This is a surface treatment used in manufacturing to enhance the corrosion resistance and surface strength of metal parts or products. The anodizing process uses an electrolytic mechanism to create an oxide layer on the substrate.

The anodizing process operates on an electrolytic principle. A substrate, such as aluminum is connected to a positive electrode and acts as the anode. A highly conductive material, on the other hand, serves as the cathode (negative electrode). For example, aluminum or stainless steel are suitable cathodes for aluminum anodizing. Therefore, H₂SO₄ (15-20% by weight), CrO₃ (3-10%), and H₃PO₄ (5-10%) are commonly used electrolytes for this process.

A uniform and smooth surface is crucial for the application of anodic oxide layers.

The part should to be anodized becomes the anode and the other highly conductive metal becomes the cathode, both of which are immersed in an electrolytic cell. When current flows through this electrolytic device, the anode oxidizes and loses electrons.
Next, the metal ions react with oxygen ions, which migrate toward them due to their positive charge. Here, the O²⁻ comes from the dissociation of the electrolyte. At the anode, these react with the metal ions to form a solid metal oxide layer.
 

Dyeing: The porous layer absorbs the dye, and a variety of colors can be achieved by immersing the part in a dye bath.
Electrolytic Coloring: Metal salts are electrochemically deposited into the pores of the layer, producing long-lasting, non-fading colors.
 

The anodizing process creates dye in the surface pores, and sealing is essential to avoid the risk of corrosion, scratches, and stains forming due to these pores. If sealing is poor or missing, the porous metal oxide layer can accumulate dust and debris.
Anodized surfaces can be sealed using different techniques, cold sealing, medium temperature sealing, and heat sealing
 

There are four types of anodizing processes, based on the type of acid bath and thickness capability. They are known as: Type I, Type II, Type II, and Phosphoric Acid Anodizing.

Type I, or chromic acid anodizing, is ideal if you require a thin layer, especially for decorative and some functional applications. However, it can mimic the performance of Type II, or hardcoat, after sealing. Layer thicknesses range from 0.00002 inches to 0.0001 inches.

This is the most common type, using sulfuric acid as an electrochemical medium to form the oxide layer. Sulfuric acid anodizing uses a solution with a concentration of 15-20%. It forms a thicker oxide layer than Type I and is suitable for a wide range of applications. Thicknesses range from 0.0001 inches to 0.001 inches. Type II anodizing also offers high corrosion and wear resistance and is available in a variety of colors.

Type III is the densest and strongest type, resulting in a thicker surface oxide layer. Therefore, it is well-suited for harsh and chemical environments. Thicknesses can range from 0.0005" to 0.006". Hard anodizing is primarily used for high-performance and low-friction components. The hard anodizing process can use chromic, sulfuric, or oxalic acid as the electrolyte.

Primarily a surface treatment, not a comprehensive corrosion or wear treatment, phosphoric acid anodizing uses a 15-30% phosphoric acid solution. Unlike other types, it forms a very thin and porous oxide layer (< 0.0001 inch). It is well-suited for the application of further adhesives or primers.

When the oxide film reacts with ambient moisture, the oxide layer thickness increases further. As a result, anodized components offer strong corrosion resistance and protect the substrate from UV rays, heat damage, and the effects of the marine environment.

Besides protection, it also enhances the aesthetics of the substrate surface. Anodizing allows for virtually any surface texture, from matte to high gloss. This allows for countless color options and customization. The appearance also lasts for a long time. Furthermore, this finish can be applied to any complex and delicate component or product.

Anodizing does not increase electrical conductivity! It provides insulation.
Anodizing, especially anodized aluminum, provides electrical insulation while the underlying metal retains its conductivity. However, you can also maintain a certain degree of conductivity on the surface by controlling the film thickness.
 

Anodizing is a hard oxide coating that enhances hardness, wear resistance, and corrosion resistance. It covers all sharp corners, edges, and complex areas. Unlike other coatings, there is no risk of adhesion failure. All of these reasons extend the life of the anodized coating, and therefore the life of the underlying components.

•  Automotive parts, such as wheel covers, fuel tank caps, engine covers, trim, and control panels.
•  Lightweight aerospace components, such as skin panels, structural components, fasteners, and cabin interior items.
•  Home appliances and kitchenware.
• Electronic and electrical housings.
• Medical device housings, scalpel handles, sterilization tray handles, etc.

• Bicycle frame components vehicle battery casings
• High-performance tools and hardware
• Drone, satellite, and aircraft components

• Automotive fasteners, anodized aircraft screws, fuel system parts, and other small mechanical components.
• Nuts, bolts, pipe fittings, building hardware, decorative items, and lighting fixtures.
• Electronic housings, tool handles, furniture hardware, etc.

Anodizing is well-suited for non-ferrous metals such as aluminum, titanium, and zinc, offering both wear resistance and aesthetic appeal. Its flexibility in thickness and color makes it an ideal choice for virtually any industry using aluminum alloy components. However, achieving the desired finish requires consideration of technical factors, such as anodizing equipment, electrolyte concentration, current and voltage, treatment time, and bath filtration. Overall, anodizing is the preferred choice whenever customized aesthetics and high performance are required in harsh environments.

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