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topic 0907

Zinc plating and blackening of powdered metal

A discussion started in 1998 but continuing through 2018


Q. We want to zinc plate + black oxide seal some powder metal (MPIF 35, F-0008-25) parts. We need the black to look good aesthetically and not fall off in our hands. We need the parts to pass a fifty-hour salt spray test. The parts are small, about on cubic inch, and all have a 1/2 inch through hole.

Grant Bryant
mfgr. - Indiana


A. I have never heard of black oxide on zinc. It may be done, but I doubt it. Are you asking for a black chromate on it?

James Watts
- Navarre, Florida


A. Zinc and black chromate will easily pass a 50-hour salt spray test when applied to a suitable substrate, Grant. However, depending on the quality of the powdered metal parts, they will probably be very porous, and could basically be unsuitable for plating onto. I'd suggest that you may need to investigate vacuum impregnation with a supplier to prepare the parts before plating.

Good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Message for Mr Grant Bryant

Vacuum Impregnation is an important prerequisite prior to any kind of plating operation for a sintered component. Vacuum Impregnation helps to seal the porosities in the components , so that the plating acids do not pose a problem of leaching after the plating operation is completed .

Best regards,

Mr Saibal Sen / Mr Probal Sen
Pune, India

March 1, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello All!
I have to process the sintered porous metal with zinc plating.
Material density is 6.6 g/cc.
After plating black patches were formed and a liquid substance is oozing out from the part.

How to get out of the problem?

Balasundaram Ramamoorthy
Sintering Solutions Pvt Ltd - Chennai, Tamil nadu, India

April 2018

A. Hi Balasundaram. We added your question to a thread which already addresses the subject. You probably will not be successful in zinc plating these parts without vacuum impregnating them to remove the porosity which wicks up the chemical treatment solutions.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

April 4, 2018

A. Many sintered parts (powder metal parts) have been - and continue to be - mechanically plated with zinc without impregnation. The void volume needs to be below about 15% which would seem to be the case here. Careful rinsing and COMPLETE drying after passivation are mandatory.

Tom Rochester
Plating Systems & Technologies, Inc.  
supporting advertiser
Jackson, Michigan, USA
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