DerbyDad03 wrote:

A question entered my mind as I was sprucing up my utility trailer. I
removed the strap hinges and closure brackets, etc. so I could clean
off the rust, re-paint, etc.

There are lots of mating surfaces where rust was present on both
surfaces, such as the back of the hinge plates and the trailer itself.
I started wondering what would happen if I used a wire wheel to get
the rust off one surface, but not the other. (That's not my plan, just
my thoughts as I was working.)

All other things being equal (weather, moisture, etc) as they would
be, does the mere presence of rust on one surface make the other
surface more apt to rust?

The surfaces would have to be clean and not exposed to air or water in
order not to rust, right? A rusty metal coating would probably
encapsulate small amounts of residual rust and so exclude air and
water. Otherwise, rust will continue. Don't ask for sources.......just
my logic at work ) Now, if all rust is removed but differing metals
are in contact then I think you get electrolysis. Never seen that, but
it eats up some metals.