Anodizing is an electrochemical process convert metal component into durable, corrosion-resistant, and decorative by adding an oxide layer. It achieves an oxidized surface finish on metal components to enhance its corrosive and wear resistance properties and make it more durable.
Anodic oxide structure originated from aluminum, and it is composed of aluminum oxide. In simple words, aluminum oxide is grown from the underlying aluminum substrate. It has a highly ordered structure, and it is well suited for coloring and sealing, unlike painting or plating. This anodic component never chips or pill at any cost.
This anodizing process was first ever used in 1923 by a British Airline company to protect British seaplanes from corrosion. Anodizing is a regularly used term in the surface finishing industry. It is one of the general surface finishing processes for aluminum, titanium, and magnesium. This process is typical in manufacturing industries, aerospace, and the food industry, because of its excellent properties. Majorly it is using to prevent corrosion of any ferrous component.
Types of Aluminum Anodizing
Majorly, there are three types of anodizing processes
- Chromic Acid Anodizing
- Sulphuric Acid Anodizing
- Hard Sulphuric Anodizing
Chromic Acid Anodizing
- Chromic Acid Anodizing produces a thin layer of oxide layer on the metal.
- It’s usually in between 0.00002”-0.0001”. Although, it has a thin layer of oxide to prevents corrosion.
- Because of a thin layer of oxide formation, it is not commonly using.
Sulphuric Acid Anodizing
- It is one of the typical anodizing processes and is majorly used in all industries.
- Sulphuric Acid Anodizing may form a 0.0001”-0.001” thick oxide layer on metal so, the metal component becomes more wear-resistant, corrosion-resistant, and more durable due to its thick layer.
- Due to this type of anodizing, metal components are easily dyed and sealed.
Sulphuric Acid Anodizing
- It is used to produce a very thick layer generally 0.001”-0.002. So, the metal component becomes more durable, wear-resistant, and corrosion-resistant as compared to others.
- Due to the very thick layer of oxide layer formation, the hard-anodized metal component undergoes black dying.
- The use of this anodizing is for a specific application.
How to Anodizing aluminum
There are five steps for Anodizing process, which are as follows.
- It is the very first step and its pre-treatment process. This process first removes imperfections such as grease or oil, which can interface with the anodizing process.
- It can be done by sandblasting and emerging aluminum components into alkaline or acid-based detergent bath.
- Removing grease or oil is one of the hard processes to ensure spotting or uneven etching of the metal surface.
- This component was a wash from a detergent bath for the next step.
- Etching is the second process in which caustic or acid etch is used to remove minor imperfections in the aluminum component.
- The thin layer of aluminum material removes to create a uniform surface for the anodizing process.
- This etching process is also used to provide matt finish in the final component.
- The aluminum component is rinsed again for the anodizing process.
- After rinsing, the aluminum component is transferred to anodizing tank and dipped into electrolytic solution H2SO4 i.e sulphuric acid.
- An electric current passes through the anodizing tank.
- A cathode mounts into an anodizing tank, and an aluminum component acting as an anode.
- Due to passing of electric current through cathode and anode, oxygen ion releases, and growth of anodic coating occurs. This anodic coating grows outward and creates a fully integrated layer on the aluminum component.
- There are 3-4 types of coloring processes of aluminum anodizing such as electrolytic coloring, Integral coloring, organic coloring, and interface coloring.
- Electrolytic coloring is widely using in the industry.
- In electrolytic coloring, an anodized metal component dip into a bath of inorganic salt, and current is passed through it depending upon chemical condition and period to control coloring.
- A newly created anodizing coating is a porous structure, and it dissolves metal salt or organic dye.
- Sealing is the final stage in aluminum anodizing in which the porous surface is seal using a solution of nickel acetate.
- Sealing closes the pores and provides a uniform sealed surface.
- This final sealed surface is very much durable as compared to other processes.
What is titanium anodizing?
Titanium anodizing is an electrochemical process in which a titanium oxide layer is artificially grown on top of a titanium workpiece to prevent corrosion. This process is very similar to aluminum anodizing; the main difference is that titanium components work as an anode.
Titanium anodizing does not require a dyeing process because the titanium oxide layer refracts differently than another oxide layer. This layer acts as a film that reflects the wavelength of light. But it depends upon the thickness of the film. By adjusting the voltage during the titanium anodizing process, the color of the titanium layer can control depending upon the application.
This titanium anodizing is majorly used in the medical industry while manufacturing medical equipment because titanium anodized parts are not toxic and chemically stable. It also enhances its corrosion and wears resistance properties, and components get more durability.
Types of Titanium Anodizing:
There are two common types of titanium anodizing: Type 2 and Type 3. Type 1 is far less common and used in specialized high-temperature treatments.
The purpose of type II titanium anodizing is to prevent metal surfaces from the wear. It prevents seizing and friction.
Its use is most common in aerospace industries because titanium coating can sustain extreme temperatures from -70 to 260-degree c and is compatible with the fluid of the airplanes.
It is using in naval applications due to its corrosion resistance property against humidity and salty water.
Titanium anodizing parts are in grey.
The purpose of the type III titanium anodizing is to give color to different parts for easy understanding.
During the surgery, the surgeon directly asks for the blue cutter rather than a specific size cutter. So in these cases, it is necessary to have type III titanium anodizing on different parts.
During the bone fixation plate surgery, different color screws can fix as per the sequence and size. In this condition surgeon directly ask for the specific color screw rather than its size.
This type III titanium anodizing is also using in jewelry applications.
Difference between Type II and Type III Titanium Anodizing
|Type II||Type III|
|Primary Benefits||Prevent friction||Gives good visual identification|
|Biocompatible for medical devices implants||Yes||Yes|
Advantages of anodizing:
- Due to the formation of an oxide layer, metal becomes corrosion, wear resistance so, it becomes more durable.
- Anodized metal components are maintain in good color because there is no chance of peeling or chipping rather than painted products.
Health and safety
- Anodizing process is favorable to environmental safety regulation, and it’s not very harmful to human beings.
- Anodized metal components are not toxic and chemically stable.
- It is very easy to taking care of an anodized component and cost-effective because it requires only mild soap and water to keep its original shine.
- Anodizing the process is very cost-effective. It requires low maintenance and processing cost and reduces its initial cost too.
Disadvantages of anodizing:
- It is for a specific grade of aluminum.
- This process is not for Stainless steel.
- It is tough to achieve the same consistency for all types of batches.
- For a small number of components, it requires the same expensive setup.
- Due to the extensive use of chemicals for anodizing process, it constraint on limited color selection.
- Touch-upped anodized components are more noticeable as compared to air dry touch-up paint.
Application of anodizing:
- Aerospace Industry
- Medical Industry
- Automotive Industry
- Art & Sculptures
- Consumer products