base metal vs metallic element

base metal and metallic element both are nouns.

Word	Noun	Adjective	Verb	Adverb
base metal	Yes	No	No	No
metallic element	Yes	No	No	No

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

base metal: a metal that is common and not considered precious
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 base metal include metal.

base metal (noun)	metallic element (noun)
a metal that is common and not considered precious	any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.