fingersix - electrolysis will occur in a cooling system of dissimilar metals. Remember the definition of a galvanic cell is two dissimilar metals in the presence of a liquid.
Its been a long time since I looked at a Periodic Table to see which metal is on top, but one item for which we are often asked (and don't have) is the various spacers which Ford used under their carburetors. These had coolant passing through them, were made of aluminum, and most have been destroyed by the electrolysis bugs. Same thing is true of the water-jacketed aluminum carburetors used by Chrysler and DeSoto in the early 1950's. The throttle bodies on the vast majority of these look like a window screen!
Antifreeze has inhibitors. Inhibitors grow old and don't work as well (same, unfortunately is true of humans). In the case of antifreeze, changing annually will restore the protection.
Jon.
