CN114182132A - Preparation method of salt solution corrosion-resistant nanoparticle reinforced Mg-Al alloy - Google Patents

Preparation method of salt solution corrosion-resistant nanoparticle reinforced Mg-Al alloy Download PDF

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CN114182132A
CN114182132A CN202111431804.3A CN202111431804A CN114182132A CN 114182132 A CN114182132 A CN 114182132A CN 202111431804 A CN202111431804 A CN 202111431804A CN 114182132 A CN114182132 A CN 114182132A
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alloy
corrosion
melt
aluminum
alpha
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王奎
李浩楠
徐高鹏
蒋海燕
王渠东
丁文江
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Shanghai Jiaotong University
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1036—Alloys containing non-metals starting from a melt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/10—Alloys containing non-metals
    • C22C1/1036—Alloys containing non-metals starting from a melt
    • C22C1/1047—Alloys containing non-metals starting from a melt by mixing and casting liquid metal matrix composites
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C23/00—Alloys based on magnesium
    • C22C23/02—Alloys based on magnesium with aluminium as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/0089—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with other, not previously mentioned inorganic compounds as the main non-metallic constituent, e.g. sulfides, glass

Abstract

The invention discloses a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy. The method introduces the nanoparticles into the alloy melt by adding the nanoparticles in batches and assisting with a variable-frequency high-energy ultrasonic treatment method, and adopts a mold with relatively low cooling speed to carry out cooling forming. Because the cooling speed in the solidification process is low, the solidification speed at the front edge of a solid-liquid interface is not enough to engulf the nano particles dispersed in the melt, so that the nano particles can be pushed to the surface of primary alpha-Mg and can be pushed to the surface of the primary alpha-Mg and eutectic beta-Mg17Al12Enrichment at the phase interface to form a nanoparticle layer and hinder Cl～Further penetration of ions at the grain boundaries slows alloy corrosion. In addition, the nano-particle layer can block Al fusant diffusion, so that a large amount of Al fusant atoms are supersaturated and dissolved in alpha-Mg groups in a solid solution modeIn the body, the electric potential of the alpha-Mg matrix is increased, and the beta-Mg matrix is reduced17Al12The potential difference of the phases is greatly reduced, and the alpha-Mg and the beta-Mg are greatly reduced17Al12The galvanic corrosion speed between the Mg and the Al alloy, thereby enhancing the corrosion resistance of the Mg-Al alloy in a neutral saline water environment.

Description

Preparation method of salt solution corrosion-resistant nanoparticle reinforced Mg-Al alloy
Technical Field
The invention belongs to the technical field of corrosion-resistant Mg-Al alloy, and particularly relates to a preparation method of salt solution corrosion-resistant nanoparticle reinforced Mg-Al alloy, which relates to a method for reinforcing Mg-Al alloy by neutral salt water corrosion-resistant nanoparticles.
Background
Mg-Al alloy, especially AZ91 alloy, is widely used in the fields of aerospace, automobile light weight and the like because of its advantages of light weight, good castability, high specific strength, high specific stiffness and the like. However, magnesium has high chemical activity, a standard electrode potential of-2.34V, and is the lowest among structural metal materials, and therefore, Mg and Mg alloys thereof have extremely poor corrosion resistance. For AZ91 alloy, its microstructure is mainly composed of alpha-Mg phase and a great deal of dissimilarity eutectic structure beta-Mg precipitated along grain boundary17Al12Phase composition. Since the beta phase has a self-corrosion potential of-1.3V, which is 0.3V higher than that of magnesium (1.6V), the alpha-Mg phase (anode) and the beta-Mg phase17Al12Galvanic corrosion prior to phase (cathodic) is the main corrosion mechanism for AZ91 alloy. How to inhibit galvanic corrosion and improve the corrosion resistance of the AZ91 alloy has very important significance for promoting and expanding the development and application of AZ91 and Mg-Al magnesium alloy materials.
At present, the corrosion resistance of Mg-Al alloy, especially AZ91 alloy, is mainly studied at home and abroad by alloying treatment. For example, it has been found by researchers that the addition of main group elements (Ca, etc.) or rare earth elements (Y, Sm, Nd, etc.) can improve the corrosion resistance of AZ91 alloy by forming intermetallic compounds such as Al with Al by the addition of alloy elements2Ca and Al2Sm and the like, these intermetallic compounds being capable of replacing beta-Mg17Al12The phase is used as a cathode to participate in corrosion, and alloy corrosion is inhibited. In addition, the addition of some elements, such as Y and Nd, can reduce the alpha-Mg phase and beta-Mg17Al12The potential difference between the phases slows down the galvanic corrosion rate, thereby improving the corrosion resistance of the alloy. However, alloying treatment has some problems, for example, the addition of Ca can improve the corrosivity of the AZ91 alloy, but can reduce the mechanical property of the alloy at normal temperature; intermetallic compounds formed after the addition of some elements cause more severe galvanic corrosion, such as Mg3Bi2And Mg3Sb2Etc.; although rare earth elements are beneficial to improving the corrosion resistance of AZ91 alloy, the scarcity and strategic resource of rare earth elements still limit the application of rare earth elements. Therefore, it is necessary to find a new, alternative corrosion-resistant method without compromising the mechanical properties.
The method comprises the steps of adding thermodynamically stable and chemically stable nano TiCN ceramic particles into Mg-Al alloy melt, dispersing the particles into the alloy melt by adding the improved particles in batches and assisting in a variable-frequency high-energy ultrasonic treatment method, and then molding by adopting a mold with a lower cooling speed. The corrosion resistance of the alloy is obviously improved by testing means such as electrochemistry, scanning and the like.
Disclosure of Invention
The invention aims to provide a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy aiming at the defect problem in the traditional alloying treatment.
The invention aims to utilize the nano particles as a reinforcement, so that the corrosion resistance of Mg-Al alloy can be obviously improved, and the defects in the traditional alloying treatment can be overcome, namely the mechanical property is damaged while the corrosion resistance is improved. Provides a new way for the corrosion resistance research of Mg-Al alloy, in particular AZ91 alloy.
The purpose of the invention can be realized by the following scheme:
the invention provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, which comprises the following steps:
s1, dividing the nano particles to be added into a plurality of parts, wrapping the parts with aluminum foil to obtain particle aluminum packages, and preserving heat;
s2, uniformly mixing the raw materials of magnesium, aluminum and zinc, heating to melt, and then preserving heat to obtain an alloy melt;
s3, cooling the alloy melt obtained in the step S2, and adding the granular aluminum packets obtained in the step S1 into the alloy melt one by one; when the particle aluminum package is added, firstly pressing the particle aluminum package into the alloy melt, and then carrying out ultrasonic oscillation treatment;
and S4, heating and preserving heat of the alloy melt processed in the step S3, casting, controlling the cooling speed to be 5-10K/S, and cooling to obtain the alloy.
As an embodiment of the present invention, the Mg — Al alloy is an AZ91 alloy.
In one embodiment of the present invention, the nanoparticles in step S1 are TiCN nanoceramic particles, and have a particle size of 50 to 100 nm. Excessive nanoparticle sizes, such as those on the submicron or micron scale, are detrimental to corrosion because large size particles exacerbate localized corrosion of the particles, which is not the case with nanoparticles. If the particle size is too small, the clustering phenomenon becomes serious, which is not favorable for ultrasonic dispersion.
In one embodiment of the present invention, the nanoparticles are added in an amount of 0.5 to 2 vol.% based on the volume percentage of the base alloy in step S1. If the addition amount exceeds 2 vol%, the corrosion resistance is better than that of the original matrix, because the addition amount is too large, the clustering phenomenon of particles is serious, and the local corrosion of clustered particles is increased.
As an embodiment of the present invention, each part of the nanoparticles in step S1 is 0.2 vol.% to 0.25 vol.% in terms of the volume percentage of the base alloy. The volume percentage is preferably 0.25 vol.%.
In one embodiment of the present invention, the temperature in step S1 is 250 to 300 ℃. At this temperature, the aluminum foil can be melted rapidly after being added to the melt. The heat preservation is carried out in a heat preservation furnace.
As an embodiment of the present invention, the raw material in step S2 includes the following components by weight percentage: 8.7-9.8% of aluminum, 0.5-1.2% of zinc and the balance of magnesium. The magnesium, the aluminum and the zinc are all industrial pure magnesium, pure aluminum and pure zinc, and the purity reaches 99.9 percent.
In one embodiment of the present invention, the heating temperature in step S2 is 720 to 740 ℃, and the holding time is 25 to 30 min.
As an embodiment of the present invention, after the heat-insulating operation in step S2, dross on the surface of the melt is removed, refining and stirring are performed to mix the melt uniformly, and a second heat-insulating operation is performed to remove surface dross, thereby obtaining an alloy melt for use. The heat preservation is to ensure that the alloy is more fully melted and the components are more uniform, and also has the function of removing scum, and the scum is formed on the surface after the heat preservation, so the heat preservation is carried out before and after refining.
According to one embodiment of the invention, the refining time is 5-10 min, and the second heat preservation time is 10-15 min.
In one embodiment of the present invention, the temperature after the temperature reduction in step S3 is 670 to 690 ℃. The temperature is preferably 680 ℃. The temperature is the optimal temperature obtained by multiple experiments, the temperature is too high, and the viscosity of the melt is low; the temperature is too low and the viscosity of the liquid is too high. Too high or too low is detrimental to the subsequent ultrasound dispersion of the particles.
As an embodiment of the invention, in the step S3, the granular aluminum packet is pressed into the middle lower part of the alloy melt when being added into the alloy melt, kept for 10-15 min, and then subjected to ultrasonic vibration treatment. The step is to melt the aluminum foil and separate the nano particles, and the step of placing the aluminum foil in the middle lower part of the melt is to prevent the particles from floating on the surface of the melt and to enable the particles to be completely dispersed in the melt, and if the aluminum foil is directly placed in the melt, the aluminum foil floats on the surface, so the aluminum foil needs to be placed in the middle lower part of the melt.
As an embodiment of the present invention, the ultrasonic oscillation treatment in step S3 specifically includes: and (3) immersing a probe of an ultrasonic generator into a position 20-25 mm below the liquid level of the alloy melt, starting an ultrasonic generation switch, and taking out the ultrasonic probe after selecting variable-frequency ultrasonic vibration for 10-15 min. The nano ceramic particles coated by the aluminum foil can be well and uniformly dispersed in the obtained alloy melt through batch and variable-frequency ultrasonic vibration. The ultrasonic treatment has a good effect on dispersing the nano particles, and the particles cannot be well dispersed in the melt without ultrasonic treatment, so that the nano particle layer distributed on the grain boundary cannot be obtained in the solidification process, and the improvement on the corrosion performance cannot be realized. After the ultrasonic oscillation treatment, the next batch of particles is added, and the process is repeated when each batch is added. Until the final addition amount of the nanoparticles is the target addition amount.
In one embodiment of the present invention, the temperature of the step S4 is 720-740 ℃, and the time of heat preservation is 10-15 min. The heating and the heat preservation are to ensure that the melt has better fluidity in the subsequent pouring process and can better fill the mold.
As an embodiment of the present invention, the whole process of step S4 is performed under a protective atmosphere. The shielding gas is CO2And SF6The volume ratio is 1: 1. Oxygen can be isolated under the protective atmosphere, and the magnesium melt is prevented from burning.
The invention also provides application of the salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy in a neutral brine corrosion environment. The application is particularly the application in the preparation of neutral brine corrosion resistant products.
For Mg-Al alloy, the corrosion mechanism is mainly alpha-Mg and beta-Mg17Al12The addition of particles can be in alpha-Mg and beta-Mg17Al12Forming a corrosion barrier layer at the interface to inhibit Cl-The penetration of (2).
The invention uses a frequency conversion high-energy ultrasonic vibration method to add aluminum foil wrapped nano particles into AZ91 alloy melt in batches, so as to achieve the purpose of uniformly dispersing the nano particles in magnesium liquid. And secondly, selecting a cooling mould with relatively low cooling speed (about 5K/s) in the solidification process, and carrying out gravity casting molding. Because the cooling speed of the alloy melt in the solidification process is low, the solidification speed at the front edge of a solid-liquid interface is not enough to engulf the nano particles dispersed in the melt, so that the nano particles can be pushed to the surface of primary alpha-Mg and can be positioned on the surface of the primary alpha-Mg and eutectic beta-Mg17Al12And (4) enriching at the phase interface to form a nanoparticle layer. As the particles are ceramic inert particles and have a crystallography matching relation with alpha-Mg, stronger bonding force can be provided and the bonding force can be resistedHindered Cl～Further penetration of ions at the grain boundaries slows alloy corrosion. In addition, the enriched nano-particle layer formed at the grain boundary can block Al fusant diffusion, so that a large amount of Al fusant atoms are supersaturated and dissolved in the alpha-Mg matrix in a solid solution manner, the potential of the alpha-Mg matrix is improved, and the beta-Mg matrix is reduced17Al12The potential difference of the phases is greatly reduced, and the alpha-Mg and the beta-Mg are greatly reduced17Al12The galvanic corrosion speed between the two layers can achieve the purpose of improving the corrosion resistance of the Mg-Al alloy.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with the traditional dispersion method of adding nano particles at one time and assisting constant frequency ultrasonic treatment, the dispersion method of adding nano particles at one time and assisting variable frequency high energy ultrasonic treatment adopted by the invention has the advantages that the problem of serious particle clusters caused by adding a large amount of particles at one time is solved, and the problems of serious ultrasonic power loss, poor dispersion effect and the like caused by long-time operation in a constant frequency mode can be reduced by adopting the variable frequency high energy ultrasonic vibration method. The method has the characteristics of high efficiency, stability and good dispersion effect.
(2) Through electrochemical performance tests, the corrosion current of the nano-particle reinforced AZ91 alloy in 3.5 wt.% NaCl is 2.039 muA-cm～2Corrosion current 17.81 μ A cm with AZ91 alloy without added particles～2Compared with the prior art, the corrosion resistance of the alloy can be improved by 88.5 percent, and the alloy has obvious corrosion inhibition effect in neutral salt water.
(3) The nano-particle reinforced Mg-Al alloy can break through the defect that the corrosion performance and the mechanical property are not matched in the traditional alloy treatment method. While the corrosion performance is improved, the nano particles can be used as a strengthening phase to block dislocation movement and improve the mechanical property of the alloy.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention to its proper form. It is obvious that the drawings in the following description are only some embodiments, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a Tafel polarization curve test plot of examples 1-3 of the present invention and comparative examples 1-3 in a 3.5 wt.% NaCl solution;
FIG. 2 is a graph of electrochemical impedance measurements of examples 1 to 3 of the present invention and comparative examples 1 to 3 in a 3.5 wt.% NaCl solution;
FIG. 3 is a graph of the morphology of examples 1 to 3 of the present invention and comparative example 1 after etching in a 3.5 wt.% NaCl solution;
FIG. 4 is a longitudinal depth profile after examples 1-3 and comparative example 1 of the present invention have been etched in a 3.5 wt.% NaCl solution, where a is the longitudinal depth profile of comparative example 1, b is the longitudinal depth profile of example 1, c is the longitudinal depth profile of example 2, and d is the longitudinal depth profile of example 3;
FIG. 5 is a distribution diagram of nanoparticles in an alloy, wherein a is a distribution diagram of nanoparticles which are not added in batches in comparative example 2, and b is a distribution diagram of nanoparticles which are added in batches in example 3;
FIG. 6 is a graph showing the distribution of nanoparticles at different cooling rates, wherein a is the distribution of nanoparticles at a cooling rate of 5K/s in comparative example 3, and a is the distribution of nanoparticles at a cooling rate of 60K/s in example 3;
FIG. 7 is a schematic illustration of the nanolayers of the alloy of example 3 at the grain boundaries.
Detailed Description
The technical solution of the present invention is further specifically described below with reference to specific examples and drawings. It should be understood that the following specific examples are illustrative only and are not limiting upon the present invention. The described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any inventive work belong to the protection scope of the present invention.
Example 1
The embodiment provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, wherein the content of nanoparticles is 0.5% of the volume fraction of a basic alloy, and the specific steps are as follows:
s1, dividing TiCN nano ceramic particles with the content of 0.5% of the volume fraction of the basic alloy into 2 parts, wrapping the particles with aluminum foil, and obtaining particle aluminum wraps, wherein the minimum measurement unit of the nano particles is 0.25 vol%, and keeping the temperature to 300 ℃ for later use;
s2, uniformly mixing 99.9-99.99% of pure magnesium, 99.9-99.99% of pure aluminum and 99.9-99.99% of pure zinc according to the proportion of AZ91 alloy components, 9% of aluminum, 9% of zinc and the balance of magnesium, placing the mixture in a smelting furnace, heating to 740 ℃, preserving heat for 30min after the raw materials are completely melted, stirring to uniformly mix alloy melt, removing scum on the surface of the melt after heat preservation operation, refining for 10min, stirring to uniformly mix the melt, preserving heat for 10min again and removing the scum on the surface to obtain the alloy melt;
s3, adding the granular aluminum packets in the step S2 into the alloy melt in the step S1 one by one, and controlling the temperature of the alloy melt to be 680 ℃; when each particle aluminum package is added, firstly pressing the particle aluminum package into the middle lower part of the alloy melt, keeping for 10min, then immersing a probe of an ultrasonic generator into a position 20-25 mm below the liquid level of the alloy melt, starting an ultrasonic generation switch, selecting variable frequency ultrasonic vibration for 10min, taking out the ultrasonic probe, and then adding the next batch of particles. Note that the above process is to be followed for each batch addition. Until the final addition amount of the nano particles is the target addition amount;
and S4, heating the alloy melt processed in the step S3 to 740 ℃, preserving heat for 10min, casting the alloy melt into a Y-shaped iron mold, controlling the cooling speed to be 5K/S, and cooling to obtain the alloy.
Example 2
This example provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, which is similar to example 1, except that: the nanoparticle content was 1.0% of the volume fraction of the base alloy.
Example 3
This example provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, which is similar to example 1, except that: the content of the nano particles is 2.0 percent of the volume fraction of the base alloy.
Comparative example 1
This comparative example was prepared in the same manner as example 1 to obtain a set of Mg-Al alloys containing no nanoparticles for comparison.
Comparative example 2
The comparative example provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, which is similar to that of example 1 and is characterized in that: the nanoparticles were not added in portions, but were added directly at once.
Comparative example 3
The comparative example provides a preparation method of a salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy, which is similar to that of example 1 and is characterized in that: the cooling rate was 60K/s.
And (3) performance testing: the polarization curve and the electrochemical impedance spectrum were tested by the Princeton electrochemical workstation. The test system is a three-electrode system, wherein the counter electrode is a graphite electrode, the reference electrode is a saturated KCl electrode, and the area of the test surface is 1cm2. Firstly, soaking a sample in 3.5 wt.% NaCl solution for 1h, and carrying out impedance spectroscopy test after the open-circuit potential is stable. The test frequency range of the impedance spectrum is 100000HZ at the beginning to 0.01HZ at the end. Then, a polarization curve test is carried out, the tested potential range is +/-0.25V vs OCP, and the scanning speed is 1mV/s.
Note that the graphs of the examples were analyzed to analyze the corrosion performance of the alloys as a function of the amount of particulate added.
The results are shown in fig. 1, 2 and the following table, fig. 1 is the results of Tafel polarization curve test of the examples and comparative examples in 3.5 wt.% NaCl solution, and fig. 2 is the results of electrochemical impedance test of the examples and comparative examples in 3.5 wt.% NaCl solution. It can be seen that the corrosion performance of the AZ91 alloy gradually improved with increasing nanoparticle content. Among them, the alloy containing 2.0 vol.% of NPs is the best in corrosion resistance, and the polarization resistance is from 261.36. omega. cm～2Increased to 1211.39 Ω · cm～2The corrosion current is from 17.81 muA cm～2Reduced to 2.039 muA-cm～2The corrosion resistance efficiency can reach 88.5 percent. Fig. 3 is the morphology of the examples and comparative examples after etching for 24h in a 3.5 wt.% NaCl solution, from which it can also be seen that the maximum etching depth of the AZ91 alloy decreases from 605 μm to 217 μm with increasing nanoparticle content. Similarly, fig. 4 is the longitudinal depth profile of the example and the comparative example after 24h corrosion in 3.5 wt.% NaCl solution, and it can be seen that as the particle content increases, the alloy corrodes the surface cracks to change from coarse cracks to fine cracks, and meanwhile, the O content gradually decreases, and the specific gravity of the corrosion product gradually decreases, further proving that the addition of the nanoparticles has a good inhibition effect on the corrosion of AZ91 magnesium alloy in neutral brine. In addition, 2.0 vol.% in the optimum addition amount compares the corrosion performance of the AZ91 alloy after one-time addition and batch addition, as shown in fig. 1, fig. 2 and table 1, it can be seen that the corrosion performance of the alloy after one-time addition is far inferior to that of the alloy after batch addition, even worse than that of the alloy without particles, which further illustrates that the dispersibility of the particles added in batches is better, the clusters are fewer, and thus the local cluster corrosion is greatly reduced. Finally, studies were made on alloys solidified at a high cooling rate (60K/s), and comparing the corrosion resistance of alloys cooled at around 5K/s, as shown in fig. 1, fig. 2 and table 1, the corrosion resistance was reduced because nanoparticles were phagocytosed by the solidified solid-liquid interface at the high cooling rate, a nano layer could not be formed, corrosion could not be inhibited, and the corrosion resistance was reduced. Compared with the base alloy without the added particles, the corrosion performance is similar.
TABLE 1
Figure BDA0003380390390000071
From fig. 5, it is clear that the effect of the non-portioned addition and the portioned addition are compared, both in an amount of 2.0 vol.%. The power of the ultrasonic probe in the high-temperature environment is reduced along with the loss of time. And can be rendered ultrasonically dispersible if too many nanoparticles are added at onceThe effect is greatly reduced, and the obtained result is as shown in fig. 5a, the clustering phenomenon of the nanoparticles is serious, and the clusters are relatively large-sized clusters, which are not pushed by a solidified solid-liquid interface in the solidification process, but are phagocytized, so that the clusters are distributed in the crystal. Thereby causing localized corrosion without utilizing the alloy corrosion properties. By adopting the batch adding method and the variable frequency ultrasonic treatment method, the particles added in batches can be well dispersed under the condition of low power loss of the ultrasonic probe, and finally, the dispersion result obtained by dispersing for a plurality of times is good by continuously adding for a plurality of times, as shown in fig. 5 b. Because the dispersion effect of the melt is good, the melt can be pushed by a solidified solid-liquid interface in the solidification process and finally enriched at a crystal boundary to form a shell layer, thereby effectively inhibiting Cl～The penetration of ions at the grain boundary improves the corrosion resistance.
As shown in fig. 6, the cooling rate should not be too high here, because too high a cooling rate would make the solid-liquid interface shift speed during solidification too fast, so that the particles are engulfed into the crystal and not distributed in the grain boundary. As can be seen from the figure, the nanoparticles are distributed at the grain boundaries at 5K/s and within the crystal at 60K/s. The particles are distributed within the crystal and their corrosion inhibiting effect is lost. Thereby having no promotion effect on the corrosion performance of the alloy.
Compared with the conventional one-time addition of the nanoparticles, the nanoparticle shell is formed by the fact that the particles are spontaneously adsorbed on the alpha-Mg surface through own Brownian motion and are not influenced by the cooling speed, and therefore the shell distributed in the grain boundary is not as dense as the particles added in batches. According to the invention, by adding the components in batches and controlling the cooling speed to be about 5K/s, most of dispersed particles can be pushed to a crystal boundary by a solid-liquid interface with a lower speed to form a shell layer with better compactness, and importantly, the dispersed particles are not distributed in the crystal and cannot cause local corrosion of the particles. In addition, by utilizing the method provided by the invention, a coherent relationship exists between partial nano particles and Mg at a grain boundary, so that the method has better lattice matching degree and can provide better bonding force.
As shown in FIG. 7, since the corrosion of AZ91 alloy is galvanic corrosion, corrosion occurredThe sites of erosion will preferentially occur at the interface of the beta phase with the alpha-Mg, i.e., the grain boundaries. The nano-layer can block Cl～And secondly, Al fusant atoms in the alpha-Mg can be inhibited from diffusing from the alpha-Mg, so that the Al fusant atoms are supersaturated and solid-dissolved in an alpha-Mg matrix, and the potential of the alpha-Mg matrix is improved. The galvanic corrosion between the beta phase and the alpha-Mg is mainly caused by the overlarge potential difference between the two phases, and the potential difference between the two phases is reduced and the galvanic corrosion rate is greatly reduced when the potential of the alpha-Mg matrix is increased. The nano-shell layer thus inhibits corrosion in both respects. More intuitively, it can be seen from electrochemical tests that the nano shell formed by the conventional method has insufficient compactness, poor binding force, poor corrosion inhibition capability and even aggravated corrosion. The corrosion performance in this application can be improved by up to 88.5% compared to the substrate.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of through the inventive work should be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.

Claims (10)

1. A preparation method of salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy is characterized by comprising the following steps:
s1, dividing the nano particles to be added into a plurality of parts, wrapping the parts with aluminum foil to obtain particle aluminum packages, and preserving heat;
s2, uniformly mixing the raw materials of magnesium, aluminum and zinc, heating to melt, and then preserving heat to obtain an alloy melt;
s3, cooling the alloy melt obtained in the step S2, and adding the granular aluminum packets obtained in the step S1 into the alloy melt one by one; when the particle aluminum package is added, firstly pressing the particle aluminum package into the alloy melt, and then carrying out ultrasonic oscillation treatment;
and S4, heating and preserving heat of the alloy melt processed in the step S3, casting, controlling the cooling speed to be 5-10K/S, and cooling to obtain the alloy.
2. The method according to claim 1, wherein the nanoparticles in step S1 are TiCN nano-ceramic particles having a particle size of 50-100 nm.
3. The method of claim 1, wherein the nanoparticles are added in an amount of 0.5-2 vol.% based on the volume percentage of the base alloy in step S1.
4. The method of claim 1, wherein the volume percentage of each nanoparticle in the base alloy in step S1 is 0.2 vol.% to 0.25 vol.%.
5. The preparation method according to claim 1, wherein the raw material in the step S2 comprises the following components in percentage by weight: 8.7-9.8% of aluminum, 0.5-1.2% of zinc and the balance of magnesium.
6. The method according to claim 1, wherein the heating temperature in step S2 is 720-740 ℃, and the holding time is 25-30 min.
7. The method according to claim 1, wherein the temperature after the temperature reduction in step S3 is 670 to 690 ℃.
8. The preparation method according to claim 1, wherein the granular aluminum packet in the step S3 is pressed into the middle lower part of the alloy melt when being added into the alloy melt, kept for 10-15 min, and then subjected to ultrasonic vibration treatment.
9. The method according to claim 1, wherein the temperature in step S4 is 720-740 ℃, and the holding time is 10-15 min.
10. Use of the salt solution corrosion resistant nanoparticle reinforced Mg-Al alloy of claim 1 in a neutral brine corrosion environment.
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CN112941384A (en) * 2021-01-11 2021-06-11 南昌大学 Method for preparing carbon nano material reinforced AZ91 alloy semi-solid slurry

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CN107083508A (en) * 2017-04-17 2017-08-22 扬州峰明光电新材料有限公司 A kind of polynary enhanced heat-proof corrosion-resistant magnesium alloy and its manufacture method
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