What Is Anodizing?

Anodized Steel
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Anodizing is a method of increasing the corrosion resistance of a metal part by forming a layer of oxide on its surface. 

Anodizing, Explained

The process of creating this protective oxide coating is achieved electrolytically.

The metal part to be treated -- generally aluminum -- is first submerged in an electrolytic solution bath along with a cathode. When a current is passed through the acid solution hydrogen is released from the cathode and oxygen forms on the surface of an anode.

This results in a metal oxide film growing on the surface of the part being treated.

Depending on the end-use application and the anodizing process used, the oxide layer that can be grown on an aluminum part can be more than 100 times as thick as an oxide layer that would naturally on an aluminum part just exposed to oxygen. 

Because the metal part being treated forms the anode in this electrolytic circuit the process is referred to as 'anodizing'. 

Anodized aluminum and aluminum alloy parts are more corrosion and wear resistant than non-treated parts. They also protect against galling - wear caused by friction when two parts are rubbed together - of threaded components. 

This results in anodized parts having longer life spans than non-anodized parts. 

Anodizing Aluminum

While anodizing aluminum allows the metal to keep its natural appears, the pores in the protective oxide layer also to provide a better surface for the adhesion of paints and glues.

 

While various metals, including titanium, hafnium, zinc and magnesium, can be protected by applying an anodized layer, by far the process is most commonly applied to aluminum and aluminum alloys.

Different types of anodizing methods are generally characterized by the type of electrolytic solution used.

 Chromic acid (referred to as Type I) was used in the first commercial anodizing facilities in the 1920s. Nowadays, however, the most common electrolytic solutions for anodizing are produced using sulfuric acid (referred to as Type II or Type III depending on the exact process used).

Anodized aluminum parts are commonly found in aircraft and architectural components, as well as consumer goods such as appliances (refrigerators, microwaves, and barbecues), sporting goods (baseball bats, golf carts, and fishing equipment) and electronics (televisions, smart phones, and computers).