Does Aluminum Rust?

After an aggressive young architect confronted me about the corrosive properties of aluminum at last month’s CSI Show in Los Angeles, I felt a little inept at my understanding of what happens to aluminum when it begins to breakdown. So, just like any professional, I went back to the books and sharpened my knowledge on what exactly happens when the elements start to work against aluminum.

Aluminum does not rust, however it does corrode. When aluminum corrodes the process is known as oxidation. Just like any other corrosive process, oxidation occurs when aluminum is exposed to the elements. This process occurs at different rates based on the type of finish covering the metal and the particular environment that the metal is exposed to.

When one examines rusting steel they will notice how the metal discolors (typically a “redish-orange” color) and begins to flake away. As the flakes fall away, more bare steel is exposed and begins to rust, which eventually leads to complete disintegration. Aluminum corrodes in a completely different manner.

When aluminum begins to oxidize, a white coating begins to form on the metal. This coating actually hardens and creates a protective layer over the exposed aluminum. This coating does not deteriorate and fall away like rust, but instead needs to be physically scraped off. The corrosion process is actually halted by this white coating unless someone removes it and exposes the raw aluminum below.

This natural process known as oxidation is actually mimicked and sped up when the metal is anodized in the factory. Clear or colored anodizing is simply the oxidation process on “steroids.” Anodizing is well known for its sturdiness as a final finish for aluminum products and trims, which is why many architects and builders prefer to have their aluminum anodized instead of simply painted.