Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.

The process is called anodizing because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than do bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light.

Anodizing: The Ultimate Guide

Taking surface finish into consideration when manufacturing metal components is vital.

Metal finishes enhance the part’s overall aesthetics and durability among other ideal properties.

Anodizing is a popular surface finishing option for different metals.

This guide takes you through all the basics of anodization you need to know, like types, benefits, design considerations, cost, and common applications among others.

What Is Metal Anodizing

Anodizing is a finishing process for metals that uses electrolytic oxidation of material surface to form a protective oxide coating.

The process forms a hard, non-conductive, non-corrosive, durable, and reflective oxide finish on the external surface of anodized part.

Ordinarily, anodizing increases the natural oxide thickness to enhance part durability, aesthetics, and corrosion resistance.

It also makes paint adhesion on surface material easy, thus commonly used as a pre-treatment for parts to be dyed, bonded, or coated.

Types Of Anodizing Process

Anodizing process is available in different types, and each type of this process provides unique results.

The common types include the following;

Type I – Chromic Acid Anodizing

It is the oldest type of anodizing, commonly known for softer anodized layers, which are relatively thinner than the regular finishes.

The thinner coated oxide coating of this anodizing process is often expressed in micro-inches ranging from 20 to 100.

Even so, it still leads to parts with enhanced corrosion resistance but with least color absorption when dyed.

It is unsuitable for applications where decoration is a concern since it is mostly dyed black.

Type II – Sulfuric Acid Anodizing

This anodizing subtype used sulfuric acid rather than chromic acid.

It yields a slightly thicker surface layer on the metal component.

Besides, it has a thickness range of 0.0002 to 0.001 inches and is usually most suitable for paint adhesion and corrosion resistance.

Type II anodizing also exhibits better energy-efficient than Type I anodizing.

Type III- Hardcoat Anodizing

It also uses sulfuric acid but often yields a thicker anodized layer than Type II anodizing.

Hardcoat anodized components exhibit the best abrasion resistance and color dyeing potential.

Hence, it is an ideal process for parts that are exposed to extreme wear or immensely corrosive settings.

Even so, it may not be an ideal anodizing option for parts with exceptionally tight tolerances.

Titanium Anodizing

This process is predominantly used for coloring titanium and finding stress cracks in base material.

It exhibits high adhesion for paint and dry film lubricant.

Therefore, it is mostly common in medical, aircraft, and spacecraft parts.

Bright Dip Anodizing

It is a surface anodizing process that uses phosphoric and nitric acid to yield an almost mirror-like appearance.

As such, you will commonly find it used in car parts production and flashlights among others.

Architectural Anodizing

It is an ideal anodizing option where appearance and durability are a concern.

Thus, you may consider it for parts designed to support exterior of a structure permanently.

Suitable Materials For Anodizing

You can use anodizing coating method on a wide range of metallic materials and still attain best results.

Such materials include the following;

  • Aluminum – It is arguably the popular material where anodizing is used. Anodized aluminum parts are used in different applications such as construction, automotive, aircraft, medical devices, etc.
  • Zinc – It is usually anodized in a few instances, especially where a deep green color is desired. This material forms a hard and wear-resistant oxide layer, thus suitable for different applications.
  • Titanium – In many instances, this material is often anodized for use in dental implants, jewelry, and artwork. Mostly, this is attributed to tendency of the titanium to form brighter colors from anodizing process.
  • Magnesium – There are instances when it is anodized to prime for painting. However, it needs additional treatment or sealing to enhance corrosion resistance.
  • Ferrous metals – Mostly, it is anodized using nitric acid to create a hard, wear-resistant oxide layer.

Mechanical Design Strategies For Anodizing

Metal anodizing process

Metal anodizing process

Here are the notable design guideline for anodizing different metal surfaces;

  • Coverage limitations

Often, the part hardly forms an oxide layer at a point it is connected to the power source; thus, tooling needs to consider this aspect.

Alternatively, features must be formed into the component to be held from a non-critical surface.

  • Sealing required

Since the oxide coatings are generally porous, a sealing treatment is incorporated to minimize micro-cracks and prevent chemical decomposition.

  • Dimensional effects

You should always know that the material surface will always rise as oxide layer builds up on the outer part.

Thus, in applications with relatively tight tolerance, the additional layer must be accounted for and dimensioned.

  • Fatigue effects

Anodizing either increases or decreases fatigue life of a component by minimizing corrosion pitting or spreading surface cracks, respectively.

Hence, the effects always depend on the material and specific application.

  • Thermal stress cracking

When subjected to temperatures beyond 350K, most anodized layers are prone to thermal stress cracking.

Ideal Equipment For Anodizing Process

Typical machinery for anodizing process may consist of several automatic anodize tanks.

Such tanks feature integrated CNC machines, which help in anodization.

However, to complete the anodizing process, it is advisable for the anodizing systems to have multiple tanks for accomplishing the anodize process.

Here are the notable equipment you should have to complete this process;

  • Chillers

They are useful when it comes to evening out metallic oxide deposition.

The cooling process is often aided by air-chillers or water-chillers.

Often, these chillers use temperatures valves and sensors to maintain the desired temperature.

  • Rectifiers

It is the system controlling the current in anodizing process.

Rectifiers help in maintaining temperature and voltage at optimal levels.

How Anodizing Works

Metal anodizing process

Metal anodizing process

Anodizing primarily involves submerging a metal into an electrolytic bath.

Ideally, the entire process may appear quite complex since it involves numerous electrochemical reactions taking place.

However, it is relatively straightforward and cost-effective.

The first step in anodizing process entails cleaning the metal part thoroughly before undergoing anodization process.

Essentially, it is important because it removes impurities likely to hinder the process’s efficiency.

Second step involves placing the metal part into an electrolytic solution bath where there is application of a direct electric current.

This forms a positive electric charge in the metal and a negative electric charge in the solutions electrolyte plates.

The subsequent electrochemical reaction forms a pore on metal’s surface, enabling metal’s substrate to bond with negatively charged oxygen ions in solution.

Hence, this creates an anodic oxide layer on the surface of the respective metal part.

This layer forms a durable and more resistant barrier than the underlying metal layer.

Establishing Successful Anodizing Process

You can use several techniques to determine whether a part has undergone a successful anodizing process.

Some of these ways include the following;

Check For Color Dispersal

An ideal anodizing process always portrays a consistent surface with uniform color dispersal.

Some anodizing effects you need to look out for on your finished anodized component include the following;

  • Insufficient agitation in the anodizing process
  • Anodizing burns due to high current densities

Matte Finish

A complete anodizing process often creates a unique matte finish, which you ought to look for.

Do A Scratch Test

Scrape a coin on the surface of anodized metal.

If it forms a visible scratch, then it is likely the part is not fully anodized.

Ideally, a fully anodized part is often scratch-resistant.

 Anodized aluminum

Anodized aluminum

Advantages Of Anodizing Metals

Anodizing different metals present various benefits to the end-user and the particular application.

Such advantages include the following;

  • Enhances aesthetics

You can use a clear anodized finish to protect an already acceptable appearance of components.

It can also be used to supplement the general aesthetics with a simple color addition.

Of course, there is a significant degree of expertise needed for precise color accuracy and repeatability.

However, you can be certain of obtaining extremely desirable and professional appearance results.

  • Durability

This surface finishing process extends the service lifespan of a metal part since it improves abrasion and corrosion resistance.

Notably, the increased durability enables such parts to resist faster wearing out during installation, handling, and regular use.

  • Health and safety

Ordinarily, anodized finishes tend to be non-toxic, chemically stable, and produce few harmful effects on the environment.

Thus, anodizing is an environmentally-safe operation.

  • Economical

In the long run, anodizing parts is cost-effective since it reduces maintenance needs.

And this is imperative since it leads to significant cost savings you would otherwise incur in new purchases or repairs.

  • Improves material properties

Anodizing significantly enhances material properties on part’s surface.

Some of these properties include weather, scratch, and corrosion resistance among others.

Besides, the oxide layer created through this process is integrated to be part of the component.

Also, the outer anodized metal layer has insulating properties; hence the part may have lower electrical conductivity.

Design Considerations For Anodizing

Usually, anodizing is used in different industries for various projects.

However, when designing for metal anodizing, it is fundamental to have in mind a few considerations for a successful outcome.

Such considerations include the following;

  • Hardness

Anodizing is common with increasing surface of a part relatively far beyond its typical base material.

Thus, it is fundamental to establish the best techniques to approach this effect to ensure it doesn’t interfere with final results.

  • Conductivity

When you anodize a metal, it increases its thermal and electrical resistance.

However, if you are experiencing challenges with thermal or electrical insulation, you can use a mask to retain a bare-metal finish if full conductivity is required.

  • Dimensions

Once anodizing process is over, there will be dimensional alterations to the bare metal part.

Technically, dimensional growth changes based on type of anodization, but it’s generally 50% of total anodic thickness.

Thus, you must establish the oxide layer thickness when determining tolerances, particularly for mating surfaces.

  • Color matching

It can be tricky to attain a true color match, especially if the parts are not necessarily treated in same batch.

Also, color fading seems to be a quite common problem for anodized coatings.

As such, it is important to carefully dial in the process of each part.

  • Combined coatings

You can add secondary processes to anodized parts by heating or treating the surface to enhance properties.

However, it is important to reach out to a coating specialist if you have special needs for your anodized parts.

Color Options For Anodized Parts

Anodized aluminum knob

Anodized aluminum knob

Essentially, anodizing provides different colors, which is advantageous since it makes it easy to select the right one for your application.

However, the specific color for anodized parts is dependent on the specific metal you are anodizing.

Nevertheless, the common color options you can get with this surface finish process include the following;

  • Gold
  • Yellow
  • Red
  • Violet
  • Blue
  • Black
  • Brown
  • Green
  • Pink
  • Grey
  • Olive drab

Cost Of Anodizing

Ideally, the cost-effectiveness of anodizing is one of the reasons it is quite popular in different applications.

Even so, the actual cost of this process is dependent on a host of factors such as part dimension, part shape, part quantity, color, and type of anodizing.

Simply put, dying a relatively complex part is likely to be more expensive to anodize than a simple part without a color finish.

Besides, the specific company you are dealing with also determines the exact cost of anodizing.

Some companies are relatively affordable, whereas others tend to be a bit costlier.

Therefore, it is recommended to always inquire from the particular entity you are getting the anodized parts from to determine the actual cost.

In general, though, this process is relatively cost-effective.

Common Applications Of Anodizing

In essence, anodizing is high quality and economical surface finishing technique.

As such, you are likely to find most of its parts used in a wide range of applications across different industries.

Some common applications you will find this component include the following;

  • Consumer goods
  • Automotive
  • Architecture
  • Homeware
  • Aerospace
  • Consumer Electronics
  • Jewelry
  • Medical equipment
  • Kitchenettes
  • Light fixtures
  • Satellites

It is apparent that anodizing has an immense wide application throughout numerous industries.

Of course, the process may vary as far as complexity and cost are concerned.

However, the ultimate product performs and exhibits superiority to original component significantly.

Contact us today for high quality anodized parts from China.

Scroll to Top