Δplus The superior surface

Our objective was to improve significantly corrosion protection of Cr(VI)-free surfaces in a swaged state.

Fig.: Swaged fittings after 300 hours salt spray testing (Test implemented by: Technical College South Westphalia / School for Technology and Business, Laboratory for Corrosion Protection)

The initial situation (Cr(VI)

  • 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 basis 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 conclusion

There is no passivation that is able to achieve the positive characteristics of a Cr(VI) coating with its "self-healing effect." The basic layer of zinc is not suitable for mechanically stressed components, since it cannot offer the required level of corrosion protection with passivation and sealing.

To achieve a practice oriented level of corrosion protection, the basic layer must already be more resistant!

The solution: Δplus

  • 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.

Essential properties

  • Highest levels of corrosion resistance against red rust, even after handling and assembly.
  • The zinc-nickel basic layer is many times more corrosion resistant than zinc.
  • White rust appears only in form of a light grey haze. No "blooming" (voluminous white corrosion degradation product / zinc oxide).
  • Demonstrably better corrosion resistance compared to the previous standard (A3C)
  • Proven standard in the European automobile industry for many years

By converting to Δplus, you obtain a Cr(VI)-free alternative that meets the highest demands on corrosion resistance.

Corrosion resistance

(Salt spray test according to DIN EN ISO 9227):
  • White rust does not exist, since there is no "blooming" of zinc possible. There is only a light grey haze.
  • Resistance to red rust (fitting): > 720 hours in unpressed state
  • Resistance to red rust (socket): > 500 hours in swaged state


  • The total layer thickness is 5 - 10 µm at a nickel content in the basic layer (ZnNi) of 12 %.
  • Corrosion resistance against red rust (swaged) > 500 h
  • Corrosion resistance against red rust (non-swaged) > 720 h
  • Assembly behavior is not affected by the new surface finish Δplus, since the coefficient of friction, due to a special surface treatment, remains unchanged in comparison to yellow chromizing (A3C).
  • Ecological compatibility conforms with EU Scrap Car Directive No. 2000/53/EG.
  • Product color is transparent, silver.
  • Paintable with commonly available enamels, however, painting test is recommended.
  • Δplus is compatible with all commercially available hydraulic media.
  • Allergy test according to DIN EN 1811 has been absolved. All limiting values were comfortably met.