technical article from Blue Sea Systems
Corroded connections are the main cause of high resistance connections that cause equipment to quit working or to work poorly. Frequently high resistance connections are the result of corrosion on the surface of unplated brass and copper conductors. Of the common plating materials used in electrical applications Nickel (Ni), Gold (Au), Tin (Sn) and Silver (Ag), tin is the best choice for marine electrical applications.
Although tin does corrode (oxidize), the tin oxide layer is a thin brittle layer that is very ductile. When two tin plated surfaces are mated under pressure the brittle surface layer of tin oxide will crack and displace allowing the lower pure tin layers to cold weld, forming An airtight bond that inhibits further oxidation in the connection.
Tin is, interestingly, not a particularly good conductor, but since the thickness of the plating is usually only about .0005", the distance the current travels is very short and therefore not high in resistance.
Original article from Blue Sea Systems