MY110203A - Non-chromated oxide coating for aluminium substrates - Google Patents

Abstract

(A.) A PROCESS FOR FORMING A COBALT CONVERSION COATING ON A METAL SUBSTRATE, THEREBY IMPARTING CORROSION RESISTANCE AND PAINT ADHESION PROPERTIES. THE INVENTION WAS DEVELOPED AS A REPLACEMENT FOR THE PRIOR ART CHROMIC ACID PROCESS. THE PROCESS INCLUDES THE STEPS OF: (A) PROVIDING A COBALT CONVERSION SOLUTION COMPRISING AN AQUEOUS SOLUTION CONTAINING A SOLUBLE COBALT-III HEXAVALENT COMPLEX, THE CONCENTRATION OF THE COBALT-III HEXAVALENT COMPLEX BEING FROM ABOUT 0.01 MOLE PER LITER OF SOLUTION TO THE SATURATION LIMIT OF THE COBALT-III HEXAVALENT COMPLEX, AND ACETIC ACID; AND (B) CONTACTING THE SUBSTRATE WITH THE SOLUTION FOR A SUFFICIENT AMOUNT OF TIME, WHEREBY THE COBALT CONVERSION COATING IS FORMED. THE SUBSTRATE MAY BE ALUMINUM OR ALUMINUM ALLOY, AS WELL AS CD PLATED, ZN PLATED, ZN-NI PLATED, AND STEEL. THE COBALT-III HEXAVALENT COMPLEX MAY BE PRESENT IN THE FORM OF [CO(NH3)6]X3 WHEREIN X IS CI, BR, NO3, CN, SCN, PO4, SO4, C2H3O2, OR CO3. (B.) A CHEMICAL CONVERSION COATING SOLUTION FOR PRODUCING THE COBALT CONVERSION COATING ON A METAL SUBSTRATE, THE SOLUTION INCLUDING AN AQUEOUS SOLUTION CONTAINING A SOLUBLE COBALT-III HEXAVALENT COMPLEX, THE CONCENTRATION OF THE COBALT-III HEXAVALENT COMPLEX BEING FROM ABOUT 0.01 MOLE PER LITER OF SOLUTION TO THE SATURATION LIMIT OF THE COBALT-III HEXAVALENT COMPLEX. THE COBALT CONVERSION SOLUTION MAY BE PREPARED BY A BATH MAKEUP SEQUENCE INCLUDING THE STEPS OF: (A) DISSOLVING A COBALT-II SALT; (B) THEN DISSOLVING A METAL NITRATE SALT; AND (C) THEN ADDING AMMONIUM ACETATE. (C.) A COATED ARTICLE EXHIBITING CORROSION RESISTANCE AND PAINT ADHESION PROPERTIES, THE ARTICLE INCLUDING: (A) A METAL SUBSTRATE; AND (B) A COBALT CONVERSION COATING (310) FORMED ON THE SUBSTRATE, THE COBALT CONVERSION COATING INCLUDING ALUMINIUM OXIDE A12O3 AS THE LARGEST VOLUME PERCENT, AND COBALT OXIDES COO, CO3O4 AND CO2O3.(FIG. 2)