Anodizing and Chromating Aluminum Castings

1 Feb 2022

Anodizing and chromating are finishing process that give castings erosion protection. There are three main types of finishing processes:

  • Chemical Conversion (chemical film and chromating)
  • Conventional Anodizing (Type II)
  • Hard Coat Anodizing (Type III)

Parts may go through a single operation, or a series of operations, depending on its end application.

anodizing and chromating

1. Chemical Conversion

Chemical conversion processes are the least expensive and least protective of the 3 finishing processes.

Chemical Film

  • Class 1A (gold) – more protective
  • Class 3 (clear) – thinner, used for electrical conductivity

Chromate Conversion

Advantages of chromate conversion are cost and its dielectric properties. However, these finishes have low durability.

While the coating is clear in color, class 1A (also known as trivalent chromate) is more protective than class 3. Class 3 coatings are thinner and used for electrical conductivity.

2. Conventional Anodizing

Type II anodizing is great for its corrosion resistance, appearance, colorful options, and oxidation protection, all within a reasonable cost.

Disadvantages of type II anodizing include insulating properties and low wear resistance. The coating is easily scratched.

3. Hard Coat Anodizing

Hard coat anodizing, also referred to as type III anodizing, is the most protective of the 3 finishing processes. Other advantages include…

  • Wear resistance
  • Corrosion resistance
  • Strong insulation
  • Heat transfer properties

Unfortunately, hard coat anodized parts are limited on color options.

Restrictive Anodizing

Sometimes, parts have areas that need anodized, and areas that need preserved. That’s where restrictive anodizing comes in. Sections can be excluded from anodizing by…

  • Plugging (ex: critical threads)
  • Taping
  • Painting (example: contours)


Please reach out to our sales team to learn more about the casting and finishing process. We are eager to help in any way we can! Give us a call at 812-537-2275

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