Replacing Hexavalent Chromium in Passivations on Zinc Plated Parts
The use and benefits of passivations based upon hexavalent compounds, particularly on zinc plated parts, are well established and understood in finishing. Through the changing attitudes within society, the continued long-term use of this technology is under question and review. We examine the background and comment on the alternative strategies available that are most likely to commercially succeed . . .

 

By Paul C. Wynn, Business Manager
and Craig V. Bishop, Special Projects Director
McGean-Rohco (UK) Ltd.

 

 

TABLE VII TABLE VIII
TABLE VII TABLE VIII

TABLE IX—Corrosion Protection CrIII Passivations
Electrodeposit Passivate W C# Hrs*
Alkaline Zn CrIII Yellow 96-200
Alkaline Zn Fe CrIII Yellow 96-200
Alkaline Zn Ni CrIII Yellow 200-400
Alkaline Zn Fe CrIII Black 100-200
Alkaline Zn Ni CrIII Black 400+
# White Corrosion (after "gray veil")
* Heat 120C for 24 Hrs prior to ASTM B117 salt spray

TABLE X—Corrosion Protection Non-Chromium
Electrodeposit Passivate> W C# Hrs*
Alkaline Zn NCr Yellow 80-200
Alkaline Zn Fe NCr Yellow 80-200
Alkaline Zn Ni NCr Yellow 200+
Alkaline Zn Fe NCr Black 50-100
Alkaline Zn Ni NCr Black 100-200
> With clear topcoat applied
# White Corrosion (after "grey veil")
* Heat 120oC for 24 Hrs prior to ASTM B117 salt spray

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