Magnesium AZ91D vs. Plastic PPS GF40

Compare Magnesium AZ91D vs. Plastic PPS GF40 strength, stiffness, weight and thermal properties.

Plastic PPS GF40Bulk polymer (molded or machined)

Mechanical	Magnesium AZ91D	Plastic PPS GF40
Yield strength	150MPa1	not given (tensile used)
Ultimate tensile strength	230MPa118% stronger	tensile strength195MPa2
Flexural strength	not sourced	285MPa2
Elongation at break	3%11.58x more ductile	strain at break1.9%2
Young's modulus (stiffness)	45GPa13.06x stiffer	14.7GPa2
Density	1,810kg/m³1	1,650kg/m³2
Strength to weight	82.9kN·m/kg	118kN·m/kg43% higher
Stiffness to weight	24.9MN·m/kg2.79x higher	8.91MN·m/kg
Poisson's ratio	base material0.353	0.354
Shear modulus	16.7GPa3.06x stiffer in shear	5.44GPa
Bulk modulus	50GPa3.06x higher	16.3GPa
Speed of sound	4,986m/s1.67x faster	2,985m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Magnesium AZ91D	Plastic PPS GF40
Thermal conductivity	72W/m·K1360x more heat through a fin	0.2W/m·K4
Thermal expansion	25µm/m·K1	parallel12µm/m·K22.08x less
100 mm part over a 50 °C swing	125µm growth	60µm growth2.08x less
Specific heat	1,050J/kg·K1	not sourced
Heats up and cools (diffusivity)	37.9mm²/s	not sourced
Thermal shock resistance	6,240W/m43.4x more resistant	144W/m
Melting point	melting range470–595°C1	DSC280°C2
Glass transition	not sourced	DSC90°C2
Max service temperature	not sourced	HDT 1.8 MPa270°C2

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources4 documents: Magnesium Elektron, Celanese, 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 PPS GF40: Celanese Fortron 1140L4 (PPS, 40% glass fibre), injection moulding; FORTRON PPS Short-Term Properties Guide (PPS-012, 2016); thermal conductivity and Poisson for 40% glass-reinforced Fortron from the Fortron PPS Design Manual (PPS-050, 2013).

1
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
2
Fortron PPS Short-Term Properties Guide (PPS-012)CelanesePlastic PPS GF40 · Ultimate tensile strength: tensile strength, 5 mm/minPlastic PPS GF40 · Flexural strength: flexural strength at breakPlastic PPS GF40 · Elongation at break: strain at break, 5 mm/minPlastic PPS GF40 · Young's modulus (stiffness): typical, 1 mm/minPlastic PPS GF40 · Density: typicalPlastic PPS GF40 · Thermal expansion: parallel (flow), mean -50 to 90 °CPlastic PPS GF40 · Melting point: DSC, 10 °C/minPlastic PPS GF40 · Glass transition: DSC, 10 °C/minPlastic PPS GF40 · Max service temperature: HDT 1.8 MPa
3
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)
4
Fortron PPS Design Manual (PPS-050)CelanesePlastic PPS GF40 · Poisson's ratio: glass-reinforced Fortron PPS (class value, not grade-specific)Plastic PPS GF40 · Thermal conductivity: 40% glass-reinforced Fortron, 25 °C (not grade-specific)

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 PPS GF40?

Plastic PPS GF40 is stronger: its tensile strength is 195 MPa against yield strength 150 MPa for Magnesium AZ91D (30%).

Which is lighter, Magnesium AZ91D or Plastic PPS GF40?

Plastic PPS GF40 is lighter: 1,650 kg/m³ against 1,810 kg/m³ for Magnesium AZ91D.

Which is stiffer, Magnesium AZ91D or Plastic PPS GF40?

Magnesium AZ91D is stiffer: Young's modulus 45 GPa against 14.7 GPa for Plastic PPS GF40, so the same part in Magnesium AZ91D deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Plastic PPS GF40?

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 PPS GF40 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Magnesium AZ91D	Plastic PPS GF40
Stiff rod or tie (tension)	lighter	2.79x heavier
Stiff beam (bending)	lighter	1.59x heavier
Stiff panel or plate	lighter	32% heavier
Strong rod or tie	43% heavier	lighter
Strong beam	31% heavier	lighter
Strong panel or plate	25% 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 is more ductile, Magnesium AZ91D or Plastic PPS GF40?

Magnesium AZ91D stretches further before it breaks: 3% elongation at break against 1.9% for Plastic PPS GF40.

Thermal

Which conducts heat better, Magnesium AZ91D or Plastic PPS GF40?

Magnesium AZ91D conducts heat better: 72 W/m·K against 0.2 W/m·K for Plastic PPS GF40.

Which expands less with temperature?

Plastic PPS GF40 expands less: 12 µm/m·K against 25 µm/m·K for Magnesium AZ91D.