Anodizing of Aluminum and Alloys: Coloring Current State and Development Trends
Aluminum is one of the most abundant elements on Earth, accounting for more than 8 % of the total crustal mass. It is commonly used for many applications in several industries, including construction, transportation, electronics, aerospace, and defense systems. However, this element is quite reactive and often subject to corrosion, so several surface treatments and coating processes are utilized in order to protect the material from the attack of both corrosive elements and their combined effect. Anodizing of aluminum and its alloys is a process used to enhance surface properties of the material, including its resistance and corrosion resistance. In addition, anodizing can also be used to produce colored finishes which are suitable for decorative purposes.
Anodizing is an electrochemical process during which the substrate material is immersed in an electrolytic solution and subjected to an electric current. This process causes the oxidation of the alumina layer, which is growing in thickness and adheres to the substrate surface. Anodizing has several advantages over traditional coatings such as painting and plating, as it is more ecofriendly and cost effective. Also, the coloring of anodized aluminum is usually much more uniform and durable than in the case of other processes, showing resistance to scratches and abrasion.
The most commonly used model in anodizing of aluminum and its alloys is the sulfuric acid anodizing process. In this method, the aluminum is placed in a sulfuric acid anodizing bath and a current of low voltage is applied between the anode and cathode. The-verflow sulfuric acid anodizing bath is heated to 50 ¯C. A thin oxide film is formed between the aluminum particles and the cathode. The coloring of the anodized aluminum is mainly a result of the formation of this oxide film, giving it different shades of a brownish color.
In addition to the traditional sulfuric acid anodizing process, some other anodizing methods can also be used to produce colored finishes, such as chromic acid anodizing, boric acid anodizing, and dichromate anodizing. Each of these methods can produce a variety of colored finishes which are suitable for different applications. The chromic acid anodizing process is used to produce a black or gray colored finish, while the boric acid anodizing process can produce a blue colored finish. Moreover, the dichromate anodizing process is mainly used for yellow, gold and other metallic colored finishes.
The anodizing of aluminum and its alloys is expected to see significant growth in the coming years, as the demand for aluminum products and components is expected to increase. In addition, the development of new anodizing technologies and processes will enable the production of new colored finishes and applications. Finally, good knowledge of the various anodizing processes, their requirements and limitations will be essential to the successful implementation of anodizing of aluminum and its alloys.
