Anodizing color deviations

Background on the subject of color deviations in anodized colors

All anodized colors shown in our web shop are sample images
An anodized color is not a coating but is created by coloring the artificially created oxide layer. (anodising)
Due to material and throughput batches, there may be color deviations in the individual components of a single shifter
The high-strength (copper-containing) aluminum from which our turned and milled parts are produced tends to have a slight yellow/brown cast

Especially with our anodized color "grey" these nuances are relatively clearly visible, this is not a defect but can be described as follows:
“ANODIZING SHOWS WHAT'S BELOW"

Here is some information about color differences of anodized parts:

Mechanical surface treatment

In general, the surface of untreated aluminum can be given a silvery or

describe it as metallic matt shiny. But if you look at this surface in detail and maybe even under the microscope, you get completely new impressions. If one also takes into account the alloy and the distribution of trace elements, significant differences in the apparently uniform material can suddenly be detected. However, these differences in the microstructure and varying alloy components are of essential importance for the coloring of aluminium. Anodized colors are based on the inclusion of molecules in the micropores of the aluminum surface and the resulting different light reflections. The arrangement of the pores largely depends on the mechanical processing of the metal surface. (e.g. turning/milling/brushing)

Since the surface treatment is always directional, the reflection behavior and thus the color impression are also directional. The pore structure created during anodizing is also influenced by impurities in the aluminum, which can vary even within a batch of a production solder. Due to the surface structure, which varies depending on the direction, appears at

color anodized surfaces depending on the viewing angle and light intensity a different color impression. This can be observed even within a device.

aluminum alloys

Anodizing is an important process for coloring aluminum surfaces. But not only the color is changed during anodizing. In addition, anodizing also improves resistance to weather influences and hand perspiration.

Aluminum is a very common material in motorsport. However, the term aluminum is not entirely correct. Aluminum in its pure form is practically not used because it is much too soft. It is therefore mixed with alloying components that improve properties such as hardness or strength. So the correct term is aluminum alloy.

The mixing ratio of the individual alloy components is subject to production-related fluctuations. These fluctuations may only be within a defined, very small tolerance range. Although the fluctuations are hardly recognizable, they still have an influence on the anodizing process.

layer thickness

The paint layer must be at least 20 micrometers (0.02 millimeters) thick on average. It must also not be less than 16 microns at any measurement point.

For comparison, an average hair is about 60 micrometers (0.06 millimeters) thick. So the layer thickness after anodizing is 3 times thinner than your hair. But even if it sounds as if the paint layer is very thin, it is a real powerhouse. By anodizing

The anodizing process and coloring

Aluminum does not rust! In contact with atmospheric oxygen, aluminum forms a natural protective surface that prevents rusting (oxidation). This protective surface is called the oxide layer. The special thing about it is that it repairs itself and is only a few nanometers thick. For comparison, your hair is 100,000 times thicker than the protective layer.

When anodizing, the protective layer grows 200 times to 20 micrometers. Hence the name: electrolytic oxidation. The aluminum is placed in a chemical bath that is electrified. The oxide layer increases in size during a chemical reaction. The advantages of this layer are increased surface hardness and higher corrosion resistance. The surface becomes less sensitive to scratches and is better protected from the weather.

During the enlargement of the oxide layer, pores form in the surface. These pores are filled with color particles in a color bath. The structure of the aluminum is therefore retained even after coloring. No layer of color is applied, but the color particles are stored in the top layer.

In the last step, the pores are closed so that the color particles remain in the pores and no other particles can penetrate. For this, the aluminum is "cooked" with the absorbed color particles. During a chemical reaction, the necks of the pores close and the color particles are trapped in the pores.

formation of color differences

As already mentioned, the outcome of a chemical reaction depends on the environment and your reactants.

The most important step during anodizing is the formation of pores in the oxide layer. This is influenced by the temperature of the aluminum and the bath. If the temperature changes by just a few degrees, the formation of pores also changes.

The chemical composition of the bath also changes during the anodizing process. Substances are absorbed by the aluminum and other substances are released into the bath. Therefore, after some time, the bath is diluted and used substances are added. These fluctuations also cause altered pore formation.

The fluctuation in pore formation becomes visible as soon as the color particles have settled in the pores. If the pores are particularly large, many color particles can collect there. If the pores are smaller, not as many paint particles accumulate as with large pores. The hue changes accordingly.

Due to the many factors influencing the anodizing process, the change in color can only be influenced to a certain extent. If there must be no fluctuations in the finished product, then the product must be anodized "in one go".

Summary

During anodizing, there will be slight color differences, which are unavoidable.

DIN 17611 is used to assess whether the color difference represents a defect