Originally Posted by sgschwend
Clear Alodine or Chromate Conversion. Check it out, looks like you could do this yourself.
Certainly not a robust as anodized, but for interior surfaces should do well. At HP there was many aluminum sheet metal parts coated that way and they held up very well for many years.
Both answers are correct; anodized is best, and alodine is good.
If stress is involved, see if shot-peening is doable.
(A retired aircraft A.M.E.)