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As the second most abundant metal on the planet, it comes as no surprise that aluminum is one of the most widely used metals. This highly versatile metal boasts a range of desirable characteristics and properties. Because of its popularity and widespread use, it’s imperative to have a clear understanding of the conditions that may shorten the lifespan of the metal, particularly aluminum corrosion. Let’s take a closer look at aluminum corrosion as well as how to prevent aluminum corrosion. 

Understanding Aluminum Corrosion 

Most metals naturally want to return to their original oxidized state. This conversion is called corrosion. However, the corrosion of any metal can substantially reduce its strength and cause partial fractures, cracks, and even total failure.

In the simplest sense, aluminum corrosion is the decay of aluminum molecules into its oxides. This results in the degradation of its chemical and physical properties. The severity and degree of corrosion that happens over time are based on material and the operating environment. 

Does Aluminum Rust?

Rusting, on the other hand, is a specialized form of corrosion that only iron and steel go through. Rust is the layman’s term for iron oxide, which is when steel or iron undergoes the process of oxidation.

In other words, rust is when the iron oxidizes and starts to flake off. This flaking then exposes fresh metal underneath, which then oxidizes, flakes, and constantly repeats. However, aluminum doesn’t rust. 

How Corrosion Resistant Is Aluminum?

Most experts on corrosion agree that aluminum resists corrosion well. Even so, it’s often necessary to protect it against corrosion based on the alloy, environment, application, and use of the aluminum component. 

• 1000-Series Aluminum: Aluminum grade 1100 is pure commercial aluminum. This material boasts excellent corrosion resistance and is typically used in food processing and chemical industries. 
• 3000-Series Aluminum: Alloy 3003 falls within this series and is undoubtedly the most widely used of all aluminum alloys. This is a pure, commercial-grade aluminum material enhanced by Manganese and Copper, which represents a 20% boost in strength. 3000-Series aluminum also offers excellent corrosion resistance. 
• 5000-Series Aluminum: Another very popular aluminum alloy is the 5052 alloy, which offers the highest strength of any non-heat-treatable grade. Alloy 5052 is widely used in marine atmospheres and environments with saltwater because of its remarkable corrosion resistance. 
• 6000-Series Aluminum: As one of the most versatile heat-treatable alloys, 6061 offers the trifecta of good strength, good aesthetics, and better corrosion resistance. On the other hand, Alloy 6063 is known as a structural alloy because of its great finishing, high tensile, and high corrosion resistance properties. 

While strain-hardenable alloys of 1000, 3000, and 5000 series and age-hardenable alloys of the 6000 series offer robust corrosion resistance, copper-containing alloys of 2000 and 7000 series are not sufficiently resistant to corrosion in humid environments. Because of this, these aluminum copper-containing alloys may require special treatment to prevent corrosion.

How to Prevent Aluminum Corrosion?

Aluminum corrosion can be a very serious problem, so you should take every necessary step to prevent corrosion of aluminum. A few of the top steps and best practices include:

1. Understand the Power of Choice. The first and most important thing you can do is to choose the right alloy. As a rule of thumb, 1000, 3000, and 5000 series aluminum will provide you with the highest level of resistance. 
2. Modify Surface Properties. Modifying the surface properties by applying chemical conversion coating, cladding, powder coating, anodizing, or boehmite coatings. 
3. Offer Protection. Knowing that certain environments can expedite corrosion, you can protect it by utilizing continuous protective coatings of lacquer or paint. 
4. Consider the Medium. You can minimize the effects of galvanic corrosion, which is caused by placing two dissimilar metals — such as steel and aluminum — next to each other. 

 Do you have questions about aluminum and aluminum corrosion? Email us at ProvenProductivity@bossard.com with any questions!

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The short answer is yes, aluminum does rust, although corrosion is a better technical term for what happens to this ubiquitous metal. The following are 10 types of corrosion that can affect aluminum.

1. Uniform Corrosion appears as pits that measure one micrometer in diameter, producing a constant decrease in thickness over the entire surface of the metal. This corrosion typically appears in highly acidic or alkaline media with dissolution rates ranging from a few micrometers per hour to a few micrometers per year.
2. Pitting Corrosion puts unevenly shaped depressions on the surface of the aluminum due to contact with liquid media such as surface water, seawater, and humid air. The corrosion pits are covered with white gelatin made from alumina. 
3. Trans-Granular and Intergranular (Intercrystalline) Corrosion is microscopic, affecting metals at the granular level. This type of corrosion often reduces the mechanical properties of aluminum that leads to the destruction of components. Propagation of intergranular corrosion usually begins as pits.
4. Exfoliation Corrosion selectively affects the planes that run parallel to the direction of the rolling or extrusion. The thin sheets of metal between these planes peel off, which gives rise to the term “exfoliation.” 
5. Stress Corrosion combines a corrosive environment with mechanical stresses, such as bending. By themselves, each of these factors does not affect the aluminum. But putting them together causes problems. Creating alloys with high mechanical strength can reduce stress corrosion.
6. Filiform Corrosion affects only lacquered aluminum, making the surface look different. It is a superficial attack, measuring only a few tens of microns. It starts from coating defects like scratches, holes, or cut edges, and usually appears only after several years.
7. Waterline Corrosion, as the name implies, occurs at the part of the metal that is just below the surface of water. It happens due to the difference in aeration between the surface of the liquid and the area directly underneath it.
8. Cavitation happens when the hydrodynamic pressure is greater than the vapor pressure of a moving liquid. Gas bubbles inside the liquid, which then crash against the metal at high speed, producing rounded cavities. Because the natural oxide film is destroyed, the aluminum suffers when the film is constantly torn and reformed. This type of corrosion usually happens within a few hours or days, depending on the speed and temperature of the liquid. Externally hardening the metal can help resist this type of corrosion.
9. Erosion happens due to moving media such as a flowing liquid, which produces scratches and undulations in the aluminum that match the direction of the flow. Among the ways of reducing erosion are controlling the speed of the fluid, using corrosion inhibitors, or streamlining the shape of the aluminum to minimize turbulence.
10. Microbiological Corrosion in aluminum is caused by certain types of bacteria in an organic carbon source. These bacteria transform organic substances into carbon dioxide, organic acids, and metabolites that are released into the environment. The environment and not the bacteria corrode the aluminum. One way to prevent this corrosion is to use disinfectants that dissolve in water or other liquid.

Want more information on aluminum corrosion in fasteners or other applications? Please contact us at ProvenProductivity@bossard.com.

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