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Applying trivalent chromate conversion coating to zinc plating before hydrogen de-embrittlement baking

Q. We are zinc platers here in Melbourne, Australia. We are searching for a chromate passivation products that can withstand the temperatures of hydrogen de-embrittlement baking without loosing their NSS performance. i.e. at present we plate, bake and then chromate. What we want to do is plate and chromate on our automatic line and then bake as the last op sequence.

Does anyone have any suggestions?

If yes, we'd like to hear from you

Jim Griffin
- Melbourne, Australia.
1999

A. Dear Mr. Jim,

What you want is possible only if the material is not very porous or if the occluded Hydrogen is not very high.

Try trivalent Blue passivation followed by a five minute immersion in boiling water then go for de-embrittlement, which will not affect the passivation too much.

regards

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

1999

A. Hi Jim. Also be aware of the face that some specifications forbid this practice (of chromating before de-embrittlement), and that Khozem's thoughtful remedy of boiling in water for five minutes will leach some of the chromate away (I'd say 'most of it' except that trivalent chromates today are highly proprietary and different from each other, so it's hard to make a universal statement).

Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 28, 2012