[JamesL]

The problem with using aluminum plates/sheets for diy casing is that it scratches really really easily, and attracts oil/dirt like a magnet.

I like the look of brushed and polished aluminum, and sheet metal+wood makes for cheap diy cases, but I can't justify using it when it'll look dull and scratched up one week after.

The only thing I've tested is some polyurethane I had on hand, which gave it a a unappealing yellow-tinted film.
I've considered anodizing, but getting it done professionally is very cost-ineffecient unless I have it done in mass quantities, and I'm not sure about diy-anodizing.

Does anyone with experience have any suggestions?

 

[MoodySteve]

Clean and, if you wish, polish the metal to the appearance that you like. Then, spray a few layers of acrylic clear coat (e.g. Krylon). This will protect the surface from scratches quite effectively. You can even sand the clear coat down for a nice, smooth finish.

Powder coating is also quite effective against scratches, but it's unlikely that most DIYers have access to the necessary equipment. Plus, glossy power coats pick up smudges very easily.

 

[amphead]

A reliable method is to use 320 sandpaper to scratch up the surface, then wash with water and 409 cleaner. Rinse and dry, then get acid etch primer in the can from your automotive paint supply store. Spray with the primer, following directions on the can. You can then spray with any color urethane automotive paint for a durable finish, also from the automotive paint supply store.