Solution for metal article treatment, method for production of corrosion-resistant chromium(iii)-based coating on metal substrate and article containing coated metal substrate (variants)

FIELD: coating of metal articles, in particular corrosion-resistant chemical conversion coatings.

SUBSTANCE: coating of structural alloys, preferably aluminum and aluminum-based alloys is carried out by treatment in acid aqueous solution containing water soluble chromium(III) compounds, fluoride, and corrosion strength improving additive (preferably nitrotris(methylene)triphosphonic acid. Claimed method includes treatment of metal substrate with said solution free from hexavalent chromium. Article contains metal substrate, coated as described above. Article may also contain anodized aluminum substrate with sealed coat comprising trivalent chromium and phosphorus applied on anodized coat.

EFFECT: trivalent chromium-based chemical conversion coating free from hexavalent chromium; effective stable coating solution.

23 cl, 8 dwg, 2 tbl, 1 ex

 

The technical field to which the invention relates.

The present invention relates to a method for producing a corrosion resistant conversion coatings based on trivalent phosphonate chromium for corrosion protection of structural alloys, preferably of aluminum and aluminum alloys for the aircraft industry and other metals, namely iron/steel, zinc or galvanized steel, etc. Other fields of application of such coatings include dense coating on anodized aluminum and coatings to improve the service life of bonded aluminum structures.

The level of technology

Conversion coatings are widely used in the processing of metal surfaces to improve the efficiency of corrosion inhibition and adhesion of subsequently applied layer of paint. When applying conversion coatings, chemical reactions occur between the metal and the solution in the bath, during which the metal surface is converted or modified in a thin film with the desired performance characteristics. First of all, conversion coatings used for the surface treatment of metals, such as steel, zinc, aluminum and magnesium. It is known that the conversion coatings based on chromium are the most effective coatings for aluminum and magnesium. However, use the previously installed conversion coatings based on chromium, in General, contained highly toxic hexavalent chromium. Hexavalent chromium is a significant risk to the production staff and process waste is extremely expensive.

To solve the problems associated with the use of conversion coatings containing hexavalent chromium, attempts were made use of conversion coatings based on trivalent chromium, which are more acceptable from the point of view of environmental protection. In U.S. patent No 4171231, 5304257 and 5374347 described solutions of trivalent chromium for use in the formation of conversion coatings on metal surfaces. Corrosion protection, which is provided with coatings based on trivalent chromium, developed or described in these patents, mainly due to the conversion of trivalent chromium to hexavalent chromium, or by adding an oxidizing agent in solution for coating, placed in a bath, or during subsequent processing of the formed conversion coating oxidizing agent, or adding corrosion inhibitors in solution for coating, is placed in the bath. In other words, the disadvantage of such methods of obtaining coatings based on trivalent chromium is lower efficiency of corrosion protection in comparison with coatings on the basis of six is Alentova chromium, and the fact that protection is achieved mainly by the oxidation of trivalent chromium to hexavalent chromium in the coating composition or in solution, is placed in the bath. However, according to the present method described in this invention, more effective protection against corrosion is provided by the adsorption of phosphonate groups contained in the organic compounds based on aminophosphonic acid with long-chain functional groups on the surface of the aluminum oxide with the formation of covalent bonds Al-O-P and by forming a grid of hydrophobic layer on all active corrosion sites on the surface. Another disadvantage of such methods with the use of trivalent chromium and acid aqueous solutions is the formation in the bath for processing during the time of sludge containing chromium. The sediment leads to the loss of material in solution and affects the quality of coverage, if the concentration of major components falls below the required and desired levels.

In this regard, the main objective of the present invention is to develop a conversion coating based on trivalent chromium with the same corrosion resistant properties compared with the conversion coating based on hexavalent chromium, and development of effective sustainable solution to the CSP is itia products placed in a tub because these organic aminophosphonate acids known for their ability to the formation of chelate compounds and complexes with trivalent metal ions, namely Cr+3, Al+3etc.

The invention

The above object is achieved with the use of the present invention according to the attached claims.

According to the present invention the acidic aqueous solution for the treatment of metallic products free from hexavalent chromium and contains a water-soluble compound of trivalent chromium, a water-soluble compound of fluoride and an additive for improving the corrosion resistance, which effectively increases the protective properties against corrosion and reduces the deposition of trivalent chromium in the course of time. The additive includes a chelating agent or multidentate ligands, for example, includes only the group of phosphonic acid or in combination with acetate groups as ligands. Preferred additives for the inhibition of corrosion include derivatives aminophosphonic acids, for example salts and esters, such as nitrilotri(methylene)triphosphonate acid (NTMP), hydroxy-, aminoalkylphosphonic acid, ethylimino(methylene)phosphonic acid, diethylaminoethylamine acid and the like, and these compounds can be is used each individually or in combination with each other as derivatives, with significant solubility in water.

The invention also features a method of obtaining a corrosion-resistant coatings based on trivalent chromium on metal substrates, in particular of aluminum and aluminum alloy, in which the processing of the substrates mentioned acid aqueous solution, and the product containing the metal substrate with a conversion coating of trivalent chromium, obtained by the above method, or article containing an aluminum substrate with a coating that has an anodized coating on the aluminum substrate and sealed coating on the anodized surface, and sealed floor contains trivalent chromium and phosphorus.

List of drawings and other materials

Figure 1 shows a micrograph obtained by scanning electron microscope (SEM), cover-based phosphonate trivalent chromium deposited on the alloy AI 2024, increasing h.

Figure 2 presents energy dispersive x-ray spectrum (EDX spectrum) 1 for SAM coverage on the basis of the NTMP-15 printed on AI 2024.

Figure 3 presents the EDX spectrum 2 for SAM coverage on the basis of the NTMP-15 printed on AI 2024.

4 shows the EDX spectrum of the 3 for SAM coverage on the basis of the NTMP-15 printed on AI 2024.

Figure 5 shows SEM coating on the Nove phosphonate trivalent chromium, printed on AI 6061, increase h.

Figure 6 presents the EDX spectrum 1 for SAM coverage on the basis of the NTMP-15 printed on AI 6061.

Figure 7 presents the EDX spectrum 2 for SAM coverage on the basis of the NTMP-15 printed on AI 6061.

On Fig presents the EDX spectrum 3 for SAM coverage on the basis of the NTMP-15 printed on AI 6061.

Information confirming the possibility of carrying out the invention

The present invention relates to a method for producing a corrosion-resistant coatings based on trivalent chromium deposited on a metal, particularly aluminum or aluminum alloys used in the aircraft industry, as well as to obtain more effective acid aqueous solution for use in the method.

The method of obtaining corrosion resistant coatings based on trivalent chromium on substrates of aluminum and aluminum alloy includes processing substrates acidic aqueous solution not containing hexavalent chromium and containing a water-soluble compound of trivalent chromium, a water-soluble compound of fluoride and additive, which increases the efficiency of corrosion inhibition and may reduce the formation of compounds of trivalent chromium. According to the present invention, the additive includes a chelating agent or a di - or multidentate ligand. Basically the content of the additive sostav the et from 5 parts per million (ppm) to 100 parts per million calculated on the total composition of the solution for coating, preferably from 5 parts per million to 30 parts per million or 15 parts per million to 30 parts per million calculated on the total composition of the solution for coating. Preferred additives for the inhibition of corrosion include derivatives aminophosphonic acids, for example salts and esters, such as nitrilotri(methylene)triphosphonate acid (NTMP), hydroxy-, aminoalkylphosphonic acid, ethylimino(methylene)phosphonic acid, diethylaminoethylamine acid and the like, and these compounds may be used each individually or in combination with each other as derivatives with significant solubility in water. Suitable additives as corrosion inhibitor and stable in solution compounds, primarily, is nitrilotri(methylene)triphosphonate acid (NTMP).

A dilute acidic aqueous solution comprises a water-soluble compound of trivalent chromium, a water-soluble compound of fluoride and connection aminophosphonic acid. The content of compounds of trivalent chromium in the solution is from 0.2 g/l to 10 g/l, preferably from 0.2 g/l to 8.0 g/l or 0.5 g/l to 8.0 g/l), the content of compounds of fluoride ranges from 0.2 g/l to 20.0 g/l, preferably from 0.2 g/DL to 18.0 g/l or 0.5 g/l to 18.0 g/l). Rabaul the config solution of trivalent chromium to cover cook so to the pH value ranged from 2.5 to 4.0, preferably from 3.5 to 4.0.

Found that when using solution for coating in which the content of the trivalent chromium is 100 parts per million to 300 parts per million, the content of compounds of fluoride from 200 parts per million to 400 parts per million and the contents of the connection aminophosphonic acid as a corrosion inhibitor ranges from 10 parts per million to 30 parts per million, there is an exceptionally high protection against corrosion and reduce deposition of trivalent chromium during the time in comparison with a solution for coatings that do not contain aminophosphonic acid. This conclusion is confirmed by the following example.

Example

Prepare three main source solution:

Solution: 8.0 g/l salt of chromium (III) in deionized water (DW),

solution B: 18,0 g/l salt containing fluoride, DV,

the solution NTMP: 1000 parts per million NTMP in the far East.

These solutions are prepared by the following method:

The solution: initial solution of sulphate of chromium (III) is prepared by dissolving 8.0 g of sulfate trivalent chromium obtained by the company Fluka, milwakee (Milwaukee), Wisconsin, USA, in 1 l of the active ingredient. Before use the solution is balance. Solution B: the original solution floreciente potassium is prepared by dissolving 18.0 g of the compounds obtained by the company Aldrich, milwakee, state Whisk is sin, USA 1 l DV. The solution is made up to complete dissolution and stabilization. The solution NTMP is prepared by dissolving 0.1 ml of 50 wt.%-aqueous solution of NTMP received by the company Sigma-Aldrich, St. Louis (St.Louis, Missouri, USA, in 100 ml of DW. Various diluted solutions to cover, placed in a bath for coating, prepared in accordance with the compositions listed in table I. One of the solutions for coating is prepared in the absence of the NTMP and use it as a reference solution to cover for evaluating the effect NTMP on the characteristics of corrosion. The pH value of all of these solutions are placed in the tub to cover, is the range from 3.5 to 4.0.

Table 1.

Compositions of solutions to cover, when placed in the tub to cover
Marking solutionSolution A (ml)Solution B (ml)DV (ml)NTMP (ml)
Control, in the absence of NTMP1001001800 
NTMP-5100100180010
NTMP-10100100180020
NTMP-15100100180030
NTMP-20100100180040
NTMP-25100100180050
NTMP-30100100180060

All solutions prepared immediately before processing samples. Samples of alloys of Al 2024-T3 and Al 6061-T6 size 3"×3" (7.62 cm×7.62 cm) is applied coating in two parallel experiments. The coatings are formed by the following method:

1) All samples for testing mechanically treated on both sides with the use of abrasive scotch brite and then clean using a soft clean cloths Kimwipes in the flow of water. Before diving into the bath with a solution for coating the samples washed with DV and dried with a paper towel.

2) the Samples to be tested are immersed in the bath with solutions for coating and incubated for 10 min at room temperature.

3) Then the samples coated washed DV and dried in air for at least 24 hours

On the surface of the alloy Al 2024 and Al 6061 formed conversion coating blue-pink-purple in colour, containing mixed oxides of chromium and phosphorus. For the obtained coating define a coating weight and characteristics to which Rosie. In the case of coatings, including NTMP-15 determine morphological characteristics using the methods of SEM/x-ray photoelectron spectroscopy (XPS).

It is shown that the mass of all of the formed coating is from 0.15 mg/square inch to 0.5 mg/square inch (0,023 mg/cm2to 0,077 mg/cm2).

Corrosion-resistant properties determine when keeping the samples under the conditions tested in salt spray according to ASTM b 117. The results are given in table II.

Morphological characteristics of coatings: the coating on the basis of trivalent chromium and NTMP-15, formed on the samples of Al 2024 and Al 6061, research using the methods of SAM/ADRS. SAM coating on the sample of Al 2024 shown in figure 1, and the EDX spectra of the specified coating on the sample of Al 2024 is shown in Fig.2-4. Similarly MSAM coverage on the basis of the NTMP-15 on the sample of Al 6061 shown in figure 5, and the EDX spectra shown in Fig.6-8. Data MSAM and ADRS indicate the presence in a conversion coating of phosphorus atoms along with chromium atoms. We can assume that the groups aminophosphonic acid adsorbed on the surface of aluminum oxide and form a chemical bond Al-O-P.

The present invention may have other embodiments, or may be implemented in any other way without from is lonene from the idea or essence of the invention. Therefore, the described embodiment of the invention can be considered in all respects as illustration and not as limitation, and the volume of claims is determined by the attached claims and assumes that it covers all possible changes within the equivalence of concepts.

1. Acid aqueous solution for processing metal products, characterized in that it is free from hexavalent chromium and contains a water-soluble compound of trivalent chromium, a water-soluble compound of fluoride and additives to improve corrosion resistance.

2. The acidic aqueous solution according to claim 1, characterized in that the additive is nitrilotri(methylene)triphosphonate acid (NTMP).

3. The acidic aqueous solution according to claim 1, characterized in that the content of the additive is from 5 parts per million to 100 parts per million calculated on the total composition of an acid aqueous solution.

4. The acidic aqueous solution according to claim 2, characterized in that the content of the additive is from 5 parts per million to 100 parts per million calculated on the total composition of an acid aqueous solution.

5. The acidic aqueous solution according to claim 1, characterized in that the content of the additive is from 5 parts per million to 30 parts per million calculated on the total composition of an acid aqueous solution.

6. The acidic aqueous solution according to claim 2, characterized in that the sod is neigh additive is from 5 parts per million up to 30 parts per million calculated on the total composition of an acid aqueous solution.

7. The acidic aqueous solution according to claim 3, characterized in that the content of the compound of trivalent chromium in the solution is from 0.2 g/l to 8.0 g/l, the content of compounds of fluoride ranges from 0.2 g/l to 18.0 g/l, and the pH value of the solution is from 3.5 to 4.0.

8. The acidic aqueous solution according to claim 4, characterized in that the content of the compound of trivalent chromium in the solution is from 0.5 g/l to 8.0 g/l, the content of compounds of fluoride is from 0.5 g/l to 18.0 g/l, and the pH value of the solution is from 3.5 to 4.0.

9. The acidic aqueous solution according to claim 5, characterized in that the content of the compound of trivalent chromium in the solution is from 0.2 g/l to 10.0 g/l, the content of compounds of fluoride ranges from 0.2 g/l to 20.0 g/l, and the pH value of the solution is from 2.5 to 4.0.

10. The acidic aqueous solution according to claim 6, characterized in that the content of the compound of trivalent chromium in the solution is from 0.5 g/l to 8.0 g/l, the content of compounds of fluoride is from 0.5 g/l to 18.0 g/l, and the pH value of the solution is from 3.5 to 4.0.

11. The acidic aqueous solution according to claim 1, characterized in that the additive is a chelating agent or multidentate ligand.

12. A method of obtaining a corrosion-resistant coatings based on trivalent chromium on metal substrates, cha is in the surrounding area, aluminium and aluminium alloy, characterized in that the handle substrate acidic aqueous solution, free from hexavalent chromium and containing a water-soluble compound of trivalent chromium, a water-soluble compound of fluoride and additive to improve the properties of corrosion resistance.

13. The method according to item 12, characterized in that the additive is used chelating agent or multidentate ligand.

14. The method according to item 12, characterized in that the additive is used NTMP.

15. The method according to item 13, wherein the chelating agent or multidentate ligand chosen from the group comprising amino acids, aminomethyl, alkylester acid, ethylimino(methylene)phosphonic acid, Diethylaminoethanol acid, diethylenetriaminepentaacetic acid, N,N'-di(2-hydroxybenzyl)Ethylenediamine-N,N'-diuksusnoi acid and mixtures thereof.

16. The method according to item 12, wherein the use solution with the content of the chelate supplements from 5 parts per million to 100 parts per million calculated on the total composition of an acid aqueous solution.

17. The method according to item 12, wherein the use solution with the content of the chelate supplements from 5 parts per million to 30 parts per million calculated on the total composition of an acid aqueous solution.

18. The method according to item 12, wherein the use solution from staranimolinar trivalent chromium in solution of 0.2 g/l to 10.0 g/l, compounds of fluoride from 0.2 g/l to 20.0 g/l and the value of pH from 2.5 to 4.0.

19. The method according to 14, wherein the use solution with a content of compounds of trivalent chromium in the solution is from 0.5 g/l to 8.0 g/l, compounds of fluoride from 0.5 g/l to 18.0 g/l and the value of pH from 3.5 to 4.0.

20. Article containing a metal substrate with a coating, wherein the coating is a conversion coating based on trivalent chromium, obtained by means of the method according to item 12.

21. The product according to claim 20, characterized in that the metal substrate is aluminum.

22. The product according to claim 20, characterized in that the metal substrate is anodized aluminum.

23. The product containing aluminum substrate with a coating, characterized in that it has an anodized coating on the aluminum substrate and sealed coating on the anodized surface, and sealed floor contains trivalent chromium and phosphorus.



 

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19 cl, 5 tbl, 5 ex

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19 cl, 1 tbl

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27 cl, 1 tbl

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