Alkaline composition and method for cleaning zinc-magnesium surfaces

Abstract

The present invention relates to a method for cleaning a surface of a substrate using an aqueous alkaline composition having a pH value of less than 10.0, which composition comprises, in addition to water, hydroxide anions a1), at least one complexing agent a2), at least one surfactant a3), and optionally at least one of condensed phosphate and borate anions a4), the surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy.The present invention also relates to a method for cleaning the surface using the aqueous alkaline composition, a substrate having at least one cleaned surface obtainable therefrom, a method for chemically pretreating the cleaned substrate surface by further using an aqueous coating composition suitable for forming, preferably, a conversion coating on the surface, and a substrate having at least one chemically pretreated surface obtainable therefrom.

Description

[Technical Field]

[0001] The present invention relates to a method for using an aqueous alkaline composition for cleaning a surface of a substrate, wherein the surface is at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy. The present invention also relates to a method for cleaning the surface, a substrate having at least one cleaned surface obtainable therefrom, a method for chemically pretreating the cleaned substrate surface by further using an aqueous coating composition suitable for forming a conversion coating on the surface, and a substrate having at least one chemically pretreated surface obtainable therefrom. [Background technology]

[0002] In the automotive OEM industry, manufactured car bodies or their components are typically cleaned with alkaline cleaning compositions to remove surface impurities that may physically or chemically deposit substrate residues, such as oils, lubricants, particles, oxidation products, etc., on the metal surface prior to subsequent coating processes (i.e., application of conversion coatings, electro-deposited coatings, and additional coatings), because such impurities often cause defects in the subsequent chemical pretreatment and additional coating layers.

[0003] Currently, the automotive industry typically uses alkaline cleaners containing various complexing agents, such as alkalinity sources, phosphonic acids, and (poly)phosphates or borates. These cleaners are typically operated in a relatively high pH range of 10-11, because this range typically offers the best compromise between sufficient cleaning performance to achieve the desired overall removal of residual oils, lubricants, particles, oxidation products, etc., and gentle treatment of the often multi-metallic car body or its components, achieving only a low etching rate of these metal substrates.

[0004] Conventional cleaning solutions, particularly those operating at pH values ​​in the range of 10 to 11 or higher, are described in EP 0 536 823 A1 A, EP 0 541 034 A2, and WO 2009 / 050035 A1. EP 0 536 823 A1 A discloses a method for cleaning metal surfaces, comprising preparing a cleaning solution containing sodium silicate and / or potassium silicate and a surfactant, treating the metal surface with the solution, subjecting the solution to ultrafiltration through an ultrafiltration membrane to regenerate the solution, and recycling the permeate of the solution after ultrafiltration. The cleaning solution is disclosed therein to have a pH value of <12.0. In the examples of EP 0 536 823 A1 A, a number of cleaning solutions are individualized, each having a pH value of approximately 11.5. EP 0 541 034 A2 discloses a method for degreasing metals, which comprises contacting the metal to be treated with a phosphate-free degreasing solution, the degreasing solution containing an alkali silicate, a water-soluble polycarboxylate, and a nonionic surfactant, and first meeting certain conditions, including a pH in the range of 10.5 to 12.5, and then controlling the degreasing solution by adding a specific agent to the degreasing solution. The use of silicates in cleaning solutions is often disadvantageous because they can cause dry marks on the cleaned parts and deposits in the tanks and nozzles of cleaning machines. Furthermore, when a cleaning solution containing silicates is used for pre-cleaning, it is often observed that the coating weight of a subsequently applied chemical conversion coating is undesirably low. WO 2009 / 050035 A1 relates to an aqueous alkaline cleaning composition for cleaning metal surfaces, which contains at least one nonionic surfactant based on a specific ethoxylated alkyl alcohol, which surfactant acts in a demulsifying manner.

[0005] Metal substrates traditionally used in the automotive industry are often composed of cold-rolled steel (CRS), various forms of galvanized steel (e.g., hot-dip galvanized steel (HDG) or electrogalvanized steel (EG)), aluminum, and / or various alloys of these materials. In recent years, zinc-magnesium (ZM) substrates have gained popularity and are considered a new type of metal substrate for use in the automotive industry. ZM is a steel product coated with a zinc-aluminum-magnesium alloy, which offers improved corrosion performance compared to other types of steel, such as HDG, as disclosed, for example, in S. Schuerz et al., Corrosion Science 2010, 52, 3271-3279. However, zinc-magnesium is a relatively difficult substrate to treat. In the automotive industry, the use of standard mild alkaline cleaners in the relatively high pH range of 10-11, as described above, often results in problems with either the cleaning process (e.g., insufficient surface wetting after cleaning) and / or paint adhesion / corrosion performance after applying standard coatings / paints. These problems are particularly true when conversion coating compositions, such as those based on zirconium cations, fluorides, and silanes, are used as chemical pretreatments (after cleaning has been performed) to form a conversion coating layer on the surface of a substrate.

[0006] Therefore, there is a need to provide a method for effectively cleaning substrates made from ZM, or at least substrates having a surface composed of ZM, which method does not result in the drawbacks observed when using conventional cleaning compositions known in the prior art, especially those having a relatively high pH value above 10.0. In particular, there is a need to provide such a method which does not adversely affect the corrosion resistance of these substrates, and in particular shows improved corrosion resistance, and does not result in poor adhesion properties after subsequent application of further coatings, in particular conversion coatings, on the cleaned surface, and wherein the resulting cleaned ZM surface should have excellent wettability even after cleaning. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] EP 0 536 823 A1 A [Patent Document 2] EP 0 541 034 A2 [Patent Document 3] WO 2009 / 050035 A1 [Non-patent literature]

[0008] [Non-Patent Document 1] S. Schuerz et al., Corrosion Science 2010, 52, 3271-3279 Summary of the Invention [Problem to be solved by the invention]

[0009] The object underlying the present invention is therefore to provide a method for effectively cleaning substrates made from ZM, or at least substrates having a surface composed of ZM, which method does not result in the drawbacks observed when using conventional cleaning compositions known in the prior art, in particular cleaning compositions having a relatively high pH value above 10.0. In particular, the object underlying the present invention is to provide such a method which does not adversely affect the corrosion resistance of these substrates, in particular exhibiting improved corrosion resistance, and which does not result in poor adhesion properties after subsequent application of further coatings, in particular conversion coatings, on the cleaned surface, wherein the resulting cleaned ZM surface should also have excellent wettability after cleaning. [Means for solving the problem]

[0010] This object has been solved by the subject matter of the present claims and the preferred embodiments thereof disclosed herein, ie the subject matter described herein.

[0011] A first subject of the present invention is the use of an aqueous alkaline composition having a pH value of less than 10.0 for cleaning the surface of a substrate, wherein the composition contains, in addition to water, at least components a1) to a4), which are different from one another, namely as component a1) at least one alkalinity-inducing source, as at least one component a2) at least one complexing agent, as at least one component a3), at least one surfactant, and As at least one component a4), at least one of an optionally condensed phosphate anion and a borate anion wherein said surface is at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy.

[0012] A further subject of the present invention is a method for cleaning at least one surface of at least one substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy, the method comprising at least step 1) and optionally step 2), namely 1) at least partially contacting at least one surface of at least one substrate with an aqueous alkaline composition used in the present invention, as defined herein and hereinafter, having a pH value of less than 10.0 for cleaning the substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy; and 2) optionally rinsing the cleaned surface obtained after step 1) with water Includes.

[0013] A further subject of the present invention is a substrate having at least one cleaned surface, said substrate being obtainable by the cleaning method of the invention as defined herein and below.

[0014] A further subject of the present invention is a method for the chemical pretreatment of at least one cleaned surface of at least one substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy, the cleaning being carried out in accordance with the inventive cleaning method as defined herein and below, the method for chemical pretreatment comprising at least step 3) and optionally step 4), i.e. 3) contacting at least one cleaned surface of at least one substrate with an aqueous, preferably acidic, coating composition suitable for forming a coating film, in particular a conversion coating film, at least partially on said surface, wherein the aqueous coating composition is different from the aqueous alkaline composition used in the present invention as defined herein and below, 4) optionally curing or drying the coating film obtained after step 3) to obtain a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness of less than 0.5 μm. Includes.

[0015] A further subject of the present invention is a substrate comprising at least one surface, wherein said at least one surface has been pretreated according to the chemical pretreatment method of the present invention.

[0016] It has been particularly surprising to find that the aqueous alkaline cleaning compositions used in the present invention, having a pH value of less than 10.0, lead to improved corrosion resistance of substrates made from ZM or substrates having at least a surface made from ZM, especially when used in combination with thin film technology, i.e., when at least a conversion coating is applied over the cleaned substrate surface, such as a conversion coating formed using an acidic aqueous composition comprising zirconium and / or titanium cations, fluoride anions, and optionally at least one organosilane. In this regard, it has been found that poor corrosion resistance is only observed when non-inventive aqueous alkaline cleaning compositions having a pH value greater than 10.0 are used instead.

[0017] Furthermore, it has been unexpectedly found that the use of aqueous alkaline cleaning compositions having a pH value of less than 10.0 to clean substrates made from ZM or substrates having at least a surface made from ZM provides highly efficient removal of Mg from the exterior surface of zinc-magnesium alloys, as demonstrated by X-ray photoelectron spectroscopy (XPS) measurements, while simultaneously providing excellent cleaning performance, particularly when spray times of more than 20 seconds, e.g., more than 40 seconds or more than 60 seconds, are used. In this regard, it has been found that the efficiency of Mg removal from the exterior surface is significantly reduced, particularly when non-inventive aqueous alkaline cleaning compositions having a pH value greater than 10.0 are used instead. In this context, it has been found that efficient removal of Mg from the exterior surface directly correlates with the corrosion performance of zinc-magnesium substrates after complete paint buildup, particularly when using acidic aqueous conversion coating compositions comprising zirconium and / or titanium cations, fluoride anions, and optionally at least one organosilane.

[0018] Furthermore, it has been found that the aqueous alkaline cleaning compositions used in the present invention having a pH value of less than 10.0 provide excellent adhesion between the surface of the cleaned substrate and a conversion coating applied thereover, particularly a conversion coating formed using an acidic aqueous composition comprising zirconium and / or titanium cations, fluoride anions, and, optionally, at least one organosilane.

[0019] Furthermore, the resulting cleaned surfaces of the substrates used were found to exhibit excellent wettability after cleaning. DETAILED DESCRIPTION OF THE INVENTION

[0020] The term "comprises" in the sense of the present invention preferably means "consisting of", for example, in relation to the aqueous alkaline cleaning composition used in the present invention, which has a pH value of less than 10.0, or in relation to the aqueous composition being suitable for at least partially forming a coating film on the surface.For example, in relation to both of these compositions described herein above, in addition to all essential components present therein, it is also possible for one or more of the further optional components specified below to be included therein.All components may in each case be present in their preferred embodiments, as specified below.

[0021] The percentages and amounts by weight (wt%) of any of the components shown below present in each composition are in each case based on the total weight of each composition and add up to 100 wt%.

[0022] How to use for cleaning A first subject of the present invention is the use of an aqueous alkaline composition for cleaning the surface of a substrate, wherein said surface is at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy.

[0023] Base material The substrate has at least one surface made at least partially from at least one steel, and the steel is at least partially coated with at least one zinc-aluminum-magnesium alloy (ZM). Thus, the surface is made at least partially from steel, and the steel at least partially comprises a layer containing, or preferably made from, at least one zinc-aluminum-magnesium alloy. Thus, the substrate has at least one metallic surface. Preferably, not only is at least one surface of the substrate metallic, but the entire substrate is metallic. ZM is known to those skilled in the art, as described, for example, in S. Schuerz et al., Corrosion Science 2010, 52, 3271-3279. ZM substrates and substrates having at least one surface made at least partially from ZM are commercially available. Preferably, the layer comprising or preferably made of at least one zinc-aluminium-magnesium alloy contains >80.0% by weight of zinc, <15.0% by weight of Al, and <5.0% by weight of Mg, in each case calculated as metal, based on the total weight of the layer. The sum of all elements present in the alloy layer is 100% by weight. Preferably, the weight of the alloy layer of at least one zinc-aluminium-magnesium alloy present on the steel surface is <800 g / m 2 , preferably <500 g / m 2 is.

[0024] Preferably, the substrate used is a conductive substrate that is commonly used and known to those skilled in the art. The substrate can have any geometric shape and form, such as a coil or a sheet, and can be an automobile part, including an automobile part such as a wheel part and other workpieces. A particularly suitable substrate is a part of an automobile body or a complete automobile body for production.

[0025] Aqueous alkaline compositions The aqueous alkaline composition has a pH value of less than 10.0 and comprises, in addition to water, at least one alkalinity-inducing source as component a1), at least one complexing agent as component a2), at least one surfactant as component a3), and at least one optionally condensed phosphate anion and / or borate anion as component a4). Components a1) to a4) are different from one another. The aqueous alkaline composition can be prepared from a concentrate containing at least components a1) to a4) by diluting the concentrate with water.

[0026] Preferably, the aqueous alkaline composition has a pH value in the range of >7.5 to <10.0 or ≦9.9, more preferably >8.0 to <10.0 or ≦9.9, even more preferably >8.5 to <10.0 or ≦9.9, even more preferably >9.0 to <10.0 or ≦9.9, even more preferably >9.2 to <10.0 or ≦9.9, even more preferably >9.4 or ≧9.5 to <10.0 or ≦9.9 or ≦9.8. Preferably, the pH value is measured at 55°C. The pH value can be adjusted in particular with component a1), in particular sodium hydroxide and / or potassium hydroxide and / or carbonates, for alkalinity adjustment, or, if acidity adjustment is required, with at least one inorganic acid, in particular phosphoric acid and / or boric acid.

[0027] The term "aqueous" in relation to the aqueous composition used in step 1) in the sense of the present invention preferably means that the composition contains at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, and most preferably at least 90% by weight of water, based on the total content of organic solvents and inorganic solvents, including water.Thus, the aqueous composition may contain at least one organic solvent other than water, but in an amount less than the amount of water present.Preferably, the aqueous composition contains at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, and most preferably at least 90% by weight of water, based on its total weight in each case.

[0028] Preferably, the aqueous alkaline composition has a temperature in the range of 40 to 70°C, preferably 45 to 60°C, more preferably 50 to 55°C.

[0029] The total amount of all components (constituents) present in the aqueous alkaline composition used in step 1) totals 100% by weight. The aqueous alkaline composition may be a dispersion or a solution. Preferably, it is a solution.

[0030] Preferably, the aqueous alkaline composition is free of or essentially free of silicates. "Essentially free" in this context means that at least no silicates are intentionally added, although residual silicates may be present as impurities. Preferably, the amount of silicates present in the aqueous alkaline composition does not exceed 100 ppm calculated as SiO. Thus, preferably, the aqueous alkaline composition contains a maximum amount of silicates of <100 ppm calculated as SiO.

[0031] Component a1) As component a1), at least one alkalinity-inducing source (alkalinity source) is present. Any type of alkalinity-inducing source, in particular anion source, can be used. Preferably, at least one hydroxide anion and / or carbonate anion source, preferably a metal salt, such as sodium hydroxide and / or potassium hydroxide and / or carbonate, in particular potassium hydroxide and / or carbonate, is used to prepare the aqueous alkaline composition. Thus, the aqueous alkaline composition preferably comprises hydroxide and / or carbonate anions as component a1). Most preferred as component a1) is a carbonate, preferably a carbonate derived from potassium carbonate.

[0032] Preferably, the aqueous alkaline composition comprises at least one alkalinity-inducing source present as component a1) in an amount such that the required alkalinity and the required pH value of less than 10.0 are met. More preferably, the aqueous alkaline composition comprises at least one alkalinity-inducing source present as component a1) in an amount of 0.2 to 20 g / L, even more preferably 1.0 to 10 g / L, and even more preferably 3 to 8 g / L. As described hereinabove, the aqueous alkaline composition can be prepared from a concentrate by diluting the concentrate with water. Preferably, the concentrate comprises at least one alkalinity-inducing source present as component a1) in the composition in an amount of 5 to 300 g / L, more preferably 10 to 200 g / L, and even more preferably 20 to 100 g / L.

[0033] Component a2) At least one complexing agent is present as at least one component a2). Suitable complexing agents are known to those skilled in the art.

[0034] Preferably, the at least one complexing agent present as at least one component a2) is selected from (i) carboxylic acids, their salts, derivatives, in particular esters, and mixtures thereof (wherein the carboxylic acids in each case include polymeric carboxylic acids), (ii) sulfamic acid, (iii) derivatives of phosphonic acid, such as phosphonic acid, phosphonates, and esters thereof, (iv) polyols, in particular having two or more OH groups (wherein the polyols include polymeric polyols), and (v) polyethyleneimine, and mixtures of (i) to (v). More preferably, the at least one complexing agent present as at least one component a2) is selected from (i) carboxylic acids, their salts, derivatives, in particular esters, and mixtures thereof (wherein the carboxylic acids in each case include polymeric carboxylic acids), (iii) derivatives of phosphonic acid, such as phosphonic acid, phosphonates, and esters thereof, and mixtures thereof. Even more preferably, the at least one complexing agent present as at least one component a2) is selected from (i) carboxylic acids, their salts, derivatives thereof, in particular esters, and mixtures thereof, where the carboxylic acid in each case comprises a polymeric carboxylic acid. Exemplary suitable complexing agents include HEDP (1-hydroxyethylidene-1,1-diphosphonic acid), EDTMP (ethylenediaminetetra(methylenephosphonic acid)), MGDA-Na3 (methylglycinediacetic acid trisodium salt), DTPA-Na5 (diethylenetriaminepentaacetic acid pentasodium salt), PBTC-Na4 (2-phosphonobutane-1,2,4-tricarboxylic acid tetrasodium salt), polyethyleneimine, amidosulfonic acid, and mixtures thereof.

[0035] Preferably, the aqueous alkaline composition comprises at least one complexing agent present as at least one component a2) in an amount of 0.2 to 10 g / L, more preferably 0.2 or 0.5 to 5 g / L, even more preferably 0.5 to 3 g / L.

[0036] Component a3) As at least one component a3) at least one surfactant is present.

[0037] The term surfactant (surface-active agent) as used herein is preferably used in accordance with the Römpp Lexikon "Lacke und Druckfarben" (Publisher: Ulrich Zorll, Editor: Hans-Juergen P. Adler-Stuttgart; New York: Thieme, 1998; term: "tenside" pages 557 and 558). Surfactants have a demulsifying effect.

[0038] Suitable surfactants are known to those skilled in the art and are disclosed, for example, in WO 2020 / 200838 A1.

[0039] Preferably, the at least one surfactant is selected from non-ionic surfactants, anionic surfactants and / or cationic surfactants, most preferably from non-ionic surfactants.

[0040] Suitable nonionic surfactants include, in particular, C6 to C 14 and alkylphenol alkoxylates, in particular alkylphenol ethoxylates, having an alkyl chain of C8-C6 and a degree of alkoxylation of 5 to 30 moles per mole of phenol. 22 , preferably C 10 ~C 18 and containing 1 to 20, preferably 1 to 5, glucosidic units, fatty acid amide alkoxylates, fatty acid alkanolamide alkoxylates, N-alkyl glucamides, or else block copolymers of ethylene oxide, propylene oxide and / or butylene oxide, and alkoxylated C8-C 22Alcohols, such as fatty alcohol alkoxylates, oxo-treated alcohol alkoxylates, and gelbet alcohol alkoxylates, may be alkoxylated with ethylene oxide, propylene oxide, butylene oxide, and / or mixtures thereof, as block or random copolymers. The alcohols preferably have 8 to 18 carbon atoms; the degree of alkoxylation is generally in the range of 2 to 50 moles, preferably 3 to 20 moles, of at least one of the alkylene oxides listed per mole of alcohol. The alkylene oxide head group may further comprise the following so-called end-capping groups as modifications: benzyl, methyl, and / or tert-butyl capping.

[0041] Depending on the application, the following anionic surfactants in particular can be used: fatty alcohol sulfates with an alkyl chain length of 8 to 22, preferably 10 to 18, carbon atoms, such as lauryl sulfate, cetyl sulfate, myristyl sulfate, palmityl sulfate or stearyl sulfate, alkyl ether sulfates with an alkyl chain length of 8 to 22, preferably 10 to 18, carbon atoms, and linear C8-C 20 Alkylbenzene sulfonates or other alkane sulfonates and soaps, e.g., C8-C 24 Sodium or potassium salts of carboxylic acids.

[0042] Cationic surfactants that can be used depending on the application include, in particular, quaternary mono- and di-(C7-C 25 Alkyl)dimethylammonium compounds, ester quaternary compounds, especially C8-C 22 Quaternary esterified mono-, di- and trialkanolamines, C7-C, esterified with carboxylic acids 25 Alkylamine, N,N-dimethyl-N-(hydroxy-C7-C 25 alkyl)ammonium salts and / or imidazoline quats.

[0043] However, as outlined above, the at least one surfactant is preferably at least one nonionic surfactant. For most applications, anionic surfactants have too high a foaming tendency, and cationic surfactants often adhere to the metal surface, which can result in problems with the deposition of subsequently applied conversion coatings.

[0044] Preferably, the aqueous alkaline composition comprises at least one surfactant as at least one component a3) in an amount of 0.3 to 10.0 g / L, more preferably 0.4 to 5.0 g / L, even more preferably 0.5 to 3.5 g / L.

[0045] Component a4) At least one of optionally condensed phosphate anions and borate anions is present as at least one component a4). When phosphate anions are present, they can be in condensed form, such as in the case of pyrophosphate (diphosphate), and / or in non-condensed form. In other words, a mixture of both forms can also be present. The term "phosphate" also includes polyphosphates, such as tripolyphosphate. Those skilled in the art will understand that the term "phosphate anions and / or borate anions" specifically refers to such phosphate anions and / or borate anions, i.e., inorganic anions themselves. These anions can be generated from suitable inorganic phosphate anion and / or borate anion-generating precursors, such as sodium phosphate and / or potassium phosphate and / or sodium borate and / or potassium borate. In particular, it will be apparent to those skilled in the art that the term "phosphate and / or borate anions" does not include organic phosphates and / or borates in which at least one phosphate and / or borate group is covalently bonded to an organic moiety, such as, for example, organic phosphate polyetheresters.

[0046] Preferably, at least optionally condensed phosphate anions are present as component a4), preferably both condensed phosphate anions (e.g. diphosphate anions) and non-condensed phosphate anions are present as component a4), and preferably the aqueous alkaline composition is free or essentially free of borate.

[0047] Preferably, the aqueous alkaline composition comprises as at least one component a4) at least one of optionally condensed phosphate anions and borate anions, more preferably at least optionally condensed phosphate anions, even more preferably both condensed and non-condensed phosphate anions, calculated as P2O5, in an amount of 0.5 g / L to 10 g / L, more preferably 1.0 to 8 g / L.

[0048] Optional components The aqueous alkaline composition may contain, in addition to components a1) to a4), an optional further component, which is similarly different from any of components a1) to a4).

[0049] Preferably, the aqueous alkaline composition comprises at least one hydrotope as optional component a5), which is used as a co-additive to maintain at least one surfactant a3) in solution within the composition. An example of a suitable hydrotope is an alkali metal salt of a carboxylic acid, such as potassium octanoate. Preferably, when present, at least one optional component a5) is present in the composition in an amount of 0.2 to 6.0 g / L, more preferably 0.3 to 5.0 g / L, and even more preferably 0.5 to 4.0 g / L.

[0050] Preferably, the aqueous alkaline composition can be obtained from the concentrate by dilution with water, preferably deionized water, wherein the concentrate, i.e. before dilution, comprises in addition to water: at least one alkalinity-inducing source, preferably hydroxide anions and / or carbonate anions, in particular carbonate anions, which can be obtained by incorporating suitable metal salts, such as hydroxides and / or carbonates of sodium and / or potassium, in particular potassium carbonate, into the concentrate in an amount ranging from 5 to 7% by weight, based on the total weight of the concentrate, at least one complexing agent, preferably chosen from carboxylic acids, their salts, derivatives thereof, in particular esters, and mixtures thereof, wherein the carboxylic acids comprise polymeric carboxylic acids in an amount ranging from 1 to 5% by weight, in each case based on the total weight of the concentrate, at least one surfactant, preferably at least one nonionic surfactant, in an amount ranging from 1 to 6% by weight, based on the total weight of the concentrate, at least one source of both optionally condensed (e.g. pyrophosphate) phosphate anions, including optionally condensed phosphate anions and / or borate anions, preferably optionally condensed phosphate anions, including polyphosphate anions, more preferably polyphosphate anions, and non-condensed phosphate anions, in an amount of 5 to 25% by weight, preferably 10 to 22% by weight, even more preferably 14 to 20% by weight, in each case based on the total weight of the concentrate, said at least one source being preferably a metal phosphate, including metal polyphosphates and / or metal pyrophosphates, for example trisodium phosphate and / or tripotassium phosphate, in particular tripotassium phosphate, and / or tetrasodium pyrophosphate and / or tetrapotassium pyrophosphate, in particular tetrapotassium pyrophosphate, and / or sodium or potassium tripolyphosphate; , more preferably said at least one source is a metal polyphosphate and / or metal pyrophosphate such as tetrasodium pyrophosphate and / or tetrapotassium pyrophosphate, in particular tetrapotassium pyrophosphate, and / or sodium or potassium tripolyphosphate, in particular potassium tripolyphosphate, and if sources of both at least one non-condensed phosphate and at least one condensed phosphate are used, the at least one source of condensed phosphate anions is preferably in an amount ranging from 2.5 to 12.5% ​​by weight, preferably from 5 to 11% by weight, even more preferably from 7 to 10% by weight, based on the total weight of the concentrate, and the at least one source of non-condensed phosphate anions is preferably in an amount ranging from 2.5 to 12.5% ​​by weight, preferably from 5 to 11% by weight, even more preferably from 7 to 10% by weight, based on the total weight of the concentrate, and Optionally, at least one hydrotope as an auxiliary additive to maintain in solution the at least one surfactant, preferably at least one nonionic surfactant, in an amount ranging from 7 to 10% by weight based on the total weight of the concentrate.

[0051] Preferably, the aqueous alkaline composition can be obtained from a concentrate by dilution with water, preferably deionized water, and the concentrate is present in the diluted composition in an amount of 5 to 60 g / L, more preferably 15 to 40 g / L, even more preferably 20 to 30 g / L, based on the total weight of the composition (obtained after dilution of the concentrate).

[0052] Cleaning method A further subject of the present invention is a method for cleaning at least one surface of at least one substrate, wherein said surface is made at least in part of at least one steel coated with at least one zinc-aluminum-magnesium alloy, the method comprising at least step 1) and optionally step 2). The method of the present invention may also comprise one or more further optional additional steps.

[0053] All preferred embodiments described herein above in relation to the method of use of the present invention and its preferred embodiments are also preferred embodiments of the cleaning method of the present invention.

[0054] The cleaning method including the cleaning step 1) preferably represents a part of the pretreatment. As used herein, the term "pretreatment" is preferably used in accordance with the term "surface pretreatment" defined in the Römpp Lexikon "Lacke und Druckfarben" (publisher: Ulrich Zorll, editor: Hans-Juergen P. Adler-Stuttgart; New York: Thieme, 1998; term: "Oberflaechenvorbehandlung" p. 417). On metal substrates or substrates with metal surfaces, including the relevant ZM substrates used according to the present invention, the first step(s) of the surface treatment, according to DIN 50902:1994-07, is often one or more cleaning step(s) with an aqueous or non-aqueous cleaning composition (also referred to as "surface treatment step(s)"). In the present case, said step(s) comprises the use of an aqueous alkaline cleaning composition.

[0055] In accordance with the above-mentioned internationally valid definition of "pretreatment" of a metal substrate, the pretreatment method according to the invention therefore preferably represents a surface preparation cleaning step and encompasses, for example, the chemical pretreatment step 3) and the cleaning step 1) of the method according to the invention, which differ from the chemical pretreatment method according to the invention described below.

[0056] Process 1) In step 1), at least one surface of at least one substrate, which surface is made of at least one steel coated at least in part with at least one zinc-aluminum-magnesium alloy, is contacted at least in part with the aqueous alkaline composition used in the present invention, which has a pH value of less than 10.0, to clean the substrate.

[0057] The term "at least partially" preferably means in this context, according to the general understanding of the term, that in some cases it may be desirable or sufficient to contact not the entire surface of the substrate with the cleaning composition. When only a portion of the surface is contacted with the composition, it is typically the same portion for all steps of the method. However, it is generally desirable to contact the entire surface of the substrate.

[0058] The "contacting" in step 1) can be a spraying, dipping, or roll-coating process, or any combination thereof. The aqueous alkaline composition can also be applied by dipping the surface or manually by wiping or brushing. Preferred are spraying, dipping, roll-coating, or any combination thereof, and most preferred is spraying.

[0059] The treatment time, i.e. the period during which the surface is in contact with the aqueous alkaline composition in step 1), is preferably 15 seconds to 20 minutes, more preferably 30 seconds to 10 minutes, most preferably 40 seconds to 5 minutes, for example 1 to 3 minutes.

[0060] Preferably, contacting step 1) is carried out by spraying the aqueous alkaline composition used in the present invention at least partially onto at least one surface of at least one substrate, more preferably for a period of >10 seconds or >20 seconds, more preferably for a period of >30 seconds or >40 seconds.

[0061] Optional step 2) Following optional step 2), the cleaned surface obtained after step 1) is rinsed with water. For rinsing, tap water or deionized water can be used, preferably deionized water.

[0062] Further optional steps Following step 1) and optionally step 2), one or more of the following optional steps may be carried out in this order: Step A-1): A step of subjecting the surface of the substrate to acidic or alkaline pickling, i.e., etching, and then rinsing the surface of the substrate; Step B-1): contacting the surface of the substrate with an aqueous composition comprising at least one mineral acid, the aqueous composition being different from the aqueous alkaline composition used in step 1) and the aqueous composition used in step 3); and Step C-1): A step of rinsing the surface of the substrate obtained after contact in step A-1) and / or B-1).

[0063] The optional step B-1) preferably serves to remove oxides, undesirable alloying elements, skins, brushing dust, etc. from the surface of the substrate, thereby further activating the surface for the subsequent conversion treatment in step 3). Preferably, the at least one mineral acid of the composition in step B-1) is sulfuric acid and / or nitric acid, more preferably sulfuric acid.

[0064] The rinsing step C-1) and the optional rinsing step 2) are preferably carried out using deionized water or tap water.

[0065] Substrate with a cleaned surface A further subject of the present invention is a substrate having at least one cleaned surface, said substrate being obtainable by the cleaning method of the invention as defined herein and below.

[0066] All preferred embodiments described herein above in relation to the inventive method of use and the inventive cleaning method, and in each case the preferred embodiments thereof, are also preferred embodiments of the inventive substrate having a cleaned surface.

[0067] Chemical Pretreatment Methods A further subject of the present invention is a method for chemical pretreatment of at least one cleaned surface of at least one substrate, wherein said surface is at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy, and wherein cleaning is carried out in accordance with the inventive cleaning method defined herein and below, the method for chemical pretreatment comprising at least step 3) and optionally also step 4). The inventive method may comprise one or more further optional additional steps.

[0068] All preferred embodiments, and in each case preferred embodiments thereof, described herein above in relation to the inventive method of use, the inventive cleaning method and the inventive substrate having a cleaned surface are also preferred embodiments of the inventive chemical pretreatment method.

[0069] The term "chemical pretreatment" is used in accordance with EN ISO 4618:2006 (E / F / D) (terminology: 2.41 "chemical pretreatment") to refer to a chemical treatment applied to a surface before applying a coating material. According to this standard, treatments such as chromate treatment, phosphate treatment, and oxalate treatment, which are included in the term "chemical conversion treatment," belong to chemical pretreatment and are therefore distinct from the (subsequent) coating step in which a coating material, i.e., a coating composition such as a powder coating composition, an electrodeposition coating composition, or an aqueous or non-aqueous liquid coating material, is applied. In addition to chemical conversion treatments such as chromate treatment, phosphate treatment, and oxalate treatment, chemical surface pretreatment can be achieved with common passivating and film-forming compositions, including aqueous compositions such as those required as chemical pretreatment compositions in step 3).

[0070] Process 3) In step 3), at least one cleaned surface of at least one substrate is at least partially contacted with an aqueous, preferably acidic, coating composition suitable for at least partially forming a coating film on said surface, wherein the aqueous coating composition is different from the aqueous alkaline composition used in the present invention. The aqueous composition used in step 3) represents a chemical pretreatment composition.

[0071] The term "at least partially" preferably means in this context, in accordance with the general understanding of said term, that in some cases it may be desirable or sufficient to contact less than the entire surface of the substrate with the chemical pretreatment composition. If only a portion of the surface is contacted with the composition, it is typically the same portion for all steps of the method. However, it is generally desirable to contact the entire surface of the substrate.

[0072] The "contacting" in step 3) can be a spraying, dipping, roll coating process, or any combination thereof. The aqueous composition can also be applied by dipping the surface or manually by wiping or brushing. Preferred are spraying, dipping, roll coating, or a combination thereof.

[0073] The treatment time, i.e., the period during which the surface is in contact with the aqueous composition in step 3), is preferably 15 seconds to 20 minutes, more preferably 30 seconds to 10 minutes, and most preferably 45 seconds to 5 minutes, for example 1 minute to 3 minutes. The temperature of the aqueous composition used in step 3) is preferably 5 to 50°C, more preferably 15 to 45°C, and most preferably 25 to 40°C.

[0074] Preferably, the coating film formed in step 3) is a conversion coating. Therefore, preferably, the aqueous coating composition is a conversion coating composition (or conversion treatment composition). Therefore, preferably, by carrying out step 3), a conversion coating is formed on the surface of the substrate that has come into contact with the aqueous composition. The term "conversion treatment composition" defines, in accordance with the common understanding of the term, a composition that, when applied to a base metal, produces a surface layer containing compounds of the base metal (often called a conversion coating) and anions of the environment (ISO 2080:2008(E / F), terminology: 2.3 "conversion treatment").

[0075] The term "aqueous" in relation to the aqueous composition used in step 3) in the sense of the present invention preferably means a composition containing at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, and most preferably at least 90% by weight of water, based on the total content of organic solvents and inorganic solvents, including water.Thus, the aqueous composition may contain at least one organic solvent other than water, but in an amount less than the amount of water present.Preferably, the aqueous composition contains at least 50% by weight, preferably at least 60% by weight, more preferably at least 70% by weight, particularly preferably at least 80% by weight, and most preferably at least 90% by weight of water, in each case based on its total weight.

[0076] Preferably, the aqueous composition used in step 3) is acidic. Preferably, the acidic aqueous composition has a pH value in the range of 0.5 to 6.5. Preferably, the pH value is measured at room temperature (23°C). The pH value of the acidic aqueous composition is more preferably in the range of 1.0 to 6.0, even more preferably in the range of 2.0 or 3.0 to 5.5. The pH can preferably be adjusted using nitric acid, aqueous ammonia and / or sodium carbonate, as needed.

[0077] The total amount of all components (constituents) present in the aqueous composition used in step 3) is 100% by mass. The aqueous composition may be a dispersion or a solution. Preferably, it is a solution.

[0078] Preferably, the aqueous composition used in step 3) of the chemical pretreatment method does not contain chromium ions, such as Cr(VI) and / or Cr(III) ions.

[0079] The aqueous composition used in step 3) may contain oxalate and / or phosphate anions, particularly if acidic.

[0080] Preferably, the aqueous composition contains fluoride anions in an amount ranging from 10 to 2000 mg / L, more preferably from 15 to 1500 mg / L, even more preferably from 20 to 1000 mg / L, even more preferably from 25 to 500 mg / L, in each case calculated as fluorine. As outlined below, complex fluorides, such as zirconium, titanium, and / or hafnium complexes formed with fluoride ions, are preferably present in the composition, e.g., by coordination of fluoride anions to zirconium, titanium, and / or hafnium cations in the presence of water. Alternatively, fluoride anions may be generated by adding other water-soluble fluoride compounds, such as fluorides (other than complex fluorides of Ti, Zr, and / or Hf) and hydrofluoric acid to the composition. Free fluoride content is determined using a fluoride ion-sensitive electrode according to the method disclosed in the "Methods" section.

[0081] Preferably, the aqueous composition contains at least one metal cation selected from the group consisting of titanium ions, zirconium ions, and hafnium ions, and mixtures thereof, more preferably titanium ions, zirconium ions, and mixtures thereof, and even more preferably zirconium ions. Preferably, the aqueous composition contains at least one metal cation selected from the group consisting of titanium ions, zirconium ions, and hafnium ions, and mixtures thereof, in an amount ranging from 5 to 2000 mg / L, more preferably from 7.5 to 1500 mg / L, even more preferably from 10 to 1000 mg / L, even more preferably from 15 to 500 mg / L, and even more preferably from 20 to 300 mg / L, in each case calculated as metal. Preferably, a precursor metal compound is used to generate the at least one metal cation. Preferably, the precursor metal compound is water-soluble. The solubility is determined at a temperature of 20°C and atmospheric pressure (1.013 bar). Particularly preferred zirconium, titanium, and / or hafnium compounds are complex fluorides of these metals. The term "complex fluorides" includes singly and multiply protonated forms, as well as deprotonated forms. It is also possible to use mixtures of such complex fluorides. Complex fluorides in the sense of the present invention are, for example, zirconium, titanium and / or hafnium complexes formed with fluoride ions in the composition by coordination of fluoride anions to zirconium, titanium and / or hafnium cations in the presence of water. The content of at least one metal cation can be monitored and determined by means of ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy), which is described below in the "Methods" section.

[0082] Preferably, the aqueous composition contains at least one organosilane, preferably in an amount of 5 to 1000 mg / L, more preferably 5 to 500 mg / L. Examples include (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane and / or (3-glycidyloxypropyl)triethoxysilane, and / or vinyltrimethoxysilane. Preferably, the at least one organosilane is present therein in a hydrolyzed form.

[0083] Preferably, the aqueous, preferably acidic coating composition used in step 3) comprises at least one metal ion selected from the group consisting of titanium ions, zirconium ions and hafnium ions, and mixtures thereof, fluoride anions, and optionally at least one organosilane.

[0084] Optionally, the aqueous composition may contain additional components, such as other metal cations (other than Zr, Ti, and / or Hf), such as Cu cations, and / or at least one water-soluble polymer, for example, a water-soluble polymer having at least one functional group selected from acid groups, hydroxyl groups, and mixtures thereof. The solubility is measured at a temperature of 20°C and atmospheric pressure (1.013 bar). Preferably, the at least one water-soluble polymer is a homopolymer or copolymer obtainable from the polymerization of at least one ethylenically unsaturated monomer, wherein at least a portion of the monomers has at least one functional group selected from acid groups, hydroxyl groups, and mixtures thereof, more preferably a homopolymer or copolymer obtainable from the polymerization of at least one vinyl monomer and / or (meth)acrylic monomer, wherein at least a portion of the monomers has at least one functional group selected from acid groups, hydroxyl groups, and mixtures thereof.

[0085] Preferably, the film obtained after step 3) is dried or cured, preferably the conversion layer formed after drying has a coating mass determined by XRF (X-ray fluorescence spectroscopy): 0.5 to 500 mg / m, calculated as metal. 2 , more preferably 1 to 400 mg / m 2 , and even more preferably 3 to 350 mg / m 2 , and even more preferably 5 to 300 mg / m 2 zirconium, titanium and / or hafnium ions, preferably zirconium and / or titanium ions, especially zirconium ions.

[0086] Optional step 3a) Optionally, step 3) can be followed by a rinsing step, whereby the film obtained after step 3) is rinsed with water, preferably deionized water.

[0087] Optional step 4) According to optional step 4), the coating film obtained after step 3) is optionally cured or dried, preferably dried, to obtain a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness of less than 0.5 μm.

[0088] The drying or curing step 4) can preferably be carried out at a temperature in the range of, for example, 15° C. to 100° C., more preferably at a temperature in the range of 18° C. to 95° C., in particular at a temperature in the range of 20° C. to 90° C. "Drying" in the sense of the present invention means physical drying, in particular by evaporation of water originally present in the composition(s) used, while "curing" further comprises a chemical reaction between at least two components originally present in the composition(s) and / or between at least one component originally present in the composition(s) and suitable functional groups present on the metal surface or in the conversion coating, for example if a water-soluble polymer is present in the aqueous composition.

[0089] Preferably, the cured or dried coating layer obtained after step 4) has a dry film thickness in the range of 1 nm to <500 nm, more preferably 10 nm to 250 nm, especially 80 nm to 150 nm.

[0090] Substrate with a chemically pretreated surface A further subject of the present invention is a substrate comprising at least one surface, wherein said at least one surface has been pretreated according to the chemical pretreatment method of the present invention.

[0091] All preferred embodiments, and in each case preferred embodiments, described herein above in relation to the inventive method of use, the inventive cleaning method, the inventive substrate having a cleaned surface, and the inventive chemical pretreatment method are also preferred embodiments of the inventive substrate having a chemically pretreated surface.

[0092] For example, at least one further step 5), i.e. 5) applying a coating material composition comprising at least one film-forming polymer onto the film obtained after step 3) or onto the dried or cured, preferably dried, film; In the chemical pretreatment method of the present invention, it is possible to apply one or more further coating films onto at least one surface of the substrate obtained after step 3), or preferably after step 4), of the chemical pretreatment method of the present invention.

[0093] The coating material composition can be, for example, an electrodeposition coating composition, a primer coating composition, a basecoat composition, or a topcoat, including a clearcoat composition. Of course, multiple compositions can be applied in succession to form multi-layer coating systems, as is conventionally used, for example, in the automotive industry.

[0094] method 1. VDA621-415 corrosion test VDA 621-415 (predecessor to VDA 233-102) is a weekly cyclic corrosion test to determine the corrosion resistance of the samples under investigation. A one-week cycle consists of 1) a salt spray phase (24 hours of 5% NaCl salt spray at 35°C), 2) a first condensed water climate phase (96 hours of temperature and humidity at 40°C, 85% RH (relative humidity)), and 3) a second condensed water climate phase (ambient conditions, i.e., 48 hours at 25°C, 50% RH). The total duration of the test is 10 weeks. Undermining (undercreep) (both the overall average and maximum undermining) was determined after the test.

[0095] 2. Volvo Mild Winter (VMW) corrosion test Volvo Mild Winter was carried out in a rain-free ACT-Chamber (ACT = Accelerated Corrosion Test) and consisted of 24-hour cycles, including 6 hours at 10°C and 95% relative humidity (RH) and 6 hours at 15°C and 65% relative humidity (RH), with two 6-hour ramps for changing conditions during the cycle. The total duration of the test was 6 weeks (42 cycles). Undermining (undercreep) (both overall average and maximum undermining) was determined after the test.

[0096] 3. Determining wettability (wetting) The test is conducted in a beaker or a 5-liter spray cabin for a standard panel size of 190 x 105 mm. The test panel is immersed or sprayed in the test cleaning solution for 1 minute, then rinsed in a vertical rinse bath (the entire panel must be immersed and removed from the rinse bath at least five times). The degree of wetting is evaluated 10 seconds after the panel is removed from the rinse bath and held vertically. The minimum cleaning time (MCT) is achieved when at least 95% of the surface is wetted with water (small non-wetted areas are permitted only at the panel edges). If this condition is not met, the cleaning and rinsing procedure must be repeated at 1-minute intervals until the above-mentioned wetting condition is met. A freshly oiled test panel must then be immersed for the total time equal to the previously required 1-minute run. This is necessary because the rinsing step between cleaning steps improves degreasing performance.

[0097] The MCT is achieved when the wettable surface is 95% or greater without any intervening rinsing steps.

[0098] 4. XPS Measurement XPS analysis was performed on a Phi Versa Probe 5000 spectrometer using monochromated Al Kα radiation. The XPS system was calibrated according to ISO 15472:2001. The BE (binding energy) of Au 4f7 / 2 is 84.00 eV, and the BE of Cu2p3 / 2 is 932.62 eV. All samples were mounted insulated to ground and neutralized with a built-in charge neutralizer during measurements. Measurements were performed at three non-overlapping sample positions using a 200 μm x 200 μm spot size. Survey scan analysis was performed with a pass energy of 117.4 eV, an energy step size of 0.5 eV, an acquisition range of -5 eV to 1350 eV, and a dwell time of 600 ms per point. High-resolution analysis of the C 1s signal was performed in the same analytical region with a pass energy of 23.5 eV, an energy step size of 0.1 eV, and a dwell time of 1200 ms per point in the range 278.0-300.0 eV. The C 1s-detail spectrum had regions defined by the following characteristics: U2 Tougaard (section -650,0,0) Fit AV width = 20 End (eV binding energy): 292.9 Onset (eV binding energy): 281.9.

[0099] The spectra were then fitted to determine the exact position of the hydrocarbon peaks based on the following model, and charge corrected so that the hydrocarbon peak maximum was at 284.8 eV for all samples:

[0100] [Table 1]

[0101] The survey spectra were then analyzed using standard XPS analysis software CasaXPS (Fairley N, (2021) CASA-XPS, 2.3.50Rev1-0D, Casa Software Ltd) for the full range of elements of interest according to the range characteristics shown in the table below.

[0102] [Table 2]

[0103] For quantification, the relative sensitivity coefficients and transmission functions provided by the instrument manufacturer were used to calculate the elemental ratios of Zn, Mg, Al, and Ca in atomic % units based on the quantitative results for the following regions (the spectral onsets vary within a range of +-0.1 eV):

[0104] 5. Determination of free fluoride content Free fluoride content is determined using a fluoride ion-selective electrode. The electrode is calibrated using at least three master solutions with known fluoride concentrations. The calibration process generates a calibration curve. This curve is then used to determine the fluoride content.

[0105] 6. ICP-OES The amount of a specific element, such as zirconium, titanium, or hafnium, in a sample under analysis is determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) in accordance with DIN EN ISO 11885 (dated September 1, 2009). The sample is thermally excited in an argon plasma generated by a radio-frequency magnetic field, and the light emitted by electronic transitions is visualized as spectral lines of the corresponding wavelengths and analyzed using an optical system. There is a linear relationship between the intensity of the emitted light and the concentration of the element in question. Prior to implementation, calibration measurements are performed using known element standards (reference standards) as a function of the specific sample under analysis. These calibrations can be used to determine the concentration of unknown solutions, such as titanium, zirconium, or hafnium. [Example]

[0106] The following examples further illustrate the present invention but are not to be construed as limiting its scope.

[0107] 1. Cleaning Composition 1.1 Cleaning composition CCC1 (for comparison) A comparative cleaning composition, CCC1, was prepared from a concentrated starting solution, the components of which are shown in Table 1a.

[0108] [Table 3]

[0109] The starting solution used was the commercially available product Gardoclean® S 5411, to which a nonionic surfactant and potassium octanoate were added. The resulting starting solution was diluted with deionized water. The resulting diluted solution was used as the process bath. This bath contained the starting solution obtained above in an amount of 20 g / L and had a temperature of 55°C.

[0110] The pH value of the process bath was 10.5. Hereinafter, this bath will be referred to as CCC1.

[0111] 1.2 Cleaning composition ICC1 (invention) A cleaning composition ICC1 of the present invention was prepared from a concentrated starting solution, the components of which are shown in Table 1b.

[0112] [Table 4]

[0113] The starting solution used was the commercially available product Gardoclean® S 5201 / 4. This starting solution was diluted with deionized water. The resulting diluted solution was used as the process bath. The bath contained 20 g / L of starting solution and had a temperature of 55°C. 2-Phosphonobutane-1,2,4-tricarboxylic acid was used as the complexing agent.

[0114] The pH value of the process bath was 9.5. Hereinafter, this bath will be referred to as ICC1.

[0115] 2. Cleaning and coating methods Two commercially available zinc-magnesium substrates (namely ZM70 and ZM100) were investigated. The substrates were treated, i.e. cleaned, with composition CCC1 (comparative example, pH value 10.5) or ICC1 (invention, pH value 9.5). Both compositions were applied using a spray application (pressure: 1 bar) for different time frames, i.e. 20 seconds for CCC1 and 70 seconds for ICC1.

[0116] After cleaning, the cleaned substrates underwent a further contact step to apply a conversion coating to the cleaned surface. This was followed by two rinsing steps, one with tap water and one with deionized water. For this purpose, the substrate surface was contacted with a commercially available acidic aqueous composition (Oxsilan® 9835) containing, inter alia, zirconium cations, fluoride anions, and an organosilane. The contacting step was carried out by immersing the substrate surface in the acidic aqueous composition for 180 seconds in each case. The acidic aqueous composition was heated to 35°C before immersion. This was followed by two rinsing steps, one with tap water and one with deionized water. The rinsing step was followed by a drying step with air blowing. Finally, a commercially available electrocoating (Cathoguard® 800) was applied to the converted surface of the substrate and baked at 175°C for 25 minutes.

[0117] 3. Investigating the properties of cleaned and coated substrates The coated substrates obtained after carrying out the method described in item 2. herein were investigated according to the method described in the "Methods" section.

[0118] The wettability and undermining values ​​of the coated substrates determined after VMW corrosion testing are summarized in Table 3a. The wettability and undermining values ​​of the coated substrates after performing the VDA621-415 corrosion testing are summarized in Table 3b.

[0119] [Table 5]

[0120] [Table 6]

[0121] The data presented clearly demonstrate the positive effect of the alkaline cleaners used in this invention on the corrosion performance of ZM substrates, especially when used at spray times that allow for sufficient cleaning performance, and especially when used in combination with suitable conversion coatings such as Oxsilan® products.

[0122] The surfaces of zinc-magnesium substrates are relatively heterogeneous, with uneven elemental distributions including Mg / Al / Zn-rich and Zn-rich regions. It has been observed that the use of ICC1 at a pH below 10.0, e.g., 9.5, can very efficiently remove Mg from the exterior surfaces of zinc-magnesium alloys, as demonstrated by X-ray photoelectron spectroscopy (XPS) measurements according to the method described in the "Methods" section. In particular, conditions using ICC1 at a pH below 10.0, e.g., 9.5, and a long spray time of 70 seconds were shown to very efficiently remove Mg from the exterior surfaces of both ZM70 and ZM100, while simultaneously achieving good cleaning performance. In contrast, CCC1 demonstrated very low Mg removal efficiency from the exterior surfaces. When using conversion coating chemistries such as Oxsilan®, which are based on zirconium, fluoride, and silane, efficient Mg removal directly correlates with the corrosion performance of zinc-magnesium alloys after the coating is fully applied.

[0123] The at% values ​​of Al, Mg, and Ca obtained from the XPS measurements are shown in Table 3c below, in comparison with the at% value of zinc obtained.

[0124] [Table 7]

[0125] The data presented highlight that Mg is removed very efficiently from the exterior surface when ICC1 is applied. Although a decrease in Mg is also observed with CCC1 compared to the reference sample, the XPS data clearly show that ICC1 removes Mg much more efficiently. Interestingly, the same trend is observed for Ca.

Claims

1. A method for cleaning the surface of a substrate using an aqueous alkaline composition having a pH value of less than 10.0, wherein the composition contains, in addition to water, at least one of the following components a1) to a4), which are different from one another: as component a1) at least one alkalinity-inducing source, as at least one component a2), at least one complexing agent, as at least one component a3), at least one surfactant, and As at least one component a4), at least one of optionally condensed phosphate anions and borate anions Including, A method of use wherein said surface is at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy.

2. 2. The use according to claim 1, wherein the aqueous alkaline composition has a pH value in the range of >7.5 to <10.0 or ≦9.9, preferably >8.0 to <10.0 or ≦9.9, more preferably >8.5 to <10.0 or ≦9.9, even more preferably >9.0 to <10.0 or ≦9.

9.

3. The aqueous alkaline composition is free or essentially free of silicates, preferably SiO ２ 3. Use according to claim 1 or 2, containing a maximum amount of silicates of <100 ppm, calculated as a function of time.

4. 3. Use according to claim 1 or 2, wherein at least optionally condensed phosphate anions are present as component a4), preferably both condensed and non-condensed phosphate anions, including polyphosphate anions, are present as component a4), and preferably the aqueous alkaline composition is free or essentially free of borate.

5. 3. Use according to claim 1 or 2, wherein the aqueous alkaline composition has a temperature in the range of 40 to 70°C, preferably 45 to 60°C, more preferably 50 to 55°C.

6. 3. Use according to claim 1 or 2, wherein the aqueous alkaline composition comprises hydroxide anions and / or carbonate anions as component a1) and / or comprises at least one component a1) in an amount of 0.2 to 20 g / L, even more preferably 1.0 to 10 g / L, even more preferably 3 to 8 g / L.

7. the at least one complexing agent present as at least one component a2) is selected from (i) carboxylic acids, their salts, derivatives, in particular esters, and mixtures thereof, (ii) sulfamic acid, (iii) phosphonic acid, phosphonates, and derivatives of phosphonic acid, such as esters, (iv) polyols, in particular having two or more OH groups, and (v) polyethyleneimine, and mixtures of (i) to (v), preferably from (i) carboxylic acids, their salts, derivatives, in particular esters, and mixtures thereof, (iii) phosphonic acid, phosphonates, and derivatives of phosphonic acid, such as esters, and mixtures thereof, more preferably from (i) carboxylic acids, their salts, derivatives, in particular esters, and mixtures thereof, 3. The method of claim 1 or 2, wherein in each case the carboxylic acid comprises a polymeric carboxylic acid and the polyol comprises a polymeric polyol.

8. 3. Use according to claim 1 or 2, wherein the at least one surfactant present as the at least one component a3) is selected from non-ionic surfactants, anionic surfactants and / or cationic surfactants, most preferably selected from non-ionic surfactants.

9. The aqueous alkaline composition comprises: the at least one complexing agent as the at least one component a2) in an amount of 0.2 to 10 g / L, preferably 0.2 or 0.5 to 5 g / L, more preferably 0.5 to 3 g / L, and / or said at least one surfactant as said at least one component a3) in an amount of 0.3 to 10.0 g / L, more preferably 0.4 to 5.0 g / L, even more preferably 0.5 to 3.5 g / L, and / or P ２ O ５ as the at least one component a4), in an amount of 0.5 g / L to 10 g / L, preferably 1.0 to 8 g / L, calculated as 3. The method of claim 1 or 2, comprising:

10. A method for cleaning at least one surface of at least one substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy, said method comprising at least step 1) and optionally step 2), i.e. 1) at least partially contacting said at least one surface of said at least one substrate with the aqueous alkaline composition having a pH value of less than 10.0 according to claim 1 for cleaning a substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy; and 2) optionally rinsing the cleaned surface obtained after step 1) with water. A method comprising:

11. 11. The method of claim 10, wherein contacting step 1) is carried out by spraying the aqueous alkaline composition as defined in claim 1 at least partially onto said at least one surface of said at least one substrate, preferably for a period of >10 seconds or >20 seconds, more preferably for a period of >30 seconds or >40 seconds.

12. A substrate having at least one cleaned surface obtainable by the method of claim 10.

13. A method for chemical pretreatment of at least one cleaned surface of at least one substrate, said surface being at least partially made of at least one steel at least partially coated with at least one zinc-aluminum-magnesium alloy, and cleaning being carried out according to the cleaning method of claim 10, wherein the method for chemical pretreatment comprises at least step 3) and optionally step 4), i.e. 3) contacting the at least one cleaned surface of the at least one substrate with an aqueous, preferably acidic, coating composition suitable for forming a coating film, in particular a conversion coating film, at least partially on the surface, wherein the aqueous coating composition is different from the aqueous alkaline composition of claim 1, 4) optionally curing or drying the coating film obtained after step 3) to obtain a cured or dried coating layer, wherein the obtained cured or dried coating layer preferably has a dry film thickness of less than 0.5 μm. A method comprising:

14. 14. The method according to claim 13, wherein the aqueous, preferably acidic coating composition used in step 3) comprises at least one metal ion selected from the group consisting of titanium ions, zirconium ions and hafnium ions, and mixtures thereof, fluoride anions, and optionally at least one organosilane.

15. A substrate comprising at least one surface, said at least one surface having been pretreated according to the method of claim 13.

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