Although most grades of aluminum have sufficient appearance and corrosion resistance in many cases, it is sometimes necessary to further improve these properties. This can be achieved by a process called oxidation. Anodizing is a metal coating process, which can increase the amount of aluminum oxide on the surface of aluminum substrate, thereby potentially improving its corrosion resistance and changing its appearance. Although many different aluminum alloys and grades can be anodized, some are more suitable for this process than other aluminum alloys.
The following aluminum alloys are most suitable for anodizing process:
5xxx series
6xxx series
7xxx series
The anodizing process can increase the size of the aluminum oxide layer on most aluminum alloys. However, the coating of alumina may lack the required amount of protection on some alloys. In addition, some alloys may have a layer of aluminum oxide after the anodizing process, leaving undesirable colors, such as unattractive yellow, brown or dark gray. Although there are some changes between each alloy, the following is a summary of the problems that may be encountered when anodizing aluminum alloys by series type:
1xxx series
This series covers pure aluminum. Aluminum in this series can be anodized. The resulting alumina layer is transparent and somewhat glossy. Because the bottom pure aluminum is relatively soft, compared with other series of aluminum alloys, these anodized aluminum is easily damaged and lacks mechanical properties.
2XXX series
This series is used to specify aluminum alloyed with copper. The copper in these alloys produces a very strong and hard aluminum alloy. Although copper is useful for improving the mechanical properties of aluminum, unfortunately, it makes these alloys unsuitable for anodizing. During anodic oxidation, the oxide layer of 2XXX aluminum series alloy is yellow shadow, which is generally considered unattractive. In addition, the protective effect of the anodized layer on the underlying aluminum alloy is poor.
3xxx series
Aluminum alloyed with manganese is divided into this series. Although the anodized layer provides good protection for the manganese alloy aluminum substrate, it will produce a bad brown color. In addition, this brown color may vary from substrate to substrate, especially from grade to grade. This makes it difficult to maintain similar colors in 3xxx series aluminum components.
4xxx series
4xxx series is composed of silicon alloy and aluminum. The anodized 4xxx material is well protected by the aluminum oxide layer produced by the anodizing process. However, it is important to note that the 4xxx series has a dark grey that lacks aesthetic appeal. 4xxx aluminum alloy is usually used for welding other alloys, such as 6xxx. However, if these welding components are anodized, the color of the welding metal will not match that of the base metal.
5xxx series
This series specifies an aluminum alloy with manganese. During anodic oxidation, 5xxx series alloy has a solid and clear oxide layer. They are excellent candidates for anodic oxidation; However, there are some important considerations when anodizing on 5xxx series alloys. For example, some alloying elements, such as manganese and silicon, need to be kept within a certain range; In addition, the anodizing process used is also important. These alloys can generally be replaced by 4xxx series alloys for welding filler metal, so that the resulting weld is not different in color from the rest of the anodized aluminum component.
6xxx series
6xxx series is made for magnesium and silicon alloy aluminum. These alloys are excellent candidates for anodic oxidation. The oxide layer after the anodizing process is transparent and provides excellent protection. 6xxx series alloys are often used in structural applications because of their excellent mechanical properties and easy anodization.
7xxx series
This series of alloy aluminum uses zinc as its main alloy element. It completes the anodic oxidation process well. The subsequent oxide layer is transparent and provides good protection. If the zinc content is too high, the oxide layer produced by anodic oxidation will turn brown.
