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Zinc plating with blue passivation is yellowish at holes

adv.
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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.

61615-1b 61615-1a

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

Thivaharan veeman
- 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,

pic of Ted Mooney
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.

Popatbhai B. Patel
electroplating consultant - Roseville, Michigan

February 29, 2024

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