Metallgesellschaft Aktiengesellschaft

Peter Mischke

Werner Rausch

Dieter Hauffe

Gisela Beege

Disclosed is a process of producing phosphate coatings on surfaces which consist of aluminum or its alloys and of at least one of the materials steel and galcanized steel by spraying or by spraying and dipping. Uniform phosphate layers having a high cover factor are obtained by the use of a phosphating solution which contains about 0.4 to about 0.8 g/l Zn, about 10 to about 20 g/l P.sub.2 O.sub.5, at least one accelerator and about 80 to about 220 mg/l fluoride ('F(el)'), as determined by a fluoride-sensitive electrode immersed into the bath solution and in which the content of free acid (FA) (in points) has been adjusted to and is maintained at a value corresponding to FA=(0.5 to 1.0)+K wherein K is calculated as K=(0.002 to 0.012).times.F(el). The free acid (FA) content is preferably adjusted to and maintained at FA=(0.04 to 0.06).times.C.sub.P.sbsb.2.sub.O.sbsb.5 +K and the content of free acid (FA) is determined using K=(0.003 to 0.009).times.F(el). The process is particularly suitable for preparing the surfaces for being painted, preferably by electrophoretic dip painting.

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Frankfurt am Main, Germany

Peter Mischke