Using AC on Stainless question

While switching from welding aluminum to SS, I turned the amp down to 55 but forgot and left the AC on. I noticed right away when starting the torch and switched to DC.

The thing is, I was trying to repair an already rejected airplane muffler that was very dark SS with cracks and corrosion all over.

I surprised myself by actually welding areas that I previously tried welding with a harbor freight TIG that just burned holes in it. The welds looked like a row of dog turds but I could actually fill holes over 3/8" wide in Old SS that was only .033" thick.

I guess my question is if AC would help clean the old/corroded SS as in aluminum and if it would help welding thin SS.

For fun,
I have welded mild steel with AC. I believe you don't get as quality of weld, but it will work, but not as good as it should. It'll sure pull up the mill scale.

Just for giggles, I tried some mild steel with DCEP and it balled my tip instantaneously. I was trying some very thin sheet metal. Very interesting attempt but I'd never seen a badly balled tungsten TIP before.