The initial situation

  • Previous standard: zinc coating (applied by electroplating, thickness 8 - 12 µm) with chromate layer (0.3 µm)
  • This surface finish has proven to be optimal for mechanically stressed components
  • Good corrosion protection, up to 100 hours until occurrence of white rust (salt spray test according to DIN 50021)
  • The decisive factor for good corrosion protection is the ″self-healing effect″ of the chromate layer in case of damage: the Cr(VI)-ions ″flow″ to the damaged area and close it up. This effect can only be achieved with Cr(VI)

The problem (zinc)

  • The basic is the same zinc layer as used in yellow chromizing.
  • Instead of the chromate layer, a passivation and additional sealing layer is used.
  • Should the sealing layer be damaged, corrosion problems are the consequence.
  • In this case, there is no ″self-healing effect″ as there is with a Cr(VI) surface.

The solution: plus

  • A zinc-nickel basic layer is many times more corrosion resistant compared to zinc.
  • A passivation with subsequent sealing provides a higher gloss finish and improves frictional properties.
  • Zinc-nickel does not develop pronounced white rust like zinc, but merely a light grey haze.