A method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding

Abstract

The application relates to a method for preparing an aluminum nitride ceramic coating on the surface of aluminum and its alloy by liquid low-temperature plasma electrolytic nitriding, and relates to the field of surface modification of aluminum and its alloy. The method is used for solving the problems that the existing method for preparing an AlN ceramic substrate generally needs high-temperature sintering, the sintering temperature is as high as 1800 DEG C, and it is difficult to sinter to be dense. The method comprises the following steps: 1, pretreating the surface of an aluminum or aluminum alloy sample; 2, configuring a non-aqueous electrolyte system capable of generating nitrogen; 3, heating the non-aqueous electrolyte system, placing the pretreated aluminum or aluminum alloy sample in the electrolyte system capable of generating nitrogen, taking a stainless steel plate or a stainless steel pool as a cathode, taking the pretreated aluminum or aluminum alloy sample as an anode, continuously feeding N2 into the electrolyte system, and carrying out liquid low-temperature plasma electrolytic nitriding treatment. The application provides a safe, efficient, environment-friendly, easy-to-operate and strong-designable method for preparing an AlN ceramic coating on the surface of aluminum or aluminum alloy.

Description

Technical Field

[0001] The present invention relates to the field of surface modification of aluminum and its alloys, and in particular to a method for preparing aluminum nitride ceramic coatings by liquid low-temperature plasma electrolytic nitriding on the surfaces of aluminum and its alloys. Background Art

[0002] Aluminum nitride (AlN) has the characteristics of high strength, high volume resistivity, high insulation withstand voltage, thermal expansion coefficient, good matching with silicon, etc. It is widely used in the field of ceramic electronic substrates and packaging materials, and its performance far exceeds that of aluminum oxide. At present, the preparation of AlN ceramic substrates usually requires high-temperature sintering, with the sintering temperature reaching as high as 1800°C, and it is difficult to sinter densely. Therefore, there is an urgent need to find a technology that is simple to operate and can prepare AlN ceramic substrates at low temperatures below 1000°C or even below 100°C. Micro-arc oxidation technology can prepare corresponding oxides on the surface of light alloys under normal temperature conditions, but it is difficult to achieve in-situ preparation of non-oxides. Based on this, the present invention provides a method for preparing aluminum nitride ceramic coatings by liquid low-temperature plasma electrolytic nitridation in a non-aqueous electrolyte system, which can grow AlN ceramic coatings in situ on aluminum alloy surfaces, and is expected to become an ideal substrate material for high-power integrated circuit packaging. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the existing methods for preparing AlN ceramic substrates usually require high-temperature sintering, with the sintering temperature reaching up to 1800°C, and are difficult to sinter densely. Instead, a method for preparing aluminum nitride ceramic coatings by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys is provided.

[0004] The present invention provides a method for preparing an AlN ceramic coating on the surface of aluminum or aluminum alloy, which is safe, efficient, environmentally friendly, easy to operate and highly designable.

[0005] A method for preparing aluminum nitride ceramic coatings on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding is specifically completed in the following steps:

[0006] 1. Pre-treating the surface of the aluminum or aluminum alloy sample to obtain a pre-treated aluminum or aluminum alloy sample;

[0007] 2. Configure a non-aqueous electrolyte system that can generate nitrogen;

[0008] The non-aqueous electrolyte system capable of generating nitrogen in step 2 comprises ammonium chloride and sodium nitrite;

[0009] 3. Heat the non-aqueous electrolyte system to generate nitrogen; place the pretreated aluminum or aluminum alloy sample in the electrolyte that can generate nitrogen, use a stainless steel plate or a stainless steel cell as the cathode, and the pretreated aluminum or aluminum alloy sample as the anode, continuously introduce N2 into the electrolyte, and the surface of the aluminum or aluminum alloy sample in the electrolyte is assisted by N2 to undergo liquid low-temperature plasma electrolytic nitriding treatment, forming an AlN ceramic coating in situ, thereby obtaining an aluminum or aluminum alloy sample with an aluminum nitride ceramic coating on the surface.

[0010] Principle of the present invention:

[0011] A special non-aqueous electrolyte system is designed. When the electrolyte temperature is greater than 85°C, a large amount of nitrogen can be generated. The electrical parameters are controlled by applying high voltage and a large pulse ratio. Under the action of discharge plasma, aluminum or aluminum alloy reacts with nitrogen to grow an AlN ceramic coating in situ. Nitrogen is also passed through the electrolyte to provide an adequate nitrogen source for full reaction with the aluminum substrate, ensuring the uniform and complete preparation of the AlN ceramic coating. In addition, the non-aqueous electrolyte system will not cause AlN hydrolysis, ensuring the formation of a uniform and complete ceramic coating on the surface of the aluminum substrate. The prepared uniform and dense AlN ceramic coating has excellent electrical insulation, corrosion resistance and good thermal conductivity, and can be used as a ceramic heat dissipation substrate to replace traditional packaging methods.

[0012] The method for preparing aluminum nitride ceramic coating by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys provided by the present invention has the following advantages:

[0013] (1) The present invention designs a non-aqueous electrolyte system that can generate nitrogen. The difference between this system and conventional electrolytes is that this system includes a non-aqueous electrolyte of saturated ammonium chloride and saturated sodium nitrite, which can generate a non-oxide ceramic coating in situ;

[0014] (2) nitrogen is introduced into the electrolyte system to assist in the preparation of the aluminum nitride ceramic coating, further ensuring that there is sufficient nitrogen to react under liquid low-temperature plasma conditions to form the AlN ceramic coating;

[0015] (3) The aluminum nitride ceramic coating on the surface of aluminum and its alloys prepared by the present invention has high electrical insulation and thermal conductivity, and has potential application prospects in the field of electronic packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of preparing aluminum nitride ceramic coatings by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys according to the present invention;

[0017] Figure 2 The non-aqueous electrolyte system capable of generating nitrogen prepared in Example 1, (a) is the electrolyte system at room temperature, and (b) is the electrolyte system heated at 85°C;

[0018] Figure 3 This is a SEM image of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0019] Figure 4 This is the XRD pattern of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0020] Figure 5 The macroscopic morphology of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0021] Figure 6 The bonding strength of the aluminum nitride ceramic coating on the aluminum surface prepared in Examples 1 to 3;

[0022] Figure 7 The electrical insulation properties of the aluminum nitride ceramic coatings on the aluminum surface prepared in Examples 1 to 3;

[0023] Figure 8 The thermal conductivity properties of the aluminum nitride ceramic coatings on the aluminum surface prepared in Examples 1 to 3. DETAILED DESCRIPTION

[0024] The following examples further illustrate the present invention, but should not be construed as limiting the present invention. Without departing from the essence of the present invention, modifications and substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0025] Specific embodiment 1: This embodiment is a method for preparing aluminum nitride ceramic coating by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys, which is specifically completed in the following steps (such as Figure 1 shown):

[0026] 1. Pre-treating the surface of the aluminum or aluminum alloy sample to obtain a pre-treated aluminum or aluminum alloy sample;

[0027] 2. Configure a non-aqueous electrolyte system that can generate nitrogen;

[0028] The non-aqueous electrolyte system capable of generating nitrogen in step 2 comprises ammonium chloride and sodium nitrite;

[0029] 3. Heat the non-aqueous electrolyte system to generate nitrogen; place the pretreated aluminum or aluminum alloy sample in the electrolyte that can generate nitrogen, use a stainless steel plate or a stainless steel cell as the cathode, and the pretreated aluminum or aluminum alloy sample as the anode, continuously introduce N2 into the electrolyte, and the surface of the aluminum or aluminum alloy sample in the electrolyte is assisted by N2 to undergo liquid low-temperature plasma electrolytic nitriding treatment, forming an AlN ceramic coating in situ, thereby obtaining an aluminum or aluminum alloy sample with an aluminum nitride ceramic coating on the surface.

[0030] This embodiment uses a non-aqueous electrolyte system that can generate N2, and with the assistance of N2, achieves a high-temperature effect and a substantial pressure gradient in the impact local electric field of strong pulse discharge and plasma discharge. When aluminum and its alloys fully react with N2, an AlN ceramic coating with a porous structure is formed, which is expected to become an ideal substrate material for high-power integrated circuit packaging.

[0031] The AlN ceramic coating on aluminum or aluminum alloys provided by this invention utilizes plasma nitridation technology to form a high-electrical-insulation / high-thermal-conductivity AlN ceramic coating on the surface of an aluminum or aluminum alloy substrate in a single step. Current existing technologies have not been able to achieve the in-situ preparation of AlN ceramic coatings on aluminum alloy surfaces. Furthermore, this technology can produce AlN ceramic coatings with excellent performance at low cost and at temperatures below 100°C, demonstrating its significant originality and potential as an ideal substrate material for high-power integrated circuit packaging.

[0032] Specific Embodiment 2: This embodiment differs from Specific Embodiment 1 in that the surface of the aluminum or aluminum alloy sample is pretreated in step 1 by polishing the surface of the aluminum or aluminum alloy sample with 600#, 1000#, and 1200# sandpaper, followed by ultrasonic cleaning with acetone and deionized water. The other steps are the same as those in Specific Embodiment 1.

[0033] In this embodiment, the purpose of polishing the surface of the aluminum or aluminum alloy sample with 600#, 1000#, and 1200# sandpaper in sequence is to remove burrs on the surface and corners of the aluminum and its alloy sample, remove surface foreign matter, and reduce the roughness of the aluminum and its alloy sample;

[0034] In this embodiment, the ultrasonic cleaning time using acetone is 10 minutes to 20 minutes to remove organic pollutants on the surface of the aluminum and its alloy samples;

[0035] In this embodiment, the ultrasonic cleaning time using deionized water is 20 minutes to 40 minutes to wash away organic residues on the surface, and the surface is air-dried for use.

[0036] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the sodium nitrite in step 2 is sodium nitrite crystals. The other steps are the same as those in specific embodiment 1 or 2.

[0037] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the sodium nitrite in step 2 is a saturated sodium nitrite solution. The other steps are the same as those in specific embodiments 1 to 3.

[0038] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the molar ratio of ammonium chloride to sodium nitrite in the non-aqueous electrolyte system capable of generating nitrogen in step 2 is 1:1. The other steps are the same as those in specific embodiments 1 to 4.

[0039] In this embodiment, the non-aqueous electrolyte system is heated to above 85° C. in order to allow ammonium chloride and sodium nitrite to react. The reaction equation is as follows:

[0040] NaNO2+NH4Cl==NH4NO2+NaCl(1);

[0041] NH4NO2=N2↑+2H2(2);

[0042] The above reaction formula can generate nitrogen in the electrolyte, which is beneficial for aluminum or aluminum alloy to react in a nitrogen-rich environment to form an AlN ceramic coating.

[0043] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: in step 3, 99.99% pure N2 at a pressure of 0.1 MPa is continuously introduced into the electrolyte. The other steps are the same as specific embodiments 1 to 5.

[0044] In this embodiment, the purpose of introducing 99.99% nitrogen at an atmospheric pressure of 0.1 MPa is to assist in the preparation of the aluminum nitride ceramic coating, ensuring sufficient nitrogen to react the aluminum substrate under liquid low-temperature plasma discharge conditions to form the AlN ceramic coating.

[0045] Specific Embodiment 7: This embodiment differs from Specific Embodiments 1 to 6 in that the parameters for the liquid low-temperature plasma electrolytic nitridation treatment described in step 3 include: an electrolyte temperature of 85°C to 100°C, a pulse voltage of 500V to 900V, and a nitridation treatment time of 10 minutes to 60 minutes. The other steps are the same as Specific Embodiments 1 to 6.

[0046] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the aluminum nitride ceramic coating on the surface of the aluminum or aluminum alloy sample in step 3 is a porous structure and is divided into two layers: the inner layer is a dense layer, and the outer layer is a porous layer. The other steps are the same as Specific Embodiments 1 to 7.

[0047] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the thickness of the aluminum nitride ceramic coating on the surface of the aluminum or aluminum alloy sample in step 3 is 5 μm to 100 μm, and the porosity is 5% to 20%. The other steps are the same as specific embodiments 1 to 8.

[0048] Specific Embodiment 10: This embodiment differs from Specific Embodiments 1 to 9 in that the aluminum nitride on the surface of the aluminum or aluminum alloy sample in step 3 has excellent mechanical properties (high bonding strength and scratch resistance), high electrical insulation, corrosion resistance, and good thermal conductivity, with an electrical insulation of ≥2000V. The other steps are the same as Specific Embodiments 1 to 9.

[0049] The following examples are used to verify the beneficial effects of the present invention:

[0050] Example 1: A method for preparing aluminum nitride ceramic coatings on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding, which is specifically completed in the following steps:

[0051] 1. The surface of the pure aluminum sample was polished with 600#, 1000#, and 1200# sandpaper in sequence to remove burrs on the surface and corners of the pure aluminum sample, remove surface foreign matter, and reduce the roughness of the aluminum and its alloy samples; then, acetone was used for ultrasonic cleaning for 20 minutes to remove organic pollutants on the surface of the aluminum and its alloy samples; finally, deionized water was used for ultrasonic cleaning for 20 minutes to wash away organic residues on the surface, and the sample was air-dried for use to obtain the pretreated aluminum sample;

[0052] 2. Configure a non-aqueous electrolyte system that can generate nitrogen;

[0053] The non-aqueous electrolyte system capable of generating nitrogen in step 2 comprises ammonium chloride, sodium nitrite and deionized water, wherein the molar ratio of ammonium chloride to sodium nitrite is 1:1, and the sodium nitrite is a saturated solution;

[0054] 3. The non-aqueous electrolyte system is heated to generate nitrogen; the pretreated aluminum sample is placed in the electrolyte capable of generating nitrogen, with the stainless steel cell as the cathode and the pretreated aluminum sample as the anode, and nitrogen with a purity of 99.99% at a pressure of 0.1 MPa is continuously introduced into the electrolyte. The surface of the aluminum sample in the electrolyte is assisted by nitrogen to undergo liquid low-temperature plasma electrolytic nitridation treatment, thereby forming an AlN ceramic coating in situ, thereby obtaining an aluminum sample having an AlN ceramic coating with a porous structure;

[0055] The parameters of the liquid low-temperature plasma electrolytic nitriding treatment described in step three include: an electrolyte temperature of 85° C., a pulse voltage of 600 V (constant voltage mode), and a nitriding treatment time of 20 minutes under stirring conditions.

[0056] The prepared coating surface presents a porous structure with a roughness of 1.7 μm, a porosity of about 15%, and a coating thickness of 12 μm.

[0057] Figure 2The non-aqueous electrolyte system capable of generating nitrogen prepared in Example 1, (a) is the electrolyte system at room temperature, and (b) is the electrolyte system heated at 85°C;

[0058] from Figure 2 It can be seen that the electrolyte is light yellow, and after heating it, the color of the electrolyte changes slightly and a large amount of nitrogen is generated.

[0059] Figure 3 This is a SEM image of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0060] Depend on Figure 3 It can be seen that the coating surface presents a porous structure with a roughness of 1.7 μm, a porosity of about 15%, and a coating thickness of 12 μm.

[0061] Figure 4 This is the XRD pattern of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0062] Figure 4 The horizontal axis 2Theta represents 2θ, and the vertical axis Intensity represents intensity, and the unit is arbitrary unit, which represents relative intensity. Figure 4 It can be seen that the main phase component of the AlN ceramic coating prepared on the pure aluminum surface is AlN phase, indicating that a ceramic coating with AlN as the main phase is formed on the aluminum surface under the induction of liquid low-temperature plasma discharge.

[0063] Figure 5 The macroscopic morphology of the aluminum nitride ceramic coating on the aluminum surface prepared in Example 1;

[0064] from Figure 5 It can be seen that the AlN ceramic coating is evenly prepared on the surface of the aluminum substrate.

[0065] Example 2: A method for preparing aluminum nitride ceramic coatings on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding, which is specifically completed in the following steps:

[0066] 1. The surface of the pure aluminum sample was polished with 600#, 1000#, and 1200# sandpaper in sequence to remove burrs on the surface and corners of the pure aluminum sample, remove surface foreign matter, and reduce the roughness of the aluminum and its alloy samples; then, acetone was used for ultrasonic cleaning for 30 minutes to remove organic pollutants on the surface of the aluminum and its alloy samples; finally, deionized water was used for ultrasonic cleaning for 30 minutes to wash away organic residues on the surface, and the sample was air-dried for use to obtain the pretreated aluminum sample;

[0067] 2. Configure a non-aqueous electrolyte system that can generate nitrogen;

[0068] The non-aqueous electrolyte system capable of generating nitrogen in step 2 comprises ammonium chloride, sodium nitrite and deionized water, wherein the molar ratio of ammonium chloride to sodium nitrite is 2:1, and the sodium nitrite is a saturated solution;

[0069] 3. The non-aqueous electrolyte system is heated to generate nitrogen; the pretreated aluminum sample is placed in the electrolyte capable of generating nitrogen, with the stainless steel cell as the cathode and the pretreated aluminum sample as the anode, and nitrogen with a purity of 99.99% at a pressure of 0.1 MPa is continuously introduced into the electrolyte. The surface of the aluminum sample in the electrolyte is assisted by nitrogen to undergo liquid low-temperature plasma electrolytic nitridation treatment, thereby forming an AlN ceramic coating in situ, thereby obtaining an aluminum sample having an AlN ceramic coating with a porous structure;

[0070] The parameters of the liquid low-temperature plasma electrolytic nitriding treatment described in step three include: an electrolyte temperature of 95° C., a pulse voltage of 700 V (constant voltage mode), and a nitriding treatment time of 30 minutes under stirring conditions.

[0071] The surface of the prepared coating presents a porous structure with a roughness of 1.8 μm, a porosity of about 16%, and a coating thickness of 26 μm.

[0072] Example 3: A method for preparing aluminum nitride ceramic coatings on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding, which is specifically completed in the following steps:

[0073] 1. The surface of the pure aluminum sample was polished with 600#, 1000#, and 1200# sandpaper in sequence to remove burrs on the surface and corners of the pure aluminum sample, remove surface foreign matter, and reduce the roughness of the aluminum and its alloy samples; then, acetone was used for ultrasonic cleaning for 40 minutes to remove organic pollutants on the surface of the aluminum and its alloy samples; finally, deionized water was used for ultrasonic cleaning for 40 minutes to wash away organic residues on the surface, and the sample was air-dried for use to obtain the pretreated aluminum sample;

[0074] 2. Configure a non-aqueous electrolyte system that can generate nitrogen;

[0075] The non-aqueous electrolyte system capable of generating nitrogen in step 2 comprises ammonium chloride, sodium nitrite and deionized water, wherein the molar ratio of ammonium chloride to sodium nitrite is 1:2, and the sodium nitrite is a saturated solution;

[0076] 3. The non-aqueous electrolyte system is heated to generate nitrogen; the pretreated aluminum sample is placed in the electrolyte capable of generating nitrogen, with the stainless steel cell as the cathode and the pretreated aluminum sample as the anode, and nitrogen with a purity of 99.99% at a pressure of 0.1 MPa is continuously introduced into the electrolyte. The surface of the aluminum sample in the electrolyte is assisted by nitrogen to undergo liquid low-temperature plasma electrolytic nitridation treatment, thereby forming an AlN ceramic coating in situ, thereby obtaining an aluminum sample having an AlN ceramic coating with a porous structure;

[0077] The parameters of the liquid low-temperature plasma electrolytic nitriding treatment described in step three include: an electrolyte temperature of 100° C., a pulse voltage of 750 V (constant voltage mode), and a nitriding treatment time of 40 minutes under stirring conditions.

[0078] The surface of the prepared coating presents a porous structure with a roughness of 2.5 μm, a porosity of about 30%, and a coating thickness of 46 μm.

[0079] Figure 6 The bonding strength of the aluminum nitride ceramic coating on the aluminum surface prepared in Examples 1 to 3;

[0080] Figure 7 The electrical insulation properties of the aluminum nitride ceramic coatings on the aluminum surface prepared in Examples 1 to 3;

[0081] Figure 8 Thermal conductivity properties of aluminum nitride ceramic coatings on aluminum surfaces prepared in Examples 1 to 3;

[0082] from Figures 6 to 8 It can be seen that:

[0083] The coating prepared in Example 1 has excellent mechanical properties (bonding strength of 42 MPa); excellent electrical insulation (breakdown voltage of 552±12 V; insulation resistance of 168±9 MΩ); high corrosion resistance (neutral salt spray resistance>1500 h); and good thermal conductivity (179±12 W / mK).

[0084] The coating prepared in Example 2 has excellent mechanical properties (bonding strength of 38 MPa); excellent electrical insulation (breakdown voltage of 1092±34 V; insulation resistance of 199±8 MΩ); high corrosion resistance (neutral salt spray resistance >1500 h); and good thermal conductivity (163±9 W / mK).

[0085] The coating prepared in Example 3 has excellent mechanical properties (bonding strength reaches 35 MPa); excellent electrical insulation (breakdown voltage reaches 1190±29 V; insulation resistance reaches 263 MΩ); high corrosion resistance (neutral salt spray resistance >1500 h); and good thermal conductivity (154±14 W / mK).

Claims

1. A method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding, characterized in that The preparation method is specifically completed according to the following steps:

1. Pre-treating the surface of the aluminum or aluminum alloy sample to obtain a pre-treated aluminum or aluminum alloy sample; 2. Configure an electrolyte system that can generate nitrogen; The electrolyte system capable of generating nitrogen in step 2 is composed of ammonium chloride, sodium nitrite and deionized water; the sodium nitrite is a saturated solution; 3. Heating the electrolyte system to generate nitrogen; placing the pretreated aluminum or aluminum alloy sample in the electrolyte capable of generating nitrogen, using a stainless steel plate or a stainless steel cell as a cathode and the pretreated aluminum or aluminum alloy sample as an anode, continuously introducing N2 into the electrolyte, and assisting the surface of the aluminum or aluminum alloy sample in the electrolyte with N2 to undergo liquid low-temperature plasma electrolytic nitriding treatment, thereby forming an AlN ceramic coating in situ, and obtaining an aluminum or aluminum alloy sample having an aluminum nitride ceramic coating on the surface; The parameters of the liquid low-temperature plasma electrolytic nitriding treatment described in step three include: electrolyte temperature of 85°C to 100°C, pulse voltage of 500V to 900V, and nitriding treatment time of 10min to 60min.

2. The method for preparing aluminum nitride ceramic coating by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys according to claim 1, characterized in that The specific method for pretreating the surface of the aluminum or aluminum alloy sample in step 1 is: polishing the surface of the aluminum or aluminum alloy sample with 600#, 1000#, and 1200# sandpaper in sequence, and then ultrasonically cleaning it with acetone and deionized water in sequence.

3. The method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding according to claim 1, characterized in that The molar ratio of ammonium chloride to sodium nitrite in the electrolyte system capable of generating nitrogen in step 2 is (1-2):(1-2).

4. The method for preparing aluminum nitride ceramic coating by liquid low-temperature plasma electrolytic nitriding on the surface of aluminum and its alloys according to claim 1, characterized in that In step 3, N2 with a purity of 99.99% at a pressure of 0.1 MPa is continuously introduced into the electrolyte.

5. The method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding according to claim 1, characterized in that In step 3, the aluminum nitride ceramic coating on the surface of the aluminum or aluminum alloy sample has a porous structure and is divided into two layers, the inner layer is a dense layer, and the outer layer is a porous layer.

6. The method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding according to claim 1, characterized in that In step 3, the aluminum nitride ceramic coating on the surface of the aluminum or aluminum alloy sample has a thickness of 5 μm to 100 μm and a porosity of 5% to 20%.

7. The method for preparing aluminum nitride ceramic coating on the surface of aluminum and its alloys by liquid low-temperature plasma electrolytic nitriding according to claim 1, characterized in that The aluminum nitride on the surface of the aluminum or aluminum alloy sample in step 3 has excellent electrical insulation, corrosion resistance and good thermal conductivity, and the electrical insulation is ≥2000V.

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