After parts fabrication, manufacturers tend to apply some finishes and post-processing operations to improve aesthetics and the general features of the material.
Anodization is one of the most effective such finishes. The process involves coating the metal with a more stable and resistant component of the metal, usually its oxide.
And since aluminum is the most common material for manufacturing, this post-processing operation is common with aluminum. Like all finishes, anodizing aluminum improves the appearance of the metal.
It enhances its mechanical and chemical features, improving its resistance to corrosion, scratch, rusting, etc. In addition, it increases the tensile strength to almost three times that of regular aluminum.
This article provides information on the processes involved in anodizing aluminum, its benefits, design tips, and everything you need to know before choosing this finish for your parts.
What is Anodized Aluminum?
Anodized aluminum refers to aluminum material that has gone through an electrochemical finishing – anodization. The process involves dipping the metal in a series of tanks in the presence of an electric current, where the metal’s external surface gets coated with an anodic oxide finish. The resulting aluminum is durable, corrosion and scratch resistant and has a better appearance.
Besides improving the mechanical and chemical properties of the metal, anodizing allows for better adhesion for glues and paint primers. The anodic layer gives the metal a unique finish that could be transparent with more excellent light reflective properties or thick with better adhesive features.
Since the extra (anodized) layer is formed from the metal itself, there’s less tendency for it to flake or peel off, improving the reliability and durability of the metal.
Anodizing is an effective way of improving the strength of a metal without increasing its weight. For example, anodized aluminum retains the lightweight property of aluminum, but it is about three times stronger than standard aluminum.
Though anodization is more common in aluminum, the process is suitable for other metals like zinc, magnesium and titanium.
How the Process of Anodizing Aluminum Works
Are you looking to anodize your aluminum parts? Then it is vital you first understand the process and how it works. Thinking about the procedure, it may seem complex and overwhelming, being an electrolytic process.
However, it’s pretty straightforward, making it a popular finishing option in most industries.
Steps to Anodizing Aluminum Parts
General anodizing occurs in a two-step process.
Step 1: Cleaning
Whether it’s a CNC machined part, or sheet metal fabrication, anodizing is suitable for almost all aluminum parts. Before the electrochemical process, the metal pieces must be appropriately cleaned, with an ideal cleaning agent, such as a non-etching alkaline detergent.
This helps rid the aluminum surface of impurities, oils, contaminants, etc. The presence of these impurities can reduce the effectiveness of the anodizing process.
Step 2: Anodizing
The aluminum part is dipped into a bath containing the electrolyte with direct current. During the anodizing process, positive charge forms around the aluminum, while negative charges move towards the other plate in the electrolyte.
The electrochemical reaction creates pores on the aluminum surface, allowing negatively charged oxide ions to bond. These oxides bond with aluminum to form the anodic layer of aluminum oxide that coats the metal. The aluminum oxide, which possesses significantly improved resistance against external than regular aluminum, now acts as the barrier, covering the metal surface.
Different Types of Anodizing Aluminum Process
There exist three main types of anodizing aluminum parts. Each method results in an anodized aluminum; however, there may exist some variation in the thickness and aesthetic appeal of the end product.
Type I Anodization
It is the primary and traditional form of anodizing. It involves using chromic acid as an electrolyte. The result is a thin coat of about 0.0001 inches around the metal surface.
Because of the thin anodized layer, there is less color absorption upon dying. However, there is a significant increase in mechanical and chemical properties.
Type II Anodization
This process uses the sulfuric acid electrolytic solution. It gives rise to a thicker anodized layer around the aluminum part, up to 0.0002 inches. Therefore, there is an increase in the adhesive property, making it more suitable for dyeing and coloration, compared to the type 1 chromic acid anodization.
Type III Anodization
This type is similar to the second because it also uses sulfuric acid. However, it is called hard a no fixing because it produces a thicker anodized layer (> 0.001 inches).
The increased coating ensures they possess better abrasion, and corrosion resistance, with improved adhesion to dyes and colors.
However, the thick layer makes it less suitable for parts having high precision and tight tolerance requirements.
Type I anodization, using chromic acid, used to be the popular choice since 1900, when this finishing operation was discovered. However, in recent times, the Type II and III process, using sulfuric acid, is soon becoming the go-to anodizing method.
Another method involves coating the aluminum surface with alodine – a chemical film. The end product of the process resembles parts that have undergone anodization.
Which Type of Anodizing Should You Choose? What’s the Difference?
Having obtained a complete understanding of the different types of anodizing. It is essential to know the ideal one to select for your fabrication.
For example, we already mentioned that the Type III anodization is unsuitable for parts with tight tolerance and dimensional accuracy requirements.
Below is a brief description of deciding which type to use for your design.
- Type I (Chromic Acid): The anodize layer is thin, though it provides effective resistance against corrosion. It is suitable for creating aircraft and automotive parts.
- Type II (Sulfuric Acid): The parts formed from this form of anodizing are thicker than those of type I. Though they still maintain a high level of dimensional accuracy. Therefore, they are suitable for aircraft and automotive components. However, they are a more standard finish for consumer and homeware goods.
- Type III: The anodized layer from this anodization is robust, thicker than the previous ones. This type of anodizing is preserved for components that face harsh and extreme chemicals and temperatures. Because of their thickened layer, they offer improved electrical insulation and are used for robust metal parts for military purposes. Also, they are suitable for valves, pistons, gears and other components that require a tough finish.
What Are the Color Options for Anodized Aluminum?
We mentioned earlier that anodized aluminum parts have deeper pores, allowing better retention of dyes, colors and other pigments.
That said, beyond the typical clear, transparent standard aluminum, it is common for manufacturers to brandish this finish in more appealing colors. Anodized aluminum may appear in black, blue, silver, gold, red, purple, etc.
The coloration works by injecting the dye or pigments into the deeper empty pores of the anodized aluminum. Immediately, the due reaches the surface of the metal, assuming the selected color. And since it is buried deep into the metal, it tends not to fade or scratch off, retaining the visual effect for a long time.
Remember that one of the benefits of this finish is the freedom it affords machinists to color their metal in desirable colors.
So you can be assured that whatever color or dye you choose will give you long-lasting desirable visual effects. At Kemal, we offer your anodized aluminum in any color variation you request.
Advantages Of Anodized Aluminum
We have briefly mentioned some of the benefits of anodized aluminum. However, let’s take a more detailed review of the advantages.
Anodizing aluminum parts increases the resistance to abrasion, corrosion, scratch, etc. There is an overall increase in mechanical strength, increasing the durability of the metal.
Also, since the anodic layer is a component of the metal itself – aluminum oxide, there is less tendency for it to peel off or flake.
Cleaning is an essential step in anodization – it rids the metal of contaminants and impurities. Also, after the process, the wears and scars that may arise from handling, assembling or even the fabrication of this component are not visible, as the metal adopts a unique, beautiful anodic finish.
Moreover, simple cleaning or rinsing the aluminum part with water and mild soap restores the anodic appearance.
Enhanced Aesthetic Appeal
One of the main benefits of anodizing is the improved appearance it provides. Like many other finishes and post-processing operations, it enhances the quality and surface properties of the aluminum part. Besides, it allows the integration of different color and dye variations.
You could have anodized aluminum brandishing blue, black, grey, gold, etc. Likewise, it could be transparent with enhanced light-reflective properties.
Typical aluminum tends to have a smooth surface, making retaining lubricating oils challenging. However, after anodization, the metal has more profound pores within the metal that allow for better adhesion and retention of lubricant – oils or films. This feature also allows anodized aluminum to retain color and dyes better than regular aluminum.
The pores are holes through which the lubricants, dyes, adhesives, or paints flow upon application to the metal surface. So, since anodized metals have deeper pores, they can absorb more of these liquids.
Health and Safety
The electrochemical process is not hazardous to humans – likewise, the after-effect of this finish. For example, anodized aluminum is used in the creation of cooking utensils.
This is because they retain their chemical stability. They are heat resistant, do not decompose, nor are they toxic. In addition, since anodizing just involves coating the metal with its oxides which is usually a naturally occurring substance, this shows more credence to the safety of anodized metals.
The anodizing process is relatively cheap. Though compared to other finishes like painting, it may seem more expensive.
However, since it requires little to no maintenance cost, even after long-term use of the anodized structure. Then, it is safe to say that it’s a cost-effective finish.
In all, the main benefit of this finish is the enhanced performance, increased lifespan and durability of the aluminum products.
Design Tips for Anodizing Aluminum
Anodizing aluminum parts is pretty straightforward, especially if you fully understand the process. Below we will discuss some crucial tips to help you streamline the finishing operation.
Remember that anodization increases the thickness of your parts, so when fabricating components with high precision specifications, you need to create allowance. You must factor in the extra thickness during the design and measurement stage. Also, avoid the type III method of anodization when working on parts that require tight tolerances.
Consider More Than One Coating
Beyond anodization, some machinists may apply additional finishes to metal surfaces to enhance the resistance further. Polishing and painting are typical post-processing operations that you can combine with anodization.
Your part’s strength and other mechanical requirements may determine the kind of anodization you use. For example, you should use type III anodization if the design calls for a robust and sturdy aluminum component.
Consider Edges and Corners
It is crucial that you leave an allowance of about 0.5mm around the edges and corners of the workpiece. This helps curb overheating or burning upon exposure to high amounts of electric current during anodization.
Applications for Anodizing Aluminum
As we have reiterated, anodized aluminum is stronger and more durable than regular metal. Also, it is safe and poses no health risk. In addition, the process – especially type I and II anodization do not alter parts that require tight tolerances.
Therefore, anodized aluminum parts are a mainstay in several world industries. Metal parts with this finish are regularly used in the following sectors:
- Consumer and homeware goods
Besides the industrial applications of anodized aluminum. Below is a list of the common use of these metals with this finishing.
- Kitchen equipment and utensils
- Refrigerator parts
- Light fixtures
- Radio equipment
- Window frames
- Electronic casings
- Photo equipment
- Patio covers
- Bathroom accessories
- Building wall switch plates, etc.
How to Identify if the Anodizing Process is Successful?
There are several ways to identify and determine if the aluminum anodizing process is successful.
This is particularly important for those who perform anodization at home. You may not be sure if there was enough electric current or if anodization occurred at all.
Here are valuable tips to follow.
Presence of a Matte Finish
An anodize metal surface will appear gloss-like, shining more than regular paint. After anodizing, the metal loses some elements of its metallic luster.
An effective way to confirm if a metal, such as aluminum, is anodized is to check its conductivity using a digital multimeter. Generally, aluminum is one of the best conductors of electricity.
However, the oxide coating around the metal increases its electrical resistance by inhibiting the flow of electrons and electricity through the metal. Therefore an anodized aluminum will exhibit lower conductivity and higher resistance than expected.
Anodized parts are usually scratch resistant. Therefore, if you scrape a coin or any metallic object on the aluminum part and quickly notice a blemish, that part has yet to be anodized. It probably was polished or just painted.
Kemal: Your Expert Aluminum Anodizing Partner
Indeed, anodizing aluminum is straightforward. In fact, we earlier mentioned you can perform it at home.
However, beyond understanding the procedure, you need to partner with an expert to ensure successful anodization of your fabrication, especially if you are manufacturing large volumes or large-sized parts.
At Kemal, we provide top-quality manufacturing services and post-processing solutions for your project. Regardless of your fabrication needs and design specifications, we offer on-demand services, ensuring that your part meets all detailed requirements.
Our facilities boast of the latest machines, ensuring that your fabrication is just as you requested or even better than your imagination.
Beyond anodizing, our team of experts are skilled in CNC machining, injection molding, 3D manufacturing and other rapid prototyping technologies with suitable finishing operations to go with each fabrication.
Anodizing is a quality, efficient and cost-effective finish for any metal. However, since aluminum is the most used metal for fabricating parts, the process is more commonly used for this metal.
Also, it provides considerable mechanical strength to the metal that can rival steel. Moreover, it enhances corrosion resistance among other chemical properties.
Besides anodizing, there are other practical finishes to improve your metal surfaces. However, anodization is one of the most effective, ensuring you upgrade the metal at a low cost.
When looking to anodize your aluminum parts, or engage in any custom fabrication, you should consider partnering with an expert to ensure a smooth and accurate project.