CN114262923B - Double-layer composite film on magnesium alloy surface, preparation method and application thereof - Google Patents
Double-layer composite film on magnesium alloy surface, preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of magnesium alloy surface treatment, and particularly discloses a magnesium alloy surface double-layer composite film, a preparation method and application thereof. The method comprises the following steps: pretreating magnesium alloy to obtain a matrix; dissolving alkaline hydroxide and phosphate into water to obtain micro-arc oxidation electrolyte; and taking the substrate as an anode, taking an inert electrode as a cathode, immersing the anode and the cathode into the micro-arc oxidation electrolyte, and performing micro-arc oxidation treatment to generate an MgO film on the surface of the anode in situ and a hydrotalcite film on the surface of the MgO film, thereby obtaining the magnesium alloy surface double-layer composite film. The invention utilizes micro-arc oxidation treatment to realize in-situ generation of the MgO/LDHs double-layer composite film layer on the surface of the magnesium alloy, thereby solving the technical problems that the preparation of the double-layer composite film layer on the surface of the magnesium alloy can only be realized by a two-step method in the prior art, and the preparation process is tedious and is not beneficial to industrial popularization.
Description
Technical Field
The invention belongs to the technical field of magnesium alloy surface treatment, and particularly relates to a magnesium alloy surface double-layer composite film, a preparation method and application thereof.
Background
Magnesium and magnesium alloy have similar density, specific strength and elastic modulus to human bone, and magnesium is also an essential trace element in human body, and the content is inferior to calcium, sodium and potassium, and even if excessive magnesium ions are generated in body fluid of human body, the magnesium alloy can be discharged out of the body through metabolism. Therefore, magnesium and magnesium alloy have considerable development prospect as biological materials. However, the electrode potential of magnesium and magnesium alloy is lower, the corrosion resistance is poorer, the corrosion speed is difficult to control after being implanted into a human body, and the mechanical strength of the implant is lost prematurely. This phenomenon clearly limits the further development of magnesium and magnesium alloys in the biological field.
In recent years, surface modification studies on magnesium alloys have been attracting attention in order to reduce the initial degradation rate of biodegradable magnesium alloys. At present, many methods for preparing magnesium alloy biological coatings through surface modification, such as plasma spraying, electrochemical deposition, sol-gel method, bionic growth method, micro-arc oxidation method and the like, exist. The coating obtained by plasma spraying has larger residual stress with the matrix; and the bonding strength between the coating obtained by the electrochemical deposition method, the sol-gel method and the bionic growth method and the matrix is low. In contrast, the micro-arc oxidation treatment can form a ceramic coating on the surface of the magnesium alloy, so that the corrosion resistance of the magnesium alloy can be improved, and the magnesium alloy has excellent wear resistance and bonding strength. However, a large amount of gas is released under the high-temperature sintering effect in the micro-arc oxidation process, so that a surface oxide layer forms a plurality of pores and microcracks. The presence of a large number of voids and microcracks significantly reduces the corrosion resistance of the oxide layer. Therefore, the hole sealing treatment on the surface of the micro-arc oxidation layer is very important.
Layered double hydroxide composite metal oxides, also known as hydrotalcite (LDH), are distinguished by flexibility of the components and anion exchange, and have been widely used for coating protection of metals. The research shows that the LDH coating on the surface of the magnesium alloy has the characteristics of environmental friendliness, self-healing, excellent corrosion resistance and the like. Meanwhile, hydrotalcite has good biocompatibility and cell adhesion. The LDHs coating is combined with the biological magnesium alloy micro-arc oxidation coating, so that the purpose of hole sealing is achieved, and the biocompatibility of the whole material is improved. At present, the technology for preparing the MgO/LDHs composite coating is realized by a two-step method, namely, firstly, an oxide layer is generated on the surface of the magnesium alloy by micro-arc oxidation, and then hydrotalcite is attached to the surface of the MgO coating by a hydrothermal method, a coprecipitation method or an electrochemical deposition method. Although such a preparation process effectively improves the corrosion resistance of the material, there are still process drawbacks such as the following: (1) The preparation conditions relate to high temperature and high pressure, which is not beneficial to industrial production; (2) The binding force between the two coatings is limited by a two-step method; (3) The preparation process is complicated, the time consumption is long, and the industrial popularization is not facilitated. Therefore, there is a need for further improvements in the technology for preparing magnesium alloy MgO/LDHs double-layer composite films.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides a magnesium alloy surface double-layer composite film, a preparation method and application thereof, and aims to realize in-situ generation of an MgO/LDHs double-layer composite film layer on the magnesium alloy surface by micro-arc oxidation treatment, thereby solving the technical problems that the preparation of the magnesium alloy surface double-layer composite film layer can only be realized by a two-step method in the prior art, and the preparation process is complicated and is not beneficial to industrial popularization.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a magnesium alloy surface double-layer composite film, the method comprising the steps of: (1) Polishing, cleaning and drying the magnesium alloy to obtain a matrix; (2) Dissolving alkaline hydroxide and phosphate into water to obtain micro-arc oxidation electrolyte; (3) And taking the substrate as an anode, taking an inert electrode as a cathode, immersing the anode and the cathode into the micro-arc oxidation electrolyte, and performing micro-arc oxidation treatment to generate an MgO film on the surface of the anode in situ and a hydrotalcite film on the surface of the MgO film, thereby obtaining the magnesium alloy surface double-layer composite film.
Preferably, in the step (3), the treatment voltage of the micro-arc oxidation treatment is 100-800V, the treatment time is 120-1200 s, the frequency is 500-1500 Hz, the duty ratio is 0-30%, and the temperature of the micro-arc oxidation electrolyte is below 40 ℃ in the micro-arc oxidation treatment process.
Preferably, the treatment voltage of the micro-arc oxidation treatment is 300-500V, and the treatment time is 420-900 s.
Preferably, the alkaline hydroxide is sodium hydroxide, potassium hydroxide or calcium hydroxide; the phosphate is one or more of trisodium phosphate, sodium hydrogen phosphate and ammonium hydrogen phosphate.
Preferably, the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 1-12 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 5-30 g/L.
Preferably, the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 4-10 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 10-18 g/L.
Preferably, the magnesium alloy is magnesium aluminum alloy, magnesium silver alloy or magnesium manganese alloy.
Preferably, the inert electrode is a stainless steel plate, a platinum sheet or a graphite carbon rod.
According to another aspect of the present invention, there is provided a magnesium alloy surface double-layer composite film prepared according to the above-described preparation method, the magnesium alloy surface double-layer composite film including an MgO film formed on a surface of a magnesium alloy and a hydrotalcite film formed on a surface of the MgO film.
Preferably, the hydrotalcite film is a cross-linked nano-sheet structure.
In general, the above technical solutions conceived by the present invention can achieve at least the following advantageous effects compared to the prior art.
(1) By utilizing the instantaneous high temperature and high pressure generated in the micro-arc oxidation treatment process, after magnesium oxide is formed on the surface of the magnesium alloy, a water-skid layer (LDHs layer) is rapidly grown on the surface of the magnesium oxide, so that the MgO/LDHs composite film is prepared on the surface of the magnesium alloy by adopting a one-step method. Namely, the MgO/LDHs double-layer composite film can be generated in situ on the surface of the magnesium alloy only by one-step micro-arc oxidation process, the preparation process is simple and easy to control, and high-temperature and high-pressure conditions are not needed; the raw materials are easy to obtain, the cost is low, and the method is suitable for industrial production and popularization.
(2) The instantaneous high temperature and high pressure generated in the micro-arc oxidation treatment process quickens the generation of the water-skid layer, and realizes the one-step generation of the MgO/LDHs double-layer composite film layer in a short time. Solves the problems that in the prior art, a two-step method, such as a hydrothermal method, is needed to generate the LDHs layer with a treatment time of several hours or even more than ten hours, and the preparation process is long in time and complex in equipment.
(3) The invention strictly controls the technological conditions (voltage, time, frequency and duty ratio) of the micro-arc oxidation treatment to generate the MgO/Mg-Al LDHs double-layer composite film so as to avoid the problems of decomposition of the LDHs film layer, structural defects of an oxide layer, incomplete film layer and the like. And meanwhile, the concentration of alkaline hydroxide and the concentration of phosphate in the micro-arc oxidation electrolyte are strictly controlled, so that the LDHs film layer with compact structure and uniform thickness can be obtained.
(4) The MgO/Mg-Al LDHs double-layer composite film prepared by the method provided by the invention is compact and uniform, has good bonding force with a substrate, and the obtained hydrotalcite film increases the roughness of the surface of the film, thereby being beneficial to bonding with other organic coatings.
(5) The water-skid layer prepared by the method provided by the invention has a three-dimensional cross-linked structure, namely, the LDHs film has a nano-sheet structure which is cross-linked with each other, and plays a role of a barrier when contacting with a corrosive medium, so that the diffusion path of the corrosive medium can be effectively increased, and the corrosion resistance of magnesium alloy is improved.
Drawings
FIG. 1 (A) is a High Angle Annular Dark Field (HAADF) diagram of a magnesium alloy surface bilayer composite film prepared by example 1 of the present invention;
FIGS. 1 (B) - (G) are energy spectrum (EDX) diagrams of the corresponding regions of FIG. 1;
fig. 1 (H) is a transmission electron microscope Bright Field (BFTEM) image of a cross section of a double-layer composite film on a magnesium alloy surface prepared in example 1 of the present invention;
FIGS. 1 (I) - (J) are high-resolution transmission electron microscope (HRTEM) images of cross sections of double-layer composite films on the surface of a magnesium alloy prepared in example 1 of the present invention;
FIGS. 2 (A) - (C) are Scanning Electron Microscope (SEM) images of the surfaces of the double-layer composite film on the surface of the magnesium alloy prepared in example 1 of the present invention;
FIG. 3A is a Scanning Electron Microscope (SEM) image of the surface of a double-layer composite film on the surface of a magnesium alloy prepared in example 1 of the present invention at one viewing angle;
FIG. 3B is a Scanning Electron Microscope (SEM) image of the surface of the magnesium alloy surface double-layer composite film prepared in example 1 of the present invention at another viewing angle;
FIG. 4 is a Scanning Electron Microscope (SEM) image of a cross section of a double-layer composite film on the surface of a magnesium alloy prepared in example 1 of the present invention;
FIG. 5 is a Scanning Electron Microscope (SEM) image of a cross section of a double-layer composite film on the surface of a magnesium alloy prepared in example 2 of the present invention;
FIG. 6 is a Scanning Electron Microscope (SEM) image of a cross section of a double-layer composite film on the surface of a magnesium alloy prepared in example 3 of the present invention;
FIG. 7 is a Scanning Electron Microscope (SEM) image of a cross section of a double-layer composite film on the surface of a magnesium alloy prepared in example 4 of the present invention;
FIG. 8 is a Scanning Electron Microscope (SEM) image of a cross section of a double-layer composite film on the surface of a magnesium alloy prepared in example 5 of the present invention;
FIG. 9 is a graphical representation of XRD phase analysis of a magnesium aluminum alloy surface bilayer composite membrane in accordance with the present invention as compared to an untreated magnesium aluminum alloy substrate in accordance with example 2;
FIG. 10 is a graph depicting polarization curves of a magnesium aluminum alloy surface double-layer composite film, a magnesium aluminum alloy surface MgO single film layer and an untreated magnesium aluminum alloy substrate in 0.9% NaCl corrosive medium in example 3 according to the present invention;
FIG. 11A is a Nyquist chart depicting the electrochemical impedance of the double layer composite film on the surface of the magnesium aluminum alloy, the MgO single film layer on the surface of the magnesium aluminum alloy, and the untreated magnesium aluminum alloy substrate in a 0.9% NaCl corrosive medium in accordance with the present invention;
FIG. 11B is a chart showing the electrochemical impedance Bode of the double-layer composite film on the surface of the magnesium-aluminum alloy, the MgO single film layer on the surface of the magnesium-aluminum alloy and the untreated magnesium-aluminum alloy matrix in a 0.9% NaCl corrosion medium according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The embodiment of the invention provides a preparation method of a magnesium alloy surface double-layer composite film, which comprises the following steps:
(1) Polishing, cleaning and drying the magnesium alloy step by step to obtain a matrix;
(2) Dissolving alkaline hydroxide and phosphate into water to obtain micro-arc oxidation electrolyte;
(3) And taking the substrate as an anode and an inert electrode as a cathode, immersing the anode and the cathode into the micro-arc oxidation electrolyte, performing micro-arc oxidation treatment to generate an MgO film in situ on the surface of the anode and a hydrotalcite film (LDHs) on the surface of the MgO film, taking out the anode after the micro-arc oxidation treatment is completed, cleaning and drying to obtain the double-layer composite film formed on the surface of the magnesium alloy. Wherein the treatment voltage of the micro-arc oxidation treatment is 100-800V, the treatment time is 120-1200 s, the frequency is 500-1500 Hz, the duty ratio is 0-30%, and the temperature of the micro-arc oxidation electrolyte is below 40 ℃ in the micro-arc oxidation treatment process.
It should be noted that, the invention strictly controls the technological conditions (processing voltage, processing time, frequency, duty ratio) of the micro-arc oxidation treatment, and too low or too high of these parameters mainly affects the amount of energy supply required in the reaction, and the breakdown and discharge conditions cannot be achieved when the energy is low; and too high energy may lead to decomposition of the LDHs film or defects of the oxide layer. For example, if the processing voltage is less than 100V, the discharge voltage for the substrate cannot be obtained, and the micro-arc oxidation phenomenon does not occur, and thus the oxide layer and the LDHs layer cannot be formed. If the treatment voltage is more than 800V, the spark discharge phenomenon is too severe, and a large amount of generated gas can generate huge pores and cracks on the surface of the coating, so that the coating is incomplete, and the LDHs layer is decomposed due to the excessively high instantaneous temperature. A duty cycle of 0 means that the energization is continued with less influence on the micro-arc oxidation process, and thus a double-layer film can be produced. However, too high a duty cycle may result in too long power-off time to generate LDHs layers.
As a preferable scheme, the treatment voltage of the micro-arc oxidation treatment is 300-500V, and the treatment time is 420-900 s. The MgO/Mg-Al LDHs double-layer composite film prepared under the condition is more compact and uniform and has better bonding force with a substrate.
In some embodiments, the alkaline hydroxide is sodium hydroxide, potassium hydroxide, or calcium hydroxide; the phosphate is one or more of trisodium phosphate, sodium hydrogen phosphate and ammonium hydrogen phosphate. Wherein the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 1-12 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 5-30 g/L. The alkaline hydroxide mainly affects the pH of the solution, and the growth of the film needs to be in a proper pH range, and too low or too high a pH causes the film to decompose. The ion concentration of phosphate radical obviously influences the morphology of LDH, when the concentration of phosphate in the micro-arc oxidation electrolyte is less than 5g/L, only a small amount of LDH layers exist in local areas and pores are larger, and when the concentration of phosphate in the micro-arc oxidation electrolyte is too high to be more than 30g/L, the LDH layers start to change in structure and do not have a cross-linked nano-sheet structure.
As a preferable scheme, the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 4-10 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 10-18 g/L. The MgO/Mg-Al LDHs double-layer composite film prepared under the condition is more compact and uniform and has better bonding force with a substrate.
In some embodiments, the magnesium alloy is a magnesium aluminum alloy, a magnesium silver alloy, or a magnesium manganese alloy.
In some embodiments, the inert electrode is a stainless steel plate, a platinum sheet, or a graphite carbon rod.
The embodiment of the invention also provides a magnesium alloy surface double-layer composite film prepared by the preparation method, which comprises an MgO film formed on the surface of the magnesium alloy and a hydrotalcite film formed on the surface of the MgO film. Wherein the hydrotalcite film has a cross-linked nano-sheet structure. The cross-linked nano sheet structure can play a role of a barrier when the magnesium alloy is contacted with a corrosive medium, can effectively increase the diffusion path of the corrosive medium and improve the corrosion resistance of the magnesium alloy.
The preparation method of the double-layer composite film on the surface of the magnesium alloy can be applied to the surface treatment of the magnesium alloy, and combines the LDHs coating with the biological magnesium alloy micro-arc oxidation coating, so that the purpose of hole sealing is achieved, and the biocompatibility of the whole material is improved.
The technical scheme of the invention is further described by the following specific embodiments:
example 1
The embodiment provides a preparation method of a double-layer composite film on the surface of a magnesium alloy, wherein the magnesium alloy is a magnesium-aluminum alloy, and the method specifically comprises the following steps:
(1) Pretreatment of magnesium alloy: and (3) polishing the surface of the magnesium-aluminum alloy step by using 600, 800, 1500 and 2000-mesh sand paper respectively, removing the surface oxide layer, ultrasonically cleaning in absolute ethyl alcohol for 15min, and blowing with a blower to dry with cold air.
(2) Preparing a micro-arc oxidation electrolyte: 6g of NaOH and 12g of Na are respectively weighed at room temperature 3 PO 4 Adding deionized water to dissolve to 1L, and stirring by magnetic force to dissolve completely to obtain micro-arc oxidation electrolyte.
(3) Micro-arc oxidation treatment: the pretreated magnesium-aluminum alloy is used as an anode, a stainless steel sheet is used as a cathode, and the cathode and the anode are immersed in the micro-arc oxidation electrolyte (ice water bath), wherein the distance between the cathode and the anode plate is 5cm. Applying a direct current pulse voltage to perform micro-arc oxidation treatment, wherein the technological parameters are as follows: voltage: 400V; frequency: 1000Hz; duty cycle: 10%; micro-arc oxidation electrolyte temperature: 4-10 ℃; the treatment time is as follows: 600s.
(4) Immediately taking out an anode sample after the micro-arc oxidation treatment, washing the surface of the anode with absolute ethyl alcohol, and drying by cold air to obtain the magnesium-aluminum alloy with the MgO/LDHs double-layer composite film layer, wherein the double-layer composite film comprises an MgO film formed on the surface of the magnesium-aluminum alloy and an LDHs film formed on the surface of the MgO film.
The thickness of the MgO film in the magnesium-aluminum alloy with the MgO/LDHs double-layer composite film layer prepared by the steps in the embodiment is 3.05+/-0.07 mu m, and the thickness of the LDHs film is 50-100 nm (see figure 4).
Example 2
The embodiment provides a preparation method of a double-layer composite film on the surface of a magnesium alloy, wherein the magnesium alloy is a magnesium silver alloy, and the method specifically comprises the following steps:
(1) Pretreatment of magnesium alloy: and (3) polishing the surface of the magnesium-silver alloy step by using 600, 800, 1500 and 2000-mesh sand paper respectively, removing the surface oxide layer, ultrasonically cleaning in absolute ethyl alcohol for 15min, and blowing with a blower to dry with cold air.
(2) The preparation method of the micro-arc oxidation electrolyte comprises the following steps: respectively weighing 10g of NaOH and 18g of Na at room temperature 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
(3) Micro-arc oxidation treatment: the pretreated magnesium-silver alloy is used as an anode, a platinum sheet is used as a cathode, and the cathode and the anode are immersed in the electrolyte (ice water bath), wherein the distance between the cathode and the anode is 5cm. Applying a direct current pulse voltage to perform micro-arc oxidation treatment, wherein the technological parameters are as follows: voltage: 300V; frequency: 800Hz; duty cycle: 20% of a base; micro-arc oxidation electrolyte temperature: 4-10 ℃; the treatment time is as follows: 720s.
(4) And immediately taking out the anode sample after the micro-arc oxidation treatment, washing the surface of the anode with absolute ethyl alcohol, and drying with cold air to obtain the magnesium-silver alloy with the MgO/LDHs double-layer composite film layer, wherein the double-layer composite film comprises an MgO film formed on the surface of the magnesium-silver alloy and an LDHs film formed on the surface of the MgO film.
The thickness of the MgO film in the magnesium-aluminum alloy with the MgO/LDHs double-layer composite film layer prepared by the steps in the embodiment is 3.17+/-0.90 mu m, and the thickness of the LDHs film is 50-100 nm (see figure 5).
Example 3
The embodiment provides a preparation method of a double-layer composite film on the surface of a magnesium alloy, wherein the magnesium alloy is a magnesium-manganese alloy, and the method specifically comprises the following steps:
(1) Pretreatment of magnesium alloy: and (3) polishing the surface of the magnesium-manganese alloy step by using 600, 800, 1500 and 2000-mesh sand paper respectively, removing the surface oxide layer, ultrasonically cleaning in absolute ethyl alcohol for 15min, and blowing with a blower to dry with cold air.
(2) The preparation method of the micro-arc oxidation electrolyte comprises the following steps: respectively weighing 5g of NaOH and 24g of Na at room temperature 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
(3) Micro-arc oxidation treatment: the pretreated magnesium-manganese alloy is used as an anode, a graphite carbon rod is used as a cathode, and the cathode and the anode are immersed in the electrolyte (ice water bath), wherein the distance between the cathode and the anode plates is 5cm. Applying a direct current pulse voltage to perform micro-arc oxidation treatment, wherein the technological parameters are as follows: voltage: 500V; frequency: 600Hz; duty cycle: 5%; micro-arc oxidation electrolyte temperature: 4-10 ℃; the treatment time is as follows: 480s.
(4) Immediately taking out the anode sample after the micro-arc oxidation treatment, washing the surface with absolute ethyl alcohol, and drying with cold air to obtain the magnesium-manganese alloy with the MgO/LDHs double-layer composite film layer, wherein the double-layer composite film comprises an MgO film formed on the surface of the magnesium-manganese alloy and an LDHs film formed on the surface of the MgO film.
The thickness of the MgO film in the magnesium-aluminum alloy with the MgO/LDHs double-layer composite film layer prepared by the steps in the embodiment is 4.13+/-0.31 mu m, and the thickness of the LDHs film is 50-100 nm (see figure 6).
Example 4
This example differs from example 1 in that in step (2), the preparation method of the micro-arc oxidation electrolyte is as follows: 1g of NaOH and 5g of Na are respectively weighed at room temperature 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
In the step (3), during the micro-arc oxidation treatment, the voltage is 100V, the treatment time is 120s, the frequency is 500Hz, and the duty ratio is 0%.
Referring to fig. 7, a magnesium-manganese alloy having a MgO/LDHs double-layer composite film layer including a MgO film formed on the surface of the magnesium-manganese alloy and an LDHs film formed on the surface of the MgO film can be prepared by the method provided in this example.
Example 5
This example differs from example 1 in that in step (2), the preparation method of the micro-arc oxidation electrolyte is as follows: respectively weighing 12g of NaOH and 30g of Na at room temperature 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
In the step (3), during the micro-arc oxidation treatment, the voltage is 800V, the treatment time is 1200s, the frequency is 1500Hz, and the duty ratio is 30%.
Referring to fig. 8, a magnesium-manganese alloy having a MgO/LDHs double-layer composite film layer including a MgO film formed on the surface of the magnesium-manganese alloy and an LDHs film formed on the surface of the MgO film can be prepared by the method provided in this example.
Example 6
The difference between this example and example 1 is that the micro-arc oxidation treatment was performed at a treatment voltage of 300V for a treatment time of 420s, naOH was replaced with potassium hydroxide, and Na 3 PO 4 Replaced by sodium hydrogen phosphate。
Example 7
The difference between this example and example 1 is that the micro-arc oxidation treatment was performed at a treatment voltage of 500V for a treatment time of 900s, naOH was replaced with calcium hydroxide, and Na was replaced with 3 PO 4 And replaced with ammonium hydrogen phosphate.
Example 8
This example differs from example 1 in that in step (2), the preparation method of the micro-arc oxidation electrolyte is as follows: at room temperature, 4g of NaOH and 10g of Na are respectively weighed 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
Example 9
This example differs from example 1 in that in step (2), the preparation method of the micro-arc oxidation electrolyte is as follows: respectively weighing 10g of NaOH and 18g of Na at room temperature 3 PO 4 Deionized water is added for constant dissolution to 1L, and the electrolyte is obtained by fully dissolving the deionized water through magnetic stirring.
Comparative example 1
This comparative example differs from example 1 in that Na is used 3 PO 4 Replaced by Na 2 SiO 3 The prepared film layer only has an MgO layer, but has no LDHs layer.
Characterization example 1
In this example, the magnesium aluminum alloy surface double-layer composite film prepared according to example 1 was subjected to cross-sectional morphology and surface morphology characterization by a high-angle annular dark field (HAADF) and a high-resolution transmission electron microscope (HRTEM).
Referring to fig. 1 (a) - (J), the cross-sectional morphology of the magnesium-aluminum alloy surface double-layer composite film prepared according to example 1 is shown. It is observed through High Angle Annular Dark Field (HAADF) that the inner layer (adjacent to the substrate) of the film of the composite coating is relatively dense in structure, and that there is a partial microporous structure in the layer, which is characteristic of typical micro-arc oxidation layers. The outer layer of the composite film layer then exhibits a cross-linked nanoplatelet structure. The energy spectrum and high resolution analysis are carried out on the composite film layer, and the main constituent elements of the inner film layer are Mg and O, while the main constituent elements of the outer film layer are Mg, al, P, na; in combination with the high resolution results, the inner layer of the membrane is mainly composed of MgO, and the outer layer of the membrane is composed of Mg-Al LDH.
Referring to fig. 2 (a) - (C) and fig. 3A, 3B, the surface morphology of the magnesium-aluminum alloy surface double-layer composite film prepared according to example 1 is shown. It can be seen that the double-layer composite film comprises an MgO film formed on the surface of the magnesium-manganese alloy and an LDHs film formed on the surface of the MgO film, namely, the inner film layer is the MgO film, the outer film layer is the LDHs film, the pores of the MgO layer of the inner film layer are more and are accompanied by partial microcracks, mg-Al LDHs nano sheets vertically grow on the outer side of the double-layer composite film, and the nano sheets are mutually crosslinked, uniformly cover the surface of the MgO layer and play a certain hole sealing role.
Characterization example 2
In this example, the XRD phase of the magnesium-aluminum alloy surface double-layer composite film prepared according to example 1 was compared with that of the untreated magnesium-aluminum alloy substrate. As shown in fig. 9, the Mg alloy mainly has Mg characteristic diffraction peaks and is accompanied by weak MgAl characteristic diffraction peaks. XRD of the MgO/Mg-Al LDHs double-layer composite film shows sharp MgO characteristic diffraction peaks, which shows that MgO has higher crystallinity. Furthermore, no diffraction peak of mg—al LDH characteristics was observed, since the layer thickness was thin and the detection limit of XRD was not reached.
Characterization example 3
In this example, the polarization curves of the magnesium-aluminum alloy surface double-layer composite film prepared according to example 1, the magnesium-aluminum alloy surface MgO single-layer film prepared according to comparative example 1, and the untreated magnesium-aluminum alloy substrate in 0.9% NaCl corrosive medium are shown. As shown in fig. 10, the self-corrosion current of the untreated magnesium aluminum alloy is significantly greater than that of the magnesium aluminum alloy surface double-layer composite film prepared according to example 1, wherein the self-corrosion current of the MgO/Mg-Al LDHs double-layer composite film prepared according to example 1 is the lowest, and the self-corrosion potential is in the opposite trend. The corrosion resistance of the magnesium aluminum alloy after micro-arc oxidation is obviously improved under the combined action of the MgO layer and the Mg-Al LDHs layer.
Characterization example 4
In this example, electrochemical resistances of the magnesium-aluminum alloy surface double-layer composite film prepared according to example 1, the magnesium-aluminum alloy surface MgO single-layer prepared according to comparative example 1, and the untreated magnesium-aluminum alloy substrate in 0.9% NaCl corrosive medium are compared. As shown in fig. 11A and 11B, compared with untreated magnesium aluminum alloy, the impedance modulus of the MgO/Mg-Al LDHs double-layer composite film layer at 10MHz is enlarged by 3 orders of magnitude and is higher than that of the MgO single-layer film, which fully proves that the double-layer composite film layer effectively improves the corrosion resistance of the magnesium aluminum alloy.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (5)
1. The preparation method of the double-layer composite film on the surface of the magnesium alloy is characterized by comprising the following steps of:
(1) Polishing, cleaning and drying the magnesium-aluminum alloy to obtain a matrix;
(2) Dissolving alkaline hydroxide and phosphate into water to obtain micro-arc oxidation electrolyte;
(3) Immersing the anode and the cathode into the micro-arc oxidation electrolyte, applying direct-current pulse voltage, and performing micro-arc oxidation treatment, wherein the micro-arc oxidation treatment adopts a constant voltage mode to generate an MgO film on the surface of the anode in situ and a magnesium-aluminum LDHs hydrotalcite film with a cross-linked nano-sheet structure on the surface of the MgO film, so as to obtain the magnesium-aluminum alloy surface double-layer composite film;
in the step (3), the treatment voltage of the micro-arc oxidation treatment is 100-800V, the treatment time is 120-1200 s, the frequency is 500-1500 Hz, the duty ratio is 0-30%, and the temperature of the micro-arc oxidation electrolyte in the micro-arc oxidation treatment process is below 40 ℃;
the alkaline hydroxide is sodium hydroxide, potassium hydroxide or calcium hydroxide; the phosphate is one or more of trisodium phosphate, sodium hydrogen phosphate and ammonium hydrogen phosphate;
the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 1-12 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 5-30 g/L.
2. The preparation method of claim 1, wherein the concentration of the alkaline hydroxide in the micro-arc oxidation electrolyte is 4-10 g/L, and the concentration of the phosphate in the micro-arc oxidation electrolyte is 10-18 g/L.
3. The method of claim 1, wherein the inert electrode is a stainless steel plate, a platinum sheet, or a graphite carbon rod.
4. A magnesium alloy surface double-layer composite film prepared by the preparation method according to any one of claims 1 to 3, wherein the magnesium alloy surface double-layer composite film comprises an MgO film formed on the surface of the magnesium alloy and a hydrotalcite film formed on the surface of the MgO film.
5. The magnesium alloy surface bilayer composite film according to claim 4, wherein the hydrotalcite film has a cross-linked nano-sheet structure.
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