Types of Anodizing Processes and Their Applications

Introduction

Anodizing is not one process with fixed specifications. It is a family of processes that differ in electrolyte, layer thickness, and properties. Choosing the right type determines how well a part resists corrosion and wear, how it looks, and what it costs. This article covers the main types of anodizing, where each is used, and how to choose the right one for your product.

The main types of anodizing

1. Chromic acid anodizing (Type I)

Produces a very thin layer compared with other types, keeps part dimensions almost unchanged, and has little effect on the fatigue strength of the metal. It has long been associated with aerospace and military applications. Its use is declining worldwide because of environmental and health restrictions on hexavalent chromium compounds.

2. Sulfuric acid anodizing (Type II)

The most widely used type in the world for decorative and protective anodizing. It gives a medium-thickness layer with pores that take dye easily, combining corrosion protection with an attractive appearance. It is used for architectural profiles, appliance handles, shower cabin profiles, accessories, and decorative parts. ISO 7599 covers this kind of decorative and protective anodic coating.

3. Hard anodizing (Type III)

Runs under different conditions (lower temperature and higher current density) to produce a much thicker and harder layer, suited to parts exposed to heavy wear, such as industrial equipment components, pistons, and cylinders. Its appearance is usually darker, its color options are limited, and it has its own standard, ISO 10074.

Coloring methods in anodizing

Coloring is not a separate type of anodizing but a step after the layer is formed. The most common methods are:

Dyeing: after anodizing, the part is immersed in a dye solution absorbed by the pores, which are then sealed. This gives colors such as gold and black.
Electrolytic coloring: metal salts are deposited inside the pores using electric current. It is mostly used for darker shades and has good light fastness.
Natural finish: the silver produced by anodizing without any coloring, very popular in clean modern designs.

How to choose the right type

For appearance and protection together: decorative and protective anodizing is the natural choice for most consumer and architectural products.
For parts under heavy wear: hard anodizing fits better, keeping in mind its effect on appearance and dimensions.
For critical dimensions: account for layer growth in the design, since the layer grows into and out from the surface in roughly similar proportions.
For outdoor use: ask for a thicker layer and good sealing, and prefer light-fast colors.

The final finish: bright or matte?

Besides the anodizing type, surface preparation before anodizing decides the final look. Chemical polishing gives a bright finish, while etching or sanding gives a matte or brushed finish. Agree on the finish with your supplier along with the anodizing type and color.

Anodizing at Golden East (GETI)

Golden East Trading & Industry (GETI) provides decorative and protective anodizing for aluminum profiles in silver, gold, and black, with bright, matte, and brushed finishes, for products such as appliance handles, shower cabin profiles, heat sinks, and decorative profiles. We measure layer thickness according to ISO 7599.

Frequently asked questions

What is the difference between Type II and Type III?

Type II is a medium-thickness layer that accepts color and suits decorative and protective uses. Type III is a thicker, harder layer designed for wear resistance in engineering applications.

Are all colors available in anodizing?

No. Anodizing gives a metallic look in specific colors, and the range differs between factories, so ask your supplier for its actual colors and request a sample.

Conclusion

Choosing the right anodizing type starts with one simple question: what does the part need most, appearance, wear resistance, or dimensional precision? The right answer improves product quality, extends its life, and lowers maintenance costs.