Alcoa Wear-Ever pure-aluminum cookware

Example of pure aluminum's water-corrosion resistance. The 5000-series aluminum-magnesium alloys for seawater service contrast with copper-bearing aluminum's poor saltwater performance.

Aluminum chloride isn't anywhere near as stable as magnesium chloride. It has to do with the relative stability of chlorides and oxides. Pure aluminum has wonderful atmospheric and water corrosion resistance. One of the companies founded by Alcoa was Wear-Ever, the pots and pans — that's relatively pure aluminum. You start putting copper and other things in aluminum — just like the nickel in the magnesium — and you create your own little concentration cell, anode and cathode. Copper alloys are not happy in salt water. Aluminum-magnesium alloys are actually very good in seawater, so the 5000-series aluminum alloys are good.