What is anodizing?

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What is anodizing?

In CNC machining manufacturing, anodizing is a key surface finishing method. Anodizing is an electrochemical oxidation process. In this process, a metal or alloy part is used as an anode, and electrolysis is used to form a thin film of oxide on its surface. The metal oxide film changes the surface condition and properties. It makes the part stronger with a higher surface finish.

What is the anodizing process?

1. Degrease

Put the workpiece into a 50℃ water tank to remove the oil on the surface of the workpiece.

2. Alkali washing

Put the parts into the alkali tank at 50℃ to remove the oxidation layer on the surface of the workpiece.

3. Acid washing

Put the component into the nitric acid tank at room temperature to remove the dirt on the surface of the component.

4. Chemical polishing

Hang the workpiece in the phosphoric acid tank at 92℃, and chemically polish the surface of the part to add gloss.

5. Anodic oxidation treatment

Hanging the power supply in a specific acid tank at a temperature of 21℃ to form an oxide film on the surface of the workpiece.

6. Dyeing

The workpiece is hung in the dyeing tank at 55 degrees Celsius to produce bright colors according to the customer’s color requirements.

7. Seal the hole

At 95 degrees Celsius, the workpiece is hung in a hole-sealing tank with a hole sealer. The workpiece holes are sealed to prevent damage to the oxide film of the workpiece.

8. Drying

Dry the moisture on the surface of the piece at a temperature of 50 degrees.


How many types of anodizing?

Chromic acid anodizing

Type I anodizing uses chromic acid to form an oxide film on the surface of the machining part, but this oxide film is relatively thin, it is less than 0.0001 inch. However, it does not affect the assembly of precision parts.

The film has low porosity and is not suitable for dyeing, so it can be used without closure.

The chromic acid anodized film has a strong bonding strength with organic paint. It is not only a good base layer for paint but also widely used as a bonding part for rubber

Sulfuric acid anodizing

Type II anodizing uses sulfuric acid instead of chromic acid to form an oxide layer on machined parts. The thickness of this oxide film is 0.0002 to 0.001 inches. It is thicker than chromic acid anodizing and therefore has better wear and corrosion resistance.

In addition, because of the use of sulfuric acid, a porous structure can be built up on the part. This makes it easier to absorb dye coatings. So it is possible to produce prototypes and parts with different colors.

Hard Sulfuric Acid Anodizing

Type III anodizing also uses sulfuric acid as the electrolyte solution. However, after being oxidized, a hard oxidized coat is generated on the part’s surface. This is why this process is called hard anodizing. Because the anodizing process is performed at a high current, high voltage, and low temperature, it produces a thicker oxidation layer. The thickness will be greater than > 0.001 inches.

After being anodized, the component is generally dark in color, so hard anodizing is generally dyed black.

Because the surface coating is thicker after anodizing, it may not be suitable for precision parts that require tight tolerances. Because he may affect the assembly of the spare part.


What’s the Difference between each type of anodizing?

Type Type-I (Chromic Acid) Type-ll (sulfuric Acid) Type-III (Hard Anodized)
Corrosion Resistance Good Good Excellent
Coating Thickness 0.08-0.25 μm 2.54-25 μm 12.7-80 μm
Abrasion resistance Poor Moderate Excellent
Appearance Primary Coat Clear or Dyed Hard Clear or Hard Black
Environment Friendly No Yes Yes


What are the advantages of anodizing?

Corrosion resistance

Many metals are easy to corrode. And the Anodizing film is oxide, which has high corrosion resistance.

High hardness

The hardness of the anodized film is about HV100, the hardness of the ordinary anodized film is about HV300, and the hard anodized film can reach about HV500.

The anodized film not only has high hardness but also has good wear resistance. Especially, the porous anodized film on the surface layer has the ability to absorb lubricants, which further improves the wear resistance of the surface.

Strong adsorption ability

The Anodizing film is a multi-hole structure with strong adsorption capacity. The holes can be filled with various paints, lubricants, and resins. This can enhance the protection, insulation, wear resistance, and decorative properties of metal parts.

Good insulation properties

The anodized film does not have conductive properties anymore. So the anodized metal becomes a good insulating material.

Excellent heat resistance

This is because of the low thermal conductivity of the anodized coating, which is resistant to temperatures of about 1500°C.

Multi-color selection

The anodized film is porous and can be filled with different color dyes to enhance the appearance of the product.

Longer life

Because the anodized film penetrates deep into the holes of the metal component, it hardly peels or chips, so it lasts longer.


What metals can be anodized?

  • anodizing aluminum
  • anodizing brass
  • anodizing copper
  • Anodizing titanium
  • Anodizing steel
  • Anodizing  Magnesium

FAQS About anodization

Is anodization a coating?

Anodizing is a type of coating material. This coating consists of an oxide film formed on a metal part by electrolysis.

Can you remove anodizing

The Anodizing film can be removed by alkaline washing. However, after alkali washing, the product surface needs to be neutralized and dried to avoid oxidation.

Is anodized rust-proof?

Yes, The anodizing film prevents the metal from rusting by isolating it from the air or other corrosive materials.

How long does anodized last?

Anodizing is a durable surface treatment method. Depending on the thickness of the anodized film and the quality of the anodizing, anodized products can last up to 20 years.

Can anodized be scratched?

The surface of the metal parts will be scratched, but the color will not be removed. Because the dye is deep into the holes of the parts.

Does anodizing fade in sunlight?

Unfortunately, anodized parts are affected by ultraviolet light from the sun and fade. That is, the color will lighten. But some measures can be taken to reduce this effect.

  • Choose a better-quality dye
  • Increase the dye saturation of the gaps
  • Improve the quality of the seal

how much does anodizing cost?

The minimum cost for anodizing is between 60-120usd. Other costs will depend on coating thickness, type of anodizing, and type and size of material.

How can you tell if the metal is anodized?

The easiest test method is using a magnet and an ammeter. This is because after anodizing, the CNC part is not magnetic or conductive.


On-demand CNC Machining prototyping and parts with Custom Finishes and low volume manufacturing.

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