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Passivation of fasteners

Sir, I am student of surface coatings,i am studying "corrosion science" as one of the subject. My query is regarding fasteners used specifically in automotive industry. Usual problem of corrosion comes in picture due to fasteners only ( what I found) , so my question is: Which passivation should be used black, yellow, olive green or Dacrotizing. And why?

Ashish Gupta
student - Kanpur, Uttar Pradesh, India
2003

2003

None of the above :-)

The European Union has effectively banned the use of hexavalent chromate conversion coatings on automotive fasteners. Therefore only clear, trivalent chromates must be used on zinc plating. The black, yellow, and olive green should not be used. There is also a hex-free system to replace the conversion coating on Dacromet, offered by by the same manufacturer, and called Geomet.

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

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