Conversion Coatings

Abstract The sections in this article are Phosphate Conversion Coatings Overview Historical Perspectives Overview of Process and Reaction Mechanisms Degreasing Activation Phosphating Posttreatment The Nature of the Phosphate Layer Morphology Chemical and Surface Composition Thermal and Chemical Properties Electrochemical Properties and Characterization Methods Porosity and Coverage Measurements In Situ Monitoring of the Phosphating Reaction Corrosion Resistance Measurements Chromate Conversion Coatings Overview Chromate Conversion Coatings: Definition and Applications Historical Perspectives Substrates Aluminum Zinc Magnesium Cadmium Steel Stainless Steels Chromate Conversion Coating Types Alkaline Chromate and Dichromate Formulations Acidic Chromium–phosphate Acidic Chromium–chromate Accelerated Chromium–chromate Chromate Conversion Coating Formation Chromium–chromate Coatings Chromium–phosphate Coatings Cr(VI) andCr(VI) Speciation Activators and Accelerators Coating Formation on Metallurgical and Structural Defects CCCMorphology, Structure, and Composition Corrosion Protection Corrosion Protection Mechanisms Aging and Heating Macroscopic Characteristics of Chromate Conversion Coatings CCCWeight, Thickness, and Color Chemical and Corrosion Resistance Mechanical and Thermal Stability Paint Adhesion Electrical Contact Resistance Chromate‐free Coatings Sol–gel Coatings Hydrothermal Coatings from Alkaline Solutions Rare Earth Metal Coatings