Nanoparticle-reinforced magnesium-based composite material and method for producing same

Abstract

The present application relates to a kind of nanoparticle reinforced magnesium-based composite material and its preparation method, the method includes the following steps: nanoparticle is uniformly dispersed with salt with water, obtain nanoparticle salt solution;Nanoparticle salt solution is dried, obtain the mixture of nanoparticle and salt;Nanoparticle and salt mixture are placed under high temperature condition to make salt melt, obtain molten salt-based nanofluid;Magnesium is added to molten salt-based nanofluid and melts, forms smelting system;Smelting system is carried out high-temperature heat preservation treatment, then after solidification, nanoparticle reinforced magnesium-based composite material is prepared.The present application is based on liquid metallurgy method, at high temperature, without using protective gas, also can avoid the oxidation combustion of nanoparticle and magnesium melt at high temperature, without mechanical stirring, also can realize the good compounding of nanoparticle and magnesium melt, can avoid the problem that more pore, inclusion defects are in composite material, is favorable to improve the mechanical properties of material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium-based composite material, and particularly relates to a kind of nano-particle reinforced magnesium-based composite material and a preparation method thereof. BACKGROUND

[0002] The particle reinforced magnesium-based composite material has low density, high strength, rigidity and good anti-creep performance, and can be applied in machinery, electronics, aviation, medicine and daily industry. Reducing the size of the reinforcing body from micron level to nanometer level (nano-particle) can significantly improve the mechanical properties of the matrix, while the elongation of the matrix alloy is maintained. To manufacture the nano-metal particle reinforced magnesium-based composite material with excellent mechanical properties, the first major problem is that the nano-particle is more likely to burn than the ceramic nano-particle, and the nano-particle is easy to agglomerate due to its small particle size. Therefore, it is difficult to uniformly disperse the metal nano-particle in the magnesium melt.

[0003] Currently, there are various forms of preparation methods for the nano-particle reinforced magnesium-based composite material, and the main methods include powder metallurgy, friction stir processing and stir casting.

[0004] The powder metallurgy for preparing the nano-particle reinforced magnesium-based composite material is limited by the oxidation of the nano-particle and magnesium powder, which ultimately affects the overall performance of the composite material. The magnesium powder is flammable, explosive and easy to oxidize, which poses a great safety hazard.

[0005] The action area of the friction stir processing is limited to the metal matrix near the stirring head, which is not suitable for processing and dispersing of thick metal. At the same time, due to the disorder of the severe plastic deformation process, the stability of the composite material performance is poor, and the size constraint is high.

[0006] As for the stir casting method, firstly, due to the physicochemical properties of the nano-particle, especially the nano-metal particle, the surface is easy to adsorb impurities, causing agglomeration. The nano-metal particle is also easy to oxidize and burn at a relatively low temperature of 50-100°C, resulting in poor dispersion effect. Secondly, the magnesium and magnesium alloy melt is also easy to burn at high temperature due to its activity, and a protective film (such as magnesium fluoride film) needs to be formed on the surface of the magnesium or magnesium alloy melt to protect the melt from burning. However, the formation of the protective film hinders the combination of the magnesium or magnesium alloy melt and the nano-reinforcing body, leading to difficulty in their combination. In order to promote the dispersion and combination of the nano-reinforcing body and the magnesium or magnesium alloy melt, mechanical stirring measures need to be taken. Under mechanical stirring, the protective film on the surface of the melt and the protective gas in the crucible will enter the melt, eventually causing an increase in the porosity and inclusion defects of the magnesium-based composite material, resulting in a decrease in the mechanical properties of the material.

[0007] Therefore, these methods still have technical deficiencies for the preparation of the nano-particle reinforced magnesium-based composite material.

[0008] In view of the above, it is necessary to provide a new kind of nanoparticle reinforced magnesium matrix composite material and a preparation method thereof. SUMMARY

[0009] In order to solve one or more technical problems in the prior art, the present application provides a kind of nanoparticle reinforced magnesium matrix composite material and a preparation method thereof.The present application is based on liquid metallurgy method, at high temperature, without using protective gas, also can avoid the oxidation combustion of nanoparticle and magnesium melt at high temperature, without mechanical stirring, also can realize the good composite of nanoparticle and magnesium melt, can avoid the problem of more pores, inclusion defects in composite material, is beneficial to improve the mechanical properties of material.

[0010] The present application provides a kind of nanoparticle reinforced magnesium matrix composite material and a preparation method thereof in the first aspect, the method comprises the following steps:

[0011] (1) uniformly disperse nanoparticle with salt with water, obtain nanoparticle salt solution;

[0012] (2) nanoparticle salt solution is dried, obtains the mixture of nanoparticle and salt;

[0013] (3) the mixture of nanoparticle and salt is placed under high temperature condition to make salt melt, obtain molten salt based nanofluid;

[0014] (4) to molten salt based nanofluid join magnesium and make magnesium melt, form smelting system;

[0015] (5) the smelting system is carried out high temperature heat preservation treatment, again after solidification, prepare nanoparticle reinforced magnesium matrix composite material.

[0016] Preferably, the nanoparticle is metal carbide nanoparticle or pure metal nanoparticle;And / or the salt is chloride of alkali metal and / or fluoride of alkali metal.

[0017] Preferably, the metal carbide nanoparticle is TiC nanoparticle, the pure metal nanoparticle is Ti nanoparticle;And / or the salt is at least two kinds of NaCl, CaF2, NaF, KCl, MgF2, CaCl2.

[0018] Preferably, the nanoparticle is Ti nanoparticle, the salt is the mixture of NaCl, CaF2, MgF2 and CaCl2, preferably, the salt is mixed by NaCl, CaF2, MgF2 and CaCl2 with mass ratio (4-6) :(0.5-1.5) :(0.5-1.5) :(2-4).

[0019] Preferably, the nanoparticles are TiC nanoparticles, and the salt is a mixture of NaCl, CaF2 and CaCl2, preferably, the salt is a mixture of NaCl, CaF2 and CaCl2 with a mass ratio of (6-8):(4-6):(4-6).

[0020] Preferably, in step (1), the dispersion is carried out by stirring for 0.5-1.5h, preferably 1h, and ultrasonic treatment for 2-4h, preferably 3h.

[0021] Preferably, in step (1), the mass ratio of the nanoparticles to the salt is 1:(8-12), preferably 1:10.

[0022] Preferably, in step (2), the drying temperature is 180-250℃, preferably 200℃, and the drying time is 10-20h, preferably 12h; and / or in step (3), the mixture of the nanoparticles and the salt is placed in a graphite crucible and melted at 700-750℃.

[0023] Preferably, in step (4), magnesium is added to the molten salt based nanofluid at 750-780℃ and melted to form a smelting system with a layered structure of the molten salt based nanofluid and the magnesium melt; and / or in step (5), the high temperature holding treatment is carried out at 780-900℃, preferably 800-820℃, and the high temperature holding treatment time is 1-3h, preferably 2h.

[0024] Preferably, the volume ratio of the magnesium to the amount of the nanoparticles is 100:(1-12), preferably 100:(5-12).

[0025] The present application provides, in a second aspect, a nanoparticle reinforced magnesium matrix composite prepared by the method of the first aspect of the present application.

[0026] Compared with the prior art, the present application has at least the following beneficial effects:

[0027] (1) The present application realizes preliminary modification of the nanoparticles by pre-dispersing the nanoparticles in the salt at room temperature, reduces the surface pollution and the surface oxide of the nanoparticles, and is conducive to promoting the wetting and compounding of the nanoparticles and the magnesium melt. The present application forms a molten salt-based nanofluid at high temperature, effectively avoids the oxidation and combustion of the magnesium melt under the protection of the molten salt-based nanofluid, does not need to use a protective gas to form a protective film on the surface of the magnesium melt for protection, and does not need to use mechanical stirring to promote the dispersion and compounding of the nanoparticles and the magnesium melt, so that the nanoparticles and the magnesium melt can be well compounded. Since the present application does not need to use mechanical stirring, the problems of pores and inclusion defects of the magnesium-based composite material can be obviously avoided, and the mechanical properties of the material can be improved. The volume fraction of the nanoparticles in the obtained nanoparticle reinforced magnesium-based composite material can reach 5% to 10%.

[0028] (2) The present application pre-disperses the nanoparticles in the salt at room temperature, performs surface modification on the nanoparticles, creates good conditions for the wetting of the nanoparticles and the magnesium melt, significantly reduces the wetting angle of the nanoparticles and the magnesium melt at high temperature, and effectively reduces the agglomeration of the nanoparticles due to the double electric layer effect of the surface of the nanoparticles in the molten salt. The nanoparticles are uniformly distributed in the magnesium and are well dispersed.

[0029] (3) Unlike the relatively low smelting temperature (about 750°C) in the prior art, the present application effectively avoids the oxidation and combustion of the magnesium melt and the nanoparticles under the protection of the molten salt-based nanofluid, and especially can realize the compounding of the magnesium melt and the nanoparticles at a higher temperature. With the increase of the temperature, the wettability of the nanoparticles and the magnesium melt is significantly improved, which is another key to realize the compounding of the nanoparticles and the magnesium melt. The method of the present application can realize higher temperature smelting, such as smelting at 900°C or higher than 900°C in an atmospheric state. In addition, it is well known that titanium nanoparticles are particularly prone to combustion and are difficult to be used to prepare a titanium nanoparticle reinforced magnesium-based composite material by liquid metallurgy without introducing other alloy powders or protective layers. However, the present application can also avoid the oxidation and combustion of titanium nanoparticle metal under the protection of the molten salt-based nanofluid. The present application is the first to realize the preparation of a titanium nanoparticle reinforced magnesium-based composite material by liquid metallurgy without mixing alloy powders into the titanium nanoparticles or introducing a protective layer on the surface of the titanium nanoparticles. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a preparation flowchart of the present application.

[0031] Figure 2 is a physical property analysis spectrum (XRD spectrum) of the nanoparticle reinforced magnesium-based composite material prepared in Example 1 of the present application.

[0032] Figure 3is a physical property analysis pattern (XRD pattern) of the nanoparticle reinforced magnesium-based composite material prepared in Example 2 of the present application.

[0033] Figure 4 is a micro-morphology pattern (SEM pattern) of the nanoparticle reinforced magnesium-based composite material prepared in Example 1 and Comparative Example 2 of the present application; in the figure, (a) corresponds to the nanoparticle reinforced magnesium-based composite material prepared in Example 1, and (b) corresponds to the nanoparticle reinforced magnesium-based composite material prepared in Comparative Example 2.

[0034] Figure 5 is a quasi-static compression stress-strain curve of the nanoparticle reinforced magnesium-based composite material prepared in Example 3 of the present application. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0036] The present application provides, in a first aspect, a preparation method of a self-dispersed and self-protected nanoparticle reinforced magnesium-based composite material, and the method comprises the following steps:

[0037] (1) uniformly dispersing the nanoparticles and the salt with water to obtain a nanoparticle salt solution; in the present application, the water may be, for example, distilled water, the nanoparticles may be, for example, metal carbide nanoparticles and / or pure metal nanoparticles, and the salt may be, for example, a chloride of an alkali metal and / or a fluoride of an alkali metal; in the present application, the dispersing is performed, for example, by stirring and ultrasonic in sequence, specifically, the nanoparticles and the salt mixed in a certain proportion are added to distilled water, and the nanoparticles are pre-dispersed by using a stirring coupling ultrasonic method to prepare a nanofluid at room temperature, i.e. the nanoparticle salt solution; in the present application, the amount of the water may be, for example, 3-5 times the total mass of the nanoparticles and the salt;

[0038] (2) drying the nanoparticle salt solution to obtain a mixture of the nanoparticles and the salt, i.e. to obtain a solid uniform mixture of the nanoparticles and the salt;

[0039] (3) melting the salt under high temperature conditions to obtain a molten salt-based nanofluid; specifically, the uniformly mixed mixture of the nanoparticles and the salt is added to a graphite crucible (also referred to as a graphite smelting crucible) under high temperature, so that the salt is quickly melted to form a molten salt-based nanofluid at high temperature;

[0040] (4) adding magnesium into the molten salt based nanofluid and melting the magnesium to form a smelting system; specifically, for example, adding magnesium ingot into the molten salt based nanofluid, the magnesium, due to its high density, sinks to the bottom of the graphite crucible and melts quickly, and the smelting system is formed from top to bottom, and the layered structure of the molten salt based nanofluid and the magnesium melt is formed, i.e. the smelting system with the layered structure of the molten salt based nanofluid and the magnesium melt is formed;

[0041] (5) subjecting the smelting system to high-temperature holding treatment, and then solidifying to obtain a nano-particle reinforced magnesium matrix composite material; based on the good wettability of the nano-particles with the magnesium melt at high temperature and the significant reduction of the viscosity of the molten salt at high temperature, during the high-temperature holding treatment, the nano-particles in the molten salt based nanofluid will be transferred from the molten medium of the molten salt based nanofluid to the magnesium melt through spontaneous Brownian thermal motion, and finally a magnesium matrix composite material rich in nano-particle reinforcements is obtained; preferably, the volume fraction of the nano-particles contained in the nano-particle reinforced magnesium matrix composite material is 5% to 10%.

[0042] It is particularly pointed out that the steps (1) to (5) in the present application do not need to use a protective gas and are directly carried out in an atmospheric state (atmospheric environment).

[0043] The method for preparing a nano-particle reinforced magnesium matrix composite material of the present application overcomes the technical deficiencies of the powder metallurgy method, the friction stir method, the stir casting method and other methods, and is based on liquid metallurgy. The nano-particles are pre-dispersed in the salt at room temperature to achieve preliminary modification of the nano-particles, reduce the surface pollution and the oxides on the surface of the nano-particles, and facilitate the wettability and compounding of the nano-particles with the magnesium melt. The present application constructs a molten salt based nanofluid at high temperature through a suitable high-temperature thermal dispersion medium, avoids oxidation and combustion of the nano-particles and the magnesium melt at high temperature without using a protective gas, creates high-temperature conditions for wettability and dispersion while protecting the magnesium melt from oxidation and combustion, and realizes good compounding of the nano-particles with the magnesium melt without mechanical stirring, which can avoid the problems of many pores and inclusions in the composite material and is beneficial to improving the mechanical properties of the material. The pre-dispersion of the nano-particles in the salt at room temperature in the present application modifies the surface of the nano-particles, creates good conditions for the wettability of the nano-particles with the magnesium melt, significantly reduces the wetting angle of the nano-particles with the magnesium melt at high temperature, and effectively reduces the agglomeration of the nano-particles due to the double electric layer effect on the surface of the nano-particles in the molten salt. The nano-particles are uniformly distributed in the magnesium and are well dispersed.

[0044] According to some preferred embodiments, the nano-particles are metal carbide nano-particles or pure metal nano-particles; and / or the salt is a chloride of an alkali metal and / or a fluoride of an alkali metal.

[0045] According to some preferred embodiments, the metal carbide nanoparticles are TiC nanoparticles, the pure metal nanoparticles are Ti nanoparticles; and / or the salt is at least two of NaCl, CaF2, NaF, KCl, MgF2, CaCl2; the present application does not make specific limitations on the particle size and source of TiC nanoparticles and Ti nanoparticles, and products available on the market or prepared by existing methods can be directly used; the present application does not make specific limitations on the source of NaCl, CaF2, NaF, KCl, MgF2, CaCl2, and products available on the market can be directly used.

[0046] According to some preferred embodiments, the nanoparticles are Ti nanoparticles, and the salt is a mixture of NaCl, CaF2, MgF2 and CaCl2, preferably, the salt is a mixture of NaCl, CaF2, MgF2 and CaCl2 with a mass ratio of (4-6):(0.5-1.5):(0.5-1.5):(2-4), more preferably, the salt is a mixture of NaCl, CaF2, MgF2 and CaCl2 with a mass ratio of 5:1:1:3.

[0047] It is well known that titanium nanoparticles are particularly prone to combustion, and it is difficult to realize the preparation of titanium nanoparticle reinforced magnesium matrix composites by liquid metallurgy without introducing other alloy powders or protective layers, but in the protection of the molten salt-based nanofluid, the titanium nanoparticle metal particles can also avoid oxidation and combustion, and the present application realizes the preparation of titanium nanoparticle reinforced magnesium matrix composites by liquid metallurgy without mixing alloy powders into titanium nanoparticles or introducing a protective layer on the surface of titanium nanoparticles for the first time.

[0048] According to some preferred embodiments, the nanoparticles are TiC nanoparticles, and the salt is a mixture of NaCl, CaF2 and CaCl2, preferably, the salt is a mixture of NaCl, CaF2 and CaCl2 with a mass ratio of (6-8):(4-6):(4-6), more preferably, the salt is a mixture of NaCl, CaF2 and CaCl2 with a mass ratio of 7:5:5.

[0049] The present application preferably mixes the salt and the nanoparticles in a suitable system in proportion to the characteristics of the magnesium matrix and to the different nanoparticle reinforcements; the present application finds that the salt can first remove the surface contaminants and the surface oxides of the nanoparticles, and second remove the surface oxides of the magnesium melt at high temperature; the present application preferably matches the salt with the nanoparticles and the magnesium melt, if the salt does not match the nanoparticles and the magnesium melt, first, there will be impurities on the surface of the nanoparticles, and second, the surface oxides of the magnesium melt are more difficult to be wetted, which will result in that the nanoparticles cannot be well compounded with the magnesium melt at high temperature spontaneously; in the present application, the surface contaminants and the surface oxides of the nanoparticles and the surface oxides of the magnesium melt will exist in the salt in the form of impurities after being treated by the salt, and will not enter the magnesium melt through spontaneous Brownian motion, and finally after the salt and impurities on the cast ingot are removed, the nanoparticle reinforced magnesium matrix composite material in the present application can be obtained, which can effectively solve the problem of more impurities in the nanoparticle reinforced magnesium matrix composite material in the prior art.

[0050] According to some preferred embodiments, in step (1), the dispersion is carried out by stirring (room temperature stirring) and ultrasonic (room temperature ultrasonic) in sequence, the stirring time is 0.5-1.5 h (for example 0.5, 1 or 1.5 h) preferably 1 h, and the ultrasonic time is 2-4 h (for example 2, 2.5, 3, 3.5 or 4 h) preferably 3 h; the present application does not make specific limitations on the conditions of the stirring (for example magnetic stirring) and ultrasonic, and conventional operations can be used; in the present application, the room temperature is for example 15-35℃; and / or in step (1), the mass ratio of the nanoparticles to the salt is 1:(8-12) (for example 1:8, 1:8.5, 1:9, 1:9.5, 1:10, 1:10.5, 1:11, 1:11.5 or 1:12) preferably 1:10.

[0051] According to some preferred embodiments, in step (2), the drying temperature is 180-250℃ (for example 180℃, 200℃, 220℃ or 250℃) preferably 200℃, and the drying time is 10-20 h (for example 10, 12, 14, 16, 18 or 20 h) preferably 12 h; and / or in step (3), the mixture of the nanoparticles and the salt is placed at 700-750℃ (for example 700℃, 710℃, 720℃, 730℃, 740℃ or 750℃) to melt the salt, preferably the mixture of the nanoparticles and the salt is placed in a graphite crucible to melt the salt at 700-750℃; in the present application, the smelting crucible is a high-temperature and oxidation-resistant graphite crucible (also referred to as a graphite smelting crucible) and is provided with a crucible cover.

[0052] According to some preferred embodiments, in step (4), the magnesium is added to the molten salt-based nanofluid and melted to form a smelting system having a layered structure of the molten salt-based nanofluid and the magnesium melt at 750-780°C (e.g. 750°C, 760°C, 770°C or 780°C); and / or in step (5), the temperature of the high-temperature holding treatment is 780-900°C (e.g. 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C), preferably 800-820°C (e.g. 800°C, 810°C or 820°C), and the time of the high-temperature holding treatment is 1-3h (e.g. 1, 1.5, 2, 2.5 or 3h), preferably 2h; in the present application, after the magnesium is melted to form the smelting system, it is more preferable that the temperature of the high-temperature holding treatment is 800-820°C, so as to match the critical temperature at which the wettability of the nanoparticles and the magnesium melt is improved; in the prior art, due to the problem of easy oxidation and combustion of the nanoparticles and the magnesium melt, it is generally not thought to increase the smelting temperature, because the higher the smelting temperature, the easier the oxidation of the nanoparticles and the magnesium melt, and in the prior art, a protective film is formed on the surface of the magnesium melt by the protective gas to protect, and due to the barrier of the protective film, even if the smelting temperature is increased, the wettability between the nanoparticles and the magnesium melt is not obviously improved; unlike the relatively low smelting temperature (about 750°C) in the prior art, in the present application, the magnesium melt and the nanoparticles can be protected from oxidation and combustion under the protection of the molten salt-based nanofluid, and in particular, the magnesium melt and the nanoparticles can be compounded at a higher temperature, and with the increase of the temperature, the wettability of the nanoparticles and the magnesium melt is significantly improved, which is another key to realize the compounding of the nanoparticles and the magnesium melt, and the method of the present application can realize smelting at a higher temperature, such as smelting at 900°C or higher than 900°C under atmospheric conditions.

[0053] According to some preferred embodiments, the volume ratio of the magnesium to the amount of the nanoparticles is 100:(1-12) (e.g. 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11 or 100:12), preferably 100:(5-12) (e.g. 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11 or 100:12); the volume fraction of the nanoparticles in the nanoparticles reinforced magnesium matrix composite prepared by the present application can reach 5%-10%, and the increase of the volume fraction of the nanoparticles can effectively improve the mechanical strength of the nanoparticles reinforced magnesium matrix composite; based on the characteristics of the nanometer-sized reinforcing agent, the nanoparticles reinforced magnesium matrix composite can maintain good plasticity compared with the micrometer-sized reinforcing agent, while the volume fraction of the nanoparticles in the nanoparticles reinforced magnesium matrix composite prepared by the prior art can only reach about 2%.

[0054] According to some specific embodiments, the method for preparing the nanoparticles reinforced magnesium matrix composite of the present application comprises the following steps:

[0055] ① Chemical material

[0056] The chemical material used in the present application is: magnesium, distilled water, nanoparticles (metal carbide ceramic or pure metal), at least two kinds of mixed salt selected from NaCl, CaF2, MgF2 and CaCl2, and graphite smelting crucible.

[0057] Pure magnesium: purity 99.9%;

[0058] Nanoparticles: titanium, average particle size 50 nm; in some other specific embodiments, nanoparticles: titanium carbide, average particle size 50 nm;

[0059] Smelting crucible: graphite smelting crucible;

[0060] NaCl: solid solid, purity 99.9%;

[0061] CaF2: solid solid, purity 99.9%;

[0062] MgF2: solid solid, purity 99.9%;

[0063] CaCl2: solid solid, purity 99.9%;

[0064] Distilled water.

[0065] ②Titanium nanoparticles are prepared according to the amount of magnesium (pure magnesium), and the amount of the nanoparticles is 5% of the volume of the pure magnesium.

[0066] ③Mix NaCl, CaF2, MgF2, CaCl2 in the proportion of (5:1:1:3) by mass, to obtain salt, then mix the nanoparticles and the salt in the proportion of (1:10) by mass, and then disperse them in distilled water.

[0067] ④Stir the solution of the nanoparticles and the salt for 1 hour by magnetic stirring.

[0068] ⑤After stirring, ultrasonically treat the solution of the nanoparticles and the salt for 3 hours to obtain a uniformly dispersed solution of the nanoparticles and the salt.

[0069] ⑥Dry the solution of the nanoparticles and the salt at 200℃ for 12 hours to obtain a mixture of the nanoparticles and the salt.

[0070] ⑦Preheat a graphite crucible to 750℃, and then add the mixture of the nanoparticles and the salt into the graphite crucible, melt the salt at 750℃ to form a molten salt-based nanofluid at high temperature, and then increase the temperature to 780℃. The time for melting the salt at 750℃ is not specifically limited in the present application, and the salt can be completely melted. For example, the time for melting the salt can be 15-30 minutes in the present application.

[0071] ⑧Add a pure magnesium ingot into the molten salt-based nanofluid at 780℃. The magnesium, due to its high density, sinks to the bottom of the crucible, and is rapidly melted in the molten salt-based nanofluid. The molten salt-based nanofluid and the magnesium melt form a layered structure from top to bottom. The time for melting the magnesium is not specifically limited in the present application, and the magnesium can be completely melted. For example, the time for completely melting the magnesium can be 15-30 minutes in the present application.

[0072] ⑨Cover the graphite crucible, and increase the temperature of the smelting system to 800℃ and keep it for 2 hours. The titanium nanoparticles have good wettability with the magnesium melt at 800℃, and the viscosity of the molten salt is significantly reduced. Therefore, the titanium nanoparticles are transferred from the molten salt-based nanofluid medium to the magnesium melt by spontaneous Brownian thermal motion.

[0073] ⑩Take out the graphite crucible from the smelting furnace, and solidify it at room temperature. The magnesium and the salt are separated, and the nanoparticles and the magnesium melt are well compounded to obtain a nanoparticle-reinforced magnesium-based composite material.

[0074] The present application provides, in a second aspect, a nanoparticle-reinforced magnesium-based composite material prepared by the preparation method described in the first aspect of the present application.

[0075] The present application will be further described below by way of examples, but the scope of protection of the present application is not limited to these examples.

[0076] Example 1

[0077] (1) 5% volume fraction of TiC nanoparticles is prepared according to the amount of magnesium (pure magnesium ingot), that is, the volume ratio of pure magnesium to TiC nanoparticles is 100:5; then NaCl, CaF2, and CaCl2 are mixed in a mass ratio of 7:5:5 to obtain a salt, and the TiC nanoparticles are uniformly mixed with the salt in a mass ratio of 1:10, and then dispersed in distilled water (the amount of distilled water is 3 times the mass of the sum of TiC nanoparticles and salt), first stirred at room temperature for 1 hour by magnetic stirring, and then ultrasonically treated at room temperature for 3 hours to obtain a uniformly dispersed nanoparticle salt solution.

[0078] (2) The nanoparticle salt solution is dried at 200°C for 12 hours to obtain a mixture of nanoparticles and salt.

[0079] (3) The graphite crucible is preheated to 750°C, and the mixture of nanoparticles and salt is added to the graphite crucible, and the salt is quickly melted at 750°C to form a molten salt-based nanofluid at high temperature, and then the temperature is raised to 780°C.

[0080] (4) The pure magnesium ingot is added to the molten salt-based nanofluid at 780°C, and the magnesium is melted in the molten salt-based nanofluid, and the magnesium sinks to the bottom of the graphite crucible due to its high density, forming a smelting system with a layered structure of molten salt-based nanofluid and magnesium melt.

[0081] (5) The lid of the graphite crucible is covered, the temperature of the smelting system is raised to 820°C, and the graphite crucible is taken out of the smelting furnace after being kept at temperature for 2h, and the solidified salt and impurities on the cast ingot are removed to obtain a nanoparticle reinforced magnesium matrix composite; steps (1) to (5) of this example are all carried out directly in the atmosphere without introducing a protective gas.

[0082] The micro-morphology diagram (SEM diagram) of the nanoparticle reinforced magnesium matrix composite prepared in this example is shown in Figure 4 From Figure 4 It can be seen that in this example, the TiC nanoparticles are uniformly distributed and well dispersed in the magnesium without stirring.

[0083] Example 2

[0084] (1) According to the amount of magnesium (pure magnesium ingot), 5% volume fraction of Ti nanoparticles is prepared, i.e. the volume ratio of pure magnesium to Ti nanoparticles is 100:5; then NaCl, CaF2, MgF2, CaCl2 are mixed in a mass ratio of 5:1:1:3 to obtain a salt, the Ti nanoparticles are uniformly mixed with the salt in a mass ratio of 1:10, and then dispersed into distilled water (the amount of distilled water is 3 times the mass of the sum of Ti nanoparticles and salt), first stirred at room temperature for 1 hour by magnetic stirring, and then ultrasonically treated at room temperature for 3 hours to obtain a uniformly dispersed nanoparticle salt solution.

[0085] (2) The nanoparticle salt solution is dried at 200℃ for 12 hours to obtain a mixture of nanoparticles and salt.

[0086] (3) The graphite crucible is preheated to 750℃, and the mixture of nanoparticles and salt is added into the graphite crucible, the salt is quickly melted at 750℃ to form a molten salt based nanofluid at high temperature, and then the temperature is increased to 780℃.

[0087] (4) The pure magnesium ingot is added into the molten salt based nanofluid at 780℃, the magnesium is melted in the molten salt based nanofluid, and the magnesium will sink to the bottom of the graphite crucible due to its high density to form a smelting system with a layered structure of molten salt based nanofluid and magnesium melt.

[0088] (5) The lid of the graphite crucible is covered, the temperature of the smelting system is increased to 800℃, and the graphite crucible is taken out of the smelting furnace after being kept at 800℃ for 2 hours, and then solidified at room temperature to obtain an ingot, and the solidified salt and impurities on the ingot are removed to obtain a nanoparticle reinforced magnesium matrix composite; steps (1) to (5) in this embodiment are all carried out in the atmosphere without introducing a protective gas.

[0089] Example 3

[0090] Example 3 is basically the same as Example 1, except that:

[0091] In step (1), 11% volume fraction of TiC nanoparticles is prepared according to the amount of magnesium (pure magnesium ingot), i.e. the volume ratio of pure magnesium to TiC nanoparticles is 100:11.

[0092] The quasi-static compression stress-strain curve of the nanoparticle reinforced magnesium matrix composite prepared in this embodiment is shown in Figure 5 , wherein the quasi-static compression stress-strain curve of pure magnesium corresponds to the quasi-static compression stress-strain curve of the as-cast pure magnesium ingot tested. Figure 5

[0093] Example 4

[0094] ​Example 4 is basically the same as Example 1, except that:

[0095] (3) The graphite crucible is preheated to 750℃, and the mixture of nanoparticles and salt is added into the graphite crucible, so that the salt is quickly melted at 750℃ to form a molten salt-based nanofluid at high temperature.

[0096] (4) The pure magnesium ingot is added into the molten salt-based nanofluid at 750℃, so that the magnesium is melted in the molten salt-based nanofluid, and the magnesium will sink to the bottom of the graphite crucible due to its high density, forming a smelting system with a layered structure of molten salt-based nanofluid and magnesium melt.

[0097] (5) The lid of the graphite crucible is covered, the temperature of the smelting system is kept at 750℃, and the graphite crucible is taken out of the smelting furnace after being kept in the smelting furnace for 2h, and solidified at room temperature to obtain an ingot, and the solidified salt and impurities on the ingot are removed to obtain a nanoparticle reinforced magnesium matrix composite; steps (1) to (5) of this embodiment are all carried out in the atmosphere without protection gas.

[0098] It is found that the smelting system in this embodiment is kept at 750℃, which cannot effectively improve the wettability between TiC nanoparticles and magnesium melt, resulting in poor compounding of the two, and finally the compressive strength and hardness of the nanoparticle reinforced magnesium matrix composite are relatively low, and there is no great improvement compared with the compressive strength and hardness of pure magnesium material.

[0099] Example 5

[0100] Example 5 is basically the same as Example 1, except that:

[0101] (3) The graphite crucible is preheated to 750℃, and the mixture of nanoparticles and salt is added into the graphite crucible, so that the salt is quickly melted at 750℃ to form a molten salt-based nanofluid at high temperature, and then the temperature is raised to 780℃.

[0102] (4) The pure magnesium ingot is added into the molten salt-based nanofluid at 780℃, so that the magnesium is melted in the molten salt-based nanofluid, and the magnesium will sink to the bottom of the graphite crucible due to its high density, forming a smelting system with a layered structure of molten salt-based nanofluid and magnesium melt.

[0103] (5) The lid of the graphite crucible is covered, the temperature of the smelting system is kept at 780℃, and the graphite crucible is taken out of the smelting furnace after being kept in the smelting furnace for 2h, and solidified at room temperature to obtain an ingot, and the solidified salt and impurities on the ingot are removed to obtain a nanoparticle reinforced magnesium matrix composite; steps (1) to (5) of this embodiment are all carried out in the atmosphere without protection gas.

[0104] The melting system in the embodiment is kept at 780℃, which cannot effectively improve the wettability between the TiC nanoparticles and the magnesium melt, resulting in poor compounding of the two, and the compressive strength and hardness of the finally prepared nanoparticle reinforced magnesium matrix composite are low, and the compressive strength and hardness of the finally prepared nanoparticle reinforced magnesium matrix composite are not greatly improved compared with those of pure magnesium material.

[0105] Comparative Example 1

[0106] (1) 5% volume fraction of TiC nanoparticles was prepared according to the amount of magnesium (pure magnesium ingot), that is, the volume ratio of pure magnesium to TiC nanoparticles was 100:5; then NaCl, CaF2 and CaCl2 were mixed in a mass ratio of 7:5:5 to obtain a salt, and the TiC nanoparticles and the salt were uniformly mixed in a mass ratio of 1:10 to obtain a mixture of nanoparticles and salt.

[0107] (2) The graphite crucible was preheated to 750℃, and the mixture of nanoparticles and salt was added to the graphite crucible, and the salt was quickly melted at 750℃ to form a high-temperature molten salt-based nanofluid, and then the temperature was raised to 780℃.

[0108] (3) The pure magnesium ingot was added to the molten salt-based nanofluid at 780℃, and the magnesium was melted in the molten salt-based nanofluid, and the magnesium sank to the bottom of the graphite crucible due to its high density, forming a melting system with a layered structure of molten salt-based nanofluid and magnesium melt.

[0109] (4) The lid of the graphite crucible was covered, the temperature of the melting system was raised to 820℃, and the graphite crucible was kept in the melting furnace for 2h, then the graphite crucible was taken out of the melting furnace and solidified at room temperature to obtain an ingot, and the solidified salt and impurities on the ingot were removed to obtain a nanoparticle reinforced magnesium matrix composite.

[0110] Steps (1) to (4) in the embodiment are all carried out in the atmosphere without protection gas.

[0111] The nanoparticle reinforced magnesium matrix composite prepared in the comparative example has unevenly dispersed TiC nanoparticles and contains more impurities.

[0112] Comparative Example 2

[0113] ​(1) According to the amount of magnesium (pure magnesium ingot) to prepare 5% volume fraction of TiC nanoparticles, that is, the volume ratio of pure magnesium to TiC nanoparticles is 100:5; then NaCl, CaF2, CaCl2 are mixed in a mass ratio of 7:5:5 to obtain a salt, and TiC nanoparticles and the salt are mixed uniformly in a mass ratio of 1:10, and then dispersed into distilled water (the amount of distilled water is 3 times the mass of TiC nanoparticles and the salt), first magnetic stirring for 1 hour at room temperature, and then ultrasonic at room temperature for 3 hours to obtain a uniformly dispersed nanoparticle salt solution.

[0114] (2) The nanoparticle salt solution is dried at 200°C for 12 hours to obtain a mixture of nanoparticles and salt.

[0115] (3) The graphite crucible is preheated to 750°C, and the mixture of nanoparticles and salt is added to the graphite crucible, and the salt is quickly melted at 750°C to form a molten salt-based nanofluid at high temperature, and then the temperature is raised to 780°C.

[0116] (4) At 780°C, the pure magnesium ingot is added to the molten salt-based nanofluid, and the magnesium is melted in the molten salt-based nanofluid, and when the magnesium is melted, mechanical stirring is carried out at a speed of 200 rpm for 30 min, so that the TiC nanoparticles enter the magnesium melt from the molten salt, and the heating and stirring are stopped; then solidify at room temperature to obtain an ingot, remove the solidified salt and impurities on the ingot, and obtain a nanoparticle reinforced magnesium matrix composite; The steps (1) to (4) of the present comparison example are not protected by a gas, but are directly carried out in an atmospheric environment.

[0117] The present comparison example is stirred, but the TiC nanoparticles in the nanoparticle reinforced magnesium matrix composite prepared have poor dispersion effect and contain more impurities; The micro-morphology graph (SEM graph) of the nanoparticle reinforced magnesium matrix composite prepared by the present comparison example is shown in Figure 4

[0118] Comparative Example 3

[0119] (1) The pure magnesium ingot is melted at 750°C, and the pure magnesium melt is obtained after melting; Carbon dioxide and sulfur tetrafluoride mixed gas are introduced for protection during the melting process, and the volume ratio of carbon dioxide to sulfur tetrafluoride is 45:1.

[0120] (2) Add the mixture of salt and nanoparticles to the 750°C pure magnesium melt; when the salt is melted, stir; wherein the salt is mixed by NaCl, CaF2, CaCl2 in a mass ratio of 7:5:5, and the nanoparticles are TiC nanoparticles; the salt and TiC nanoparticles are mixed uniformly in a mass ratio of 10:1 to obtain a mixture of salt and nanoparticles; the amount of TiC nanoparticles is 5% of the volume amount of pure magnesium melt.​

[0121] (3) At 750℃, under mechanical stirring at 200rpm for 20min, TiC nanoparticles entered the magnesium melt from the molten salt, and the heating and stirring were stopped; the mixture melt was solidified at room temperature to obtain an ingot.

[0122] (4) The solidified salt and impurities on the ingot were removed to obtain a nanoparticle reinforced magnesium matrix composite; in the present comparative example, except for step (1), no protective gas was introduced, and the process was directly carried out in an atmospheric environment.

[0123] The TiC nanoparticles in the nanoparticle reinforced magnesium matrix composite prepared in the present comparative example had poor dispersion effect, and contained more impurities.

[0124] The mechanical properties of the nanoparticle reinforced magnesium matrix composite prepared in each example and each comparative example were tested, and the results are shown in Table 1; wherein, the hardness test refers to the test standard GB / T 4340.3-2012; the compression strength test refers to the test standard GB / T 7314-2017.

[0125] Table 1

[0126]

[0127] The part of the present application not described in detail is the technology known to those skilled in the art.

[0128] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present application.

Claims

1. A method for preparing a nanoparticle-reinforced magnesium-based composite material, characterized in that, The method includes the following steps: (1) Disperse the nanoparticles and salt evenly with water to obtain a nanoparticle salt solution; the nanoparticles are Ti nanoparticles, and the salt is a mixture of NaCl, CaF2, MgF2 and CaCl2 in a mass ratio of (4~6):(0.5~1.5):(0.5~1.5):(2~4); or the nanoparticles are TiC nanoparticles, and the salt is a mixture of NaCl, CaF2 and CaCl2 in a mass ratio of (6~8):(4~6):(4~6); (2) The nanoparticle salt solution is dried to obtain a mixture of nanoparticles and salt; the drying temperature is 180~250℃ and the drying time is 10~20h; (3) The mixture of nanoparticles and salt is placed at a high temperature of 700~750℃ to melt the salt and obtain molten salt-based nanofluid; (4) Add magnesium to the molten salt-based nanofluid at 750~780℃ and melt the magnesium to form a smelting system with a layered structure of molten salt-based nanofluid and magnesium melt; (5) The smelting system with a layered structure of molten salt-based nanofluid and magnesium melt is subjected to high-temperature heat preservation treatment and then solidified to obtain nanoparticle-reinforced magnesium-based composite material; the temperature of the high-temperature heat preservation treatment is 780~900℃ and the time of the high-temperature heat preservation treatment is 1~3h; during the high-temperature heat preservation treatment, the nanoparticles in the molten salt-based nanofluid are transferred from the molten molten salt-based nanofluid medium to the magnesium melt through spontaneous Brownian thermal motion.

2. The preparation method according to claim 1, characterized in that: In step (1), the dispersion is carried out by stirring and sonication in sequence, the stirring time is 0.5~1.5h, and the sonication time is 2~4h.

3. The preparation method according to claim 2, characterized in that: The stirring time is 1 hour.

4. The preparation method according to claim 2, characterized in that: The ultrasound session lasted for 3 hours.

5. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of the nanoparticles to the salt is 1:(8~12).

6. The preparation method according to claim 5, characterized in that: In step (1), the mass ratio of the nanoparticles to the salt is 1:

10.

7. The preparation method according to claim 1, characterized in that: In step (2), the drying temperature is 200°C, and the drying time is 12 hours; and / or In step (3), the mixture of nanoparticles and salt is placed in a graphite crucible and the salt is melted at 700~750°C.

8. The preparation method according to claim 1, characterized in that: In step (5), the temperature of the high-temperature heat preservation treatment is 800~820℃, and the time of the high-temperature heat preservation treatment is 2h.

9. The preparation method according to claim 1, characterized in that: The volume ratio of magnesium to nanoparticles is 100:(1~12).

10. The preparation method according to claim 9, characterized in that: The volume ratio of magnesium to nanoparticles is 100:(5~12).

11. A nanoparticle-reinforced magnesium-based composite material prepared by any one of claims 1 to 10.

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