Yes, the aluminum can become weakly magnetic in the presence of an external magnetic field. But once it’s no longer influenced by that field, it no longer is. It cannot, on its own, hold a magnetic charge as it has an eneven amount of electrons. So the only way to demagnetize your CD is to do it while it is being subjected to whatever magnetic field or electromagnetic field within the guts of your player or transport. Hmm...Sounds like a tweak waiting for an inventor!
