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Metal finishing Q&As since 1989
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Zinc plating with blue passivation is yellowish at holes
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Q. Hi everyone, need help. My company does zinc plating with blue trichrome passivation. We are encountering yellowish issue at hole areas.
Information on our process:
Degrease
Electroclean
Rinse
Acid pickling
Predip( NaOH)
Zinc bath (alkaline non-cyanide)
Rinse
Bright dip
Rinse
Blue passivation (tri Cr)
Rinse x4
Hot water (70 °C)
Blow dry
Oven dry (60 °C) 10 min
We have tried
1) change blue passivation solution
2) change bright dip solution
3) change rinse water
All specifications follow supplier spec
I'm suspecting the hot water & oven drying temperature may cause this issue?
Can anyone help me on the root cause & troubleshooting
- Perak malaysia
November 29, 2023
A. Hi Thivaharan
While we await someone with actual experience with this particular problem, I would suspect inadequate agitation in the chromate tank, or rinsing which is either not quick enough or not thorough enough.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. I think you can try after zinc plate, 5-6 seconds 1% by vol. nitric acid dip, follow up rinses then go to trivalent blue dip.
![popat patel](../portraits/popat_patel.jpg)
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan
February 29, 2024
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