CN112941360B - Preparation method of carbon nano tube reinforced aluminum alloy semi-solid slurry - Google Patents

Preparation method of carbon nano tube reinforced aluminum alloy semi-solid slurry Download PDF

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CN112941360B
CN112941360B CN202110030634.1A CN202110030634A CN112941360B CN 112941360 B CN112941360 B CN 112941360B CN 202110030634 A CN202110030634 A CN 202110030634A CN 112941360 B CN112941360 B CN 112941360B
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CN112941360A (en
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闫洪
刘智彬
熊俊杰
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Nanchang 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
    • C22C1/1005—Pretreatment of the non-metallic additives
    • C22C1/1015—Pretreatment of the non-metallic additives by preparing or treating a non-metallic additive preform
    • 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
    • C22C1/12—Making non-ferrous alloys by processing in a semi-solid state, e.g. holding the alloy in the solid-liquid phase
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
    • C22C21/08—Alloys based on aluminium with magnesium as the next major constituent with silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
    • C22C2026/002—Carbon nanotubes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C26/00—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes
    • C22C2026/008—Alloys containing diamond or cubic or wurtzitic boron nitride, fullerenes or carbon nanotubes with additional metal compounds other than carbides, borides or nitrides

Abstract

The invention provides a preparation method of carbon nano tube reinforced aluminum alloy semi-solid slurry, belonging to the technical field of metal material manufacturing. A preparation method of carbon nano tube reinforced aluminum alloy semi-solid slurry comprises the following steps: under the condition of fusion casting, refining and deslagging the Al-Mg-Si alloy, and then using a bell jar to carry out Al-CNTs-KAlF under the protection of argon gas4Pressing the intermediate precast block into the alloy melt, applying 2.1-3.2kW high-energy ultrasonic in the adding process, then quickly reducing the temperature to 610-650 ℃ for heat preservation, carrying out secondary high-energy ultrasonic for a short time, then quickly quenching with water, and finally preparing the uniformly spheroidized semi-solid structure under the preferable process conditions. The invention has safe operation and stable process, and the prepared semi-solid slurry has obviously refined matrix structure compared with the original matrix structure without the intermediate precast block under the same condition, the carbon nano tube and the alloy matrix have good interface combination, and the distribution of the secondary phase is more uniform.

Description

Preparation method of carbon nano tube reinforced aluminum alloy semi-solid slurry
Technical Field
The invention belongs to the technical field of metal material manufacturing, and particularly relates to a preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry.
Background
In recent years, green and low-carbon lifestyles are vigorously advocated, and scientific exploration is also struggling to find breakthrough in green development. At present, automobiles are more and more personalized, and the additional devices further increase the weight of the automobile body, so that the light weight of parts is a necessary choice for realizing the purposes of weight reduction of the automobile body and emission reduction of tail gas of automobile enterprises. For this reason, more and more body parts are gradually replaced by aluminium alloy parts, such as: housing parts such as a cylinder block, a cylinder head, a hub, and a transmission case, and body covers such as a door, a bonnet, and a roof. However, the performance requirements of simple aluminum alloy can not be completely met, and the defects that the strength of castings is insufficient or cold stamped parts are easy to crack exist, and the like exist, so that the aluminum-based composite material with excellent performance is particularly important.
Carbon Nanotubes (CNTs), a tubular article made of graphite hexagonal lattice curls, have excellent properties of high temperature resistance, corrosion resistance, high strength, high elastic modulus, thermal conductivity, and electrical conductivity. The tensile strength of the carbon nano tube can reach 10-250GPa, which is about 100 times of that of steel, and the density of the carbon nano tube is less than 1/7 of the steel, and is at least one order of magnitude higher than that of the conventional graphite fiber. Its elastic modulus can reach 1000GPa, is equivalent to that of diamond, is about 5 times that of steel, is a material with highest specific strength which can be prepared at present, and is known as "super fiber". Therefore, the carbon nano tube is used as a nano reinforced material to prepare the aluminum matrix composite, and the strength, elasticity, fatigue resistance and other properties of the composite can be greatly improved.
However, the performance improvement and popularization and application of the carbon nanotube reinforced aluminum matrix composite are limited by the widely applied preparation processes (such as powder metallurgy, melt stirring, and the like) at home and abroad at present for the following reasons: the carbon nano tube is easy to agglomerate and wind in a matrix, has poor bonding property with an alloy matrix, and has complex preparation process of the composite material. In the publication No. CN109666818A entitled "a method for preparing composite integration of carbon material and aluminum alloy", carbon nanotubes are used as aluminum alloy reinforcement to improve the mechanical properties of the matrix obtained by semi-solid chilling of the alloy. The ZL101A alloy semi-solid slurry is prepared through the process, and semi-solid bars can be obtained through chilling, but the method is complex in process flow, high in equipment cost, large in alloy melt viscosity in the semi-solid state, poor in interface binding capacity, and easy to agglomerate through the carbon material mixed powder sprayed in a spinning mode. In the publication No. CN108588464A entitled "a method for preparing carbon nanotube reinforced aluminum matrix composite", a semi-solid alloy melt is rolled to prepare a carbon nanotube reinforced aluminum matrix composite casting. The process is advanced, but the carbon nano tube is placed in a melting crucible of a casting and rolling machine and is heated and melted along with a furnace, and the carbon nano tube is easy to burn because the specific gravity of the carbon nano tube is too small relative to the alloy and the carbon nano tube floats in the melting process before the alloy is completely melted. In publication No. CN109735736A entitled "method for preparing low-density metal matrix composite", a non-metallic material containing graphene or/and carbon nanotubes is added into a low-density metal material melt such as metallic aluminum, metallic copper or a mixture thereof, and is stirred and mixed to prepare semi-solid metal matrix composite slurry, and the semi-solid metal matrix composite slurry is die-cast into a composite material. The process is simple and operable, but the density of the non-metallic material containing graphene or/and carbon nano tubes is smaller than that of the metallic material, the non-metallic material is easy to agglomerate on the surface layer of a melt in the high-speed stirring process after being added, the dispersibility of the carbon nano tubes and the like in the obtained semi-solid metal-based composite slurry is poor, the semi-solid metal-based composite slurry is not chilled after being die-cast, the crystal grains in the material are easy to grow, and the semi-solid spherical crystal structure is difficult to obtain. Aiming at the problems, the research on novel casting preparation technology is developed, the uniform composite preparation process of the carbon nano tube and the aluminum alloy is explored, and the shortening of the cycle time of the preparation process and the forming of complex components are very important.
The metal semi-solid forming process was originally proposed and developed by professor Flemings, etc. in the 70 th 20 th century, and semi-solid forming is forming by utilizing the characteristic of non-dendritic state of metal material in the process of converting from solid state to liquid state or from liquid state to solid state. Compared with the traditional casting and forging process, the metal semi-solid forming process has many advantages, such as stable mold filling, no turbulence and splashing, and less gas entrapment; the deformation resistance is small, the equipment investment is reduced, and the energy is saved; the forming temperature is low, and the service life of the die is long; the solidification shrinkage is small, the precision of a workpiece is high, the workpiece is almost formed in a near-net shape, and raw materials are saved; the internal structure of the formed part is compact, the hole defects are few, and the mechanical property is high; the solidification time is shortened, the production efficiency is high, and the like. Therefore, the semi-solid forming process for researching the carbon nano tube reinforced aluminum matrix composite material has wide prospect. Semi-solid slurry making is one of the keys of semi-solid forming technology, and the core of the semi-solid slurry making is the thinning and spheroidizing of metal grains.
The existing method for preparing the semi-solid slurry mainly comprises a mechanical stirring method, an electromagnetic stirring method, a strain induced melt activation method, a near liquid phase line method, a high-energy ultrasonic method and the like. The mechanical stirring method has the following disadvantages: the molten metal is easily polluted and corroded by the stirrer, a stirring blind area exists, the uniformity of the slurry is insufficient, gas and impurities are easily involved in the stirring process, and the quality of the semi-solid blank is further influenced. The electromagnetic stirring method has the following disadvantages: stirring equipment is expensive, the electromagnetic gap of the device is large, magnetic leakage is serious, and part of energy cannot be used for stirring the metal melt, so that the production cost is greatly increased. The strain-induced melt activation method has the following disadvantages: an additional pre-deformation process is required, the cost is increased, and the size of the prepared semi-solid blank is smaller. The near liquid phase line method has the following disadvantages: the preparation period is long, and the pouring temperature of the melt is difficult to accurately control.
Disclosure of Invention
The invention aims to provide carbon nano tube reinforced aluminumA method for preparing alloy semi-solid slurry. The method realizes the purpose of reinforcing the matrix of the carbon nano tube by the methods of ultrasonic dispersion and stirring mixing of powder used by the precast block, vacuum sintering of the precast block and ultrasonic fusion casting. The method has the advantages that: the carbon nanotube is Al-CNTs-KAlF4The intermediate precast block is added, so that the carbon nano tube is prevented from floating upwards in the adding process, and the interface wetting of the carbon nano tube and the aluminum alloy melt is improved by adding the potassium tetrafluoroaluminate; high-energy ultrasonic waves are introduced into the metal melt, the generated transient high temperature and high pressure change the local balance, the surface tension of the liquid surface is reduced, strong local impact is generated, and a strong scattering effect can be generated on an agglomerated phase; the addition of the carbon nano tube can also refine the grain size of the aluminum-magnesium-silicon alloy.
The invention is realized by the following technical scheme:
a preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry comprises the following steps:
1) mixing the carbon nano tube with aluminum powder and potassium tetrafluoroaluminate by using ultrasound to obtain a mixed solution;
2) vacuum filtering the mixed solution, drying in a vacuum drying oven, sintering the dried powder in a vacuum hot pressing sintering furnace to obtain the aluminum powder-carbon nano tube-potassium tetrafluoroaluminate (Al-CNTs-KAlF)4) The middle precast block is cut into small particles and coated by aluminum foil paper for later use;
3) cutting Al-Mg-Si matrix alloy into small pieces, placing the small pieces into a graphite crucible, placing the graphite crucible into a resistance furnace, heating to 760-4Pressing the intermediate precast block into the alloy melt, adding the precast block and simultaneously applying high-energy ultrasound;
4) and 3) after the high-energy ultrasonic treatment is finished, quickly reducing the temperature of the melt to 610-650 ℃, preserving the temperature, applying secondary ultrasonic treatment for 60-90s, and immediately quenching the slurry obtained by the secondary ultrasonic treatment to obtain a semi-solid structure with fine grains.
Further, the specific step of mixing in step 1) is to mix the carbon nanotubes with absolute ethanol according to 2.5-3.5g of carbon nanotubes mixed with 100ml of ethanol, and then to place the mixture into an ultrasonic instrument for ultrasonic dispersion treatment for 100-480 minutes, wherein the ultrasonic power is 400-480W, and the frequency is 35-45 kHz; mixing aluminum powder, potassium tetrafluoroaluminate powder and absolute ethyl alcohol according to the proportion that each 150ml of ethanol is mixed with 40-50g of aluminum powder and 2.5-3.5g of potassium tetrafluoroaluminate, and mixing for 150min by mechanical stirring at the stirring speed of 100-; and then uniformly adding the mixed and dispersed aluminum powder-potassium tetrafluoroaluminate ethanol mixed solution into the carbon nano tube ethanol dispersion liquid after ultrasonic treatment, continuing to perform ultrasonic dispersion with the power of 750-800W and the frequency of 35-45kHz, and simultaneously performing mechanical stirring with the stirring speed of 200-250r/min and the duration of 120-180 min.
A large number of researches show that the carbon nano tube can refine alpha-Al phase and Mg of the aluminum alloy2The Si phase plays a role in promoting the spheroidization of crystal grains, so that the internal microstructure of the aluminum alloy is optimized, and the performance of the alloy material is improved.
Furthermore, the Carbon Nano Tubes (CNTs) have the outer diameter of 20-60nm, the length of 10-30 mu m and the purity of more than or equal to 99.5 percent; the purity of the aluminum powder is more than or equal to 99.9 percent, and the granularity is 100-200 meshes.
Further, the sintering temperature in the step 2) is 400-450 ℃, the hot-pressing pressure is 40-60MPa, and the pressure maintaining time is 2-3 h; in particular, Al-CNTs-KAlF is obtained after sintering4The mass percentage of CNTs in the intermediate precast block is 5-10%, KAlF4The mass ratio of the carbon nano tube to the CNTs is 1:1, and the balance is Al.
Further, the Al-Mg-Si matrix alloy in the step 3) comprises the following elements in percentage by mass: 0.8 to 1.2 percent of magnesium, 0.4 to 0.8 percent of silicon, 0.15 to 0.4 percent of copper and the balance of aluminum.
Further, after the base alloy in the step 3) is completely melted, hexachloroethane accounting for 0.2-0.3 wt% of the melt mass is added for refining and slagging off.
Further, step 3) pressing in Al-CNTs-KAlF4The CNTs are added into the intermediate precast block in an amount of 0.5 to 1.5 wt.% of the total amount of the alloy melt, and KAlF4The ratio of the amount of the CNTs to the amount of the CNTs added is 1: 1.
Further, the high-energy ultrasonic operation method in the step 3) is that an ultrasonic amplitude transformer probe is immersed into the alloy melt, the ultrasonic power is applied to the alloy melt to be 2.1-3.2kW, the frequency is 18-22kHz, and the time is 10-15 min; argon is filled in the whole ultrasonic process for protection.
Compared with other methods, the high-energy ultrasonic method has fewer defects, can obtain an ideal non-dendritic crystal semi-solid structure in a short time, and really realizes low energy consumption and high efficiency. When high-energy ultrasound is applied to the melt, acoustic cavitation and acoustic flow effects can be generated, and high-temperature and high-pressure shock waves generated by the acoustic cavitation effect play an important role in the aspects of breaking crystal grains, promoting nucleation, destroying a boundary layer and the like. Meanwhile, the carbon nano tubes can be promoted to be uniformly dispersed in the melt through an ultrasonic casting method and to be better infiltrated with the alloy melt, which plays an important role in obtaining fine and round semi-solid crystal grains.
Further, the parameters of the secondary ultrasound except time in the step 4) are consistent with the ultrasound in the step 3).
Further, the water quenching temperature in the step 4) is 20-30 ℃, and the water quenching is carried out and then the drying is carried out in a temperature field of 40-50 ℃.
Compared with the prior art, the invention has the beneficial effects that:
1) the fine characteristics of the carbon nano tube are utilized to refine the crystal grains of the aluminum-magnesium-silicon alloy; 2) adding potassium tetrafluoroaluminate to improve the interface bonding strength of the carbon nano tube and the aluminum alloy melt; 3) the high-energy ultrasonic is applied to promote the uniform dispersion of the carbon nano tube in the aluminum alloy melt; 4) and in the semi-solid temperature range, applying secondary ultrasound to further spheroidize the semi-solid slurry structure.
The invention has safe operation, stable process and low energy consumption, the semi-solid structure of the prepared composite material is obviously refined, the carbon nano tube and the alloy matrix interface are well combined, and the secondary phase distribution is relatively uniform.
Detailed Description
The present invention will be further described with reference to specific examples, but the present invention is not limited to the following examples. The process is conventional unless otherwise specified, and the starting materials are commercially available from the open literature.
Example 1
A preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry comprises the following steps:
(1) mixing a proper amount of carbon nanotubes with the outer diameter of 20-60nm, the length of 10-30 mu m and the purity of more than or equal to 99.5 percent with absolute ethyl alcohol in a beaker according to the proportion that every 100ml of the ethyl alcohol is mixed with 3.0g of the carbon nanotubes, and then putting the mixture into an ultrasonic instrument for ultrasonic dispersion treatment for 120min, wherein the ultrasonic power is 450W and the frequency is 40 kHz; mixing aluminum powder with the purity of more than or equal to 99.9 percent and the granularity of 100-200 meshes, potassium tetrafluoroaluminate powder and absolute ethyl alcohol in a beaker according to the mixing ratio of 45g of aluminum powder and 3.0g of potassium tetrafluoroaluminate in 150ml of ethanol, and mixing for 120min by mechanical stirring at the stirring speed of 120 r/min; and then uniformly adding the mixed and dispersed aluminum powder-potassium tetrafluoroaluminate ethanol mixed solution into the carbon nano tube ethanol dispersion solution subjected to ultrasonic dispersion, continuously performing ultrasonic dispersion with the power of 780W and the frequency of 40kHz, and simultaneously performing mechanical stirring at the stirring speed of 220r/min for 150min to obtain a mixed solution.
(2) And (2) filling the mixed solution prepared in the step (1) into a suction filtration instrument, performing vacuum suction filtration to obtain a paste, and drying the paste in a vacuum drying oven at 80 ℃.
(3) Sintering the dried powder in a vacuum hot-pressing sintering furnace at 425 ℃ under 50MPa for 2.5h to obtain Al-CNTs-KAlF4A middle prefabricated block, wherein the CNTs accounts for 8 percent by mass, KAlF4The mass ratio of the prefabricated blocks to the CNTs is 1:1, and the balance is Al, and the prefabricated blocks are cut into small particles and coated by aluminum foil paper for later use.
(4) Cutting Al-Mg-Si matrix alloy (the mass percent of Mg in the alloy is 1.0%, the mass percent of Si is 0.6%, the mass percent of Cu is 0.25%, and the balance is Al) into small blocks, putting the small blocks into a dried graphite crucible, putting the graphite crucible into a resistance furnace, heating to 770 ℃, and preserving heat for 30 min.
(5) After the alloy is completely melted, hexachloroethane accounting for 0.25 wt.% of the melt mass is added for refining and slagging off. Then using bell jar to make Al-CNTs-KAlF4Pressing the intermediate prefabricated block into the alloy melt, wherein the addition amount of CNTs accounts for 1.0 wt.% of the total weight of the alloy melt, and KAlF4The addition amount of the CNTsThe ratio of the amounts is 1: 1. Applying high energy ultrasound while adding the pre-agglomerate particles: immersing an ultrasonic amplitude transformer probe into the alloy melt, and applying ultrasonic power of 2.8kW, frequency of 20kHz and time of 13 min; argon is filled in the whole ultrasonic process for protection.
(6) And (3) after the high-energy ultrasonic is applied, when the temperature of the melt is rapidly reduced to 630 ℃, applying secondary ultrasonic to the semi-solid slurry for 80s, wherein the rest ultrasonic parameters are the same as those in the step (5). And immediately carrying out water quenching on the slurry obtained by the secondary ultrasound after the secondary ultrasound is finished, wherein the water quenching temperature is 25 ℃, and drying in a 45 ℃ temperature field after the water quenching is finished to obtain a semi-solid structure with fine grains.
The semi-solid state crystal grain structure of the aluminum-based composite material prepared under the condition of the embodiment is fine, and the average crystal grain size is compared with that of the aluminum-based composite material which is not added with Al-CNTs-KAlF under the same condition4The matrix alloy of the intermediate precast block is reduced by 47.6%, and the average shape factor is correspondingly improved by 28.7%.
Example 2
A preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry comprises the following steps:
(1) mixing a proper amount of carbon nanotubes with the outer diameter of 20-60nm, the length of 10-30 mu m and the purity of more than or equal to 99.5 percent with absolute ethyl alcohol in a beaker according to the proportion that 2.5g of the carbon nanotubes are mixed in per 100ml of the ethanol, and then putting the mixture into an ultrasonic instrument for ultrasonic dispersion treatment for 100min, wherein the ultrasonic power is 400W, and the frequency is 35 kHz; mixing aluminum powder with the purity of more than or equal to 99.9 percent and the granularity of 100-200 meshes, potassium tetrafluoroaluminate powder and absolute ethyl alcohol in a beaker according to the mixing ratio of 40g of aluminum powder and 2.5g of potassium tetrafluoroaluminate into 150ml of ethanol liquid, and mixing for 100min by mechanical stirring at the stirring speed of 100 r/min; and then uniformly adding the mixed and dispersed aluminum powder-potassium tetrafluoroaluminate ethanol mixed solution into the carbon nano tube ethanol dispersion solution subjected to ultrasonic dispersion, continuously performing ultrasonic dispersion with the power of 750W and the frequency of 35kHz, and simultaneously performing mechanical stirring at the stirring speed of 200r/min for 120min to obtain a mixed solution.
(2) And (2) filling the mixed solution prepared in the step (1) into a suction filtration instrument, performing vacuum suction filtration to obtain a paste, and drying the paste in a vacuum drying oven at 80 ℃.
(3) Sintering the dried powder in a vacuum hot-pressing sintering furnace at the sintering temperature of 400 ℃, the hot-pressing pressure of 40MPa and the pressure maintaining time of 2h to obtain Al-CNTs-KAlF4A middle prefabricated block, wherein the CNTs accounts for 5 percent by mass, KAlF4And (3) cutting the prefabricated blocks into small particles according to the mass ratio of 1:1 to the CNTs, and coating the small particles with aluminum foil paper for later use.
(4) Cutting Al-Mg-Si matrix alloy (the mass percent of Mg in the alloy is 1.0%, the mass percent of Si is 0.6%, the mass percent of Cu is 0.25%, and the balance is Al) into small blocks, putting the small blocks into a dried graphite crucible, putting the graphite crucible into a resistance furnace, heating to 760 ℃, and preserving heat for 25 min.
(5) After the alloy is completely melted, hexachloroethane accounting for 0.2 wt.% of the melt mass is added for refining and slagging off. Then using bell jar to mix Al-CNTs-KAlF4Pressing the intermediate prefabricated block into the alloy melt, wherein the addition amount of CNTs accounts for 0.5 wt.% of the total weight of the alloy melt, and KAlF4The ratio of the amount of (2) to the amount of CNTs is 1: 1. Applying high energy ultrasound while adding the pre-agglomerate particles: immersing an ultrasonic amplitude transformer probe into the alloy melt, and applying ultrasonic power of 2.1kW, frequency of 20kHz and time of 10 min; argon is filled in the whole ultrasonic process for protection.
(6) And (3) after the high-energy ultrasonic is applied, when the temperature of the melt is rapidly reduced to 610 ℃, applying secondary ultrasonic to the semi-solid slurry for 60s, wherein the rest ultrasonic parameters are the same as those in the step (5). And immediately carrying out water quenching on the slurry obtained by the secondary ultrasound after the secondary ultrasound is finished, wherein the water quenching temperature is 20 ℃, and drying in a temperature field of 40 ℃ after the water quenching is finished to obtain a semi-solid structure with fine grains.
The semi-solid state crystal grain structure of the aluminum-based composite material prepared under the condition of the embodiment is fine, and the average crystal grain size is compared with that of the aluminum-based composite material which is not added with Al-CNTs-KAlF under the same condition4The matrix alloy of the intermediate precast block is reduced by 37.8%, and the average shape factor is correspondingly improved by 20.6%.
Example 3
A preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry comprises the following steps:
(1) mixing a proper amount of carbon nanotubes with the outer diameter of 20-60nm, the length of 10-30 mu m and the purity of more than or equal to 99.5 percent with absolute ethyl alcohol in a beaker according to the proportion that every 100ml of the ethanol is mixed with 3.5g of the carbon nanotubes, and then putting the mixture into an ultrasonic instrument for ultrasonic dispersion treatment for 150min, wherein the ultrasonic power is 480W and the frequency is 45 kHz; mixing 50g of aluminum powder and 3.5g of potassium tetrafluoroaluminate powder which have the purity of more than or equal to 99.9 percent and the granularity of 100-200 meshes with absolute ethyl alcohol in a beaker according to the proportion that each 150ml of ethanol is mixed with the aluminum powder and the potassium tetrafluoroaluminate for 150min by mechanical stirring, wherein the stirring speed is 140 r/min; and then uniformly adding the mixed and dispersed aluminum powder-potassium tetrafluoroaluminate ethanol mixed solution into the carbon nano tube ethanol dispersion solution subjected to ultrasonic dispersion, continuously performing ultrasonic dispersion with the power of 800W and the frequency of 45kHz, and simultaneously performing mechanical stirring at the stirring speed of 250r/min for 180min to obtain a mixed solution.
(2) And (2) filling the mixed solution prepared in the step (1) into a suction filtration instrument, performing vacuum suction filtration to obtain a paste, and drying the paste in a vacuum drying oven at 80 ℃.
(3) Sintering the dried powder in a vacuum hot-pressing sintering furnace at the sintering temperature of 450 ℃, under the hot-pressing pressure of 60MPa and under the pressure maintaining time of 3h to obtain Al-CNTs-KAlF4A middle prefabricated block, wherein the CNTs accounts for 10 percent by mass, KAlF4The mass ratio of the prefabricated blocks to the CNTs is 1:1, and the balance is Al, and the prefabricated blocks are cut into small particles and coated by aluminum foil paper for later use.
(4) Cutting Al-Mg-Si matrix alloy (the mass percent of Mg in the alloy is 1.0%, the mass percent of Si is 0.6%, the mass percent of Cu is 0.25%, and the balance is Al) into small blocks, putting the small blocks into a dried graphite crucible, putting the graphite crucible into a resistance furnace, heating to 780 ℃, and preserving heat for 30 min.
(5) After the alloy is completely melted, hexachloroethane accounting for 0.3 wt.% of the melt mass is added, and refining and slagging-off are carried out. Then using bell jar to make Al-CNTs-KAlF4Pressing the intermediate prefabricated block into the alloy melt, wherein the addition amount of CNTs accounts for 1.5 wt.% of the total weight of the alloy melt, and KAlF4The ratio of the amount of the CNTs to the amount of the CNTs added is 1: 1. Applying high energy ultrasound while adding the pre-block particles: immersing an ultrasonic amplitude transformer probe into the alloy melt, and applying ultrasonic power of 3.2kWThe frequency is 20kHz, and the time is 15 min; argon is filled in the whole ultrasonic process for protection.
(6) And (3) after the high-energy ultrasonic is applied, when the temperature of the melt is rapidly reduced to 650 ℃, applying secondary ultrasonic to the semi-solid slurry for 90s, wherein the rest ultrasonic parameters are the same as those in the step (5). And immediately carrying out water quenching on the slurry obtained by the secondary ultrasound after the secondary ultrasound is finished, wherein the water quenching temperature is 30 ℃, and drying in a 50 ℃ temperature field after the water quenching is finished to obtain a semi-solid structure with fine grains.
The semi-solid state crystal grain structure of the aluminum-based composite material prepared under the condition of the embodiment is fine, and the average crystal grain size is compared with that of the aluminum-based composite material which is not added with Al-CNTs-KAlF under the same condition4The matrix alloy of the intermediate precast block is reduced by 41.8%, and the average shape factor is correspondingly improved by 25.9%.
The above-described embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made by one skilled in the art, and any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A preparation method of carbon nanotube reinforced aluminum alloy semi-solid slurry is characterized by comprising the following steps:
1) mixing the carbon nano tube with aluminum powder and potassium tetrafluoroaluminate by using ultrasound to obtain a mixed solution;
2) vacuum-filtering the mixed solution, drying in a vacuum drying oven, sintering the dried powder in a vacuum hot-pressing sintering furnace to obtain intermediate prefabricated blocks of aluminum powder-carbon nano tube-potassium tetrafluoroaluminate, cutting the prefabricated blocks into small particles, and coating the small particles with aluminum foil paper for later use;
3) cutting Al-Mg-Si matrix alloy into small blocks, putting the small blocks into a graphite crucible, putting the crucible into a resistance furnace, heating to 760-;
4) step 3) after the high-energy ultrasound is finished, rapidly reducing the temperature of the melt to 610-650 ℃, preserving the temperature and applying secondary ultrasound, wherein the ultrasound time is 60-90s, and immediately performing water quenching on slurry obtained by the secondary ultrasound after finishing to obtain a semi-solid tissue with small grains;
the mixing in the step 1) comprises the following specific steps: mixing the carbon nano tube with absolute ethyl alcohol according to the proportion that each 100ml of ethyl alcohol is mixed with 2.5-3.5g of the carbon nano tube, then placing the mixture into an ultrasonic instrument for ultrasonic dispersion treatment for 100-480 min, wherein the ultrasonic power is 400-480W, and the frequency is 35-45 kHz; mixing aluminum powder, potassium tetrafluoroaluminate powder and absolute ethyl alcohol according to the proportion that each 150ml of ethanol is mixed with 40-50g of aluminum powder and 2.5-3.5g of potassium tetrafluoroaluminate, and mixing for 150min by mechanical stirring at the stirring speed of 100-; and then uniformly adding the mixed and dispersed aluminum powder-potassium tetrafluoroaluminate ethanol mixed solution into the carbon nano tube ethanol dispersion liquid after ultrasonic treatment, continuing to perform ultrasonic dispersion with the power of 750-800W and the frequency of 35-45kHz, and simultaneously performing mechanical stirring with the stirring speed of 200-250r/min and the duration of 120-180 min.
2. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry as claimed in claim 1, wherein the carbon nanotube has an outer diameter of 20-60nm, a length of 10-30 μm and a purity of more than or equal to 99.5%; the purity of the aluminum powder is more than or equal to 99.9 percent, and the granularity is 100-200 meshes.
3. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry according to claim 1, wherein the sintering temperature in the step 2) is 400-450 ℃, the hot-pressing pressure is 40-60MPa, and the pressure-holding time is 2-3 h;
the mass percent of the carbon nano tubes in the aluminum powder-carbon nano tube-potassium tetrafluoroaluminate intermediate precast block obtained after sintering is 5-10%, the mass ratio of the potassium tetrafluoroaluminate to the carbon nano tubes is 1:1, and the balance is aluminum.
4. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry as claimed in claim 1, wherein the Al-Mg-Si matrix alloy of step 3) comprises the following elements in percentage by mass: 0.8 to 1.2 percent of magnesium, 0.4 to 0.8 percent of silicon, 0.15 to 0.4 percent of copper and the balance of aluminum.
5. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry as claimed in claim 1, wherein the step 3) of pressing the aluminum powder-carbon nanotube-potassium tetrafluoroaluminate intermediate preform into the aluminum powder-carbon nanotube-potassium tetrafluoroaluminate intermediate preform, wherein the addition amount of the carbon nanotube accounts for 0.5-1.5 wt.% of the total amount of the alloy melt, and the ratio of the addition amount of the potassium tetrafluoroaluminate to the addition amount of the carbon nanotube is 1: 1.
6. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry according to claim 1, wherein the high-energy ultrasonic operation method in the step 3) is to immerse an ultrasonic amplitude transformer probe into the alloy melt, and the ultrasonic power is 2.1-3.2kW, the frequency is 18-22kHz, and the time is 10-15 min; argon is filled in the whole ultrasonic process for protection.
7. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry according to claim 1, wherein the parameters of the secondary ultrasound except time in the step 4) are consistent with those of the ultrasound in the step 3).
8. The method for preparing the carbon nanotube reinforced aluminum alloy semi-solid slurry according to claim 1, wherein the water quenching temperature in the step 4) is 20-30 ℃, and the carbon nanotube reinforced aluminum alloy semi-solid slurry is dried in a temperature field of 40-50 ℃ after water quenching.
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