Fatigue Strength of Anodized Aluminum

Question:

I have a question about an article on the web that was attributed to you. The article can be found at www.pfonline.com/articles/clinics/0503cl_alum1.html. In that article you wrote, “Another interesting fact about dichromate sealing is that it can largely overcome the loss of fatigue properties caused by the anodic coating, especially hardcoat.” You’re right, that is interesting. Can you elaborate on this? Perhaps there’s a simple description of the mechanism, or maybe you know about some published tests that I can peruse. Thanks for any insight you can offer. D.V.

Answer:

Thanks for your question.  If I were to write that article again the word I might leave out would be “largely” simply because it leaves a lot of room for interpretation.  It is a demonstrated fact that sealing in general, and dichromate sealing in particular, does ameliorate somewhat the loss of fatigue strength in anodized aluminum.

Here are some references that talk a little about this, although not in great detail. If you are at a university, as your e-mail address indicates, you undoubtedly have access to these publications and can pursue it further.

The Surface Treatment and Finishing of Aluminum and Its Alloys, by S. Wernick, R. Pinner and P.G. Sheasby, Fifth Edition, Vol 2, pg 720.

Technology of Anodizing Aluminum, by A.W. Brace and P.G. Sheasby, pg 282.

The Technology of Anodizing Aluminum, by Arthur W. Brace, Third Edition, pg 285.  (Not the same as the second ref, but almost.)
 You can take it from here.  Let me know if I may be of further assistance.