Why does rust/corrosion appear to “dribble” from the edges of metal surfaces, or from between two pieces of metal?

Question

When looking at rusty objects I’ve noticed that some rust looks like its “dribbling” down from the edges of metal surfaces where two metal parts are directly touching, like where rivets/bolts are holding metal panels in place, almost like the rust is a liquid leaking out from beneath the metal. Why does it form like that?

In: 7

Answer 1

When two different metals make contact, the less noble material oxides more easily. It’s basically what happens in s battery. This is why you will use galvanized steel. The zinc layer is less noble and oxidizes before the steel does, making the steel last longer.

Edit; my phone seems to have an issue with the word “different”