Materials / Compare
Aluminum vs. Steel AISI 4340
Compare Aluminum vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.
| Try it on a partA bracket to run stress or thermal on, free in your browser | Open in LessCAD | Open in LessCAD |
|---|---|---|
| Mechanical | ||
| Yield strength | 276MPasourcetypical, 0.2% offset, .500 in dia specimen | 1,035MPasourcetypical, transverse |
| Ultimate tensile strength | 310MPasourcetypical | 1,140MPasourcetypical, transverse |
| Elongation at break | 17%sourcetypical, in 4D, 0.500 in dia specimen | 18%sourcetypical, transverse |
| Young's modulus (stiffness) | 68.3GPasourcetypical | 200GPasourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Density | 2,700kg/m³sourcenominal | 7,840kg/m³sourcetypical |
| Strength to weight | 102kN·m/kg | 132kN·m/kg29% higher |
| Stiffness to weight | 25.3MN·m/kg | 25.5MN·m/kg |
| Poisson's ratio | 0.33sourcetypical (handbook physical constant) | 0.32sourceMIL-HDBK-5J design value (AISI 4340, quenched and tempered) |
| Shear modulus | 25.7GPa | 75.7GPa2.95x stiffer in shear |
| Bulk modulus | 67GPa | 185GPa |
| Speed of sound | 5,030m/s | 5,049m/s |
| Thermal | ||
| Thermal conductivity | 167W/m·Ksourcetypical, 20 °C | 37.5W/m·Ksourcetypical |
| Thermal expansion | 23.6µm/m·Ksourcetypical, mean 20-100 °C | 11.3µm/m·Ksourcemean, -18 to 93 °C |
| 100 mm part over a 50 °C swing | 118µm growth | 56.5µm growth2.09x less |
| Specific heat | 896J/kg·Ksourcetypical, at 100 °C | 448J/kg·Ksourcetypical |
| Heats up and cools (diffusivity) | 69mm²/s6.47x faster | 10.7mm²/s |
| Thermal shock resistance | 19,159W/m1.64x more resistant | 11,678W/m |
| Melting point | 582–652°Csourcesolidus-liquidus | not sourced |
| Values for | 6061-T6/T651, Kaiser Aluminum typical properties (sheet, coil & plate datasheet); Poisson from MIL-HDBK-5J | 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 stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 276 MPa for Aluminum (3.75x).
Which is lighter, Aluminum or Steel AISI 4340?
Aluminum is lighter: 2,700 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.
Which is stiffer, Aluminum or Steel AISI 4340?
Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 68.3 GPa for Aluminum, so the same part in Steel AISI 4340 deflects less under the same load.
Which is lighter for the same job, Aluminum or Steel AISI 4340?
For the same stiffness or strength: Aluminum 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 | Aluminum | Steel AISI 4340 |
|---|---|---|
| Stiff rod or tie (tension) | about equal | about equal |
| Stiff beam (bending) | lighter | 1.7x heavier |
| Stiff panel or plate | lighter | 2.03x heavier |
| Strong rod or tie | 29% heavier | lighter |
| Strong beam | lighter | 20% heavier |
| Strong panel or plate | lighter | 50% 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 or Steel AISI 4340?
Aluminum conducts heat better: 167 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 23.6 µm/m·K for Aluminum.