Magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer and preparation method

Abstract

The present invention provides a magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer (hereinafter referred to as Mg-Al-LDH magnesium alloy) and a preparation method thereof. The preparation method of the Mg-Al-LDH magnesium alloy includes: using a magnesium alloy as a substrate, and in-situ growing a layer of magnesium hydroxide on the surface of the substrate by a hydrothermal method, which serves as an intermediate transition layer, and then growing Mg-Al-LDH above the transition layer again by the hydrothermal method, finally forming an Mg-Al-LDH film layer with excellent corrosion resistance on the magnesium alloy surface. Compared with the prior art, the Mg-Al-LDH magnesium alloy composite material film layer prepared by the hydrothermal method of the present invention has smaller grains, better densification, and stronger bonding force with the substrate. While the composite material has good corrosion resistance, it can still maintain good mechanical and plastic properties.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface corrosion protection, and in particular relates to a magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer and a preparation method thereof. Background Art

[0002] As global energy and environmental issues become increasingly prominent, researchers have a stronger demand for lightweight design of metal materials. Magnesium alloys have the advantages of low density, high specific strength, large elastic modulus, high damping, and excellent biocompatibility. Among current metal materials, magnesium alloys are the best choice to meet the requirements of lightweight material design. Magnesium alloys are being increasingly used in fields such as automobiles, aerospace, electronics, and biomedicine. Although magnesium alloys have many attractive performance advantages, their inherent performance disadvantages make it difficult to expand their application range. Magnesium has a low standard electrode potential and active chemical properties, which makes magnesium alloy products extremely prone to corrosion in the service environment. Therefore, the corrosion problem is also a key factor hindering the large-scale application of magnesium alloys in industry.

[0003] The main methods to improve the corrosion resistance of magnesium alloys are divided into two directions: one is to increase the electrode potential of the magnesium alloy itself through purification and alloying, or to form a protective oxide film in the service environment to enhance its own resistance to the environment. However, while improving the corrosion resistance, it will affect the mechanical properties, plasticity and stability of the matrix, and it is impossible to achieve a simultaneous improvement in the mechanical properties, plasticity, stability and corrosion resistance of the alloy. The second is to modify and coat the surface of the magnesium alloy to isolate the alloy from the medium to achieve improved corrosion resistance. However, existing surface technologies generally have many shortcomings such as complex processes, poor interface effects, and environmental unfriendliness. Therefore, how to form an environmentally friendly film layer on the surface of the magnesium alloy and improve the corrosion resistance of the alloy while ensuring that the mechanical properties, plasticity and stability of the alloy are not affected is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a magnesium alloy composite material having a magnesium-aluminum layered double hydroxide film layer, and its preparation method comprises the following steps:

[0005] (1) After polishing the surface of the magnesium alloy, the sample was immersed in a mixed solution of 40-55 g / L soluble alkali and 8-12 g / L soluble phosphate at 70-85° C. for 8-15 minutes to remove residual oil on the surface of the sample, and then washed with deionized water and dried to obtain a magnesium alloy with a clean surface, wherein the magnesium alloy is one of AZ31 magnesium alloy and AZ91 magnesium alloy;

[0006] (2) Mix a soluble base, a soluble carbonate, and deionized water to obtain a solution with a pH of 13 - 14, where the concentration of the soluble carbonate is 0.08 - 0.12 mol / L. Place the magnesium alloy with a clean surface obtained in step (1) in the solution, and carry out a hydrothermal reaction under the conditions of 155 - 165 °C and 540 - 750 KPa for 30 - 50 min. After washing and drying, a magnesium alloy with magnesium hydroxide crystals uniformly dispersed on the surface is obtained;

[0007] (3) Mix a soluble magnesium salt and a soluble aluminum salt with deionized water to obtain solution A, where the molar ratio of Mg 2+ to Al 3+ is 2.8:1 - 3.2:1, the concentration of Al 3+ is 0.045 - 0.055 mol / L, and the concentration of Mg 2+ is 0.12 - 0.18 mol / L; Mix a soluble base 1 with deionized water to obtain an alkali solution B with a concentration of 0.05 - 0.2 mol / L; Mix a soluble base 2 and a soluble nitrate with deionized water to obtain a mixed solution C with a pH value of 9.5 - 10.3, where the concentration of the soluble nitrate is 0.08 - 0.12 mol / L; Add solution A and solution B to solution C, continuously stir and control the pH value to be 8.3 - 8.7 to obtain a suspension D. Place the magnesium alloy obtained in step (2) in suspension D, and carry out a hydrothermal reaction at 123 - 128 °C and 200 - 250 KPa for 14 - 16 h. After washing and drying, a magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer is obtained.

[0008] Further, in step (1), the soluble base is any combination of sodium hydroxide or potassium hydroxide, and the soluble phosphate is any combination of sodium phosphate or potassium phosphate.

[0009] Further, in step (2), the soluble base is any combination of sodium hydroxide, potassium hydroxide, or lithium hydroxide, and the soluble carbonate is any combination of sodium carbonate or potassium carbonate.

[0010] Further, in step (3), the soluble magnesium salt is any combination of magnesium nitrate, magnesium chloride, or magnesium sulfate, and the soluble aluminum salt is any combination of aluminum nitrate, aluminum chloride, or aluminum sulfate.

[0011] Further, in step (3), the soluble base 1 and the soluble base 2 are any combination of sodium hydroxide or potassium hydroxide, and the soluble nitrate is any combination of sodium nitrate or potassium nitrate.

[0012] Further, the grain size of the magnesium hydroxide in the magnesium alloy with magnesium hydroxide crystals uniformly dispersed on the surface described in step (2) is 200 - 350 nm.

[0013] Further, the grain size of the layered double hydroxide in the magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer described in step (3) is 100 - 250 nm.

[0014] Advantages of the present invention

[0015] Compared with the prior art, through the synergistic effect of raw materials, raw material ratio, process and parameters, the obtained magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer (hereinafter referred to as Mg-Al-LDH magnesium alloy) of the present invention has the following advantages:

[0016] (1) The present invention does not require additional equipment, and the experimental process is simple.

[0017] (2) The magnesium hydroxide layer component prepared in the primary hydrothermal stage of the present invention has fine and uniform grains, and the structure and morphology are controllable.

[0018] (3) CO3 provided in the early stage of the primary hydrothermal stage of the present invention 2- reacts with Mg generated by the dissolution of the magnesium alloy matrix 2+ to form a deposit of Mg5(CO3)4(OH)2·5H2O, which decomposes into magnesium hydroxide subsequently, promoting the formation of magnesium hydroxide in a strongly alkaline environment. Therefore, an in-situ grown anhydrous magnesium hydroxide conversion layer is obtained, replacing the water-containing magnesium hydroxide produced by the traditional hydrothermal method. The reaction is controlled to occur only on the surface of the magnesium alloy matrix, that is, an in-situ reaction is carried out, using only the Mg on the surface layer of the magnesium alloy as the reaction raw material, without reacting with the Mg in the mother liquor. Therefore, the binding force between magnesium hydroxide and the alloy matrix is more stable, making the growth of magnesium hydroxide denser, uniformly coating the surface of the matrix, and providing better corrosion protection for the matrix.

[0019] (4) Since the present invention realizes the effective control of the composition, structure and morphology of the magnesium hydroxide film layer, and utilizes the similar crystal structure and adjustable surface morphology between the magnesium hydroxide film layer and LDH to provide favorable conditions for the nucleation and growth of the LDH film layer. In addition, the dissolution and deposition re-equilibration process of magnesium hydroxide in the secondary hydrothermal solution also provides effective ions for the nucleation and growth of LDH, making the binding force between LDH and the magnesium alloy matrix stronger, effectively improving the structure and properties of the film layer. At the same time, the formation of impurities such as aluminum hydroxide in the mother liquor is reduced, which is more conducive to the growth of the Mg-Al-LDH coating.

[0020] (5) Compared with the prior art, the Mg-Al-LDH coating formed under lower pH conditions, that is, under low alkalinity conditions with a pH value of 8.3 - 8.7, of the present invention has finer grains, a dense structure, and a controllable thickness.

[0021] In summary, compared with the prior art, the nucleation rate of the present invention is higher, the magnesium hydroxide crystals and the crystals on the surface layer of the composite material are finer, and can evenly and tightly cover the surface of the substrate. Among them, the grain size of magnesium hydroxide in the magnesium alloy with magnesium hydroxide crystals evenly dispersed on the surface is 200-350 nm; the grain size of the double hydroxide in the magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer is 100-250 nm.

[0022] The results show that: compared with the prior art, the alloy material obtained by the present invention can improve the corrosion resistance without sacrificing the mechanical properties and plasticity. Among them, the corrosion potential is higher and the corrosion current density is smaller, that is, the corrosion resistance is more excellent. In addition, only the processes and parameters within the scope of the claims of the present invention can achieve the effect of simultaneously improving the mechanical properties, plasticity and corrosion resistance of the composite material. This significant improvement is achieved by the synergistic effect of raw materials, reaction ratios, processes and parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 (a) and (b) are respectively the SEM comparison diagrams of AZ31 magnesium alloy 1 obtained in step (2) of Example 1 and AZ31 magnesium alloy composite material 1 obtained in step (3);

[0024] Figure 2 (a) and (b) are respectively the SEM comparison diagrams of AZ31 magnesium alloy 4 obtained in step (2) of Comparative Example 1 and AZ31 magnesium alloy composite material 4 obtained in step (3);

[0025] Figure 3 is the small-angle grazing incidence X-ray diffraction comparison pattern of AZ31 magnesium alloy 1 obtained in step (2) of Example 1 and AZ31 magnesium alloy composite material 1 obtained in step (3).

[0026] According to the diffraction peaks of magnesium hydroxide in the diffraction pattern of AZ31 magnesium alloy 1 and the SEM image of AZ31 magnesium alloy 1, Figure 1 (a) The fine grains with a grain size of 200-350 nm are magnesium hydroxide; according to the diffraction peaks of LDH in the diffraction pattern of AZ31 magnesium alloy composite material 1 and the SEM image of AZ31 magnesium alloy 1, the fine grains with a grain size of 100-250 nm are Mg-Al-LDH. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0028] Example 1

[0029] The preparation steps of AZ31 magnesium alloy composite material 1 with a magnesium-aluminum layered double hydroxide film layer are as follows:

[0030] (1) After the surface of AZ31 magnesium alloy was polished smooth, it was immersed in a mixed solution of 50 g / L sodium hydroxide and 10 g / L sodium phosphate at 80 °C for 10 min to remove the residual oil on the surface of the sample. The sample was then washed with deionized water and dried to obtain AZ31 magnesium alloy with a clean surface.

[0031] (2) Sodium hydroxide, sodium carbonate and deionized water are mixed to obtain a solution with a pH value of 14, wherein the concentration of sodium carbonate is 0.1 mol / L, and the AZ31 magnesium alloy with a clean surface obtained in step (1) is placed in the solution, and a hydrothermal reaction is carried out at 160° C. and 618.3 kPa for 40 min. After washing and drying, an AZ31 magnesium alloy 1 with magnesium hydroxide crystals uniformly dispersed on the surface is obtained.

[0032] (3) Mix magnesium nitrate and aluminum nitrate with deionized water to obtain solution A, in which Mg 2+ With Al 3+ The molar ratio is 3:1, Al 3+ The concentration of Mg is 0.05mol / L, 2+ The concentration of the mixture is 0.15 mol / L; sodium hydroxide is mixed with deionized water to obtain a 0.1 mol / L sodium hydroxide solution B; sodium hydroxide and sodium nitrate are mixed with deionized water to obtain a mixed solution C with a pH value of 10, wherein the concentration of sodium nitrate is 0.1 mol / L; solution A and solution B are added to solution C, and the suspension D is obtained after continuous stirring and controlling the pH value to 8.5. The AZ31 magnesium alloy 1 obtained in step (2) is placed in the suspension D, and a hydrothermal reaction is carried out at 125° C. and 232.2 kPa for 15 h, and then an AZ31 magnesium alloy composite material 1 (Mg-Al-LDH magnesium alloy composite material 1) with a magnesium-aluminum layered double hydroxide film layer is obtained after washing and drying.

[0033] according to Figure 1 (a) and Figure 3 The step (2) obtains a magnesium hydroxide crystal AZ31 magnesium alloy 1 with uniformly dispersed magnesium hydroxide crystals on the surface. The magnesium hydroxide crystals are uniformly dispersed on the surface of the AZ31 magnesium alloy 1, and the grain size thereof is 200 to 350 nm. The Mg-Al-LDH nucleates and grows on the magnesium hydroxide crystals, and finally the LDH grains of the Mg-Al-LDH film layer obtained in the step (3) are relatively small. Figure 1 (b) and Figure 3 ,The grain size is 100~250nm, and the LDH grows relatively densely, which makes the gap between adjacent crystals smaller and evenly covers the substrate, achieving full coverage of the substrate and providing better protection for the substrate.

[0034] The fitting results of the potentiodynamic polarization curve of the AZ31 magnesium alloy composite material 1 with a magnesium-aluminum layered double hydroxide film layer obtained in step (3) in a 3.5 wt% NaCl saturated Mg(OH)2 solution show that the corrosion potential (E corr ) is -1.07 V / SCE, and the corrosion current density (Icorr) is 9.53×10 -9 A·cm -2 . According to the reports in the prior art, the smaller the corrosion current density, the better the corrosion resistance of the film layer.

[0035] Example 2

[0036] The preparation steps of the AZ31 magnesium alloy composite material 2 with a magnesium-aluminum layered double hydroxide film layer are as follows:

[0037] (1) After polishing the surface of the AZ31 magnesium alloy smoothly, it is soaked in a mixed solution of 48 g / L sodium hydroxide and 8 g / L sodium phosphate at 75 °C for 8 min to remove the residual oil on the sample surface. Then, it is washed with deionized water and dried to obtain the AZ31 magnesium alloy with a clean surface.

[0038] (2) Sodium hydroxide, sodium carbonate, and deionized water are mixed to obtain a solution with a pH value of 13.6, where the concentration of sodium carbonate is 0.08 mol / L. The AZ31 magnesium alloy with a clean surface obtained in step (1) is placed in the solution, and a hydrothermal reaction is carried out under the conditions of 158 °C and 591.5 KPa for 35 min. After washing and drying, the AZ31 magnesium alloy 2 with uniformly dispersed magnesium hydroxide crystals formed on the surface is obtained.

[0039] (3) Magnesium nitrate and aluminum nitrate are mixed with deionized water to obtain solution A, where the molar ratio of Mg 2+ to Al 3+ is 2.8:1, the concentration of Al 3+ is 0.045 mol / L, and the concentration of Mg 2+ is 0.126 mol / L; sodium hydroxide is mixed with deionized water to obtain a 0.08 mol / L sodium hydroxide solution B; sodium hydroxide and sodium nitrate are mixed with deionized water to obtain a mixed solution C with a pH value of 9.8, where the concentration of sodium nitrate is 0.08 mol / L; solution A and solution B are added to solution C, and it is continuously stirred and its pH value is controlled to be 8.3 to obtain a suspension D; the AZ31 magnesium alloy 2 obtained in step (2) is placed in the suspension D, and a hydrothermal reaction is carried out under the conditions of 123 °C and 219.2 KPa for 14.5 h. After washing and drying, the AZ31 magnesium alloy composite material 2 with a magnesium-aluminum layered double hydroxide film layer (Mg-Al-LDH magnesium alloy composite material 2) is obtained.

[0040] The Mg-Al-LDH film layer obtained in step (3) has dense LDH growth and uniformly covers the substrate, achieving full coverage of the substrate and providing better protection for the substrate.

[0041] The potentiodynamic polarization curve fitting results of the Mg-Al-LDH magnesium alloy composite 2 obtained in step (3) in a 3.5 wt% NaCl saturated Mg(OH)2 solution show that the corrosion potential (E corr ) is -1.11 V / SCE, and the corrosion current density (Icorr) is 1.13×10 -8 A·cm -2 . It shows good corrosion resistance.

[0042] Example 3

[0043] The preparation steps of the AZ31 magnesium alloy composite 3 with a magnesium-aluminum layered double hydroxide film layer are as follows:

[0044] (1) After polishing the surface of the AZ31 magnesium alloy smoothly, it is soaked in a mixed solution of 52 g / L sodium hydroxide and 12 g / L sodium phosphate at 85 °C for 12 min to remove the residual oil on the specimen surface. Then, it is washed with deionized water and dried to obtain the AZ31 magnesium alloy with a clean surface.

[0045] (2) Sodium hydroxide, sodium carbonate, and deionized water are mixed to obtain a solution with a pH value of 13.8, where the concentration of sodium carbonate is 0.11 mol / L. The AZ31 magnesium alloy with a clean surface obtained in step (1) is placed in the solution, and a hydrothermal reaction is carried out at 162 °C and 655 KPa for 50 min. After washing and drying, the AZ31 magnesium alloy 3 with uniformly dispersed magnesium hydroxide crystals formed on the surface is obtained.

[0046] (3) Magnesium nitrate and aluminum nitrate are mixed with deionized water to obtain solution A, where the molar ratio of Mg 2+ to Al 3+ is 3.2:1, the concentration of Al 3+ is 0.055 mol / L, and the concentration of Mg 2+The concentration is 0.176 mol / L; sodium hydroxide and deionized water are mixed to obtain sodium hydroxide solution B with a concentration of 0.1 mol / L; sodium hydroxide and sodium nitrate are mixed with deionized water to obtain mixed solution C with a pH value of 10.2, where the concentration of sodium nitrate is 0.12 mol / L; solution A and solution B are added to solution C, and after continuous stirring and controlling the pH value to 8.7, suspension D is obtained; the AZ31 magnesium alloy 3 obtained in step (2) is placed in suspension D, and a hydrothermal reaction is carried out under the conditions of heat preservation at 127 °C and 247.2 KPa for 16 h, and then after washing and drying, an AZ31 magnesium alloy composite material 3 (Mg-Al-LDH magnesium alloy composite material 3) with a magnesium-aluminum layered double hydroxide film layer is obtained.

[0047] The Mg-Al-LDH film layer LDH obtained in step (3) grows densely and uniformly covers the substrate, realizing full coverage of the substrate and providing better protection for the substrate.

[0048] The potentiodynamic polarization curve fitting results of the Mg-Al-LDH magnesium alloy composite material 3 obtained in step (3) in a 3.5 wt% NaCl saturated Mg(OH)2 solution are that the corrosion potential (E corr ) is -1.09 V / SCE, and the corrosion current density (Icorr) is 1.16×10 -8 A·cm -2 . It shows good corrosion resistance.

[0049] Comparative Example 1

[0050] An AZ31 magnesium alloy composite material 4 with a magnesium-aluminum layered double hydroxide film layer, and its preparation method is as follows:

[0051] (1) After the magnesium alloy surface is polished smoothly, the surface of the substrate is cleaned in ethanol by ultrasonic waves to remove the residual oil on the surface of the specimen. The specimen is taken out, rinsed with deionized water, and then dried by cold air blowing to obtain a magnesium alloy substrate with a smooth and clean surface.

[0052] (2) Sodium hydroxide and deionized water are mixed to obtain a solution with a pH value of 10. The AZ31 magnesium alloy with a clean surface obtained in step (1) is placed in the solution, and a hydrothermal reaction is carried out under the conditions of heat preservation at 125 °C and 232.2 KPa for 1.5 h. After washing and drying, an AZ31 magnesium alloy 4 coated with magnesium hydroxide crystals is obtained.

[0053] (3) Magnesium nitrate and aluminum nitrate are mixed with deionized water to obtain solution A, where the molar ratio of Mg 2+ to Al 3+ is 3:1, the concentration of Al 3+ is 0.02 mol / L, and the concentration of Mg 2+The concentration is 0.06 mol / L; sodium hydroxide and deionized water are mixed to obtain sodium hydroxide solution B with a concentration of 0.05 mol / L; solution B and solution A are mixed, and then continuously stirred to obtain suspension C with a pH value of 10; the AZ31 magnesium alloy 4 obtained in step (2) is placed in suspension C, and a hydrothermal reaction is carried out under the conditions of heat preservation at 120 °C and 198.6 KPa for 18 h, and then after washing and drying, the AZ31 magnesium alloy composite material 4 with a magnesium-aluminum layered double hydroxide film layer is obtained.

[0054] According to Figure 2 (a), the AZ31 magnesium alloy 4 obtained in step (2) is the AZ31 magnesium alloy with magnesium hydroxide crystals coated on the surface. The grain size of the magnesium hydroxide crystals is about 800 - 1000 nm. The Mg-Al-LDH film layer LDH obtained in step (3) shows a larger grain size. According to Figure 2 (b), the grain size is 1000 - 1300 nm. Although it plays a certain role in delaying the corrosion of the matrix, due to the relatively large LDH grains, the distance between the grains is relatively large, and this loose structure cannot achieve full coverage of the matrix, so the corrosion resistance is weak.

[0055] The fitting result of the potentiodynamic polarization curve of the AZ31 magnesium alloy composite material 4 with a magnesium-aluminum layered double hydroxide film layer obtained in step (3) in a 3.5 wt% NaCl saturated Mg(OH)2 solution shows that the corrosion potential (E corr ) is -1.25 V / SCE, and the corrosion current density (Icorr) is 5.03×10 -7 A·cm -2 .

[0056] Table 1 Corrosion potential and current density of the AZ31 magnesium alloy composite materials obtained in Examples 1 - 3 and Comparative Example 1

[0057]

[0058] In summary: Compared with the comparative example, although the comparative example uses a similar process to the present invention, the process parameters in the comparative example are not within the scope of the claims of the present invention. As a result, the corrosion resistance of the magnesium alloy composite material obtained in the comparative example is lower than the lowest corrosion resistance of the alloy material obtained in the present invention. In addition, compared with the prior art, the present invention can significantly improve the bonding force between the film layer and the matrix by adjusting the process, raw materials, ratio, and the synergistic effect of relevant process parameters, so that all the Mg 2+ in the initially formed magnesium hydroxide comes from the magnesium alloy matrix, while the Mg 2+Partially derived from the substrate and partially from the mother liquor, this makes the connection degree between the film layer and the substrate unstable, which will also bring instability to the growth of the composite film layer in the later stage; in addition, compared with the prior art, the nucleation rate of the present invention is higher, and the magnesium hydroxide crystals and the crystals of the finally obtained material are finer; the present invention also reduces the formation of impurities such as aluminum hydroxide; the results show that: compared with the prior art, the alloy material obtained by the present invention has a higher corrosion potential and a smaller corrosion current density, that is, the corrosion resistance is more excellent. It can be seen from the three examples of the present invention that: under the condition of different process parameters in the three examples, the material obtained in Example 1 has the most excellent corrosion resistance. Therefore, it can be concluded that the most excellent corrosion resistance of the material obtained by the present invention is achieved by the synergistic effect of raw materials, reaction ratio, process and parameters. In addition, compared with the prior art, the present invention can significantly improve the corrosion resistance of the material while maintaining good mechanical properties and plasticity of the substrate material. Compared with the prior art which is difficult to simultaneously improve the mechanical properties, plasticity and corrosion resistance of the material, the present invention has achieved remarkable technical effects.

Claims

1. A magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer, characterized in that, It is prepared by the following method steps: (1) After polishing the surface of the magnesium alloy smoothly, put it into a mixed solution of 40 - 55 g / L soluble alkali and 8 - 12 g / L soluble phosphate. After heat preservation and soaking at 70 - 85 °C for 8 - 15 min, remove the residual oil on the surface of the sample, and then wash and dry it with deionized water to obtain a magnesium alloy with a clean surface. The magnesium alloy is one of AZ31 magnesium alloy and AZ91 magnesium alloy; (2) Mix soluble alkali, soluble carbonate and deionized water to obtain a solution with a pH of 13 - 14, where the concentration of soluble carbonate is 0.08 - 0.12 mol / L. Place the magnesium alloy with a clean surface obtained in step (1) in the solution, and carry out hydrothermal reaction under the conditions of 155 - 165 °C and 540 - 750 KPa for 30 - 50 min. After washing and drying, obtain a magnesium alloy with magnesium hydroxide crystals uniformly dispersed on the surface; (3) Mix soluble magnesium salt and soluble aluminum salt with deionized water to obtain solution A, where the molar ratio of Mg 2+ to Al 3+ is 2.8:1 to 3.2:1, the concentration of Al 3+ is 0.045 - 0.055 mol / L, and the concentration of Mg 2+ is 0.12 - 0.18 mol / L; mix soluble base 1 with deionized water to obtain alkaline solution B with a concentration of 0.05 - 0.2 mol / L; mix soluble base 2 and soluble nitrate with deionized water to obtain mixed solution C with a pH value of 9.5 - 10.3, where the concentration of soluble nitrate is 0.08 - 0.12 mol / L; add solution A and solution B into solution C, continuously stir and control the pH value to be 8.3 - 8.7 to obtain suspension D, place the magnesium alloy obtained in step (2) in suspension D, carry out hydrothermal reaction at 123 - 128 °C and 200 - 250 KPa for 14 - 16 h, and then obtain a magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer after washing and drying; In step (3), the soluble alkali 1 and soluble alkali 2 are any combination of sodium hydroxide or potassium hydroxide.

2. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, wherein: In step (1), the soluble alkali is any combination of sodium hydroxide or potassium hydroxide, and the soluble phosphate is any combination of sodium phosphate or potassium phosphate.

3. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, wherein: In step (2), the soluble alkali is any combination of sodium hydroxide or potassium hydroxide or lithium hydroxide, and the soluble carbonate is any combination of sodium carbonate or potassium carbonate.

4. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, characterized in that: In step (3), the soluble magnesium salt is any combination of magnesium nitrate, magnesium chloride or magnesium sulfate, and the soluble aluminum salt is any combination of aluminum nitrate, aluminum chloride or aluminum sulfate.

5. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, characterized in that: In step (3), the soluble nitrate is any combination of sodium nitrate or potassium nitrate.

6. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, characterized in that: The grain size of magnesium hydroxide in the magnesium alloy with magnesium hydroxide crystals uniformly dispersed on the surface described in step (2) is 200 - 350 nm.

7. The magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer according to claim 1, characterized in that: The grain size of the layered double hydroxide in the magnesium alloy composite material with a magnesium-aluminum layered double hydroxide film layer described in step (3) is 100 - 250 nm.

Images