Originally Posted by
Andrew R Stewart
rosefarts- I find that you are correct, I think what I am remembering is corrosion of the non Ti part, like seat posts, in a Ti frame. In NC we removed more then a few "welded" in place from various bikes of non steel construction. We saw a lot of bikes that spent a lot of time on the coast that were hard to deal with. Andy
The “welding” of seatposts and other parts is less about galvanic action between the two metals than it is about corrosion of each metal. Aluminum, for example, can react along crystallite boundaries without being in contact with other metals. All that is needed is the salt. With aluminum and steel, it’s also not galvanic action that is the main cause of the “welding”. Both steel and aluminum react with salt and make an oxide. The oxide of both is of a lower density and larger volume which is what causes the binding of the parts together.
Titanium, as well as aluminum, have what is called a high stacking fault energy which means, essentially, the atomic crystalline structure has lots of faults that can catch when the metal slides on a surface. In threads, either material can break off bits that jam the threads. Add in a bit of corrosion of the aluminum and things go south quickly.