Method for coating aluminum

Claim 1

A PROCESS FOR COATING ALUMINUM WHICH CONSISTS ESSENTIALLY OF THE STEPS OF CONTACTING A SURFACE OF ALUMINUM WITH AN AQUEOUS ACIDIC CLEANING SOLUTION CONSISTING ESSENTIALLY OF THE PHOSPHATE ION, THE FLUORIDE ION AND A METAL ION SELECTED FROM THE GROUP CONSISTING OF ZINC, MANGANESE, AND IRON, SAID SOLUTION HAVING A PH IS THE RANGE OF ABOUT 1.8 TO ABOUT 3.2, THE PHOSPHATE IONS BEING PRESENT IN AN AMOUNT OF AT LEAST 0.1% BY WEIGHT, THE METAL ION BEING PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TO FORM THE PHOSPHATE SALT WITH THE PHOSPHATE IONS PRESENT AND THE FLUORIDE IONS BEING EQUIVALENT TO AN AMOUNT, WHICH WHEN ADDED AS HF IS FROM ABOUT 0.02 TO 0.3% BY WEIGHT IN EXCESS OF THAT REQUIRED TO FORM AIFX, WHERE X IS 1.1 TO 1.2, WITH THE ALUMINUM INTORDUCED INTO THE SOLUTION BY THE WORK BEING TREATED, MAINTAINING SAID SOLUTION IN CONTACT WITH THE ALUMINUM SURFACE FOR A TIME SUFFICIENT TO EFFECT CLEANING THEREOF, WATER RINSING THE SURFACE, THEREAFTER FORMING A CHROMATE CHEMICAL CONVERSION COATING ON SAID RINSED SURFACE.