I also read on this forum that Aluminum Sulphate (Al2(SO4)3) will dissolve the ferrous metals and leave the aluminum in tact. You can pick it up at the depot or other hardware/garden stores. Its used to change the pH of your soil so your hydrangea turn blue. I found this somewhere else, not sure if its true (i hate chemisty) but it looks good:
"At first glance, you might think that nothing will happen: ferrous and ferric sulfates are both soluble in water, and aluminum is above iron in the activity series, so we cannon get a precipitation or a single replacement reaction.
However, aluminum sulfate is actually an acidic compound. It will hydrolyze in aqueous solution (this equation only occurs to a small degree - not all of the Al3+ ions will react, and soluble complex ions with hydroxide ligands might be formed instead of solid aluminum hydroxide, but the idea is the same):
Al2(SO4)3 + 6H2O <----> 2Al(OH)3 + 3HSO4- + 3H+
These hydrogen ions are below iron in the activity series, and so iron will be oxidized in acidic solutions, usually forming Fe2+ (and H2 gas as the other product).
Thus, a plausible reaction would be:
2Al3+(aq) + 6H2O(l) + 3Fe(s) -----> 3Fe2+(aq) + 2Al(OH)3(s) + 3H2(g)"