EP1200641B1 - Pretreatment of aluminum surfaces with chrome-free solutions - Google Patents

Description

The invention relates to a method for the pretreatment of Workpieces with a surface of aluminum or Aluminum alloys for chipless forming and / or the bonding by welding or gluing with similar pretreated or otherwise otherwise precoated workpieces or optionally Pre-treated parts made of steel and / or galvanized and / or alloy-galvanized steel and for a subsequent anti-corrosive treatment by Phosphating, by a 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, in the second stage rinsed with water and in the third stage finally with an aqueous, chemical Wets conversion coatings forming solution and the Liquid film is dried. This will be on the Metal formed a thin, non-metallic coating, the in accordance with selected composition of Treatment liquid and the reaction conditions the Can significantly improve surface quality. So can z. B. coatings of paints, adhesives and plastics, optionally in the form of films, by a material greater liability and a considerably increased Corrosion protection, if they are on such pretreated metal are applied.

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

Due to the presence of hexavalent chromium this is Method of disadvantage in common that in particular Precautions when applying the coating agent and the handling of the coated metal required are.

To those with the use of solutions, the hexavalent Chromium, to avoid associated disadvantages, sees another process category for applying Conversion coatings especially for aluminum surfaces, a treatment with compositions based on the fluoroanions zircons and / or Titans (US-A-41 48 670, FR-A-942 789, EP-A-106 389, EP-A-825 280).

Recently, the use of workpieces with attained Surfaces of aluminum or aluminum alloys in Vehicle construction is becoming increasingly important. Essential reasons this is the reduction of vehicle weight, but also the favorable recyclability of such workpieces. It is generally customary for vehicles to consist of several usually previously non-cutting formed parts, made of Workpieces with aluminum or aluminum surfaces Aluminum alloys are made, but also with such Steel and / or galvanized steel and / or Alloy galvanized steel to connect. By far main forms of joining respectively Joining is welding or gluing.

At the joining of the parts regularly closes one. anticorrosive treatment, depending on Texture of the connected parts of one Phosphating treatment, a chromium-free Conversion treatment, a primer order or a Lacquer can exist.

Thus a perfect connection of the parts with surfaces made of aluminum or aluminum alloys with each other or with parts made of steel and / or galvanized or alloy-galvanized steel guaranteed It must be ensured that the surfaces of the Aluminum or aluminum alloy free of Aluminum oxide or oxides possibly Alloy components of aluminum are. One yourself this offering pickling treatment does not lead to the goal since the aluminum surface after a short time with a covering new oxide layer.

In order to solve the problem outlined above, the process 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 non-cutting and / or cutting deformation process, and / or bonded 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 condition-containing 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 11730 mg / m ² , preferably 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 17780 mg / m ² , preferably from 0.18 to 7.04 mg / m ² (each indicated as zirconium metal).

The concept of the present invention Previous studies have shown that a Variety of those described in EP-B-700 452 Design options too less favorable Results, especially with regard to the first chemical conversion treatment reached temporary Corrosion protection and for the production of Welded joints of important volume resistance, to lead.

The object of the invention is to provide a method for Pre-treatment of workpieces with a surface made Aluminum or aluminum alloys for the non-cutting Forming and / or joining by welding or Gluing with similarly pretreated or optionally otherwise precoated workpieces or parts made of steel and / or galvanized and / or alloy galvanized Steel and a subsequent permanent anti-corrosive treatment by phosphating, by a chrome-free conversion treatment, by primer application or to provide painting regularly Workpieces with a sufficiently low Volume resistance with good adhesive pull shear values and good temporary Corrosion protection leads.

a) mit einer Mineralsäure enthaltenden wäßrigen, sauren Lösung im Tauchen oder Spritzen beizt,

b) mit Wasser spült,

c) mit einer wäßrigen, sauren Lösung, die chrom- und polymerfrei ist und im wesentlichen aus Ti und Zr als komplexe Fluoride in einem Gewichtsverhältnis von Ti : Zr von 2:1 bis 1:2 sowie ggf. aus kolloidaler Kieselsäure besteht, in der Weise in Kontakt bringt, daß nach dem nachfolgenden Auftrocknen ein Schichtgewicht von 2 bis 15 mg/m² (ber. als Ti/Zr-Metall) resultiert,

man beim In-Kontakt-Bringen des Werkstückes Lösungen einsetzt, die bei Tauch- oder Spritz-Applikation 300 bis 700 mg/l Fluorid (ber. als Fluoro-Anion) enthalten und einen pH-Wert von 4,0 bis 5,0 aufweisen und bei Applikation im Rollenauftragsverfahren 5000 bis 15000 mg/l Fluorid (berechnet als Fluoro-Anion) enthalten und einen pH-Wert von 1,0 bis 3,0 aufweisen.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,

c) with an aqueous, acidic solution which is chromium and polymer-free and consists essentially of Ti and Zr as complex fluorides in a weight ratio of Ti: Zr from 2: 1 to 1: 2 and optionally of colloidal silica, in the Contact, that after the subsequent drying a layer weight of 2 to 15 mg / m ² (calculates as Ti / Zr metal),

When contacting the workpiece, solutions are used which contain 300 to 700 mg / l fluoride (calculated as fluoroanion) in the case of immersion or spray application and have a pH of 4.0 to 5.0 and 5,000 to 15,000 mg / l fluoride (calculated as fluoroanion) when applied by roller coating and have a pH of 1.0 to 3.0.

It has been found that neither in the application of solutions containing only fluorotitanate or only fluorozirconate, nor in the application of solutions in which the weight ratio of titanium: zirconium outside the weight ratio of 2: 1 to 1: 2 or, in the application of solutions that lead to coating weights of titanium / zirconium outside the range of 2 to 15 mg / m ² (over. As titanium / zirconium metal), satisfactory results are achieved with respect to the task. With regard to the adjustment weight to be set, it is therefore of crucial importance that, depending on the type of application with respect to the concentration of the fluoro anions and the pH differently procured solutions are used.

To achieve the objective pursued by the invention It is also essential that the workpieces with a Mineral acid-containing aqueous, acidic solution in Dipping or spraying, pickling. An alkaline Cleaning, for example, has the emergence of Titanium / zirconium layers with bad ones Volume resistance values result. The same applies to Layers made using polymer-containing solutions which are why within the according to the invention to be used solutions must be polymer-free.

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 is a Prevent cleaning / degreasing stage or the Pickling process is to lead in the way that one simultaneous cleaning / degreasing takes place. The latter can done by adding surfactant to the pickling solution.

As a method for phosphating are those which with solutions based on zinc phosphate, in particular according to the low-zinc technology, or with Alkaline phosphate work, in the foreground. The solutions can by adding further small amounts of polyvalent cations, such as calcium, magnesium, nickel, Copper or manganese, be modified.

For chromium-free conversion treatment get in particular Acid solutions of the fluoro complexes of titanium, zirconium, Hafnium, but also boron and silicon, optionally with a content of organic polymer, used.

As a primer so-called reaction primer or Adhesive base be applied.

The pretreatment of the workpieces according to the invention provides a sufficient, temporary corrosion protection for longer storage times safely. During this time takes place no negative influence on the weldability, in particular electrical resistance welding, or the bondability. Also is overlooking the Weldability ensures that the volume resistance Practical on all surface areas of the workpiece is equal to.

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 with or without water rinsing. For application without water rinse, it is advantageous excess treatment solution by squeezing rollers too remove.

In the treatment of sheet or strip is the application the treatment solution according to the roll coater method especially advantageous. It allows one in a single operation defined setting of the desired wet film thickness.

Following the above Types of application of the solution, the workpiece is dried or the solution dried up. Object temperatures of 30 to 90 ° C are special advantageous.

To approach the treatment fluids are Usually concentrates used with low salt Water, preferably demineralized water, on each be diluted to be adjusted. Especially it is advantageous for the purpose of avoiding the entry of Alkali ions, the required fluoro anions of the zirconium and Titans with the help of the free acids and the If necessary, the respective pH value by adding ammonia adjust.

The pickling of the workpieces (process step a)) happens with a mineral acid-containing aqueous, acidic Solution. It can be carried out electrolytically or chemically. At the Electrolytic pickling is as mineral acid phosphoric acid particularly suitable. The pickling chemically, the because of the less complex apparatus in the Usually preference is given to using nitric acid or Nitric acid / hydrofluoric acid are made. Corresponding A preferred embodiment of the invention are the Workpieces with a solution in spraying or dipping pickled, the surfactant, hydrogen fluoride and sulfuric acid contains, with solutions that are 3 to 8 g / l Sulfuric acid, 50 to 150 mg / l not complexed, free fluoride and 1 to 3 g / l nonionic surfactant ' contained, have been found to be particularly suitable. When Nonionic surfactants are ethylene oxide adducts Fatty alcohols and, for example, abietic acid especially suitable.

The measurement of the free fluoride was done with a fluoride-sensitive Electrode performed, with the calibration the electrode was made with solutions whose pH identical to that of the solution to be tested.

In order to achieve layers with an optimum resistance to dryness 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 Water flushing - according to step b) - takes place preferably in several rinsing stages, being particularly advantageous, the rinse water cascade the workpiece to lead contrary. It should be the last Rinsing be carried out with demineralized water. By the subsequent to the pickling and rinsing stage Treatment according to step c) prevents the ' Workpieces with a surface of aluminum or Aluminum alloy re-growth of an oxide layer occurs.

A further advantageous embodiment of the invention provides for the workpieces in step c) to be brought into contact with a solution containing colloidal silica.
Due to the content of the solution of silica, the paint adhesion is improved in a subsequent coating. An adverse effect on the volume resistivity does not occur. A particularly suitable silica is fumed silica having an average particle size of 10 to 25 nm. Particularly advantageous coating weights are between 2 and 30 mg / m ² (calculated as Si). On the basis of these data, the silicic acid concentrations to be set in the respective treatment solutions used in stage c) can be determined in a simple manner on the basis of a few experiments. When applying the solution in the roll coater method, it can be easily calculated on the amount of wet film to be applied.

In the case of a subsequent stage c) Subsequent treatment by non-cutting forming sees another advantageous embodiment of the invention, to the Workpieces apply a lubricant. This acts in particular mineral oil-based forming oils containing fully synthetic or native, or um Dry lubricants based on polyethylene / polyacrylate.

It is before the permanent anti-corrosive treatment usually convenient, cleaning and Intermediate water scavenging stages. At a designated Primer or varnish application is recommended a previous one Drying. If a chrome-free Conversion treatment should be able to join Application in diving or spraying also wet in wet, d. H. without previous drying, to be worked. at Application according to the roll coater method is one Intermediate drying indispensable. In the case of one subsequent phosphating treatment, which also wet in wet, it is appropriate, a Activation treatment, for example with a titanium and Phosphate-containing activating agent to provide.

With the aid of the method according to the invention regularly get workpieces with layers, the one perfect deformation and / or gluing or as a result of low and uniform over the workpiece surface Electric volume resistance is impeccable and allow easy welding. In addition, are the workpieces for a subsequent permanent Corrosion protection treatment ideally suited.

The invention will be more apparent from the following examples explains:

Examples

6 g/l Schwefelsäure (100 %-ig)

100 mg/l Flußsäure (100 %-ig)

2 g/l nichtionisches Tensid, bestehend aus ethoxyliertem Fettalohol und ethoxylierter Abietinsäure im Gewichtsverhältnis 1:1.

With the exception of a sheet set, which was cleaned alkaline (Example 1), sheets of quality aluminum AA 6016 and AA 5182 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%)

2 g / l nonionic surfactant consisting of ethoxylated fatty alcohol and ethoxylated abietic acid in a weight ratio of 1: 1.

bei der Legierung AA 5182 0,3 bis 0,4 g/m² und

bei der Legierung AA 6016 0,2 bis 0,3 g/m²

betrug. Hierzu waren Behandlungszeiten zwischen 5 und 20 sec erforderlich.

The pickling process was conducted in such a way that the pickling

for the alloy AA 5182 0.3 to 0.4 g / m ² and

for the alloy AA 6016 0.2 to 0.3 g / m ²

amounted to. For this treatment times between 5 and 20 sec were required.

Subsequently, the workpieces were thoroughly with Water, in the last stage with demineralized water, rinsed. The measured at the single sheet Volume resistances for alloy AA 5182 6 bis 8 μ-ohms, with the alloy AA 6016 9 to 11 μ-ohms.

This was followed by treatment with solutions of hexafluoric acids of titanium and / or zirconium, the data of which are reproduced in Table 1 with regard to the concentration of titanium and / or zirconium, the pH and the application form. If necessary, the pH was adjusted with ammonia solution. example Concentration in mg / l PH value application Ti Zr TiF6 ZrF6 TiF6 + ZrF6 1 354 360 1197 810 2007 2.4 diving 2 354 360 1197 810 2007 2.4 diving 3 362 1074 1224 2416 3640 1.9 rollcoater 4 1075 360 3634 810 4444 1.8 rollcoater 5 700 0 2367 0 2367 2 diving 6 60 60 203 135 338 4.2 splash 7 120 120 406 270 676 4.1 diving 8th 1328 1328 4490 2987 7477 2 rollcoater 9 60 60 203 135 338 4.2 diving 10 0 40 0 90 90 4.2 diving 11 60 60 203 135 338 4.2 diving 12 60 60 203 135 338 4.2 diving 13 2700 2600 9128 5849 14977 1.8 rollcoater

The application of the solutions, which had room temperature, was done by dipping or according to the roll coater method, wherein the immersion time or wet film thickness were selected in such a way that the in 2.1 column 2 Table 2 referred weights (calculated as titanium or. Zirconium metal) resulted. In the case of application by dipping or spraying, excess treatment solution was removed by squeezing rollers, and then the treated surface was dried. The drying or the drying in the roll coater application was carried out at 60 ° C. For example Circulation (mg / m ² ) Contact resistance Adhesive pull shear values (N / mm ² ) 6016 Ti 5182 Ti 6016 Zr 5182 Zr 6016 directly 5182 6016 n.30 5182 days 6016 beginning 5182 6016 20 Rdn 5182 SCAB 1 10 10 114 147 12.6 11.2 2 10 10 30 92 12.2 3 3 8th 21 52 13.1 11.4 4 8th 3 49 80 12.8 11.2 5 10 40 68 13.3 11.0 6 2 2 4 8th 14.2 13.0 7 6 6 22 23 13.3 12.4 8th 4 4 12 20 13.5 13.0 9 6 7 4 5 18 10 31 34 15.8 16.8 11.5 10 8th 8th 26 38 45 95 16.4 17.4 12.1 11 5 4 3 4 11 9 27 36 15.7 16.8 11.8 12 4 4 4 4 10 18 24 35 15.3 16.7 15.3 14.7 13 4 4 4 4 21 30 17.8 16, 7

Columns 3 and 4 of Table 2 show the volume resistances in μ-ohms obtained in the case of single sheet measurements and the adhesive pull shear values in N / mm ² . The measurement of the volume resistances was carried out immediately after the drying / drying (first row "directly") and after a storage of 30 days (second row "n. 30 days"). It was made in accordance with DVS bulletin 2929 with copper electrodes with a diameter of 20 mm. The adhesive tensile shear values were determined by means of tensile shear tests in accordance with DIN 53283 using a commercially available two-component epoxy adhesive. The first row of column 4 of Table 2 gives the measurements obtained immediately after bonding, the second row indicates the measurements obtained after 30 days salt spray-condensation change test according to VDA 621-415.

The measured values in Table 2 can be seen from the following. The proof of the need for an acidic Pickling in step a) made in Example 1 Treatment of aluminum sheets with an alkaline Cleaner leads to sheets with good adhesive pull shear properties, but with extremely bad Duch resistances.

Example 2 shows that due to a too high Weight of the dressing in the treatment according to step c) obtained layer very high Volume resistances - especially after storage for 30 days - received become.

In Examples 3 to 5 and 10 are indeed the obtained support weights in the desired range, however are due to the titanium / zirconium ratio in the Treatment solution for process step c) of about 1: 3 (Example 3) or about 3: 1 (Example 4) or as a result of Zirconium free (Example 5) or the freedom from titanium (Example 10) of the solution obtained Volume resistances, especially after 30 days Storage, unacceptable.

In contrast, Examples 6 to 9 and 11 to 13, that in compliance with the conditions essential to the invention regarding the nature of the pickling treatment, the Ti / Zr ratio, the generated contact weight, the respective concentration and pH ranges of Treatment solutions layers with extremely good Volume resistances at the same time good Adhesive properties are obtained.

The results of the corrosion protection were in all cases Good.

Claims (5)

1. Method of pretreating workpieces having a surface of aluminium or aluminium alloys for non-cutting shaping and/or for joining by welding or adhesive bonding to workpieces that have been pretreated in the same manner or optionally precoated in a different manner or to optionally precoated parts of steel and/or galvanised and/or alloy-galvanised steel, and also for subsequent permanent anticorrosive treatment by phosphating, by a chrome-free conversion treatment, by application of a primer or by lacquering, wherein the workpieces

   a) are pickled using an aqueous acidic solution containing a mineral acid, by immersion or spraying,

   b) are rinsed with water,

   c) are brought into contact with an aqueous acidic solution that is chrome- and polymer-free and consists substantially of Ti and Zr as complex fluorides in a ratio by weight of Ti:Zr of from 2:1 to 1:2, and optionally of colloidal silica, in such a manner that a layer weight of from 2 to 15 mg/m² (calculated as Ti/Zr metal) is obtained after subsequent drying, the solutions with which the workpiece is brought into contact, in the case of application by immersion or spraying, contain from 300 to 700 mg/l of fluoride (calculated as fluoro anion) and have a pH value of from 4.0 to 5.0 and, in the case of application by the roller application process, contain from 5000 to 15,000 mg/l of fluoride (calculated as fluoro anion) and have a pH value of from 1.0 to 3.0.
2. Method according to claim 1, wherein the workpieces are pickled using a solution containing surfactant, hydrofluoric acid and sulfuric acid.
3. Method according to claim 2, wherein the workpieces are pickled using a solution that contains 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 non-ionic surfactant.
4. Method according to one or more of claims 1 to 3, wherein, in the case of pretreatment of the workpieces for non-cutting shaping, a lubricant is applied prior to the shaping process.
5. Method according to one or more of claims 1 to 4, wherein treatments comprising cleaning, rinsing with water and, optionally, activation are carried out prior to the permanent anticorrosive treatment.