Does aluminum rust? It’s a valid question and one that a lot of folks think they have the answer to, but you may be surprised by what I have to tell you about aluminum and its ability to stand up to corrosion.
Aluminum is seen as a rockstar of corrosion resistance and is one of the few metals, along with stainless steel, that can hold up to exterior and coastal exposures over long periods of time. You already know that aluminum can last outside for decades, but what you want to know is does aluminum rust, right?
The short answer is, yes, aluminum does rust. It just rusts in a different way than steel and iron rust. When exposed to oxygen, it forms aluminum oxide, just like steel forms iron oxide, but the difference lies in the chemical makeup of these two oxides.
Iron oxide (rust) is a soft red colored metal that begins to expand and flake off as it is chemically transformed which exposes more of the underlying steel or iron to the air and the process continues until the metal is completely transformed to iron oxide.
Aluminum oxide is different. It is actually quite hard and serves as a protective coating around the underlying aluminum. It doesn’t flake off like iron oxide and therefore, once the outer layer of aluminum “rusts” the process stops and the aluminum is protected. Couple that with the fact that it is a grayish color very similar to aluminum, and you may never even notice your aluminum’s rust.
How to Treat Bare Aluminum
That aluminum rust can protect bare aluminum indefinitely, but what if you want to paint the aluminum? In that case, you’ll need to sand off the aluminum oxide coating and get to clean aluminum, since most coatings don’t adhere well to aluminum oxide.
Don’t plan for a paint job on any aluminum surface to last long if you haven’t sanded and cleaned it thoroughly prior to painting. Make sure to find a metal primer specifically designed for aluminum surfaces as well, since most basic primers and paints are not designed for this application.