A multi-layer structure thermal barrier coating on a magnesium alloy surface and a preparation method thereof

Abstract

The application discloses a magnesium alloy surface multilayer structure thermal barrier coating and a preparation method thereof, and belongs to the technical field of metal material surface coating. The magnesium alloy surface multilayer structure thermal barrier coating comprises a ceramic layer, a Ni-P layer and a Ni layer arranged on the surface of a magnesium alloy base body in sequence from inside to outside. The ceramic layer, the Ni-P layer and the Ni layer are used as the intermediate layer of the magnesium alloy surface multilayer structure thermal barrier coating, the thermal conductivity and the thermal expansion coefficient of the ceramic layer, the Ni-P layer and the Ni layer are gradiently reduced, the interface thermal effect mismatching problem between a metal base body and a thermal barrier coating under a conventional thermal barrier coating is effectively relieved, the thermal shock life of the thermal barrier coating is improved, and the heat resistance of the thermal barrier coating is improved. Moreover, the ceramic layer, the Ni-P layer and the Ni layer have a synergistic effect, the magnesium alloy surface multilayer structure thermal barrier coating can resist oxidation and delay thermal corrosion under the erosion of a corrosive medium and a high-temperature state, and has good corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface coating of metal materials, and in particular to a multi-layer structure thermal barrier coating on the surface of a magnesium alloy and a preparation method thereof. BACKGROUND

[0002] Magnesium alloy has been widely used in various industries due to its low density, high specific strength and rigidity, and easy processing. However, magnesium alloy is chemically active and has a low equilibrium potential (-2.37 V), which makes it prone to corrosion in humid air, seawater, and acidic media. In order to better preserve and apply magnesium alloy, certain protective measures need to be taken. In addition, the melting point of magnesium alloy is relatively low, and its long-term use temperature is below 200℃. The working temperature of high-temperature components such as marine ship turbine blades will reach 400℃, which exceeds the commonly used working temperature range of magnesium alloy, restricting the use of magnesium alloy at higher temperatures. In order to improve the performance of magnesium alloy, surface coating treatment technology is often used to treat the surface of magnesium alloy.

[0003] Thermal barrier coating is a ceramic material with high temperature resistance, corrosion resistance, and good thermal insulation performance deposited on the surface of an alloy substrate according to a certain process route. Thermal barrier coating is generally connected to the metal surface through a metal bonding layer and composed of an outer ceramic layer. Thermal barrier coating can relieve interfacial stress, improve the bonding strength between the coating and the substrate, enhance thermal shock resistance and prolong service life. The ceramic layer has the characteristics of large thermal expansion coefficient, good heat resistance, and low thermal conductivity, and the metal bonding layer has strong oxidation resistance and high temperature resistance. However, the working environment of turbine blade thermal barrier coating is harsh, and it is easily affected by corrosion medium, high temperature oxidation, and fatigue failure. In order to further alleviate the mismatch of interfacial thermal effects between the metal surface and the thermal barrier coating, improve the corrosion resistance of the coating, and reduce the interfacial stress, a multi-layer thermal barrier coating structure system has been developed, which introduces an intermediate layer between the metal surface and the metal bonding layer to reduce the failure caused by the mismatch of thermal expansion coefficients between the metal surface and the metal bonding layer, and improve the bonding strength and thermal shock service life of the coating.

[0004] Currently, there are some related reports on multi-layer thermal barrier coating structure system:

[0005] Patent CN201810749678.8 discloses a novel structural thermal barrier coating (TBC) for magnesium alloy surfaces and its preparation method. The coating, composed of a Ni-P / Al / Ni-P transition layer, a NiCoCrAlY bonding layer, and a YSZ ceramic top layer, significantly improves the thermal shock life of the TBC. The novel Ni-P / Al / Ni-P "sandwich" transition layer structure addresses the problem of poor interfacial bonding stability between the TBC and the magnesium alloy substrate caused by plasma flame oxidation and ablation of the magnesium alloy substrate during the APS process, as well as thermal expansion mismatch between the coating and the substrate. This significantly improves the bonding strength and high-temperature thermal shock life of the TBC on the magnesium alloy surface.

[0006] Patent CN202011201622.2 discloses a novel magnesium alloy thermal barrier coating and its preparation method. An adhesive layer is generated in situ on a magnesium alloy substrate. The upper layer of the adhesive layer is a loose and porous micro-arc oxidation layer, and the lower layer is a dense micro-arc oxidation layer. Subsequently, an 8YSZ ceramic surface layer is prepared on the adhesive layer using atmospheric plasma spraying technology, thereby preparing a new YSZ / PEO / Mg thermal barrier coating system. The micro-arc oxidation layer has a high bonding strength with the substrate. At the same time, the loose and porous structure of the upper micro-arc oxidation layer increases the contact area with the surface YSZ layer, forming a structure in which YSZ is embedded in the upper layer of the micro-arc oxidation layer, thereby improving the bonding strength between the metal surface layer and the adhesive layer.

[0007] Patent CN201010196233.5 discloses a method for preparing thermal barrier coatings on the surfaces of aluminum, magnesium alloys and their composite materials. The method comprises the following steps: first, the surface of the aluminum, magnesium alloys and their composite materials is electrolytically oxidized to form a film medium using a silicate and phosphate system plasma electrolyte; then, electrophoretic deposition is performed on the basis of the plasma electrolytic oxidation film using an electrophoretic deposition electrolyte to obtain a thermal barrier coating on the surface of the aluminum, magnesium alloys and their composite materials. The obtained plasma electrolytic oxidation-electrophoretic composite ceramic layer has a smooth surface, firm bonding, controllable thickness, is dense and porous, and has good thermal insulation and thermal shock resistance. The layer is suitable for working parts with surfaces of various sizes and complex shapes.

[0008] Patent CN201310320747.0 discloses a thermal barrier coating containing a hot corrosion-resistant transition primer and its preparation method. A uniform, dense nickel-phosphorus coating is deposited on the surface of ductile iron. This coating serves as a transition layer between the substrate and the thermal barrier coating and as a substrate protective coating. The thermal barrier coating is then deposited on top of this coating. By improving the interdiffusion between the bonding layer and the substrate, the coating significantly improves the corrosion resistance of the ductile iron and the thermal shock resistance of the thermal barrier coating, extending the service life of the thermal barrier coating. The uniform, dense nickel-phosphorus coating, with a thickness of 20 to 35 microns, can be deposited on the surface of the ductile iron, significantly improving the corrosion resistance of the ductile iron.

[0009] Patent CN201711291622.4 discloses a preparation method of thermal barrier coating with antioxidant protective film, YSZ@Ni nano core-shell particles are mixed with NiCoCrAlY binder metal powder by grinding; 2%wt PVA124 binder is mixed with NiCoCrAlY3 / YSZ@Ni7 mixed powder, a pre-coating layer is pre-coated on the substrate, and dried for use. The thermal barrier coating is prepared by laser cladding. The advantage is that a protective oxidation film is formed during the coating preparation process, not only excellent heat insulation performance, but also excellent oxidation resistance, and the connection between the ceramic layer and the substrate is improved, thus prolonging the service life of the coating.

[0010] However, the above-mentioned multilayer thermal barrier coating structure system is easy to corrode in a humid and high temperature environment, which greatly limits the application of the multilayer structure thermal barrier coating on the surface of the magnesium alloy. Therefore, it has potential significance to develop a new multilayer structure thermal barrier coating on the surface of the magnesium alloy and a preparation method thereof for improving the corrosion inhibition process of the thermal barrier coating on the magnesium alloy substrate, improving the bonding strength and heat resistance of the thermal barrier coating on the surface of the magnesium alloy, and realizing the application of the thermal barrier coating on the magnesium alloy turbine blade. SUMMARY

[0011] Therefore, the technical problem to be solved by the present application is to provide a multilayer structure thermal barrier coating on the surface of a magnesium alloy and a preparation method thereof. The multilayer structure thermal barrier coating on the surface of the magnesium alloy has good heat resistance, corrosion resistance and interface bonding force.

[0012] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0013] The present application provides a multilayer structure thermal barrier coating on the surface of a magnesium alloy, which comprises a ceramic layer, a Ni-P layer and a Ni layer arranged in turn from inside to outside on the surface of a magnesium alloy substrate. Preferably, the main component phase of the ceramic layer is MgAl2O4 and MgO;

[0014] Preferably, the Ni-P layer contains 10-12wt% of phosphorus element and 88-90wt% of nickel element;

[0015] More preferably, the Ni-P layer contains 10-11wt% of phosphorus element and 89-90wt% of nickel element;

[0016] Further preferably, the Ni-P layer contains 10wt% of phosphorus element and 90wt% of nickel element.

[0017] Preferably, the Ni layer contains 98-99.6wt% of nickel element and 0.4-2wt% of oxygen element.

[0018] More preferably, the Ni layer contains 99-99.6wt% of nickel element and 0.4-1wt% of oxygen element.

[0019] Further preferably, the Ni layer contains 99.6wt% of nickel element and 0.4wt% of oxygen element.

[0020] The magnesium alloy surface multilayer structure thermal barrier coating has the ceramic layer, the Ni-P layer and the Ni layer arranged in the magnesium alloy substrate surface from inside to outside as the intermediate layer of the thermal barrier coating, the thickness of the intermediate layer is controlled, and the magnesium alloy surface multilayer structure thermal barrier coating with long thermal shock life and good thermal corrosion delaying capacity is obtained.

[0021] The thickness of the intermediate layer is the sum of the thickness of the ceramic layer, the thickness of the Ni-P layer and the thickness of the Ni layer.

[0022] Preferably, the thickness of the ceramic layer is 15-20um; more preferably, 16-20um; further preferably, 20um.

[0023] Preferably, the thickness of the Ni-P layer is 30-40um; more preferably, 30-35um; further preferably, 30um. Preferably, the thickness of the Ni layer is 40-100um; more preferably, 65-100um; further preferably, 100um. In some specific embodiments of the present application, preferably, the thickness of the Ni layer is 45um, 65um or 100um.

[0024] The thermal conductivity and the thermal expansion coefficient of the ceramic layer, the Ni-P layer and the Ni layer in the intermediate layer are gradiently reduced, and the interface thermal effect mismatching problem between the metal substrate and the thermal barrier coating of the conventional thermal barrier coating is effectively alleviated.

[0025] And under the synergistic effect of the ceramic layer and the Ni layer, the magnesium alloy surface multilayer structure thermal barrier coating can play a good antioxidation and thermal corrosion delaying effect under the corrosion medium erosion and high temperature state.

[0026] Preferably, the magnesium alloy surface multilayer structure thermal barrier coating further comprises a metal bonding layer and a ceramic thermal insulation layer.

[0027] Preferably, the metal bonding layer and the ceramic thermal insulation layer are arranged in the surface of the Ni layer from inside to outside.

[0028] Preferably, the metal bonding layer is selected from a NiCrAlY layer.

[0029] Preferably, the thickness of the NiCrAlY layer is 80-150um; more preferably, 100um.

[0030] Preferably, the ceramic thermal barrier layer is selected from 8YSZ layer.

[0031] Preferably, the thickness of the 8YSZ layer is 150-300 μm. More preferably, 250 μm.

[0032] The present application also provides a preparation method of the magnesium alloy surface multilayer structure thermal barrier coating, comprising the following steps:

[0033] 1) placing the surface treated magnesium alloy substrate into a micro-arc oxidation electrolyte solution to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy substrate by arc discharge;

[0034] 2) sequentially performing surface sensitization, activation and reduction treatment on the micro-arc oxidation ceramic layer obtained in step 1), and then performing chemical plating of Ni-P coating on the surface of the micro-arc oxidation ceramic layer to obtain a Ni-P coating;

[0035] 3) performing electrodeposition of Ni coating on the surface of the above Ni-P coating to obtain a Ni coating;

[0036] 4) sequentially performing plasma spraying of NiCrAlY powder as a metal bonding layer and spraying of 8YSZ powder as a ceramic thermal barrier layer on the surface of the prepared Ni coating to finally prepare a magnesium alloy surface multilayer structure thermal barrier coating.

[0037] The magnesium alloy surface multilayer structure thermal barrier coating prepared by the preparation method can improve the occlusion state and chemical stability of the interface between the thermal barrier coating and the magnesium alloy substrate, enhance the corrosion inhibition process of the thermal barrier coating on the magnesium alloy substrate, improve the bonding strength between the magnesium alloy surface and the thermal barrier coating, and improve the heat resistance and corrosion resistance of the thermal barrier coating.

[0038] The process parameters include the composition of the micro-arc oxidation electrolyte solution, the Ni-P plating solution and the Ni deposition solution, and the experimental parameters during the preparation of the micro-arc oxidation ceramic layer, the Ni-P coating and the Ni coating.

[0039] In the preparation method of the magnesium alloy surface multilayer structure thermal barrier coating, the surface treated magnesium alloy substrate in step 1) is preferably a magnesium alloy substrate obtained by sequentially cleaning with anhydrous ethanol and acetone and then drying.

[0040] Preferably, the micro-arc oxidation electrolyte solution in step 1) is a mixed solution of 8-10 g / L sodium metaaluminate, 3-5 g / L sodium fluoride, 2-4 g / L sodium citrate, 2-4 g / L sodium hydroxide and 1-3 g / L sodium tetraborate.

[0041] In some specific embodiments of the present application, the alkali sodium aluminate electrolyte solution in step 1) is preferably a mixed solution of 10 g / L sodium metaaluminate, 3 g / L sodium fluoride, 3 g / L sodium citrate, 2 g / L sodium hydroxide and 2 g / L sodium tetraborate.

[0042] Preferably, the Ni-P plating solution used in step 2) is a mixed solution of 20-25 g / L NiSO4·6H2O, 7-10 g / L CH3COONa, 15-20 g / L NH4HF, 20-25 g / L NaH2PO2·H2O and 8-10 mL / L HF.

[0043] The pH of the Ni-P plating solution is preferably 6.0-6.5.

[0044] In some specific embodiments of the present application, the Ni-P plating solution used in step 2) is preferably a mixed solution of 20 g / L NiSO4·6H2O, 10 g / L CH3COONa, 20 g / L NH4HF, 20 g / L NaH2PO2·H2O and 10 mL / L HF.

[0045] Preferably, the pH of the Ni-P plating solution is 6.0-6.5.

[0046] Preferably, the sensitizing solution used in step 2) is SnCl2 and HCl.

[0047] The concentration of SnCl2 is preferably 1 g / L, and the concentration of HCl is preferably 1 mL / L.

[0048] Specifically, the magnesium alloy substrate with the micro-arc oxidation ceramic layer obtained in step 1) is placed in the sensitizing solution and sensitized at room temperature.

[0049] The sensitizing time is preferably 1 min.

[0050] The sensitizing treatment can form a dense film layer with a reducing effect on the surface of the micro-arc oxidation ceramic layer, which is conducive to forming more activation centers during activation.

[0051] After the sensitizing treatment, the magnesium alloy substrate with the micro-arc oxidation ceramic layer is activated.

[0052] The activation solution used in step 2) is preferably PdCl2 and HCl.

[0053] The concentration of PdCl2 is preferably 1 g / L, and the concentration of HCl is preferably 1 mL / L.

[0054] Specifically, the sample after step 1) is placed in the activation solution and activated at room temperature.

[0055] The activation time is preferably 1 minute.

[0056] The above activation treatment can make the Pd activation center distributed on the surface of the ceramic layer of micro-arc oxidation, and the Pd activation center can act as a crystallization center to promote the formation of the Ni-P layer.

[0057] The reducing solution used in step 2) is preferably NaH2PO2.

[0058] The concentration of NaH2PO2 is preferably 2 g / L.

[0059] Specifically, the sample after step 1) is placed in the activation solution and activated at room temperature.

[0060] The activation time is preferably 1 minute.

[0061] The above activation treatment can make the Pd activation center distributed on the surface of the ceramic layer of micro-arc oxidation, and the Pd activation center can act as a crystallization center to promote the formation of the Ni-P layer.

[0062] In the preferred embodiment of the present application, the Ni deposition solution used in step 3) for electrodeposition of the Ni coating is a mixed solution of 280-300 g / L of NiSO4·6H2O, 40-60 g / L of NiCl2 and 30-40 g / L of H3BO3.

[0063] In some specific embodiments of the present application, the Ni deposition solution used in step 3) for electrodeposition of the Ni coating is preferably a mixed solution of 300 g / L of NiSO4·6H2O, 40 g / L of NiCl2 and 30 g / L of H3BO3.

[0064] Preferably, the pH of the Ni deposition solution is 4-5; more preferably 4.5.

[0065] In the preferred embodiment of the present application, the time for electrodeposition of the Ni coating in step 3) is 1-4 hours.

[0066] In the preferred embodiment of the present application, the constant voltage for forming the ceramic layer of micro-arc oxidation in step 1) is 460-480 V, and the working frequency is 500-510 Hz. In some specific embodiments of the present application, the constant voltage for forming the ceramic layer of micro-arc oxidation in step 1) is 460 V, and the working frequency is 500 Hz.

[0067] Preferably, the reaction temperature for chemical plating of the Ni-P coating in step 2) is 80-85°C, and the reaction time is 1-1.5 hours.

[0068] In some embodiments of the present application, the reaction temperature of the electroless Ni-P coating in step 2) is 80℃, and the reaction time is 1h.

[0069] Preferably, the reaction temperature of the electrodeposited Ni coating in step 3) is 40-50℃, the current density is 4-8A / cm 2 , and the pulse duty cycle is 40-50%. In some embodiments of the present application, the reaction temperature of the electrodeposited Ni coating in step 3) is 50℃, the current density is 8A / cm 2 , and the pulse duty cycle is 40%.

[0070] Preferably, when the plasma spraying of the NiCrAlY powder as the metal bonding layer and the spraying of the 8YSZ powder as the ceramic thermal barrier layer in step 4) is performed, the process parameters are as follows:

[0071] the spraying current is 500-600A;

[0072] the argon flow rate is 45-47SLPM;

[0073] the hydrogen flow rate is 7-9SLPM;

[0074] the spraying distance is 80-100mm.

[0075] In some embodiments of the present application, preferably, the process parameters are as follows:

[0076] the spraying current is 550A;

[0077] the argon flow rate is 45SLPM;

[0078] the hydrogen flow rate is 9SLPM;

[0079] the spraying distance is 100mm.

[0080] Compared with the prior art, the magnesium alloy surface multilayer structure thermal barrier coating provided by the present application comprises a ceramic layer, a Ni-P layer and a Ni layer arranged in turn from the inside to the outside on the surface of a magnesium alloy substrate. The ceramic layer, the Ni-P layer and the Ni layer are used as the intermediate layer of the magnesium alloy surface multilayer structure thermal barrier coating, and the thermal conductivity and the thermal expansion coefficient of the ceramic layer, the Ni-P layer and the Ni layer decrease in a gradient manner, which effectively alleviates the problem of the mismatch of the interface thermal effect between the metal substrate and the thermal barrier coating of the conventional thermal barrier coating, improves the thermal shock life of the thermal barrier coating, and improves the heat resistance of the thermal barrier coating. Moreover, the ceramic layer, the Ni-P layer and the Ni layer have a synergistic effect, and the magnesium alloy surface multilayer structure thermal barrier coating can resist oxidation and delay hot corrosion under the erosion of the corrosion medium and in the high-temperature state, and has good corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0081] Figure 1A structure diagram of the multilayer structure thermal barrier coating on the surface of the magnesium alloy according to the present application, wherein 1 is a magnesium alloy substrate, 2 is a multilayer structure thermal barrier coating, 21 is a micro-arc oxidation ceramic layer, 22 is a chemical plating Ni-P layer, 23 is an electrodeposition Ni layer, 24 is a NiCrAlY metal bonding layer, and 25 is an 8YSZ outer ceramic layer;

[0082] Figure 2 A preparation flow chart of the multilayer structure thermal barrier coating on the surface of the magnesium alloy according to the present application;

[0083] Figure 3 An XRD diagram of the ceramic layer in the multilayer structure thermal barrier coating on the surface of the magnesium alloy prepared in Example 1;

[0084] Figure 4 An XRD diagram of the Ni-P layer in the multilayer structure thermal barrier coating on the surface of the magnesium alloy prepared in Example 1;

[0085] Figure 5 An XRD diagram of the Ni layer in the multilayer structure thermal barrier coating on the surface of the magnesium alloy prepared in Example 1;

[0086] Figure 6 An SEM morphology diagram of the section of the intermediate layer in the multilayer structure thermal barrier coating on the surface of the magnesium alloy prepared in Example 3. DETAILED DESCRIPTION

[0087] In order to further illustrate the present application, the multilayer structure thermal barrier coating on the surface of the magnesium alloy and the preparation method thereof provided by the present application are described in detail below in combination with examples.

[0088] The outer ceramic layer described below is the ceramic thermal barrier layer described above.

[0089] The NiCrAlY powder described below is purchased from Beijing General Research Institute of Mining and Metallurgy, and the specific structure is Ni 24.87 Cr 4.62 Al 0.58 Y; the 8YSZ powder is purchased from Beijing General Research Institute of Mining and Metallurgy, and the model is ZrO2-8%Y2O3; other reaction raw materials and reagents are all ordinary commercially available products.

[0090] Example 1

[0091] A multilayer structure thermal barrier coating on the surface of a magnesium alloy and a preparation method thereof, comprising the following steps:

[0092] Step one: 10g sodium metaaluminate, 3g sodium fluoride, 3g sodium citrate, 2g sodium hydroxide, 2g sodium tetraborate were weighed and dissolved in deionized water respectively, then mixed and dissolved in deionized water to 1L as alkali metal sodium aluminate electrolyte solution. The sample was placed in the electrolyte, and a micro-arc oxidation ceramic layer (20μm) was obtained under constant voltage 460V and working frequency 500Hz. The sample was cleaned with deionized water and dried in a vacuum drying oven for use;

[0093] Step two: 1g / L SnCl2 and 1mL / L HCl were dissolved in deionized water to prepare a sensitizing solution. The micro-arc oxidation ceramic layer was placed in the sensitizing solution for sensitization treatment to form a film layer with reducing effect on the surface of the micro-arc oxidation ceramic layer. The time was 1min, and the sample was taken out and washed with deionized water. 1g / L PdCl2 and 1mL / L HCl were dissolved in deionized water to prepare an activating solution. The sensitized sample was placed in the activating solution for activation treatment. The time was 1min, and the sample was taken out and washed with deionized water. 2g / L NaH2PO2 was dissolved in deionized water to prepare a reducing solution. The activated sample was placed in the reducing solution for reduction treatment to reduce the insufficient Pd. The time was 1min;

[0094] Step three: 20g NiSO4·6H2O, 10g CH3COONa, 20g NH4HF, 20g NaH2PO2·H2O, and 10mL HF were dissolved in deionized water respectively, and then added to the NiSO4·6H2O solution in sequence and mixed uniformly. The volume was made up to 1L with deionized water, and appropriate thiourea was added as a stabilizer. Finally, the pH was adjusted to 6.0-6.5 with ammonia water. The chemical plating solution was heated to 80℃ using a water bath, and the reduced sample was placed in the chemical plating solution for 1h to obtain a Ni-P coating (30μm thick);

[0095] Step four: The chemical plating sample was subjected to oil removal treatment and dried in a vacuum drying oven for use. 300g / L NiSO4·6H2O and 40g / L NiCl2 were dissolved in deionized water respectively. After the NiSO4·6H2O solution and the NiCl2 solution were mixed and stirred uniformly, 30g / L H3BO3 was added and stirred. Finally, the volume was made up to 1L with deionized water, and a lubricant, sodium dodecyl sulfate, was added. The pH was adjusted to 4.5 with 1wt% H2SO4 solution. The prepared electrodeposition plating solution was heated to 50℃ using a water bath, and the oil-removed sample was placed in the electrodeposition plating solution. The current density was adjusted to 8A / cm 2 , the duty cycle was 40%, and the electrodeposition time was 1h to obtain a Ni coating (45μm thick);

[0096] Step five: the sample is subjected to oil removal treatment, and is placed in a vacuum drying oven for drying. The sample after oil removal is subjected to sand blasting treatment, the spray gun is 10 cm away from the surface of the sample, the spraying time is 30 s, the pressure is 30 MPa, the surface of the sample after sand blasting is subjected to plasma spraying treatment, NiCrAlY powder is used as a metal bonding layer (100 μm in thickness), 8YSZ powder is used as a ceramic thermal barrier layer (250 μm in thickness), plasma spraying is performed, and finally a magnesium alloy surface multilayer structure thermal barrier coating is prepared. The spraying current is 550 A, the argon flow rate is 45 SLPM, the hydrogen flow rate is 9 SLPM, and the spraying distance is 100 mm.

[0097] Figure 3 The XRD pattern of the ceramic layer (micro-arc oxidation ceramic layer) in the magnesium alloy surface multilayer structure thermal barrier coating prepared in Example 1. From Figure 3 It can be seen that the micro-arc oxidation ceramic layer is mainly composed of MgO and MgAl2O4. The formation of MgAl2O4 is conducive to improving the corrosion resistance of the micro-arc oxidation ceramic layer.

[0098] Figure 4 The XRD pattern of the Ni-P layer in the magnesium alloy surface multilayer structure thermal barrier coating prepared in Example 1. From Figure 4 It can be seen that the diffraction peak at 2θ = 45° forms a diffuse scattering nickel diffraction main peak, and a broadening appears, and the second and third strong peaks disappear, indicating that the phosphorus atoms enter the face-centered cubic nickel lattice, causing the lattice to distort, so that the main peak appears obvious broadening, indicating that the electroless Ni-P coating is in an amorphous state.

[0099] Figure 5 The XRD pattern of the Ni layer in the magnesium alloy surface multilayer structure thermal barrier coating prepared in Example 1, wherein the diffraction peaks at 44°, 52° and 76° correspond to the (111), (200) and (220) crystal planes of face-centered cubic nickel, respectively.

[0100] Example 2

[0101] A magnesium alloy surface multilayer structure thermal barrier coating and a preparation method thereof, comprising the following steps:

[0102] Step one: 10 g of sodium metaaluminate, 3 g of sodium fluoride, 3 g of sodium citrate, 2 g of sodium hydroxide, and 2 g of sodium tetraborate are weighed, and are sequentially dissolved in a proper amount of deionized water, and then are mixed to be uniform. The mixed solution is made into an alkali metal sodium aluminate electrolyte solution by being made constant volume to 1 L with deionized water. The sample is placed in the electrolyte, and a micro-arc oxidation ceramic layer (20 μm) is obtained under a constant voltage of 460 V and a working frequency of 500 Hz. The sample is washed with deionized water and is placed in a vacuum drying oven for drying.

[0103] Step two: 1 g / L SnCl2, 1 mL / L HCl were dissolved with deionized water, and the sensitizing solution was prepared by stirring. The micro-arc oxidation ceramic layer was placed in the sensitizing solution for sensitization treatment, so that a film layer with reducing effect was generated on the surface of the micro-arc oxidation ceramic layer. The time was 1 min, and the sample was taken out and washed with deionized water. 1 g / L PdCl2, 1 mL / L HCl were dissolved with deionized water, and the activating solution was prepared by stirring. The sensitized sample was placed in the activating solution for activation treatment, and the time was 1 min. The sample was taken out and washed with deionized water. 2 g / L NaH2PO2 was dissolved with deionized water, and the reducing solution was prepared by stirring. The activated sample was placed in the reducing solution for reduction treatment to reduce the insufficient Pd, and the time was 1 min.

[0104] Step three: 20 g of NiSO4·6H2O, 10 g of CH3COONa, 20 g of NH4HF, 20 g of NaH2PO2·H2O, and 10 mL of HF were weighed and dissolved with deionized water and stirred, respectively, and then sequentially added to the NiSO4·6H2O solution and mixed uniformly. Deionized water was used to make up to 1 L, and appropriate thiourea was added as a stabilizer. Finally, ammonia water was used to adjust the pH to 6.0-6.5. The chemical plating solution was heated to 80°C using a water bath box, the reduced sample was placed in the chemical plating solution, and the reaction time was 1 h to obtain a Ni-P coating (thickness of 30 μm).

[0105] Step four: The chemical plating sample was subjected to oil removal treatment and placed in a vacuum drying oven for drying. 300 g / L of NiSO4·6H2O, 40 g / L of NiCl2, and 30 g / L of H3BO3 were dissolved with deionized water, respectively. The NiSO4·6H2O solution and the NiCl2 solution were mixed and stirred uniformly, and then the H3BO3 solution was added and continued to be stirred. Finally, deionized water was used to make up to 1 L, and a lubricant, sodium dodecyl sulfate, was added. A 1 wt% H2SO4 solution was used to adjust the pH to 4.5. The prepared electrodeposition plating solution was heated to 50°C using a water bath box. The oil-removed sample was placed in the above electrodeposition plating solution, the current density was adjusted to 8 A / cm 2 , the duty cycle was 40%, the electrodeposition time was 2 h, and a Ni coating (thickness of 65 μm) was obtained.

[0106] Step five: the sample is subjected to oil removal treatment, placed in a vacuum drying oven for drying. The sample after oil removal is subjected to sand blasting treatment, the spray gun is 10 cm away from the sample surface, the spraying time is 30 s, the pressure is 30 MPa, the surface of the sample after sand blasting is subjected to plasma spraying treatment in sequence, NiCrAlY powder is sprayed as a metal bonding layer (thickness is 100 μm), 8YSZ powder is sprayed as a ceramic thermal barrier layer (thickness is 250 μm), and finally a magnesium alloy surface multilayer structure thermal barrier coating is prepared. Among them, the spraying current is 550 A, the argon flow is 45 SLPM, the hydrogen flow is 9 SLPM, and the spraying distance is 100 mm.

[0107] Example 3

[0108] A magnesium alloy surface multilayer structure thermal barrier coating and a preparation method thereof, comprising the following steps:

[0109] Step one: 10 g of sodium metaaluminate, 3 g of sodium fluoride, 3 g of sodium citrate, 2 g of sodium hydroxide, and 2 g of sodium tetraborate are weighed and dissolved in a proper amount of deionized water in sequence, then mixed uniformly, and then deionized water is used to make the mixed solution constant volume to 1 L to obtain an alkali metal sodium aluminate electrolyte solution. The sample is placed in the electrolyte, and a micro-arc oxidation ceramic layer (20 μm) is obtained under a constant voltage of 460 V and a working frequency of 500 Hz. The sample is washed with deionized water and dried in a vacuum drying oven for use;

[0110] Step two: 1 g / L SnCl2 and 1 mL / L HCl are dissolved in deionized water to prepare a sensitizing solution. The micro-arc oxidation ceramic layer is placed in the sensitizing solution for sensitization treatment, so that a film layer with reducing effect is generated on the surface of the micro-arc oxidation ceramic layer, and the time is 1 min. The sample is taken out and washed with deionized water. 1 g / L PdCl2 and 1 mL / L HCl are dissolved in deionized water to prepare an activating solution. The sensitized sample is placed in the activating solution for activation treatment, and the time is 1 min. The sample is taken out and washed with deionized water. 2 g / L NaH2PO2 is dissolved in deionized water to prepare a reducing solution. The activated sample is placed in the reducing solution for reduction treatment to reduce the insufficient Pd, and the time is 1 min;

[0111] Step three: 20 g of NiSO4·6H2O, 10 g of CH3COONa, 20 g of NH4HF, 20 g of NaH2PO2·H2O, and 10 mL of HF are respectively dissolved in deionized water and stirred, then sequentially added to the NiSO4·6H2O solution and mixed uniformly, and then deionized water is used to make the solution constant volume to 1 L. Appropriate thiourea is added as a stabilizer, and finally ammonia water is used to adjust the pH to 6.0-6.5. The chemical plating solution is heated to 80°C by using a water bath box, the reduced sample is placed in the chemical plating solution, and the reaction time is 1 h to obtain a Ni-P coating (thickness is 30 μm);

[0112] Step 4: Degrease the chemical plating sample and place it in a vacuum drying oven for drying. Dissolve 300g / LNiSO4·6H2O, 40g / L NiCl2, and 30g / L H3BO3 in deionized water respectively, mix the NiSO4·6H2O solution and the NiCl2 solution, stir them evenly, then add them to the H3BO3 solution and continue stirring. Finally, dilute the volume to 1L with deionized water, add lubricant sodium lauryl sulfate, and adjust the pH to 4.5 with 1wt% H2SO4 solution. Heat the prepared electroplating solution to 50°C in a water bath, place the deoiled sample in the above electroplating solution, and adjust the current density to 8A / cm 2 , duty cycle 40%, electrodeposition time 4h, and Ni coating (thickness 100μm) was obtained;

[0113] Step 5: Degrease the sample and place it in a vacuum drying oven for drying. The degreased sample is sandblasted with the spray gun at a distance of 10 cm from the sample surface, for 30 seconds at a pressure of 30 MPa. Plasma spraying is then performed on the sandblasted sample surface, with NiCrAlY powder sprayed as a metal bonding layer (100 μm thick) and 8YSZ powder sprayed as a ceramic insulation layer (250 μm thick). Finally, a multilayer thermal barrier coating is prepared on the magnesium alloy surface. The spraying current is 550 A, the argon flow rate is 45 SLPM, the hydrogen flow rate is 9 SLPM, and the spraying distance is 100 mm.

[0114] Figure 6 This is an SEM morphology image of the cross section of the middle layer of the multilayer thermal barrier coating on the surface of the magnesium alloy prepared in Example 3. The dotted line portion represents the junction of the magnesium alloy substrate, the micro-arc oxidation ceramic layer, the electroless Ni-P layer, and the electrodeposited Ni layer. The SEM cross-sectional morphology image clearly shows that the adhesion between the various parts is good, with no obvious gaps. The strength of the interlayer adhesion of the thermal barrier coating is the key to maintaining the performance of the thermal barrier coating.

[0115] Step 1: Weigh 10g of sodium metaaluminate, 3g of sodium fluoride, 3g of sodium citrate, 2g of sodium hydroxide, and 2g of sodium tetraborate, dissolve them in an appropriate amount of deionized water, mix until uniform, and dilute the mixture to 1L with deionized water to form an alkali metal sodium aluminate electrolyte solution. Place the sample in the electrolyte and obtain a micro-arc oxidation ceramic layer (20μm) at a constant voltage of 460V and an operating frequency of 500Hz. Rinse with deionized water and dry in a vacuum drying oven for later use.

[0116] Step two: the sample was subjected to oil removal treatment, and the sample after oil removal was subjected to sand blasting treatment, the spray gun was 10 cm away from the surface of the sample, the spraying time was 30 s, the pressure was 30 MPa, and the surface of the sample after sand blasting was subjected to plasma spraying treatment in sequence, NiCrAlY powder was sprayed as a metal bonding layer (thickness of 100 μm), and 8YSZ powder was sprayed as a ceramic thermal barrier layer (thickness of 250 μm), and finally a magnesium alloy surface multilayer structure thermal barrier coating was prepared. Among them, the spraying current is 550 A, the argon flow is 45 SLPM, the hydrogen flow is 9 SLPM, and the spraying distance is 100 mm. Comparative example 2

[0117] A magnesium alloy surface multilayer structure thermal barrier coating and a preparation method thereof, comprising the following steps:

[0118] Step one: 4.5 g of sodium hydroxide, 4.5 g of sodium carbonate, and 5 g of sodium phosphate were weighed, dissolved in 200 mL of deionized water, mixed uniformly to prepare an alkali washing solution, heated to 60°C, and the sample was placed in the alkali washing solution to remove excess oil on the surface of the sample. Washed clean with deionized water, weigh 12.5 g of CrO3, measure 10 mL of HNO3 with a graduated cylinder, dissolve and mix uniformly in 200 mL of deionized water to prepare an acid washing solution, place the alkali washed sample in the acid washing solution, and react for 3 min under room temperature and ultrasonic vibration conditions to remove the metal oxide film on the surface of the sample. Take out and wash with deionized water; weigh 10 g of NH4HF2, measure 20 mL of H3PO4 with a graduated cylinder, dissolve and mix uniformly in 200 mL of deionized water to prepare an activation solution, place the acid washed sample in the activation solution, and react for 1.5 min under room temperature and ultrasonic vibration conditions to form a dense oxide film layer on the surface of the sample to reduce the corrosion of the plating solution to the magnesium alloy substrate during electroless plating. Take out and wash with deionized water for standby;

[0119] Step two: 20 g of NiSO4·6H2O, 10 g of CH3COONa, 20 g of NH4HF, and 20 g of NaH2PO2·H2O were weighed and dissolved in deionized water with stirring, respectively, and then added to the NiSO4·6H2O solution in sequence, mixed uniformly, and then diluted with deionized water to 1 L. Add appropriate thiourea as a stabilizer, and finally adjust the pH to 6.0-6.5 with ammonia water. Heat the electroless plating solution to 80°C using a water bath, place the reduced sample in the electroless plating solution, and react for 1 h to obtain a Ni-P coating (thickness of 30 μm);

[0120] Step three: the electroless plating sample was treated with oil removal, and was placed in a vacuum drying oven for drying. 300 g / L NiSO4·6H2O, 40 g / L NiCl2, 30 g / L H3BO3 were dissolved in deionized water respectively, the NiSO4·6H2O solution and the NiCl2 solution were mixed and stirred uniformly, then the H3BO3 solution was added and stirred, finally the solution was diluted to 1 L with deionized water, a lubricant sodium dodecyl sulfate was added, and the pH was adjusted to 4.5 with 1 wt% H2SO4 solution. The prepared electrodeposition plating solution was heated to 50°C using a water bath, and the oil-removed sample was placed in the electrodeposition plating solution, the current density was adjusted to 8 A / cm 2 , the duty cycle was 40%, and the electrodeposition time was 4 h to obtain a Ni coating (100 μm thick);

[0121] Step four: the sample was treated with oil removal, and was placed in a vacuum drying oven for drying. The oil-removed sample was treated with sand blasting, the spray gun was 10 cm away from the sample surface, the spraying time was 30 s, and the pressure was 30 MPa. The surface of the sand-blasted sample was treated with plasma spraying in sequence, NiCrAlY powder was sprayed as a metal bonding layer (100 μm thick), and 8YSZ powder was sprayed as a ceramic thermal barrier layer (250 μm thick), and finally a magnesium alloy surface multilayer structure thermal barrier coating was prepared. The spraying current was 550 A, the argon flow rate was 45 SLPM, the hydrogen flow rate was 9 SLPM, and the spraying distance was 100 mm.

[0122] Comparative example 3

[0123] The same as example 3, the only difference is the thickness, and the thermal shock life obtained is lower than that of example 3.

[0124] A magnesium alloy surface multilayer structure thermal barrier coating and a preparation method thereof, comprising the following steps:

[0125] Step one: 10 g of sodium metaaluminate, 3 g of sodium fluoride, 3 g of sodium citrate, 2 g of sodium hydroxide, and 2 g of sodium tetraborate were weighed and dissolved in deionized water in sequence, and then mixed uniformly. The mixed solution was diluted to 1 L with deionized water to obtain an alkali metal sodium aluminate electrolyte solution. The sample was placed in the electrolyte, and a micro-arc oxidation ceramic layer (20 μm) was obtained under a constant voltage of 460 V and a working frequency of 500 Hz. The sample was washed with deionized water and dried in a vacuum drying oven for use;

[0126] Step two: 1g / L SnCl2, 1mL / L HCl were dissolved with deionized water, and the sensitizing solution was prepared by stirring. The micro-arc oxidation ceramic layer was placed in the sensitizing solution for sensitization treatment, so that a film layer with reducing effect was generated on the surface of the micro-arc oxidation ceramic layer. The time was 1 min, and the sample was taken out and washed with deionized water. 1g / L PdCl2, 1mL / L HCl were dissolved with deionized water, and the activating solution was prepared by stirring. The sensitized sample was placed in the activating solution for activation treatment, and the time was 1 min. The sample was taken out and washed with deionized water. 2g / L NaH2PO2 was dissolved with deionized water, and the reducing solution was prepared by stirring. The activated sample was placed in the reducing solution for reduction treatment to reduce the insufficient Pd, and the time was 1 min.

[0127] Step three: 20g NiSO4·6H2O, 10g CH3COONa, 20g NH4HF, 20g NaH2PO2·H2O, and 10mL HF were weighed and dissolved with deionized water and stirred, respectively, and then sequentially added to the NiSO4·6H2O solution and mixed uniformly. Deionized water was added to make the volume 1L. Appropriate thiourea was added as a stabilizer. Finally, ammonia water was added to adjust the pH to 6.0-6.5. The chemical plating solution was heated to 80°C using a water bath box. The reduced sample was placed in the chemical plating solution, and the reaction time was 1h to obtain a Ni-P coating (thickness of 30μm).

[0128] Step four: The chemical plating sample was subjected to oil removal treatment and dried in a vacuum drying oven for standby. 300g / L NiSO4·6H2O, 40g / L NiCl2, 30g / L H3BO3 were dissolved with deionized water, respectively. The NiSO4·6H2O solution and the NiCl2 solution were mixed and stirred uniformly, and then the H3BO3 solution was added and continued to be stirred. Finally, deionized water was added to make the volume 1L. Lubricant sodium dodecyl sulfate was added, and 1wt% H2SO4 solution was used to adjust the pH to 4.5. The prepared electrodeposition plating solution was heated to 50°C using a water bath box. The oil-removed sample was placed in the above electrodeposition plating solution, and the current density was adjusted to 8A / cm 2 , the duty cycle was 40%, and the electrodeposition time was 6h to obtain a Ni coating (thickness of 130μm).

[0129] Step five: the sample was treated by oil removal, and was dried in a vacuum drying oven. The sample after oil removal was treated by sand blasting, the distance between the spray gun and the sample surface was 10 cm, the spraying time was 30 s, the pressure was 30 MPa, and the sample surface after sand blasting was treated by plasma spraying, NiCrAlY powder was used as the metal bonding layer (100 μm in thickness), and 8YSZ powder was used as the ceramic thermal barrier layer (250 μm in thickness), and then the magnesium alloy surface multilayer structure thermal barrier coating was prepared by plasma spraying. The spraying current was 550 A, the argon flow rate was 45 SLPM, the hydrogen flow rate was 9 SLPM, and the spraying distance was 100 mm.

[0130] The thermal shock resistance of the magnesium alloy surface multilayer structure thermal barrier coatings prepared in Examples 1-3 and Comparative Examples 1-3 was tested. Specifically, six groups of magnesium alloy multilayer structure thermal barrier coatings were placed in a 400 ℃ tube furnace for 15 min, and then were taken out and cooled in cold water for 2 min for one thermal cycle test. The thermal shock life of the six kinds of magnesium alloy multilayer structure thermal barrier coatings was tested by such a cycle, and the test results are shown in Table 1.

[0131] Table 1 Thermal shock resistance test results of magnesium alloy multilayer structure thermal barrier coatings prepared in Examples 1-3 and Comparative Examples 1-3

[0132]

[0133]

[0134] As shown in Table 1, the thermal shock life of Comparative Example 2 without the micro-arc oxidation ceramic layer MAO was significantly lower than that of Example 3, which indicated that the micro-arc oxidation ceramic layer MAO could improve the thermal shock life and improve the heat resistance of the magnesium alloy surface multilayer structure thermal barrier coating.

[0135] In addition, as shown in Table 1, within a certain range, as the electro-deposition Ni time increased, the electro-deposition Ni layer thickness increased, and the thermal shock life also increased, which indicated that the heat resistance of the thermal barrier coating increased with the increase of the coating thickness. However, when the electro-deposition Ni time was too long (6 h), the electro-deposition Ni layer thickness was too thick (130 μm), which would cause the adhesion of the Ni layer to decrease, thereby reducing the thermal shock life, such as the thermal shock life of Comparative Example 3 was 135 times.

[0136] Specifically, when the electro-deposition Ni time was 4 h, the Ni layer thickness reached 100 μm, the MAO / Ni-P / Ni 4hThe thermal cycle number of the / NiCrAlY / 8YSZ thermal barrier coating is greater than 200, and the thermal shock life of the thermal barrier coating is optimal. When the electrodepositing time of the Ni increases from 4h to 6h and the thickness increases from 100μm to 130μm, the thermal shock life of the coating decreases from greater than 200 to 135, because the adhesion of the electrodepositing Ni coating decreases with the increase of the thickness of the coating, the adhesion between the coatings is small when the coating is too thick, which leads to the peeling of the coating and the decrease of the heat resistance and the thermal shock life.

[0137] The corrosion resistance of the / ceramic layer of micro-arc oxidation / chemically plated Ni-P layer / electrodepositing Ni layer / NiCrAlY metal bonding layer / 8YSZ outer ceramic layer multilayer structure thermal barrier coating prepared on the surface of the magnesium alloy in Examples 1-3 is tested compared with the multilayer structure thermal barrier coating prepared on the surface of the magnesium alloy in Comparative Examples 1-3. Specifically, 6 groups of 1cm 2 The bottom of the magnesium alloy multilayer structure thermal barrier coating sample is welded with a copper wire and cured with epoxy resin, 3.5% NaCl solution is used as the corrosion medium, a three-electrode system is used, saturated calomel electrode is used as the reference electrode, platinum electrode is used as the counter electrode, and the sample is used as the working electrode. The open circuit potential of the sample is measured first, and then the open circuit potential ±0.6V is selected as the scanning interval, and the scanning rate is 0.01V / s. The test results are shown in Table 2.

[0138] Table 2: Corrosion resistance test results of the magnesium alloy multilayer structure thermal barrier coatings prepared in Examples 1-3 and Comparative Examples 1-3

[0139]

[0140]

[0141] As shown in Table 2, the corrosion current density of Example 3 is less than that of Comparative Example 2, and the corrosion potential is greater than that of Comparative Example 2, which indicates that the micro-arc oxidation ceramic layer MAO improves the corrosion resistance of the multilayer structure thermal barrier coating on the surface of the magnesium alloy.

[0142] This is because the micro-arc oxidation ceramic layer has a synergistic effect with the chemically plated Ni-P layer and the Ni deposition layer, which can play a good role in oxidation resistance and delay of thermal corrosion under the erosion of the corrosion medium and high temperature.

[0143] The electrochemical test results in Table 2 show that the MAO / Ni-P / Ni 4h / NiCrAlY / 8YSZ prepared in Example 3 has the best corrosion resistance effect.

[0144] The corrosion current density of the examples 1-3 is less than that of the comparative examples 1 and 2, and the corrosion potential is greater than that of the comparative examples 1 and 2, which indicates that the corrosion resistance of the examples 1-3 is better than that of the comparative examples 1 and 2. This shows that the Ni-P layer and the Ni layer and the ceramic layer of micro-arc oxidation have a synergistic effect to achieve good corrosion resistance.

[0145] In addition, by comparing the examples 1-3 with the comparative example 3, it can be seen that the corrosion current density of the example 3 is less than that of the comparative example 3, and the corrosion potential is greater than that of the comparative example 3, which indicates that the corrosion resistance of the example 3 is better than that of the comparative example 3. The corrosion current density of the example 1 is greater than that of the comparative example 3, but the corrosion potential is less than that of the comparative example 3, which indicates that the corrosion resistance of the comparative example 3 is better than that of the example 1, which may be because the higher coating thickness of the comparative example 3 can delay the corrosion of the corrosion ions to a certain extent. However, according to the thermal shock life results in Table 1, the thermal shock life of the comparative example 3 is less than that of the example 1, so the corrosion resistance of the comparative example 3 is better than that of the example 1, but the thermal resistance is poor, and the coating thickness is too high, which does not meet the actual application requirements.

[0146] In summary, the magnesium alloy multilayer structure thermal barrier coating described in the present application not only meets the requirements of thermal resistance (thermal shock life) in practical applications, but also meets the requirements of corrosion resistance.

[0147] Therefore, in order to make the magnesium alloy surface multilayer structure thermal barrier coating described in the present application have excellent thermal resistance, corrosion resistance and bonding strength, the thickness of the electrodeposited Ni layer should not be too thick, and the electrodeposition time should be controlled within a certain range.

[0148] The above examples are only used to help understand the method of the present application and its core idea. It should be noted that for those skilled in the art, without departing from the principles of the present application, the present application can be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A multi-layer thermal barrier coating on the surface of a magnesium alloy, characterized in that: The invention comprises a ceramic layer, a Ni-P layer and a Ni layer sequentially arranged on the surface of the magnesium alloy substrate from the inside to the outside; The main components of the ceramic layer are MgAl2O4 and MgO; The multi-layered thermal barrier coating on the surface of the magnesium alloy further comprises a metal bonding layer and a ceramic thermal insulation layer; The metal bonding layer and the ceramic heat insulation layer are sequentially arranged on the surface of the Ni layer from the inside to the outside; The metal bonding layer is selected from NiCrAlY layer; The ceramic insulation layer is selected from 8YSZ layer; The ceramic layer is prepared according to the following method: placing the surface-treated magnesium alloy substrate in a micro-arc oxidation electrolyte solution to perform micro-arc oxidation by arc discharge to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy substrate; The Ni layer is prepared by electrodeposition, and the Ni deposition solution used in the electrodeposited Ni coating is a mixed solution of 280-300 g / L NiSO4•6H2O, 40-60 g / L NiCl2 and 30-40 g / L H3BO3; the pH of the Ni deposition solution is 4-5; and the time for electrodepositing the Ni coating is 1-4 h.

2. The multi-layer thermal barrier coating on the surface of magnesium alloy according to claim 1, characterized in that: The Ni-P layer contains 10-12 wt% of phosphorus and 88-90 wt% of nickel; The Ni layer contains 98-99.6 wt % of nickel and 0.4-2 wt % of oxygen.

3. The multi-layer thermal barrier coating on the surface of magnesium alloy according to claim 1, characterized in that: The thickness of the ceramic layer is 15-20 μm; The thickness of the Ni-P layer is 30-40 μm; The thickness of the Ni layer is 40-100 μm.

4. The multi-layered thermal barrier coating on the surface of magnesium alloy according to claim 1, characterized in that: The thickness of the NiCrAlY layer is 80-150 μm; The thickness of the 8YSZ layer is 150-300 μm.

5. A method for preparing a multilayer thermal barrier coating on a magnesium alloy surface, characterized in that: The following steps are involved: 1) placing the surface-treated magnesium alloy substrate in a micro-arc oxidation electrolyte solution to form a micro-arc oxidation ceramic layer on the surface of the magnesium alloy substrate by arc discharge; 2) performing surface sensitization, activation, and reduction treatments on the micro-arc oxidized ceramic layer obtained in step 1), and then performing chemical Ni-P plating on the surface of the micro-arc oxidized ceramic layer to obtain a Ni-P coating; 3) Electrodepositing a Ni coating on the surface of the Ni-P coating to obtain a Ni coating; the Ni deposition solution used in the electrodeposition of the Ni coating is a mixed solution of 280-300 g / L NiSO4•6H2O, 40-60 g / L NiCl2, and 30-40 g / L H3BO3; the pH of the Ni deposition solution is 4-5; and the electrodeposition time of the Ni coating is 1-4 hours; 4) NiCrAlY powder is plasma sprayed on the surface of the Ni coating prepared above as a metal bonding layer and 8YSZ powder is sprayed as a ceramic thermal insulation layer, and finally a multilayer thermal barrier coating on the surface of the magnesium alloy is prepared.

6. The preparation method according to claim 5, wherein The micro-arc oxidation electrolyte solution in step 1) is a mixed solution of 8-10 g / L sodium aluminate, 3-5 g / L sodium fluoride, 2-4 g / L sodium citrate, 2-4 g / L sodium hydroxide and 1-3 g / L sodium tetraborate.

7. The preparation method according to claim 5, wherein The Ni-P plating solution used in the electroless Ni-P coating in step 2) is a mixed solution of 20-25 g / L NiSO4·6H2O, 7-10 g / L CH3COONa, 15-20 g / L NH4HF, 20-25 g / L NaH2PO2·H2O and 8-10 mL / L HF; The pH of the Ni-P plating solution is 6.0-6.

5.

8. The preparation method according to claim 5, wherein The constant voltage for forming the ceramic layer by micro-arc oxidation in step 1) is 460-480 V, and the operating frequency is 500-510 Hz; The reaction temperature of the chemical Ni-P plating in step 2) is 80-85° C., and the reaction time is 1-1.5 h; The reaction temperature of the electrodeposition Ni coating in step 3) is 40-50°C, and the current density is 4-8 A / cm 2 , the pulse duty cycle is 40~50%; In step 4), when plasma spraying NiCrAlY powder as a metal bonding layer and spraying 8YSZ powder as a ceramic thermal insulation layer, the process parameters used are: Spraying current 500~600 A; Argon flow rate 45~47 SLPM; Hydrogen flow rate 7~9 SLPM; Spraying distance 80~100 mm.

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