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Aluminum Anodizing Colors: Understanding The Coloring of Aluminum Products

Views: 50     Author: Site Editor     Publish Time: 2022-06-08      Origin: Site


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Upon completing the manufacturing process, achieving surface smoothness becomes paramount. Among the various methods available, anodizing stands out as a reliable choice for aluminum and other materials due to its ability to yield durable and aesthetically pleasing results. A thorough understanding of the anodizing process is essential, especially regarding coloring techniques and the selection of aluminum anodizing colors.

By exploring anodizing and its application in coloring aluminum products, this article aims to provide insights into its functionality and significance in the manufacturing process.

What is Anodizing?

Anodizing serves as an electrolytic passivation technique primarily employed to augment the thickness of the oxide layer on metal components. By harnessing the innate oxidizing propensity of metals, particularly alloys like aluminum, this method regulates oxide layer formation electrochemically, thereby mitigating further oxidation. Beyond bolstering mechanical properties and augmenting aesthetics via diverse chemical reactions that yield various colors, anodizing also fortifies the metal's resistance against corrosion and enhances adhesion.

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Types of Anodizing

Anodizing techniques can be classified according to various parameters. Firstly, based on current type, they encompass direct current anodizing, alternating current anodizing, and pulse current anodizing. Secondly, electrolyte-dependent categorization includes sulfuric acid anodizing, oxalic acid anodizing, chromic acid anodizing, phosphoric acid anodizing, mixed acid anodizing, and natural coloring anodizing primarily employing sulfonic organic acid solutions. Lastly, anodizing methods are differentiated by film properties, featuring ordinary film, hard film (thick film), porcelain film, bright modification layer, and semiconductor action of the blocking layer, among others.

Anodizing Process Flow

To conduct anodizing effectively, several sequential procedures are followed. Initially, chemical degreasing involves immersing the material in a solution like Na3PO4 (60g/L) and Na2CO3 (40g/L) at 40°C for 3 minutes. Subsequently, alkali etching is carried out utilizing an alkaline solution, such as NaOH (40g/L), for a similar duration. Following this, the workpiece undergoes water washing to remove residues. Brightening is then achieved by treating the surface with an acidic solution, like HNO3 (40g/L), for 15 seconds, followed by further water washing. The anodizing process ensues, involving immersion in a H2SO4 solution (180g/L) at a current density of 1.4A/dm2 for 30 minutes at a temperature of 18~22°C. Post-anodizing, sealing is executed for 10 minutes, with options including boiling water sealing or mischmetal sealing. Finally, the workpiece undergoes water washing and drying to conclude the process.


It's important to note that the outlined anodizing process is a general framework, subject to adjustments based on material type and desired outcomes. For instance, aluminum products aiming for heightened brightness might necessitate supplementary mechanical polishing steps. Moreover, to enhance decorative properties, the anodized workpiece can undergo dyeing or electrolytic coloring. Hence, selecting the appropriate process flow and conditions should be guided by specific application requirements.

Considerations for Anodizing Process

Electrolyte Selection: The electrolyte chosen significantly impacts the quality and thickness of the oxide film. Chromium-containing electrolytes, like chromic acid, are favored for producing robust oxide films with excellent wear and corrosion resistance. However, careful control of composition and concentration is essential to prevent adverse reactions.

Temperature and Time Control: Maintaining appropriate oxidation temperature and duration is vital for achieving a durable and visually appealing anodized film. Optimal temperatures typically range between 200-400°C, with precise timing dependent on aluminum alloy properties and desired thickness. Overly prolonged exposure may result in uneven or excessively thick films, while insufficient time could compromise hardness and wear resistance.

Pre-Anodizing Preparation: Thorough cleaning of aluminum profiles before anodizing is imperative to eliminate grease, dust, and impurities, ensuring effective electrolyte adhesion to the material surface. Subsequent cleaning and drying post-treatment are equally crucial to prevent interference with oxide film formation by residual substances.

Post-Anodizing Steps: Immediate sealing of anodized aluminum profiles, through methods like polyurethane paint application, safeguards against degradation by air, moisture, and other contaminants. Additionally, avoiding harsh impacts and friction preserves the integrity of the anodized film.

Laboratory Conditions: Maintaining a dry laboratory environment is essential to prevent moisture interference during the anodizing process.

Safety Measures: Adherence to safety protocols, including wearing protective gear and supervision, is paramount. Prohibited actions such as using tank water for handwashing or stirring tank liquid directly with hands must be strictly enforced.

Advantages of Anodizing

Enhanced Corrosion Resistance: Anodizing facilitates the formation of a protective oxide film on metal surfaces, boosting density and corrosion resistance.

Superb Decorative Capabilities: Anodizing enables the creation of transparent oxide films that can be dyed in vibrant hues. Additionally, specialized treatments can achieve effects akin to ceramic coatings, enhancing decorative appeal.


Enhanced Hardness and Wear Resistance: Anodizing results in a substantial increase in the hardness and wear resistance of the metal or its alloy, achieving levels ranging from 250 to 500 kg/mm2.

Superb Heat Resistance: The hard anodized film boasts an impressive melting point of up to 2320K.

Outstanding Insulating Properties: Anodized films exhibit remarkable insulation, withstanding breakdown voltages of up to 2000V.

Effective Heat Dissipation: While anodizing offers low thermal conductivity, it excels in heat dissipation, particularly through far-infrared radiation. Consequently, anodized metal components are often utilized as radiators and other heat dissipation elements.

Prevention of Peeling: Unlike plating or painting processes, anodizing erodes the substrate while continually growing and integrating with the base material. As a result, it does not peel off over time.

Applications of Anodizing

Enhancement of Mechanical Components: Anodizing serves to bolster the wear and corrosion resistance of mechanical parts, consequently elongating their operational lifespan.


Aircraft and Automotive Components: Anodizing treatment enhances the wear and corrosion resistance of aircraft and automotive parts, alongside providing decorative appeal.

Precision Instruments and Communication Devices: Anodizing treatment fortifies the wear and corrosion resistance of precision instruments and communication devices, while also adding a decorative touch.

Construction Materials: Anodizing treatment bolsters the wear and corrosion resistance of building materials, exemplified by its widespread use in aluminum curtain walls, doors, and windows for both interior and exterior building decor.

Electronic Device Housings: Anodizing treatment strengthens the wear and corrosion resistance of electronic device casings, while concurrently elevating their aesthetic appeal.


Everyday Items: Anodizing treatment elevates the wear and corrosion resistance of common household objects, while simultaneously imparting a decorative finish.


Reflecting on the anodizing and coloring processes of aluminum components, it's evident that one of the primary advantages of aluminum anodizing lies in its capacity to introduce diverse colors onto the surface. This not only enhances both the mechanical properties and visual appeal but also aligns with market preferences. Additionally, among the four coloring methods, electrophoretic coloring stands out as the most effective, utilizing electrochemical deposition and a selection of suitable salt solutions to generate an array of colors.

Undoubtedly, the aluminum anodizing process entails complexity, involving a blend of chemistry, materials science, and engineering manufacturing. However, by opting for our ZONZE anodizing services, clarity prevails. Our team of materials science and mechanical engineering specialists ensures the delivery of top-tier aluminum anodizing, offering you the freedom to select the ideal color palette for your project.

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