Anodizing AA380

Usually the silicon in aluminum casting alloys makes for splotchy and off color anodizing. Black is the worst this way. Stripping and polishing will not improve the results. Usually it only makes it worse.

Silicon is needed in cast aluminum alloys to get them to flow into a mold when molten. Common wrought aluminum alloys black anodize nicely because they don't contain silicon.

I don't know what your economics are for this project; but if you want to spend some money trying something different take a look at PVD coating (sputtering) the part with pure aluminum thick enough to work with the anodizing process. You'll likely need to polish the part between the coating and anodizing steps.

I have no experience with anodizing pure aluminum in sputtered coating form. Maybe make some test coupons out of other aluminum die castings first if the casting is valuable to you.

Ed Weldon

The anodic coat on an alloy for casting with a high content of silicone is very porous. Hence it turns out to be a good base for a PVDF coat.

If you want to have specifically an anodised surface you should look for a company that does hard anodising. The process is done at a temperature of -2°C and with a coat of 80-100 microns it becomes black on it's own without colouring. The surface is however dull. If you can give it a bright look you can buff the surface with cotton brushes. It will give it a gloss on the surface.

You should know that hard anodising is expensive.

Sputtering is not a good solution for an anodic coat, it tends to peel of.