Galvanic Corrosion - You need to know this!

Galvanic corrosion may also be referred to as bimetallic corrosion and it is a reaction between two dissimilar metals.

Metals have different electrical properties depending on their composition and when two different metals come into contact with each other, the results can be catastrophic.

A disposable alkaline battery gets it's energy from the internal reaction between the zinc metal and manganese dioxide.   The zinc material is called the anode and the manganese is known as the cathode.   There is a reaction between these two materials and the reaction can be fueled by adding a substance such as salty water to the process.  As the reaction takes place, the electrons leave the zinc anode and it eventually deteriorates until the cell dies.

The same type of reaction happens with fasteners of dissimilar metals and the composition of your materials should always be considered when choosing a fastening product.

You've just ordered an aluminum pool fence and decide you want to use only the best stainless steel hardware to install the brackets.   The connection between the stainless fasteners and aluminum material will cause a galvanic reaction.  This reaction combined with a wet environment and pool chemicals will disintegrate the contact points of the aluminum structure within a few years.  This is the same reason they warn against mixing different types of fittings in a plumbing application.  You shouldn't see a copper to cast iron connection without some type of electrically isolated (dielectric) fitting.

You may have noticed applications where a steel screw or rivet was used to attach an aluminum soffit panel or rain gutter and the hole where the fastener was installed has corroded away.  Aluminum engine heads and intake manifolds corrode where they come into contact with steel bolts or spark plug threads.  The Statue of Liberty underwent it's renovation in the 1980's because the copper exterior had come into contact with the iron structure and caused it to corrode.

To prevent this reaction and stop corrosion, fasteners are often coated or electroplated.  You can also use isolating washers to prevent the two materials from coming into contact with each other.  Whatever the application, make sure the fasteners you're using are right for the job and will not cause more harm than good.

If you have questions about fastener materials and platings we're always welcome to answer them.