CO2 lasers can’t engrave aluminium, however it is possible to ‘bleach’ anodised coatings to white or to ablate painted coatings. You can use a specific coating made for bonding with the aluminium, such as Cermark or moly spray.
I use a product called Trotec Alumark, which is aluminium sheet, anodised and coated. You ablate away the coating and are left with the anodised sheet showing through.
My settings are 250mm/s at 25% power, with a scan of 0.05mm/500dpi on ~100W
Distance will depend on the focal length of your lens.
There’s nothing special about engraving coatings on aluminium than any other material, like wood, plastic. Get your speed/power right by going through a materials check.