Process for phosphating metal surfaces

In a process comprising cleaning and phosphating metal surfaces, the improvement wherein the surfaces without previous activation are contacted in a temperature range of from 30.degree. C. to 70.degree. C. with an aqueous solution consisting essentially of:

• (a) from about 10 to about 40 g/l of Ca.sup.2+ ions,
• (b) from about 10 to about 40 g/l of Zn.sup.2+ ions,
• (c) from about 10 to about 100 g/l of PO.sub.4.sup.3- ions,
• (d) an accelerator selected from the group consisting of
• (i) about 10 to about 100 g/l of nitrate ions and
• (ii) about 0.1 to about 2.0 g/l of organic nitro compounds,
• (e) up to about 10 g/l of Ni.sup.2+ ions, and
• (f) up to abut 10 g/l of simple, complex, or mixed simple and complex fluoride ions,
• said solution having a pH value in the range from about 2.0 to about 3.8, a ratio of free acid to total acid from about 1:4 to 1:100, and a ratio by weight of Zn.sup.+2 ions to Ca.sup.+2 ions of about 1:0.5 to about 1:1.5;
• said process producing on the metal surfaces a phosphate layer containing scholzite in an areal density between about 3 and about 9 g/m.sup.2.