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topic 47183

Manganese phosphating and black oxide on gun parts


My company is supplying MIM parts to a gun company. We've had problems with the manganese phosphate applied to the parts. The coating is not sticking and shows inconsistent coloration. The customer has suggested we black oxide the parts first. Somehow this doesn't seem right. Any suggestions would be appreciated.


John Aiello
Buyer - Guilford, Connecticut, USA


Black oxide is more of an alternative to phosphating than a pretreatment for it. But guess number 1 is that the parts simply aren't clean.

Ted Mooney, amadeya42.com Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Good afternoon:

You could be having problems due to excess porosity in the MIM parts. This could be trapping chemicals from your phosphating process which bleed out later.

Steve Bizub
- St Louis, Missouri


There is no surface porosity on a MIM part. It not like a pressed powdered metal part. At the sintering temperature there would be no organic residuals on the surface. The parts are being bead blasted and solvent cleaned prior to phosphating. The steel is MIM 8620. I'm beginning to think our problems are more process related than material related because we do get some good batches.

John Aiello
- Guilford, Connecticut, USA


Solvent clean is ok to remove gross oil contamination but is never enough to guarantee a clean surface.
Solvent clean first (to avoid oil in the Bead Blaster [linked by editor to product info at Amazon] ) Hot aqueous alkaline clean rinse, water break test, (possibly an acid dip to ensure all the alkali has gone and to activate the metal) phosphate.

geoff smith
Geoff Smith

February 11, 2008

Good Day

first check your material

second check you cleaning steps

third you suppose to check your phosphating solution by laboratory and confirm that balanced or not

Yasser Metwalli Osman
- U.A.E, Ajman

Black Manganese phosphate on S7 MIM Tool steel

January 9, 2018

Q. We have a difficult time getting manganese phosphate black on MIM S7 gun parts. We get shades of grey and green. I've been told that post phosphate and water rinse and dip in antimony tartrate will blacken the metal. The Mil-Spec also mentions a dye but I haven't found anyone who knows anything about this. It is essential that these parts be jet black to match the other parts of the firearm.
John Aiello

John Aiello
distributor - Guilford Connecticut
^- -^

January 10, 2018

A. Hi John!

Check accelerator additions and iron content in your bath, green shades are iron phosphate deposits and usually means you have iron dissolved in your bath (there should be no iron, and you should have some accelerator in excess to work your line smoothly).

Check this and the other parameters in your manganese bath and you should get black phosphate. If not, I would talk to your vendor to improve the deposit darkness.

Best regards!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

January 11, 2018

Q. Instead of MIL-DTL-16232 [link is to free spec at Defense Logistics Agency, dla.mil] Type M Class 2 should the spec be changed to Class 4? Class 4 allows color dying or a post dip in an inorganic salt.

John Aiello [returning]
- Guilford, Connecticut

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