Anodizing Aluminum 101: How to Anodize Aluminum Parts

Anodizing Aluminum-feature image

Lastest Updated On April 16th, 2022 

The anodizing process is perfect for several materials, however, the most important and commonly used one is aluminum. If you are new to machining, you might not be familiar with anodizing. The anodizing process can make a layer of oxide on metal parts and prove helpful for increasing the visual qualities of metal parts.

This guide will take you through everything you need to know about anodizing aluminum. We will discuss what anodizing aluminum is, how to anodize aluminum and the benefits of aluminum anodization. Let’s check more.

What Is Anodized aluminum?

Anodized aluminum has been treated with an electrolytic process to harden and protect the metal. This process creates a layer of oxide on the surface of the aluminum that is more durable and corrosion-resistant than the metal itself. This oxide layer can provide corrosion protection to metal parts.

Anodized aluminum is often used in applications where the metal needs to be strong and resistant to the elements. The anodizing process can also be used to change the color of the aluminum, giving it a unique finish that is both durable and stylish.

How Does Aluminum Anodizing Work?

It is possible to anodize an aluminum part no matter what manufacturing method. The anodizing aluminum process is a cost-effective and simple method, so it has a wide range of applications for various industries.

Before understanding how anodized aluminum works, we should first know the selection of anodizing materials and the preparations that need to be done before anodizing the parts.

Materials for Anodizing Process

different colors of anodizing aluminum parts

Anodizing process is an electrochemical process that makes a metal surface durable, decorative, and corrosion protection. Aluminum is suitable for conductive materials, and it is one of the most suitable for anodizing. Some other non-ferrous metals can also be anodized, such as titanium and magnesium.

The anodizing process is not suitable for stainless steel and steel due to the formation of rust. Rust can not prove good to make a tight and corrosion-resistant coating on steel, while aluminum contains natural oxide layer to protect the underneath metal parts.

The aluminum oxide can not apply to a plating or paint surface, and aluminum oxide can fully integrate with the underlying aluminum substrate. It can not peel and has a highly porous structure for secondary processing of coloring and sealing.

The specular characteristics and features of anodized surface and finishes have proved aluminum are one of the highly selected materials for various sectors. Some main advantage of anodizing aluminum which makes it is a widely used material to produce thousands of industrial products.

  1. It can use to make the tallest building structure, such as Illinois and the Willis Tower in Chicago.

  2. It requires less maintenance and provides durable exteriors, curtain walls, ceilings, lobbies, floors, and commercial buildings.

  3. It is considered an eco-friendly material and protects satellites from a harsh environment.

Tips for Surface Preparation Before Anodizing

Make use of mechanical finishing techniques when necessary. Etching alone isn’t enough to correct pre-existing surface defects like scratches and dents. If these are evident in a part’s surface, you might as well use mechanical polishing techniques like grinding, buffing, and sandblasting.

Be mindful of your packaging. Before sending out your parts for anodizing, make sure that you have packed them to be dent-proof and well-cushioned. Additionally, avoid sticking a tape directly to the surface to be anodized.

Ensure that your parts are properly cleaned and degreased. Look out for uncleaned swarf seated on blind holes, fingerprints on the surface (avoid handling parts with bare hands!), and residual oils from the fabrication processes.

Remove steel inserts like rivets and pins on parts to be anodized as these can corrode differently throughout the different treatment processes.

How to Anodize Aluminum Parts: Step by Step

anodizing aluminum process

The working principle behind anodized aluminum parts involves inducing the oxidation of aluminum by submerging it into an electrically conductive acid electrolyte solution where oxygen ions are released. This method uses anodic films to get aesthetic effects.

To further understand the process of anodizing aluminum parts, here are 4 major steps involved:

Step 1: Pre-treating

The pretreatment process involves achieving a visible finish and a clean work part.

Cleaning: Pretreatment cleaning is important to remove residual grease, oils, and other impurities from a previous fabrication process like extrusion or CNC aluminum machining to avoid impurities and inconsistencies in the finished part.

Etching: The surface finish of a part before anodizing is relevant because it will dictate the quality of your final result. Tweaking your desired surface finish can be done through etching, where minor imperfections on the surface are corrected while being prepared for anodizing.

Step 2: Anodic Oxide

After the surface is prepared, the parts will go through the anodizing step, submerged into a bath of sulfuric acid electrolyte solution (which may vary depending on the type of anodizing process chosen). The electrolyte solution has many positive and negative ions and is an electrically conductive solution.

The positive ions can attract the negative plates and the negative ions to the positive anode. An electric current causes it in the circuit. The negative ion attracts the aluminum parts, which is the positive anode. The aluminum parts will serve as an anode.

At the same time, a cathode is installed within the tank to allow an active passing of electrical current through the system and induce the release of oxygen ions from the electrolytic solution. This process will create aluminum oxide into the substrate, which is also called a barrier layer. But it rougher than the aluminum surface.

Step 3: Coloring

The anodic coating formed on the surface layer is porous by the structure, which allows the addition of color into the part. Various ways of adding colors to an anodized part involve submerging it into dyes or dissolved metal salts. This process achieves finishes like black anodized aluminum, gold, black, nickel, and stainless.

Step 4: Sealing

To close the porous surface created in anodizing and provide a uniform surface, the parts are subjected to a final step that will submerge them into a nickel acetate solution. Sealing ensures long-lasting color and prevents further corrosion for the anodized part.

Different Types Of Anodizing Aluminum Process

So, what’s so different about anodizing aluminum compared to other finishes is its process. The majority of protective covers are added to the material, while in anodize aluminum, the cover is formed by removing positive ions from the surface of aluminum parts. There are three major types of anodizing processes on aluminum parts, resulting in the different finishes and appearances we see on several products.

Type I – Chromic Acid Anodize

This type uses a chromic acid solution to create a thin coating (from 0.5 to 2.5 microns) on parts. Chromic acid anodizing produces the thinnest coating and least color absorption among the three major types. Although the coating is relatively thin, it protects the aluminum part against corrosion and is an effective first coat for powder-coated or painted finishes.

Type II Sulfuric Acid Anodizing

Type II anodizing is the most commonly used method for anodizing aluminum parts, where it is used as the anodizing solution. It produces an anodized layer of 2.5 up to 25 microns. The porous nature of this process is perfect for absorbing dyes well. Type II is not good for parts having tight tolerances.

Type III Hardcoat Anodizing( hard anodizing)

This hard anodizing process is also done on a sulfuric acid solution. However, the layer produced is much thicker and denser than the normal sulfuric acid anodization. The hardness of the aluminum oxide of type III is equivalent, and the difference in hard coats thickness can alter the surface appearance of the substrate. This is used for tough applications where superior abrasion and corrosion resistance are needed, such as medical devices.

Which type of Anodizing is the best for you?

different color in aluminum anodizing

It’s not easy to step to choose the most suitable type of anodizing and know-how anodizing works. You should choose the anodizing process by considering the various applications of aluminum parts. A highly qualified company can suggest which type of anodizing is best for your project. You can choose the best anodizing aluminum parts by comparing different types of anodizing.

  1. Type 1 has specific properties such as good corrosion resistance and uses chromic acid to make a thin layer acting on the surface of parts. Type 1 is good for aircraft parts manufacturing.

  2. Type II anodizing is mostly used for the applications of architecture and aircraft. Type II uses sulfuric acid instead of chromic acid to create thick coatings of anodized layer on parts. Type II has moderate wear resistance and uses sulfuric acid to make a thick layer on the surface of the aluminum part.

  3. Type III is best for parts that can withstand chemical exposure and high temperature. Type III has the same features as type II but has some results variations. Type III creates a layer of corrosion and is used to make sturdy metal parts.

The Benefits Of Anodizing Aluminum Parts

There are many advantages to anodizing your parts, and here are some of the reasons why you may need to anodize:

Aesthetics- Anodized parts add a little hint of elegance and enhance a part’s overall surface finish.

Durability- The whole process of anodizing improves a part’s overall corrosion and abrasion resistance which heavily contributes to the extension of the lifespan of the work part.

Ease of maintenance- The corrosion and abrasion resistance of anodized aluminum make it hard for the part to incur dents and wear that may cause additional fabrication and restoration processes.

Color Stability- Unlike other plating methodologies used in the industry, anodized parts do not chip off or peel because of their structure.

Economical- Anodizing aluminum cost is a cheap way of achieving a desirable finish with impressive surface properties.

Have Improved Insulating Property-Outer anodized layer of anodizing aluminum parts has insulating properties and has low electrical conductivity. So a reason for choosing aluminum to anodized parts.

Design Tips And Considerations For Anodizing Aluminum

Dimensional Considerations

Remember that you need to compensate for the anodizing thickness in arriving at your final part dimension and designation of feature tolerances.

Hardness Requirements

Be mindful of your applications and their tensile strength requirements to know what hardness you need to call out on your parts design.

Color Matching

Manage your expectations when setting up your desired color as different metals and alloys react to various dyeing compounds and coloring parameters.

Combined Coatings

Anodized parts may also be subjected to secondary coating processes like painting and Teflon impregnation to further enhance their corrosion resistance and structural integrity.

Conductivity

Testing the conductivity is an easy way to check the anodization of aluminum parts. It can check the conductivity of the surface by using a digital multimeter. Anodic layers can be good insulators, and they can be applied with a clear chemical conversion coat in certain areas.

Saves Energy

Aluminum reduces energy demand and contributes to the product’s life cycle. It can serve both a conductive and structural purpose and preserves the structure, wiring, and space.

Application Of Anodized Aluminum

Oxidation pool

In such a way, Anodizing has revolutionized the aluminum fabrication industry due to its excellent and impressive enhancement of mechanical and aesthetic properties. This can be seen in almost any walk of life:

  • Aerospace and Defense Industry

  • Medical Industry

  • Automotive Industry

  • Consumer electronics

  • Custom parts

  • Architecture and construction industries

  • Prototyping and product development

  • Housewares

  • Hydraulic fittings

Many end product uses and functional benefits of anodized aluminum offer great design opportunities for users and companies.

Conclusion

Anodizing is an important process to manufacture products and involves submerging aluminum components into an electrolytic solution and chemical baths. It has large applications for many industries and proves helpful in providing a safe living style. This process has variations in its cost and complexity, but it ensures you get better and high-quality end products.

At WayKen, we offer professional aluminum anodizing service that will give you the best value with our high-quality processes, quick turn-around time, and competitive pricing. If you have any quotations or projects to review, please don’t hesitate to contact us. Here, we can offer practical advice on different parts finishing services that can help enhance your prototypes and parts.

FAQ

1. Is Anodizing Aluminum Expensive?

Anodizing aluminum is a cost-effective process, but some variables are required to consider before assessing the cost of aluminum. These variables are anodizing type, thickness, lead time, pre-processing requirements, dimension of aluminum materials, and anodizing process. These factors are responsible for an increase or decrease in cost.

2. Can aluminum be anodized at home?

Anodizing aluminum is a simple and easy process, and you can do it at home. Try to use small aluminum pieces so they can submerge in small quantities of acid. You need to find small aluminum parts to perform anodize aluminum process. You require sulfuric acid, a cathode, aluminum wire, distilled water, an acid neutralizer, a power source, tanks, eye protection, and gloves.

3. What colors can you anodize aluminum?

Anodizing aluminum process is open to all rainbows colors, and they are different from other methods and techniques such as paint and powder coating. Many factors are involved, such as grade, finish tapes and sizes.

4. Can you anodize aluminum twice?

when your anodized aluminum parts are open to wear and tear, it may cause damage to items so that anodizing parts can be repeated. You can do it either by using chromate conversion or applying other methods. It can restore the appearance and provides much better adhesion for paint primers. It will make your aluminum component more protective and appealing.

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