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Chromate Conversion Coatings

MPP Group applies chromate conversion coatings to zinc plated products as well as to mill finish aluminum.

Chromate conversion coating is a type of conversion coating used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, and tin alloys. It is primarily used as a corrosion inhibitor, primer, decorative finish, or to retain electrical conductivity.

“Chem-Film” or chromic acid used in the bath, is more commonly known as hexavalent chromium. This type of bath is still the most widely used, however hexavalent chromium is toxic and, thus, highly regulated, so new non-hexavalent chromium based processes are now available.

Irridite and Alodine are names of commonly used Chromate Conversion Solutions.

MPP Location providing this process: Missouri

Zinc

Chromating is commonly performed on zinc-plated parts to make them more durable. The chromate coating acts like a paint, protecting the zinc from white corrosion, this can make the part several times more durable depending on chromate layer thickness.

The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black. Darker coatings generally provide more corrosion resistance.

ISO 4520 specifies chromate conversion coatings on electroplated zinc and cadmium coatings. ASTM B633 Type II and III specify zinc plating plus chromate conversion on iron and steel parts.