A preparation method of a self-densifying micro-arc oxidation coating for a magnesium alloy

Abstract

The present invention provides a method for preparing a self-densifying micro-arc oxidation coating on a magnesium alloy, comprising the following steps: cutting the magnesium alloy into specimens of required size; polishing and rinsing the specimens to obtain magnesium alloy specimens after drying; preparing a mixed solution of potassium fluoride with a concentration of 0.2-0.4 mol / L and potassium dihydrogen phosphate or sodium dihydrogen phosphate with a concentration of 0.01-0.03 mol / L, and adjusting the pH of the mixed solution to 6-8 to obtain an electrolytic solution; connecting the electrolytic solution, the magnesium alloy specimen and a micro-arc oxidation power supply into a working circuit; turning on the micro-arc oxidation power supply to carry out micro-arc oxidation on the magnesium alloy specimen to form a film for 10-45 minutes; taking out the magnesium alloy specimen after micro-arc oxidation film formation, rinsing and drying. The method for preparing a self-densifying micro-arc oxidation coating on a magnesium alloy provided by the present invention has small pore size, high densification and strong corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-arc oxidation coating preparation, and particularly relates to a method for preparing a self-sealing micro-arc oxidation coating on a magnesium alloy. Background Art

[0002] Poor corrosion resistance is an important factor restricting the large-scale application of magnesium alloys. At present, by adjusting the electrolyte and electrical parameters, a micro-arc oxidation coating is grown on the surface of a magnesium alloy by means of arc discharge to generate instantaneous high temperature and high pressure. This coating can significantly improve the wear resistance, corrosion resistance, high-temperature impact resistance, and electrical insulation of the magnesium alloy, and has been widely applied to fields such as aviation and electronic products.

[0003] However, the coatings prepared by the existing micro-arc oxidation technology all have a relatively high porosity, which affects the coating life. Because currently, alkaline electrolytes are mainly used for micro-arc oxidation, and the arc discharge is very intense, which easily leads to relatively large pore sizes in the film layer. And these pores will significantly reduce the corrosion resistance of micro-arc oxidation products. Therefore, after the micro-arc oxidation treatment of the magnesium alloy, a sealing treatment is also required.

[0004] Therefore, there is an urgent need for a new method for preparing a micro-arc oxidation coating on a magnesium alloy to reduce the pore size of the micro-arc oxidation coating and improve the densification and corrosion resistance of the micro-arc oxidation coating on the magnesium alloy. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a self-sealing micro-arc oxidation coating on a magnesium alloy with low pore size, high densification, and strong corrosion resistance.

[0006] To solve the above technical problem, the present invention provides a method for preparing a self-sealing micro-arc oxidation coating on a magnesium alloy, including the following steps:

[0007] Cut the magnesium alloy into specimens of the required size;

[0008] After grinding and rinsing and drying the specimens, obtain magnesium alloy specimens;

[0009] Prepare a mixed solution of potassium fluoride with a concentration of 0.2 - 0.4 mol / L and potassium dihydrogen phosphate or sodium dihydrogen phosphate with a concentration of 0.01 - 0.03 mol / L, and adjust the pH of the mixed solution to 6 - 8 to obtain an electrolytic solution;

[0010] Connect the electrolytic solution, the magnesium alloy specimen, and the micro-arc oxidation power supply into a working circuit;

[0011] Set the power supply voltage to 350 - 380 V, the current density to 2 - 4 A / dm 2 ², the frequency to 250 - 1000 Hz, and the positive and negative duty cycles to 30% - 50%, and turn on the micro-arc oxidation power supply to carry out micro-arc oxidation film formation on the magnesium alloy specimen for 10 - 45 min;

[0012] Take out the magnesium alloy sample after micro-arc oxidation to form a film, rinse and dry it.

[0013] Further, the magnesium alloy is cut into samples with sizes of 15mm×15mm×5mm or 25mm×25mm×5mm by wire cutting.

[0014] Further, the grinding of the sample is to grind the sample successively with 240-mesh, 600-mesh, and 1000-mesh silica sandpapers.

[0015] Further, the rinsing and drying of the sample is to rinse it with alcohol and then blow it dry.

[0016] Further, adjusting the pH of the mixed solution is to add sodium hydroxide solution to the mixed solution to control the pH of the mixed solution at 6 - 8.

[0017] Preferably, the pH of the mixed solution is controlled at 6.5 - 7.5.

[0018] More preferably, the pH of the mixed solution is controlled at 7.0.

[0019] Further, the rinsing and drying of the magnesium alloy sample after micro-arc oxidation to form a film is to rinse it with deionized water and air-dry it in the air.

[0020] Preferably, the micro-arc oxidation film-forming time of the magnesium alloy sample is controlled at 20 - 30 min.

[0021] More preferably, the micro-arc oxidation film-forming time of the magnesium alloy sample is controlled at 30 min.

[0022] A preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy provided by the present invention uses a mixed solution of potassium fluoride and potassium dihydrogen phosphate or sodium dihydrogen phosphate as the electrolyte for micro-arc oxidation. By controlling the pH of the electrolyte and the micro-arc oxidation time, the intense arc light in the current micro-arc oxidation preparation of magnesium alloy coatings can be changed into fine arc light, so that the pore size of the magnesium alloy micro-arc oxidation coating can be reduced from 10 - 15 microns to 1 - 3 microns. Moreover, a preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy provided by the present invention utilizes the liquid-phase filling and cooling sintering phenomena caused by the temperature gradient during the arc discharge process of the electrolyte. When forming the film, the coating is denser, and the self-sealing of the coating pores can be realized, greatly improving the corrosion resistance of the magnesium alloy micro-arc oxidation coating. At the same time, a preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy provided by the present invention sets the power supply voltage at 350 - 380 V during the micro-arc oxidation process. Using a lower voltage can reduce the probability of burning the micro-arc oxidation workpiece. Description of the Drawings

[0023] Figure 1 Flow chart of the preparation method of the self-densifying micro-arc oxidation coating on magnesium alloy provided by the embodiment of the present invention;

[0024] Figure 2 Macroscopic discharge morphology during the micro-arc oxidation process in the preparation method of the self-densifying micro-arc oxidation coating on magnesium alloy provided by the embodiment of the present invention;

[0025] Figure 3 Scanning electron microscope surface morphology diagram of the micro-arc oxidation coating in the preparation method of the self-densifying micro-arc oxidation coating on magnesium alloy provided by the embodiment of the present invention;

[0026] Figure 4 Macroscopic discharge morphology during the micro-arc oxidation process in the preparation method of the traditional alkaline micro-arc oxidation coating on magnesium alloy provided by the comparative example of the present invention;

[0027] Figure 5 Scanning electron microscope surface morphology diagram of the micro-arc oxidation coating in the preparation method of the traditional alkaline micro-arc oxidation coating on magnesium alloy provided by the comparative example of the present invention. Detailed implementation manners

[0028] See Figure 1 , a preparation method of a self-densifying micro-arc oxidation coating on magnesium alloy provided by the embodiment of the present invention, includes the following steps:

[0029] Step 1) Cut the magnesium alloy into specimens with a size of 15mm×15mm×5mm or 25mm×25mm×5mm by wire cutting.

[0030] Step 2) Polish the specimens successively with 240-mesh, 600-mesh and 1000-mesh silicon dioxide sandpapers, then rinse with alcohol and dry, to obtain magnesium alloy samples for standby.

[0031] Step 3) Prepare a mixed solution of potassium fluoride with a concentration of 0.2-0.4mol / L and potassium dihydrogen phosphate with a concentration of 0.01-0.03mol / L, or prepare a mixed solution of potassium fluoride with a concentration of 0.2-0.4mol / L and sodium dihydrogen phosphate with a concentration of 0.01-0.03mol / L. And adjust the pH of the mixed solution to 6-8 with sodium hydroxide solution to obtain the micro-arc oxidation electrolyte.

[0032] Step 4) Connect the prepared micro-arc oxidation electrolyte, magnesium alloy specimen and micro-arc oxidation power supply into a working circuit.

[0033] Step 5) Set the power supply voltage to 350-380V, the current density to 2-4A / dm 2 ², the frequency to 250-1000Hz, the positive and negative duty cycles to 30%-50%, turn on the micro-arc oxidation power supply and carry out micro-arc oxidation for film formation for 10-45min to form a layer of micro-arc oxidation coating on the surface of the magnesium alloy specimen.

[0034] Step 6) Take out the magnesium alloy sample after micro-arc oxidation film formation, rinse it with deionized water, and then air-dry it, so that a self-compacting micro-arc oxidation coating is formed on the surface of the magnesium alloy.

[0035] Among them, the pH of the mixed solution is preferably 6.5 - 7.5, more preferably 7.0.

[0036] Among them, the time for micro-arc oxidation film formation of the magnesium alloy is preferably 20 - 30 min, more preferably 30 min.

[0037] The following specifically describes a method for preparing a self-compacting micro-arc oxidation coating on a magnesium alloy provided by an embodiment of the present invention through examples and comparative examples.

[0038] Example 1

[0039] A method for preparing a self-compacting micro-arc oxidation coating on a magnesium alloy includes the following steps:

[0040] (1) Cut the magnesium alloy into 15 mm × 15 mm × 5 mm by wire cutting;

[0041] (2) Polish the sample with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and blow-dry it with alcohol;

[0042] (3) Dissolve 113 g of potassium fluoride and 11 g of potassium dihydrogen phosphate in 4 L of deionized water, adjust the pH to 7.1 with sodium hydroxide solution, and stir evenly;

[0043] (4) Connect the above-prepared electrolyte solution, micro-arc oxidation power supply, and magnesium alloy sample into a working circuit;

[0044] (5) Set the power supply voltage to 370 V, current density to 3 A / dm 2 , frequency to 500 Hz, positive and negative duty cycle to 30%, and carry out a 30-min micro-arc oxidation film formation process;

[0045] (6) Take out the sample, rinse it with deionized water, and air-dry it.

[0046] In the method for preparing a self-compacting micro-arc oxidation coating on a magnesium alloy provided in this example, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 2 shown. The surface morphology of the micro-arc oxidation coating obtained by the method for preparing a self-compacting micro-arc oxidation coating on a magnesium alloy provided in the embodiment of the present invention is as Figure 3 shown.

[0047] Example 2

[0048] A method for preparing a self-compacting micro-arc oxidation coating on a magnesium alloy includes the following steps:

[0049] (1) Cut the magnesium alloy into 15 mm × 15 mm × 5 mm by wire cutting;

[0050] (2) Polish the specimen with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and dry it with alcohol;

[0051] (3) Dissolve 80 g of potassium fluoride and 5 g of potassium dihydrogen phosphate in 4 L of deionized water, adjust the pH to 8 with sodium hydroxide solution, and stir evenly;

[0052] (4) Connect the above-prepared electrolyte solution, micro-arc oxidation power supply, and magnesium alloy specimen into a working circuit;

[0053] (5) Set the power supply voltage to 350 V, current density to 2 A / dm 2 , frequency to 300 Hz, positive and negative duty cycle to 35%, and carry out the micro-arc oxidation film-forming process for 30 min;

[0054] (6) Take out the specimen, rinse it with deionized water, and air-dry it.

[0055] In the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in this example, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 2 shown. The surface morphology of the micro-arc oxidation coating obtained by the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in the embodiment of the present invention is as Figure 3 shown.

[0056] Example 3

[0057] A preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy, comprising the following steps:

[0058] (1) Cut the magnesium alloy into 25 mm × 25 mm × 5 mm by wire cutting;

[0059] (2) Polish the specimen with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and dry it with alcohol;

[0060] (3) Dissolve 100 g of potassium fluoride and 15 g of potassium dihydrogen phosphate in 4 L of deionized water, adjust the pH to 7.3 with sodium hydroxide solution, and stir evenly;

[0061] (4) Connect the above-prepared electrolyte solution, micro-arc oxidation power supply, and magnesium alloy specimen into a working circuit;

[0062] (5) Set the power supply voltage to 380 V, current density to 4 A / dm 2 , frequency to 1000 Hz, positive and negative duty cycle to 50%, and carry out the micro-arc oxidation film-forming process for 30 min;

[0063] (6) Take out the specimen, rinse it with deionized water, and air dry it.

[0064] In the preparation method of the self-densifying micro-arc oxidation coating for magnesium alloy provided in this embodiment, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 2 shown. The surface morphology of the micro-arc oxidation coating obtained by the preparation method of the self-densifying micro-arc oxidation coating for magnesium alloy provided in the embodiment of the present invention is as Figure 3 shown.

[0065] Example 4

[0066] A preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy includes the following steps:

[0067] (1) Cut the magnesium alloy into 15 mm × 15 mm × 5 mm by wire cutting;

[0068] (2) Grind the specimen with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and blow dry with alcohol;

[0069] (3) Dissolve 90 g of potassium fluoride and 15 g of potassium dihydrogen phosphate in 4 L of deionized water, adjust the pH to 6.5 with sodium hydroxide solution, and stir evenly;

[0070] (4) Connect the above-prepared electrolyte solution to a micro-arc oxidation power supply and a magnesium alloy specimen to form a working circuit;

[0071] (5) Set the power supply voltage to 360 V, the current density to 3 A / dm 2 , the frequency to 800 Hz, and the positive and negative duty cycles to 40%, and carry out a 20-minute micro-arc oxidation film-forming process;

[0072] (6) Take out the specimen, rinse it with deionized water, and air dry it.

[0073] In the preparation method of the self-densifying micro-arc oxidation coating for magnesium alloy provided in this embodiment, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 2 shown. The surface morphology of the micro-arc oxidation coating obtained by the preparation method of the self-densifying micro-arc oxidation coating for magnesium alloy provided in the embodiment of the present invention is as Figure 3 shown.

[0074] Example 5

[0075] A preparation method of a self-densifying micro-arc oxidation coating for magnesium alloy includes the following steps:

[0076] (1) Cut the magnesium alloy into 15 mm × 15 mm × 5 mm by wire cutting;

[0077] (2) Grind the specimen with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and blow dry with alcohol;

[0078] (3) Dissolve 90 g of potassium fluoride and 15 g of potassium dihydrogen phosphate in 4 L of deionized water, adjust the pH to 6.5 with sodium hydroxide solution, and stir evenly.

[0079] (4) Connect the above-prepared electrolyte solution, micro-arc oxidation power supply, and magnesium alloy sample into a working circuit.

[0080] (5) Set the power supply voltage to 380 V, the current density to 3 A / dm 2 , the frequency to 500 Hz, and the positive and negative duty cycles to 50%, and carry out the micro-arc oxidation film-forming process for 15 minutes.

[0081] (6) Take out the sample, rinse it with deionized water, and air-dry it.

[0082] In the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in this example, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 2 shown. The surface morphology of the micro-arc oxidation coating obtained by the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in the embodiment of the present invention is as Figure 3 shown.

[0083] Comparative Example

[0084] The preparation method of the traditional alkaline micro-arc oxidation coating of magnesium alloy includes the following steps:

[0085] (1) Cut the magnesium alloy into 15 mm × 15 mm × 5 mm by wire cutting.

[0086] (2) Grind the sample with 240#, 600#, and 1000# silicon carbide sandpaper, and rinse and dry it with alcohol.

[0087] (3) Dissolve 80 g of sodium silicate, 12 g of potassium fluoride, and 8 g of sodium hydroxide in 4 L of deionized water, and stir evenly.

[0088] (4) Connect the above-prepared electrolyte solution, micro-arc oxidation power supply, and magnesium alloy sample into a working circuit.

[0089] (5) Set the power supply voltage to 450 V, the current density to 3 A / dm 2 , the frequency to 500 Hz, and the positive and negative duty cycles to 30%, and carry out the micro-arc oxidation film-forming process for 30 minutes.

[0090] (6) Take out the sample, rinse it with deionized water, and air-dry it.

[0091] In the preparation method of the traditional alkaline micro-arc oxidation coating of magnesium alloy provided in this comparative example, the macroscopic discharge morphology during the micro-arc oxidation process is as Figure 4As shown. The SEM surface morphology of the micro-arc oxidation coating obtained by the preparation method of the traditional alkaline micro-arc oxidation coating of magnesium alloy provided in this comparative example is as Figure 5 shown.

[0092] From Figure 2 and Figure 4 comparison, it can be seen that in the preparation method of the traditional alkaline micro-arc oxidation coating of magnesium alloy provided in the comparative example of the present invention, the micro-arc oxidation is intense arc light, while in the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in the example of the present invention, the micro-arc oxidation has been improved from intense arc light to fine arc light. Since the smaller the arc light, the less likely the coating is to be damaged during the arc discharge process, and the more beneficial it is to reduce the influence of coating pore defects on the corrosion resistance of the coating. Therefore, in the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in the example of the present invention, through the improvement of the electrolyte composition and the optimized control of the electrolyte pH and the micro-arc oxidation time, the corrosion resistance of the magnesium alloy micro-arc oxidation coating is better.

[0093] From Figure 3 and Figure 5 comparison, it can be seen that the micropore size of the micro-arc oxidation coating obtained by the preparation method of the traditional alkaline micro-arc oxidation coating of magnesium alloy provided in the comparative example of the present invention is relatively large, reaching 10-15 microns, which will significantly reduce the corrosion resistance of the coating. While the micropores of the micro-arc oxidation coating obtained by the preparation method of the self-densifying micro-arc oxidation coating of magnesium alloy provided in the example of the present invention are smaller, within 1-3 microns, and many of its micropores are self-filled. Therefore, the corrosion resistance of the magnesium alloy micro-arc oxidation coating obtained in the example of the present invention is better.

[0094] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of a self-densifying micro-arc oxidation coating for a magnesium alloy, characterized in that, It includes the following steps: Cut the magnesium alloy into specimens of the required size; After grinding and rinsing and drying the specimens, magnesium alloy specimens are obtained; Prepare a mixed solution of potassium fluoride with a concentration of 0.2 - 0.4 mol / L and potassium dihydrogen phosphate or sodium dihydrogen phosphate with a concentration of 0.01 - 0.03 mol / L, and adjust the pH of the mixed solution to 6 - 8 to obtain an electrolytic solution; wherein, adjusting the pH of the mixed solution is to add sodium hydroxide solution to the mixed solution to control the pH of the mixed solution at 6 - 8; Connect the electrolytic solution, the magnesium alloy specimen and the micro-arc oxidation power supply into a working circuit; Set the power supply voltage to 350 - 380V, the current density to 2 - 4A / dm 2 , the frequency to 250 - 1000Hz, the positive and negative duty cycles to 30% - 50%, turn on the micro-arc oxidation power supply to carry out micro-arc oxidation on the magnesium alloy sample for 10 - 45 minutes to form a film, and the micropores of the micro-arc oxidation coating of the magnesium alloy obtained are 1 - 3 microns. Utilize the liquid-phase filling and cooling sintering phenomena caused by the temperature gradient during the arc discharge process of the electrolyte, and the coating is denser when the micro-arc oxidation film is formed, realizing the self-sealing of the pores of the micro-arc oxidation coating of the magnesium alloy; Take out the magnesium alloy specimen after micro-arc oxidation film formation, rinse and dry it.

2. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The magnesium alloy is cut into specimens with a size of 15mm×15mm×5mm or 25mm×25mm×5mm by wire cutting.

3. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The grinding of the specimen is to grind the specimen successively with 240-mesh, 600-mesh, and 1000-mesh silica sandpaper.

4. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The rinsing and drying of the specimen is to rinse it with alcohol and then blow it dry.

5. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The pH of the mixed solution is controlled at 6.5 - 7.

5.

6. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 5, characterized in that: The pH of the mixed solution is controlled to be 7.

0.

7. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The rinsing and drying of the magnesium alloy specimen after micro-arc oxidation film formation is to rinse it with deionized water and air-dry it.

8. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 1, characterized in that: The micro-arc oxidation film formation time of the magnesium alloy specimen is controlled within 20 - 30 min.

9. The preparation method of the self-densifying micro-arc oxidation coating for a magnesium alloy according to claim 8, characterized in that: The micro-arc oxidation film formation time of the magnesium alloy specimen is controlled to be 30 min.

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