What Does Iron Do to Aluminum Fencing?

Galvanic Corrosion

• Galvanic corrosion occurs when metals with different corrosion potentials are brought into contact in the presence of an electrolytic solution. Outdoor fencing made from iron and aluminum tends to corrode when it is exposed to moisture from precipitation, sprinklers or atmospheric water vapor. The difference in electrical potential between the two metals allows electrons to flow from one metal to the other, causing one to corrode when the metals are wet. The greater the difference in corrosive potential, the more quickly the more active metal, known as the anode, corrodes. Aluminum fencing with iron fittings slowly corrodes, since these metals have relatively similar corrosion potentials.

Protective Coatings

• Covering the iron fittings of your aluminum fencing with a protective coating prevents galvanic corrosion. Any coating or covering that physically and electrically separates the two metals is effective. Non-metallic paint is an effective method for preventing galvanic corrosion in most cases. Consider using a rubberized or plastic coating if you expect the aluminum and iron fittings of your fence to rub together, since a damaged paint coating does not protect fencing and can increase the rate of corrosion under certain circumstances.

Protective Fixtures

• If painting or coating the fence is not an option, install cathodic protection to prevent damage to the iron and aluminum parts of your fence. Attaching metal strips with a higher corrosive potential than the iron and aluminum fittings of the fence causes the metal strips to corrode instead of your fence. Zinc roofing strips have a higher corrosive potential than iron or aluminum, and protects the fence from damage.

Considerations

• The relative area of the iron and aluminum parts of your fencing affects how much the metals corrode. If the aluminum parts have a significantly larger area than the iron parts, the amount and rate of corrosion increases. The environment around the fence also affects the rate of galvanic corrosion. If you live in a wet climate, precipitation and moisture in the air increases the rate of corrosion. If you live near the ocean or your fence is near a road that is salted during the winter, exposure to saltwater also increases the rate of galvanic corrosion.