Anodized aluminum is valued for its properties, corrosion resistance, and gleaming finish. Besides this, anodized aluminum is incredible because it can be colored during the anodizing process. So, there are colorful varieties of aluminum for use. In this article, you will learn all about the anodized aluminum colors including the anodizing color chart, the type of anodizing colors, costs, and more.
What is Anodized Aluminum?
Anodized aluminum goes through an electrochemical treatment to develop a harder, thicker, and more decorative skin with a color coating. This process forms a layer on the surface of the metal comprising aluminum oxides and enables the formation of a colored dye layer. So, the aluminum is dyed in various colors.
What is Color Anodized Aluminum?
This is a procedure of giving color to aluminum during the anodizing process of aluminum. Aluminum can thus be anodically colored in almost any shade up to black, gold, bronze, and any primary color of the rainbow. The final layer produced is opaque and permeable, thus enabling the formation of a dye or metallic salt for a durable color.
Complete Process of Anodized Aluminum Coloring
The aluminum coloring process of anodizing uses several stages to improve the naturally forming oxide layer on the aluminum surface, resulting in increased hardness level, capability of sporting a shade, and corrosion resistance.
1. Cleaning and Pre-Treatment
Anodizing requires the aluminum surface to be cleaned thoroughly to remove oils, dirt, and other extra material over the surface. This step helps minimize anodizing defects that may be on the surface of the aluminum product to achieve the best finish. Pre-treatment methods include:
- Alkaline cleaning: Cleans the surface and destroys the effect of grease, oils, and other surface films.
- Etching: The aluminum is immersed in a concentration of sodium hydroxide to reduce the surface roughness of the piece’s surface to give the piece a flat dull appearance. This step assists in enhancing the formation surface for anodizing.
2. Desmutting
When the etching is complete, there will always be some sort of aluminum smut on the surface to be cleaned off. The smut can be removed by desmutting bath often nitric or sulfuric acid enables a smooth finish that does not have the smut. This step is important for alloy purposes as copper and silicon since they scar the structure after etching.
3. Electrolytic oxidation or anodizing
Here the aluminum is submerged in an acid electrolyte solution preferred to sulfuric acid (Type II anodizing). It allows electric current to be passed through a solution where the aluminum is an anode and the cathode is usually lead or aluminum.
Furthermore, the electrochemical process enables oxygen ions from electrolytes to come and deposit on the aluminum surface and form an aluminum oxide layer that is thick and porous. The anodic layer is:
- Porous: Enables dyeing or Coloring.
- Corrosion-resistant: It is much more resistant than aluminum that has not been treated.
- Controlled in thickness: Thickness depends upon the anodizing parameters. It can vary from 0.5 to 25 microns for decorative anodizing and hard anodizing is up to 150 microns.
4. Coloring
After anodizing forms the porous aluminum oxide layer on the surface it is ready to be coloured. There are several methods for introducing color during the anodizing process:
A. Integral Coloring
This is a method in which color can be introduced in the process of anodizing aluminum. The color develops the oxidation reaction concerning the organic acids and metallic salts. Integral coloring comes up with deeper and more metallic, i.e. bronze, black, and gold.
B. Electrolytic Coloring: Two-Step Process
Anodized aluminum is submerged in an electrolyte bath, i.e. metallic salt that contains tin, cobalt, or nickel after the anodizing process. Then it allows the current to pass through the solution and helps deposit the metallic particles into the pores of the oxide layer. So, it can create colors host, ranging from bronze, and black to champagne.
C. Organic Dyeing
In this process, the anodized aluminum is immersed right into a colored bathtub that enters the pores of the oxide layer. The range of color can be achieved when dyeing is broad. It provides conspicuous colors, i.e. blue, red, green, yellow, and many other colors. It seeps into the pores when anodizing is being done to give a deep and uniform color
D. Interference Coloring
Interference coloring is more complex since it includes the deposition of metallic oxides into the anodized surface to produce an active layer where light wave interferes. This results in iridescent or metallic effects with deeper colorations of gold, blue, or green such as that of the interference pattern.
5. Sealing
Finally, their surface is sealed with a clear sealant in order to close the pores of the anodized aluminum. Sealing can be done using several methods:
- Hot Water Sealing: The most frequent procedure is to heat the colored anodized aluminum in boiling water, which is about 95°C – 100°C. The heat results in the opening up of pores to take in moisture but once this water is taken into the pores they expand and close hence no further corrosion or harm to the colored surface.
- Cold Sealing: This is the process of placing the anodized aluminum into a bath with an option for using nickel fluoride or cobalt salts. This is however faster but comparatively costly and this yields a slightly dissimilar surface texture.
- Mid-temperature Sealing: Combination of hot and cold sealing techniques which results in better control in the final look of the anodized surface.
Sealing also lowers the ability of the aluminum to wear out, fade from the effects of the UV light, or decline from other external factors thus allowing the color to last longer.
6. Rinsing and Drying
After sealing, the anodized aluminum is washed with clean water and dried completely. After wash, the surface must be properly dried to avoid having water stains or marks on the finished surface.
Different Techniques We Can Use to Color the Anodized Aluminum
Here are the main techniques to color anodized aluminum:
- Integral Coloring: In anodizing, color depends on organic acids or metallic salts used during the process. It creates colors such as bronze and black but mostly gives dark metallic shades.
- Electrolytic Coloring: One anodizing process in which metal dyes such as tin or cobalt are deposited on the anodized layer that produces colors, i.e. bronze, black, and champagne.
- Organic Dyeing: Anodized aluminum can be immersed in a dye bath, resulting in a selection of bright colors including; red, blue, and green.
- Interference Coloring: Metallic oxides are precipitated with a range of interference colors, i.e. gold, blue, and green.
- Combination Coloring: This may include dyeing and special electrode methods, i.e. electro-coloring to effect preferred or multilayered hues.
Can the Colour of Anodized Aluminium be Changed?
Yes, anodized aluminum can be refinished and subsequently given a new color. But, to do that, the first strip off the existing anodized coat. This is mostly achieved through chemical stripping, mechanical sanding, and re-anodizing aluminum. However, this causes a problem with the material mechanical properties and is utilized only when necessary.
Acids Used to Color of Anodize Aluminium
Several acids are used to color anodized aluminum, each with its benefits:
- Sulfuric Acid (Type II): The most commonly used anodizing acid that covers virtually all the anodizing colors and accompanying uses.
- Chromic Acid (Type I): Recognized for specifying a slender yet, anti-corrosive oxide layer is applied in aerospace engineering.
- Phosphoric Acid: Useful for application in bright dipping process for decorative coatings.
- Organic Acids: Good for attaining particular shades and lusters using sulfuric acid.
- Oxalic Acid: Famous for painting automobiles in yellow or gold.
Key Considerations When Choosing an Anodized Aluminum Color
When you’re choosing an anodized aluminum color, consider the following:
- Application: Where will aluminum be utilized? If you are using it outdoors, UV stability is required.
- Durability: Type III anodizing may not be sufficient for ‘rugged’ applications and a harder surface might require type 50 anodizing or other types of anodizing.
- Aesthetic Appeal: The color should harmonize with the design and branding is associated with the specific product.
- Environmental Exposure: Lighting and climate play an essential role in the fading of the color.
- Cost: They are different in price because the anodizing process is different or one of the colors is used less often.
What to Do If the Anodized Part’s Color Isn’t What You Expected?
If you want to reverse color on anodized aluminum, there is a way for you to do this the first is by using chemical etching solutions which could help strip the anodized layer. For the other method, you’re allowed to mechanically rub the surface so that the raw aluminum can show through in a non-smooth manner. The anodized layer is removed from the aluminum and then the aluminum can again be anodized in the color, preferred.
Benefits of Coloring Anodized Aluminum
The following are the pros of anodized aluminum coloring.
- Durability: These coatings provide better protection from corrosive elements and better protection from scratches.
- Aesthetic Appeal: Most often have a variety of colors and finishes.
- UV Resistance: Green and other colored fabrics do not readily develop and fade when exposed to the sunlight
- Environmentally Friendly: Anodizing also has fewer toxic chemicals than in painting It is also a better way of protecting aluminum surfaces.
- Increased Surface Hardness: Anodized aluminum as we know is harder tested than normal aluminum.
Drawbacks of Coloring Anodized Aluminum
The following are the cons of anodized aluminum coloring
- Cost: Color anodizing is costly compared to simple anodizing.
- Limited Color Palette: This can be a challenge depending on the color needed, or wanting a bright white or certain light shade of a color.
- Surface Irregularities: A few imperfections present on the aluminum can get amplified after anodizing has been done.
- Potential for Color Variations: Batches may come in slightly different colors.
- Complex Removal: When undertaken, re-anodizing takes some time and is also detrimental to the surface of the aluminum part.
Different Types of Aluminum Anodizing Coloring
The following are the different types of Aluminum Anodizing;
- Natural/Clear Anodizing: Retains the appearance of aluminum with improved durability, go to clear anodized aluminum page to know more.
- Bronze Anodizing: Often used for architectural projects its appearance has a rich metal reflection.
- Black Anodizing: It has characteristics of electronic gadgets and automobile parts offering a trendy outlook, go to black anodized aluminum page to know more about this black anodizing color.
- Bright Anodizing: Usually accomplished by a blazing dipping method and provides a brilliant or luminously reflective surface.
- Two-Step Anodizing: Comprises anodizing of the aluminum then dyeing and sealing the material resulting in a colorful list of colors.
There is only a few of them but not limited to those colors, any color can be anodized on the aluminum parts, if you have aluminum part that needs special anodizing surface finish, you can contact us.
What is the cost of Anodized Aluminum?
The cost of anodized aluminum varies according to the kind of anodizing done, the size of the aluminum part, and the color. On average, anodizing will set you between $2 and $10 per square foot, for custom colors and finishes, costs increase.
Anodized Aluminum Coloring Chart with Estimated Cost
So, here is the Anodized Aluminum Coloring chart along with estimated costs;
| Color | Application | Cost Range (Per Sq. Ft.) |
| Natural (Clear) | Industrial, Automotive, Construction | $2 – $5 |
| Black | Electronics, Automotive, Aerospace | $3 – $6 |
| Bronze | Architectural, Consumer Products | $4 – $7 |
| Gold | Jewelry, Decorative Hardware, Architecture | $5 – $8 |
| Red | Consumer Electronics, Automotive | $4 – $7 |
| Blue | Aerospace, Marine, Consumer Goods | $4 – $7 |
| Green | Military, Outdoor Equipment | $5 – $8 |
| Custom Colors | High-end Consumer Goods, Design Elements | Varies (depending on complexity) |
Applications of Anodized Aluminum Coloring
So, here are some of the important applications of anodized aluminum coloring in different industries;
- Architecture: Applied in door and window sills, curtain walling, and decorative strips.
- Automotive: Anodized aluminum is widely used as a trim and exterior part
- Electronics: Anodized colors are incorporated in devices such as telephones and computers.
- Aerospace: Utilized as a design feature and element for operational use in planes.
- Consumer Goods: Anodized aluminum can be used in most home products for example clothing irons, utensils, and home facilities like tables and chairs.
Conclusion
In conclusion, anodized aluminum represents high durability, and versatility and allows any color that can be commercially useful in different fields. Knowledge of the anodizing process, the various colors, and the factors to consider in color selection will be useful in getting the right job done. So, this article gives a complete guide to anodized aluminum colors.
Frequently Asked Questions
Q1. Some claim that anodization can be done at home, is it true?
Yes, it needs specific tools and other things to do it right and make it look good.
Q2. How long do Anodized aluminum products last?
Without sealing, anodized aluminum can serve about 20 to 30 years without fading its color and corrosion.
Q3. Is this anodizing method environmentally friendly?
Anodizing is however believed to be more environmentally friendly than all other coating processes because of the least toxic chemicals it utilizes.
Q4. Can anodized aluminum be welded?
Yes, but the anodized layer needs to be guarded before the beginning of welding, and the layer might need reestablishment after the welding.
Q5. Can I paint over anodized aluminum?
Yes, but before painting, the surface of the material that is to be painted has to be cleaned well and etched.