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Corrosion protection of phosphate and oil

Hello, This is Jeff Martin Wintle. I am trying ascertain properly what offers the corrosion protection in the finish phosphate and oil. Is it the phosphate or the oil? Assuming the corrosion protection comes mostly from the oil, does the base phosphate offer any protection? Is there a difference betwixt zinc phosphate or mag phosphate?

Jeff Wintle
quality administrator - Birmingham, Alabama, USA
July 19, 2011

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Hi, Jeff. This comes up absolutely constantly, with people forever wanting to know the salt spray resistance of bare phosphate, etc., so if you patiently search the site you'll find all kinds of insights. But, basically, the oil provides the corrosion resistance while the phosphate provides an adherent, amorphous or crystalline but absorbant base to hold the oil. So the effect is symbiotic. Without the oil, the phosphate does little; but without the phosphate, the oil can run off to too thin a covering for significant protection.

Today's phosphate coatings can be complex; there's no longer just iron, zinc and manganese, but tri-cationic and so forth, so the old axioms may not hold 100 percent anymore. But in simple generic terms, manganese are the thickest, iron are the thinnest, and the oil-holding capacity and corrosion resistance tend to be in proportion to the thickness of the phosphate coating.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 20, 2011

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What Ted said above per se', PLUS, if a hex chrome seal (do to send to Europe) is used with or without the oil the corrosion protection is greatly enhanced. Also the manganese process is usually used only for lubricity and metal "break-in".

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

July 21, 2011