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topic 1557

Coef. of Friction of Anodized Aluminum as function of surface finish?


Does anybody have any data (or know where to look) for coefficient of friction of anodized aluminum (specifically 2219)and how it varies with varying surface finish? I have limited data from one supplier, but it is based on tests of coupons with a 4 RMS finish. I have parts that will be machined to ~ 32 RMS and I'd like to know what to expect after anodize.

Mark Lipschutz
- Aerojet Propulsion Division


I think that the coefficient of friction is independent of surface finish and more dependent on the ambient conditions such as presence of oxygen or nitrogen or vacuum, etc. Data for the same samples may vary from place to place because the test conditions are not exactly the same. Besides, what emthod do you want to use? There is a pin-on-disk method and reciprocating pin method. Friction also depends on the pin material. I would suggest you create your own data by sending samples to a lab. Another suggestion, call a material science faculty at a University nearby and get a clear idea what needs to be done. One expert I know is Dr. Sampath, Prof. Mech. Eng., Colo. State Univ., Ft. Collins, CO.

Mandar Sunthankar
- Fort Collins, Colorado


I can say that the basic coefficient of friction for aluminium to aluminium is stated as 1.4 in "The Friction and Lubrication of Solids" [affil. link to book on Amazon] Vol.1 by Bowden and Tabor. However you have also stated that the material will be anodized after surface finishing. This would lead me to believe that the coefficient of friction will be largely dependent on the anodizing process film that will be deposited onto the surface. There is a large variety of anodizing finishes available from Hard anodize to standard clear and coloured anodizes. I would suggest that you first consider the wear and pressure characteristics of the anodize film before concerning yourself with the characteristics of the aluminium base metal beneath, as this will give you a mean time before failure of the anodize and hence the point at which the aluminium becomes the contributing frictional element.

Charles D. Balmer
- Concord Elevator

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