Method and device for indirect ultrasonic preparation of semi-solid alloy based on SEED method

Abstract

This application belongs to the field of semi-solid alloys, and more specifically, relates to a method and apparatus for preparing semi-solid alloys by indirect ultrasonication based on the SEED method. The proposed method for preparing semi-solid alloys by indirect ultrasonication based on the SEED method involves gradient design of the supercooling degree and target solid fraction of the alloy melt. By simultaneously subjecting the alloy melt to eccentric rotation and indirect ultrasonication, and with step-by-step set process parameters for eccentric rotation and indirect ultrasonication, the nucleation and spheroidization processes of solid grains during the cooling process of the alloy melt are precisely controlled. Compared with the existing SEED method, this significantly reduces the primary phase size of solid grains in the slurry and increases the proportion of spheroidal crystals.

Description

Technical Field

[0001] This application belongs to the field of semi-solid alloys, and more specifically, relates to a method and apparatus for indirect ultrasonic preparation of semi-solid alloys based on the SEED method. Background Technology

[0002] Semi-solid forming technology is an advanced manufacturing technology that directly shapes semi-solid metal blanks with special microstructures and forming properties, located at temperatures between the solidus and liquidus lines, into parts. This technology enables efficient near-net-shape forming of complex components under relatively low forming loads, playing a crucial role in improving the quality and performance utilization of metal materials, extending mold life, and achieving energy conservation and emission reduction. The ability to prepare semi-solid slurries with fine and uniformly distributed spherulitic microstructures is fundamental to semi-solid forming technology. Existing methods for improving the refinement and spheruliticity of alloy microstructures mainly include the following:

[0003] (1) Mechanical stirring method: During the solidification process of molten metal, stirring elements are used to vigorously stir the molten metal to affect the growth of alloy structure. However, this method is prone to problems such as corrosion of stirring elements, contamination of semi-solid slurry and uneven structure when preparing semi-solid slurry.

[0004] (2) Electromagnetic stirring method achieves stirring of molten metal by applying a rotating magnetic field to the molten metal, which refines the grain structure and makes the structure more uniform. Compared with mechanical stirring method, electromagnetic stirring method does not directly contact the molten metal phase and is less likely to cause pollution. However, this method has high requirements for equipment, high energy consumption, and high production cost.

[0005] (3) Inclined plate method: Liquid metal is poured onto a cooling plate equipped with a condensation device and condensation channel, allowing the liquid metal to cool to a semi-solid state and then flow into a mold to prepare a semi-solid slurry. This method has low equipment requirements and is simple to operate. However, the slurry is extremely prone to air entrapment and inclusion, resulting in defects such as porosity.

[0006] (4) Direct ultrasound-assisted method involves placing an ultrasonic amplitude transformer directly below the molten metal surface to transfer wave energy into the molten metal. The cavitation effect (formation and collapse of bubbles) and acoustic flow effect (internal flow of the liquid) of ultrasound are used to break up dendritic structures, promoting grain refinement and spheroidization. This method can achieve effective grain refinement at lower temperatures and reduces environmental pollution. However, the sound pressure of ultrasound decreases sharply with increasing distance. When the volume of the molten metal is too large, the microstructure farther from the ultrasonic head is difficult to refine. Furthermore, direct ultrasound can lead to corrosion of the ultrasonic amplitude transformer and contamination of the molten metal.

[0007] (5) The SEED method, short for Swirling Enthalpy Equilibrium Device, involves pouring the melt into a rotating container (such as an inclined rotating drum). By controlling the rotation speed and cooling rate, the melt forms a uniform solid-liquid two-phase region (the solid phase ratio is usually 30%~60%) under shear force. When preparing semi-solid metal slurry using the SEED method, the heat exchange mainly relies on the drum to cool the superheated melt. As heat exchange proceeds, the temperature of the drum increases, the temperature difference between the drum and the melt decreases, the heat exchange rate slows down, and the preparation time is longer. This further increases the probability of gas entrapment and oxide inclusions, thus affecting the quality and performance of the casting.

[0008] Existing mechanical stirring methods are prone to contamination of the molten metal and corrosion of the stirring elements; electromagnetic stirring methods have high production costs and high equipment requirements; inclined plate methods are prone to problems such as air entrapment and inclusions; ultrasonic amplitude transformers have a good cavitation effect near the ultrasonic amplitude transformer, but the effect is not good at positions away from the ultrasonic amplitude transformer; the SEED method relies on the cylinder to cool and exchange heat for the superheated molten metal, but the preparation time is long, and it is prone to air entrapment, oxidation inclusions, and uneven microstructure. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this application aims to provide a method and apparatus for indirect ultrasonic preparation of semi-solid alloys based on the SEED method. This method addresses the technical problems existing in the current SEED method for preparing semi-solid alloys, such as long preparation time, easy gas entrapment, oxidation inclusions, and uneven microstructure, as well as the problems of sound pressure attenuation, easy corrosion of the amplitude transformer, and contamination of the melt caused by direct ultrasonication.

[0010] To achieve the above objectives, in a first aspect, this application provides a method for indirect ultrasonic preparation of semi-solid alloys based on the SEED method, comprising the following steps:

[0011] (1) The alloy melt placed in the slurry container is heated to above the liquidus line to eliminate the genetic nuclei, and a protective gas is introduced into the slurry container;

[0012] (2) When the alloy melt cools down to the liquidus temperature, the slurry container is rotated eccentrically at the first rotation speed, and an asymmetric shear flow is generated inside the alloy melt, thus initially establishing melt convection;

[0013] (3) Cool the alloy melt to the temperature corresponding to the first target solid fraction, increase the eccentric rotation speed to the second rotation speed to promote uniform nucleation of the melt, and subject the alloy melt to indirect ultrasound. Under the first ultrasound power, use the transient high pressure generated by cavitation effect and acoustic flow effect to excite heterogeneous nucleation and suppress the formation of local dendrites; the first target solid fraction is 20-25%;

[0014] (4) Further cool the alloy melt to the temperature corresponding to the second target solid fraction, further increase the eccentric rotation speed to the third rotation speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and increase the power of the indirect ultrasound to the second ultrasound power to break up the grain agglomerates, and use acoustic flow disturbance to suppress the ripening of the primary alloy grains; the second target solid fraction is 35-45%;

[0015] (5) Reduce the eccentric rotation speed to the fourth rotation speed to maintain the convection intensity of the semi-solid slurry, and reduce the indirect ultrasonic power to the third ultrasonic power to continuously suppress the ripening of the primary grains of the alloy through micro-disturbance, thereby obtaining a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, the fourth rotation speed is less than the third rotation speed, and greater than or equal to the first rotation speed.

[0016] Preferably, in step (1), the alloy melt is superheated to 80-120°C above the liquidus line for 30-80 seconds to eliminate genetic nuclei.

[0017] Preferably, in step (2), the first rotational speed is 20-40 rpm, the eccentricity is set to 10-15 mm, and the rotation time is 10-15 s.

[0018] Preferably, in step (3), the temperature is reduced to the temperature corresponding to the first target solid fraction at a rate of 15-20℃ / min; in step (3), the second rotation speed is 60-90 rpm; the first ultrasonic power is 1-1.5 kW, and the ultrasonic time is 20-30 s.

[0019] Preferably, step (4) further cools the temperature to the temperature corresponding to the second target solid fraction at a rate of 8-15℃ / min.

[0020] More preferably, the third rotation speed in step (4) is 140-160 rpm; the second ultrasonic power is 1.5-2 kW, and the ultrasonic time is 20-60 s.

[0021] More preferably, the fourth rotation speed in step (5) is 70-90 rpm, the third ultrasonic power is 0.4-0.6 kW, and the ultrasonic time is 10-20 s.

[0022] According to another aspect of the present invention, a semi-solid alloy preparation apparatus for implementing the method is provided, comprising an eccentric rotating device, a slurry container placed on the eccentric rotating device, a plurality of ultrasonic amplitude transformers disposed on the outer wall of the slurry container, and an ultrasonic control unit; wherein:

[0023] The multiple ultrasonic amplitude transformers are evenly distributed on the outer wall of the slurry container.

[0024] Preferably, the distance between the end of each ultrasonic amplitude transformer and the wall of the slurry container is 1-3 mm, and the 1-3 mm distance is filled with a solid coupling agent.

[0025] Preferably, the solid coupling agent is a copper foil.

[0026] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0027] (1) The present invention proposes a method for preparing semi-solid alloys by indirect ultrasound based on the SEED method. By designing the supercooling degree and target solid fraction of the alloy melt in a gradient manner, the alloy melt is simultaneously subjected to eccentric rotation and indirect ultrasound. With the step-by-step setting of eccentric rotation and indirect ultrasound process parameters, the nucleation and spheroidization process of solid grains during the cooling process of the alloy melt is precisely controlled. Compared with the existing SEED method, the primary phase size of solid grains in the slurry is significantly reduced and the proportion of spheroids is increased.

[0028] (2) The present invention combines eccentric rotation with indirect ultrasound. The enthalpy balance is controlled by eccentric rotation, and the micro-cavitation disturbance is achieved by indirect ultrasound, which prevents the occurrence of chilled layer, breaks dendritic structure, promotes grain refinement and spheroidization, and makes the structure uniform.

[0029] (3) The present invention uses indirect ultrasound, and the ultrasonic amplitude transformer does not come into direct contact with the melt, thus avoiding corrosion of the ultrasonic amplitude transformer by the melt.

[0030] (4) The present invention solves the problem of sound pressure attenuation in ultrasound assistance to a certain extent by combining eccentric rotation with indirect ultrasound in a spatiotemporal synergy. Compared with the existing SEED method, it significantly shortens the preparation time of semi-solid alloy and quickly prepares semi-solid slurry.

[0031] (5) The device for preparing semi-solid alloys by indirect ultrasound based on the SEED method provided by the present invention has a simple structure. Ultrasonic amplitude rods are evenly arranged on the wall of the slurry container. Each ultrasonic amplitude rod has a certain distance from the wall of the slurry container. The gap is filled with a solid coupling agent to transfer ultrasonic energy to the melt. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the preparation process of semi-solid alloys based on the SEED method using indirect ultrasonication, provided in an embodiment of this application.

[0033] Figure 2 This is a schematic diagram of an apparatus for indirect ultrasonic preparation of semi-solid alloys based on the SEED method provided in an embodiment of this application;

[0034] Figure 3This is a schematic diagram of the distribution of ultrasonic amplitude transformers uniformly arranged on the wall of the paddle container provided in the embodiments of this application;

[0035] Figure 4 This is a temperature-solid fraction curve of aluminum A356 alloy provided in Example 1 of this application;

[0036] Figure 5 These are the crystal phase diagrams of the semi-solid alloys prepared in the embodiments and comparative examples of this application; wherein content (a) is the crystal phase diagram of the aluminum A356 semi-solid slurry of Comparative Example 1, content (b) is the crystal phase diagram of the aluminum A356 semi-solid slurry prepared by the method of Example 1, and content (c) is the crystal phase diagram of the aluminum A356 semi-solid slurry prepared by Comparative Example 2.

[0037] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0038] 1-Pulp container; 2-Eccentric rotating device; 3-Ultrasonic amplitude transformer; 4-Ultrasonic control unit. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0040] Existing mechanical stirring methods are prone to contamination of the molten metal and corrosion of the stirring elements; electromagnetic stirring methods have high production costs and demanding equipment requirements; tilting plate methods are prone to problems such as air entrapment and inclusions; ultrasonic amplitude transformers have good cavitation effects near the transformer, but the effect is poor at locations far from the transformer; the SEED method relies on the cylinder to cool and transfer heat to the overheated melt, but the preparation time is long, and it is prone to air entrapment, oxidation inclusions, and uneven microstructure. Based on this, this invention proposes an indirect ultrasonic preparation method for semi-solid alloys based on the SEED method. The main inventive concept is to overcome the inherent dendrite growth tendency of alloys by actively and effectively intervening in the natural solidification process, and, under industrially feasible conditions, attempt to stably, efficiently, and repeatedly prepare semi-solid slurries with fine (micrometer-scale), uniform, spherical primary phases and precisely controllable solid phase fraction.

[0041] This invention provides a method for indirect ultrasonic preparation of semi-solid alloys based on the SEED method, such as... Figure 1 As shown, it includes the following steps:

[0042] (1) Melt overheating: The alloy melt placed in the slurry container on the eccentric rotating device is overheated to above the liquidus line to eliminate the inherited crystal nuclei, and a protective gas is introduced into the slurry container;

[0043] (2) Rotation initialization to start thermal enthalpy balance: When the alloy melt cools down to the liquidus temperature, the eccentric rotation device is started, so that the slurry container rotates eccentrically at the first speed. Asymmetric shear flow is generated inside the alloy melt, and melt convection is initially established, laying the foundation for thermal enthalpy balance.

[0044] (3) Nucleation and enthalpy balance: The alloy melt is cooled to the temperature corresponding to the first target solid fraction, the eccentric rotation speed is increased to the second rotation speed to promote uniform nucleation of the melt, and the alloy melt is subjected to indirect ultrasound. Under the first power, the transient high pressure generated by cavitation effect and acoustic flow effect is used to excite heterogeneous nucleation and suppress the formation of local dendrites; the first target solid fraction is 20-25%;

[0045] (4) Spheroidization and microstructure refinement: The alloy melt is further cooled to the temperature corresponding to the second target solid fraction, and the eccentric rotation speed is further increased to the third rotation speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and the power of indirect ultrasound is increased to the second power to break up the grain agglomerates, and the acoustic flow disturbance is used to suppress the ripening of the primary grains of the alloy; the second target solid fraction is 35-45%;

[0046] (5) Steady-state control of the structure: reduce the eccentric rotation speed to the fourth rotation speed to maintain the convection intensity of the semi-solid slurry, and reduce the indirect ultrasonic power to the third power to continuously suppress the ripening of the primary grains of the alloy through micro-disturbance, so as to obtain a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, the fourth rotation speed is less than the third rotation speed, and greater than or equal to the first rotation speed.

[0047] This invention first initiates eccentric rotation when the alloy melt is cooled to the liquidus temperature, generating asymmetric shear flow within the melt, improving the overall heat transfer efficiency, eliminating temperature gradients, and suppressing the growth of large-sized dendrites. Then, the eccentric rotation speed is increased, and indirect ultrasound is simultaneously initiated. Rotational shearing macroscopically breaks down dendrites, while ultrasonic cavitation microscopically refines the grains, allowing the primary phase size to be reduced to 30-60 micrometers. Further cooling appropriately increases the solidity, and combined with increased eccentric rotation speed and ultrasonic power, grain agglomerates are broken down, suppressing the maturation of primary alloy grains. Finally, the eccentric rotation speed and ultrasonic power are reduced to maintain the convection intensity of the semi-solid slurry and continuously suppress the maturation of primary alloy grains, resulting in a semi-solid alloy.

[0048] This invention achieves macroscopic enthalpy balance and shear spheroidization during the eccentric rotation-dominant stage of the alloy melt placed in a slurry container, while the ultrasonic strengthening stage refines the microstructure and inhibits ripening. The dual-field stabilization stage ensures microstructure uniformity and solidity accuracy. This breakthrough overcomes the limitations of the traditional SEED method, which relies on single mechanical shearing, and provides a new approach for the efficient preparation of semi-solid slurries. Furthermore, this invention lowers the nucleation barrier through ultrasonic cavitation, reducing the need for supercooling and improving the accuracy of solidity control.

[0049] In some embodiments, the alloy melt in step (1) is superheated to 80-120°C above the liquidus line for 30-80 seconds to eliminate genetic nuclei.

[0050] In some embodiments, in step (2), the first rotational speed is 20-40 rpm, the eccentricity is set to 10-15 mm, and the eccentric rotation time at the first rotational speed is 10-15 s.

[0051] In some embodiments, step (3) involves cooling to the temperature corresponding to the first target solid fraction at a rate of 15-20℃ / min; the second rotation speed in step (3) is 60-90 rpm; the first ultrasonic power is 1-1.5 kW, and the ultrasonic time is 20-30 s.

[0052] In some embodiments, step (4) further cools the temperature to the temperature corresponding to the second target solid fraction at a rate of 8-15℃ / min; the third rotation speed in step (4) is 140-160 rpm; and the second ultrasonic power is 1.5-2 kW.

[0053] In some embodiments, the fourth rotation speed in step (5) is 70-90 rpm, the third ultrasonic power is 0.4-0.6 kW, and the ultrasonic time is 10-20 s.

[0054] In preparing semi-solid alloys, this invention gradually increases the solid fraction in the alloy melt by controlling the melt undercooling, eccentric rotation speed, and indirect ultrasonic power and time. This optimizes the microstructure, reduces component segregation, improves slurry stability, enhances slurry rheological properties, and facilitates subsequent processing. For a specific alloy type, the alloy composition can be input into JMatPro (Java-based Materials Properties) software to obtain the temperature-solid fraction curve, thereby determining the temperature corresponding to the target solid fraction.

[0055] The term "solid fraction" or "solid percentage" used in this invention specification refers to the volume percentage of solid phase in the alloy melt.

[0056] The present invention also provides a semi-solid alloy preparation apparatus for implementing the method, such as... Figure 2 and Figure 3 As shown, it includes an eccentric rotating device 2, a slurry container 1 placed on the eccentric rotating device, multiple ultrasonic amplitude transformers 3 disposed on the outer wall of the slurry container, and an ultrasonic control unit 4; wherein:

[0057] like Figure 3 As shown, the plurality of ultrasonic amplitude transformers 3 are evenly distributed on the outer wall of the slurry container, and the distance between the end of each ultrasonic amplitude transformer 3 and the wall of the slurry container is 1-3 mm. A solid coupling agent is filled in the 1-3 mm gap, which helps to transfer ultrasonic energy to the melt. This indirect ultrasonic method also avoids corrosion caused by direct contact between the ultrasonic amplitude transformers and the melt. The ultrasonic control unit is used to control the ultrasonic power and time of the ultrasonic amplitude transformers. The number of ultrasonic amplitude transformers can be 3-6.

[0058] In some embodiments, the solid coupling agent is a copper foil, preferably a soft copper foil with a thickness in the micrometer range, such as electrolytic copper foil or rolled copper foil. A high-temperature resistant adhesive is used to bond the soft copper foil to the gap between the ultrasonic amplitude transformer and the container. High-temperature resistant adhesives such as Aremco 645 and Cotronics 989 are used.

[0059] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0060] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0061] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0062] The embodiments of this application are described below with reference to the accompanying drawings.

[0063] Comparative Example 1

[0064] Comparative Example 1 uses the traditional SEED method to prepare a semi-solid alloy, the specific method of which is as follows:

[0065] (1) The aluminum A356 alloy melt placed in the crucible on the eccentric rotating device is superheated to 100°C above the liquidus line and held for 1 minute to eliminate the inherited crystal nuclei, and argon gas is introduced as a protective gas.

[0066] (2) After cooling for 1 minute, when the alloy melt is cooled to the liquidus temperature of 616℃, start the eccentric rotation to 30 rpm with an eccentricity of 12 mm and rotate for 20 seconds. Continue to rotate to generate asymmetric shear flow inside the melt and initially establish melt convection.

[0067] (3) Increase the eccentric speed to 160 rpm and rotate for 80 s to promote uniform nucleation of the melt.

[0068] (4) After the rotation stops, let the melt stand for 60 seconds to allow the solid particles to settle initially. Open the valve at the bottom of the container to allow the residual liquid phase to seep out and drain. A semi-solid slurry is obtained in 50 seconds.

[0069] Example 1

[0070] use Figure 2 The prepared apparatus shown is used to prepare a semi-solid alloy. This apparatus includes an eccentric rotating device 2, a slurry container 1 (crucible) placed on the eccentric rotating device, three ultrasonic amplitude transformers 3 disposed on the outer wall of the crucible, and an ultrasonic control unit 4; wherein:

[0071] like Figure 3 As shown, three ultrasonic amplitude transformers 3 are evenly arranged at 120° angles on the outer wall of the crucible, with the end of each ultrasonic amplitude transformer 3 1.5 mm away from the crucible wall. Multiple layers of electrolytic copper foil, each approximately 100 μm thick, are filled within this 1.5 mm gap. The process is as follows:

[0072] (1) The aluminum A356 alloy melt placed in the crucible on the eccentric rotating device is superheated to 100°C above the liquidus line and held for 1 minute to eliminate the inherited crystal nuclei, and argon gas is introduced as a protective gas.

[0073] (2) When the temperature of the alloy melt is 616℃ after cooling for 1 minute, start the eccentric rotation to the first speed of 30 rpm and the eccentric distance is 12 mm. Continue to rotate for 15 seconds to generate asymmetric shear flow inside the melt and initially establish melt convection.

[0074] (3) such as Figure 4 As shown, according to the temperature-solid fraction relationship curve of the alloy, when the solid fraction is 25%, the alloy temperature is 601℃. After 35s, the alloy melt is cooled to the lower limit temperature of 601℃ for the first target solid fraction of 25%, and the eccentric rotation speed is increased to the second rotation speed of 90rpm to promote uniform nucleation of the melt. At the same time, the alloy melt is subjected to indirect ultrasound for 20s. Under the first ultrasonic power of 1.2kW, the transient high pressure generated by cavitation effect and acoustic flow effect is used to excite heterogeneous nucleation and suppress the formation of local dendrites.

[0075] (4) such as Figure 4As shown, when the solid fraction is 40%, the alloy temperature is 586℃. After 40 seconds, the alloy melt is cooled to the temperature corresponding to the second target solid fraction of 40%, which is 586℃. The eccentric rotation speed is further increased to a third speed of 150 rpm to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize. Simultaneously, the power of the indirect ultrasound is increased to a second ultrasound power of 1.8 kW to break up the grain agglomerates. Ultrasound is performed for 30 seconds. Acoustic flow disturbance is used to suppress the ripening of the primary alloy grains.

[0076] (5) Reduce the eccentric rotation speed to the fourth rotation speed of 70 rpm to maintain the convection intensity of the semi-solid slurry, and simultaneously reduce the indirect ultrasonic power to the third ultrasonic power of 0.5 kW, and ultrasonic for 15 s to continuously suppress the ripening of the alloy primary grains by micro-disturbance, so as to obtain a semi-solid alloy.

[0077] Comparative Example 2

[0078] The preparation apparatus is the same as in Example 1. The difference lies in the preparation method, which is as follows:

[0079] (1) The aluminum A356 alloy melt placed in the crucible on the eccentric rotating device is superheated to 100°C above the liquidus line and held for 1 minute to eliminate the inherited crystal nuclei, and argon gas is introduced as a protective gas.

[0080] (2) After 1 minute, when the alloy melt cools down to the liquidus temperature of 616℃, start the eccentric rotation to 150rpm with an eccentricity of 12mm, and at the same time turn on the ultrasonic power of 1.6KW. Stir continuously for 80s, cool down for 75s, until the solid fraction reaches 40% to obtain a semi-solid slurry.

[0081] Table 1. Relevant parameters for preparing semi-solid alloy slurries in different comparative examples and embodiments.

[0082]

[0083] Table 1 shows the primary phase sizes prepared in different comparative examples and embodiments. The metallographic images were binarized using ImageJ software, and the average value was taken after counting at least five grains using the equivalent circle diameter method. The proportion of spherical crystals was automatically calculated using the morphological analysis module of Olympus Stream software, with a shape factor F > 0.8 as the criterion. The crystal phase diagrams of the semi-solid alloy slurries prepared in different comparative examples and embodiments are shown below. Figure 5 As shown, Figure 5 Content (a) is a crystal phase diagram of the aluminum A356 semi-solid slurry of Comparative Example 1, and content (b) is a crystal phase diagram of the aluminum A356 semi-solid slurry prepared by the method of Example 1. Figure 5Content (c) shows the crystal phase diagram of the aluminum A356 semi-solid slurry prepared in Comparative Example 2. As can be seen from the diagram, compared to the other two methods, the aluminum A356 semi-solid slurry prepared in Example 1 has a more uniform microstructure, finer primary phase size, and a higher proportion of spheroidal crystals. This indicates that Example 1, through process control of the supercooled nucleation and grain spheroidization maturation of the alloy melt, and by using step-by-step control of eccentric rotation and indirect ultrasound, not only has a shorter preparation cycle but also better preparation results for the semi-solid alloy slurry. Comparative Example 1 uses the traditional SEED method, while Comparative Example 2 uses both eccentric rotation and indirect ultrasound control, but the rotation speed of the eccentric rotation and the power of the indirect ultrasound remain unchanged. Although the total time is the same as in Example 1, the final semi-solid alloy obtained has a larger primary phase size and a much smaller proportion of spheroidal crystals compared to Example 1.

[0084] This invention achieves macroscopic enthalpy balance and shear spheroidization during the rotation-dominant stage through the spatiotemporal synergy of rotational enthalpy balance (global heat flux control) and indirect ultrasound (micro-area cavitation disturbance). The ultrasound-enhanced stage refines micrograins and suppresses ripening. The dual-field stabilization stage ensures microstructure uniformity and solidity accuracy. This breakthrough overcomes the limitations of traditional SEED methods, which rely on single mechanical shearing, and provides a new approach for the efficient preparation of semi-solid slurries. The method for preparing semi-solid alloys in this invention is simple and requires minimal equipment. It cleverly solves the technical problems of existing SEED methods, such as long preparation time, easy gas entrapment, oxidation inclusions, and uneven microstructure, as well as the problems of sound pressure attenuation, easy corrosion of the amplitude transformer, and melt contamination associated with direct ultrasound.

[0085] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for indirect ultrasonic preparation of semi-solid alloys based on the SEED method, characterized in that, Includes the following steps: (1) Heat the alloy melt placed in the slurry container to above the liquidus line and introduce protective gas into the slurry container; (2) When the alloy melt cools down to the liquidus temperature, the slurry container is rotated eccentrically at the first rotation speed to initially establish melt convection inside the alloy melt; (3) Cool the alloy melt to the temperature corresponding to the first target solid fraction, increase the eccentric rotation speed to the second rotation speed to promote uniform nucleation of the melt, and perform indirect ultrasound on the alloy melt to excite heterogeneous nucleation under the first ultrasound power and suppress the formation of local dendrites; the first target solid fraction is 20-25%; (4) Further cool the alloy melt to the temperature corresponding to the second target solid fraction, and increase the eccentric rotation speed to the third rotation speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and increase the power of the indirect ultrasound to the second ultrasound power to break up the grain agglomerates, and use acoustic flow disturbance to suppress the ripening of the primary grains of the alloy; the second target solid fraction is 35-45%; (5) Reduce the eccentric rotation speed to the fourth rotation speed to maintain the convection intensity of the semi-solid slurry, and reduce the indirect ultrasonic power to the third ultrasonic power to continuously suppress the ripening of the primary grains of the alloy through micro-disturbance, thereby obtaining a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, the fourth rotation speed is less than the third rotation speed, and greater than or equal to the first rotation speed.

2. The method as described in claim 1, characterized in that, In step (1), the alloy melt is superheated to 80-120°C above the liquidus line for 30-80 seconds.

3. The method as described in claim 1, characterized in that, Step (2) The first rotation speed is 20-40 rpm, the eccentricity is set to 10-15 mm, and the rotation time is 10-15 s.

4. The method as described in claim 1, characterized in that, Step (3) Cool down to the temperature corresponding to the first target solid fraction at a rate of 15-20℃ / min; Step (3) The second rotation speed is 60-90 rpm; the first ultrasonic power is 1-1.5 kW, and the ultrasonic time is 20-30 s.

5. The method as described in claim 1, characterized in that, Step (4) Cool down to the temperature corresponding to the second target solid fraction at a rate of 8-15℃ / min.

6. The method as described in claim 1, characterized in that, The third rotation speed in step (4) is 140-160 rpm; the second ultrasonic power is 1.5-2 kW, and the ultrasonic time is 20-60 s.

7. The method as described in claim 1, characterized in that, In step (5), the fourth rotation speed is 70-90 rpm, the third ultrasonic power is 0.4-0.6 kW, and the ultrasonic time is 10-20 s.

8. An apparatus for preparing a semi-solid alloy as described in any one of claims 1 to 7, characterized in that, The system includes an eccentric rotating device (2), a slurry container (1) placed on the eccentric rotating device, multiple ultrasonic amplitude transformers (3) disposed on the outer wall of the slurry container, and an ultrasonic control unit (4); wherein: The multiple ultrasonic amplitude rods (3) are evenly distributed on the outer wall of the slurry container (1).

9. The preparation apparatus as described in claim 8, characterized in that, The distance between the end of each ultrasonic amplitude rod (3) and the wall of the slurry container is 1-3 mm, and the 1-3 mm distance is filled with solid coupling agent.

10. The preparation apparatus according to claim 9, characterized in that, The solid coupling agent is copper foil.

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