Anodized metal is any metal that gains an oxide layer through a process called anodizing, which gives the metal new properties and unique uses. To create anodized metal, a certain metal has to be placed in an oxide solution and a cathode electrode is used to adhere the oxygen to the metal. Only certain metals can be used; all of them are nonferrous, meaning they do not contain iron. Unlike other layers that are added to metal and chip or wear, this layer is permanently affixed to the metal. After being anodized, the metal becomes harder and more resistant; it also can be used in a battery and can be dyed.
To create anodized metal, a sample of the metal has to be placed in an oxide solution. This solution, commonly referred to as an electrolyte, contains salts and oxides. A cathode electrode is then placed in the solution and, by use of electricity, the oxygen becomes excited and bonds with the nearest suitable material — the metal. The oxide layer normally adds about 0.006 of an inch (150 micrometers) or less to the metal, so most people will rarely notice the size difference.
The anodizing process can only occur with three base metals, and some metals made from those bases. The three base metals are magnesium, aluminum and titanium, all of which easily react with oxygen, making it easier for the oxide layer to form. If any of these metals are alloyed with iron, then they can no longer be turned into anodized metal, because iron does not react properly with oxygen.
There are other processes that add layers to metal, but anodized metal is typically more permanent. Most of these processes add a layer on top of the metal, which can be prone to chipping off after several months or years. The anodizing process affixes the oxygen to the inside and outside of the metal, making the layer permanent. If this layer wears, it is typically from the entire metal wearing or someone forcibly removing the layer.
When anodized metal gains its oxide coating, it is changed and given special properties. The physical properties gained are better wear, corrosion and heat resistance; a harder surface; and the metal's ability to better adhere to other surfaces. This is the same process required to make an anode, which is used in batteries and circuits, so anodized metal can be placed in these. The oxide layer changes the metal’s pore structure, so it also can accept dye in a process known as color anodizing.