aluminium vs metallic element

aluminium and metallic element both are nouns.

Word	Noun	Adjective	Verb	Adverb
aluminium	Yes	No	No	No
metallic element	Yes	No	No	No

As nouns, metallic element is a hypernym of aluminium; that is, metallic element is a word with a broader meaning than aluminium:

aluminium: a silvery ductile metallic element found primarily in bauxite
metallic element: any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.

Other hypernyms of aluminium include metal.

aluminium (noun)	metallic element (noun)
a silvery ductile metallic element found primarily in bauxite	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.