It is my understanding that metals are a crystal lattice of ions, held together by delocalized electrons, which move freely through the lattice (and conduct electricity, heat, etc.).
If two pieces of the same metal are touched together, why don’t they bond?
It seems to me the delocalized electrons would move from one metal to the other, and extend the bond, holding the two pieces together. If the electrons don’t move freely from one piece to the other, why would this not happen when a current is applied (through the two pieces)?
Asked by jcw in physics.stackexchange
Metals will bond on contact, and it works pretty much as you’ve described it. However, this only happens in a vacuum.
It’s called cold welding, and it’s something that needs to be designed around when building satellites.
Metals in the atmosphere will form an oxide layer, or contain other contaminants on the surface, preventing cold welding.