Aluminum has a corrosion-resistant and wear-resistant oxide layer. Therefore, pure aluminum is corrosion resistant. However, aluminum with other alloying elements can be corroded unless a thick layer of aluminum oxide can be made to protect it. To prevent corrosion and wear of aluminum alloys, a technique was developed to create this thick protective aluminum oxide layer. One way to form this oxide layer is through a process called it.

Anodizing, the electrochemical oxidation of metals or alloys. Aluminum and its alloys form an oxide film on the aluminum product (anode) under the corresponding electrolyte and specific process conditions due to the action of the applied current. Unless otherwise specified, it usually refers to sulfuric acid.

In order to overcome defects such as surface hardness and wear resistance of aluminum alloys, expand the scope of application, and prolong service life, surface treatment technology has become an indispensable part of the use of aluminum alloys, and anodizing technology is the most widely used and most successful .

What is anodizing?

Anodizing is a process used to promote the formation of aluminum oxide layers on substrates faster or thicker than normal under natural conditions. While anodizing does work on several other substrates, aluminum responds most effectively to anodizing. It first became popular in the 1920s as a way to prevent corrosion of aluminum parts. Since then, it has been used not only for corrosion resistance, but also for wear-resistant and stained aluminum. Since alumina is not as conductive as aluminum, it can also be used for electrical insulation purposes. It has many benefits, but the caveat is that it will not increase the strength of the aluminum beneath the anodized surface.

How is anodizing performed?

Anodizing aluminum is considered an electrochemical process. It involves dipping aluminum alloys into tanks filled with electrolytes. This solution contains an acid; the type of acid depends on the application. Once submerged, current flows through the aluminum. Anodized aluminum was used as the anode. The cathode is also placed in the tank; usually aluminum or lead. The electric current causes the aluminum to oxidize. The anodizing process leaves a thicker layer of aluminum oxide than natural oxidation.

What is anodizing for?

Anodizing is most commonly used to improve the corrosion resistance of certain types of aluminum alloys. Aluminum alloys subject to marine environments often benefit from anodizing. Ship hulls, dock components and oil rig structures are common examples of these.

Anodizing is also used for wear control. Unoxidized aluminum is a relatively soft material compared to steel or titanium. Aluminum oxide, on the other hand, is an extremely hard material. In fact, aluminum oxide is often used in sandpaper due to its hardness. When the anodizing process forms an aluminum oxide layer on the outside of the aluminum alloy, since aluminum oxide is a hard material, its wear resistance is greatly improved. Anodizing for wear-resistant applications includes aluminum parts that are subject to constant motion and contact with other materials.

Staining is another popular application for anodized aluminum. The aluminum oxide layer formed on aluminum alloys during anodizing is porous. This allows some of the dye to be absorbed by the oxide layer. Aluminum alloys that could not be dyed before can now be made in a variety of colors. Anodized aluminum stain applications include artwork and aluminum signage.

Which metals can be anodized?

Aluminum is the most common anodized material. However, there are several other types of materials that can be anodized. Magnesium can be anodized, but its applications are very limited. Titanium is probably the second most common material, but is still far less popular than aluminum. Some materials should not be anodized at all. Carbon steel will only corrode if it is anodized.