CN115074707B - Method for synthesizing double-layer composite film on magnesium alloy surface in one step and magnesium alloy material obtained by same - Google Patents

Method for synthesizing double-layer composite film on magnesium alloy surface in one step and magnesium alloy material obtained by same Download PDF

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CN115074707B
CN115074707B CN202210392073.4A CN202210392073A CN115074707B CN 115074707 B CN115074707 B CN 115074707B CN 202210392073 A CN202210392073 A CN 202210392073A CN 115074707 B CN115074707 B CN 115074707B
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CN115074707A (en
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朱继元
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Guilin University of Technology
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1225—Deposition of multilayers of inorganic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/24—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials for applying particular liquids or other fluent materials
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
    • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
    • C23C18/1229—Composition of the substrate
    • C23C18/1241—Metallic substrates

Abstract

The invention belongs to the technical field of magnesium alloy surface treatment, and particularly relates to a method for synthesizing a double-layer composite film on the surface of a magnesium alloy in one step and an obtained magnesium alloy material. The method comprises the following steps: 1) Pretreating the magnesium alloy to obtain the magnesium alloy with a clean surface; 2) Immersing the magnesium alloy obtained in the step 1) into a surface treatment liquid, heating to perform hydrothermal reaction, and cleaning and drying the magnesium alloy after the reaction is finished to obtain compact Mg (OH) 2 Bottom film and K with porous support-like microstructure 2 Al 2 Si 4 O 12 ·xH 2 A magnesium alloy sample of the O upper film; 3) Immersing the magnesium alloy sample obtained in the step 2) into a solution of stearic acid in ethanol for modification treatment, and then taking out, cleaning and drying to obtain the magnesium alloy with the stearic acid modified double-layer composite film, which has excellent corrosion resistance and stable hydrophobicity.

Description

Method for synthesizing double-layer composite film on magnesium alloy surface in one step and magnesium alloy material obtained by same
Technical Field
The invention belongs to the technical field of magnesium alloy surface treatment, and particularly relates to a method for synthesizing a double-layer composite film on the surface of a magnesium alloy in one step and an obtained magnesium alloy material.
Background
The magnesium alloy is used as a degradable green environment-friendly material, has excellent mechanical properties of small density, high strength, strong ductility and the like, and is widely applied to the fields of medical treatment, automobile industry, aerospace and the like. However, magnesium alloys have poor corrosion resistance and are extremely susceptible to corrosion in practical applications, and many treatments have been proposed to improve the corrosion resistance, including conversion coatings, surface modification, chemical inhibition, and the like. Among them, the conversion coating method is receiving attention as the most cost-effective and practical method.
In order to obtain the magnesium alloy corrosion-resistant coating which is simple and environment-friendly in preparation process, has excellent corrosion protection performance and low in manufacturing cost, in recent years, the preparation method is continuously optimized and improved. Zeolite has excellent properties such as adsorptivity, ion exchange property, acid and alkali resistance, high temperature resistance, etc., and is often used as a filler to enhance corrosion resistance of the prepared coating, and the methods currently involved include a coating method, a sol-gel method, a dip coating method, a hot pressing method, and an electrodeposition method. However, the sample prepared by the method is often faced with the problems of poor adhesion performance of the coating, incomplete coating coverage, complex preparation process, limited improvement of corrosion protection effect and the like. Calabrese et al, filled with zeolite, prepared a silane sol-gel coating on the magnesium alloy surface, and as the zeolite loading increased, the corrosion resistance of the coating gradually increased, but the adhesion properties of the coating were consequently deteriorated. The magnesium alloy surface after the alkaline pretreatment of Rotella et al uses zeolite as a filler, a coating with good adhesion performance and controllable thickness is prepared by a dip coating method, and the highest coverage rate reaches 97%, but compared with the magnesium alloy, the corrosion improvement efficiency is only improved by 8 times, and the corrosion protection performance is improved only limitedly. In addition, banerjee et al formed a uniform zeolite film on the surface of AZ91D magnesium alloy by in situ crystallization using tetrapropylammonium hydroxide (TPAOH) and Structure Directing Agent (SDA), but the corrosion current density of the prepared samples was only increased by 1 order of magnitude compared to the bare magnesium alloy substrate, and the preparation process was complicated, and the used drugs were expensive, limiting practical applications.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a method for synthesizing a double-layer composite film on the surface of a magnesium alloy in one step and an obtained magnesium alloy material.
The technical scheme provided by the invention is as follows:
method for synthesizing double-layer composite film on magnesium alloy surface in one step
A method for synthesizing a double-layer composite film on the surface of a magnesium alloy in one step comprises the following steps:
1) Pretreating the magnesium alloy to obtain the magnesium alloy with a clean surface;
2) Immersing the magnesium alloy obtained in the step 1) into a surface treatment liquid, heating to perform hydrothermal reaction, and cleaning and drying the magnesium alloy after the reaction is finished to obtain compact Mg (OH) 2 Bottom film and K with porous support-like microstructure 2 Al 2 Si 4 O 12 ·xH 2 O upper film magnesium alloy sample, x is 3-12, hereinafter abbreviated as M-Z/CH;
3) Immersing the magnesium alloy sample obtained in the step 2) into a solution of stearic acid in ethanol for modification treatment, and then taking out, cleaning and drying to obtain a magnesium alloy with a stearic acid modified double-layer composite film, which is hereinafter abbreviated as M-Z/CH@SA;
wherein, in step 2):
the surface treatment liquid comprises SiO 2 KOH, ethylenediamine tetraacetic acid, ca (OH) 2 The weight ratio of each component to the solvent deionized water is (0.0184-0.0192) 1, (0.069-0.071) 1, (0.090-0.092) 1, (0.0226-0.0234) 1;
the hydrothermal reaction conditions are as follows: heating to 190-210 deg.C, preferably 200 deg.C, and maintaining the temperature for 90-105min.
Based on the technical scheme, the method for synthesizing the double-layer composite film on the surface of the magnesium alloy in one step can be realized. The film is mainly made of compact Mg (OH) 2 Bottom film and K with porous support-like microstructure 2 Al 2 Si 4 O 12 ·xH 2 The composition of the O upper film reduces the corrosion current on the surface of the magnesium alloy after stearic acid modification by about 3 orders of magnitude compared with the Mg matrix, the slow release rate reaches 99.96%, and the contact angle is stabilized at about 125 degrees. The result shows that the obtained magnesium alloy has excellent corrosion resistance and stable hydrophobicity. Meanwhile, the preparation process is simple, efficient and environment-friendly, and has good application prospect.
The principle of the reaction process is as follows:
the magnesium alloy reacts with the mixed solution, as shown in fig. 6, mg in the sample reacts with ethylenediamine tetraacetic acid (EDTA) in the mixed solution to generate Mg 2+ ，Mg 2+ With OH in alkaline solution - The reaction takes place to produce Mg (OH) 2 And (3) depositing the precipitate (1) on the surface of the magnesium alloy substrate. Al in the sample is affected in alkaline solution with OH - React to generate AlO 2- (2). Nano SiO 2 Powder in solution with OH - React to form SiO 3 2- And is present in the solution (3). With increasing heating time, the surface of the Mg matrix is gradually coated with Mg (OH) 2 Completely covered and tends to stabilize (parts a, c in FIG. 6), and subsequently K is present in the solution + ，SiO 3 2- ，AlO 2 - And H 2 O reacts (4) to form K 2 Al 2 Si 4 O 12 ·xH 2 O, and in Mg (OH) 2 The layer surface gradually crystallized (parts b and d in fig. 6).
Mg + +2OH - ＝Mg(OH) 2 (1)
2Al+2OH - +2H 2 O＝2AlO 2 - +3H 2 (2)
SiO 2 +2OH - ＝SiO 3 2- +H 2 O (3)
2K + +2AlO 2 - +4SiO 3 2- +(x+4)H 2 O＝K 2 Al 2 Si 4 O 12 ·xH 2 O+8 OH - (4)
Specifically, in step 1), the magnesium alloy is AZ91D magnesium alloy. Compared with other types of magnesium alloy, the alloy directly contains a certain amount of Al element, so that Al atoms are provided for the reaction process, the reaction is promoted, and the AZ91D magnesium alloy has better treatment effect.
Specifically, in step 2), siO is used 2 The particle size of (2) is 8000-10000 mesh, preferably 8000 mesh. Too large particle size can lead to uneven morphology of the film layer, and thus poor treatment effect.
Specifically, in step 2), the reaction vessel used is a muffle furnace.
Specifically, in step 3), the magnesium alloy sample obtained in step 2) is immersed in a solution of stearic acid in ethanol and allowed to stand for modification treatment, wherein the standing time is 40-60min, preferably 50min.
The invention also provides the magnesium alloy with the double-layer composite film on the surface, which is prepared by the method.
The magnesium alloy provided by the invention has excellent corrosion resistance and stable hydrophobicity.
Drawings
FIG. 1 is an SEM image of the surface of an M-Z/CH@SA sample from section 2.1 of the detailed description of the invention, (a, c, e) for 90min and (b, d, f) for 105min.
FIG. 2 is an XRD diffraction pattern of the M-Z/CH@SA film described in section 2.2 of the detailed description.
FIG. 3 is a surface infrared spectrum of the M-Z/CH@SA film in section 2.2 of the detailed description.
FIG. 4 is an XPS full scan profile of an M-Z/CH@SA film in section 2.2 of the detailed description.
FIG. 5 is an XPS narrow scan spectrum of an M-Z/CH@SA film in section 2.2 of the detailed description, (a) K2p region (b) O1s region (C) C1s region (d) Mg1s region (e) Si2p region (f) Ca2p region.
FIG. 6 is a schematic diagram of the hydrothermal reaction of the present invention.
FIG. 7 is a plot of dynamic potential polarization curves for AZ91D magnesium alloy, M-Z/CH samples and M-Z/CH@SA samples in section 2.3 and in 3.5wt.% NaCl solution, according to the specific embodiment.
FIG. 8 is a Nyquist plot of each sample in section 2.3 of the detailed description in 3.5wt% aqueous NaCl.
FIG. 9 is a Bode plot of |Z| versus frequency in 3.5wt% aqueous NaCl solution for each sample from section 2.3 of the present embodiments.
FIG. 10 is a Bode plot of phase angle versus frequency in 3.5wt% aqueous NaCl solution for each sample from section 2.3 of the present embodiments.
FIG. 11 is an equivalent circuit model of the AZ91D magnesium alloy in section 2.3 in the embodiment in 3.5wt% NaCl aqueous solution
FIG. 12 is an equivalent circuit model of the M-Z/CH@SA sample in section 2.3 of the detailed description in 3.5wt% aqueous NaCl.
FIG. 13 is an image (parts a, b) of an M-Z/CH sample film from section 2.4 of the detailed description after image polishing with droplet contact; M-Z/CH@SA sample film and droplet contact image static water contact angle image (parts c, d).
Detailed Description
The principles and features of the present invention are described below with examples only to illustrate the present invention and not to limit the scope of the present invention.
1.1 materials
The material is AZ91D magnesium alloy (89.1% -90.8% of Mg, 8.5% -9.5% of Al, 0.45% -0.9% of Zn and 0.17% -0.4% of Mn), which is purchased by Hebei Teng stone metal materials limited company (Chen table), and cut into the specification of 40mm multiplied by 20mm multiplied by 5 mm. Absolute ethyl alcohol (C) 2 H 6 O, AR) was purchased from Tianjin Fuyu fine chemical Co., ltd., 8000 mesh nano SiO 2 The powder was purchased from Shanghai Yuan Jiang chemical Co., ltd., potassium hydroxide (KOH, AR), calcium hydroxide (Ca (OH) 2 AR), ethylenediamine tetraacetic acid (EDTA, AR) and stearic acid (98%) are supplied by Shanghai Yi En chemical technologies limited. The heating process used was carried out using a high-temperature box furnace (KSL-1700X) available from Hefei Kogyo materials technology Co., ltd.
1.2 method
The AZ91D magnesium alloy sheet is polished by 500 mesh SiC sand paper and 1000 mesh SiC sand paper respectively, and then is sequentially put into deionized water and absolute ethyl alcohol for ultrasonic cleaning for 10 minutes, so as to remove impurities on the surface of the magnesium alloy and fat-soluble substances insoluble in water.
8000-mesh nano SiO 2 Adding 0.94g of powder, 1.75g of KOH solid and 4.55g of ethylenediamine tetraacetic acid (EDTA) into a beaker containing 25ml of deionized water, and stirring uniformly by ultrasonic waves to obtain a solution A; ca (OH) is taken again 2 Adding 1.15g of particles and 1.75g of KOH solid into another beaker containing 25ml of deionized water, and stirring by ultrasonic to dissolve the particles to obtain a solution B; and then mixing and uniformly stirring the solution A and the solution B, adding the mixed solution and the pretreated AZ91D magnesium alloy sheet into a reaction kettle liner with the volume of 100ml, and putting into a horse boiling furnace for heating, wherein the heating temperature and the heat preservation temperature are 200 ℃ and the heating time is 90-105min. And taking out the sample after the reaction kettle is completely cooled, washing with a large amount of deionized water, and drying to obtain the M-Z/CH sample.
And preparing 4g of stearic acid and 30ml of absolute ethyl alcohol into a stearic acid-ethanol solution, placing the M-Z/CH sample into the stearic acid-ethanol solution, standing for 50min, taking out, washing and airing to finally prepare the M-Z/CH@SA sample.
1.3 characterization of samples
The surface morphology of the samples was studied by scanning electron microscopy (SEM, SU5000, HITACHI,5.0KV, tokyo, japan). The chemical composition and valence state of the samples were measured with x-ray photoelectron spectroscopy (XPS, 250Xi,Thermo scientific,Waltham,Massachusetts,America) and an alkα x-ray source (hν= 1486.6 eV). By Fourier transform infrared spectrometer (FTIR, IRAffin)ity-1S, shimadzu corporation, 4000-450cm -1 Chemical composition of the samples was measured by X-ray diffractometer (XRD, smartlab9, rigaku company; and (3) target: cuKa;40kv,150ma; wavelength: 1.54056, tokyo, japan) studied the phase structure of the sample. Static Contact Angles (CA) were measured using a contact angle measuring instrument (SDC-200, sancen, inc.) and the average contact angles were obtained by measuring with 6. Mu.L drops (deionized water) at 4 different locations of the sample, respectively.
1.4 evaluation of Corrosion Performance
To study the corrosion resistance of the membranes, CS2350H electrochemical workstation (marchand instruments, marchand, china) was used to evaluate the corrosion resistance of the materials using a conventional three electrode device with a platinum plate as the auxiliary electrode, a reference electrode being an Ag/AgCl (saturated KCl) electrode, and 3.5wt% aqueous nacl as the electrolyte. Test material as working electrode with an exposure area of 1cm 2 The test was performed at room temperature. Using Tafel extrapolation, the corrosion potential (Ecorr) and the corrosion current density (Icorr) were extracted by means of CView software and the polarization resistance (Rp, Ω cm) was calculated 2 ) The initial potential of potential scanning is-0.5V, the termination potential is 1V, the potential interval of data acquisition is 0.5mV, and the sample is contacted with the solution for 30 minutes before testing, so that the stability of the surface of the sample is ensured.
2.1 Characterization of M-Z/CH@SA films
FIG. 1 shows SEM images of the surface of (90-105 min) M-Z/CH@SA samples prepared under different heating times based on the method described in section 1.2. As can be seen from the SEM low-magnification image (parts a and b of fig. 1), irregular protrusions are randomly distributed on the surface of the sample, and compared with the sample (part a of fig. 1) heated for 90min, the surface protrusions of the sample (part b of fig. 1) heated for 105min have larger size, parts of the protrusions are connected with each other, and the whole surface has more obvious fluffy feeling. In the high-power image, a dense and flat film is formed on the surface of the sample after heating for 90min, and a plurality of elongated microstructures with cilia-like characteristics are attached to the surface of the film (part c of fig. 1). As the heating time increased, the sample surface of 105min spread over the support-like microstructure having a porous characteristic (part d of fig. 1), while it was observed that a large number of elongated cilia-like microstructures were interspersed in the porous support-like microstructure, which also explains why the sample exhibited a remarkable fluffy feeling in the SEM low-magnification image. The result shows that as the reaction proceeds, a layer of dense and flat film is formed on the surface of the sample, a large number of slender cilia-like microstructures are attached to the surface of the film, and as the reaction time increases, the slender cilia-like microstructures are continuously formed and interlaced with each other, and finally a layer of porous supporting-like microstructures is formed on the film. The random distribution of the irregular projections on the surface of the sample is formed by the aggregation of columnar crystals and elongated cilia structures (part e of fig. 1), and after heating for 105min, the elongated cilia-like microstructures will completely cover these projections and also form surface irregular projections which also have porous support-like microstructures (part f of fig. 1).
2.2 analysis of surface Components
M-Z/CH@SA films were prepared based on the method in section 1.2 and both at a heating time of 105min. FIG. 2 is an XRD diffraction pattern of a sample of M-Z/CH@SA, showing characteristic peaks at 18.5 °, 32.9 °, 38.0 °, 50.8 °, 58.7 °, 62.1 °, 68.2 °, 68.9 °, 72.1 °, respectively corresponding to Mg (OH) 2 (001) (100) (101) (102) (110) (111) (103) (200) (201) in PDF (044-1482), the peak type is narrower and the intensity is higher, indicating that the crystal grain is larger. The samples also showed characteristic peaks at 10.7 °, 12.4 °, 16.5 °, 17.6 °, 19.8 °, 20.7 °, 21.6 °, 27.4 °, 28.0 °,30.2 °, 32.8 °, 35.2 °, which are derived from K 2 Al 2 Si 4 O 12 ·xH 2 O (PDF 016-0692), determined by crystal planes (110) (002) (112) (022) (211) (103) (220) (310) (311) (321) (303) (323), has lower heights and intensities of diffraction peaks and wider peak areas, indicating K contained in the film layer 2 Al 2 Si 4 O 12 ·xH 2 The grains of the O species are smaller. In addition, the samples showed characteristic peaks at 18.2 °, 34.2 °, 36.9 °, 50.9 °, 64.7 °, 72.1 °, belonging to Ca (OH) 2 The (001) (011) (002) (110) (103) (202) crystal face of (PDF 089-2779), characteristic peaks at 30.2 DEG and 60.5 DEG, are composed of SiO 2 The (110) (211) crystal plane of (PDF 015-0026) is determined, and the peak patterns of the two substances are not obvious, indicating Ca (OH) 2 And SiO 2 The loading of these two substances is low and the crystallization is weak, and the distribution in the film is more dispersed.
As shown in FIG. 3, the chemical composition of the surface of the M-Z/CH@SA sample was analyzed by Fourier transform infrared spectrometer (FTIR), wherein a represents stearic acid and b represents the M-Z/CH@ sample, as shown in FIG. 3 part a, at wave number 2916cm -1 And 2848cm -1 Nearby occurrence of-CH 2 -and CH 3 C-H stretching vibration absorption peak with wave number of 1703cm -1 The position corresponds to the stretching vibration absorption peak of carbonyl (C=O) in the-COOH group. M-Z/CH@SA sample modified by stearic acid is 2916cm -1 And 2848cm -1 C-H bond stretching vibration absorption peak corresponding to peak value at wave number does not have peak shift, and is 1700-1725 cm -1 The free-COOH band in the wavenumber range disappeared, but at 1576cm -1 The vibration absorption peak of carboxylate (c=o) appears correspondingly nearby, and the peak shift phenomenon occurs. And at a wavenumber of 934cm -1 the-OH bending vibration at the same is also greatly reduced. It can be seen that CH in stearic acid 3 (CH 2 ) 12 COO-functional groups reacted with the sample surface and stearic acid was successfully modified to the M-Z/CH@SA sample surface.
In order to further detect the chemical composition of the film and determine the characteristics thereof, XPS analysis was performed on the sample, and an XPS full scan spectrum of the M-Z/CH@SA film is shown in FIG. 4, wherein the film mainly contains K, O, C, mg, si, ca and other elements.
The narrow scan spectra of K2p, O1s, C1s, mg1s, si2p and Ca2p are shown in FIG. 5, section a, b, C, d, e, f. The characteristic element K2p narrow scan spectrum is shown in part (a) of fig. 5, the binding energy of the K2p3/2 peak and the K2p1/2 peak is concentrated at 293.2eV and 296eV, and is mainly represented by oxidation state signals of potassium, O1s is composed of two characteristic peaks (part b of fig. 5), the first group of peaks is carbon-oxygen double bonds (c=o) and is characterized by binding energy of 531.5eV-532eV, which is mainly represented by chemical state of silicate, and the other group of peaks is located at-533 eV due to carbon-oxygen single bonds (C-O) and hydroxyl groups (-OH). The C1s peak can be divided into three characteristic peaks (part C in FIG. 5), the first set of peaksIs a carbon-carbon single bond (C-C), characterized by a binding energy of 284.8eV, the binding energy of the second set of peaks being related to a carbon-oxygen single bond (C-O) at-286 eV, the third set of peaks being at-288.5 eV due to carboxyl groups (O-c=o). As shown in part (d) of FIG. 5, the narrow scanning spectrum of the characteristic element Mg1s is divided into two characteristic peaks, wherein the first group of peaks are located at 1303eV and represent Mg simple substance, the second group of peaks are located at 1304.5eV and represent oxidation state signals of Mg, and the main component of the narrow scanning spectrum is Mg (OH) by combining XRD result analysis 2 . The characteristic peak of Si2p is located at-102 eV and is represented as a chemical state of silicate (part e in fig. 5). The characteristic peaks of Ca2p1/2 and Ca2p3/2 are located at 351eV and 347.5eV, respectively, and represent the oxidation state of Ca (FIG. 5 f). Experimental results show that the surface film layer of the M-Z/CH@SA sample mainly contains Mg (OH) in combination with the analysis result of XRD 2 And K 2 Al 2 Si 4 O 12 ·xH 2 O。
2.3 Corrosion protection
M-Z/CH@SA films were prepared based on the method in section 1.2 and both at a heating time of 105min. FIG. 7 shows dynamic potential polarization curves of AZ91D magnesium alloy, M-Z/CH sample and M-Z/CH@SA sample in 3.5wt% NaCl solution, table 1 below shows corrosion potential (E corr ) And corrosion current density (I) corr ) The corrosion inhibition efficiency (. Eta.) of the film calculated from the formula (1) is also given 0 corr Corrosion current density for Mg matrix, I corr Is the corrosion current density of the sample.
Figure GDA0003809498770000101
As shown in Table 1, the corrosion current density (I 0 corr ) 3.1503 ×10 -5 A/cm 2 Corrosion potential (E corr ) is-1.1996V. Corrosion current Density (I) of M-Z/CH and M-Z/CH@SA samples corr ) And corrosion potential (E) corr ) 7.1812 ×10 respectively -8 A/cm 2 ，1.4086×10 -8 A/cm 2 and-0.93089V, -0.89433V. According to electrochemical theory, the material with better corrosion resistance has I corr And E is corr Is low. I of M-Z/CH sample compared with AZ91D magnesium alloy corr About 2.5 orders of magnitude lower, I for the M-Z/CH@SA sample corr Reduced by about 3 orders of magnitude and E of both corr Has a positive value lower than that of the Mg matrix, but wherein the M-Z/CH@SA sample has E corr Positive values are lower. The results show that the M-Z/CH and M-Z/CH@SA samples prepared by experiments both remarkably improve the corrosion resistance of the magnesium alloy, the film corrosion inhibition rate of the M-Z/CH sample is 99.77%, the corrosion inhibition rate of the modified M-Z/CH@SA sample film layer is more than 99.96%, and meanwhile, the corrosion inhibition rate of the modified M-Z/CH@SA sample film layer is I corr And E is corr The positive values of (2) are also the lowest, so the M-Z/CH@SA sample possesses the best corrosion protection performance.
Table 1 electrochemical data of polarization curves obtained from samples
Figure GDA0003809498770000102
To characterize the corrosion resistance of the samples, figures 8,9, 10 show the nyquist plot, |z| versus frequency baud plot and the phase angle versus frequency baud plot of the M-Z/CH samples, M-Z/ch@sa samples and AZ91D magnesium alloy in 3.5wt% aqueous nacl, with fitted data connected by curves and scattered points as measured data points.
In the Nyquist diagram (FIG. 8), the capacitance semicircle diameter is related to the charge transfer resistance, and a larger capacitance semicircle diameter indicates that the sample has better corrosion resistance, and the capacitance semicircle diameter of the magnesium alloy is about 250Ω·cm -2 In contrast, the capacitance semicircle diameters of the M-Z/CH sample and the M-Z/CH@SA sample are far higher than those of the magnesium alloy matrix, and compared with the M-Z/CH sample, the capacitance semicircle diameter of the modified M-Z/CH@SA sample is higher and is about 1 multiplied by 10 6 Ω·cm -2 About 4 orders of magnitude higher than the magnesium alloy matrix. The M-Z/CH@SA sample has excellent corrosion resistance. This can also be seen from the baud plot of |z| versus frequency (fig. 9), which generally shows that the higher the value of |z| the better the corrosion resistance, the data indicate that the value of |z| for the M-Z/ch@sa sample is 3.5 orders of magnitude higher than that for the magnesium alloy matrix, and is greater than that for the M-The value of Z/CH sample is 1 order of magnitude higher. The high phase angle in the high frequency domain indicates that the sample has good rejection performance, and the large modulus in the low frequency domain indicates that the corrosion resistance is enhanced, as shown in fig. 10, the Z/ch@sa sample shows a higher phase angle in both the high frequency domain and the low frequency domain. The results show that the M-Z/CH@SA sample has excellent corrosion protection performance.
FIGS. 11 and 12 are equivalent circuit models (ECs) for AZ91D magnesium alloy and Z/CH@SA samples, respectively. In the circuit, the solution resistance is Rs, the film resistance is Rh, the Rf, the charge transfer resistance is Rct, and because the surface structure of the sample is complex and uneven, a Constant Phase Element (CPE) is used for replacing a pure capacitor, so that the circuit is provided with a non-ideal capacitor for circuit fitting, and the constant phase element has a better fitting effect in an equivalent circuit compared with the pure capacitor. Experimental data shows that the Rct of the magnesium alloy matrix is 572.5 omega, compared with the Rct of the M-Z/CH@SA sample which is 4.7941 ×10 6 Omega, far higher than magnesium alloy matrix. M-Z/CH@SA samples were also demonstrated to have excellent corrosion protection properties, and the detailed fit data are shown in Table 2.
Table 2 equivalent circuit fitting results
Figure GDA0003809498770000111
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2.4 wettability of hydrophobic films
In order to explore the film protection mechanism, the wettability of the surfaces of the M-Z/CH sample (heating for 105 min) and the M-Z/CH@SA sample (heating for 105 min) is studied, and experiments show that deionized water droplets are absorbed by the film at the moment of contacting the surface of the M-Z/CH sample (part a in fig. 13), and the result shows that the surface of the M-Z/CH sample which is not modified by stearic acid has strong adsorption force on water, and the surface film shows super hydrophilicity. This also results in the sample being exposed to the solution containing the corrosive medium, which will be absorbed by the membrane and spread throughout the sample along the membrane coverage. To prove the guesswork, M-Z/CH samples after corrosion performance testing in 3.5wt% NaCl aqueous solution were taken, and the samples were polished to remove the surface film and expose the magnesium alloy matrix. The red marked area is the area where the sample is in direct contact with the corrosive medium during the corrosion performance test (part b in fig. 13), and it can be observed that the sample has pitting holes not only in the direct contact area but also in the non-direct contact area. The results show that the aqueous solution containing NaCl is truly adsorbed and diffused by the surface film of the M-Z/CH sample when the corrosion performance test is carried out, so that the whole sample is corroded. Thus, while the membrane of the M-Z/CH sample does improve the corrosion protection performance of the Mg matrix, the super-hydrophilicity of the membrane prevents the sample from corrosion protection.
In fig. 13 (c, d part) is a contact angle image of the surface of the M-Z/ch@sa sample, the M-Z/ch@sa sample modified by stearic acid shows a remarkable hydrophobic property, and the average contact angle is 125 ° as measured at 4 different positions of the M-Z/ch@sa sample by a contact angle meter. The hydrophobicity of the surface of the modified M-Z/CH@SA sample prevents the solution containing the corrosive medium from adsorbing and diffusing on the membrane, and greatly limits the direct contact between the corrosive medium in the solution and the sample, so that the M-Z/CH@SA sample has more excellent corrosion protection effect compared with the sample before modification.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims (4)

1. The method for synthesizing the double-layer composite film on the surface of the magnesium alloy in one step is characterized by comprising the following steps:
1) Pretreating magnesium alloy to obtain magnesium alloy with clean surface, wherein the magnesium alloy is AZ91D magnesium alloy;
2) Immersing the magnesium alloy obtained in the step 1) into a surface treatment liquid, heating to perform hydrothermal reaction, and cleaning and drying the magnesium alloy after the reaction is finished to obtain compact Mg (OH) 2 Bottom film and K with porous support-like microstructure 2 Al 2 Si 4 O 12 ·xH 2 A magnesium alloy sample of the O upper film, wherein x is 3-12;
3) Immersing the magnesium alloy sample obtained in the step 2) into a solution of stearic acid in ethanol for modification treatment, and then taking out, cleaning and drying to obtain the magnesium alloy with the stearic acid modified double-layer composite film;
wherein, in step 2):
the surface treatment liquid comprises SiO 2 KOH, ethylenediamine tetraacetic acid, ca (OH) 2 The weight ratio of each component to solvent deionized water is (0.0184-0.0192) 1 (0.069-0.071) 1 (0.090-0.092) 1 (0.0226-0.0234) 1, siO used 2 The grain diameter of the particles is 8000-10000 meshes;
the hydrothermal reaction conditions are as follows: heating to 190-210 deg.C and maintaining the temperature for 90-105min.
2. The method for synthesizing the double-layer composite film on the surface of the magnesium alloy in one step according to claim 1, wherein the method comprises the following steps: in step 2), the reaction vessel used was a muffle furnace.
3. The method for synthesizing the double-layer composite film on the surface of the magnesium alloy in one step according to claim 1, wherein the method comprises the following steps: in the step 3), immersing the magnesium alloy sample obtained in the step 2) into a solution of stearic acid in ethanol for standing for modification treatment, wherein the standing time is 40-60min.
4. A magnesium alloy having a surface provided with a double-layer composite film, prepared by the method according to any one of claims 1 to 3.
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