Smut?

[scocklin]

I am trying to anodize some very old sailboat cleats (of an unknown alloy) for a boat I am rebuilding. I washed off the aluminum cleats with simple green, degreased them and stripped them with Caswell stripper. When I pulled the cleats out of the stripper I noticed a dark film on them. Not knowing for sure I assumed that this was smut. I rinsed off the cleats and put them into the de-oxidizer/de-smut tank for 5 minutes, I then pulled them out and they where a bright aluminum almost white with heavy etching the dark film was gone.

Was this smut and what is smut? Can I have a polished surface on the cleats?

[M_D]

Yes, that was smut. Chances are good it is cast aluminum, although it may be extruded aluminum capable of being anodized nicely. Cast aluminum can be difficult to anodize and get a good appearance. Polishing the aluminum before anodizing doesn’t cause any problems I am aware of, as long as it is cleaned properly afterwards. Although I can't verify it from personal experience, I have read that polishing cast aluminum may alleviate some of the problems generally encountered.

[Fibergeek]

To expound on what M_D said:

Cast aluminum can be more difficult to anodize, but its certainly not impossible. It will save you some frustration if you put off castings (if that is what it is) until you gain more experience with easy to anodize barstock. Buy a length of generic 1/4' x1"x6' aluminum bar at your local hardware store (or "home center") which is practically assured to be 6061 or 6062, both easy to anodize. Cut it up and get some practice.

Cast aluminum contains by necessity substantial amounts of silicon, and other not anodizable metals, these are in solution with the aluminum and the effect is slower anodize growth with time. It will become important that you take agitation requirements seriously, and be certain that the electrolyte temperature stays between 70 and 75 deg. F., throughout the entire anodization. Anodizing at the higher end of the LCD range will also help. If you don't you will learn the bad effects of excessive dissolution.

[scocklin]

You’re both absolutely right! The aluminum cleats have casting holes under the fasteners. I will put these pieces aside for now. Again thank you.