CN109735887B - Preparation method of magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating - Google Patents
Preparation method of magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating Download PDFInfo
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Abstract
The magnesium alloy surface coating with excellent corrosion resistance is prepared. According to the method, a magnesium alloy sample subjected to pretreatment is subjected to micro-arc oxidation in advance, then the micro-arc oxidation sample is placed in deionized water for hydrothermal reaction, and finally the magnesium-manganese hydrotalcite/micro-arc oxidation coating is formed on the surface of the alloy. The coating prepared by the invention has lower corrosion current density, not only can effectively repair holes and cracks of the micro-arc oxidation layer, but also can well adsorb anions in a corrosive solution, and effectively improves the corrosion resistance of the alloy. The invention has simple process, easy operation, low cost and wide popularization feasibility.
Description
Technical Field
The invention relates to a magnesium alloy surface treatment technology, in particular to a preparation method of a magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating.
Background
Magnesium and its alloy have good mechanical and physical properties, such as high specific strength, impact resistance, good shock absorption, good electromagnetic shielding property, good biocompatibility and the like, so that the magnesium and its alloy are ideal materials in the application fields of automobile lightweight, aerospace, electronic industry and the like. However, since the magnesium alloy has a disadvantage of poor corrosion resistance and thus cannot be used on a large scale, the magnesium alloy is often surface-treated industrially to improve the corrosion resistance.
Magnesium alloy surface treatments such as chemical oxidation, anodic oxidation, metal coating, etc. can improve the corrosion resistance of the alloy, but also have problems of environmental pollution, high cost, etc., and are difficult to mass-produce. The micro-arc oxidation has the advantages of simple technology, high efficiency and no pollution, and can form a compact ceramic layer on the surface of the alloy. The principle is that a magnesium alloy sample is placed into electrolyte in a pulse electric field environment as an anode, an oxide film on the surface of the sample is broken down under high pressure to generate a large amount of micro-arc discharge, and magnesium atoms react with oxygen ions in the electrolyte to form a magnesium oxide ceramic coating under high temperature and high pressure in a micro-area generated in the discharge process. However, holes, cracks and the like are easily formed in the micro-arc oxidation process, so that pretreatment or post-treatment is required to reduce defects and improve the corrosion resistance of the alloy.
Hydrotalcite is a kind of anion intercalation type layered compound, also called layered double-hydroxy composite metal hydroxide, and its chemical formula is [ M2+ 1-xM3+ x(OH)2]x+Am- x/m•nH2O, wherein M2+And M3+Metal cations representing the host layer plate, Am-Are exchangeable interlayer guest anions. The hydrotalcite has a series of excellent physicochemical properties such as good catalysis, fire resistance, magnetism and the like due to the adjustability of the composition and the structure and the interchangeability of interlayer ions, so that the hydrotalcite material has wide application prospects in the fields of catalytic adsorption, magnetism, fire retardants, metal corrosion prevention and the like. Good ion exchange capacity of hydrotalcite coating to capture and limit Cl by ion exchange-Thereby effectively inhibiting Cl-The erosive effect of (c).
In recent years, research on preparation of aluminum alloy micro-arc oxidation/hydrotalcite coating has been carried out, and people can effectively relieve corrosion of the alloy by preparing the hydrotalcite coating on the surface of the aluminum alloy micro-arc oxidation layer. However, the research on the magnesium alloy micro-arc oxidation/hydrotalcite coating is very few, the preparation process is complex, divalent ions need to be additionally introduced, and the cost and the process flow are increased.
The micro-arc oxidation coating of the magnesium alloy has a large number of cracks and holes, and the large cracks and holes easily form corrosion channels, so that the corrosion of the alloy is accelerated. And carrying out hydrothermal treatment on the micro-arc oxidation sample in a reaction kettle to obtain the micro-arc oxidation/hydrotalcite coating. According to the preparation process, deionized water is directly used as a reaction liquid for hydrothermal treatment, a hydrothermal reaction mixed solution is not required to be prepared, trivalent ions are introduced, the divalent magnesium ions and the trivalent manganese ions of the micro-arc oxidation layer are used for synthesizing the hydrotalcite, the process is simple and easy to operate, and the obtained coating can effectively relieve the corrosion of the magnesium alloy.
Disclosure of Invention
The invention aims to provide a preparation method of a magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating, which directly adopts deionized water as reaction liquid to carry out hydrothermal treatment, does not need to prepare a hydrothermal reaction mixed solution, introduces trivalent ions, synthesizes hydrotalcite through divalent magnesium ions and trivalent manganese ions of a micro-arc oxidation layer, has simple working procedures and easy operation, and can effectively relieve the corrosion of magnesium alloy.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating comprises the following steps:
(1) pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: performing micro-arc oxidation on the dried magnesium alloy sample in a constant current mode to obtain a manganese-micro-arc oxidation sample;
(3) and (3) performing hydrothermal reaction, namely putting the manganese-micro arc oxidation sample obtained in the step (2) into deionized water for hydrothermal reaction to prepare the magnesium-manganese hydrotalcite/micro arc oxidation coating.
The electrolyte for micro-arc oxidation in the step (2) comprises the following components: 5-20g/L of sodium silicate, 5-30g/L of potassium hydroxide, 1-10g/L of potassium fluoride and 0-2g/L of potassium permanganate.
The processing time of the constant current mode micro-arc oxidation in the step (2) is 5-20min, and the frequency is 600-.
The temperature of the hydrothermal reaction in the step (3) is 100-150 ℃, and the reaction time is 1-30 h.
Further, the preparation method is applied to the preparation of the anti-corrosion magnesium alloy.
The invention has the advantages that:
(1) the hydrotalcite is used as a novel inorganic functional material, has the characteristics of memory effect, thermal stability, interchangeability of interlayer anions and the like due to the adjustability of the composition and the structure, and has wide application prospect.
(2) The magnesium-manganese hydrotalcite/micro-arc oxidation coating is prepared by a hydrothermal method, and the corrosion resistance of the micro-arc oxidation alloy sample is effectively improved due to the unique layered structure of the hydrotalcite.
(3) The method does not need to prepare a hydrothermal reaction mixed solution, has simple and efficient process, low cost, environmental protection and no pollution, can obviously reduce the corrosion current density of the magnesium alloy, and widens the application range of the magnesium alloy.
(4) The magnesium-manganese hydrotalcite/micro-arc oxidation coating can effectively delay the corrosion speed of the magnesium alloy and prolong the service life of the magnesium alloy.
(5) The magnesium-manganese hydrotalcite/micro-arc oxidation coating has certain adsorption property and can be used as an adsorption coating.
Drawings
FIG. 1 is an XRD of a coating of micro-arc oxidation, manganese-micro-arc oxidation and magnesium-manganese hydrotalcite/micro-arc oxidation.
FIG. 2 is an SEM image of a micro-arc oxidation, manganese-micro-arc oxidation and magnesium-manganese hydrotalcite/micro-arc oxidation coating; wherein (a) is micro-arc oxidation, (b) is manganese-micro-arc oxidation, and (c-d) is magnesium-manganese hydrotalcite/micro-arc oxidation coating.
FIG. 3 is an EDS diagram of magnesium manganese hydrotalcite/micro-arc oxidation coating.
FIG. 4 is a dynamic polarization curve of micro-arc oxidation, manganese-micro-arc oxidation and magnesium-manganese hydrotalcite/micro-arc oxidation coating.
Detailed Description
Example 1 preparation method of magnesium-manganese hydrotalcite/micro-arc oxidation coating
(1) Pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: performing micro-arc oxidation on the dried magnesium alloy sample in a constant current mode, wherein the treatment time is 20min, and the frequency is 800Hz to obtain a manganese-micro-arc oxidation sample; the micro-arc oxidation electrolyte comprises the following components: 20g/L of sodium silicate, 30g/L of potassium hydroxide, 10g/L of potassium fluoride and 2g/L of potassium permanganate.
(3) And (3) performing hydrothermal reaction, namely putting the manganese-micro arc oxidation sample obtained in the step (2) into deionized water for hydrothermal reaction at the temperature of 120 ℃ for 15 hours to prepare the magnesium-manganese hydrotalcite/micro arc oxidation coating.
Example 2
(1) Pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: performing micro-arc oxidation on the dried magnesium alloy sample in a constant current mode, wherein the treatment time is 5min, and the frequency is 600Hz, so as to obtain a manganese-micro-arc oxidation sample; the micro-arc oxidation electrolyte comprises the following components: 5g/L of sodium silicate, 5g/L of potassium hydroxide, 1g/L of potassium fluoride and 1g/L of potassium permanganate.
(3) And (3) performing hydrothermal reaction, namely putting the manganese-micro arc oxidation sample obtained in the step (2) into deionized water for hydrothermal reaction at the reaction temperature of 100 ℃ for 10 hours to prepare the magnesium-manganese hydrotalcite/micro arc oxidation coating.
Example 3
(1) Pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: performing micro-arc oxidation on the dried magnesium alloy sample in a constant current mode, wherein the treatment time is 10min and the frequency is 700Hz, and thus obtaining a manganese-micro-arc oxidation sample; the micro-arc oxidation electrolyte comprises the following components: 10g/L of sodium silicate, 10g/L of potassium hydroxide, 5g/L of potassium fluoride and 2g/L of potassium permanganate.
(3) And (3) performing hydrothermal reaction, namely putting the manganese-micro arc oxidation sample obtained in the step (2) into deionized water for hydrothermal reaction at the temperature of 120 ℃ for 15 hours to prepare the magnesium-manganese hydrotalcite/micro arc oxidation coating.
Comparative example 1 preparation method of micro-arc oxidation coating
(1) Pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: the dried magnesium alloy sample is subjected to micro-arc oxidation in a constant current mode, and the electrolyte for micro-arc oxidation comprises the following components: 20g/L of sodium silicate, 30g/L of potassium hydroxide and 10g/L of potassium fluoride; the treatment time is 20min, the frequency is 800Hz, and the micro-arc oxidation sample is obtained.
Comparative example 2 preparation method of manganese-micro arc oxidation coating
(1) Pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: the dried magnesium alloy sample is subjected to micro-arc oxidation in a constant current mode, and the electrolyte for micro-arc oxidation comprises the following components: 20g/L of sodium silicate, 30g/L of potassium hydroxide, 10g/L of potassium fluoride and 2g/L of potassium permanganate; the treatment time is 10min, and the frequency is 800Hz, so that the manganese-micro arc oxidation sample is obtained.
The coatings prepared in the examples and the comparative examples are subjected to X-ray diffraction, and the diffraction patterns of the coatings are analyzed, so that the magnesium-manganese hydrotalcite/micro-arc oxidation coating in the example 1 has diffraction peaks of (003) and (006) crystal planes of hydrotalcite, and the hydrotalcite coating is formed on the surface of a micro-arc oxidation sample (figure 1).
SEM representation is carried out on the coatings prepared in the examples and the comparative examples, and as can be seen from figure 2, the magnesium alloy sample in the comparative example 1 forms a compact coating after micro-arc oxidation, but a large number of volcanic-shaped holes with different sizes exist and obvious cracks are distributed, and the holes and the cracks are easy to form rapid corrosion channels to accelerate the corrosion of the surface of the magnesium alloy. After potassium permanganate is added into the electrolyte of comparative example 2, more fine holes appear on the surface of a manganese-micro-arc oxidation sample, the number of the holes is increased, and after hydrothermal reaction (example 1), a lamellar hydrotalcite coating is formed on the surface of a magnesium-manganese hydrotalcite/micro-arc oxidation sample, the holes can be effectively covered by the hydrotalcite coating, and meanwhile, the special layered structure of the hydrotalcite coating can capture and limit chloride ions through ion exchange, so that the corrosion speed of magnesium alloy is remarkably reduced.
As can be seen from the EDS spectrum (figure 3), Mg and O are mainly distributed on the surface of the sample, and a compact MgO ceramic layer is formed on the surface of the alloy after micro-arc oxidation. In addition, Al, Si and Mn are uniformly distributed on the surface of the sample, wherein Si is introduced from electrolyte in the process of micro-arc oxidation, hydrotalcite formed by Al, Mn and the like uniformly grows on the micro-arc oxidation layer, holes and cracks are effectively covered, and the micro-arc oxidation layer is not damaged.
The dynamic polarization curves of the magnesium alloy micro-arc oxidation, the manganese-micro-arc oxidation and the magnesium-manganese hydrotalcite/micro-arc oxidation coating in 3.5 wt% sodium chloride solution in the examples and the comparative examples are shown in figure 4. The corrosion current density and the self-corrosion potential in the dynamic polarization curve are important standards for measuring the corrosion resistance of the sample, and the smaller the corrosion current density is, the higher the self-corrosion potential is, and the better the corrosion resistance of the magnesium alloy is. As shown in fig. 4, the corrosion potential of the manganese-micro arc oxidation coating formed after adding potassium permanganate remains unchanged basically, and the corrosion current increases, indicating that the corrosion resistance of the alloy is not improved by adding potassium permanganate into the electrolyte under the current experimental conditions, but the corrosion potential of the magnesium-manganese hydrotalcite/micro arc oxidation coating is unchanged after hydrothermal reaction, but the corrosion current density is obviously reduced, indicating that the corrosion resistance of the magnesium-manganese hydrotalcite/micro arc oxidation coating is obviously higher than that of the micro arc oxidation coating, because the magnesium-manganese hydrotalcite covers the holes and cracks of the micro arc oxidation coating, the penetration of chloride ions is effectively blocked, and meanwhile, the unique property of the hydrotalcite coating, namely, the hydrotalcite coating has good ion exchange property, can capture and limit the chloride ions, thereby effectively delaying the corrosion degree of the magnesium alloy.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (2)
1. The preparation method of the magnesium alloy magnesium-manganese hydrotalcite/micro-arc oxidation corrosion-resistant coating is characterized by comprising the following steps of:
(1) pretreatment: grinding the surface of a magnesium alloy sample to be smooth, and then washing and drying;
(2) micro-arc oxidation of magnesium alloy: performing micro-arc oxidation on the dried magnesium alloy sample in a constant current mode to obtain a manganese-micro-arc oxidation sample;
(3) hydrothermal reaction, namely putting the manganese-micro arc oxidation sample obtained in the step (2) into deionized water for hydrothermal reaction to prepare magnesium-manganese hydrotalcite/micro arc oxidation coating; the electrolyte for micro-arc oxidation in the step (2) comprises the following components: 5-20g/L of sodium silicate, 5-30g/L of potassium hydroxide, 1-10g/L of potassium fluoride and 0-2g/L of potassium permanganate; the processing time of the constant current mode micro-arc oxidation in the step (2) is 5-20min, and the frequency is 600-; the temperature of the hydrothermal reaction in the step (3) is 100-150 ℃, and the reaction time is 1-30 h.
2. Use of the process according to claim 1 for the production of corrosion-resistant magnesium alloys.
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