all strong bases (alkalis) will attack aluminium.
its pretty good at dissolving tissue and fat too if you've seen fight club you may remember the scene where brad pitt gives ed norton a chemical burn on his hand when making the soap. the powder he used was lye which reacts with the moisture on his skin to form sodium hydroxide or caustic soda.
the fumes can cause pulmonary edema . nasty stuff but really useful!
Unfortunately this is the only "before" picture. it's the one from the ebay listing. you cant tell from the picture what a heap it was. you also can't tell how stuck the seatpost was!