- 27 July 2024
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Despite its enhanced anti-corrosion properties, aluminum can also rust. Depending on external conditions, environmental parameters and related factors, aluminum products can oxidize over time. However, corrosion processes do not occur as quickly as with steel and its alloys. They can also be prevented or significantly slowed down by taking advantage of certain properties of aluminum alloys.
The metal's resistance to external influences is determined by the thickness of the oxide layer on its surface. The main property and difference of aluminum alloys is their ability to regenerate and almost completely restore their original properties. So, does aluminum rust? Aluminum can enter into an active chemical reaction with oxygen only at high temperatures. Under normal conditions, the oxide layer protects the surface and prevents the metal particles from reacting with the surrounding oxygen molecules. So whether aluminum rusts depends most on external conditions.
At temperatures up to 200C, aluminum actively gives off heat to the environment, and at temperatures above this value it begins to react with sulfur, forming sulfides. In turn, at 2000C it forms nitrides and carbides. These properties are used in industry and manufacturing to obtain the necessary substances, alloys and oxidation products. Corrosion of aluminum is also theoretically possible when in contact with water. However, aluminum can only react with water in the absence of an oxide layer. This is practically impossible under natural and everyday conditions. Therefore, an aluminum product very rarely rusts when exposed to water.
When interacting with bases, sodium derivatives are formed, and when interacting with acids, oxides and salts are released. Any type of acid can destroy the oxide layer and then the surface of aluminum.
Aluminum alloys can be destroyed by the external environment, chemical reagents and temperature. In some cases, electric current can become a catalyst for the process. The ability to behave passively in certain aggressive environments is the main criterion for the metal's resistance to corrosion. The protection of aluminum against rust depends on the following parameters:
- The concentration of the aggressive reagent.
- The ambient temperature.
- The presence of process catalysts.
- The quality of the alloy.
- The condition of the surface oxide layer.
Alloy purity is a critical factor. If aluminum has many foreign impurities, air pockets and casting defects, then aluminum corrosion is more intense.
When interacting with oxygen, aluminum enters a passive state. At the first contact with air, the surface is covered with an oxide layer several micrometers thick. Typically, this value is 0.01-0.02 microns. Sulfur compounds contained in industrial exhaust have no effect on the alloy. However, as soon as alkali appears in the environment, the decomposition process is activated. Even room temperature is sufficient for this. An example is the corrosion of some of the components located in the engine compartment.
When the protection of aluminum against rust has failed, intensive measures must be taken to remove the corrosion. Fortunately, corroded aluminum can be easily cleaned. The most popular method is mechanical, which can restore the original properties of the surface. However, the use of chemicals can also have the opposite effect, leaving a "chemical residue." Corroded aluminum can also be cleaned mechanically.
The simplest method is to sandblast the part with a fine mixture of electrocorundum. This method does not destroy the surface layer and effectively removes the first corrosion foci. One chemical method is cleaning in a 40-50% potassium hydrogen fluoride solution. This cleaning method involves alternately immersing the product in a cold and hot solution. Alloys can also be cleaned with dehydrated alkali. However, this method can only be used in laboratory conditions, as it requires careful work with reagents.
