No oil wanted/needed

[pontiac428]

So what we have assumed was “etching” of the surface is really just a stain that will eventually fade away? Am I reading that correctly?

Yessir, that's my claim. A little bit of lye will knock it off, but that can stain too for similar reasons. After welding you can clean the area with mild abrasive and polish it back up, no real harm done, it's all skin deep.

 

[K_Ridley]

I knew an old Harley mechanic who would put the cases in a dishwasher to clean them up. He said it worked great to get them clean until one day he forgot to take them out before his wife got home from work. After that it was back to scrubbing them with degreaser.

 

[pontiac428]

If the part is polished, dishwasher is okay, but know that the phosphate in detergent will bind fast to aluminum and aluminum oxides and form a very tough insoluble mineral layer when the pH is high. You've seen it with cheap cookware. Strong ionic detergents and aluminum stick together and will ruin a presentation finish that isn't polished smooth or waxed. There are times you might want that, like to form a base for painting, so it depends on the application.

 

[Bone Head]

No dishwasher here and just as well. I'll use mineral spirits first, then acetone.