Anodized Aluminum Guide

Aluminum has a protective oxide layer of Al2O3 that prevents aluminum from corroding. Taking advantage of this property, aluminum is anodized and an oxide layer is artificially formed on the surface of the sample through an electrolytic reaction. This layer is corrosion resistant, durable, and aesthetically pleasing. A good surface finish can extend the life of the material by increasing fatigue life and improving wear resistance.

Different colors can be produced using anodizing. It can also be done by using pigments and dyes to adhere them to the porous oxygen layer after anodizing. This article will guide you on how anodizing works and how to apply different colors on aluminum substrates.

How does anodizing work?

Anodizing is the process of adding an oxide layer to the surface of a metal. It increases the thickness of the metal and also provides corrosion and wear resistance. Thus, increasing the life of the material. Sometimes it is also used for the aesthetics of the metal.

The process starts by immersing the metal substrate in an electrolyte solution. The metal substrate acts as an anode and is connected to the positive terminal of the battery. While the negative terminal is connected to a metal bath containing an electrolyte solution. Electrolytes such as sulfuric acid and sodium phosphate are used for this purpose. When current flows through the electrodes, the metal substrate acts as an anode and attracts oxygen ions from the solution, while the metal bath acts as a cathode. Due to the electrolytic reaction, a layer of oxide forms on the surface of the metal.

Anodizing is popular with aluminum alloys, and sometimes the process is also used for titanium and magnesium.

Basics of Aluminum Anodizing Process

Aluminum anodizing is a method of improving the surface of aluminum by creating a durable oxide layer through an electrochemical reaction. This layer, also known as the anodic film, improves corrosion and wear resistance by providing decorative and coloring options.

Aluminum anodizing is performed in the following steps:

Cleaning

This process is used to remove grease/oil from the substrate that may interfere with the anodizing process. This is done by immersing the substrate in an acidic or alkaline cleaner.

Etching

Before anodizing, alkaline or acid etching is used to remove minor defects on the aluminum surface. In this step, a thin layer of aluminum is removed to create a new surface for the anodizing process.

Aluminum Anodizing Colors

After removing the etchant, the aluminum is anodized by immersing it in a sulfuric acid bath. By supplying an electric current to the cathode, a porous oxide layer forms on the surface.

Coloring

Metal salts or organic dyes can be introduced into the porous oxide layer if any coloring is required.

Sealing

In the final step, the porous surface is sealed by immersing the substrate in a nickel acetate solution and a highly durable surface is created.

 

 

Anodizing of aluminum is classified into different types such as chromic acid anodizing, sulfuric acid anodizing, and hard anodizing, each type depending on the specific use. Aluminum anodizing is widely used in industries such as automotive, aerospace, electronics, and construction.

Aluminum Anodizing Dyes

Anodizing dyes are applied after the anodizing process when an oxide layer is formed on the surface. This is done by immersing the aluminum substrate in a dye bath. The dye is then absorbed by the porous oxide layer under controlled temperature and pressure. These dyes can provide you with custom color anodizing.

Different types of dyes are used in the industry:

Acid dyes:

They contain organic compounds used to dye aluminum under acidic conditions. Examples include acid red 88, acid blue 90, acid black 1, etc.

Metal complex dyes

Common examples of these dyes are nickel sulfate dyes, cobalt sulfate dyes, copper sulfate dyes, etc.

Organic pigments

Organic pigments also provide a wide range of colors and are stable. For example: Phthalocyanine Green, Quinacridone Red, Perylene Violet, etc.

Color Matching (Various Colors for Aluminum)

Color matching is done by using specific dyes of the desired color. Aluminum is mostly available in gray, which is neutral and modern. Adding color to aluminum also depends on the method chosen. There are different methods for adding color.

Electrolytic Coloring

This process is done by immersing the aluminum substrate in a bath containing metal salts and then providing an electric current. The common colors used in this process are basically bronze and black. The colored surfaces produced by this technique are UV resistant.

Dip Dyeing

In this method, the anodized aluminum is immersed in a dye tank. When the pores are completely filled with dye, the substrate surface is boiled in an iodine water tank. It is available in a variety of colors, but unlike electrolytic coating, it is not UV resistant. Integral coloring and interference coloring are also used in the industry.

Color matching of anodized aluminum is a subtractive color process, unlike painting which is an additive color method. Usually, you see the color reflected from the surface of the material. The anodized film acts as a filter, the light passes through the porous layer and is reflected by the aluminum surface underneath. This adds to the complexity of the process.

Anodized Aluminum Color Chart

The anodized aluminum chart shows a comparison between the anodizing process and the range of colors it can provide. These charts also depend on the grade of aluminum used and its surface finish. Here is a standard anodized aluminum color chart for better understanding.

The question is what color can aluminum be anodized to. Aluminum can be ionized to a variety of colors and you will have to see some examples:

Purple anodized aluminum: Purple is obtained when red and blue anodizing dyes are mixed.

Orange anodized aluminum: Orange anodized aluminum is made from a dye called Acid Orange 7.

Gray anodized aluminum: Gray is obtained by using a dye called Acid Black 1.

Red anodizing: Red is the result of Acid Red 88 dye.

Colored anodized aluminum

Colored anodized aluminum is made using three types of anodizing processes. In the Type I anodizing process, the substrate is placed in a colored electrolyte solution, which creates a porous oxide film. Most of the time, this method is done before painting the substrate. This process also produces bronze anodized aluminum. The Type II process uses a sulfuric acid electrolyte. It is generally used before dyeing. When the substrate is immersed in it, its porous structure absorbs the dye. Type III contains a mixture of sulfuric acid and dissolved aluminum parts. It increases the surface hardness of the material.

Color Anodized Aluminum: The Process

First, anodizing of aluminum is done by electrolysis. The material is then immersed in a tank containing dyes or organic pigments. Coloring can also be done using a simple electrolytic process and depends on the electrolyte mixture used for the coloring process.

Multicolor Anodized Aluminum

Multicolor anodizing is done by selecting a mask on the substrate. First, the substrate is carefully cleaned after applying a mask on the selected areas. After that, the substrate is immersed in the electrolyte solution. An anodized layer is formed over the exposed areas. When the desired thickness is reached, the mask is removed and a substrate with different colors is obtained. This type of anodizing color variation is required only in applications where aesthetics or color coding are required.

Hard Anodized Aluminum Colors

Hard anodizing, also known as Type III anodizing, produces components with different colors. These colors depend on the grade of aluminum and the thickness of the oxide layer. Clear anodized aluminum, before dyeing, has a dark gray or bronze gray color. After dyeing, it can achieve a full black effect. On this basis, they must major in the course. Class I undyed samples have a dark gray or black and bronze gray color. This class is usually not used for decorative purposes. In Class 2 hard coat anodizing, black is preferred in most cases. The following figure shows the hard natural anodized aluminum color.

Hard Anodizing Process

The hard anodizing process is slightly different from the conventional anodizing process. First, the substrate is placed in a sulfuric acid electrolyte tank containing 180 grams of acid per liter. After that, bubbles are bubbled out of the solution. Further circulation of air helps to maintain the temperature of the sulfuric acid at a temperature close to the freezing point. Subsequently, the oxygen in the electrolyte forms a layer of oxygen on the surface of the substrate. The current is continuously applied to achieve the desired thickness.

 

 

The thickness of anodized hard coatings ranges from 13 to 150 microns. This thickness range is much higher than Type I and Type II anodizing.

 

Can you change the color of anodized aluminum?

Yes, anodized aluminum can be customized to any color you want. It can be done by using dyes or processes such as electrolytic coloring.

Dyes

After aluminum is anodized, the dyeing process is as simple as immersing the sample in a bath containing dissolved organic/inorganic dyes. This is a short process, typically taking ten minutes for the dye to penetrate the porous anodic coating and become trapped within it. The final color depends on several key factors, including the thickness of the anodic film, dye concentration, immersion time, and temperature.

Electrolytic Coloring

The process involves immersing the anodized aluminum in an acidic bath containing metal salts and then passing an alternating current through it to deposit the metal salts onto the anodized surface. The color produced depends on the size of the ions and the voltage applied. A wide range of colors can be achieved with different electrolytes such as tin, nickel, and cobalt.

How to Clean Colored Anodized Aluminum

The process of cleaning colored anodized aluminum is very simple. Simply wash with warm water, but if there is stubborn dirt, rinse thoroughly with a soft cloth and a mild soap solution. To keep the surface finish intact, it is important to avoid using harsh acidic or alkaline cleaners and use gentle pressure when cleaning.

Anodized Aluminum Paint Colors

Anodized aluminum paint colors are applied on anodized aluminum to further improve the appearance. Different paints can be applied on anodized aluminum, such as acrylic paint, epoxy paint, and polyurethane paint. For applying the paint, any method can be used, such as spraying, brushing, or dipping. The final substrate is mainly used for architectural and customer products.

Factors to Consider When Selecting Anodized Aluminum Colors

The color matching process of anodized aluminum is very challenging because it acts as a filter rather than a reflector. In order to achieve color consistency in anodized aluminum, several factors need to be observed. Each aluminum grade varies in color and hue to achieve the best results. It is necessary to choose the right grade. The type of metal surface treatment can be matte or shiny. Therefore, for color matching, consider samples with uniform finish. Increasing the number of dyes and layers will cause color changes. The last factor to consider is the crystal structure of the material, and the correct reflection angle must be ensured because the lattice structure affects the way anodized aluminum reflects light.

Why Choose Tuofa Custom Anodized Aluminum Service?

China PANS is known for its CNC machining, but it also offers services like aluminum anodizing. The skills and capabilities of the workforce are sufficient to handle the complexity of the problem. You should choose TuoFa because they:

Modern technology
Customer satisfaction
Low price

Customer satisfaction is the top priority of the organization. At TuoFa, small to large quantities of samples can be anodized. Functional prototypes are also available, which will save time and materials.

Common Problems and Strategies

Does anodized aluminum wear out?

Yes, anodized aluminum will wear out over time. The oxide layer produced by anodizing has good wear resistance, but it is not immune. Factors such as environment, weather, and wear and tear can cause the oxide layer to wear out. By avoiding harsh cleaning and regular inspections, you can extend the life of anodized aluminum.

How much does anodizing aluminum service cost?

The cost of anodizing aluminum service depends on the grade and temper number of aluminum, size, complex shape, type of anodizing, and the number of aluminum samples that can be anodized. You must consult different industries, and if they offer the same surface treatment, then you must compare and choose the one that can provide excellent processing at a low cost.

Is hard anodized aluminum suitable for induction?

No, hard anodized aluminum cannot be inductive, and cookware made with this type of aluminum is not suitable for stovetops because there is no induction between the stovetop and the hard anodized aluminum. Cookware mostly uses magnetic materials for induction purposes. Hard aluminum that is specially made through this process has a base made of magnetic materials such as stainless steel.