[Amps] Pretreatment of Aluminum for painting

[N7KA@comcast.net]

I do believe ALODINE provides an insulating surface.  The best preparation of aluminum for paint processes is a chromate surface.  This is accomplished per MIL-C-5541 (ANSI has a different specification number for thsi process).  This is a conductive surface treatment and normally yields the light yellow to brownish color depending upon length the parts are subjected to the chemical conversion process.
The process is usually done with a series of tanks used to clean, coat, and rinse parts.  There are 2 classes of coatings based upon the requirement for a very low surface resistance (Class 1A) or a normal conductive surface (Class 3).  Some chemical conversion can be performed in clear color and must be specified.
There is a new process that does not use chromates that we are investigating at work.  Because of the heavy metal attributes of chromate we do NOT do this process ourself, but send it out to be done.  A non-chromate process would allow us to do it in-house and save a lot of $$ and lessen use of chromates (hopeful eliminate 99% of our chromate use requirements).
I do some painting of aluminum at home and usually get good results by ensuring the surface is clean of any oils.  I clean with alcohol and use several light coatings of paint.  Most I then bake in the oven at about 170F, let your wife go away for the weekend, or she might get very upset at this happening in HER oven.  Often after this I will allow the part to relax in the New Mexico sun to continue in a natural baking process. The paint hardens very nicely.
 If I can find a shop that does powder coatng (and does it within hobby budget) I will have all projects painted in this manner.  Powder coat is probably the best commercial coatings available.
I may have digressed a bit but hopefully the info will be helpful to the readers.  I am sure others have had success with other processes.  I for one would be interested in other results.
73 de Arne N7KA