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.