Everyone talks about using d/a sanders on rust. D/A sanders should be used for feathering broken paint edges, key marks, rock chips,etc.It can be used for stripping paint although this process takes time but less messy than chemical. If the metal is pitted it will need to be cleaned completely. Depending on how badly the metal is pitted will determine if it should be sandblasted or if it can be cleaned with a 3M #07468
Clean-N- strip disc. All of this should be followed by some type of good quality self etching primer or a sealer, this depends on who you are talking to. Everyone has their preference.