What is Anodizing

Highlights:

  • Anodizing Aluminum enhances properties of  for increased hardness, durability, corrosion and wear resistance
  • Chromic Acid Anodize Type I thickness – .00005”-.0001”
  • Sulfuric Acid Anodize Type II thickness – .0001”-.0008”
  • Hardcoat Anodize Type III thickness – .0008”-.003”
  • Can be dyed in many colors
  • MIL holds numerous aerospace Prime and Nadcap approvals
  • Can be used as a pre-treatment for other coatings

Aluminum alloys are extremely valuable and low-maintenance materials that, due to their high temperature control and overall versatility, can be used in a variety of applications from cooking to automotive to use in air and space craft. They are not, however, very hard materials. Unlike pure aluminum, they are not self-passivating and are therefore more susceptible to corrosion and wear. In order to better utilize the benefits of aluminum and to achieve enhanced durability, hardness, corrosion and wear resistance, these industries and others have turned to the process of Aluminum Anodizing.

What is Anodizing?

Many people have mistaken anodizing for a plating process. This is inaccurate, as the surface to be anodized does not receive a superficial coating deposited in the same manner as a surface to be plated. Plating is a process where a coating is applied to the surface. Anodizing is a process that modifies the surface. By applying electricity to aluminum, the parts become the anode against the cathode in a completed electrical circuit while immersed in an electrolyte acid bath. The electricity and acid batch work together to open the surface’s texture and crystal structure, and build the thickness of the natural oxide layer. In this same process the surface also has increased hardness which is crucial in the many applications for anodized aluminum.

Depending on the type required, MIL can provide an anodize thickness range as follows:

  • Chromic Acid Anodize (Type I) .00005”-.0001”
  • Sulfuric Acid Anodize (Type II) .0001”-.0008”
  • Hardcoat Anodize (Type III) .0008”-.003”

As the surface texture and crystal structure is modified, the anodized surface becomes ideal for absorption of dyes in color application. From black to gold to red to many other colors, anodized aluminum surfaces offer color stability under ultraviolet rays and do not chip where a painted surface would.

After the parts are immersed in an electrolyte solution made up of chromic, sulfuric, boric sulfuric acid, or are dyed, they are sealed per specification or purchase order requirements. This forces the pores that have been opened to swell shut and prevent unwanted dye or other fluid absorption, and provide the corrosion resistance that bare aluminum does not have.

While an anodized aluminum part can stand up on its own, the process can also be used as a pre-treatment for other coatings processes. Anodized surfaces provide increased adhesion under coatings such as Solid Film Lubricant and Prime and Paint, for optimal performance and endurance.

In order to take advantage of the many inherent qualities that aluminum has to offer, anodizing of the surface can enhance the product for durability that far outlasts bare aluminum. MIL can provide a number of different types of anodize, ranges of thickness and color, and multiple sealing solutions. Magnetic Inspection Laboratory also retains numerous aerospace Prime and Nadcap approvals to support these process requirements.

Aluminum alloy parts

Aluminum alloy parts

What is anodizing

One of MIL's anodizing lines

Magnetic Inspection Laboratory Anodizing

Electrolyte solution

Anodizing MIL gold

Many colors available, such as gold