CA2247144A1 - Zinc-phosphatizing method using low nickel and/or cobalt concentrations - Google Patents

Abstract

Described is a method of phosphatizing steel, aluminium or galvanized or alloyplated steel or aluminium surfaces by spraying the surface with, or dipping the surface in, a zinc-containing phosphatization solution for between 3 seconds and 8 minutes. The method is characterized in that the phosphatization solution contains 0.2 to 3 g/l of zinc ions, 3 to 50 g/l of phosphate ions, 1 to 100 mg/l of nickel or cobalt ions, as well as one or more accelerators and not more than 0.5 g/l of nitrate ions. Optional additives are lithium, copper and/or manganese.

Description

ZINC-PHOSPHATIZING METHOD USING LOW NICKEL AND/OR
COBALT CONCENTRATIONS
This invention relates to processes forphosphatizing metal surfaces using aqueous, acidic phosphatizing solutions which contain zinc and phosphate ions and a maximum of 1 00ppm of nickel and/or cobalt ions. The present invention also relates to the use of such a process as a preparatory treatment for metal surfaces for subsequent painting, in particular electrophoretic painting or powder painting. The process is applicable to the treatment of surfaces of steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-aluminized steel.

Metals are phosphatized so as to produce solidly grown together layers of metal phosphates on the metal surfaces, which, alone, improve corrosion resistance and, in combination with paints or other organic coatings, contribute to a substantial increase in paint adhesion and resistance to infiltration when subjected to corrosives. This type of phosphatizing process has been known for a long time. In the case of preparatory treatment prior to painting, in particular electrophoretic painting, the low zinc phosphatizing process in which the phosphatizing solutions have relatively low concentrations of zinc ions of, for instance, from 0.5 to 2 g/l, is particularly suitable. One essential feature of such low zincphosphatizing baths is the ratio, by weight, of phosphate ions to zinc ions, which is usually greater than 8 and may have values of up to 30.

It has been shown that phosphate layers having much improved anti-corrosion and paint adhering properties may be formed by also using other polyvalentcations in the zinc phosphate baths. By way of example, low zinc processes with the addition of, e.g., from 0.5 to 1.5 g/l of manganese ions and, e.g., from 0.3 to 2.0 g/l of nickel ions find wide application as the so-called trication process for preparing metal surfaces for painting, for example for cathodic electrophoretic painting of car bodies.

Since nickel and also cobalt, which may be used as an alternative, are classified as critical from a toxicological and effluent point of view, there is a need forphosphatizing processes which provide a similar level of performance as thetrication process, but which manage with much lower bath concentrations of nickel and/or cobalt. Recently,phosphatizing processes have been developed which operate without nickel at all. These have the disadvantage, however, that not all the metal surfaces used in the automobile industry are reliably provided with equally good finishes.

DE-A-20 49 350 discloses a phosphatizing solution which contains, as essential constituents, from 3 to 20 g/l of phosphate ions, from 0.5 to 3 g/l of zinc ions, from 0.003 to 0.7 g/l of cobalt ions or from 0.003 to 0.04 g/l of copper ions or, preferably, from 0.05 to 3 g/l of nickel ions, from 1 to 8 g/l of magnesium ions, from 0.01 to 0.25 g/l of nitrite ions and from 0.1 to 3 g/l of fluoride ions and/or from 2 to 30 g/l of chloride ions. Accordingly, this process describes a zinc/magnesium phosphatizing procedure, wherein the phosphatizing solution also contains one of the ions cobalt, copper or preferably nickel. This type of zinc/magnesiumphosphatizing procedure did not succeed industrially.

EP-B-18 841 concerns a chlorate/nitrite accelerated zincphosphatizing solution containing, inter alia, from 0.4 to 1 g/l of zinc ions, from 5 to 40 g/l of phosphate ions and optionally at least 0.2 g/l, preferably from 0.2 to 2 g/l, of one or more ions selected from nickel, cobalt, calcium and manganese. ThereFore, the optional nickel or cobalt concentration is at least 0.2 g/l. In the examples, nickel concentrations of 0.53 and 1.33 g/l are quoted.

EP-A-141 341 relates to phosphatizing solutions which contain, in addition to from 10 to 50 g/l of zinc, nickel or cobalt in amounts of from 0.1 to 5 g/l. In this case, it is not a matter of low zinc phosphatizing, but a primer coat for immobile structures, such as bridges. EP-A-287 133 describes a zinc phosphatizing solution which may optionally contain cobalt in amounts of up to 0.3 g/l. The solution contains from 5 to 30 g/l of nitrate as an essential component.

An object of the present invention is to provide a heavy metal-poorphosphatizing process which achieves the performance of the trication phosphatizing process on the various materials used in the automobile industry. This object is achieved by a process for phosphatizing metal surfaces of steel, galvanized or alloy-galvanized steel and/or of aluminum, in which the metal surfaces are brought into contact with a zinc-containing phosphatizing solution by spraying or immersing for a period of between 3 seconds and 8 minutes, characterized in that the phosphatizing solution contains:

from 0.2 to 3 g/l of zinc ions;
from 3 to 50 g/l of phosphate ions, calculated as P04;

from 1 to 100 mg/l of nickel and/or cobalt ions;
one or more accelerators selected from:
from 0.3 to 4 g/l of chlorate ions, from 0.01 to 0.2 g/l of nitrite ions, from 0.05 to 2 g/l of m-nitrobenzenesulphonate ions, from 0.05 to 2 g/l of m-nitrobenzoate ions, from 0.05 to 2 g/l of ~-nitrophenol, from 0.005 to 0.15 g/l of hydrogen peroxide in free or bound form, from 0.1 to 10 g/l of hydroxylamine in free or bound form, from 0.1 to 10 g/l of a reducing sugar;
and no more than 0.5 g/l of nitrate ions.

The zinc concentration is preferably between about 0.3 and about 2 g/l, in particular between about 0.8 and about 1.6 g/l. Zinc concentrations above 1.6 g/l, for example between 2 and 3 g/l, bring only very slight advantages to the process, but, on the other hand, increase the production of sludge in the phosphatizing bath. Such a zinc concentration may be produced in a working phosphatizing bath if additional zinc gets into the phosphatizing bath, when phosphatizing galvanized surfaces, due to etching. Nickel and/or cobalt ions in the concentration range mentioned of from about 1 to about 100 mg/l each, in combination with the lowest possible nitrate concentration of not more than about 0.5 9/l improve the anti-corrosive effect and paint adherence as compared with phosphatizing baths which do not contain any nickel or cobalt or which have a nitrate concentration of more than 0.5 g/l.
Preferably, nickel concentrations are from about 1 to about 50 mg/l and/or cobalt concentrations are from about 5 to about 100 mg/l. This achieves a beneficial compromise between the eflectiveness of the phosphatizing baths on the one hand and the requirements for effluent treatment of the rinsing water on the other hand.

German Patent application 195 00 927.4 discloses that amounts of lithium ions of from about 0.2 to about 1.5 g/l improve the anti-corrosive effect achievable using zincphosphatizing baths. Lithium concentrations of from 0.2 to about 1.5 g/l, in particularfrom about 0.4 to about 1 g/l also have a beneficial effect on the anti-corrosive effect achieved in the heavy metal-poor phosphatizing process according to the present invention. Thephosphatizing solutions may also contain from about 0.001 to about 0.03 g/l of copper ions instead of or in addition to the lithium. Such a copper concentration, especially in combination withhydroxylamine as accelerator, leads to a further improvement in the anti-corrosive effect. If the process according to the present invention is intended for use as a spraying procedure, copper concentrations of from about 0.001 to about 0.01 g/l are particularly beneficial. When used as an immersion procedure, copper concentrations of from 0.005 to 0.02 g/l are preferred.

A further improvement in the anti-corrosive effect may be achieved if thephosphatizing solution contains additional manganese ions in addition to or instead of the lithium and/or copper ions. In this case, the manganese is preferably present in oxidation state 2.
Manganese concentrations of from about 0.003 to about 0.1 g/l represent a beneficial compromise between the effectiveness of thephosphatizing bath and the requirements for effluent treatment and are therefore preferred. Higher manganese concentrations of from about 0.1 to about 4 g/l in particular from about 0.5 to about 1.5 g/l, may offer further advantages with regard to the anti-corrosive effect and may be used when effluent treatment and the waste disposal of sludge do not present any problems.

Specific cation combinations represent a good and therefore preferred compromise between the effectiveness of the phosphatizing bath and the effluent treatment and sludge waste disposal required. In this context, in one preferred embodiment of the present invention, phosphatizing solutions are used which contain zinc ions, cobalt ions and copper ions in the previously mentioned amounts, but which contain no manganese ions. In a second preferred embodiment, phosphatizing baths are used which contain zinc ions, cobalt ions and manganese ions in the previously mentioned amounts, but which contain no nickel or copper ions. In a third preferred embodiment, phosphatizing solutions are used which contain zinc ions, cobalt ions and lithium ions, and which optionally contain manganese ions. In a fourth preferred embodiment, phosphatizing solutions are used which contain zinc ions, nickel ions and lithium ions in the previously mentioned amounts and which optionally contain manganese ions.
Apart from the previously mentionedcations, which are incorporated into the phosphate layer or which at least have a positive effect on crystal growth in the phosphate layer, the phosphatizing baths generally contain sodium, potassium and/or ammonium ions to adjust the free acid. The expression "free acid" is familiar to those skilled in thephosphatizing art.
The method for determining free acid and total acid used for present purposes is given in the examples. Free acid and total acid are an important regulating parameter forphosphatizing baths since they have a large effect on the weight of the layer. Values for free acid between 0 and 1.5 points for phosphatizing individual parts and of up to 2.5 points for strip phosphatizing, and values for total acid between about 15 and about 30 points lie within the technically conventional range and are suitable in the context of the present invention.

In the case of phosphatizing baths which are intended to be suitable for different substrates, it has been conventional to add free and/orcomplexed fluoride in amounts of up to 2.5 g/l of total fluoride, of which up to 1 g/l is free fluoride. The presence of this amount of fluoride is also of advantage in phosphatizing baths according to the present invention. In the absence of fluoride, the aluminum concentration in the bath should not exceed 3 mg/l. In the presence of fluoride, higher Al concentrations may be tolerated due to complex formation, provided the concentration of non-complexed Al does not exceed 3 mg/l. The use of fluoride-containing baths is therefore advantageous if the surfaces beingphosphatized consist at least partly of aluminum or contain aluminum. In these cases, it is beneficial to use notcomplexed fluoride, but only free fluoride, preferably at a concentration of from 0.5 to 1.0 g/l.

When phosphatizing zinc surfaces, the phosphatizing baths do not necessarily have to contain so-called accelerators. When phosphatizing steel surfaces, however, the phosphatizing solution should contain one or more accelerators. Such accelerators are common in the prior art as components of zincphosphatizing baths. They are understood to be substances which chemically bond the hydrogen being produced at the metal surface as a result of attack by the acid in the pickling solution and are themselves reduced. Oxidizing accelerators also have the effect of oxidizing to the trivalent state iron(ll) ions released on steel surfaces due to attack by the pickling solution so that they may be precipitated as iron(lll) phosphate.

Phosphatizing baths according to the present invention may contain one or more of the following components as accelerators:

from 0.3 to 4 g/l of chlorate ions, from 0.01 to 0.2 g/l of nitrite ions, from 0.05 to 2 g/l of m-nitrobenzenesulphonate ions, from 0.05 to 2 g/l of m-nitrobenzoate ions, from 0.05 to 2 g/l Of ~2-nitrophenol, from 0.005 to 0.15 g/l of hydrogen peroxide in free or bound form, from 0.1 to 10 g/l of hydroxylamine in free or bound form, from 0.1 to 10 g/l of a reducing sugar.

When phosphatizing galvanized steel, the phosphatizing solution should contain as little nitrate as possible. Nitrate concentrations of 0.5 g/l should not be exceeded because at higher nitrate concentrationsthere is a risk of producing so-called"specks". These are white, crater-like defects in the phosphate layer. In addition, the adhesion of paint to galvanized surfaces is impaired.

The use of nitrite as an accelerator leads to technically satisfactory results, especially on steel surfaces. For industrial safety reasons (risk of evolving nitrous gases), however, it is recommended that the use of nitrite as an accelerator be avoided. This is also advisable for technical reasons when phosphatizing galvanized surfaces because nitrate may be formed from nitrite; this, as explained above, may lead to the problem of speck formation and to reduced adhesion of a paint to zinc.

For environmental reasons, hydrogen peroxide and, for technical reasons, hydroxylamine, which offers the possibility of a simplified formulation when more needs to be added to solutions at a later stage, are particularly preferred as accelerators. The mutual use of these two accelerators, however, is not advisable sincehydroxylamine is decomposed by hydrogen peroxide. If hydrogen peroxide is used in free or bound form as an accelerator, concentrations of from 0.005 to 0.02 g/l of hydrogen peroxide are particularly preferred. In this case, hydrogen peroxide may be added to the phosphatizing solutions as such. It is also possible, however, to use hydrogen peroxide in bound form as compounds which provide hydrogen peroxide in the phosphatizing bath due to hydrolysis reactions. Examples of such compounds are persalts, such as perborates, percarbonates, peroxosulphates or peroxodisulphates. Further suitable sources of hydrogen peroxide are ionic peroxides, such as alkali metal peroxides. A preferred embodiment of the present invention involves the use of a combination of chlorate ions and hydrogen peroxide when phosphatizing by animmersion process. In this embodiment, the concentration of chlorate may be, for example, from 2 to 4 g/l and the concentration of hydrogen peroxide may be from 10 to 50 ppm.

The use of reducing sugars as accelerators is known from US-A-5 378 292. They may be used in accordance with the present invention in amounts between about 0.01 and about 10 g/l, preferably between about 0.5 and about 2.5 g/l. Examples of this type of sugar are galactose, mannose and, in particular, glucose (dextrose).

Another preferred embodiment of the present invention involves usinghydroxylamine as accelerator. Hydroxylamine may be used as the free base, as a hydroxylamine complex, as an oxime, which represents the condensation product of hydroxylamine with a ketone, or in the form of hydroxylammonium salts. If freehydroxylamine is added to the phosphatizing bath or to a phosphatizing bath concentrate, it is mainly present as ahydroxylammonium cation due to the acidic character of these solutions. When used as a hydroxylammonium salt, the sulphates and phosphates are particularly appropriate. In the case of phosphates, the acid salts are preferred due to the better solubility thereof.Hydroxylamine or compounds thereof are added to the phosphatizing bath in amounts such that the theoretical concentration of free hydroxylamine is between 0.1 and 10 g/l, preferably between 0.3and 5 g/l. In this case it is preferred that the phosphatizing baths contain only hydroxylamine as accelerator, if necessary together with a maximum of 0.5 g/l of nitrate. Therefore, in a preferred embodiment phosphate baths are used which do not contain any of the other known accelerators, such as nitrite, oxo-anions of halogens, peroxides or nitrobenzenesulphonate. As a positive side effect, hydroxylamine concentrations above about 1.5 g/l reduce the risk of rust formation at places on the components to be phosphatized which are inadequately surrounded by liquid.

In practice, it has been shown that the accelerator hydroxylamine may also be slowly inactivated if no metal parts to be phosphatized are introduced into thephosphatizing bath.
Surprisingly, it has been shown that inactivation of hydroxylamine may be greatly retarded if one or more aliphatichydroxycarboxylic or aminocarboxylic acids having from 2 to 6 carbon atoms are also added in a total amount of from 0.01 to 1.5 9/l. In this case, the carboxylic acids are preferably selected from glycine, lactic acid, gluconic acid, tartronic acid, malic acid, tartaric acid and citric acid, wherein citric acid, lactic acid and glycine are particularly preferred.

EP-A-361 375 discloses adding from 0.3 to 5 g/l, preferably from 1 to 3 g/l, of formic acid to nickel-containing phosphatizing baths. The formic acid causes more intense deposition of nickel on the metal surface and/or greater incorporation of nickel in the phosphate crystals.

It may be assumed that this effect may also be transposed to cobalt. Addition of formic acid is also beneficial for the purposes of the scope of the present invention with its low concentrations of nickel and/or cobalt.

When using the phosphatizing process on steel surfaces, iron goes into solution in the form of iron(ll) ions. If the presentphosphatizing baths do not contain substances which are able to oxidize iron(ll~, the divalent iron is transformed into the trivalent state as a result of atmospheric oxidation so that it may precipitate as iron(lll) phosphate. This is the case, for example, when using hydroxylamine. Therefore, iron(ll) concentrations may be built up in phosphatizing baths which are well above the concentrations contained in baths which contain oxidizing agents. In this context, iron(ll) concentrations of up to 50ppm are normal, while values up to 500 ppm may also occur for short periods during the production cycle. In the phosphatizing process according to the present invention, such iron(ll) concentrations are not damaging. When prepared using hard water, thephosphatizing baths may also contain the hardness-producing cations Mg(ll) and Ca(ll) in a total concentration of up to 7mmol/1.
Mg(ll) or Ca(ll) may also be added to the phosphatizing baths in amounts of up to 2.5 g/l.

The ratio, by weight, of phosphate ions to zinc ions in thephosphatizing baths may vary between wide limits, provided it is between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred. With respect to the data on phosphate concentration, the total phosphorus content of the phosphatizing bath is regarded as being present in the form of phosphate ions P043 . Therefore, when calculating the amounts, the fact that, at the pH of phosphate baths, which is generally from about 3 to about 3.6, only a very small proportion of the phosphate is actually in the form of triply charged anions, is ignored. Rather, at this pH
it would be expected that the phosphate is mainly present as singly chargeddihydrogen-phosphate anions, togetherwith small amounts of undissociated phosphoric acid and doubly charged characteriz anions.

Phosphatizing baths are generally sold in the form of aqueous concentrates which are adjusted to the application concentration by addition of water on site. For stability reasons, these concentrates contain an excess of free phosphoric acid so that, on diluting to the bath concentration, the free acid value is initially too high and the pH is too low. The free acid value is lowered to the desired range by adding alkalis, such as sodium hydroxide, sodium carbonate or ammonia. Furthermore, it is known that the concentration of free acid may rise with time during the use of phosphatizing baths due to consumption of the layer-forming cations and optionally by decomposition reactions of the accelerator. In this case, the free acid value has to be re-adjusted to the desired range by adding alkali from time to time. This means that the concentrations of alkali metal ions or ammonium ions in thephosphatizing baths may vary between wide limits and that they tend to increase over the lifetime of the phosphatizing baths as a result of neutralising the free acid. The weight ratio of alkali metal ions and/or ammonium ions to, for example, zinc ions, may therefore be very low in freshly prepared phosphatizing baths, ~or example < 0.5, and in the extreme case may even be 0, while it generally increases over time as a result of bath maintenance procedures, so that the ratio may become > 1 and values up to 10 and above may be acceptable. Low zinc phosphatizing baths generally require the addition of alkali metal ions or ammonium ions in order to be able to adjust the free acid to the required range with the desired ratio by weight of P043_: Zn > 8. Analogous considerations may also be used with respect to the ratios of alkali metal ions or ammonium ions to other bath constituents, for example to phosphate ions.

In the case of lithium-containing phosphatizing baths, the use of sodium compounds for adjusting the free acid should be avoided because the beneficial effect of lithium on the anti-corrosive effect is suppressed by too high a concentration of sodium. In this case, basic lithium compounds are preferably used for adjusting the free acid. Potassium compounds are also suitable for assisting this procedure.

In principle, it does not matter in what form the layer-forming or layer-influencingcations are introduced into the phosphatizing baths. Nitrates should be avoided, however, in order not to exceed the upper limit for nitrate concentration according to the present invention. The metal ions are preferably used in the form of those compounds which do not introduce foreign ions to the phosphatizing solution. Therefore, it is most beneficial to use the metals in the form of oxides or carbonates thereof. Lithium may also be used assulphate and copper preferably as acetate. The types of phosphatizing solution which satisfy the ecological objectives of the process particularly well are those which contain, in addition to zinc ions, not more than a total of 0.5 g/l of other divalent cations.

Phosphatizing baths according to the present invention are suitable for phosphatizing surfaces of steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-aluminized steel. The expression "aluminum" in this context includes industrially conventional aluminum alloys, such as AIMg05Si14. The materials mentioned may, as is increasingly conventional in the automobile industry, also be present side-by-side.

Thus, parts of a car body may also consist of already prepared material, such as a material prepared by the BONAZINK0 process. In this case, the basic material is firstchromatized or phosphatized and then coated with an organic resin. Thephosphatizing process according to the present invention then leads to phosphatizing of damaged areas in this prepared layer or to phosphatizing of the untreated other side.

The process is applicable to immersion, spraying or spray/immersion procedures. It may be used, in particular, in the automobile industry, where treatment times between 1 and 8 minutes, in particular from 2 to 5 minutes, are conventional. Use for stripphosphatizing in steel works, wherein the treatment times are between 3 and 12 seconds, however, is also possible. When used in strip phosphatizing processes, it is advisable to set the bath concentrations in the upper half of each of the preferred ranges according to the present invention. For example, the zinc concentration may be from 1.5 to 2.5 g/l and the concentration of free acid may be from 1.5 to 2.5 points. Galvanized steel, in particular electrolytically galvanized steel, is particularly suitable as a substrate for stripphosphatizing.

As is also conventional with other known phosphatizing baths, appropriate bath temperatures are between 30 and 70~C, regardless of the field of application, the temperature range between 45 and 60~C being preferred.

The phosphatizing process according to the present invention is particularly intended for treating the metal surfaces mentioned prior to painting, for example beforecathodic electrophoretic painting, as is conventional in the automobile industry. Furthermore, it is suitable as a preparatory treatment prior to powder painting, as is used for example for domestic appliances. The phosphatizing process is to be regarded as one step in the technically conventional preparatory treatment sequence. In this sequencephosphatizing is conventionally preceded by the steps of cleansing/degreasing, intermediate rinsing and activating, wherein activating is generally performed using activating agents which contain titanium phosphate. Phosphatizing according to the present invention may optionally be followed by a passivating post-treatment, with or without intermediate rinsing. Treatment baths containing chromic acid are widely used for this type of passivating post-treatment. For reasons of industrial safety, to protect the environment and also for waste disposal reasons, however, there is a tendency to replace these chromium-containingpassivating baths with chromium-free treatment baths. For this purpose, purely inorganic bath solutions, in particular those based on zirconium compounds, or else organic-reactive bath solutions, for example those based on poly(vinylphenols), are known. It is known from German Patent application 195 11 573.2 that specific phosphatizing processes may be followed by a passivating post-rinsing using an aqueous solution having a pH of from about 3 to about 7 which contains from 0.001 to 10 g/l of one or more of the followingcations: lithium ions, copper ions and/or silver ions. This type of post-rinsing is also suitable for improving the anti-corrosive effect of the phosphatizing process according to the present invention, in particular if thephosphatizing solution does not contain copper. An aqueous solution which contains from 0.002 to 1 g/l of copper ions is preferably used for this purpose. The copper is preferably used as the acetate.
In particular, this type of post-rinsing solution preferably has a pH of from 3.4 to 6 and a temperature of from 20 to 50~C.

An intermediate rinsing procedure using fullydeionized water is generally performed between this post-passivating procedure and the painting procedure which conventionally follows it.

Examples The phosphatizing process according to the present invention and comparison processes were tested on ST 1405 steel sheets and on electrolytically galvanized steel sheets such as are used in the automobile industry. The following procedure, conventional when producing car bodies, was performed as an immersion process:

1. Cleansing with an alkaline cleanser (RIDOLINE~ 1559, Henkel KGaA), made up as 2 % in tap water, 55~C, 4 minutes.

2. Rinsing with tap water, room temperature, 1 minute.

3. Activating with a titanium phosphate-containingactivating agent (FIXODINE, C9112, Henkel KGaA), made up as 0.1 % in fullydeionized water, room temperature, 1 minute.

4. Phosphatizing with phosphatizing baths in accordance with Table 1, 4 minutes,temperature 55~C. In addition to the cations mentioned in Table 1, the phosphatizing baths contained sodium ions, if required, to adjust the free acid value.Li-containing phosphatizing baths did not contain sodium. All the baths contained 0.95 g/l of SiF62-and 0.2 g/l of F-.

The free acid value was 1.0 - 1.1 points and the total acid value was 23 - 25 points.
The value in points of free acid is to be understood to be the consumption in ml of 0.1 N caustic soda solution by 10 ml of bath solution, whentitrated to give a pH of 3.6.
Similarly, the value in points of total acid is the consumption in ml to give a pH of 8.2.

5. Rinsing with tap water, room temperature, 1 minute.

6. Post-passivating with a chromium-freepassivating agent based on complex zirconium fluorides (DEOXYLYTE~ 54 NC, Henkel KGaA) 0.25 % strength in fully deionized water, pH 4.0, temperature 40~C, 1 minute (symbol in Table 1: "Zr"). Alternatively, post-passivation was performed using a post-rinsing solution which contained 50 mg/l of Cu(ll) (as acetate), pH = 3.6 (adjusted with acetic acid), temperature 45~C, 1 minute (symbol in Table 1: "Cu").

7. Rinsing with fully deionized water.

8. Air-blowing with compressed air.

The mass per unit area (~coating weight") was determined by dissolution in 5 % strength chromic acid solution in accordance with DIN 50942. They were in the range 1.5- 3.5 g/m2.

The phosphatized test sheets were coated with a cathodicelectrophoretic paint from BASF
(FT 85-7042). The anti-corrosive effect for electrolytically galvanized steel was tested over 5 cycles in a test under changing climatic conditions according to VDA 621 -415. The result is given in Table 1 as the paint penetration at a scratch (half-width of scratch). Table 1 also contains the results, as a "K value", of a gravel impact test according to a VW standard (the smaller K, the better the paint adhesion~.

The anti-corrosive effect for steel sheets was tested by a salt spray test according to DIN
50021 (1008 hours). Table 1 gives the paint penetration at a scratch (half-width of scratch).

CA 02247l44 l998-08-l9 Table 1: Phosphatizing baths, post-passivation and anti-corrosive results (steel: salt spray test; galvanized steel: changing climate test) Bath components (g/l) Comp Comp Comp Ex. 1 Ex. 2 Ex. 3 Ex. 4 Zn(II) 1.1 1.1 1.1 1.1 1.1 1.1 1.0 PO43~ 15 15 15 15 15 15 16 Ni(II) - 0.025 0.025 0.025 0.025 0.025 0.012 Co(II) _ _ 0.05 - - 0 05 Mn(II) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Cu(II) Li(I) - - _ 0 5 Glucose (NH30H)2SO4 1.8 1.8 1.8 1.8 1.8 1.8 1.7 Formic acid - _ _ _ _ _ Post-rinsing Zr Zr Zr Zr Cu Zr Zr Paint gap steel (mm) 1.3 0.8 0.8 0.8 0.7 0.7 0.9 Paint gap galvanized steel 1.7 2.2 2.0 1.6 1.6 1.4 1.4 (mm) K value 6 9 8 5 5 4 5 CA 02247l44 l998-08-l9 Table 1 (cont.):

Bath components (g/l) Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Zn(II) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Ni(lI) 0.012 0.012 0.012 0.012 0.025 - -Co(II) - 0.05 0 05 - - O 05 0 05 Mn(II) 1.0 - 0.05 0.05 - - 0.05 Cu(II) ~ ~ - ~ ~ 0.01 Li(I) 0.5 0.5 - 0.5 0.5 NO~- - - - - - - -Glucose (NH30H)2SO4 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Formic acid Post-rinsing Cu Cu Zr Zr Zr Zr Cu Paint gap steel (rnm) 0.7 1.0 0.8 0.6 0.8 0.6 0.7 Paint gap galvanized steel 1.5 1.4 1.6 1.4 1.6 1.3 1.5 (rnm) Kvalue 4 6 6 5 6 4 5 CA 02247l44 l998-08-l9 Table 1 (cont):

Bath components (g/l) Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Zn(II) 1.0 1.0 1.0 1.0 1.0 Ni(II) - 0.012 0.012 - 0.012 Co(II) 0.05 0.05 0.05 0.02 0.05 Mn(II) - 0.05 0.05 1.0 0.05 Cu(II) Li(I) 0 5 ~ ~ 1.0 H202 0.013 Glucose - - 2.0 (NH~OH)2SO4 1.7 1.7 1.7 Formic acid - - - - 2.0 Post-rinsing Zr Zr Zr Zr Zr Paint gap steel (mm) 0.8 0.9 1.0 0.8 0.7 Paintgap galvanized steel 1.4 1.5 1.5 1.4 1.4 (mm) Kvalue 5 5 5 5 4

Claims (14)

1. A process for phosphatizing metal surfaces of steel, galvanized or alloy-galvanized steel and/or of aluminium, in which the metal surfaces are brought into contact with a zinc-containing phosphatizing solution by spraying or immersing for a period between 3 seconds and 8 minutes, characterized in that the phosphatizing solution contains 0.2 to 3 g/l of zinc ions 3 to 50 g/l of phosphate ions, calculated as PO4, 12 to 100 mg/l of nickel and/or 1 to 100 mg/l of cobalt ions, 0.1 to 10 g/l of hydroxylamine in free or bonded form, and no more than 0.5 g/l of nitrate ions.

2. A process according to Claim 1, characterized in that the phosphatizing solution contains 12 to 50 mg/l of nickel ions and/or 5 to 100 mg/l of cobalt ions.

3. A process according to one or both of Claims 1 and 2, characterized in that the phosphatizing solution also contains 0.2 to 1.5 g/l of lithium ions.

4. A process according to one or more of Claims 1 to 3, characterized in that the phosphatizing solution also contains 1 to 30 mg/l of copper ions.

5. A process according to one or more of Claims 1 to 4, characterized in that the phosphatizing solution also contains 3 to 100 mg/l of manganese ions.

6. A process according to one or more of Claims 1 to 4, characterized in that the phosphatizing solution also contains 0.1 to 4 g/l of manganese ions.

7. A process according to one or more of Claims 1 to 4, characterized in that the phosphatizing solution contains zinc ions, cobalt ions and copper ions and does not contain manganese ions.

8. A process according to one or more of Claims 1 to 6, characterized in that the phosphatizing solution contains zinc ions, cobalt ions and manganese ions and does not contain nickel or copper ions.

9. A process according to one or more of Claims 1 to 6, characterized in that the phosphatizing solution contains zinc ions, cobalt ions and lithium ions and optionally manganese ions.

10. A process according to one or more of Claims 1 to 6, characterized in that the phosphatizing solution contains zinc ions, nickel ions and lithium ions and optionally manganese ions.

11. A process according to one or more of Claims 1 to 10, characterized in that the phosphatizing solution also contains fluoride in amounts of up to 2.5 g/l oftotal fluoride, of which up to 1 g/l is free fluoride, each being calculated as F-.

12. A process according to one or more of Claims 1 to 11, characterized in that the phosphatizing solution also contains a total of 0.01 to 1.5 g/l of one or more aliphatic hydroxycarboxylic or aminocarboxylic acids with 2 to 6 carbon atoms.

13. A process according to one or more of Claims 1 to 12, characterized in that the phosphatizing solution also contains 0.3 to 5 g/l of formic acid.

14. A process according to one or more of Claims 1 to 13, characterized in that the phosphatizing solution contains, in addition to zinc ions, no more than a total of 0.5 g/l of other divalent cations.