While you're at it, sand all the other areas you treated for rust to smooth them out and prepare them for painting. Any spots you've sanded down to the bare metal must be primed before you paint ...
Let the solution soak the fence for an hour and then rinse the metal with some soapy water. From here, you can take your cleaning a step further by painting your fence with a protective rust ...
So if there's aluminum, magnesium, or a pot metal on the car ... chemical dipping is the most thorough way to remove all paint and rust from a car body. It gets to places that physical medias ...