Most steel parts provided by Superlite are either powder coated or zinc plated. However, the following parts aren’t coated and they quickly begin to pit even when kept in a climate controlled garage:
Ball joint plates (4x)
Lower shock pins (4x)
Rear suspension pushrods (2x)
Toe links (2x)
Rear suspension k-brace support rods (2x)
I’ve have also fabricated a bunch of brackets, backer plates, rocker support arms and other parts that need rust protection. Powder coating works great in many applications, but it chips too easily in areas where wrenching is done (e.g., pushrods, shock pins, shock brackets, etc.). In addition, even when applied with electrostatic spray it’s typically 3-5 mils thick which can conceal cracks during a visual inspection or increase a critical dimension (e.g., shock pins).
Cadmium was the premium automotive corrosion protection, but it’s highly toxic and illegal in most states. After doing some research it seams that zinc-nickel is the premium replacement for cadmium. When compared to zinc, zinc-nickel offers ~4x better corrosion protection and is ~2x harder.
Zinc-nickel is comparatively new and not nearly as common as zinc, nickel, chrome, etc. I called over 20 places and they all had large minimums. One place had a one ton minimum, really? I was about to give up when I found Sav-on Plating who provides a variety of high-volume plating services to the aerospace, healthcare and automotive industries. However, they have a reasonable $250 minimum charge for 5-micron zinc-nickel plating. While their zinc plating is done via racks their zinc-nickel is done via barrels so size is limited. That said, all of my parts fit in the barrel and the minimum would have covered about twice the volume that I sent.
One concern with most plating is hydrogen embrittlement. Apparently, steel with an ultimate tensile strength of less than 1,000 MPa (~145,000 psi) or a hardness of less than 32 HRC (hydrogen assisted cracking) is not generally considered susceptible to hydrogen embrittlement. The hardest parts that I’m plating are non-heat treated 4130 alloy steel which has an ultimate tensile strength of 670 MPa (97,200 psi). That said I had the parts baked for 14 hours at 400° F per the table above just to be safe. That cost an additional $50.
I also decided to have a passivization and clear layer applied which added another $50. Apparently the passivization layer can discolor the finish a bit, so if you want a brighter more consistent finish I’d skip the passivization.
Most of the car has a machined or brushed aluminum finish so I didn’t want a polished finish. I removed the pitting and rust with a combination of a belt sander, a Dremel with an abrasive wheel and a tube polisher with a surface finishing belt. The only parts that I did polish where the shock pins because I wanted to ensure that they’d glide easily into the shock’s monoballs.
