METHOD OF PHOSPHATING METAL SURFACES

In a process of phosphatizing metal surfaces, which at least partly consist of iron or steel, in accordance with the low-zinc technology, the metal surfaces are brought in contact with aqueous acid phosphatizing solutions at a temperature of 30 to 65° C. for a period of 1 to 8 min, which solutions contain0.4 to 2.0 g/l Zn7 to 25 g/l P2O50.005 to 0.5 g/l peroxide (calc. as H2O2)0.01 to 10 g/l formate (calc. as formate ion),are free from chlorate and added nitrite, and in which the weight ratio of free P2O5 to total P2O5 has been adjusted to a value in the range from 0.03 to 0.20, and the content of free acid has been adjusted to a value in the range from 0.5 to 2.5. After contact with the phosphatizing solution, the workpiece is rerinsed with water, which has been adjusted with mineral acid to a pH of from 3.6 to 5.0. The phosphatizing solutions may contain in addition up to 30 g/l nitrate as well as manganese, magnesium, calcium, lithium, tungstate, vanadate, molybdate or combinations thereof, possibly also nickel and/or cobalt, each in an amount of up to 3 g/l, possibly also up to 0.030 g/l copper. The weight ratios Mn:Zn, Mg:Zn, Ca:Zn and possibly (Ni and/or Co):Zn should each be not more than 2:1.