One-step cleaning and chemical pretreatment method and composition for use in said method

Abstract

The present invention relates to a method comprising at least step 1), namely contacting at least one metallic surface of at least one substrate at least in portion with an aqueous acidic composition AAC for cleaning and chemically pretreating said surface, wherein composition AAC is free or essentially free of fluoride anions and comprises, besides water, at least constituents a2) and a3), and optionally one or both of a1) and a4), namely optionally at least one of Zr, Ti, and Hf cations as a1), at least one surfactant as a2) in an amount in a range of from 0.5 to 12.5 wt.-%, based on the total weight of the composition, at least one copolymer bearing at least one kind of acid groups in an amount in a range of from 5 to 50 000 mg / L as a3), and optionally at least one corrosion inhibitor as a4), a cleaned and chemically pretreated substrate obtainable by this method, composition AAC as such, a concentrate usable for its preparation, a use of composition AAC simultaneously as cleaning and chemical pretreatment composition, to a method of coating aforementioned cleaned and chemically pretreated substrate, and to a coated substrate obtainable by said method.

Description

[0001] 2024P00038WO I L024883PCT 1 February 17, 2026 Chemetall GmbH

[0002] One-step cleaning and chemical pretreatment method and composition for use in said method

[0003] The present invention relates to a method comprising a step of simultaneously cleaning and chemically pretreating a metallic surface of a substrate, to a cleaned and chemically pretreated substrate obtainable by this method, to a composition as such for use in said step, to a concentrate usable for the preparation of said composition, to a use of said composition simultaneously as cleaning and chemical pretreatment composition, to a method of coating aforementioned cleaned and chemically pretreated substrate, and to a coated substrate obtainable by said method.

[0004] Background of the invention

[0005] Aluminum materials and / or aluminum alloy materials, e.g., used for architectural construction elements made of aluminum and / or aluminum alloys in indoor and outdoor areas are typically cleaned and often additionally pickled prior to any conversion coating applied on their surfaces. These steps are necessary to ensure a sufficient corrosion protection and good adhesion to subsequently applied coatings such as powder coatings.

[0006] Typical cleaners used for the aforementioned applications are mild alkaline immersion cleaners operating at temperatures of about 45 to about 60 °C. The use of such relatively high temperatures is, however, disadvantageous in terms of energy consumption from an ecological and economic viewpoint. As mentioned above, often a pickling step is furthermore necessary to remove any existing oxide layers and / or intermetallic particles from the surface of the aluminum and / or aluminum alloy materials. Conventionally used pickling solutions comprise mineral acids such as sulfuric acid and / or phosphoric acid and a low amount of hydrofluoric acid, which are mixed with surfactants. The pickling step is performed at temperature between about 35 and 45 °C, depending on the type of intended application and the material used. The use of such still relatively high temperatures is, however, disadvantageous in terms of energy consumption from an ecological and economic viewpoint as in case of the aforementioned cleaners. Typically, conversion coatings to be applied onto the cleaned and pickled surfaces are based on Ti- and or Zr-fluoride complexes, which build a respective metal oxide layer on the surfaces and thereby protect the aluminum and / or aluminum alloy material against filiform corrosion. In particular for ecological reasons, however, the use of fluoride ions in such conversion coating compositions is undesired. Often, also polymers are additionally used in the conversion coating technology to provide a good adhesion to subsequently applied coatings such as powder coatings. A combination of, e.g., Ti-, Zr-, and / or Hf-compounds and copolymers bearing carboxylic acid and / or phosphonic acid groups in conversion coating compositions is described in WO 2016 / 096777 A1. A combination of, e.g., Ti-, Zr-, and / or Hf-compounds and copolymers bearing carboxylic acid and phosphonic acid groups in conversion coating compositions is described in WO 2020 / 049132 A1.

[0007] In general, from an ecological and economic point of view, using two or three different process steps such as cleaning, pickling, and performing a conversion coating is disadvantageous, e.g., in terms of material and energy consumption. There is thus a tendency towards reducing such treatment steps as much as possible. For example, in ON 117604536 A, a process is disclosed, in which the conversion coating step is incorporated into in the cleaning2024P00038WO I L024883PCT 2 February 17, 2026 Chemetall GmbH

[0008] step. The cleaner according to CN 117604536 A inter alia comprises an inorganic acid such as a combination of sulfamic acid and hydrofluoric acid. As mentioned above, in particular for ecological reasons the use of fluoride ions is, however, undesired.

[0009] In addition, the conventional conversion coating compositions including the ones disclosed in CN 117604536 A do not always provide conversion coatings with both a sufficiently high corrosion resistance such as a sufficiently high filiform corrosion resistance and a sufficiently high adhesion to any subsequently applied coatings such as powder coatings. Furthermore, often due to an etching rate, which it too high, an undesired high concentration of trivalent aluminum cations may result in the conversion bath, in particular when aluminum and / or aluminum alloy containing substrates are used, which may have a negative impact on bath stability and bath lifetime.

[0010] Thus, there is a need to provide aqueous compositions, which are suitable to be used simultaneously for both cleaning of and for providing a conversion coating film on metallic surfaces of substrates, in particular aluminum and / or aluminum alloy containing surfaces of substrates, allow an efficient cleaning of the surfaces and at the same time provide conversion coatings with both an excellent corrosion resistance such as filiform corrosion resistance and a sufficient adhesion to any subsequently applied coatings such as powder coatings, lead only to a low etching rate in particular on aluminum and / or aluminum alloy containing surfaces of substrates in order to increase stability of the treatment bath and of its lifetime as much as possible, and which are furthermore suitable to be formulated as compositions that are free or essentially free of fluoride anions without any negative impact on corrosion protection and substrate adhesion compared to conventionally used fluoride anions containing compositions.

[0011] Problem

[0012] It has been therefore an objective underlying the present invention to provide aqueous coating compositions, which are suitable to be used simultaneously for both cleaning of and for providing a conversion coating film on metallic surfaces of substrates, in particular aluminum and / or aluminum alloy containing surfaces of substrates, allow an efficient cleaning of the surfaces and at the same time provide conversion coatings with both an excellent corrosion resistance such as filiform corrosion resistance and a sufficient adhesion to any subsequently applied coatings such as powder coatings, lead only to a low etching rate in particular on aluminum and / or aluminum alloy containing surfaces of substrates in order to increase stability of the treatment bath and of its lifetime as much as possible, and which are furthermore suitable to be formulated as compositions that are free or essentially free of fluoride anions without any negative impact on corrosion protection and substrate adhesion compared to conventionally used fluoride anions containing compositions.

[0013] Solution

[0014] This objective has been solved by the subject-matter of the claims of the present application as well as by the preferred embodiments thereof disclosed in this specification, i.e. by the subject matter described herein.2024P00038WO I L024883PCT 3 February 17, 2026 Chemetall GmbH

[0015] A first subject-matter of the present invention is a method of simultaneously cleaning and chemically pretreating a metallic surface of a substrate comprising at least step 1) and optionally one or more of steps 2) and 3), namely

[0016] 1) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous acidic composition AAC for cleaning and chemically pretreating said surface,

[0017] wherein the aqueous acidic composition AAC comprises, besides water, at least constituents a2) and a3), and optionally one or both of a1) and a4), which are different from one of another, namely optionally at least one of zirconium, titanium, and hafnium cations as constituent a1), at least one surfactant as constituent a2), preferably in an amount in a range of from 0.5 to 12.5 wt.-%, based on the total weight of the composition,

[0018] at least one polymer, which is a homopolymer or copolymer, preferably a copolymer, bearing at least one kind of acid groups, preferably in an amount in a range of from 5 to 50 000 mg / L, as constituent a3), and

[0019] optionally at least one corrosion inhibitor as constituent a4),

[0020] wherein the aqueous acidic composition AAC is free or essentially free of fluoride anions,

[0021] 2) optionally rinsing the cleaned and chemically pretreated surface obtained after step 1) at least once with water and / or at least once with an aqueous rinsing composition ARC, and

[0022] 3) optionally curing and / or drying the cleaned and chemically pretreated surface obtained after step 1) or after optional step 2).

[0023] A further subject-matter of the present invention is a substrate having at least one metallic surface, wherein said surface is an at least in portion cleaned and chemically pretreated surface, which is obtainable by the inventive method of cleaning and chemical pretreatment as defined hereinbefore and hereinafter.

[0024] A further subject-matter of the present invention is an aqueous acidic composition AAC as defined hereinbefore and hereinafter or a concentrate, from which said aqueous acidic composition AAC is at least obtainable by dilution with water and, optionally further, by pH adjustment.

[0025] A further subject-matter of the present invention is a use of the aqueous acidic composition AAC as defined hereinbefore and hereinafter simultaneously as cleaning and chemical pretreatment composition, preferably in the cleaning and chemical pretreatment method as defined hereinbefore and hereinafter, more preferably also for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon.2024P00038WO I L024883PCT 4 February 17, 2026 Chemetall GmbH

[0026] A further subject-matter of the present invention is a method of coating of at least one cleaned and chemically pretreated metallic surface of at least one substrate, wherein cleaning and chemical pretreatment of the at least one metallic surface has been carried out according to the inventive method of simultaneous cleaning and chemical pretreatment as defined hereinbefore and hereinafter or by making use of an inventive aqueous composition AAC, the method of coating further comprising at least step 4), namely

[0027] 4) applying at least one coating material composition comprising at least one film-forming polymer and / or resin onto the cleaned and chemically pretreated surface obtained after step 1) or after optional step 2) as defined hereinbefore and hereinafter or after optional step 3) as defined hereinbefore and hereinafter, i.e., in the latter case onto a dried or cured, preferably dried, layer, which in turn is obtainable from drying or curing according to optional step 3), in particular of a film obtainable from having performed step 1).

[0028] A further subject-matter of the present invention is a substrate having at least one metallic surface, wherein said surface is a coated surface being obtainable by the inventive coating method as defined hereinbefore and hereinafter.

[0029] It has been in particular surprisingly found that the aqueous acidic composition AAC can be used both as cleaning and as chemical pretreatment composition at the same time and hence allows simultaneously cleaning and chemically pretreating metallic surfaces of suitable substrates, in particular surfaces at least partially made of at least one kind of aluminum and / or at least one kind of an aluminum alloy. Thus, only one process step for both cleaning and chemical pretreatment is necessary, which is both ecologically and economically advantageous compared to conventional processes, in which cleaning, pickling, and surface treatment such as chemical pretreatment are performed in two or even three steps in total. In addition, it has been found in this context that the cleaning and chemical pretreatment step making use of composition AAC can be performed at lower temperatures such as, e.g., at temperatures between 25 and 30 °C including room temperature, compared to conventional prior art cleaning and pickling processes, which often are performed at higher temperatures such as between 45 and 60 °C, and, therefore, is very energy-efficient.

[0030] Further, it has been surprisingly found in this regard that cleaning can be performed in an effective manner via the inventive method, e.g., in that any oil and / or dirt is completely removed from the surface of the metallic substrates, and that the metallic surfaces can be effectively protected, in particular against filiform corrosion, at the same time by providing a coating film onto said surfaces via chemical pretreatment. It has been in particular found in this regard that a synergetic action of the surfactant a2) and the polymer a3) allows an efficient cleaning of the surface and at the same time a sufficient deposition of the polymer onto the metallic surface in order to provide a conversion coating film.

[0031] In addition, it has been found that it is possible to formulate composition AAC as a composition, which is free of fluoride anions or essentially free of fluoride anions, and to use said composition in the inventive cleaning and2024P00038WO I L024883PCT 5 February 17, 2026 Chemetall GmbH

[0032] chemical pretreatment method, which is advantageous from the viewpoint of environmental health safety (EHS). In addition, it has been surprisingly found that using composition AAC being free of fluoride anions or being essentially free of fluoride anions does not have any negative impacts on the coating film (conversion film) formation on the metallic surface, although free fluoride anions are known to often initiate conversion film formation. In addition, using composition AAC being free of fluoride anions or being essentially free of fluoride anions has the advantage that the fluoride content does not need to be measured during the chemical pretreatment method: this usually has to be done in case of fluoride anions containing compositions, since an amount of fluoride anions, which is too high, may lead to a Zr- / Ti- / Hf-oxides formation being too high and too dense, which in turn can negatively affect the adhesion to any subsequently applied coatings. Therefore, in case of conventional fluoride anions containing compositions it is necessary to monitor the bath and measure the concentration of fluoride anions in the bath to avoid the aforementioned adhesion issue, which is not necessary when performing the inventive method.

[0033] Further, it has been found that by using composition AAC in the inventive method, an excellent adhesion to any subsequently applied coatings such as powder coatings is achieved.

[0034] Moreover, it has been in particular surprisingly found that when the metallic surfaces are at least partially made of at least one kind of aluminum and / or at least one kind of an aluminum alloy, any undesired formation of trivalent aluminum cations is minimized by using the composition AAC, which in turn positively affects the stability of the treatment bath and its lifetime, in particular since the etching rate has been found to be rather low when using composition AAC compared with conventional fluoride anions containing compositions, since a high etching rate usually results in a high concentration of trivalent aluminum cations in the bath. It has been particularly found that the low etching rate can be achieved by making use of the polymer constituent a3), which functions as an only weak acid. In contrast, much higher etching rates are observed when using strong acids such as sulfuric or nitric acid. In addition, no undesired sludge formation has been observed as well when performing the inventive method making use of composition AAC.

[0035] Detailed description of the invention

[0036] The term "comprising” in the sense of the present invention, in connection for example with the aqueous acidic composition AAC, has the meaning of "consisting of'. With regard, e.g., to said composition, it is possible - in addition to all mandatory constituents present therein - for one or more of the further optional constituents identified hereinafter to be also included therein. All constituents may in each case be present in their preferred embodiments as identified below.

[0037] The proportions and amounts in wt.-% (% by weight) of any of the constituents given hereinafter, which are present in each of the compositions add up to 100 wt.-%, based in each case on the total weight of the respective composition.2024P00038WO I L024883PCT 6 February 17, 2026 Chemetall GmbH

[0038] The inventive method is a method of simultaneously cleaning and chemically pretreating a metallic surface of a substrate comprising at least step 1) and optionally one or more of steps 2) and 3). Hence, step 1) combines a cleaning and conversion coating and optionally also a pickling operation in one single step. The method may comprise further steps performed after each of steps 1), 2) and 3).

[0039] Chemical pretreatment is a term known by a person skilled in the art and in particular is part of a pretreatment method.

[0040] The cleaning operation performed in step 1) of the inventive method preferably represents part of a pretreatment and more preferably represents the pretreatment. The term "pretreatment” as used herein is preferably used in accordance with the term "surface pretreatment” as defined in Rdmpp Lexikon "Lacke und Druckfarben” (Publisher: Ulrich Zorll, Editor: Hans-Jurgen P. Adler - Stuttgart; New York: Thieme, 1998; term: "Oberflachenvorbehandlung” page 417). On metallic substrates or substrates having metallic surfaces, according to DIN 50902: 1994-07, the first step(s) of a surface treatment is / are often one or more (chemical) cleaning step(s) with aqueous or nonaqueous cleaning compositions (also called "surface preparation step”). In the present case, there is no need to perform a separate cleaning step as step 1) already combines a cleaning and conversion coating and optionally also a pickling operation in one single step. Hence, as a cleaning is already performed when carrying out step 1), preferably, the inventive method does not comprise any cleaning steps other than step 1).

[0041] The term "chemical pretreatment” is used in accordance with EN ISO 4618:2006 (E / F / D) (term: 2.41 "chemical pretreatment”), which represents any chemical process applied to a surface prior to the application of a coating material. According to this standard, e.g., treatments like chromatizing (chromating) and phosphatizing and oxalating, which can be subsumed under the term "conversion treatment”, belong to the chemical pretreatment and thus are to be distinguished from (subsequent) coating steps, wherein coating materials, i.e., coating material compositions such as powder coating compositions, electrodeposition coating compositions, aqueous or nonaqueous liquid coating materials are applied. Besides conversion treatments such as chromatizing (chromating) and phosphating, the chemical surface pretreatment may be achieved with passivation compositions and thin-film forming compositions in general, including the aqueous composition AAC, which is mandatorily used as chemical pretreatment composition in step 1). Hence, step 1) of the method represents a chemical pretreatment step and the aqueous composition AAC used therein represents a chemical pretreatment composition (besides its parallel suitability also as a cleaning composition as outlined hereinbefore).

[0042] Preferably, the inventive cleaning and chemical pretreatment method (and also not any pretreatment method, of which the chemical pretreatment method is part of) does not comprise any further contacting steps, in which any composition such as a further pre-rinse composition and / or such as a further aqueous composition different from2024P00038WO I L024883PCT 7 February 17, 2026 Chemetall GmbH

[0043] AAC, e.g., for use as chemical pretreatment composition, is used. Hence, preferably, the inventive method does not comprise any chemical pretreatment steps other than step 1).

[0044] Preferably, the inventive cleaning and chemical pretreatment method (and also not any pretreatment method, of which the chemical pretreatment method is part of) does not contain any step involving any treatment with chromium ions such as Cr(VI) ions and / or Cr(lll) ions.

[0045] Preferably, the inventive cleaning and chemical pretreatment method (and also not any pretreatment method, of which the chemical pretreatment method is part of) does not comprise any pickling step.

[0046] Substrate

[0047] In step 1) of the cleaning and chemical pretreatment method at least one metallic surface of at least one substrate is contacted with composition AAC.

[0048] The substrate used in step 1) contains at least one metallic surface. The term "metallic surface” in the sense of the present invention preferably means that the surface of the substrate used is at least partially made of at least one metal, i.e., that at least one region of said surface is made of at least one metal and / or alloy thereof. Preferably, the overall surface of the substrate is made of at least one metal and / or alloy thereof, more preferably, the whole substrate is made of at least one metal and / or alloy thereof, i.e., the substrate consists of at least one metal and / or alloy thereof. If a substrate comprises areas of different metals, such substrate is herein denoted as "multi-metallic substrate” as a subclass of metallic substrates. Such multi-metallic substrates can be subjected to step 1) of the cleaning and chemical pretreatment method and can be coated in the same treatment bath.

[0049] The at least one metallic surface of the substrate may be optionally pre-coated, but preferably is not pre-coated.

[0050] Preferably, the substrate used is an electrically conductive substrate, which is used customarily and known to the skilled person. The substrate can have all sorts of geometry and shape such as coils, foils and sheets as well as represent parts such as automotive parts including vehicle parts such as wheel parts. Particularly suitable substrates are profiles, e.g., for use in the field of architecture.

[0051] Preferably, the at least one metallic surface of the at least one substrate is at least partially made of at least one kind of aluminum and / or at least one kind of an aluminum alloy. More preferably, the at least one metallic surface as such is made of at least one kind of aluminum and / or at least one kind of an aluminum alloy, and even more preferably said substrate as such is made of at least one kind of aluminum and / or at least one kind of an aluminum alloy.

[0052] Examples of aluminum alloys are aluminum magnesium alloys, aluminum magnesium silicon alloys, aluminum copper alloys, aluminum zinc alloys, and aluminum zinc copper alloys. The term "alloy” is known to the person2024P00038WO I L024883PCT 8 February 17, 2026 Chemetall GmbH

[0053] skilled in the art, e.g., from DIN EN 12258-1:2012, 2.2.1. For the purposes of the present invention, the term "alloy” preferably encompasses substances having metallic properties and being composed of two or more elements so combined that they cannot readily be separated by physical means. In case of an aluminum alloy said alloy preferably contains more than 50 wt.-%, more preferably more than 75 wt.-%, even more preferably more than 80 wt.-%, of aluminum, based on the total weight of the alloy. In particular suitable are aluminum magnesium alloys, including, but not limited to AA5005, aluminum magnesium silicon alloys, including, but not limited to AA6014, AA6016, AA6022, AA6060, AA6061 and AA6063 as well as AA6111, cast alloys - e.g., AISI7Mg, AISIOMg, AISHOMg, AISIHMg, AISI12Mg - as well as forge alloys - e.g., AISIMg. Aluminum magnesium alloys, including AA5005, as well as aluminum magnesium silicon alloys, including AA6060 and AA6063, are commonly used in the field of, e.g., aluminum finishing and / or for the treatment of wheels and / or in other vehicle parts such as electrical vehicle parts, e.g., battery housings. Suitable are all alloys including aluminum copper alloys of the so-called AA1000, especially AA1050, AA2000, AA3000, especially AA3003, AA4000, AA5000, AA6000, AA7000 as well as AA8000 series. An example of the AA2000 series is AA2024. An example of the AA7000 series is AA7075. AA2024 and AA7075 are often used in the aerospace industry. Further examples of suitable substrates with metallic surfaces are steel substrates, which bear a coating made of aluminum and / or at least one kind of aluminum alloy on their surface such as the commercially available products Galvalume® and Galfan®. Preferably, however, the metallic surface does not comprise steel and / or a steel alloy in any amount exceeding the amount of aluminum and / or of the alloy thereof present therein. More preferably, the metallic surface does not comprise any steel and / or a steel alloy at all. Also particular suitable are aluminum silicon alloys, including, but not limited to A356, aluminum silicon copper alloys including, but not limited to A319. A356 is often used in the aerospace industry.

[0054] Step 1)

[0055] According to step 1) at least one metallic surface of at least one substrate is contacted at least in portion with an aqueous acidic composition AAC for cleaning and chemically pretreating said surface.

[0056] The term "at least in portion” preferably means in this context, in accordance with the general understanding of said term, that in some cases it might be desired or sufficient to contact not the whole surface of the substrate with the composition AAC. If only part of the surface is contacted with said composition, it is typically the same part for all steps of the method. However, generally, it is desired to contact the whole surface of the substrate.

[0057] The "contacting” according to step 1) can be, e.g., a spraying, a dipping (immersing) or a roll coating (rolling) step or any combination thereof. The aqueous acidic composition AAC can also be applied by flooding the surface or even manually by wiping or brushing. Preferred is spraying, dipping or roll coating or any combination thereof, most preferred is spraying or dipping.

[0058] The treatment time, i.e., the period of time the surface is contacted with the aqueous acidic composition AAC in step 1), is preferably from 15 seconds to 20 minutes, more preferably from 10 seconds to 10 minutes, and most preferably 30 seconds to 7.5 minutes, as for example 1 to 5 minutes.2024P00038WO I L024883PCT 9 February 17, 2026 Chemetall GmbH

[0059] Preferably, contacting step 1) is performed by spraying, dipping or roll coating, more preferably by spraying or dipping, preferably for a period of >10 to 10 minutes, more preferably for a period of >30 seconds to 7.5 minutes, even more preferably for a period of 1 minute to 5 minutes.

[0060] The temperature of the aqueous acidic composition AAC used in step 1) is preferably of from 5 to <45 °C, more preferably of from 15 to 40 °C, even more preferably of from 17.5 to 35 °C, yet more preferably of from 17.5 to 30 or to 25 °C. Most preferably, the aqueous acidic composition AAC used in step 1) has room temperature (17.5 to 23.5 °C).

[0061] Preferably, the aqueous acidic composition AAC is suitable to form a coating film such as a conversion coating film at least in portion onto the metallic surface of the substrate.

[0062] Aqueous acidic composition AAC used in step 1)

[0063] The aqueous acidic composition AAC comprises, besides water, at least constituents a2) and a3) and optionally one or both of a1) and a4), which are different from one of another, namely optionally at least one of zirconium, titanium, and hafnium cations as constituent a1), at least one surfactant as constituent a2), at least one polymer bearing at least one kind of acid groups as constituent a3), and optionally at least one corrosion inhibitor as constituent a4).

[0064] Preferably, the aqueous acidic composition AAC used in step 1) has a pH value in a range of from 0.10 to <7.0, more preferably of from 0.25 to 6.0, even more preferably of from 0.50 to 5.0, yet more preferably of from 0.75 to 4.0 or to 3.5, still more preferably of from 1.0 or 3.0, most preferably of from 1.5 or 2.5. Acidity of the composition AAC, in particular in the ranges defined hereinbefore, is required in order to ensure that etching of the metallic surface, in particular of the aluminum and / or aluminum alloy surface, is sufficient.

[0065] The pH value can be in particular adjusted by using a suitable pH adjusting constituent, in particular sodium and / or potassium hydroxide and / or sodium and / or potassium and / or ammonium carbonate for alkaline adjustment, or can be in particular adjusted in case acidic adjustment is needed by at least one inorganic acid such as sulfuric and / or nitric acid and / or phosphoric acid and / or by at least one organic acid such as methyl sulfonic acid. However, preferably pH adjustment is not needed and the pH is adjusted by the presence of polymer constituent a3) alone.

[0066] The temperature of the aqueous acidic composition AAC is preferably of from 5 to <45 °C, more preferably of from 15 to 40 °C, even more preferably of from 17.5 to 35 °C, yet more preferably of from 17.5 to 30 or to 25 °C. Most preferably, the aqueous acidic composition AAC used in step 1) has room temperature (17.5 to 23.5 °C).

[0067] The aqueous acidic composition AAC can be a dispersion or solution. Preferably, it is a solution. Solubility is determined at a temperature of 20°C and atmospheric pressure (1.013 bar).2024P00038WO I L024883PCT 10 February 17, 2026 Chemetall GmbH

[0068] The aqueous acidic composition AAC is preferably

[0069] free or essentially free of any chromium ions such as Cr(VI) cations and / or Cr(lll) cations, more preferably is free of chromium ions or comprises a maximum amount of chromium ions of <10 mg / L, calculated as metal, and / or is

[0070] free or essentially free of any nickel ions such as Ni(ll) cations and / or Ni(lll) cations, more preferably is free of nickel ions or comprises a maximum amount of nickel ions of <10 mg / L, calculated as metal, and / or is

[0071] free or essentially free of any phosphate anions, more preferably is free of phosphate anions or comprises a maximum amount of phosphate anions of <10 mg / L, calculated as phosphate.

[0072] "Essentially free” in this context means in each case that at least on purpose none of the aforementioned constituents and / or any precursors for generating said constituents is added, but it may not be ruled out that any residues of any of the constituents may be present as impurities and / or may be present in amounts being naturally present in water.

[0073] The aqueous acidic composition AAC is free or essentially free of fluoride anions. "Essentially free” in this context means that no fluoride anions and / or any precursors for generating fluoride anions is added on purpose, but it may not be ruled out that any fluoride anions may be present as impurities and / or may be present in amounts being naturally present in water. Preferably, the aqueous acidic composition AAC is free of fluoride anions or comprises a maximum amount of fluoride anions of <10.0 mg / L, more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <5.0 mg / L, even more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <2.0 mg / L, still more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <1.0 mg / L, yet more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <0.1 mg / L, in each case calculated as fluorine (F).

[0074] The term "aqueous” with respect to the aqueous acidic composition AAC used in step 1) in the sense of the present invention preferably means that the composition is a composition containing at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-% in particular at least 80 wt.-%, most preferably at least 90 wt.-% of water, based on its total content of organic and inorganic solvents including water. Thus, the aqueous composition may contain at least one organic solvent besides water - however, in an amount lower than the amount of water present.

[0075] Preferably, the aqueous acidic composition AAC contains at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-% in particular at least 80 wt.-%, most preferably at least 90 wt.-% of water, in each case based on its total weight.2024P00038WO I L024883PCT 11 February 17, 2026 Chemetall GmbH

[0076] Preferably, the amount of organic solvent(s) present in the aqueous acidic composition AAC does not exceed 5 wt.-%, yet more preferably does not exceed 2.5 wt.-%, even more preferably is lower than 2.0 wt.-%, yet more preferably is at most 1.0 wt.-% or at most 0.5 wt.-% or at most 0.2 wt.-%, still more preferably is at most 0.1 wt.-% or at most 0.05 wt.-% or at most 0.02 wt.-%, in each case based on the total weight of the composition. Examples of organic solvents are methanol, ethanol, ethylene glycol n-butyl ether, ethylene glycol n-propyl ether, propylene glycol n-propyl ether, propylene glycol n-butyl ether and mixtures thereof. Preferably, no organic solvents at all are added on purpose to the composition AAC.

[0077] Preferably, the aqueous acidic composition AAC has a solid content in a range of from 2.5 to 35.0 wt.-%, more preferably of from 3.5 to 30.0 wt.-%, even more preferably of from 4.0 to 25.0 wt.-%, still more preferably of from 4.5 to 20.0 wt.-%, even more preferably of from 5.0 to 15.0 wt.-%. The solid content is determined according to the method disclosed in the 'method' section.

[0078] Optional constituent a 1 )

[0079] At least one of zirconium, titanium, and hafnium cations is optionally present as constituent a1) in composition AAC. Preferably, at least one of zirconium, and titanium cations is present as optional constituent a1) in composition AAC. More preferably, zirconium cations are present as optional constituent a1) in composition AAC.

[0080] Preferably, zirconium cations are not used as constituent a1) and more preferably composition AAC does not or does essentially not comprise zirconium cations. Preferably, titanium cations are not used as constituent a1) and more preferably composition AAC does not or does essentially not comprise titanium cations. "Essentially free” in this context means that no zirconium cations and / or any precursors for generating such cations are added on purpose, but it may not be ruled out that any zirconium cations may be present as impurities and / or may be present in amounts being naturally present in water. The same applies with respect to titanium cations.

[0081] Preferably, the aqueous acidic composition AAC comprises constituent a1), more preferably at least one of zirconium and titanium cations, even more preferably zirconium cations, if present, in an amount in a range of from 1.0 to 2000 mg / L, more preferably of from 5.0 to 1 500 mg / L, even more preferably of from 10.0 to 1 000 mg / L, still more preferably of from 15.0 to 750 mg / L, yet more preferably of from 20.0 to 500 mg / L, even more preferably of from 22.5 to 250 mg / L, yet more preferably of from 25.0 to 150 mg / L, most preferably of from 25.0 to 100 mg / L, in each case calculated as metal.

[0082] The content of constituent a1) can be monitored and determined by the means of ICP-OES (optical emission spectroscopy with inductively coupled plasma). Said method is described hereinafter in the 'method' section.

[0083] Preferably, a precursor metal compound is used to generate constituent a1). Preferably, the precursor metal compound is water-soluble. Solubility is determined at a temperature of 20°C and atmospheric pressure (1.013 bar).2024P00038WO I L024883PCT 12 February 17, 2026 Chemetall GmbH

[0084] In case zirconium cations are present as constituent a1), these are preferably added in form of zirconyl compounds as, e.g., zirconyl nitrate, zirconyl acetate, zirconium carbonate and / or zirconium gluconate and / or zirconium nitrate, the latter one being particularly preferred. The same similarly applies to titanium and hafnium cations: here the respective titanium and / or hafnium compounds can be used accordingly.

[0085] Optionally, constituent a1) is used in a complexed form thereof with the aid of at least one complexing agent, which is discussed hereinafter as optional constituent a8). Preferably, a complexed form of a1) by means of a8) is prepared first and then included into the composition AAC.

[0086] Preferably, complex fluorides of zirconium, titanium, and hafnium cations are not used as precursor metal compounds, since the aqueous acidic composition AAC is free or essentially free of fluoride anions.

[0087] Constituent a2)

[0088] At least one surfactant is present as constituent a2) in composition AAC.

[0089] The term surfactant (surface active agent) as used herein is preferably used in accordance with the term "tenside” as defined in Rdmpp Lexikon "Lacke und Druckfarben” (Publisher: Ulrich Zorll, Editor: Hans-Jurgen P. Adler -Stuttgart; New York: Thieme, 1998; term: "tenside” pages 557 and 558). Suitable surfactants are known to a person skilled in the art and, e.g., disclosed in WO 2020 / 200838 A1.

[0090] Preferably, the at least one surfactant is selected from non-ionic, anionic, and cationic surfactants and mixtures thereof, more preferably from non-ionic surfactants, anionic surfactants, and mixtures thereof.

[0091] Suitable non-ionic surfactants include in particular alkylphenol alkoxylates, especially alkylphenol ethoxylates, having Ce to C14 alkyl chains and a degree of alkoxylation of 5 to 30 mol per mole of phenol, alkylpolyglucosides having an alkyl chain length of C4 to C22, preferably Cs to C22, more preferably C to Cis, and containing 1 to 20, preferably 1 to 5, glucoside units, fatty acid amide alkoxylates, fatty acid alkanolamide alkoxylates, N-alkylglucamides or else block copolymers consisting of ethylene oxide, propylene oxide and / or butylene oxide, and alkoxylated Cs to C22 alcohols such as fatty alcohol alkoxylates, oxo-process alcohol alkoxylates and Guerbet alcohol alkoxylates, where the alkoxylation may take place with ethylene oxide, propylene oxide, butylene oxide and / or a mixture of these, as a block copolymer or random copolymer. The alcohols preferably have 8 to 18 carbon atoms; the degree of alkoxylation ranges typically between 2 to 50 mol, preferably 3 to 20 mol, of at least one of the stated alkylene oxides per mole of alcohol. The alkylene oxide head group may additionally contain the following so-called end-capping groups as a modification: benzyl, methyl, and / or tert-butyl capping. An example of a commercially suitable non-ionic surfactant is Lutensol® TO. Further examples are Plurafac® and Pluronic® types.2024P00038WO I L024883PCT 13 February 17, 2026 Chemetall GmbH

[0092] Depending on application, the following anionic surfactants in particular can be used: fatty alcohol sulfates having alkyl chain lengths of 8 to 22, preferably 10 to 18, carbon atoms, for example lauryl sulfate, cetyl sulfate, myristyl sulfate, palmityl sulfate or stearyl sulfate, alkyl ether sulfates having alkyl chain lengths of 8 to 22, preferably 10 to 18, carbon atoms, and linear Cs to C20 alkylbenzenesulfonates or else alkanesulfonates and soaps, such as sodium or potassium salts of Cs to C24 carboxylic acids, as well as sulfosuccinates. Examples of a commercially suitable anionic surfactants are Disponil® ALS and Disponil® FES types.

[0093] Cationic surfactants employed, depending on application, are in particular quaternary mono- and di-(Cz-C25 alkyl)dimethylammonium compounds, ester quats, especially quaternary esterified mono-, di- and trialkanolamines esterified with C8-C22 carboxylic acids, and C7 to C25 alkylamines, N,N-dimethyl-N-(hydroxy-C7-C25 alkyl)ammonium salts and / or imidazoline quats.

[0094] As outlined above, however, the at least one surfactant preferably is at least one non-ionic surfactant. Within the majority of applications, the foaming tendency of anionic surfactants is too high, while cationic surfactants often attach to the metallic surface, and may consequently give rise to problems within the deposition of conversion coating films to be subsequently applied.

[0095] Preferably, the aqueous acidic composition AAC comprises the at least one surfactant as constituent a2) in an amount of from 0.5 to 12.5 wt.-%, more preferably of from 1.0 to 10.0 wt.-%, even more preferably of from 1.5 to 8.0 wt.-%, yet more preferably of from 2.0 to 7.5 wt.-%, in each case based on the total weight of the composition.

[0096] Preferably, the aqueous acidic composition AAC comprises the at least one surfactant as constituent a2) in an amount of from 0.3 to 10.0 g / L, more preferably of from 0.4 to 5.0 g / L, even more preferably of from 0.5 to 3.5 g / L.

[0097] Constituent a3)

[0098] At least one polymer, which is a homopolymer or copolymer, preferably a copolymer, bearing at least one kind of acid groups is present as constituent a3) in composition AAC. The acid groups of said polymer such as carboxylic acid groups can be present in the form of free acid groups and / or in deprotonated forms and / or in the form of salts thereof. Said polymer may function as film-forming polymer, but does not necessarily have to, in particular, when said polymer is a water-soluble polymer.

[0099] The polymer being present as constituent a3) in the aqueous acidic composition AAC is preferably able to attack the metallic surface such as the aluminum- and / or aluminum alloy-based surface and to bind to thereto and to form a conversion coating film, and is preferably also able to provide excellent adhesion to any subsequently applied coating film such as a powder coating film. At the same time preferably also a sufficient etching can be achieved by means of the polymer constituent a3).2024P00038WO I L024883PCT 14 February 17, 2026 Chemetall GmbH

[0100] Preferably, the at least one polymer bearing at least one kind of acid groups is water-soluble. Solubility in water is determined at 23 °C, atmospheric pressure and at pH 7.0 as outlined in the ‘methods' section.

[0101] Preferably, the at least one polymer bearing at least one kind of acid groups is present as constituent a3) in the aqueous acidic composition AAC in an amount in a range of from 5 to 50000 mg / L, more preferably of from 50 to 30 000 mg / L, even more preferably of from 100 to 20 000 mg / L, still more preferably of from 200 to 15000 mg / L, yet more preferably of from 250 to 10 000 mg / L, even more preferably of from 500 to 7 500 mg / L, yet more preferably of from 750 to 5000 mg / L, even more preferably of from 1 000 to 4500 mg / L, most preferably of from 1 500 or 2000 to 4000 or to 3500 mg / L.

[0102] Preferably, the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC has a weight average molecular weight in a range of from 10000 g / mol to 250000 g / mol or to 200000 g / mol or to 150 000 g / mol or to 100000 g / mol, more preferably of from 15000 g / mol to 125000 g / mol or to 90000 g / mol, still more preferably of from 20 000 g / mol to 80 000 g / mol, yet more preferably of from 30 000 g / mol to 75000 g / mol. The weight average molecular weight is determined according to the method as outlined in the ‘methods' section.

[0103] Preferably, the at least one polymer bearing at least one kind of acid groups and being present as constituent a3) in the aqueous acidic composition AAC is a homopolymer or copolymer, more preferably a copolymer, obtainable from polymerization of at least two different kinds of ethylenically unsaturated monomers. Preferably, at least as one kind of ethylenically unsaturated monomers at least one kind of (meth)acrylic monomers is used.

[0104] The term "(meth)acrylic” means "acrylic” and / or "methacrylic”. Similarly, "(meth)acrylate” means acrylate and / or methacrylate. The polymer being present as constituent a3) can be regarded as a "(meth)acrylic polymer”, when it is formed at least partially from "acrylic monomers” and / or "methacrylic monomers”, but it additionally may contain non-acrylic and / or non-methacrylic monomeric units if other ethylenically unsaturated monomers such as vinyl monomers, e.g., styrene, have been additionally used for its preparation. Preferably, the polymer is formed from more than 20 wt.-%, even more preferably of from more than 25 wt.-%, still more preferably of more than 30 wt.-%, yet more preferably of more than 35 wt.-%, of (meth)acrylic monomers.

[0105] Preferably, the at least one polymer being present as constituent a3) is a (meth)acrylic homopolymer in case precisely one kind of (meth)acrylic monomers is used for its polymerization, or is a (meth)acrylic copolymer in case at least two kinds of (meth)acrylic monomers, which are different from one another, or at least one kind of (meth)acrylic monomers and at least one kind of further monomers are used for its polymerization, wherein said at least one kind of further monomers are ethylenically unsaturated monomers, which are not (meth)acrylic monomers.

[0106] Preferably, the at least one kind of acid groups of polymer constituent a3) are selected from carboxylic acid groups, phosphorous containing acid groups such as phosphonic acid groups, and sulfonic acid groups, and mixtures thereof, more preferably from carboxylic acid groups, phosphorous containing acid groups such as phosphonic acid2024P00038WO I L024883PCT 15 February 17, 2026 Chemetall GmbH

[0107] groups, and mixtures thereof. Most preferably, at least carboxylic acid groups are present as acid groups, e.g., as only acid groups or in combination with phosphonic acid groups.

[0108] Suitable ethylenically unsaturated monomers, which bear carboxylic acid groups, are suitable (meth)acrylic monomers such as acrylic acid, and methacrylic acid, and / or are suitable non-(meth)acrylic monomers such as maleic acid, and mixtures thereof.

[0109] Suitable ethylenically unsaturated monomers, which bear phosphorous containing acid groups, are suitable (meth)acrylic monomers such as, e.g., 2-(meth)acryloyloxyethyl phosphate, 3-(meth)acryloyloxypropyl phosphate, 4-(meth)acryloyloxybutyl phosphate, 10-(meth)acryloyloxydecyl dihydrogen phosphate, ethyl-2-[4-(dihydroxyphosphoryl)-2-oxabutyl] (meth)acrylate and 2,4,6-trimethylphenyl-2-[4-(dihydroxyphosphoryl)-2-oxabutyl] (meth)acrylate, and / or are suitable non-(meth)acrylic monomers such as vinyl monomers such as vinyl phosphonic acid, vinyl phosphonic acid in a form at least partially esterified with a Ci-s alkyl alcohol, vinyl phosphoric acid in a form at least partially esterified with a Ci-s alkyl alcohol, and mixtures thereof.

[0110] It is also possible to introduce the phosphorous containing acid groups afterwards in a polymer analogous reaction. Preferably, in case of introducing said acid groups after the polymerization has taken place, a monomer comprising a suitable moiety for later modification is used for polymerization to generate a precursor structural unit. Preferably, at least one monomer selected from the group consisting of preferably (meth)acrylic monomers having at least one epoxide group is used. Most preferred is glycidyl (meth)acrylate. For introducing the at least one phosphorous containing acid groups a suitable phosphorous containing compound is used, preferably a compound having at least one phosphorous containing group, which can react with the epoxide moiety after ring opening of the epoxide group and form the at least one phosphorous containing acid groups. Preferably, the phosphorous containing compound is selected from the groups consisting of phosphoric acid including polyphosphoric acid, P2O5, and phosphoryl chloride, as well as phosphonic acid and / or esters and / or derivatives thereof such as octyl phosphonic acid, and leads to formation of at least one phosphorous containing acid groups selected from phosphonic acid groups and / or partial esters and / or salts thereof. However, this approach is not preferred.

[0111] Preferably, the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC, which is a homopolymer or copolymer, more preferably a copolymer, bears at least carboxylic acid groups as acid groups, wherein said carboxylic acids are more preferably present in structural units of the polymer, which are obtainable from polymerization of (meth)acrylic acid monomers, even more preferably of acrylic acid monomers.

[0112] Preferably, the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC is a homopolymer or copolymer, more preferably a copolymer, which is obtainable from polymerization of at least (meth)acrylic acid monomers, more preferably of acrylic acid monomers, and at least one further and preferably acid functional monomer different from (meth)acrylic acid, wherein said at least one further acid functional monomer is more preferably selected from maleic acid, vinyl phosphonic acid, and mixtures thereof. It is also or alternatively2024P00038WO I L024883PCT 16 February 17, 2026 Chemetall GmbH

[0113] possible to further employ non-functional ethylenically unsaturated monomers such as vinyl methyl ether, in particular when maleic acid is used as acid-functional monomer.

[0114] Preferably, if the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC is a copolymer, it bears at least two different kinds of structural units SU1 and SU2. At least one of SU1 and SU2 bears the at least one kind of acid groups, preferably both of SU1 and SU2 each bear at least one kind of acid groups. The kinds of acid groups can be the same such as in case of a copolymer obtainable from acrylic acid and maleic acid or can be different from one another such as in case of a copolymer obtainable from acrylic acid and vinyl phosphonic acid.

[0115] Preferably, the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC is a copolymer and

[0116] contains structural units SU1 derivable from at least one suitable ethylenically unsaturated monomer, preferably from at least one (meth)acrylic monomer, which contains at least one acid group such as at least one carboxylic acid group, wherein said at least one (meth)acrylic monomer is most preferably acrylic acid, and further

[0117] contains structural units SU2 derivable from at least one suitable ethylenically unsaturated monomer, preferably from at least one non-(meth)acrylic monomer, which contains at least one acid group such as at least one carboxylic acid group and / or at least one phosphorous containing acid group such as at least one phosphonic acid group, wherein said at least one non-(meth)acrylic monomer is most preferably maleic acid and / or vinyl phosphonic acid,

[0118] wherein said polymer preferably contains structural units SU1 in an amount in a range of from 35 to 95 wt.-%, preferably of from 40 to 90 wt.-%, more preferably of from 45 to 85 wt.-%, even more preferably of from 47.5 to 80 wt.-%, and structural units SU2 in an amount in a range of from 5 to 65 wt.-%, preferably of from 10 to 60 wt.-%, more preferably of from 15 to 55 wt.-%, even more preferably of from 20 to 52.5 wt.-%,

[0119] wherein the sum of all structural units, of course, adds up to 100 wt.-% in each case.

[0120] Preferably, the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC, in case it is a copolymer, is not a block copolymer. Rather, preferably it is a statistical or alternating copolymer.

[0121] It is also possible to use two different kinds of polymer constituents a3) such as at least one copolymer as defined hereinbefore such as a copolymer of maleic acid and acrylic acid in combination with a homopolymer such as poly (meth)acrylic acid.2024P00038WO I L024883PCT 17 February 17, 2026 Chemetall GmbH

[0122] Optional constituent a4)

[0123] At least one corrosion inhibitor is present as optional constituent a4) in composition AAC. Preferably, constituent a4) is present in composition AAC.

[0124] Preferably, the at least one corrosion inhibitor is present in the aqueous acidic composition AAC in an amount in a range of from 0.005 to 1.5 wt.-%, more preferably of from 0.010 to 1.25 wt.-%, even more preferably of from 0.010 to 1.00 wt.-%, based on the total weight of the composition.

[0125] Preferably, the at least one corrosion inhibitor is present in the aqueous acidic composition AAC in an amount in a range of from 0.001 to 10.0 mmol / L, more preferably of from 0.005 to 7.5 mmol / L, even more preferably of from 0.010 to 5.0 mmol / L, yet more preferably of from 0.050 to 2.5 mmol / L, most preferably of from 0.100 to 1.0 mmol / L.

[0126] Preferably, the corrosion inhibitor as such is solid or is liquid at 23 °C and atmospheric pressure.

[0127] Preferably, the at least one corrosion inhibitor has a water solubility at 23 °C of less than 40 g / L, more preferably of less than 30 g / L, even more preferably of less than 20 g / L, yet more preferably of less than 15 g / L, even more preferably of less than 10 g / L, still more preferably of less than 7.5 g / L, yet more preferably of less than 5.0 g / L, still more preferably of less than 2.5 g / L, most preferably of less than 1 g / L.

[0128] Some suitable corrosion inhibiting constituents are, e.g., described in S. Gangopadhyay et al., J. Coat. Technol. Res. 2018, 15 (4), p. 789-807, M. L. Zheludkevich et al., Chem. Mater. 2007, 19, p. 402-411 and S. B. Ulaeto et al., Progress in Organic Coatings 2019, 136, 105276.

[0129] Preferably, the corrosion inhibitor is an inorganic or organic constituent, more preferably is an organic compound, even more preferably an organic compound having at least one cycloaliphatic, heterocycloaliphatic, aromatic and / or heteroaromatic moiety, still more preferably having at least one C3-C4o-cycloaliphatic moiety, at least one C3-C40-heterocycloaliphatic moiety, which comprises at least one heteroatom and / or at least one heteroatom group, wherein the heteroatom is in each case preferably selected from O, N and S, at least one C5-C4o-aromatic moiety and / or at least one C5-C4o-heteroaromatic moiety, which comprises at least one heteroatom and / or at least one heteroatom group, wherein the heteroatom is in each case preferably selected from O, N and S. Yet more preferably, the organic compound comprises at least one C3-C25-cycloaliphatic moiety, at least one C3-C25-heterocycloaliphatic moiety, which comprises at least one heteroatom and / or at least one heteroatom group, wherein the heteroatom is in each case preferably selected from O, N and S, at least one C5-C25-aromatic moiety and / or at least one C5-C25-heteroaromatic moiety, which comprises at least one heteroatom and / or at least one heteroatom group, wherein the heteroatom is in each case preferably selected from O, N and S.

[0130] Suitable corrosion inhibitors are, e.g., disclosed in L. K. M. O. Goni et al., Chem. Asian J. 2021, 16, 1324-1364, and includes heterocyclic compounds such as imidazoles, pyrazoles, oxazoles, pyridindes, triazines, tetrazines,2024P00038WO I L024883PCT 18 February 17, 2026 Chemetall GmbH

[0131] diazines (such as pyrazines, pyridazines and pyrimidines), indoles, triazoles, tetrazoles, thiazoles, thiadiazoles, and mixtures thereof. Exemplary compounds are 2-(3-Methoxyphenyl)-4,5-diphenyl-1 H-imidazole, 1-Benzylimidazole, 3-Methoxy-4-(1 ,4,5-triphenyl-1 H-imidazol-2-y l)phenol, 2-(4-Methoxyphenyl)- 1 ,4,5-triphenyl-1 H-imidazole, 4-Methoxy-2-naphthalen-1-yl-4,5-dihydro-1 H-imidazole, 2-(4-Methoxyphenyl)-4,5-diphenyl-imidazole, 6-Phenyl-2,3,5,6-tetrahydroimidazo[2,1-b][1,3]thiazole, (E)-N‘-(4-Chlorobenzylidene)-2-(3,5-dimethyl-1 H-pyrazol-1-yl)-acetohydrazide, (E)-5-(4-(dimethylamino)phenyl)-3-(4-(dimethylamino)styryl)-2,3-dihydro-1 H-pyrazole-1-carbothioamide, 6'-Amino-3'-methyl-2-oxo-1'-phenyl-1'H-spiro[indoline-3,4'-pyrano-[2,3-c]pyrazole]-5' -carbonitrile, (E)-5-Amino-3-(methoxyphenyl)-N'-(1-(4-methoxyphenyl)ethylidene)-1H-pyrazole-4-carbohydrazide, 5-(4-(Dimethylamino)phenyl)-3-phenyl-4,5-dihydro-1 Hpyrazole-1 -carboxamide, 4,4’-((2-hydroxy-4-methoxyphenyl)methylene)-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol), 4-((E)-((E)-3-(4-methoxyphenyl)allylidene)amino)-1 , 5-d i methy l-2-pheny I- 1 H-py razol-3(2 / - / )-one, 3, 3'-(1 , 4-pheny lene)bis-(2-imino-2,3-dihydrobenzo[d]oxazole-5,3-diyl)bis(4-ethylbenzenesulfonate), 2,5-bis(2-pyridyl)-1,3,4-oxadiazoles, E)-2-(2-(pyren-2-yl)vinyl)benzol[d]oxazole, 2-Methyl-2-{4-[5-(6-methylpyridin-2-yl)-[1,3,4]oxadiazol-2-yl]-phenyl}-propionitrile, 2-Phenyl-4-[(E)-1-(4-sulfanylanilino)-methylidene]-1,3-oxazole-5(4H)-one, 2-Butyl-hexahydropyrrolo[1,2-b][1,2]oxazole, 4-{[(4-Ethyl-2-phenyl-4,5-dihydro-1,3-oxazol-4-yl)-methoxy]methyl}benzene- 1-sulfonate, 5-((4,5-dihydro-oxazol-2-yl)methyl)quinoline-8-ol, N-(Benzo[d]thiazole-2-ylimino)ethylaniline, Methyl (E)-2-(((E)-4-chlorobenzylidene)hydrazono)-5-(4-chlorophenyl)-2,3-dihydrothiazole-4-carboxylate, (S)-6-Phenyl-2,3,5,6-tetrahydroimidazo[2, 1-b]thiazole hydrochloride, 3-((4-Amino-2-methylpyrimidin-5-yl)methyl)-5-(2-hydroxyethyl)-4-methylthiazol-3-ium chloride, 4-(2-Aminothiazole-4-yl)phenol, 4-(Pyridin-3-yl)thiazol-2-amine, 2-Amino-4-(4-methoxyphenyl)-thiazole, 2-Amino-(4-bromophenyl)-thiazole, 2-Amino-4-methyl-1,3-thiazole-5-carboxylate, 2-Amino-5-(4-nitrophenyl)-1,3,4-thiadiazole, 2-Amino-5-(2-methoxyphenyl)-1,3,5-thiadiazole, N,N'-(1 , 4-pheny lenebis(methanyly I idene)) bis-(5-methylth i o)- 1 , 3,4-thiadi azol -2-amine), 5-Amino-1 ,3-thiadiazole-2-thiol, 2.5-Dimercapto-1 , 3, 4-th i ad i azol e, (4-Dimethylamino-benzylidene)-[1 , 3,4] thi adi azol -2-yl-ami ne, 5,5'- Disulfanediylbis-1,3,4-thiadiazol-2-amine, 3,3’-((4-methylthio)phenyl)methylene)-bis(1 H-indole), 1-Methyl-9H-pyridol[3,4-b]indole, Indole, 5-Chloro-1-(2-dimethylamino)ethyl)-indoline-2, 3-dione, 3-(phenyl(piperidin-1-yl)methyl)-1 H-indole, 1-Allyl-5-chloro-indoline-2, 3-dione, Benzotriazole, 5-Methyl-1 H-benzotriazole, 5-Methyl benzoxazole-2-tione, 2-(2-Chlorophenyl)-1H-benzimidazole, 1 ,4-Bis(2-(4-chlorophenyl)-1 Hbenzo[d]imidazole-1-yl)butane, Methyl-5-benzoyl-2-benzimidazole carbamate, Decyl-2-[(5-methylisoxazol-2-yl)methyl]benzimidazole, 2-(2-(4-Chlorophenyl)-1 H)benzo[d]imidazole-1-yl)-N-(3,5-dimethylphenyl)acetamide, 2-Mercaptobenzothiazole and sodium phosphate dibasic dehydrate, 2-Amino-5-chloropyridine, 6-Bromo-2-(4-methoxyphenyl)-3-nonyl-3Himidazo[4,5-b]pyridine, Pyridine, 1 ,4,7-Tris[hydrogen(6-methylpyridin-2-yl)phosphonate]-1 ,4,7-triazacyclononane, 2,4-Diamino-7-hydroxy-5-(phenylthiol)-5Hchromeno[2,3-b]pyridine-3-carbonitrile, 2-(Dibutylamino)-4,6-Dimercapto-1 ,3,5-Triazine, 6-((1,3,4-thiadiazol-2-yl)thio)-N2-(3-(dimethylamino)propyl)-N4-octyl-1 ,3, 5, -trizine-2, 4-diamine, 1 , 3- Bis-(5, 6-d i ph eny I- 1 , 2,4-tri azin-3-y l)thiourea, 1 ,3,5-T ris-(4-methoxyphenyl)- 1.3.5-triazine, 5-(2-Hydroxyethyl)-1,3,5-triazine-2-thione, Triazine-Methionine, 6-Dibutylamino-1 ,3,5-triazine-2,4-dithiolmonosodium, 6-Dibutylamino-1,3,5-triazine-2,4-dithiolmonosodium, 6-(4-Hydroxyphenyl)-3-mercapto-7,8-di hy d ro-[ 1 ,2, 4]triazol [4,3-b] [1 , 2, 4,5] tetrazi ne, 3,6-Bis(2-methoxyphenyl)-1 , 2-di hyd ro- 1 , 2, 4,5-tetrazi ne, E)-N- {(Thiophene-2-yl)methylene}-pyrazine-2-carboxamide, 2,5-Dimethylpyrazine, 4-(6-Phenyl-pyridazin-3-ylsulafnyl)-2024P00038WO I L024883PCT 19 February 17, 2026 Chemetall GmbH

[0132] butyric acid ethyl ester, 1-((3,6-Di(pyridine-2-yl)pyridazine-4-yl)methyl)-indoline-2, 3-dione, (6-Phenyl-pyridazin-3-ylsulfanyl)-acetic acid (2,4-dihydroxy-benzylidene)-hydrazine, 5-Styryl-2, 7-dithioxo-2, 3,5,6, 78-hexahydropyrimido-[4,5-d]pyrimidin-4(1 H)-one, 6-Phenyl-2H-pyridazine-3-thione, 2-(6-Chloropyridazin-3-yl)-2-phenylacetone, Acenaptho[1,2-b]pyrazine, 8,8-Dimethyl-5-p-tolyl-8,9-dihydro-1 H-chromeno(;)pyridmidine-2,4,6(3H,5H,7H)-trione, 4-Mercaptopyrazolo-pyrimidine, 5-(4-hydroxyphenyl)-10-((3R,5S,6R)-2,4,5-trihydroxy-6- (hydroxymethyl)tetrahydro-2H-pyran-3-yl)-9, 10-dihydropyrido[2,3-d:6,5-d]dipyrimidine-2,4,6,8(1 H,3H,5H,7H)-tetraone, 5-((2-(4-nitrophenyl)-1 H-benzo[d]imidazol-1-yl)methyl)quinolin-8-ol, 2,3-di(furan-2-yl)quinoxaline, 4-(1-((4-hydroxynaphthalen-1-yl)methyl)-5-methyl-1H-benzo[d]imidazol-2-yl)benzoic acid, 4,4’,4”,4”'-(porphyrin-5, 10,15,20-tetrayl)tetrakis(benzoic acid), 1 ,2,4,7,9,10-hexaazacyclo-pentadeca-10, 15-dien-3,5,6,8-tetraone, 1 ,2, 4, 7, 9, 10-hexaazacyclo-pentadeca-10, 15-di en-3, 5, 6, 8-tetraone, 1 -phenyl-1 , 2-d i hy d ron aph tho [ 1 ,2-e]- [1 ,3]oxazin-3-one, 8-Hyd roxyqu i noline, 2-amino-4-(4-(dimethylamino)phenyl)-7-hydroxy-1 , 4-d i hydroq ui noline-3-carbonitrile, 2-(Di butylami no)-4, 6-d i mercapto- 1 , 3, 5-triazine, 1 ,3,5-T ris(4-methoxyphenyl)-1 ,3,5-triazine, 2-(4-Methoxyphenyl)-4,5-diphenyl-imidazole, (E)-2-(2-(Pyren-2-yl)vinyl)benzo[d]oxazole, 6'-Amino-3'-methyl-2-oxo-1'-phenyl-1'Hspiro[indoline-3,4'-pyrano[2,3-c]pyrazole]-5' -carbonitrile, 5-(3-Aminophenyl)tetrazole, Ethyl-2-Amino-4-methyl-1 ,3-thiazole-5-carboxylate, 1 ,2,4-Triazole, and mixtures thereof.

[0133] Examples of corrosion inhibiting constituents are also azole moiety containing compounds such as benzotriazole and benzothiazole, and further also compound such as 3-amino-1 H-triazole, 3-amino-5-mercapto-1,2,4-triazole, 1,2,4-triazole, 5-methyl-1H-benzotriazole, 3-amino-5-methylthio-1H-1,2,4-triazole, and 3-mercapto-1,2,4-triazole. Additional examples are benzimidazole, 1 -methylbenzimidazole, 1 -phenylbenzimidazole, and 2-phenyl-benzimidazole. Further examples are 3-methylsalicylic acid, 4-methylsalicylic acid, 5-methylsalicylic acid, 6-methylsalicylic acid, 3-sulfosalicylic acid, 4-sulfosalicylic acid, 5-sulfosalicylic acid, 6-sulfosalicylic acid, 3-aminosalicylic acid, 4-aminosalicylic acid, 5-aminosalicylic acid, 6-aminosalicylic acid, and thiosalicylic acid and salts thereof. Further examples are quercetine and urea as well as 2,6-diamino-2-mercaptopyrimidine.

[0134] Preferably, the at least one corrosion inhibitor being present as constituent a4) in composition AAC exhibits an inhibition efficiency of at least 40%, more preferably of at least 60%, still more preferably of at least 80%, yet more preferably of at least 85%, in in at least one of three different aqueous electrolytic solutions thereof, each of which contain the at least one corrosion inhibitor in an amount in a range of from 0.1 to 5.0 wt.-%, based on the total weight of the aqueous solution, wherein said three different aqueous electrolytic solutions differ from each other in their pH values, which are 3.0, 7.0, or 9.0, respectively, wherein the at least one corrosion inhibitor preferably exhibits the aforementioned inhibition efficiency in at least two of said three aqueous solutions and more preferably in all three aforementioned aqueous solutions, and wherein the inhibition efficiency is determined via an electrochemical testing procedure in terms of determining linear polarization resistance (LPR) and / or electrochemical impedance spectroscopy (EIS) and / or potentiodynamic scan (PDS). By this method it is determined if and to what extent the at least one corrosion inhibitor is able to reduce the corrosion current density and the limiting current of the cathodic reaction taking place in an electrolytic cell.2024P00038WO I L024883PCT 20 February 17, 2026 Chemetall GmbH

[0135] Optional constituent a5)

[0136] Optionally, aqueous acidic composition AAC comprises copper cations as constituent a5), preferably in an amount in a range of from 0 or 1 to 1 000 mg / L, more preferably of from 0 or 1 to 500 mg / L, even more preferably of from 0 or 1.5 to 250 mg / L, still more preferably of from 0 or 2 to 150 mg / L, yet more preferably of from 0 or 2.5 to 100 mg / L, even more preferably of from 0 or 5 to 50 mg / L, most preferably of from 0 or 7.5 to 30 mg / L, in each case calculated as metal. It has been found that the presence of copper ions has a positive effect on increasing the Zr and / or Ti coating weight of the chemically pretreated substrate, when Zr and / or Ti cations are present as optional constituent a1).

[0137] Optional constituent a6)

[0138] Optionally, aqueous acidic composition AAC comprises zinc cations as constituent a6), preferably in an amount in a range of from 0 or 5 to 5000 mg / L, more preferably of from 0 or 10 to 2500 mg / L, even more preferably of from 0 or 25 to 1 000 mg / L, still more preferably of from 0 or 50 to 750 mg / L, yet more preferably of from 0 or 100 to 600 mg / L, in each case calculated as metal. It has been found that the presence of zinc ions has a positive effect on the corrosion resistance.

[0139] Optional constituent a7)

[0140] Optionally, aqueous acidic composition AAC comprises at least one organosilane and / or at least one hydrolysis and / or condensation product thereof as constituent a7).

[0141] Examples of hydrolysis and / or condensation products of organosilanes that can be formed in the presence of water are organosiloxanes and polyorganosiloxanes. The term "organo” in "organosilane” preferably means that at least one organic group is present, which is connected directly to a silicon atom via a carbon atom and can consequently not be subjected to hydrolysis.

[0142] Preferably, optional constituent a7) has at least one functional group selected from (meth)acrylate groups, alkylaminoalkyl groups, alkylamino groups, alkyltetrasulfide groups, amino groups, aminoalkyl groups, carboxyl groups, epoxy groups such as glycidoxy groups, isocyanato groups, mercaptoalkyl groups, succinic anhydride groups, imido groups, imino groups, and / or ureido groups (urea groups).

[0143] Examples of suitable organosilanes are, e.g., aminoalkyltrialkoxysilanes, such as, preferably, 2-aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutyltriethoxysilane, bis(2-ethyltrimethoxysilyl)amine, bis(3-propyltrimethoxysilyl)amine, bis(4-butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine, bis(3-propyltriethoxysilyl)amine and / or bis(4-butyltriethoxysilyl)amine. Further examples of suitable organosilanes are 1 ,2-bis(triethoxysilyl)ethane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, (3-glycidyloxypropyl)triethoxysilane, and / or vinyltrimethoxysilane.2024P00038WO I L024883PCT 21 February 17, 2026 Chemetall GmbH

[0144] Optionally, at least one aminoalkyltrialkoxysilane and / or at least one hydrolysis and / or condensation product thereof is present as optional constituent a7).

[0145] Preferably, optional constituent a7) is present in the composition AAC in such an amount that results in a content of Si in a range of from 1 or 5 to 500 mg / L, more preferably of from 7.5 to 250 mg / L, even more preferably of from 10 to 100 mg / L, still more preferably of from 20 to 80 mg / L, most preferably of from 25 to 50 mg / L, in each case calculated as elemental silicon. The amount of Si can be measured according to the method described in the ‘methods' section, i.e., by ICP-OES.

[0146] Optional constituent a8)

[0147] Optionally, aqueous acidic composition AAC comprises at least one complexing agent as constituent a7).

[0148] Preferably, the at least one complexing agent a8) is suitable to complex constituent a1), and more preferably is selected from organic compounds bearing at least one kind of functional groups, which are able to coordinate to constituent a1) in water, even more preferably is selected from organic compounds bearing at least one kind of functional groups selected from OH-groups, carboxylic acid groups, salts and / or derivatives such as esters thereof, and mixtures thereof, still more preferably is selected from organic compounds bearing both at least one OH-group and at least one carboxylic acid group, a salts and / or a derivatives such as an ester thereof. Examples of suitable complexing agents a8), which bear both at least one OH-group and at least one carboxylic acid group are lactic acid, citric acid, gluconic acid, and galactaric acid. Citric acid is particularly preferred.

[0149] Complexing agent a8) may be an organic compound, which is suitable to form at least one organic metalate with constituent a1), wherein the metal of the metalate is selected from Ti, Zr and Hf, more preferably from Ti and Zr. Hence, most preferably, the metalate corresponds to a titanate and / or zirconate, in particular to a zirconate in this case.

[0150] Preferably, complexing agent a8) comprises at least one organic group, that is suitable to form at least one organic metalate with constituent a1). Preferably, the organic group(s) are bonded to constituent a1), more preferably to titanium and / or zirconium via divalent oxygen atoms. Preferably, constituent a8) comprises at least one alkoxide groups, wherein each alkoxide group preferably represents a -O-Ci-Cs group, more preferably a -O-C3-C8 group. Even more preferably, each alkoxide group has 3 to 6, still more preferably 3 to 4 carbon atoms. Examples of alkoxide groups are n-butyl alkoxides, n-propyl alkoxides, isopropyl alkoxides. Exemplary metalates such as titanates and / or zirconates formed by constituents a1) and a8) are tetra-n-butyl zirconate (available under the trade name Tyzor® NBZ), tetra-n-propyl titanate (available under the trade name Tyzor® TPT by Dorf Ketal) and titanium acetyl acetonate (available under the trade names Tyzor® AA 75, Tyzor® AA 65 and Tyzor® AA 105 by Dorf Ketal).2024P00038WO I L024883PCT 22 February 17, 2026 Chemetall GmbH

[0151] More preferably, complexing agent a8) is selected from organic compounds comprising an organic group, which comprises both at least one OH-group and at least one carboxylic acid group, such as citric acid. Citrates of a1) can be, e.g., prepared by reacting a suitable alkoxide of a1) such as titanium tetra-isopropylate and / or zirconium tetra-isopropylate with citric acid, e.g., in a molar ratio of about 1:1. Formed isopropanol may be distilled of afterwards.

[0152] Further, suitable metal halogenides (with the metal being selected from Ti, Zr and Hf) can react with suitable organic compounds, which comprise at least one OH-group under hydrogen halide cleavage to build the desired complex.

[0153] Preferred suitable complexing agents for use as constituent a8) are selected from glycolic acid, gluconic acid, lactic acid, 2-hydroxybutanoic acid, leucic acid, glyceric acid, malic acid, citric acid, tartaric acid, fumaric acid, maleic acid, mandelic acid, quinic acid, aromatic hydroxy carboxylic acids such as, e.g., salicylic acid and other hydroxy carboxylic acids as well as keto acids, glycerin, oxalic acid aspartic acid, and asparagine, nitrogen-containing complexing agents such as N,N,N',N'-tetrakis(2-hydroxyethyl)ethylene-diamine and / or N,N,N',N'-tetrakis(2-hydroxypropyl)-ethylenediamine and mixtures thereof. Nitrogen-containing complexing agents are, e.g., described in WO 2008 / 155568 A1 and WO 2008 / 155569 A1.

[0154] Preferably, the molar ratio of complexing agent a8) to constituent a1) is in a range of from 0.5 to 1.0 to 8.0 to 1.0, more preferably of from 0.5 to 1.0 to 6.0 to 1.0, even more preferably of from 1.0 to 1.0 to 3.0 to 1.0.

[0155] Preferably, the aqueous composition comprises the at least one complexing agent present as constituent a8) in an amount of from 0.25 to 3.0 wt.-%, more preferably of from 0.5 to 2.5 wt.-%, based on the total weight of the composition.

[0156] Further optional constituent(s)

[0157] The aqueous acidic composition AAC may contain one or more further optional constituent(s).

[0158] Optionally, the aqueous acidic composition AAC further comprises at least one kind of metal cations selected from the group of cations of metals of the 1stto 3rdsubgroup (copper, zinc and scandium groups) and 5thto 8thsubgroup (vanadium, manganese and iron groups) of the periodic table of the elements including the lanthanides as well as the 2ndmain group of the periodic table of the elements (alkaline earth metal group), lithium and bismuth and / or tin, except of copper and zinc ions, which may already be present as optional constituents a5) and a6). More preferably the aqueous acidic composition AAC further optionally comprises at least one kind of metal cations selected from the group consisting of cations of cerium and other lanthanides, iron, calcium, cobalt, magnesium, manganese, molybdenum, niobium, tantalum, yttrium, vanadium, lithium, bismuth, and tin, and mixtures thereof.

[0159] Optionally, the aqueous acidic composition AAC further comprises at least one of the following constituents: one or more waxes, one or more wetting agents and one or more defoamers and / or rheology additives.2024P00038WO I L024883PCT 23 February 17, 2026 Chemetall GmbH

[0160] Optional step 2)

[0161] According to optional step 2) the cleaned and chemically pretreated surface obtained after step 1) is rinsed at least once with water and / or at least once with an aqueous rinsing composition ARC, preferably at least once with water.

[0162] Preferably, the water used in optional step 2) has a pH value <5.0, more preferably <4.8, even more preferably is in a range of from 3.5 to 4.7 or of from 3.8 to 4.6 or of from 3.9 to 4.5.

[0163] The term "rinsing” preferably means, in accordance with the general understanding of this term, a removal of excessive parts of the aqueous acidic composition AAC, which was contacted with the surface in step 1) directly preceding the optional rinsing step. Tap water and / or deionized water can be used for rinsing in optional step 2). As outlined hereinbefore, optional step 2) can be performed more than once. It is hence possible, e.g., to perform a rinsing in step 2) once with tap water followed by rinsing with deionized water or vice versa. If optional step 2) is performed, it is preferably carried out twice, first with tap water and then with deionized water. If optional step 2) is performed, it is also possible to be carried out just once, either with tap water or with deionized water.

[0164] It is, however, possible that optional rinsing step 2) is not performed. This has the advantage that less water to be used in total for performing the method is necessary. In addition, a rinsing zone in the setup and pretreatment line used for performing the cleaning and chemical pretreatment method is not necessary.

[0165] Optional step 3)

[0166] According to optional step 3) the cleaned and chemically pretreated surface obtained after step 1) or after optional step 2) is subjected to drying and / or curing. In particular, at least the portion of the metallic surface of the substrate that has been contacted with the aqueous acidic composition AAC in step 1) or that has been rinsed according to optional step 2) is subjected to drying and / or curing.

[0167] Optional step 3) is performed in order to obtain a cured or dried coating layer. Preferably, by performing the optional step 3) of drying or curing, more preferably of drying, the conversion coating film obtained after step 1) is dried or cured, preferably dried. As a result, dried or cured, preferably dried, a conversion coating layer from the conversion coating film is obtained.

[0168] Drying and / or curing may be performed in particular, when in a step 4) as outlined hereinafter, a coating material composition is subsequently applied. However, step 3) is only optional and, hence, further method steps such as step 4) may be carried out without drying and / or curing the film obtained after having performed step 1) and optionally step 2). In particular, it is possible to apply a coating material composition such as an electrodeposition coating material composition in a step 4) as outlined hereinafter onto a wet film obtained after having performed step 1) and optional step 2), although in such a case preferably prior to that step 3) is carried out.2024P00038WO I L024883PCT 24 February 17, 2026 Chemetall GmbH

[0169] The drying or curing step 3) may be preferably performed (if performed at all), e.g., at a temperature in the range of 15°C to 180°C, more preferably at a temperature in the range of 25°C to 150°C, in particular at a temperature in the range of 50°C to 130°C. "Drying” in the sense of the present invention means physical drying by evaporation of in particular water originally present in the composition(s) used, whereas "curing” further includes a chemical reaction between at least two constituents originally present in the composition(s) and / or between at least one constituent originally present in the com posit! on (s) and a suitable functional group present on the metallic surface or in the conversion film. Once a film is dried, the resulting product can be regarded as a layer.

[0170] Preferably, the dry layer thickness of a conversion layer formed after drying or curing, preferably drying, the film obtainable after step 3), is below 0.5 m. Preferably, the obtained cured or dried coating layer obtained after step 3) has a dry film thickness in a range of from 1 nm to <500 nm, more preferably of from 10 nm to 250 nm.

[0171] Substrate obtainable by cleaning and chemical pretreatment method

[0172] A further subject-matter of the present invention is a substrate having at least one metallic surface, wherein said surface is an at least in portion cleaned and chemically pretreated surface, which is obtainable by the inventive method of cleaning and chemical pretreatment as defined hereinbefore and hereinafter.

[0173] All preferred embodiments described above herein in connection with the cleaning and chemical pretreatment method and preferred embodiments thereof are also preferred embodiments of the substrate obtainable by this method.

[0174] Preferably, the cleaned and chemically pretreated surface comprises a cured or dried coating layer, when step 3) is performed. Preferably, said cured or dried coating layer has a dry film thickness in a range of from 1 nm to <500 nm, more preferably of from 10 nm to 250 nm.

[0175] The cleaned and chemically pretreated surface preferably has a coating weight of Zr, Ti, and / or Hf, if optional constituent a1) had been present in the composition AAC, preferably of Zr and / or Ti, more preferably of Zr, in each case calculated as metal, in a range of from 1 to 200 mg / m2, more preferably of from 2 to 100 mg / m2, still more preferably of from 3 to 50 mg / m2, even more preferably of from 4 to 25 mg / m2, most preferably of from 5 to 15 mg / m2, determined in each case via XRF measurements as outlined in the ‘methods' section.

[0176] Aqueous acidic composition AAC & concentrate

[0177] A further subject-matter of the present invention is an aqueous acidic composition AAC as defined hereinbefore and hereinafter or a concentrate, from which said aqueous acidic composition AAC is at least obtainable by dilution with water and, optionally further, by pH adjustment.2024P00038WO I L024883PCT 25 February 17, 2026 Chemetall GmbH

[0178] All preferred embodiments described above herein in connection with the cleaning and chemical pretreatment method, the substrate obtainable by said method, and in each case preferred embodiments thereof are also preferred embodiments of the composition AAC and the concentrate as such.

[0179] Preferably, aqueous coating composition AAC can be prepared from a concentrate by dilution of the concentrate with water.

[0180] The concentrate used to produce the aqueous coating composition AAC typically contains the constituents of the aqueous coating composition AAC to be produced in the desired proportions, but at a higher concentration. Such concentrate is diluted with water to the desired concentrations of the constituents as disclosed hereinbefore to form aqueous coating composition AAC. If necessary, the pH value of the composition may be adjusted after dilution as well as outlined hereinbefore. Of course, it is also possible to further add any of the optional constituents of the composition to the water used for dilution or to add any of the optional or some of the necessary constituents after diluting the concentrate with water. It is, however, preferred that the concentrate already contains all necessary constituents.

[0181] Preferably, the aqueous coating composition AAC is obtainable from a concentrate by dilution with water, preferably with deionized water, such that the concentrate is present in the composition after dilution in an amount of from 5 to 60 g / L, more preferably 10 to 40 g / L, even more preferably of from 15 to 30 g / L, based on the total weight of the composition (obtained after dilution of the concentrate).

[0182] Preferably, the concentrate is diluted with water in a weight ratio of 1:5000 to 1:10, more preferably of 1:1000 to 1:10, even more preferably of 1:300 to 1:10, still more preferably of 1:150 to 1:10, yet more preferably of 1:50 to 1:10, even more preferably of 1:20 to 1:5, most preferably of 1:10 or 1:5 to 1:2, to produce the aqueous coating composition AAC.

[0183] Use

[0184] A further subject-matter of the present invention is a use of the aqueous acidic composition AAC as defined hereinbefore and hereinafter simultaneously as cleaning and chemical pretreatment composition, preferably in the cleaning and chemical pretreatment method as defined hereinbefore and hereinafter, more preferably also for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon.

[0185] All preferred embodiments described above herein in connection with the cleaning and chemical pretreatment method, the substrate obtainable by said method, the composition AAC and the concentrate as such, and in each case preferred embodiments thereof are also preferred embodiments of the aforementioned inventive use.2024P00038WO I L024883PCT 26 February 17, 2026 Chemetall GmbH

[0186] Coating method

[0187] A further subject-matter of the present invention is a method of coating of at least one cleaned and chemically pretreated metallic surface of at least one substrate, wherein cleaning and chemical pretreatment of the at least one metallic surface has been carried out according to the inventive method of simultaneous cleaning and chemical pretreatment as defined hereinbefore and hereinafter or by making use of an inventive aqueous composition AAC, the method of coating further comprising at least step 4), namely

[0188] 4) applying at least one coating material composition comprising at least one film-forming polymer and / or resin onto the cleaned and chemically pretreated surface obtained after step 1) or after optional step 2) as defined hereinbefore and hereinafter or after optional step 3) as defined hereinbefore and hereinafter, i.e., in the latter case onto a dried or cured, preferably dried, layer, which in turn is obtainable from drying or curing according to optional step 3), in particular of a film obtainable from having performed step 1).

[0189] All preferred embodiments described above herein in connection with the cleaning and chemical pretreatment method, the substrate obtainable by said method, the composition AAC and the concentrate as such, the aforementioned inventive use, and in each case preferred embodiments thereof are also preferred embodiments of the inventive coating method.

[0190] The coating material composition applied in step 4) is different from the aqueous acidic composition AAC. The coating material composition used in step 4) preferably comprises at least one polymer being suitable as filmforming binder, which preferably is different from constituent a3) of composition AAC.

[0191] Preferably, the coating material composition used in step 4) is a powder coating composition and is applied after having performed step 3). Any conventional powder coating composition may be used in such a step such as a polyester powder coating composition.

[0192] Alternatively, the coating material composition used in step 4) can be, e.g., an electrodeposition coating composition, a primer coating composition, a basecoat composition, or a topcoat including a clearcoat composition. It is, of course, possible to apply more than one coating composition subsequently to form a multilayer coating system, which is conventionally used, e.g., in the automotive industry. However, most preferably, the coating composition used in step 4) is a powder coating composition and is applied after step 3).

[0193] Preferably, the at least one coating material composition is applied in step 4) onto the present dried or cured, more preferably dried, coating layer, which in turn is obtainable from drying or curing, preferably from drying, the coating film formed by having performed step 1) and optionally 2), wherein drying or curing, preferably drying, of the2024P00038WO I L024883PCT 27 February 17, 2026 Chemetall GmbH

[0194] resulting film in turn preferably is performed according to optional step 3) of the inventive method of cleaning and chemical pretreatment.

[0195] Substrate obtainable by coating method

[0196] A further subject-matter of the present invention is a substrate having at least one metallic surface, wherein said surface is a coated surface being obtainable by the inventive coating method as defined hereinbefore and hereinafter.

[0197] All preferred embodiments described above herein in connection with the cleaning and chemical pretreatment method, the substrate obtainable by said method, the composition AAC and the concentrate as such, the aforementioned inventive use, the inventive coating method, and in each case preferred embodiments thereof are also preferred embodiments of the of the substrate obtainable by this method.2024P00038WO I L024883PCT 28 February 17, 2026 Chemetall GmbH

[0198] METHODS

[0199] 1. Solid content

[0200] The solid content (non-volatile content) was determined via DIN EN ISO 3251:2019:09 at 105 °C for 60 min.

[0201] 2. ICP-OES

[0202] The amounts of certain elements in a sample under analysis, such as of zirconium, titanium, hafnium etc., was determined using inductively coupled plasma atomic emission spectrometry (ICP-OES) according to DIN EN ISO 11885 (date: September 1, 2009). A sample was subjected to thermal excitation in an argon plasma generated by a high-frequency field, and the light emitted due to electron transitions became visible as a spectral line of the corresponding wavelength and was analyzed using an optical system. There is a linear relation between the intensity of the light emitted and the concentration of the element in question. Prior to implementation, using known element standards (reference standards), the calibration measurements were carried out as a function of the particular sample under analysis. These calibrations could be used to determine concentrations of unknown solutions such as the concentration of the amount of titanium, zirconium, and hafnium.

[0203] 3. XRF (X-ray fluorescence spectroscopy)

[0204] XRF (X-ray fluorescence spectroscopy) was used for determining the coating weight in mg / m2of certain (tracer) element(s) such as Ti, Zr, Hf, and / or Si in a layer such as the conversion layer resulting from applying the chemical pretreatment composition to a substrate. XRF analyses were performed on the following instruments: Panalytical Axios max or Malvern Panalytical Zetium. There was one calibration per substrate for the particular element required. The calibrations were based on the data of the ICP measurements (the surface of the panels used for calibration was detached and measured by ICP; ICP uses standards traceable to NIST). The samples were circular blanks with a diameter of 4 cm.

[0205] 4. pH measurements

[0206] pH measurements were done using the device "WTW pH 330 I” with the following pH

[0207] electrode: "SI Analytics BlueLine 28 pH”. The calibration was done with three buffer solutions (traceable to SRM from NIST and PTB) with the following pH values: 4, 7, 10.

[0208] 5. Average molecular weight

[0209] The number average molecular weight (Mn) was determined by means of gel permeation chromatography (GPC) in accordance with DIN 55672-1 (date: August 2007). Besides the number-average molecular weight, this method may also be used to determine the weight-average molecular weight (Mw) and also the polydispersity d (ratio of weight average molecular weight (Mw) to number-average molecular weight (Mn)). An aqueous phosphate buffer (0.01 mol / L) having a pH of 7.4 and further containing 0.01 mol / L NaNa was used as eluent. The determination was made against polymethyl methacrylate standards. The column material consists of styrene-divinylbenzene copolymers.2024P00038WO I L024883PCT 29 February 17, 2026 Chemetall GmbH

[0210] 6. Glass transition temperature

[0211] The glass transition temperature was measured by means of DSC measurements in accordance with DIN EN ISO 11357-2 (2019-03).

[0212] 7. Water solubility

[0213] Water solubility is measured at 23 °C (at atmospheric pressure and at pH 7.0). The measurement method including sample preparation is described in OECD Guideline 105.

[0214] 8. Crosscut Testing

[0215] The crosscut test is used to ascertain the strength of adhesion of a coating on a substrate in accordance with DIN EN ISO 2409:2020-12. Cutter spacing is 2 mm. Assessment takes place on the basis of characteristic cross-cut values in the range from 0 (very good adhesion) to 5 (very poor adhesion). The crosscut test is performed before and after exposure for 240 hours in a condensation clima according to DIN EN ISO 6270-2 CH:2018-04 (at constant humidity). Each of the tests is performed three times and an average value is determined.

[0216] 9. CASS corrosion test and delamination

[0217] A cyclic corrosion test according to DIN EN ISO 9227 CASS:2017-07 (copper-accelerated acetic acid-salt spray test) was performed for 240 h. The coated substrates were then investigated for their level of filiform corrosion according to DIN EN ISO 4628-10:2024-06.

[0218] 10. Oil removal and water break test

[0219] The test was carried out in a 5 L beaker for standard panel sizes of 190 x 105 mm. The test panel was immersed in the composition to be tested for 1 min and subsequently rinsed in a vertical rinsing bath (the entire panel must be dipped in and pulled out of the rinsing bath for at least 5 times). The degree of wettability was evaluated 10 seconds after the panel had been removed from the rinsing bath and held in a vertical position. The minimum cleaning time (MOT) was achieved, if at least 95% of the surface was wetted by water (small non-wetted areas are only allowed at the panel edges). If this condition is not met the cleaning and rinsing procedure must be repeated in 1 min intervals until the wettability conditions are met as described above. Afterwards, a new oiled test panel must be immersed for as long as the combined duration of the previously required 1 min runs. This is necessary, as the rinsing steps between the cleaning steps improve the degreasing performance2024P00038WO I L024883PCT 30 February 17, 2026 Chemetall GmbH

[0220] EXAMPLES

[0221] The following examples further illustrate the invention but are not to be construed as limiting its scope.

[0222] 1. Cleaning and chemical pretreatment compositions (as compositions AAC)

[0223] 1.1 Composition ICC1 (inventive)

[0224] An aqueous composition comprising 10 g / L of a commercially available surfactant 1 (a non-ionic fatty alcohol sulfate bearing ethylene oxide units) and 10 g / L of a commercially available copolymer of maleic acid and acrylic acid was prepared. Sulfuric acid was added for pH adjustment and the resulting pH value of the composition was pH 3.5. The resulting composition was used as composition ICC1 in form of a treatment bath having a temperature of about 60 °C.

[0225] 1.2 Composition ICC2 (inventive)

[0226] A composition ICC2 was prepared in the same manner as composition ICC1 except that instead of 10 g / L surfactant 1 another commercially available surfactant, i.e., 10 g / L of surfactant 2 (a sulfosuccinate) was used.

[0227] 1.3 Composition CCC1 (comparative)

[0228] A composition CCC1 was prepared in the same manner as composition ICC1 except that 15 g / L of surfactant 1 and no copolymer was used. Further, the composition had a pH of 4.0 after addition of sulfuric acid.

[0229] 1.4 Composition CCC2 (comparative)

[0230] A composition CCC2 was prepared in the same manner as composition ICC2 except that 15 g / L of surfactant 2 and no copolymer was used. Further, the composition had a pH of 4.0 after addition of sulfuric acid.

[0231] 1.5 Composition CCC3 (comparative)

[0232] A composition CCC3 was prepared in the same manner as composition ICC1 except that a commercially available copolymer of maleic acid and ethylene was used. Further, the composition had a pH of about 10.5 after addition of an alkalinity inducing source (no sulfuric acid was added).

[0233] 1.6 Composition CCC4 (comparative)

[0234] A composition CCC4 was prepared in the same manner as composition ICC2 except that a commercially available copolymer of maleic acid and ethylene was used. Further, the composition had a pH of about 10.5 after addition of an alkalinity inducing source (no sulfuric acid was added).2024P00038WO I L024883PCT 31 February 17, 2026 Chemetall GmbH

[0235] 2. Cleaning and chemical pretreatment as well as coating method

[0236] 2.1 Two different commercially available aluminum substrate panels were investigated, i.e., AA6060 (substrate S1), and Circal 6060 being a recycled aluminum alloy (substrate S2).

[0237] Each of the substrates was treated, i.e., cleaned and chemically pretreated, by making use of one of compositions ICC1, ICC2 or one of compositions CCC1 to CCC4. All compositions were applied using spray application (pressure: 1 bar) for 10 seconds.

[0238] After having been cleaned and chemically pretreated, the substrates were rinsed once with deionized water using dip application.

[0239] Following the rinsing steps, a drying step was performed for 8 minutes at 120 °C.

[0240] 2.2 Finally, a commercially available powder coating material (C1 or C2 class) was applied and dried / cured at 175 °C for 25 minutes.

[0241] 3. Investigation of the properties of the cleaned and chemically pretreated as well as coated substrates

[0242] 3.1 The substrates obtained after the method described hereinbefore in item 2.1 were then investigated according to the methods described in the ‘methods' section in terms of oil removal capability and by performing the water break test.

[0243] Excellent results were obtained in case of both ICC1 and ICC2 on both substrates S1 and S2. Good results were obtained in case in case of both CCC3 and CCC4 on both substrates S1 and S2

[0244] Insufficient results were obtained in case of both CCC1 and CCC2 on both substrates S1 and S2.

[0245] 3.2 The substrates obtained after the method described hereinbefore in item 2.2 were then investigated according to the methods described in the ‘methods' section in terms of the CASS test in order to measure corrosion resistance and the crosscut test in order to measure wet adhesion. The results are shown in Table 1.2024P00038WO I L024883PCT 32 February 17, 2026 Chemetall GmbH

[0246] Table 1

[0247]

Claims

2024P00038WO I L024883PCT 33 February 17, 2026 Chemetall GmbHCLAIMS1. A method of simultaneously cleaning and chemically pretreating a metallic surface of a substrate comprising at least step 1) and optionally one or more of steps 2) and 3), namely1) contacting at least one metallic surface of at least one substrate at least in portion with an aqueous acidic composition AAC for cleaning and chemically pretreating said surface, wherein the aqueous acidic composition AAC comprises, besides water, at least constituents a2) and a3), and optionally one or both of a1) and a4), which are different from one of another, namelyoptionally at least one of zirconium, titanium, and hafnium cations as constituent a1),at least one surfactant as constituent a2) in an amount in a range of from 0.5 to 12.5 wt.-%, based on the total weight of the composition,at least one polymer, which is a copolymer, bearing at least one kind of acid groups, as constituent a3), in an amount in a range of from 5 to 50 000 mg / L, andoptionally at least one corrosion inhibitor as constituent a4),wherein the aqueous acidic composition AAC is free or essentially free of fluoride anions,2) optionally rinsing the cleaned and chemically pretreated surface obtained after step 1) at least once with water and / or at least once with an aqueous rinsing composition ARC, and3) optionally curing and / or drying the cleaned and chemically pretreated surface obtained after step 1) or after optional step 2).

2. The method according to claim 1 , characterized in that the at least one metallic surface of the at least one substrate is at least partially made of at least one kind of aluminum and / or at least one kind of an aluminum alloy, preferably in that said at least one metallic surface as such is made of at least one kind of aluminum and / or at least one kind of an aluminum alloy, more preferably in that said substrate as such is made of at least one kind of aluminum and / or at least one kind of an aluminum alloy.

3. The method according to claim 1 or 2, characterized in that the aqueous acidic composition AAC used in step 1) has a pH value in a range of from 0.10 to <7.0, preferably of from 0.25 to 6.0, more preferably of from 0.50 to 5.0, yet more preferably of from 0.75 to 4.0 or to 3.5, still more preferably of from 1.0 or 3.0, most preferably of from 1.5 or 2.5.2024P00038WO I L024883PCT 34 February 17, 2026 Chemetall GmbH4. The method according to one or more of the preceding claims, characterized in that the aqueous acidic composition AAC comprises optional constituent a1), preferably at least one of zirconium and titanium cations, more preferably zirconium cations, if present, in an amount in a range of from 1.0 to 2000 mg / L, preferably of from 5.0 to 1 500 mg / L, more preferably of from 10.0 to 1 000 mg / L, still more preferably of from 15.0 to 750 mg / L, yet more preferably of from 20.0 to 500 mg / L, even more preferably of from 22.5 to 250 mg / L, yet more preferably of from 25.0 to 150 mg / L, most preferably of from 25.0 to 100 mg / L, in each case calculated as metal.

5. The method according to one or more of the preceding claims, characterized in that the at least one surfactant being present as constituent a2) in the aqueous acidic composition AAC is selected from nonionic, anionic, and cationic surfactants and mixtures thereof, preferably from non-ionic surfactants, anionic surfactants, and mixtures thereof, wherein said at least one surfactant is preferably present in the aqueous acidic composition AAC in an amount in a range of from 1.0 to 12.5 wt.-%, more preferably of from 1.0 to 10.0 wt.-%, even more preferably of from 1.5 to 8.0 wt.-%, yet more preferably of from 2.0 to 7.5 wt.-%, in each case based on the total weight of the composition.

6. The method according to one or more of the preceding claims, characterized in that the at least one polymer bearing at least one kind of acid groups and being present as constituent a3) in the aqueous acidic composition AAC is a copolymer obtainable from polymerization of at least two different kinds of ethylenically unsaturated monomers.

7. The method according to one or more of the preceding claims, characterized in that the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC, which is a homopolymer or copolymer, preferably a copolymer, bears at least carboxylic acid groups as acid groups, wherein said carboxylic acids are preferably present in structural units of the polymer, which are obtainable from polymerization of (meth)acrylic acid monomers, more preferably of acrylic acid monomers.

8. The method according to one or more of the preceding claims, characterized in that the at least one polymer being present as constituent a3) in the aqueous acidic composition AAC is a homopolymer or copolymer, preferably a copolymer, which is obtainable from polymerization of at least (meth)acrylic acid monomers, preferably of acrylic acid monomers, and at least one further preferably acid functional monomer different from (meth)acrylic acid such as maleic acid and / or vinyl phosphonic acid.

9. The method according to one or more of the preceding claims, characterized in that the at least one polymer bearing at least one kind of acid groups is present as constituent a3) in the aqueous acidic composition AAC in an amount in a range of from 50 to 50000 mg / L, preferably of from 50 to 30000 mg / L, more preferably of from 100 to 20 000 mg / L, still more preferably of from 200 to 15000 mg / L, yet more preferably of from 250 to 10000 mg / L, even more preferably of from 500 to 7500 mg / L, yet more preferably2024P00038WO I L024883PCT 35 February 17, 2026 Chemetall GmbHof from 750 to 5000 mg / L, even more preferably of from 1 OOOto 4500 mg / L, most preferably of from 1 500 or 2000 to 4000 or to 3500 mg / L.

10. The method according to one or more of the preceding claims, characterized in that the at least one corrosion inhibitor being present as optional constituent a4) is present in the aqueous acidic composition AAC in an amount in a range of from 0.005 to 1.5 wt.-%, preferably of from 0.010 to 1.25 wt.-%, more preferably of from 0.010 to 1.00 wt.-%, based on the total weight of the composition, and / or in an amount in a range of from 0.001 to 10.0 mmol / L, preferably of from 0.005 to 7.5 mmol / L, more preferably of from 0.010 to 5.0 mmol / L, yet more preferably of from 0.050 to 2.5 mmol / L, most preferably of from 0.100 to 1.0 mmol / L.

11. The method according to one or more of the preceding claims, characterized in that the aqueous acidic composition AAC is free of fluoride anions or comprises a maximum amount of fluoride anions of <10.0 mg / L, preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <5.0 mg / L, more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <2.0 mg / L, even more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <1.0 mg / L, yet more preferably is free of fluoride anions or comprises a maximum amount of fluoride anions of <0.1 mg / L, in each case calculated as fluorine (F).

12. An aqueous acidic composition AAC as defined in one or more of claims 1 to 11 or a concentrate, from which said aqueous acidic composition AAC is at least obtainable by dilution with water and, optionally further, by pH adjustment.

13. A use of the aqueous acidic composition AAC according to claim 12 simultaneously as cleaning and chemical pretreatment composition, preferably in the method as defined in one or more of claims 1 to 11, preferably also for providing or improving adhesion of metallic surfaces of substrates to one or more further coating layers present thereon.

14. A method of coating of at least one cleaned and chemically pretreated metallic surface of at least one substrate, wherein cleaning and chemical pretreatment of the at least one metallic surface has been carried out according to the method according to one or more of claims 1 to 11 or by making use of aqueous acidic composition AAC according to claim 12, the method of coating further comprising at least step 4), namely4) applying at least one coating material composition, preferably at least one powder coating material composition, comprising at least one film-forming polymer and / or resin onto the cleaned and chemically pretreated surface obtained after step 1) as defined in claim 1 or after optional2024P00038WO I L024883PCT 36 February 17, 2026 Chemetall GmbHstep 2) as defined in claim 1 or after optional step 3) as defined in claim 1, preferably after step 3) as defined in claim 1.

15. A substrate having at least one metallic surface, wherein said surface is an at least in portion cleaned and chemically pretreated surface, which is obtainable by the method according to one or more of claims 1 to 11, or wherein said surface is a coated surface being obtainable by the method according to claim 14, wherein the cleaned and chemically pretreated surface preferably has a coating weight of Zr, Ti, and / or Hf if optional constituent a1) had been present in the composition AAC, more preferably of Zr and / or Ti, even more preferably of Zr, in each case calculated as metal, in a range of from 1 to 200 mg / m2, more preferably of from 2 to 100 mg / m2, still more preferably of from 3 to 50 mg / m2, even more preferably of from 4 to 25 mg / m2, most preferably of from 5 to 15 mg / m2.

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