Although most grades of aluminum have sufficient appearance and corrosion resistance in many cases, these properties sometimes need to be further improved. This can be achieved through a process called anodizing. Anodizing is a metal coating process, which can increase the alumina content on the surface of aluminum substrate, so as to potentially improve its corrosion resistance and change its appearance. Although many different aluminum alloys and grades can be anodized, some are more suitable for this process than others.
The following aluminium alloys are best suited to the anodising process:
The anodising process can increase the size of the aluminium oxide layer on most aluminium alloys. However, the coating of aluminium oxide may lack the desired amount of protection on some alloys. Furthermore, some alloys may have a layer of aluminium oxide after the anodisation process that leaves an undesirable colour, such as an unattractive yellow, brown, or dark grey. While there are some variations from each alloy to alloy, here is a summary of what one will likely encounter when anodising an aluminium alloy by their series type:
This series includes pure aluminum. This series of aluminum can be anodized. The resulting alumina layer is transparent and a little shiny. Because the pure aluminum in the bottom layer is relatively soft, these anodized aluminum are easy to be damaged, and their mechanical properties are poor compared with other series of aluminum alloys.
This series is used to represent copper aluminum alloy. The copper in these alloys forms a very hard aluminum alloy. Although copper helps to improve the mechanical properties of aluminum, unfortunately, it makes these alloys unsuitable for anodizing. When anodized, 2XXX aluminum series alloys have an oxide layer with a yellow shadow, which is usually not considered attractive. In addition, the layer produced by anodizing provides poor protection for the underlying aluminum alloy.
Aluminum alloys containing manganese belong to this series. Although the anodized layer provides good protection for the manganese alloy aluminum substrate, it creates an unpopular brown. In addition, this Brown will vary from substrate to substrate, especially in different grades. This makes it difficult for 3xxx series aluminum components to maintain similar colors.
Manganese containing aluminum alloy belongs to this series. Although the anodized layer provides good protection for the manganese alloy aluminum substrate, it creates an unpopular brown. In addition, this kind of Brown will vary according to different substrates, especially in different grades. This makes it difficult for 3xxx series aluminum components to maintain similar colors.
This series specifies an aluminum alloy with manganese. When anodized, 5xxx series alloys have a strong and clear oxide layer. They are excellent candidates for anodizing; However, there are some important considerations when anodizing 5xxx series alloys. For example, some alloying elements, such as manganese and silicon, need to be kept within a range; In addition, the anodizing process used is also important. These alloys can usually replace the welding filler metal with 4xxx series alloys, so that the resulting weld is not different from the color of other anodized aluminum components.
6xxx series is made for aluminum alloy containing magnesium and silicon. These alloys are excellent candidates for anodizing. The oxide layer follows the anodic oxidation process, is transparent and provides good protection. Because 6xxx series alloys have good mechanical properties and are easy to anodize, they are often used in structural applications.
Zinc is the main alloy element in this series of aluminum alloys. It can well adapt to the anodic oxidation process. The subsequent oxide layer is clear and provides great protection. If the zinc content is too high, the oxide layer produced by anodizing will turn brown.