A method for preparing a rare earth passivation film on a magnesium alloy surface

Abstract

The present application relates to the technical field of corrosion resistance of metal materials, and particularly relates to a preparation method of a rare earth passivation film on a magnesium alloy surface. The preparation method comprises the following steps: performing surface pretreatment on the magnesium alloy; immersing the pretreated magnesium alloy into a passivation solution containing yttrium oxide and hydrogen peroxide to perform passivation treatment; after the passivation is completed, cleaning and drying the sample to obtain the magnesium alloy covered with the rare earth passivation film on the surface. The preparation method is used to prepare the passivation film on the magnesium alloy surface, and the corrosion resistance of the AZ31B magnesium alloy is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of corrosion resistance research technology for metallic materials, and in particular to a method for preparing a rare earth passivation film on the surface of a magnesium alloy. Background Technology

[0002] Magnesium alloys, due to their high specific strength, excellent electromagnetic shielding properties, and good biocompatibility, show broad application prospects in aerospace, automotive, electronics and communications, and biomedical fields. However, magnesium (Mg) is chemically highly reactive, with a low standard electrode potential. Although a natural oxide film can form on its surface during use, this natural oxide film is porous and cannot provide effective corrosion protection to the substrate. Especially in harsh environments or specific media such as high humidity, salt spray, or acidic conditions, the corrosion resistance of magnesium alloys significantly decreases, severely limiting their widespread application in environments requiring high corrosion resistance. Therefore, developing efficient and environmentally friendly surface protection technologies to improve the corrosion resistance of magnesium alloys has become a current research hotspot and challenge.

[0003] To improve the corrosion resistance of magnesium alloys, researchers have developed various surface treatment technologies, such as anodizing, micro-arc oxidation, electroless plating, organic coatings, and chemical conversion treatments. Among these, chemical conversion treatment has demonstrated outstanding competitiveness in the field of metal surface engineering due to its significant advantages, including no limitations on workpiece shape and size, simple operation, low cost, uniform and rapid film formation, and strong adhesion to subsequent organic coatings. Traditional chemical conversion treatment processes mainly include alkaline washing, acid etching, and drying. Currently, chromate conversion treatment and phosphate conversion treatment are relatively mature applications. However, although chromate conversion films have excellent corrosion resistance and self-healing capabilities, hexavalent chromium is highly toxic and carcinogenic, seriously harming the environment and human health, and its use is subject to increasingly stringent regulations. Therefore, the development of chromium-free, environmentally friendly, and efficient chemical conversion treatment technologies is particularly urgent. Summary of the Invention

[0004] Based on the above, this invention provides a method for preparing a rare earth passivation film on the surface of a magnesium alloy. This invention can improve the corrosion resistance of AZ31B magnesium alloy, extend its service life, and reduce the usage and protection costs of AZ31B magnesium alloy.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a rare earth passivation film on a magnesium alloy surface, comprising the following steps: Surface pretreatment of magnesium alloys; The pretreated magnesium alloy was immersed in a passivation solution containing yttrium oxide (Y2O3) and hydrogen peroxide (H2O2) for passivation treatment. After passivation, the sample is cleaned and dried to obtain a magnesium alloy with a rare earth passivation film on the surface.

[0006] In this invention, Y2O3 is used as a film-forming agent and H2O2 solution is used as a promoter.

[0007] The second technical solution of the present invention is a method for improving the corrosion resistance of magnesium alloys, wherein a passivation film is prepared on the surface of magnesium alloys using the above-mentioned preparation method to improve the corrosion resistance of magnesium alloys.

[0008] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a single rare earth yttrium oxide (Y2O3) modification technique. By adding an appropriate amount of rare earth, the electrochemical activity of the AZ31B magnesium alloy surface is reduced, significantly improving the corrosion resistance of the AZ31B magnesium alloy, while also enhancing the film adhesion and self-healing ability.

[0009] The principle behind this invention for improving the corrosion resistance of magnesium alloys lies in the fact that electrochemical corrosion is a common form of metal corrosion. Because AZ31B magnesium alloy contains a second phase β-Mg... 17 Al 12 This phase, which has a potential difference with the magnesium matrix, causes the magnesium matrix to preferentially dissolve as an anode, thus accelerating the corrosion of AZ31B magnesium alloy, especially in Cl-containing alloys. - Corrosion is particularly accelerated in the medium. Adding appropriate amounts of rare earth elements can reduce the electrochemical activity of the AZ31B magnesium alloy surface and decrease Cl... - The adsorption of corrosive ions increases the polarization resistance, thereby inhibiting the rate of electrochemical corrosion reaction. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a process flow diagram of the preparation of rare earth passivation film on the surface of AZ31B magnesium alloy according to the present invention; Figure 2 Circuit diagram for fitting AC impedance spectroscopy of an electrochemical workstation; Figure 3 The AC impedance diagram for the blank group in Example 1; Figure 4 The polarization curves for the blank group in Example 1; Figure 5 The AC impedance diagrams for different passivation times in Example 2 are shown. Figure 6 The graph shows the polarization curves for different passivation times in Example 2. Figure 7 SEM images of the surface morphology of magnesium alloys after passivation in the blank group and Examples 2-4 are shown. Among them, (a) blank, (b) passivation time of 50 min in Example 2 (1 wt.%, 20℃, 50 min), (c) passivation temperature of 20℃ in Example 3 (2 wt.%, 20℃, 50 min), and (d) rare earth mass fraction of 1 wt.% in Example 4 (1 wt.%, 40℃, 50 min). Figure 8 Impedance diagrams at different passivation temperatures in Example 3; Figure 9 The graph shows the polarization curves at different passivation temperatures in Example 3. Figure 10 Impedance diagrams for different rare earth mass fractions in Example 4; Figure 11 This is a polarization curve diagram of different rare earth mass fractions in Example 4. Detailed Implementation

[0012] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0013] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0014] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0015] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0016] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0017] Unless otherwise specified, "room temperature" in this invention refers to 20~30℃.

[0018] The first aspect of this invention provides a method for preparing a rare earth passivation film on a magnesium alloy surface, comprising the following steps: Surface pretreatment of magnesium alloys; The pretreated magnesium alloy was immersed in a passivation solution containing yttrium oxide (Y2O3) and hydrogen peroxide (H2O2) for passivation treatment. After passivation, the sample is cleaned and dried to obtain a magnesium alloy with a rare earth passivation film on the surface.

[0019] In this invention, Y2O3 is used as a film-forming agent and H2O2 solution is used as a promoter.

[0020] In a preferred embodiment of the present invention, the passivation solution contains 1% to 5% yttrium oxide, 2.4% to 2.5% hydrogen peroxide, and the balance being deionized water, by mass percentage.

[0021] In a preferred embodiment of the present invention, the passivation treatment conditions are set as follows: the passivation temperature is 20~60℃, and the passivation time is 20~60 minutes.

[0022] In a preferred embodiment of the present invention, the surface pretreatment includes: sanding with sandpaper, polishing with polishing cloth, cleaning with anhydrous ethanol, rinsing with deionized water, and then drying.

[0023] In a preferred embodiment of the present invention, the drying conditions are set as follows: drying at 200°C for 10 minutes.

[0024] In a preferred embodiment of the present invention, the magnesium alloy is AZ31B magnesium alloy.

[0025] In a preferred embodiment of the present invention, the cleaning step includes washing with anhydrous ethanol and distilled water in sequence; the drying is natural air drying.

[0026] A second aspect of the present invention provides a method for improving the corrosion resistance of magnesium alloys, wherein a passivation film is prepared on the surface of the magnesium alloy using the above-described preparation method to improve the corrosion resistance of the magnesium alloy.

[0027] This invention significantly improves the corrosion resistance of AZ31B magnesium alloy: when the rare earth content is 1 wt.%, the temperature is room temperature, and the passivation time is 50 min, the system exhibits the maximum capacitive arc diameter (1262.2 mm). The self-corrosion potential reached its maximum at approximately -0.714 V, which was 0.12 V higher than the control group (without any passivation treatment). This phenomenon is due to the passivation effect of yttrium oxide, which significantly improves the stability of the passivation film.

[0028] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0029] The Y2O3 used in the embodiments of this invention was purchased from Chengdu Ounrui Chemical Reagent Co., Ltd., with a purity of ≥99.9% and a particle size of 1-5 micrometers.

[0030] The testing method involved in this invention is as follows: Electrochemical detection: A CHI660D electrochemical workstation was used for detection. The passivated sample was placed in 3.5 wt.% NaCl, and a three-electrode testing system (working electrode, platinum sheet as auxiliary electrode, and saturated calomel electrode as reference electrode) was used for testing. AC impedance spectroscopy was measured at room temperature and pressure, with EIS measured at the open-circuit potential. The EIS test frequency was 10 kHz for the high frequency and 1 Hz for the low frequency, with the open-circuit potential being the initial voltage. Polarization curve testing was performed at a scan rate of 0.01 V / s, with the voltage set to 0 V for the high potential and -1.0 V for the low potential, and 1 s for the number of scan segments.

[0031] Scanning electron microscopy (SEM) examination: 1 cm × 1 cm × 10 mm AZ31B magnesium alloy. Parameter settings were: magnification 4894x, working distance 8.5 mm, accelerating voltage 10.00 kV, beam current 25 pA, beam spot size 6.0.

[0032] The circuit diagram used when fitting the circuit using Zview software is attached. Figure 2 .

[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1 (Blank Group) Take an AZ31B magnesium alloy plate and cut it into samples with dimensions of 1 cm × 1 cm × 0.1 cm (for scanning electron microscopy surface morphology observation) and 3 cm × 1 cm × 0.1 cm (for electrochemical performance testing).

[0035] The pretreatment steps are as follows: The sample surface is successively polished with 500-grit and 900-grit water-based sandpaper to remove the surface oxide layer and impurities; then, the polished surface is polished with a polishing cloth to obtain a smooth and clean surface. The polished sample is immersed in anhydrous ethanol and ultrasonically cleaned at room temperature for 1 min (the purpose is to remove oil; this invention does not specifically limit the ultrasonic power, and the ultrasonic power commonly used by those skilled in the art can be used); after removal, it is rinsed 2-3 times with deionized water; finally, it is placed in an oven and dried at 200℃ for 10 min to obtain the pretreated blank sample. The impedance and polarization diagram of the blank sample are shown below. Figure 3 and Figure 4 As shown. By Figure 3 and Figure 4 It can be seen that the impedance and self-corrosion potential of the blank sample are relatively small, with detailed values ​​of 340 Ω and -0.714 V, respectively.

[0036] The pretreated blank samples were directly subjected to electrochemical tests and surface morphology observations, serving as a control group.

[0037] Example 2 (Single rare earth yttrium oxide passivation film - passivation time gradient optimization) According to the mass fractions, 90.7 parts of deionized water, 8.3 parts of 30 wt.% H2O2 solution, and 1 part of Y2O3 were mixed to obtain a passivation solution with a Y2O3 mass fraction of 1%. The blank sample prepared in Example 1 was immersed in the passivation solution and passivated in a 20°C water bath for 20–60 min (five gradients were set: 20 min, 30 min, 40 min, 50 min, and 60 min; timing began when the blank sample was placed in the passivation solution). After passivation, the sample was removed and washed successively with anhydrous ethanol and distilled water, then allowed to air dry naturally to obtain an AZ31B magnesium alloy sample with a rare earth passivation film on its surface. Its impedance and polarization diagrams are shown below. Figure 5 and Figure 6 As shown.

[0038] Depend on Figure 5 and Figure 6 It can be seen that: the AC impedance curve is as follows Figure 5 As shown, the impedance arc radius gradually increases to its maximum value from 20 min to 50 min, and then decreases from 50 min to 60 min. After reaching its maximum value, the impedance arc radius decreases slightly. Existing research indicates that a larger impedance arc radius results in greater charge transfer resistance, making the corrosion reaction more difficult and leading to better corrosion resistance of the coating. Therefore, yttrium oxide passivation provides the best corrosion resistance for AZ31B magnesium alloy at a passivation time of 50 min. The polarization curves are shown below. Figure 6As shown, the self-corrosion potential gradually increases to its maximum value from 20 min to 50 min; from 50 min to 60 min, the self-corrosion potential shows a decreasing trend, and is still greater than that of the control group. The self-corrosion potential first rises to its maximum value and then decreases. Previous studies have shown that the higher the self-corrosion potential, the stronger the corrosion resistance. Therefore, yttrium oxide passivation provides the best corrosion resistance for AZ31B magnesium alloy at a passivation time of 50 min. Experimental results show that the optimal passivation time is 50 min. At this time, the corrosion resistance is optimal, i.e., the self-corrosion potential is the largest and the impedance spectrum capacitive arc radius is the largest, with a self-corrosion potential of -0.726 V and an impedance value of 1262.2 Ω. Compared to the control group, the self-corrosion potential increases by 0.014 V, and the impedance value increases by 922.2 Ω.

[0039] Example 3 (Single rare earth yttrium oxide passivation film - passivation temperature gradient optimization) According to the mass fractions, 89.7 parts of deionized water, 8.3 parts of 30 wt.% H2O2 solution, and 2 parts of Y2O3 were mixed to obtain a passivation solution with a Y2O3 mass fraction of 2%. The blank sample prepared in Example 1 was immersed in the passivation solution and passivated for 50 minutes in a water bath at 20-60℃ (five temperature gradients were set: 20℃, 30℃, 40℃, 50℃, and 60℃, with timing starting from the moment the blank sample was placed in the passivation solution). After passivation, the sample was removed and washed successively with anhydrous ethanol and distilled water, then allowed to air dry naturally, resulting in an AZ31B magnesium alloy sample with a rare earth passivation film on its surface. Its impedance and polarization diagrams are shown below. Figure 8 and Figure 9 As shown.

[0040] Depend on Figure 8 and Figure 9 It can be seen that: the AC impedance curve is as follows Figure 8 As shown, the impedance arc radius decreases gradually from 20 ℃ to 60 ℃, reaching its minimum value, and exhibits a decreasing trend. Therefore, yttrium oxide passivation provides the best corrosion resistance to AZ31B magnesium alloy at a passivation temperature of 20 ℃. The polarization curves are shown below. Figure 9 As shown, the self-corrosion potential gradually decreases to a minimum as the temperature increases from 20 ℃ to 50 ℃, and increases slightly from 50 ℃ to 60 ℃, both exceeding those of the control group. The self-corrosion potential first decreases to a minimum and then increases slightly. Therefore, yttrium oxide passivation provides the best corrosion resistance for AZ31B magnesium alloy at a passivation temperature of 20 ℃. The experimental results show that the optimal passivation temperature is 20 ℃. At this temperature, the corrosion resistance is optimal, with the highest self-corrosion potential and the largest capacitive arc radius in the impedance spectrum. The self-corrosion potential is -0.718 V, and the impedance value is 789.37 Ω. Compared to the control group, the self-corrosion potential increases by 0.022 V, and the impedance value increases by 449.37 Ω.

[0041] Example 4 (Single rare earth yttrium oxide passivation film - rare earth mass fraction gradient optimization) Based on a mass fraction of 100 parts, 8.3 parts of a 30 wt.% H2O2 solution, 1-5 parts of Y2O3, and the remainder deionized water were mixed to obtain passivation solutions with Y2O3 mass fractions of 1%, 2%, 3%, 4%, and 5%. The blank sample prepared in Example 1 was immersed in the passivation solution and passivated for 50 minutes in a 20°C water bath (timing started when the blank sample was placed in the passivation solution). After passivation, the sample was removed and washed successively with anhydrous ethanol and distilled water, then allowed to air dry naturally, resulting in an AZ31B magnesium alloy sample with a rare earth passivation film on its surface. Its impedance and polarization diagrams are shown below. Figure 10 and Figure 11 As shown.

[0042] Depend on Figure 10 and Figure 11 It can be seen that: the AC impedance curve is as follows Figure 10 As shown, the impedance arc radius gradually decreases from 1% to 5% of the mass fraction, reaching a minimum value, and is still larger than the value of the blank group, indicating a decreasing trend. A larger impedance arc radius means greater charge transfer resistance, making corrosion reaction more difficult and resulting in better corrosion resistance of the coating. Therefore, yttrium oxide passivation at a passivation mass fraction of 1% provides the best corrosion resistance for AZ31B magnesium alloy. The polarization curves are shown below. Figure 11 As shown, as the mass fraction increases from 1% to 3%, the self-corrosion potential gradually decreases to a minimum, rises to a maximum from 3% to 4%, and decreases again from 4% to 5%. After decreasing to a minimum, the self-corrosion potential rises to a maximum again, and then decreases slightly. Therefore, yttrium oxide passivation provides the best corrosion resistance for AZ31B magnesium alloy when the passivation mass fraction is 1%. The experimental results show that the optimal mass fraction of yttrium oxide for passivation is 1 wt.%. At this point, the corrosion resistance is optimal, i.e., the self-corrosion potential is the largest and the impedance spectrum capacitive arc radius is the largest, with a self-corrosion potential of -0.724 V and an impedance value of 1262.2 Ω. Compared to the blank group, the self-corrosion potential increases by 0.016 V, and the impedance value increases by 922.2 Ω.

[0043] The surface morphology of the identified optimal condition group was analyzed using SEM to explore its surface morphology characteristics, such as... Figure 7 As shown. Figure 7 In the middle (a) is the blank control group, which only underwent cleaning and drying treatment before surface morphology detection. Figure 7 As shown in (a), no obvious corrosion-resistant coating was observed on the surface of the magnesium alloy; Figure 7 (b) shows the optimal passivation conditions for yttrium oxide: passivation time 50 min, passivation temperature 20 ℃, and mass fraction 1 wt.%. Surface morphology was then examined after passivation. Figure 7(c) shows the surface morphology after passivation with yttrium oxide for 50 min, 20 ℃, and 2 wt.% by mass. Figure 7 (d) Surface morphology was examined after passivation with yttrium oxide for 50 min, at a passivation temperature of 40 ℃, and with a mass fraction of 1 wt.%. All three images show a clearly resistant corrosion coating, which is significantly better than under other conditions. Figure 7 The coating on surface (b) is the most uniform and shows no obvious cracks, indicating the best passivation effect.

[0044] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a rare earth passivation film on a magnesium alloy surface, characterized in that, Includes the following steps: Surface pretreatment of magnesium alloys; The pretreated magnesium alloy was immersed in a passivation solution containing yttrium oxide and hydrogen peroxide for passivation treatment. After passivation, the sample is cleaned and dried to obtain a magnesium alloy with a rare earth passivation film on the surface.

2. The preparation method according to claim 1, characterized in that, The passivation solution contains 1% to 5% yttrium oxide, 2.4% to 2.5% hydrogen peroxide, and the balance is deionized water, by mass percentage.

3. The preparation method according to claim 1, characterized in that, The passivation conditions are set as follows: passivation temperature is 20~60℃, and passivation time is 20~60 minutes.

4. The preparation method according to claim 1, characterized in that, The surface pretreatment includes: sanding with sandpaper, polishing with polishing cloth, cleaning with anhydrous ethanol, rinsing with deionized water, and then drying.

5. The preparation method according to claim 4, characterized in that, The drying conditions are set as follows: dry at 200°C for 10 minutes.

6. The preparation method according to claim 1, characterized in that, The magnesium alloy is AZ31B magnesium alloy.

7. The preparation method according to claim 1, characterized in that, The cleaning steps include washing with anhydrous ethanol and distilled water in sequence; the drying is natural air drying.

8. A method for improving the corrosion resistance of magnesium alloys, characterized in that, A passivation film is prepared on the surface of a magnesium alloy using the preparation method described in any one of claims 1 to 7, so as to improve the corrosion resistance of the magnesium alloy.

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