After the manufacturing process, some applications require surface treatment. Among the various methods, Anodized Aluminum Colors and other materials stands out because it produces durable and aesthetically pleasing products.
Aluminium anodising creates a protective layer on the surface of aluminium products, preventing corrosion and increasing their durability. Anodised aluminium colours include blue, red, green, black, silver, gold, orange, purple, pink and more. These colours are permanently applied through the anodising process to improve stability, durability, surface finish and wear resistance.
This article explores the Anodized Aluminum Colors selection, technology and influencing factors of aluminium anodising colours. You will also learn how to fully customise colours for specific applications in your industry.
Let’s first understand the aluminum anodizing process. Aluminum anodizing is an electrochemical process that adds a wear-resistant oxide layer to the surface of aluminum products. This can improve the quality and appearance of the product, making it durable, wear-resistant and corrosion-resistant, and aesthetically pleasing.
The anodizing process involves an electrochemical cell reaction, where the aluminum part is the anode. An inert material serves as the cathode, and an acidic electrolyte is used. There are three types of anodizing processes, and each type has different coating strengths. These differences come from differences in the electrolyte, electrodes, and energy used in the process.
Type 1 anodising uses chromic acid as the electrolyte and aluminium as the anode. When an electric current is passed through the electrolyte, the positive particles on the anode form tiny grooves on the surface. These grooves oxidise to form an oxide layer which increases the resistance to heat and corrosion compared to untreated aluminium products.
In Type 2 anodising, sulphuric acid replaces chromic acid, providing a stronger solution. This allows the orthoaluminium particles to be blasted more effectively than in Type 1. As a result, the micro-grooves formed are deeper and the oxide layer thicker. These characteristics contribute to the improved paint retention of Type 2 aluminium parts.
Ideal for heavy-duty aluminium products, Type 3 anodising uses higher voltage and stronger sulphuric acid. This process differs from other types in that it produces a thicker, more durable oxide layer, which increases wear resistance. The resulting aluminium products are particularly suitable for heavy-duty applications in harsh environments.
Colour anodising of aluminium refers to the formation of an artificial oxide layer on the surface of aluminium and the addition of colour to enhance its functionality and aesthetics. Unlike coatings such as painting and electroplating, colour anodising will not flake off or fade over time.
The benefits of color anodizing include:
Colour anodised aluminium offers a range of options, making it attractive to those who prioritise colour in their purchases. It enhances aesthetics without compromising the metallic look of the aluminium component. It creates different colours and finishes to differentiate branding and marketing efforts. If you value aesthetics in your application, this is undoubtedly your best choice.
The extended life of anodised aluminium products provides economic benefits through reduced maintenance and operating costs. The added protective layer of anodised aluminium colour enhances wear and corrosion resistance. This is particularly beneficial in harsh environments exposed to corrosive substances.
The value of anodising is that it forms a well-structured oxide layer around the metal, preserving its quality and preventing corrosion. The added colour layer increases corrosion resistance, making it particularly suitable for harsh environments.
Adding colour to the aluminium surface through anodising not only enhances its appearance, but also reduces friction. This makes it suitable for applications where low friction is required. This property makes anodised aluminium versatile and functional.
The anodising process can give aluminium surfaces a variety of Anodized Aluminum Colors, including blue, red, green, black, silver, gold, bronze, orange, purple, pink and more. The aluminium alloys obtained during the manufacturing process usually have a variety of colours. As a result, the colours available in anodised aluminium are very numerous.
The Anodized Aluminum Colors of anodised aluminium range from light to dark. Factors such as anodising layer thickness, immersion time, colour concentration and power supply level can affect the colour intensity. Using sulphuric acid as the electrolyte can produce brown and black, followed by red, blue, gold and bronze. In addition, clear anodising produces a transparent, uniform film which improves durability and stability. Common anodising colours for industrial products include brown, black and clear (silver), which account for approximately 80% of anodising applications. The following anodised aluminium colour chart briefly introduces some colours and their components.
The aim of this step is to thoroughly clean the surface of the aluminium workpiece and remove any grease deposits. This ensures optimum deposition of oxidising ions, resulting in a uniform oxide layer. In addition, addressing the moisture content prevents the formation of white spots in the anodised layer. This helps to maintain the quality of the workpiece.
Once the surface has been cleaned, the workpiece is immersed in an etch solution to remove the native oxide. This step removes a fine layer of oxide to ensure a uniform, contamination-free surface. The part is then rinsed to remove any residual etch solution.
After obtaining a surface free of impurities, the workpiece is placed in an electrolytic solution of sulphuric acid. When preparing the solution, one part of sulphuric acid must be added to three parts of water to prevent the formation of harmful gases. The aluminium workpiece, which acts as the anode, is connected to promote the deposition of oxide ions.
The flow of current through the solution forms an oxide layer and bubbles appear near the anode. If no bubbles appear, the power supply should be switched off to check the connection. The aluminium oxide layer initially formed is thin and uniform (barrier layer).
Once formed, the current is increased to create pores in the surface to allow the coloured layer to adhere. This current is maintained for approximately 45 minutes and the colour of the anodised layer changes to brown and then yellow. At the end of the anodising process, the surface is thoroughly rinsed to remove any residual electrolyte.
Once the anodising process is complete, you have a number of options for adding Anodized Aluminum Colors to your workpiece. There are four ways to colour anodised aluminium and each method is explained below.
Sealing is a key step in anodising where dye molecules are trapped in the pores to prevent absorption of unwanted molecules. Sealing is performed in hot water at 93ºC, forming hydrated aluminium oxide crystals that close the pores. Metal salts can also be deposited after dissolving in hot water at 86ºC. Sealing increases corrosion resistance, making the coating more ideal and improving material performance.
Unlike paint, anodised colours are subtractive rather than additive. In standard colour perception, materials reflect what they do not absorb. Anodising is slightly different: the film formed transmits light to the aluminium base and reflects it back through the film. This turns the anodised layer into a filter rather than a reflector. This concept is crucial for accurate colour matching.
Achieving colour consistency is challenging, especially between batches. Successful colour matching of anodised aluminium requires an understanding of the above concepts and the key factors that affect the appearance of anodised colours. To ensure colour consistency, the following factors should be considered during the anodising process.
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