1100-O (annealed) commercially pure aluminium, Kaiser Aluminum Tube & Pipe Alloy 1100 Technical Data (Rev. 05/06), typical properties; specific heat from Hydro EN AW-1050A (99.5% Al) extruded-products datasheet (10/2018).
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 1100-O stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 35 MPa for Aluminum 1100-O (29.6x).
Which is lighter, Aluminum 1100-O or Steel AISI 4340?
Aluminum 1100-O is lighter: 2,710 kg/m³ against 7,840 kg/m³ for Steel AISI 4340.
Which is stiffer, Aluminum 1100-O or Steel AISI 4340?
Steel AISI 4340 is stiffer: Young's modulus 200 GPa against 69 GPa for Aluminum 1100-O, so the same part in Steel AISI 4340 deflects less under the same load.
Which is lighter for the same job, Aluminum 1100-O or Steel AISI 4340?
For the same stiffness or strength: Aluminum 1100-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 1100-O
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
10.2x heavier
lighter
Strong beam
3.31x heavier
lighter
Strong panel or plate
1.88x 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 conducts heat better, Aluminum 1100-O or Steel AISI 4340?
Aluminum 1100-O conducts heat better: 222 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 1100-O.