Magnesium AZ91D vs. Titanium Ti-6Al-4V

Compare Magnesium AZ91D vs. Titanium Ti-6Al-4V strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	150MPasourcetypical, 0.2% tensile yield, ambient temperature	885MPasourcetypical, plate (>0.187 in), annealed, 0.2% offset
Ultimate tensile strength	230MPasourcetypical, ambient temperature	940MPasourcetypical, plate, annealed
Elongation at break	3%sourcetypical, ambient temperature	16%sourcetypical, in 2 in., plate annealed
Young's modulus (stiffness)	45GPasourcetypical	107–122GPasourcetypical range, 20 °C
Density	1,810kg/m³sourcetypical	4,430kg/m³sourcenominal
Strength to weight	82.9kN·m/kg	200kN·m/kg2.41x higher
Stiffness to weight	24.9MN·m/kg	25.8MN·m/kg4% higher
Poisson's ratio	0.35sourcebase material: AZ91C casting (MIL-HDBK-5J handbook physical constant)	0.342sourcemean of TIMET measurements
Shear modulus	16.7GPa	42.7GPa2.56x stiffer in shear
Bulk modulus	50GPa	121GPa
Speed of sound	4,986m/s	5,084m/s
Thermal
Thermal conductivity	72W/m·Ksourcetypical	6.6W/m·Ksourcetypical, 20 °C, mill annealed
Thermal expansion	25µm/m·Ksourcetypical, temperature range not stated	9µm/m·Ksourcetypical, mean 0-100 °C
100 mm part over a 50 °C swing	125µm growth	45µm growth2.78x less
Specific heat	1,050J/kg·Ksourcetypical	580J/kg·Ksourcetypical, 20 °C
Heats up and cools (diffusivity)	37.9mm²/s14.7x faster	2.57mm²/s
Thermal shock resistance	6,240W/m1.67x more resistant	3,730W/m
Melting point	470–595°Csourcemelting range	1,630–1,650°Csourcemelting range
Max service temperature	not sourced	400°Csourceupper recommended use temperature
Values for	ELEKTRON AZ91D magnesium die-casting alloy, as cast; Magnesium Elektron datasheet 475 (7/01), typical properties; Poisson from MIL-HDBK-5J for AZ91C castings.	TIMETAL 6-4 (Ti-6Al-4V Grade 5) annealed plate typical (TIMET properties manual) + TIMET datasheet TMC-0150 physical properties

Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Is Magnesium AZ91D stronger than Titanium Ti-6Al-4V?

Titanium Ti-6Al-4V is stronger: its yield strength is 885 MPa against 150 MPa for Magnesium AZ91D (5.9x).

Which is lighter, Magnesium AZ91D or Titanium Ti-6Al-4V?

Magnesium AZ91D is lighter: 1,810 kg/m³ against 4,430 kg/m³ for Titanium Ti-6Al-4V.

Which is stiffer, Magnesium AZ91D or Titanium Ti-6Al-4V?

Titanium Ti-6Al-4V is stiffer: Young's modulus 115 GPa against 45 GPa for Magnesium AZ91D, so the same part in Titanium Ti-6Al-4V deflects less under the same load.

Which is lighter for the same job, Magnesium AZ91D or Titanium Ti-6Al-4V?

For the same stiffness or strength: Magnesium AZ91D is lighter for a stiff beam (bending), stiff panel or plate; Titanium Ti-6Al-4V is lighter for a stiff rod or tie (tension), strong rod or tie, strong beam.

Part that must be	Magnesium AZ91D	Titanium Ti-6Al-4V
Stiff rod or tie (tension)	4% heavier	lighter
Stiff beam (bending)	lighter	1.53x heavier
Stiff panel or plate	lighter	1.79x heavier
Strong rod or tie	2.41x heavier	lighter
Strong beam	33% heavier	lighter
Strong panel or plate	about equal	about equal

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 conducts heat better, Magnesium AZ91D or Titanium Ti-6Al-4V?

Magnesium AZ91D conducts heat better: 72 W/m·K against 6.6 W/m·K for Titanium Ti-6Al-4V.

Which expands less with temperature?

Titanium Ti-6Al-4V expands less: 9 µm/m·K against 25 µm/m·K for Magnesium AZ91D.

Among 72 materials

Stiffness against density

Strength against density