Magnesium AZ31B-H24 vs. Steel AISI 4340

Compare Magnesium AZ31B-H24 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	220MPasourcetypical, H24, 0.5-6 mm, 0.2 % proof stress	1,035MPasourcetypical, transverse
Ultimate tensile strength	290MPasourcetypical, H24, 0.5-6 mm	1,140MPasourcetypical, transverse
Elongation at break	13%sourcetypical, H24, 0.5-6 mm, gauge 5.65√A	18%sourcetypical, transverse
Young's modulus (stiffness)	44.8GPasourcetypical (handbook physical constant)	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	1,769kg/m³sourcenominal	7,840kg/m³sourcetypical
Strength to weight	124kN·m/kg	132kN·m/kg6% higher
Stiffness to weight	25.3MN·m/kg	25.5MN·m/kg
Poisson's ratio	0.35sourcetypical (handbook physical constant)	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	16.6GPa	75.7GPa4.56x stiffer in shear
Bulk modulus	49.8GPa	185GPa
Speed of sound	5,032m/s	5,049m/s
Thermal
Thermal conductivity	76.9W/m·Ksourcetypical (temper/temperature not stated)	37.5W/m·Ksourcetypical
Thermal expansion	26.8µm/m·Ksourcetypical (temperature range not stated)	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	134µm growth	56.5µm growth2.37x less
Specific heat	1,040J/kg·Ksourcetypical	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	41.8mm²/s3.92x faster	10.7mm²/s
Thermal shock resistance	9,159W/m	11,678W/m27% more resistant
Max service temperature	149°Csourcestated application limit	not sourced
Values for	AZ31B-H24 sheet 0.016-0.062 in., MIL-HDBK-5J Table 4.2.1.0(b) (AMS 4377); strengths are S-basis MINIMUMS	Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

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 AZ31B-H24 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 220 MPa for Magnesium AZ31B-H24 (4.7x).

Which is lighter, Magnesium AZ31B-H24 or Steel AISI 4340?

Magnesium AZ31B-H24 is lighter: 1,769 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Magnesium AZ31B-H24 or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 44.8 GPa for Magnesium AZ31B-H24, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Magnesium AZ31B-H24 or Steel AISI 4340?

For the same stiffness or strength: Magnesium AZ31B-H24 is lighter for a stiff beam (bending), stiff panel or plate, strong beam, strong panel or plate; Steel AISI 4340 is lighter for a strong rod or tie.

Part that must be	Magnesium AZ31B-H24	Steel AISI 4340
Stiff rod or tie (tension)	about equal	about equal
Stiff beam (bending)	lighter	2.1x heavier
Stiff panel or plate	lighter	2.69x heavier
Strong rod or tie	6% heavier	lighter
Strong beam	lighter	1.58x heavier
Strong panel or plate	lighter	2.04x heavier

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 AZ31B-H24 or Steel AISI 4340?

Magnesium AZ31B-H24 conducts heat better: 76.9 W/m·K against 37.5 W/m·K for Steel AISI 4340.

Which expands less with temperature?

Steel AISI 4340 expands less: 11.3 µm/m·K against 26.8 µm/m·K for Magnesium AZ31B-H24.

Among 59 materials

Stiffness against density

Strength against density