Sized seatpost

[Spudalumps]

I have a aluminium seatpost stuck in a aluminium frame. I will be trying to use a vice to apply some pressure although I’m just curious on how it is bonded on the microscopic level. Is it a chemical welding caused by natural corrosion or is that only between aluminium seatposts and steel/ carbon frames?

 

[gtturbo]

Slightly off topic but a tip I found from when I had a ali seatpost stuck in a ti frame. If you get one of those pipe freezing kits that plumbers use to replace sections of pipe without draining the system and then put it round the seatpost, not the frame, and freeze it. I found it caused the post to shrink just enough to get it moving and out. No damage to either the frame or post. The only damage is £15 or so for the kit, especially if it doesnt work. I'm generally a fan of the vice method but it does tend to fubar the seatpost.

 

[CassidyAce]

(I think the title of the thread contains a typo at the moment.)

Galvanic corrosion occurs between dissimilar metals when in electrical contact, e.g. when wet. It shouldn't happen between an aluminium seat post and an aluminium seat tube. If the seat post and seat tube are not pure aluminium but aluminium alloy there might be some galvanic effect, the extent depending on the alloys used and quantities, but it's likely to be small. Someone more specialised in this field might be able to give more detail but I would be surprised if there's any chemical bonding between your seat post and seat tube.