EP3350357B1 - Pre-treating aluminum surfaces with zirconium- and molybdenum-containing compositions - Google Patents

Description

The invention relates to a method for pretreating 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 optionally otherwise precoated workpieces or with optionally pretreated parts made of steel and/or galvanized and/or alloy-galvanized steel, as well as for subsequent anti-corrosive treatment by phosphating, by a chromium-free conversion treatment, by applying a primer or by painting.

For the chemical surface treatment of metals, for example in preparation for the application of paints, adhesives and plastics, processes are known in which the metal surface is cleaned in the first stage, rinsed with water in the second stage and finally wetted with an aqueous solution that forms chemical conversion coatings in the third stage and the liquid film is dried. This forms a thin, non-metallic coating on the metal which, if the composition of the treatment liquid and the reaction conditions are selected accordingly, can significantly improve the surface quality. For example, coatings made of paints, adhesives and plastics, possibly in the form of films, can be characterized by significantly better adhesion and considerably increased corrosion protection if they are applied to metal that has been pretreated in this way.

Processes of the aforementioned type work, for example, with an aqueous solution containing hexavalent chromium, trivalent chromium, alkali ions and silicon dioxide in certain proportions and produces coatings for electrical insulation, for corrosion protection and as a primer for paints and the like ( DE-AS 17 69 582 ).

Due to the presence of hexavalent chromium, these processes have the disadvantage that particular precautions are required when applying the coating agent and handling the coated metal.

In order to avoid the disadvantages associated with the use of solutions containing hexavalent chromium, another category of processes for applying conversion coatings specifically for aluminium surfaces involves treatment with compositions based on the fluoro anions of zirconium and/or titanium ( US-A-41 48 670 , FR-A-942 789 , EP-A-106 389 , EP-A-825 280 ).

In recent times, the use of workpieces with surfaces made of aluminum or aluminum alloys in vehicle construction has become increasingly important. The main reasons for this are the reduction in vehicle weight, but also the favorable recyclability of such workpieces. It is generally common practice to connect vehicles from several parts, usually previously formed without chipping, 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 connection or assembly are welding or gluing.

The joining of the parts is usually followed 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 application or a coating.

In order to ensure that parts with surfaces made of aluminum or aluminum alloys are properly bonded to each other or to parts made of steel and/or galvanized or alloy-galvanized steel, it must be ensured that the surfaces of the aluminum or aluminum alloy are free of aluminum oxide or oxides of any alloy components of the aluminum. A pickling treatment that would be suitable for this purpose does not achieve the desired result, as the aluminum surface is covered with a new oxide layer after a very short time.

To solve the problem outlined above, the procedure of EP-B-700 452 proposes to bring surfaces made of aluminium or its alloys into contact with an aqueous solution containing complex fluorides of the elements boron, Silicon, titanium, zirconium or hafnium, individually or in a mixture with one another, in fluoro anion concentrations of 100 to 4000 mg/l in total and with a pH value of 0.3 to 3.5. Between pretreatment and permanent corrosion-protective conversion treatment, the parts made of aluminum or its alloys are subjected to a non-cutting and/or machining deformation process and/or are bonded to one another or to parts made of steel and/or galvanized and/or alloy-galvanized steel by gluing and/or welding. The solution, which may contain polymers of a certain nature, can be applied by spraying, dipping or using the no-rinse process, whereby in the case of the no-rinse process the wet film quantity should be between 2 and 10, preferably between 4 and 6 ml/m ² of metal surface. Regardless of the form of application of the solution, it is advantageous to dry at temperatures between 40 and 85 °C. For cleaning purposes, the parts made of aluminum or its alloys are cleaned with acid or alkali before the first conversion treatment; preferably, cleaning steps and intermediate rinsing with water and/or with activating rinsing baths are carried out 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 amount of wet film on the other hand, in the case of application of a solution containing fluoro titanate, a coating of 0.06 to 11.73 mg/m ² , preferably 0.12 to 7.04 mg/m ² (in each case stated as titanium metal) results and in the case of application of a solution containing fluoro zirconate, a coating of 0.09 to 17.78 mg/m ² , preferably 0.18 to 7.04 mg/m ² (in each case stated as zircon metal).

The investigations preceding the conception of the present invention have shown that a large number of the EP-B-700 452 The design options described lead to less than advantageous results, particularly with regard to the temporary corrosion protection achieved with the first chemical conversion treatment and the volume resistance which is important for the production of welded joints.

With the US6,020,030A disclosed method in which a If an organophosphorus compound is used to pretreat aluminum substrates, good adhesive bonding can be achieved. However, the process is susceptible to bath contamination by aluminum ions, which must therefore be removed using an ion exchange resin.

A treatment of workpieces with a surface made of aluminium or aluminium alloys with compositions based on the fluoro anions of zirconium and/or molybdate is described in each of the publications DE 102012017438 A1 , CN104294258A , EP1200641A1 , WO 2005/021834 A1 , US 2003/213533 A1 and EP2532769A1 disclosed.

The object of the invention is to provide a method for pretreating workpieces with a surface made of aluminum or aluminum alloys for non-cutting forming and/or joining by welding or gluing, in particular for joining by gluing, with similarly pretreated or otherwise precoated workpieces or with parts made of steel and/or galvanized and/or alloy-galvanized steel, in particular with similarly pretreated workpieces, as well as a subsequent permanent corrosion-protection treatment by phosphating and/or by a chromium-free conversion treatment as well as by applying primer and/or painting, in particular by phosphating and a chromium-free conversion treatment as well as by painting, which regularly leads to workpieces with a sufficiently low volume resistance and at the same time good phosphatability and adhesive adhesion.

Preferably, the process according to the invention should also lead to good temporary corrosion protection values and be largely insensitive to bath contamination by aluminum ions.

1. a) mit einer Mineralsäure enthaltenden wässrigen, sauren Lösung im Tauchen oder Spritzen beizt,
2. b) mit Wasser spült und
3. c) mit einer wässrigen, sauren Lösung, die chromfrei ist und Zr als komplexes Fluorid sowie Mo als Molybdat in einem Gewichtsverhältnis (berechnet als Zr-/Mo-Metall) von Zr : Mo von 15 : 1 bis 3,5 : 1 enthält, durch Tauch- oder Spritz-Applikation in Kontakt bringt, sodass nach dem nachfolgenden Auftrocknen ein Schichtgewicht von jeweils 2 bis 15 mg/m² an Zr und Mo resultiert, wobei die Lösung 100 bis 800 mg/l Zr und 30 bis 100 mg/l Mo (ber. als Zr-/Mo-Metall) enthält und einen pH-Wert von 2,5 bis 4,5 aufweist, und wobei die Lösung zusätzlich mindestens ein Polymer ausgewählt aus der Gruppe bestehend aus Poly(meth)acrylsäure, (Meth)acrylsäure-Copolymeren, Polyvinylphosphonsäure, Vinylphosphonsäure-Copolymeren und Maleinsäure-Copolymeren enthält.

The object is achieved on the one hand by designing the method of the type mentioned at the outset according to the invention in such a way that the workpieces

1. (a) pickling with an aqueous acidic solution containing mineral acid by immersion or spraying,
2. b) rinse with water and
3. 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 15 : 1 to 3.5 : 1, by immersion or spray application, so that after subsequent drying a layer weight of 2 to 15 mg/m ² of Zr and Mo results, whereby 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, and wherein the solution 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.

During dip or spray application, it has been shown that neither the application of solutions containing only fluorozirconate or only molybdate, nor 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, nor the application of solutions that lead to coating weights of zirconium and molybdenum outside the range of 2 to 15 mg/m ² , achieves satisfactory results with regard to the task.

Preferably, the aqueous, acidic solution in step c) in the case of dip or spray application contains Zr and Mo in a weight ratio of 15:1 to 5:1, particularly preferably 13:1 to 7:1 and very particularly preferably 11:1 to 9:1. Preferably, in the case of dip or spray application, the resulting layer weight after drying is 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.

When applied by immersion or spray, the aqueous solution preferably contains 250 to 700 mg/l Zr and 30 to 80 mg/l Mo, particularly preferably 400 to 600 mg/l Zr and 40 to 60 mg/l Mo, and very particularly preferably 475 to 525 mg/l Zr and 45 to 55 mg/l Mo.

Furthermore, when applied by immersion or spray, the aqueous solution preferably has a pH of 3.1 to 4.3 and particularly preferably 3.6 to 4.0 and preferably a temperature of 20 to 50 °C and particularly preferably 20 to 30 °C.

1. a) mit einer Mineralsäure enthaltenden wässrigen, sauren Lösung im Tauchen oder Spritzen beizt,
2. b) mit Wasser spült und
3. c) mit einer wässrigen, sauren Lösung, die chromfrei ist und Zr als komplexes Fluorid sowie Mo als Molybdat in einem Gewichtsverhältnis (berechnet als Zr-/Mo-Metall) von Zr : Mo von 2 : 1 bis 1 : 2 enthält, durch Applikation im Rollenauftragungsverfahren in Kontakt bringt, so dass nach dem nachfolgenden Auftrocknen ein Schichtgewicht von jeweils 2 bis 15 mg/m² an Zr und Mo resultiert, wobei die Lösung 0,4 bis 7,5 g/l Zr und 0,4 bis 7,5 g/l Mo (ber. als Zr-/Mo-Metall) enthält und einen pH-Wert von 1,0 bis 3,0 aufweist, und wobei die Lösung zusätzlich mindestens ein Polymer ausgewählt aus der Gruppe bestehend aus Poly(meth)acrylsäure, (Meth)acrylsäure-Copolymeren, Polyvinylphosphonsäure, Vinylphosphonsäure-Copolymeren und Maleinsäure-Copolymeren enthält und die Konzentration des mindestens einen Polymers zwischen 100 und 600 mg/l liegt.

On the other hand, the object is achieved by designing the method of the type mentioned at the outset according to the invention in such a way that the workpieces

1. a) with an aqueous, acidic solution containing mineral acid by immersion or spraying,
2. b) rinse with water and
3. 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 using a roller application method, so that after subsequent drying a layer weight of 2 to 15 mg/m ² of Zr and Mo results, wherein the solution contains 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 value of 1.0 to 3.0, and wherein the solution 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 and the concentration of the at least one polymer is between 100 and 600 mg/l lies.

When applying using the roller application method, it has been shown that neither the application of solutions containing only fluorozirconate or only molybdate, nor the application of solutions in which the weight ratio (calculated as Zr/Mo metal) of zirconium : molybdenum is outside the weight ratio of 2 : 1 to 1 : 2, nor the application of solutions that lead to coating weights of zirconium and molybdenum outside the range of 2 to 15 mg/m ² , achieves satisfactory results with regard to the task.

Preferably, the aqueous, acidic solution in step c) when applied by the roller application process contains Zr and Mo in a weight ratio of 1.7:1 to 1:1.7, particularly preferably 1.4:1 to 1:1.4 and very particularly preferably 1.1:1 to 1:1.1.

When applied using the roller application method, the result after drying is preferably a layer 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. When applied using the roller application method, the aqueous solution preferably contains 1.0 to 6.0 g/l Zr and 1.0 to 6.0 g/l Mo, particularly preferably 2.0 to 4.0 g/l Zr and 2.0 to 4.0 g/l Mo and very particularly preferably 2.8 to 3.2 g/l Zr and 2.8 to 3.2 g/l Mo.

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

With regard to the defined coating weight of zirconium and molybdenum (2 to 15 mg/m ² ) to be set in each case, it is of crucial importance that, depending on the type of application - dip or spray application on the one hand, application using the roller application method on the other hand - aqueous, acidic solutions of different compositions are used in step c) with regard to the concentration and ratio of the fluorozirconate and molybdate anions and the pH value.

The aqueous, acidic solution in step c) can be provided by previously diluting 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.

In order to achieve the aim pursued with the invention, it is also essential that the workpieces are pickled with an aqueous, acidic solution containing mineral acid by immersion or spraying. Alkaline cleaning, for example, results in the formation of zirconium/molybdenum layers with poor volume resistance values.

The workpieces pretreated according to the invention can be joined to workpieces that have been pretreated in the same way or, if appropriate, precoated in a different way, e.g. phosphated workpieces, with surfaces made of aluminum or its alloys. If a connection to parts made of steel and/or galvanized and/or alloy-galvanized steel is intended, these parts can have bare or precoated surfaces. A suitable precoating can be, for example, a phosphate layer with a layer weight of a maximum of 2 g/m ² or a layer of a conductive primer.

If the workpieces are oiled, a cleaning/degreasing step must be carried out before the pickling process or the pickling process must be carried out in such a way that cleaning/degreasing takes place at the same time. The latter can be done by adding surfactant to the pickling solution.

Phosphating treatment processes that use solutions based on zinc phosphate, particularly low-zinc technology, or alkali phosphate are the most popular. The solutions can be modified by adding small amounts of other polyvalent cations, such as calcium, magnesium, nickel, copper or manganese.

For chromium-free conversion treatment, acidic solutions of the fluoro complexes of titanium, zirconium, hafnium, but also silicon, optionally with a content of 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. It is particularly preferably one which can be hydrolyzed to an aminopropylsilanol and/or to 2-aminoethyl-3-aminopropylsilanol and/or a bis(trimethoxysilylpropyl)amine.

So-called reaction primers or adhesion primers can be applied as primers.

The pretreatment of the workpieces according to the invention ensures sufficient, temporary corrosion protection for longer storage periods. During this time, there is no negative influence on the weldability, in particular on electrical resistance welding, or on the bondability. With regard to weldability, it is also guaranteed that the volume resistance is practically the same on all surface areas of the workpiece.

Workpieces within the meaning of the present invention are strip, sheet metal and individual parts such as profiles.

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

Following the 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 are usually used to prepare the treatment liquids, which are diluted with low-salt water, preferably demineralized water, to the concentrations to be set. In order to avoid the introduction of alkali ions, it is particularly advantageous to introduce the required fluoro anions of the zirconium using the free acid and to adjust the respective pH value if necessary by adding ammonia. The molybdate, on the other hand, 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 such as, in particular, molybdic acid.

The pickling of the workpieces (process stage a)) is carried out with an aqueous, acidic solution containing mineral acid. It can be carried out electrolytically or chemically. In electrolytic pickling, phosphoric acid is a particularly suitable mineral acid. Chemical pickling, which is generally preferred because it requires less equipment, can be carried out with nitric acid or nitric acid/hydrofluoric acid. According to a preferred embodiment of the invention, the workpieces are pickled by spraying or dipping with a solution that contains surfactant, sulfuric acid and a compound selected from the group consisting of hydrofluoric acid, phosphoric acid and iron(III) sulfate, preferably hydrogen fluoride, with solutions containing 3 to 8 g/l sulfuric acid, 50 to 150 mg/l non-complexed, free fluoride and 1 to 3 g/l non-ionic surfactant having proven to be particularly suitable. Non-ionic surfactants are ethylene oxide adducts. fatty alcohols and, for example, abietic acid.

The measurement of free fluoride was carried out using a fluoride-sensitive electrode, whereby the electrode was calibrated using solutions whose pH was identical to that of the solution to be tested.

In order to achieve layers with an optimal volume resistance in the subsequent treatment according to stage c), the pickling process should be carried out in such a way that a metal removal of approximately 0.1 to 0.6 g/m ² of workpiece surface is achieved.

The water rinsing following the pickling of the workpieces - according to stage b) - preferably takes place in several rinsing stages, whereby it is particularly advantageous to direct the rinsing water in a cascade-like manner in the opposite direction to the workpiece. The last rinsing stage should be carried out with fully demineralized water. The treatment following the pickling and rinsing stage according to stage c) prevents the renewed growth of an oxide layer on the workpieces with a surface made of aluminum or aluminum alloy.

According to 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.

Preferred (meth)acrylic acid-maleic acid copolymers are used as (meth)acrylic acid copolymers and preferred vinylphosphonic acid-acrylic acid copolymers are vinylphosphonic acid-acrylic acid copolymers. Polyacrylic acid and acrylic acid copolymers are particularly suitable as polymers, and in the latter case, acrylic acid-maleic acid copolymers are particularly suitable.

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

The (meth)acrylic acid copolymer used preferably 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, particularly preferably between 135 and 290 mg/l and very particularly preferably between 170 and 180 mg/l. By using the at least one polymer, a layer weight of Zr and Mo that is more independent of the spraying time, preferably largely independent of it, can be achieved in the target range of 2 to 15 mg/m ² in each case. This is particularly advantageous because it allows similar layer weights to be achieved even at different belt speeds. However, no negative effects on the volume resistance can be observed due to the polymer content.

In the case of a subsequent treatment by chipless forming following stage c), a further advantageous embodiment of the invention provides for a lubricant to be applied to the workpieces. This particularly involves mineral oil-based forming oils, which can be fully synthetic or native, or dry lubricants based on polyethylene/polyacrylate.

Before the permanent anti-corrosive treatment, it is usually advisable to carry out cleaning and water rinsing steps. If a primer or paint application is planned, it is advisable to dry it beforehand. If a chrome-free conversion treatment is to follow, the application can be carried out wet-on-wet, i.e. without prior drying, when dipping or spraying. When applying using the roll coater method, Intermediate drying is essential. In the case of a subsequent phosphating treatment, which can also be carried out wet-on-wet, it is advisable to provide an activation treatment, for example with an activating agent containing titanium and phosphate.

Using the method according to the invention, workpieces are regularly obtained with layers that allow perfect forming and/or bonding or, due to the low and uniform electrical resistance across the workpiece surface, perfect and problem-free welding. In addition, the workpieces are ideally suited for subsequent permanent corrosion protection treatment.

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

Examples of implementation:

With the exception of one set of sheets that was cleaned with alkali (comparative example VB2 in Tab. 1 ), sheets made of aluminum alloys of quality AA 6111 and AA 5754 were first pickled to remove grease at a temperature of 50 °C by immersion or spraying. The pickling solution contained 6 g/l sulfuric acid (100%), 100 mg/l hydrofluoric acid (100%) and 2 g/l non-ionic 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 removal was 0.05 to 0.2 g/m ² for the AA 5754 alloy and 0.05 to 0.4 g/m ² for the AA 6111 alloy. This required treatment times of between 5 and 20 seconds.

The workpieces were then thoroughly rinsed with water, and in the last step with demineralized water. The volume resistances measured on the individual sheets were approximately 60 µ-Ohm for the AA 5754 alloy and approximately 13 µ-Ohm for the AA 6111 alloy.

This was followed by treatment with solutions of zirconium hexafluoric acid and/or molybdate, each of which optionally contained a polymer or copolymer, and whose data regarding the concentration of zirconium and/or molybdenum and (co)polymer, the pH value and the application temperature are shown in Table 1, for 6 seconds by tip application. If necessary, the pH value was adjusted with ammonia solution. Excess treatment solution was removed by squeezing rollers and the treated surface was then dried.

1. A: Polyacrylsäure, MW = ca. 60.000 g/mol in kolloidaler Lösung,
2. B: Acrylsäure-Maleinsäure-Copolymer, MW = ca. 70.000 g/mol,
3. C: Polyacrylsäure, MW = ca. 250.000 g/mol,
4. D: Vinylphosphonsäure-Acrylsäure-Copolymer, MW = 4000 bis 70.000 g/mol.

Tabelle 1: Beispiel B7 ist nicht erfindungsgemäß (Vgl.-) Bsp. Konzentration in mg/l pH-Wert Temp. in °C Zr Mo ZrF₆ ^2- MoO₄ ^2- ZrF₆ ^2-+ MoO₄ ^2- Polymer 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 23 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 Tabelle 2: Beispiel B7 ist nicht erfindungsgemäß (Vgl.-) Bsp. Schichtgewicht (mg/m²) Durchgangswiderstand (µ-Ohm) AA6111 AA 5754 AA6111 AA 5754 Zr Mo Zr Mo 0 d 30 d 0 d 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 Tabelle 3: Beispiel B7 ist nicht erfindungsgemäß (Vgl.-) Bsp. Phosphatierbarkeit (+/o/-) modifiz. APGE-Test (bestandene Zyklen) AA 6111 AA 5754 AA 6111 AA 5754 VB1 n.g. n.g. 10-30 10-30 B1 + + ≥ 45 ≥ 45 B2 + + ≥ 45 ≥ 45 B3 + + ≥ 45 ≥ 45 B4 + + ≥ 45 ≥ 45 B5 + + ≥ 45 ≥ 45 B6 + + ≥ 45 ≥ 45 VB2 + - n.g. n.g. B7 + o ≥ 45 ≥ 45 VB3 - - n.g. n.g. VB4 o - n.g. n.g. VB5 o - n.g. n.g. n.g. = nicht gemessen The polymers A to D in Table 1 were the following:

1. A: Polyacrylic acid, MW = approx. 60,000 g/mol in colloidal solution,
2. B: Acrylic acid-maleic acid copolymer, MW = approx. 70,000 g/mol,
3. C: polyacrylic acid, MW = approx. 250,000 g/mol,
4. D: Vinylphosphonic acid-acrylic acid copolymer, MW = 4000 to 70,000 g/mol.

<b>Table 1</b>: Example B7 is not according to the invention (See) Example Concentration in mg/l PH value Temp. in °C Zr Mon _ZrF6 ^2- _MoO4 ^2- ZrF ₆ ^2- + MoO ₄ ^2- polymer 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 23 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 (See) Example Coating weight (mg/m ² ) Volume resistance (µ-Ohm) AA6111 AA5754 AA6111 AA5754 Zr Mon Zr Mon 0 d 30 days 0 d 30 days VB1 26 4 37 7 25 38 62 100 B1 9 5 14 6 8th 10 9 11 B2 2 6 5 7 9 11 13 15 B3 4 8th 8th 7 12 14 13 15 B4 3 5 10 6 7 8th 10 12 B5 3 5 8th 8th 10 14 4 16 B6 2 1 4 2 13 14 5 7 VB2 7 12 8th 3 26 25 18 33 B7 7 4 9 6 15 15 6 15 VB3 18 8th 24 12 67 73 40 79 VB4 6 4 8th 6 26 44 9 21 VB5 4 3 8th 8th 19 22 9 18 (See) Example Phosphating ability (+/o/-) modified APGE test (cycles passed) AA6111 AA5754 AA6111 AA5754 VB1 ng ng 10-30 10-30 B1 + + ≥ 45 ≥ 45 B2 + + ≥ 45 ≥ 45 B3 + + ≥ 45 ≥ 45 B4 + + ≥ 45 ≥ 45 B5 + + ≥ 45 ≥ 45 B6 + + ≥ 45 ≥ 45 VB2 + - ng ng B7 + O ≥ 45 ≥ 45 VB3 - - ng ng VB4 O - ng ng VB5 O - ng ng ng = not measured

Column 2 in Table 2 shows the layer weights of Zr and Mo in mg/m ² achieved in this way. The individual layer weights were measured using X-ray fluorescence analysis (XRF).

Column 3 of Table 2 also shows the volume resistances obtained from individual sheet measurements in µ-Ohm. The volume resistances were measured immediately after drying/drying (first row "0 d" in each case) and after storage for 30 days (second row "30 d" in each case). They were carried out in accordance with leaflet 2929 (from September 2001) of the German Association for Welding and Related Processes (DSV) using copper electrodes with a diameter of 20 mm.

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

1. 1. 15 Min. Tauchen in eine 5 Gew.-%-ige Lösung von NaCl in destilliertem Wasser,
2. 2. 105 Min. Trocknen in einer trockenen Umgebung,
3. 3. 22 Std. bei kontrollierter Temperatur und Luftfeuchtigkeit: 50 °C und 90 % rel. LF,
4. 4. 4 Wiederholungen der Schritte 1. bis 3., und
5. 5. 48 Std. bei 50 °C und 90 % rel. LF.

The adhesive bond was determined using a modified APGE (Arizona Proving Ground Equivalent) test. For this purpose, two test plates (each 56.25 x 25 x 0.25 mm) were coated with a standard industrial dry lubricant and glued together using a suitable standard industrial adhesive. Six pairs of such test plates were then screwed together at their respective ends to form a chain, which was subjected to a tensile stress of 2400 N. The following climate program was used for each test week:

1. 1. Immerse for 15 minutes in a 5 wt.% solution of NaCl in distilled water,
2. 2. 105 min. drying in a dry environment,
3. 3. 22 hours at controlled temperature and humidity: 50 °C and 90 % RH,
4. 4. 4 repetitions of steps 1 to 3, and
5. 5. 48 hours at 50 °C and 90 % relative humidity.

A sequence of steps 1 to 3 represents a cycle by definition. A cycle was considered to have passed if the adhesive bond between all test plates in the chain held up. The test was considered to have passed overall if if at least 45 cycles have been passed.

The phosphatability was determined using scanning electron microscope images. A "+" in Table 3 means a closed, fine-crystalline phosphate layer, an "o" a closed, coarsened phosphate layer (crystals with > 20 µm edge length) and a "-" a non-closed or non-existent phosphate layer.

The following can be deduced from the measured values in Tables 2 and 3. The treatment of the aluminium sheets with an alkaline cleaner carried out in comparison example VB2 to demonstrate the necessity of an acid pickling treatment in stage a) leads to sheets with poor volume resistances (18 µ-Ohm for AA 5754 and 26 µ-Ohm for AA 6111).

Comparative example VB1 shows that due to an excessive Zr coating weight of the layer obtained during treatment according to step c) (37 mg/m ² for AA 5754 and 26 mg/m ² for AA 6111), very high volume resistances are obtained - especially after storage for 30 days (100 µ-Ohm for AA 5754 and 38 µ-Ohm for AA 6111).

In the comparative examples VB4 and VB5, 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), the volume resistances obtained are not acceptable, especially for AA 6111 (26 and 44 µ-Ohm for VB4 and 19 and 22 µ-Ohm for VB5).

In the case of comparative example VB3 with a too low pH value of 2.1, excessively high Zr deposits (24 mg/m ² for AA 5754 and 18 mg/m ² for AA 6111) as well as much too high volume resistances (40 or 79 µ-Ohm for AA 5754 and 67 or 73 µ-Ohm for AA 6111) are observed.

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

In addition, it is clear from Table 3 that all examples B1 to B7 on both AA 5754 and AA 6111 passed the modified APGE test - i.e. at least 45 cycles each - while this is clearly not the case for the comparison example VB1 , which only passed 10 to 30 cycles each. The other comparison examples VB2 to VB5 were not subjected to the modified APGE test due to the poor results already obtained for the layer weight and volume resistance ( Table 2, see above).

With regard to phosphatability (see Table 3 ), all examples B1 to B7 (with the exception of B7 for AA 5754) always show a closed, fine-crystalline phosphate layer ("+"), while the comparative examples VB2 to VB5 on AA 5754 only show a non-closed to non-existent phosphate layer ("-") and (with the exception of VB2 ) also show significantly worse results on AA 6611.

1. i) Alkalische Reinigung (60 °C ; 180 s)
2. ii) Spülen (Stadtwasser; RT, 60 s)
3. iii) Aktivieren (Titanphosphat; RT, 30 s)
4. iv) Phosphatieren (Trikationen; 53 °C, 180 s)
5. v) Spülen (Stadtwasser; RT, 30 s)
6. vi) Passivieren (Zirkoniumfluorid; RT, 45 s)
7. vii) Nachspülen (VE-Wasser; RT, 30 s)
8. viii) Trocknen (Umluftofen; 100°C ; 7 min)

The test plates of Examples B6 and B7 pretreated according to the invention as well as a non-pretreated bare test plate VB6 were also subjected to a multi-stage corrosion protection treatment consisting of the following steps:

1. i) Alkaline cleaning (60 °C ; 180 s)
2. ii) Rinse (mains water; RT, 60 s)
3. iii) Activation (titanium phosphate; RT, 30 s)
4. iv) Phosphating (trications; 53 °C, 180 s)
5. v) Rinse (town water; RT, 30 s)
6. vi) Passivation (zirconium fluoride; RT, 45 s)
7. vii) Rinse (deionized water; RT, 30 s)
8. viii) Drying (convection oven; 100°C ; 7 min)

After subsequent electrocoating and topcoating, a filiform corrosion test was carried out in accordance with DIN EN 3665 (average values according to DIN EN ISO 4628-8) and a cyclic corrosion test according to VDA 621-415 (average values according to DIN EN ISO 4628-8) were carried out. The lower the measured infiltration in mm, the better the corrosion protection. The results can be found in the following table. <b>Table 4:</b> Example B7 is not according to the invention (See) Example Filament (mm) VDA-Temperature (mm) AA6111 AA5754 AA6111 AA5754 VB6 0.8 0.1 0.1 0.1 B6 0.8 0.1 0.1 0.1 B7 1.0 0.1 0.1 0.1

The corrosion protection for B6 and B7 is comparable to that for VB6 . The pretreatment according to the invention therefore has no adverse effect on the protection subsequently achieved by a corrosion-protective treatment.

Claims (16)

1. A process for the pretreatment of workpieces having a surface of aluminum or aluminum alloys for noncutting forming and/or for joining by welding or adhesive bonding to similarly pretreated or otherwise precoated workpieces or to parts composed of steel and/or galvanized and/or alloy-galvanized steel and also for a subsequent permanent corrosion-protecting treatment by phosphating, by means of a chromium-free conversion treatment, by application of primer or by surface coating, wherein the workpieces are

   a) pickled by means of an aqueous, acidic solution comprising mineral acid by dipping or spraying,

   b) rinsed with water and

   c) brought into contact with an aqueous, acidic solution which is chromium-free and comprises 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 by application by dipping or spraying so as to result, after subsequent drying, in a layer weight of in each case from 2 to 15 mg/m² of Zr and Mo, where the solution comprises from 100 to 800 mg/l of Zr and from 30 to 100 mg/l of Mo (calculated as Zr/Mo metal) and has a pH of from 2.5 to 4.5, and where the solution additionally 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 maleic acid copolymers.
2. The process according to claim 1, wherein the parts composed of steel and/or galvanized and/or alloy-galvanized steel are precoated.
3. The process according to claim 1 or 2, wherein the aqueous, acidic solution in step c) comprises Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr/Mo metal) of Zr : Mo of 13 : 1 to 7 : 1.
4. A process for the pretreatment of workpieces having a surface of aluminum or aluminum alloys for noncutting forming and/or for joining by welding or adhesive bonding to similarly pretreated or otherwise precoated workpieces or to parts composed of steel and/or galvanized and/or alloy-galvanized steel and also for a subsequent permanent corrosion-protecting treatment by phosphating, by means of a chromium-free conversion treatment, by application of primer or by surface coating, wherein the workpieces are

   a) pickled by means of an aqueous, acidic solution comprising mineral acid by dipping or spraying,

   b) rinsed with water and

   c) brought into contact with an aqueous, acidic solution which is chromium-free and comprises Zr as 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 by the roller application method so as to result, after subsequent drying, in a layer weight of in each case from 2 to 15 mg/m² of Zr and Mo, where the solution comprises from 0.4 to 7.5 g/l of Zr and from 0.4 to 7.5 g/l of Mo (calculated as Zr/Mo metal) and has a pH of from 1.0 to 3.0, and where the solution additionally 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 maleic acid copolymers and the concentration of the at least one polymer is between 100 and 600 mg/l.
5. The process according to claim 4, wherein the parts composed of steel and/or galvanized and/or alloy-galvanized steel are precoated.
6. The process according to claim 4 or 5, wherein the aqueous, acidic solution in step c) comprises Zr as 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.
7. The process according to any of claims 1 to 6, wherein the at least one polymer is polyacrylic acid and/or an acrylic acid-maleic acid copolymer.
8. The process according to any of claims 1 to 7, wherein the workpieces are pickled by means of a solution comprising surfactant, hydrofluoric acid and sulfuric acid.
9. The process according to claim 8, wherein the workpieces are pickled by means of a solution comprising from 3 to 8 g/l of sulfuric acid, from 50 to 150 mg/l of free fluoride and from 1 to 3 g/l of nonionic surfactant.
10. The process according to any of claims 1 to 9, wherein in the case of pretreatment of the workpieces for noncutting forming, a lubricant is applied before the forming process.
11. The process according to any of claims 1 to 9, wherein cleaning and rinsing-with-water treatments or cleaning, rinsing-with-water and activation treatments are carried out before the permanent corrosion-protecting treatment.
12. An aqueous acidic solution for the pretreatment of workpieces having a surface of aluminum or aluminum alloys, wherein the solution is chromium-free and comprises 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, where the solution comprises from 100 to 800 mg/l of Zr and from 30 to 100 mg/l of Mo (calculated as Zr/Mo metal) and has a pH of from 2.5 to 4.5, where the aqueous acidic solution additionally 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 maleic acid copolymers.
13. A concentrate from which a solution according to claim 12 is obtainable by dilution with water or an aqueous solution and optionally adjustment of the pH.
14. An aqueous acidic solution for the pretreatment of workpieces having a surface of aluminum or aluminum alloys, wherein the solution is chromium-free and comprises Zr as complex fluoride and Mo as molybdate in a weight ratio (calculated as Zr/Mo metal) of Zr : Mo of 2 : 1 to 1 : 2, where the solution comprises from 0.4 to 7.5 g/l of Zr and from 0.4 to 7.5 g/l of Mo (calculated as Zr/Mo metal) and has a pH of from 1.0 to 3.0, where the aqueous, acidic solution additionally 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 maleic acid copolymers and the concentration of the at least one polymer is between 100 and 600 mg/l.
15. A concentrate from which a solution according to claim 14 is obtainable by dilution with water or an aqueous solution and optionally adjustment of the pH.
16. A workpiece having a surface of aluminum or aluminum alloys, wherein the workpiece has been pretreated by means of a process according to any of claims 1 to 11.