Clients sometimes ask us why we insist on changing gutter brackets when we replace their eavestrough systems. Our reasoning is sometimes because the profiles are different, while at other times there is a conflict of metals. The latter case can cause galvanic corrosion weakening the materials, and potentially the lifespan of the system itself.
Galvanic Corrosion Where and What Is That?
Galvanic corrosion occurs when two different metals with dissimilar electrochemical properties touch each other. However, this reaction is only possible in the presence of a facilitator such as a corrosive environment, or an electrolytic liquid able to complete the reaction.
When the right circumstances are present, the two metals begin a chemical reaction whereby the stronger one corrodes the other. The winner in the dual is the one with the greater potential. If you are thinking this sounds like an electrochemical battery, you are on to something.
The Electrochemical Reaction Behind Galvanic Corrosion
All metal types have different electrical potentials, which relate to their positively charged particles. The metal with the stronger pull appropriates charged particles from the weaker one. This causes the latter to corrode more rapidly, while the former metal becomes stronger. This galvanic corrosion as we describe it has the following characteristics:
- It is localized around the area where contact with the other metal takes place.
- This decay may present as craters, depressions and holes in the weaker metal.
- It has a uniform overall character, although the rest of the surface is unchanged.
How Aluminum Corrodes in The Presence of a Different Metal
The actual impact will vary depending on the structure of the other metal:
- The effect is slight when pairing with galvanized steel, and may be limited to the galvanized fasteners only.
- Screws, nuts, bolts from ordinary steel may rust, stain the aluminum and spoil the finish.
- The reaction between aluminum and stainless steel, including screws and brackets is minimal.
Therefore the combination to look out for is mixing aluminum and mild steel. We typically use aluminum hangers with aluminum gutters, and steel hangers with steel gutters, unless the design of the steel hanger is inferior to the aluminum option in our opinion.
If an architectural design forces us to use aluminum in close proximity with mild steel, we insulate the latter with paint, or another neutral coating. The best way to control any galvanic corrosion that still does occur is to keep the surfaces clean. This information comes to you with compliments of Valiant Exteriors in Calgary.
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Image: Galvanic Corrosion Around Bolt in Aluminum Plate (Government of Canada)