WATER ACID SOLUTION, PROCESS TO COVER THE SURFACE OF A METAL, COATING, AND, WATER CONCENTRATED COMPOSITION, COATING

摘要

The corrosion resistance and paint adhesion of aluminium and its alloys is improved by contacting the aluminium (or aluminium alloy) surface with an aqueous acid solution containing polyacrylic acid or an ester thereof and at least one of H2ZrF6, H2TiF6 and H2SiF6, the pH of the solution being less than 3.5. The waste disposal problems associated with conventional chromate phosphate coating processes are avoided. The coating solution may be replenished with a concentrate containing polyacrylic acid or an ester thereof, at least one of H2ZrF6, H2TiF6 and H2SiF6, and a source of free fluoride, preferably hydrofluoric acid, to complex dissolved aluminium.