Rare earth passivation solution as well as preparation method and application thereof

Abstract

The invention relates to the technical field of corrosion resistance of metal materials, in particular to a rare earth passivation solution and a preparation method and application thereof. The rare earth passivation solution provided by the invention comprises the following components in parts by mass: 3-8 parts of a film-forming agent, 10-20 parts of an accelerant and 70-85 parts of water, wherein the film-forming agent is cerium chloride and praseodymium chloride; and a magnesium alloy is placed in the rare earth passivation solution to be soaked, and preparation of the rare earth passivation film on the surface of the magnesium alloy is completed. The mixed rare earth cerium chloride and praseodymium chloride synergistic modification technology is adopted, and the corrosion resistance of the AZ31 magnesium alloy is remarkably improved through the structural design of the composite passive film.

Description

Technical Field

[0001] The present invention relates to the technical field of corrosion resistance of metal materials, and in particular to a rare earth passivation solution, a preparation method and application thereof. Background Art

[0002] Magnesium alloys have the core advantages of low density and high specific strength, as well as excellent thermal conductivity, outstanding shock absorption performance, and good environmental compatibility. They also exhibit remarkable strength-plasticity matching characteristics: at room temperature, the tensile strength can reach 230MPa and the yield strength can reach 180MPa. However, certain shortcomings of magnesium and magnesium alloys (such as poor corrosion resistance in the environment and higher cost compared to aluminum) limit the widespread application of magnesium alloys. They are mainly susceptible to environmental factors such as moisture and acid rain, and oxidative corrosion occurs, which can form galvanic corrosion with Cl- as the triggering medium, greatly increasing their use and maintenance costs.

[0003] In order to improve the corrosion resistance of magnesium alloys, surface treatment technology is a commonly used and effective method. Compared with other surface pretreatment methods, chemical conversion treatment has the advantages of simple operation, low cost, uniform film layer and fast reaction speed. Its process generally includes alkaline washing, acid etching, drying and other steps. It has the advantages of being unaffected by the shape and size of the workpiece and having strong bonding with organic coatings, and has shown significant competitiveness in the field of surface engineering. Traditional chemical conversion films, especially chromate conversion films, can provide good protection, but because they contain highly toxic hexavalent chromium (Cr 6+ ), poses serious environmental pollution and human health risks. Therefore, the development of environmentally friendly (chromium-free) and efficient chemical conversion technologies has become a research hotspot. Among them, rare earth conversion treatment technology is considered a promising alternative due to the unique properties of rare earth elements (such as corrosion inhibition and catalysis).

[0004] However, the existing rare earth passivation technology still has some problems that need to be solved: the long-term protective effect of some rare earth passivation films, especially the corrosion resistance in harsh environments (such as high Cl- concentration), still needs to be optimized to reach or exceed the level of chromate films; the bonding strength between the film layer and the magnesium alloy substrate, as well as the density and stability of the film layer itself are sometimes not ideal, affecting its long-term protective effect and support for subsequent coatings. When the film layer is damaged by external forces (such as scratches) or local corrosion, traditional rare earth passivation films usually lack the ability to prevent corrosion from spreading, resulting in protection failure; the development of efficient, stable, and easy-to-industrial rare earth passivation solution formulas and processes for specific grades of magnesium alloys (such as the widely used AZ31) still needs in-depth exploration. In response to the above technical difficulties, especially to improve corrosion resistance, enhance film bonding, and give the passivation film a multi-layer thickness to achieve the goal of preventing corrosion or crack propagation, it is urgent to develop new and efficient rare earth passivation solutions. Summary of the Invention

[0005] The purpose of the present invention is to provide a rare earth passivation solution and a preparation method and application thereof, so as to solve the problems existing in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a rare earth passivation solution, comprising the following components by weight: 3 to 8 parts of a film-forming agent, 10 to 20 parts of a promoter, and 70 to 85 parts of water;

[0008] The film-forming agents are cerium chloride and praseodymium chloride.

[0009] Optionally, the mass ratio of the cerium chloride to the praseodymium chloride is 1:0.3-3.

[0010] Optionally, the accelerator is a hydrogen peroxide solution.

[0011] Optionally, the concentration of the hydrogen peroxide solution is 25-35 wt.%.

[0012] The present invention also provides a method for preparing the rare earth passivation solution, comprising the following steps: mixing a film-forming agent, a promoter and water to obtain the rare earth passivation solution.

[0013] The present invention also provides a method for preparing a rare earth passivation film on a magnesium alloy surface, which is characterized by comprising the following steps:

[0014] The magnesium alloy is placed in the above rare earth passivation solution and immersed to complete the preparation of the rare earth passivation film on the surface of the magnesium alloy.

[0015] Optionally, the magnesium alloy is AZ31 magnesium alloy.

[0016] Optionally, the soaking temperature is 40-50° C. and the soaking time is 20-25 minutes.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention adopts the synergistic modification technology of mixed rare earths of cerium chloride and praseodymium chloride, and accurately controls the formation and structure of the passivation film by adjusting key parameters such as the mass ratio of the mixed rare earths, the passivation temperature, and the amount of hydrogen peroxide added. The key to this technology is: Pr 3+ With Ce 3+When the pH locally rises, a Pr(OH)3 / Ce(OH)3 colloid is generated, dynamically sealing film defects. Furthermore, an innovative gradient composite passivation film structure was designed to address the varying film-forming rates of different rare earth mixture ratios with the magnesium alloy matrix. This structure results in a passivation film on the surface of AZ31 magnesium alloy with a dense inner layer and an amorphous outer layer. The dense inner layer effectively blocks substrate corrosion, while the amorphous outer layer acts as a stress buffer and inhibits crack propagation. This synergistic effect significantly improves the corrosion resistance of AZ31 magnesium alloy while simultaneously reducing its cost of use and subsequent protection.

[0019] The maximum resistance of the rare earth passivation film on the surface of the AZ31 magnesium alloy prepared by the present invention can reach 5161.3Ω, which is 3570Ω higher than that of the blank group, and the maximum self-corrosion potential can reach -0.684V, which is 0.020V higher than that of the blank group. 3 + / Ce 3+ The synergistic effect of mixed rare earths significantly improves the stability of the passivation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart for preparing a rare earth conversion film on the surface of an AZ31 magnesium alloy material according to the present invention;

[0021] Figure 2 This is the circuit diagram used for impedance fitting in the present invention;

[0022] Figure 3 The AC impedance spectra of the samples of Examples 1 to 5 are shown;

[0023] Figure 4 Polarization curves of samples from Examples 1 to 5;

[0024] Figure 5 The AC impedance diagrams of samples of Example 1 and Comparative Examples 1 to 6 are shown;

[0025] Figure 6 Polarization curves of samples of Example 1 and Comparative Examples 1 to 6;

[0026] Figure 7 Impedance spectra of different alloy materials of Example 1 and Comparative Examples 7 to 12;

[0027] Figure 8 Polarization curves of different alloy materials of Example 1 and Comparative Examples 7 to 12;

[0028] Figure 9The SEM images of the samples of Comparative Example 1, Example 1, Comparative Example 10, and Comparative Example 12 are shown, wherein (a) is the sample of Comparative Example 1, (b) is the sample of Comparative Example 10, (c) is the sample of Example 1, and (d) is the sample of Comparative Example 12;

[0029] Figure 10 This is the EDS graph of the sample of Example 1. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0032] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0033] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0035] The raw materials used in the present invention can be obtained commercially or prepared using existing technologies.

[0036] The present invention provides a rare earth passivation solution, comprising the following components by weight: 3 to 8 parts of a film-forming agent, 10 to 20 parts of a promoter, and 70 to 85 parts of water;

[0037] In the present invention, the rare earth passivation solution includes 3 to 8 parts of the film-forming agent, preferably 4 to 7 parts, more preferably 5 to 6 parts, and most preferably 4 parts.

[0038] In the present invention, the film-forming agents are cerium chloride and praseodymium chloride; the mass ratio of cerium chloride to praseodymium chloride is 1:0.3-3, for example, 1:1, 2:2, 4:4, 1:3, 3:1, etc.

[0039] In the present invention, the rare earth passivation solution includes 10 to 20 parts of a promoter, preferably 12 to 19 parts, more preferably 14 to 18 parts, and even more preferably 16 to 17 parts. The promoter is a hydrogen peroxide solution, and the concentration of the hydrogen peroxide solution is 25 to 35 wt.%, preferably 27 to 34 wt.%, more preferably 28 to 32 wt.%, and even more preferably 29 to 30 wt.%.

[0040] In the present invention, the rare earth passivation solution includes 70 to 85 parts of water, preferably 72 to 82 parts, more preferably 70 to 78 parts, and even more preferably 75 to 76 parts.

[0041] The present invention also provides a method for preparing the rare earth passivation solution, comprising the following steps: mixing a film-forming agent, a promoter and water to obtain the rare earth passivation solution.

[0042] The present invention also provides a method for preparing a rare earth passivation film on a magnesium alloy surface, which is characterized by comprising the following steps:

[0043] The magnesium alloy is placed in the above rare earth passivation solution and immersed to complete the preparation of the rare earth passivation film on the surface of the magnesium alloy.

[0044] In the present invention, the magnesium alloy is AZ31 magnesium alloy.

[0045] In an embodiment of the present invention, the AZ31 magnesium alloy needs to be pretreated before immersion, and the pretreatment method is: the AZ31 magnesium alloy is customized into rectangular thin die-cast sheets with specifications of 1cm×1cm×1mm for surface morphology and chemical valence state detection and 3cm×1cm×1mm for electrochemical detection such as polarization curves and impedance spectra; the AZ31 magnesium alloy sample is placed in deionized water for cleaning at room temperature for 1 minute, and then immersed in anhydrous ethanol for cleaning at room temperature for 1 minute. The treated sample is placed in an oven for drying at 120°C for 1 hour to complete the pretreatment.

[0046] In the present invention, the soaking temperature is 40-50° C., preferably 40° C.; the soaking time is 20-25 min, preferably 20 min.

[0047] In the embodiment of the present application, after the soaking is completed, the obtained AZ31 magnesium alloy needs to be cleaned, degreased and dried, wherein the cleaning and degreasing is to clean the passivated AZ31 magnesium alloy by using distilled water and anhydrous ethanol successively; and the drying is to air dry the cleaned AZ31 magnesium alloy.

[0048] The technical solutions provided by the present application are described in detail below in combination with the embodiments, but they should not be understood as limiting the protection scope of the present application.

[0049] In the embodiment of the present application, the purity of praseodymium chloride is ≥99.99%, the purity of cerium chloride is ≥99.99%, and the concentration of hydrogen peroxide solution is 30 wt.%.

[0050] Embodiment 1

[0051] 1g of cerium chloride, 3g of praseodymium chloride, 16.67g of hydrogen peroxide solution and 79.33g of deionized water are mixed to prepare a rare earth passivation solution;

[0052] (1) Pretreatment of AZ31 magnesium alloy: the AZ31 magnesium alloy is customized to have a size of 1cm×1cm×1mm, which is used for surface morphology and chemical valence state detection, and a size of 3cm×1cm×1mm, which is used for electrochemical detection such as polarization curve and impedance spectrum; the AZ31 magnesium alloy sample is cleaned in deionized water at room temperature for 1min, and then is cleaned in anhydrous ethanol at room temperature for 1min; and the treated sample is dried in an oven at 120℃ for 1h, to complete the pretreatment.

[0053] (2) The pretreated AZ31 magnesium alloy is soaked in the rare earth passivation solution at 40℃ for 20min; the passivated AZ31 magnesium alloy sample is cleaned successively by using anhydrous ethanol and deionized water; and the AZ31 magnesium alloy sample is naturally air dried, to complete the preparation of the rare earth conversion film on the surface of the AZ31 magnesium alloy material.

[0054] Embodiment 2

[0055] The difference from Embodiment 1 is only that 2g of cerium chloride, 2g of praseodymium chloride, 16.67g of hydrogen peroxide solution and 79.33g of deionized water are mixed to prepare a rare earth passivation solution; and the AZ31 magnesium alloy is treated by using the rare earth passivation solution.

[0056] Embodiment 3

[0057] The difference from Embodiment 1 is only that 3g of cerium chloride, 1g of praseodymium chloride, 16.67g of hydrogen peroxide solution and 79.33g of deionized water are mixed to prepare a rare earth passivation solution; and the AZ31 magnesium alloy is treated by using the rare earth passivation solution.

[0058] Example 4

[0059] The only difference from Example 1 is that 4 g of cerium chloride, 4 g of praseodymium chloride, 14.67 g of hydrogen peroxide solution and 77.33 g of deionized water are mixed to prepare a rare earth passivation solution; and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0060] Example 5

[0061] The only difference from Example 1 is that the pretreated AZ31 magnesium alloy is placed in a rare earth passivation solution and immersed at 50° C. for 20 minutes.

[0062] Comparative Example 1

[0063] Only pretreatment was performed on AZ31 magnesium alloy.

[0064] Comparative Example 2

[0065] The only difference from Example 1 is that 4 g of cerium chloride, 16.67 g of hydrogen peroxide solution and 79.33 g of deionized water are mixed to prepare a rare earth passivation solution; and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0066] Comparative Example 3

[0067] The only difference from Example 1 is that 4 g of praseodymium chloride, 16.67 g of hydrogen peroxide solution and 79.33 g of deionized water are mixed to prepare a rare earth passivation solution; and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0068] Comparative Example 4

[0069] The only difference from Example 1 is that the AZ31 magnesium alloy is replaced by AZ91D magnesium alloy.

[0070] Comparative Example 5

[0071] The only difference from Example 1 is that the AZ31 magnesium alloy is replaced by 301 stainless steel magnesium alloy.

[0072] Comparative Example 6

[0073] The only difference from Example 1 is that the AZ31 magnesium alloy is replaced by 304 stainless steel magnesium alloy.

[0074] Comparative Example 7

[0075] The only difference from Example 1 is that 3 g of CeCl3, 2.5 g of hydrogen peroxide solution, and 94.5 g of water are mixed to prepare a rare earth passivation solution; and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0076] Comparative Example 8

[0077] The only difference from Example 1 is that 10 g of citric acid, 10 g of hydrogen peroxide solution, 2.06 g of sodium molybdate, 2.22 g of CeCl3, and 75.72 g of deionized water are used to prepare a rare earth passivation solution, and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0078] Comparative Example 9

[0079] The only difference from Example 1 is that 10 g of hydrogen peroxide solution, 4 g of citric acid and 86 g of water are mixed to prepare a rare earth passivation solution; and the rare earth passivation solution is used to treat the AZ31 magnesium alloy.

[0080] Comparative Example 10

[0081] The only difference from Example 1 is that the pretreated AZ31 magnesium alloy is placed in a rare earth passivation solution and immersed at 20° C. for 20 minutes.

[0082] Comparative Example 11

[0083] The only difference from Example 1 is that the pretreated AZ31 magnesium alloy is placed in a rare earth passivation solution and immersed at 30° C. for 20 minutes.

[0084] Comparative Example 12

[0085] The only difference from Example 1 is that the pretreated AZ31 magnesium alloy is placed in a rare earth passivation solution and immersed at 60° C. for 20 minutes.

[0086] Test Case

[0087] A CHI760E electrochemical workstation was used to test a 3cm×1cm×1mm AZ31 magnesium alloy. The passivated samples of Examples 1 to 5 and Comparative Examples 1 to 12 were placed in 3wt.% NaCl and tested using a three-electrode test system (working electrode, platinum sheet as auxiliary electrode, saturated calomel electrode as reference electrode). At room temperature and pressure, the AC impedance spectroscopy (EIS) test frequency was 100,000 Hz high frequency, 0.5 Hz low frequency, and the open circuit potential was the initial voltage. For polarization curve testing, the scan rate was 10 mV per second, the voltage was set to 0V for the high potential, and -1.4V for the low potential. When fitting using Zview software, the circuit diagram used is shown in the attached figure. Figure 2 The test results are as follows. Figures 3 to 10 As shown in Table 1:

[0088] Table 1 Impedance values ​​and polarization corrosion potential values ​​of AZ31 magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 12

[0089] sample Self-corrosion potential / V Impedance value Z' / Ω Example 1 -0.684 5161.3 Example 2 -0.733 2969.6 Example 3 -0.742 2765.0 Example 4 -0.715 2635.7 Example 5 -0.704 4467.6 Comparative Example 1 -0.704 1590.5 Comparative Example 2 -0.732 3145.1 Comparative Example 3 -0.742 3194.4 Comparative Example 4 -0.735 2588.2 Comparative Example 5 -0.717 3284.5 Comparative Example 6 -0.715 3542.5 Comparative Example 7 -0.734 3147.1 Comparative Example 8 -0.741 2592.4 Comparative Example 9 -0.716 2149.5 Comparative Example 10 -0.718 3194.4 Comparative Example 11 -0.698 3857.9 Comparative Example 12 -0.670 3450.9

[0090] Polarization curves show that the more positive the corrosion voltage and the smaller the corrosion current, the better the corrosion resistance of the coating. A larger capacitance arc radius in the AC impedance spectrum corresponds to a smaller constant, and the resulting Faraday current impedance is larger, indicating that the film layer has a greater resistance effect, making it more difficult for reactions to occur on the electrode surface, and thus, the better the corrosion resistance. Figure 3 and Figure 4 These are the AC impedance spectra and polarization curves of Examples 1 to 5. Figure 5 and Figure 6 These are the AC impedance diagrams and polarization curves of samples of Example 1 and Comparative Examples 1 to 6. Figure 7 and Figure 8 The following are the AC impedance diagrams and polarization curves of the samples of Example 1 and Comparative Examples 7 to 12. Figures 3 to 8 As shown in Table 1, a comparison of the corrosion potential and impedance spectrum values ​​of the five examples and the 12 comparative examples shows that Example 1 has the highest impedance spectrum value of 5161.3Ω and the highest corrosion potential of -0.684V, indicating that it has the best corrosion resistance. Therefore, AZ31 magnesium alloy has the best corrosion resistance in this rare earth passivation solution.

[0091] Scanning electron microscopy (SEM) examination: 1cm×1cm×1mm AZ31 magnesium alloy. The SEM conditions used were: ETD detector, SE signal mode, magnification 4894x, working distance 8.5mm, accelerating voltage 10.00kV, beam current 25pA, and spot size 6.0.

[0092] Comparative Example 1( Figure 9 (a)), Comparative Example 10 ( Figure 9 (b)), Example 1 ( Figure 9 (c)), Comparative Example 12 ( Figure 9 (d)) SEM image Figure 9 As shown by Figure 9 It can be seen that there are uneven scratches of varying depths on the surface of Comparative Example 1. However, it can be clearly seen that there are no scratches on the surface of Example 1, and there is a thin film of uneven thickness on the surface. A large number of lumps are formed on the surface of Comparative Example 10, and a uniform and smooth film is formed on the bottom. The passivation film formed on the surface of Comparative Example 12 is uneven, and cracks of varying sizes are formed. It can be seen from the electron microscope scanning image that as the passivation temperature increases, the passivation film formed shows that when the passivation temperature is 40°C (Example 1), it is optimal, but when the passivation temperature is gradually increased, cracks will appear in the passivation film, thereby reducing its corrosion resistance. Combining the polarization diagram and the impedance spectrum, it is concluded that the best passivation temperature is 40°C.

[0093] Energy dispersive spectrometer (EDS) detection: 1cm×1cm×1mmAZ31 magnesium alloy, the EDS diagram of Example 1 is as follows Figure 10 As shown by Figure 10It can be seen that a relatively uniform oxide film has formed on the surface of the magnesium alloy, adhering to the substrate material, but it does not completely cover the substrate. Scanning images (a), (b), (c), (d), (e), (f), and (d) show the distribution of Mg, Al, Ce, Mn, Cl, and Mn in the rare earth cerium salt passivation film on the passivated AZ31Mg-A surface. The oxide film is primarily composed of cerium and praseodymium, but since it does not completely cover the substrate, metallic elements such as Mg and Al are also present in the elemental distribution.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A rare earth passivation solution, characterized in that: The method comprises the following components in parts by weight: 3 to 8 parts of a film-forming agent, 10 to 20 parts of an accelerator, and 70 to 85 parts of water; The film-forming agents are cerium chloride and praseodymium chloride.

2. The rare earth passivation solution according to claim 1, wherein The mass ratio of the cerium chloride to the praseodymium chloride is 1:0.3-3.

3. The rare earth passivation solution according to claim 1, wherein The accelerator is hydrogen peroxide solution.

4. The rare earth passivation solution according to claim 3, wherein The concentration of the hydrogen peroxide solution is 25-35 wt.%.

5. The method for preparing the rare earth passivation solution according to any one of claims 1 to 4, characterized in that: The following steps are involved: The film-forming agent, the accelerator and water are mixed to obtain a rare earth passivation solution.

6. A method for preparing a rare earth passivation film on a magnesium alloy surface, characterized in that: The following steps are involved: The magnesium alloy is placed in the rare earth passivation solution according to any one of claims 1 to 4 and immersed therein to complete the preparation of the rare earth passivation film on the surface of the magnesium alloy.

7. The preparation method according to claim 6, characterized in that The magnesium alloy is AZ31 magnesium alloy.

8. The preparation method according to claim 6, characterized in that The soaking temperature is 40-50° C. and the soaking time is 20-25 minutes.

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