"Paul Hovnanian P.E." wrote
Does the brass/galvanized iron interface cause this kind of corrosion?

Probably contributes to it, brass and zinc/galvanized-steel being at
opposite ends of the galvanic scale. Maybe a stainless steel chain would
fare better. Taking the brass out of direct contact with with the steel
would reduce but probably not totally eliminate galvanic current. Painting
the brass might help. Simplest thing might be to pull it up every 2-3 years
for maintenance.