A chromium-free passivating agent and passivation treatment method thereof

Abstract

The present invention belongs to the technical field of material surface treatment, and discloses a chromium-free passivator and a passivation treatment method thereof. The chromium-free passivator of the present invention comprises components: heteropoly acid, fluorine-containing compound, organophosphine compound, organic acid salt, hydrolyzed silane polymer; heteropoly acid comprises Dawson type 10-molybdenum 8-vanadium diphosphoric acid. The chromium-free passivator of the present invention takes Dawson type 10-molybdenum 8-vanadium diphosphoric acid as the main component, and rationally compounding it with fluorine-containing compound, organophosphine compound, organic acid salt, and hydrolyzed silane polymer, so that the chromium-free passivator of the present invention can form a passivation film with strong corrosion resistance on the surface of aluminum alloy, the color is the original color of aluminum alloy or close to the original color, the color is uniform, and there is no corrosion spot after more than 100h of bare film neutral salt spray test, the passivation film is basically discolored, and the color remains uniform; at the same time, the chromium-free passivator of the present invention does not contain trivalent chromium and hexavalent chromium, and has good environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface treatment, and particularly relates to a chromium-free passivating agent and a passivation treatment method thereof. Background Art

[0002] Aluminum alloys are highly active and easily corroded, so anti-corrosion treatment is required on the surface. Traditional hexavalent chromium passivation can form a dense and corrosion-resistant passivation film, but due to the high toxicity of hexavalent chromium, it is carcinogenic and not environmentally friendly. At present, the market mainly uses trivalent chromium passivation technology to replace hexavalent chromium passivation technology, but the trivalent chromium passivation technology has the following problems: the passivation oxidation ability of trivalent chromium is significantly lower than that of hexavalent chromium, resulting in significantly lower corrosion resistance of its trivalent chromium passivation film than that of hexavalent chromium passivation film, and because trivalent chromium is easily oxidized into carcinogenic hexavalent chromium in the solution, the wastewater of the trivalent chromium passivation treatment process is prone to contain hexavalent chromium, which is also not environmentally friendly. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a chromium-free passivating agent, which can form a passivating film on the surface of an aluminum alloy with strong corrosion resistance and a color that is the original color of the aluminum alloy or close to the original color, with uniform color, and no corrosion spots after a bare film neutral salt spray test for more than 100 hours, and the passivating film basically does not change color, and the color remains uniform; at the same time, the chromium-free passivating agent of the present invention does not contain trivalent chromium or hexavalent chromium, and has good environmental protection.

[0004] The first aspect of the present invention provides a chromium-free passivating agent, comprising components: heteropoly acid, fluorine-containing compound, organic phosphine compound, organic acid salt, hydrolyzed silane polymer; the heteropoly acid comprises Dawson type 10-molybdenum 8-vanadium diphosphoric acid.

[0005] Preferably, the heteropoly acid further comprises at least one of silicotungstic acid, silicomolybdic acid and phosphotungstic acid.

[0006] Preferably, the fluorine-containing compound includes at least one of potassium fluorozirconate, potassium fluorotitanate, fluorosilicic acid, and fluoroboric acid. The fluorine-containing compound used in the present invention can accelerate the film formation speed and enhance the protective effect of the chromium-free passivation bare film, so that the obtained chromium-free passivation bare film has better effects in all aspects.

[0007] Preferably, the organic phosphine compound includes at least one of polyaminopolyether methylenephosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, and sodium ethylenediaminetetramethylenephosphonate. The organic phosphine compound used in the present invention can form an organic phosphine and metal salt complex, which can further enhance the firmness of the chromium-free passivation bare film on the surface of the aluminum alloy, and can also improve the corrosion resistance, and can meet the ultra-high requirements of the firmness and corrosion resistance of the passivation film layer for the chromium-free passivation bare film treatment of ADC12 die-cast aluminum on the market.

[0008] Preferably, the organic acid salt includes at least one of tetrasodium iminodisuccinate, tetrasodium glutamate diacetate, and pentasodium diethylenetriamine pentaacetate. The organic acid salt used in the present invention is a metal ion complexing agent with excellent performance, which can assist in forming a metal ion chelating layer on the surface of the aluminum alloy during the passivation treatment, making the chromium-free passivation bare film layer very uniform and further enhancing the firmness of the chromium-free passivation film layer, and can also help further improve the corrosion resistance of the chromium-free passivation bare film surface.

[0009] Preferably, the preparation method of the chromium-free passivating agent is: mixing the components and stirring them evenly.

[0010] The second aspect of the present invention provides the use of the chromium-free passivating agent of the present invention in the passivation and corrosion protection of aluminum alloy surfaces.

[0011] A third aspect of the present invention provides a surface passivation treatment method for an aluminum alloy, comprising the following steps:

[0012] The chromium-free passivating agent of the present invention is mixed with water and stirred evenly to obtain a bath solution;

[0013] The aluminum alloy is immersed in a bath solution for passivation treatment to form a passivation film on the surface of the aluminum alloy.

[0014] Preferably, the pH of the bath solution is 3.5-4.0, the temperature of the bath solution is 20-40° C., and the passivation treatment time is 2-10 min.

[0015] Preferably, the passivation treatment time is 6-10 minutes.

[0016] Preferably, the passivation treatment time is 10 minutes.

[0017] Preferably, the preparation method of the Dawson type 10-molybdenum 8-vanadium diphosphoric acid comprises the following steps:

[0018] Sodium metavanadate, sodium molybdate, sodium dihydrogen phosphate and phosphoric acid are mixed, heated and reacted to obtain the Dawson type 10-molybdenum 8-vanadium diphosphoric acid.

[0019] Preferably, the chemical equation for the preparation reaction of the Dawson type 10-molybdenum 8-vanadium diphosphoric acid is as follows:

[0020] 10Na2MoO4+8NaVO3+2NaH2PO4+14H + →H 14 [P2Mo 10 V8O 62 ].

[0021] Preferably, the preparation method of the Dawson type 10-molybdenum 8-vanadium diphosphoric acid comprises the following steps:

[0022] Sodium metavanadate, sodium molybdate, sodium dihydrogen phosphate and water are mixed, stirred, heated to 90-95°C, phosphoric acid is added, and the mixture is heated to 100-110°C, kept under reflux for 4-5 hours, and then cooled to below 40°C to obtain the Dawson type 10-molybdenum 8-vanadium diphosphoric acid (H 14 [P2Mo 10 V8O 62 ]).

[0023] A fourth aspect of the present invention provides an aluminum alloy, wherein the aluminum alloy is surface passivated using the chromium-free passivating agent described in the present invention.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The chromium-free passivator of the present invention uses Dawson type 10-molybdenum 8-vanadium diphosphoric acid as a main component, has a relatively high oxidation electrode potential close to the electrode potential of hexavalent chromium, and has a passivation oxidation ability very close to that of hexavalent chromium. The Dawson type 10-molybdenum 8-vanadium diphosphoric acid is rationally compounded with a fluorine-containing compound, an organic phosphine compound, an organic acid salt, and a hydrolyzed silane polymer, so that the metal ion chelating ability is improved while having a high passivation oxidation ability, so that the chromium-free passivator of the present invention can form a passivation film on the surface of the aluminum alloy with strong corrosion resistance and a color that is the original color of the aluminum alloy or close to the original color, and the color is uniform and consistent, and no corrosion spots are found after a bare film neutral salt spray test for more than 100 hours, and the passivation film is basically not discolored, and the color remains uniform and consistent; at the same time, the chromium-free passivator of the present invention does not contain trivalent chromium or hexavalent chromium, and has good environmental protection.

[0026] The chromium-free passivating agent of the present invention is mainly composed of Dawson type 10-molybdenum 8-vanadium diphosphoric acid with strong self-repairing ability. The high-valent molybdenum and vanadium can quickly absorb oxygen in the air and oxidize to a high-valent state when reduced to a low-valent state. The passivation film layer formed in this way has very similar performance to the hexavalent chromium passivation film layer, has strong repairing ability, and the stability and firmness of the passivation film are basically equivalent to those of the hexavalent chromium passivation film; at the same time, molybdenum and vanadium can be maintained in a relatively high valence state during long-term use, and the bath liquid has good stability, thereby avoiding the problem that the traditional trivalent chromium is easily oxidized to a higher valence state or reduced to a lower valence state, and the content of the higher or lower valence chromium in the bath liquid must be frequently analyzed and adjusted in time during the production process. DETAILED DESCRIPTION

[0027] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0028] Unless otherwise specified, the raw materials, reagents and devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0029] The hydrolyzed silane polymer used in the examples is selected from Nanjing Gutian Chemical Co., Ltd., model number SW3005.

[0030] The preparation method of the Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution used in the embodiment comprises the following steps:

[0031] 82 g of sodium metavanadate was added to 200 g of deionized water, and the mixture was stirred. Then, 200 g of sodium molybdate was added, and the mixture was stirred for 10 min. Then, 26 g of sodium dihydrogen phosphate was added, and the mixture was stirred for 10 min to obtain a mixed solution.

[0032] The mixed solution was heated to 93°C, and then 240 g of phosphoric acid with a mass concentration of 85% was added to the mixed solution, and the mixture was heated to 106°C, and kept refluxed for 5 hours under boiling conditions;

[0033] After the reaction was completed, the temperature was lowered to below 40° C. to obtain a dark red, clear and transparent Dawson-type 10-molybdenum 8-vanadium diphosphoric acid solution.

[0034] Example 1

[0035] A chromium-free passivating agent, composed of the following components in parts by mass:

[0036] 10 parts of potassium fluorozirconate, 5 parts of silicotungstic acid, 10 parts of hydrolyzed silane polymer, 3 parts of polyaminopolyether methylenephosphonic acid, 2 parts of tetrasodium iminodisuccinate, 20 parts of Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution, and 50 parts of deionized water.

[0037] The preparation method of the chromium-free passivating agent of this embodiment is: mix the components and stir them evenly.

[0038] The components of the chromium-free passivation bath solution are as follows: 100 g / L of the chromium-free passivating agent of this embodiment, and the balance is deionized water; the pH of the bath solution is 3.5-4.0; and the temperature of the bath solution is 30°C.

[0039] A surface passivation treatment method for an aluminum alloy comprises the following steps:

[0040] The ADC12 die-cast aluminum alloy is immersed in the above-mentioned chromium-free passivation bath solution for passivation treatment for 2-10 minutes to form a passivation film on the surface of the ADC12 die-cast aluminum alloy.

[0041] The ADC12 die-cast aluminum alloy that had been passivated for 2 minutes, 6 minutes, and 10 minutes was tested for the chromium-free passivation film performance. The test results are shown in Table 1.

[0042] Table 1

[0043]

[0044]

[0045] Example 2

[0046] A chromium-free passivating agent, composed of the following components in parts by mass:

[0047] 10 parts of potassium fluorotitanate, 5 parts of silicomolybdic acid, 10 parts of hydrolyzed silane polymer, 3 parts of 2-phosphonobutane-1,2,4-tricarboxylic acid, 2 parts of tetrasodium glutamate diacetate, 20 parts of Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution, and 50 parts of deionized water.

[0048] The preparation method of the chromium-free passivating agent of this embodiment is: mix the components and stir them evenly.

[0049] The components of the chromium-free passivation bath solution are as follows: 100 g / L of the chromium-free passivating agent of this embodiment, and the balance is deionized water; the pH of the bath solution is 3.5-4.0; and the temperature of the bath solution is 30°C.

[0050] A surface passivation treatment method for an aluminum alloy comprises the following steps:

[0051] The ADC12 die-cast aluminum alloy is immersed in the above-mentioned chromium-free passivation bath solution for passivation treatment for 2-10 minutes to form a passivation film on the surface of the ADC12 die-cast aluminum alloy.

[0052] The ADC12 die-cast aluminum alloy that had been passivated for 2 minutes, 6 minutes, and 10 minutes was tested for the chromium-free passivation film performance. The test results are shown in Table 2.

[0053] Table 2

[0054]

[0055]

[0056] Example 3

[0057] A chromium-free passivating agent, composed of the following components in parts by mass:

[0058] 5 parts of fluorosilicic acid, 5 parts of fluoroboric acid, 5 parts of phosphotungstic acid, 10 parts of hydrolyzed silane polymer, 3 parts of sodium ethylenediaminetetramethylenephosphate, 2 parts of pentasodium diethylenetriaminepentaacetate, 20 parts of Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution, and 50 parts of deionized water.

[0059] The preparation method of the chromium-free passivating agent of this embodiment is: mix the components and stir them evenly.

[0060] The components of the chromium-free passivation bath solution are as follows: 100 g / L of the chromium-free passivating agent of this embodiment, and the balance is deionized water; the pH of the bath solution is 3.5-4.0; and the temperature of the bath solution is 30°C.

[0061] A surface passivation treatment method for an aluminum alloy comprises the following steps:

[0062] The ADC12 die-cast aluminum alloy is immersed in the above-mentioned chromium-free passivation bath solution for passivation treatment for 2-10 minutes to form a passivation film on the surface of the ADC12 die-cast aluminum alloy.

[0063] The ADC12 die-cast aluminum alloy that had been passivated for 2 minutes, 6 minutes, and 10 minutes was subjected to a chromium-free passivation film performance test. The test results are shown in Table 3.

[0064] Table 3

[0065]

[0066]

[0067] Comparative Example 1 (the difference from Example 1 is that the Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution is replaced with 12-phosphotungstic acid)

[0068] A chromium-free passivating agent, composed of the following components in parts by mass:

[0069] 10 parts of potassium fluorozirconate, 5 parts of silicotungstic acid, 10 parts of hydrolyzed silane polymer, 3 parts of polyaminopolyether methylenephosphonic acid, 2 parts of tetrasodium iminodisuccinate, 20 parts of 12-phosphotungstic acid, and 50 parts of deionized water.

[0070] The preparation method of the chromium-free passivating agent of this comparative example is: mix the components and stir them evenly.

[0071] The composition of the chromium-free passivation bath solution is as follows: 100 g / L of the chromium-free passivating agent of this comparative example, and the balance is deionized water; the pH of the bath solution is 3.5-4.0; and the temperature of the bath solution is 30°C.

[0072] A surface passivation treatment method for an aluminum alloy comprises the following steps:

[0073] The ADC12 die-cast aluminum alloy is immersed in the above-mentioned chromium-free passivation bath solution for passivation treatment for 2-10 minutes to form a passivation film on the surface of the ADC12 die-cast aluminum alloy.

[0074] The ADC12 die-cast aluminum alloy that had been passivated for 2 minutes, 6 minutes, and 10 minutes was tested for the performance of the chromium-free passivation film. The test results were as follows:

[0075] After passivation treatment for 2 minutes, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 20 hours of neutral salt spray test.

[0076] After 6 minutes of passivation treatment, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 50 hours of neutral salt spray test.

[0077] After passivation treatment for 10 minutes, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 80 hours of neutral salt spray test.

[0078] Comparative Example 2 (the difference from Example 1 is that tetrasodium iminodisuccinate is replaced by sodium nitrate)

[0079] A chromium-free passivating agent, composed of the following components in parts by mass:

[0080] 10 parts of potassium fluorozirconate, 5 parts of silicotungstic acid, 10 parts of hydrolyzed silane polymer, 3 parts of polyaminopolyether methylenephosphonic acid, 2 parts of sodium nitrate, 20 parts of Dawson type 10-molybdenum 8-vanadium diphosphoric acid solution, and 50 parts of deionized water.

[0081] The preparation method of the chromium-free passivating agent of this comparative example is: mix the components and stir them evenly.

[0082] The composition of the chromium-free passivation bath solution is as follows: 100 g / L of the chromium-free passivating agent of this comparative example, and the balance is deionized water; the pH of the bath solution is 3.5-4.0; and the temperature of the bath solution is 30°C.

[0083] A surface passivation treatment method for an aluminum alloy comprises the following steps:

[0084] The ADC12 die-cast aluminum alloy is immersed in the above-mentioned chromium-free passivation bath solution for passivation treatment for 2-10 minutes to form a passivation film on the surface of the ADC12 die-cast aluminum alloy.

[0085] The ADC12 die-cast aluminum alloy that had been passivated for 2 minutes, 6 minutes, and 10 minutes was tested for the performance of the chromium-free passivation film. The test results were as follows:

[0086] After passivation treatment for 2 minutes, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 80 hours of neutral salt spray test.

[0087] After 6 minutes of passivation treatment, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 200 hours of neutral salt spray test.

[0088] After passivation treatment for 10 minutes, the ADC12 die-cast aluminum alloy began to produce corrosion spots after 350 hours of neutral salt spray test.

[0089] It can be seen from the test results of the above Examples 1-3 and Comparative Examples 1-2 that after the ADC12 die-cast aluminum alloy is subjected to surface passivation treatment with the chromium-free passivator of the present invention, a chromium-free passivation film of original color or close to original color can be generated on the surface, and the passivation film has very excellent corrosion resistance and can pass the bare film neutral salt spray test for 500 hours without corrosion spots; while Comparative Examples 1 and 2 have significantly reduced corrosion resistance due to changes in the components in the chromium-free passivator system of the present invention.

[0090] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A chromium-free passivating agent, characterized in that: The invention comprises components: a heteropoly acid, a fluorine-containing compound, an organic phosphine compound, an organic acid salt, and a hydrolyzed silane polymer; the heteropoly acid comprises Dawson type 10-molybdenum 8-vanadium diphosphoric acid, and the Dawson type 10-molybdenum 8-vanadium diphosphoric acid is prepared by a preparation method comprising the following steps: Sodium metavanadate, sodium molybdate, sodium dihydrogen phosphate and water are mixed, stirred, heated to 90-95° C., phosphoric acid is added, and the mixture is heated to 100-110° C., kept at reflux for 4-5 hours, and then cooled to below 40° C. to obtain the Dawson type 10-molybdenum 8-vanadium diphosphoric acid; The chemical formula of the Dawson type 10-molybdenum 8-vanadium diphosphoric acid is H 14 [P2Mo 10 V8O 62 ]; The fluorine-containing compound includes at least one of potassium fluorozirconate, potassium fluorotitanate, fluorosilicic acid, and fluoroboric acid; The organic phosphine compound includes at least one of polyamino polyether methylene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, and sodium ethylenediaminetetramethylenephosphonate; The organic acid salt includes at least one of tetrasodium iminodisuccinate, tetrasodium glutamate diacetate, and pentasodium diethylenetriamine pentaacetate.

2. The chromium-free passivating agent according to claim 1, characterized in that: The heteropoly acid further comprises at least one of silicotungstic acid, silicomolybdic acid and phosphotungstic acid.

3. Use of the chromium-free passivator according to claim 1 or 2 in passivation and corrosion protection of aluminum alloy surfaces.

4. A surface passivation treatment method for aluminum alloy, characterized in that: The steps include: Mixing the chromium-free passivating agent according to claim 1 or 2 with water, stirring evenly, to obtain a bath solution; Immersing the aluminum alloy in a bath solution for passivation treatment to form a passivation film on the surface of the aluminum alloy; The pH of the bath solution is 3.5-4.0, the temperature of the passivation treatment is 20-40° C., and the time of the passivation treatment is 2-10 min.

5. An aluminum alloy, characterized in that: The aluminum alloy is surface passivated using the chromium-free passivator described in claim 1 or 2.

Images