A £4.00 felt disc that you put it an angle grinder, I then use brown soap, followed by blue soap, it should come up like a mirror, that's tomorrows job, polish both sides.
Got some proper buffing cloth wheels, but they are too big, better on a bench grinder.
I first was introduced to aluminium polishing at 17 when I stuffed my Honda wet dream down the road and chewed up the engine cover.
I sanded it down with progressive grades of sandpaper and luckily at college the lecturer allowed me the use of there polishing equipment.
What I didn't realise was that I was getting covered in polishing crap, so when I got home, my girlfriend thought I had been down the mines.
The important thing was I learnt that you could with patience polish aluminium to a brilliant finish, with little cost.