Anodizing

Anodizing: Durable Protection and Aesthetics for Aluminum Parts

In anodizing, an aluminum part is immersed in an electrolytic solution, usually dilute sulfuric acid. By passing an electric current through the solution, the aluminum surface reacts with oxygen, resulting in the formation of an aluminum oxide layer. This layer is porous and can later be sealed for additional protection. The process consists of several steps, including surface pretreatment (cleaning and degreasing), anodizing, optional staining and finally sealing the pores to optimize corrosion resistance.

Different Types of Anodization

We offer three main types of anodizing, each suitable for specific applications:

• Type I (thin layer): This process uses dilute chromic acid and creates a thin layer of 5-10 microns. Ideal for decorative applications or when weight is an important factor.
• Type II (standard): The most common form of anodization, performed with sulfuric acid, producing a layer of 15-25 microns. Provides both aesthetic benefits and basic protection against wear and corrosion.
• Type III (hard anodizing): Occurs at colder temperatures and higher current ratings, resulting in a thicker layer of 25-100 microns. Perfect for heavy industrial applications where extreme wear resistance and corrosion protection are required.

Material compatibility

Anodizing is only possible with aluminum and its alloys because the process depends on the natural oxidation of this metal. Pure aluminum and 1000-series alloys are excellent for decorative anodizing because of their smooth and uniform oxide layer. Alloys with more silicon or copper, such as the 2000- and 6000-series, may form darker and less uniform oxide layers, but remain functionally effective.

Benefits of Anodizing

Anodizing offers several performance advantages. First, it increases wear resistance because the aluminum oxide layer formed is much harder than the base material. This is especially useful for parts exposed to constant wear. In addition, it provides excellent corrosion protection, especially in humid and aggressive environments. The anodization layer also acts as an electrical insulator, which can be useful in electronic applications. In addition, it offers aesthetic benefits by allowing parts to be anodized in different colors, which is both functional and visually appealing.

Applications and Industries

Anodizing is widely used in various industries:

• In the electronics industry, it provides protection and insulation for components such as housings of smartphones and laptops.
• In the automotive sector, it improves the durability and appearance of automotive parts.
• The aerospace industry uses hard anodizing for structural components that require extreme durability and safety.
• The mechanical engineering and consumer goods industries also apply anodizing for functional and visually appealing products.

Customization and Process Optimization

Within the anodization process, we offer several customization options to meet specific customer needs. For example, we can adjust the thickness of the oxide layer to optimize wear resistance or corrosion protection. We also offer color choices, where parts can be anodized in different colors.

The color in anodization is created by coloring the porous aluminum oxide layer before it is sealed. This is done by dipping the aluminum in a bath of dye after anodization. The result is a colored, protective layer that also contributes to the aesthetics of the product. However, it is important to note that anodizing does not offer the same precision in color matching as paint processes, for example.

Why not exact RAL colors?

The use of standard RAL colors is not possible with anodizing due to the nature of the process. The final color depends on several factors, including the composition of the aluminum alloy, the thickness of the anodization layer and the exact process conditions. This makes it difficult to reproduce colors consistently in accordance with a predefined color standard such as RAL. Anodized colors are often vibrant and durable, but color tone can vary and is difficult to accurately predict or match to an exact RAL value.

Color adjustment between batches

Another point to consider is that the color may vary slightly between different batches. This is because parts are treated in the same bath for each batch. With a new order, the parts are re-anodized, and the exact process conditions may differ. This may result in slight color variations between batches. We do our best to ensure color consistency, but slight variation between production orders is technically unavoidable.

Pretreatment for milling marks

When a smooth surface without visible milling marks is desired, we strongly recommend surface treatment prior to anodizing. This is especially important with Type I and Type II anodizing, because the anodizing layer is relatively thin (5-10 microns and 15-25 microns, respectively) and not thick enough to mask any unevenness, such as milling marks. Without appropriate pretreatment, these marks often remain visible after anodizing.

Recommended treatments to achieve a smoother surface include mechanical polishing, brushing or glass bead blasting. Mechanical polishing creates a very smooth and shiny surface, while brushing creates a more textured but even pattern. Glass bead blasting gives the aluminum a matte, uniform finish and can effectively remove minor blemishes. Applying these treatments before the anodizing process achieves a much tighter and visually appealing finish.

Available Color Options

When anodizing aluminum, different colors can be achieved through the use of dyes during the anodizing process. The color options available depend on the exact anodizing method, the dyes used, and the surface finish of the aluminum. Here is a list of common color options available from anodizing:

Standard anodizable colors:

• Silver (natural)
• Black
• Gold
• Blue
• Red
• Green
• Purple
• Yellow
• Orange
• Pink
• Bronze/brown (light to dark)
• Gray (light to dark)

Special effects (sometimes available):

• Second color with gradient (when double anodizing)
• Metal color effects (in the case of brushed aluminum, for example)
• Satin/matt vs. glossy (surface finish can affect perceived color)

The exact hue and brightness of these colors can vary depending on factors such as the thickness of the anodic layer, the dye used, and the finish of the material. Some colors, such as black and silver, are easier to reproduce and are often chosen for applications where color consistency is important. Other colors can vary in intensity and saturation.

Environmental friendliness

Anodizing is generally environmentally friendly because the process uses non-toxic materials and the resulting layer is inert, meaning it does not emit harmful substances. We comply with REACH and RoHS directives, which means that our processes meet the strictest environmental standards. In addition, we optimize our energy and water consumption and treat wastewater carefully to minimize environmental impact.

Quality Control and Inspection

Our quality controls are rigorous and follow established procedures to ensure that each anodized part meets the highest standards. We measure the thickness of the anodization layer to ensure it is consistent across the entire part. Optical inspections ensure that aesthetic quality, such as staining and finish, meets customer requirements. Our processes meet key industry standards, such as MIL-A-8625, which ensures that our customers receive reliable, high-quality results.