Letter 34090

Galvanic corrosion of chem-filmed aluminum  

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I have a unit that is made of aluminum (6061)that has been chem filmed to Mil-C-5541 [link is to spec at TechStreet] -3. In installation, it interfaces with two 300 series stainless steel pins. In humid environments, will the chromate conversion coating, although conductive, serve as a barrier between the aluminum and stainless or do I still risk galvanic corrosion where they contact?

Lou Volka
Aerospace manufacturer - Farmingdale, New York, USA

I would suspect that the pins will scratch through the film to create direct contact with the aluminum, which creates a potential for galvanic corrosion. SS is not as active in causing galvanic corrosion of aluminum as is plain steel, but there is certainly a possibility, especially in the crevice of the pin bore where the SS will tend to lose passivity.

You could check test assemblies with a voltmeter to see if you have electric conductivity between the pin and aluminum. If you have a low resistance, there is electical continuity and a potential for galvanized corrosion.

Good luck.

Larry Hanke materials testing laboratory Minneapolis, Minnesota

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