A bright white ceramic film on magnesium alloy surface and its preparation method and application

Abstract

The present invention belongs to the technical field of magnesium alloy surface treatment, and specifically discloses a bright white ceramic film on the surface of a magnesium alloy, and a preparation method and application thereof. The preparation method of the bright white ceramic film on the surface of a magnesium alloy provided by the present invention comprises the following steps: using a pretreated magnesium alloy as an anode, and adopting bipolar pulse constant current micro-arc oxidation in an electrolyte to oxidize the pretreated magnesium alloy to obtain a magnesium alloy with a bright white ceramic film; wherein the electrolyte comprises sodium aluminate, a strong base, sodium fluoride, potassium titanate, sodium stannate, triethanolamine and water. The present invention selects sodium aluminate, a strong base, sodium fluoride, potassium titanate, sodium stannate and triethanolamine as the electrolyte, and combines the bipolar pulse constant current micro-arc oxidation process, so that the ceramic film prepared on the surface of the magnesium alloy presents a bright white color, and also greatly improves the hardness and corrosion resistance of the ceramic film.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy surface treatment, and in particular relates to a bright white ceramic film on the surface of a magnesium alloy and a preparation method and application thereof. Background Art

[0002] Magnesium alloys are widely used in aerospace, electronic devices and other fields because of their advantages such as low density, high strength, good electromagnetic shielding performance, and easy recycling, high degree of reuse, and high surface content. Therefore, the further development of the various advantages of magnesium alloys has become the top priority at this stage. However, poor oxide films are easily generated on the surface of magnesium alloys, which makes the corrosion resistance of magnesium alloys poor, seriously limiting the development of magnesium alloys. In order to overcome the defects of magnesium alloy corrosion resistance, the prior art usually performs surface treatment on magnesium alloys to generate a film layer with good corrosion resistance, and can further improve its aesthetics, so that magnesium alloys can be used in more environments. At present, the surface film layer of magnesium alloys is usually grayish white, but its film layer has poor corrosion resistance, and the obtained ceramic film layer is not suitable in many environments; however, the bright white ceramic layer material has good light reflectivity and excellent corrosion resistance, which can increase the use of the material. However, there is no literature record of the preparation method of white ceramic film on the surface of magnesium alloys. Therefore, it is of great significance to prepare a bright white ceramic film on the surface of magnesium alloys to improve corrosion resistance and application fields. Summary of the invention

[0003] In view of this, the present invention provides a bright white ceramic film on the surface of a magnesium alloy, and a preparation method and application thereof. By selecting sodium aluminate, strong alkali, sodium fluoride, potassium titanate, sodium stannate and triethanolamine as electrolytes, and combining a bipolar pulse constant current micro-arc oxidation process, the ceramic film prepared on the surface of the magnesium alloy presents a bright white color, and the hardness and corrosion resistance of the ceramic film are greatly improved.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0005] The present invention provides a method for preparing a bright white ceramic film on the surface of a magnesium alloy, comprising the following steps:

[0006] Using the pretreated magnesium alloy as an anode, bipolar pulse constant current micro-arc oxidation is used in an electrolyte to obtain a magnesium alloy with a bright white ceramic film;

[0007] The electrolyte comprises sodium aluminate, a strong base, sodium fluoride, potassium titanate, sodium stannate, triethanolamine and water.

[0008] Compared with the prior art, the present invention provides a method for preparing a bright white ceramic film on the surface of a magnesium alloy, wherein sodium aluminate and a strong alkali are used as a basic electrolyte to improve the hardness of the film layer; further, by adding potassium titanate and sodium stannate, the surface smoothness can be further improved while reducing the amount of electrolyte used in the film-making process, so that the prepared ceramic film is bright white; there is an interaction between potassium titanate and sodium stannate, which can greatly improve the corrosion resistance and hardness of the bright white ceramic film on the surface of the magnesium alloy; the addition of triethanolamine makes the solute in the electrolyte evenly dispersed in the solution; the present invention carries out a bipolar pulse constant current micro-arc oxidation process in a specific electrolyte, wherein the bipolar pulse constant current micro-arc oxidation process makes the potassium titanate and sodium stannate in the electrolyte fully exert a synergistic effect, so that the prepared film layer is dense, has a small pore size and is bright white, and can further improve the corrosion resistance and hardness of the film layer.

[0009] Preferably, the electrical parameters of the bipolar pulse constant current micro-arc oxidation include a current density of 5A / dm 2 -7A / dm 2 , the power supply frequency is 1300Hz-1600Hz, and the duty cycle is 35%-50%.

[0010] The specific electrical parameters of bipolar pulse constant current micro-arc oxidation can give full play to the effects of various electrolytes in the electrolyte, reduce the arc starting voltage and termination voltage of bipolar pulse constant current micro-arc oxidation, ensure the integrity of the film layer, and further promote the preparation of bright white ceramic films; setting a higher power supply frequency is also conducive to giving full play to the synergistic effect of potassium titanate and sodium stannate, so that the prepared ceramic film layer has the characteristics of dense surface, small pore size and excellent corrosion resistance.

[0011] Preferably, the oxidation time of the bipolar pulse constant current micro-arc oxidation is 10 min-15 min.

[0012] Preferably, the mass concentration of the sodium aluminate is 5 g / L-15 g / L.

[0013] Preferably, the mass concentration of the strong base is 1 g / L-5 g / L.

[0014] Preferably, the mass concentration of the sodium fluoride is 0.5 g / L-2 g / L.

[0015] Preferably, the mass concentration of potassium titanate is 0.2 g / L-1.5 g / L.

[0016] Preferably, the mass concentration of the sodium stannate is 0.5 g / L-1 g / L.

[0017] Preferably, the volume concentration of the triethanolamine is 1 mL / L-2 mL / L.

[0018] The preferred electrolyte concentration preparation can fully exert the role of the solutes in each electrolyte in the bipolar pulse constant current micro-arc oxidation process, and through the synergistic effect, the bright white ceramic film on the surface of the magnesium alloy finally prepared is bright white, thereby improving the corrosion resistance of the film layer.

[0019] It should be further explained that the sodium aluminate, potassium titanate and sodium stannate need to be ball-milled, filtered, dried and ground.

[0020] The specific technical parameters of ball milling, filtration, drying and grinding treatment all adopt conventional operations of the prior art.

[0021] Preferably, the cathode in the bipolar pulse constant current micro-arc oxidation process is stainless steel.

[0022] Preferably, the strong base is potassium hydroxide or sodium hydroxide.

[0023] Preferably, the pretreatment step is: grinding the magnesium alloy with sandpaper, and then polishing, cleaning and drying to obtain the magnesium alloy.

[0024] Preferably, the specifications of the sandpaper used for polishing are 240#, 360#, 600#, 1000# and 1500# respectively.

[0025] It should be further explained that SiC sandpaper with specifications of 240#, 360#, 600#, 1000# and 1500# was used for grinding until there were no scratches on the surface of the workpiece. The workpiece was polished with a metallographic polishing machine, washed with deionized water, and then ultrasonically cleaned with 95% ethanol aqueous solution, and then taken out and dried.

[0026] As a preferred embodiment, the metallographic polishing machine adopts nylon polishing cloth.

[0027] As a preferred embodiment, the frequency of the ultrasonic cleaning is 40KHz, and the time of the ultrasonic cleaning is 3min-5min.

[0028] It should be further explained that the preparation method also includes washing the magnesium alloy after bipolar pulse constant current micro-arc oxidation treatment with cold water at 10°C-15°C for 2min-4min, and then washing the surface with 75% ethanol solution and drying it.

[0029] The present invention provides a bright white ceramic film on the surface of a magnesium alloy, which is prepared by the method for preparing the bright white ceramic film on the surface of a magnesium alloy.

[0030] Preferably, the thickness of the bright white ceramic film on the surface of the magnesium alloy is 15 μm-35 μm.

[0031] The present invention also provides an application of the method for preparing the bright white ceramic film on the surface of the magnesium alloy in preparing the bright white ceramic film on the surface of the AZ31B magnesium alloy.

[0032] The bright white ceramic film on the surface of the magnesium alloy provided by the present invention, when prepared on the surface of AZ31B magnesium alloy, has a dense and smooth surface, a small pore size, and excellent hardness and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a SEM image of the bright white ceramic film prepared in Example 1 of the present invention;

[0034] Figure 2 The potentiodynamic polarization curves of the bright white ceramic film prepared in Example 1 of the present invention and the AZ31B magnesium alloy without the bright white ceramic film prepared on the surface in a 3.5% NaCl solution;

[0035] Among them, 1 is the potentiodynamic polarization curve of AZ31B magnesium alloy without preparing bright white ceramic film on the surface, and 2 is the potentiodynamic polarization curve of the bright white ceramic film prepared in Example 1. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing a bright white ceramic film on the surface of a magnesium alloy, comprising the following steps:

[0039] (1) Cutting the AZ31B magnesium alloy into square pieces with a size of 30 mm×30 mm×1 mm, grinding the AZ31B magnesium alloy with SiC sandpaper of specifications of 240#, 360#, 600#, 1000# and 1500# in sequence until there are no scratches on the surface, polishing the surface with a nylon polishing cloth until the appearance is smooth and bright, washing with deionized water and then ultrasonically cleaning with 95% ethanol aqueous solution, taking out and drying, and obtaining the treated AZ31B magnesium alloy; wherein the frequency of ultrasonic cleaning is 40 KHz, and the time of ultrasonic cleaning is 3 min;

[0040] (2) Sodium aluminate, potassium titanate and sodium stannate are placed in a ball mill, 95% ethanol solution is added, the speed is set to 300 r / min, the program is set to alternate clockwise and counterclockwise rotation, clockwise rotation for 20 min, counterclockwise rotation for 120 min, with a 10 min interval in between, and the cycle is repeated 3 times. After ball milling, the slurry is filtered, and after filtration, the solid medicine is placed in a culture dish, sealed with plastic wrap, and placed in a drying oven at 100°C for 7 h. After drying, it is ground for 30 min until it is completely loose before use; wherein, the mass ratio of zirconia balls to medicines (sodium aluminate, potassium titanate and sodium stannate) is 10:1, and the mass ratio of large balls (diameter 9 mm), medium balls (diameter 6 mm) and small balls (diameter 3 mm) of zirconia balls is 2:3:5; the amount of 95% ethanol solution added is more than the amount of medicines (sodium aluminate, potassium titanate and sodium stannate) and grinding balls;

[0041] (3) adding the treated sodium aluminate, potassium titanate and sodium stannate, potassium hydroxide, sodium fluoride, and triethanolamine into water and stirring until dissolved to obtain an electrolyte; wherein the mass concentration of sodium aluminate is 15 g / L, the mass concentration of potassium hydroxide is 1 g / L, the mass concentration of sodium fluoride is 2 g / L, the mass concentration of potassium titanate is 0.2 g / L, the mass concentration of sodium stannate is 0.5 g / L, and the volume concentration of triethanolamine is 2 mL / L;

[0042] (4) adding the treated AZ31B magnesium alloy obtained in step (1) into the prepared electrolyte, using the AZ31B magnesium alloy as the anode and the stainless steel as the cathode, and performing bipolar pulse constant current micro-arc oxidation treatment; wherein the electrical parameters of the bipolar pulse constant current micro-arc oxidation are set to a current density of 7A / dm 2 , the power frequency is 1300Hz and the duty cycle is 50%;

[0043] (5) The workpiece obtained in step (4) was taken out and washed with cold water at 10° C. for 4 minutes, and then the surface was cleaned with a 75% ethanol solution and dried to obtain a bright white ceramic film with a thickness of 15 μm.

[0044] Example 2

[0045] This embodiment provides a method for preparing a bright white ceramic film on the surface of a magnesium alloy, comprising the following steps:

[0046] (1) Cutting the AZ31B magnesium alloy into square pieces with a size of 30 mm×30 mm×1 mm, grinding the AZ31B magnesium alloy with SiC sandpaper of specifications of 240#, 360#, 600#, 1000# and 1500# in sequence until there are no scratches on the surface, polishing the surface with a nylon polishing cloth until the appearance is smooth and bright, washing with deionized water and then ultrasonically cleaning with 95% ethanol aqueous solution, taking out and drying, and obtaining the treated AZ31B magnesium alloy; wherein the frequency of ultrasonic cleaning is 40 KHz, and the time of ultrasonic cleaning is 5 min;

[0047] (2) Sodium aluminate, potassium titanate and sodium stannate are placed in a ball mill, 95% ethanol solution is added, the speed is set to 300 r / min, the program is set to alternate clockwise and counterclockwise rotation, clockwise rotation for 10 min, counterclockwise rotation for 10 min, 5 min interval in between, repeat the cycle twice, filter the slurry after ball milling, place the solid medicine in a culture dish after filtration, seal it with plastic wrap, place it in a drying oven at 80°C for 10 h, grind it for 20 min after drying, and use it until it is completely loose; wherein, the mass ratio of zirconia balls to medicines (sodium aluminate, potassium titanate and sodium stannate) is 10:1, and the mass ratio of large balls (diameter 9 mm), medium balls (diameter 6 mm) and small balls (diameter 3 mm) of zirconia balls is 2:3:5; the amount of 95% ethanol solution added is more than the amount of medicines (sodium aluminate, potassium titanate and sodium stannate) and grinding balls;

[0048] (3) adding the treated sodium aluminate, potassium titanate and sodium stannate, sodium hydroxide, sodium fluoride, and triethanolamine into water, stirring until dissolved, to obtain an electrolyte; wherein the mass concentration of sodium aluminate is 5 g / L, the mass concentration of sodium hydroxide is 5 g / L, the mass concentration of sodium fluoride is 0.5 g / L, the mass concentration of potassium titanate is 0.2 g / L, the mass concentration of sodium stannate is 1 g / L, and the volume concentration of triethanolamine is 2 mL / L;

[0049] (4) adding the treated AZ31B magnesium alloy obtained in step (1) into the prepared electrolyte, using the AZ31B magnesium alloy as the anode and the stainless steel as the cathode, and performing bipolar pulse constant current micro-arc oxidation treatment; wherein the electrical parameters of the bipolar pulse constant current micro-arc oxidation are set to a current density of 5 A / dm 2 , the power frequency is 1600Hz and the duty cycle is 35%;

[0050] (5) The workpiece obtained in step (4) was taken out and washed with cold water at 15° C. for 2 min. The surface was then cleaned with a 75% ethanol solution and dried to obtain a bright white ceramic film with a thickness of 35 μm.

[0051] Example 3

[0052] This embodiment provides a method for preparing a bright white ceramic film on the surface of a magnesium alloy, comprising the following steps:

[0053] (1) Cutting the AZ31B magnesium alloy into square pieces with a size of 30 mm×30 mm×1 mm, grinding the AZ31B magnesium alloy with SiC sandpaper of specifications of 240#, 360#, 600#, 1000# and 1500# in sequence until there are no scratches on the surface, polishing the surface with a nylon polishing cloth until the appearance is smooth and bright, washing with deionized water and then ultrasonically cleaning with 95% ethanol aqueous solution, taking out and drying, and obtaining the treated AZ31B magnesium alloy; wherein the frequency of ultrasonic cleaning is 40 KHz, and the time of ultrasonic cleaning is 4 min;

[0054] (2) Sodium aluminate, potassium titanate and sodium stannate are placed in a ball mill, 95% ethanol solution is added, the speed is set to 300 r / min, the program is set to alternate clockwise and counterclockwise rotation, clockwise rotation for 15 min, counterclockwise rotation for 15 min, with an interval of 8 min in between, and the cycle is repeated 3 times. After ball milling, the slurry is filtered, and after filtration, the solid medicine is placed in a culture dish, sealed with plastic wrap, and placed in a drying oven at 90°C for 8 h. After drying, it is ground for 25 min until it is completely loose before use; wherein, the mass ratio of zirconia balls to medicines (sodium aluminate, potassium titanate and sodium stannate) is 10:1, and the mass ratio of large balls (diameter 9 mm), medium balls (diameter 6 mm) and small balls (diameter 3 mm) of zirconia balls is 2:3:5; the amount of 95% ethanol solution added is more than the amount of medicines (sodium aluminate, potassium titanate and sodium stannate) and grinding balls;

[0055] (3) adding the treated sodium aluminate, potassium titanate and sodium stannate, potassium hydroxide, sodium fluoride and triethanolamine into water and stirring until dissolved to obtain an electrolyte; wherein the mass concentration of sodium aluminate is 7 g / L, the mass concentration of potassium hydroxide is 3 g / L, the mass concentration of sodium fluoride is 2 g / L, the mass concentration of potassium titanate is 1 g / L, the mass concentration of sodium stannate is 0.8 g / L, and the volume concentration of triethanolamine is 1.5 mL / L;

[0056] (4) adding the treated AZ31B magnesium alloy obtained in step (1) into the prepared electrolyte, using the AZ31B magnesium alloy as the anode and the stainless steel as the cathode, and adopting bipolar pulse constant current micro-arc oxidation treatment; wherein the electrical parameters of the bipolar pulse constant current micro-arc oxidation are set to a current density of 5.5 A / dm 2 , the power frequency is 1400Hz and the duty cycle is 40%;

[0057] (5) The workpiece obtained in step (4) was taken out and washed with cold water at 13° C. for 3 min, and then the surface was cleaned with a 75% ethanol solution and dried to obtain a bright white ceramic film with a thickness of 20 μm.

[0058] Example 4

[0059] Compared with Example 1, the difference between this embodiment and Example 1 is that the mass concentration of sodium stannate is increased to 1.5 g / L, and the other operating steps are the same as those in Example 1.

[0060] Example 5

[0061] Compared with Example 1, the difference between this embodiment and Example 1 is that the mass concentration of potassium titanate is increased to 2 g / L, and the other operating steps are the same as those in Example 1.

[0062] Example 6

[0063] Compared with Example 1, the difference between this embodiment and Example 1 is that the power supply frequency in step (4) is set to 600 Hz, and the other operation steps are the same as those in Example 1.

[0064] Example 7

[0065] Compared with Example 1, the difference between this embodiment and Example 1 is that the current density in step (4) is set to 8A / dm 2 , other operation steps are the same as those in Example 1.

[0066] Comparative Example 1

[0067] Compared with Example 1, the difference between this comparative example and Example 1 is that potassium titanate is replaced by an equal amount of sodium tungstate, and the other operating steps are the same as Example 1, and no bright white ceramic film is obtained.

[0068] Comparative Example 2

[0069] Compared with Example 1, the difference between this comparative example and Example 1 is that sodium stannate is replaced by an equal amount of EDTA-2Na, and the other operating steps are the same as Example 1, and no bright white ceramic film is obtained.

[0070] Application Examples

[0071] The magnesium alloys prepared in Examples 1-7 of the present invention and Comparative Examples 1-2 and the ceramic films on their surfaces were measured for corrosion potential, corrosion current density and polarization resistance in a NaCl solution with a mass concentration of 3.5% using a three-electrode mode; wherein the electrode system consists of a working electrode, a reference electrode and a counter electrode, the working electrode is the product prepared in Examples 1-7 of the present invention and Comparative Examples 1-2, the reference electrode is a saturated calomel electrode, and the counter electrode is a platinum sheet; the parameters of the three-electrode mode are: an initial potential of -2V, a termination potential of 1V, and a scanning speed of 2mV / s.

[0072] The color measurement provided by the present invention adopts the "Lab Standard Colorimetric System" recommended by the International Committee of Stationary Elements (CIE), and the testing equipment is a 3nh spectrophotometer. The ceramic films prepared in Examples 1-7 and Comparative Examples 1-2 are measured at 10 points on the front and back surfaces, respectively, and the L*, a*, and b* of the measured samples are recorded respectively. The sum of the absolute values ​​of the three numbers is the blackness obtained by the test.

[0073] Ten points were selected from the surfaces of the ceramic membranes prepared in Examples 1-7 and Comparative Examples 1-2, and the microhardness was measured using an HVS-1000Z microhardness tester produced by Shanghai Aolong Xingdi Testing Equipment Co., Ltd. The indenter used was a diamond tetrahedron with an angle of 136°, the loading load was 0.5 g, the holding time was 10 s, and the accuracy was 0.1 HV. The specific test results are shown in Table 1.

[0074] Table 1 Test results

[0075]

[0076] As shown in Table 1, the corrosion potential of the bright white ceramic film on the surface of the magnesium alloy prepared in the embodiment of the present invention can reach -0.021V, and the corrosion current density can be reduced to 1.33×10 -8 A / cm 2 , the polarization resistance can reach 1.49×10 8 Ω·cm 2 , indicating that the bright white ceramic film provided by the present invention has excellent corrosion resistance and high hardness; Figure 1-2 It can be seen that the bright white ceramic film layer provided by the present invention has no cracks on the surface, and has a small pore size and uniform distribution. The film layer has good density and can effectively prevent the corrosion of the metal in the corrosive environment. The corrosion resistance is significantly improved compared with the untreated AZ31B magnesium alloy.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bright white ceramic film on the surface of a magnesium alloy, characterized in that: The steps include: Using the pretreated magnesium alloy as an anode, bipolar pulse constant current micro-arc oxidation is used in an electrolyte to obtain a magnesium alloy with a bright white ceramic film; The electrolyte includes sodium aluminate, strong alkali, sodium fluoride, potassium titanate, sodium stannate, triethanolamine and water; the electrical parameters of the bipolar pulse constant current micro-arc oxidation are: the current density is 5A / dm 2 -7A / dm 2 , the power supply frequency is 1300Hz-1600Hz, and the duty cycle is 35%-50%.

2. The method for preparing a bright white ceramic film on the surface of a magnesium alloy according to claim 1, characterized in that: The oxidation time of the bipolar pulse constant current micro-arc oxidation is 10 min-15 min.

3. The method for preparing a bright white ceramic film on the surface of a magnesium alloy according to claim 1, characterized in that: The mass concentration of the sodium aluminate is 5g / L-15g / L; and / or The mass concentration of the strong base is 1g / L-5g / L; and / or The mass concentration of the sodium fluoride is 0.5 g / L-2 g / L; and / or The mass concentration of potassium titanate is 0.2 g / L-1.5 g / L; and / or The mass concentration of the sodium stannate is 0.5 g / L-1 g / L; and / or The volume concentration of the triethanolamine is 1 mL / L-2 mL / L.

4. The method for preparing a bright white ceramic film on the surface of a magnesium alloy according to claim 1 or 3, characterized in that: The cathode in the bipolar pulse constant current micro-arc oxidation process is stainless steel; and / or The strong base is potassium hydroxide or sodium hydroxide.

5. The method for preparing a bright white ceramic film on the surface of a magnesium alloy according to claim 1, characterized in that: The preparation steps of the pretreated magnesium alloy are: grinding the magnesium alloy with sandpaper, and then polishing, cleaning and drying to obtain the pretreated magnesium alloy.

6. The method for preparing a bright white ceramic film on the surface of a magnesium alloy according to claim 5, characterized in that: The specifications of the sandpaper used in the polishing are 240#, 360#, 600#, 1000# and 1500# respectively.

7. A bright white ceramic film on the surface of a magnesium alloy, characterized in that: The bright white ceramic film is prepared by the method for preparing a bright white ceramic film on the surface of a magnesium alloy as described in any one of claims 1 to 6.

8. The bright white ceramic film on the surface of magnesium alloy according to claim 7, characterized in that: The thickness of the bright white ceramic film on the surface of the magnesium alloy is 15 μm-35 μm.

9. Use of the method for preparing a bright white ceramic film on the surface of a magnesium alloy according to any one of claims 1 to 6 in preparing a bright white ceramic film on the surface of an AZ31B magnesium alloy.

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