How Color Is Created in Anodized Aluminum

The book explains the principle behind color changes in anodized aluminum, and combines this with metal surface treatment technology to reveal the effects of the thickness of the anodized film, the composition of the electrolyte, and voltage on the formation of color. This helps users master practical methods for precise control of marking results.

Why does anodized aluminum change color when engraved?

When people first hear about anodized aluminum, their first reaction is usually to ask, "Where do the colors come from?In fact, this has to do with an "optical game" of the oxide film.Anodizing involves immersing aluminum in an electrolyte and then passing a current through it, which creates an oxide layer on the surface of the metal. The thickness of this layer affects the way in which light is reflected and refracted, and this in turn determines the color of the surface.For example, when the coating is about 0.3 micrometers thick, interference of the light makes the surface appear golden; if it is thicker, it may appear blue or purple.

Three factors that affect color changes.

Relation of Oxidation Film Thickness to Color.

The thickness of the oxide layer determines the depth of color.To precisely control color, the time, voltage, and temperature must be strictly controlled.For example, when the voltage is increased, the oxidation reaction speeds up, the film layer becomes thicker, and the color gradually shifts from light gold to dark brown.

The "invisible" effect of electrolyte composition.

The composition of the electrolyte is not chosen at random. The proportion of sulfuric acid, oxalic acid or a mixture of acids can vary, and the porosity and structure of the oxide film will also change.For example, oxalic acid electrolyte is easier to use to produce dense oxide films, and the colors it produces are more saturated. It is suitable for use in situations where a bright mark is needed.

A small space.

Voltage is like a dial that regulates color.Under low voltage (for example, 10 V), the film grows slowly and the color is lighter, making it suitable for fine patterns. Under high voltage (for example, 30 V), the film grows more quickly, and the color is darker. However, if the voltage is not well controlled, the film will not be uniform.

Color control techniques for practical use.

First, we make a small sample and test it.

Don't get too eager to start the machine! First use scraps to test the effects of different combinations of parameters.Recording the voltage, time, temperature, and resulting color, they build up a "color card library." The next time they have a similar need, they can quickly adjust the parameters.

Don't forget about the environment.

The colors produced in summer and winter may be different! The electrolyte temperature rises, accelerating the reaction and causing too rapid an increase in the film thickness.They suggested that the operation be moved to a temperature-controlled workshop, or that the cooling time be adjusted according to the season.

The post-treatment sealing is very important.

The color may appear a little "washed out" right after the anodizing process, but this is because the pores in the oxide film have not yet been sealed.After the holes are sealed with boiling water or steam, the color stabilizes and the stone's resistance to corrosion is enhanced.

Common Problems and Solutions

What if the colors are uneven?

First check to see if the clamps are making good contact.If it's a large area, then it's probably a problem with circulation of the electrolyte, and the solution might be to clean the tank or add a stirring device.

How can the problem of the colors fading quickly be solved?

Eighty percent of the time, the reason is that the sealing hasn't been done properly. You can try lengthening the sealing time, or using a sealing agent with a nickel salt.If a part will be exposed to a highly acidic or basic environment, a double layer of coating is recommended.

How to keep the color consistent in complex patterns.

When anodizing fine logos, it is possible to divide the process into two stages: First, use low pressure to anodize the details, then use high pressure to anodize the entire piece.Although the process is more complicated, the result is that the edges do not turn black.