NL2017768B1 - Acidic aqueous composition for preparing a corrosion resistant coating on a metal substrate, method using the composition, and post-treatment composition - Google Patents

Abstract

The invention relates to an acidic aqueous composition for preparing a corrosion resistant layer on substrates of aluminium, aluminium alloys, anodized aluminium, aluminized steel, zinc or zinc alloy coated steel, wherein the composition comprises: trivalent chromium (Cr3+): 0.04 – 6 g/l zirconium (Zr4+): 0.08 – 8 g/l total fluoride (F-): 0.1 - 9 g/l stabilizing agent comprising a hydroxyl carboxylic acid or corresponding base(s) thereof (calculated as the acid):: 0.2 - 9 g/l wherein the molar ratio Zr4+ : Cr3+ is in the range of 0.8 : 1 to 2.0 : 1; the molar ratio Zr4+ : F- is in the range of 1: 5.5 to 1.0 : 2.0; and pH is in the range of 3.0 – 5.0. The invention also relates to an application method of this acidic aqueous composition, as well as to a post-rinse composition.

Description

Θ 2017768

NL BI 2017768

Patent center

The Netherlands

BI PATENT @ Int. CL:

C23C 22/34 (2017.01) C25D 11/24 (2017.01) C23C 22/83 (2017.01) (21) Application number: 2017768 © Application submitted: 11/11/2016

(30) Priority: (73) Patent holder (s): 02/09/2016 EN 2017407 AD Productions B.V. in HEIJNINGEN. (Tl) Application registered: (72) Inventor (s): 09/03/2018 Richard Johannes van der Net in DORDRECHT. (43) Application published: Robin Arthur Langelaar - in BERGEN OP ZOOM. Patent granted: 09/03/2018 (74) Agent: ir. H.V. Mertens et al. In Rijswijk. (45) Patent issued: 09/03/2018

(54) ACIDIC AQUEOUS COMPOSITION FOR PREPARING A CORROSION RESISTANT COATING ON A METAL SUBSTRATE, USING THE COMPOSITION, AND POST-TREATMENT COMPOSITION © The invention relates to an acidic aqueous composition for preparing a corrosion resistant layer on substrates or aluminum, aluminum alloys, anodized aluminum, aluminized steel, zinc or zinc alloy coated steel, comprising the composition:

trivalent chromium (Cr ³⁺ ): 0.04 - 6 g / l zirconium (Zr ⁴⁺ ): 0.08 - 8 g / l total fluoride (F): 0.1 - 9 g / l stabilizing agent comprising a hydroxyl carboxylic acid or corresponding base ( s) ther (calculated as the acid) :: 0.2 - 9 g / l in the molar ratio Zr ⁴⁴ : Cr ³⁴ is in the range of 0.8: 1 to 2.0: 1; the molar ratio Zr ⁴⁴ : F- is in the range or 1: 5.5 to 1.0: 2.0; and pH is in the range of 3.0 - 5.0.

The invention also relates to an application method of this acidic aqueous composition, as well as to a post-rinse composition.

This patent has been granted regardless of the attached result of the research into the state of the art and written opinion. The patent differs from the documents originally submitted. All submitted documents can be viewed at the Netherlands Patent Office.

P32869NL01 / JV

ACIDIC AQUEOUS COMPOSITION FOR PREPARING A CORROSION RESISTANT COATING ON A METAL SUBSTRATE, USING THE COMPOSITION, AND POSTTREATMENT COMPOSITION

The invention relates to an acidic aqueous composition for preparing a corrosion-resistant coating on a metal substrate, a method of providing a corrosion-resistant coating on a metal substrate, as well as a post-treatment composition, in particular for use in said method.

In the art mechanical and chemical treatment of metal surfaces for enhancing (bare) corrosion resistance, as well as for improving bonding to a applied applied coating such as an adhesive layer, paint layer, lacquer layer or other finishing layer and enhancing the corrosion resistance or the thus coated final product is well known. E.g. mechanical treatment such as grit blasting has been used to improve adhesion, when chemical treatment steps were not practical to apply. Chemical treatment of metal surfaces or zinc (alloy) coated steel, mild steel, or aluminum and their alloys with aqueous chromate (chromium VI) solutions results in a so called “chromate conversion layer”, which offers corrosion resistance and improved adhesion.

It has been recognized that these chromate-based aqueous solutions suffer from the toxicity of the Cr ⁶⁺ component. Cr ⁶⁺ is classified as carcinogenic and will be banned from most industrial applications involving high exposure risks for the operating staff. Disposal of the toxic treatment composition is also a problem, although to a lesser extent if the hexavaient chromium is converted into the comparatively innocuous trivalent chromium. However, such a conversion brings about additional costs and expenses.

Therefore, in the art there is a need for treatments that are substantially free of hexavaient chromium compounds, that offer corrosion resistance and bonding performance to the metal surfaces treated similar to those obtained by treating these metal surfaces with conventional solutions containing hexavaient chromium. Proposals for satisfying this need, which are based on Cr (lll) typically in combination with one or more other active components such as zirconium, are known.

From US 2011/0293841 A1 an aqueous solution for forming a protective coating on a metal surface is known that includes Cr ₂ (GF ₆ ), in which G is a Group IV-B element (Zr, Ti or Hf), in particular Cr ₂ (ZrF ₆ ) 3 at least one polymer having a variety of carboxylic acid groups such as polyacrylic acid and copolymers or methyl vinyl ether and maleic acid, and at least one polymer having a variety of hydroxyl groups for example polyvinyl alcohols and homopolymers or copolymers or hydroxyethyl methacrylate, and / or at least one polymer having a various or both carboxylic acid and hydroxyl acid groups exemplified by free-radical

-2 copolymers or hydroxyl-ethyl methacrylate and methacrylic acid, containing the composition contains less than 500 ppm or alkali metal ions and less than 200 ppm or halide ions relative to chromium. Application of a high purity Cr ₂ (ZrF ₆ ) 3 solution, is said to improve the corrosion resistance of the metal substrate. The Zr: Cr molar ratio is typically determined by the stoichiometry of the compound, but due to the optional presence of other components the weight ratio Zr: Cr is typically in the range of 2.4: 1 - 3.0: 1, most typically 2.6: 1 -2.8: 1. Any metal may be treated, with apparently good results being obtained on zinc, zinc ally, aluminum and aluminum alloy surfaces. The addition of organo-functional silanes such as aminoproyl triethoxysilane may improve adhesion of subsequently applied coatings such as paints to the treated surfaces, while maintaining good corrosion results. For a working bath the pH or a treatment solution including the above polymers is in a range from 2.5 - 4.0, more typically 2.8-3.2.

US 6375726 B1 has disclosed an acidic aqueous solution for the protection and surface treatment of aluminum, aluminum alloys and coated aluminum substrates against corrosion. The solution comprises at least one trivalent chromium salt such as trivalent chromium sulphate, at least one alkali metal hexafluorozirconate in combination with at least one water-soluble or dispersible thickening agent and a water-soluble surfactant. The corrosion resistant aluminum substrates of this invention have improved adhesion for overlaying coatings e.g. paints and a lower electrical resistance contact.

WO 2006/088519 A2 discloses an acidic aqueous solution for treating metal substrates, such as aluminum alloy or iron alloy or a metal substrate having a pre-existing metal coating for example anodized aluminum to improve adhesion bonding and corrosion protection, which comprises water soluble trivalent chromium compounds, fluorozirconates, fluorometallic compounds, zinc compounds, thickeners, surfactants, and at least about 0.001 moles per liter of the acidic solution or at least one polyhydroxy and / or carboxylic compound as the stabilizing agent for the aqueous solution. The carboxylic compounds contain one or more carboxylic functional groups having the formula R-COO- where R is hydrogen or a lower molecular weight organic radical or functional group, and can be used in the form of their acids or salts. The stabilizers are said to result in improved shelf life and working stability of the solutions. According to this document after treating with the acidic aqueous solution, application of a strong oxidizing solution can yield a film having additional corrosion resistance, which is presumed to be due to the formation of hexavalent chromium in the film derived from the trivalent chromium.

Furthermore, an acidic, aqueous composition that contains a trivalent chromium compound, an organo-functional silane, and a compound or a group IV-B element, is known from US 2009/0280253 A1. The composition is said to protect metal surfaces, preferably aluminum and aluminum alloys, against corrosion and improves their paint adhesion. The trivalent

-3chromium compound may include chromium fluoride and optionally others, such as chromium nitrate. The organo-functional silane is preferably an aminopropyltriethoxy silane, and the compound of a group IV-B element is preferably fluorozirconic acid. The composition can either be three-in-place or rinsed before a further coating layer has been applied. The composition may also include at least one polymer having a variety of both carboxylic functional groups, alone or with hydroxyl groups. The document also discloses a process using the aqueous composition either with or without the organo-functional silane along with a sealing step following the application of the aqueous composition; where the sealing step involves applying a sealing composition, including an organo-functional silane, to the metal surface.

From US 2015/0020925 A1 a process for surface treatment or a part made of aluminum, magnesium, or one of the alloys, is known in order to protect the part from corrosion. The method comprises consecutively immersing the part in a first aqueous bath containing a corrosion-inhibiting metal salt such as trivalent chromium salt and an oxidizing compound such as K ₂ ZrF ₆ , and a second aqueous bath containing an oxidizing compound like hydrogen peroxide and a corrosion -inhibiting rare-earth salt. The method can be carried out for the chemical conversion of aluminum or the alloys, and of magnesium or the alloys, parts that have not been previously treated, or after anodizing the part to seal the anodic layer.

US 6648986 B1 teaches an acidic aqueous solution that contains a water soluble trivalent chromium compound, a water soluble fluoride compound, an alkaline pH adjustment reagent and provided with a solution stability additive for reducing precipitation or trivalent chromium over time. The solution stability additive comprises a complexing agent that is selected from the group consisting of organic acids (single coordination acids and bidentate chelating compounds) and amino acids. The concentration of the solution stability additive varies based on the complexing capability of the additive.

US 2010/0132843 A1 discloses a low sludge trivalent chromium based conversion coating bath that forms corrosion resistant coatings on aluminum and aluminum alloys by immersion in aqueous solutions containing trivalent chromium ions and fluorometallate ions followed by optional rinsing. Trivalent chromium coated aluminum also serves as an effective base for paint primers.

It is an object of the invention to provide a stable treatment solution based on Cr (lll) for providing a substrate of aluminum, aluminum alloys, anodized aluminum, aluminized steel, zinc or zinc alloy coated steel with a layer, that protects the substrate against corrosion and / or offers adhesion for a subsequently applied (typically organic) coating such as paint, and / or for an adhesive bonding system, or at least an alternative treatment solution.

-4 Another object is to provide such a stable treatment solution that offers an enhanced layer formation.

A further object is to provide a method or apply a treatment composition to such a metal substrate in order to achieve corrosion resistance and / or adhesion.

Another object is to provide such a method that does not result in Cr ⁶⁺ species in the deposited layer that are easily released from the treated product under severe conditions. According to a first aspect the invention provides an acidic aqueous composition for preparing a corrosion resistant layer on substrates of aluminum, aluminum alloys, anodized aluminum, zinc or zinc alloy coated steel, aluminized steel, containing the composition comprises:

trivalent chromium (Cr ³⁺ ): 0.04-6 g / i zirconium (Zr ⁴⁺ ): 0.08-8 g / i total fluoride (F '): 0.1-9 g / i

stabilizing agent comprising a hydroxyl carboxylic acid or corresponding base (s) (calculated as the acid): 0.2 - 9 g / l in the molar ratio Zr ⁴⁺ : Cr ³⁺ is in the range of 0.8: 1 to 2.0: 1 ;

the molar ratio Zr ⁴⁺ : F is in the range or 1: 5.5 to 1.0: 2.0; and pH is in the range of 3.0 - 5.0.

It has been shown that the aqueous composition according to the invention when used as a bath is stable in time and does not form deposits and / or sludge in the bath. When applied to a surface of aluminum, aluminum alloys and anodized aluminum, zinc or zinc alloy coated steel, the surface, which is essentially free of Cr ⁶⁺ , shows good corrosion resistance and if present, durable bonding to a applied paint system or adhesive bonding system.

The acidic aqueous composition according to the invention comprises as main active components trivalent chromium, tetravalent zirconium and fluoride in specific concentrations and ratios, as well as one or more hydroxyl carboxylic acids as stabilizing agent. Thereby a stable solution is provided with less fluoride with respect hexafluozirconic acid (H ₂ ZrF ₆ ) or ((alkali) metal) salt, with the ratio Zr: F = 1: 6.

Trivalent chromium is present in an amount or 0.04-6 g / l, preferably 0.2-1.0 g / l. If the amount of chromium (III) is lower, then within industrially acceptable processing times, the rate of layer formation is low resulting in a layer having insufficient thickness and thus inadequate protection and / or bonding.

The trivalent chromium can be derived from organic chromium salts, in particular citrate, glycolate, tartrate, and combinations. Another attractive route for receiving trivalent chromium is by reducing chromic acid (H ₂ CrO ₄ ) with chemical agents that can be oxidized by chromic acid like methanol or hydrogen peroxide leaving no residual products in the starting

-5solution after heating. Another attractive source for trivalent chromium and fluoride is using CrF3.4H2O as a starting material. This compound is hardly soluble in water, but accompanied by acidic components like HF, acidic hydroxyl carboxylic stabilizing agents and water soluble acidic polymers or combinations thereof, it is. HF is preferably used as it does not introduce extraneous anions other than those required.

Tetravalent zirconium is present in an amount of 0.08-8 g / l, preferably in the range or 0.2-2.0 g / l. Suitable starting materials include hexafluozirconic acid and its ammonium salt, zirconium salts or lactate, carbonate, glycolate and citrate, ammonium zirconium carbonate and zirconium triethanol amine, and combinations thereof. The high zirconium content is believed to enhance co-precipitation of Cr and Zr as Cr (OH) ₃ and Zr (OH) ₄ and more layer formation.

Fions are present in the range of 0.1-9 g / l, preferably 0.2-2.0 g / l. The fluoride can be obtained from HF, alkali metal fluoride such as sodium fluoride, ammonium bi fluoride (ABF), chromium fluoride, hexafluorozirconic acid and its ammonium salt, as well as combinations thereof. If hexafluo zirconic acid is used as a starting material, at least one other zirconium component is present, otherwise the ratio of Zr: F is not within the required range High fluoride content compared to Cr and Zr results in excessive etching hindrance layer formation. Without being bound to any theory it is believed that fluoride content in the solution according to the invention will prevent over-etching during layer formation and might prevent accumulation of fluorides in the layer that could weave the conversion layer during exposure in corrosive environment.

Low fluoride contents have the opposite effect and may reduce stability of the composition.

In addition to the concentration ranges, apply the following molar ratio.

the molar ratio Zr ⁴⁺ : Cr ³⁺ is in the range of 0.8: 1 to 2.0: 1; preferably 0.9: 1 - 1.3: 1, such as

1.04: 1.0;

and the molar ratio Zr ⁴⁺ : F is in the range of 1: 5.5 to 1.0: 2.0.

Then the molar ratio Cr ³⁺ : F is in the range or 1: 11 to 1: 1.6.

The acidic aqueous comprises a stabilizing agent being a hydroxy carboxylic acid or a corresponding base in a concentration of 0.2-9 g / l, preferably in the range of 0.2-5 g / l, more preferably 0.3-3 g / l (calculated as the acid). The stabilizing agent can be used as the acid or a water soluble salt. Suitable hydroxyl carboxylic acids are lactic acid, citric acid, malic acid, tartaric acid, glycolic acid, gluconic acid and combinations thereof. The stabilizing agent may be introduced in the composition by the chromium or zirconium compound as well as shown above in the form of the zirconium and / or chromium (III) salt of the conjugated base of the hydroxy carboxylic acid, or as a similar part of the pH adjusting agents as discussed below. The stabilizing agent acts to stabilize the solution as a dipping

-6bath having the composition according to the invention in time, which bath would otherwise be at the given concentrations and ratios of its components deteriorate rapidly It is assumed that the acid becomes part of the resulting layer comprising the hydroxides and oxides of chromium and zirconium. Higher contents of hydroxyl carboxylic acid results in coating layers that are sensitive to dissolving. Too low contents will cause instability and sludge forming of the composition during operation, typically a process bath for dipping, over time .. The composition according to the invention has a pH in the range of 3.0-5.0, preferably 3.44.4. If the pH is too low then the formation of the protective layer on the substrate is limited by the simultaneous attack or the formed layer by the acidic components. Thus the composition as a whole offer, a balance between components and the amount, their functional properties and processing possibilities. In order to set the acidity at the required level the composition may contain pH adjusting agents, typically bases, such as one or more alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and ammonia. As said before, the pH adjusting agent may be a source of the base of the hydroxyl carboxylic acid stabilizing agent. Examples include lactate, citrates or ammonium and / or sodium and the like. Advantageously the pH adjusting agent is present in amount or 0-1.0 g / l. The alkali metal cations do not - or to a negligible extent - affect the formation of the protective layer. When the pH rises to values above 5, the composition can easily become instable. At pH less than 3.0 it is hard to form substantial coating weight in view of corrosion resistance.

The composition may also include one or more water-soluble surfactants for improving the wetting properties, advantageously in a concentration of 0-1.0 g / l, preferably 0.001-0.5 g / l. Surfactants that can be used in the composition according to the invention include acid stable low foaming anionic and non-ionic surfactants like alkaryl sulfonates and poly ethylene glycol fatty amines. The surfactant provides uniform wetting of the substrate. If the amount of surfactant is too high, it can cause excessive foaming in the process.

Other optional components of the composition according to the invention include water soluble polymers and organo-functional silanes and / or their hydrolysed oligomers. The water soluble polymers include homopolymers and copolymers that are preferably based on the following monomers: acrylic acid, methacrylic acid, vinyl alcohol, vinyl ether, maleic acid, monohydroxy acrylic ester, vinylphosphonic acid, vinylsulphonic acid, methyl vinyl ether, monohydroxy methacrylic ester and combinations of, up to 4.0 g / l, preferably 0.01-4.0 g / l, more preferably 0.1-1 g / l. These polymers improve wetting behavior of the treatment composition, as well as adhesion or subsequently applied organic coatings. Too high concentrations will reduce wet adhesion or an organic coating. The concentration of silanes or oligomers, if present, ranges up to 4.0 g / l. Advantageously the reactive functional group is at least one selected from a mercapto group, an amino group, a vinyl group, an

-7epoxy group and a methacryloxy group, advantageously in an amount or 1 to 40 mg / l based on Si.

According to a second aspect the invention relates to a method of treating a substrate of aluminum, aluminum alloy, anodized aluminum, aluminized steel, zinc or zinc alloy coated steel for corrosion protection, adhesion or an organic coating or adhesive bonding system, which method comprises a step of applying the acidic aqueous solution according to the invention as explained above onto a substrate of aluminum, aluminum alloy, anodized aluminum, aluminized steel, zinc or zinc alloy coated steel.

Typically the metal surface to be treated with the composition according to the invention is pre-treated using known mechanical and / or chemical pre-treatment processes or combination to obtain a legible surface, which typically requires the surface to be roughened and to be substantial free of rest, fat, oil and the like. Mechanical pre-treatment processes include grit blasting, shot peening and abrading. Chemical pre-treatment includes e.g. (acidic / alkaline) degreasing, de-oxidation, desmutting, pickling. Typically each chemical pretreatment is followed by a rinsing step using tap water or demineralised water. Combinations of mechanical pre-treatment and chemical pre-treatment in any order is also possible. The surface may be anodized in case or aluminum or its alloys. Typically treatment according to the invention or bare aluminum will form a conversion layer. Treating anodized aluminum according to the invention will result in a sealing layer.

The way of applying the composition according to the invention to the metal surface is not limited. However, homogeneity and uniformity of the applied law film on the substrate before drying will be advantageous. Suitable application methods include spraying, dipping, wiping, brushing, roll coating and the like. Excess of treatment fluid on parts with intricate geometries can be removed with compressed air. After applying the acidic aqueous composition one or more rinsing steps with demi water are performed, preferably the last rinsing step with demi water having an electrical conductivity in the range of 5-200 micros, and a drying step of drying the thus rinsed substrate, in particular at a temperature in the range of 10-50 ° C. Advantageously the method according to the invention is performed with the composition having a temperature in the range of 10-80 ° C, preferably 15-50 ° C. Typically the processing time ranges from 1-30 minutes, preferably from 3-15 minutes. Processing times or less than 3 minutes are practically not feasible on an industrial scale in view or reproducible coating results. Processing times or more than 30 minutes may interfere with other operations on a continuous production line.

The coating weight, as measured by XRF after drying, is typically in the range of 5-200 mg Cr / m ² , such as 15-100 mg Cr / m ² . For a composition according to this invention coating weight can be controlled by adjusting concentration, pH, bath temperature and immersion time. Too high coating weights will give corrosion resistance, but may reduce adhesion properties and

-8increase the surface electrical resistivity. Low electrical resistivity of the metal surface is important for certain applications as it prevents build-up or static electricity and will not influence welding properties.

For certain alloys, in particular those copper containing aluminum alloys as used in the aerospace technical field such as 2024 and 7075, it has appeared advantageously to conduct a further treatment step. This further treatment step comprises post-treating the substrate that has been treated with the acidic aqueous composition, with a second acidic aqueous composition including an oxidizing agent and an acidifying component, which second composition has a pH in the range of 1-5, preferably 1-3. It has been shown that the risk of formation of Cr ⁶⁺ in the formed protective layer is reduced by using the acidic second solution. Cr ⁶⁺ was less than the detection limit (<0.03 pg / cm ² ) in the used second solution and in the thus obtained protective layer.

Advantageously the oxidizing component is a water soluble peroxide, preferably hydrogen peroxide. Hydrogen peroxide functions as a reducer with respect to Cr ⁶⁺ in an acidic environment. Thus trivalent chromium will not be converted into hexavalent chromium. The concentration of the oxidizing component ranges typically from 10-100 g / l, preferably from 25100 g / l.

The acidifying component is present in a concentration of 0.2-20 g / l, preferably 0.5-5.0 g / l. The acidifying component is advantageously a non-halogenated inorganic acid such as nitric acid, or a metal salt, excluding rare earth metals, preferably a salt or aluminum, zirconium and / or trivalent chromium, preferably the nitrate salt. These acidic components should not dissolve the applied coating by the first composition nor etch aluminum. Nitric acid is a strong acid but has not been shown to attack the coating from the first solution. Other strong acids such as hydrogen chloride and sulphuric acid are too aggressive towards the first deposited layer. The second composition should be acidic enough to avoid formation of hexavalent chromium.

The temperature of the second composition is preferably in the range of 10-50 ° C, more preferably at ambient temperature, like 20-30 ° C. Such a low temperature is advantageous in order to avoid fast decomposition or peroxides.

Treating time is typically 1-30 minutes, preferably 3-15 minutes.

Suitable application methods for the second composition include spraying, dipping, wiping, brushing, roll coating and the like.

In a third aspect the invention relates to an acidic aqueous composition (2 ^nd composition) for post-treatment of a substrate of aluminum, aluminum alloy, anodized aluminum, aluminized steel, zinc or zinc coated alloy, in particular aluminum alloy treated with a trivalent chromium based conversion coating (according to the first aspect of this invention), which composition

-9 companies an oxidizing agent and an acidifying component and has a pH in the range of 1-5, preferably 1-3.

The features disclosed above related to the concentrations and components of this second composition in the method according to the invention similarly apply to this acidic aqueous composition.

The invention is illustrated by the following Examples

Composition 1 and 2 as indicated in Table 1 were prepared from commercially available compounds.

Table 1. Examples starting Compositions

Composition 1 (wt.%) Composition 2 (wt.%) Comparative Example (wt.%) Zirconium triethanolamine (13.8 wt.% Zr) 4 Hexafluoro zirconium acid (19.8 wt.% Zr) 1.41 Ammonium zirconium carbonate (14.8 wt.% Zr) 4.5 4.5 Chromium trifluoride * 4 H ₂ O (28.7 wt.% Cr) 1.51 1.03 10.8 Hydrogen fluoride (20%) 0.9 0.9 Malic acid (99%) 0.9 0.7 Remainder water Zr: Cr molar ratio 1.1: 1 1.3: 1 1: 3: 1 Zr: F mol ratio 1: 4.8 1: 3.6 1: 3.6 Stability (no suspension or gel formed) > 240 days > 240 days <1 day

From these starting Compositions first solutions were prepared by dilution with demi water as indicated in Table 2.

Table 2 First treating solutions

Application solution bath 1 [Zr] g / L [Cr] g / L [F] g / L pH 20 wt.% Of Composition 1 1.66 0.87 1.65 3.9 8 wt.% Or Composition 2 0.53 0.24 0.4 3.9

Below Table 3 shows the various (optional) method steps and the conditions, which are carried out according to the invention.

Table 3. General Process Conditions.

Product Concentric tration [wt.%] Immersion time [min] Temp. [° C] pH Alkaline degreasing Cleaner ABF 3.0 3-7 50-55 9-10 Tap water rinsing Acidic deoxidation / desm utting Adeox 11 3.5 3-7 15-25 1- 3 Tap water rinsing Demi water ringing First treating Composition bath 1 8 wt.% Of Composition 2 5- 20 2- 20 [5-15] 10-80 [30 - 45] 3-5 [3.4 - 4.4] Demi water ringing Forced hot air drying (optionally) 10-80 [40-60] Post-rinse composition bath 2 post-rinse example # 2 or Table 4 0 -60 [3-7] 5-60 [15-30] 1-5 [1-3] Demi water ringing Forced hot air drying (optionally) 10-80 [40 - 60]

[..] represent preferred ranges.

- 11 Table 4 shows data of the resulting layer weight of a conversion coating applied to AA2024 steel using 8 wt% solution of composition under varying process time, using varying immersion (dipping) times, pH and T conditions.

Table 4 Effect of varying process conditions on the resulting layer weight of the conversion coating on AA2024 (expressed in mg Cr / m ² ) using 8 wt.% Of composition 2

pH = 4.2; T = 40 ° C Immersion t [min] 2 5 10 Coating weight {mg Cr / m ² } 12.5 18.8 24.1 pH = 4.2; t = 5 min Temperature bath 1 [°} 30 35 40 Coating weight {mg Cr / m ² } 13.7 16.3 18.8 t = 5 min; T = 40 ° C pH bath 1 3.8 4 4.2 Coating weight {mg Cr / m ² } 11.6 13.3 16.3

Table 5 shows the corrosion test result of 2024 aluminum alloy, as well as the Cr ⁶⁺ content.

Table 5. Examples Aluminum alloy 2024 treated by 20% or Composition 1 at 40 ° C for 10 minutes, followed by a post-rinse.

Example Post rinse bath 2 composition Corrosion rating Salt Spray Test ASTM B117 after 168 hours Hexavalent chromium measured after boiling water extraction 1 None > 5 pits 2 Al (NO ₃ ) ₃ * 9H ₂ O, 4.33 g / l + H ₂ O ₂ (30%) 50 g / l 2 pits <0.03 pg / cm ² 3 Sulfuric Acid (1M) 5.33 g / LH ₂ O ₂ (30%) 50 g / l 2 pits <0.03 pg / cm ² 4 H ₂ O ₂ (30%) 50 g / l 1 burner 0.09 pg / cm ² 5 HNO ₃ (1M) 34.63 g / LH ₂ O ₂ (30%) 50 g / l 3 pits <0.03 pg / cm ²

Table 6-8 present the corrosion results of various metal substrates when treated according to the invention.

- 12 Table 6. Overview corrosion test results various aluminum alloys treated with 8 wt.% Composition 2, optionally followed by post-rinse AI (NO ₃ ) ₃ * 9H ₂ O, 4.33 g / l + H ₂ O ₂ (30% ) 50 g / l at room temperature during 5 minutes

Aluminum Alloy First treatment bath 1 Post rinse bath 2 Neutral Salt Spray <5 burner ASTM B117 AA2024-T3 no no <8 hrs AA2024-T3 y no > 168 hr AA2024-T3 y y > 500 hr AA5005 y no > 1000 hr AA5754 y no > 1000 hr AA6060 y no > 1000 hr AA6061-T6 y no > 1500 hr AA6061-T6 y yes > 3000 hr AA6063 y no > 1000 hr

Table 7. Standard boric acid / sulphuric acid anodizing procedure on 2024 aluminum alloy 2024. Anodized coating thickness 5 pm. Anodized layer is treated / sealed with Composition 2 at 2 different concentrations (T = 40 ° C, t = 10 minutes) without post rinse.

Example Immersion time [min] Bath temperature [° C] Cone. Cr ³⁺ [g / L] Sealed according to to this invention Measured Cr Corrosion rating Salt Spray Test ASTM B117 1 - - - - completely corroded in 24 h 2 10 40 0.5 80 Cr mg / m ² no pits after 168 h 3 10 40 0.25 40 Cr mg / m ² 3 pits after 168 h

Table 8. HDG (hot dip galvanized) Steel experiment

Substrate fresh hot dipped galvanized steel cooled down to 80 ° C Corrosion test Humidity 100% RH, 40 ° C Time to 5% white rest formation Corrosion test: ASTM B117 Neutral salt spray test Time to 5% white rest formation No treatment <12 hours <2 hours 10 wt.% Composition 2, Room Temperature, 10 minutes 500 hours 48 hours

Claims (20)

CONCLUSIONS An acidic aqueous composition for producing a corrosion-resistant layer on substrates of aluminum, aluminum alloys, anodized aluminum, zinc or zinc alloy coated steel, or aluminized steel, the composition comprising: trivalent chromium (Cr ³⁺ ): 0.04 - 6 g / i zirconium (Zr ⁴⁺ ): 0.08-8 g / L total fluoride (F): 0.1 - 9 g / i stabilizer comprising a hydroxycarboxylic acid or corresponding base (s) (calculated as the acid): 0.2-9 g / l with the molar ratio of Zr ⁴⁺ : Cr ³ * 0.8: 1 - 2.0: 1; the molar ratio is Zr ⁴⁺ : F '1: 5.5 -1.0: 2.0; and the pH is in the range of 3.0 - 5.0. The composition of claim 1, wherein the concentration of trivalent chromium (Cr ³⁺ ) is in the range of 0.2 -1.0 g / l. The composition according to claim 1 or 2, wherein the zirconium concentration (Zr ⁴⁺ ) is in the range of 0.2 - 2.0 g / l. The composition according to any of the preceding claims, wherein the fluoride ion concentration (F ') is in the range of 0.2 - 2.0 g / l. A composition according to any one of the preceding claims, wherein the concentration of hydroxycarboxylic acid stabilizer is in the range of 0.2 - 5, and is preferably 0.3 - 3 g / l. The composition according to any of the preceding claims, wherein the pH is in the range of 3.4 - 4.4. Composition according to any of the preceding claims, comprising one or more water-soluble surfactants in a concentration of 0-1.0 g / l, preferably 0.001 - 0.5 g / l, pH-adjusting means in a concentration of 0-1.0 g / l, water-soluble polymers, organofunctional silanes or oligomers in a concentration of 0 - 4.0 g / l. A method for treating a substrate of aluminum, aluminum alloy, anodized aluminum, zinc, zinc alloy coated steel or aluminized steel for corrosion protection, adhesion of a coating and / or glue, which comprises applying an acidic aqueous composition according to any of the preceding claims on the substrate of aluminum, aluminum alloy, anodized aluminum, zinc, or zinc alloy coated steel or aluminized steel. The method of claim 8, wherein the composition has a temperature in the range of 10-80 ° C, preferably 15-50 ° C. The method according to claim 8 or 9, wherein the treatment time is 1-30 minutes, preferably 3-15 minutes. 11. Method as claimed in any of the foregoing claims 8-10, further comprising one or more steps of rinsing the treated substrate with demineralised water, wherein preferably the last rinsing step with demineralised water having a conductivity in the range of 5 200. microS takes place. The method according to any of the preceding claims 8-11, wherein the coating weight is in the range of 5 - 200 mg Cr / m2, measured with XRF after drying. A method according to any of the preceding claims 8-12, further comprising after rinsing with demineralized water, a step of drying the rinsed substrate, preferably at a temperature of 10-50 ° C. The method of any one of the preceding claims, further comprising a step of post-treating the substrate treated with the acidic aqueous composition of any one of claims 1 to 12 with a second acidic aqueous composition comprising an oxidizer and an acidic component and has a pH in the range of 1-5, preferably 1-3. The method of claim 14, wherein the oxidizer is a water-soluble peroxide, preferably hydrogen peroxide. A method according to claim 14 or 15, wherein the oxidizer concentration is 5-100 g / l, preferably 8-50 g / l. A method according to any one of the preceding claims 14-16, wherein the concentration of acidic component is 0.2 - 20 g / l, preferably 0.5 - 5.0 g / l. 18. A method according to any one of the preceding claims 14-17, wherein the acid component is a salt of aluminum, zirconium or trivalent chromium, preferably a nitrate salt. A method according to any one of the preceding claims, wherein the temperature of the second composition is 10 - 50 ° C, preferably 20 - 30 ° C. The method according to any of the preceding claims, wherein the treatment time with the second composition is 1-30 minutes, preferably 3-15 minutes. The invention relates to an acidic aqueous composition for preparing a corrosion-resistant layer on substrates of aluminum, aluminum alloys, anodized aluminum, aluminized steel, 5 zinc or zinc alloy coated steel, comprising the composition: