Plenty of topics on here about refurbing bare metal frames.
TL;DR version: strip the lacquer with some paint stripper like Nitromors (which is not nearly as good as it used to be); then polish up with some wet’n’dry (start on about 600 grit, finish with 1200 or so — depends a. It on the condition of the frame); final buff with wire wool; then polish with some Peek or Autosol.
It’ll come up lovely and shiny!
Word of warning... some alu can be a bit tough as it’s anodised. The anodised outer layer is much harder than the regular alloy. Anodised aluminium is not necessarily the funky coloured stuff.