Appearance of Clear Anodized Coatings on 6061 Alloy
How do you achieve clear anodizing that is bright and clear?
Q. I recently sent some 6061 alloy aluminum parts to an outside anodizer for clear anodizing, and the parts returned with a dull gray color. The anodizer said this was normal, but I have seen products labeled as clear anodized, and they are bright and clear. How do they achieve this?—W.G.
A. It is difficult to picture exactly what you describe, but the normal appearance of etched and anodized 6061 alloy would be a matte, silver-gray look. Alloy 6063 with the same finish will generally appear a little more silver than gray. Alloy 6463, a good “bright” alloy, would look somewhat bright and reflective when polished to a high specularity, given little or no etch, and then anodized with a very thin coating. This would be especially true if that alloy were also chemically brightened as part of the cleaning process prior to anodizing.
The examples sited above might suggest that the appearance of an anodized part depends on the alloy and the finish. Since you are a machining company, you probably machine alloys such as 6061, 2024 and 7075. Among these three alloys, the latter two will usually have a “brighter,” more silvery appearance then the 6061. The higher iron and silicon in 6061 make it a good alloy to machine, but not a great alloy for “brightness.” So the alloying constituents and the methods used to finish the part are what determine the appearance. Perhaps your anodizer can help you select the proper alloy and call out the finish that will provide the look that you want.
The following anodizing process overviews are provided as a means of introduction to aerospace anodizing
Electropolishing can be a pretreatment for anodizing or a substitute for bright dipping. Either way, it improves the surface of the aluminum...
Anodizing for pre-prep bonding bridges the gap between the metallic and composite worlds, as it provides a superior surface in many applications on aluminum components for bonding to these composites.