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Analysis of Anodic Oxidation Process

Anodizing is an electrochemical surface treatment process mainly used for surface treatment of aluminum and its alloys. By applying current to aluminum in the electrolyte, a dense layer of aluminum oxide film is formed on its surface. This oxide film can not only improve the corrosion resistance, wear resistance, and hardness of the material, but also impart different colors and functionalities to the material through dyeing or sealing treatment.

The basic principle of anodizing

Electrochemical reaction:

In the electrolyte, aluminum serves as the anode and undergoes an oxidation reaction upon being energized, resulting in the formation of aluminum oxide (Al ₂ O3) on the surface.

Cathodes are usually made of inert materials such as lead or stainless steel, which mainly serve to conduct electricity.

Formation of oxide film:

The oxide film consists of two layers: a dense barrier layer near the substrate and a porous outer layer.

The thickness of the barrier layer is proportional to the voltage, and the thickness of the porous layer is proportional to the oxidation time.

Selection of electrolyte:

Common electrolytes include sulfuric acid, oxalic acid, chromic acid, etc.

Sulfuric acid anodizing is the most common process and is suitable for most aluminum alloys.

Process flow of anodizing

Pre processing:

Oil removal: Remove surface oil stains.

Alkali washing: Remove natural oxide film.

Acid washing: neutralize residual alkali solution and activate the surface.

Anodizing:

Immerse the aluminum material in the electrolyte and apply electricity for oxidation.

Control voltage, current density, temperature, and time to achieve the desired film thickness and performance.

Staining (optional):

Using the porous structure of the oxide film, coloring is achieved by adsorbing dyes.

Common dyes include organic dyes and inorganic salts.

Sealing treatment:

Seal the micropores of the oxide film with hot water, steam, or chemical sealing agents to improve corrosion resistance and wear resistance.

Post processing:

Clean, dry, and if necessary, apply coating or polishing.

Characteristics and advantages of anodizing

Performance improvement:

Improve hardness (up to 200-300 HV).

Enhance corrosion resistance (high chemical stability of oxide film).

Improve wear resistance (high and dense oxide film hardness).

Decorative:

Multiple colors can be achieved through dyeing.

The surface glossiness can be adjusted to meet different appearance requirements.

Functionality:

The oxide film has good insulation performance and can be used for electronic components.

Porous structures can be used for adsorbing lubricants or functional coatings.

application area 

Construction industry:

Surface treatment of aluminum alloy doors, windows, and curtain walls.

Automotive industry:

Surface protection of engine components and wheel hubs.

electronic product:

Decoration and protection of mobile phone cases and laptop cases.

Aerospace:

Lightweight and corrosion-resistant treatment of aircraft structural components.

Common Problems and Solutions

Uneven oxide film:

Reason: Uneven current distribution or inconsistent electrolyte concentration.

Solution: Optimize electrode design and regularly stir the electrolyte.

Uneven staining or fading:

Reason: Inconsistent porosity of oxide film or incomplete sealing of pores.

Solution: Strictly control the oxidation process parameters to ensure sufficient sealing of the holes.

Film layer detachment:

Reason: Incomplete pre-treatment or excessive oxide film.

Solution: Strengthen pre-processing and control the film thickness within a reasonable range.

Future Development Trends

Green and environmentally friendly:

Develop electrolytes and processes with low pollution and energy consumption.

Multi functionality:

Combining nanotechnology to endow the oxide film with self-cleaning and antibacterial properties.

Intelligence:

Introduce automation equipment to improve process accuracy and consistency.

Anodizing, as a mature surface treatment technology, has broad application prospects in industrial production and daily life. With the continuous advancement of technology, its process efficiency and functionality will be further improved.