Dissimilar Metals & Galvanic Corrosion

Did you know? Metals can react with each other and speed up the corrosion process.

The Fastener Factory is here to help you understand dissimilar metals and the dangerous combinations that can lead to corrosion and potential project disasters.

What makes metals corrosive?

Different metals have different properties and in order to understand a metal's susceptibility to corrosion, you must understand the nobility of the metal and its galvanic scale. The noblility of a metal determines how resistant it is to corrosion. Noble metals are more miserly with their electrons, compared to basic metals. Basic metals give away electrons more easliy. How easily a metal gives up its electrons is what determines its place on the galvanic scale and the more basic they are the faster and higher chance of corrosion. In the same environment, a metal like aluminium or zinc will give up its electrons more easily than a metal like stainless steel. This ability to retain electrons makes stainless steel more resistant to corrosion.

Why do dissimilar metals react with each other?

When dissimilar metals are used together, galvanic corrosion may occur. Galvanic corrosion happens when dissimilar metals rub against one another in wet or grimy environments. A good example of this is using stainless steel screws on an aluminium sheet. In addition to being better at holding on to its own electrons (more noble), stainless steel more easily takes electrons from aluminium.

What metals should I use together?

In order to avoid galvanic corrosion, you should avoid metals on opposite ends of the galvanic scale. If there’s a large gap in the nobility of two metals, they are unlikely to be compatible. Since stainless steel and aluminium have a large gap in nobility, they’re dissimilar. That means pairing them up will have a higher chance of leading to galvanic corrosion. On the other hand, metals like copper and stainless steel are similar. That’s why stainless steel pipes and copper tubing work well together. The same goes for copper and lead or tin. They’re similar enough that they usually don’t need to be insulated from one another.

 

Environmental Effect

Corrosion between dissimilar metals can be enhanced by their environment. When dissimilar metals come into contact with electrolytes such as condensation, rainwater or other sources such as oil, dirt and airborne particles, it can produce an electrochemical reaction. That’s why galvanic corrosion is increased in moist or humid environments. Bacteria and other grime can also act as an instigator between metals.

Reduce the likelyhood of corrosion on your next job.

Understanding dissimilar metals and other corrosion causes can help you safeguard against disasters. In order to prevent galvanic corrosion, these measures can be implemented:

  • Insulate the two metals
  • Use electroplating or cathodic protection systems, or protective layers like paint, plastic or rubber
  • Keep metals away from ionic compounds such as bases, acids and salts.
  • Select metals that are simliar in nobility.