Crown molding that is made of metal of any kind, for example, steel or aluminum, can indeed rust, if not properly taken care of. One way to prevent that from happening is to use protective paints that prevent rust. This type of paint comes in several colors, and you can just paint it on to protect the metal. If you want crown molding that doesn’t rust, you need to get vinyl or wooden molding.
While each of the kinds of molding has its advantages and disadvantages, metal crown molding is one of the better types, since it can’t be damaged by insects or rot. The best way to prevent the rusting of crown molding is to only install it in areas where there is not enough moisture to damage it.