Aluminum vs galvanized vs stainless tubing for fence with railing?
Thick wall Aluminum can work, but you'll likely need to sand or grind it annually. Salt air and Aluminum don't really like each other, they're only cordial most of the time.

Stainless Steel is your only real option and will be vastly stronger as well as maintenance free the longest. It too can be sanded and ground back to new way down the road. Burnish it with the shiny side of aluminum foil after a renewal to deposit a fresh layer of chromium and nickel.