I wonder how the entire bottom is so messed up, but the rest of completely spotless. It's like the bottom was removed, soaked in water, and then put the transformer and everything back.
I tried cleaning it with some drain cleaner, but I'm guessing it was too dilute (only 1-5%). Here's what I got after an hour:
I'll get some pure sodium hydroxide and try again.
Hello, maybe it's a silly question, but that piece seem die-casted, are you sure
it's aluminium alloy and not zinc alloy (some zamak) ?
If so probably the NaOH stripping procedure will not be that effective.
Zama will have a density similar to steel, while Al will have less than half.
If it's Al, if you have access to nitric acid (not easy but maybe you can)
the NaOH+distilled water+HNO3 procedure is very effective in restoring
aluminium parts. Some Al alloys work better, some become dark
after NaOH. The NaOH becomes hot during the process and after
a while starts eating fast, careful with threads.
Fabio.