Guides/Comparisons
Steel vs aluminium
steel-vs-aluminiumSteel and Aluminium at a glance
This page compares Steel and Aluminium using only values that carry a source, a test condition and an evidence level. Ranges run across temper, heat treatment and product form, measured at room temperature where the source says so.
- Yield strength: the ranges overlap (Steel 170 to 1,330 MPa; Aluminium 29 to 510 MPa).
- Tensile strength: the ranges overlap (Steel 310 to 1,600 MPa; Aluminium 60 to 572 MPa).
- Density: Steel is higher (Steel 7.67 to 8.03 g/cm³; Aluminium 2.65 to 2.84 g/cm³), about 2.9 times the midpoint of Aluminium.
- Young's modulus: Steel is higher (Steel 190 to 210 GPa; Aluminium 57.2 to 79 GPa), about 2.9 times the midpoint of Aluminium.
- Thermal conductivity: Aluminium is higher (Steel 25 to 93 W/(m·K); Aluminium 120 to 229 W/(m·K)), about 3.0 times the midpoint of Steel.
- Melting point: Steel is higher (Steel 1,432 to 1,526 °C; Aluminium 490 to 660 °C), about 2.6 times the midpoint of Aluminium.
- Thermal expansion: Aluminium is higher (Steel 3.44 to 14.6 ppm/K; Aluminium 21.4 to 25 ppm/K), about 2.6 times the midpoint of Steel.
- Yield strength for each unit of density (calculated from each grade's midpoint values): Steel 32.6 to 115 MPa per g/cm³; Aluminium 10.7 to 180 MPa per g/cm³.
"Higher" means the whole range is higher, not just one value. Where a value is a specified minimum, the table says "at least".
Side by side
| Property | Steel | Aluminium |
|---|---|---|
| Yield strength | 170 to 1,330 MPa | 29 to 510 MPa |
| Tensile strength | 310 to 1,600 MPa | 60 to 572 MPa |
| Density | 7.67 to 8.03 g/cm³ | 2.65 to 2.84 g/cm³ |
| Young's modulus | 190 to 210 GPa | 57.2 to 79 GPa |
| Thermal conductivity | 25 to 93 W/(m·K) | 120 to 229 W/(m·K) |
| Melting point | 1,432 to 1,526 °C | 490 to 660 °C |
| Service temperature | no data | 65 to 160 °C |
| Thermal expansion | 3.44 to 14.6 ppm/K | 21.4 to 25 ppm/K |
| Yield strength per densitycalculated | 32.6 to 115 MPa per g/cm³ | 10.7 to 180 MPa per g/cm³ |
When to use which
| Material | Best for | Weakest at |
|---|---|---|
| A36 structural carbon steel | Welded and bolted structural frames, girders and shapes that will be painted or galvanized | Rusts outdoors and corrodes first when it touches copper or tin in a wet electrolyte; minimum strength falls above 650 °F (343 °C) |
| Carbon steel 1018 | Machined shafts, pins and gears, and cost-sensitive structural parts that are coated against rust | Rust in moist air and salt unless it is coated, and strength that depends on whether the bar was cold drawn or hot rolled |
| Carbon steel 1045 | Forged or machined axles, shafts, gears and machine parts that need more strength than low-carbon steel, and that are coated against rust | Rust in moist air and salt unless it is coated, and strength that depends on whether the bar was cold drawn, hot rolled, normalised or annealed |
| Carbon steel 1215 | Screw-machine parts such as bushings, inserts, pins, studs and couplings, where machining speed and surface finish matter more than weldability (Alro; Titanium Industries) | Welding and fatigue. Alro says it is difficult to weld, and Titanium Industries says it fails in parts under severe fatigue stress |
| Alloy steel AISI 4130 | Aircraft and motorsport tube, sheet and bar, and oil and gas parts, where weldability and strength after heat treatment both matter | Hydrogen gas and salt solutions: in one laboratory study the threshold stress intensity fell from 88 to 32 MPa√m as hydrogen pressure rose from 21 to 69 MPa, and salt solution cut corrosion-fatigue life |
| Alloy steel AISI 4140 | Machine parts and structures in medium and large sections that need high strength and toughness after quenching and tempering | Hydrogen gas, which cut notched strength by about 60 percent in one room-temperature study, and dilute sulfuric acid, which corroded it at 176.87 mpy |
| Carbon steel 1010 | Formed, drawn and welded parts, and light structural parts, where cost and ductility matter | Rust in moist air and salt unless it is coated, and strength that depends on the processing condition |
| Carbon steel 1070 | Springs, shafts and hand tools that are heat treated and kept dry or coated (tensile strength 640 to 700 MPa in the supplier range) | Corrosion, which is poor without a coating, brittleness once fully hardened, and poor weldability |
| Alloy steel AISI 4340 | Large sections that need high tensile strength and toughness after quenching and tempering, such as aircraft landing gear, gears and shafts (voestalpine, Saky Steel). | Toughness at the highest strength levels: the minimum Charpy impact energy falls from 42 J at condition U to 9 J at condition Z (voestalpine). No corrosion data were read for this grade. |
| Aluminium alloy 6061 | A light, workable structural metal with good corrosion resistance (the NASA handbook ranks 6061 best of the heat-treatable aluminium alloys for corrosion) | Galvanic attack when coupled to more noble metals, especially in sea water (NASA handbook); typical strength values are marked not for design |
| Aluminium alloy 7075-T6 | High-strength aluminium parts where low mass and wrought forms such as tube, plate, bar or forging are useful | Stress-corrosion cracking in the short-transverse direction in T6, and relatively poor corrosion resistance in industrial and marine environments |
| Aluminium alloy 2024 | A high-strength wrought aluminium alloy for aircraft fittings and structural parts (the datasheets list these uses; ASM typical T4 yield strength is 324 MPa) | Stress-corrosion cracking of the 2024-T351 temper in seacoast and salt-water conditions (NASA 1981), and pitting in salt water |
| Aluminium alloy 5052 | Welded sheet and tank or marine-style parts at medium strength, where the temper is named and checked (the datasheets rate its seawater resistance very good) | Strength depends on temper (yield 13 ksi annealed to 37 ksi in H38), and no measured seawater corrosion rate was found in the sources read |
| Aluminium-magnesium alloys (5XXX series) | Welded, corrosion-resistant sheet and plate at moderate strength (5083 is sold for ship building and pressure vessels) | Strength per alloy is modest next to heat-treated 6061, and 5083 is not recommended above 65 °C because of grain-boundary attack |
| Aluminium-lithium alloy 2195 | Welded cryogenic tanks where friction stir welding keeps most of the strength (NASA reports, 1998 to 2008) | Fusion welding, which hot-cracks and needs repairs, and corrosion resistance, which the supplier calls poor |
| Aluminium | Light, cheap electrical and thermal conduction, and a positive-electrode foil that stays passive in common lithium-ion electrolytes | Strength: annealed pure aluminium has a typical yield strength near 22 to 29 MPa, so it is not a structural metal on its own |
| Aluminium alloy 1050 | Formed sheet, chemical plant and heat-transfer parts that need very good corrosion resistance and easy forming more than strength (Smiths and Righton list these uses) | Low strength in the soft tempers (Smiths gives 100 to 135 N/mm2 typical tensile for 1050A H14, and 1200 O is 70 to 105 N/mm2); no measured corrosion test data were read |
| Aluminium alloy 2011 | Small, complex, high-precision machined parts made on automatic lathes, such as screws, bolts, gears, fasteners and fittings (suppliers rate machinability very good to excellent) | Weldability (rated poor to extremely poor by the sources) and corrosion resistance (rated low to moderate, and anodising or another surface treatment is advised) |
| Aluminium alloy 2014 | High-strength structural parts for aerospace and defence, where a 460 MPa minimum tensile strength in T651 plate is needed and the part is clad or painted against corrosion | Corrosion resistance (poor in water and salt, with pitting and galvanic attack in sea water), and welding, which is difficult and prone to cracking |
| Aluminium alloy 2017 | High-strength machined parts and rivets in aircraft-type structures, in the T4 temper (supplier rates machinability excellent, strength very good) | Weldability (only resistance welding is suitable, per the AircraftMaterials datasheet) and corrosion resistance (rated moderate by the supplier, with no test data found for this grade) |
| Aluminium alloy 2017A | Machined structural parts and solid rivets in the T4 temper (supplier rates machinability Excellent, yield strength 276 MPa) | Welding (resistance welding only, per the Smith and AircraftMaterials datasheets) and corrosion resistance (rated moderate by one supplier and good by another, with no test data for this grade) |
| Aluminium alloy 2219 | Launch-vehicle and cryogenic tankage where weldability and fracture toughness matter (Smith datasheet: readily weldable, good fracture toughness; Alloys International: launch vehicle and cryogenic tanks) | Ductility in thick plate, where 5-inch T87 plate showed below 1 % in the short-transverse direction (NASA 2021), and general corrosion resistance, which Wikipedia describes as lower than other aluminium alloys |
| Aluminium alloy 3003 | Sheet and formed parts that need moderate strength, good workability and weldability, and resistance to atmospheric corrosion, such as storage tanks, chemical equipment and heat exchangers, with the temper named | Strength depends on temper, from 14 to 19 ksi tensile in O to 27 ksi minimum in H18, and no seawater rating or measured corrosion rate for 3003 was found in the sources read |
| Aluminium alloy 5083 | Welded marine structures and pressure vessels kept at or below 65 °C, where seawater resistance and strength matter (supplier datasheets) | Service above 65 °C, where the suppliers advise against use. It is a non-heat-treatable alloy (Dinco sheet). No space-environment data were found. |
| Aluminium alloy 5251 (AlMg2) | Welded marine and sheet-metal structures where seawater corrosion resistance and weldability matter more than peak strength, at 2.69 g/cm3 | Strength compared with heat-treatable alloys: H22 minimum proof stress is 120 MPa, and a good weld reaches only about 160 MPa (Smith) |
| Aluminium alloy 5754 (AlMg3) | Welded structures and marine or chemical service where seawater corrosion resistance matters, at a density of about 2.67 g/cm3 | Strength against heat-treatable aluminium alloys, since strength comes from the temper, and the risk of sensitisation in magnesium-rich grades held warm for long periods (no temperature threshold for this grade was verified) |
| Aluminium alloy 6013 | Light structural aluminium for aerospace and general structural use: 2.71 g/cm3 density, and 350 MPa yield in the T651 temper (supplier page) | Dust and chips ignite readily during machining (Hydro SDS). No fatigue, fracture-toughness or T6 temper data was opened, and the sources disagree on thermal expansion |
| Aluminium alloy 6063 | Architectural extrusions such as window and door frames, rails and trim that need a smooth anodised finish (Alloys International; AZoM). | Strength: Alloys International says 6061 is the higher-strength choice for structural parts, and no space-environment, cryogenic or galvanic data were found for 6063. |
| Aluminium alloy 6082 | Structural parts that must be strong but light: T6 and T651 plate with minimum proof stress 255 MPa and density 2.70 g/cm3 | Strength in the weld zone, which the supplier says is lowered by welding, and pitting or intergranular attack in chloride solution (lab immersion test at 50 °C) |
| Aluminium alloy 7050 (AA7050) | Thick, high-strength aerospace structure in the over-aged T74 or T7451 conditions, where high yield strength and good exfoliation resistance are needed | Weld zones: friction-stir welds of 7050-T7451 showed less cracking resistance than 7075-T651 welds in constant extension rate tests (2003 study) |
| Aluminium alloy 8011 (AA8011) | Thin, light foil and fin stock: 2.71 g/cm3 density with 210 to 220 W/(m·K) thermal conductivity in H19 foil at 20 °C | Yield strength and corrosion data are missing from this profile, and no spacecraft use was found in any source read |
Where each is used
| Material | Use |
|---|---|
| A36 structural carbon steel | General construction and structural framing |
| A36 structural carbon steel | Girders, structural shapes and angle iron |
| A36 structural carbon steel | Bolted and welded structural joints |
| Carbon steel 1018 | Shafts, pins and gears |
| Carbon steel 1018 | Low-stress structural components |
| Aluminium alloy 6061 | Launch vehicle and spacecraft structures (aluminium alloys, 6061 named as a structural alloy) |
| Aluminium alloy 6061 | Simulated propellant tanks of 6061-T3 sheet (ground impact tests, not flown) |
| Aluminium alloy 6061 | Fittings, couplings, hinge pins, valves and valve parts, and hydraulic and brake pistons |
| Aluminium alloy 7075-T6 | Aircraft structures and airframe parts |
| Aluminium alloy 7075-T6 | High-pressure hydraulic units |