Process for preparing zinc phosphate coatings containing manganese and magnesium

A process for producing zinc phosphate coatings containing manganese and magnesium on metal surfaces selected from the group consisting of steel, zinc, aluminum, the alloys thereof, and combinations thereof by contacting the metal surfaces by a method selected from the group consisting of spraying, spray-immersion, immersion, and combinations thereof with an aqueous solution consisting essentially of the following components:

• 0.4 to 0.6 g/l of zinc(II) ions,
• 0.9 to 1.1 g/l of manganese(II) ions,
• 1. 4 to 1.6 g/l of magnesium(II) ions,
• 12.0 to 16.0 g/l of phosphate ions,
• 1.0 to 5.0 g/l of nitrate ions,
• 0.4 to 0.6 g/l of fluoride ions,
• and, optionally,
• 0.2 to 0.8 g/l of nickel(II) ions,
• and, necessarily, an accelerator component selected from the group consisting of:
• 0.02 to 0.2 g/l of nitrite ions,
• 0.4 to 1 g/l of chlorate ions,
• 0.2 to 1.0 g/l of an organic oxidizing agent,
• and combinations of any two or of all of these,
• wherein the aqueous solution has a free acid content of 0.6 to 1.8 points and a total acid content of from 15 to 30 points and Na.sup.+ ions are present in the amount necessary to adjust the free acid.