WO2017046139A1

WO2017046139A1 - Pre-treating aluminum surfaces with zirconium- and molybdenum-containing compositions

Info

Publication number: WO2017046139A1
Application number: PCT/EP2016/071657
Authority: WO
Inventors: Norbert Maurus; Thomas Wendel; Dr. Nawel Souad KHELFALLAH
Original assignee: Chemetall Gmbh
Priority date: 2015-09-15
Filing date: 2016-09-14
Publication date: 2017-03-23
Also published as: DE102016217507A1; RU2750923C1; CN108350579A; MX2018003246A; KR20180053306A; ZA201802301B; CA2996465A1; US20180237919A1; EP3350357A1; JP2018527467A

Abstract

The invention relates to a method for pre-treating workpieces with a surface made of aluminum or aluminum alloys for a forming process without machining and/or for a connection process by welding or adhering with identically pre-treated or optionally otherwise pre-coated workpieces or with optionally pre-coated parts made of steel and/or galvanized steel and/or alloy galvanized steel and for a subsequent permanently corrosion-protective treatment by means of a phosphating process, a non-chromate conversion treatment, a primer application process, or by painting. The workpiece is a) pickled with an aqueous acid solution containing mineral acid in an immersion or spraying process, b) rinsed with water, and c) brought into contact with an aqueous acid solution, which is free of chromate and contains Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr/Mo metal) of Zr : Mo from 15 : 1 to 3.5 : 1, using an immersion or spraying application such that after the subsequent drying process, a layer weight of 2 to 5 mg/m² of Zr and Mo results in each case, wherein the solution contains 100 to 800 mg/l of Zr and 30 to 100 mg/l of Mo (calculated as Zr/Mo metal) and has a pH value of 2.5 to 4.

Description

Pre-treatment of aluminum surfaces with zirconium and molybdenum-containing compositions

The invention relates to a method for the pretreatment of workpieces with a surface made of aluminum or aluminum alloys for non-cutting forming and / or joining by welding or gluing with similarly pretreated or otherwise otherwise precoated workpieces or with optionally pretreated parts made of steel and / or galvanized and / or alloy-galvanized steel, and for subsequent corrosion-protective treatment by phosphating, by chromium-free conversion treatment, by primer application or by painting.

For the chemical surface treatment of metals, for example as a preparation for the application of paints, adhesives and plastics, methods are known in which in the first stage, the metal surface cleaned, rinsed in the second stage with water and finally in the third stage with an aqueous, wets chemical conversion coatings forming solution and the liquid film is dried. As a result, a thin, non-metallic coating is formed on the metal, which can decisively improve the surface quality with appropriately selected composition of the treatment liquid and the reaction conditions. So z. B. coatings of paints, adhesives and plastics, optionally in the form of films, characterized by a much greater adhesion and a considerably increased corrosion protection when applied to such pretreated metal.

Method of the aforementioned type work z. B. with an aqueous solution containing hexavalent chromium, trivalent chromium, alkali metal ions and silica in certain proportions and coatings for electrical insulation, for corrosion protection and as a primer for paints and the like produced (DE-AS 17 69 582).

Due to the presence of hexavalent chromium, this method has the common drawback that, in particular, precautions are required in the application of the coating agent and the handling of the coated metal. In order to avoid the drawbacks associated with the use of solutions containing hexavalent chromium, another category of processes for applying conversion coatings specifically for aluminum surfaces provides a treatment with compositions based on the zirconium and / or titanium fluoroanions (US Pat. A-41 48 670, FR-A-942 789, EP-A-106 389, EP-A-825 280).

More recently, the use of workpieces with surfaces of aluminum or aluminum alloys has become increasingly important in vehicle construction. The main reasons for this are the reduction in vehicle weight, but also the favorable recyclability of such workpieces. In this case, it is generally customary to connect vehicles made of a plurality of parts which as a rule have previously been formed without cutting and which consist of workpieces with surfaces made of aluminum or aluminum alloys, but also with those made of steel and / or galvanized steel and / or alloy-galvanized steel. By far the most important forms of joining or joining are welding or gluing. The joining of the parts is regularly followed by an anti-corrosive treatment which, depending on the nature of the connected parts, can consist of a phosphating treatment, a chromium-free conversion treatment, a primer application or a coating.

To ensure proper connection of the parts with surfaces of aluminum or aluminum alloys with each other or with parts made of steel and / or galvanized or alloy-galvanized steel, it must be ensured that the surfaces of the aluminum or aluminum alloy free of aluminum oxide or oxides of any alloying constituents of aluminum are. A suitable pickling treatment does not lead to the goal, since the aluminum surface is coated with a new oxide layer after a short time.

In order to solve the problem outlined above, the method of EP-B-700 452 envisages contacting surfaces of aluminum or its alloys with an aqueous solution prior to a second permanent anticorrosion treatment for pretreatment, comprising complex fluorides of the elements boron, Contain silicon, titanium, zirconium or hafnium individually or in admixture with each other in concentrations of the fluoro-anions of 100 to 4000 mg / l and have a pH of 0.3 to 3.5. Between pre-treatment and permanent anti-corrosive conversion treatment, the parts made of aluminum or its alloys are subjected to a chipless and / or cutting deformation process, and / or connected to one another or to parts made of steel and / or galvanized and / or alloy-galvanized steel by gluing and / or welding. The application of the optionally polymers containing certain state of the art solution can be done by spraying, dipping or no-rinse method, wherein in the case of the no-rinse method, the wet film amount between 2 to 10, preferably between 4 and 6 ml / m ² metal surface should. Regardless of the form of application of the solution, it is advantageous to dry at temperatures between 40 and 85 ° C. For the purpose of cleaning, the parts made of aluminum or its alloys are acid or alkaline cleaned prior to the first conversion treatment, and cleaning steps and intermediate rinses with water and / or activating rinsing baths preferably take place before the permanent corrosion-protective treatment.

From the information on the concentrations of fluoro-anions of the solutions to be applied on the one hand and the wet film amount on the other hand results in the case of the order of a fluoro-titanate-containing solution an edition of 0.06 to 1 1, 73 mg / m ² , preferably from From 0.12 to 7.04 mg / m ² (in each case given as titanium metal) and, in the case of the order of a solution containing fluorozirconate, an overlay of from 0.09 to 17.78 mg / m ² , preferably from 0, 18 to 7.04 mg / m ² (each indicated as zirconium metal). The investigations preceding the conception of the present invention have shown that a multiplicity of the possibilities of embodiment described in EP-B-700 452 lead to less favorable results, in particular with regard to the temporary corrosion protection achieved with the first chemical conversion treatment and the volume resistivity which is important for the production of welded joints , to lead.

With the method disclosed in US 6,020,030 A, in which a Although organophosphorus compound is used for the pretreatment of aluminum substrates, it is true that good adhesive adhesion can be achieved. However, the method is susceptible to bath contamination by aluminum ions, which therefore must be removed by means of an ion exchange resin. The object of the invention is a method for the pretreatment of workpieces with a surface made of aluminum or aluminum alloys for non-cutting forming and / or joining by welding or gluing, in particular for bonding by gluing, with similarly pretreated or otherwise otherwise precoated workpieces or with Parts made of steel and / or galvanized and / or alloy galvanized steel, in particular with similarly pretreated workpieces, and to provide a permanent corrosion protection treatment by phosphating and / or by a chrome-free conversion treatment and by primer application and / or painting, in particular by phosphating and a Chrome-free conversion treatment as well as varnishing, which regularly leads to workpieces with a sufficiently low volume resistance and at the same time good phosphatability and adhesive adhesion.

In addition, the method according to the invention should moreover lead to good temporary corrosion protection values and be largely insensitive to bath contamination by aluminum ions.

The object is achieved, on the one hand, by configuring the method according to the invention in such a way that the workpieces a) are immersed in a dipping or spraying with a mineral acid-containing aqueous, acidic solution,

b) rinsing with water and

c) with an aqueous, acidic solution which is chromium-free and contains Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 15: 1 to 3.5: 1, brought by dipping or spraying application in contact, so that after the subsequent drying a coating weight of 2 to 15 mg / m ² of Zr and Mo results, the Solution contains 100 to 800 mg / l Zr and 30 to 100 mg / l Mo (calculated as Zr / Mo metal) and has a pH of 2.5 to 4.5.

In the dipping or spraying application, it has been shown that neither in the application of solutions containing only fluorozirconate or only molybdate, nor in the application of solutions in which the weight ratio (calculated as Zr / Mo metal) of zirconium: molybdenum is outside the weight ratio of 15: 1 to 3.5: 1, or in the application of solutions that lead to contact weights of zirconium and molybdenum outside the range of 2 to 15 mg / m ² , with respect to the task satisfactory results be achieved.

The aqueous, acidic solution in step c) preferably contains Zr and Mo in a weight ratio of 15: 1 to 5: 1, more preferably from 13: 1 to 7: 1 and very particularly preferably from 1: 1 by immersion or spraying : 1 to 9: 1.

After dehydration, a coating weight of 2 to 12 mg / m ² , particularly preferably 2 to 10 mg / m ² and very particularly preferably 2 to 8 mg / m ² of Zr and Mo preferably results in the case of immersion or spray application ,

Preferably, the aqueous solution contains 250 to 700 mg / l Zr and 30 to 80 mg / l Mo, more preferably 400 to 600 mg / l Zr and 40 to 60 mg / l Mo and most preferably 475 in the case of immersion or spray application to 525 mg / l Zr and 45 to 55 mg / l Mo.

Furthermore, the aqueous solution in the case of immersion or spray application preferably has a pH of from 3.1 to 4.3 and more preferably from 3.6 to 4.0 and preferably a temperature of from 20 to 50 ° C. and more preferably from 20 to 30 ° C on. On the other hand, the object is achieved by the method of the type mentioned according to the invention is designed such that the workpieces a) with a mineral acid-containing aqueous, acidic solution in the dipping or spraying,

b) rinsing with water and

c) with an aqueous, acidic solution which is chromium-free and contains Zr as a complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 2: 1 to 1: 2, by application in the

Roller coating method brings into contact, so that after the subsequent drying, a coating weight of 2 to 15 mg / m ² of Zr and Mo results, the solution 0.4 to 7.5 g / l Zr and 0.4 to 7.5 contains g / l Mo (calc. as Zr / Mo metal) and has a pH of 1.0 to 3.0. When applied by the roll application method, it has been found that neither in the application of solutions containing only fluorozirconate or only molybdate, nor in the application of solutions in which the weight ratio (calculated as Zr / Mo metal) of zirconium: Molybdenum outside the weight ratio of 2: 1 to 1: 2, or when applying solutions that lead to contact weights of zirconium and molybdenum outside the range of 2 to 15 mg / m ² , satisfactory results are achieved with respect to the task.

Preferably, the aqueous, acidic solution in step c) when applied by roller coating Zr and Mo in a weight ratio of 1, 7: 1 to 1: 1, 7, more preferably from 1, 4: 1 to 1: 1, 4 and all more preferably from 1, 1: 1 to 1: 1, 1.

After application in a roller application method, after drying preferably results in a coating weight of 2 to 12 mg / m ² , more preferably from 2 to 10 mg / m ² and most preferably from 2 to 8 mg / m ² of Zr and Mo. the aqueous solution when applied by roller coating 1, 0 to 6.0 g / l Zr and 1, 0 to 6.0 g / l Mo, more preferably 2.0 to 4.0 g / l Zr and 2.0 to 4 , 0 g / l Mo and most preferably 2.8 to 3.2 g / l Zr and 2.8 to 3.2 g / l Mo.

Furthermore, the aqueous solution preferably has a pH of from 1.4 to 2.7, and particularly preferably from 1.8 to 2.5, when applied by the roller application method on.

Inn With regard to the defined coating weight of zirconium and molybdenum (2 to 15 mg / m ² ) to be set, it is of decisive importance that, depending on the type of application - dipping or spraying application on the one hand, application in the roll application method on the other - In terms of concentration and ratio of the fluoro-zirconate and molybdate anions and the pH differently sourced aqueous, acidic solutions in step c) are used.

The aqueous, acidic solution in step c) can by prior dilution of a corresponding concentrate, preferably by a factor of 1: 30 to 1: 100, more preferably by a factor of about 1:50, preferably with water and optionally adjusting the pH value can be provided.

In order to achieve the objective pursued by the invention, it is furthermore essential that the workpieces are pickled with a mineral acid-containing aqueous, acidic solution by dipping or spraying. Alkaline cleaning, for example, results in the formation of zirconium / molybdenum layers with poor volume resistivity values.

The compound of the invention pretreated workpieces can be pre-coated with similar pretreated or possibly otherwise, for. As phosphated workpieces, done with surfaces of aluminum or its alloys. If intended to be joined to steel and / or galvanized and / or alloy galvanized steel parts, these parts may have bare or precoated surfaces. A suitable pre-coating can, for. Example, a phosphate layer with a maximum coating weight of 2 g / m ² or a layer of a conductive primer.

If the workpieces are oiled, the pickling process must be preceded by a cleaning / degreasing stage or the pickling process must be carried out in such a way that simultaneous cleaning / degreasing takes place. The latter can be done by adding surfactant to the pickling solution. As a method for Phosphatierbehandlung are those who work with solutions based on zinc phosphate, in particular according to the low-zinc technology, or with alkali metal phosphate in the foreground. The solutions may be modified by the addition of further small amounts of polyvalent cations, such as calcium, magnesium, nickel, copper or manganese.

For chromium-free conversion treatment, in particular acid solutions of the fluoro complexes of titanium, zirconium, hafnium, but also silicon, optionally containing organic polymer, are used.

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

The at least one organosilane preferably has at least one amino group. Particularly preferably it is one which can be hydrolyzed to an aminopropylsilanol and / or to 2-aminoethyl-3-amino-propyl-silanol and / or a bis (trimethoxysilylpropyl) amine.

As primers so-called reaction primer or primer can be applied.

The pre-treatment of the workpieces according to the invention ensures adequate, temporary corrosion protection for longer storage times. During this time, there is no negative influence on the weldability, in particular the electrical resistance welding, or the bondability. Also, with regard to the weldability, it is ensured that the volume resistance is practically the same on all surface areas of the workpiece.

Workpieces in the context of the present invention are tape, sheet metal and individual parts, such as profiles.

The application of the solution according to step c) can be done by spraying or dipping each with or without water rinse. When applied without water rinse, it is advantageous to remove excess treatment solution by squeezing rollers. In the treatment of sheet or strip, the application of the treatment solution by the roll coater method is particularly advantageous. It allows a defined setting of the desired wet film thickness in one operation.

Following the types of application of the solution described above, the workpiece is dried or the solution is dried. Object temperatures of 30 to 90 ° C are particularly advantageous.

Concentrates which are diluted with low-salt water, preferably demineralized water, to the concentrations to be respectively adjusted are usually used to prepare the treatment liquids. To avoid the entry of alkali ions, it is particularly advantageous to introduce the required fluoro-anions of the zirconium with the aid of the free acid and to adjust the respective pH-value by adding ammonia if required. In contrast, the molybdate is advantageously introduced as ammonium heptamolybdate and / or sodium heptamolybdate, preferably as ammonium heptamolybdate and particularly preferably as ammonium heptamolybdate x 7 H ₂ O.

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

The pickling of the workpieces (process step a)) is done with a mineral acid-containing aqueous, acidic solution. It can be carried out electrolytically or chemically. In the case of electrolytic pickling, phosphoric acid is particularly suitable as the mineral acid. The pickling by chemical means, which is given preference because of the apparatus less laborious procedure in the rule, can be made with nitric acid or nitric acid / hydrofluoric acid. According to a preferred embodiment of the invention, the workpieces are pickled with a solution by spraying or dipping containing surfactant, sulfuric acid and a compound selected from the group consisting of hydrofluoric acid, phosphoric acid and iron (III) sulfate, preferably hydrogen fluoride, wherein solutions, containing 3 to 8 g / l of sulfuric acid, 50 to 150 mg / l of non-complexed free fluoride and 1 to 3 g / l of nonionic surfactant have been found to be particularly suitable. Nonionic surfactants are ethylene oxide Adducts to fatty alcohols and, for example, abietic acid are particularly suitable.

The measurement of the free fluoride was carried out with a fluoride-sensitive electrode, wherein the calibration of the electrode was carried out with solutions whose pH was identical to that of the solution to be tested. In order to achieve layers with an optimum volume resistance in the subsequent treatment according to step c), the pickling process should be carried out in such a way that a metal removal of about 0.1 to 0.6 g / m ² workpiece surface is obtained.

The subsequent to the pickling of the workpieces flushing - according to step b) - is preferably carried out in several rinsing stages, and it is particularly advantageous to perform the rinse water cascade-like the workpiece in the opposite direction. The last rinse step should be carried out with demineralized water. The subsequent to the pickling and rinsing step treatment according to step c) prevents the re-growth of an oxide layer occurs on the workpieces with a surface made of aluminum or aluminum alloy.

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

The (meth) acrylic acid copolymers used are preferably (meth) acrylic acid / maleic acid copolymers and the vinylphosphonic acid copolymers vinylphosphonic acid / acrylic acid copolymers. As polymers, in particular polyacrylic acid and acrylic acid copolymers and in the latter especially acrylic acid-maleic acid copolymers are suitable.

Preferably, the poly (meth) acrylic acid used has a number average molecular weight (MW) in the range from 4,000 to 300,000 g / mol, more preferably from 50,000 to 250,000 g / mol and most preferably from 100,000 up to 250,000 g / mol.

Preferably, the (meth) acrylic acid copolymer used has a number average molecular weight (MW) in the range from 4,000 to 100,000 g / mol and particularly preferably from 60,000 to 80,000 g / mol.

The polyvinylphosphonic acid or vinylphosphonic acid copolymer used preferably has a number average molecular weight (MW) in the range from 4,000 to 70,000 g / mol and particularly preferably in the range from 10,000 to 30,000 g / mol.

The concentration of the at least one polymer is between 100 and 600 mg / l, preferably between 100 and 400 mg / l, more preferably between 135 and 290 mg / l and most preferably between 170 and 180 mg / l. By using the at least one polymer, a coating weight of Zr and Mo which is more independent of the injection time and preferably largely independent of coating weight in the target range of 2 to 15 mg / m ² can be achieved in spray application. This is particularly advantageous because even at different tape speeds similar coating weights can be achieved. Negative effects on the volume resistivity, however, are not observed by the polymer content.

In the case of a subsequent treatment at step c) by non-cutting forming a further advantageous embodiment of the invention provides to apply a lubricant to the workpieces. These are in particular mineral oil-based forming oils, which may be fully synthetic or native, or dry lubricants based on polyethylene / polyacrylate.

Before the permanent corrosion-protective treatment, it is usually useful to intervene cleaning and Wasserspülstufen. If a primer or varnish application is planned, prior drying is recommended. If a chromium-free conversion treatment is to follow, it is also possible to work wet on wet, ie without prior drying, when applied by dipping or spraying. For application according to the roll coater method is an intermediate drying essential. In the case of a subsequent phosphating treatment, which may also be done wet-on-wet, it is expedient to provide an activating treatment, for example with a titanium and phosphate-containing activating agent. With the aid of the method according to the invention, workpieces with layers are regularly obtained which permit perfect deformation and / or gluing or, as a result of the small electrical resistance which is uniform over the workpiece surface, a perfect and trouble-free welding. In addition, the workpieces are ideally suited for a subsequent permanent corrosion-protective treatment.

The invention will be explained in more detail with reference to the following non-limiting exemplary embodiments.

EXAMPLES

With the exception of a sheet set, which was cleaned alkaline (Comparative Example VB2 in Tab. 1), sheets of aluminum alloys of quality AA 61 1 1 and AA 5754 were first degreased at a temperature of 50 ° C in dipping or spraying degreasing. The pickling solution contained 6 g / l sulfuric acid (100%), 100 mg / l hydrofluoric acid (100%) and 2 g / l nonionic surfactant consisting of ethoxylated fatty alcohol and ethoxylated abietic acid in a weight ratio of 1: 1.

The pickling process was carried out in such a way that the pickling rate for the alloy AA 5754 was 0.05 to 0.2 g / m ² and for the alloy AA 61 1 1 0.05 to 0.4 g / m ² . For this treatment times between 5 and 20 seconds were required.

Subsequently, the workpieces were thoroughly rinsed with water, in the final stage with demineralized water. The volume resistances measured on the single sheet were about 60 μ-ohms for the AA 5754 alloy and about 13 μ-ohms for the AA 61 1 1 alloy. This was followed by treatment with solutions of hexafluoric acid zirconium and / or molybdate, which optionally each contained a polymer or copolymer and their data in terms of the concentration of zirconium and / or molybdenum and (co) polymer, the pH and the Application temperature are shown in Tab. 1, for 6 sec. By pointed application. If necessary, the pH was adjusted with ammonia solution. Excess treatment solution was removed by squeezing rollers and then the treated surface was dried.

The polymers A to D in Table 1 were the following:

A: polyacrylic acid, MW = about 60,000 g / mol in colloidal solution,

B: acrylic acid-maleic acid copolymer, MW = about 70,000 g / mol,

C: polyacrylic acid, MW = approx. 250,000 g / mol,

D: Vinylphosphonic acid-acrylic acid copolymer, MW = 4000 to 70,000 g / mol. Table 1:

(Comp.) Concentration in mg / l pH Temp. Ex. Value

Zr Mo ZrF ₆ ^{2 "} Mo0 ₄ ^2" ZrF ₆ ^{2 "} + polyin ° C

MoO ₄ ^{2 "} mer

VB1 500 50 1125 83 1208 A: 250 3.6 50

B1 500 50 1125 83 1208 A: 250 3,6 30

B2 500 50 1125 83 1208 B: 500 3,6 30

B3 500 50 1125 83 1208 C: 175 3.6 23

B4 500 50 1125 83 1208 D: 250 3,6 23

B5 300 80 675 132.8 807.8 C: 175 3.9 23

B6 600 40 1350 66.4 1416.4 C: 350 3.6 3.6

VB2 500 50 1125 83 1208 C: 175 3.6 23

B7 500 50 1125 83 1208 0 3,6 23

VB3 500 50 1125 83 1208 C: 175 2.1 23

VB4 500 25 1128 41.5 1166.5 C: 175 3.6 23

VB5 100 50 225 83 308 C: 175 3.6 23

Table 2:

(Comp.) Layer weight Volume resistance Ex. (Mg / m ² ) (μ-ohm)

AA6111 AA5754 AA6111 AA5754

Zr Mo Zr Mo Od 30 d Od 30 d

VB1 26 4 37 7 25 38 62 100

B1 9 5 14 6 8 10 9 11

B2 2 6 5 7 9 11 13 15

B3 4 8 8 7 12 14 13 15

B4 3 5 10 6 7 8 10 12

B5 3 5 8 8 10 14 4 16

B6 2 1 4 2 13 14 5 7

VB2 7 12 8 3 26 25 18 33

B7 7 4 9 6 15 15 6 15

VB3 18 8 24 12 67 73 40 79

VB4 6 4 8 6 26 44 9 21

VB5 4 3 8 8 19 22 9 18

Table 3:

ng = not measured

Column 2 in Table 2 shows the layer weights of Zr achieved in this manner and of Mo in mg / m ² . The measurement of the individual coating weights was carried out by means of X-ray fluorescence analysis (XRF).

In column 3 of Tab. 2, the volume resistances obtained in single-sheet measurements are also reproduced in μ-ohms. The measurement of the volume resistances was carried out immediately after the drying / drying (in each case first row "0 d") and after storage for 30 days (in each case the second row "30 d"). It was carried out according to leaflet 2929 (dated September 2001) of the German Association for Welding and allied processes e.V. (DSV) with copper electrodes with a diameter of 20 mm.

Columns 2 and 3 of Table 3 show the corresponding phosphatabilities or the results of the modified APGE test described below in passed cycles.

Adhesive adhesion was determined using a modified APGE (Arizona Proving Ground Equivalent) test. To this end, two test slides (each 56.25 x 25 x 0.25 mm) were coated with a dry lubricant customary in the industry and bonded using a suitable industrial adhesive. Six such test plate pairs were then bolted at their respective ends to a chain which was subjected to a tensile stress of 2400 N. The following climate program was used per test week:

1 . 15 min. Immersion in a 5% strength by weight solution of NaCl in distilled water,

2. 105 min. Drying in a dry environment,

3. 22 hours at controlled temperature and humidity: 50 ° C and 90% rel.

LF,

4. 4 repetitions of steps 1. to 3., and

5. 48 hours at 50 ° C and 90% rel. LF.

A sequence of steps 1. to 3. represents a cycle by definition. One cycle was passed if the adhesive bond between all of the test slides on the chain withstood. The test was passed as a whole, if at least 45 cycles were passed.

The phosphatability was determined by scanning electron microscope images. Thus, a "+" - in Table 3, a closed, finely crystalline phosphate layer, an "o" a closed, coarsened phosphate layer (crystals with> 20 μιτι edge length) and a "-" a non-closed to nonexistent phosphate layer.

The following can be found in the measured values in Tab. 2 and 3. The treatment of the aluminum sheets with an alkaline cleaner carried out to demonstrate the necessity of an acidic pickling treatment in stage a) in Comparative Example CB2 leads to sheet metals having poor volume resistivities (18 μ-ohms for AA 5754 and 26 μ-ohms for AA 61 1 1).

Comparative Example VB1 reveals that owing to an excessively high Zr support weight, the layer obtained in the treatment according to step c) (37 mg / m ² at AA 5754 and 26 mg / m ² at AA 61 1 1) has very high volume resistivities - in particular a storage of 30 days - be obtained (100 μ-ohms for AA 5754 and 38 μ-ohms for AA 61 1 1).

In the comparative examples VB4 and VB5, although the coating weights obtained are in the desired range, but due to the zirconium / molybdenum ratio in the treatment solution for process step c) of 20: 1 (see VB4) and 2: 1 (see VB5) are the obtained Volume resistances, especially for AA 61 1 1, are not acceptable (26 or 44 μ-ohms for VB4 and 19 or 22 μ-ohms for VB5).

In the case of Comparative Example VB3 with a too low pH of 2.1 become too high Zr conditions (24 mg / m ² for AA 5754 and 18 mg / m ² for AA 61 1 1) and much too high volume resistances (40 or 79 μ-ohms for AA 5754 and 67 or 73 μ-ohms for AA 61 1 1).

In contrast, examples B1 to B7 show that, in compliance with the conditions essential to the invention, with regard to the type of pickling treatment, the Zr / Mo ratio, the produced coating weight, the respective Concentration and pH ranges of the treatment solutions layers with extremely good volume resistances at the same time good adhesive properties are obtained.

In addition, it can be seen from Table 3 that all Examples B1 to B7 on both AA 5754 and AA 61 1 1 have passed the modified APGE test - ie at least 45 cycles in each case - while for Comparative Example VB1 only 10 in each case to 30 passed cycles clearly does not apply. The other comparative examples VB2 to VB5 were no longer subjected to the modified APGE test because of the poor results (Table 2, see above) already present in the coating weight or volume resistance.

With regard to the phosphatability (see Tab. 3), all examples B1 to B7 (with the exception of B7 for AA 5754) always show a closed, finely crystalline phosphate layer ("+"), while Comparative Examples VB2 to VB5 on AA 5754 only one non-closed bis have absent phosphate coating ("-") and (with the exception of VB2) on AA 661 1 significantly worse results.

The pretreated test slides of Examples B6 and B7 and a non-pretreated bare test slide VB6 were further subjected to a multistage anticorrosive treatment consisting of the following steps: i) Alkaline purification (60 ° C., 180 s)

ü) rinsing (city water, RT, 60 s)

iü) activation (titanium phosphate, RT, 30 s)

iv) phosphating (trications, 53 ° C, 180 s)

v) rinsing (city water, RT, 30 s)

vi) passivation (zirconium fluoride, RT, 45 s)

vii) Rinse (deionized water, RT, 30 s)

viii) drying (convection oven, 100 ° C, 7 min)

After subsequent electrocoating and topcoating, a filiform corrosion test according to DIN EN 3665 (average values according to DIN EN ISO 4628-8) as well as a cyclic corrosion test according to VDA 621-415 (average values according to DIN EN ISO 4628-8). The lower the measured infiltration in mm, the better the corrosion protection. The results are shown in the following table. Table 4:

The corrosion protection of B6 and B7 is similar to that of VB6. The pretreatment according to the invention therefore does not adversely affect the protection subsequently achieved by a corrosion-protective treatment.

Claims

claims:

1 . Process for the pretreatment of workpieces with a surface made of aluminum or aluminum alloys for chipless forming and / or joining by welding or gluing with identically pretreated or otherwise precoated workpieces or optionally precoated parts made of steel and / or galvanized and / or alloy-galvanized steel and for a subsequent permanent corrosion-protective treatment by phosphating, by a chromium-free conversion treatment, by primer application or by painting characterized in that the workpieces a) with a mineral acid-containing aqueous, acidic solution in the dipping or spraying,

b) rinsing with water and

c) with an aqueous, acidic solution which is chromium-free and Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr-

Mo / metal) of Zr: Mo of 15: 1 to 3.5: 1, brings by dip or spray application in contact, so that after the subsequent drying a coating weight of 2 to 15 mg / m ² of Zr and Mo resulting in the solution containing 100 to 800 mg / l Zr and 30 to 100 mg / l Mo (calc. as Zr / Mo metal) and having a pH of 2.5 to 4.5.

2. The method according to claim 1, characterized in that the aqueous, acidic solution in step c) Zr as a complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 13: 1 to 7 : 1 contains.

3. A process for the pretreatment of workpieces with a surface made of aluminum or aluminum alloys for chipless forming and / or bonding by welding or gluing with similarly pretreated or otherwise otherwise precoated workpieces or optionally precoated parts made of steel and / or galvanized and / or alloy-galvanized Steel as well as for a subsequent permanent corrosion-protective treatment by phosphating, by a chromium-free conversion treatment, by primer application or by painting, characterized in that the workpieces a) with a mineral acid-containing aqueous, acidic solution in the dipping or spraying,

b) rinsing with water and

c) with an aqueous, acidic solution which is chromium-free and contains Zr as a complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 2: 1 to 1: 2, by application in the roll application process, so that after the following

Drying a layer weight of 2 to 15 mg / m ² each of Zr and Mo, the solution containing 0.4 to 7.5 g / l Zr and 0.4 to 7.5 g / l Mo (calc. / Mo-metal) and has a pH of 1.0 to 3.0.

4. The method according to claim 3, characterized in that the aqueous, acidic solution in step c) Zr as a complex fluoride and Mo as molybdate in a

Weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 1, 4: 1 to 1: 1, 4 contains.

5. The method according to any one of claims 1 to 4, characterized in that the aqueous, acidic solution in step c) additionally at least one polymer selected from the group consisting of poly (meth) acrylic acid, (meth) acrylic acid copolymers, polyvinylphosphonic acid, vinylphosphonic Contains copolymers and maleic acid copolymers.

6. The method according to claim 5, characterized in that the at least one polymer is polyacrylic acid and / or an acrylic acid-maleic acid copolymer.

7. The method according to any one of claims 1 to 6, characterized in that the workpieces are mixed with a surfactant, hydrofluoric acid and sulfuric acid-containing solution.

8. The method according to claim 7, characterized in that the

Workpieces with a solution containing 3 to 8 g / l of sulfuric acid, 50 to 150 mg / l free fluoride and 1 to 3 g / l nonionic surfactant.

9. The method according to any one of claims 1 to 8, characterized in that applying in the event of pretreatment of the workpieces for the non-cutting forming prior to the forming process, a lubricant.

10. The method according to any one of claims 1 to 8, characterized in that one carries out before the permanent corrosion-protective treatment cleaning, Wasserspül- and optionally activation treatments.

1 1. Aqueous acid solution for the pretreatment of workpieces having a surface of aluminum or aluminum alloys characterized in that it is chromium-free and Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 15: 1 to 3.5: 1, wherein the solution contains 100 to 800 mg / l Zr and 30 to 100 mg / l Mo (calc. As Zr / Mo metal) and has a pH of 2.5 to 4 , 5.

12. Concentrate, from which by dilution with water or an aqueous solution and optionally adjusting the pH, a solution according to claim

1 1 is available.

13. Aqueous acidic solution for pretreating workpieces with a surface made of aluminum or aluminum alloys, characterized in that it is chromium-free and Zr as a complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr / Mo metal) of Zr: Mo of 2: 1 to 1: 2, wherein the solution contains 0.4 to 7.5 g / l Zr and 0.4 to 7.5 g / l Mo (calc. As Zr / Mo metal) and a pH Value of 1.0 to 3.0.

14. Concentrate from which a solution according to claim 13 is obtainable by dilution with water or an aqueous solution and optionally adjusting the pH.

15. workpiece having a surface made of aluminum or aluminum alloys, characterized in that it has been pretreated by a method according to any one of claims 1 to 10.