Aluminum ADC12 vs. Steel AISI 4340

Compare Aluminum ADC12 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	149MPasourceone test result, 0.2% proof stress, as cast, ASTM tensile bar (Daiki)	1,035MPasourcetypical, transverse
Ultimate tensile strength	345MPasourceone test result, as cast, ASTM tensile bar (Daiki)	1,140MPasourcetypical, transverse
Elongation at break	2.3%sourceone test result, as cast, ASTM tensile bar (Daiki)	18%sourcetypical, transverse
Young's modulus (stiffness)	79.8GPasourcestandard value (S.S.Aluminum)	200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Density	2,680kg/m³sourcemeasured (Daiki)	7,840kg/m³sourcetypical
Strength to weight	55.6kN·m/kg	132kN·m/kg2.37x higher
Stiffness to weight	29.8MN·m/kg17% higher	25.5MN·m/kg
Poisson's ratio	not sourced	0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered)
Shear modulus	not sourced	75.7GPa
Bulk modulus	not sourced	185GPa
Speed of sound	5,457m/s	5,049m/s
Thermal
Thermal conductivity	125W/m·Ksourcemeasured on specimens cut from a 50 x 100 x 5 mm flat die casting (Daiki)	37.5W/m·Ksourcetypical
Thermal expansion	21µm/m·Ksourcemeasured, temperature range not stated (Daiki)	11.3µm/m·Ksourcemean, -18 to 93 °C
100 mm part over a 50 °C swing	105µm growth	56.5µm growth1.86x less
Specific heat	911J/kg·Ksourcemeasured (Daiki)	448J/kg·Ksourcetypical
Heats up and cools (diffusivity)	51.2mm²/s4.8x faster	10.7mm²/s
Thermal shock resistance	not sourced	11,678W/m
Melting point	515–582°Csourcesolidus-liquidus (Daiki)	not sourced
Values for	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.	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 Aluminum ADC12 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 149 MPa for Aluminum ADC12 (6.95x).

Which is lighter, Aluminum ADC12 or Steel AISI 4340?

Aluminum ADC12 is lighter: 2,680 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Aluminum ADC12 or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 79.8 GPa for Aluminum ADC12, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Aluminum ADC12 or Steel AISI 4340?

For the same stiffness or strength: Aluminum ADC12 is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate, strong panel or plate; Steel AISI 4340 is lighter for a strong rod or tie, strong beam.

Part that must be	Aluminum ADC12	Steel AISI 4340
Stiff rod or tie (tension)	lighter	17% heavier
Stiff beam (bending)	lighter	1.85x heavier
Stiff panel or plate	lighter	2.15x heavier
Strong rod or tie	2.37x heavier	lighter
Strong beam	24% heavier	lighter
Strong panel or plate	lighter	11% 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, Aluminum ADC12 or Steel AISI 4340?

Aluminum ADC12 conducts heat better: 125 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 21 µm/m·K for Aluminum ADC12.

Among 72 materials

Stiffness against density

Strength against density