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anodizing aluminum

What is Aluminum Anodizing and How Does it Work?

Aluminum anodizing is a remarkable coating technique that serves a two-fold purpose for your parts: Strengthening the part mechanically and providing good aesthetics. This technique has advanced in recent times. Now, it is a go-to option for most aluminum parts. This surface finishing is also suitable for magnesium and titanium. However, today we will discuss aluminum anodizing in detail and its functionality. Without further ado, let us dive right into it!

What is Aluminium Anodizing?

anodizing process

Aluminum anodizing is an electrochemical process by nature and involves controlled passivation of aluminum surfaces for unanimous and even surface layer protection. Now you might be wondering that aluminum forms its oxide layer naturally, so why anodize it then?

The dilemma in the natural oxide layer is its uneven nature, poor protection, and very thin dimensionally. The controlled dipping of charged aluminum in an acidic electrolytic bath forms a very aesthetically pleasing yet rugged layer on its surface that is durable, corrosion-resistant, and also can be colored for applications.

Techniques for Anodizing Aluminum

There are two broad categories for anodizing aluminum surfaces classified by their coating thickness and applications. Let us have a peek into these:

Anodizing Type II: Standard Anodizing (clear or color)

This is the most elementary form of anodizing. It is also referred to as standard or decorative anodizing. It is great for applications where aesthetics is the primary concern. The maximum coating thickness is 25 μm. Specifically, parts dyed black using this technique have a thickness range of 8 – 12 μm, whereas, for clear coatings, it ranges from 4 – 8 μm.

You might be thinking that what is this form of anodization then useful for?

Well, it is great for:

  • Resistance to corrosion
  • Good for appearance
  • Applications where limited wear resistance is required
  • Great for welded parts
  • Also useful for mating parts where tight tolerances are required

Anodizing Type III: Hard Coating

As the name suggests, this form of anodizing offers thicker coatings, i.e., up to 125 μm. It is covered under Military Standard Specifications in MIL-A-8625. The average thickness range of this coating is usually around 50 μm. It produces robust, high-density coatings suitable for:

  • Flame resistance
  • Easily maintainable
  • Is more resistant to peeling, chipping, or flaking
  • Specifically useful for medical instruments due to their non-contaminating nature

However, it must be noted that Hard Coating is more expensive than Standard Anodizing but more durable.

Applications of Anodized Aluminum

Three main industries where anodized aluminum plays a major role are:

  • Mechanical and aerospace: Wheel trims, aircraft panels, and material for control units are some examples. It might be interesting for you to know that NASA’s Space Station incorporates anodized aluminum for trusses and handrails! Anodized aluminum provides superior thermal stability and superb optical properties allowing for clear visibility of handrails to astronauts. Hard coating is specifically used in dental equipment and the marine industry.
  • Construction and architecture: Window panes made of anodized aluminum are all around us. Moreover, it is also being used to create masterpieces of exterior artwork that can sustain environmental degradation.
  • Consumer goods: Numerous products ranging from refrigerators, dryers, televisions, and microwave ovens are made from anodized aluminum which serves a twofold purpose: longevity and aesthetics for consumer goods. OEMs highly rely on hard coating for their products.

Costing Aspect of Anodization

With the technical details covered, it is vital for you, as our reader, to know the factors that account for the cost incurred in anodizing your aluminum parts. We will discuss these categorically and one at a time.

1. Type of Anodization Process

The first and foremost question is: What is the required level of thickness of the coating and where will the part be used? Is its application inclined towards aesthetics or durability or perhaps a balance of both?

For the consideration of the thickness of the coating, it is important to understand that there is no direct proportional rule of thickness with regard to cost. In most cases, narrower coating ranges are more expensive. It is harder to control the surface finish of a thinner coating. For instance, a thinner finish for hard coating is really expensive.

Which type of anodization to use among the types aforementioned depends on the context of the application of the specific part. If military parts or computer accessories are in consideration, without a doubt, hard coating is the primary choice.

2. Dimensions and Number of Surfaces

Of course, the dimensions of surfaces to be anodized play a key factor. The more extensive the dimensions, the more is the cost incurred. However, a key point that most companies forget to highlight is that intricacy of the surface is also a vital aspect in cost estimation for anodization. Very complex contours result in more cost.

3. Arrangement on Anodizing Racks

It is important to understand that a part of the cost gets derived from the time spent on preparing the anodizing bath. There is manpower and operations involved behind this process i.e. preparation of surfaces, testing, packaging etc. For instance, the cost of anodizing short bars with light profiles will be higher due to large number of operations. On the other hand, heavy profiled long aluminum bars are also costly to anodize considering more involvement of manpower. The management of anodization of your parts is also part of our longterm experience in this field which enables us to offer market competitive rates with resounding quality.


We hope that this article helped you grasp the concepts and ideas behind the surfaces of anodized aluminum. We believe that it is good for our customers to have sound preliminary knowledge of the services they are being offered. You can always contact us for advice on aluminum anodizing finishing. We also offer free project reviews and cost estimation for your parts with quick procedures so that you can get your parts made at the earliest!

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Hey there, I’m Sam!

From AT-Machining, I’m a CNC Machining Expert in this field for more than 20 years.  We offer cost-effective machining services from China. Ask for a quote for your ongoing or upcoming projects now!

Best Regards, Sam, Co-Founder

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