PROCESS OF PRODUCING PHOSPHATE COATINGS

摘要

In a process of producing phosphate coatings on composite parts consisting of steel and galvanized steel, which comprises alkaline cleaning, rinsing with an aqueous rinsing bath, and phosphatizing with zinc phosphate, the formation of a non-uniform coating and of spots is avoided by the use of a rinsing bath which contains at least 0.2 g/l alkali borate, at least 0.1 g/l alkali silicate and at least 0.05 g/l alkali nitrite, and which preferably contains said components in a total up to 5 g/l. If the composite parts are to be activated with an activating bath which contains titanium phosphate before the zinc phosphate solution is applied, the activating bath must contain at least 1 g/l and preferably up to 4 g/l tetraalkalipyrophosphate. The process in accordance with the invention can be used to special advantage for preparing composite parts of steel and galvanized steel for being subsequently painted, particularly by electrophoretic dip painting.