Summary for yellow chromate color Discussion
Yellow chromate color vs. corrosion resistance is discussed as a mostly process-related issue rather than a direct quality indicator. Juergen Schroeder asked whether a deeper yellow on zinc-plated inserts means a thicker chromate film and better or worse corrosion resistance, or whether it is only an optical effect. Jonathan Timms replied that higher drying temperatures can produce a more iridescent color, and that excessive drying temperature can hurt NSST results; however, he said a slight color difference usually does not significantly affect corrosion resistance in normal service life unless the parts are not passivated properly. A second answer added that the issue may lie in passivation and post-passivation handling, noting that after drying, parts should be stored properly because acid fumes can spoil the passivation color.
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 Schroeder
plastic 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