DE69915372T2 - FERRATE CONVERSION LAYERS ON METAL SUBSTRATES - Google Patents

Abstract

A method employing oxide film conversion coatings prepared using ferrate (VI) as the oxidizing agent is disclosed. Metal substrates or surfaces, such as aluminum, aluminum alloys or other metals, are contacted with an aqueous solution comprising ferrate (VI) anions to form a corrosion resistant conversion coating on the surface thereof. The ferrate anion concentration is preferably between about 0.0166 % and about 1.66 % by weight. The coating process is carried out by dipping, spraying, or painting at temperatures ranging from 25 DEG C to 100 DEG C for a period of time ranging from about 1 second to about 5 minutes.

Description

BACKGROUND THE INVENTION

Territory of invention

The The present invention relates to a method for forming a Conversion layer on metal surfaces or substrates.

State of technology

in the In general, chemical conversion layers are formed chemically, by causing the surface of the metal is "converted" into a tightly adherent layer, with either the entire or a part of the conversion layer of an oxidized form of the substrate metal consists. Chemical conversion layers can give the substrate high corrosion resistance give as well as strong binding affinity for paint. The industrial application from paint to metals generally requires use a chemical conversion layer, especially if the performance requirements are high.

Although Aluminum protects itself against corrosion by forming a natural oxide layer, the protection is not complete. In the presence of moisture and electrolytes, aluminum alloys corrode, in particular aluminum alloys with a high copper content, much faster than pure aluminum.

in the Generally, there are two types of treatment methods Aluminum, for a cheap Conversion layer to form. The first is by anodic oxidation (Anodization), the aluminum component in a chemical bath submerged, such as a chrome or sulfuric acid bath, and an electric current through the aluminum component and the chemical bath is passed. The conversion layer on the surface The aluminum component provides corrosion resistance and a bonding surface for organic Topcoats.

Of the second type of process is by chemical preparation of a conversion layer, the usual is referred to as a chemical conversion layer by the Aluminum component of a chemical solution is subjected, such as about a chromic acid solution, but without using an electric current in the process. The chemical solution can be applied by immersion application, by manual application or by spray application be applied. The resulting conversion layer on the surface The aluminum component provides corrosion resistance and a bonding surface for organic Topcoats.

conversion layers chromate-based have been widely used in applications where maximum corrosion protection is a point. immersion of aluminum or aluminum alloys in a chromate conversion coating bath leads to a thick, corrosion resistant Film consisting of hydrated Cr (III) and Al (III) oxides. The reaction is driven by the reduction of high quality Cr (VI) ions and the oxidation of the Al metal. Some of the benefits of one Chromate conversion layer include hydrophobicity and self-healing properties one.

Many aluminum structural parts, as well as Cd-plated, Zn-plated, Zn-Ni-plated and steel parts, in the aerospace industry are currently being treated using this chromic acid process technology. It has been shown that chromic acid conversion films, as formed on aluminum substrates, meet a 168 hour corrosion resistance criterion, but serve primarily as a surface substrate for paint adhesion. Because of their relative thinness and low layer weights (40-150 milligrams / ft ² ), chromic acid conversion layers do not reduce the fatigue life of the aluminum structure.

environmental regulations in the United States, especially in California, and in other states, however, the contents of hexavalent chromium compounds, the in flows and emissions from metal finishing procedures are allowed drastically reduce. Accordingly, chemical conversion coating processes, replace the hexavalent chromium compounds.

Some the strongest explored non-chromate conversion layers used in the treatment of aluminum alloy based materials are used described below.

Sol-gel technology uses polymers or metal oxides, either alone or mixed, to complex by the hydrolysis of suitable precursor compounds form. Sol-gels can Powder or thin Form films that inhibit corrosion on substrates.

Fluorozirconium coating technology used complexed transition metal salts, around a thin one Film similar to a substrate material to create a conversion layer. Specifically, zirconium mixed with fluorine to produce fluorozirconium which reacts with the part surface reacts to form a coating.

Cobalt-based coatings use cobalt and molybdenum to treat substrate materials. The generated layers are low in the electrical resistance and are good for corrosion resistance.

Rare earth metal (REM) salts can by hot diving can be applied to protective layers on substrate materials produce. REMs provide corrosion resistance by providing a protective one Create oxide film.

Potassium permanganate solutions can be used to produce manganese oxide films on substrates. Manganese oxide films, that result from potassium permanganate treatment are correct largely coincide with the corrosion resistance from conventional Chromium oxide films used in conversion layers. Potassium permanganate coatings are very effective in protecting aluminum alloys.

Fluorotitanium coatings precipitated from acid solutions with organic polymers, require some process steps and can usually be carried out at ambient temperatures. Although these Coatings in a wide range of applications they are not in the aerospace industry used.

Talc coatings, typically applied to aluminum substrates are corrosion resistant. These Polycrystalline layers are deposited by precipitation of Aluminum-lithium compounds and other anions in an alkaline Saline.

anodizing is a process where a metal surface is converted to an oxide layer which makes a tough, Adhesive surface layer produced becomes. A thick oxide layer can be made by placing a Part in an electrolytic solution submerged and an electric current is passed through, similar to Electroplate. Then can the pores of the film, by placing the part in boiling water, to be sealed. As a result, the oxide changes from one Shape into another.

In spite of There is still a need for a conversion coating solution of these alternatives a stable, corrosion resistant Conversion layer on metal surfaces will form without toxic To contain or produce chemicals. There is also a need for a conversion coating solution, the improved corrosion protection on a variety of substrate materials and under a variety of conditions. In addition, it would be desirable if the conversion layer has a suitable surface for Provide absorption of organic coatings or paints would.

US-A-2,850,416 discloses a composition and method for treating Metals, such as steel or aluminum, using a Solution, the 0,5-5% Ferrate (VI) contains and a pH of 7-11 having. The solution contains preferably sodium salts as a buffer or stabilizer.

FR-A-616,849 discloses a composition and method for treating ferrous metals using a solution containing NaOH, Na ₂ CO ₃ , PbO ₂ and Na ₂ FeO ₄ .

According to one aspect of this invention, there is provided a solution for forming a conversion layer on a metal surface, wherein the solution comprises ferrate (VI) (FeO ₄ ^2- ) anions at a concentration of 1-100 mmol / L and one or more transition metal oxa ions, which are selected from the group consisting of permanganate, molybdate, vanadate, tungstate and combinations thereof, and wherein the solution has a pH greater than 13.5.

According to another aspect of this invention, there is provided a solution for forming a conversion layer on a metal surface, wherein the solution comprises ferrate (VI) (FeO ₄ ^2- ) anions at a concentration of 1-100 mmol / L and one or more transition metal oxyanions which are selected from the group consisting of permanganate, molybdate, vanadate, tungstate and combinations thereof, and wherein the solution has a pH between 13 and 13.5.

Preferably comprises the solution continue one or more additional Oxidizing agents selected are from the group consisting of peroxide, hypochlorite, ozone and Combinations thereof.

advantageously, the ferrate (VI) -oxyanion is provided by a compound, the selected is a sodium ferrate (VI) salt, a potassium ferrate (VI) salt, a solution of ferrate (VI) in potassium hydroxide, a solution of ferrate (VI) in sodium hydroxide and mixtures thereof.

Preferably comprises the solution further ethylenediaminetetraacetic acid.

advantageously, comprises the solution continue a salt that is selected is from an alkali metal or an alkaline earth metal nitrate, chloride, fluoride or combinations thereof.

The invention also relates to a method of treating a metal surface, which comprises cleaning and deoxidizing the metal surface, rinsing the deoxidized metal surface with water, In contacting the deoxidized and purged metal surface with an aqueous oxidizing solution at a temperature in the range of 25 to 100 ° C, allowing the metal surface to be oxidized by the oxidizing solution, and removing the oxidized metal surface from contact with the solution, characterized in that the oxidizing solution is an aqueous solution comprising ferrate (VI) (FeO ₄ ^2- ) at a concentration of 1 to 100 mmol / l and one or more transition metal oxyanions selected from the group consisting of permanganate, Molybdate, vanadate, tungstate and combination thereof, and wherein the solution has a pH of greater than 13.5.

In a further aspect, the invention provides a method of treating a metal surface which comprises cleaning and deoxidizing the metal surface, rinsing the deoxidized metal surface with water, contacting the deoxidized and rinsed metal surface with an aqueous oxidizing solution at a temperature in the range of 25 to 100 ° C C, allowing the metal surface to be oxidized by the oxidizing solution, and removing the oxidized metal surface from contact with the solution, characterized in that the oxidizing solution is an aqueous solution containing ferrate (VI) (FeO ₄ ^2- ) at a concentration of 1 to 100 mmol / l and one or more transition metal oxyanions selected from the group consisting of permanganate, molybdate, vanadate, tungstate and combination thereof, and wherein the solution has a pH between 13 and 13 , 5.

suitably the ferrate (VI) is selected of a sodium ferrate (VI) salt, a potassium ferrate (VI) salt, a solution of ferrate (VI) in potassium hydroxide, a solution of ferrate (VI) in sodium hydroxide and mixtures thereof.

advantageously, the metal surface is selected from Aluminum, aluminum alloy, steel or other ferrous metals.

Prefers comprises the solution continue a salt that is selected is an alkali metal or a Alkaline earth metal nitrate, chloride, fluoride or combinations thereof.

suitably become the metal surfaces with the oxidizing solution for between 1 second and 5 minutes in contact.

advantageously, For example, the ferrate solution has a transition metal oxyanion concentration in between 0.1 and 5 wt .-% on.

Prefers comprises the aqueous oxyanion solution on one or more additional ones Oxidizing agents selected are made of peroxide, hypochlorite, ozone and combinations thereof.

suitably comprises the aqueous solution on Ethylenediaminetetraacetic acid.

The Procedure may additionally the step include that the oxidized metal surface with a post-treatment solution which contains one or more compounds which are selected of an alkali metal silicate, an alkali metal borate, an alkali metal phosphate or mixtures thereof to provide an oxide film conversion layer.

The Method may further include that the oxide film conversion layer is brought into contact with lithium nitrate.

The Procedure may additionally include that the Oxide film conversion layer contacted with calcium hydroxide becomes.

Optional The process may further precede the steps of cleaning the metal surface contacting the metal surface with ferrate solution and / or Influence of boiling water or anodization on the purified Metal surface, around an oxide or aqueous oxide layer to build.

It is also optional, the conversion layer surface, the formed by ferrate oxidation, with an aftertreatment solution in To bring contact that contains one or more compounds that selected are made of an alkali metal silicate, an alkali metal borate, a Alkali metal phosphate, lithium nitrate, magnesium hydroxide, calcium hydroxide, Barium hydroxide or mixtures thereof. Preferably, the Concentration of one or more connections between about 0.015 and about 5 wt .-%. When calcium hydroxide is used, the preferred concentration is between about 0.06 and about 0.09 wt.%, and preferably solution prepared in water in the absence of carbon dioxide. The aftertreatment is preferably at a solution temperature between about 10 ° C and about 100 ° C for one Period of between about 1 minute and about 20 minutes.

SHORT DESCRIPTION THE DRAWINGS

In order that the above-mentioned features and advantages of the present invention may be understood in detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof illustrated in the accompanying drawings. It should however, it should be noted that the appended drawings illustrate only typical embodiments of this invention and, therefore, are not intended to limit its scope, as the invention may be capable of other equally effective embodiments.

1 Figure 4 is a graph showing the stability of conversion layers in salt mists prepared with two ferrate concentrations without oxyanions, with molybdate, with permanganate, and with both molybdate and permanganate.

2 Figure 9 is a table showing the resistance of ferrate conversion layers to salt spray made from various ferrate solutions with and without pretreatment steps or post-sealing steps.

DETAILED DESCRIPTION THE INVENTION

The The present invention provides a conversion coating process prepared a stable and corrosion resistant oxide film on the surface of Metal substrates using ferrate (VI) as the oxidizing agent forms. The conversion coating process uses an aqueous solution which Ferrate anions, preferably with a ferrate anion concentration between 1 millimolar (about 0.0166 wt% and 100 millimolar (about 1.66 wt%).) The solution also closes one or more transition metal oxyanions which form stable metal oxides in the layers and as inhibitors act against the corrosion of the coated metal. The transition metal oxyanions are selected from permanganate, molybdate, vanadate, tungstate and combinations the same, preferably at a concentration of between about 0.1 and about 5% by weight. The coating process is carried out at Temperatures ranging between 25 ° C and 100 ° C and with a contact time, which is between 1 second and 5 minutes. The conversion layer Can be manufactured on different metal surfaces or substrates be, including, but not limited to this Aluminum, aluminum alloys, steels (eg carbon steels and stainless steels) and other ferrous metals. The pH of the ferrate solution is 13 to 13.5 or more than 13.5.

Optional, but preferably, the surface of the metal substrate is pretreated, before using the aqueous ferrate solution in Contact is brought. Most preferably, the metal surface is through Sonication in acetone for Cleaned for 30 minutes, then in an alkaline solution cleaned. The cleaned metal surface can then be deoxidized solution submerged, such as LNC deoxidizers (Oakite Products Inc., Berkeley Heights, New Jersey) to remove any residual oxide film from the metal surface to remove. If the metal is aluminum or an aluminum alloy is, can the cleaned surface boiling water or anodization exposed to an oxide layer to build.

moreover For example, the invention may be an optional aftertreatment method for the conversion layer lock in. After the metal surface with a ferrate-containing conversion coating solution has been oxidized the conversion layer is sealed with an aftertreatment solution, containing a sealant, that selected is from an alkali metal silicate, an alkali metal borate, a Alkali metal phosphate, lithium nitrate, magnesium hydroxide, calcium hydroxide or barium hydroxide, the most preferred sealant Calcium hydroxide is. The preferred conditions for the aftertreatment shut down a sealant concentration between about 0.015 and about 5 wt .-%, a solution temperature between about 10 ° C and about 100 ° C and a contact time between about 1 minute and about 20 minutes. When calcium hydroxide is used, the after-treatment solution contains on most preferably between about 0.06 and about 0.09 weight percent calcium hydroxide and is mixed with water with a reduced carbon dioxide concentration produced.

Of the Post-treatment step, for example using calcium hydroxide, is carried out, By reducing the concentration of carbon dioxide in water, one solution formed by adding calcium hydroxide with the water at a reduced concentration is brought together with carbon dioxide, and contact between the metal surface and the solution will be produced. The concentration of carbon dioxide in water can but will be reduced by any known method preferably reduced by heating the water, most preferably to a temperature between 50 ° C and 100 ° C. Other methods of reducing carbon dioxide concentration in the water close that Passing the water through an electro-osmosis pump, passing it through of carbon dioxide through a hydrophobic membrane, the use of carbon dioxide scavengers or centrifuging the water. It is important that the carbon dioxide content the water is reduced because the amount of carbon dioxide present in water at room temperature will provide a solution that will not the desired Conversion layer generated.

Aluminum or other substrate plates made with ferrate conversion layers are submerged in one or more post-treatment solutions, such as alkali metal silicate and calcium hydroxide, between 80 ° C and 100 ° C for 1 minute to 20 minutes. Preferably, the treated aluminum plates are post-treated by immersing first in an aqueous solution containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate at 100 ° C for 20 minutes and second in a aqueous solution containing 2.4 wt .-% alkali metal silicate, at 80 ° C for 2 minutes. Optionally, the aqueous calcium hydroxide solution may further include manganese, molybdenum, or a combination thereof which form stable metal oxides in the layers and act as corrosion inhibitor inhibitors of the layers.

The present invention provides a method that can be used to coat metal substrates with a non-toxic oxide film conversion layer that exhibits corrosion resistance comparable to chromate conversion layers. Ferrate contains iron in a ⁺⁶ oxidation state (Fe ⁶⁺ ) and thus is quite useful as a powerful oxidizer. Suitable forms of ferrate include, but are not limited to, sodium ferrate salts, potassium ferrate salts, solutions of ferrate in potassium hydroxide, solutions of ferrate in sodium hydroxide, and mixtures thereof.

Ferrate (VI) for use in the solution The present invention can be made in a number of ways become. The ferrate (VI) anion can be generated by adding an aqueous solution of Iron nitrate is provided complexed with ethylenediaminetetraacetic acid, and Hydroxide ions. A strong oxidant, such as hydrogen peroxide, becomes subsequently to the solution added to oxidize the iron (III) to ferrate (VI).

Ferrat can also be produced by electrochemical processes. Generally ferrous metal can be used as the anode, with one made of carbon, Nickel or other suitable material produced cathode. In an alkaline solution becomes a current over the anode and cathode applied, which leads to the oxidation of iron from either an iron compound in the anolyte or the anode itself, to Ferrat (VI). Size Volumes of relatively high concentration ferrate (VI) can be mixed with be prepared by this method. The ferrate can then be precipitated, to produce solid ferrate salts, or the solution can be used as a source of ferrate be used.

Optional can the aqueous ferrate solution Alkali metal salt or an alkaline earth metal salt as an accelerator, Activator or passivator of the conversion coating reaction. suitable Alkali metal salts or alkaline earth metal salts include nitrates, Chlorides and fluorides, preferably lithium nitrate, lithium chloride and sodium nitrate, but are not limited thereto. The preferred alkali metal salt concentration is between about 0.1 and about 5.0% by weight.

Optional can stabilize the aqueous ferrate solution be by adding one or more additional oxidants or ethylenediaminetetraacetic to the ferrate solution be added. additional Oxidizing agents can selected are made of peroxides, hypochlorite and ozone. The concentration of additional Oxidizing agent is preferably between about 0.1 and about 0.5% by weight. The presence of other oxidants keeps the iron in the ferrate solution in a + 6 oxidation state.

Example 1. Preparation of aluminum or aluminum alloy plates

Comparative example

Provided Unless otherwise stated, in the following examples, aluminum or aluminum alloy plates. Before contacting of the plates with a coating solution, the plates were passed through Sonication in acetone for 30 minutes prepared. They were then treated with an alkaline cleaning solution (such as about 4215 NCLT, available by Elf Atochem - Turco Products Division, Westminster, California) for 10 minutes at 50 ° C to 60 ° C. The plates were subsequently rinsed with deionized water and in a deoxidizing solution with 15% LNC deoxidizer (Oakite Products Inc., Berkeley Heights, New Jersey) for Submerged for 10 minutes at room temperature. Optionally, the cleaned plates then exposed to boiling water or anodization to form an oxide layer. The plates were then thoroughly with rinsed with deionized water and allowed to dry.

Example 2. Aluminum or aluminum alloy plates treated with conversion coating solutions, the ferrate (VI) in combination with one or more oxyanions or salts

Aqueous solutions from Ferrate (VI) at concentrations between 0.0166% (1 mM) and 1.66% (100 mM) ferrate (VI), with or without 0.5% sodium nitrate, 1.0% to 3.0% of one or more of lithium chlorite or lithium nitrate produced. Aluminum plates that had been produced as described in Example 1, were used in this conversion coating solution for between Submerged for 1 second and 5 minutes at temperatures between 25 ° C and 80 ° C. The plates were subsequently thoroughly rinsed with deionized water, in the air for Dried for 48 to 94 hours and tested with salt spray according to ASTM B-117 test method (Samples were placed at an angle of 15 °).

Example 3. Aluminum or aluminum alloy plates treated with conversion coating solutions, the ferrate (VI) and EDTA at low hydroxide concentrations in combination with a or more oxyanions or salts

Aqueous solutions from Ferrate (VI) with EDTA at concentrations between 0.0166% to 1.66% ferrate (VI) at a pH between 13 and 13.5 were prepared. The solutions could also 1.0% to 3.0% of one or more of potassium permanganate and potassium molybdate and 0.5% to 1.0% of one or more of Lithium chloride, lithium nitrate or sodium nitrate. Aluminum panels, prepared as described in Example 1 were used in these conversion coating solutions of submerged between 1 second and 10 minutes at temperatures between 25 ° C and 80 ° C. The plates were subsequently thoroughly rinsed with deionized water, in the air for Dried for 48 to 94 hours and tested with salt spray according to ASTM B-117 test method (Samples were placed at an angle of 15 °).

Example 4. Aluminum or aluminum alloy plates treated with conversion coating solutions, containing only ferrate (VI) and then treated with post-sealants

Comparative example

Aqueous solutions from Ferrate (VI) with concentrations in a range between 3 to 80 mmol / l Ferrate (VI) were prepared. Aluminum plates, made like described in Example 1, were in each of the solutions for periods in a range of 1 Submerged for 5 minutes at a temperature in the range between 25 ° C and 80 ° C. The treated aluminum panels then received a post-treatment, by first in an aqueous solution, the Containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate, at 100 ° C for 20 Minutes and second in an aqueous solution containing 2.4% by weight of alkali metal silicate contained, at 80 ° C. for 2 minutes were submerged. The plates were then thoroughly with rinsed with deionized water, in the air for Dried for 48 to 94 hours and sprayed with salt spray according to the ASTM B-117 test method tested (samples were placed at an angle of 15 °).

Example 5. Aluminum or aluminum alloy plates treated with conversion coating solutions, the ferret (VI) in combination with one or more oxyanions or salt, and then treated with post-sealants

Aqueous solutions from Ferrate (VI) with concentrations between 3-10 mmol / l ferrate (VI), with or without 0.5% sodium nitrate, 1.0% to 3.0% of one or more of Potassium permanganate and potassium molybdate and 0.5% to 1.0% of one or more of lithium chloride or lithium nitrate were prepared. The aluminum plates prepared as described in Example 1, were in this conversion coating solution for between 1 second and 5 Submerged minutes at temperatures between 25 ° C and 80 ° C. The treated ones Aluminum panels were then given an aftertreatment by first in an aqueous solution, the Containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate, at 100 ° C for 20 Minutes and second in an aqueous solution containing 2.4% by weight of alkali metal silicate contained, at 80 ° C. for 2 minutes were submerged. The plates were then thoroughly with rinsed with deionized water, in the air for Dried for 48 to 94 hours and tested by salt spray fog according to the ASTM B-117 test method (Samples were placed at an angle of 15 °).

Example 6. Aluminum or aluminum alloy plates treated with conversion coating solutions, the ferrate (VI) and EDTA at low hydroxide concentrations in Contain combination with one or more oxyanions or salts, and subsequently treated with post-sealants

Aqueous solutions from Ferrate (VI) with EDTA at concentrations between 0.0166% to 1.66% ferrate (VI) at a pH between 13 and 13.5 were prepared. The solutions could also 1.0% to 3.0% of one or more of potassium permanganate and potassium molybdate and from 0.5% to 1.0% of one or more of lithium chloride, lithium nitrate or sodium nitrate. Aluminum plates were prepared as described in Example 1, were in these conversion coating solutions for between 1 second to 5 seconds Submerged minutes at temperatures between 25 ° C and 80 ° C. The treated ones Aluminum plates were subsequently in one or more Aftertreatment solutions such as alkali metal silicate and calcium hydroxide, between 80 ° C and 100 ° C for 1 minute submerged for up to 20 minutes. The plates were then with rinsed with deionized water, in air for 48 dried to 94 hours and salt spray fog tested according to the ASTM B-117 test method (Samples were placed at an angle of 15 °).

Example 7. Stabilization of ferrate (VI) in the conversion coating solution

The ferrate (VI) anions in the conversion coating solution can be stabilized by the addition of oxidizing agents such as peroxides, hypochlorites, ozone or other oxidizing agents become. The concentrations of these oxidizers can be varied between 0.1 and 0.5 wt.%.

Claims (18)

A solution for forming a conversion layer on a metal surface, wherein the solution comprises ferrate (VI) (FeO ₄ ^2- ) anions at a concentration of 1-100 mmol / L and one or more transition metal oxyanions selected from the group consisting permanganate, molybdate, vanadate, tungstate and combinations thereof, and wherein the solution has a pH greater than 13.5. A solution for forming a conversion layer on a metal surface, wherein the solution comprises ferrate (VI) (FeO ₄ ^2- ) anions at a concentration of 1-100 mmol / L and one or more transition metal oxyanions selected from the group consisting permanganate, molybdate, vanadate, tungstate and combinations thereof, and wherein the solution has a pH between 13 and 13.5. solution according to claim 1 or 2, characterized in that it continues one or more additional ones Comprises oxidizing agent, which are selected from the group consisting of peroxide, hypochlorite, ozone and combination the same. solution according to claim 1, 2 or 3, characterized in that the ferrate (VI) oxyanion is provided by a compound that is selected of a sodium ferrate (VI) salt, a potassium ferrate (VI) salt, a solution of ferrate (VI) in potassium hydroxide, a solution of ferrate (VI) in sodium hydroxide and mixtures thereof. solution according to one of the claims 1 to 4, characterized in that it further comprises ethylenediaminetetraacetic acid. solution according to one of the claims 1 to 5, characterized in that it further comprises a salt which selected is from an alkali metal or an alkaline earth metal nitrate, chloride, fluoride or combinations thereof. A method of treating a metal surface, which comprises cleaning and deoxidizing the metal surface, rinsing the deoxidized metal surface with water, contacting the deoxidized and rinsed metal surface with an aqueous oxidizing solution at a temperature in the range of 25 to 100 ° C, allowing the metal surface to pass through the metal surface oxidizing solution, and removing the oxidized metal surface from contact with the solution, characterized in that the oxidizing solution is an aqueous solution containing ferrate (VI) (FeO ₄ ^2- ) at a concentration of 1 to 100 mmol / and one or more transition metal oxyanions selected from the group consisting of permanganate, molybdate, vanadate, tungstate and combination thereof, and wherein the solution has a pH greater than 13.5. A method of treating a metal surface, which comprises cleaning and deoxidizing the metal surface, rinsing the deoxidized metal surface with water, contacting the deoxidized and rinsed metal surface with an aqueous oxidizing solution at a temperature in the range of 25 to 100 ° C, allowing the metal surface to pass through the metal surface oxidizing solution, and removing the oxidized metal surface from contact with the solution, characterized in that the oxidizing solution is an aqueous solution containing ferrate (VI) (FeO ₄ ^2- ) at a concentration of 1 to 100 mmol / and one or more transition metal oxyanions selected from the group consisting of permanganate, molybdate, vanadate, tungstate and combination thereof, and wherein the solution has a pH between 13 and 13.5. Method according to claim 7 or 8, characterized that this Ferrate (VI) selected is derived from a sodium ferrate (VI) salt, a potassium ferrate (VI) salt, a solution of ferrate (VI) in potassium hydroxide, a solution of ferrate (VI) in sodium hydroxide and mixtures thereof. Method according to claim 7, 8 or 9, characterized that the metal surface selected is made of aluminum, aluminum alloy, steel or other ferrous metals. Method according to one of claims 7 to 10, characterized that the solution further comprises a salt, that selected is from an alkali metal or an alkaline earth metal nitrate, chloride, fluoride or combinations thereof. Method according to one of claims 7 to 11, characterized that the metal surfaces with the oxidizing solution for between 1 second and 5 minutes in contact. Method according to one of claims 7 to 12, characterized that the Ferrate solution a transition metal oxyanion concentration between Has 0.1 and 5 wt .-%. A method according to any one of claims 7 to 13, characterized in that the aqueous oxyanion solution further comprises one or more additional oxidizing agents selected from Pe roxide, hypochlorite, ozone and combinations thereof. Method according to one of claims 7 to 14, characterized that the aqueous solution on ethylenediaminetetraacetic includes. Method according to one of claims 7 to 15, characterized that it includes the step that the oxidized metal surface with a post-treatment solution is contacted, which contains one or more compounds, the selected are made of an alkali metal silicate, an alkali metal borate, a Alkali metal phosphate or mixtures thereof to form an oxide film conversion layer provide. Method according to claim 16, characterized in that that it further comprises that the Oxide film conversion layer brought into contact with lithium nitrate becomes. Method according to claim 16 or 17, characterized that it further comprises that the oxide film conversion layer is contacted with calcium hydroxide.