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Corrosion protection for aluminum blade shaft on variable pitch fan




I am a mechanical engineer. We make a variable pitch fan, and use an aluminum shaft to mount our blades on. Due to fatigue issues with anodizing, I want to get away from it. The fan may be exposed to salt (radiator fan on highway trucks). What options do I have for coating the exposed area of the shaft. I am looking at 6061-T6 or 7075-T73 alloys. A simple spray on coating would be ideal.

Jon McCallum
- Edmonton, Alberta, Canada
2003



1. Chromic Acid Anodizing is the best answer. The aircraft industry still uses it to get corrosion protection without fatigue problems. There are still a few chromic anodizing shops around.

2. Second best is a light chromate followed by powder coat. Do not put the chromate on too heavy as the coating will shear and the paint peel.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
2003


What about electroless nickel plating? Does EN have any effect on Fatigue? If we get a scratch through the coating, will the aluminum sacrifice for the nickel?

Jon McCallum
- Edmonton, Alberta, Canada
2003



If the electroless nickel coating becomes compromised, yes, it will cause galvanic corrosion of the aluminum. However, millions of aluminum automobile wheels are successfully electroless nickel plated before decorative nickel-chrome plating. I would not expect electroless nickel plating to severely impact fatigue strength, but I think Mr. Probert offered some sound options.

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




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