Method for in-situ synthesis of CePO4 micro-arc oxidation composite coating

Abstract

The invention discloses a method for in-situ synthesis of a CePO4 micro-arc oxidation composite coating. The method comprises the following steps: carrying out decontamination treatment on the surface of a magnesium alloy sample; a micro-arc oxidation solution is added into an electrolytic cell, the treated magnesium alloy sample serves as an anode, a stainless steel barrel serves as a cathode, and the magnesium alloy sample and the stainless steel barrel are immersed into the micro-arc oxidation solution; adding a Ce source into the micro-arc oxidation solution, wherein the Ce source is a 0-5g / L Ce (CH3CO2) 3 * xH2O solution; and an electrolytic tank is externally connected with a stirrer and a water cooling system, micro-arc oxidation treatment is conducted in a constant-current mode, and the MAO / CePO4 composite coating is obtained. The micro-arc oxidation coating containing CePO4 is synthesized on the surface of the magnesium alloy in situ, so that the wear resistance and corrosion resistance of the magnesium alloy are improved.

Description

Technical Field

[0001] The invention relates to a method for in-situ synthesizing a CePO4 micro-arc oxidation composite coating, and belongs to the field of corrosion-resistant composite coatings of metal materials. Background Art

[0002] Magnesium and its alloys have excellent properties such as low density, high specific strength, and good recyclability, and have broad application prospects in the fields of automobiles, aerospace, biomedicine, and electronic products. However, the electrochemical activity of magnesium alloys is too high, which makes them extremely susceptible to corrosion. This characteristic seriously limits the application of magnesium alloys. In order to solve the problem of magnesium alloys' poor corrosion resistance, scientific researchers have introduced many surface treatment measures to improve the corrosion resistance of magnesium alloys. Micro-arc oxidation (MAO) is widely used in the field of protection, and its film layer has high adhesion to the substrate, high hardness and high corrosion resistance. However, as the application environment becomes increasingly harsh, relying on traditional micro-arc oxidation coatings can no longer meet people's needs.

[0003] Rare earth elements play a significant role in improving material performance and are favored by researchers. Rare earth (RE)-based coatings on magnesium alloys have very broad research prospects. Among them, the rare earth element Ce has corrosion inhibition and self-healing properties. The Ce compound CePO4 itself has excellent chemical stability. After corrosion and hydrolysis, CePO4 generates water-insoluble Ce(OH)3. In addition, CePO4 is a very excellent lubricating phase with excellent sliding ability. Therefore, the rare earth element Ce can effectively compensate for the defects of the micro-arc oxidation ceramic layer and improve the corrosion resistance of the film layer. Unlike the direct addition of particles, in-situ synthesis of micro-arc oxidation can make the target substance and the micro-arc oxidation film layer more tightly bonded and more evenly distributed, greatly improving performance. However, for active metals such as magnesium alloys, excessive ions lead to uncertainty in the reaction process, limiting the development and further application of in-situ synthesis. Thus, this application uses a simple micro-arc oxidation process to in-situ synthesize a CePO4-containing micro-arc oxidation coating on the surface of a magnesium alloy, thereby providing better protection for the magnesium alloy substrate, inhibiting the occurrence of corrosion processes, and improving the wear and corrosion resistance of the magnesium alloy. This method is simple, feasible, and easy to operate, and the resulting magnesium alloy MAO / CePO4 composite coating has high wear and corrosion resistance. Summary of the Invention

[0004] The present invention designs and develops a method for in-situ synthesis of CePO4 micro-arc oxidation composite coating, which in-situ synthesizes CePO4-containing micro-arc oxidation coating on the surface of magnesium alloy, thereby improving the wear resistance and corrosion resistance of magnesium alloy.

[0005] The technical solution provided by the present invention is:

[0006] A method for in-situ synthesis of a CePO4 micro-arc oxidation composite coating, comprising:

[0007] Decontamination treatment is performed on the surface of the magnesium alloy sample;

[0008] Add micro-arc oxidation solution into the electrolytic cell, use the treated magnesium alloy sample as the anode and the stainless steel barrel as the cathode, and immerse them in the micro-arc oxidation solution;

[0009] Adding a Ce source to the micro-arc oxidation solution, which is a 0-5 g / L Ce(CH3CO2)3·xH2O solution;

[0010] The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

[0011] Preferably, the electrical parameters for micro-arc oxidation treatment in the constant current mode include:

[0012] The processing frequency is 800HZ;

[0013] The duty cycle is 15%;

[0014] The current density is 24A / dm 2 ;

[0015] The micro-arc oxidation time was 10 min.

[0016] Preferably, the micro-arc oxidation solution is composed of:

[0017] 20g / L (NaPO3)6 solution and 10g / L NaF solution.

[0018] Preferably, the decontamination treatment includes:

[0019] The surface of the magnesium alloy specimen was polished step by step using metallographic sandpapers of #120, #600, #800, and #1200 in sequence;

[0020] The polished magnesium alloy specimens were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 3 to 5 minutes, respectively, to obtain magnesium alloy specimens with residues and oil removed.

[0021] Preferably, the (NaPO 3 ) 6 solution, the NaF solution, the Ce(CH 3 CO 2 ) 3 ·xH 2 O solution, the anhydrous ethanol and the isopropanol are all chemically pure or higher.

[0022] The present invention provides the following beneficial effects: A micro-arc oxidation coating containing CePO₄ is synthesized in situ on the surface of a magnesium alloy through a simple micro-arc oxidation process, thereby providing enhanced protection for the magnesium alloy substrate, inhibiting the occurrence of corrosion processes, and improving the wear and corrosion resistance of the magnesium alloy. This method is simple, feasible, and easy to operate, and the resulting magnesium alloy MAO / CePO₄ composite coating exhibits high wear and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1( a ) is a low-magnification SEM image of the coating surface of the Ce-0 sample described in the present invention.

[0024] FIG1( b ) is a high-magnification SEM image of the coating surface of the Ce-0 sample described in the present invention.

[0025] FIG1( c ) is a low-magnification SEM image of the coating surface of the Ce-2.5 sample described in the present invention.

[0026] FIG1( d ) is a high-magnification SEM image of the coating surface of the Ce-2.5 sample described in the present invention.

[0027] FIG1(e) is a low-magnification SEM image of the coating surface of the Ce-5 sample described in the present invention.

[0028] FIG1( f ) is a high-magnification SEM image of the coating surface of the Ce-5 sample described in the present invention.

[0029] FIG2( a ) is an XRD pattern of the surfaces of four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0030] FIG2( b ) is a high-resolution spectrum of the Ce element in the XPS spectrum of the Ce-5 sample coating of the present invention.

[0031] FIG3( a ) shows the COF curves of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0032] Figure 3(b) shows the wear profile trajectories of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0033] Figure 4 These are the Tafel curves of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0034] Figure 5 These are the Nyquist diagrams of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0035] Figure 6This is the Bode modulus diagram of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0036] Figure 7 This is the Bode phase angle diagram of the four samples of AZ31B, Ce-0, Ce-2.5 and Ce-5 described in the present invention.

[0037] FIG8( a ) is a low-magnification SEM image of the Ce-0 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days.

[0038] FIG8( b ) is a high-magnification SEM image of the Ce-0 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days.

[0039] FIG8( c ) is a low-magnification SEM image of the Ce-2.5 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days.

[0040] FIG8( d ) is a high-magnification SEM image of the Ce-2.5 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days.

[0041] FIG8( e ) is a low-magnification SEM image of the Ce-5 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days.

[0042] FIG8( f ) is a high-magnification SEM image of the Ce-5 sample coating of the present invention after being immersed in a 3.5 wt . NaCl solution for 14 days. DETAILED DESCRIPTION

[0043] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0044] As shown in Figures 1-8, the present invention provides a method for in-situ synthesis of a CePO4 micro-arc oxidation composite coating, which in-situ synthesizes a CePO4-containing micro-arc oxidation coating on the surface of a magnesium alloy to improve the wear resistance and corrosion resistance of the magnesium alloy, comprising:

[0045] Decontamination treatment is performed on the surface of the magnesium alloy sample;

[0046] The surfaces of the magnesium alloy samples were polished step by step using metallographic sandpapers of #120, #600, #800, and #1200, respectively. The polished magnesium alloy samples were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 5 minutes, respectively, to remove residues and oil stains.

[0047] Add micro-arc oxidation solution into the electrolytic cell, use the treated magnesium alloy sample as the anode and the stainless steel barrel as the cathode, and immerse them in the micro-arc oxidation solution;

[0048] The composition of the micro-arc oxidation solution is:

[0049] 20g / L (NaPO3)6 solution and 10g / L NaF solution.

[0050] Adding a Ce source to the micro-arc oxidation solution, which is a 0-5 g / L Ce(CH3CO2)3·xH2O solution;

[0051] The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

[0052] The electrical parameters for micro-arc oxidation treatment in constant current mode include:

[0053] The processing frequency is 800HZ;

[0054] The duty cycle is 15%;

[0055] The current density is 24A / dm 2 ;

[0056] The micro-arc oxidation time was 10 min.

[0057] Example 1

[0058] Decontamination treatment is performed on the surface of the magnesium alloy sample;

[0059] The surfaces of the magnesium alloy samples were polished step by step using metallographic sandpapers of #120, #600, #800, and #1200, respectively. The polished magnesium alloy samples were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 5 minutes, respectively, to remove residues and oil stains.

[0060] Micro-arc oxidation is carried out in a phosphoric acid system using a constant current mode. At room temperature, a micro-arc oxidation solution is added to the electrolytic cell, and the treated magnesium alloy sample is used as the anode and the stainless steel barrel is used as the cathode, which are immersed in the basic micro-arc oxidation solution.

[0061] The basic micro-arc oxidation solution consists of 20 g / L (NaPO3)6 solution and 10 g / L NaF solution;

[0062] A Ce source was added to the basic micro-arc oxidation solution, which was a 0 g / L Ce(CH3CO2)3·xH2O solution. That is, the magnesium alloy sample in this embodiment was only subjected to micro-arc oxidation treatment without the introduction of a Ce source.

[0063] The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

[0064] The electrical parameters set for micro-arc oxidation treatment in constant current mode include:

[0065] The processing frequency is 800HZ;

[0066] The duty cycle is 15%;

[0067] The current density is 24A / dm 2 ;

[0068] The micro-arc oxidation time was 10 min.

[0069] The prepared MAO / CePO4 composite coating was numbered and set as Ce-0.

[0070] Example 2

[0071] Decontamination treatment is performed on the surface of the magnesium alloy sample;

[0072] The surfaces of the magnesium alloy samples were polished step by step using metallographic sandpapers of #120, #600, #800, and #1200, respectively. The polished magnesium alloy samples were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 5 minutes, respectively, to remove residues and oil stains.

[0073] Micro-arc oxidation is carried out in a phosphoric acid system using a constant current mode. At room temperature, a micro-arc oxidation solution is added to the electrolytic cell, and the treated magnesium alloy sample is used as the anode and the stainless steel barrel is used as the cathode, which are immersed in the basic micro-arc oxidation solution.

[0074] The basic micro-arc oxidation solution consists of 20 g / L (NaPO3)6 solution and 10 g / L NaF solution;

[0075] A Ce source of 2.5 g / L Ce(CH3CO2)3·xH2O solution was added to the basic MAO solution;

[0076] The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

[0077] The electrical parameters set for micro-arc oxidation treatment in constant current mode include:

[0078] The processing frequency is 800HZ;

[0079] The duty cycle is 15%;

[0080] The current density is 24A / dm 2 ;

[0081] The micro-arc oxidation time was 10 min.

[0082] The prepared MAO / CePO4 composite coating was numbered and set to Ce-2.5.

[0083] Example 3

[0084] Decontamination treatment is performed on the surface of the magnesium alloy sample;

[0085] The surfaces of the magnesium alloy samples were polished step by step using metallographic sandpapers of #120, #600, #800, and #1200, respectively. The polished magnesium alloy samples were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 5 minutes, respectively, to remove residues and oil stains.

[0086] Micro-arc oxidation is carried out in a phosphoric acid system using a constant current mode. At room temperature, a micro-arc oxidation solution is added to the electrolytic cell, and the treated magnesium alloy sample is used as the anode and the stainless steel barrel is used as the cathode, which are immersed in the basic micro-arc oxidation solution.

[0087] The basic micro-arc oxidation solution consists of 20 g / L (NaPO3)6 solution and 10 g / L NaF solution;

[0088] A Ce source of 5 g / L Ce(CH3CO2)3·xH2O solution was added to the basic MAO solution;

[0089] The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

[0090] The electrical parameters set for micro-arc oxidation treatment in constant current mode include:

[0091] The processing frequency is 800HZ;

[0092] The duty cycle is 15%;

[0093] The current density is 24A / dm 2 ;

[0094] The micro-arc oxidation time was 10 min.

[0095] The prepared MAO / CePO4 composite coating was numbered and set as Ce-5.

[0096] The morphology of the MAO / CePO4 composite coatings prepared in Examples 1 to 3 was analyzed, as shown in Figures 1(a) to (f):

[0097] As can be seen from Figure 1(a), the surface of the Ce-0 coating is highly undulating and has a large number of micropores and cracks.

[0098] As can be seen from Figure 1(b), cracks appear in the pores of the Ce-0 coating, which penetrate through the pores. These open pores provide channels for corrosive media to enter the substrate, which is not conducive to the wear and corrosion resistance of the film.

[0099] It can be seen from Figure 1(c) that the surface flatness and smoothness of the Ce-2.5 coating are significantly improved compared to the Ce-0 sample.

[0100] As can be seen from Figure 1(d), pores sealed by sealing materials begin to appear on the surface of the Ce-2.5 sample coating, which reduces the surface defects of the micro-arc oxidation layer and helps to improve the corrosion resistance of the coating.

[0101] It can be seen from Figure 1 (e) that there is a significant difference in the surface morphology of the Ce-5 sample coating and the Ce-0 sample coating. The surface of the MAO / CePO4 composite coating is significantly smoother than that of the MAO coating, and the degree of surface protrusions, the number and size of holes and cracks on the film layer are significantly reduced.

[0102] As can be seen from Figure 1(f), sealing materials appeared at the pores of the Ce-5 sample coating, and a material that was clearly different from the MAO layer was formed at the edge of the pores. This sealing material sealed the pores, reduced the surface defects of the MAO coating, and was beneficial to improving the corrosion resistance of the film.

[0103] It can be seen that compared with the composite coating without adding Ce source, after adding Ce source, the smoothness and flatness of the coating surface are significantly improved, the number of pore defects on the micro-arc oxidation surface is significantly reduced, the micropores are closed, and the porosity of the film surface is reduced. Especially when the addition amount of Ce source is 5g / L, the effect is optimal.

[0104] The composition analysis was carried out. AZ31B magnesium alloy was used as a comparative example. The XRD composition characterization was carried out together with the surfaces of Ce-0, Ce-2.5 and Ce-5 samples prepared in Examples 1 to 3. The XPS spectrum characterization was also carried out on the coating of Ce-5 sample. As shown in Figure 2(a), the main components of different samples are Mg, MgO, Mg 3( Among them, since phosphates such as Mg3(PO4)2 and CePO4 formed by micro-arc oxidation often overlap at 15-34° and form amorphous peaks containing phosphates, the CePO4 phase cannot be clearly determined. Therefore, XPS spectrum detection was performed on the Ce-5 sample coating.

[0105] As shown in Figure 2(b), the typical characteristics of Ce element can be seen, that is, the Ce 3d 5 / 2 and Ce3d3 / 2 The characteristic peaks are composed of two double peaks. 5 / 2 The binding energies of Ce3d are 882.35eV and 885.4eV respectively. 3 / 2 The binding energies of the two species are 900.45eV and 904.62eV respectively. They are both attributed to Ce. 3+ .

[0106] It was finally determined that in the MAO / CePO4 composite coating prepared by the micro-arc oxidation in-situ synthesis method, the in-situ synthesized CePO4 grew together with the micro-arc oxidation ceramic layer and was contained in the film layer, rather than the residual Ce in the electrolyte. 3+ Adsorbed on the surface of micro-arc oxidation coating.

[0107] Conduct friction performance analysis

[0108] AZ31B magnesium alloy was used as a comparative example and subjected to ball-on-disc friction and wear tests together with Ce-0, Ce-2.5 and Ce-5 samples prepared in Examples 1 to 3. As can be seen from Figure 3(a) and Table 1, since the AZ31B substrate has no coating protection, it is ground into the substrate by the friction ball at the beginning of the ball-on-disc friction process. After about 3 minutes of running-in, the AZ31 substrate has been deeply penetrated into the body by the friction ball. Due to the effect of hard ceramic particles in the friction process, the COF peak of the Ce-0 sample coating is significantly higher than that of the Ce-0 sample. The AZ31B matrix, without the auxiliary effect of the CePO4 reinforcing phase, the protective effect of the film layer was completely broken through after about 3 minutes of friction; the Ce-2.5 sample coating had a stronger protective effect than the Ce-0 sample. The Ce-2.5 sample persisted for more than 5 minutes during the friction running-in process, and the protective effect of the film layer was completely broken through; the Ce-5 sample resisted the longest time during the friction process, about 15 minutes, and in the early stage of friction, due to the enhanced film layer effect and lubrication effect brought by CePO4, the COF curve of the film layer grew slowly and slowly.

[0109] Table 1

[0110] Project Number Comparative Example AZ31 Example 1Ce-0 Example 2Ce-2.5 Example 2Ce-5 Wear time 3min 3min More than 5 minutes 15min

[0111] As can be seen from Figure 3(b) and Table 2, since the AZ31B substrate is not protected during the friction process, its wear scar profile has the largest length and depth, which are 1449.014 μm and 83.578 μm, respectively. The length and depth of the wear scar profile of the Ce-0 coating sample are slightly lower than those of AZ31, which are 1291.242 μm and 70.845 μm, respectively. The length and depth of the wear scar profile of the Ce-2.5 coating sample are further reduced, which are 1233.115 μm and 66.244 μm, respectively. Since the Ce-5 coating sample has the longest resistance to friction, its wear scar profile length and depth are most significantly reduced compared with those of AZ31B, Ce-0 and Ce-2.5 coatings, which are 1228.963 μm and 55.909 μm, respectively.

[0112] Table 2

[0113] Project Number Comparative Example AZ31 Example 1Ce-0 Example 2Ce-2.5 Example 2Ce-5 Wear scar length 1449.014μm 1291.242μm 1233.115μm 1228.963μm Wear scar depth 83.578μm 70.845μm 66.244μm 55.909

[0114] It can be seen that compared with the composite coating without adding Ce source, the overall friction resistance of the composite coating is significantly improved after adding Ce source. During the ball-disc friction process, the friction resistance time is increased from 3min to 15min, and the depth and width of the wear scar are significantly reduced. Especially when the addition amount of Ce source is 5g / L, the wear resistance effect is optimal.

[0115] Conduct corrosion resistance test:

[0116] AZ31B magnesium alloy was used as a comparative example and electrochemical tests were carried out together with Ce-0, Ce-2.5 and Ce-5 samples prepared in Examples 1 to 3 to test their corrosion resistance. The corrosion resistance of the coating was characterized by polarization curves and electrochemical impedance spectroscopy, and the lower corrosion current density (I corr ) usually indicates that the coating has strong corrosion resistance, and the corrosion potential (E corr ) is mainly manifested as a tendency to corrosion. At the same time, the larger the capacitor arc radius, the better the corrosion resistance of the coating.

[0117] like Figure 4 As shown in the figure and Table 3, it can be seen that the AZ31B bare magnesium substrate has the highest corrosion current density of 9.284×10 -4 A / cm 2 and the lowest corrosion potential of -1.478V; the corrosion current density and corrosion potential of Ce-0 sample coating are slightly higher than those of AZ31, which are 4.957×10 -5 A / cm 2 and -1.411V; the corrosion current density and corrosion potential of Ce-2.5 sample coating are slightly higher than those of Ce-0, which are 2.278×10 -5 A / cm2 and -1.402V; the corrosion resistance of Ce-5 coating was significantly improved, with the lowest corrosion current density of 7.318×10 -7 A / cm 2 and the highest corrosion potential of -1.405V.

[0118] Table 3

[0119] Project Number Comparative Example AZ31 Example 1Ce-0 Example 2Ce-2.5 Example 2Ce-5 Corrosion current density <![CDATA[9.284×10 -4 A / cm 2 ]]> <![CDATA[4.957×10 -5 A / cm 2 ]]> <![CDATA[2.278×10 -5 A / cm 2 ]]> <![CDATA[7.318×10 -7 A / cm 2 ]]> Corrosion potential -1.478V -1.411V -1.402V -1.405V

[0120] like Figure 5 As shown in the figure and Table 4, the Ce-5 sample coating exhibits the largest semicircular arc (3570Ω·cm 2 ), much higher than the Ce-2.5 sample coating (1610Ω·cm 2 ), Ce-0 sample coating (608Ω·cm 2 ) and AZ31B substrate (61.3Ω·cm 2 ) The larger the capacitor arc radius, the better its corrosion resistance.

[0121] Table 4

[0122] Project Number Comparative Example AZ31 Example 1Ce-0 Example 2Ce-2.5 Example 2Ce-5 Capacitor arc radius <![CDATA[61.3Ω·cm 2 ]]> <![CDATA[608Ω·cm 2 ]]> <![CDATA[1610Ω·cm 2 ]]> <![CDATA[3570Ω·cm 2 ]]>

[0123] The corrosion resistance of the coating can be evaluated by the impedance modulus at the lowest frequency (|Z| 0.01HZ ) and the angle at the highest frequency. The higher the low-frequency impedance modulus of the coating and the higher the high-frequency angle, the better the corrosion resistance and film integrity of the surface coating. After testing, the impedance modulus of the samples in the low-frequency region are as follows: Ce-5 sample coating (1.03×10 4 Ω·cm 2 )>Ce-2.5 sample coating (3.07×10 3 Ω·cm 2 )>Ce-0 sample coating (1.37×10 3 Ω·cm 2 )>AZ31B substrate (402Ω·cm 2 The order of the phase angles in the high-frequency region of the samples is: Ce-5 sample coating (45.1°) > Ce-0 sample coating (35.7°) > Ce-2.5 sample coating (31.9°) > AZ31B substrate (2.75°). Figure 6 and 7 shown.

[0124] Therefore, the MAO / CePO4 composite coating prepared by in-situ synthesis of CePO4 using the one-step micro-arc oxidation method provided by the present invention has significantly improved corrosion resistance compared to MAO coatings, reaching the level of performance enhancement achieved by conventional micro-arc oxidation coatings using a secondary coating. Furthermore, the one-step micro-arc oxidation in-situ synthesis method used in the present invention offers the advantages of simple operation, low cost, and high preparation efficiency.

[0125] To perform a macro soak test:

[0126] AZ31B magnesium alloy was used as a comparative example, along with the Ce-0, Ce-2.5, and Ce-5 samples prepared in Examples 1 to 3, and immersed in a 3.5 wt. NaCl solution for 14 days to test the macroscopic corrosion resistance of the composite film. As shown in Figure 8(a), after 14 days of immersion, the coating surface of the Ce-0 sample showed obvious shedding. As shown in Figure 8(b), the surface of the Ce-0 sample showed wrinkled, fine shedding due to corrosion. As shown in Figure 8(c), after 14 days of immersion, the shedding area on the coating surface of the Ce-2.5 sample was significantly smaller than that of the Ce-0 sample. As shown in Figure 8(d), the wrinkled shedding on the surface of the Ce-2.5 sample due to corrosion was significantly less than that of the Ce-0 sample, and the pores in the film layer still retained the sealant. As shown in Figure 8(e), after immersion for 14 days, the coating surface of the Ce-5 sample did not show the phenomenon of peeling due to corrosion as in the other examples. Instead, attachments adsorbed on the coating surface appeared. As shown in Figure 8(f), the morphology of corrosion products at the pores on the coating surface of the Ce-5 sample showed a dense lamellar structure. This behavior of generating sealing materials due to corrosion hydrolysis and sealing the surface defects of the micro-arc oxidation coating is beneficial to improving the corrosion resistance of the micro-arc oxidation coating of magnesium alloy.

[0127] From the above analysis, it can be seen that this method is simple, feasible and easy to operate, and the prepared magnesium alloy MAO / CePO4 composite coating has high wear resistance and high corrosion resistance protective properties.

[0128] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for in-situ synthesis of CePO4 micro-arc oxidation composite coating, characterized in that: include: Decontamination treatment is performed on the surface of the magnesium alloy sample; Add micro-arc oxidation solution into the electrolytic cell, use the treated magnesium alloy sample as the anode and the stainless steel barrel as the cathode, and immerse them in the micro-arc oxidation solution; Adding a Ce source to the micro-arc oxidation solution, which is a 0-5 g / L Ce(CH3CO2)3·xH2O solution; The electrolytic cell was connected to an external stirrer and a water cooling system, and micro-arc oxidation treatment was carried out in a constant current mode to obtain a MAO / CePO4 composite coating.

2. The method for in-situ synthesis of CePO4 micro-arc oxidation composite coating according to claim 1, characterized in that: The electrical parameters for micro-arc oxidation treatment in the constant current mode include: The processing frequency is 800HZ; The duty cycle is 15%; The current density is 24A / dm 2 ; The micro-arc oxidation time was 10 min.

3. The method for in-situ synthesis of CePO4 micro-arc oxidation composite coating according to claim 2, characterized in that: The micro-arc oxidation solution is composed of: 20g / L (NaPO3)6 solution and 10g / L NaF solution.

4. The method for in-situ synthesis of CePO4 micro-arc oxidation composite coating according to claim 2, characterized in that: The decontamination treatment comprises: The surface of the magnesium alloy specimen was polished step by step using metallographic sandpapers of #120, #600, #800, and #1200 in sequence; The polished magnesium alloy specimens were ultrasonically treated with anhydrous ethanol and isopropyl alcohol for 3 to 5 minutes, respectively, to obtain magnesium alloy specimens with residues and oil removed.

5. The method for in-situ synthesis of CePO4 micro-arc oxidation composite coating according to claim 4, characterized in that: The (NaPO 3 ) 6 solution, the NaF solution, the Ce(CH 3 CO 2 ) 3 · xH 2 O solution, the anhydrous ethanol and the isopropanol are all chemically pure or higher.

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