Anodized Aluminum

Anodized Aluminum: Anodization Process of Coloring Aluminum!

Anodized Aluminum: Anodization Process of Coloring Aluminum!

Aluminum is one of the most used metals in the fabrication and manufacturing industries, be it metallic sheets, metal pieces, machine parts, or any decorative item. It is durable and long-lasting and has excellent resistance against corrosion and rusting. Perhaps, this is why this metal has become so popular in most markets as a raw material.

The process of converting the raw mined element into the end products involves many steps. Out of these, the most important is the application of colors on the surface through the process of anodization. It ensures the durability of the surface finish and the overall appearance and enhances the look and texture.

If you are curious about the anodization process of coloring aluminum, delve deep into this upcoming discussion to clarify all your doubts and understand it deeper. 

Anodized aluminum basics- a brief overview of the process

Anodizing the aluminum is based on an electrolytic reaction where the material to be coated is used as the anode (positive terminal) while the material with which coating needs to be applied forms the cathode (negative terminal). The electrolyte (the liquid part of the cell) is mainly acidic that facilitates the process, and speeds up the process. 

When electricity is passed through the terminals and into the electrolyte, ionic reactions occur, and the coating is applied on the material’s surface at the anode. 

Benefits of using the anodized aluminum 

Anodized Aluminum parts

Anodizing aluminum is quite important during metal fabrication in various industries, starting from cookware manufacturing companies to the appliance framing market. Below are some of the major perks of anodizing the metal:

  • Enhances the aesthetics

    The anodization will help in improving the aesthetics of different aluminum end products. For example, decorative products made from this raw material have colored anodized surfaces so that they can have the expected visual appeal for the end-users. 

  • Reduces the hassles of maintenance

    With anodized material covering the material’s surface, you won’t have to worry about enduring maintenance hassles. Therefore, you can easily use the end products without worrying about regular maintenance and care. In addition, unlike naked metal surfaces, the anodized one will maintain its surface texture for a long time, without scratches, wear and tear, and more. 

  • Stabilizes the color

    The anodization process introduces chrome stability as the particles are infused within the grooves on the surface created by electricity. Therefore, the chrome layer is not subjected to direct corrosion, further improving the color retention property. 

Types of the anodizing process for aluminum 

Anodized Aluminum parts

Anodization is done in three different processes, based on the requirements of the end-users and the features to be included. In this section below, we have briefly defined these three processes for your clarification. 

  • Process type 1: Chromic Acid anodization 

    This is the lightest anodization process where the chromic acid acts as the electrolyte. As it cannot ionize completely when electricity is passed, the coating layer over the aluminum product has a maximum thickness of 0.0001 inches. This process makes sure that the colors incorporated are stable and can prevent corrosion. 

  • Process type 2: Sulfuric acid anodization

    If the aluminum product needs to be dyed, sulfuric acid is used for applying the color coating over its surface. Due to the high ionization level of the chemical electrolyte in an aqueous state, the chrome compound is coated with even thickness, measuring between 0.0002 inches to 0.001 inches.

  • Process type 3: Hardcoat anodization

    In the Hardcoat anodization process, a thicker coating is applied over the aluminum surface, having a thickness of more than 0.001 inches. As a result, it is more resistant to corrosion and wear and tear, which is why this process is used to make hard anodized cooking utensils, mechanical spare parts, and more. 

Introduction to anodizing colors- a brief overview

The anodizing colors are made with different compounds to efficiently serve the purpose, i.e., improving surface strength, durability, and color stability. There are many options for anodizing the metal surface in an aesthetically pleasing manner. However, the process of applying the color coats isn’t easy. It involves a series of steps and needs precision and accuracy for better results.

Therefore, proper care is taken when choosing the colors based on aluminum texture, grade, end expectations, resistance against corrosion, and more. If there is a slight mistake associated with the choice, the results won’t be pleasant, and it might destroy the material also. 

Process of anodizing aluminum with different colors

Aluminum surfaces are painted with different chromes via anodization in a series of steps explained in the below section. This will help you understand what happens in the factories and how it ensures improvement in the overall material’s strength, lifetime, and durability. 

  • Step 1: Surface cleaning and etching

    The products are rinsed thoroughly in large water tanks to remove any physical impurity present on the metallic surface. Liquid detergents are used because they won’t cause leaching or surface corrosion of pure metal. 

    Once cleaning is done, the wet surfaces are dried with an air blower and then passed for etching. Etching is a process via which the surfaces of different products are polished multiple times till they become shiny and smooth in texture. Also, etching removes any trace of other metals from the aluminum surfaces as they can cause improper chemical reactions. 

  • Step 2: Coating with a film layer

    Once the surface gets etched, a proper film is added as the basic coating. As there are three processes for forming this build layer, it is imperative to choose the best one to help achieve all the desired properties and features. As aluminum is mainly used in alloy form to make the products, the type of the alloy will determine the size and shape of the film pores. On the other hand, the electrolyte concentration, supplied voltage, and the tank temperature determine the pore depth or overall coat thickness. 

  • Step 3: Addition of the colors

    Four different methods are applied to add the colors over the build film layer on the aluminum product’s surface. Based on the process chosen, several factors will be impacted like: 

    • Color intensity 
    • Depth of the film
    • Color retention ability
    • Surface smoothness
    • Texture 

    Since both the visual appeal and strength of the product will depend on the color coat, make sure to choose the process of application as per the requirements. 

  • Step 4: Surface sealing 

    Sealing is always done at the end of the anodization process. As the color layer added over the built film will have numerous pores, it is important to seal their mouth so that the corrosive factors cannot directly contact the original metal surface. 

    For this, powdered dye is poured over the product’s surface so that they can seal all the pores and maintain structural and visual integrity.

Process of anodizing aluminum with different colors

CNC Machining Surface Sand Blast

1. Electrolysis 

In this process, an acid salt is used in an aqueous solution as the electrolyte, which increases the absorption rate of the molecules. This helps seal the pores and offers UV-resistant properties so that the product can easily withstand the sun rays. However, the main problem is that the electrolysis process limits the use of color shades. Usually, you can use black, bronze, gold, nickel, chromium, and other colors that can be applied over the product surfaces. 

2. Dipping method

The dipping method is used to apply color coats with different shades, both brighter to darker ones. Here, the product is placed inside a tank where dye solution is present. Once the chemical reaction is triggered, the dye molecules fill up the pores until they are sealed. The main drawback of this technique is the absence of UV-resistant properties from the surface of the end product. 

3. Interference coloring

The interference coloring technique is used when the light rays interact with the dye molecules and suffer inference. The pores increase in size during the process and, therefore, accommodate more dye molecules to seal the entire surface. 

4. Integration method

In this method, the anodizing colors are integrated with the chrome molecules present inside the metal alloy. Therefore, the colors obtained are mainly black and bronze. One of the main benefits of the integration coloring method is the excellent abrasion resistance of the surface against scratches and other damages. 

How to match the colors for anodized aluminum?

Going by the simple optical mechanism, we can view the colors of a material’s surface based on the polychromatic radiations that are absorbed by it within the visible light spectrum. For example, a yellow dress will absorb the yellow radiations in the white light and reflect the rest of the wavelengths. When your eyes receive the reflected radiations, the lens will find what wavelength is missing and form the same color vision. Therefore, you can see a yellow dress in front of you. 

Even though the same mechanism is applicable for anodization, there is a slight difference. The anodized layer won’t reflect the light as expected. Rather, it allows the radiations to pass through and strike the base layer. Since it is made from aluminum having a clean and smooth surface, the light radiations are reflected easily. Therefore, the colors perceived by your eyes will be lighter in intensity and also in the shade because the anodizing layer acts as a filter. 

Matching process of the color with aluminum

The same color can create different visuals as the anodizing layer acts as the filter. For example, a light coating will create darker color while the hardened coat will lighten the intensity. Therefore, it is important to choose a color that will ideally match the anodized layer and the base material features. 

In the below section, we have described a few factors that need to be considered for appropriate color matching. 

  • Grade of the base material

    As it is the base metal absorbing the light and reflecting the rest, you need to focus on its color and tone. These two features differ according to the grade of the metal. For example, you can find the metal alloy having light silver shade, bronze metallic shade, dark grey shade, and more. So, you have to pick the color based on the grade so that the perceived color is similar to the expected one.

  • Finish type

    If the finish of the aluminum base surface is smooth and clean, the light won’t be scattered, and therefore, regular reflection will occur. This will cause your eyes to gather most of the radiation, intensifying the color. On the other, if the base material has an uneven surface, it will cause irregular reflection or scattering of the chrome rays. Again, this will reduce the color intensity. 

  • Dyes used and their types 

    The final color that your eyes will perceive will depend on the layers of dye used and the number of the chromes. For example, multiple dyes need to be used to match the color intensity or create unique shades. Similarly, if there is more than one layer of the dye, the reflection will happen at every stage, and therefore, the intensity will differ. 

Process of anodizing aluminum with different colors

The aluminum surfaces are colored in two different ways- anodization and painting. These two processes are much different from each other. For example:

  1. Color stability is more for anodized aluminum than the painted material, which is why the former products can last for a long time and create a high visual appeal.

  2. Also, anodized aluminum is resistant to abrasions, corrosions, and wear and tear. But the painted surfaces are not immune to these surface damages.

Conclusion 

In this complete guide, we have discussed everything you should know about anodized aluminum, its coloring, and several other facts. If you deal in metal fabrication, this guide will assist you in offering results as per the market standards and expectations. Besides, anodizing is a very tedious process. So, with the help of this guide, you can avoid making mistakes, be it in choosing the color or sealing the pores.

Scroll to Top