Aluminum 6063-T6 vs. Magnesium AZ91D

Compare Aluminum 6063-T6 vs. Magnesium AZ91D strength, stiffness, weight and thermal properties.

Mechanical	Aluminum 6063-T6	Magnesium AZ91D
Yield strength	215MPa143% stronger	150MPa2
Ultimate tensile strength	240MPa1	230MPa2
Elongation at break	12%14x more ductile	3%2
Young's modulus (stiffness)	69GPa11.53x stiffer	45GPa2
Density	2,700kg/m³1	1,810kg/m³249% lighter
Strength to weight	79.6kN·m/kg	82.9kN·m/kg4% higher
Stiffness to weight	25.6MN·m/kg3% 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	5,055m/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 6063-T6	Magnesium AZ91D
Thermal conductivity	201W/m·K12.79x more heat through a fin	72W/m·K2
Thermal expansion	23.4µm/m·K1	25µm/m·K2
100 mm part over a 50 °C swing	117µm growth7% less	125µm growth
Specific heat	901J/kg·K4	1,050J/kg·K217% higher
Heats up and cools (diffusivity)	82.6mm²/s2.18x faster	37.9mm²/s
Thermal shock resistance	not sourced	6,240W/m
Melting point	melting range615–655°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 6063-T6: 6063-T6 extruded tube, Kaiser Aluminum Tube & Pipe Alloy 6063 Technical Data (Rev. 05/06), typical properties; specific heat from Hydro EN AW-6063 extruded-products datasheet (Rev.4, 03/2023).
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 6063 Tube & Pipe Technical Data, Rev. 05/06Kaiser Aluminumarchived copyAluminum 6063-T6 · Yield strength: typical, T6, 0.0625 in specimenAluminum 6063-T6 · Ultimate tensile strength: typical, T6Aluminum 6063-T6 · Elongation at break: typical, T6, in 4DAluminum 6063-T6 · Young's modulus (stiffness): typicalAluminum 6063-T6 · Density: nominal, 20 °CAluminum 6063-T6 · Thermal conductivity: typical, T6, 20 °CAluminum 6063-T6 · Thermal expansion: typical, mean 20-100 °CAluminum 6063-T6 · 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-6063 (Rev. 4, 2023)Hydroarchived copyAluminum 6063-T6 · Specific heat: typical, 20 °C (Hydro EN AW-6063)

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 6063-T6 stronger than Magnesium AZ91D?

Aluminum 6063-T6 is stronger: its yield strength is 215 MPa against 150 MPa for Magnesium AZ91D (43%).

Which is lighter, Aluminum 6063-T6 or Magnesium AZ91D?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 2,700 kg/m³ for Aluminum 6063-T6.

Which is stiffer, Aluminum 6063-T6 or Magnesium AZ91D?

Aluminum 6063-T6 is stiffer: Young's modulus 69 GPa against 45 GPa for Magnesium AZ91D, so the same part in Aluminum 6063-T6 deflects less under the same load.

Which is lighter for the same job, Aluminum 6063-T6 or Magnesium AZ91D?

For the same stiffness or strength: Aluminum 6063-T6 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 6063-T6	Magnesium AZ91D
Stiff rod or tie (tension)	lighter	3% heavier
Stiff beam (bending)	20% heavier	lighter
Stiff panel or plate	29% heavier	lighter
Strong rod or tie	4% heavier	lighter
Strong beam	17% 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, Aluminum 6063-T6 or Magnesium AZ91D?

Aluminum 6063-T6 stretches further before it breaks: 12% elongation at break against 3% for Magnesium AZ91D.

Thermal

Which conducts heat better, Aluminum 6063-T6 or Magnesium AZ91D?

Aluminum 6063-T6 conducts heat better: 201 W/m·K against 72 W/m·K for Magnesium AZ91D.

Which expands less with temperature?

Aluminum 6063-T6 expands less: 23.4 µm/m·K against 25 µm/m·K for Magnesium AZ91D.