Guide To The Types of Aluminum Corrosion Process

Aluminum is the 2nd most abundant metals we obtain from the earth. Moreover, it has several excellent features. This makes it ideal for metalworking. There is a variety of fabrication processes that we practice on aluminum. However, there are a few conditions that decrease the lifespan of metals. Aluminum corrosion decreases its functional strength by causing structural damage. The metal may develop cracks and partial fractures. It may eventually result in complete material failure. The following guide will help you grasp the types of corrosion affecting aluminum.

 

What Is Aluminum Corrosion Process?

It refers to the slow degradation of aluminum molecules into oxides. This changes its physical and chemical features. Aluminum is both naturally reactive and passive. It first reacts with oxygen in the environment to form an oxide. The resultant oxide layer is a protective covering.

Additionally, it does not flake off easily. The corrosion process is slow, unlike deliberate ones such as laser etching. It can take place over months or years. Understanding its different variations is key. It may help you in reducing or preventing their occurrence.

 

What Kind of Processes For Aluminum Parts Finishing?

• Atmospheric

It is the most common type of aluminum corrosion process. It occurs due to exposure to natural elements. Three subcategories exist depending on the level of moisture. These are wet, dry, and damp. The level of moisture varies depending on the environment. Additionally, temperature, wind direction, and changes in precipitation may increase it.

The concentration and variety of pollutants in the airplay a notable role. Atmospheric corrosion increases if the design does not allow for moisture drainage. The creation of pockets for condensation rain is a harmful design flaw.

• Galvanic

We also call it dissimilar metal corrosion. It occurs when you connect aluminum to noble metal. The connection can either be physical or through an electrolyte. A noble metal is anything lower than aluminum in the reactivity series.

You can easily form a galvanic cell by placing aluminum and brass close to each other in brine. The aluminum easily corrodes as it forms the anode. A classic case is in boats that have brass fittings close to aluminum fittings. Galvanic corrosion is faster than atmospheric corrosion.

• Pitting

It is a type of corrosion that has small holes on the metal’s surface. Luckily, these holes do not affect the material’s strength. However, it presents an aesthetic issue. Eventually, it may contribute to material failure. It generally occurs in areas with salt in the atmosphere. The presence of chloride ions is a key factor. This may be worse in the presence of acidic and alkaline salts. Pitting corrosion occurs if the salt’s potential is lower than the alloy’s potential.

• Crevice

As one of the aluminum corrosion process. Unintentional design flaws and overlapping material contribute to crevice formation. These pockets may collect salty water and lead to crevice corrosion. Even minute gaps between bolts and structures are enough to initiate this corrosion. With time, the aluminum dissolves and precipitates in the brine. The ionic aluminum absorbs oxygen and hydroxide ions forming the aluminum hydroxide. The reduction of oxygen makes the crevice acidic. Additionally, chloride ions present to accelerate the corrosion.

• Intergranular

With aluminum, the grain boundary differs electrochemically from its alloy microstructure. This results in an electrochemical potential forming between the two. Therefore, an exchange of electrons occurs. There are different Intergranular corrosion that occurs on the basis of the metallic structure. It may also result from thermochemical treatments. Additionally, it varies depending on its position on the aluminum alloy series. For instance, the 6xxx series is less prone to intergranular corrosion.

• Exfoliation

It is a special form of intergranular corrosion that takes place in aluminum alloys, Which is common in those with marked directional structures. It is especially evident in products that we form using cold or hot rolling processes, and it occurs along with the microstructure of elongated grain boundaries. The term exfoliation arises from the fact that the corrosion product appears voluminous. This gives the illusion of elevation from the material surface. The corrosion expands both the upwards and sideways. This contributes to pressure buildup in the product.

Eventually, a wedging action takes place starting from the surface. It then moves to the rest of the product. Ultimately, the material weakens and severe delamination occurs. The surface may have pitting, flaking, and blistering.

• General Corrosion

We can also call it a uniform aluminum corrosion process. It occurs uniformly on an aluminum’s surface. It results from the constant exposure to the highly alkaline or acidic medium. Additionally, it may arise from exposure to a high electrochemical potential. A classic example is the rusting of aluminum in an acidic solution. The high or low PH distorts the stable oxide layer on the aluminum surface. This exposes them to underlying reactive metal. The materials’ thickness gradually decreases. It eventually dissolves completely.

Understanding the different types of corrosion is helpful in their management. If you have any further inquiries, contact us at Creatingway.

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