Lay it out and have a go with oxualic acid (ospho) and scrub it clean.and rinse a few times.
Then get some rubber gloves and allow it to hang in a pail of Rustolium aluminum paint , and dunk the entire length a foot at a time.
Surface rust does nor weaken the chain a bit (its weak already compared to line ) so its mostly a cosmetic deal.
Re galvanising used to be easy to have done , but now there are so many rules that its frequently cheaper just to by new, should the time come.
AS always you get what you pay for , a good brand of US chain , NOT Chinese recast scrap iron , if you dont want to sell your boat to the insurance guys.