Galvanic Corrosion Test for Titanium Anodize (AMS 2487)
February 14, 2022
Q. We are an aerospace metal finisher who anodizes titanium per the AMS2487 [affil. link to spec at Techstreet] specification. That spec requires, among a lot of others, a periodic test for 'galvanic corrosion'. The method specified is to tightly fasten a titanium anodized 1" x 6" flat plate to a similarly sized, bare, 1100 alloy aluminum plate using nylon bolts through (2) holes in the opposite ends. You expose that assembly to salt spray ASTM B117 [affil. link to spec at Techstreet]
for one week and then 'check for evidence of galvanic corrosion'.
I can find no spec governing that test and nothing that might give a hint of what a pass or fail would look like. Obviously, the bare aluminum is going to corrode -- especially at the junction of the two plates, because unlike in a standard salt spray test where a single, almost vertically inclined panel is exposed to salt fog such that any salt moisture ultimately beads off of the surface of the panel), the fastened-panel salt solution would just 'sit' between the panels, causing way more corrosion than would be experienced on a single panel whose salt solution mostly beads and drops off.
We have very spotty success with multiple labs in passing the test, in my opinion because they don't accurately interpret 'evidence of galvanic corrosion'.
Any experience or guidance would be helpful. I really can't see how the AMS organization can specify a test with such loose pass/fail criteria as that!
- Gardena, California
A. Hi Mike. Just a guess, but maybe you're supposed to tape or mask the edges because the corrosion you are looking for is not between the two panels but on the outside of the panels?
I also agree with you that if a spec calls for some kind of testing it ought to say what constitutes passing or failing the test :-)
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey