Tom G. says:
Try autosol for chrome.
For Aluminum, I do the sanding approach, using wet/dry
sandpaper (sometimes I use it wet, sometimes I use it
dry). 220 is a good starting point, but some bad
scratches require coarser grades first. then 320,
then 400, then 600, then 1000, then 1500, and THEN I
rub out with mothers aluminum polish (although I think
autosol is ok too).