Disclosed is a process for phosphating a galvanized surface, particularly
of galvanized steel wherein the surface is contacted for up to 10 seconds
with a phosphating solution which contains accelerator, particularly
nitrate,
0.5 to 5.0 g/l zinc,
3 to 20 g/l phosphate (calculated as P.sub.2 O.sub.5),
0.3 to 3 g/l magnesium
at a weight ratio of magnesium: zinc=(0.5 to 10):1 and has an S value in
the range from 0.2 to 0.4 preferably in the range from 0.2 to 0.3, and is
replenished with a concentrate in which the weight ratio of zinc to
phosphate (calculated as P.sub.2 O.sub.5) is in the range from (0 to 1):8.
It is particularly desirable to use a phosphating solution which contains
up to 1.5 g/l zinc, preferably 0.5 to 1 g/l zinc, at a weight ratio of
magnesium: zinc of (0.5 to 3:1, nickel ions in an amount of up to 1.5 g/l,
preferably in an amount of up to 0.5 g/l and simple or complex fluoride in
an amount of up to 3 g/l, preferable 0.1 to 1.5 g/l (calculated as F in
each case).
A special advantage is afforded by the use of the process to treat
galvanized steel strip which is subsequently painted or coated with a
preformed organic film.
