Anodizing 101: Everything You Need to Know About Surface Finishing

anodizing cnc machined parts

Anodizing is a surface finishing process that is commonly used to enhance the appearance and durability of metal parts. It involves creating a controlled oxidation layer on the surface of the metal, which can improve corrosion resistance, increase wear resistance, and provide an attractive finish.

The anodizing process typically begins with cleaning and preparation of the metal part to be anodized. This can involve degreasing and chemical treatments to remove any oils, dirt, or other contaminants that may be present on the surface. Once the part is clean, it is immersed in an electrolytic solution and an electrical current is applied. This causes an oxide layer to form on the surface of the metal, which can range in thickness from a few microns to several hundred microns.

There are several different types of anodizing processes, each of which can produce different results. For example, sulfuric acid anodizing is a common type of anodizing that is often used for aluminum parts. This process creates a thin, hard, and porous oxide layer on the surface of the aluminum, which can be dyed or sealed to create a range of different colors and finishes.

Other types of anodizing processes include hard anodizing, chromic acid anodizing, and phosphoric acid anodizing, each of which has its own unique properties and applications.

Overall, anodizing is a versatile surface finishing process that can be used to improve the performance and appearance of metal parts for a wide range of applications.

Pro & Cons


  1. Corrosion resistance: Anodizing can greatly improve the corrosion resistance of metal parts, which can make them more durable and long-lasting.
  2. Wear resistance: Anodizing can also increase the wear resistance of metal parts, making them more resistant to scratches, abrasions, and other types of damage.
  3. Aesthetic appeal: Anodizing can create a range of attractive colors and finishes on metal parts, which can enhance their aesthetic appeal and make them more visually appealing.
  4. Environmental benefits: Anodizing is an environmentally-friendly process that does not produce harmful byproducts or waste materials.


  1. Cost: Anodizing can be a relatively expensive process, especially for small-scale production runs or custom parts.
  2. Limited color options: While anodizing can create a range of colors and finishes, the options are still somewhat limited compared to other surface finishing techniques.
  3. Dimensional changes: Anodizing can cause slight dimensional changes in metal parts, which can affect their fit and function in some applications.
  4. Surface defects: If metal parts are not properly cleaned and prepared before anodizing, surface defects such as pits and streaks can occur, which can affect the appearance and performance of the parts.

Design Tips

  1. Material selection: The material selected for the custom machined parts should be suitable for anodizing. Materials commonly used for anodizing include aluminum, titanium, magnesium, and certain grades of steel. It is important to select a material that can provide the desired level of corrosion resistance, wear resistance, and other properties.
  2. Surface finish requirements: The surface finish of the custom machined parts should be carefully considered to ensure that it is compatible with anodizing. Anodizing can highlight surface imperfections, so it is important to ensure that the surface finish is as smooth and uniform as possible. Any scratches, tool marks, or other surface defects can be visible after anodizing.
  3. Tolerances and dimensional changes: Anodizing can cause slight dimensional changes in custom machined parts, so it is important to consider this when designing the parts. Any tolerances or critical dimensions should be carefully specified to ensure that they are maintained after anodizing.
  4. Part geometry: The geometry of the custom machined parts should also be considered when designing for anodizing. Anodizing is a surface treatment, so it may not be possible to anodize certain areas of complex parts. It is important to design parts with this in mind to ensure that the desired areas are anodized.
  5. Color and finish requirements: The desired color and finish of the anodized parts should also be considered when designing for anodizing. The type of anodizing process used can affect the color and finish, so it is important to specify the desired outcome in advance.


Is anodizing cheaper than painting?

Anodizing is typically more expensive than painting, as it is a more involved and specialized process. However, anodizing can provide superior durability and corrosion resistance compared to painting, which may make it a better long-term investment in certain applications.

How long does anodized last?

The lifespan of an anodized finish can vary depending on a variety of factors, including the type of anodizing process used, the material being anodized, and the environment in which the part is used. Generally speaking, anodized finishes can last for many years, even in harsh or corrosive environments.

Why can’t you anodize steel?

Steel cannot be anodized because it does not contain enough aluminum or other anodizable metals to form a suitable oxide layer. However, steel can be treated with other types of surface coatings or finishes to provide similar benefits.

Does anodizing chip off?

Anodizing can chip or wear off in certain circumstances, such as in high-impact or abrasive environments. However, this is relatively rare and is usually only a concern for parts that will be subjected to significant wear and tear.

What metals Cannot be anodized?

Metals that cannot be anodized include those that do not contain enough aluminum or other anodizable metals, such as copper, brass, and most types of stainless steel.

How can you tell if metal is anodized?

Anodized metal can often be identified by its characteristic color and texture. Anodized aluminum, for example, will typically have a hard, smooth, and somewhat glossy surface with a range of colors available depending on the anodizing process used.

Can aluminum be anodized twice?

Yes, aluminum can be anodized multiple times to achieve a thicker or more durable oxide layer. However, this may require additional preparation and processing steps to ensure the best possible outcome.


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