Why is Aluminum Anodized?

by | Oct 12, 2016 | Aluminium

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When you buy high quality rectangular aluminum tubing, it may be anodized. Most people understand that anodizing is a process of placing a finish on metals but it is not like painting or powder coating. The process of anodizing is a special method designed to protect and beautify. Here is more about anodizing to give you a better idea of what happens.

Why Anodize?

Anodizing is a finishing method which provides natural protection to aluminum. It places a layer of aluminum oxide on the outer surface and this increases resistance to wear and also makes it more resistant to corrosion. In addition, anodizing provides a degree of lubrication and allows the metal to dissipate heat easier. Plus, it increases adhesion properties and can greatly improve the appearance.


The process of anodizing involves passivation. This is how a layer of aluminum oxide is placed on the outer surface. Have you ever noticed the green colored patina which forms on copper over time? This is a natural passivation process creating copper oxide and it protects the copper from further corrosion. Items like rectangular aluminum tubing utilize passivation created by a special finishing process.

To passivate, aluminum is placed in liquid electrolyte and then an electric current is passed into the liquid. This forms an aluminum oxide layer on the outer surface. By controlling the amount of current and time in the electrolyte, the desired effects can be achieved.

Aluminum oxide is a very tough and durable material. In fact, it has a level of hardness which rivals natural diamonds. This is why it offers such excellent protection and is often used to protect non ferrous type metals.


Did you know the process of anodizing is often used to give things like rectangular aluminum tubing different colors? Anodizing changes the chemical structure of the metal and when aluminum oxide is mixed with various dies, they can easily adhere. In fact, it is a much more efficient process than simply painting, because the color actually soaks into the metal. This makes it almost impossible to scratch off and it does not wear away easily.

Standard and Type III Anodizing

There are two basic types of anodizing methods. Type III is also called hard dipped anodizing and provides a more dense coating than Type II (conventional). Type III produces a very durable surface which is much more resistant to electrical conductivity than conventional anodizing. Welding is often done before anodizing because the coating will need to be removed if welding is required afterward.

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