Method for sequentially forming a conversion layer on a component including a steel surface

Abstract

The present invention relates to a method for the corrosion protection pretreatment of a plurality of components in series, the components being at least partially made of iron and / or steel, each of the components in series being subjected to a first conversion step, then a rinsing step and thereafter a second conversion step, the first and second conversion steps each comprising contacting the components with an aqueous acidic conversion solution based on compounds of the elements Zr and / or Ti dissolved in water, the aqueous conversion solution of the second conversion step further comprising copper ions.

Description

[Technical field]

[0001] The present invention relates to a method for the corrosion protection pretreatment of a plurality of components in series, the components being at least partially made of iron and / or steel, each of the components in series being subjected to a first conversion step, then a rinsing step and thereafter a second conversion step, the first and second conversion steps each comprising contacting the components with an aqueous acidic conversion solution based on compounds of the elements Zr and / or Ti dissolved in water, the aqueous conversion solution of the second conversion step further comprising copper ions. [Background technology]

[0002] In the corrosion protection pretreatment of components with surfaces made of materials such as iron, steel, galvanized steel and / or aluminum, thin film passivation based on amorphous conversion layers based on oxides and hydroxides of the elements Zr and / or Ti has been widely established as an alternative to phosphating, whereby crystalline coatings are formed. Efforts to further develop this type of conversion coating are essentially aimed at establishing a chromium-free passivation and resource saving that provides an excellent adhesive base for the subsequently applied paint system, with the aim of achieving a corrosion protection comparable to that of tricational zinc phosphate treatments. In particular in the case of amorphous thin films obtained from conversion processes in acidic aqueous solutions containing water-soluble compounds of the elements Zr and / or Ti, a controlled film formation and the formation of a coating with as few defects as possible are of great importance. In particular, in this case, it is difficult to influence the rate of film formation in thin diffusion films on metal surfaces, where an alkaline pH leads to a coating based on hydroxides and oxides of the elements Zr and / or Ti, so that the conversion of conversion processes mainly based on fluorocomplexes of the elements Zr and / or Ti is as complete as possible. This is to prevent fluorides from remaining in the thin film, which may cause localized film defects in contact with corrosive media.For example, EP 1 455 002 A1 reports that the corrosion behavior and the film adhesion to subsequent electrocoating can be improved by reducing the proportion of fluorides in the conversion coating.In order to effectively reduce the fluoride content in the conversion coating, EP 1 455 002 A1 proposes adding magnesium, calcium, Si-containing compounds, zinc, or copper to the conversion solution, and alternatively or in combination with this, drying the conversion coating or post-rinsing it with an alkaline aqueous composition.

[0003] The prior art also makes efforts to improve the quality of conversion coatings through the sequential formation of coatings. For example, in EP 2 318 566 A1, it is shown that cascading the rinsing water of the conversion process into a pre-rinse before the actual conversion process is favorable for the formation of an amorphous coating based on the elements Zr and / or Ti, in particular on the steel surface, which protects against corrosion. According to EP 2 318 566 A1, during the pre-rinse, an initial slight conversion of the surface takes place, which is favorable for the subsequent formation of the actual conversion layer. According to the teaching of EP 2 971 234 A1, sequential layer construction by conversion in successive wet-chemical steps carried out independently of one another is also used to improve the adhesion of the coating to correspondingly pretreated steel surfaces. A two-stage process for the formation of a conversion coating based on elements of group 2 IIIb / IVb of the periodic table, in particular the element Zr, consisting of an acidic fluoride-containing solution, is described. This is particularly suitable for subsequent electrocoating and can be carried out on a variety of metal substrates. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] EP 1 455 002 A1 [Patent Document 2] EP 2 318 566 A1 [Patent Document 3] EP 2 971 234 A1 Summary of the Invention [Problem to be solved by the invention]

[0005] Based on this prior art, the object of the present invention is to provide an alternative method for providing conversion coatings with as few defects as possible for a wide variety of metals, which have improved protection against corrosive peeling after coating formation. The method must be able to be carried out with as few resources as possible and must be particularly suitable for treating components in series. In order to improve the process quality, a sufficient improvement in corrosion protection and coating adhesion on at least steel and / or iron surfaces must also be achieved in a stable manner during the pretreatment of a series of components, compared to the prior art. [Means for solving the problem]

[0006] This object is achieved by a method for sequentially forming a conversion coating in two treatment steps interrupted by a rinsing step, the conversion solutions each containing water-soluble compounds of the elements Zr and / or Ti, the conversion solution in the second conversion step further containing copper ions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Specifically, the present invention relates to a method for pretreating a plurality of series components, the series components being at least partially formed of iron and / or steel, the method comprising subjecting each of the series components to the sequential steps (i) to (iii) of: (i) a first conversion step of providing an aqueous conversion solution (I) having a pH in the range of 2.5 to 5.0 and containing at least 0.10 mmol / kg of compounds of the elements Zr and / or Ti and free fluoride dissolved in water; (ii) a rinsing step of providing an aqueous rinsing solution (II) having a pH in the range of 5.0 to 10.0, a concentration of compounds of the elements Zr and / or Ti dissolved in the water that is at least 5 times lower than in the aqueous conversion solution (I), and containing less than 0.25 mmol / kg of free fluoride; (iii) a second conversion step of providing an aqueous conversion solution (III) having a pH in the range of 2.5 to 5.0 and comprising at least 0.10 mmol / kg of a compound of the elements Zr and / or Ti dissolved in water and at least 15 μmol / kg of copper ions dissolved in water; and successively contacting at least the surface of the iron and / or steel of the component with each of the aqueous solutions (I) to (III).

[0008] The corrosion protection pretreatment of components in series is when a number of components are contacted with the treatment solutions provided in each treatment step of the method of the invention and usually stored in a system tank, the individual components being contacted sequentially and therefore at different times, the system tank being the vessel into which the treatment solutions intended for the corrosion protection pretreatment in series are introduced.

[0009] When referring in the present invention to the pretreatment of components made of metallic materials, in particular to the pretreatment on the surface of iron and steel materials subjected to the pretreatment of the present invention, all materials containing more than 50 at% of each element are included. Anticorrosive pretreatment always affects the surface of the component and therefore the surface of the metallic material. The material can be a homogeneous material or a coating. According to the present invention, galvanized steel grades are composed of both material steel and material zinc, and it can happen that the surface of the steel is exposed at the cutting edge and cylindrical grinding points of an automobile body made of galvanized steel, in which case there is a pretreatment of material steel according to the present invention.

[0010] In the present invention, insofar as the concentration of an active ingredient or compound is referred to as the amount of substance per kilogram, this is the amount of substance based on the weight of the respective total composition.

[0011] The components to be pretreated according to the invention may in particular be three-dimensional structures of any shape and design resulting from a manufacturing process, including semi-finished products such as strips, sheets, rods, pipes, and composite structures assembled from said semi-finished products, in particular automobile bodies, which are preferably interconnected by gluing, welding and / or flanging to form a composite structure.

[0012] With regard to the process steps, solutions (I) to (III) are considered to be "provided" in the sense of the process of the invention if they are prepared or prepared for contacting as defined in each process step (i) to (iii) or are carried out during contacting as defined.

[0013] In comparison with a conversion treatment by a single contact with an acidic aqueous solution containing Zr and / or Ti compounds and free fluorides dissolved in water (conventional single-step conversion layer formation), the multi-step pretreatment of the present invention provides a defect-free conversion layer with a low fluoride content and a significantly reduced tendency for corrosive peeling of the subsequently formed coating system. For this, the combination of a first conversion step with a second conversion step carried out after a rinsing step in a conversion solution containing copper ions dissolved in water is essential, as a mere reduction of the fluoride content in the converted coating after the first conversion step by a rinsing step carried out with a rinsing solution substantially free of free fluoride ions (i.e. less than 0.25 mmol / kg, preferably less than 0.10 mmol / kg, very particularly preferably less than 0.05 mmol / kg of free fluoride) is not sufficient, in particular for a sufficient performance in terms of corrosion protection for steel and / or iron surfaces of the components in series.

[0014] The amount of free fluoride in the relevant step of the pretreatment of the present invention can be determined potentiometrically using a fluoride-sensitive measuring electrode at 20° C. in the relevant donor solution after calibration with a fluoride-containing buffer without pH buffer.

[0015] The formation of the conversion layer in steps (i) and (iii) is carried out with a conversion solution which forms an amorphous oxide / hydroxide coating based on the elements Zr and / or Ti and accordingly comprises compounds of the elements Zr and / or Ti dissolved in water. The term "dissolved in water" includes molecularly dissolved species and compounds which dissociate in aqueous solution to form hydrated ions. Typical examples of these compounds are titanyl sulfate (TiO(SO4)), titanyl nitrate (TiO(NO3)2) and / or hexafluorotitanic acid (H2TiF6) and their salts, or ammonium zirconium carbonate ((NH4)2ZrO(CO3)2) and / or hexafluorozirconic acid (H2ZrF6) and their salts. The compounds dissolved in water are preferably selected in the conversion step from fluoro acids and / or fluoro complexes of the elements Zr and / or Ti. The formation of this type of conversion layer is particularly preferred, since conversion layers based on fluoro acids and / or fluoro complexes of the element Zr provide improved coating adhesion.

[0016] It is also advantageous for the formation of a very homogeneous and dense amorphous conversion layer, particularly in the first conversion step, that the pH of the conversion solution is not set to be acidic, in order to keep the pickling rate as low as possible during the formation of the conversion layer. Overall, therefore, both conversion steps (i) and (iii) are preferred, in which the pH in each case is above 3.0, more preferably above 3.5, particularly preferably above 4.0, but preferably below 4.5, since otherwise the precipitation of sparingly soluble hydroxides of the elements Zr and / or Ti in the solution can only be controlled continuously within a narrow process window during the sequential processing of several components.

[0017] Particularly preferred is an embodiment of the method according to the invention, in which the majority of the layer formation has already taken place in the first conversion step, and the second conversion step serves exclusively to repair defects in the converted coating formed in the first step by deposition of a relatively small additional coating on the elements Zr and / or Ti, supported by local cementation of copper at point defects in the converted layer. Surprisingly, it was found in the present invention that excessive precipitation of Zr and / or Ti in the second conversion step leads to a significant deterioration of the corrosion protection properties. This applies in particular to the iron and / or steel surfaces of components pretreated according to the invention.

[0018] Thus, the contact with the aqueous conversion solution (I) in the first conversion step of step (i) is carried out in such a way that the surface of the steel and / or iron is treated with a concentration of at least 20 mg / m 2 based on the elements Zr and / or Ti in each case. 2 The time for forming a coating of at least 150 mg / m2 is preferably at least 150 mg / m2. 2 More than 100 mg / m 2 More particularly preferably 80 mg / m 2 It is preferred that the process of the present invention not be run for such a long time that thicker coatings are obtained.

[0019] As already mentioned above, in relation to such contacting carried out in the first conversion step, this is advantageous for corrosion protection and paint adhesion, especially on steel and / or iron surfaces, and therefore it is preferred to carry out the contacting with the aqueous conversion solution (III) in the second conversion step of step (iii) in such a way that the surface of the steel and / or iron is in a concentration of 15 mg / m based on the elements Zr and / or Ti in each case. 2 More than 12 mg / m 2 More particularly preferably more than 10 mg / m 2 Preferably, the coverage on at least these surfaces is at least 2 mg / m2, but not continuing to an increase in coverage of more than 2 mg / m2. 2 It is also preferred that the increasing time continue.

[0020] In this way, the layer formation in the conversion step of the method according to the invention for corrosion protection pretreatment is optimally adjusted.

[0021] Preferred embodiments of the method of the invention are shown and explained below with reference to the individual process steps and method implementations which are particularly advantageous with respect to the objectives underlying the invention.

[0022] First conversion step: In the first conversion step, it is necessary to produce a conversion coating based on oxide / hydroxide compounds of the elements Ti and / or Zr as homogeneously as possible and at the same time to meet the requirements of process economy. The treatment time required for this, i.e. the contact time with the conversion solution at a temperature in the range of 10-60° C., should be in the range of 10 s to 300 s. To ensure this, the method according to the invention is preferred, in which in the aqueous conversion solution (I) of the first conversion step in step (i), the proportion of compounds of the elements Zr and / or Ti dissolved in water is preferably at least 0.15 mmol / kg, more preferably at least 0.25 mmol / kg, particularly preferably at least 0.30 mmol / kg. For reasons of process economy, the content of compounds of the elements Zr and / or Ti dissolved in water should be significantly less than 10.0 mmol / kg, particularly preferably less than 5.0 mmol / kg.

[0023] However, depending on the type and surface properties of the metal substrate, in particular the steel substrate, and the required pickling speed, a certain proportion of free fluoride is necessary in any case. In principle, it is advantageous and therefore preferred if in the aqueous conversion solution (I) of the first conversion step in step (i) the proportion of free fluoride is at least 0.5 mmol / kg, particularly preferably at least 1.0 mmol / kg, very particularly preferably at least 1.5 mmol / kg. However, for reasons of process economy and in order to prevent rust formation on the steel and / or iron surfaces, especially after the rinsing step, the proportion of free fluoride should preferably be less than 8.0 mmol / kg, particularly preferably less than 6.0 mmol / kg, very particularly preferably less than 5.0 mmol / kg.

[0024] In the conversion aqueous solution (I) of the first conversion step of step (i), TIFF2024524451000001.tif1353 [where F / mM and Me / mM are the free fluoride (F) or reduced zirconium and / or titanium (Me) concentrations subtracted in mmol / kg] If the quotient λ according to is greater than 0.80, preferably greater than 1.20, particularly preferably greater than 1.60, a good balance between pickling speed and layer formation can be achieved, and therefore such conversion solutions are preferred in the present invention.

[0025] The preferred source of free fluoride in the first conversion step of step (i) of the method of the present invention is hydrofluoric acid and its water-soluble salts, such as ammonium difluoride and sodium fluoride, and complex fluorides of the elements Zr, Ti and / or Si, in particular complex fluorides of the element Si. Thus, in the phosphating process according to the second embodiment of the present invention, the source of free fluoride is preferably selected from hydrofluoric acid and its water-soluble salts, and / or complex fluorides of the elements Zr, Ti and / or Si. The salts of hydrofluoric acid are dissolved in deionized water (κ<1 μS cm ) at 60° C. -1 ) is at least 1 g / L, calculated as F, is water-soluble within the meaning of the present invention.

[0026] Rinsing process: The rinsing step in step (ii) of the sequential conversion coating process according to the invention serves, on the one hand, to completely or partially remove or dilute the soluble residues, particles and active components adhering on the component from step (i) of the preliminary wet-chemical process. On the other hand, the removal of the soluble residues should in particular result in the soluble fluoride species contained in the conversion coating, thus conditioning the first conversion coating for the subsequent passivating deposition of oxide / hydroxide Zr and / or Ti compounds and the cementation of copper in the second conversion step. It has been found that the rinsing solution may be substantially free of active components based on metal or semi-metal elements, which are simply consumed by the metal surfaces of the component brought into contact with the rinsing solution by deposition. Thus, the rinse solution may simply be municipal or deionized water, or may further contain, if desired, additional surface-active compounds, such as redox-active compounds ("depolarizers") to optimize the conditioning of the metal surfaces accessible at point defects, or non-ionic or anionic surfactants to optimize wetting with the rinse solution.

[0027] For the purpose of the rinsing step, it is therefore essential that the aqueous rinsing solution (II) supplied in the rinsing step has a concentration of the compounds of the elements Zr and / or Ti dissolved in water that is at least 5 times lower, preferably at least 10 times lower, particularly preferably at least 20 times lower, very particularly preferably at least 50 times lower than the aqueous conversion solution (I), in each case containing less than 0.25 mmol / kg, preferably less than 0.10 mmol / kg, particularly preferably less than 0.05 mmol / kg of free fluoride, and preferably less than 0.10 mmol / kg of the compounds of the elements Zr and / or Ti dissolved in water. In this case, the continuous reduction of the soluble fluoride species in the conversion coating can also be achieved by contacting the conversion coating with a rinsing solution that contains a concentration of the compounds of the elements Zr and / or Ti dissolved in water that is 5 times, for example more than 100 times, more dilute. This rinsing step comprises several immediately successive rinsing steps, preferably not more than three for reasons of process economy, with a rinsing solution (II) containing at least one compound of elemental Zr and / or Ti dissolved in water, the concentration of which is reduced by a factor of five.

[0028] Thus, in view of the objectives pursued with the rinsing step, which is to provide conditioning for the subsequent passivating deposition of Zr and / or Ti oxide / hydroxide compounds and for the cementation of copper, it is advantageous and therefore preferred in the present invention for the rinsing solution (II) of the rinsing step to comprise metal ions of elemental copper, nickel and cobalt dissolved in water in a total amount of less than 50 μmol / kg, preferably less than 15 μmol / kg.

[0029] In the present invention, the pH of the rinsing solution is in the range of 5.0 to 10.0. However, it has been found that an alkaline rinsing solution can be disadvantageous in that alkalinity is introduced into the second conversion step, which must be compensated for by regrinding with an acidic substance, further promoting the precipitation of active ingredients and the formation of sludge. It is therefore preferred in the present invention that in step (ii), the aqueous rinsing solution (II), preferably at least the rinsing solution of the final rinsing step of the rinsing step, has a pH of more than 6.0 but less than 9.5, particularly preferably less than 8.5.

[0030] In another embodiment, it could be shown that the conditioning of the steel and / or iron surface provided with the first conversion layer for the subsequent passivating deposition of Zr and / or Ti oxide / hydroxide compounds and for the cementation of copper in the second conversion step is promoted by the fact that redox active compounds (called "depolarizers") are added to the rinsing solution, which inhibit the production of hydrogen at the metal surface. Thus, in a preferred embodiment of the process according to the invention, the aqueous rinsing solution (II) of the rinsing step of step (ii) further comprises at least 0.1 mmol / kg, more preferably at least 0.5 mmol / kg, particularly preferably at least 1 mmol / kg, but preferably at most 10 mmol / kg, particularly preferably at most 6 mmol / kg, of a depolariser selected from nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, hydrogen peroxide in free or combined form, hydroxylamine in free or combined form and reducing sugars, preferably selected from nitrite ions, nitroguanidine, hydroxylamine in free or combined form and hydrogen peroxide in free or combined form, particularly preferably selected from nitrite ions.

[0031] As already explained, the rinsing step can be carried out in several successive rinsing steps, ensuring that each rinsing solution (II) has a pH in the range of 5.0 to 10.0, a concentration of compounds of the elements Zr and / or Ti dissolved in water that is at least 5 times lower than in the aqueous conversion solution (I), and contains less than 0.25 mmol / kg, preferably less than 0.10 mmol / kg, particularly preferably less than 0.05 mmol / kg, of free fluoride. In a preferred embodiment, the contact with each rinsing solution provided in the rinsing step of step (ii) is carried out by immersion and / or spraying. Preferably, immersion is carried out first, followed by spraying, and preferably by immersion and spraying.

[0032] Second conversion step: As already explained, the conversion of the metal surface of the component brought about in the second conversion step mainly serves the subsequent passivating deposition of oxide / hydroxide Zr and / or Ti compounds. Therefore, for reasons of process economics and to ensure compliance with the process window, in the method of the invention, a relatively low active content of Zr and / or Ti in the conversion solution of the second conversion step can be advantageous for optimizing the anticorrosive properties of the subsequently formed conversion layer. Therefore, the method of the invention is preferred, in which in the conversion solution (III) of the second conversion step of step (iii), the proportion of compounds of element Zr and / or Ti dissolved in water is less than 1.00 mmol / kg, preferably less than 0.80 mmol / kg, more preferably less than 0.70 mmol / kg, particularly preferably less than 0.60 mmol / kg.

[0033] In the second conversion step, the amount of free fluoride is optional, and it should be noted that the downstream conversion step should not be set to be too mordanted at the same time to prevent local defects in the conversion coating. Nevertheless, for short process time windows, a small amount of free fluoride can be useful for the cementation of copper ions and the subsequent accelerated passivation deposition of Zr and / or Ti oxide / hydroxide. Therefore, in order to support the increase in the coverage on Zr and / or Ti, it is preferable that the proportion of free fluoride in the conversion solution (III) of the second conversion step of step (iii) is less than 3.00 mmol / kg, preferably less than 2.50 mmol / kg, particularly preferably less than 2.00 mmol / kg, but preferably at least 0.1 mmol / kg, more preferably at least 0.2 mmol / kg. Suitable sources of free fluoride in the second conversion step of step (i) of the method of the present invention are the same as those described in connection with the first conversion step.

[0034] The corrosion protection and coating adhesion, which are not fully achieved until the second conversion step, can be optimized by the amount of copper ions contained in the conversion solution (III). It has been found that the conversion solution (III) of the second conversion step of step (iii) should preferably contain more than 40 μmol / kg, particularly preferably more than 50 μmol / kg. However, for reasons of process economy and in order to avoid extensive cementation of metallic copper, particularly if the components have been additionally pretreated with a zinc surface, it is preferred that the conversion solution (II) contains not more than 500 μmol / kg, particularly preferably not more than 300 μmol / kg, very particularly preferably not more than 200 μmol / kg of copper ions dissolved in water. Suitable sources of copper ions dissolved in water are water-soluble salts such as copper nitrate (Cu(NO3)2), copper sulfate (CuSO4) and copper acetate (Cu(CH3COO)2).

[0035] Implementation of the method and substrates: For the implementation of the method according to the invention, it has been found to be advantageous, firstly for the removal of soluble residues from the first conversion layer and finally for the passivating deposition of oxide / hydroxide compounds of the elements Zr and / or Ti and the cementation of copper, to transfer the components from the "wet-in-wet" step to both the rinsing step and the second conversion step. According to the invention, for reasons of process economy, a method in which there is no drying step between steps (i) and (iii) is also preferred.

[0036] The anticorrosive pretreatment of the method of the invention relates to the implementation of the method for providing an amorphous conversion coating based on oxide / hydroxide compounds of the elements Zr and / or Ti, which provides an excellent paint adhesion primer for the subsequently applied paint system. It is therefore preferred according to the invention that after step (iii) with an intermediate rinsing step, but preferably without an intermediate drying step, the coating of the component is carried out using a paint system, preferably electrocoating, particularly preferably cathodic electrocoating.

[0037] In this context, the rinsing step is used exclusively to completely or partially remove from the component to be coated soluble residues, particles and active ingredients carried over from the previous wet chemical step (iii) adhering to the component, the metallic or semi-metallic active ingredients being already consumed by the contact of the metallic surface of the component with the rinsing liquid and not contained in the rinsing liquid itself. The rinsing liquid may therefore simply be municipal water or deionized water or, if necessary, a rinsing liquid containing a surface-active compound to improve the wetting with the rinsing liquid. The surface-active compound is preferably a non-ionic surfactant selected from alkoxylated alkyl alcohols and / or alkoxylated fatty amines, especially in the case of a subsequent electrocoating to improve the coverage. It is ethoxylated and / or propoxylated, the number of alkylene oxide units being preferably not more than 20, more preferably not more than 16, but more preferably at least 4, particularly preferably at least 8, the alkyl groups preferably having at least 10 carbon atoms, more preferably at least 12 carbon atoms, and having the following formula: HLB = 20·(1-M l / M) [In the formula, M l is the molar mass of the lipophilic group of the nonionic surfactant, and M is the molar mass of the nonionic surfactant. The HLD value calculated by the above is realized in the range of 12 to 16.

[0038] The drying step according to the invention is the drying of the components brought about by controllable technical precautions, for example by the supply of heat or the supply of directed air.

[0039] The contact of the steel and / or iron components or surfaces with the aqueous solutions (I)-(III) of steps (i)-(iii) is not optional for the success of the method of the invention, traditional methods such as, for example, immersion, spraying and jetting being preferred. The same applies to the contact times in each treatment step, which in each case are preferably in the range of 10-300 seconds. The temperatures of the conversion solutions (I)-(III) at the time of contact are preferably in the range of 10-60°C, particularly preferably 25-55°C, very particularly preferably 30-50°C.

[0040] With regard to components, it has been found that the method of the invention is very suitable for the corrosion protection pretreatment of a series of components made of different metal materials. The series of components preferably have a zinc and / or aluminum surface in addition to a steel and / or iron surface. Suitable metal materials whose surfaces can be subjected to corrosion protection in the method of the invention can be, in addition to steel and iron, zinc, electrolytic (ZE), hot-dip galvanized (Z), alloy galvanized (ZA), (ZF) and (ZM) and (ZM), aluminized (AZ), (AS) rolled steel, as well as the light metals aluminium, magnesium and their alloys. EXAMPLES

[0041] Working Example The advantages of the method sequence according to the invention are explained below on the basis of the anticorrosive pretreatment and cathodic electrocoating of individual steel sheets (CRS).

[0042] Alkaline degreasing at 55° C. for 90 seconds by spray application using a composition (pH 10.5) consisting of the following process chemicals from I. Henkel AG & KGaA: 20g / L Bonderite® C-AK 2011 1g / L Bonderite® C-AD 1270 II. Alkaline cleaning by immersion application at 55° C. for 120 seconds using a composition (pH 11.0) consisting of the following process chemicals from Henkel AG & KGaA: 20g / L Bonderite® C-AK 2011 1g / L Bonderite® C-AD 1270 III. Deionized water (κ<1μScm) by immersion application -1 ) Rinse with IV. A first conversion step at 35° C. for 120 seconds by dip coating with a composition (pH 4.0) made from the following process chemicals from Henkel AG & KGaA: Variant (A) containing 6 g / L of Bonderite® M-NT 1800 gives: 30 mg / kg Zr 4mg / kg copper 34mg / kg free fluoride Variant (B) containing 16.6 g / L Bonderite® M-AD 110, 15 g / L Bonderite® M-NT 12001 MU gives: 150mg / kg Zr 4mg / kg copper 33mg / kg free fluoride V. Deionized water by immersion application (κ<1μScm -1 ) Rinse with

[0043] VI. A second conversion step by dip coating at 35° C. for 30 seconds using a nitric acid composition (pH 4.0) from Henkel AG & KGaA consisting of the following process chemicals: Variant (A) containing 6 g / L of Bonderite® M-NT 1800 gives: 30 mg / kg Zr 4mg / kg copper 27mg / kg free fluoride Variant (B) containing 30.0 g / L of Bonderite® M-NT 1800 gives: 150mg / kg Zr 4mg / kg copper 29mg / kg free fluoride Variant (C) containing 2.5 g / L of Bonderite® M-PT 54 NC gives: 150mg / kg Zr 17mg / kg free fluoride VII. Deionized water (κ<1μScm) for immersion applications -1 ) Rinse with VIII. Drying with Compressed Air IX. Dry film thickness ??g / m 2 Cathodic dip coating with CathoGuard® 800 (BASF Coatings AG) at

[0044] The percentage of free fluoride was adjusted with aqueous ammonium bifluoride solution, and the pH was adjusted with ammonium bicarbonate.

[0045] The pretreated, electrocoated sheets were then aged for 6 weeks for 30 cycles according to the VW PV 1210 Alternating Climate Test and the scribe release after aging was measured.

[0046] The results show that the method according to the invention results in a significant improvement in corrosion protection compared to the two-stage conversion process without an intermediate rinsing step (Table 1: V3 vs. E1). The presence of copper ions in the second conversion step is also important for sufficient corrosion protection (Table 1: V4 vs. E2). Also, the 10 mg / m 2 concentration of Zr in the second conversion step 2 An increase in layer weight less than or the content of compounds of elemental Zr in the second conversion step dissolved in water has proven to be favorable for preventing corrosive delamination after electrodeposition (Table 1: E3 vs. E4 and E1 vs. E2).

[0047] TIFF2024524451000002.tif101157

Claims

1. 1. A method for corrosion protection pre-treating a plurality of series members, the series members being at least partially formed of iron and / or steel, the method comprising the steps of: (i) a first conversion step of providing an aqueous conversion solution (I) having a pH in the range of 2.5 to 5.0 and comprising compounds of elemental Zr and / or Ti dissolved in water at a concentration of at least 0.10 mmol / kg and free fluoride; (ii) a rinsing step of providing an aqueous rinsing solution (II) having a pH in the range of 5.0 to 10.0, a concentration of compounds of elemental Zr and / or Ti dissolved in the water that is at least 5 times lower than that of the aqueous conversion solution (I), and a free fluoride content of less than 0.25 mmol / kg; (iii) a second conversion step providing an aqueous conversion solution (III) having a pH in the range of 2.5 to 5.0 and comprising at least 0.10 mmol / kg of compounds of elemental Zr and / or Ti dissolved in water and at least 15 μmol / kg of copper ions dissolved in water; and sequentially contacting at least the surface of the iron and / or steel of the component with each of the aqueous solutions (I) to (III).

2. The contact with the aqueous conversion solution (I) in the first conversion step of step (i) is carried out in such a way that the surface of the steel and / or iron is in a concentration of at least 20 mg / m based on the elements Zr and / or Ti in each case. ２ The time for forming a coating of at least 150 mg / m ２ More than 100 mg / m ２ More than, very particularly preferably, 80 mg / m ２ 2. The method of claim 1, wherein the method is not carried out for a time so long as to obtain a coating of greater than 100%.

3. The contact with the aqueous conversion solution (III) in the second conversion step of step (iii) is carried out in such a way that the surface of the steel and / or iron is in a concentration of 15 mg / m based on the elements Zr and / or Ti in each case. ２ More than 12 mg / m ２ More than, very particularly preferably, 10 mg / m ２ Preferably, the coating on at least these surfaces is at least 2 mg / m², but not until an increase of more than 2 mg / m² occurs. ２ 3. The method of claim 2, wherein the increasing time continues.

4. 4. The method according to any one of claims 1 to 3, characterized in that in the aqueous conversion solution (I) of the first conversion step of step (i), the proportion of compounds of elemental Zr and / or Ti dissolved in water is at least 0.15 mmol / kg, preferably 0.25 mmol / kg, more preferably at least 0.30 mmol / kg.

5. 4. The method according to claim 1, wherein the proportion of free fluoride in the aqueous conversion solution (I) of the first conversion step of step (i) is at least 0.5 mmol / kg, preferably at least 1.0 mmol / kg, very particularly preferably at least 1.5 mmol / kg, but preferably less than 8.0 mmol / kg, particularly preferably less than 6.0 mmol / kg, very particularly preferably less than 5.0 mmol / kg.

6. In the conversion aqueous solution (I) of the first conversion step of step (i), a compound represented by the formula (1): where F / mM and Me / mM are the free fluoride (F) or reduced zirconium and / or titanium (Me) concentrations subtracted in mmol / kg. The method according to any one of claims 1 to 3, characterized in that the quotient λ according to is greater than 0.80, preferably greater than 1.20, particularly preferably greater than 1.

60.

7. 4. The method according to claim 1, wherein in the aqueous conversion solution (III) of the second conversion step of step (iii), the proportion of compounds of the elements Zr and / or Ti dissolved in water is less than 1.00 mmol / kg, preferably less than 0.80 mmol / kg, more preferably less than 0.70 mmol / kg, particularly preferably less than 0.60 mmol / kg.

8. 4. The method according to claim 1, wherein in the aqueous conversion solution (III) of the second conversion step of step (iii), the proportion of free fluoride is less than 3.00 mmol / kg, preferably less than 2.50 mmol / kg, particularly preferably less than 2.00 mmol / kg, but preferably at least 0.1 mmol / kg, particularly preferably at least 0.2 mmol / kg.

9. 4. The method according to claim 1 , wherein the aqueous conversion solution (III) of the second conversion step of step (iii) contains more than 40 μmol / kg, preferably more than 50 μmol / kg, but preferably not more than 500 μmol / kg, particularly preferably not more than 300 μmol / kg, very particularly preferably not more than 200 μmol / kg of copper ions dissolved in water.

10. 4. The method according to any of claims 1 to 3, characterized in that in the conversion steps (i) and (iii) the compounds of element Zr and / or Ti dissolved in water are selected from fluorocomplexes of element Zr and / or Ti, preferably fluorocomplexes of element Zr.

11. 4. The method according to claim 1, wherein the aqueous rinsing solution (ii) of the rinsing step in step (ii) further comprises a depolarizer in a concentration of at least 0.1 mmol / kg, preferably at least 0.5 mmol / kg, particularly preferably at least 1 mmol / kg, but preferably not more than 10 mmol / kg, particularly preferably not more than 6 mmol / kg, selected from nitrate ions, nitrite ions, nitroguanidine, N-methylmorpholine N-oxide, hydrogen peroxide in free or bound form, hydroxylamine in free or bound form, and reducing sugars, preferably selected from nitrite ions, nitroguanidine, hydroxylamine in free or bound form, and hydrogen peroxide in free or bound form, particularly preferably selected from nitrite ions.

12. 4. The method according to claim 1, wherein the aqueous conversion solutions of the conversion steps in steps (i) and (iii) each have a pH of above 3.0, preferably above 3.5, particularly preferably above 4.0, but preferably below 4.

5.

13. 4. The method according to claim 1, wherein in the rinsing step of step (ii), the contacting with the supplied rinsing solution is carried out by immersion and / or spraying, preferably by immersion and spraying, with immersion being carried out first and then spraying.

14. 4. The method according to claim 1, wherein after step (iii) with an intermediate rinsing step but preferably without an intermediate drying step, the coating of the component is carried out using a coating system, preferably electrocoating, particularly preferably cathodic electrocoating.

15. 4. The method according to claim 1, wherein the elements in series have, in addition to steel and / or iron surfaces, also zinc and / or aluminum surfaces.

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