The properties of aluminium include: low density, excellant malleability, easy machining, high strength, great corrosion resistance and good thermal/electrical conductivity.
Steel is a general term for iron containing small amounts of carbon, manganese and other elements. The properties of steel include: electrical conductivity, malleability, ductility, strength and it's durability.
The selection of grade and type must initially meet the corrosion resistance requirements. Additional physical properties need to be considered to achieve needed performance requirements.