Method and device for preparing semi-solid alloy through indirect ultrasound based on SEED method

Abstract

The invention belongs to the field of semi-solid alloy, and particularly relates to a method and device for preparing semi-solid alloy through indirect ultrasound based on an SEED method. According to the method for preparing the semi-solid alloy through indirect ultrasound based on the SEED method, gradient design is carried out on the supercooling degree and the target solid-phase fraction of the alloy melt, eccentric rotation and indirect ultrasound are carried out on the alloy melt at the same time, eccentric rotation and indirect ultrasound process parameters which are set step by step are matched, and the semi-solid alloy is prepared. The nucleation and spheroidizing processes of solid crystal grains in the alloy melt cooling process are finely controlled, and compared with an existing SEED method, the method has the advantages that the primary phase size of the solid crystal grains in slurry is remarkably reduced, and the proportion of spherical crystals is increased.

Description

Technical Field

[0001] The present application belongs to the field of semi-solid alloys, and more specifically, to a method and apparatus for indirectly ultrasonically preparing semi-solid alloys based on the SEED method. Background Art

[0002] Semi-solid forming technology is an advanced manufacturing technique that directly forms parts from semi-solid metal blanks at a temperature between the solidus and liquidus lines, possessing unique microstructures and forming properties. This technology enables efficient near-net-net forming of complex components at low forming loads, playing a significant role in improving the quality and performance utilization of metal materials, extending mold life, and reducing energy consumption and emissions. The ability to prepare a semi-solid slurry with fine and evenly distributed semi-solid spherulites is fundamental to semi-solid forming technology. Existing methods for improving alloy microstructure refinement and spheroidization primarily include the following: (1) Mechanical stirring method: During the solidification process of the metal melt, a stirring element is used to vigorously stir the metal melt to influence the growth of the alloy structure. However, this method is very likely to cause corrosion of the stirring element, contamination of the semi-solid slurry, and uneven structure when preparing the semi-solid slurry.

[0003] (2) Electromagnetic stirring: Electromagnetic stirring is a method of stirring the molten metal by applying a rotating magnetic field to the molten metal, thereby refining the grain structure and making the structure uniform. Compared with mechanical stirring, electromagnetic stirring does not directly contact the molten metal and is less likely to cause contamination. However, this method has high equipment requirements, high energy consumption, and high production costs.

[0004] (3) The inclined plate method pours the molten metal onto a cooling plate equipped with a condensation device and condensation channels. After cooling, the molten metal reaches a semi-solid state and flows into a mold to prepare a semi-solid slurry. This method does not require high equipment requirements and is simple to operate. However, the slurry is very prone to air entrainment and inclusions, resulting in defects such as pores.

[0005] (4) Direct ultrasonic-assisted method: By placing the ultrasonic horn directly below the melt surface, the wave energy is transferred to the metal melt, and the cavitation effect (formation and rupture of bubbles) and acoustic streaming effect (internal flow of liquid) of the ultrasound are used to break up the dendrite structure and promote grain refinement and spheroidization. This method can achieve effective grain refinement at a lower temperature and reduce environmental pollution. However, the sound pressure of ultrasound decays sharply with increasing distance. When the volume of the metal melt is too large, the tissue far away from the ultrasonic head is difficult to be refined. In addition, direct ultrasound can cause corrosion of the ultrasonic horn and contamination of the melt.

[0006] (5) The SEED method, also known as the Swirling Enthalpy Equilibrium Device, involves pouring the melt into a rotating container (such as an inclined rotating drum). By controlling the rotational speed and cooling rate, the melt forms a uniform solid-liquid two-phase region (the solid phase ratio is usually 30% to 60%) under the action of shear force. When preparing semi-solid metal slurry using the SEED method, the drum is mainly used to cool the overheated melt for heat exchange. As the heat exchange proceeds, the drum temperature rises, the temperature difference with the melt decreases, the heat exchange rate slows down, and the preparation time is prolonged, which further increases the probability of gas entrainment and oxidation inclusions, thereby affecting the quality and performance of the casting.

[0007] The existing mechanical stirring method is prone to contamination of the metal melt and corrosion of the stirring elements; the electromagnetic stirring method has high production costs and high equipment requirements; the inclined plate method is prone to problems such as air entrapment and inclusions; there is a good cavitation effect near the ultrasonic horn, but the effect is poor at a distance from the ultrasonic horn; the SEED method relies on a cylinder to cool and heat the overheated melt, but the preparation time is long, it is prone to air entrapment, oxidation inclusions, and uneven microstructure. Summary of the Invention

[0008] In response to the defects of the existing technology, the purpose of this application is to provide a method and device for indirect ultrasonic preparation of semi-solid alloys based on the SEED method, aiming to solve the technical problems existing in the existing SEED method semi-solid alloy preparation process, such as long preparation time, easy gas entrainment, oxidation inclusions, uneven microstructure, and direct ultrasound sound pressure attenuation, easy corrosion of the amplitude rod and contamination of the melt.

[0009] To achieve the above objectives, in a first aspect, the present application provides a method for preparing a semi-solid alloy by indirect ultrasonication based on the SEED method, comprising the following steps: (1) heating the alloy melt in a slurry container to above the liquidus to eliminate inherited crystal nuclei, and introducing a protective gas into the slurry container; (2) When the alloy melt is cooled to the liquidus temperature, the slurry container is rotated eccentrically at a first speed to generate an asymmetric shear flow inside the alloy melt and initially establish melt convection; (3) cooling the alloy melt to a temperature corresponding to a first target solid fraction, increasing the eccentric speed to a second speed to promote uniform nucleation of the melt, and indirectly ultrasonicating the alloy melt, using the transient high pressure generated by the cavitation effect and the acoustic streaming effect at a first ultrasonic power to stimulate heterogeneous nucleation and inhibit the formation of local dendrites; the first target solid fraction is 20-25%; (4) further cooling the alloy melt to a temperature corresponding to a second target solid fraction, further increasing the eccentric speed to a third speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and increasing the power of the indirect ultrasound to a second ultrasound power to break up the grain agglomerates and suppress the ripening of the primary grains of the alloy by using acoustic flow disturbance; the second target solid fraction is 35-45%; (5) reducing the eccentric speed to a fourth speed to maintain the convection intensity of the semi-solid slurry, and reducing the indirect ultrasonic power to a third ultrasonic power to continuously micro-perturb and suppress the ripening of the primary grains of the alloy, thereby obtaining a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, and the fourth speed is less than the third speed and is greater than or equal to the first speed.

[0010] Preferably, in step (1), the alloy melt is superheated to 80-120° C. above the liquidus for 30-80 seconds to eliminate genetic nuclei.

[0011] Preferably, in 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.

[0012] Preferably, in step (3), the temperature is lowered to a temperature corresponding to the first target solid fraction at a rate of 15-20°C / 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.

[0013] Preferably, in step (4), the temperature is further lowered at a rate of 8-15°C / min to a temperature corresponding to the second target solid fraction.

[0014] Further 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.

[0015] Further preferably, 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.

[0016] According to another aspect of the present invention, there is provided a semi-solid alloy preparation device for implementing the method, comprising an eccentric rotating device, a slurry container placed on the eccentric rotating device, a plurality of ultrasonic horns provided on the outer wall of the slurry container, and an ultrasonic control unit; wherein: The plurality of ultrasonic horns are evenly distributed on the outer wall of the pulp container.

[0017] Preferably, the distance between the end of each ultrasonic horn and the wall of the slurry container is 1-3 mm, and a solid coupling agent is filled in the distance of 1-3 mm.

[0018] Preferably, the solid coupling agent is metal copper foil.

[0019] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: (1) The present invention proposes a method for preparing semi-solid alloys by indirect ultrasound based on the SEED method. By gradient designing the supercooling degree and target solid phase fraction of the alloy melt, the alloy melt is simultaneously subjected to eccentric rotation and indirect ultrasound, and the eccentric rotation and indirect ultrasound process parameters are set in steps, the nucleation and spheroidization process of the solid grains during the cooling process of the alloy melt are precisely controlled. Compared with the existing SEED method, the primary phase size of the solid phase grains in the slurry is significantly reduced, and the proportion of spherical crystals is increased.

[0020] (2) The present invention coordinates eccentric rotation with indirect ultrasound, controls the thermal enthalpy balance through eccentric rotation, and uses indirect ultrasound to achieve micro-cavitation disturbance, prevent the occurrence of the chill layer, break the dendrite structure, promote the refinement and spheroidization of grains, and make the organization uniform.

[0021] (3) The present invention adopts indirect ultrasound, and the ultrasonic amplitude transformer does not come into direct contact with the melt, thereby avoiding corrosion of the ultrasonic amplitude transformer by the melt.

[0022] (4) The present invention solves the problem of sound pressure attenuation in ultrasound-assisted technology to a certain extent through the spatiotemporal coordination of eccentric rotation and indirect ultrasound. Compared with the existing SEED method, the preparation time of semi-solid alloy is significantly shortened, and semi-solid slurry is quickly prepared.

[0023] (5) The device for indirect ultrasonic preparation of semi-solid alloys based on the SEED method provided by the present invention has a simple structure. Ultrasonic amplitude transformers are evenly arranged on the wall of the slurry container. Each ultrasonic amplitude transformer 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is a schematic diagram of the preparation process of a semi-solid alloy prepared by indirect ultrasonication using the SEED method according to an embodiment of the present application; Figure 2 Schematic diagram of a device for indirect ultrasonic preparation of semi-solid alloys based on the SEED method provided in an embodiment of the present application; Figure 3 This is a schematic diagram of the distribution of ultrasonic horns evenly distributed on the wall of the paddle container provided in an embodiment of the present application; Figure 4 This is a temperature-solid phase ratio relationship curve of aluminum A356 alloy provided in Example 1 of the present application; Figure 5It is a crystal phase diagram of the semi-solid alloy prepared in the examples and comparative examples of the present 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 in comparative example 2.

[0025] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1- slurry container; 2- eccentric rotating device; 3- ultrasonic horn; 4- ultrasonic control unit. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0027] 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; the inclined plate method is prone to problems such as air entrapment and inclusions; the ultrasonic horn has a good cavitation effect near the ultrasonic horn, but the effect is poor at locations far from the horn; the SEED method relies on a cylinder to cool and heat the superheated melt, but this method takes a long time to prepare, is prone to air entrapment, oxidation inclusions, and produces an uneven microstructure. Based on these considerations, the present invention proposes a method for indirect ultrasonic preparation of semi-solid alloys based on the SEED method. The main inventive concept is to overcome the alloy's inherent tendency to dendrite growth by actively and effectively intervening in the natural solidification process. Under industrially feasible conditions, this method attempts to stably, efficiently, and reproducibly prepare a semi-solid slurry with a fine (micrometer-level), uniform, spherical primary phase and a precisely controllable solid phase fraction.

[0028] The present invention provides a method for preparing semi-solid alloys by indirect ultrasonic treatment based on SEED method, such as Figure 1 As shown, the following steps are included: (1) Melt overheating: The alloy melt in the slurry container placed on the eccentric rotating device is overheated to above the liquidus to eliminate the inherited crystal nuclei, and protective gas is introduced into the slurry container; (2) Rotation initialization to start thermal enthalpy balance: When the alloy melt is cooled to the liquidus temperature, the eccentric rotating device is started to make the slurry container rotate eccentrically at a first speed, and an asymmetric shear flow is generated inside the alloy melt, and melt convection is initially established, laying the foundation for thermal enthalpy balance; (3) Nucleation and enthalpy balance: The alloy melt is cooled to a temperature corresponding to a first target solid fraction, the eccentric speed is increased to a second speed, uniform nucleation of the melt is promoted, and the alloy melt is subjected to indirect ultrasound, and the transient high pressure generated by the cavitation effect and the acoustic streaming effect is used at a first power to stimulate heterogeneous nucleation and suppress the formation of local dendrites; the first target solid fraction is 20-25%; (4) Spheroidization and microstructure refinement: The alloy melt is further cooled to the temperature corresponding to the second target solid fraction, and the eccentric speed is further increased to the third speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and the power of the indirect ultrasound is increased to the second power to break up the grain agglomerates and use the acoustic flow disturbance to inhibit the ripening of the primary grains of the alloy; the second target solid fraction is 35-45%; (5) Microstructure steady-state control: reducing the eccentric speed to the fourth speed to maintain the convection intensity of the semi-solid slurry, and reducing the indirect ultrasonic power to the third power to continuously micro-perturb and suppress the ripening of the primary grains of the alloy, thereby obtaining a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, and the fourth speed is less than the third speed and is greater than or equal to the first speed.

[0029] The present invention first starts eccentric rotation when the alloy melt is cooled to the liquidus temperature, so as to generate asymmetric shear flow inside the melt, improve the heat transfer efficiency of the entire melt, eliminate temperature gradients, and inhibit the growth of large-sized dendrites; then the eccentric speed is increased, and indirect ultrasound is started at the same time, and the dendrites are macroscopically broken by rotational shearing, and the grains are microscopically refined by ultrasonic cavitation, so that the primary phase size can be broken to 30-60 microns; then the temperature is further lowered to appropriately increase the solid phase ratio, and the eccentric speed and ultrasonic power are increased to break the grain agglomerates and inhibit the ripening of the primary grains of the alloy; finally, the eccentric speed and ultrasonic power are reduced to maintain the convection intensity of the semi-solid slurry and continuously micro-perturb to inhibit the ripening of the primary grains of the alloy, so as to obtain a semi-solid alloy.

[0030] The present invention achieves macroscopic thermal enthalpy balance and shear spheroidization during the eccentric rotation-dominated phase by combining eccentric rotation and indirect ultrasonic coordinated control of the alloy melt placed in the slurry container; microscopic grain refinement and ripening suppression are achieved during the ultrasonic strengthening phase; and the dual-field stabilization phase ensures structural uniformity and solid fraction accuracy. This method breaks through 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. The present invention uses ultrasonic cavitation to reduce the nucleation barrier, minimize supercooling requirements, and improve solid fraction control accuracy.

[0031] In some embodiments, the alloy melt in step (1) is superheated to 80-120° C. above the liquidus for 30-80 seconds to eliminate genetic nuclei.

[0032] In some embodiments, in step (2), the first rotation speed is 20-40 rpm, the eccentric distance is set to 10-15 mm, and the eccentric rotation time at the first rotation speed is 10-15 s.

[0033] In some embodiments, step (3) is cooled at a rate of 15-20°C / min to a temperature corresponding to the first target solid fraction; 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.

[0034] In some embodiments, step (4) further cools the mixture to a temperature corresponding to the second target solid fraction at a rate of 8-15°C / min; the third rotation speed in step (4) is 140-160 rpm; and the second ultrasonic power is 1.5-2 kW.

[0035] 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.

[0036] When preparing semi-solid alloys, the present invention gradually increases the solid fraction in the alloy melt by controlling the melt undercooling, eccentric rotation speed, and indirect ultrasonic power and duration. This optimizes the microstructure, reduces compositional segregation, enhances slurry stability, and improves slurry rheological properties, facilitating subsequent processing. For a specific alloy type, the alloy composition can be input into JMatPro (Java-based Materials Properties) software to generate a temperature-solid fraction curve for the alloy, thereby determining the temperature corresponding to the target solid fraction.

[0037] The "solid phase ratio" or "solid phase fraction" mentioned in the present specification refers to the volume percentage of the solid phase in the alloy melt.

[0038] The present invention also provides a semi-solid alloy preparation device for implementing the method, such as Figure 2 and Figure 3 As shown, it includes an eccentric rotating device 2, a pulp container 1 placed on the eccentric rotating device, a plurality of ultrasonic horns 3 and an ultrasonic control unit 4 arranged on the outer wall of the pulp container; wherein: like Figure 3As shown, the multiple ultrasonic horns 3 are evenly distributed on the outer wall of the slurry container, with the end of each ultrasonic horn 3 spaced 1-3 mm from the container wall. This 1-3 mm gap is filled with a solid coupling agent, which helps transfer ultrasonic energy to the melt. This indirect ultrasonic method also avoids corrosion caused by direct contact between the ultrasonic horns and the melt. An ultrasonic control unit is used to control the ultrasonic power and timing of the ultrasonic horns. The number of ultrasonic horns can range from 3 to 6.

[0039] In some embodiments, the solid coupling agent is a metal copper foil, preferably a soft metal copper foil with a thickness in the micrometer range, such as electrolytic copper foil or rolled copper foil. High-temperature resistant adhesive, such as Aremco 645 or Cotronics 989, is used to adhere the soft metal copper foil to the gap between the ultrasonic horn and the container.

[0040] The embodiments of the present invention are implemented on 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 based on conventional conditions.

[0041] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0042] In the following examples, the process parameters without specific conditions are generally based on conventional conditions.

[0043] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0044] Comparative Example 1 Comparative Example 1: A semi-solid alloy was prepared using the conventional SEED method. The specific method is as follows: (1) The aluminum A356 alloy melt in the crucible on the eccentric rotating device is superheated to 100 °C above the liquidus for 1 minute to eliminate the inherited crystal nuclei, and the protective gas argon is introduced; (2) After cooling for 1 minute, when the alloy melt is cooled to the liquidus temperature of 616°C, the eccentric rotation is started to 30 rpm, the eccentric distance is 12 mm, and the rotation is continued for 20 seconds to generate asymmetric shear flow inside the melt and initially establish melt convection; (3) Increase the eccentric speed to 160 rpm and rotate for 80 s to promote uniform nucleation of the melt.

[0045] (4) After the rotation stops, the melt is allowed to stand for 60 seconds to allow the solid phase particles to initially settle. The valve at the bottom of the container is opened to allow the residual liquid phase to seep out and drain. A semi-solid slurry is obtained after 50 seconds.

[0046] Example 1 use Figure 2 The preparation device shown prepares semi-solid alloys. The preparation device includes an eccentric rotating device 2, a slurry container 1 (crucible) placed on the eccentric rotating device, three ultrasonic horns 3 arranged on the outer wall of the crucible, and an ultrasonic control unit 4; wherein: like Figure 3 As shown, three ultrasonic horns 3 are evenly arranged at 120 degrees on the outer wall of the crucible, and the distance between the end of each ultrasonic horn 3 and the crucible wall is 1.5 mm. In addition, multiple layers of electrolytic copper foil with a thickness of about 100 μm are filled in the 1.5 mm gap. According to the following method: (1) The aluminum A356 alloy melt in the crucible on the eccentric rotating device is superheated to 100 °C above the liquidus for 1 minute to eliminate the inherited crystal nuclei, and the protective gas argon is introduced; (2) After cooling for 1 minute, when the liquidus temperature of the alloy melt is 616°C, start the eccentric rotation to the first speed of 30 rpm, the eccentric distance is 12 mm, and continue to rotate for 15 seconds to generate asymmetric shear flow inside the melt and initially establish melt convection; (3) If Figure 4 As shown in the temperature-solid fraction relationship curve of the alloy, when the solid fraction is 25%, the alloy temperature is 601°C. After 35 seconds, the alloy melt is cooled to 601°C, the lower limit temperature of the first target solid fraction of 25%. The eccentric speed is increased to a second speed of 90 rpm to promote uniform nucleation of the melt. At the same time, the alloy melt is subjected to indirect ultrasound for a duration of 20 seconds at a first ultrasonic power of 1.2 kW. The transient high pressure generated by the cavitation effect and the acoustic streaming effect is used to stimulate heterogeneous nucleation and suppress the formation of local dendrites. (4) If Figure 4 As shown, when the solid fraction was 40%, the alloy temperature was 586°C. After 40 seconds, the alloy melt was cooled to 586°C, corresponding to the second target solid fraction of 40%. The eccentric speed was further increased to the third speed of 150 rpm to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize. The indirect ultrasonic power was simultaneously increased to the second ultrasonic power of 1.8 kW to break up grain agglomerates. Ultrasonication was continued for 30 seconds. Acoustic streaming perturbation was used to suppress the ripening of the primary grains of the alloy. (5) The eccentric speed was reduced to the fourth speed of 70 rpm to maintain the convection intensity of the semi-solid slurry, and the indirect ultrasonic power was simultaneously reduced to the third ultrasonic power of 0.5 kW, and the ultrasonic time was 15 s to suppress the ripening of the primary grains of the alloy by continuous micro-disturbance, thereby obtaining a semi-solid alloy.

[0047] Comparative Example 2 The preparation apparatus is the same as that in Example 1. The difference is that the preparation method is as follows: (1) The aluminum A356 alloy melt in the crucible on the eccentric rotating device is superheated to 100 °C above the liquidus for 1 minute to eliminate the inherited crystal nuclei, and the protective gas argon is introduced; (2) One minute later, when the alloy melt is cooled to the liquidus temperature of 616°C, the eccentric rotation is started to 150 rpm, the eccentric distance is 12 mm, and the ultrasound is turned on at the same time. The ultrasonic power is 1.6 kW, and the stirring time is continued for 80 s. The temperature is cooled for 75 s until the solid phase ratio reaches 40% to obtain a semi-solid slurry.

[0048] Table 1 Parameters of semi-solid alloy slurries prepared in different comparative examples and examples

[0049] The sizes of primary phases prepared in different comparative examples and examples in Table 1 were binarized using ImageJ software. The average value was obtained by counting more than 5 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 the shape factor F>0.8 as the judgment standard. The crystal phase diagrams of the semi-solid alloy slurries prepared in different comparative examples and examples are shown in Figure 1. 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 5 Content (c) is a crystal phase diagram of the aluminum A356 semi-solid slurry prepared in Comparative Example 2. As can be seen from the figure, compared with the other two methods, the aluminum A356 semi-solid slurry prepared in Example 1 has a more uniform microstructure, a finer primary phase size, and a higher proportion of spherical crystals. This demonstrates that Example 1, by controlling the supercooling nucleation of the alloy melt and the grain spheroidization and ripening process, and by utilizing step-by-step control of eccentric rotation and indirect ultrasound, not only shortens the preparation cycle but also achieves 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 maintains the same eccentric rotation speed and indirect ultrasound power. Although the total duration is the same as in Example 1, the resulting semi-solid alloy has a larger primary phase size and a much smaller proportion of spherical crystals than in Example 1.

[0050] This invention achieves macroscopic enthalpy balance and shear spheroidization during the rotation-dominant phase through the spatiotemporal synergy of rotational enthalpy balance (global heat flow control) and indirect ultrasound (micro-cavitation perturbation). Microscopic grain refinement and ripening suppression are achieved during the ultrasound-enhanced phase, while microstructure uniformity and solid fraction accuracy are ensured during the dual-field stabilization phase. This overcomes the limitations of the traditional SEED method, which relies solely on mechanical shearing, and provides a new approach for the efficient preparation of semi-solid slurries. The present invention's method for preparing semi-solid alloys is simple and requires minimal equipment. It cleverly addresses the technical challenges of existing SEED methods for preparing semi-solid alloys, including long preparation times, prone to gas entrainment, oxide inclusions, and microstructural inhomogeneity, as well as direct ultrasound, which presents acoustic pressure attenuation, susceptible to horn corrosion, and contamination of the melt.

[0051] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A method for preparing semi-solid alloys by indirect ultrasonication based on the SEED method, characterized in that: The steps include: (1) heating the alloy melt in a slurry container to above the liquidus, and introducing a protective gas into the slurry container; (2) When the alloy melt is cooled to the liquidus temperature, the slurry container is rotated eccentrically at a first speed to initially establish melt convection inside the alloy melt; (3) cooling the alloy melt to a temperature corresponding to a first target solid fraction, increasing the eccentric speed to a second speed to promote uniform nucleation of the melt, and indirectly ultrasonicating the alloy melt to stimulate heterogeneous nucleation at a first ultrasonic power to inhibit the formation of local dendrites; the first target solid fraction is 20-25%; (4) further cooling the alloy melt to a temperature corresponding to a second target solid fraction, and increasing the eccentric speed to a third speed to mechanically peel off the dendrite arms and force the crystal nuclei to spheroidize; and increasing the power of the indirect ultrasound to a second ultrasound power to break up the grain agglomerates and suppress the ripening of the primary grains of the alloy by using acoustic flow disturbance; the second target solid fraction is 35-45%; (5) reducing the eccentric speed to a fourth speed to maintain the convection intensity of the semi-solid slurry, and reducing the indirect ultrasonic power to a third ultrasonic power to continuously micro-perturb and suppress the ripening of the primary grains of the alloy, thereby obtaining a semi-solid alloy; and the third ultrasonic power is less than the first ultrasonic power, and the fourth speed is less than the third speed and is greater than or equal to the first speed.

2. The method according to claim 1, wherein In step (1), the alloy melt is superheated to 80-120°C above the liquidus for 30-80 seconds.

3. The method according to claim 1, wherein In 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 according to claim 1, wherein Step (3) cooling at a rate of 15-20°C / min to a temperature corresponding to the first target solid fraction; 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.

5. The method according to claim 1, wherein Step (4) cooling at a rate of 8-15°C / min to a temperature corresponding to the second target solid fraction.

6. The method according to claim 1, wherein In step (4), the third rotation speed is 140-160 rpm; the second ultrasonic power is 1.5-2 kW, and the ultrasonic time is 20-60 s.

7. The method according to claim 1, wherein 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. A semi-solid alloy preparation device for implementing the method according to any one of claims 1 to 7, characterized in that: It comprises an eccentric rotating device (2), a pulp container (1) placed on the eccentric rotating device, a plurality of ultrasonic horns (3) arranged on the outer wall of the pulp container, and an ultrasonic control unit (4); wherein: The plurality of ultrasonic horns (3) are evenly distributed on the outer wall of the pulp container (1).

9. The preparation device according to claim 8, characterized in that The distance between the end of each ultrasonic horn (3) and the wall of the slurry container is 1-3 mm, and the distance of 1-3 mm is filled with a solid coupling agent.

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

Images