CN113846366A - Preparation method of corrosion-resistant micro-arc oxidation composite coating - Google Patents
Preparation method of corrosion-resistant micro-arc oxidation composite coating Download PDFInfo
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- CN113846366A CN113846366A CN202111372507.6A CN202111372507A CN113846366A CN 113846366 A CN113846366 A CN 113846366A CN 202111372507 A CN202111372507 A CN 202111372507A CN 113846366 A CN113846366 A CN 113846366A
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/026—Anodisation with spark discharge
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/024—Anodisation under pulsed or modulated current or potential
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/04—Anodisation of aluminium or alloys based thereon
- C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C21/00—Alloys based on aluminium
- C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
- C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
Abstract
The invention discloses a preparation method of a corrosion-resistant micro-arc oxidation composite coating, which comprises the following steps: preparing micro-arc oxidation electrolyte added with nano silicon carbide; and placing the aluminum alloy matrix and the micro-arc oxidation electrolyte added with the nano silicon carbide into micro-arc oxidation equipment, and performing micro-arc oxidation reaction for 10 minutes at constant pressure of 500V, thereby preparing the corrosion-resistant micro-arc oxidation SiC composite coating on the surface of the aluminum alloy matrix. The porosity of the corrosion-resistant micro-arc oxidation composite coating prepared by the invention is obviously reduced, the subsequent hole sealing treatment of the coating is not needed, the whole electrochemical impedance of the coating is high, and the corrosion expansion speed is slow after local damage occurs, so that the problem that the aluminum alloy is easy to corrode when used as a battery box body can be solved, the corrosion resistance of the aluminum alloy is greatly enhanced, the coating thickness is more uniform, the compactness is better, and the coating is better combined with an aluminum alloy matrix.
Description
Technical Field
The invention relates to the technical field of aluminum alloy surface treatment, in particular to a preparation method of a corrosion-resistant micro-arc oxidation composite coating.
Background
The 6-series aluminum alloy has good mechanical property, excellent welding property and higher specific strength; the 6 series aluminum alloy has more magnesium and silicon alloy characteristics, so that the processing performance is excellent, the electroplating property and the high toughness are good, and the alloy is not deformed after processing; the 6 series aluminum alloy material is compact and free of defects, is easy to polish and color film, and has excellent oxidation effect.
In order to reduce the weight of the automobile body and reduce the energy consumption, the electric automobile enterprise generally selects aluminum alloy as a battery box material, and the material can reduce the mass of the box body by 40-50% on the premise of ensuring the rigidity. In recent years, 6-series aluminum alloy (for example, 6061 aluminum alloy) is adopted as a new energy automobile battery tray or box material, and the mainstream trend is shown. However, the aluminum alloy battery box is exposed or directly becomes a part of the chassis of the automobile, so that the aluminum alloy can not be prevented from contacting substances having a corrosion effect on the aluminum alloy, and in order to achieve the purpose of good heat dissipation of the battery, a protective cover can not be additionally arranged at the bottom of the battery box by some electric automobile manufacturers, so that the aluminum alloy battery box still faces the risk of corrosion failure.
The micro-arc oxidation process can generate a continuous and compact ceramic oxide film on the surface of a metal material in situ, the oxide film has high bonding strength with a metal matrix, has the characteristics of good wear resistance, corrosion resistance, high-temperature impact resistance, electric insulation and the like, and is more suitable for coating modification of valve metals such as aluminum alloy and the like. The micro-arc oxidation process is easy to operate and environment-friendly, and the coating prepared by the micro-arc oxidation process is uniform, compact and good in binding force from the viewpoint of coating quality, so that the micro-arc oxidation process has great superiority compared with other coating modification methods. In the prior art, the ceramic coating prepared by the micro-arc oxidation process on the surface of the aluminum alloy has high porosity, and the coating needs to be subjected to hole sealing treatment subsequently to reduce and narrow micropores on the surface of the coating, so that the coating has good corrosion resistance.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a preparation method of a corrosion-resistant micro-arc oxidation composite coating, which aims to solve the technical problems in the prior art. The porosity of the corrosion-resistant micro-arc oxidation composite coating prepared by the invention is obviously reduced, the subsequent hole sealing treatment of the coating is not needed, the whole electrochemical impedance of the coating is high, and the corrosion expansion speed is slow after local damage occurs, so that the problem that the aluminum alloy is easy to corrode when used as a battery box body can be solved, the corrosion resistance of the aluminum alloy is greatly enhanced, the coating thickness is more uniform, the compactness is better, and the coating is better combined with an aluminum alloy matrix.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a corrosion-resistant micro-arc oxidation composite coating comprises the following steps:
and 2, placing the aluminum alloy matrix and the micro-arc oxidation electrolyte added with the nano silicon carbide into micro-arc oxidation equipment, and performing micro-arc oxidation reaction for 10-15 minutes at constant pressure of 500V, so that the corrosion-resistant micro-arc oxidation SiC composite coating is prepared on the surface of the aluminum alloy matrix.
Preferably, the adding of the nano silicon carbide powder in the process of preparing the micro-arc oxidation electrolyte comprises the following steps: adding sodium hydroxide, sodium silicate, sodium hexametaphosphate and nano silicon carbide powder into water according to the proportion of using 2g of sodium hydroxide, 10g of sodium silicate, 15g of sodium hexametaphosphate and 3g of nano silicon carbide powder per liter of water, and uniformly mixing to prepare the micro-arc oxidation electrolyte added with nano silicon carbide.
Preferably, the aluminum alloy substrate is pretreated before micro-arc oxidation; the pretreatment comprises the following steps: and (3) polishing the surface of the aluminum alloy matrix, then carrying out ultrasonic cleaning, and then immersing the aluminum alloy matrix into absolute ethyl alcohol for sealing, thus finishing the pretreatment.
Preferably, the aluminum alloy substrate is 6 series aluminum alloy with the mark of 6061.
The corrosion-resistant micro-arc oxidation SiC composite coating is prepared by adopting the preparation method of the corrosion-resistant micro-arc oxidation SiC composite coating.
The surface of the aluminum alloy part is provided with the corrosion-resistant micro-arc oxidation SiC composite coating.
Compared with the prior art, the preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the invention adds the nano silicon carbide particles into the micro-arc oxidation electrolyte, and adopts a special voltage-lifting mode and a constant-voltage control operation mode in the micro-arc oxidation process, so that the porosity of the prepared corrosion-resistant micro-arc oxidation SiC composite coating is obviously reduced, the subsequent hole sealing operation of the coating is not needed, the whole electrochemical impedance of the coating is high, and the corrosion expansion speed is slow after local damage occurs, so that the problem that the aluminum alloy is easy to corrode as a battery box body is solved, the corrosion resistance of the aluminum alloy is greatly enhanced, the corrosion resistance of the aluminum alloy as a battery box body material of an electric automobile is improved, the coating thickness is more uniform, the compactness is better, and the coating is better combined with an aluminum alloy matrix.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a macro topography diagram of an aluminum alloy substrate and a micro-arc oxidized SiC composite coating prepared in embodiment 1 of the invention.
Fig. 2 is a schematic diagram of a coating thickness and a schematic diagram of a cross-sectional EDS line scan element of the micro-arc oxidized SiC composite coating prepared in example 1 of the present invention.
FIG. 3 is a micro-topography of a single micro-arc oxidation coating without SiC in the prior art and a micro-arc oxidation SiC composite coating prepared in the embodiment 1 of the invention.
FIG. 4 is a phase composition diagram of XRD of a single micro-arc oxidation coating without SiC in the prior art and a micro-arc oxidation SiC composite coating prepared in the embodiment 1 of the invention.
FIG. 5 is a graph comparing the mode resistance values of an aluminum alloy substrate, a single micro-arc oxidation coating without SiC in the prior art and a micro-arc oxidation SiC composite coating prepared in example 1 of the present invention.
FIG. 6 is a comparison graph of corrosion current densities of an aluminum alloy substrate, a single micro-arc oxidation coating without SiC added in the prior art, and a micro-arc oxidation SiC composite coating prepared in example 1 of the present invention.
FIG. 7 is a partial impedance diagram of a single micro-arc oxidation coating without SiC added in the prior art and a micro-arc oxidation SiC composite coating prepared in the embodiment 1 of the invention.
Detailed Description
The technical scheme in the embodiment of the invention is clearly and completely described below by combining the attached drawings in the embodiment of the invention; it is to be understood that the described embodiments are merely exemplary of the invention, and are not intended to limit the invention to the particular forms disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The terms that may be used herein are first described as follows:
the terms "comprising," "including," "containing," "having," or other similar terms of meaning should be construed as non-exclusive inclusions. For example: including a feature (e.g., material, component, ingredient, carrier, formulation, material, dimension, part, component, mechanism, device, process, procedure, method, reaction condition, processing condition, parameter, algorithm, signal, data, product, or article of manufacture), is to be construed as including not only the particular feature explicitly listed but also other features not explicitly listed as such which are known in the art.
When concentrations, temperatures, pressures, dimensions, or other parameters are expressed as ranges of values, the ranges are to be understood as specifically disclosing all ranges formed from any pair of upper, lower, and preferred values within the range, regardless of whether ranges are explicitly recited; for example, if a numerical range of "2 ~ 8" is recited, then the numerical range should be interpreted to include ranges of "2 ~ 7", "2 ~ 6", "5 ~ 7", "3 ~ 4 and 6 ~ 7", "3 ~ 5 and 7", "2 and 5 ~ 7", and the like. Unless otherwise indicated, the numerical ranges recited herein include both the endpoints thereof and all integers and fractions within the numerical range.
The preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the invention is described in detail below. Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to the person skilled in the art. Those not specifically mentioned in the examples of the present invention were carried out according to the conventional conditions in the art or conditions suggested by the manufacturer. The reagents or instruments used in the examples of the present invention are not specified by manufacturers, and are all conventional products available by commercial purchase.
The invention provides a preparation method of a corrosion-resistant micro-arc oxidation composite coating, which comprises the following steps:
step A, pretreatment of an aluminum alloy matrix: and polishing the surface of the aluminum alloy matrix, performing ultrasonic cleaning after polishing, and immersing the aluminum alloy matrix into absolute ethyl alcohol for sealing after cleaning, thereby obtaining the pretreated aluminum alloy matrix.
Step B, using 2g of sodium hydroxide (NaOH) and 10g of sodium silicate (Na) per liter of water2SiO3) 15g of sodium hexametaphosphate ((NaPO)3)6) And 3g of nano silicon carbide powder, sequentially adding sodium hydroxide, sodium silicate, sodium hexametaphosphate and nano silicon carbide powder into water (preferably ultrapure water), and uniformly mixing to obtain the micro-arc oxidation electrolyte added with nano silicon carbide.
And step C, pouring the micro-arc oxidation electrolyte added with the nano silicon carbide in the step B into micro-arc oxidation equipment, completely soaking the aluminum alloy substrate pretreated in the step A in the micro-arc oxidation electrolyte to be used as a power supply anode, and taking a stainless steel electrolytic cell as a power supply cathode to perform micro-arc oxidation, starting the micro-arc oxidation equipment, and performing micro-arc oxidation reaction for 10-15 minutes under constant voltage control of 500V, so that the corrosion-resistant micro-arc oxidation SiC composite coating is prepared on the surface of the aluminum alloy substrate.
Specifically, the preparation method of the corrosion-resistant micro-arc oxidation composite coating can comprise the following embodiments:
(1) the aluminum alloy matrix is 6 series aluminum alloy with the mark of 6061, and the aluminum alloy matrix comprises, by mass, 0.8-1.2% of Mg, 0.4-0.8% of Si, 0.15-0.4% of Cu, 0.15% of Mn, 0.25% of Zn, 0.04-0.35% of Cr, 0.15% of Ti, less than or equal to 0.7% of Fe, and the balance of Al. The formula of the micro-arc oxidation electrolyte is specially designed for the 6061 aluminum alloy with the components, so that the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix has good corrosion resistance without hole sealing treatment, the coating thickness is more uniform, the compactness is better, and the coating is better combined with the aluminum alloy matrix.
(2) The micro-arc oxidation conditions comprise operation voltage, voltage lifting mode and oxidation time; the specific operating voltage is 500V; the boosting mode is that the voltage is adjusted from 0V to 50V, the voltage is increased by 50V every 30 seconds from 50V to 200V, the voltage is controlled to be increased by 25V every minute from 200V to 500V, the voltage is oxidized for 10-15 minutes at 500V, the voltage is reduced quickly after the oxidation is finished, the voltage is adjusted from 500V to 100V, then to 50V, and finally to 0V; by adopting the voltage boosting mode, after the voltage reaches 500V, the voltage is controlled at constant voltage for 500V to perform micro-arc oxidation reaction for 10-15 minutes, and then the voltage reduction mode is adopted, so that the prepared corrosion-resistant micro-arc oxidation SiC composite coating has good quality, and micro-arc oxidation equipment can be protected.
Further, taking an aluminum alloy block as an example to illustrate the preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the invention, the aluminum alloy block is used as an aluminum alloy substrate, the aluminum alloy block is firstly polished by using 240#, 800#, 1200# silicon carbide abrasive paper until no obvious scratch is formed on the surface of the aluminum alloy block, then the aluminum alloy block is immediately subjected to ultrasonic cleaning, and after the cleaning is finished, the aluminum alloy block is immediately immersed in absolute ethyl alcohol for sealing and standby application, so that a pretreated aluminum alloy block is obtained; and soaking the pretreated aluminum alloy block in a microarc oxidation electrolyte added with nano silicon carbide, performing microarc oxidation reaction for 10-15 minutes under constant pressure control of 500V, turning off a power supply and a control cabinet, taking out the aluminum alloy substrate, flushing the microarc oxidation electrolyte on the surface by using tap water, and drying by using a hair drier to obtain the aluminum alloy substrate with the corrosion-resistant microarc oxidation SiC composite coating.
Compared with the prior art, the preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the invention at least has the following advantages:
(1) according to the corrosion-resistant micro-arc oxidation SiC composite coating prepared by the invention, nano silicon carbide particles exist in the coating, compared with the coating without nano silicon carbide, the porosity of the corrosion-resistant micro-arc oxidation SiC composite coating prepared by the invention is obviously reduced, and the subsequent hole sealing operation of the coating is not required.
(2) The silicon carbide nano particles have the advantages of low preparation cost, small preparation difficulty, flexible and various preparation methods, stable chemical property, high heat conductivity coefficient, small thermal expansion coefficient and good wear resistance, and meanwhile, the silicon carbide nano particles have high hardness, the Mohs hardness is 9.5, and the silicon carbide nano particles can resist oxidation at high temperature next to the hardest diamond (10 grades) in the world, so that the prepared corrosion-resistant micro-arc oxidation SiC composite coating has higher heat conductivity coefficient, smaller thermal expansion coefficient, better wear resistance, higher hardness and better oxidation resistance at high temperature by adopting the nano silicon carbide particles.
(3) According to the preparation method of the corrosion-resistant micro-arc oxidation composite coating, a constant-pressure control operation mode is adopted in the preparation process, and compared with constant-current control, the prepared coating is more uniform in thickness, better in coating compactness and more corrosion-resistant.
(4) The preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the invention has the characteristics of environmental protection, few preparation steps, simple operation and low cost.
In conclusion, the porosity of the corrosion-resistant micro-arc oxidation composite coating prepared by the embodiment of the invention is obviously reduced, the subsequent hole sealing treatment of the coating is not needed, the whole electrochemical impedance of the coating is high, and the corrosion expansion speed is low after local damage occurs, so that the problem that the aluminum alloy is easy to corrode when used as a battery box body is solved, the corrosion resistance of the aluminum alloy is greatly enhanced, the coating thickness is more uniform, the compactness is better, and the coating is better combined with an aluminum alloy matrix.
In order to more clearly show the technical scheme and the technical effects provided by the present invention, the following detailed description is provided for the preparation method of the corrosion-resistant micro-arc oxidation composite coating provided by the embodiment of the present invention with specific embodiments.
Example 1
A preparation method of a corrosion-resistant micro-arc oxidation composite coating comprises the following steps:
step a, pretreating an aluminum alloy substrate: drilling a hole on an aluminum alloy matrix test piece with the thickness of 30 multiplied by 40 multiplied by 5mm, wherein the drilling position is at the center (vertical to the thickness direction of the test piece) which is about 3mm away from a narrow side, then carrying out coarse grinding by using 240# silicon carbide abrasive paper, removing obvious processing scratches on the surface of the aluminum alloy matrix test piece, and then carrying out fine grinding by using 800# and 1200# silicon carbide abrasive paper, immediately putting the aluminum alloy matrix test piece into an ultrasonic cleaning machine for cleaning after the fine grinding effect reaches the surface finish without obvious scratches and consistent lines, immediately immersing the aluminum alloy matrix test piece into a beaker filled with absolute ethyl alcohol for liquid sealing and sealing the beaker after the cleaning is finished, and preventing the surface of the aluminum alloy from being oxidized too fast, thereby obtaining the pretreated aluminum alloy matrix test piece.
Step b, preparing a micro-arc oxidation electrolyte: preparing a micro-arc oxidation electrolyte according to a formula that sodium hydroxide is 2g/L (2g/L represents 2g of water per liter), sodium silicate is 10g/L (10g/L represents 10g of water per liter), sodium hexametaphosphate is 15g/L (15g/L represents 15g of water per liter), and nano silicon carbide powder is 3g/L (3g/L represents 3g of water per liter), wherein 3000mL of pure water is added into a beaker in a first step, 6g of sodium hydroxide is added into the pure water in the beaker in a second step, 30g of sodium silicate is added into the pure water in the beaker in a third step, 45g of sodium hexametaphosphate is added into the pure water in the beaker in a fourth step, 9g of nano silicon carbide powder is added into the beaker, the next raw material is added after one raw material is completely added and stirred until the next raw material is completely dissolved, and the nano silicon carbide powder is added, and mixing and dispersing the nano silicon carbide powder uniformly to prepare the micro-arc oxidation electrolyte added with the nano silicon carbide. The micro-arc oxidation electrolyte needs to be replaced every time the micro-arc oxidation operation is performed, and the prepared micro-arc oxidation electrolyte needs to be used within 24 hours every time, so that the micro-arc oxidation electrolyte is prevented from deteriorating.
Step c, micro-arc oxidation: and micro-arc oxidation equipment is adopted to carry out micro-arc oxidation on the pretreated aluminum alloy matrix test piece, the micro-arc oxidation equipment can adopt a micro-arc oxidation preparation device in the prior art, and the structure of the micro-arc oxidation equipment comprises a power supply, a control cabinet, a transformer, a stirrer and a stainless steel electrolytic tank with water cooling circulation. Pouring the micro-arc oxidation electrolyte added with the nano silicon carbide in the step b into a stainless steel electrolytic tank of micro-arc oxidation equipment, and (b) passing an aluminum wire through the drilled hole on the aluminum alloy matrix test piece pretreated in the step (a), hanging the aluminum wire on an anode steel bar, connecting the pretreated aluminum alloy matrix test piece with the anode of a power supply, using the stainless steel electrolytic tank as the cathode of the power supply, the pretreated aluminum alloy matrix test piece is completely soaked in the micro-arc oxidation electrolyte added with the nano silicon carbide, placing the pretreated aluminum alloy matrix test piece, starting a stirrer to enable ions and particles in the micro-arc oxidation electrolyte to fully contact the pretreated aluminum alloy matrix test piece in a micro-arc oxidation reaction, finally connecting a cooling water inlet pipe with a faucet, introducing a cooling water outlet pipe into a discharge tank, and enabling the cooling water to flow in a downward-feeding and upward-discharging mode; opening a power supply of the micro-arc oxidation equipment, starting a control cabinet, entering a system control panel, selecting a manual constant voltage, setting an initial voltage of 50V, increasing 50V every 30 seconds from 50V to 200V, controlling the voltage to rise by 25V every minute from 200V to 500V, oxidizing for 10 minutes at 500V after the voltage reaches 500V, and after the oxidation is finished, quickly reducing the voltage, adjusting the voltage from 500V to 100V, then to 50V, and finally to 0V; and when the voltage is reduced to be below 20V, the control cabinet and the power supply can be closed, the aluminum alloy matrix test piece is taken out, the residual electrolyte on the surface of the aluminum alloy matrix test piece is washed away by tap water, and the aluminum alloy matrix test piece is dried by a blower, so that the corrosion-resistant micro-arc oxidation SiC composite coating is prepared on the surface of the aluminum alloy matrix test piece, and the aluminum alloy matrix test piece with the corrosion-resistant micro-arc oxidation SiC composite coating on the surface is obtained.
Specifically, the aluminum alloy matrix test piece with the corrosion-resistant micro-arc oxidation SiC composite coating on the surface prepared in the embodiment 1 of the invention can be subjected to a parallel experiment, wherein the parallel experiment is to perform micro-arc oxidation on two or more aluminum alloy matrixes in the same system, one is used for detecting the appearance and quality of the coating, and the other is used for performing a corrosion resistance experiment on the coating.
Further, in order to prove the superiority of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in the embodiment 1 of the invention, the aluminum alloy matrix test piece with the corrosion-resistant micro-arc oxidation SiC composite coating on the surface in the embodiment 1 of the invention is cut, the size of a working surface is cut to 10mm multiplied by 10mm, the cut aluminum alloy matrix test piece is divided into three parts, one part is sent to be subjected to SEM detection, and the surface appearance and the thickness of the coating are observed and represented; the other part is sent to be subjected to XRD object image composition analysis to prove that the corrosion-resistant micro-arc oxidation SiC composite coating is successfully prepared; and thirdly, embedding the SiC composite coating in resin for electrochemical test, testing the impedance modulus value and the corrosion current density of the corrosion-resistant micro-arc oxidation SiC composite coating, and comparing the impedance modulus value and the corrosion current density with the testing values of a single micro-arc oxidation coating and an aluminum alloy matrix which are not added with SiC in the prior art, thereby obtaining the following results:
(1) as shown in fig. 1, a macro topography of an aluminum alloy substrate and the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy substrate test piece in embodiment 1 of the invention; wherein, fig. 1a is a macro topography of an aluminum alloy matrix, and fig. 1b is a macro topography of a corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of an aluminum alloy matrix test piece in embodiment 1 of the invention. As can be seen from fig. 1: the surface of the aluminum alloy substrate is successfully prepared with the corrosion-resistant micro-arc oxidation SiC composite coating.
(2) As shown in fig. 2, a schematic diagram of a coating thickness and a schematic diagram of cross-sectional EDS linear scan elements of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in example 1 of the present invention; wherein, fig. 2a is a schematic diagram of a coating thickness of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the present invention, and fig. 2b is a schematic diagram of a cross-sectional EDS energy spectrum line scan element of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the present invention. As can be seen from fig. 2 a: the cross section thickness of the corrosion-resistant micro-arc oxidation SiC composite coating marked by the light gray indicating line is about 8-10 mu m, and the coating is firmly combined with the matrix; as can be seen from fig. 2 b: the characteristic curves of the three elements of Cu, Fe and Si have mutation at 9 micrometers, which proves that the characteristic curves are the boundary of the coating and the matrix, and the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in the embodiment 1 of the invention is well combined with the aluminum alloy matrix.
(3) As shown in fig. 3, is an SEM micro-topography of a single micro-arc oxidation coating without SiC added in the prior art and the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the present invention; wherein, FIG. 3a is an SEM micro-topography of a single micro-arc oxidation coating without adding SiC in the prior art; FIG. 3b is an SEM microscopic morphology of the corrosion-resistant micro-arc oxidized SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the invention. As can be seen from fig. 3: the number of micropores and the number of holes of the single micro-arc oxidation coating without adding SiC are more than those of the corrosion-resistant micro-arc oxidation SiC composite coating in the embodiment 1 of the invention, which shows that the silicon carbide added in the invention plays a role in hole sealing, and the coating becomes smoother.
(4) As shown in fig. 4, it is an XRD phase composition diagram of the single micro-arc oxidation coating without SiC added in the prior art and the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the present invention; wherein, fig. 4a is a phase composition diagram of XRD of the single micro-arc oxidation coating without SiC added in the prior art, and fig. 4b is a phase composition diagram of XRD of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in embodiment 1 of the present invention. As can be seen from fig. 4: in the XRD curve of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in the embodiment 1 of the invention, the main phases are Al and alpha-Al2O3、γ-Al2O3And SiC, Al is from aluminum alloy matrix, and Al of two crystal forms2O3The appearance of diffraction peaks indicates the aluminum alloyThe surface of the gold matrix fully reacts with the micro-arc oxidation electrolyte, aluminum on the surface of the aluminum alloy matrix test piece is oxidized into an aluminum oxide ceramic phase, namely, the coating is generated in an in-situ growth mode, and the appearance of SiC diffraction peaks shows that nano SiC particles are uniformly dispersed in the coating.
(5) FIG. 5 is a graph showing the comparison of the impedance mode values of an aluminum alloy substrate, a single micro-arc oxidation coating without SiC added in the prior art, and a corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of an aluminum alloy substrate test piece in example 1 of the present invention. As can be seen from fig. 5: after 8 hours and 25 ℃ soaking in 3.5 percent NaCl corrosive liquid, the impedance of the aluminum alloy matrix is lowest (4.89 multiplied by 10)4Ω·cm2) The single micro-arc oxidation coating without SiC in the prior art has slightly strong impedance (3.09 multiplied by 10)5Ω·cm2) The resistance mode value of the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in the embodiment 1 of the invention is the highest (4.08 multiplied by 10)6Ω·cm2) The resistance module value of the corrosion-resistant micro-arc oxidation SiC composite coating added with SiC is improved by 10 times compared with that of a single micro-arc oxidation coating without the SiC and is improved by nearly 100 times compared with that of an aluminum alloy matrix, which shows that the corrosion resistance of the prepared corrosion-resistant micro-arc oxidation SiC composite coating can be greatly improved by adding the SiC.
(6) As shown in fig. 6, it is a comparison graph of corrosion current density of an aluminum alloy matrix, a single micro-arc oxidation coating without SiC added in the prior art, and a corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of an aluminum alloy matrix test piece in example 1 of the present invention. As can be seen from the potentiodynamic polarization curve of fig. 6: the corrosion-resistant micro-arc oxidation SiC composite coating prepared in the embodiment 1 of the invention has the most positive corrosion potential (-0.63V) and the lowest corrosion current density (37.797 nA/cm)2) The corrosion resistance of the corrosion-resistant micro-arc oxidation SiC composite coating is strongest, and the corrosion resistance of the aluminum alloy can be obviously improved.
(7) The coating plays a role in protecting the aluminum alloy matrix, but the coating is inevitably scratched due to mechanical external force and the like during the running of an automobile, corrosion failure starts at the damaged part of the coating, and therefore local impedance detection needs to be carried out on the scratched defect part of the coating. Are not added in the prior art respectivelyA single micro-arc oxidation coating of SiC and the corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of the aluminum alloy matrix test piece in the embodiment 1 of the invention are preformed with a scratch of 0.2mm multiplied by 1mm, and the impedance of the coating defect is tested by using a micro-area electrochemical test system, so that a local impedance diagram shown in FIG. 7 can be obtained; wherein, fig. 7a is a local impedance diagram of a single micro-arc oxidation coating without SiC in the prior art, and fig. 7b is a local impedance diagram of a corrosion-resistant micro-arc oxidation SiC composite coating prepared on the surface of an aluminum alloy matrix test piece in embodiment 1 of the present invention. As can be seen from fig. 7: the central position of the scanning area has a low impedance value, the part corresponds to the position of the scratch, the cloud picture is wholly in a valley shape, the cloud picture is expanded outwards from the scratch area, and the impedance value is gradually increased; in comparison, the corrosion-resistant micro-arc oxidized SiC composite coating of the embodiment 1 of the invention in FIG. 7b has the maximum local impedance value (3.48X 10)6Ω) compared to the maximum local impedance of the single micro-arc oxidation coating of prior art without SiC addition (1.05 × 10) of fig. 7a4Omega) is improved by about 300 times, which shows that when the coating is locally damaged due to mechanical external force and the like, the corrosion-resistant micro-arc oxidation SiC composite coating added with SiC has higher local impedance and stronger corrosion resistance than the single micro-arc oxidation coating without adding SiC in the prior art; even if the corrosion-resistant micro-arc oxidation SiC composite coating added with SiC is locally damaged, the corrosion expansion speed of the corrosion-resistant micro-arc oxidation SiC composite coating is much slower than that of a single micro-arc oxidation coating without the SiC in the prior art.
In conclusion, the porosity of the corrosion-resistant micro-arc oxidation composite coating prepared by the embodiment of the invention is obviously reduced, the subsequent hole sealing treatment of the coating is not needed, the whole electrochemical impedance of the coating is high, and the corrosion expansion speed is low after local damage occurs, so that the problem that the aluminum alloy is easy to corrode when used as a battery box body is solved, the corrosion resistance of the aluminum alloy is greatly enhanced, the coating thickness is more uniform, the compactness is better, and the coating is better combined with an aluminum alloy matrix.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Claims (6)
1. The preparation method of the corrosion-resistant micro-arc oxidation composite coating is characterized by comprising the following steps of:
step 1, adding nano silicon carbide powder in the process of preparing the micro-arc oxidation electrolyte so as to prepare the micro-arc oxidation electrolyte added with nano silicon carbide;
and 2, placing the aluminum alloy matrix and the micro-arc oxidation electrolyte added with the nano silicon carbide into micro-arc oxidation equipment, and performing micro-arc oxidation reaction for 10-15 minutes at constant pressure of 500V, so that the corrosion-resistant micro-arc oxidation SiC composite coating is prepared on the surface of the aluminum alloy matrix.
2. The method for preparing the corrosion-resistant micro-arc oxidation composite coating according to claim 1, wherein the adding of the nano silicon carbide powder in the process of preparing the micro-arc oxidation electrolyte comprises the following steps: adding sodium hydroxide, sodium silicate, sodium hexametaphosphate and nano silicon carbide powder into water according to the proportion of using 2g of sodium hydroxide, 10g of sodium silicate, 15g of sodium hexametaphosphate and 3g of nano silicon carbide powder per liter of water, and uniformly mixing to prepare the micro-arc oxidation electrolyte added with nano silicon carbide.
3. The method for preparing the corrosion-resistant micro-arc oxidation composite coating according to claim 1 or 2, wherein the aluminum alloy substrate is pretreated before being subjected to micro-arc oxidation;
the pretreatment comprises the following steps: and (3) polishing the surface of the aluminum alloy matrix, then carrying out ultrasonic cleaning, and then immersing the aluminum alloy matrix into absolute ethyl alcohol for sealing, thus finishing the pretreatment.
4. The method for preparing the corrosion-resistant micro-arc oxidation composite coating according to claim 1 or 2, wherein the aluminum alloy substrate is 6 series aluminum alloy with the mark of 6061.
5. A corrosion-resistant micro-arc oxidation SiC composite coating, which is characterized by being prepared by the preparation method of the corrosion-resistant micro-arc oxidation SiC composite coating according to any one of claims 1 to 4.
6. An aluminum alloy part characterized in that the surface of the aluminum alloy part is provided with the corrosion-resistant micro-arc oxidized SiC composite coating according to claim 5.
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