Sacrificial anodes are highly active metals which are attached to less active metals to attract the electrolytes that would normally corrode and weaken the less active metal. The mere presence of the anode helps draw the elements that would normally corrode the other metal away from it.
Sacrificial anodes are usually made of zinc or magnesium or are made of an alloy of magnesium and aluminum. Zinc and aluminum are used mostly in salt water applications. These anodes can be found in the forms of plating that goes over other metal, alloys or as galvanization. Sacrificial anodes are often found on hulls of ships, pipelines and off-shore platforms.