Aluminum ADC12 vs. Magnesium AZ91D

Compare Aluminum ADC12 vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

Mechanical	Aluminum ADC12	Magnesium AZ91D
Yield strength	one test result149MPa1	150MPa2
Ultimate tensile strength	one test result345MPa11.5x stronger	230MPa2
Elongation at break	one test result2.3%1	3%230% more ductile
Young's modulus (stiffness)	standard value79.8GPa31.77x stiffer	45GPa2
Density	measured2,680kg/m³4	1,810kg/m³248% lighter
Strength to weight	55.6kN·m/kg	82.9kN·m/kg49% higher
Stiffness to weight	29.8MN·m/kg20% higher	24.9MN·m/kg
Poisson's ratio	not sourced	base material0.355
Shear modulus	not sourced	16.7GPa
Bulk modulus	not sourced	50GPa
Speed of sound	5,457m/s9% faster	4,986m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Aluminum ADC12	Magnesium AZ91D
Thermal conductivity	125W/m·K41.74x more heat through a fin	72W/m·K2
Thermal expansion	measured21µm/m·K419% less	25µm/m·K2
100 mm part over a 50 °C swing	105µm growth19% less	125µm growth
Specific heat	measured911J/kg·K4	1,050J/kg·K215% higher
Heats up and cools (diffusivity)	51.2mm²/s35% faster	37.9mm²/s
Thermal shock resistance	not sourced	6,240W/m
Melting point	solidus-liquidus515–582°C4	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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Sources5 documents: Daiki Aluminium Industry, Magnesium Elektron, S.S. Aluminum, U.S. Department of Defense

Aluminum ADC12: JIS ADC12 (Al-Si-Cu, about A383 / EN AC-46100) high-pressure die-casting alloy, as cast; physical properties from Daiki Aluminium Industry (ADC12 ingot producer) measured values; modulus from S.S.Aluminum (ADC12 ingot producer) standard 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
NA Alloys Product DataDaiki Aluminium IndustryAluminum ADC12 · Yield strength: one test result, 0.2% proof stress, as cast, ASTM tensile bar (Daiki)Aluminum ADC12 · Ultimate tensile strength: one test result, as cast, ASTM tensile bar (Daiki)Aluminum ADC12 · Elongation at break: one test result, as cast, ASTM tensile bar (Daiki)
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
Die-Casting Alloys (ダイカスト用合金)S.S. AluminumAluminum ADC12 · Young's modulus (stiffness): standard value (S.S.Aluminum)
4
DIK365 Product DataDaiki Aluminium IndustryAluminum ADC12 · Density: measured (Daiki)Aluminum ADC12 · Thermal conductivity: measured on specimens cut from a 50 x 100 x 5 mm flat die casting (Daiki)Aluminum ADC12 · Thermal expansion: measured, temperature range not stated (Daiki)Aluminum ADC12 · Specific heat: measured (Daiki)Aluminum ADC12 · Melting point: solidus-liquidus (Daiki)
5
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 Aluminum ADC12 stronger than Magnesium AZ91D?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 149 MPa for Aluminum ADC12 (1%).

Which is lighter, Aluminum ADC12 or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,680 kg/m³ for Aluminum ADC12.

Which is stiffer, Aluminum ADC12 or Magnesium AZ91D?

Aluminum ADC12 is stiffer: Young's modulus 79.8 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum ADC12 deflects less under the same load.

Which is lighter for the same job, Aluminum ADC12 or Magnesium AZ91D?

For the same stiffness or strength: Aluminum ADC12 is lighter for a stiff rod or tie (tension); Magnesium AZ91D is lighter for a stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate.

Part that must be	Aluminum ADC12	Magnesium AZ91D
Stiff rod or tie (tension)	lighter	20% heavier
Stiff beam (bending)	11% heavier	lighter
Stiff panel or plate	22% heavier	lighter
Strong rod or tie	49% heavier	lighter
Strong beam	49% heavier	lighter
Strong panel or plate	49% 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, Aluminum ADC12 or Magnesium AZ91D?

Magnesium AZ91D stretches further before it breaks: 3% elongation at break against 2.3% for Aluminum ADC12.

Thermal

Which conducts heat better, Aluminum ADC12 or Magnesium AZ91D?

Aluminum ADC12 conducts heat better: 125 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Aluminum ADC12 expands less: 21 µm/m·K against 25 µm/m·K for Magnesium AZ91D.