Aluminum 1100-O vs. Magnesium AZ91D

Compare Aluminum 1100-O vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

Mechanical	Aluminum 1100-O	Magnesium AZ91D
Yield strength	35MPa1	150MPa24.29x stronger
Ultimate tensile strength	90MPa1	230MPa22.56x stronger
Elongation at break	35%111.7x more ductile	3%2
Young's modulus (stiffness)	69GPa11.53x stiffer	45GPa2
Density	2,710kg/m³1	1,810kg/m³250% lighter
Strength to weight	12.9kN·m/kg	82.9kN·m/kg6.42x higher
Stiffness to weight	25.5MN·m/kg2% higher	24.9MN·m/kg
Poisson's ratio	not sourced	base material0.353
Shear modulus	not sourced	16.7GPa
Bulk modulus	not sourced	50GPa
Speed of sound	5,046m/s1% 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 1100-O	Magnesium AZ91D
Thermal conductivity	222W/m·K13.08x more heat through a fin	72W/m·K2
Thermal expansion	23.6µm/m·K1	25µm/m·K2
100 mm part over a 50 °C swing	118µm growth6% less	125µm growth
Specific heat	base material901J/kg·K4	1,050J/kg·K217% higher
Heats up and cools (diffusivity)	90.9mm²/s2.4x faster	37.9mm²/s
Thermal shock resistance	not sourced	6,240W/m
Melting point	melting range640–655°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: Kaiser Aluminum, Magnesium Elektron, U.S. Department of Defense, Hydro

Aluminum 1100-O: 1100-O (annealed) commercially pure aluminium, Kaiser Aluminum Tube & Pipe Alloy 1100 Technical Data (Rev. 05/06), typical properties; specific heat from Hydro EN AW-1050A (99.5% Al) extruded-products datasheet (10/2018).
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
Alloy 1100 Tube & Pipe Technical Data, Rev. 05/06Kaiser Aluminumarchived copyAluminum 1100-O · Yield strength: typical, O, 0.0625 in specimenAluminum 1100-O · Ultimate tensile strength: typical, OAluminum 1100-O · Elongation at break: typical, O, in 4DAluminum 1100-O · Young's modulus (stiffness): typicalAluminum 1100-O · Density: nominal, 20 °CAluminum 1100-O · Thermal conductivity: typical, O, 20 °CAluminum 1100-O · Thermal expansion: typical, mean 20-100 °CAluminum 1100-O · Melting point: melting range
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
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
Technical Datasheet, Extruded Products: Alloy EN AW-1050AHydroAluminum 1100-O · Specific heat: base material: commercially pure aluminium EN AW-1050A (Hydro), 20 °C

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 1100-O stronger than Magnesium AZ91D?

Magnesium AZ91D is stronger: its yield strength is 150 MPa against 35 MPa for Aluminum 1100-O (4.29x).

Which is lighter, Aluminum 1100-O or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,710 kg/m³ for Aluminum 1100-O.

Which is stiffer, Aluminum 1100-O or Magnesium AZ91D?

Aluminum 1100-O is stiffer: Young's modulus 69 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum 1100-O deflects less under the same load.

Which is lighter for the same job, Aluminum 1100-O or Magnesium AZ91D?

For the same stiffness or strength: Aluminum 1100-O 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 1100-O	Magnesium AZ91D
Stiff rod or tie (tension)	lighter	2% heavier
Stiff beam (bending)	21% heavier	lighter
Stiff panel or plate	30% heavier	lighter
Strong rod or tie	6.42x heavier	lighter
Strong beam	3.95x heavier	lighter
Strong panel or plate	3.1x 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 1100-O or Magnesium AZ91D?

Aluminum 1100-O stretches further before it breaks: 35% elongation at break against 3% for Magnesium AZ91D.

Thermal

Which conducts heat better, Aluminum 1100-O or Magnesium AZ91D?

Aluminum 1100-O conducts heat better: 222 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Aluminum 1100-O expands less: 23.6 µm/m·K against 25 µm/m·K for Magnesium AZ91D.