An aqueous acidic zinc phosphate solution which contains at least 6 g/l of Zn, at least 5 g/l P.sub.2 O.sub.5, at least 1.0 g/l of an accelerator, calculated as ClO.sub.3, from about 1 to about 50 g/l of sulfate ion, which solution has a total acid number of at least 20, a weight ratio of free P.sub.2 O.sub.5 of 0.2-0.6:1 and a weight ratio of P.sub.2 O.sub.5 : Zn: ClO.sub.3 of 1:0.5-4.0: 0.01-1.0. The phosphatizing bath preferably contains from about 1 to 5 g/l chlorate in combination with at least 8 g/l nitrate, with a weight ratio of P.sub.2 O.sub.5 : NO.sub.3 of 1:0.2-6.0. The baths may be used to form phosphate coatings on ferrous metal surfaces using immersing or flow coating techniques and the phosphate coatings formed are found to have increased thickness and adhesion or coalescence to the metal surface.