WO1996022406A1

WO1996022406A1 - Lithium-containing zinc phosphating solution

Info

Publication number: WO1996022406A1
Application number: PCT/EP1996/000039
Authority: WO
Inventors: Bernd Mayer; Jürgen Geke; Karl-Heinz Gottwald; Karl-Dieter Brands
Original assignee: Henkel Kommanditgesellschaft Auf Aktien; Brands, Thomas
Priority date: 1995-01-16
Filing date: 1996-01-08
Publication date: 1996-07-25
Also published as: AR000711A1; DE19500927A1; ZA96302B; AU4484496A; TR199600035A2

Abstract

An acid, aqueous phosphating solution containing 0.2 to 3 g/l zinc(II) and 3 to 50 g/l phosphate, calculated as PO43-, additionally containing 0.2 to 1.5 g/l lithium(I).

Description

'Lithiumhaitiqe zinc phosphating solution'

The invention relates to processes for phosphating metal surfaces with aqueous, acid phosphating solutions which contain zinc and phosphate ions as well as lithium ions, and to their use as pretreatment of the metal surfaces for subsequent painting, in particular electro-dip painting or powder painting. The method can be used for the treatment of surfaces made of steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-aluminized steel.

The phosphating of metals pursues the goal of producing metal phosphate layers which are firmly adhered to the metal surface and which in themselves already improve the corrosion resistance and, in conjunction with paints and other organic coatings, lead to a substantial increase in paint adhesion and resistance to infiltration when exposed to corrosion contribution. Such phosphating processes have long been known. The low-zinc phosphating processes, in which the phosphating solutions have comparatively low zinc ion contents of e.g. B. 0.5 to 2 g / 1. An essential parameter in these low-zinc phosphating baths is the weight ratio of phosphate ion to zinc ions, which is usually in the range> 8 and can assume values of up to 30.

It has been shown that by using other polyvalent cations in the zinc phosphating baths, phosphate layers with significantly improved corrosion protection and paint adhesion properties can be formed. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / 1 manganese ions and z. B. 0.3 to 2.0 g / 1 nickel ions widely used as a so-called trication process for the preparation of metal surfaces for painting, for example for the cathodic electrodeposition of car bodies.

However, the high content of nickel ions in the phosphating solutions of the trication processes and of nickel and nickel compounds in the phosphate layers formed has disadvantages insofar as nickel and nickel compounds are classified as critical from the point of view of environmental protection and workplace hygiene. Lately, low-zinc phosphating processes have therefore been increasingly described which, without the use of nickel, lead to high-quality phosphate layers similar to the nickel-containing processes. Concerns about the accelerators nitrite and nitrate are also being raised due to the possible formation of nitrous gases.

For example, DE-A-3920296 describes a phosphating process which dispenses with nickel and uses magnesium ions in addition to zinc and manganese ions. The phosphating baths described here contain, in addition to 0.2 to 10 g / 1 nitrate ions, further oxidizing agents which act as accelerators, selected from nitrite, chlorate or an organic oxidizing agent.

EP-A-60 716 discloses low-zinc phosphating baths which contain zinc and manganese as essential cations and which can contain nickel as an optional component. The necessary accelerator is preferably selected from nitrite, nitrobenzenesulfonate or hydrogen peroxide.

EP-A-228 151 also describes phosphating baths which contain zinc and manganese as essential cations. The phosphating accelerator is selected from nitrite, nitrate, hydrogen peroxide, m-nitrobenzenesulfonate, m-nitrobenzoate or p-nitrophenol. In dependent claims, the nitrate content is specified at 5 to about 15 g / 1 and an optional nickel content between 0.4 and 4 g / 1. The exemplary embodiments for this all contain both nickel and nitrate.

EP-A-321 059 teaches zinc phosphating baths which, in addition to 0.1 to 2.0 g / 1 zinc and an accelerator, also 0.01 to 20 g / 1 tungsten in the form of a soluble tungsten compound, preferably alkali metal or ammonium tungstate or -s licowungstamate, alkaline earth metal silicotungstate or boro- or silicotungstic acid. The accelerator is selected from nitrite, nitrobenzenesulfonate or hydrogen peroxide. Optional components include nickel in amounts of 0.1 - 4 g / 1 and nitrate in amounts of 0.1 - 15 g / 1.

DE-C-27 39 006 describes a phosphating process for surfaces made of zinc or zinc alloys which is free of nitrate and ammonium ions. In addition to an essential zinc content in amounts between 0.1 and 5 g / 1, 1 to 10 parts by weight of nickel and / or cobalt are required per part by weight of zinc. Hydrogen peroxide is used as an accelerator. From the point of view of workplace hygiene and environmental protection, cobalt is not an alternative to nickel.

DE-A-40 13 483 discloses phosphating processes with which similarly good corrosion protection properties can be achieved as with the trication processes. These processes do without nickel and instead use copper in low concentrations, 0.001 to 0.03 g / 1. Oxygen and / or other oxidizing agents having the same effect are used to oxidize the divalent iron formed in the pickling reaction of steel surfaces to the trivalent stage. Nitrite, chlorate, bromate, peroxy compounds and organic nitro compounds such as nitrobenzenesulfonate are specified as such. WO93 / 20259 modifies this process by adding hydroxylamine, its salts or complexes in an amount of 0.5 to 5 g / 1 hydroxylamine as a modifying agent for the morphology of the phosphate crystals formed.

The use of hydroxylamine and / or its compounds to influence the shape of the phosphate crystals is known from a number of published publications. EP-A-315 059 specifies the particular effect of the use of hydroxylamine in phosphating baths in the fact that the phosphate crystals still form in steel in a desired columnar or bulbous form when the zinc concentration in the phosphating bath corresponds to that for low Zinc process exceeds the usual range. This makes it possible to use phosphate baths with zinc concentrations up to 2 g / 1 and with weight ratios of phosphate to zinc down to 3.7. No further statements are made about advantageous cation combinations of these phosphate baths, but nickel is used in all cases in the patent examples.

The use of lithium ions in phosphating baths has occasionally been described in the literature. In a monograph from 1950 (W. Machu: "The Phosphating" Verlag Chemie Weinheim 1950, p. 146) it is mentioned that the addition of LiNÜ3 to phosphating baths lowers the free acid. From the gas evolution it is concluded that Li increases the speed of the (pickling? -) reaction.

DE-B-23 27 304 describes a peroxide-accelerated phosphating process which is kept very general with regard to its parameters, the phosphating solution containing zinc ions and being essentially free of those components which give water-soluble salts when neutralized with calcium hydroxide, so that the rinsing water can be cleaned by neutralization with calcium hydroxide and returned to the phosphating duct. As a potential constituent of such a phosphating bath, lithium is stated in amounts of 0.04 to 20 g / l, among many others. US-A-3458364 teaches a phosphating solution which contains 0.02 to 20 g / l of an aliphatic polycarboxylic acid having 2 to 6 carbon atoms to avoid rust formation. Other essential components of the phosphating solution are 1 to 20 g / 1 zinc, 2.5 to 40 g / 1 phosphate and 0.2 to 1 g / 1 iron. The solution preferably additionally contains 2.5 to 80 g / 1 nitrate and 1 to 40 g / 1 lithium, beryllium, magnesium, calcium, strontium, cadmium or barium. DE-B-12 87 412, which also relates to a phosphating solution which contains chelating polycarboxylic acids having 2 to 6 carbon atoms, is closely related to this. In addition to zinc ions, this solution contains 1 to 10 g / 1 iron (II). Other optional components are nickel, cobalt, lithium, bismuth, cerium and manganese in quantities of up to 0.5 g / l. In one embodiment, 4.7 mg / 1 lithium are used. Without further details of the concentration, US Pat. No. 3,676,224 claims a phosphating solution which, in addition to phosphate and zinc ions, contains one or more of the metals calcium, magnesium, lithium, beryllium, strontium, cadmium and barium as so-called modifying ions. The Exemplary embodiments contain between 1.09 and 1.62 g / 1 zinc, between 4.94 and 12.4 g / 1 phosphate and no lithium.

The object of the invention is to provide phosphating baths which are free of nickel or the similarly questionable cobalt, which is dangerous for environmental and workplace hygiene reasons.

This object is achieved by an acidic, aqueous phosphating solution containing

0.2 to 3 g / 1 zinc (II) and

3 to 50 g / 1 phosphate, calculated as PO 3-

characterized in that the solution additionally

Contains 0.2 to 1.5 g / 1 lithium (I).

Lithium is preferably used as a water-soluble salt, in particular as a hydroxide, carbonate, nitrate or sulfate. Since phosphating baths are solutions, all metals, including those listed below as optional, are present as ions.

The phosphating baths according to the invention can contain further divalent metal ions, the positive effect of which on the corrosion protection of zinc phosphate layers is known in the prior art. It is therefore preferred that the phosphating solution according to the invention additionally contains one or more of the following cations:

0.2 to 4 g / 1 manganese (II), 0.2 to 2.5 g / 1 magnesium (II), 0.2 to 2.5 g / 1 calcium (II). 0.01 to 0.5 g / 1 iron (II). 0.001 to 0.03 g / 1 copper (II)

The presence of manganese is particularly preferred. The possibility of the presence of divalent iron depends on the accelerator system described below. The presence of iron (II) in the mentioned concentration range requires an accelerator which does not have an oxidizing effect on these ions. Hydroxylamine is an example of this.

The phosphating baths are preferably, but not necessarily, free of nickel and cobalt. This means that these elements or ions are not deliberately added to the phosphating baths. In practice, however, it cannot be ruled out that such constituents may be traced into the phosphating baths via the material to be treated. In particular, it cannot be ruled out that when phosphating steel coated with zinc-nickel alloys, nickel ions are introduced into the phosphating solution. However, the expectation of the phosphating baths according to the invention is that under technical conditions the nickel concentration in the baths is below 0.01 g / 1, in particular below 0.0001 g / 1.

In a manner similar to that described in EP-A-321 059, the presence of soluble compounds of hexavalent tungsten also has advantages in terms of corrosion resistance and paint adhesion in the phosphating baths according to the invention. Phosphating solutions which additionally contain 20 to 800 mg / 1, preferably 50 to 600 mg / 1 of tungsten in the form of water-soluble tungstates, silicotungstates and / or borotungstates can be used in the phosphating processes according to the invention. The anions mentioned can be used in the form of their acids and / or their water-soluble salts, preferably ammonium salts.

In the case of phosphating baths which are said to be suitable for different substrates, it has become customary to add free and / or complex-bound fluoride in amounts of up to 2.5 g / 1 total fluoride, of which up to 800 mg / 1 free fluoride. The presence of such amounts of fluoride is also advantageous for the phosphating baths according to the invention. In the absence of fluoride, the aluminum content of the bath should not exceed 3 mg / 1. In the presence of fluoride, higher Al contents are tolerated as a result of the complex formation, provided the concentration of the non-complexed AI does not exceed 3 mg / 1. The use of fluoride-containing baths is therefore advantageous if the surfaces to be phosphated are at least partially Made of aluminum or containing aluminum. In these cases it is expedient not to use any fluoride bound to the complex, but only free fluoride, preferably in concentrations in the range from 0.5 to 1.0 g / l.

For the phosphating of zinc surfaces, it is not absolutely necessary that the phosphating baths contain so-called accelerators. For the phosphating of steel surfaces, however, it is necessary that the phosphating solution contain one or more accelerators. Such accelerators are known in the prior art as components of zinc phosphate baths. These are substances that chemically bind the hydrogen generated by the acid pickling on the metal surface by reducing them themselves. Oxidizing accelerators also have the effect of oxidizing released iron (II) ions to the trivalent stage by the pickling attack on steel surfaces, so that they can precipitate out as iron (III) phosphate.

The phosphating baths according to the invention can contain one or more of the following components as accelerators:

0.3 to 1.5 g / 1 chlorate ion,

0.01 to 0.2 g / 1 nitrite ion,

0.05 to 2 g / 1 m-nitrobenzenesulfonate ions,

0.05 to 2 g / 1 m nitrobenzoate ions,

0.05 to 2 g / 1 p-nitrophenol,

0.005 to 0.15 g / 1 hydrogen peroxide in free or bound form,

0.1 to 10 g / 1 hydroxylamine in free or bound form.

In addition, nitrate ions in amounts of up to 10 g / l can be present as co-accelerators, which can have a particularly favorable effect on the phosphating of steel surfaces. When phosphating galvanized steel, however, it is preferred that the phosphating solution contain as little nitrate as possible. Nitrate concentrations of 0.5 g / l should preferably not be exceeded, since at higher nitrate concentrations there is a risk of so-called "speck formation". This means white, crater-like defects in the phosphate layer. The use of nitrite as an accelerator leads to technically satisfactory results, in particular on steel surfaces. For reasons of occupational safety (risk of developing nitrous gases), however, it is advisable to avoid nitrite as an accelerator. For the phosphating of galvanized surfaces, this is also advisable for technical reasons, since nitrite can form from nitrite, which, as explained above, can lead to the problem of speck formation.

Hydrogen peroxide is preferred for reasons of environmental friendliness, and hydroxylamine is particularly preferred as an accelerator for technical reasons because of the simplified formulation options for replenishing solutions. However, using these two accelerators together is not advisable since hydroxylamine is decomposed by hydrogen peroxide. If hydrogen peroxide in free or bound form is used as an accelerator, concentrations of 0.005 to 0.02 g / l of hydrogen peroxide are particularly preferred. The hydrogen peroxide can be added as such to the phosphating solution. However, it is also possible to use hydrogen peroxide in bound form as compounds which give hydrogen peroxide in the phosphating bath by hydrolysis reactions. Examples of such compounds are persalts such as perborates, percarbonates, peroxosulfates or peroxodisulfates. Ionic peroxides, such as, for example, alkali metal peroxides, are suitable as further sources of hydrogen peroxide.

Hydroxylamine can be used as a free base, as a hydroxylamine complex or in the form of hydroxylammonium salts. If free hydroxylamine is added to the phosphating bath or a phosphating bath concentrate, it will largely exist as a hydroxylammonium cation due to the acid character of these solutions. When used as a hydroxylammonium salt, the sulfates and the phosphates are particularly suitable. In the case of the phosphates, the acid salts are preferred due to the better solubility. Hydroxylamine or its compounds are added to the phosphating bath in such quantities that the calculated concentration of the free hydroxylamine is between 0.1 and 10 g / 1, preferably between 0.2 and 6 g / 1 and in particular between 0. 3 and 2 g / 1. Preferred concentrations of lithium ions in the phosphating baths according to the invention are in the range from 0.4 to 1 g / l. Phosphate baths which contain lithium as the only monovalent cation are particularly preferred. Depending on the desired ratio of phosphate ions to the divalent cations and the lithium ions, it may be necessary to add further basic substances to the phosphating baths in order to set the desired free acid. In this case, ammonia is preferably used, so that the lithium-containing phosphating baths can additionally contain ammonium ions in the range from about 0.5 to about 2 g / l. The use of basic sodium compounds such as sodium hydroxide solution is less preferred since the presence of sodium ions in the lithium-containing phosphating baths deteriorates the corrosion protection properties of the layers obtained.

Particularly good corrosion protection results are obtained with phosphating baths that contain manganese (II) in addition to zinc and lithium. The manganese content of the phosphating bath should be between 0.2 and 4 g / l, since with lower manganese contents the positive influence on the corrosion behavior of the phosphate layers is no longer given and with higher manganese contents there is no further positive effect. Contents between 0.3 and 2 g / 1 and in particular between 0.5 and 1.5 g / 1 are preferred. The zinc content of the phosphating bath is preferably set to values between 0.45 and 1.5 g / l. As a result of the pickling removal during the phosphating of zinc-containing surfaces, it is possible, however, that the current zinc content of the working bath rises to up to 3 g / l. The form in which the zinc and manganese ions are introduced into the phosphating baths is in principle irrelevant. It is particularly advisable to use the oxides and / or the carbonates as the zinc and / or manganese source.

When the phosphating process is used on steel surfaces, iron in the form of iron (II) ions dissolves. If the phosphating baths according to the invention do not contain any substances which have a strong oxidizing effect on iron (II), the divalent iron changes to the trivalent state primarily as a result of air oxidation, so that it can precipitate out as iron (III) phosphate. Therefore, egg II) contents can be built up in the phosphating baths which are clearly above the contents which Baths containing oxidizing agents. In this sense, iron (II) concentrations of up to 50 ppm are normal, although values of up to 500 ppm can also occur briefly in the production process. Such iron (II) concentrations are not detrimental to the phosphating process according to the invention.

The weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided that it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred. For this calculation, the total phosphorus content of the phosphating bath is considered to be present in the form of phosphate ions P0_; 3 ~. Accordingly, the known fact that the pH values of the phosphating baths, which are usually in the range from about 3 to about 3.6, only a very small part of the phosphate in the form of the triple negative is disregarded when calculating the quantitative ratio charged anions. At these pH values, it is rather to be expected that the phosphate is present primarily as a single negatively charged dihydrogenphosphate anion, together with smaller amounts of undisociated phosphoric acid and double negatively charged hydrogenphosphate anions.

As a further parameter for controlling phosphating baths, the free acid and total acid contents are known to the person skilled in the art. The method of determining these parameters used in this document is given in the example section. Values of the free acid between 0 and 1.5 points in the case of partial phosphating, in the case of band phosphating up to 2.5 points and the total acid between about 15 and about 30 points are within the technically customary range and are suitable for the purposes of this invention.

Phosphating baths are usually sold in the form of aqueous concentrates which are adjusted to the application concentrations on site by adding water. For reasons of stability, these concentrates can contain an excess of free phosphoric acid, so that when diluted to a bath concentration, the value of the free acid is initially too high or the pH is too low. By adding alkalis such as preferably lithium hydroxide, lithium carbonate or ammonia, optionally also basic potassium or (less preferred) sodium compounds, the Free acid value lowered to the desired range. Furthermore, it is known that the free acid content during use of the phosphating baths can increase over time due to the consumption of the layer-forming cations and, if appropriate, through decomposition reactions of the accelerator. In these cases it is necessary to readjust the value of the free acid to the desired range from time to time by adding alkalis. This means that the contents of alkali metal or ammonium ions in the phosphating baths can fluctuate within wide limits and tend to increase over the course of the service life of the phosphating baths due to the dulling of the free acid. The weight ratio of alkali metal and / or ammonium ions to zinc ions, for example, can therefore be very low in freshly prepared phosphating baths, for example <0.5 and in extreme cases even 0, while it usually increases over time due to bath maintenance measures, so that the Ratio> 1 and can take values up to 10 and larger. Low-zinc phosphate baths generally require the addition of alkali metal or ammonium ions in order to be able to adjust the free acid to the desired value range at the desired weight ratio POt -: Zn> 8. Analogous considerations can also be made regarding the proportions of alkali metal and / or ammonium ions to other bath components, for example phosphate ions.

Phosphating baths according to the invention are suitable for phosphating surfaces made of steel, galvanized or alloy-galvanized steel, aluminum, aluminized or alloy-alloyed steel. The term "aluminum" includes the technically customary aluminum alloys such as AlMg0.5Sil, 4. The materials mentioned can - as is becoming increasingly common in automotive engineering - also coexist. The method is suitable for use in immersion, spraying or spray / immersion processes. It can be used in particular in automobile construction, where treatment times between 1 and 8 minutes, in particular 2 to 5 minutes, are common. However, it can also be used for strip phosphating in the steel mill, with treatment times between 3 and 12 seconds. When used in tape phosphating processes, it is advisable to set the bath concentrations in the upper half of the ranges preferred according to the invention. For example, the Zinc content in the range from 1.5 to 2.5 g / 1, the lithium content in the range from 0.5 to 1.5 g / 1, the manganese content in the range from 1.5 to 3 g / 1 and the content of free acid are in the range of 1.5 to 2.5 points. A particularly suitable substrate for strip phosphating is galvanized steel, in particular electrolytically galvanized steel.

As is also common with other phosphating baths of the prior art, the suitable 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 phosphating process according to the invention is intended in particular for treating the metal surfaces mentioned before painting, for example before cathodic electrocoating, as is customary in automobile construction. It is also suitable as a pre-treatment before a powder coating, such as that used for household appliances. The phosphating process is to be seen as a sub-step of the technically customary pretreatment chain. In this chain, the steps of cleaning / degreasing, rinsing and activating are usually preceded by the phosphating, the activation usually being carried out using activating agents containing titanium phosphate. After intermediate rinsing, the phosphating according to the invention can optionally be followed by a passivating aftertreatment. Treatment baths containing chromic acid are widely used for such a passivating aftertreatment. For reasons of work and environmental protection and for reasons of disposal, however, there is a tendency to replace these chromium-containing passivation baths with chromium-free treatment baths. Purely inorganic bath solutions, in particular based on zirconium compounds, or also organic-reactive bath solutions, for example based on poly (vinylphenols), are known for this. An intermediate rinse with demineralized water is generally carried out between this post-passivation and the usually subsequent coating. Embodiments 1 to 16 - Comparative Examples 1 to 3

The phosphating processes according to the invention and the comparative processes were checked on steel sheets (St 1405), on aluminum sheets of the alloy AlMgO, 5Sil, 4 and on steel sheets (ZE) electrolytically galvanized on both sides, as are used in automobile construction. The following process step (in the dipping or spraying process) used in body production was carried out:

1. For immersion processes: cleaning with an alkaline cleaner (Ridoline ^R 1559, Henkel KGaA), preparation 2% in city water, 60 ° C, 4 minutes.

For spraying processes: cleaning with an alkaline cleaner (Ridoline ^R C1250, Henkel KGaA), approach 0.5% in city water, 60 ° C, 2 minutes.

2. Rinse with deionized water in spraying or dipping, room temperature, 1 minute.

3. Activation with an activating agent containing titanium phosphate in immersion (Fixodine ^R C 9112, Henkel KGaA), approach 0.2% in deionized water, room temperature, 2 minutes.

4. Phosphating with phosphating baths (bath temperature, unless otherwise stated, 50 ° C.) according to Table 1. In addition to the cations mentioned, the phosphating baths contained 0.5 to 2 g / 1 ammonium ions to adjust the free acid and Fe (II ) in the range 50 - 60 ppm. Sodium and hydroxylamine were used as sulfate. Demineralized water was used for all baths. For example, the bath of Example 1 was obtained by dissolving the following substances in completely deionized water in the order given: 16.56 g / 1 85% phosphoric acid

1.25 g / 1 ZnO

2.09 g / 1 nC03

2.48 g / 1 FeS04 x 7 H ₂ 0

2.86 g / 1 34% solution of H ₂ SiFö

0.57 g / 1 40% solution of HF

1.63 g / 1 (NH ₃ 0H) ₂ S04

1.72 g / 1 LiOH

The bath of Example 2 additionally contained 4.57 g / l LiSO 4 x H ₂ 0.

The free acid score is understood to mean the consumption in ml of 0.1 normal sodium hydroxide solution in order to titrate 10 ml of bath solution up to a pH of 3.6. Similarly, the total acid score indicates consumption in ml up to a pH of 8.2.

5. Rinse with deionized water by spraying or dipping, room temperature, 1 minute.

6. Blow dry with compressed air

Current density / potential measurements were carried out as a short test for the corrosion protection effect of the layers. This method is described, for example, in A.Losch, JWSchultze, D. Speckmann: "A New Electronic Method for the Determination of the Free Surface of Phosphate Layers", Appl. Surf. Be. 5.2, 29-38 (1991). For this purpose, the phosphated sample sheets were clamped in a sample holder made of polyamide, which left a surface of 43 cm ² to be examined free. The measurements were carried out under oxygen-free conditions (flushing with nitrogen) in an electrolyte with pH = 7.1, which contained 0.32 M H3BO3, 0.026 M Na ₂ B4θ7'10H 0 and 0.5 M NaNθ3. A standard mercury electrode with a normal potential EQ - 0.68 volts was used as the reference electrode. The samples were first immersed in the electrolyte solution for 5 minutes without applying an external potential. Then cyclic Voltamograms between -0.7 and 1.3 volts compared to the standard mercury electrode with a potential change of 20 mV / s were recorded. For evaluation, the current density at a potential of -0.3 volts, the maximum value of the current density in the range between 0 and 0.8 volts and the minimum value of the current density in the range between 0.5 and 1.3 volts, in each case based on the standard - Mercury electrode, read. Negative current densities at a potential of -0.3 volts indicate a reduction in layer components. High current densities in the measuring ranges from 0 to 0.8 volts and from 0.5 to 1.3 volts indicate a poor barrier effect, low current densities indicate a good barrier effect of the phosphate layers against corrosive currents.

Layer weights when phosphating different substrates and selected results of current density / potential measurements are contained in Table 2.

Table 1: Continued component Vera1.3 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16

Zn (II) (g / 1) 1 1 1 ⁱ 1 ⁱ 1 l 1 l 1 1 1 1 1

Phosphate (g / 1) 14 14 14 14 14 14 14 14 14

LUD (g / D - 0.25 0.5 0.75 1 1.25 0.5 0.5 0.5

Mn (II) (g / 1) 1 1 1 1 1 1 1 1 1

Ni (II) (g / D -

Mg (II) (g / 1) -

Na (I) (g / 1) 0 0.8 88 0.8 0.8 0.8 0.8 0.8 1 0.25

SiF ₆ 2- (g / 1) 0.0, 9966 0.96 0.96 0.96 0.96 0.96 0.96 0.96

F "free (g / 1) 0 0.22222 0.22 0.22 0.22 0.22 0.22 0.22 0.22 0.7

NH ₂ 0H (g / 1) 0 0, .6666 0.66 0.66 0.66 0.66 0.66 0.66 0.66 0.66 m-nitrobenzene - - I sulfonic acid (g / 1)

H ₂ 0 ₂ (mg / 1) - pH 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3

Free acid 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8

(Points)

Total acid 23 23 23 23 23 23 23 23 23

(Points)

Application diving diving diving diving diving diving diving diving diving

Time (seconds) 180 180 180 180 180 180 180 180 180

Claims

claims

1. Containing acidic, aqueous phosphating solution

0.2 to 3 g / 1 zinc (II) and

3 to 50 g / 1 phosphate, calculated as PO4 ³ -,

characterized in that the solution additionally

Contains 0.2 to 1.5 g / 1 lithium (I).

2. Phosphating solution according to claim 1, characterized in that it additionally contains one or more of the following cations:

0.2 to 4 g / 1 manganese (II),

0.2 to 2.5 g / 1 magnesium (II),

0.2 to 2.5 g / 1 calcium (II),

0.01 to 0.5 g / 1 iron (II).

0.001 to 0.03 g / 1 copper (II).

3. phosphating solution according to one or both of claims 1 and 2, da¬ characterized in that it additionally

20 to 800 mg / 1 tungsten

contains in the form of water-soluble tungstates, S licowungstamates and / or Borowolfra ate in the form of their acids and / or in the form of their water-soluble salts.

4. Phosphating solution according to one or more of claims 1 to 3, characterized in that it additionally contains fluoride in amounts of up to 2.5 g / 1 total fluoride, of which up to 800 mg / 1 free fluoride.

5. Phosphating solution according to one or more of claims 1 to 3, characterized in that it additionally contains one or more of the following components as accelerators: 0.3 to 1.5 g / 1 chlorate

0.01 to 0.2 g / 1 nitrite ion,

0.05 to 2 g / 1 m-nitrobenzenesulfonate ions,

0.05 to 2 g / 1 m nitrobenzoate ions,

0.05 to 2 g / 1 p-nitrophenol,

0.005 bbiiss 00,, 115 g / 1 hydrogen peroxide in free or bound form,

0.1 to 10 g / 1 hydroxylamine in free or bound form.

6. phosphating solution according to claim 5, characterized in that it contains 0.005 to 0.02 g / 1 hydrogen peroxide in free or bound form as accelerator.

7. phosphating solution according to claim 5, characterized in that it contains 0.2 to 6 g / 1 hydroxylamine as an accelerator in free or bound form.

8. phosphating solution according to one or more of claims 1 to 7, characterized in that it contains 0.4 to 1 g / 1 lithium (I).

9. phosphating solution according to one or more of claims 1 to 8, da¬ characterized in that it has a free acid content in the range of 0 to 2.5 points and / or a total acid content in the range of 15 to 30 points.

10. A method for phosphating surfaces of steel, galvanized or galvanized steel and / or of aluminum or its alloys, characterized in that the surfaces with a phosphating solution according to one or more of claims 1 to 9, the temperature in the range of 30 up to 70 ° C, for a period of 3 seconds to 8 minutes by spraying, dipping or spray dipping.

11. The method according to claim 10 for the treatment of the surfaces before a cathodic electrocoating or before a powder coating.