Anodic oxidation of other metals
In addition to aluminum and aluminum alloys, other metals such as magnesium, copper, titanium, and zinc can also be surface-treated using anodizing technology to produce oxide films with specific properties to meet different usage requirements. Although not as widely used as aluminum anodizing, anodizing technology for these metals plays an important role in their respective fields. By forming unique oxide films, the metal surfaces are endowed with special properties such as corrosion resistance, wear resistance, insulation, and decorative effects. For example, the anodized film on magnesium alloys can effectively improve their poor corrosion resistance, enabling their wider application in the aerospace and automotive industries; the anodized film on titanium has good biocompatibility, providing a high-quality surface treatment solution for the medical device field.
Anodizing of magnesium and magnesium alloys is an important means to solve their poor corrosion resistance. Magnesium is a more active metal than aluminum, and its natural oxide film has weak protective properties and is prone to corrosion. Through anodizing, a 5-20 micron thick oxide film (mainly composed of magnesium oxide and magnesium hydroxide) is formed on the surface of the magnesium alloy, which can significantly improve its corrosion resistance. The electrolyte commonly used for anodizing of magnesium alloys is an alkaline solution (such as sodium hydroxide, sodium carbonate solution), or a solution containing fluoride or phosphate. In terms of process parameters, the voltage is usually 30-80V, the current density is 1-5A/dm², and the processing time is 10-30 minutes. The resulting oxide film is brittle, so it is often used in combination with processes such as painting to further enhance the protective effect. Magnesium alloy anodizing technology is widely used in aerospace, military industry, 3C products and other fields, such as drone bodies and mobile phone cases.
Anodizing copper and copper alloys is primarily used to improve their surface hardness, wear resistance, and decorative properties. Copper easily oxidizes and discolors in air, affecting its appearance and performance. Anodizing creates a layer of copper oxide or cuprous oxide on the surface, resulting in colors such as brown, black, or blue, which provides both decorative and protective properties. The electrolytes used for anodizing copper and copper alloys are typically alkaline solutions (such as sodium carbonate or sodium hydroxide) or acidic solutions (such as chromic acid or sulfuric acid). In alkaline electrolytes, a cuprous oxide film forms on the copper surface, resulting in a red or yellow color; in acidic electrolytes, a cupric oxide film forms, resulting in a black color. Process parameters include a voltage of 5-20V, a current density of 1-3A/dm², and a treatment time of 5-20 minutes. After the oxide film is formed, it can be sealed or coated with a clear varnish to improve corrosion resistance and stability. Anodizing copper and copper alloys is commonly used in decorative items, musical instruments, electronic components, and other products.
Anodizing titanium and its alloys has found applications in high-end applications due to its unique properties. Titanium inherently possesses excellent corrosion resistance and biocompatibility, and anodizing further optimizes its surface properties. The resulting oxide film (primarily composed of titanium dioxide) exhibits excellent wear resistance, insulation, and biocompatibility. A variety of electrolytes are used for anodizing titanium and its alloys, including sulfuric acid, phosphoric acid, and oxalic acid. By adjusting process parameters (such as voltage and current density), the thickness and color of the oxide film can be controlled, achieving a seamless integration of decorative and functional properties. For example, at varying voltages, titanium anodized films can exhibit a variety of colors, including gold, blue, and purple, achieving an aesthetically pleasing appearance without the need for dyeing. In the medical field, the oxide film on the surface of anodized titanium alloy implants promotes osseointegration and improves implant stability. In the aerospace field, the high-temperature stability and wear resistance of the oxide film make it suitable for high-temperature components such as engine parts.
Anodizing of zinc and zinc alloys is mainly used to improve their corrosion resistance and paint adhesion. Zinc is a commonly used protective coating material, but its own corrosion resistance is limited. Anodizing can form a layer of zinc oxide film on its surface to enhance its protective performance. The electrolyte for anodizing zinc and zinc alloys is mostly chromate solution or phosphate solution. The resulting oxide film is porous and can improve the adhesion with the coating. It is often used for surface pretreatment of automotive parts, hardware products, etc. In terms of process parameters, the voltage is 10-30V, the current density is 1-5A/dm², and the processing time is 5-15 minutes. After the oxide film is formed, it is usually passivated or painted to further improve corrosion resistance.
While anodizing technologies for other metals have their own unique characteristics, they are generally developing in a more environmentally friendly and functional manner. The development of new environmentally friendly electrolytes has reduced the use of toxic substances, such as the use of chromium-free electrolytes in copper and zinc anodizing. The development of functional oxide films has expanded their application areas, such as the bioactivation treatment of titanium alloy anodized films. The application of composite treatment technologies (such as combining anodizing with plating and coating) has further enhanced the overall performance of metal surfaces. In the future, as industry’s requirements for material performance continue to increase, anodizing technologies for other metals will play a significant role in even more niche areas, providing a richer range of solutions for surface modification of metal materials.
