Anodizing non-ferrous metals such as aluminum or titanium helps to protect them against corrosion as well as improve their aesthetics if used for decorative purposes. The bond that results from anodizing is also superior to that of any bonding achieved via painted coatings.
Under the MIL-A-8625 standard, there are three types of anodization:
- – Type I, which uses a chromatic acid bath
- – Type II, which uses a sulfuric acid bath
- – Type III, which also uses a sulfuric acid bath, but in a much thicker oxide layer.
Type I is the oldest form of anodizing and produces a softer and more ductile film. This type can be used as a pre-coating to paint finishes. Type II anodizing is often used with such materials as decorative finishing work, electronic products, military and aerospace hardware, and automotive and sporting goods. Type III is used for protective coatings on functional parts such as gears, pistons, and electronics that may be exposed to extreme wear. This type is also referred to as “hard anodizing.”
Accurately testing anodized coatings is very important in determining their effectiveness. But which method you use to test them largely depends on the type and purpose of the anodization. For example, to determine the strength of a thicker, hard anodized coating (Type III for protective), you should use the instrumented indentation (nanoindentation) method to test its hardness. Conversely, with decorative anodized coatings (Type II for color coating), where the hue of the coating is the primary concern (for proper colorization), you’ll need to ensure the correct substrate alloy is being coated, as the alloy’s specific properties will affect the color of the anodized layer. Even a very minor variation in an alloy’s properties can result in different colored hues being applied during the anodization process. To avoid this, you’ll need to measure the electrical conductivity of the alloy making up the base material. For this task, an instrument using the eddy current method for material analysis should be used.
Instruments:
Sources:
A Guide to Anodizing Aluminum and Other Metals (Fast Radius):
https://www.fastradius.com/resources/anodizing-guide/
Type II and Type III Anodizing – What are the Benefits? (Lincoln Industries.com):
https://www.lincolnindustries.com/blog/articles/1-1-2022/type-ii-type-iii-anodizing-what-are-benefits
Anodizing (Wikipedia):
https://en.wikipedia.org/wiki/Anodizing
Quality Control for Decorative Anodized Coatings (HelmutFischer.com):
https://www.helmut-fischer.com/quality-control-for-decorative-anodized-coatings
Mechanical Testing of Anodized Coatings (HelmutFischer.com):
https://www.helmut-fischer.com/mechanical-testing-of-anodized-coatings
Leave A Comment