Aluminum 3003-O vs. Steel AISI 4340

Compare Aluminum 3003-O vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

Mechanical	Aluminum 3003-O	Steel AISI 4340
Yield strength	40MPa1	1,035MPa225.9x stronger
Ultimate tensile strength	110MPa1	1,140MPa210.4x stronger
Elongation at break	30%11.67x more ductile	18%2
Young's modulus (stiffness)	69GPa1	200GPa3
Density	2,730kg/m³12.87x lighter	7,840kg/m³2
Strength to weight	14.7kN·m/kg	132kN·m/kg9.01x higher
Stiffness to weight	25.3MN·m/kg	25.5MN·m/kg
Poisson's ratio	not sourced	0.323
Shear modulus	not sourced	75.7GPa
Bulk modulus	not sourced	185GPa
Speed of sound	5,027m/s	5,049m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Aluminum 3003-O	Steel AISI 4340
Thermal conductivity	193W/m·K15.15x more heat through a fin	37.5W/m·K2
Thermal expansion	23.2µm/m·K1	mean11.3µm/m·K22.05x less
100 mm part over a 50 °C swing	116µm growth	56.5µm growth2.05x less
Specific heat	not sourced	448J/kg·K2
Heats up and cools (diffusivity)	not sourced	10.7mm²/s
Thermal shock resistance	not sourced	11,678W/m
Melting point	melting range640–655°C1	not sourced

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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Sources3 documents: Kaiser Aluminum, Carpenter Technology, U.S. Department of Defense

Aluminum 3003-O: 3003-O (annealed) aluminium-manganese alloy, the heat-exchanger tube and brazing alloy, Kaiser Aluminum Tube & Pipe Alloy 3003 Technical Data (Rev. 05/06), typical properties; specific heat from the NIST cryogenic 3003-F fit at 293 K.
Steel AISI 4340: Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

1
Alloy 3003 Tube & Pipe Technical Data, Rev. 05/06Kaiser Aluminumarchived copyAluminum 3003-O · Yield strength: typical, O, 0.0625 in specimenAluminum 3003-O · Ultimate tensile strength: typical, OAluminum 3003-O · Elongation at break: typical, O, in 4DAluminum 3003-O · Young's modulus (stiffness): typicalAluminum 3003-O · Density: nominal, 20 °CAluminum 3003-O · Thermal conductivity: typical, O, 20 °CAluminum 3003-O · Thermal expansion: typical, mean 20-100 °CAluminum 3003-O · Melting point: melting range
2
Lescalloy 4340 VAC-ARC Data SheetCarpenter Technologyarchived copySteel AISI 4340 · Yield strength: typical, transverseSteel AISI 4340 · Ultimate tensile strength: typical, transverseSteel AISI 4340 · Elongation at break: typical, transverseSteel AISI 4340 · Density: typicalSteel AISI 4340 · Thermal conductivity: typicalSteel AISI 4340 · Thermal expansion: mean, -18 to 93 °CSteel AISI 4340 · Specific heat: typical
3
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseSteel AISI 4340 · Young's modulus (stiffness): MIL-HDBK-5J design value (AISI 4340, quenched and tempered)Steel AISI 4340 · Poisson's ratio: MIL-HDBK-5J design value (AISI 4340, quenched and tempered)

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 3003-O stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 40 MPa for Aluminum 3003-O (25.9x).

Which is lighter, Aluminum 3003-O or Steel AISI 4340?

Aluminum 3003-O is lighter: 2,730 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.

Which is stiffer, Aluminum 3003-O or Steel AISI 4340?

Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 69 GPa for Aluminum 3003-O, so the same part in Steel AISI 4340 deflects less under the same load.

Which is lighter for the same job, Aluminum 3003-O or Steel AISI 4340?

For the same stiffness or strength: Aluminum 3003-O is lighter for a stiff beam (bending), stiff panel or plate; Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.

Part that must be	Aluminum 3003-O	Steel AISI 4340
Stiff rod or tie (tension)	about equal	about equal
Stiff beam (bending)	lighter	1.69x heavier
Stiff panel or plate	lighter	2.01x heavier
Strong rod or tie	9.01x heavier	lighter
Strong beam	3.05x heavier	lighter
Strong panel or plate	1.77x 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 3003-O or Steel AISI 4340?

Aluminum 3003-O stretches further before it breaks: 30% elongation at break against 18% for Steel AISI 4340.

Thermal

Which conducts heat better, Aluminum 3003-O or Steel AISI 4340?

Aluminum 3003-O conducts heat better: 193 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 23.2 µm/m·K for Aluminum 3003-O.