at break: typical, ambient temperatureMagnesium AZ91D · Young's modulus (stiffness): typicalMagnesium AZ91D · Density: typicalMagnesium AZ91D · Thermal conductivity: typicalMagnesium AZ91D · Thermal expansion: typical, temperature range not statedMagnesium AZ91D · Specific heat: typicalMagnesium AZ91D · Melting point: melting range
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Ultradur B 4300 G6 Product InformationBASFPlastic PBT GF30 · Ultimate tensile strength: stress at break, 23 °CPlastic PBT GF30 · Flexural strength: typical, 23 °CPlastic PBT GF30 · Elongation at break: strain at break, 23 °CPlastic PBT GF30 · Young's modulus (stiffness): typical, 23 °CPlastic PBT GF30 · Density: typicalPlastic PBT GF30 · Thermal conductivity: typical (DIN 52612-1)Plastic PBT GF30 · Thermal expansion: longitudinal (flow), mean 23-55 °CPlastic PBT GF30 · Specific heat: typical, 23 °CPlastic PBT GF30 · Melting point: DSC (ISO 11357)Plastic PBT GF30 · Max service temperature: HDT 1.8 MPa
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MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseMagnesium AZ91D · Poisson's ratio: base material: AZ91C casting (MIL-HDBK-5J handbook physical constant)
Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Mechanical
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).
Thermal
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.