Aluminium vs Magnesium
Aluminium and Magnesium are genuine alternatives to one another — a choice somebody actually makes — and differ on 5 measured properties, density most clearly.
Aluminium vs Magnesium
Aluminium
Al
The most abundant metal in the Earth's crust, and until the 1880s more valuable than gold because nobody could extract it cheaply.
Magnesium
Mg
The lightest structural metal in common use, and one that burns with a light bright enough to have been used for photography.
| Property | Aluminium | Magnesium |
|---|---|---|
| Atomic number | 13 higher | 12 |
| Density | 2.7 g/cm³ higher | 1.738 g/cm³ |
| Electrical conductivity Only one of the two has a figure we can stand behind, so there is nothing to compare. | 37.7 MS/m | Not known |
| Melting point | 660.32 °C higher | 649 °C |
| Mohs hardness Mohs hardness is an ordinal scale: values can be ranked, but differences and ratios between them are not meaningful. | about 2.75 higher | about 2.5 |
| Molar mass | 26.982 g/mol higher | 24.305 g/mol |
| Tensile strength Only one of the two has a figure we can stand behind, so there is nothing to compare. | 70–130 MPa | Not known |
| Thermal conductivity Only one of the two has a figure we can stand behind, so there is nothing to compare. | 237 W/(m·K) | Not known |
Choosing between them
Magnesium is recorded as a substitute for Aluminium — lighter.
What it gives up: Burns, corrodes galvanically, and creeps — which keeps it to castings rather than structure.
Partial substitute, on the evidence cited above.