Which Alloys of Aluminum Can Be Anodized?
Theoretically, all the alloys of aluminum can be anodized. However, in practice the alloy must be properly selected to achieve the desired mechanical properties of the part while also providing an acceptable appearance. The following is provided as a guideline:
These “pure” aluminum alloys are relatively soft and provide a clear, bright finish for cans and architectural applications (e.g. 1100 or 1175). The 1000 series alloys are not suitable for hardcoating.
The 2000 series is alloyed with copper. These are very strong and hard materials, developed for the aerospace industry (e.g. 2219 or 2224). They are not suitable for decorative applications since a yellow, non-weather resistant coating is achieved. Special current control techniques are required for wear resistant (hardcoating) applications.
These alloys incorporate maganese into the alum inurn to form sheet material (e.g. 3003 or 3004). Properties are similar to the 1000 series, but a grayish brown color is produced that is difficult to match in successive batches. They can be used for cans, lighting and as a base for painted architectural products.
The 4000 series should be avoided due to the high silicon content which forms a heavy black smut when anodized. The coating formed is dark gray in appearance. Some of these alloys (e.g. 4043 and 4343) have been used for dark gray architectural finishes.
Magnesium is the primary alloying constituent in the strong, ductile 5000 series. These are important alloys, producing clear, corrosion resistant coatings. Applications include lighting, food utensils, boats (e.g. 5052 or 5252) and architecture (e.g. 5005 or 5657).
These are strong, ductile alloys that provide clear coatings with good properties for structural and architectural applications (e.g. 6063 or 6463). The alloying elements are magnesium and silicon. Some of these alloys are strengthened by heat treatment and are thus suitable for hardcoating (e.g. 6061 or 6101).
The 7000 series is alloyed with magnesium and zinc, which imparts strength and ductility for clear, corrosion resistant automotive trim (e.g. 7029, 7046 or 7075). These alloys can also be used for hardcoating.