JCL Precision Part Co.,Ltd.

How Does Aluminum Anodization Work?

Aluminum anodizing involves applying a durable layer of aluminum oxide to aluminum items, making them more durable and resistant to corrosion and wear. After the anodizing process, it is possible to dye this layer to improve its aesthetic.

This fluid is typically weakened by sulfuric acid. On account of the reverberation of the electrical flow, the adversely charged oxygen particles in the electrolyte are drawn to the decidedly charged aluminum surface. At the point when oxygen particles and aluminum molecules meet up, they make an intense aluminum oxide covering. Anodizing can be grouped into three primary sorts: Type I uses chromic acid, Type II uses sulfuric acid, and Type III outcomes in a hard covering.


1. What is Anodizing? 

Manufacturers safeguard metals like aluminum by applying a specific oxide layer. They complete this oxide process through anodizing. The manufacturers just immerse the metal in a specialized liquid and electrically charge it as part of the process. The metal forms an extreme layer on its surface when exposed to electric flow. Through anodizing, manufacturers make the metal aesthetically good and pretty. This anodizing method protects the metal from rust, wear, and scratch harm. Several industries use anodizing in their fields, like automation and aviation, to upgrade metal parts' strength and visual allure.

2. What is the Purpose of Aluminum Anodizing?

Manufacturers use anodizing aluminum mainly for two purposes; 

As we know, manufacturers strengthen the aluminum, making it impervious to harm and rust through anodizing. Improving the thickness and strength of the oxide layer on metal makes a more significant hindrance than the normally dainty layer of aluminum in the air. Thus, anodized aluminum is great for things that experience continuous use or harsh conditions.

Through anodizing, engineers make things (stylishly) that function admirably and in useful ways. The oxide layer considers the retention of colors, prompting a change in the metal's tone and color. This gives more options for how to design & plan aluminum parts. The anodized layer makes it simpler for paint, oil, and different treatments to stick to the surface.

3. How Does Anodizing Work? 

In the anodizing process, manufacturers use electricity to give the aluminum surface a special coating to give it a smooth, durable, and colorful surface. This is how anodized aluminum sheet metal works:

In the first step, manufacturers clean the aluminum metal properly. In the cleaning process, they clean it from debris and blemishes and remove natural coating or any other pollutant residue. This cleaning step is very crucial for oxide layer adhesion and uniform anodizing. 

Now, the manufacturers dip the pre-cleaned metal in an electrolyte solution known as sulfuric acid. They keep the positive (cathode) and negative (anode) electrodes (made of stainless steel or lead) in the electrolyte solution. 


Then, manufacturers pass the energy through the liquid or solution. In this phase, aluminum is positively charged when it loses negative electrons.  Simultaneously, negatively charged oxygen particles are delivered with the help of cathode electrons. So, these electrons form a thin layer of oxide sticking to the aluminum.  Manufacturers can control the thickness by changing the time, energy, temperature, and liquid concentration. Once you get the desired result, you can remove the particular component from the bath. The first oxide layer is called the barrier layer, which has no pores. After completing the process, the component can be sealed using sealing solutions. Sealing aims to make it more powerful and protect it from further wear and tear. 

4. Types of Aluminum Anodizing Processes?

Type I - Chromic Acid Anodizing: 

Using chromic acid as the liquid, this method produces the thinnest oxide layer, approximately 0.0001 inches thick, out of the three main types. It has outstanding security against rust despite the fact that it's not thick like different coatings. Because the thinner layer is not very porous, the chromic acid method has a darker finish but needs to hold the color better. However, it provides perfect adhesive bonding and corrosion resistance for paint, etc. 

Note: Today, manufacturers use it less frequently due to chronic presence, which is hazardous for the environment. 


Type II - Sulfuric Acid Anodizing: 

Sulfuric acid is the electrolyte that is most frequently used in this process. It produces a layer that is thicker and more durable than that produced by chromic acid anodizing. Sulfuric acid offers many benefits, such as wear resistance, electrical insulation, corrosion resistance, etc.  You can see its footprint in various industries like aviation, automotive, electronics, etc. It does a great job of absorbing dyes and producing various decorative colors.


Type III - Hardcoat Anodizing: 

Due to high voltage and lower temperature, hard anodizing produces a thicker and denser anodized layer than sulfuric acid anodizing. If you compare the two, you will find that the oxide layer that hard anodizing provides has much harder and anti-wear resistance qualities than standard anodizing. It offers many benefits, like thermal degradation and high defense against abrasion and chemical corrosion. Manufacturers use it in different apparatuses that demand excellent durability and wear resistance, such as hydraulic systems,  pistons, and cylinders. 


5. Which Type is Perfect for Your Project? 






Type I (Chromic Acid)

Chromic acid

It has the thinnest coating (~0.0001 in), it has good corrosion resistance qualities and has dark or limited color options

It has the thinnest layer, 

It has good corrosion resistance features, 

Has limited color options (usually black),  

It has poor wear-resistant features, 

It has good corrosion-resistance properties

It is used in Electronic components, optical housings, etc.  

Type II (Sulfuric Acid)

Sulfuric Acid

0.001" - 0.002" (25 - 50 μm)

It is the most common type, has a good balance of properties, it accepts dyes for a wide range of color, it has moderately wear-resistant & corrosion resistance properties,

We use it in Building materials, automotive parts, and consumer electronics, etc

Type III (Hard Anodizing)

Sulfuric Acid (higher voltage/concentration)

12.7-80 μm

It is the thickest and hardest layer, it has excellent wear-resistance corrosion-resistance properties, has limited color options (usually dull gray), 

You can use it in Engine components, gears, and firearms, etc.


6. Aluminum Anodizing Advantages 

Aluminum anodizing is a popular choice for a wide range of applications due to its numerous advantages. Durability and corrosion resistance are the fundamental benefits of anodizing. The anodized aluminum is shielded from damage by the extremely long-lasting layer of anodized aluminum oxide, which also protects it from scratches and even severe weather. Thus, the aluminum will endure longer and require less maintenance after some time. In addition, unlike paints and other coatings, which may chip or peel, the anodized layer is permanently bonded to the aluminum.

Anodizing also offers several aesthetic benefits. You can get an exquisite, normal metallic sparkle in various colors through aesthetic anodizing. Depending on the desired impact, this permits either a sleek and futuristic design or a conventional metallic finish. In addition, anodizing results in a surface finish that is extremely consistent and can be applied to a variety of shapes and textures, ensuring a consistent and polished appearance. Most importantly, manufacturers use it in outdoor, salty, and moisture-based projects due to its corrosion and wear resistance properties.


This makes products and architectural components look better. Additionally, the anodized metal has a long haul, without blurring, breaking, or stripping, even after stretched-out openness to daylight and antagonistic climate. 

Finally, anodized aluminum is reasonable and eco-accommodating. The anodizing process uses less energy and produces less waste than other methods of finishing surfaces. Due to its strength, treated aluminum products require less incessant substitution or resurfacing, which sets aside cash over the long haul.


7. Where is Anodized Aluminum Used?

 Anodized aluminum, known for its flexibility, is popular in many industries for its resilience, durability, and attractive appearance. Here are some common uses:

Building and Architecture: 

Anodized aluminum is commonly used for making building facades, window frames, doors, roofing parts, and other architectural features. Its resistance to rust and harsh weather makes it ideal for outdoor uses.

Consumer Goods:

Anodized aluminum is also used in dishwashers, refrigerators, laptops, smartphones, furniture parts, kitchenware, and sporting items like baseball bats and bicycle frames. It is versatile because it is sturdy, aesthetically pleasing, and simple to clean.



You can use Anodized aluminum in different transportation parts. Consider altering the components for the wheels and boats, making modifications for automobiles, and adjusting the parts required for airplanes. Some of the positive qualities of this item include its durability, resistance to rust, and lightweight design.


Anodized aluminum keeps electronic parts cool because it can take away heat. It is often used for electronic covers, supporting parts and heat sinks.

Medical Equipment:

Some medical tools and equipment use anodized aluminum because it is clean and doesn't rust.

8. Limitations of Aluminum Anodizing?

While aluminum anodizing offers benefits, it's essential also to consider the drawbacks when selecting a treatment for your aluminum components. Here are the main rules that are broken down:

Limited to Aluminum: 

Anodizing works only on aluminum and metal mixtures made with aluminum. When you use metals like steel or copper, you need to consider different ways to finish them.

Color Matching Challenges:  

Anodizing can make many different colors, but getting the same color for many things simultaneously takes work. Small color differences can happen because of mistakes in the anodizing process or slight changes in the aluminum material.

Dimensional Shifts:

During anodizing, a thin layer of oxide forms on the aluminum surface. This could lead to small changes in the size of the part, but it will be fine for most uses.

Surface Texture Alteration: 

Hard anodizing is very resistant to wear, but it can make the surface of the aluminum a little rough. Even though most projects don't need this, you should consider it if you want a really smooth finish for your project.

Vulnerability to Damage: 

Damage Vulnerability: While the anodized oxide layer is strong, it can still be damaged. The covering can get holes or be damaged by strong chemicals, making the metal underneath rust.

Limited Color Options for Hard Anodizing:

Limited options for colors are available for hard anodizing. The thick oxide coating that it provides comes with a trade-off if you want better wear resistance. Hard-anodized aluminum can only be colored in a limited range compared to other methods.

9. What Should You Know Before Anodizing Parts? 

Consider Tolerance 

Through anodizing, a thin layer is applied to your metal part. This can potentially bring about slight changes in the part's fit with other components.

If you need precise measurements, you should use Type I or Type II anodizing, which makes thinner layers.  It is possible to adjust your design early on to give it more thickness.

Check Edges & Corners

Ensure that your workpiece has smooth corners and edges so that the anodizing process can be successful. Try to make the corners round with a radius of at least 0. 5 millimeters when possible.

Avoid rough metal bits and sharp edges in your design. The strong electrical current can cause the anodized surface to be uneven or even burned.

Other Finishing Steps 

Anodizing is different from polishing or bead blasting because it uses electricity to process it instead of using mechanical methods. This means it won't fix scratches or dents on the aluminum surface. After the anodizing process, you can still see scratches and marks from machining.

Before applying a coating, consider polishing, using bead blasting, or another finishing method if the surface is smooth and consistent. Anodizing can't fix existing problems, but it can make the surface a little smoother.

Work with Small Batches 

It is recommended to work with smaller amounts when dyeing anodized items. Matching colors exactly between different groups can be hard, so this helps make the color more even.

"Coat a few small pieces simultaneously to ensure they all have the same color. "

10. How to Know the Anodizing Process is Successful 

1. Visual Inspection: 

Uniform Color:

The anodizing process was correctly performed if the part had a consistent color. Look for any changes in color, lines, or uneven spots that could be signs of uneven anodizing.

Scratch Resistance: 

The anodized layer is harder to scratch than the underlying aluminum. Use a coin to scratch the surface gently. Scratches should not be visible if the protective coating is still on.

2. Dimensional Checks:

Minor Thickness Increase:

A good anodizing process will make the part bigger. When the design requires accuracy, verify the final measurements to ensure they are the correct dimensions.


Salt Spray Test:

During the test, we placed the anodized part in a salty spray to see if it could withstand corrosion. Proper anodizing should shield against the effects of rust.


To sum up, aluminum naturally has a thin coating of oxide. Anodizing makes this coating stronger, more even, and thicker. This is done using electrolysis. Sulfuric acid is a liquid that can conduct electricity. It is kept in a tank with aluminum, which is the positive electrode. Metal oxide is made by pulling oxygen ions to the metal surface using electricity. This aluminum oxide coating is really strong. It helps metal resist wear and corrosion and makes it better at insulating electricity. By using dyes, the method can make more colorful colors. Overall, anodizing is a cost-effective way to make aluminum parts look better and work better.


How Long Will Anodized Aluminum Last? 

The longevity of indoor anodized aluminum depends on factors such as usage, environmental conditions, and the thickness of the coating. In order to increase the durability of objects outdoors, they may need to be coated with thicker layers or additional protective coatings.

Materials Diversity Needed to Anodize Aluminum? 

You can use only conductive materials like metals for anodizing. Besides aluminum, you can use titanium and magnesium for anodizing purposes. The frequent question is whether we can anodize stainless steel. The answer is big no. Due to the presence of iron oxide in steel, we cannot anodize it. 

Is Anodized Aluminum Prone to Rust? 

Aluminum doesn't rust, but it can still undergo corrosion. Anodizing by forming a protective layer increases the material's durability against rust. However, in tough situations, it might be necessary to take extra safety measures.

Popular Anodizing Colors for Aluminum? 

Anodizing has the capability to change the colors of objects like silver, black, gold, red, and blue. The type of dye and its application method will determine the range of colors that can be produced.

What Happens to Aluminum When It Is Anodized?

During anodizing, the natural oxide layer of aluminum gets thicker. This makes the aluminum stronger, more rust-resistant, and able to absorb coloring dyes. 

Why do you anodize parts? 

Factors such as the size and complexity of the parts, the type of anodizing used, and the preferred color all play a role in determining the cost of anodizing. Usually, it is a cheaper way to finish compared to others.


How do I assess the quality of anodized parts? 

You can assess the quality through color uniformity, dimensional checking, scratch resistance, and salt spray tests. 

Is anodizing expensive? 

Usually, anodizing is believed to be cheaper than other ways of finishing metals, like painting or plating.

What’s the difference between Type II and Type III anodizing? 

Type II metal is well-liked and can be used in many different ways. It forms a protective layer that is about 10 microns thick and can resist damage from rust and scraping. Manufacturers use it in many different kinds of applications. 

Type III creates a thicker and sturdier oxide layer, which can be as dense as 25 microns, in contrast to Type II. It has superior resistance to wear and is commonly utilized for durable items such as construction materials and sturdy components.