Why are zinc and magnesium used as sacrificial anodes?

Zinc and magnesium are used as sacrificial anodes because they are more chemically active than the metals they are intended to protect, such as iron or steel.12

In the context of corrosion, this process is known as cathodic protection. When a more active metal is in electrical contact with a less active metal in the presence of an electrolyte (such as water or moisture), the more active metal acts as an anode and undergoes oxidation preferentially.12

Because zinc and magnesium have a higher readiness to give up electrons, they corrode sacrificially, effectively sparing the structural metal from oxidation. This mechanism ensures that as long as the sacrificial anode remains in contact with the protected structure, the structural metal remains intact. This technique is widely employed to prevent the degradation of critical infrastructure, including ship hulls, pipelines, and water heaters.32