Chemical conversion coatings sometimes referred to as chromate conversion, chem film , Iridite or Alodine refer to a process of applying a thin barrier coating on the substrate to passivated aluminum alloys to slow the formation of corrosion. It is gelatinous film that has self-healing properties and improves paint adhesion on aluminum alloys and die castings. It can also be applied to zinc die castings.
- Materials qualified under Mil-DTL-5541F produce coatings that range in color from clear to iridescent yellow or brown.
- They are all electrically conductive and impart some measure of corrosion protection on the substrate.
- Visual inspection may be difficult since breaks in the coating are not easily seen.
- Type I is Hexavalent Chromate
- Type II is ROHS compliant, hex free chromate. This meets the ROHS and EELV requirements.
Class IA coatings are intended to provide corrosion protection as a stand alone coating and improve adhesion of subsequent operations such as paint on aluminum substrates. Class 3 chemical conversion coatings are used as a corrosion preventative film where electrical contact is still required. Many times it is applied under masking operations prior to anodic coatings in accordance with MIL-A-8625-F. The primary difference between Class IA coatings and Class three coatings is thickness.
- Aircraft industry
- Electronic cabinetry
- Aluminum stampings
- Electronic components
- Zinc die castings
- Aluminum die castings