CN107130281B

CN107130281B - Micro-arc oxidation electrolyte with low calcium-phosphorus ratio

Info

Publication number: CN107130281B
Application number: CN201710376039.7A
Authority: CN
Inventors: 于慧君; 高丹丹; 陈传忠
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2017-05-25
Filing date: 2017-05-25
Publication date: 2021-10-01
Anticipated expiration: 2037-05-25
Also published as: CN107130281A

Abstract

The invention relates to a micro-arc oxidation electrolyte with low calcium-phosphorus ratio. The micro-arc oxidation electrolyte comprises: phosphoric acid or phosphate, calcium carbonate, wherein Ca/P is less than or equal to 1/2. The results of XRD and FT-IR infrared tests of calcium-phosphorus film layers prepared on the surfaces of self-cast Mg-2Sr alloys by a micro-arc oxidation technology by adopting constant positive voltage and negative voltage show that the phases contained in the micro-arc oxidation film layers before the dipping of simulated body fluid are mainly Mg, MgO and Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like, and Ca was detected in the film layer after the immersion₂P₂O₇,Mg(OH)₂And new phases such as HA, Sr-HA and the like exist. The micro-arc oxidation film layer prepared by the method has a typical microporous structure and has no obvious microcrack, the granular corrosion products on the surface of the micro-arc oxidation film layer have high content of calcium and phosphorus phases, and the micro-arc oxidation film layer has good biocompatibility and bioactivity. Compared with the matrix, the micro-arc oxidation film layer has better corrosion resistance, and is improved by more than 2 orders of magnitude compared with the existing high-calcium low-phosphorus electrolyte.

Description

Micro-arc oxidation electrolyte with low calcium-phosphorus ratio

Technical Field

The invention belongs to the field of magnesium alloy micro-arc oxidation, and relates to a micro-arc oxidation electrolyte with a low calcium-phosphorus ratio.

Background

As a biodegradable implant material, the magnesium alloy has the following advantages: the density and the elastic modulus are relatively close to those of bone tissues, so that the stress shielding effect can be effectively reduced, and the growth of the bone tissues is promoted; has good physical property and mechanical property, and is suitable for repairing and replacing bone tissues; magnesium is a basic element contained in a human body, has no toxicity to the human body, and does not generate any side effect in the dissolving process; magnesium in the skeletal system is beneficial to bone growth and improves bone strength. However, the ideal biodegradable magnesium alloy also needs to meet the requirements of better mechanical strength and integrity, higher corrosion resistance in the initial period of implantation, uniform and controllable degradation rate, no more content of degradation products than the range capable of being absorbed by human body and the like.

The selection of strontium as an alloying element for magnesium alloy implants has potential feasibility. The strontium element and the calcium element are positioned in the second main group of the periodic table and below the calcium element, and the strontium element can promote the generation of the implant. Strontium is a trace metal element in the human body and 99% of the total amount thereof is distributed in bone tissues. The generation of strontium-containing hydroxyapatite is beneficial to bone repair. The strontium element can promote the growth, reproduction and repair of cells around the bone implant, thereby improving the bone induction and bone formation capability. In addition, researches find that the magnesium alloy containing 2 mass percent of Sr has higher mechanical property and lower corrosion resistance. In summary, the Mg-2Sr alloy can be used as a potential biocompatible magnesium-based alloy for subsequent experiments. However, magnesium degrades too rapidly in the human body to maintain its supporting effect until new bone tissue grows, and hydrogen generated by degradation is deposited around the implant to hinder wound healing, and also raises the pH around the implant, even causing alkalosis. Magnesium purification, alloying and surface modification can be used as three different solutions for enhancing corrosion resistance. In the experiment, strontium element is adopted for alloying preparation of Mg-2Sr alloy with excellent performance, and then a functional film layer is prepared on the surface of the alloy by utilizing the micro-arc oxidation technology so as to realize comprehensive utilization of alloying and surface modification. Micro Arc Oxidation (MAO), also known as microplasma oxidation, applies a voltage to the surface of metal such as Al, Mg, Ti, Zr, Nb, Ta, etc. by an electrochemical method to generate a spark discharge phenomenon, undergoes melting, eruption, crystallization, high temperature phase change under the combined action of thermochemistry, plasma chemistry and electrochemistry, and finally forms a ceramic layer by cladding and sintering on the surface of a substrate. The micro-arc oxidation film layer has high hardness, good wear resistance, better corrosion resistance and thermal stability. The ceramic film layer and the metal matrix are metallurgically bonded, so that the bonding force is strong.

The alloy matrix, the electrical parameters and the electrolyte formula comprehensively influence the performance of the micro-arc oxidation film layer. Wherein, the components from the electrolyte formula enter the film layer along with the micro-arc oxidation reaction, thereby influencing the phase composition, microstructure, corrosion resistance, binding force, biodegradability and the like of the film layer. Therefore, the electrolyte formulation is critical to the final properties of the film for a given substrate and electrical parameters.

Disclosure of Invention

In order to make up the defects of the traditional electrolyte, the invention provides a micro-arc oxidation electrolyte system added with calcium carbonate.

The invention is realized by the following modes:

the micro-arc oxidation electrolyte with low calcium-phosphorus ratio has Ca/P not more than 1/2.

Preferably, the Ca/P ratio of the electrolyte is 1/7-1/2, the preferable Ca/P ratio is 1/6-1/2, and the further preferable Ca/P ratio is 1/5-1/3.

Preferably, the calcium source used by the electrolyte is calcium carbonate, and the concentration of the calcium carbonate is 0.2-4 g/L; preferably, the concentration of calcium carbonate is 0.3-3 g/L; further preferably, the concentration of calcium carbonate is 0.5-1 g/L; most preferably, the concentration of calcium carbonate is 0.600 g/L.

The electrolyte also comprises one or more of the following components in percentage by mass: (Na)₂PO₃)₆The concentration of (A) is 1-30g/L, the concentration of KOH is 2-10g/L, NH₄HF₂Has a concentration of 5-10g/L, C₃H₈O₃The concentration of (A) is 2-10ml/L, N (CH)₂CH₂OH)₃The concentration of (A) is 2-10ml/L, H₂O₂The concentration of (B) is 1-13 ml/L.

The optimized one or more components and mass concentration of the invention are as follows: (Na)₂PO₃)₆The concentration of (A) is 1-20g/L, the concentration of KOH is 4-6g/L, NH₄HF₂Has a concentration of 6-8g/L, C₃H₈O₃The concentration of (A) is 6-8 ml/L, N (CH)₂CH₂OH)₃The concentration of (A) is 4-6ml/L, H₂O₂The concentration of (A) is 4-10 ml/L.

The invention further optimizes one or more components and concentrations as follows: (Na)₂PO₃)₆Has a concentration of 1.836g/L or 2.448g/L or 3.060g/L, a KOH concentration of 5g/L, NH₄HF₂Has a concentration of 7g/L, C₃H₈O₃Has a concentration of 5ml/L, N (CH)₂CH₂OH)₃Has a concentration of 5ml/L, H₂O₂The concentration of (2) was 7 ml/L.

Preferably, the electrolyte has a Ca/P of 1/2, 1/3, 1/4 or 1/5.

The invention also provides a preparation method of the strontium-containing hydroxyapatite micro-arc oxidation coating on the surface of the magnesium alloy, which is characterized in that the coating is prepared on the magnesium alloy substrate by adopting a micro-arc oxidation method;

the electrolyte adopted by the micro-arc oxidation method is any one of the above electrolytes;

the magnesium alloy matrix is Mg-2 Sr.

Preferably, the micro-arc oxidation treatment comprises the following specific steps: airing the pretreated magnesium alloy matrix, placing the aired magnesium alloy matrix in an electrolyte as a positive electrode, using a stainless steel groove as a negative electrode, introducing circulating cooling water to keep the temperature of the electrolyte below 50 ℃, supplying power by using a micro-arc oxidation power supply, wherein the power frequency is 500-600 Hz, the positive duty ratio is 20-40%, the negative duty ratio is 10-30%, adding negative voltage of 20-60V, and performing an electrifying reaction for 5-20 min under the constant voltage of the positive voltage of 400-500V; preferably, the micro-arc oxidation power supply has parameters of power supply frequency of 550Hz, positive duty ratio of 30 percent and negative duty ratio of 20 percent, negative voltage of 40V is added, and the micro-arc oxidation power supply is electrified and reacts for 10min under the constant voltage of positive voltage of 450V, and is a bidirectional pulse power supply, a unidirectional pulse power supply or a direct current power supply.

The invention also provides application of the electrolyte with low calcium and high phosphorus and added calcium carbonate in improving the corrosion resistance and/or the biological performance (biocompatibility or bioactivity) of the magnesium alloy micro-arc oxidation coating. The invention discovers that the following components are obtained through systematic research on the film forming rule of the micro-arc oxidation film of the magnesium-strontium alloy: different from other matrix materials, for magnesium-strontium alloy, the addition of the calcium carbonate-containing low-calcium high-phosphorus electrolyte not only can enable the micro-arc oxidation film to have better biological performance (biocompatibility or bioactivity), but also can enable the corrosion resistance of the micro-arc oxidation film to be improved by more than 2 orders of magnitude compared with the existing high-calcium low-phosphorus electrolyte.

The invention has the beneficial effects that:

1) the micro-arc oxidation film layer prepared by the invention has a typical micro-pore structure and has no obvious micro-cracks, the content of calcium and phosphorus phases in granular corrosion products on the surface of the micro-arc oxidation film layer is high, and the biological performance (biocompatibility or bioactivity) is good. Compared with the matrix, the micro-arc oxidation film layer has better corrosion resistance, and is improved by more than 2 orders of magnitude compared with the existing high-calcium low-phosphorus electrolyte.

2) The invention selects calcium gluconate, calcium lactate and calcium carbonate as calcium source and sodium hexametaphosphate as electrolyte system of phosphorus source (the ratio of calcium to phosphorus is determined to be 1:2), adopts constant positive voltage and negative voltage to prepare calcium phosphorus film XRD and FT-IR infrared test results on the surface of self-cast Mg-2Sr alloy by micro-arc oxidation technology, and shows that the phases contained in the micro-arc oxidation film before the immersion of simulated body fluid are mainly Mg, MgO, Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like, and Ca was detected in the film layer after the immersion₂P₂O₇,Mg(OH)₂And new phases such as HA, Sr-HA and the like exist. The micro-arc oxidation film layer prepared by using calcium gluconate as a calcium source has smaller thickness, and the micro-arc oxidation film layer prepared by using calcium lactate and calcium carbonate as the calcium source has larger and closer thickness. All three micro-arc oxidation film layers have typical micro-pore structures and no obvious micro-cracks are found. The simulated body fluid immersion test shows that the granular corrosion product on the surface of the micro-arc oxidation film layer prepared by using calcium carbonate as a calcium source has higher content of calcium and phosphorus phases and good biological performance (biocompatibility or bioactivity). The micro-arc oxidation film layer has better corrosion resistance than the matrix, wherein the micro-arc oxidation films B and C prepared by using calcium lactate and calcium carbonate as calcium sources have lower weight loss rate.

3) The invention adopts constant positive voltage and negative voltage to prepare the calcium-phosphorus film XRD and FT-IR infrared test results on the surface of the self-cast Mg-2Sr alloy by the micro-arc oxidation technology, and the results show that the phases contained in the micro-arc oxidation film before the immersion of the simulated body fluid are mainly Mg, MgO and Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like, additionally after soakingCa was also detected in the film layer₂P₂O₇,Mg(OH)₂And new phases such as HA, Sr-HA and the like exist. Wherein, the surface of the film layer taking calcium lactate as a calcium source becomes smoother along with the reduction of the calcium-phosphorus ratio, the sizes of micropores become finer and more uniform, and the number of micropores is obviously increased. The calcium and phosphorus ratio in the film layer with calcium carbonate as the calcium source has smaller influence on the surface appearance of the film layer. The simulated body fluid soaking test shows that under two calcium sources, the calcium-phosphorus ratio is 1:4, the granular corrosion product on the surface of the micro-arc oxidation film layer prepared by the method has high calcium-phosphorus phase content, good biological performance (biocompatibility or bioactivity), good corrosion resistance, and low weight loss rate and degradation rate.

Drawings

FIG. 1 is an XRD (X-ray diffraction) spectrum of a micro-arc oxidation film layer prepared by calcium carbonate-containing electrolytes with different calcium-phosphorus ratios;

FIG. 2 shows FT-IR spectra of micro-arc oxide films prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios;

FIG. 3 is a micro-arc oxidation film prepared by the electrolyte with calcium carbonate as the calcium source, wherein the micro-arc oxidation film is characterized by (a) C3, (b) C4 and (C) C5;

FIG. 4C 4 is a graph showing the surface topography and elemental distribution of a film;

FIG. 5 is a cross-sectional morphology and elemental analysis of a micro-arc oxide film layer prepared from a calcium carbonate-containing electrolyte, wherein (a) C3, (b) C4, (C) C5;

FIG. 6 shows the binding force of the micro-arc oxide film prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios;

FIG. 73 is a tafel polarization curve of a micro-arc oxidation film layer in an SBF in calcium carbonate-containing electrolyte system with different calcium-phosphorus ratios;

FIG. 8 is an XRD (X-ray diffraction) pattern of a micro-arc oxidation film layer prepared by calcium carbonate-containing electrolytes with different calcium-phosphorus ratios after being soaked in SBF for 21 days;

FIG. 9 is FT-IR chart of micro-arc oxide film layer prepared by calcium carbonate containing electrolyte with different calcium-phosphorus ratio after soaking in SBF for 14 days;

FIG. 10 shows the surface morphology and the atomic percentage of elements of a micro-arc oxidation film layer SBF soaked for 21 days with calcium carbonate as a calcium source C3 (a)₁,a₂)，C4(b₁,b₂)，C5(c₁,c₂)；

FIG. 11 shows the weight loss of the micro-arc oxide film prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios after soaking in SBF for different days;

FIG. 12 shows the degradation rate of the micro-arc oxidation film layer SBF prepared by calcium carbonate-containing electrolyte with different calcium-phosphorus ratios after soaking for 28 days;

FIG. 13 is a graph showing the change of pH value with time during the soaking of the micro-arc oxidation film layer SBF prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios.

Detailed Description

The following is further illustrated with reference to the examples:

example 1

1. The micro-arc oxidation film prepared in the experiment relates to three different electrolyte systems, which are respectively as follows: calcium carbonate is used as a calcium source, and the molar ratio of calcium to phosphorus is set to 1:3, 1:4 and 1:5, which are respectively defined as C3, C4 and C5. The experiment systematically contrasts and researches the performances of the micro-arc oxidation film prepared under the three different calcium source electrolyte systems, and gives the optimized calcium-phosphorus molar ratio under the calcium carbonate source.

2. Experimental materials and methods

2.1 substrate and film preparation

The matrix used in the experiment is self-cast Mg-2Sr alloy, and the method comprises the following specific steps: using atmospheric protection (SF)₆：CO₂1: 200) pure magnesium (99.99%) and magnesium-strontium intermediate alloy (Mg-21Sr (99.99%)) are melted in a resistance furnace. All raw materials and tools used for casting need to be preheated to 250 ℃. When the temperature of the furnace rises to 500 ℃, putting the preheated pure magnesium ingot. When the furnace temperature is 700 ℃, pure magnesium is completely melted and is kept warm for 20 min. Adjusting the furnace temperature to 710 ℃, adding theoretical amount of magnesium-strontium intermediate alloy (Mg-21Sr (99.99 percent)) and preserving the temperature for 20 min. The melt was stirred thoroughly and poured into a preheated graphite mold. The cast Mg-2Sr alloy is then subjected to a homogenizing anneal at 400 ℃ for 16 hours. And cutting the casting body into regular cube small blocks of 8mm multiplied by 10mm by using linear cutting equipment, and then mechanically polishing the cube small blocks by using coarse 360#, coarse 600#, fine 600# and fine 1000# abrasive paper. And finally, cleaning the mixture by using acetone, deionized water and absolute ethyl alcohol and drying the mixture for later use. Micro-meterThe calcium source used in the arc oxidation experiment is calcium carbonate CaCO₃The calcium ion molar concentration is 0.006mol/L, and the mass concentration is 0.600 g/L; the phosphorus source used in the experiment is (Na)₂PO₃)₆The concentrations are 1.836g/L, 2.448g/L and 3.060g/L respectively; the components and the concentration of the rest electrolyte are KOH,5 g/L; NH (NH)₄HF₂,7g/L；C₃H₈O₃And N (CH)₂CH₂OH)₃The concentration is 5 ml/L; h₂O₂The concentration was 7 ml/L. The calcium to phosphorus ratios were 1:3/1:4 and 1:5, respectively, and the corresponding electrolyte systems were defined as C3, C4 and C5. All the medicines used in the experiment are analytically pure. In the micro-arc oxidation experiment process, a magnesium alloy sample is used as an anode, a stainless steel groove is used as a cathode, circulating cooling water is introduced to keep the temperature of the electrolyte below 50 ℃, a micro-arc oxidation power supply is adopted to supply power, and specific electrical parameters are shown in table 1.

TABLE 1 micro-arc Oxidation of Electrical parameters

2.2. Film detection

Film layer phase composition analysis: the phase composition of the micro-arc oxide film layer was analyzed by an X-ray diffractometer (BRUKER D8Advanced, Germany and Shmadzu XRD-6100) test. The test conditions were: the method comprises the following steps of Cu target (Cu-Kalpha), tube voltage of 40kV, tube current of 30mA, scanning range of 10-90 degrees, scanning speed of 4 degrees/min and sample interval of a counter of 0.02. Detecting the change of molecular structure and functional group by using a Fourier transform infrared spectrometer (Tensor 37 model) of BROOK, Germany, and the wave number range of infrared transmission spectrum is 4000cm^-1～400cm^-1Resolution of 4cm^-1The scan time is 16 s.

2, microscopic morphology and composition analysis (SEM, EDS) of the membrane layer: the surface morphology of the film before and after soaking was analyzed by S-3400N test of Hitachi (HITACHI), and the composition of the film was analyzed by assembling JED-2300 energy spectrum analyzer (EDS) with JSM-6380LA scanning electron microscope of JEOL (JEOL). And carrying out gold spraying treatment on the non-conductive sample before testing. The gold spraying equipment adopts a KYKY SBC-12 type ion sputtering instrument developed by Beijing Zhongkou instrument technology development Limited liability company, the used target material is a gold target, the current is 20mA, and the gold spraying time is 120 s.

And 3, measuring the thickness of the film layer: the thickness of the film layer is measured by a thickness tester with the model number of Mini Test600B FN2, the thickness of the non-conductive covering layer on the non-magnetic metal substrate is selected and tested, and the final film thickness value is the average value of 5 Test values.

4, scratch test: and in the scratch method test, a diamond scriber is used for scribing the surface of the film layer under constant or continuously increased positive pressure and a certain speed until the film layer is damaged, and the corresponding critical load is used as the bonding strength of the film layer and the magnesium alloy substrate. The scratch test adopts WS-2005 scratch tester developed by Lanzhou chemical and physical research institute of Chinese academy of sciences, and the diamond cone angle is 120 degrees, and the curvature radius is 0.2 mm. The maximum loading force is 30N, the scratch speed is 30N/min, and the moving speed of the workbench is 3 mm/min.

2.3 degradation and bioactivity testing

And (3) adopting an in-vitro simulated body fluid soaking test to characterize the biological activity of the micro-arc oxidation film layer. 1.0 the SBF solution contains ions at concentrations similar to those of human plasma, and is prepared from NaCl, NaHCO₃,KCl,K₂HPO₄·3H₂O,MgCl₂·6H₂O,1.0mol/LHCl,CaCl₂And Na₂SO₄Prepared from (CH)₂OH)₃CNH₂And adjusting the pH value of the solution to 7.2-7.4 by hydrochloric acid, wherein the temperature of the solution is required to be kept at 36.5 +/-0.5 ℃ in the whole preparation process. Then the sample to be soaked is placed in a plastic bottle filled with simulated body fluid and is placed in a constant temperature water bath at 36.5 ℃. During the soaking process of the sample, the simulated body fluid is replaced every other day and is kept colorless and free of precipitate. After the sample was soaked for 1 day, 7 days, 14 days, 21 days and 28 days, the sample was taken out, washed with deionized water and acetone in this order, and then sufficiently dried with a blast type drying oven.

2.4 electrochemical Performance testing

And (3) electrochemical performance testing: the potentiodynamic polarization curve of the membrane layer was tested using a Princeton Parstat 2273 electrochemical workstation manufactured by Princeton applied Research, USA, and was coupled to the substrateAnd (6) performing line comparison. The electrochemical test adopts a standard three-electrode system, takes simulated body fluid as a corrosion medium, and samples to be tested (the area is 1.00 cm)²) A platinum sheet (area 1.00 cm) as a working electrode²) As an auxiliary electrode, an Ag/AgCl electrode is used as a reference electrode, the scanning voltage range is-2000 mV to-1300 mV, and the scanning speed is set to be 1 mV/s.

3. Results of the experiment

3.1 morphology of the membranous layer

3.1.1 phases of the film layer

FIG. 1 is an XRD (X-ray diffraction) spectrum of a micro-arc oxidation film layer prepared by calcium carbonate-containing electrolyte with different calcium-phosphorus ratios. It can be seen that the phases of the micro-arc oxidation film layers prepared by the electrolyte systems with different calcium-phosphorus ratios under the calcium source of calcium carbonate are basically consistent and are all Mg, MgO and Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like. Wherein, Ca₃(PO₄)₂The existence of The (TCP) phase indicates that Ca and P elements in the electrolyte outside the matrix are successfully introduced into the film layer through the micro-arc oxidation process. In addition, the TCP phase has good biological properties (biocompatibility or bioactivity) and degradability, and is widely used in the clinical field. After implantation in the body, the TCP phase also reacts with body fluids to form HA. Specifically, the peaks in the C3 curve are dense and relatively weak, and the peak intensities of the matrix phase Mg and MgO are weaker than those of the other two curves, which indicates that the film thickness of the C3 film layer is large, so that the X-ray hardly penetrates through the film layer to enter the matrix, the peak intensity of CaO at 37 ° in the C4 curve is strong, which indicates that the phase is well crystallized in the film layer C4, the peak intensities of the phases in the C5 curve are strong, particularly the peak intensities of the matrix Mg phase at 70 ° are high, which indicates that the thickness of the C5 film layer is likely to be small, and the X-ray easily penetrates through the film layer to enter the matrix. In summary, the phases in films C4 and C5 were more crystalline, while the presence of amorphous phase in film C3 resulted in lower peak intensity.

3.1.2 FT-IR functional group analysis of the film layer

FIG. 2 shows FT-IR spectra of micro-arc oxide films prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios, and from FIG. 2, it can be seen that the micro-arc oxide films prepared from calcium carbonate as calcium sourceNow 2915cm^-1And 1652cm^-1Treating CO₃ ^2-The characteristic peak of cleavage of (2) in addition to 3453cm^-1At 1072cm of O-H stretching vibration peak^-1And 652cm^-1The peak at (B) corresponds to PO₄ ^3-,HPO₄ ^2-Or P₂O₇ ^4-. Furthermore, below 500cm^-1The following peaks are considered to be M-O or M-F (M ═ Mg, Ca, Sr). Specifically, the FT-IR curves of the film layers C4 and C5 with the calcium carbonate to sodium hexametaphosphate ratios of 1:4 and 1:5 are similar in shape, and the characteristic peaks are wide and gentle, and when the calcium carbonate to sodium hexametaphosphate ratio is 1:3, the characteristic peak in the FT-IR curve of the film layer C3 is sharp, and is particularly reflected in 1072cm^-1A characteristic peak of phosphate group at (C3), and a C3 curve of 485cm^-1A sharper characteristic peak appears, which may be M-O or M-F (M ═ Mg, Ca, Sr). In conclusion, the change of the calcium-phosphorus ratio in the electrolyte system can affect the shape of a characteristic peak in an FT-IR curve to different degrees, and the detected functional groups in the micro-arc oxidation film layer prepared under the same calcium source are the same.

3.1.3 surface topography and compositional analysis of films

FIG. 3 is a diagram showing the morphology and elemental analysis of a micro-arc oxidation film layer prepared by using an electrolyte with calcium carbonate as a calcium source. Wherein the micropores on the surface of the film layer C3 in fig. 3(a) are distributed around the nodules, the size of the micropores is in the range of 10-20 μm, white flocculent substances are deposited inside part of the larger holes, local nodule protrusions are formed on the surface of the film layer, and elongated micro-cracks are formed on the nodules. As shown in FIG. 3(b), as the Ca/P ratio is decreased to 1:4, the number of micropores on the surface of the film layer C4 is increased, and the size of the micropores is more uniform and finer, and is between 5 μm and 10 μm. In addition, the surface of the film layer is smoother, no redundant deposit is found in the micropores, and microcracks in the film layer C4 are rare. With the further decrease of the calcium-phosphorus ratio, as shown in fig. 3(c), the surface of the film layer has local distribution of finer micropores with a size of only about 2 μm, and also has larger micropores with a size of about 15 μm. Granular sediment is fully piled in part of the larger micropores, the surface of the whole film layer is rough, and no long and thin microcrack exists. In summary, in the film layer using calcium carbonate as the calcium source, as the ratio of calcium to phosphorus is reduced, the micropores on the surface of the film layer become finer and more uniform, and then have larger micropore size, and simultaneously the surface of the film layer becomes smoother and smoother, and then the roughness is increased. And then, the results of element analysis of two different positions on the surfaces of the three film layers show that all the film layers contain Mg, O, Ca, P, F, C and other elements, and the elements except the matrix element Mg come from an electrolyte system, which shows that the components in the electrolyte successfully enter the film layers through micro-arc oxidation reaction. The Sr element of the substrate could not be detected due to the detection error and the low Sr element content in the film layer.

3.1.4 area scanning and composition analysis of the film

According to the comprehensive analysis of the experimental results, the surface scanning is carried out on the surface of the film layer of the sample C4 in the section, and according to the graph shown in FIG. 4, micropores on the surface of the film layer of C4 are more uniform, fine and distributed on the whole surface of the film layer, and no elongated deeper holes appear. The film layer is also composed of Mg, Sr, O, Ca, P, F, etc., wherein Mg, O, F, P are mainly distributed at the convex portion outside the hole, and Ca and Sr are dispersed throughout the entire region, and obviously, Ca is more densely distributed than Sr, i.e., the content is higher at the surface of the film layer, which is consistent with the analysis result of fig. 3. Secondly, three elements of Ca, P and O are simultaneously present in the convex structure and the periphery of the convex structure, and the distribution of the three elements at the holes is rare but can be detected, which shows that the positions are distributed with calcium phosphate so as to have higher bioactivity and stronger capability of inducing the generation of hydroxyapatite in simulated body fluid.

3.1.5 film section morphology and film bonding force

FIG. 5 is a sectional morphology and elemental analysis of a micro-arc oxidation film layer prepared by using an electrolyte with calcium carbonate as a calcium source. As can be seen from the figure, the bonding conditions of the micro-arc oxidation film layers prepared under the three calcium-phosphorus ratios, the matrix and the epoxy resin are different, and the thickness difference of the film layers is larger. Specifically, the thickness of the film C3 with the calcium-phosphorus ratio of 1:3 is the minimum and is about 40 μm, the connection between the dense layer and the matrix of the film is very tight, the transition between the dense layer and the loose layer is good, the thickness of the dense layer and the loose layer is slightly larger than that of the loose layer, an obvious boundary exists between the loose layer and the epoxy resin, and the peeling phenomenon is obvious; the thickness of the film C4 with the calcium-phosphorus ratio of 1:4 is about 70 μm, the film has good quality, the connection between the compact layer and the matrix is very tight, the peeling phenomenon does not occur, cracks and micropores occur in the loose layer area, which is probably caused by larger discharge sparks occurring in the micro-arc oxidation process, and the thickness of the loose layer is obviously larger than that of the compact layer. The thickness of the film layer C5 with the calcium-phosphorus ratio of 1:5 is about 50 mu m, the compact layer is thin and is tightly connected with the matrix, the transition between the compact layer and the loose layer is poor, the loose layer area is large and loose, holes and peeling phenomena occur inside the film layer, a transverse microcrack exists till the epoxy resin area, and the quality of the loose layer of the film layer is poor, which is probably caused by overlarge discharge sparks generated due to large electric conductivity in the micro-arc oxidation process. Secondly, the connection area of the loose layer to the epoxy resin shows significant cracks and crevices. From the scanning result of the section line of the film layer, the element types are still Mg, O, Ca, P, F, C, Sr and the like, the element distribution diagrams of the cross sections of the three film layers are very similar, the content of the Mg element gradually rises along the depth direction of the interior of the film layer, and the suddenly increased part is the combination area of the compact layer and the substrate. In addition, elements such as O, Ca, P, F and the like are detected in the film layer, which indicates that the elements enter the film layer through micro-arc oxidation reaction and play a certain role in changing the structure and structure of the film layer.

FIG. 6 is a schematic diagram of the bonding force of the micro-arc oxidation film layer prepared by the electrolyte using calcium carbonate as the calcium source. It can be seen from the figure that, as the calcium-phosphorus ratio decreases, the bonding force between the film and the substrate tends to increase, and the bonding force value is between 20N and 30N, specifically, the bonding forces of the C3, C4 and C5 films are respectively 21.2N,25.4N and 28.1N, which is relatively consistent with the rule expressed by the cross-sectional morphology of the film.

3.2 Corrosion resistance of the film

FIG. 7 is a Tafel polarization curve of the micro-arc oxidation film layer in SBF in different electrolyte systems, and the corrosion current I corresponding to each curve in Table 2 is obtained by extrapolation of the Tafel polarization curve_corrAnd corrosion ofVoltage E_corr. As previously mentioned, these data can qualitatively compare the corrosion propensity and corrosion rate of different materials. As can be seen from the data in FIG. 7 and Table 2, the corrosion currents of the micro-arc oxide film layers C3, C4 and C5 prepared by using calcium carbonate as a calcium source are relatively similar and are reduced by 2 orders of magnitude compared with the substrate, which means that the corrosion rates of the three film layers are relatively low and the corrosion resistance is relatively good, and the corrosion voltage is positively shifted by 0.234V to 0.508V relative to the substrate. Specifically, the corrosion voltage of the film C3 with the calcium-phosphorus ratio of 1:3 is positively shifted by 0.508V, and the corrosion current is the minimum, namely 1.889 × 10^-7A/cm²This indicates that the C3 film is the most difficult to etch and has the lowest etch rate. The corrosion current of the film C4 with the calcium-phosphorus ratio of 1:4 is positively shifted by 0.234V, and the corrosion current is still very low, only 2.002 x 10^-7A/cm²This indicates that the film C4 is more susceptible to corrosion, but the actual corrosion rate is lower, probably because the loose layer of the film C4 is looser, corrosive ions can easily enter the loose layer, but the structure of the dense layer is more uniform and dense and bonds well to the substrate, and the final corrosion rate is still lower. The corrosion voltage of the film C5 with the calcium-phosphorus ratio of 1:5 is negatively shifted by 0.347V, and the corrosion current is only 2.113 x 10^-7A/cm²This is substantially consistent with the film cross-sectional phenomena depicted in fig. 5.

TABLE 2 electrochemical test data of micro-arc oxidation film layer in different electrolyte systems

3.3 bioactivity and in vitro degradation behavior of the Membrane layer

3.3.1 analysis of Membrane phase composition and FT-IR functional groups after SBF immersion

FIG. 8 is an XRD pattern of a micro-arc oxidation film prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios after being soaked in SBF for 21 days, compared with FIG. 1, except for a TCP phase with higher solubility, the phases detected before soaking basically exist, and in addition, Ca is detected on the surface of the film after being soaked for 21 days₂P₂O₇(CCP),Mg(OH)₂HA and Ca_10-xSr_x(PO₄)₆(OH)₂(Sr-HA) etc., wherein Ca_10-xSr_x(PO₄)₆(OH)₂Is a new biocompatible apatite formed by element Sr substituting the position of element Ca in hydroxyapatite, and can promote the growth, reproduction and repair of cells around bone implant, and CCP phase is also one material with excellent biological performance, biocompatibility or bioactivity. HA is considered to be the most suitable ceramic material for hard tissue repair, it is not toxic at all, and it can bind directly to bone cells. The difference between the three curves in fig. 8 is quite clear, the peak of curve C3 being quite sharp and the peak of curves C4, C5 being relatively low. Among them, the peaks of matrix phase, CCP, HA and Sr-HA in the curve C3 are sharpest, which indicates that these phases have high crystallinity, and the corrosion products of the C3 sample after soaking are likely to be less, and the deposited layer is thinner, so that the X-ray can easily penetrate the corrosion products to reach the matrix. The peaks of the curves C4 and C5 are low and broad, indicating that the surface of the membrane layer after being soaked with C4 and C5 shows an amorphous phase, wherein the peak of HA appears at 63 ° in the curve C5 and is sharper, and the peak of HA phase appears very weak in the other two curves.

FIG. 9 shows FT-IR spectra of micro-arc oxidation film layers prepared by calcium carbonate-containing electrolytes with different calcium-phosphorus ratios after soaking in SBF for 14 days, compared with FIG. 2, FT-IR spectra of 3 soaked film layers are greatly changed, and FT-IR spectra of 3 soaked film layers are very similar and are 3700cm at the same time^-1At the position of the sharp OH^-1Shows that Mg (OH) appears in the soaked film layer₂This is in contrast to XRD after immersion which detects Mg (OH)₂The results are consistent. Secondly, 3 free water appears in 3420cm after the membrane layer is soaked^-1Has a wider tensile absorption peak, and 1439cm of FT-IR spectrum of a film layer prepared from calcium lactate after soaking^-1CO of₃ ^2-V is₃Antisymmetric telescopic peak, PO, compare with FIG. 2₄ ^3-,HPO₄ ^2-Or P₂O₇ ^4-The peak shape change of the isoradical is relatively less, and is measured by 1072cm^-1And 662cm^-1The peak shape of (A) was 1056cm^-1And 570cm^-1The peak shape of (A) and 870cm also appeared in the curve C5^-1Peak at phosphate group.

3.3.2 surface topography and compositional analysis of films

FIG. 10 is the surface morphology and elemental composition analysis of the micro-arc oxidation film layer SBF soaked for 21 days with calcium carbonate as the calcium source, specifically, from FIG. 10 (a)₁)(a₂) It can be known that after the membrane layer C3 is soaked in SBF for 21 days, the porous structure is partially retained, the corrosion of the rest part is severe, the whole surface is uneven, densely distributed corrosion cracks are found in the enlarged view, lamellar corrosion products are distributed on the surface of the membrane layer and around the micro cracks, and the corrosion products deposited at the holes are less. FIG. 10 (b)₁)(b₂) It can be seen that the surface of the film C4 is relatively flat, a small amount of microcracks appear, and granular corrosion products are accumulated deep and around the micropores, and it can be seen from the enlarged view that nanorod and nanowire-like substances appear in the corrosion products and are distributed along the corrosion cracks, and lamellar corrosion products are sandwiched in the middle. From FIG. 10 (c)₁)(c₂) The film layer is known to retain a partial complete micropore structure, a lamellar corrosion product appears in a partial area, and then the enlargement shows that a large amount of nano linear substances appear around the lamellar corrosion product, like a chrysanthemum flower, and the partial corrosion product grows at the corrosion microcrack, which indicates that the part has larger energy and is easy to nucleate. The elemental analysis results show the atomic species and proportions of the elements at the corrosion products of the three films, which all contain C, O, F, Mg, Ca, P, Sr and other elements. Specifically, the atomic numbers of the three elements of Ca, P, and O in the film layer C3 are higher, respectively 18%, 15%, and 47%, which indicates that the corrosion product contains more calcium-phosphorus compounds and has good biological properties (biocompatibility or bioactivity). The corrosion product of film C4 has a higher content of elemental O and Mg, indicating that the corrosion product contains more MgO, and secondly the content of elemental F, P, and Ca is close to about 10%. In the corrosion product of the film C5, the atomic numbers of the three elements of Ca, P and O are higher, namely 22%, 18% and 42%, respectively, and the contents of the elements of F and Mg are lower, which indicates that the film C has high corrosion resistance and high corrosion resistance5, the corrosion products on the surface contain a large amount of calcium-phosphorus compounds, thereby greatly improving the biological activity of the film.

3.3.3 weight loss and pH Change of samples

The in vitro degradation behavior of the test specimens can be evaluated by weight loss rate, degradation rate and pH curve. The weight loss rate finally expressed by the sample is the result of the combined action of the degradation of the film layer and the generation of corrosion products such as apatite and the like. According to fig. 11, the corrosion degradation rates of the three film layers before soaking for 7 days are all low, and after soaking for 14 days, the weight loss rate of the film layer C3 is the largest and is about 12%, while the weight loss rate of the film layer C4 is only 3.2%, and the weight loss rate of the film layer C5 is 8.7%. After 21 days of soaking, the weight loss rate of the film layer C4 is the lowest and is about 13%, and the weight loss rates of the film layers C3 and C5 are about 15% and 17%. In conclusion, the film layers B4 and C4 with the calcium-phosphorus ratio of 1:4 have lower weight loss rate and stronger corrosion resistance, and are beneficial to improving the stability of the implant in vivo so as to better complete the support service task, which is consistent with the electrochemical test result.

FIG. 12 shows the degradation rates of SBF of micro-arc oxide film layers prepared from calcium carbonate-containing electrolytes with different calcium-phosphorus ratios after soaking for 21 days, wherein the degradation rates of C3, C4 and C5 are 0.24015, 0.17684 and 0.19481 (mg/(cm))²D)). It can be seen that the film layer C4 with the calcium-phosphorus ratio of 1:4 has the lowest weight loss rate and degradation rate, indicating that the film layer C4 has better corrosion resistance and slower early degradation, which is beneficial to ensuring that the implant maintains the supporting task in vivo.

Fig. 13 is a graph showing the change of pH value with time during the soaking process of the micro-arc oxidation film layer SBF prepared by calcium carbonate-containing electrolyte with different calcium-phosphorus ratios. The pH of the original simulated body fluid was 7.25, which floated significantly over the 21 day soaking period. The overall trend for pH change was: the membrane layers C3, C4 and C5 respectively reach the maximum values of 9.9,8.7 and 9.1 after being soaked for 1 day, 3 days and 5 days, the pH value is obviously reduced in the subsequent soaking period, and is reduced to about 8.4 after being soaked for 11 days, the pH value floats upwards to a small extent after being soaked for 11-13 days, and is reduced and stabilized between 7.4 and 8.2 after being soaked for 13-21 days. Specifically, within one unit soaking period (2 days), the pH value rises as the soaking time is prolonged. The pH of membrane C5 was significantly higher than the pH of membrane C3 and C4 for the same soaking time. Wherein the pH of membrane C4 changed less and appeared to be at a maximum on day 3.

4 conclusion

(1) Before soaking, the micro-arc oxidation film layer mainly contains Mg, MgO and Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like, and the TCP with higher solubility in the membrane layer after soaking is cancelled and the Ca is detected₂P₂O₇(CCP),Mg(OH)₂HA and Ca_10-xSr_x(PO₄)₆(OH)₂Existence of a new phase (Sr-HA).

(2) Along with the reduction of the calcium-phosphorus ratio in the film layer taking calcium carbonate as a calcium source, micropores on the surface of the film layer become finer and more uniform firstly, then larger micropore size appears, the surface of the film layer becomes smoother firstly and smoother then the roughness is increased.

(3) The corrosion currents of the micro-arc oxidation film layers prepared by taking calcium carbonate as a calcium source are similar and are reduced by 2 orders of magnitude compared with the matrix, and the corrosion rate of the three film layers is low and the corrosion resistance is good.

(4) The surface appearance of the membrane layer after being soaked for 21 days is corroded in different degrees, the original porous structure is basically partially reserved, nanorod and nanowire-shaped substances appear in corrosion products of the membrane layers C4 and C5 and are distributed along corrosion cracks, lamellar corrosion products are mixed in the corrosion products, the atomic percentages of Ca, P and O are high, and the improvement of the biological activity of the material is urgently needed.

(5) The film C4 with the calcium-phosphorus ratio of 1:4 has lower weight loss rate and stronger corrosion resistance, the weight loss rate after being soaked in SBF for 21 days is only 13%, the early-stage degradation is also slower, the degradation rate corresponding to 21 days is the lowest in the same group, which is beneficial to improving the stability of the implant in vivo so as to better complete the supporting service task, and secondly, the change range of the pH value of the film C4 in the soaking process is smaller than that of other films and the maximum value appears on the 3 rd day.

Example 2

The micro-arc oxidation film prepared in the embodiment relates to three electrolyte systems containing different calcium sources, including more researched calcium gluconate and less researched calcium lactate, calcium carbonate and the like. The calcium content of the three calcium sources is 9%, 13% and 40%, respectively. The calcium content in the organic calcium source calcium gluconate and calcium lactate is obviously lower than that in the inorganic calcium source calcium carbonate. The experiment systematically contrasts and researches the performances of the micro-arc oxidation film layers prepared under the three different calcium source electrolyte systems, and shows the difference of the micro-arc oxidation film layers prepared by organic calcium and inorganic calcium.

2. Experimental materials and methods

2.1 substrate and film preparation

The matrix used in the experiment is self-cast Mg-2Sr alloy, and the method comprises the following specific steps: using atmospheric protection (SF)₆：CO₂1: 200) pure magnesium (99.99%) and magnesium-strontium intermediate alloy (Mg-21Sr (99.99%)) are melted in a resistance furnace. All raw materials and tools used for casting need to be preheated to 250 ℃. When the temperature of the furnace rises to 500 ℃, putting the preheated pure magnesium ingot. When the furnace temperature is 700 ℃, pure magnesium is completely melted and is kept warm for 20 min. Adjusting the furnace temperature to 710 ℃, adding theoretical amount of magnesium-strontium intermediate alloy (Mg-21Sr (99.99 percent)) and preserving the temperature for 20 min. The melt was stirred thoroughly and poured into a preheated graphite mold. The cast Mg-2Sr alloy is then subjected to a homogenizing anneal at 400 ℃ for 16 hours. And cutting the casting body into regular cube small blocks of 8mm multiplied by 10mm by using linear cutting equipment, and then mechanically polishing the cube small blocks by using coarse 360#, coarse 600#, fine 600# and fine 1000# abrasive paper. And finally, cleaning the mixture by using acetone, deionized water and absolute ethyl alcohol and drying the mixture for later use. The three calcium sources used in the micro-arc oxidation experiment are calcium gluconate Ca (C)₆H₁₁O₇)₂﹒H₂O, calcium lactate Ca (C)₃H₅O₃)₂﹒5H₂O and calcium carbonate CaCO₃The molar concentration of calcium ions is 0.006mol/L, and the mass concentration is 2.688g/L,1.848g/L,0.600g/L and 0.444g/L respectively; the remaining electrolyte composition and concentration are (Na)₂PO₃)₆,1.224g/L(0.012mol/L)；KOH,5g/L；NH₄HF₂,7g/L；C₃H₈O₃And N (CH)₂CH₂OH)₃The concentration is 5 ml/L; h₂O₂The concentration was 7 ml/L. Three groups of electrolyte systems containing different calcium salts are respectively defined as A, B and C, wherein the calcium-phosphorus ratio is 1: 2. All the medicines used in the experiment are analytically pure. In the micro-arc oxidation experiment process, a magnesium alloy sample is used as an anode, a stainless steel groove is used as a cathode, circulating cooling water is introduced to keep the temperature of the electrolyte below 50 ℃, a micro-arc oxidation power supply is adopted to supply power, and specific electrical parameters are shown in table 3.

TABLE 3 micro-arc oxidation electrical parameters

2.2. Film detection

Film layer phase composition analysis: the phase composition of the micro-arc oxidation film layer was analyzed by an X-ray diffractometer (BRUKER D8Advanced, Germany and Shmadzu XRD-6100) test. The test conditions were: the method comprises the following steps of Cu target (Cu-Kalpha), tube voltage of 40kV, tube current of 30mA, scanning range of 10-90 degrees, scanning speed of 4 degrees/min and sample interval of a counter of 0.02. Detecting the change of molecular structure and functional group by using a Fourier transform infrared spectrometer (Tensor 37 model) of BROOK, Germany, and the wave number range of infrared transmission spectrum is 4000cm^-1～400cm^-1Resolution of 4cm^-1The scan time is 16 s.

2.3 degradation and bioactivity testing

And (3) adopting an in-vitro simulated body fluid soaking test to characterize the biological activity of the micro-arc oxidation film layer. 1.0 the SBF solution contains ions at concentrations similar to those of human plasma, and is prepared from NaCl, NaHCO₃,KCl,K₂HPO₄·3H₂O,MgCl₂·6H₂O,1.0mol/L HCl,CaCl₂And Na₂SO₄Prepared from (CH)₂OH)₃CNH₂And adjusting the pH value of the solution to 7.2-7.4 by hydrochloric acid, wherein the temperature of the solution is required to be kept at 36.5 +/-0.5 ℃ in the whole preparation process. Then the sample to be soaked is placed in a plastic bottle filled with simulated body fluid and is placed in a constant temperature water bath at 36.5 ℃. During the soaking process of the sample, the simulated body fluid is replaced every other day and is kept colorless and free of precipitate. After the sample was soaked for 1 day, 7 days, 14 days, 21 days and 28 days, the sample was taken out, washed with deionized water and acetone in this order, and then sufficiently dried with a blast type drying oven.

2.4 electrochemical Performance testing

And (3) electrochemical performance testing: the potentiodynamic polarization curves of the films were tested using a Princeton partstat 2273 electrochemical workstation manufactured by princetonoriented Research, usa, and compared to the substrate. The electrochemical test adopts a standard three-electrode system, takes simulated body fluid as a corrosion medium, and samples to be tested (the area is 1.00 cm)²) A platinum sheet (area 1.00 cm) as a working electrode²) As an auxiliary electrode, an Ag/AgCl electrode is used as a reference electrode, the scanning voltage range is-2000 mV to-1300 mV, and the scanning speed is set1mV/s。

3. Conclusion

(1) When the micro-arc oxidation reaction of the electrolyte taking calcium gluconate as a calcium source occurs, electric sparks are fine and distributed sporadically, the buzzer is low, the duration is short, and the reaction energy is low; the electrolytic liquid system containing other two calcium sources generates a large amount of bubbles in the reaction process, a large amount of discharge sparks are generated and accompanied by harsh rumbling, the duration of the sparks is long, and the reaction energy is high. Thus, the thickness of layer A is less than about 25.6 μm, and the thicknesses of layers B and C are greater and closer, 37.8 and 34.0 μm, respectively.

(2) Before soaking, the micro-arc oxidation film layer mainly contains Mg, MgO and Sr₂Mg₁₇,MgF₂,CaO,CaF₂,Ca₃(PO₄)₂(TCP) and the like, and the TCP with higher solubility in the membrane layer after soaking is cancelled and the Ca is detected₂P₂O₇(CCP),Mg(OH)₂HA and Ca_10-xSr_x(PO₄)₆(OH)₂Existence of a new phase (Sr-HA).

(3) The film prepared by the micro-arc oxidation technology has better corrosion resistance, wherein the corrosion voltage and the corrosion current of the film B and the film C are obviously reduced relative to the matrix. In any soaking period, the weight loss rate of the film layers B and C is lower than that of other soaking groups, which indicates that the micro-arc oxidation film layer prepared by the electrolyte taking calcium lactate and calcium carbonate as calcium sources has lower degradation rate.

(4) By combining XRD and FT-IR infrared spectrograms and EDX elemental analysis, calcium phosphate is successfully converted into calcium apatite in the SBF soaking process. The granular corrosion product of the micro-arc oxidation film layer B prepared by using calcium lactate as a calcium source has higher content of calcium and phosphorus phases, and shows better biological performance (biocompatibility or bioactivity).

Although the present invention has been described with reference to the specific embodiments, it should be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims

1. A preparation method of a magnesium alloy surface strontium-containing hydroxyapatite micro-arc oxidation coating is characterized in that a coating is prepared on a magnesium alloy substrate by adopting a micro-arc oxidation method;

the electrolyte adopted by the micro-arc oxidation method consists of the following components: the concentration of calcium carbonate is 0.2-4g/L, (Na)₂PO₃)₆The concentration of (A) is 1-30g/L, the concentration of KOH is 2-10g/L, NH₄HF₂Has a concentration of 5-10g/L, C₃H₈O₃The concentration of (A) is 2-10ml/L, N (CH)₂CH₂OH)₃The concentration of (A) is 2-10ml/L, H₂O₂The concentration of (A) is 1-13ml/L, wherein, Ca/P is 1/5-1/3;

the magnesium alloy matrix is Mg-2Sr, and the preparation method comprises the following steps: using atmosphere to protect SF₆：CO₂1: melting magnesium with the purity of 99.99 percent and magnesium-strontium intermediate alloy Mg-21Sr with the purity of 99.99 percent in a 200 resistance furnace; all raw materials and tools used for casting need to be preheated to 250 ℃; when the temperature of the furnace rises to 500 ℃, putting the preheated pure magnesium ingot; completely melting pure magnesium at the furnace temperature of 700 ℃ and preserving heat for 20 min; adjusting the furnace temperature to 710 ℃, adding a magnesium-strontium intermediate alloy Mg-21Sr with the theoretical amount of 99.99 percent, and preserving the temperature for 20 min; fully stirring the melt and pouring the melt into a preheated graphite mold; then carrying out homogenizing annealing on the poured Mg-2Sr alloy at 400 ℃ for 16 hours;

the micro-arc oxidation treatment comprises the following specific steps: airing the pretreated magnesium alloy matrix, placing the magnesium alloy matrix in an electrolyte as a positive electrode, using a stainless steel groove as a negative electrode, introducing circulating cooling water to keep the temperature of the electrolyte below 50 ℃, and supplying power by using a micro-arc oxidation power supply, wherein the positive voltage is 450V, the frequency is 600Hz, the negative voltage is 20V, the positive duty ratio is 30%, the negative duty ratio is 20%, the ratio of the positive pulse number to the negative pulse number is 1:1, and the electrifying time is 10 min.

2. The method of claim 1, wherein the electrolyte consists of: the concentration of calcium carbonate is 0.5-1g/L g/L, (Na)₂PO₃)₆The concentration of (A) is 1-20g/L, the concentration of KOH is 4-6g/L, NH₄HF₂Has a concentration of 6-8g/L, C₃H₈O₃The concentration of (A) is 6-8 ml/L, N (CH)₂CH₂OH)₃The concentration of (A) is 4-6ml/L, H₂O₂The concentration of (A) is 4-10 ml/L.

3. The method of claim 1, wherein the electrolyte consists of: the concentration of calcium carbonate is 0.600g/L, (Na)₂PO₃)₆Has a concentration of 1.836g/L or 2.448g/L or 3.060g/L, a KOH concentration of 5g/L, NH₄HF₂Has a concentration of 7g/L, C₃H₈O₃Has a concentration of 5ml/L, N (CH)₂CH₂OH)₃Has a concentration of 5ml/L, H₂O₂The concentration of (2) was 7 ml/L.