Aluminum Anodizing - The Ultimate Guide
What is Aluminum Anodizing
The electrochemical passivation process that converts the surface layer of an aluminum substrate into an aluminum oxide layer is known as aluminum anodizing. This procedure turns the metal surface into an anodic oxide finish that is beautiful, long-lasting, and corrosion-resistant.
It also provides highly durable exteriors with minimum maintenance, revolutionized the construction of computer hardware, consumer products, home appliances, building materials, and more.
Although aluminum is ideal for anodizing, other nonferrous metals like magnesium and titanium can also be anodized. Aluminum anodizing is governed by a number of procedures and standards, the most prevalent of which come from the defense, aerospace, and automotive industries.
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Aluminum Anodizing Benefits
Aluminum products that are anodized have a long life span. Aluminum anodizing offers economic advantages by minimizing operation and maintenance cost savings.
Anodized aluminum parts are applied with anodic coatings to ensure that the colors will not peel or chip and are easily repeatable when exposed to ultraviolet rays.
Anodizing can provide a lot of color and gloss alternatives. It helps in eliminating and minimizing color variations. Anodizing also offers a metallic appearance to the products.
The aluminum anodizing process is not harmful and safe for human health. This surface finish is non-toxic, heat-resistant, will not decompose, and chemically stable.
How Anodic Coatings are Applied to Aluminum?
During the process, the aluminum part is submerged in an acid electrolytic bath. Then, by using a medium, the component will pass in an electrical charge. A release of oxygen ions from the acid electrolyte is possible when the current moves through the bath.
The oxygen ion will join the aluminum substrate creating an aluminum oxide layer. Unlike plating or painting surface finish, the underlying substrate is fully integrated with the anodic layer.
Factors to Consider When Choosing Anodic Coating
Each industry such as aerospace, defense, medical, surgical, and more requires different anodizing specifications. Mostly, defense, automotive, and aerospace industries require abrasion resistance. Thus, requires a hard coat anodizing.
For medical and surgical industries, chemical resiliency is essential. Therefore, needing an anodizing process that produces a consistent and even finish availability of a wide range of non-leaching colors, aesthetically pleasing, and chemical resistance.
Anodizing Enhances the Aluminum Part Life Cycle
Anodizing process enhances the aluminum parts with more corrosion resistance, lightweight, and extremely strong finish. The anodized surface of the aluminum components becomes very hard. Thus, preserving and extending its life.
Its high corrosion resistance makes the aluminum component suitable for transportation, processing equipment, storage, building element, and more industrial applications. It also adds durability for applications where abrasion resistance is needed.
Aluminum Anodizing - Material and Energy Saving Process
Aluminum is a good electricity conductor while the anodic coating is also an insulator. These two properties can be combined to save material and energy. The anodized aluminum part can be used for conductive and structural applications. Anodizing process provides properties that allow minimizing energy demand while enhancing the component’s life cycle.
Aluminum Anodizing: Environmentally Safe Process
The aluminum anodizing process doesn’t use any VOCs. It is a process that doesn’t use any carrier resins or vehicle solvents. The process used an extremely small amount of pigmentation or dye that is locked in a hard surface. Anodizing process doesn’t involve any toxic organic such as halogenated hydrocarbons.
During the process, anodizing will not generate any hazardous waste. In fact, wastes from the aluminum anodizing process are significant for settling solids and removing pollutants in domestic sewage.
Different Steps in Aluminum Anodizing Process
The first step is cleaning the aluminum product before anodizing. The surface with grease and dirt can be cleaned with alkaline or acidic cleaning agents.
The second step is pre-treatment to remove any imperfections or flaws from the surface. Thus, providing a smooth, clean, and visible surface. Etching and brightening are the two main processes used for pre-treatment.
Brightening is also known as bright finishing. This process cleans the leftover residues from the cleaning process of aluminum metal. A concentrated mixture of phosphoric and nitric acid is used for smoothening the aluminum surface. Thus, providing a metallic finish.
This process can provide a matte finish to the aluminum by eliminating the aluminum layer from the surface. Surface imperfections can be removed by using a hot sodium hydroxide solution.
After the pre-treatment process, the aluminum component is ready for the anodizing process. Sulfuric acid and other alternatives such as chromic acid, phosphoric acid, tartrate, borate, and organic acid are used in the process.
Anodized aluminum uses different methods to add color such as:
Electrocoloring is used in the anodizing process to provide a dark color shade. This method uses electrolyte with an inorganic metallic salt.
It is the most common way of adding color to the anodized aluminum parts. It has a thick layer that makes it scratch resistant. The dyeing method offers a wide range of color choices.
This process is the last step of aluminum anodizing. It provides corrosion resistance and leakage proof to the anodized aluminum component. This process can be done through the cold and hot methods or combinations.
Different Types of Aluminum Anodizing Process
Decorative anodizing focuses on providing an aesthetic appearance to the aluminum component while adding extra protection.
This type of aluminum anodizing is the most common. It uses chromic acid to create a ductile and thin anodized layer.
Type II aluminum anodizing uses sulfuric acid rather than chromic acid. It is an ideal choice for colorization since it can create a thicker anodized layer on the aluminum part.
This type of aluminum anodizing method also uses sulfuric acid but creates a thicker anodized layer. It is also ideal for colorization. Type III anodizing is also called hard anodizing.
Aluminum Anodizing Process Equipment
The temperature should be within the specific parameters inside the tank. It requires sufficient cooling so it does not exceed a couple of degrees temperature during the anodizing process. For the hard-coat anodizing process, a water or glycol mixture is used for cooling.
During the anodizing process, agitation can be provided by using a pump. Fumes that are generated by the tank during the process are captured by the exhaust ventilation. Exhaust ventilation with a slot hood is responsible for controlling the fume emission.
Color Options for Anodizing Aluminum
There are a variety of color options during the aluminum anodizing process. The standard color options for aluminum anodizing include black, champagne, bronze, clear, red, pink, gold, yellow, green, brown, violet, grey, and more.
Aluminum Anodizing Design Tips
If you are a beginner in aluminum anodizing processing, here are some tips for a smooth process.
Anodizing process can add extra thickness to the aluminum component. Therefore, if your application requires critical tight tolerance, you may opt for Type II or Type I aluminum anodizing.
Take Note of Corners and Edges
A significant design tip for aluminum anodizing is to ensure that all corners and edges of the component have at least 0.5mm radii. Make sure that aluminum parts are not produced with any burrs. Considering this tip may prevent overheating and burning during the process/
Use Other Surface Finishing Process
If the aluminum part is anodized directly, it may leave some scratches or marks on its surface. Due to that, in order to achieve an even surface finish, you may consider bead blasting, polishing, or other mechanical finishing prior to aluminum anodizing.
Batch by Batch Anodizing
If you decide to put color on the aluminum component, it is recommended that you perform the anodizing process in a small batch to assure an even color uniformity.
Aluminum anodizing is an affordable process that can provide different components with additional protection. Thus, this process is widely used by different industries including the following:
- Homeware sectors
- Consumer goods
- Medical, and more.
A wide range of aluminum parts is suitable for the anodizing process such as:
- Kitchen equipment
- Electronic casings
- Food preparation products
- Radio equipment
- Duct covers
- Photo equipment
- Light fixtures, and more
Below are some useful considerations to identify if you performed a successful aluminum anodizing process.
Check if the anodized part has a matte finish. Usually, anodizing creates a matte finish surface.
A simple scratch test using a coin may also help. Anodized aluminum parts are fully scratch resistant. Try scraping a coin to the surface, if it creates a scratch, the aluminum component is just likely to be polished, not anodized.
Check if the aluminum parts have uniform color dispersal.
Aluminum anodizing is a cost-effective process. However, the cost is also affected by different factors including anodizing type, shape, part dimension, color, part quantity, and more. For example, complex aluminum parts will be more costly to anodize, unlike simple aluminum parts.
Yes. Through anodizing, the aluminum parts’ surface will be added to the barrier layer. Therefore, you can assure that it will not chip or peel. Aluminum anodizing that is properly performed will last for many decades. Additionally, dyed aluminum parts through anodizing will most likely last for at least 5 years.
The aluminum parts will have more or less resistant depending on the thickness the anodized layer provides. For applications that need a strong resistance, the thickness of the parts can be increased up to 50 µm. Thicknesses can help you distinguish its use. You can refer to the following table.
|Class 5-10||5-9 microns and 10-14 microns||Parts should only be used for indoor applications.|
|Class 15||15-19 microns||Aluminum parts is a standard class for outdoor applications|
|Class 20||20-24 Microns||Suitable for applications such as marine and industrial|
|Class 25||25-29 microns||Ideal for marine and industrial applications|
Powder coating is also a surface treatment that is available for aluminum materials. In this process, the aluminum surface is coated with polyester powder to add decoration and protection. However, most manufacturers find anodizing as much better than the traditional powder coating process because of the following:
- Anodizing is an inorganic choice that can offer an excellent surface finish than organic powder coating.
- Anodizing can provide a metallic sheen appearance to the aluminum surface. Compared to powder coating, anodizing can react to both artificial and natural light.
- Powder coating may be subjected to failure and color may fade after a long time. On the other hand, anodizing can be used and can provide better performance for many decades.
Other than aluminum, other materials such as tantalum, hafnium, zinc, niobium, zirconium, titanium, and magnesium can also be anodized.
Plastic materials are also suitable for the anodizing process.
All materials that undergo anodizing process can be provided with a long-lasting life cycle, attractive appearance, and superior surface finish.
During the process, the aluminum part is subjected to a variety of chemical baths. Thus, requiring an electric terminal to hold the part during the process. Sometimes, the part needs to be hanged or mounted to hold it in the position. That part of the aluminum component is blocked and will not be anodized.
This process uses an acidic solution, thus the aluminum ions start to lose on the aluminum surface. The aluminum surface will be eroded and will react to the electrolyte’s negatively charged oxygen ion. While the erosion continues, the surface creates a barrier by forming an aluminum oxide layer and thus, preventing another erosion.
After coloring, the aluminum anodizing process provides metallic characteristics due to two factors:
- Anodizing creates a uniform electrochemical etching. Thus, leaving a rough surface. The surface becomes rougher if the pores are deeper. This will also provide more durability to the colors.
- The light that strikes from the anodized aluminum surface reacts with the colorant and bounces back to a person’s eye. Two different wavelengths will reflect causing a distinctive shine or metallic properties.
Now that you have learned and understand aluminum anodizing, you can decide if you want to anodize your aluminum component. This processing technique will satisfy your requirements if you need corrosion resistance, wear resistance, and functional aluminum parts. If you want your aluminum parts to have a visual appeal while adding extra durability, metallic sheen, and protection, you should anodize your components.