Keep your rack clean and in good working order by simply using water and soap, nothing more. All metals corrode no matter what treatment they have, so the more you keep them clean, the better they will operate and last.
Road salts are very corrosive, so you must be proactive with your rack to keep it in good condition.
NOTE: Do NOT use any lubricant as it will collect dirt and prevent the necessary friction to keep the rack arm(s) locked in place