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Galvanic Corrosion Tin Plated aluminum - Alu?

2005

Q. In our sensor application we currently have a sensor with a 6061 aluminum body that is thread mounted on a mating part of tin plated 6262 aluminum. Between the two parts is an O-ring that prevents medium leakage. In a salt spray test (SWAAT ASTM G85) leakage occurs after a few hundred cycles.
I think this is caused by a classic case of galvanic corrosion on the O-ring sealing surface of the sensor because:
- Tin is compared with aluminum the more noble metal
- Sensor and mating part are electrically coupled at the thread
- Sensor and mating share a common electrolyte (SWAAT solution)
- Sealing surface where leakage occurs is very close to where the parts are electrically coupled
- SWAAT solution contains acid (pH 3.0) and this attacks the natural aluminum oxide layer on the aluminum, rendering the aluminum more susceptible to galvanic corrosion

Now my questions:
- I am correct in assuming galvanic corrosion is the problem here?
- Could chromating (hexavalent chromium free chromating) the aluminum body of the sensor solve the problem?

Thanks in advance for all replies.

Jaap Hoftijzer
Automotive Supplier - The Netherlands

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Q. Dear sir.

I am very glad to reach here to communicate with you about some ASTM questions, thank you!

Okay, I have read some ASTM standards, but I do not know the difference between the ASTM G 85-98 and ASTM G 85-94, especially, the testing time. mainly because I do not have the standard of ASTM G thank you very and best regards!

Oota Hidetoshi
- Gunma, Japan
2005