CA2247141A1 - Zinc phosphatising using low concentration of copper and mangnese - Google Patents

Abstract

Process for phosphatizing metal surfaces of steel, zinc coated or zinc-alloy coated steel and/or of aluminium where the metal surfaces are brought into contact with a phosphatizing solution containing zinc through spraying or immersion for a time between 3 seconds and 8 minutes; the solution contains 0.2 to 3 g/l zinc ions, 3 to 50 g/l phosphate ions, calculated as PO4, 1 to 150 mg/l manganese ions, 1 to 30 mg/l copper ions and one or several accelerators.

Description

ZINC PHOSPHATIZING WITH LOW CONTENTS
OF COPPER AND MANGANESE
This invention relates to processes for phosphatizing metal surfaces using aqueous, acidic phosphatizing solutions which contain zinc and phosphate ions and a maximum of 150 ppm of manganese ions and 30 ppm of copper 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 with the objective of producing 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 these low zinc phosphatizing 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 polyvalent cations in the zinc phosphate baths. By way of example, low zinc processes with the addition of e.g., from 0.5 to 1.5 9/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 and preferably without these two metals.

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, 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/magnesium phosphatizing procedure did not succeed industrially.

EP-B-18 841 relates to a chlorate/nitrite accelerated zinc phosphatizing 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 manganese, 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-459 541 concerns phosphatizing solutions which are essentially free of nickel and which contain, apart from zinc and phosphate, from 0.2 to 4 g/l of manganese and from 1 to 30 mg/l of copper. DE-A-42 10 513 discloses nickel-freephosphatizing solutions which contain, apart from zinc and phosphate, from 0.5 to 25 mg/l of copper ions and hydroxylamine as accelerator. These phosphatizing solutions optionally also contain from 0.15 to 5 g/l of manganese.

The phosphatizing processes described in two last-mentioned documents fully satisfy the demands for anti-corrosion protection. In practice, however,phosphatizing baths are used which have a relatively high concentration of manganese of about 1 g/l. These phosphatizing baths do not, therefore comply with modern ecological requirements for working with the lowest possible concentrations of heavy metals so that as small an amount as possible of metal-containing sludge is produced during the treatment of wash-water and effluents.

An object of the present invention is to provide a heavy metal-poorphosphatizingprocess which achieves the performance of thetrication 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 150 mg/l of manganese ions;
from 1 to 30 mg/l of copper ions;
and 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.

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 ranges of from about 1 to about 50 mg/l for nickel and from about 5 to about 100 mg/l for cobalt, in combination with the lowest possible nitrate concentration of not more than about 0.5 g/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. This achieves a beneficial compromise between the effectiveness of thephosphatizing baths on the one hand and the requirements for efffluent 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 zinc phosphatizing baths. Lithium concentrations of 0.2 to about 1.5 g/l, in particular from 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.

If the present process is intended for use as a spraying procedure, copper concentrations of from about 0.002 to about 0.01 9/l are particularly beneficial. When used as an immersion procedure, copper concentrations of from 0.005 to 0.02 g/l are preferred.

Apart from the previously mentioned cations, 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 Afree acid~? is familiar to those skilled in the phosphatizing art. The method for determining free acid and total acid used for the present purposes is given in the examples. Free acid and total acid are an important regulating parameterforphosphatizing 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, of up to 2.5 points for stripphosphatizing, 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/or complexed 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, higherAI 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 being phosphatized consist at least partly of aluminum or contain aluminum. In these cases, it is beneficial to use not complexed 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 zinc phosphatizing 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 e-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 concentrations there 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 since hydroxylamine 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 thephosphatizing bath due to hydrolysis reactions. Examples of such compounds are persalts, such as perborates, percarbonates, peroxosulfates or peroxodisulfates. 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 an immersion 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 according to 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 using hydroxylamine 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 hydroxyl-ammonium salts. If free hydroxylamine is added to thephosphatizing bath or to a phosphatizing bath concentrate, it is mainly present as a hydroxylammonium cation due to the acidic character of these solutions. When used as a hydroxylammonium salt, the sulfates 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 thephosphatizing bath in amountssuch that the theoretical concentration of free hydroxylamine is between 0.1 and 10g/l, preferably between 0.3 and 5 g/l. In this case, it is preferred that thephosphatizing baths contain only hydroxylamine as accelerator, if necessary togetherwith a maximum of 0.5 g/l of nitrate. Therefore, in a preferred embodiment,phosphatizing baths are used which do not contain any of the other known accelerators, such as nitrite, oxo-anions of halogens, peroxides or nitro-benzenesulphonate. 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 byliquid.

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 the phosphatizing bath. Surprisingly it has been shown that inactivation of hydroxylamine may be greatly retarded if one or more aliphatic hydroxycarboxylicor aminocarboxylicacids having from 2 to 6 carbon atoms are also added to thephosphatizing bath in a total amount of from 0.01 to 1.5 g/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.

When using the phosphatizing process on steel surfaces, iron goes into solution in the form of iron(ll) ions. If thephosphatizing baths according to the present invention do not contain substances which are able to oxidise iron(ll), the divalent iron is transformed into the trivalent state only 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 inphosphatizing baths which are well above the concentrations contained in baths which contain oxidising agents. In this context, iron(ll) concentrations of up to 50 ppm are normal, while values up to 500 ppm may also occur for short periods during the production cycle. In thephosphatizing process according to the present invention, such iron(ll) concentrations are not damaging. When prepared using hard water, the phosphatizing baths may also contain the hardness-producing cations Mg(ll) and Ca(ll) in a total concentration of up to 7 mmol/l. 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 po4B3. Therefore, when calculating the ratio, 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 charged dihydrogen-phosphate anions, together with small amounts of undissociated phosphoric acid and doubly charged hydrogenphosphate 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 dilution 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 theconcentration of free acid may rise with time during the use ofphosphatizing 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 the phosphatizing baths may vary between wide limits and that they tend to increase over the lifetime of thephosph~ ing baths as a result of neutralizing 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 preparedphosphatizing baths, for example c 0.5, and in the extreme 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 zincphosphatizing 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 weight ratio of po34B 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-containingphosphatizing 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-influencing cations are introduced into the phosphatizing baths. Nitrates should be avoided, however, in order not to exceed the preferred upper limit for nitrate concentration. 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.

Phosphatizing baths according to the present invention are suitable forphosphatizing surfaces of steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-aluminized steel. The expression "aluminum" as used herein includes industriallyconventional aluminum alloys, such as AIMg35Si,.4. The materials mentioned may, as is increasingly conventional in the automobile industry, also be present side-by-side.

Thus, parts of the car body may also consist of already prepared material, such as a material prepared by the BONAZINK7 process. In this case, the basic material is first chromatized 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 particularfrom 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 strip phosphatizing.

As is also conventional in the case of other knownphosphatizing baths, appropriate bath temperatures are between 30 and 70 EC, regardless of the field of application, the temperature range between 45 and 60 EC 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 sequence, phosphatizing 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 toreplace these chromium-containing passivating baths with chromium-free treatmentbaths. 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 following cations: 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. 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. It is particularly preferred for such a post-rinsing solution to have a pH of from 3.4 to 6 and a temperature of from 20 to 50EC.
An intermediate rinsing procedure using fully deionized 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 onelectrolytically 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 (RIDOLINE7 1501, Henkel KGaA), made up as 2 % in tap water, 55EC, 4 minutes.

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

3. Activating with a titanium phosphate-containing activating agent (FIXODINE7 950, Henkel KGaA), made up as 0.1 % in fully deionized water, room temperature, 1 minute.

4. Phosphatizing with phosphatizing baths in accordance with Table 1, 4 minutes,temperature 55 EC. In addition to the cations mentioned in Table 1, the nitrate-free phosphatizing baths contained 0.1 g/l of iron(ll) and, if required, sodium ions to adjust the free acid value. Li-containing phosphatizing baths did not containsodium. All the baths contained 0.95 g/l of SiF62- and 0.2 g/l of F- and, as accelerator, 1.7 g/l of hydroxylammonium sulphate.

The free acid value was 1.0 - 1.1 points, the total acid value was 23 - 25 points.
The value in points of free acid is to be understood to be the consumption in mlof 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 giveapHof8.2.

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

6. Post-passivating with a chromium-free passivating agent based on complex zirconium fluorides (DEoXYLYTE7 54 NC, Henkel KGaA) 0.25 % strength in fully deionized water, pH 4.0, temperature 40EC, 1 minute.

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 2.5s 4.5 g/m2.

The phosphatized test sheets were coated with a cathodic electrophoretic paint from BASF (FT 85-7042). The anti-corrosive effect forelectrolytically 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 removal at a scribe (half-width of the gap).
Table 1 also contains the results, as a "K value", of a gravel impact test according to a \ N standard (the smaller K, the better the paint adhesion).

The anti-corrosive effect for steel sheets were tested with a salt spray test according to DIN 50021 (1008 hours). Table 1 gives the paint removal at a scribe (half-width of the gap).

- CA 02247141 1998-08-l9 Table 1: Phosphatizing baths, post-passivation and anti-corrosive results (steel: salt spray test; galvanized steel: changing climate test) Bath components Comp. Comp. Ex. I Ex. 2 Ex.3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 (g/l) I 2 Zn(II) 1-0 1-0 1-0 1.0 1.0 1.0 1.0 1.0 1.0 Po43- 14 14 14 14 14 14 14 14 14 Mn(II) 1.0 0.1 0.04 0.07 0.1 0.1 0.1 0.1 0.05 Cu(II) 0.007 - 0.007 0.007 0.007 0.007 0.007 0.007 0.007 Ni(II) ~ ~ ~ ~ ~ 0.012 - 0.012 Co(II) - - - - - - 0.05 0.05 Li(I) - - - - - - - - 0.5 Paintgap steel (mm) 0.8 1.3 0.9 0.8 0.8 0.7 0.7 0.8 0.7 Paintgap galvanized 1.4 2.2 1.6 1.6 1.5 1.4 1.5 1.4 1.4 steel (mm) Kvalue 5 8 6 5 5 5 4 4 5

Claims (10)

1. 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 at a temperature between 30 and 70°C and in which the ratio by weight of phosphate ions to zinc ions is between 3.7 and 30, by spraying or immersing for a period between 3 seconds and 8 minutes, characterised in that the phosphatizing solution does not contain lanthanum compounds but does contain 0.2 to 2 g/l of zinc ions 3 to 50 g/l of phosphate ions, calculated as PO4 -3, 1 to 100 mg/l of manganese ions, 1 to 30 mg/l of copper ions and one or more accelerators selected from 0.3 to 4 g/l of chlorate ions, 0.01 to 0.2 g/l of nitrite ions, 0.05 to 2 g/l of m-nitrobenzenesulphonate ions, 0.05 to 2 g/l of m-nitrobenzoate ions, 0.05 to 2 g/l of p-nitrophenol, 0.005 to 0.15 g/l of hydrogen peroxide in free or bonded form, 0.1 to 10 g/l of hydroxylamine in free or bonded form, 0.1 to 10 g/l of a reducing sugar.

2. A process according to claim 1 wherein the phosphatizing solution also contains from 1 to 50 mg/l of nickel ions and/or from 5 to 100 mg/l of cobalt ions.

3. A process according to one or both of claims 1 and 2 wherein thephosphatizing solution also contains from 0.2 to 1.5 g/l of lithium ions.

4. A process according to one or more of claims 1 to 3 wherein thephosphatizing solution contains from 5 to 20 mg/l of copper ions when used in an immersion process and from 2 to 10 mg/l of copper ions when used in a spray process.

5. A process according to one or more of claims 1 to 4 wherein the phosphatizingsolution also contains fluoride in amounts of up to 2.5 g/l of total fluoride, of which up to 1 g/l is free fluoride, each being calculated as F-.

6. A process according to one or more of claims 1 to 5 wherein the phosphatizingsolution contains as accelerator from 5 to 150 mg/l of hydrogen peroxide in freeor bound form.

7. A process according to one or more of claims 1 to 5 wherein the phosphatizingsolution contains as accelerator from 0.1 to 10 g/l of hydroxylamine in the free or bound form.

8. A process according to claim 7 wherein the phosphatizing solution also contains a total of from 0.01 to 1.5 g/l of one or more aliphatic hydroxycarboxylic or aminocarboxylic acids having from 2 to 6 carbon atoms.

9. A process according to one or more of claims 1 to 8 wherein the phosphatizing solution contains not more than 0.5 g/l of nitrate.

10. A process according to one or more of claims 1 to 9 wherein, after treating the metal surface with the phosphatizing solution and before painting, a passivatingpost-rinsing is performed using an aqueous solution having a pH of from 3 to 7 which contains a total of from 0.001 to 10 g/l of one or more of the following cations: lithium ions, copper ions and/or silver ions.