Method for Preparing In-situ Synthesized Nanoparticle Reinforced Aluminum Matrix Composite by Centrifugal Reaction

Abstract

The present invention relates to the technical field of aluminum matrix composites, and particularly to the preparation of nanoparticle-reinforced aluminum matrix composites by centrifugal reaction and its preparation method, including: S1. Melting a first AlSi12 eutectic alloy crucible, heating it to 600 ± 10 °C, holding the temperature, and adjusting the crucible rotation speed until the liquid surface of the eutectic alloy adheres tightly to the inner wall of the crucible in a "U" shape to obtain Material 1; S2. Adding mixed salts to Material 1, after the mixed salts are completely melted, adding a second AlSi12 eutectic alloy to the crucible, keeping the crucible temperature not higher than 650 °C, after reacting for 10 - 20 min, slowly reducing the rotation speed to 0, skimming the slag after the liquid surface is stable, and performing desalting treatment to obtain Material 2; S3. Heating Material 2 to 760 - 780 °C, adding intermediate metals, controlling the temperature to 700 - 720 °C, adding elements prone to burning loss for melt refining treatment, and casting to obtain the nanoparticle-reinforced aluminum matrix composite, solving the problems in the traditional process that are difficult to control during the reaction process, such as small reaction interface, long reaction duration, and large heat release.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum matrix composites, and particularly to a method for preparing nano-particle reinforced aluminum matrix composites by centrifugal reaction and its preparation method. Background Art

[0002] Nano-particle reinforced aluminum matrix composites have excellent comprehensive mechanical properties and have broad application prospects in the fields of aerospace, weapons, ships, electronics, automobiles, etc. The preparation method of nano-particle reinforced aluminum matrix composites by the fluorine salt method has the advantages of simple process and low cost, and is considered to be the most potential in-situ synthesis method for preparing nano-particle reinforced aluminum matrix composites for engineering applications. The fluorine salt method forms TiB2 (or ZrB2) nano-particles through the thermite reaction of liquid titanium aluminum with titanium salts (or zirconium salts) and boron salts. On the one hand, the thermite reaction is an exothermic reaction, the reaction process is violent, the reaction products are numerous and miscellaneous, and the size range is wide, which is difficult to control. At present, the method of appropriately reducing the reaction temperature is mainly used for control. On the other hand, the contents of Ti element and B element in titanium salts and boron salts are low, and their mass fractions are 19.9% and 8.6% respectively. Even if the recovery rates of Ti element and B element in the reaction process are 100%, 7 kg of mixed salts are required to synthesize 1 kg of TiB2. When preparing 5 wt.% TiB2 / Al composites, the weight of the mixed salts accounts for 36.8% of the alloy weight, that is, the molten salt occupies one-third of the crucible volume. A large amount of molten salt continuously undergoes violent reactions at the alloy liquid and molten salt interface through convection, causing the melt at the reaction interface to continuously heat up and the reaction products to grow rapidly. In addition, a large amount of residual molten salt enters the melt, resulting in many problems such as particle agglomeration and difficulty in melt purification. In order to obtain enhanced particles with high size concentration and good dispersion, technicians at home and abroad generally choose a lower reaction temperature and simultaneously implement strong stirring (including electromagnetic stirring and mechanical stirring).

[0003] Chinese Patent No. 202011306962.1 discloses a method for preparing in-situ nano-particle reinforced aluminum matrix composites at low temperature. The reaction temperature is 660-670 °C. A high-speed mechanical stirring is applied on the melt surface to form a vortex, and the mixed salts are added into the vortex on the melt surface for 15 minutes of reaction. This technology suppresses particle agglomeration by applying rapid mechanical stirring at the reaction interface, improves the dispersion and size of particles. When adding salts to the surface vortex, a large amount of air will be introduced into the melt, resulting in a large amount of residual molten salts, oxides and gases in the melt, increasing the melt viscosity and bringing difficulties to the melt purification treatment. The research by Liu Zhengcai et al. (Research Status of TiB2 Particle Reinforced Aluminum Matrix Composites by Mixed Salt Method [J]. Hot Working Technology, 2021, 12(50) pp: 17-21) shows that low-speed stirring cannot effectively break clusters, high-speed stirring will increase hydrogen absorption and oxidation, and introduce surface impurities, thus reducing the mechanical properties of the composite material.

[0004] Chinese patents 202011571152.9, 202011571153.3, and 202011571141.0 propose a system and method for preparing in-situ self-generated aluminum matrix composites by pulsed magnetic field, with a reaction temperature of 700 - 760 °C and simultaneous vacuum pumping; Chinese patent 200510029902.9 discloses a method for preparing in-situ particle-reinforced high-temperature-resistant aluminum matrix composites, with a reaction temperature of 680 - 800 °C. After the reaction is completed, alloying elements are added and vacuum pumping and standing are performed. After the reaction is completed, the residual salts in the melt are not processed in a timely manner, and the addition of alloying elements will cause the melt viscosity to further increase, making it increasingly difficult to purify the melt. The reaction temperature is relatively high, and the influence of the rising reaction temperature on the reaction process is not involved; in order to avoid the problem of difficult melt purification caused by introducing residual molten salts into the melt by the fluorine salt method, Chinese patent 202111585762.9 proposes a method for preparing controllable TiB2 in-situ reinforced aluminum matrix composites, using boron alloy and aluminum-titanium alloy or pure titanium as raw materials, reacting at 800 - 850 °C, and using argon gas refining for degassing. It can be seen that the prior art does not involve residual molten salt purification technology, let alone the technology of increasing the reaction interface by centrifugal force to control the reaction rate, particle size, and dispersion.

[0005] Currently, the prior art all adopts the method of reacting at the reached temperature for reaction temperature control. The present invention discovers that when the melting amount is in the range of hundreds of kilograms to tons, the melt temperature during the reaction process rises by about 80 - 100 °C. The substantial rise in the melt temperature leads to an increase in the reaction rate, while the convection or diffusion rate (constant mechanical stirring or equal-power acoustic-magnetic coupling field) remains unchanged, which is bound to cause the growth or aggregation of the reinforcing particle size, ultimately resulting in a large span of the reinforcing particle size range and uneven dispersion. During the reaction process, molten salts inevitably enter the interior of the melt, causing an increase in the melt viscosity. The publicly available technical solutions usually adopt traditional methods for melt purification treatment before pouring. In fact, alloying will cause the melt viscosity to further increase, making it more difficult to purify the melt. Further improving the controllability of the reaction process and obtaining nano-reinforcing particles with consistent size, morphology, and uniform dispersion, as well as a pure melt, are problems that scientific research and technical personnel in this field are committed to solving. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a preparation method for in-situ synthesized nano-particle-reinforced aluminum matrix composites that reacts stably at extremely low temperatures.

[0007] The first aspect of the present invention provides a preparation method for centrifugal reaction to prepare nano-particle-reinforced aluminum matrix composites, and the preparation method includes the following steps:

[0008] S1. Melt the first AlSi12 eutectic alloy crucible, heat it up to 600 ± 10 °C, keep it warm, and adjust the crucible rotation speed until the liquid surface of the eutectic alloy adheres tightly to the inner wall of the crucible in a "U" shape to obtain Material 1;

[0009] S2. Add mixed salts to Material 1. After the mixed salts are completely melted, continue to add the second AlSi12 eutectic alloy to the crucible. Keep the crucible temperature not higher than 650 °C. After reacting for 10 - 20 min, slowly reduce the rotation speed to 0. After the liquid surface is stable, skim the slag and perform desalting treatment to obtain Material 2;

[0010] S3. Heat Material 2 to 760 - 780 °C, add intermediate metals, control the temperature to 700 - 720 °C, add easily burned elements for melt refining treatment, and pour to obtain the nano-particle reinforced aluminum matrix composite material.

[0011] In some embodiments, the rotation speed of the crucible in S1 is adjusted to 3000 - 4000 r / min.

[0012] The applicant found during the exploration process that if the rotation speed of the crucible is too low, the depression degree of the liquid surface is insufficient, or it is difficult to form a "U" - shaped liquid surface, which is not conducive to establishing a sufficient reaction interface and results in low reaction efficiency. If the rotation speed is too high, high - density reinforcement particles will agglomerate under the action of centrifugal force and be hindered by the crucible side wall, and it will increase energy consumption and equipment manufacturing costs. The definition of the "U" shape in the present invention is: during the rotation of the crucible, the liquid surface that adheres tightly to the inner wall of the crucible is higher than the liquid surface at the bottom of the crucible, and it can be considered that a "U" shape is formed.

[0013] Furthermore, the vertical distance from the highest point to the lowest point of the "U" - shaped liquid surface is 2 / 3 - 3 / 4 of the height of the crucible.

[0014] In some embodiments, the mixed salts are a mixture of potassium hexafluorotitanate and potassium tetrafluoroborate after baking.

[0015] Furthermore, the molar ratio of Ti atoms to B atoms in potassium hexafluorotitanate and potassium tetrafluoroborate is 1:2.

[0016] In some embodiments, the addition amount of the second AlSi12 eutectic alloy is 5 - 10 wt% of the addition amount of the mixed salts.

[0017] If the addition amount of the second AlSi12 eutectic alloy is too low, the expected temperature - lowering effect cannot be achieved. If the addition amount is too high, the melt temperature is lower than the liquidus, which is not conducive to the dispersion of micro - nano reinforcement particles in the melt.

[0018] The addition sequence of the second AlSi12 eutectic alloy plays a crucial role. The melting rate of AlSi12 added to the melt is much higher than that of the mixed salt. When added before or together with the mixed salt, the melt temperature first drops rapidly and then rises rapidly under the influence of the reaction heat, failing to achieve the effect of controlling the significant increase in the melt temperature during the reaction process, and thus unable to achieve the purpose of regulating the size of the reinforcing particles.

[0019] In some embodiments, the profile dimensions of the second AlSi12 eutectic alloy are all less than 30×30×30 mm.

[0020] Too large profile dimensions of the second AlSi12 eutectic alloy will cause a large local temperature drop and a long time to reach the equilibrium temperature through heat conduction, which is not conducive to achieving the control of the melt temperature uniformity. While too small profile dimensions will introduce a large amount of oxide films into the melt.

[0021] In some embodiments, the temperature of the desalting treatment is controlled at 600 - 630 °C, the pressure is not greater than 500 Pa, and the time is 15 - 30 min.

[0022] In some embodiments, the melt refining treatment is specifically: the melt refining treatment is carried out by the argon rotary injection method, with a rotation speed of 300 - 600 r / min, an argon pressure of 1 - 2 MPa, and a refining time of 15 - 25 min.

[0023] Furthermore, the intermediate metal can be selected from the types commonly used in the art, including but not limited to pure aluminum ingots.

[0024] Furthermore, the easily burned - out element can be selected from the types commonly used in the art, including but not limited to pure magnesium.

[0025] The reaction temperature in the prior art is generally 750-900 degrees, and the lowest temperature reported is 660-670 degrees. The present invention starts from adding mixed salt (600±10°C) until the reaction is completed and the slag removal operation is completed. During this stage, the temperature of the melt in the reaction process is significantly lower than that of the prior art. The applicant found that the reaction temperature has the most significant effect on the size of the enhanced particles. The higher the reaction temperature, the larger the size of the generated enhanced particles. When the reaction temperature is greater than 1000°C, a large number of enhanced particles with a size of micrometers are generated. When the reaction temperature is 700-900°C, the size distribution range of the generated enhanced particles is wide, and nanometer-level and micrometer-level particles exist at the same time. When the reaction temperature is lower than 650°C, the generated enhanced particles are almost all at the nanometer level. The use of a higher reaction temperature is conducive to the subsequent melt purification treatment because the residual salt or alkali metal in the melt volatilizes under the action of high temperature, reducing the difficulty of subsequent purification. When the reaction temperature is low, the residual salt or alkali metal in the melt is difficult to volatilize, which brings difficulties to the subsequent melt purification treatment. The present invention adopts vacuum desalination treatment after the reaction is completed by establishing a vacuum above the liquid surface to promote and accelerate the volatilization of residual salts or alkali metals in the melt, so as to reduce the difficulty of subsequent melt purification, thereby solving the problem of difficulty in melt purification caused by low-temperature reaction.

[0026] In some embodiments, the size of the nanoparticles in the nanoparticle-reinforced aluminum-based composite material is 80 to 90 nm.

[0027] In some embodiments, the elongation of the nanoparticle-reinforced aluminum-based composite material is not less than 6%.

[0028] In the present invention, the relationship between the centrifugal force on the nanoparticles and their volume and rotation speed is as follows:

[0029]

[0030] Wherein, F is the centrifugal force on the nanoparticles; ρ is the density of the nanoparticles; V is the volume of the nanoparticles; v is the linear velocity of the nanoparticles; and r is the distance from the nanoparticles to the center of rotation.

[0031] The density of the reaction product TiB2 (or ZrB2) particles is greater than that of the aluminum melt, and they quickly detach from the reaction interface under the action of centrifugal force, and their subsequent growth is inhibited. By adjusting the crucible speed, the centrifugal force on the nanoparticles is changed, and the volume of the nanoparticles detached from the reaction interface is controlled, thereby achieving the regulation of the size of the nanoparticles. At the same time, the centrifugal force helps to improve the dispersibility of the nanoparticles.

[0032] The present invention performs vacuum desalination after the reaction is completed, and the free K in the melt + , H + 、F -Ions can quickly separate from the melt, thereby achieving the purpose of removing residual molten salt in the melt, and at the same time playing the role of degassing and slag removal. First, remove the residual molten salt, and then heat up the melt for alloying. This can not only reduce the difficulty of melt purification but also avoid the further reaction of the residual molten salt after increasing the temperature, which causes the strengthening particles to continue to grow. Therefore, it is beneficial to obtain nano-strengthening particles with uniform and fine sizes and a pure alloy melt.

[0033] The second aspect of the present invention provides a nano-particle reinforced aluminum matrix composite material obtained by the described preparation method.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] In the present invention, a motor installed at the bottom of the crucible drives the crucible to rotate to generate centrifugal force. Under the action of the centrifugal force, the alloy liquid forms a "U-shaped" liquid surface close to the crucible wall. After the mixed salt melts, it spreads on the "U" liquid surface, significantly increasing the contact area between the alloy liquid and the molten salt, improving the reaction efficiency, facilitating the diffusion of reaction products, and improving the dispersion of particles. In addition, the large reaction interface increases the heat dissipation area, which is conducive to the conduction of the heat released by the reaction and further improves the stability of the reaction process. It solves the problems in the traditional process, such as small reaction interface, long reaction duration, large heat release, etc., which make the reaction process difficult to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the equipment for preparing the nano-particle reinforced aluminum matrix composite material of the present invention, where 1 - crucible; 2 - alloy melt; 3 - molten salt; 4 - motor drive keyway.

[0037] Figure 2 It is the particle size, morphology and distribution diagram of the TiB2(10wt.%) / ZL101A composite material prepared in Example 1.

[0038] Figure 3 It is the particle size, morphology and distribution diagram of the TiB2(10wt.%) / ZL114A composite material prepared in Example 2.

[0039] Figure 4 It is the particle size, morphology and distribution diagram of the TiB2(10wt.%) / ZL101A composite material prepared in Comparative Example 1.

[0040] Figure 5 It is the particle size, morphology and distribution diagram of the TiB2(10wt.%) / ZL114A composite material prepared in Comparative Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Example 1

[0043] This embodiment provides a preparation method of TiB2(10wt.%) / ZL101A composite material. The preparation method includes the following steps:

[0044] S1. Add the first AlSi12 eutectic alloy (51.3 kg) into a crucible and melt it. Heat it up to 600 ± 10 °C, keep it warm, and adjust the rotation speed of the crucible to 4000 r / min until the liquid level of the eutectic alloy adheres to the inner wall of the crucible in a "U" shape. The vertical distance from the highest point to the lowest point of the "U" - shaped liquid level is 2 / 3 of the height of the crucible, obtaining Material 1;

[0045] S2. Add 70.8 kg of mixed salts (potassium fluotitanate and potassium fluoroborate, with a Ti and B molar ratio of 1:2) to Material 1. After the mixed salts are completely melted, add 7 kg of the second AlSi12 eutectic alloy (with contour dimensions all less than 30×30×30 mm, and the addition amount is 10% of the weight of the mixed salts) to the crucible. Keep the temperature of the crucible not higher than 650 °C. After reacting for 15 min, slowly reduce the rotation speed to 0. After the liquid level is stable, skim the slag. Control the temperature at 620 - 650 °C, the pressure not greater than 500 Pa, and the time for 20 min for desalting treatment, obtaining Material 2;

[0046] S3. Heat Material 2 to 770 °C, add 32 kg of pure aluminum ingots and 2.5 kg of AlTi4 master alloy. Control the temperature to 710 °C, add 0.7 kg of the easily burned - out element pure magnesium, and perform melt refining treatment by argon rotary spraying method. The rotation speed is 500 r / min, the argon pressure is 1 MPa, and the refining time is 20 min. Then cast to obtain the nano - particle reinforced aluminum - matrix composite material.

[0047] As Figure 2 shown, the TiB2 particle size of the TiB2(10wt.%) / ZL101A aluminum - matrix composite material prepared in this embodiment is concentrated in the range of 80 - 90 nm. After T6 heat treatment, using the test method of GB / T 228.1 - 2010, the tensile strength is 398 MPa, the yield strength is 354 MPa, and the elongation is 8%.

[0048] Example 2

[0049] This embodiment provides a method for preparing TiB2(10wt.%) / ZL114A composite material, and the preparation method includes the following steps:

[0050] S1. Add the first AlSi12 eutectic alloy (52.6 kg) into a crucible and melt it. Heat it up to 600 ± 10 °C, keep it warm, and adjust the rotation speed of the crucible to 3000 r / min until the liquid surface of the eutectic alloy adheres tightly to the inner wall of the crucible in a "U" shape. The vertical distance from the highest point to the lowest point of the "U" - shaped liquid surface is 3 / 4 of the height of the crucible, obtaining Material 1;

[0051] S2. Add 70.8 kg of mixed salt into Material 1, where the atomic ratio of Ti and B is 1:2. After the mixed salt is completely melted, add 5.7 kg of the second AlSi12 eutectic alloy (the contour size is less than 30×30×30 mm, and the addition amount is 8% of the weight of the mixed salt) into the crucible. Keep the temperature of the crucible not higher than 650 °C. After reacting for 30 min, slowly reduce the rotation speed to 0. After the liquid surface is stable, skim the slag. Control the temperature at 620 - 650 °C, the pressure is not greater than 500 Pa, and the time is 20 min for desalting treatment, obtaining Material 2;

[0052] S3. Heat Material 2 to 770 °C, add 35 kg of pure Al ingot and 2.5 kg of AlTi4 master alloy. Control the temperature to 710 °C, add 0.9 kg of the easily - burned - out element pure magnesium, and carry out melt refining treatment by argon rotary injection method. The rotation speed is 600 r / min, the argon pressure is 2 MPa, and the refining time is 25 min. Then pour it to obtain the nano - particle reinforced aluminum - matrix composite material.

[0053] As Figure 3 shown, the TiB2 particle size of the TiB2(10wt.%) / ZL114A aluminum - matrix composite material prepared in this embodiment is concentrated in the range of 80 - 90 nm. After T6 heat treatment, using the test method of GB / T 228.1 - 2010, the tensile strength is 428 MPa, the yield strength is 363 MPa, and the elongation is 6%.

[0054] Comparative Example 1

[0055] This comparative example provides a method for preparing TiB2(10wt.%) / ZL101A composite material. The specific implementation method is the same as that of Example 1, except that in step S1, the first AlSi12 eutectic alloy is melted in a crucible, heated up to 600 ± 10 °C, and kept warm to obtain Material 1.

[0056] As Figure 4As shown, the particle size of TiB2 in the prepared TiB2(10wt.%) / ZL101A aluminum matrix composite is concentrated in the range of 80 - 90 nm. After T6 heat treatment, the tensile strength is 334 MPa, the yield strength is 195 MPa, and the elongation is 1.5%.

[0057] Comparative Example 2

[0058] This comparative example provides a preparation method of TiB2(10wt.%) / ZL114A composite material. The specific implementation is the same as that of Example 2, except that in step S2, the second AlSi12 eutectic alloy is not added.

[0059] As Figure 5 shown, the particle size of TiB2 in the prepared TiB2(10wt.%) / ZL114A aluminum matrix composite is concentrated at 300 nm, and the agglomeration tendency is serious. After T6 heat treatment, the tensile strength is 355 MPa, the yield strength is 280 MPa, and the elongation is 3.5%.

[0060] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a nanoparticle-reinforced aluminum matrix composite by centrifugal reaction, characterized in that, The preparation method includes the following steps: S1. Melt the first AlSi12 eutectic alloy crucible, heat it up to 600 ± 10 °C, keep it warm, adjust the crucible rotation speed to 3000 - 4000 r / min until the eutectic alloy liquid level is in a "U" shape closely attached to the inner wall of the crucible to obtain Material 1; S2. Add mixed salt to Material 1. After the mixed salt is completely melted, add the second AlSi12 eutectic alloy to the crucible. Keep the crucible temperature not higher than 650 °C. After reacting for 10 - 20 min, slowly reduce the rotation speed to 0. After the liquid level is stable, skim the slag and perform desalting treatment to obtain Material 2; The temperature of the desalting treatment is controlled at 600 - 630 °C, the pressure is not greater than 500 Pa, and the time is 15 - 30 min; S3. Heat Material 2 to 760 - 780 °C, add intermediate metal, control the temperature to 700 - 720 °C, add easily burned elements for melt refining treatment, and pour to obtain the nano-particle reinforced aluminum matrix composite material; The specific melt refining treatment is: carry out melt refining treatment by argon gas rotary injection method, with a rotation speed of 300 - 600 r / min, an argon gas pressure of 1 - 2 MPa, and a refining time of 15 - 25 min; The size of the nano-particles in the nano-particle reinforced aluminum matrix composite material is 80 - 90 nm, and the elongation rate of the nano-particle reinforced aluminum matrix composite material is not less than 6%; 2. The preparation method of the nano-particle reinforced aluminum matrix composite material prepared by centrifugal reaction according to claim 1, characterized in that, The addition amount of the second AlSi12 eutectic alloy is 5 - 10 wt% of the addition amount of the mixed salt; 3. The preparation method of the nanoparticle-reinforced aluminum matrix composite material prepared by centrifugal reaction according to claim 1, characterized in that, The mixed salt is a mixture of potassium hexafluorotitanate and potassium tetrafluoroborate after baking; 4. The preparation method of the nanoparticle-reinforced aluminum matrix composite material prepared by centrifugal reaction according to claim 1, characterized in that, The profile dimensions of the second AlSi12 eutectic alloy are all less than 30 × 30 × 30 mm; 5. A nano-particle reinforced aluminum matrix composite material obtained by the preparation method according to any one of claims 1 - 4.

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