I just recently repainted an outdoor mirror frame which had started to rust out.
I used a wire brush drill attachment and painted the worst bits with a rust converter. I wiped everything down with sugar soap then used Zinsser Bullseye 123 which is a primer, undercoat and stain blocker. Top coated with semi gloss Dulux Aquanamel. A light sand in between coats and it came up looking great.
The colour I used was Dowager Grey, which I think was a Taubmans colour. The Aquanamel will dry quite quickly, but needs to have time to harden. Preferably after painting the final coat, leave in the sun for as long as possible to "bake" it. This might take a few days. Good luck. - kacharash4