The cleaned surface of an aluminum or aluminum alloy product, for example, aluminum coil, is treated with a 0.5 to 3 second spray of a chromating bath heated to 40.degree. to 60.degree. C., said bath having a pH of 1.0 to 3.0 and containing 0.1 to 3.0 g/L of tungstate ions and/or molybdate ions, 0.5 to 4.0 g/L of hexavalent chromium ions, 5.0 to 30.0 g/L of phosphate ions, and 0.05 to 2.0 g/L of free fluoride ions. A highly corrosion-resistant, highly paint-adherent chromate coating can thereby be formed on the surface of aluminum in less time than that required by prior phosphoric acid-based chromating treatments.
An anticorrosion treatment of an aluminium/zinc alloy surface is disclosed. The treatment includes the steps of forming on the alloy surface a coating of a solution which contain 5-40 grams of molybdenum per litre of the solution, 2-19% by volume of a phosphoric acid, and a surface etchant. The treatment also includes drying the coating to form a dried coating having a loading of molybdenum of at least 10 mg/m.sup.2 of the dried coating and of phosphorus of at least 15 mg/m.sup.2 of the dried coating.
