Alochrome or Surtec it. It's a process to provide a key for painting. Lacquer just comes off cranks, i know that from experience. Electroless Nickel Plating may be an option but Nickel is extremly brittle. This means if you have any flex in the part you can get cracks. Re-anodising is worth looking at if you have a pure aluminium part, I can't reanodise my cranks due to the steel axle, the sulphuric used eats the steel. Best option would be a 50um Hard anodised coating.