Prompted by the lack of a definitive response, I did a little web
research. A wide variety of industries (e.g., cookware and window frame
makers) routinely recommend cleaning aluminum with steel wool. Notably,
however, the FAA seems to prohibit it on aircraft. One newsgroup poster
(an EI, which would be a bad environment for corrosion) said he had
direct -- bad -- experience, and would never use steel wool on aluminum
again. So it looks to me like the jury is still out. Maybe it's ok if
you live in an environment that's pretty benign with respect to
corrosion, but a bad idea if you live close to the ocean. I don't claim
to know, and I've never felt the need to clean outside aluminum, so it's
just curiosity to me.

Roy Lewallen, W7EL