Touching up black aluminium window frame
do exactly what you described just as you described.  put four or five coats on.  then:

1)  sand the new paint very carefully with 800 gr sandpaper.  use wet/dry paper and use water to lubricate.  use a block of wood as a backer to make sure you dont get too much pressure in one area or another and sand through the paint.  sand down until smooth and flush with adjacent paint.  dont worry if it looks flat and dull now.

2)  repeat with 1200 and then 1500.

3)  buff the repaired area and the adjacent area with a smooth cotton cloth (t shirt will do fine) with some brasso, toothpaste, or some other polishing agent.  polish with hand pressure and the polishing agent on the cloth until you get the same overall gloss to match. more rubbing, more shine.

4)  if a smooth finish is desired, you are done.  if you want a brushed finish (like many aluminum panels) rub very lightly with a scotchbrite pad in the same direction as the grain you are trying to match.

done!