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What Is Anodizing and How Does It Work

by: Dec 15,2023 308 Views 0 Comments Posted in Engineering Technical

Anodizing Anodized aluminum CNC machining Sheet metal titanium

What is Anodizing

Anodizing is a technology that oxidizes metal surfaces through an electrochemical process, aiming to improve the surface hardness, corrosion resistance and decorative properties of the metal. This technology is widely used in the surface treatment of aluminum, magnesium, titanium and other metals to meet the requirements for material performance in different fields.


How Does Anodizing Work

First, the process of anodizing is based on the electrochemical reaction of metal in an electrolyte. In this process, the metal surface is placed on the anode (positive electrode), and by applying an external current, an oxidation reaction occurs on the metal surface to form an oxide film. This oxide film has excellent properties, such as high hardness, good electrical conductivity, corrosion resistance, etc., allowing the metal surface to maintain good performance under various environmental conditions.

Anodized Aluminum

Anodizing is a common surface treatment for aluminum. In this process, aluminum products are pretreated and immersed in an electrolyte containing ingredients such as sulfuric acid or chromium oxide. After energization, the oxidation reaction on the metal surface occurs rapidly, forming a dense and uniform oxide film. This oxide film not only improves the hardness and wear resistance of aluminum, but also increases its corrosion resistance, making aluminum products widely used in aviation, automobiles, construction and other fields.


Anodizing Process Materials

According to its principle, anodizing is only suitable for conductive materials such as metals. However, that doesn't mean aluminum is the only option. In fact, anodized metals also include magnesium and titanium. For example, anodizing treatment on titanium can obtain a hard oxide film, improving its surface hardness and corrosion resistance, making titanium play a more important role in medical devices, aerospace and other fields.


Different Types of Aluminum Anodizing

To understand how to anodize aluminum, you need to understand the types of aluminum used in the anodizing process. There are three commonly used types of anodizing processes, each resulting in different functional and aesthetic properties.

Type I - Chromic Acid Anodizing

The Type I anodizing process uses chromic acid to create a thin coating (up to 0.0001 inches thick) on the surface of a metal part.

Although Type I is the thinnest anodized coating, it still results in parts with higher corrosion resistance. However, it also results in minimal color absorption when stained.


Type II - Sulfuric Acid Anodizing

The Type II anodizing process uses sulfuric acid instead of chromic acid. This results in a slightly thicker surface layer on the aluminum part.

Type II sulfuric acid anodizing is 0.0002 to 0.001 inch thick and is more suitable for stained parts.


Type III - Hard Coat Anodized

This is often called "hard anodizing" which also uses the sulfuric acid method. However, it produces a thicker (>0.001 inch) anodized layer than Type II.

Hard coat anodized parts offer optimal wear resistance and stain potential. However, it may not be suitable for parts with extremely tight tolerances.


The wide application of anodizing technology is not only limited to improving the basic properties of metals, but also has positive significance in environmental protection and sustainable development.

1. Environmentally friendly advantages: Compared with some traditional surface treatment methods, the anodizing process does not require the use of environmentally harmful chemicals. This reduces the negative impact on the environment during the production process and is in line with modern society's pursuit of green production.

2. Coating adhesion: The oxide film formed by anodizing usually has a certain pore structure, which can improve the adhesion of the coating. This makes it easier for metal surfaces to be coated with various coatings, such as paints, coatings or films, to suit the needs of specific applications.

3. Electrolyte optimization: With the development of science and technology, researchers continue to work hard to improve the electrolyte used in the anodizing process to improve its efficiency and reduce the demand for resources. Such optimization helps to further improve the sustainability of the process.

4. Expansion of application fields: With the continuous improvement of material performance requirements, anodizing technology has been widely used in different fields. For example, in medical device manufacturing, anodizing can improve the biocompatibility of metal surfaces, making medical devices safer and more reliable.

5. Innovative materials research: The application of anodizing technology has also promoted the research of new metal alloys and composite materials. By regulating the conditions of the anodizing process, surfaces with special properties can be obtained, providing new directions for innovation in the field of materials science.

6. Electrochemical energy storage field: Anodizing technology also has potential applications in the field of electrochemical energy storage. By changing the oxidation state of the metal surface, the performance of the electrode material can be affected, thereby improving the efficiency and cycle life of the battery.


Anodized Aluminum Design Tips

1. Pay attention to tolerances

If you know you're applying an anodizing process to an aluminum part, be aware that the process does increase the thickness of the part. This is because it can (albeit slightly) affect part tolerances.

If tight tolerances are critical, consider Type I or Type II anodizing options. You can also consider additional layer thickness during the design phase.

2. Angular

An important design tip for the anodizing process is to ensure that all edges and corners of the workpiece have a radius of at least 0.5 mm. The part design should also not contain any burrs.

The reason for these design considerations is that they help prevent the workpiece from overheating (or even burning) due to high current concentrations.

3. Consider using other decluttering steps

Anodizing is an electrochemical process. Therefore, it does not have the same effect as sandblasting or polishing. If an aluminum machined part is anodized directly, some machine marks or scratches may remain on the surface of the finished part.

Therefore, if you require a completely uniform surface finish, it may be beneficial to use polishing, sandblasting, or other mechanical finishing processes beforehand. Anodizing will make the surface of the part smoother than before.

4. Process batches

If you are tinting aluminum parts or products, it is recommended to anodize them in small batches. This ensures a greater degree of color uniformity since it is difficult to accurately match color from one batch to the next. The ideal situation for color consistency is to anodize a small batch of small parts at a time.


Industries That Frequently Use Anodizing

Aerospace.

Auto.

Architecture.

Consumer goods.

Household products industry.

Kitchen equipment.

Pipe covers.

Light fixtures.

Food preparation products.

Photo equipment.

Radio equipment.

Electronic enclosure.


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