Which aluminum alloys can be anodized?

 　　The following aluminum alloys are most suitable for anodizing processes:

　　5XXX series

　　6XXX series

　　7XXX series

　　The anodizing process can increase the size of the aluminum oxide layer on most aluminum alloys. However, aluminum oxide coatings may lack the required amount of protection on certain alloys. In addition, some alloys may have a layer of aluminum oxide after the anodizing process, leaving unwanted colors such as unattractive yellow, brown, or dark gray. Although there are some differences between each alloy, the following is a summary of the situations that may be encountered when anodizing aluminum alloys according to their series types:

　　1XXX series

　　This series covers pure aluminum. The aluminum in this series can be anodized. The resulting alumina layer is transparent and has a slight luster. Due to the relatively soft nature of the underlying pure aluminum, these anodized aluminum alloys are prone to damage and lack mechanical properties compared to other series of aluminum alloys.

　　2XXX series

　　This series is used to specify aluminum in copper alloys. The copper in these alloys creates a very sturdy and hard aluminum alloy. Although copper can be used to improve the mechanical properties of aluminum, unfortunately, it makes these alloys unsuitable for anodizing. When anodizing, the oxide layer of 2XXX aluminum series alloy is a yellow shadow, which is usually considered unattractive. In addition, the layer produced by anodic oxidation provides poor protection to the underlying aluminum alloy.

　　3XXX series

　　The classification of aluminum alloys with manganese alloys is included in this series. Although the anodized layer provides good protection for the manganese alloy aluminum substrate, it can produce an unwanted brown color. In addition, this brown color may vary depending on the substrate, especially in different grades. This makes it difficult to maintain similar colors on the 3XXX series aluminum components.

　　4XXX series

　　The 4XXX series is composed of aluminum alloy and silicon. The anodized 4XXX material is well protected by the aluminum oxide layer produced by the anodizing process. However, it should be noted that the 4XXX series has a dark gray color and lacks aesthetic appeal. 4XXX aluminum alloy is usually used for welding other alloys, such as 6XXX, but if these welding components are anodized, the weld metal will not match the color of the base metal.

　　5XXX series

　　This series represents aluminum alloyed with manganese. When anodizing, the oxide layer produced by the 5XXX series alloy is sturdy and transparent. They are excellent candidates for anodizing; However, there are some important considerations when conducting anodizing processes on 5XXX series alloys. For example, certain alloy 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 usually be replaced with the 4XXX series alloy for welding filler metal, resulting in a weld seam that differs in color from the rest of the anodized aluminum component.

　　6XXX series

　　The 6XXX series is designed for magnesium and silicon alloy aluminum alloys. These alloys are excellent candidates for anodizing. The oxide layer after the anodizing process is transparent and provides excellent protection. Due to its excellent mechanical properties and ease of anodizing, the 6XXX series alloys are often used in structural applications.

　　7XXX series

　　This series of alloy aluminum uses zinc as its main alloying element. It is well suited for anodizing processes. 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.