ZINC PHOSPHATE CONVERSION COATING COMPOSITIONS AND PROCESS.

摘要

A process for forming a zinc phosphate coating on an aluminum substrate is provided to obtain good coverage by the coating. The coating preferably has a columnar or nodular crystal morphology and a coating weight of at least about 1612 mg/m2. The aluminum substrate is contacted with a zinc phosphate conversion coating bath which contains: from about 0.4 to 2.5 g/l zinc ion; from about 5 to 26 g/l phosphate ion; from about 0.4 to 1.5 g/l fluoride ion; from about 4 to 400 mg/l ferrous ion; and from about 0.01 to 2 g/l ammonium ion. The zinc phosphate conversion coating is formable on an aluminum substrate in the presence or absence of an accelerator. Also provided is an aqueous zinc phosphate conversion coating concentrate which may be diluted with an aqueous medium in a weight ratio of about 1:10 to 1:100 to yield a zinc phosphate conversion coating bath.