What does the term 'mechanically connected' refer to in galvanic corrosion?

In the context of galvanic corrosion, the term 'mechanically connected' refers specifically to the requirement for metals to be joined in a way that facilitates the flow of electrons between them. When two different metals are electrically connected and exposed to an electrolyte (such as water), there is a potential for galvanic corrosion to occur. This happens because differences in electrode potentials between the two metals will lead to one metal corroding faster than it would if it were isolated.

For galvanic corrosion to take place, it's essential that there is an electrical pathway, allowing the flow of electrons from the anode (the metal that will corrode) to the cathode (the metal that remains protected). This connection does not necessarily require direct physical contact through mechanical bonding or gluing; rather, the key factor is that there must be an effective electronic connection permitting electron transfer.

Thus, while physical contact is often a practical aspect in many scenarios of galvanic coupling, it is the allowance of electron flow that is fundamental to galvanic corrosion, which is why the correct understanding of 'mechanically connected' emphasizes the importance of the electrical connection rather than just the physical aspect of metal contact.