What Is the Galvanic Series?
Different types of metals are considered more or less noble and are arranged accordingly in the galvanic series.
Platinum and gold are at the top (more noble, less reactive) while aluminium and zinc (less noble, more reactive) are near the bottom.
Yellow metals are somewhere in the middle, with iron and steel less noble than bronze and copper but more noble than aluminum and zinc.
Why Does Galvanic Corrosion Occur?
When different types of metal that are far apart on the galvanic series come in contact with each other, the corrosion potential of the more noble metal will be shifted to the less noble metal.
Luke Stone, Technical Service Engineer at Cortec® Corporation, says that in such cases, “things like copper are going to preferentially cause things like steel to corrode.
Things like steel are going to preferentially cause things like aluminum to corrode….”
He noted that metal contact points, such as fasteners with different metals, are a good “canary in the coal mine” to identify galvanic corrosion concerns.
How to Avoid Galvanic Corrosion Surprises
Galvanic corrosion can take people by surprise when they are only protecting one type of metal (eg steel) in a multi-metal system.
While they may have thought that the brass or aluminum in the system did not need corrosion protection due to higher corrosion resistance, Stone says that this can do a “severe disservice” by pushing corrosion attack down the line to the less noble metal.
The key to preventing galvanic corrosion (when it is not possible to electrically isolate dissimilar metals) is to choose a corrosion-preventative product—whether paint, VpCI® packaging or a liquid rust preventative that protects all types of metals in the system.
The comments above barely scratch the surface of galvanic corrosion, but they offer a major step forward in preventing it. Contact Cortec for more information
