A Chrome - Free Aluminum Oxide Conversion Coating Process

摘要

The term "conversion coating", as used in the metal finishing industry, refers to the conversion of a metal's surface into a surface that will more easily accept applied coatings and/or provide for a more corrosion resistant surface. They are rather thin (not over 600 nm thick on aluminum), quickly and easily formed, easily scratched and, if used to enhance paint adhesion, are coated shortly after being formed to prevent degradation of the conversion coating. Conversion coatings for aluminum have been in use since the early 1920's and there are a number of different products on the market. The four main types of conversion coatings, in common use, are based upon: (1) the production of a film of chromium hydroxides and/or oxides; (2) the production of a film of precipitated heavy metal phosphates; or oxides; (3) the use of various synthetic polymers, with or without heavy metal phosphates or oxides; (4) the formation of a manganese oxide - aluminum oxide film by use of permanganates. Aluminum oxide - manganese oxide based conversion coatings are particularly useful as they have excellent barrier properties and greatly enhance the adhesion of applied coatings.