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Aluminum wheel with gold anodized caliper

Conversion coatings

Why does aluminum need conversion coating in automotive applications?

Conversion coatings

Chromium-free conversion coatings are used to protect aluminum from corrosion, ensure that reliable electrical connections can be made and as an effective pre-treatment for adhesion of organic coatings. Conversion coatings produce an amorphous coating via immersion or spraying techniques.

Hexavalent chromium-free

Typically solutions used for forming conversion coatings in automotive applications solutions must be free of hexavalent chromium. Today that means solutions completely free of chromium. Until now, most non-chromium conversion coatings had been based on a combination of organic polymers and fluoride compounds.  

While these types of products have excellent paint adhesion characteristics, in most cases, they have no corrosion resistance properties, critical for protecting exposed aluminum. Based on that deficiency, we developed the Iridite range of chromium-free coatings that has proven to effective in demanding applications, such as automotive.

Where are they used?

Although coated aluminum is used in most automobile applications, there are two particular types of vehicles in which aluminum use is growing:

Electric vehicles

Battery housing and constructions use conversion coatings to provide corrosion resistance, paintability and defined electrical conductivity. Additionally, aluminum provides good thermal transfer capabilities to keep the battery cool in hot weather, while maintaining structural integrity in case of collision. Another trend for electric vehicles, is closed aluminum wheels are popular for improved aerodynamics to increase the driving range. The aluminum wheels are conversion coated to provide adhesion towards subsequent paint layers. 


These larger cars require additional lightweight considerations and there is a trend towards using aluminum brake calipers instead of cast iron. Aluminum wheels, a critical part of the look and feel of today's SUVs are conversion coated to provide adhesion towards paint layers. 

Find out more

ESI Automotive has many years of supplying aluminum conversion coatings to the automotive industry. To find out more about our chromium-free conversion coatings for EVs, SUVs and all other vehicles, please contact us today.