All About Machining Anodized Aluminum Parts

Aluminum anodizing is a very durable post-treatment method. It can not only enhance the performance and appearance of the part, but also better bond the primer and glue. Anodized surface treatment makes aluminum one of the most popular materials in the production of thousands of consumer, commercial and industrial products today.

What Is Anodized Aluminum?

Anodized aluminum is treated aluminum with excellent durability. To produce anodic aluminum oxide, use an electrochemical process in which the metal is immersed in a series of tanks, and the anode layer in one of the tanks is grown from the metal itself.Anodized aluminum parts

Anodizing is an electrochemical process that transforms a metal surface into a decorative, durable, and corrosion-resistant anodic oxide layer. Since the anodic oxide layer is formed by aluminum itself, it is a highly controlled oxidation problem, enhanced by natural phenomena, rather than being painted or coated. Therefore, the anodic oxide coating is hard, durable, and will not peel off. It will not wear out under normal conditions. Although other non-ferrous metals (such as titanium, zinc and magnesium) can also be anodized, aluminum is by far the most widely used metal. Anodized aluminum is three times harder than raw materials and 60% lighter than other competitive metals such as stainless steel and copper.

How to Anodize Aluminum Parts?

In order to anodic aluminum parts correctly, must clean and rinse the surface, and then place aluminum parts in an electrolyte containing sulfuric acid or chromic acid, which will form tiny pores (nanopores) on the aluminum surface and form many positive ions And negative ion conductive coating. An electric current is applied to the medium, and by adding a cathode, oxygen ions are released from the acid and combined with aluminum.

The combination of the aluminum surface and the negatively charged ions forms a barrier layer, which is called the surface layer that makes the part corrosion-resistant in the anodized aluminum process. The anode coating is composed of hydrated aluminum oxide, which is considered to be corrosion and abrasion resistant. The thickness of the conventional coating is 0.1 to 1.0 mil. If necessary, can apply color at this time. Finally, apply a sealant to close the nanopores and any micro cracks in the oxide layer.

The coloring process is carried out by injecting paint into the holes of the part. After the colored pigment reaches the surface, it is sealed to retain the selected color. This creates a color that will not fade and is very durable, and cannot scrape off the color on the surface because the color is actually very dark and can only be removed by grinding off the substrate.

anodized aluminun partAnodizing Aluminum Parts Process Type

There are several types of aluminum anodizing, each of which results in a unique anodic coating. Most commonly referred to as Type I-Chromic Acid Anodize, Type II-Sulfuric Acid Anodize, and Type III -Hard Anodize or Hardcoat.

Anodized Type I (Chromic Acid Anodize)

Chromic acid anodizing or anodized type I is the most basic type, using chromic acid to produce a thin and ductile anodic oxide layer on aluminum parts. The thickness of each surface is usually .00002 inches-.0001 inches (20 to 100 micro inches). This limits the use of chromic acid anodization as a decorative finish.

It is suitable for parts with strict tolerance requirements and will not change the size. But this is done using chromic acid, which is not good for the environment, and is rarely used today.

Anodized Type II (Sulfuric Acid Anodize)

Anodized Type II, also called Sulfuric Acid Anodize, is a common standard anodizing. Instead of using chromic acid, it uses sulfuric acid, based on the military specification MIL-A-8625. It is the standard specification for industrial anodized aluminum in the medical, aerospace, military and defense fields worldwide. It is particularly suitable for applications requiring hardness and wear resistance.

The thickness range of Anodized Type II process film is .0001″-.001″. The total thickness of the formed coating is 67% penetration in the substrate, which is 33% longer than the original size of the part, producing a thicker anodized layer on the part, making it more suitable for coloring. The parts can be chemically or mechanically treated before anodizing to achieve a matte (non-reflective) effect.

Anodized Type III

Type III anodizing, also known as Hard or hard coat anodizing, uses a process similar to type II anodizing, carried out in a sulfuric acid-based electrolyte, but will produce a thicker and denser coating, up to 2 mils in thickness . Thereby significantly enhance the wear resistance and corrosion resistance. Hard anodizing produces a very thick hard coating that penetrates the treated aluminum. Half of the protective oxide layer penetrates the surface, and the other half is deposited on the surface.

Hard coatings are suitable for aluminum parts in extreme wear applications that require extremely high wear resistance, or corrosive environments that require thicker, harder, and more durable coatings. It is also valuable in places where electrical insulation needs to be enhanced.

The main difference between type II and type III is that for type III anodizing, the temperature of the sulfuric acid solution is lowered and operated at a higher voltage.

Anodizing Aluminum Parts Benefits


Polar oxidation changes the aluminum base material at the molecular level, and the anodized parts will not chip or peel off, and have strong corrosion and wear resistance. The surface hardness of anodized aluminum is three times that of standard aluminum. Even if it is processed for color enhancement, it will not chip, peel, or flake. Since the anodizing process is controlled oxidation of aluminum, the product will not rust, bronze or age. Anodized aluminum parts are one of the toughest and most versatile metal products on the market.

Low cost, High Value

Because anodized aluminum is much lighter than other metal products, the cost of transportation to the job site or manufacturing plant is greatly reduced. Due to its high strength-to-weight ratio, the total cost per square foot of anodized aluminum in the project is lower than that of materials such as steel, zinc, bronze, brass and copper, while still having the same visual effect. The service life is longer than similar parts sprayed or electroplated.

Environment Friendly

Because aluminum is rich in recyclability, and is the only metal that is 100% recyclable, plus the aluminum anodizing process is very environmentally friendly, unlike spraying and electroplating, anodizing does not produce hazardous waste or interfere with the recyclability of aluminum.

Light Weight

Anodized aluminum is a lightweight metal, about 60% lighter than stainless steel, copper or brass. This makes the transportation of materials more cost-effective and can solve countless design problems. From architectural design to consumer product design, as long as lightweight, durable and attractive materials are required, anodized aluminum can provide versatile solutions.

Easy Maintenance

The parts look primitive from production and have remained in this state for many years. Soap and water or mild detergent can remove dirt and restore the finish with relative ease.


Anodized aluminum has a more beautiful appearance than anything. If kept in its natural state, the anodized aluminum is a bright new silver and can be anodized to retain a matte or bright finish. You can also choose custom textures such as stucco, brushed or pebble tones to give your product a unique look and feel.

Custom Color Options

anodization parts colorsBecause the anode layer has an open-pore structure before sealing, the anodized aluminum can be processed to make it almost the same color as any brand you imagine. The versatility of the material also means that it can be made into a similar appearance to other metals, giving you the appearance of gold, bronze, copper, stainless steel, brass, etc., without the risk of weathering.

Enhance The Abrasion Resistance Of Aluminum Products

The anodic oxide film whose chemical structure is metal oxide rather than metal has strong electrical insulation. Some aluminum materials require electrical insulation, such as a capacitive dielectric layer. This can be achieved by anodic oxidation.

(Realted Post: All About CNC Aluminum Machining )

With over 10 years of experience manufacturing precision parts, we consider anodizing a reliable, economical and proven finishing process for aluminum components. SANS machining provide anodizing finishes to our client projects. Available colors include clear, yellow, green, red, and black.

As a ISO9001:2015 certified supplier, all parts are subject to rigorous inspection and quality assurance, according to the specification required for the project which keeps your anodized parts looking their best for years on-end.

2 thoughts on “All About Machining Anodized Aluminum Parts

  1. vital says:

    Hello i have small die casting product which expose to ethanol solution for prolonged time. To protect them i need to anodizes the aluminum die casting product. But as anodization change the size and dimensions and surface roughness. Some parts movement is affected by the surface roughness.

    Can you suggest any other process or anodization of aluminum die casting product which can reduce the machining of the part after anodization, reduce surface roughness.

    I am also have a question if i machine the anodized aluminum parts the anodization will crack or affect.

    I also need cost effective coating with good resistance to ethanol and low surface roughness with low dimensions change.

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