Metal surface treatment

Abstract

The invention relates to the use of at least one polymer P obtained by free-radical copolymerization of a mixture of (i) acrylic acid; (ii) methacrylic acid; and (iii) at least one 2-hydroxyethyl methacrylate phosphate ester, for treating a metal surface intended to be bonded to another surface by an adhesive, in order to impart the resulting bond with resistance to adhesive failure.

Description

[0001] This application claims priority to Nr 20305514.0 filed in Europe on 19 May 2020, the entire contents of which are incorporated herein by reference for all purposes.

[0002] This invention relates to the field of metal-based surface treatment, and more particularly to metal surfaces intended for coating with an adhesive composition. More specifically, this invention relates to the treatment of said metal surfaces aimed at providing enhanced adhesion of the adhesive composition to said metal surface.

[0003] Several methods have been proposed to provide enhanced adhesion of film-forming organic compositions such as coatings, varnishes or adhesives to metal surfaces (especially aluminum or steel), including depositing inorganic coatings, particularly so-called "conversion coatings", on metal surfaces.

[0004] The term “conversion coating” is well known in the art and refers to a layer formed on a metal surface that is a favorable substitute for the natural oxides on the surface (especially on aluminum), and is obtained by controlled chemical formation of a film on the metal surface through reaction with chemical elements of the metal surface, such that at least some of the cations dissolved from the metal material are deposited in the conversion coating.

[0005] Typically, coatings (such as conversion coatings) are obtained by reacting a metal surface with a solution containing metal cations and fluoride ions. Chromium-containing coatings have been proposed in the past (typically obtained by reacting the surface with a solution containing H₂CrF₆), and more recently, coatings based on less toxic metals such as zirconium, titanium, or others (e.g., obtained by reacting the surface with a solution containing H₂TiF₆, H₂ZrF₆, H₂HfF₆, H₂AlF₆, H₂SiF₆, H₂GeF₆, H₂SNF₄, or HBF₄) have been proposed. Conversion coatings may include other compounds, such as silane precursors.

[0006] To improve adhesion to coatings (such as conversion coatings), it is known to add additives, especially organic polymers. In this regard, the use of polyacrylic acid has been described, for example. A typical additive is ACUMER, available from Dow Chemical Company (and previously from Rohm & Haas). TM 1510 has already provided a comprehensive description of this application. For further details on this, see in particular WO 97 / 13588, US 4,191,596 or US 4921552.

[0007] One object of the present invention is to provide a novel method for treating metal surfaces, which imparts good adhesion to film-forming organic compositions of adhesive compositions applied to the metal surfaces.

[0008] To this end, the present invention proposes the use of a specific polymer, optionally (but not necessarily) in conjunction with the formation of a conversion coating (i.e., before, during, or after), resulting in a treated metal surface exhibiting the following highly significant characteristics: good adhesion is achieved between the surface and the coated composition when coated with a film-forming composition (such as a paint, varnish, or adhesive composition). Furthermore, the surface receives excellent protection, particularly against corrosion. When a metal surface is coated with an adhesive layer, the coated surface can typically be used to ensure so-called "adhesive bonding" between the coated metal surface and another surface (typically a similar metal surface treated with the same polymer) that is in contact with all or part of the adhesive coating. In this application, the specific polymer used according to the invention allows for resistance to adhesive failure. Within the scope of the invention, the inventors have now observed that the adhesion between the adhesive and the metal surface exhibits particularly high strength, to the extent that cohesive failure occurs rather than (or at least more preferably adhesive failure) when sufficiently high mechanical stress is applied to separate the adhesive-bonded surfaces.

[0009] Adhesive failure is understood as the failure between two surfaces bonded by an adhesive occurring on one surface, while the adhesive remains on the other.

[0010] Cohesion loss effect is understood to mean that the failure between two surfaces bonded by an adhesive occurs within the adhesive itself, thus the adhesive remains on both surfaces.

[0011] The improved adhesion between two surfaces, treated with the polymer of the present invention and then assembled with an adhesive, is reflected in resistance to adhesive failure, which means that cohesive failure will instead occur, especially after aging, compared to other existing treatments.

[0012] More specifically, the present invention utilizes at least one polymer P, which is a polymer obtained by free radical copolymerization of a mixture of acrylic acid, methacrylic acid, and at least one 2-hydroxyethyl methacrylate phosphate having the following formula (a):

[0013]

[0014] Where n is 1 or 2.

[0015] Typically, polymer P is obtained by free radical copolymerization of a mixture of acrylic acid, methacrylic acid, and a mixture of several 2-hydroxyethyl methacrylate phosphates of formula (a) with different n values. Preferably, polymer P is obtained by free radical copolymerization of a mixture having the following molar ratio based on the total amount of acrylic acid, methacrylic acid, and 2-hydroxyethyl methacrylate phosphate of formula (a):

[0016] - Acrylic acid (AA): from 65% to 90%, preferably from 80% to 90% (e.g., about 83%-85%),

[0017] - Methacrylic acid (MAA): from 5% to 30%, preferably from 5% to 15% (e.g., about 11%-13%)

[0018] - 2-Hydroxyethyl methacrylate phosphate: from 2% to 12%, for example from 2% to 10%, notably from 2% to 6% (for example, about 4%).

[0019] When compared with polymers that exhibit no MAA or whose MAA is outside the above-mentioned MAA range, the above molar ratio of monomers in polymer P shows particularly good results in terms of resistance to adhesive failure. For example, when the amount of MAA in polymer P is too high, polymer P is insoluble in acidic treatment water baths and therefore cannot be used.

[0020] Furthermore, the polymer P used according to the invention preferably has a molecular weight of at least 7,500 Da, for example from 10 kDa to 1,500 kDa, for example from 10 kDa to 150 kDa, notably between 10 and 100 kDa, typically a weight-average molecular weight. Typically, the polymer P used according to the invention has a molecular weight from 10 to 40 kDa, for example from 20 to 30 kDa.

[0021] The polymer P particularly suitable for the present invention is a random copolymer having a weight-average molecular weight of about 20 to 30 kDa, which is a copolymer of acrylic acid, methacrylic acid and 2-hydroxyethyl methacrylate phosphate having formula (a), preferably in a molar ratio of about 85:11:4 or 83:13:4.

[0022] Average molecular weight (typically weight-average molecular weight) was measured using size exclusion chromatography (SEC). Notably, the SEC was equipped with a multi-angle laser scattering (MALLS) Mini Dawn TREOS detector and an Agilent concentration detector (RI detector). The SEC-MALLS system was run on a three-column Varian Aquagel OH mixed H, 8 μm, 3*30 cm at a flow rate of 1 mL / min, with the following mobile phase: 85% water, 100 mM NaCl, 25 mM NaH2PO4, 25 mM Na2HPO4-15% methanol. Polymer samples were diluted to 0.5 wt% activity in the mobile phase for at least 4 hours, then filtered through a 0.45 μm microporous filter, and 100 μL were injected into the mobile phase stream. Absolute molar masses were obtained, where the dn / dC of poly(acrylic acid) was equal to 0.1875 mL / g.

[0023] A specific object of the present invention is the use of at least one polymer P as defined above for treating a first metal surface (S1) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting resistance to adhesive failure of the bond. An additional advantage of the adhesive bond obtained according to the invention is its high resistance to corrosive and humid atmospheres, resulting in a durable adhesive bond. In most cases, the polymer is also used to obtain this additional effect (i.e., to further impart resistance to corrosive and humid atmospheres to the bond; in other words, to obtain both highly effective and durable adhesion). In other words, the use of at least one polymer P as defined above for treating a first metal surface (S1) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting resistance to adhesive failure of the bond also provides very good resistance to aging of the adhesive bond. This property can be measured by tensile testing of so-called “single lap shear” (SLS) components, as defined in ASTM D-1002 10, on newly bonded SLS components, and on SLS components aged in repeated cycles of corrosive atmosphere, humid atmosphere, or corrosive atmosphere followed by humid atmosphere, as in ASTM G85 A3. Other tests combine corrosive stress and mechanical stress (e.g., compressive load), such as Bv 101-07, the Ford Durability Stress Test for Adhesive Lap-shear Bonds, or the Arizona Proven Ground Exposure (APGE). Notably, adhesive bonding between the two surfaces S1 and S2 using the polymer P according to the invention has been shown to provide a failure phase that retains greater cohesion after aging.

[0024] Typically (but not necessarily), the second surface (S2) is also a metallic surface, having or not having the same properties as the first surface (S1). According to an advantageous embodiment, the second surface (S2) is a metallic surface also treated with a polymer P having formula (a), typically but not necessarily the same polymer P as the first surface (S1).

[0025] More generally, the polymer P used according to the invention is preferably used to treat the two surfaces (S1) and (S2) before the adhesive bonds the two surfaces, especially when (S2) is a metallic surface.

[0026] The first metal surface (S1) is preferably a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobalt-nickel alloys. The invention is particularly interested in metal surfaces of aluminum or aluminum alloys. The invention is especially interested in the fact that the surface (S1) is an aluminum or aluminum alloy metal surface.

[0027] The second surface (S2) can be a metallic or non-metallic surface.

[0028] According to an embodiment of interest, the second surface (S2) is a surface comprising a metal, advantageously selected from aluminum, steel, zinc, magnesium, titanium, copper and alloys thereof, or cobalt-nickel alloys. According to one embodiment, surfaces (S1) and (S2) are identical in nature, but they may also be different according to other possible embodiments of the invention. According to a variant of interest, both surfaces (S1) and (S2) are metallic surfaces of aluminum or aluminum alloys.

[0029] According to another possible embodiment, the second surface (S2) is a non-metallic surface, such as a plastic surface (e.g., a plastic surface based on polyamide, PEEK, or ABS); or a composite surface (based on, for example, CFRP or glass fiber reinforced plastic).

[0030] Regardless of the exact properties of surfaces (S1) and (S2), according to possible embodiments, a conversion coating can be applied to the metal surface (S1) through a reaction between the surface and the conversion composition (in other words, the conversion composition is applied to the metal surface to form a conversion coating thereon). However, according to the invention, the use of a conversion coating is not mandatory, and according to specific embodiments, a conversion coating is not applied to surface (S1). When using the conversion composition, typically:

[0031] - The conversion composition includes all or part of polymer P as an additive; and / or

[0032] - Apply the conversion coating to the surface (S1), and then apply all or part of the polymer P to the conversion coating.

[0033] The second surface (S2) can also be treated with a similar conversion coating under the same conditions, especially when the second surface (S2) is a metallic surface. However, according to the invention, the use of a conversion coating is not mandatory, and in certain embodiments, a conversion coating may not be applied to the surface (S2).

[0034] According to another possible embodiment compatible with the foregoing embodiments, all or part of the polymer P is contained in the adhesive composition applied to surfaces (S1) and (S2). According to this embodiment, the polymer can typically be introduced into the adhesive composition as a solid powder, the powder containing only the polymer or the polymer contained on the surface of the mineral filler (the powder is typically obtained by spray drying a solution or suspension of the polymer, typically in the presence of the mineral filler). According to another aspect, another specific object of the invention is a method for bonding a first metal surface (S1) to a second surface (S2) (preferably as defined above), the method comprising:

[0035] - Treat the first surface (S1) with at least one composition comprising at least one polymer P as defined above (preferably the surface (S1) is cleaned and / or activated prior to treatment with the polymer P); and

[0036] - Optionally, the second surface (S2) is treated with at least one composition comprising at least one polymer P as defined above (and preferably, the surface (S2) is cleaned and / or activated prior to treatment with the polymer P); and

[0037] - The two surfaces are bonded together by applying an adhesive composition between the surface (S1) and the surface (S2).

[0038] Within that range, compositions containing polymer P can typically be:

[0039] - Conversion compositions including polymer P; and / or

[0040] - A solution or dispersion of the polymer P, preferably applied to the surface after the conversion coating is applied to the surface to be treated; and / or

[0041] - An adhesive composition which may contain all or part of polymer P.

[0042] Typically, polymer P is present in the conversion composition and / or in a solution or dispersion applied to the conversion coating. In that case, an adhesive is applied to the surface previously treated with the polymer.

[0043] According to some specific embodiments, an additional layer is applied between the treated surface (S1) and the adhesive (this is, for example, for a metal coil or part that is treated at a first location and then bonded to a second location): in that case, a lubricant can be applied to the treated coil or part to protect it during transport and storage and to facilitate downstream operations (coil cutting, punching, stamping, forming, etc.).

[0044] According to yet another aspect, a specific object of the invention is to include materials comprising two surfaces bonded together by an adhesive, the first metal surface comprising a metal surface (S1) which is wholly or partially (i) treated with a polymer P as defined above and (ii) bonded by an adhesive to a second surface (S2) preferably defined above.

[0045] These materials include, in particular, materials having a metallic surface (S1) that is wholly or partially covered by the following:

[0046] - At least one coating (typically a conversion coating and / or paint, varnish, or adhesive layer) comprising at least one polymer P; and / or

[0047] - A layer (typically a conversion coating) containing the following: a reaction product of polymer P as defined above with a metal having a treated surface or another compound present in the layer, or polymer P tightly bonded to the other compound (e.g., through complexation, ionic bonding or hydrogen bonding).

[0048] The specific features and possible embodiments will now be described in more detail.

[0049] Metal surface (S1)

[0050] Any metal surface can be treated with the polymer P of the present invention, but the present invention is particularly suitable for treating the following metal surfaces:

[0051] - Aluminum or aluminum-based alloys; or

[0052] - Steel, such as galvanized steel (hot-dip galvanized HDG or electro-galvanized EG); or cold-rolled steel (CRS); or

[0053] - Magnesium or magnesium-based alloys; or

[0054] - Zinc or zinc-based alloys; or

[0055] - Titanium or titanium-based alloys.

[0056] The present invention is of particular interest for the metallic surfaces of aluminum and aluminum alloys (such as aluminum alloy AA 5005 tested in the appended examples or other alloys such as the 1xxx, 2xxx, 3xxx, 4xxx, 5xxxx, 6xxx, 7xxx series (such as AA1050, 2024, 3003, 5182, 5754, 6111, 6016, 6060, 6063, 6182, 7075).

[0057] Optional conversion coating

[0058] When a conversion coating is applied to one or both of surfaces (S1) and / or (S2), the conversion coating can be obtained by bringing the surface into contact with any conversion composition known from the prior art.

[0059] Contact between the metal surface and the conversion composition can be made by any means known per se, such as dip coating in a conversion bath or spray coating, as an illustrative example.

[0060] The conversion compositions used according to the present invention typically contain fluorine-containing anionic and cationic metals, such as compounds like H2CrF6, or more preferably chromium-free compounds such as H2TiF6, H2ZrF6, H2HfF6, H2AlF6, H2SiF6, H2GeF6, H2SNF4, or HBF4.

[0061] The conversion composition may also contain other compounds, such as silane precursors, and / or cerium salts, and / or terbium molybdate.

[0062] Furthermore, according to specific embodiments, the conversion composition may contain all or part of the polymer P used in the invention for surface treatment. In that case, the application of the conversion layer itself results in the surface treatment according to the invention.

[0063] In other respects, this treatment is typically obtained after the formation of the conversion layer by bringing the metal surface with the conversion layer into contact with polymer P (which can typically be applied to the conversion layer in the form of a solution or suspension of polymer P, or within a paint, varnish, or adhesive composition applied to the conversion layer).

[0064] According to specific embodiments, it is possible to use polymer P both in the conversion composition and in the adhesive composition applied to the conversion layer.

[0065] If any patent, patent application, or disclosure incorporated herein by reference conflicts with the description of this application to the extent that it may lead to ambiguity in terminology, then this description shall take precedence.

[0066] The following examples illustrate the present invention.

[0067] Example

[0068] Example 1

[0069] In this example, the polymer according to the invention has been tested, which is obtained by copolymerization of acrylic acid, methacrylic acid, and a mixture of 2-hydroxyethyl methacrylate phosphate having formula (a). The method used to produce this polymer is based on conventional free radical polymerization well known in the art.

[0070] The polymer (polymer P1) exhibits the following characteristics:

[0071] The weight-average molecular weight (Mw) was 24,000 g / mol, and the number-average molecular weight (Mn) was 12,000 g / mol. These parameters were measured using a size exclusion chromatography (SEC) instrument equipped with a multi-angle laser scattering (MALLS) Mini Dawn TREOS detector and an Agilent Technologies concentration detector (RI detector). The SEC-MALLS was run on a three-column Varian Aquagel OH mixed H, 8 μm, 3 x 30 cm column at a flow rate of 1 mL / min, with the following mobile phase: 85% water, 100 mM NaCl, 25 mM NaH₂PO₄, 25 mM Na₂HPO₄ - 15% methanol. Polymer samples were diluted to 0.5 wt% activity in the mobile phase for at least 4 hours, then filtered through a 0.45 μm microporous filter, and 100 μL were injected into the mobile phase stream. Absolute molar masses were obtained, with dn / dC of poly(acrylic acid) equal to 0.1875 mL / g.

[0072] The molar ratio of AA / MAA / 2-hydroxyethyl methacrylate phosphate with formula (a) is 83 / 13 / 4.

[0073] Performance was evaluated by single lap shear (SLS) tests before and after aging under corrosive conditions. Specimens were prepared according to the following protocol and assembled to form an SLS assembly as described in D1002-10.

[0074] Step 1 - Twenty specimens (aluminum alloy specimens: AA5754, from FBCG; 100 mm long, 25 mm wide, 3 mm thick) were all cleaned and etched together in a single combined cleaning and etching step in a 4 L bath at 50°C in a stainless steel tank for 3 minutes with gentle agitation. This bath was typically prepared by diluting a commercially available formulation, DBT ALU 200 (available from Chemtec Aertec), (5 g of DBT ALU 200 in 995 g of water). The specimens were then rinsed twice with deionized water within 1 minute.

[0075] Step 2 - The samples were then pretreated by immersion in a treatment bath for 2 minutes containing polymers at 50°C and at the concentrations shown in Table 1 below. They were then rinsed together with a stream of deionized water for 1 minute and dried at 60°C for 30 minutes.

[0076] Step 3 – Then assemble the specimens in pairs, each pair forming a so-called single-overlap shear “assembly”: Place two specimens horizontally parallel, one on top of the other, forming a 12.5 mm long and 25 mm wide overlap (“overlap area”, including one of the end areas of each of the two 25 mm wide specimens, i.e., the last 12.5 mm of the specimen’s 100 mm length). Apply structural high-T curing epoxy adhesive beads (Betamate 1496, from Dow Chemical Company) to the overlap area of ​​the lower specimen using a gun at 7 bar. Then press the upper specimen down, thus forming a 12.5 mm long and 25 mm wide bond area. Use paperclips before and during curing to maintain the integrity of the assembly. Then cure the adhesive according to the adhesive manufacturer’s guidelines, typically at 180°C for 40 minutes. Finally, remove the paperclips.

[0077] Step 4 - Perform a tensile strength test on the component obtained in Step 3.

[0078] Materials used Zwick / Roell-Z50 features jaws with a gripping component tip exceeding 50 mm and a traction speed of 10 mm / min (each jaw clamps one of a pair of bonded specimens in a 50 mm gripping area of ​​the specimen located at the end area of ​​each specimen opposite the overlapping area. The jaws are then moved to traction each specimen horizontally in the direction from the initial self-bonding area toward the gripping area).

[0079] Step 5 - After aging Perform tensile strength test II on the components obtained in step 3.

[0080] 5.1. Aging Cycle Test

[0081] The aging test was conducted according to ASTM G85 - Appendix 3 (SWAAT, 2011) in a corrosion chamber from Q-FOG, specifically in a Q-FOG CRH 600L.

[0082] Under the following conditions:

[0083] • 30 minutes of acidifying salt spray, followed by

[0084] • Soak for 90 minutes at a relative humidity >98%.

[0085] Under the following conditions:

[0086] • Room temperature - constant 49℃

[0087] • Air saturator temperature - constant 57℃

[0088] Relative humidity -> 98%

[0089] • The pH of the falling solution is between -2.8 and 3.0.

[0090] • Volume of the falling solution: -1.0 to 2.0 ml / 80 cm³ 2 / Hour

[0091] • Exposure period - 1000 hours

[0092] After the exposure period is complete, the components are washed with lukewarm water to remove and neutralize any excess acid and any remaining salt residue.

[0093] Then, all components are air-dried using forced ambient temperature, followed by an overlap shear tensile test.

[0094] 5.2 Tensile strength test

[0095] Under the conditions of tensile strength test I in step 4

[0096] The results are reported in Tables 2-4 below (values ​​are averages: these tests were performed on 3 pre-aging components and 5 post-aging components), with the following changes in step 2:

[0097]

[0098]

[0099] Table 1: Conditions for Step 2

[0100] The following are the reported performance before and after aging, and the ratio between the post-aging value and the pre-aging value (referred to as the "retention rate"):

[0101]

[0102] Table 2: Maximum Strain

[0103]

[0104] Table 3: Maximum Load

[0105]

[0106] Table 4: Maximum Energy

[0107]

[0108] Table 5: Phase after adhesive failure

[0109] (c): Cohesive fracture

[0110] (a): Adhesive fracture

[0111] (~c): Slightly cohesive fracture

[0112] Example 2

[0113] In this example, other polymers according to the invention have been tested, obtained by copolymerization of acrylic acid, methacrylic acid, and a mixture of 2-hydroxyethyl methacrylate phosphate having formula (a). The methods for producing polymers P2 and P3 are based on conventional free radical polymerization well known in the art. The method for producing P4 is based on controlled free radical polymerization.

[0114] Those polymers exhibit the following characteristics:

[0115] Polymer P2

[0116] • Weight-average molecular weight Mw = 22,000 g / mol, Mn = 13,000 g / mol.

[0117] The molar ratio of AA / MAA / 2-hydroxyethyl methacrylate phosphate having formula (a) is 77 / 11 / 12.

[0118] Polymer P3

[0119] • Weight-average molecular weight Mw = 68,000 g / mol, Mn = 26,000 g / mol.

[0120] The molar ratio of AA / MAA / 2-hydroxyethyl methacrylate phosphate having formula (a) is 77 / 11 / 12.

[0121] Polymer P4

[0122] • Weight-average molecular weight Mw = 19,000 g / mol, Mn = 10,000 g / mol.

[0123] • The molar ratio of AA / MAA / 2-hydroxyethyl methacrylate phosphate having formula (a) is 79 / 12 / 9

[0124] Comparison Examples

[0125] Comparison with polymer C0:

[0126] The polymer was prepared according to the same method as described in Example 1, but with the following molar ratio: AA / MAA / 2-hydroxyethyl methacrylate phosphate having formula (a) molar ratio = 26 / 70 / 4

[0127] The polymer is insoluble in acidic treatment baths and therefore cannot be tested.

[0128] Comparison of polymer C1: AA 100

[0129] Polyacrylic acid (100% AA) was prepared and tested.

[0130] The polymer has Mw = 26,000 g / mol and Mn = 19,000 g / mol (measured using the same method as previously described).

[0131] Comparison of polymers C2 and C3:

[0132] Two comparative polymers were prepared by replacing hydroxyethyl methacrylate phosphate with benzotriazole ethyl methacrylate. Details are given below:

[0133] general formula:

[0134]

[0135] Comparative polymer C2: 4 mol% benzotriazole methacrylate (BztMA)

[0136] MAA / AA / BztMA=76 / 20 / 4mol%

[0137] Mw = 30,000 g / mol, Mn = 15,000 g / mol (using the same measurement method as previously described).

[0138] Comparative polymer C3: 10 mol% benzotriazole methacrylate (BztMA)

[0139] MAA / AA / BztMA=67 / 23 / 10mol%

[0140] Mw = 30,000 g / mol, Mn = 15,000 g / mol (using the same measurement method as previously described).

[0141] Performance testing

[0142] Performance was evaluated by single lap shear (SLS) tests before and after aging under corrosive conditions. Specimens were prepared according to the protocol described in Example 1 and assembled to form an SLS assembly as described in D1002-10.

[0143] Two wave tests have already been conducted.

[0144] Conditions for Wave 1:

[0145] Step 1: Prepare a bath using 5% Chemtec DBT ALU 200 and heat it to 50°C. Immerse the sample in the bath for 3 minutes, and then rinse with hot water and then deionized water for 1 minute.

[0146] Step 2: Heat the bath to 50°C; adjust the pH with sulfuric acid; immerse the sample for 2 minutes, and then rinse with deionized water for 1 minute.

[0147] Conditions for wave 2:

[0148] Step 1: Prepare a bath using 5% Chemtec DBT ALU 200 and heat it to 50°C. Immerse the sample in the bath for 1 minute, and then rinse with hot water and then deionized water for 1 minute.

[0149] Step 2: Heat the bath to 50°C; adjust the pH with sulfuric acid; immerse the sample for 2 minutes, and then rinse with deionized water for 1 minute.

[0150] result

[0151] Wave 1

[0152]

[0153]

[0154] Table 6: Conditions for Step 2 - Wave 1

[0155]

[0156] Table 7: Strain under maximum load - Wave 1

[0157]

[0158]

[0159] Table 8: Maximum Load - Wave 1

[0160]

[0161] Table 9: Energy under Maximum Load - Wave 1

[0162]

[0163] Table 10: Phase after Adhesion Failure - Wave 1

[0164] c: Cohesive fracture; ~c: Slightly cohesive fracture; c / a: Simultaneous cohesive and adhesive fracture; ~a: Slightly adhesive fracture; a: Adhesive fracture

[0165] Wave 2

[0166]

[0167]

[0168] Table 11: Conditions for Step 2 - Wave 2

[0169]

[0170] Table 12: Strain under maximum load - Wave 2

[0171]

[0172]

[0173] Table 13: Maximum Load - Wave 2

[0174]

[0175] Table 14: Energy under Maximum Load - Wave 2

[0176]

[0177] Table 15: Phase after Adhesion Failure - Wave 2

[0178] c: Cohesive fracture; ~c: Slightly cohesive fracture; c / a: Simultaneous cohesive and adhesive fracture; ~a: Slightly adhesive fracture; a: Adhesive fracture

Claims

1. A process for bonding a first metal surface (SI) with a second metal surface (S2), the process comprising: - treating the first metal surface (SI) with at least one composition comprising at least one polymer P, the at least one polymer P being obtained by free-radical copolymerization of a mixture having the following molar ratios, based on the total amount of acrylic acid, methacrylic acid and 2-hydroxyethyl methacrylate phosphate ester having formula (a): - acrylic acid: from 65% to 90% - methacrylic acid: 5% to 30% - 2-hydroxyethyl methacrylate phosphate ester: 2% to 12%. the at least one polymer P being obtained by free-radical copolymerization of a mixture having the following molar ratios, based on the total amount of acrylic acid, methacrylic acid and 2-hydroxyethyl methacrylate phosphate ester having formula (a): - acrylic acid: 80% to 90% - methacrylic acid: 5% to 15% - 2-hydroxyethyl methacrylate phosphate ester: 2% to 10%. the polymer P having a molecular weight of at least 7,500 Da. the polymer P having a molecular weight of from 10 kDa to 1500 kDa. the first metal surface (SI) being a surface comprising a metal selected from the group consisting of aluminum, steel, zinc, magnesium, titanium, copper and alloys thereof, or cobalt-nickel alloys.

2. The method of claim 1, wherein, the first metal surface (SI) being a surface of aluminum or aluminum alloys. the polymer P is used to treat both the first metal surface (SI) and the second metal surface (S2) before adhesive bonding of the two surfaces. the composition comprising the polymer P is: - a conversion composition comprising the polymer P; and / or 3. The method of any one of claims 1 to 2, wherein, - a solution or dispersion of the polymer P which is applied on the surface after a conversion coating has been applied on the surface to be treated; and / or 4. The method of claim 3, wherein, - an adhesive composition comprising the polymer P.

5. The method of any one of claims 1 to 2, wherein, 9. A material comprising two adhesive-bonded surfaces, said surfaces comprising a first metal surface (SI) and a second metal surface (S2), wherein one metal surface of the first metal surface (SI) is wholly or partially (i) treated with a polymer P as defined in any one of claims 1 to 8 and (ii) adhesive-bonded to said second metal surface (S2), the first metal surface (SI) of said material being wholly or partially covered by:

6. The method of claim 5, wherein, - at least one coating comprising at least one polymer P as defined in any one of claims 1 to 8; 7. The method of any one of claims 1 to 2, wherein, and 8. The method of claim 7, wherein, ​ ​ ​ ​ ​ ​ ​ - optionally a conversion coating, said conversion coating being obtained by contacting the first metal surface (S1) with a conversion composition, wherein said conversion composition comprises one or more of H2TiF6, H2ZrF6, H2HfF6, H2AIF6, H2SiF6, H2GeF6, H2SnF4, and HBF4.

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