RU2750923C1 - Pretreatment of aluminum surfaces with compounds containing zirconium and molybdenum - Google Patents

Abstract

FIELD: chemistry; etching.

SUBSTANCE: group of inventions relates to the pretreatment of workpieces having a surface of aluminum or aluminum alloys for forming without cutting and/or joining by welding or adhesive connection with pretreated or optionally precoated workpieces or with optionally pretreated parts consisting of steel and/or galvanized and/or galvanized alloy steel. The workpieces are etched, washed with water and brought into contact with an aqueous acidic chromium-free solution containing Zr in the form of complex fluoride and Mo in the form of molybdate, in a mass ratio of Zr:Mo, calculated as metallic Zr/Mo, ranging from 15:1 to 3.5:1 or from 2:1 to 1:2. In this case, the workpieces are treated in such a way that after subsequent drying, in each case, the mass of the Zr and Mo layer is obtained, which is from 2 to 15 mg/m². A solution is used containing 100 to 800 mg/l Zr and 30 to 100 mg/l Mo calculated as metallic Zr/Mo and having a pH of 2.5 to 4.5, or a solution containing 0.4 to 7.5 g/l Zr and 0.4 to 7.5 g/l Mo calculated as metallic Zr/Mo and having a pH of 1.0 to 3.0.

EFFECT: obtaining workpieces that have corrosion protection, good phosphatibility and adhesion, as well as a low volumetric resistivity, which is almost the same on all parts of the workpiece surface.

15 cl, 4 tbl

Description

The invention relates to a method for pretreating workpieces having a surface of aluminum or aluminum alloys for forming without cutting and / or joining by welding or adhesive bonding with similarly pre-processed or optionally otherwise pre-coated workpieces or with optionally pre-treated parts consisting of steel and / or galvanized and / or alloy-galvanized steel, as well as for subsequent anticorrosive treatment by phosphating, by means of chromium-free conversion treatment, by applying a primer layer or by surface coating.

For chemical surface treatment of metals, for example, as a preparation for the application of surface coatings, adhesives and polymers, methods are known in which the metal surface is cleaned in a first stage, washed with water in a second stage, and finally wetted with an aqueous solution forming chemical conversion coatings on the third stage, and the liquid film is dried. Thus, a thin, non-metallic coating is formed on the metal, which, when the formulations of the treatment liquid and the reaction conditions are properly selected, can clearly improve the surface quality. Thus, for example, coatings consisting of surface coating formulations, adhesives and polymers, optionally in the form of films, can exhibit significantly better adhesion and markedly improved corrosion protection when applied to metal that has been pretreated in this way. ...

The methods of the above type, for example, use an aqueous solution that contains hexavalent chromium, trivalent chromium, alkali metal ions and silicon dioxide in certain proportions, and as a result, coatings are obtained for electrical insulation, for protection against corrosion and as an adhesion base for surface coatings and the like (DE-B 1769582).

As a result of the presence of hexavalent chromium, all of these methods have the disadvantage that, in particular, precautions are required for the application of the coating compositions and the treatment of the coated metal.

In order to overcome the indicated disadvantages associated with the use of solutions that contain hexavalent chromium, another category of methods provides for the deposition of conversion coatings, in particular, on aluminum surfaces, treatment with compositions based on zirconium and / or titanium fluoroanions (US-A-4148670, FR -A-942789, EP-A-106389, EP-A-825280).

Recently, in the design of a vehicle, the use of blanks with surfaces of aluminum or aluminum alloys has become increasingly important. Significant reasons for this are the reduction in vehicle weight, as well as the advantageous recyclability and reuse of such blanks. In this case, it is generally accepted to manufacture vehicles by joining together a plurality of parts, which, as a rule, were previously formed without machining and consist of blanks having surfaces of aluminum or aluminum alloys, or having surfaces of steel and / or galvanized steel. and / or alloy galvanized steel. Today, the most important forms of joining or assembly are welding or adhesive bonding.

Joining of parts is usually accompanied by an anti-corrosive treatment, which, depending on the nature of the parts to be joined, can consist of a phosphating treatment, a chromium-free conversion treatment, a primer or a top coat.

In order to guarantee a defect-free connection of parts with surfaces of aluminum or aluminum alloys to each other or to parts consisting of steel and / or galvanized or galvanized alloy steel, it is necessary to ensure that the surfaces of aluminum or aluminum alloy do not contain alumina or possible oxides of the alloying constituents of aluminum. Etching, which seems attractive in this case, does not achieve this goal, since the aluminum surface is covered with a fresh oxide layer in a very short time.

In order to solve the above problem, the method according to EP-B-700452 provides that surfaces of aluminum or their alloys are brought into contact with an aqueous solution containing complex fluorides of elements such as boron, silicon, titanium, zirconium or hafnium, either alone or in admixture with each other, in total fluoroanion concentrations ranging from 100 to 4000 mg / l and having a pH ranging from 0.3 to 35 for pretreatment prior to the second final anti-corrosive treatment. Between pretreatment and final anti-corrosive conversion treatment, parts consisting of aluminum or their alloys are formed without cutting and / or by cutting and / or joining together or with parts consisting of steel and / or galvanized and / or galvanized alloy steel by adhesive bonding and / or welding. The application of the solution, optionally containing polymers of a particular nature, can be carried out by spraying, dipping or non-washing methods, where in the case of a non-washing method, the amount of wet film is preferably in the range from 2 to 10 ml / m, preferably from 4 to 6 ml / m , metal surface. Regardless of the method in which the solution is used, it is preferable to carry out drying at temperatures in the range from 40 to 85 ° C. For the purpose of cleaning, parts consisting of aluminum or their alloys are cleaned in acidic or alkaline conditions before the first conversion treatment, where it is preferable to carry out an additional cleaning step and intermediate rinsing with water and / or activating solutions for rinsing before the final anticorrosive treatment.

Based on the data on the concentration of fluoroanions in the solutions to be used and on the amount of wet film, in the case of using a solution containing fluorotitanate, it is possible to calculate the amount of the solution to be used, which ranges from 0.06 to 11.73 mg / m ² , preferably from 0 , 12 to 7.04 mg / m ² (in each case as titanium metal) and, in the case of using a solution containing fluorozirconate, the amount used is 0.09 to 17.78 mg / m ² , preferably 0.18 up to 7.04 mg / m ² (in each case as metallic zirconium).

Studies prior to the concept of the present invention have shown that many of the process possibilities described in EP-B-700452 lead to results that are not very favorable, in particular with regard to the temporary corrosion protection achieved by the first chemical conversion treatment, and also volumetric resistivity, which is important for the production of welded joints.

A good adhesion bond can be achieved by the method disclosed in US Pat. No. 6,020,030 A, which uses an organophosphorus compound to pretreat aluminum substrates. However, the process is susceptible to contamination of the bath with aluminum ions, which must therefore be removed by using an ion exchange resin.

The object of the invention is to provide a method for pretreating workpieces having a surface of aluminum or aluminum alloys for shaping without cutting and / or joining by welding or adhesive bonding, in particular for bonding by means of an adhesive bonding, likewise pretreated or optionally otherwise pretreated coated workpieces or with parts consisting of steel and / or galvanized and / or alloy-galvanized steel, in particular with similarly pretreated workpieces, as well as subsequent finishing for corrosion protection by phosphating and / or by means of chromium-free conversion treatment, or by applying a primer layer and / or by surface coating, in particular by phosphating and chromium-free conversion treatment or by surface coating, as a result of which workpieces are usually obtained having a sufficiently low bulk resistivity, along with good phosphatibility and adhesion.

In addition, the method according to the invention will preferably result in good temporary corrosion protection values and will be substantially insensitive to contamination of the bath with aluminum ions.

Firstly, the object is achieved by means of a method of the type mentioned at the outset, configured in accordance with the invention in such a way that the workpieces

a) etched by applying an aqueous, acidic solution containing mineral acid, by immersion or spraying,

b) washed with water and

c) contact with an aqueous, acidic solution that does not contain chromium, and contains Zr in the form of complex fluoride and Mo in the form of molybdate, in a mass ratio (calculated as metallic Zr / Mo) Zr: Mo, which is 15: 1 up to 3.5: 1, by means of dipping or spraying, whereby, after subsequent drying, in each case, the mass of the Zr and Mo layer is obtained, constituting from 2 to 15 mg / m ² , where the solution contains from 100 up to 800 mg / l Zr and from 30 to 100 mg / l Mo (calculated as metallic Zr / Mo), and has a pH ranging from 2.5 to 4.5.

During application by dipping or spraying, it was found that neither during the application of solutions that contain only fluorozirconate or only molybdate, nor during the application of solutions in which the mass ratio (calculated as metallic Zr / Mo) zirconium: molybdenum is outside the range a weight ratio of 15: 1 to 3.5: 1, neither during the application of the solutions, resulting in a weight of layers of zirconium and molybdenum outside the range of 2 to 15 mg / m ² , results are not obtained that are satisfactory in achieving the object of the invention.

The aqueous, acidic solution in step c) to be applied by immersion or spraying preferably contains Zr and Mo in a weight ratio of 15: 1 to 5: 1, in particular preferably 13: 1 to 7: 1 and especially preferably 11: 1 to 9: 1.

Application by dipping or spraying, preferably after drying, results in each case in a Zr and Mo layer mass of 2 to 12 mg / m ² , in particular preferably 2 to 10 mg / m ² , and particularly preferably 2 up to 8 mg / m ² .

The aqueous solution for application by dipping or spraying preferably contains 250 to 700 mg / l Zr and 30 to 80 mg / l Mo, in particular preferably 400 to 600 mg / l Zr and 40 to 60 mg / l Mo, and particularly preferably 475 to 525 mg / l Zr and 45 to 55 mg / l Mo.

In addition, the aqueous solution for application by dipping or spraying preferably has a pH of 3.1 to 4.3, and in particular preferably 3.6 to 4.0, and also preferably has a temperature of 20 to 50 ° C, and in particular, preferably from 20 to 30 ° C.

Secondly, the object is achieved by means of a method of the type mentioned at the outset, configured in accordance with the invention in such a way that the workpieces

a) etched by applying an aqueous, acidic solution containing mineral acid, by immersion or spraying,

b) washed with water and

c) contact with an aqueous, acidic solution that does not contain chromium, and contains Zr in the form of complex fluoride and Mo in the form of molybdate, in a mass ratio (calculated as metallic Zr / Mo) Zr: Mo, ranging from 2: 1 to 1: 2, by means of a roller application method, so that after subsequent drying, in each case a Zr and Mo layer mass of 2 to 15 mg / m ² is obtained, where the solution contains from 0.4 to 7.5 g / L Zr and 0.4 to 7.5 g / L Mo (calculated as metallic Zr / Mo), and has a pH of 1.0 to 3.0.

During application by the roller application method, it was found that neither during the application of solutions containing only fluorozirconate or only molybdate, nor during application of solutions in which the mass ratio (calculated as Zr / Mo metal) zirconium: molybdenum is outside the weight ratio of 2: 1 to 1: 2, nor during the application of the solutions, which results in a weight of layers of zirconium and molybdenum outside the range of 2 to 15 mg / m ² , results are not obtained which are satisfactory in achieving the object of the invention.

The aqueous, acidic solution in step c) to be applied by the roller application method preferably contains Zr and Mo in a weight ratio of 1.7: 1 to 1: 1.7, in particular preferably 1.4 : 1 to 1: 1.4, and particularly preferably 1.1: 1 to 1: 1.1.

Application by means of a roller application method, preferably after drying, in each case results in a Zr and Mo layer weight of 2 to 12 mg / m ² , in particular preferably 2 to 10 mg / m ² , and particularly preferably from 2 to 8 mg / m ² .

The aqueous solution for application by the roller application method preferably contains from 1.0 to 6.0 g / l Zr and from 1.0 to 6.0 g / l Mo, in particular, preferably from 2.0 to 4.0 g / l Zr and 2.0 to 4.0 g / l Mo, and particularly preferably 2.8 to 3.2 g / l Zr and 2.8 to 3.2 g / l Mo.

In addition, the aqueous solution for application by the roller application method preferably has a pH of 1.4 to 2.7, and particularly preferably 1.8 to 2.5.

With regard to the target weight of the layer of zirconium and molybdenum (2 to 15 mg / m ² ) to be set in each case, it is imperative that, depending on the method of application, namely spray application or dipping or dipping using a roller, at stage c), aqueous, acidic solutions were used, which differ in the concentration and ratio of the anions of fluorozirconate and molybdate, as well as the pH value).

The aqueous, acidic solution in step c) can be obtained by preliminary dilution, preferably with water, of a suitable concentrate, preferably in a ratio of 1:30 to 1: 100, more preferably in a ratio of about 1:50, and optionally setting pH level.

To achieve the objectives of the invention, it is also important that the preforms are pickled by using an aqueous, acidic solution containing a mineral acid by immersion or spraying. In this case, alkaline refining, for example, leads to the formation of layers of zirconium / molybdenum having a low volume resistivity.

The joining of preforms that have been pretreated in accordance with the invention can be carried out with similarly pretreated or optionally otherwise precoated, for example phosphated preforms, with surfaces of aluminum or their alloys. When joining to parts consisting of steel and / or galvanized and / or alloy galvanized steel is intended, these parts may have uncoated or pre-coated surfaces. One suitable precoat can, for example, be a phosphate layer having a layer weight of not more than 2 g / m ² or a conductive primer layer.

If the workpieces are oiled, the pickling process will follow the cleaning / degreasing step, or the pickling process will be carried out in such a way that simultaneous cleaning / degreasing occurs. The latter can be achieved by adding a surfactant to the etching solution.

As the phosphating treatment methods, the foreground are methods in which solutions based on zinc phosphate are used, in particular, in accordance with technology using a low zinc content, or in which an alkali metal phosphate is used. The solutions can be modified by adding additional small amounts of multivalent cations such as calcium, magnesium, nickel, copper or manganese.

In the case of chromium-free conversion treatment, in particular, acidic solutions of fluoride complexes of titanium, zirconium, hafnium or silicon, optionally containing an organic polymer, are used.

These acidic solutions may additionally contain at least one organosilane and / or at least one product of its hydrolysis and / or at least one product of its condensation.

The at least one organosilane preferably has at least one amino group. Particular preference is given to bis (trimethoxysilylpropyl) amine or organosilane, which can be hydrolyzed to aminopropylsilanol and / or to 2-aminoethyl-3-aminopropylsilanol.

As a primer, it is possible to apply reactive primers or binders.

Pretreating the workpieces in accordance with the invention provides satisfactory, temporary corrosion protection over a relatively long storage time. During this time, there are no adverse effects on weldability, in particular in the case of resistance welding, or on adhesion. In addition, with regard to weldability, it is ensured that the bulk resistivity is substantially the same over all portions of the surface of the workpiece.

Blanks for the purposes of the present invention are strip, sheet, and discrete parts such as profiles.

The application of the solution according to step c) can be carried out by spraying or immersion, in each case with rinsing with water or without rinsing with water. In the case of application without rinsing with water, it is advantageous to remove the excess treatment solution by using squeeze rollers.

For the treatment of a sheet or strip, the application of the treatment solution by a roller application method is particularly advantageous. It allows the desired wet film thickness to be obtained in a single operation.

After the above types of solution application have been carried out, the preform is dried or the solution is evaporated. In this case, temperatures ranging from 30 to 90 ° C are particularly advantageous.

For the formulation of treatment fluids, concentrates are generally used which are diluted with water having a low salt content, preferably deionized water, to the concentrations to be adjusted in each case. In order to avoid the ingress of alkali metal ions, it is advantageous in particular to introduce the required zirconium fluoroanions by adding free acid, and to adjust the pH, if necessary, by adding ammonia. On the other hand, the molybdate is advantageously administered in the form of ammonium heptamolybdate and / or sodium heptamolybdate, preferably in the form of ammonium heptamolybdate, and particularly preferably in the form of ammonium heptamolybdate x 7 H ₂ O.

For the purposes of the present invention, the term "molybdate" also contains protonated forms such as, in particular, molybdic acid.

The etching of the workpieces (stage a of the method)) is carried out using an aqueous, acidic solution containing a mineral acid. It can be carried out electrolytically or chemically. In the case of electrolytic etching, phosphoric acid is particularly suitable as a mineral acid. The pickling by chemical method, which is generally preferred due to the simpler operating conditions from the point of view of equipment, can be carried out using nitric acid or a mixture of nitric acid / hydrofluoric acid. In a preferred embodiment, the preforms are etched by spraying or dipping using a solution containing a surfactant, sulfuric acid and a compound selected from the group consisting of hydrofluoric acid, phosphoric acid and iron (III) sulfate, preferably hydrofluoric acid. where it has been found that solutions containing from 3 to 8 g / l of sulfuric acid, from 50 to 150 mg / l of uncomplexed, free fluoride and from 1 to 3 g / l of non-ionic surfactant are particularly suitable. Adducts of ethylene oxide with fatty alcohols and, for example, abietic acid, are particularly suitable as nonionic surfactants.

The determination of the amount of free fluoride was carried out using a fluoride-sensitive electrode, where the electrode was calibrated using solutions whose pH was the same as the pH of the solution being studied.

In order to obtain layers having optimum volumetric resistivity during the subsequent processing according to step c), the etching process must be carried out in such a way as to obtain a metal removal of about 0.1 to 0.6 g / m ² per workpiece.

The water wash which follows the etching of the preforms, which corresponds to step b), is preferably carried out in several washing stages, and it is particularly advantageous to supply the wash water in a cascade-like manner in countercurrent flow to the preform. In this case, the last stage of washing will be carried out using deionized water. The treatment according to step c), which follows the etching and washing steps, prevents re-growth of the oxide layer formed on the workpieces having an aluminum or aluminum alloy surface.

In an advantageous embodiment of the invention, the solution used in step c) further comprises at least one polymer selected from the group consisting of poly (meth) acrylic acid, (meth) acrylic acid copolymers, polyvinylphosphonic acid, vinylphosphonic acid copolymers and copolymers of maleic acid.

Preference is given to using copolymers of (meth) acrylic acid and maleic acid as copolymers of (meth) acrylic acid, and copolymers of vinylphosphonic acid and acrylic acid as copolymers of vinylphosphonic acid. Particularly suitable polymers are copolymers of polyacrylic acid and acrylic acid, and in the case of the latter, in particular copolymers of acrylic acid and maleic acid.

The poly (meth) acrylic acid used preferably has a number average molecular weight (MW) which is in the range from 4000 to 300000 g / mol, in particular preferably in the range from 50,000 to 250,000 g / mol, and particularly preferably in the range from 100,000 to 250,000 g / mol.

The (meth) acrylic acid copolymer used preferably has a number average molecular weight (MW) which is in the range of 4000 to 100000 g / mol, and in particular preferably in the range of 60,000 to 80,000 g / mol.

The polyvinylphosphonic acid used or the vinylphosphonic acid copolymer used preferably has a number average molecular weight (MW) which is in the range of 4000 to 70,000 g / mol, and in particular is preferably in the range of 10,000 to 30,000 g / mol.

The concentration of at least one polymer is in the range from 100 to 600 mg / l, preferably from 100 to 400 mg / l, in particular, preferably from 135 to 290 mg / l, and particularly preferably from 170 to 180 mg / l. The use of at least one polymer makes it possible, during spraying, to achieve a layer weight of Zr and Mo in a predetermined range, in each case from 2 to 15 mg / m ² , relatively independently, preferably mainly independently of the spraying time. This is particularly advantageous since similar layer masses can be achieved even at different strip speeds. On the other hand, no adverse effects on bulk resistivity were observed as a function of polymer content.

In the case of post-processing by forming without cutting, which was carried out after step c), a further advantageous embodiment of the invention provides for the application of lubricant to the workpieces. Such lubricants are, in particular, molding oils based on mineral oil, which can be fully synthetic or natural, or dry lubricants based on polyethylene / polyacrylate.

It is generally useful to include cleaning steps and water rinsing steps prior to finishing to impart corrosion protection. In the case of the intended application of a primer or top coat, pre-drying is recommended. If a chromium-free conversion treatment is to follow, then the application by dipping or spraying can also be carried out on a wet layer, i. E. without preliminary drying. In the case of application by roller coating method, intermediate drying is mandatory. In the case of a post-treatment by phosphating, which can also be carried out on a wet bed, it is advantageous to provide an activation treatment, for example by using an activating agent containing titanium and phosphate.

The method according to the invention generally provides preforms that have layers that allow defect-free formation and / or adhesion or, as a result of low electrical volume resistivity, which is uniform over the entire surface of the preform, guarantee a defect-free and problem-free welding. In addition, the workpieces are very suitable for subsequent anti-corrosive finishing.

The invention will be illustrated in more detail using the following examples, which should not be construed as limiting.

Examples:

With the exception of metal sheet, which was cleaned under alkaline conditions (comparative example SP2 in Table 1), sheets consisting of aluminum alloys AA 6111 and AA 5754 were first subjected to degreasing etching at 50 ° C by immersion or spraying. The etching solution contained 6 g / L sulfuric acid (100% concentration), 100 mg / L hydrofluoric acid (100% concentration), and 2 g / L nonionic surfactant consisting of ethoxylated fatty alcohol and ethoxylated abietic acid acid in a mass ratio of 1: 1.

The etching process was carried out in such a way that the removal of material during etching was from 0.05 to 0.2 g / m ² in the case of the AA 5754 alloy, and from 0.05 to 0.4 g / m ² in the case of the AA 6111 alloy. For this purpose, processing times in the range of 5 to 20 seconds were required.

Subsequently, the workpieces were thoroughly washed with water, and at the last stage they were washed with deionized water. Bulk resistivities measured on one sheet were approximately 60 μΩ in the case of AA 5754 alloy, and approximately 13 μΩ in the case of AA 6111 alloy.

This was followed by treatment with solutions of hexafluorozirconic acid and / or molybdate, which in each case optionally consisted of a polymer or copolymer, and whose data on the concentration of zirconium and / or molybdenum, as well as on the (co) polymer, pH values and application temperatures are shown in Tab. ... 1, in the case of 6 seconds of spray application. If necessary, the pH was adjusted by using an ammonia solution. Excess treatment solution was removed by using squeeze rollers and the treated surface was subsequently dried.

Polymers A - D in Tab. 1 were as follows:

A: Polyacrylic acid, MW = approximately 60,000 g / mol in colloidal solution,

B: Copolymer of acrylic acid and maleic acid, MW = approximately 70,000 g / mol,

B: Polyacrylic acid, MW = approximately 250,000 g / mol,

D: Copolymer of vinyl phosphonic acid and acrylic acid, MW = 4000-70000 g / mol.

n.i. = not measured

Column 2 in Tab. 2 shows the resulting weights of the Zr and Mo layers, in mg / m ² . The determination of the amount of mass of individual layers was carried out using X-ray fluorescence (RF) analysis.

In addition, the volume resistivity in μΩ obtained during the individual measurements of the metal sheets is shown in column 3 of Tab. 2. Measurement of the volume resistivity was carried out immediately after drying / evaporation (in each case, the first group "0 d") and after storage for 30 days (in each case, the second group "30 d"). It was carried out in accordance with brochure 2929 (September 2001) Deutscher Verbandes fur Schweifien und verwandte Verfahren e.V. (German Society for Welding and Allied Technologies) (DSV), using copper electrodes having a diameter of 20 mm.

Corresponding phosphatization and the results of the modified APGE test described below, presented as the cycles that passed the test, are shown in columns 2 and 3 of Table 3.

Adhesion was determined by a modified APGE test (Arizona equivalent test site). For this purpose, two test plates (each 56.25 x 25 x 0.25 mm) were in each case coated with a commercial dry lubricant and adhesively bonded with a suitable commercial adhesive. Six such pairs of test plates were then screwed together at their respective ends so as to obtain a chain that was subjected to a tensile force of 2,400 N. For each week of testing, the following program of conditions was applied:

1. Immersion for 15 minutes in a 5% concentration by weight of a NaCl solution in distilled water,

2. Drying for 105 minutes in a dry environment,

3.22 hours at controlled temperature and atmospheric humidity: 50 ° C and 90% relative atmospheric humidity,

4.4 repetitions of steps 1-3, and

5.48 hours at 50 ° C and 90% relative atmospheric humidity. One sequence of steps 1-3 is essentially one

cycle. In each case, the cycle is considered to have passed the test successfully when the adhesive bond between all the chain test plates is held firmly. In general, the test is passed when the test passes at least 45 cycles successfully.

Phosphatization was determined by means of images obtained using a scanning electron microscope. In this case, "+" in Table 3 means a closed, fine-crystalline phosphate layer, "o" means a closed, phosphate layer of enlarged particles (the crystal has an edge length> 20 μm), and "-" means a phosphate layer , which is not closed, that is, the absence of a layer.

The set values in Tab. 2 and 3 allow us to draw the following conclusions: the treatment of aluminum sheets with an alkaline cleaning solution, which is carried out for the required acid etching in stage a) in comparative example SP2, leads to the production of sheets having low volume resistivity (18 μOhm for AA 5754 and 26 μOhm for AA 6111).

As can be seen from comparative example SP1, too high a mass of the Zr layer obtained in the case of treatment according to step c) (37 mg / m ² in the case of AA 5754 and 26 mg / m ² in the case of AA 6111) results in a very high volume resistivity, in particular, after storage for 30 days (100 μΩ in the case of AA 5754 and 38 μΩ in the case of AA 6111).

In the case of comparative examples SP4 and SP5, the weights of the layers obtained are in the desired range, however as a result of the fact that the ratio of zirconium / molybdenum in the treatment solution for process step c) is 20: 1 (see SP4) or 2: 1 (see SP5 ), the obtained volume resistivity is unacceptable, in particular, in the case of AA 6111 (26 and 44 μΩ in the case of SP4 and 19 and 22 μΩ in the case of SP5).

In the case of the comparative example of SDR, where the pH is too low, namely 2.1, undesirably high weights of the applied Zr layer were observed (24 mg / m ² for AA 5754 and 18 mg / m ² for AA 6111) as well as too high volumetric resistivity (40 and 79 μΩ for AA 5754 and 67 and 73 μΩ for AA 6111).

For comparison, examples P1-P7 show that when the conditions essential for the invention are met with respect to the type of etching, the Zr / Mo ratio, the mass of the layer obtained, the corresponding concentration and the pH ranges of the treatment solutions, layers are obtained having very good bulk resistivity, along with good adhesion properties.

Also, as can be seen from Tab. 3, all examples P1 - P7 successfully passed the modified APGE test, i.e. in each case, at least 45 cycles successfully passed the test, both in the case of AA 5754 and in the case of AA 6111, while this clearly does not apply in the case of comparative example SP1, where in each case only 10 up to 30 cycles. The other comparative examples SP2-SP5 were no longer subjected to the modified APGE test due to the already low results in terms of layer weight or bulk resistivity (Table 2, see above).

With regard to phosphatization (see Table 3), all examples P1-P7 (except P7 in the case of AA 5754) always showed a closed, finely crystalline phosphate layer ("+"), while comparative examples SP2-SP5 in in the case of AA 5754, they simply have a phosphate layer that is not closed, that is, they demonstrate the absence of a layer ("-"), and (with the exception of SP2) also show significantly lower results in the case of AA 6611.

The test plates of examples P6 and P7, which were pretreated in accordance with the invention, as well as an uncoated SPb test plate, which was not pretreated, were also subjected to anticorrosion treatments in several stages, which consisted of the following stages:

I) Alkaline purification (60 ° C; 180 s)

II) Rinsing (tap water; CT, 60 s)

III) Activation (titanium phosphate; CT, 30 s)

IV) Phosphating (trications; 53 ° C, 180 s)

V) Rinsing (tap water; CT, 30 s)

VI) Passivation (zirconium fluoride; CT, 45 s)

VII) Subsequent rinsing (demineralized water; CT, 30 s)

VIII) Drying (convection oven; 100 ° C; 7 min)

After the subsequent application of the electrophoretic coating and the top coat, a filiform corrosion test in accordance with DIN EN 3665 (mean values in accordance with DIN EN ISO 4628-8) and a cyclic corrosion test in accordance with VDA standard were carried out in each case 621-415 (average values according to DIN EN ISO 4628-8). The smaller the set migration under the coating in mm, the better the corrosion protection. The results are shown in the following table.

The corrosion protection in the case of examples P6 and P7, in each case, is comparable to the corrosion protection in the case of SP6. Thus, the pretreatment according to the invention does not adversely affect the corrosion protection subsequently obtained as a result of the anticorrosion treatment.

Claims (21)

1. A method of pretreating workpieces having a surface of aluminum or aluminum alloys for forming without cutting and / or joining by welding or adhesive bonding with pre-processed or optionally pre-coated workpieces or with optionally pre-treated parts consisting of steel and / or galvanized and / or alloy galvanized steel, and for subsequent final anticorrosive treatment by phosphating, by chromium-free conversion treatment, by applying a primer layer or by surface coating, in which the workpieces: a) etched by applying an aqueous acidic solution containing mineral acid by immersion or spraying, b) washed with water and c) contact with an aqueous acidic chromium-free solution for pretreatment, which contains Zr in the form of complex fluoride and Mo in the form of molybdate at a Zr: Mo mass ratio, calculated as metallic Zr / Mo, ranging from 15: 1 to 3.5: 1 by dipping or spraying, so that, after subsequent drying, in each case a Zr and Mo layer mass of 2 to 15 mg / m ² is obtained, the solution containing from 100 to 800 mg / l Zr and from 30 to 100 mg / L Mo, calculated as Zr / Mo metal, and has a pH of 2.5 to 4.5. 2. The method according to claim 1, in which the aqueous acidic chromium-free solution in step c) contains Zr in the form of complex fluoride and Mo in the form of molybdate at a Zr: Mo mass ratio, calculated as Zr / Mo metal, ranging from 13: 1 to 7 :one. 3. A method of pretreating workpieces having a surface of aluminum or aluminum alloys to form without cutting and / or joining by welding or adhesive bonding with pretreated or optionally precoated workpieces or with optionally pretreated parts consisting of steel and / or galvanized and / or alloy galvanized steel, and for subsequent final anticorrosive treatment by phosphating, by chromium-free conversion treatment, by applying a primer layer or by surface coating, in which the workpieces: a) etched by applying an aqueous acidic solution containing mineral acid by immersion or spraying, b) washed with water and c) contact with an aqueous acidic chromium-free solution for pretreatment, which contains Zr in the form of complex fluoride and Mo in the form of molybdate at a Zr: Mo mass ratio, calculated as metallic Zr / Mo, ranging from 2: 1 to 1: 2, by means of a roller application method, so that, after subsequent drying, in each case a Zr and Mo layer mass of 2 to 15 mg / m ² is obtained, the solution containing from 0.4 to 7.5 g / l Zr and 0.4 to 7.5 g / L Mo, calculated as Zr / Mo metal, and has a pH of 1.0 to 3.0. 4. The method according to claim 3, in which the aqueous acidic chromium-free solution in step c) contains Zr in the form of complex fluoride and Mo in the form of molybdate, with a mass ratio of Zr: Mo, calculated as metallic Zr / Mo, ranging from 1.4: 1 to 1: 1.4. 5. The method according to any one of claims. 1-4, in which the aqueous acidic chromium-free solution in step c) further contains at least one polymer selected from the group consisting of poly (meth) acrylic acid, copolymers of (meth) acrylic acid, polyvinylphosphonic acid, copolymers of vinylphosphonic acid and copolymers maleic acid. 6. The method of claim 5, wherein the at least one polymer is polyacrylic acid and / or a copolymer of acrylic acid and maleic acid. 7. A method according to any one of claims. 1-6, in which the preforms are etched with a solution containing a surfactant, hydrofluoric acid and sulfuric acid. 8. The method of claim 7, wherein the preforms are etched with a solution containing 3 to 8 g / L sulfuric acid, 50 to 150 mg / L free fluoride, and 1 to 3 g / L nonionic surfactant. 9. A method according to any one of claims. 1-8, in which, in the case of pretreating the blanks for non-cutting forming, a lubricant is used prior to the forming process. 10. The method according to any one of claims. 1-8, wherein scrubbing, rinsing with water, and optionally revitalization treatments are performed prior to the final anti-corrosive treatment. 11. Aqueous acidic chromium-free solution for pretreatment of workpieces having a surface made of aluminum or aluminum alloys, containing Zr in the form of complex fluoride and Mo in the form of molybdate at a Zr: Mo mass ratio, calculated as metallic Zr / Mo, ranging from 15: 1 to 3.5: 1, and the solution contains from 100 to 525 mg / L Zr and from 30 to 80 mg / L Mo, calculated as metallic Zr / Mo, and at least one polymer selected from the group consisting of poly (meth ) acrylic acid, copolymers of (meth) acrylic acid, polyvinylphosphonic acid, copolymers of vinylphosphonic acid and copolymers of maleic acid, with a pH ranging from 2.5 to 4.5. 12. A concentrate of an aqueous acidic chromium-free solution for pretreating workpieces having a surface of aluminum or aluminum alloys, which, when diluted with water or an aqueous solution in a ratio of from 1:30 to 1: 100, and optionally with adjusting the pH value, provides an aqueous acidic a chrome-free solution according to claim 11. 13. Aqueous acidic chromium-free solution for pretreatment of workpieces having a surface of aluminum or aluminum alloys, containing Zr in the form of complex fluoride and Mo in the form of molybdate at a Zr: Mo mass ratio, calculated as metallic Zr / Mo, ranging from 2: 1 to 1: 2, and the solution contains from 1.0 to 4.0 g / l Zr and from 0.4 to 2.0 g / l Mo, calculated as metallic Zr / Mo, and at least one polymer selected from the group consisting of poly (meth) acrylic acid, copolymers of (meth) acrylic acid, polyvinylphosphonic acid, copolymers of vinylphosphonic acid and copolymers of maleic acid, while having a pH of 1.0 to 3.0. 14. A concentrate of an aqueous acidic chromium-free solution for pretreating workpieces having a surface of aluminum or aluminum alloys, which, when diluted with water or an aqueous solution in a ratio of from 1:30 to 1: 100, and optionally with adjusting the pH value, provides an aqueous acidic a chromium-free solution according to claim 13. 15. A workpiece having a surface of aluminum or aluminum alloys, treated by a pretreatment method according to any one of paragraphs. 1-10.