After you've cast your part it still isn't done. You have the option of finishing it. You can plate it, there is a compound that will remove the oxide layer and give the aluminum another layer for plating it with what ever you wish to plate it with. Copper, bronze, gold, nickel... This zincate layer dissolve when you immerse it in the plating solution. https://caswellplating.com/zincate-8-fl-oz.html You can also polish it up but this won't last long term, and its just clear aluminum. I tried painting some boat items with Kandy paint and it has held up even though the painting method is completely wrong. Polished surface, no primer... Kandy paint if you don't know is a transparent paint. You can anodize it, which I've heard can be splotchy for castings. I haven't anodized castings but I have anodized a few other machined parts. The process is amazingly simple. The only 'difficult' part is you need a quality dye. I suppose if you must you can paint aluminum with regular opaque paint, but...?
The end use is going to be key and the amount of cost and effort you’re willing to spend both initially and in ongoing maintenance will be the deciding factors in finishing. No sense in polishing a turd. Knowing what options are available as well as their requirements and limitations will save a lot of grief and aggravation. This could turn into a great thread. Thanks for starting it. Pete
casts brass is easy plated with chrome nickel , but casts aluminum plating is not easy as of the aluminus is active metal, once remove the oxide layer by polishing process then build the zincate layer when you immerse it into plating solutions, then goes to chrome or nickel plating . But plating pocess always comes out with heat and it caused electr0plating solution temperature rise, the casts Aluminum parts' polished substrate porosity contains water and it sealed by plating layer, so once the temperature rises the porosity water will be thermal expansion and contraction, the plating layer will peel off. Our German engineer explained that control the polished substrate porosity is the key factors. why Zinc alloy (Zamak 3 ) has no such a problems, because the solid layer thickerness of casting Zamak parts is Min 1.5mm, casts aluminum parts solid layer thickness is 0.4~0.6mm. once you remove the oxide layer too much, the substrate porosity will come up. the further plating pocess will be failed. On this way, we improve our die casting mold to control the casting oxide layer quality, solved this problem. As for casts aluminumn, the anodize process seems not appropriate because of the Si element will dissolve out during anodize process and the cast aluminum become dark, not matter you put any shining or dary dye on it, the appearance looks no good. But for extrusion or forging aluminum, the Si contents is very low, the anodize quality is very good, you can dye a wonderful color appearance. Details you can check the metal hand book.
