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Due to its chemical composition, aluminum alloys are often anodized. Anodizing is an electrochemical process that creates a protective coating on the surface of a piece of metal, typically aluminum. The anodized aluminum finish provides corrosion-resistance and allows for improved durability from the protective anodized aluminum.
Anodization produces a micro-thin aluminum oxide coating that is fully integrated with the base aluminum metal. The aluminum oxide layer is relatively clear and colorless, but it has a highly porous structure that can be dyed and then coated to produce a colorful metallic gloss.
Not all aluminum alloys can be anodized successfully. Different aluminum alloys contain different types and amounts of alloying metals, which produce coatings of different properties, some of which are less desirable.
According to the Aluminum Anodizers Council (AAC), the only aluminum alloys suitable for architectural anodizing applications fall in the 5xxx and 6xxx series. For example, alloys 5005, 5657, 6063, and 6463, are labeled “Anodizing Quality (AQ).” Not all alloys within the 5xxx and 6xxx series meet the AQ qualification, though they can still be anodized satisfactorily. For example, alloy 6061 is not considered AQ, nor are 5052, 5252, or 6101.
Anodization produces a micro-thin aluminum oxide coating that is fully integrated with the base aluminum metal. The aluminum oxide layer is relatively clear and colorless, but it has a highly porous structure that can be dyed and then coated to produce a colorful metallic gloss.
Applications that Use Anodized Aluminum
Anodized aluminum is ideal for a wide range of construction and architectural applications. Notably, anodized aluminum colors will never chip, peel, or fade in sunlight, making them popular for many commercial, industrial, and consumer applications. Common applications include construction components for building exteriors, vents, window frames, doors, and other structural applications.Not all aluminum alloys can be anodized successfully. Different aluminum alloys contain different types and amounts of alloying metals, which produce coatings of different properties, some of which are less desirable.
Which Aluminum Alloys are Suitable for Anodizing?
Wrought aluminum alloy designations follow the Aluminum Association series numbers from 1xxx to 7xxx, based on chemical composition. 5xxx and 6xxx series aluminum alloys are well-suited for anodizing, given their inclusion of magnesium which offers an aesthetically pleasing color after the aluminum is anodized.
Aluminum Alloy Series |
Factors to Consider for Anodization |
| 1xxx Series | Alloys in the 1xxx series are 99% pure aluminum, with tiny amounts of alloying elements. They can be anodized, but the underlying aluminum structure is not strong enough for many applications. |
| 2xxx Series | The 2xxx series is primarily alloyed with copper, which causes any anodized coating to have a yellowish tone. The coatings produced on these alloys also do not provide a high level of protection found in other alloy series. |
| 3xxx Series | Aluminum alloys in the 3xxx series are alloyed with manganese. Anodization of these alloys produces a gray or brown coating. The coating color is difficult to match for projects requiring multiple sheets, so painted applications work best. |
| 4xxx Series | The aluminum 4xxx series is alloyed with silicon and produces a dark gray, sooty appearance when anodized. The coating provides protection, but the surface color is unappealing. |
| 5xxx Series | Alloys in the 5xxx series contain magnesium. When anodized, these alloys create a strong, clear oxide layer, as long as the alloying magnesium is kept within a certain percentage range. |
| 6xxx Series | 6xxx series aluminum alloys contain magnesium and silicon. Anodizing these alloys produces a clear and strong protective layer that makes them especially useful in architectural applications. For example, Al 6063, or architectural aluminum, can be anodized to create an aesthetically pleasing, colored finish for visual architectural and building applications such as window frames, door frames, roofs, and sign frames. |
| 7xxx Series | Aluminum alloys in the 7xxx series contain zinc. Anodizing these alloys provides a clear coating with good protection, but too much zinc in the mix may turn the coatings brown. |
Anodized Aluminum Factors for Consideration
According to the Aluminum Anodizers Council (AAC), the only aluminum alloys suitable for architectural anodizing applications fall in the 5xxx and 6xxx series. For example, alloys 5005, 5657, 6063, and 6463, are labeled “Anodizing Quality (AQ).” Not all alloys within the 5xxx and 6xxx series meet the AQ qualification, though they can still be anodized satisfactorily. For example, alloy 6061 is not considered AQ, nor are 5052, 5252, or 6101.
