sacrificial metal

In electrochemistry, a more reactive metal used to protect a less reactive metal from corrosion. When the two metals are in close contact, the more reactive will always react first. For example, zinc is used as a coating to protect steel (galvanization), chromium electroplating is used for the protection of steel and other alloys, and iron may be connected to magnesium or aluminium to prevent rusting.

This protection is known as sacrificial protection or cathodic protection. A metal such as iron oxidizes because its atoms act as anodes (positive electrodes) on contact with air or water, but if a more reactive metal is attached the iron atoms become cathodes (negative electrodes) and the more reactive metal corrodes.