Steel is an alloy of Fe iron 26 and carbon 6, + trace other elements if desired..

aluminum 13 is another element, alloyed to different recipes..

Examples,
in steel 4130 is a specific steel mix, in aluminum 7075 is also a precise description ..

there are specially drawn and heat-treated, high strength steels, that cost more to buy,
just the tube-set.

than a whole wally-world bike.

go to a proper bike shop and they will begin the demystification.