Abstract: A chromating treatment composition particularly suitable for preparing aluminum and stainless steel for clear coating comprises water, anions containing hexavalent chromium, trivalent chromium cations, phosphate ions, dry process finely divided silica, and acrylic and/or methacrylic acid polymer or copolymer in such amounts that:(A) the concentration of the total of hexavalent and trivalent chromium atoms is in the range from 1 to 60 g/L;(B) the (trivalent chromium atom)/(hexavalent chromium atom) weight ratio is in the range from 0.6 to 2.5;(C) the (phosphate ion)/(total chromium atoms in hexavalent chromium ions and trivalent chromium ions) weight ratio is in the range from 0.5 to 4.5;(D) the (dry process silica)/(total chromium atoms in hexavalent chromium ions and trivalent chromium ions) weight ratio is in the range from 0.1 to 5.

Abstract: A colorless chromate coating film is formed on a bright aluminum wheel by subjecting the surface of an aluminum wheel to a cathodic electrolytic treatment in an acidic aqueous solution containing not less than 2 g/l of hexavalent chromium ions, 20 to 2,000 ppm of sulfate ions, 10 to 400 ppm of fluorine (F) as fluoride and not less than 20 ppm of zirconium ions at a pH of 0.6 to 1.7 at a current density of 0.5 to 15 A/dm.sup.2 for at least 30 seconds, thereby forming a coating film with a chromium coating amount of 50 to 250 mg/m.sup.2.

Abstract: A durable hydrophilic surface can be formed on metals by coating them with a composition containing a first water soluble polymer based on polyacrylamide, a second water soluble polymer with at least 60 mole percent of ionizable groups such as acids and quaternary ammonium salts, and a cross linking agent. Water soluble chromium and zirconium salts that can form complexes with the first water soluble polymer are preferred crosslinking agents. The invention is particularly useful for aluminum to be used in heat exchangers.