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White rust soon after black trivalent chromating

We have this non-cyanide Zinc plating with black trivalent chromating process in our company. Recently, we encountered this white rust (like white during salt spray test) after few days in normal environment. I would like to ask what is the main cause for this kind of defect and the probable corrective action/measure for this.

Jang Almanzor
plating company employee - Manila, Philippines
July 22, 2011

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Hi,

Pls check the rinses and the drying method after the passivation, secondly have you applied any topcoat after black passivation?

Regards
Praveen

Praveen Kumar
plating process supplier
Mumbai, India
July 26, 2011

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Many years back I had a similar problem with hex black.
We found the black pass was too aggressive and was eating away too much of the zinc layer we had just deposited.
Tri black could be the same. Make sure the zn layer is thick enough 8-10 µm and rinse well between treatments and seal afterwards.

Gary

Gary Joseph
Johannesburg,
South Africa
July 27, 2011