Corrosion is a natural process that affects many materials, including metals like aluminium. But does aluminium rust? This is a common question, and the answer is not as straightforward as you might think. To understand corrosion and its effects on aluminium, it is essential to learn the fundamentals of this chemical process.
In this comprehensive guide, we will explore the basics of corrosion, the different types of corrosion, and how aluminium is affected by corrosion. With this knowledge, you will be able to make better decisions surrounding the maintenance and upkeep of aluminium objects, such as cars, buildings, and other products.
What is corrosion?
Corrosion is a natural process that causes metals to deteriorate. It is a chemical reaction that occurs when two different metals or a metal and a non-metal are exposed to a suitable environment. While corrosion only affects the outside of a material, it can be very harmful, even leading to structural damage.
To prevent this, it is essential to understand the different types of corrosion and take preventative measures. Corrosion can be divided into 3 main categories:
Galvanic corrosion, Electrochemical corrosion, and Corrosion caused by a breach of integrity. The first two types are related to different metals having different electrical potentials. And the last category deals with materials having a break in their structure.
The different types of corrosion
- Galvanic corrosion: Galvanic corrosion is electrochemical corrosion that occurs when two or more metals are immersed in an electrolyte, such as water. Galvanic corrosion occurs when two metals with different electrical potentials are in electrical contact with each other. The difference in potentials causes a current to flow between the metals, resulting in corrosion. Galvanic corrosion can occur between two aluminium alloys and other metals, such as steel. It is more likely to occur when the surface of the aluminium is scratched, dented, or otherwise damaged.
- Electrochemical corrosion: Electrochemical corrosion is another type of electrochemical reaction that occurs between a metal and a non-metal. It is the chemical reaction of a metal with the ions in a solution. This can occur in freshwater, seawater, or groundwater.
- Corrosion caused by a breach of integrity: This type of corrosion happens when the structure of a material is compromised. This can happen when two aluminium alloys are attached together with an adhesive.
How aluminium corrodes
Aluminium corrodes in a similar way to iron, forming a mixture of iron and aluminium oxides that are commonly referred to as “rust”. When iron oxidises, it forms iron oxide. Iron oxide and aluminium oxide are two different compounds with different properties. While iron oxide is grey in colour and relatively soft, aluminium oxide is white, harder than iron, and more brittle.
When aluminium oxidises, it forms aluminium oxide, which is a white powder. Aluminium oxidising does not happen as easily as iron, so aluminium does not rust as quickly. However, if the aluminium is scratched or the surface has been otherwise damaged, it is much more likely that aluminium will oxidise.
The effects of corrosion on aluminium
Corrosion of aluminium, like corrosion of any other material, significantly reduces its properties. Some of the more critical defects caused by the corrosion of aluminium include:
- Loss of rigidity: The most noticeable effect of corrosion is the loss of the original strength and rigidity of the material. Corrosion significantly decreases the tensile strength of the base material. If the corrosion is not properly controlled, it can cause the material to break.
- Reduction of strength: The yield strength of a material is the point where it is no longer able to carry a load without deformation. The corrosion can reduce the tensile strength to a point where the aluminium material becomes brittle and fractures.
- Cracking: Another critical defect caused by corrosion is cracking. The cracks can appear either within the material or at the surface. Cracking can lead to partial or total breakage of the material.
Factors that can cause corrosion of aluminium
There are a number of factors that can cause the corrosion of aluminium. These include: The surface of the aluminium must be chemically clean and free of contamination.
The parts must be properly joined with no gaps that allow water to collect. The parts must be free of stress.
How to prevent corrosion of aluminium
Aluminium is a very versatile and useful material, but it must be properly maintained to prevent the onset of corrosion. Preventive maintenance can be done through several different methods.
- Keep the surface clean: The surface of the aluminium must be kept clean and free of contaminants. This will help prevent the oxidation of aluminium by blocking water from coming into contact with it.
- Use the proper materials: When joining aluminium parts together, you must use an adhesive or a sealant recommended by the manufacturer. This will guarantee the best results in terms of chemical reaction and water resistance.
- Use protective coatings: Protective coatings can be applied to aluminium to reduce the rate of corrosion. Coatings can be applied either chemically or by spraying a liquid solution on the surface.
Corrosion protection methods for aluminium
There are a few different methods used to protect aluminium from corrosion. You can select the best option for your specific needs.
- Electrolytic coating: This is a protective coating applied to the surface of aluminium with a chemical process. It is the most common method used to protect aluminium from corrosion.
- Hard coating: This is a thin layer of solid material applied to the surface of aluminium with a chemical process. Hard coatings are harder than electrolytic coatings and can provide more protection from mechanical damage.
- Anodising: Anodising is a chemical process applied to the surface of the aluminium to create a protective coating. Anodising can produce a wider range of colours than other methods.
Aluminium corrosion repair
If corrosion has occurred, it can be repaired using a combination of methods, such as a thick coating or hard coating. You can try multiple methods and select the best option.
- Electrolytic coating: This is the most common method used to repair aluminium that has been corroded. This method produces a protective coating that is similar to an electrolytic coating.
- Thick coating: Applying a thick coating will cover the existing surface. This is a more permanent solution but has the disadvantage of changing the appearance of the surface.
- Hard coating: Hard coating will cover the existing surface with a new layer of material. This provides protection from corrosion and mechanical damage.
Conclusion
Aluminium is a very useful material that has many industrial applications. However, it is prone to corrosion and must be properly maintained to prevent the onset of corrosion.
There are a few different methods used to protect aluminium from corrosion, but the best option depends on the specific situation.
