When one considers steel, immediately one thinks of strength, toughness, robustness, etc. So, we associate the word “strong” with steel. With aluminium, we associate a silvery metal that normally looks good and is lightweight, compared to steel. And, we usually consider steel to be stronger than aluminium.
Aztex Equipment Liftwell Gates are manufactured using both steel and aluminium, for their respective strength and lightweight features.
Heavy duty scaffolding made out of aluminium
Steel is made by combining iron and carbon. Starting with iron ore (e.g., magnetite, haemetite, etc.) the metal is mined, then smelted and impurities removed. With the addition of carbon, we get carbon steel. The resulting metal is also used as a base for other metals, e.g., chrome-alloy and stainless steel. We note that the higher the amount of carbon in an alloy, the harder this becomes. Thus, we would normally consider aluminium weaker than steel—we should note however, that there are aluminium alloys that are stronger than steel.
Aluminium has bauxite as its base material. Again, this is also mined. The mined material is ground into a thick paste (alumina), which is smelted with molten cryolite (used as a flux), and shocked with electricity during manufacture. The ions separate and the residual liquid cools to become aluminium.
Comparing the two, one would say that steel is stronger and heavier than aluminium. Steel’s high strength comes with higher density. Thus, if one takes two pieces of equal volume, steel can be as much as three times the weight of aluminium. Typically, aluminium weighs 2.8 g/cm3, while steel comes at 7.8 g/cm3.
Steel’s strength makes it ideal for use in high-stress applications. However, factoring the lighter weight of aluminium, this material ranks better when considering strength-to-weight ratio. In manufacturing, one could come up with a larger aluminium piece that would provide more strength at a lower weight than the steel alternative.
With regards malleability, we note that steel is harder to work into shapes compared to aluminium. This can be overcome in manufacturing applications through the use of heat applied to the steel in high temperatures—adding to the cost and also possibly compromising other properties. Aluminium is easier to work with cold or hot, thus making it ideal for manufacturing processes like extrusion and rolling.
A short note on conductivity: aluminium is generally a better thermal conductor than steel. Hence, the use of aluminium where heat dissipation or distribution is required, e.g., heat sink applications.
Carbon steel has very poor corrosion resistance. This is the reason steel is coated or painted for use in corrosive environments, e.g., moist or salty air. This contrasts with aluminium which exhibits high oxidation and corrosion resistance. When manufactured, aluminium forms a protective oxide barrier on the skin. This acts as an inert block to further oxidation.
Note that use of chromium as an alloy in steel manufacture (minimum of 11%) makes it stainless steel. This process is also costly and makes the resulting metal more expensive than carbon steel.
Finally, we look at cost, a significant factor in choice of raw material in project use. As the cost of metals fluctuate due to market forces and use of specific alloys in manufacture, so we cannot say definitely which is cheaper in every use. We note, however, that it is commonly accepted that carbon steel is generally less expensive than a comparable aluminium alloy.
