Metal finishing Q&As since 1989
-----
Zinc plate/Yellow Chromate - color vs. corrosion resistance
Q. We are a plastic molding company and using inserts for some parts which are zinc plated and yellow chromated. Some of the parts are looking more yellow some less. Our plater told us it's because of the drying process and does not affect the quality in regard of corrosion.
My question: is the intensity of the yellow color a sign of the thickness of the chromate film and based on this affecting the resistance against corrosion or is it just an optical effect.
Juergen Schroederplastic molder - Changchun, Jilin Prov., China
2004
A. Dear Mr. Schroeder,
You're both correct in some ways. Higher drying temps will give a more iridescent colour. Although, this can have a negative effect on NSST results if the drying temp is too high. Unless you mean that some parts aren't passivated properly at all, I don't think a slight difference in colour has any significant effect on corrosion resistance in the service life of the part.
Regards,
Jonathan Timms- Hong Kong
2004
A. Problem seems in passivation and post passivation treatment, after drying pieces should be stored properly , any acid fumes will spoil the colour of passivation.
Ajay Raina
Ludhiana, Punjab, India
2004
Q, A, or Comment on THIS thread -or- Start a NEW Thread