Been mentioned a couple of times in relationship with rear leaf springs as a couple of other applications. IMHO semi-gloss black isn't an option since coil springs were not painted. If you have to use paint play with the Eastwood phosphate with a light dry overcoating of Dark Charcoal Metallic.
Not of the coatings by themselves should be considered IMHO and should be coated with a protective additional coating such as a wax or oil base