I know someone who 'dissolved' a stuck stem by sawing off the top so you can get the fork out and then soaking the enitre fork in Super strength Draino - apparently it will Eat the Aluminium but will not touch the paint or steel.
not really relevant to this thread, but anyway, a mate had a seized seat post in his pompino, he'd tried everything and eventually cut a slit down it and began to hammer a screwdriver down the tube to free it, except the screwdriver went straight through the seat tube, making an inch slit.
In exasperation, he bought a new frame and gave me the old one.
I got the post out by plugging all the holes (cork in end of seat tube in BB, allen bolts in the bottle bosses) and filling the tube with strong caustic soda solution. about six times. in the end the seatpost had been attacked enough to just pull out easily. NOT a job to be attempted inside under any circumstances, it's a real witches cauldron of harmful smoke.
so yes, caustic soda (sold for unblocking drains) attacks ally and can free the bond between steel and aluminium, leaving the steel intact. don't expect to save the aluminium part though.
not really relevant to this thread, but anyway, a mate had a seized seat post in his pompino, he'd tried everything and eventually cut a slit down it and began to hammer a screwdriver down the tube to free it, except the screwdriver went straight through the seat tube, making an inch slit.
In exasperation, he bought a new frame and gave me the old one.
I got the post out by plugging all the holes (cork in end of seat tube in BB, allen bolts in the bottle bosses) and filling the tube with strong caustic soda solution. about six times. in the end the seatpost had been attacked enough to just pull out easily. NOT a job to be attempted inside under any circumstances, it's a real witches cauldron of harmful smoke.
so yes, caustic soda (sold for unblocking drains) attacks ally and can free the bond between steel and aluminium, leaving the steel intact. don't expect to save the aluminium part though.