EP0356855B1 - Pretreatment of aluminium or aluminium alloy surfaces to be coated with organic materials without using chromium - Google Patents

Abstract

The invention relates to a process for the pretreatment of metallic surfaces before the coating with organic materials. The surfaces are initially cleaned and pickled and then contacted with aqueous solutions and/or dispersions of aluminium/zirconium complexes which can be obtained as reaction product of a chelated aluminium unit, of an organofunctional ligand and of a zirconyl halide, where the organofunctional ligand is chemically bonded to the chelated aluminium unit and to the zirconium unit. According to the invention the surfaces are subjected, before the coating with organic materials, to a subsequent treatment with aqueous solutions or emulsions and/or dispersions of one or more inorganic and/or organic film-formers.

Description

The invention relates to a process for the pretreatment of surfaces made of aluminum or aluminum alloys, in which first the cleaned, pickled and decapitated surfaces are brought into contact with an aqueous solution and / or dispersion of aluminum-zirconium complexes, the surfaces being subjected to a subsequent treatment with aqueous solutions, emulsions and / or dispersions of one or more inorganic and / or organic film formers before coating with organic materials.

DE-A-32 00 245 relates to a method for treating surfaces made of aluminum or aluminum alloys, which is also carried out in two steps. In the first step, a chemical coating is formed on the aluminum surface to be treated, solutions based on chromic acid, chromate, dichromate, chromic acid-phosphoric acid, phosphoric acid, phosphates, titanates, titanium tannic acid or zirconium fluoride being used. In the second step, the chemical covering produced is treated with solutions based on silica, silicates and / or colloidal silica. The surfaces of aluminum bodies treated in this way, in particular aluminum parts in evaporators of air conditioning systems, have improved hydrophilic properties.

F. Tödt, "Corrosion and Corrosion Protection", Walter de Gruyter & Co, 2nd edition (1961), describes various methods for protecting aluminum surfaces. On pages 422 and 670, so-called "wash primers" (reaction primers) are mentioned here, which are applied as a primer to increase the adhesive strength of paints on such surfaces. These wash primers contain zinc chromate or tetraoxy chromate and polyvinyl butural in isopropyl or butyl alcoholic phosphoric acid. Page 669 also reports on the generation of adhesive layers on aluminum surfaces. Here it is said that the surfaces are treated with solutions based on sodium carbonate and sodium chromate and then with bichromate or water glass solutions. The layers produced in this way are also intended to serve as anchoring layers for subsequent film runs or coatings.

Also in "Metals Handbook 9th Edition", Vol 5: "Surface Cleaning, Finishing, and Coating", American Society for Metals (1982), an overview of processes for pretreating metal surfaces, including aluminum surfaces, before the subsequent application of organic coatings or painted. In addition to phosphating layers, wash primers containing polyvinyl butyral, a chromate pigment and phosphoric acid are mentioned here on page 477 as "prepaint treatments". Further information on the production of such primer layers on aluminum surfaces can be found on pages 598 to 599; Phosphating layers are treated as zinc primers as an adhesive primer. Pages 647 and 648 describe organic coatings for magnesium surfaces. Here too it is said that a priming treatment is required before the application of paints, preferably chromate-containing ones Pretreatment agents are mentioned. Furthermore, it is stated here that the actual top coat is composed of different layers - prime coat, second coat and finish coat -, the prime coats being based on polyvinyl butyral, acrylates, polyurethanes, vinyl epoxy compounds or phenolic resins and containing corrosion-protecting pigments such as zinc chromate or titanium dioxide can.

The use of chromates or chromic acid in aqueous solutions to produce conversion layers on surfaces made of aluminum, aluminum alloys, zinc, cadmium, magnesium, steel and / or galvanized and alloy-galvanized steel has long been state of the art.

The conversion layers significantly improve the adhesion and the corrosion-inhibiting effect of subsequent coatings with organic materials, such as paints, powder layers or foils. Therefore, the conversion layers are used in particular on aluminum, its alloys and on zinc as corrosion-resistant coatings without a subsequent coating. Another one A well-known area of application of chromates and chromic acid is the rinsing of zinc phosphate and iron phosphate conversion layers on steel and galvanized steel. Here, too, this aftertreatment brings about a significant improvement in the adhesion of subsequent coatings with organic materials and an increase in the corrosion resistance of the coated metallic surfaces.

• 1. Reinigen in relativ milden, alkalischen, wäßrigen Lösungen,
• 2. Spülen in Frischwasser,
• 3. Beizen in starkalkalischen Lösungen,
• 4. Spülen in Frischwasser,
• 5. Dekapieren in sauren Lösungen,
• 6. Spülen in Frischwasser,
• 7. Chromatieren mit Chromat- und/oder Chromsäure-haltigen Lösungen,
• 8. Spülen in Frischwasser,
• 9. Spülen in vollentsalztem Wasser und
• 10. Trocknen der Konversionsschichten.

The following procedure is usually used to pretreat aluminum before coating it with organic materials:

• 1. cleaning in relatively mild, alkaline, aqueous solutions,
• 2. rinsing in fresh water,
• 3. pickling in strongly alkaline solutions,
• 4. rinsing in fresh water,
• 5. pickling in acidic solutions,
• 6. rinsing in fresh water,
• 7. Chromating with solutions containing chromate and / or chromic acid,
• 8. rinsing in fresh water,
• 9. Rinse in deionized water and
• 10. Drying the conversion layers.

Due to the toxic properties of chromium (VI) compounds, the wastewater generated in the control and disposal of the baths must be subjected to a special, complex treatment.

This also applies to the waste water from the above-mentioned rinsing baths, which are contaminated with chromium (VI) compounds. The particularly critical toxic properties of chromates and chromium oxides in the form of breathable dusts and aerosols require strict precautionary measures to protect the employees in the production and use of the pretreatment chemicals. The wastewater generated during production must therefore also be treated with special effort to protect the environment.

For the reasons mentioned above, there has been no lack of attempts in the past to replace the chromium (VI) compounds in the pretreatment of metals with other, less or non-toxic compounds before coating them with organic materials.

For the pretreatment of aluminum, for example, processes based on chromium (III) compounds or on the basis of zirconium and / or titanium compounds are known and are already partly in practical industrial use. The corrosion-inhibiting effects of molybdate and tungstate have also been reported in the literature. On this basis, however, there are no procedures used in practice.

The above-mentioned processes based on chromium (III) compounds as well as on the basis of zirconium and titanium compounds have either only been able to establish themselves in special fields or they are not familiar with the quality achieved or the universal application comparable to the process based on chromium (VI) compounds. The same applies to the field of rinsing for zinc and iron phosphate conversion layers.

Due to recent developments, however, is a class of substances for use in aqueous solutions for pretreating metals before coating with organic materials become interesting, which are organometallic compounds. In the past, the use of organometallic compounds in aqueous solution was prohibited because practically all known representatives of this class of substances hydrolyzed to a greater or lesser extent in aqueous solution.

US-A-4 650 526 describes a method for treating phosphated metal surfaces before coating them with organic materials. In particular, the use of certain organometallic compounds in rinse solutions to improve the adhesion of subsequent organic coatings is described. These are aluminum-zircon complexes, which are sold by Cavedon Chemical Co. under the name "CAVCOMOD". The preparation of the aluminum-zirconium complexes is described in US Patents 4,539,048 and 4,539,049.

The starting point of the present invention was the aluminum-zirconium complexes described in US Pat. No. 4,650,526. It was shown that treatment of aluminum with the aluminum-zirconium complexes alone did not give acceptable adhesion and corrosion protection values compared to a "classic" pretreatment based on chromium (VI) compounds.

Accordingly, it was an object of the present invention to improve the method for pretreating surfaces made of aluminum or aluminum alloys before coating with organic materials. Another object of the present invention was to achieve acceptable adhesion and corrosion protection values for such surfaces before coating with organic materials.

According to the invention, the above-mentioned objects are achieved by the combined use of the above-mentioned aluminum-zirconium complexes with an organic and / or inorganic film former. Conversion layers with very good adhesion and improved corrosion protection properties for subsequent organic coatings can be produced on surfaces made of aluminum and its alloys.

• a) die gereinigten, gebeizten und dekapierten Oberflächen mit Wasser spült und - ohne weitere Zwischenschritte - mit einer wäßrigen Lösung und/oder Dispersion der Aluminium-Zirkon-Komplexe in Kontakt bringt,
• b) die so behandelten Oberflächen erneut mit Wasser spült und einer nachfolgenden Behandlung mit wäßrigen Lösungen, Emulsionen und/oder Dispersionen eines oder mehrerer anorganischer und/oder organischer Filmbildner unterwirft, wobei
  • als anorganische Filmbildner Siliciumdioxid, Titandioxid und/oder Aluminiumoxid in einer Konzentration von 0,05 bis 5 g/l und
  • als organische Filmbildner Polyacrylsäure, Polyacrylate, Polyester, Polyurethane und/oder Polyepoxidverbindungen in einer Konzentration von 0,01 bis 2 g/l, jeweils bezogen auf die wäßrigen Lösungen, Emulsionen und/oder Dispersionen, eingesetzt werden,
• c) und anschließend die Beschichtung mit organischen Materialien durchführt.

The invention thus relates to a method for pretreating surfaces made of aluminum or aluminum alloys with an aqueous solution and / or dispersion of aluminum-zirconium complexes, which are obtainable as a reaction product of a chelated aluminum unit, an organofunctional ligand and a zirconyl halide, the organofunctional ligand being chemical is bound to the chelated aluminum unit and the zirconium unit before a known coating of the surfaces with organic materials, which is characterized in that

• a) rinsing the cleaned, pickled and pickled surfaces with water and - without further intermediate steps - bringing them into contact with an aqueous solution and / or dispersion of the aluminum-zirconium complexes,
• b) the surfaces treated in this way are rinsed again with water and subjected to a subsequent treatment with aqueous solutions, emulsions and / or dispersions of one or more inorganic and / or organic film formers, where
  • as inorganic film formers silicon dioxide, titanium dioxide and / or aluminum oxide in a concentration of 0.05 to 5 g / l and
  • polyacrylic acid, polyacrylates, polyesters, polyurethanes and / or polyepoxide compounds are used as organic film formers in a concentration of 0.01 to 2 g / l, in each case based on the aqueous solutions, emulsions and / or dispersions,
• c) and then carries out the coating with organic materials.

It was found that treatment of aluminum alone with the above-mentioned aluminum-zirconium complexes, as described in US Pat. No. 4,650,526, without an additional organic and / or inorganic film-forming agent, at most brings about improvements in the adhesion and the corrosion protection value of a subsequent organic coating, if you compare with untreated, only cleaned substrate. Acceptable adhesion and corrosion protection values compared to a pretreatment based on chromium (VI) compounds can, however, only be achieved with the combination of aluminum-zirconium complexes and organic and / or inorganic film formers mentioned.

The above-mentioned aluminum-zirconium complexes, as described in US-A-4,650,526, can be brought into contact with the surfaces by spraying, dipping, flooding, rolling and / or rolling up.

• (1) die Aluminiumeinheit durch die allgemeine Formel (I)
  
  
  
          Al₂(OR₁O)_aA_bB_c   (I)
  
  
  
  wiedergegeben ist, wobei
  A oder B für OH oder Fluor, Chlor, Brom und/oder Jod steht a, b und c ganze Zahlen sind und $\text{2a + b + c gleich 6}$
  
  
  ist und (OR₁O) steht für
  • (a) eine α, β- oder α, γ-Glykolgruppe und R₁ für einen Alkylrest mit 1 bis 6 C-Atomen oder
  • (b) einen α-Hydroxycarbonsäurerest der allgemeinen Formel (II)
  
  
  
  
          -OCH(R₃)COO-   (II)
  
  
  
  worin

  R₃

  für Wasserstoff oder einen Alkylrest mit 1 bis 4 C-Atomen steht,

• (2) der organofunktionelle Ligand für einen Alkyl- oder Alkenylrest, eine Alkyl- oder Aralkylcarbonsäure mit jeweils 2 bis 36 C-Atomen,
  eine aminofunktionelle Carbonsäure mit 2 bis 18 C-Atomen, eine dibasische Carbonsäure mit 2 bis 18 C-Atomen,
  ein Säureanhydrid einer dibasischen Säure mit 2 - 18 C-Atomen, eine mercaptofunktionelle Carbonsäure mit 2 - 18 C-Atomen, oder eine epoxyfunktionelle Carbonsäure mit 2 bis 18 C-Atomen steht und
• (3) die Zirkonlyhalogenideinheit durch die allgemeine Formel (III)

        ZrA_dB_e   (III)



wiedergegeben ist, wobei
A und B wie oben definiert sind und
d und e jeweils für numerische Zahlen stehen, wobei die Summe von d + e gleich 4 ist und das Stoffmengenverhältnis der chelatisierten Aluminiumeinheit zur Zirkonylhalogenideinheit 1,5 zu 10 beträgt und das Stoffmengenverhältnis von organofunktionellem Ligand zu dem gesamten Metallgehalt 0,05 bis 3 beträgt.The aluminum-zirconium complexes are available as a reaction product of a chelated aluminum unit, an organofunctional ligand and a zirconyl halide, whereby

• (1) the aluminum unit by the general formula (I)
  
  
  
  Al₂ (OR₁O) _a A _b B _c (I)
  
  
  
  is reproduced, whereby
  A or B represents OH or fluorine, chlorine, bromine and / or iodine, a, b and c are integers and $\text{2a + b + c equals 6}$
  
  
  is and (OR₁O) stands for
  • (a) an α, β or α, γ-glycol group and R₁ for an alkyl radical having 1 to 6 carbon atoms or
  • (b) an α-hydroxycarboxylic acid residue of the general formula (II)
  
  
  
  
  -OCH (R₃) COO- (II)
  
  
  
  wherein

  R₃

  represents hydrogen or an alkyl radical having 1 to 4 carbon atoms,

• (2) the organofunctional ligand for an alkyl or alkenyl radical, an alkyl or aralkyl carboxylic acid each having 2 to 36 carbon atoms,
  an amino-functional carboxylic acid with 2 to 18 C atoms, a dibasic carboxylic acid with 2 to 18 C atoms,
  an acid anhydride of a dibasic acid with 2-18 C-atoms, a mercapto-functional carboxylic acid with 2-18 C-atoms, or an epoxy-functional carboxylic acid with 2-18 C-atoms and
• (3) the zirconium halide unit represented by the general formula (III)

ZrA _d B _e (III)



is reproduced, whereby
A and B are as defined above and
d and e each represent numerical numbers, the sum of d + e being 4 and the molar ratio of the chelated aluminum unit to the zirconyl halide unit being 1.5 to 10 and the molar ratio of organofunctional ligand to the total metal content being 0.05 to 3.

In a preferred embodiment of the present invention, the above-mentioned aluminum-zirconium complexes are used in a concentration of 0.05 to 50 g / l as an aqueous solution and / or dispersion.

According to a further embodiment of the present invention, the contact time is 1 sec to 5 min at a bath temperature of 10 to 60 ° C.

The organic film formers can be brought into contact with the surfaces by spraying, dipping, flooding, rolling and / or rolling up. According to the invention, the contact time of the aqueous solutions, emulsions and / or dispersions containing the organic film formers in one embodiment is 1 sec to 5 min at a bath temperature in the range from 10 to 60 ° C.

In the same way as the organic film formers, the inorganic film formers are brought into contact with the metal surfaces to be coated in the form of aqueous solutions or dispersions in the course of 1 sec to 5 min at a temperature of 10 to 60 ° C. The inorganic film formers can be brought into contact by spraying, dipping, Flooding, rolling and / or rolling with the surface happen.

In a further preferred embodiment of the present invention, free and / or complex fluorides are added to the solutions containing aluminum-zirconium complexes in a concentration of 0.01 to 1 g / l.

R =

org. Rest

X =

reaktive Gruppe
(Funktionalität)

Die genaue Produktbezeichnung der im Handel erhältlichen Lösungen der Aluminium-Zirkon-Komplexe richtet sich nach Funktionalität und verwendetem Lösungsmittel in der Lieferform, wie der Tabelle 1 zu entnehmen ist.

The general formula (IV) of the aluminum-zirconium complexes can be represented as follows:

R =

org. rest

X =

reactive group
(Functionality)

The exact product name of the commercially available solutions of the aluminum-zircon complexes depends on the functionality and the solvent used in the delivery form, as can be seen in Table 1.

The active contents of the commercially available solutions (hereinafter zircoaluminate solution) are between 20 - 24%.

The exact explanation of the product names can be found in US-A-4,650,526, to which express reference is made here.

Examples : Reference Example I

Aluminum sheets (Al 99.5) format 100 x 200 x 0.7 mm were treated as follows:
1) Dipping in a conventional alkaline cleaner (RIDOLINE C 1515, containing sodium hydroxide, phosphates, complexing agents and nonionic surfactants). Concentration: 3% (wt.) In fresh water Time: 3 min. Temp .: 60 ° C
2) Dip rinse in fresh water Time: 1 min Temp .: RT (room temperature)
3) Remove the oxide skin by dipping in a chromium-free agent (DEOXIDIZER 395 H, containing complex fluorides in acid solution). Concentration: 2% (vol.) In fresh water Time: 1 min Temp .: 40 ° C
4) Dip rinse in fresh water Time: 1 min Temp .: RT
5) Immersion in a solution containing aluminum-zircon complexes (CAVCOMOD A) Concentration: a) 0.1% (vol.) of the delivery form b) 1% (vol.) of the delivery form Time: 3 min Temp .: RT
6) immersion rinsing as 2) and 4)
7) Dip rinse in deionized water
8) Warm air drying Time: 3 min Air temp .: 70 ° C

Example I 1

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD APG Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water Time: 3 min Temp .: RT

Example I 2

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD C Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water Time: 3 min Temp .: RT

Example I 3

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD CPM Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water Time: 3 min Temp .: RT

Example I 4

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD C-1 Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water Time: 3 min Temp .: RT

Example I 5

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD F Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water

Example I 6

Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD M Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water

Example I 7 Treatment stages 1) - 4) and 6) - 8) as reference example I 5) immersion in a "zircoaluminate solution", CAVCOMOD M 1

Concentration: a) 0.1% (vol.) of the delivery form in deionized water b) 1.0% (vol.) of the delivery form in deionized water Time: 3 min Temp .: RT

The sheets according to Reference Example I and Examples I 1 to I 7 were then coated with a polyester stove enamel (GG 92 L ex BASF Lacke und Farben AG). It is a commercially available varnish, which is designed according to binder and pigment composition for use on pretreated aluminum on objects that are exposed to the weather. A primer is not necessary. The paint was baked at 250 ° C air temperature, time: 2 min, 15 sec. Dry layer thickness: 25 - 30 µm.

The sheets were then subjected to adhesion and corrosion protection tests.

0 =

bestes Ergebnis, keinerlei Lackteilchen am Klebeband

3 =

mittleres Ergebnis, überwiegende Lackmenge am Klebeband

5 =

schlechtestes Ergebnis, gesamte Lackmenge am Klebeband

Korrosionsschutzprüfung: Neutraler Salzsprühtest nach DIN 50021.Adhesion tests: cross cut according to DIN 53151 and T-Bend according to ECCA method T 7 (ECCA = European Coil-Coating Association)
All sheets were bent through 180 ° to T 0.5 and the paint adhesion on the bending shoulder (diameter 1 sheet thickness) was assessed by pressing and peeling off an adhesive tape. The amount of paint particles adhering to the adhesive tape is rated 0 to 5.

0 =

best result, no paint particles on the tape

3 =

medium result, predominant amount of paint on the adhesive tape

5 =

worst result, total amount of paint on the adhesive tape

Corrosion protection test: Neutral salt spray test according to DIN 50021.

A continuous cut is made on the metal sheets, down to the metal surface, on which the through Corrosion caused by infiltration is determined in mm.

The adhesion and corrosion values of the sheets according to Reference Example I and Examples I 1 - I 7 are shown in Table 2.

Example II

As Examples I 1 - I 7, but after 7) followed by immersion in an aqueous (fully demineralized water) solution of a polyacrylic acid. Primal A 1 from Rohm and Haas was used. The delivery form is a 25% solution with a pH of about 2, the molecular weight of polyacrylic acid is about 60,000. Concentration: 0.5 g / l Time: 0.5 min Temp .: RT

Without further rinsing, the sheets were dried as in reference example I according to 8). The sheets were painted as in Reference Example I and subjected to the same adhesion and corrosion tests. The values are shown in Table 3.

Example III

As in Reference Example II and Examples II; however, the concentration of the polyacrylic acid used was 1 g / l.

The liability and corrosion protection values found are shown in Table 4.

Example IV

As in Reference Example I and Examples I 1 - I 7, but after 7) immersion in an aqueous silicon dioxide dispersion follows. Syton X 30 from Monsanto / Brentag was used. The delivery form of the dispersion has a solids content of 30%. The pH is 9.9. The specific surface area of the silicon dioxide particles is approximately 250 m² / g.

Zeit:

0,5 min

Temp.:

RT

The concentration of silicon dioxide in the immersion sink was 3 g / l.

Time:

0.5 min

Temp .:

RT

Without further rinsing, the sheets were dried, painted and tested as in Reference Example I.

The liability and corrosion protection values found are shown in Table 5.

Example V

As in Reference Example IV and Examples IV, but the concentration of silicon dioxide in the immersion sink was 1.5 g / l.

The liability and corrosion protection values found are shown in Table 6.

Example VI

As in Reference Example II and Examples II 1- II 7, but after 7 there was a dip in a bath which contains both the polyacrylic acid solution (Primal A-1) and the silicon dioxide dispersion (Syton X 30). Concentration: Polyacrylic acid, 0.5 g / l Concentration: SiO₂ 3.0 g / l Time: 0.5 min Temp .: RT

The liability and corrosion protection values found are shown in Table 7.

Example VII

As in reference example VI and examples VI, but the individual CAVCOMOD solutions each contained 0.5 g / l of hydrofluoric acid and the immersion time was only 8 seconds.

The liability and corrosion protection values found are shown in Table 8.

Example VIII

As in Reference Example II and Examples II, but after 7 an immersion was carried out in an aqueous dispersion of a polyacrylate. It was Plextol DV 588 from Röhm GmbH.

The basic monomers are butyl acrylate and methyl methacrylate, the dispersion in the delivery form has a solids content of 50%, the pH is 2.2 ± 0.5, the average particle diameter is 0.15 µm. Concentration: 0.5 g / l Time: 0.5 min Temp .: RT

The liability and corrosion protection values found are shown in Table 9.

Example IX

As in Reference Example IV and Examples IV, but Degussa was used as Aerosil 200 silicon dioxide. Aerosil 200 has the following characteristics: Average size of the particles: 12 nm, surface according to BET 200 m² / g, pH value in 4% aqueous dispersion: 3.6-4.3. Concentration: 3 g / l Time: 0.5 min Temp .: RT

The liability and corrosion protection values found are shown in Table 10.

The tables clearly show the positive effect of the pretreatment carried out by the process according to the invention. The adhesion of the organic coating is improved both compared to the untreated metal sheets and compared to the standard process. The corrosion protection values are significantly closer to the values achieved with the standard process than the values of the untreated sheets.

Claims (8)

1. A process for the pretreatment of surfaces of aluminium or aluminium alloys with an aqueous solution and/or dispersion of aluminium/zirconium complexes obtainable as the reaction product of a chelated aluminium unit, an organofunctional ligand and a zirconyl halide, the organofunctional ligand being chemically attached to the chelated aluminium unit and the zirconium unit, before the surfaces are coated with organic materials in known manner, characterized in that

   a) the cleaned, pickled and descaled surfaces are rinsed with water and - without further intermediate steps - are contacted with an aqueous solution and/or dispersion of the aluminium/zirconium complexes,

   b) the surfaces thus treated are rerinsed with water and subsequently treated with aqueous solutions, emulsions and/or dispersions of one or more inorganic and/or organic film formers,

   - silicon dioxide, titanium dioxide and/or aluminium oxide being used as inorganic film formers in a concentration of 0.05 to 5 g/l and

   - polyacrylic acid, polyacrylates, polyesters, polyurethanes and/or polyepoxide compounds being used as organic film formers in a concentration of 0.01 to 2 g/l,

   based on the aqueous solutions, emulsions and/or dispersions,
   and

   c) coating with the organic materials is subsequently carried out.
2. A process as claimed in claim 1, characterized in that the aluminium/zirconium complexes are contacted with the surfaces by spray, dip, flood, roller and/or roll coating.
3. A process as claimed in claim 1 or 2, characterized in that

   (1) the aluminium unit has the following general formula:
   
   
   
           Al₂(OR₁O)_aA_bB_c   (I)
   
   
   
   in which A or B stands for OH or fluorine, chlorine, bromine and/or iodine, a, b and c are integers and $\text{2a + b + c = 6}$

   

   and (OR₁O) stands for

   (a) an α-, β- or α,γ-glycol group and R₁ is an alkyl radical containing 1 to 6 C atoms or

   (b) a α-hydroxycarboxylic acid group corresponding to the general formula:
   
   
   
           -OCH(R₃)COO-   (II)
   
   
   
   in which R₃ is hydrogen or an alkyl radical containing 1 to 4 C atoms,

   (2) the organofunctional ligand stands for an alkyl or alkenyl radical, an alkyl or aralkyl carboxylic acid containing 2 to 36 C atoms,
   an aminofunctional carboxylic acid containing 2 to 18 C atoms,
   a dibasic carboxylic acid containing 2 to 18 C atoms,
   an anhydride of a dibasic acid containing 2 to 18 C atoms, a mercaptofunctional carboxylic acid containing 2 to 18 C atoms or an epoxyfunctional carboxylic acid containing 2 to 18 C atoms and

   (3) the zirconyl halide unit has the following general formula:
   
   
   
           ZrA_dB_e   (III)
   
   
   
   in which
   A and B are as defined above and
   d and e are each numbers and the sum of d + e is 4, the quantitative ratio of the chelated aluminium unit to the zirconyl halide unit is 1.5 to 10 and the quantitative ratio of the organofunctional ligand to the total metal content is 0.05 to 3.
4. A process as claimed in claims 1 to 3, characterized in that the concentration of the aluminium/zirconium complexes is 0.05 to 50 g/l.
5. A process as claimed in claims 1 to 4, characterized in that the contact time of the aluminium/zirconium complexes with the surfaces is 1 sec. to 5 mins. at a bath temperature of 10 to 60°C.
6. A process as claimed in claims 1 to 5, characterized in that free and/or complex fluorides are added to solutions containing the aluminium/zirconium complexes in a concentration of 0.01 to 1 g/l.
7. A process as claimed in claims 1 to 6, characterized in that the contact time of the inorganic and/or organic film formers is 1 sec. to 5 mins. at a temperature of 10 to 60°C.
8. A process as claimed in claims 1 to 7, characterized in that the inorganic and/or organic film formers are contacted with the surfaces by spray, dip, flood, roller and/or roll coating.