Process of forming phosphate coatings on metal surfaces

A process for forming a phosphate coating on a metal surface, comprising contacting said metal surface with an Fe(II) containing phosphating solution comprising,

• from 0.4 to 30 g/l Zn;
• from 4 to 30 g/l P.sub.2 O.sub.5 ;
• from 5 to 50 g/l NO.sub.3 ;
• from greater than 0 to 10 g/l Fe(II);
• and
• from greater than 0 to 0.3 g/l (Fe(III),
• wherein the weight ratio of free P.sub.2 O.sub.5 to total P.sub.2 O.sub.5 is (0.04 to 0.50):1, and
• replenishing said phosphating solution with Zn, NO.sub.3 and P.sub.2 O.sub.5 in a weight ratio of Zn:NO.sub. 3 :P.sub. 2 O.sub.5 =(0.80 to 0.30):(0.17 to 0.4):1, and further replenishing said phosphating solution with a compound selected from the group consisting of
• Mg, Ca, Mn, Ni, Fe, Co and Cu, with a molar ratio of
• (Mg+Ca+Mn+Ni+Fe+Co+Cu):Zn of 2:1 or less, of phosphate in a ratio of free P.sub.2 O.sub.5 to total P.sub.2 O.sub.5 of (-0.4 to +0.5):1 during replenishment, and
• wherein the Fe(II) content is adjusted by an oxidation with nitrate or nitrite derived from nitrate, optionally employed with an oxygen-containing gas, H.sub.2 O.sub.2 and nitrous gases, then
• rinsing said metal surface by a cascade of at least two aqueous rinsing baths in the opposite direction of travel of said metal surface, wherein water having a low salt content or being salt-free and derived from the phosphating bath is fed to the last rinsing bath and the overflowing water from said rinsing bath is fed to the next preceding rinsing bath and ultimately to the phosphating bath, respectively, and the low salt content or salt-free rinse water derived from the phosphating bath is withdrawn therefrom at a rate effective to permit the addition of phosphate-enriched rinsing water from the cascade of rinsing water to the phosphating bath while maintaining a desired species concentration in said phosphating bath, and further
• wherein rinse water having a low-salt content or salt-free water is removed from said phosphating bath by a process selected from the group consisting of a single effect evaporation, multiple effect evaporation, reverse osmosis and electrodialysis.