Copper C10100 vs. Magnesium AZ91D

Compare Copper C10100 vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

Mechanical	Copper C10100	Magnesium AZ91D
Yield strength	69MPa1	150MPa22.17x stronger
Ultimate tensile strength	221MPa1	230MPa2
Elongation at break	45%115x more ductile	3%2
Young's modulus (stiffness)	117GPa12.6x stiffer	45GPa2
Density	8,941kg/m³1	1,810kg/m³24.94x lighter
Strength to weight	7.72kN·m/kg	82.9kN·m/kg10.7x higher
Stiffness to weight	13.1MN·m/kg	24.9MN·m/kg1.9x higher
Poisson's ratio	0.343	base material0.354
Shear modulus	43.7GPa2.62x stiffer in shear	16.7GPa
Bulk modulus	122GPa2.44x higher	50GPa
Speed of sound	3,621m/s	4,986m/s38% faster

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Copper C10100	Magnesium AZ91D
Thermal conductivity	391W/m·K15.43x more heat through a fin	72W/m·K2
Thermal expansion	16.9µm/m·K148% less	25µm/m·K2
100 mm part over a 50 °C swing	84.5µm growth48% less	125µm growth
Specific heat	385J/kg·K1	1,050J/kg·K22.73x higher
Heats up and cools (diffusivity)	114mm²/s3x faster	37.9mm²/s
Thermal shock resistance	8,992W/m44% more resistant	6,240W/m
Melting point	melting point1,083°C1	melting range470–595°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: Copper Development Association, Magnesium Elektron, Wieland, U.S. Department of Defense

Copper C10100: C10100 oxygen-free electronic (OFE) copper, annealed to 0.050 mm grain size (OS050), 0.04 in. flat products, copper.org typical values
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.

1
C10100 Alloy (copper.org)Copper Development Associationarchived copyCopper C10100 · Yield strength: typical, 0.5% extension under load, 0.04 in. flatCopper C10100 · Ultimate tensile strength: typical, 0.04 in. flatCopper C10100 · Elongation at break: typical, 0.04 in. flatCopper C10100 · Young's modulus (stiffness): typicalCopper C10100 · Density: nominalCopper C10100 · Thermal conductivity: typical, 20 °CCopper C10100 · Thermal expansion: typical, mean 20-100 °CCopper C10100 · Specific heat: typical, 20 °CCopper C10100 · Melting point: melting point (liquidus = solidus, pure copper)
2
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
3
Wieland-K09 (Cu-OFE, C10100) Data SheetWielandCopper C10100 · Poisson's ratio: reference value at room temperature (Wieland-K09 = Cu-OFE = C10100, rolled products)
4
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 Copper C10100 stronger than Magnesium AZ91D?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 69 MPa for Copper C10100 (2.17x).

Which is lighter, Copper C10100 or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 8,941 kg/m³ for Copper C10100.

Which is stiffer, Copper C10100 or Magnesium AZ91D?

Copper C10100 is stiffer: Young's modulus 117 GPa against 45 GPa for Magnesium AZ91D, so the same part in Copper C10100 deflects less under the same load.

Which is lighter for the same job, Copper C10100 or Magnesium AZ91D?

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	Copper C10100	Magnesium AZ91D
Stiff rod or tie (tension)	1.9x heavier	lighter
Stiff beam (bending)	3.06x heavier	lighter
Stiff panel or plate	3.59x heavier	lighter
Strong rod or tie	10.7x heavier	lighter
Strong beam	8.29x heavier	lighter
Strong panel or plate	7.28x 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, Copper C10100 or Magnesium AZ91D?

Copper C10100 stretches further before it breaks: 45% elongation at break against 3% for Magnesium AZ91D.

Thermal

Which conducts heat better, Copper C10100 or Magnesium AZ91D?

Copper C10100 conducts heat better: 391 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Copper C10100 expands less: 16.9 µm/m·K against 25 µm/m·K for Magnesium AZ91D.