An apparatus for preparing a large volume semi-solid aluminum alloy slurry and a method of preparing the same

Abstract

The application relates to a device for preparing a large-volume semi-solid aluminum alloy slurry and a preparation method thereof, which comprises, from top to bottom, an eccentric composite stirring mechanism, a crucible and a three-dimensional rotating magnetic field mechanism. The eccentric composite stirring mechanism comprises a porous graphite stirring rod extending into the crucible for stirring and an eccentric stirring driving assembly for driving the porous graphite stirring rod to rotate synchronously. The three-dimensional rotating magnetic field mechanism comprises a rotating permanent magnet which can rotate around the crucible and can reciprocate along the axis of the crucible while rotating, so as to form a three-dimensional rotating magnetic field. The application has simple structure and reasonable design. Through the synergistic effect of the three-dimensional rotating magnetic field mechanism and the eccentric composite stirring mechanism, the internal flow field, magnetic field and temperature field of the melt are homogenized, the uniformity of the semi-solid slurry structure and the spheroidization rate are improved, and the stable and efficient preparation of the large-volume semi-solid aluminum alloy slurry is met.

Description

Technical Field

[0001] This invention relates to an apparatus and method for preparing large-volume semi-solid aluminum alloy slurry. Background Technology

[0002] Semi-solid metal processing (SSM) is an advanced near-net-shape forming technology that heats metallic materials to a solid-liquid coexistence region, shaping them into a semi-solid slurry with a certain solid phase fraction. The most widely used existing semi-solid slurry preparation processes involve applying a physical external force field, primarily including mechanical stirring, electromagnetic stirring, strain-induced melting activation (SIMA), spray deposition, and tilting plate methods. Among these, mechanical stirring is widely studied due to its simple equipment and low cost. However, traditional mechanical stirring typically employs a single rotating stirring method, which easily leads to the formation of central vortices and dead zones within the melt. For large-volume aluminum alloy melts, it is difficult to achieve uniform shearing and convection throughout the melt region, resulting in uneven temperature field and solid phase distribution within the slurry, ultimately causing grain coarsening and reduced spheroidization. Electromagnetic stirring technology, due to its non-contact stirring characteristics, avoids alloy slurry contamination, offers precise controllable process parameters, good process compatibility, and effectively inhibits dendrite growth and improves microstructure uniformity, making it widely used in the preparation of semi-solid aluminum alloy slurries. However, most existing electromagnetic stirring equipment uses a fixed two-dimensional rotating magnetic field, which suffers from the skin effect and has a limited magnetic field area. For large-volume melts of 10 kg or more, problems such as large temperature differences between the top and bottom of the melt, insufficient flow in local areas, and poor uniformity of the microstructure still exist, making it difficult to meet the requirements for stable preparation of large-volume semi-solid slurries. In addition, existing semi-solid slurry preparation equipment usually adopts an open-loop control method. During the slurry preparation process, parameters such as stirring speed, magnetic field strength, and gas flow rate cannot be adjusted in real time according to the melt state, resulting in poor process repeatability and stability, making it difficult to achieve precise control and continuous industrial production of large-volume semi-solid slurries.

[0003] To address the problems of traditional electromagnetic stirring, a combined electromagnetic and mechanical stirring approach has emerged. For example, a patent published by Xi'an Jiaotong University (CN109967716B) combines a weak electromagnetic stirring device with a mechanical stirring device, claiming to avoid the skin effect. However, in this approach, the mechanical stirring relies on the rotation of the base to drive the entire crucible's rotation, resulting in limited forced convection in the central region of the melt. Furthermore, while gas stirring can generate bubble disturbance, the pore size of conventional porous graphite rods is relatively large (typically >100μm), making precise control of bubble size difficult and easily leading to gas retention and localized component segregation within the slurry. With the development of large-scale integrated die-casting technology and high-performance aluminum alloy components, the demand for large-volume, high-quality semi-solid aluminum alloy slurries is increasing. Therefore, developing a method and apparatus for preparing large-volume semi-solid aluminum alloy slurries that can enhance internal convection and shearing, eliminate dead zones and temperature gradients in the flow field, and monitor and automatically adjust slurry parameters in real time is of great significance for achieving stable preparation of high-quality semi-solid aluminum alloy slurries and promoting the engineering application of semi-solid forming technology. Summary of the Invention

[0004] The present invention improves upon the above-mentioned problems. Specifically, the technical problem to be solved by the present invention is to provide an apparatus and method for preparing large-volume semi-solid aluminum alloy slurry. Through the synergistic effect of a three-dimensional rotating magnetic field mechanism and an eccentric composite stirring mechanism, the uniformity of the semi-solid slurry structure and the spheroidization rate are improved, thereby meeting the requirements for stable and efficient preparation of large-volume semi-solid aluminum alloy slurry.

[0005] The specific embodiment of the present invention is configured as follows: it includes an eccentric composite stirring mechanism, a crucible, and a three-dimensional rotating magnetic field mechanism arranged sequentially from top to bottom. The eccentric composite stirring mechanism includes a porous graphite stirring rod extending into the crucible for stirring and an eccentric stirring drive assembly for driving the porous graphite stirring rod to rotate and revolve synchronously. The three-dimensional rotating magnetic field mechanism includes a rotating permanent magnet that can rotate around the crucible. While rotating, the rotating permanent magnet can move up and down along the axial direction of the crucible to reciprocate, so as to facilitate the formation of a three-dimensional rotating magnetic field.

[0006] Furthermore, the eccentric stirring drive assembly includes a stirring motor, a planetary transmission structure, and a stirring shaft. The input end of the planetary transmission structure is connected to the stirring motor, the output end of the planetary transmission structure is connected to the stirring shaft, and the other end of the stirring shaft is connected to a porous graphite stirring rod.

[0007] Furthermore, the three-dimensional rotating magnetic field mechanism also includes a screw lifting mechanism and a permanent magnet rotary motor for driving the rotating permanent magnet to rotate. The screw lifting mechanism includes a lifting slider, a lifting rail, a screw, and a support frame. The lifting rail is longitudinally arranged on the support frame, and the rotating permanent magnet is rotatably mounted on the lifting slider. The two sides of the lifting slider are respectively slidably engaged with the lifting rail. The screw is threadedly engaged with the lifting slider. The screw is driven to rotate by the permanent magnet lifting motor, so as to drive the lifting slider, the permanent magnet rotary motor, and the rotating permanent magnet to move up and down synchronously.

[0008] Furthermore, the crucible is provided with an insulated water circulation system, which includes an outer water-cooled shell and an inner heat-insulating ceramic layer arranged sequentially from the outside to the inside. The outer water-cooled shell is provided with a coolant circulation channel.

[0009] Furthermore, the porous graphite stirring rod is externally connected to a gas supply system for introducing protective gas. The gas supply system includes a gas cylinder and a connecting gas pipe for connecting the gas cylinder and the porous graphite stirring rod. A gas flow control valve and a gas flow sensor are provided on the connecting gas pipe near the gas cylinder. The gas control valve is used to precisely control the flow rate of the protective gas.

[0010] The porous graphite stirring rod has a main air channel in the middle.

[0011] Furthermore, the porous graphite stirring rod has a rotational speed of 200–1000 r / min, a revolution speed of 20–300 r / min, and an eccentric revolution radius of 10–50 mm.

[0012] Furthermore, the rotating permanent magnet of the three-dimensional rotating magnetic field mechanism has a rotational speed of 200–1200 r / min, a lifting stroke of 50–300 mm, and a lifting speed of 5–50 mm / s.

[0013] Furthermore, a method for preparing a large-volume semi-solid aluminum alloy slurry includes the following steps: (1) Melting and holding: heating the aluminum alloy melt to 10-20°C above the liquidus and holding it at that temperature, then transferring the alloy melt to a preheated crucible; (2) Degassing and purification: covering the crucible with the crucible lid, inserting a porous graphite stirrer into the crucible, opening the gas flow control valve, and blowing protective gas out from the porous graphite stirrer through the connecting gas pipe to perform melt degassing and purification; (3) Eccentric composite stirring: when an eccentric composite stirring is formed above the alloy melt... After the protective gas atmosphere is established, the lifting motor is controlled to immerse the graphite stirring rod into the alloy melt. The protective gas is continuously introduced, and the eccentric composite stirring mechanism is started, so that the porous graphite stirring rod rotates on its own axis while simultaneously revolving eccentrically. (4) Three-dimensional rotating magnetic field treatment: At the same time as starting the eccentric composite stirring mechanism, the three-dimensional rotating magnetic field mechanism is started to form a rotating and axially moving three-dimensional rotating magnetic field. The rotating permanent magnet insulated water circulation system runs synchronously. (5) Obtaining semi-solid slurry: When the solid phase fraction of the melt reaches the target value, the slurry preparation is stopped to obtain a large volume semi-solid aluminum alloy slurry.

[0014] Furthermore, in step (5), when the solid fraction of the melt reaches 20-60%, the slurry preparation is stopped to obtain a semi-solid aluminum alloy slurry.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Eliminate dead zone in flow field: By eccentric composite stirring, the porous graphite stirring rod can rotate on its own axis and revolve eccentrically, thereby increasing the range of action on the melt and avoiding the central vortex and dead zone in flow field generated by traditional mechanical stirring, thus achieving uniform convection inside a large volume melt. (2) Three-dimensional magnetic field strengthening effect: The three-dimensional rotating magnetic field is formed by the rotation and axial reciprocating motion of the rotating permanent magnet, which enhances the flow capacity of the upper and lower regions inside the melt, effectively reduces the temperature gradient and solid phase distribution difference, and sets an outer water-cooled shell to effectively isolate the high-temperature melt from the permanent magnet. The heat is continuously removed by the circulating coolant, so that the working temperature of the rotating permanent magnet is stabilized within a safe range, avoiding high-temperature demagnetization, improving the magnetic field stability and equipment service life, and ensuring long-term stable output of the three-dimensional rotating magnetic field. (3) Realize multi-field coupled pulping: The eccentric composite stirring technology and three-dimensional rotating magnetic field technology are organically combined to construct a large-volume semi-solid pulping system with multi-field coupling of flow field, magnetic field and bubble field, which improves process stability and repeatability, and realizes precise control of large-volume semi-solid slurry. The semi-solid aluminum alloy slurry prepared by this device has the advantages of fine grains, high spheroidization rate and uniform solid phase distribution. The average size of primary α-Al grains can reach 50~100μm and the spheroidization rate can reach more than 90%. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the overall structure of the pulping device in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the three-dimensional rotating magnetic field mechanism of Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the eccentric composite stirring mechanism in Embodiment 1 of the present invention; Figure 4 This is a cross-sectional view of the porous graphite stirring rod structure in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the three-dimensional rotating magnetic field motion trajectory in Embodiment 1 of the present invention.

[0017] Figure 6 This is a partial schematic cross-sectional view of the planetary transmission in Embodiment 1 of the present invention; Figure 7 This is a flowchart of the large-volume aluminum alloy slurry preparation process in Embodiment 2 of the present invention.

[0018] Figure 8 This is a block diagram of the online closed-loop control system of Embodiment 2 of the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: Refer to Appendix Figure 1-7 As shown, an apparatus for preparing large-volume semi-solid aluminum alloy slurry is provided, comprising an eccentric composite stirring mechanism 1, a crucible 2, and a three-dimensional rotating magnetic field mechanism 3 arranged sequentially from top to bottom. The eccentric composite stirring mechanism 1 includes a porous graphite stirring rod 11 extending into the crucible for stirring and an eccentric stirring drive assembly 12 for driving the porous graphite stirring rod to rotate and revolve synchronously. The three-dimensional rotating magnetic field mechanism 3 includes a rotating permanent magnet 31 that can rotate around the crucible. While rotating, the rotating permanent magnet can move up and down along the axial direction of the crucible to reciprocate, so as to facilitate the formation of a three-dimensional rotating magnetic field.

[0021] The crucible is provided with a support 21 below it.

[0022] In this embodiment of the invention, the eccentric stirring drive assembly 12 includes a stirring motor 121, a planetary transmission structure 122, and a stirring shaft 123. The input end of the planetary transmission structure is connected to the stirring motor, the output end of the planetary transmission structure is connected to the stirring shaft, and the other end of the stirring shaft is connected to a porous graphite stirring rod.

[0023] The planetary transmission structure is existing technology, which may include a planet carrier, a gear ring 1221, a sun gear 1222, and multiple planet gears 1223. The sun gear is located in the middle of the gear ring, and the planet gears are located between the sun gear and the gear ring. The planet gears mesh with the inner ring gear of the gear ring and the sun gear, respectively. One side of the planet gear is connected to the planet carrier, and the other side of the planet gear is connected to the stirring shaft. The motor drives the sun gear to rotate, which in turn drives the multiple planet gears and the stirring shaft to both revolve around the sun gear and rotate on their own axis.

[0024] In this embodiment of the invention, the three-dimensional rotating magnetic field mechanism 3 further includes a lead screw lifting mechanism 32 and a permanent magnet rotary motor 33 for driving the rotating permanent magnet to rotate. The lead screw lifting mechanism 32 includes a lifting slider 321, a lifting slide rail 322, a lead screw 323, and a support frame 324. The lifting slide rail is longitudinally arranged on the support frame 324. The rotating permanent magnet 31 is rotatably arranged on the lifting slider. The two sides of the lifting slider are respectively slidably engaged with the lifting slide rail. The lead screw is threadedly engaged with the lifting slider. The lead screw is driven to rotate by the permanent magnet lifting motor 325, so as to facilitate the synchronous up and down movement of the lifting slider, the permanent magnet rotary motor, and the rotating permanent magnet.

[0025] The output shaft of the permanent magnet rotary motor can pass through the lifting slider and connect to the middle of the rotating permanent magnet, and a bearing can be installed at the connection.

[0026] The lead screw of the lead screw lifting mechanism can be offset from the position of the permanent magnet rotary motor. The permanent magnet rotary motor can be installed below the lifting slider and moves synchronously with the movement of the lifting slider. The lead screw is installed in front of the permanent magnet rotary motor and is driven to rotate by the permanent magnet lifting motor, thereby driving the lifting slider to move up and down.

[0027] In this embodiment of the invention, a hot water circulation system 4 is provided outside the crucible. The hot water circulation system 4 includes an outer water-cooled shell 41 and an inner heat-insulating ceramic layer 42 arranged sequentially from the outside to the inside. A coolant circulation channel 43 is provided on the outer water-cooled shell.

[0028] The aforementioned coolant circulation channel is equipped with coolant inlet and outlet.

[0029] The aforementioned inner heat-insulating ceramic layer is used to block the high-temperature heat radiation of the melt, and the water-cooled shell continuously removes heat through circulating coolant, thereby keeping the operating temperature of the rotating permanent magnet within a safe range.

[0030] The coolant flow rate of the insulated water circulation system can be 5~20L / min, the inlet water temperature can be 15~25℃, the thickness of the inner heat insulation ceramic layer can be 5~15mm, and the coolant circulation channel adopts a spiral arrangement, that is, the coolant circulation channel is spiral or similar to an S-shape.

[0031] The coolant is a water or ethylene glycol solution.

[0032] In this embodiment of the invention, the porous graphite stirring rod is externally connected to a gas supply system 5 for introducing protective gas. The gas supply system includes a gas cylinder 55 and a connecting gas pipe 51 for connecting the gas cylinder and the porous graphite stirring rod. A gas flow control valve 52 and a gas flow sensor 53 are provided on the connecting gas pipe near the gas cylinder. The gas control valve is used to precisely control the flow of protective gas.

[0033] The aforementioned connecting air pipe can pass through the stirring motor, planetary transmission structure and the middle of the stirring shaft in sequence, and then connect to the porous graphite stirring rod. Specifically, a rotary joint can be provided at the connection between the connecting air pipe and the main air channel of the porous graphite stirring rod to prevent the connecting air pipe from getting tangled.

[0034] The porous graphite stirring rod has a main air passage 54 in the middle.

[0035] The porous graphite stirring rod has a connecting part 56 at the top, which can be threaded with the stirring shaft.

[0036] The porous graphite stirring rod has a porosity of 10-30% and a pore size of 20-100 μm.

[0037] In this embodiment of the invention, the rotation speed of the porous graphite stirring rod can be 200-1000 r / min, the revolution speed can be 20-300 r / min, and the eccentric revolution radius can be 10-50 mm.

[0038] In this embodiment of the invention, the rotational speed of the rotating permanent magnet of the three-dimensional rotating magnetic field mechanism can be 200-1200 r / min, the lifting stroke can be 50-300 mm, and the lifting speed can be 5-50 mm / s.

[0039] In this embodiment of the invention, the gas flow rate of the gas supply system can be 5~50L / min, and the protective gas can be one or a mixture of two gases, namely nitrogen and argon.

[0040] In this embodiment of the invention, the rotating permanent magnet is made of neodymium iron boron (NdFeB) or aluminum nickel cobalt material, and the magnetic induction intensity can be 0.3~0.8T.

[0041] In this embodiment of the invention, a method for preparing a device for preparing large-volume semi-solid aluminum alloy slurry includes the following steps: (1) Melting and holding: heating the aluminum alloy melt to 10-20°C above the liquidus and holding it at that temperature, then transferring the alloy melt to a preheated crucible to ensure that the alloy melt does not cool too quickly before preparing the semi-solid slurry; (2) Degassing and purification: covering the crucible with the crucible lid, inserting the porous graphite stirrer into the crucible, opening the gas flow control valve, and blowing protective gas out from the porous graphite stirrer through the connecting gas pipe to perform degassing and purification of the melt; (3) (3) Core composite stirring: After a protective gas atmosphere is formed above the alloy melt, the lifting motor is controlled to immerse the graphite stirring rod into the alloy melt, and the protective gas is continuously introduced. The eccentric composite stirring mechanism is started, so that the porous graphite stirring rod rotates on its own axis while eccentrically revolving around the center; (4) Three-dimensional rotating magnetic field treatment: At the same time as starting the eccentric composite stirring mechanism, the three-dimensional rotating magnetic field mechanism is started to form a rotating and axially moving three-dimensional rotating magnetic field. The rotating permanent magnet insulated water circulation system runs synchronously; (5) Obtaining semi-solid slurry: When the solid phase fraction of the melt reaches the target value, the slurry preparation is stopped to obtain a large volume semi-solid aluminum alloy slurry.

[0042] In this embodiment of the invention, in step (5), when the solid fraction of the melt reaches 20-60%, the slurry preparation is stopped to obtain a semi-solid aluminum alloy slurry.

[0043] In this embodiment of the invention, in step (2), after degassing, the mixture can be left to stand for 1 to 3 minutes to allow residual bubbles to escape before pulping.

[0044] In this embodiment of the invention, the solid fraction at the end of slurry preparation can be 20-60%, which can be selected according to the requirements of subsequent forming processes: 20-35% for die casting, 35-50% for squeeze casting, and 50-60% for rolling forming.

[0045] In this embodiment of the invention, the crucible is made of SiC or graphite material, with a diameter of 400-500 mm and a depth of 500-600 mm.

[0046] Example 2: Based on Example 1, in this embodiment of the invention, as follows... Figure 1-8 As shown, a melt temperature sensor 6 is provided inside the crucible to detect the temperature during the slurry preparation process; a stirring speed sensor 7 is provided next to the stirring shaft to detect the stirring speed of the eccentric composite stirring mechanism; a permanent magnet speed sensor 8 is provided above the three-dimensional rotating magnetic field mechanism; wherein, the stirring speed sensor, melt temperature sensor and permanent magnet speed sensor are all sensors in the prior art.

[0047] In this embodiment of the invention, an online closed-loop control system is also included. The online closed-loop control system includes a PLC controller 9, a data acquisition module, a human-machine interface, and an actuator, which are respectively connected to a melt temperature sensor, a stirring speed sensor, and a permanent magnet speed sensor, for real-time acquisition of pulping parameters and automatic adjustment of the pulping process.

[0048] In this embodiment of the invention, the preparation method of the device for preparing large-volume semi-solid aluminum alloy slurry includes the following steps: (1) Melting and holding: The aluminum alloy melt is heated to 10~20°C above the liquidus line and held at that temperature. Then the alloy melt is transferred to a preheated crucible to ensure that the alloy melt does not cool down too quickly before preparing the semi-solid slurry; (2) Degassing and purification: The crucible lid is closed, the porous graphite stirrer is inserted into the crucible, the gas flow control valve is opened, and the protective gas is blown out from the porous graphite stirrer through the connecting gas pipe to perform degassing and purification of the melt; (3) Eccentric composite stirring: When a protective gas atmosphere is formed above the alloy melt, the lifting and lowering electric current is controlled. The machine immerses the graphite stirring rod into the alloy melt, continuously introduces protective gas, and starts the eccentric composite stirring mechanism, so that the porous graphite stirring rod rotates on its own axis while simultaneously revolving eccentrically; (4) Three-dimensional rotating magnetic field treatment: while starting the eccentric composite stirring mechanism, the three-dimensional rotating magnetic field mechanism is started to form a rotating and axially movable three-dimensional rotating magnetic field, and the rotating permanent magnet insulated water circulation system runs synchronously; (5) Online closed-loop control: the melt temperature, gas flow rate, stirring speed, and permanent magnet speed are collected in real time through the online closed-loop control system, and the pulping parameters are automatically adjusted; (6) Obtaining semi-solid slurry: when the solid phase fraction of the melt reaches 20~60%, pulping is stopped to obtain semi-solid aluminum alloy slurry.

[0049] Example 3: This example describes the preparation of a semi-solid Al-7Si alloy slurry. The Al-7Si alloy material has a weight percentage composition of Si: 7.56%, Fe: 0.117%, with the remainder being Al and unavoidable impurities. 25 kg of Al-7Si alloy melt was heated to 630 °C and held for 10 min, then transferred to a crucible preheated to 600 °C. The gas supply system was activated, and nitrogen gas was introduced through a porous graphite stirring rod at a flow rate of 15 L / min for 5 min of degassing. When the melt temperature dropped to 600 °C, the porous graphite stirring rod was immersed in the melt. The eccentric composite stirring mechanism was activated: stirring rod rotation speed: 600 r / min; revolution speed: 100 r / min; eccentric radius: 20 mm. Simultaneously, the three-dimensional rotating magnetic field mechanism was activated: rotating permanent magnet speed: 800 r / min; lifting stroke: 150 mm; lifting speed: 20 mm / s. An online closed-loop control system monitored the melt temperature, stirring speed, permanent magnet speed, and gas flow rate in real time. Slurry preparation was stopped when the solid fraction reached 30%.

[0050] Example 4: This example describes the preparation of a semi-solid A356 alloy slurry. The weight percentage composition of the A356 alloy is: Si: 6.93%, Mg: 0.38%, Fe: 0.17%, Cu: 0.01%, Mn: 0.01%, Zn: 0.01%, Ti: 0.15%, Ni: 0.05%, with the remainder being Al. 30 kg of A356 alloy melt was heated to 620℃ and held for 10 min, then transferred to a preheated crucible at 595℃. The gas supply system was activated, and nitrogen gas was introduced through a porous graphite stirring rod at a flow rate of 20 L / min for a degassing time of 5 min. The stirring rod's rotation speed was 600 r / min; its revolution speed was 120 r / min; and its eccentricity radius was 25 mm. Simultaneously, a three-dimensional rotating magnetic field mechanism was activated: the rotating permanent magnet rotated at 1000 r / min; its lifting stroke was 200 mm; and its lifting speed was 25 mm / s. Pulping time: 25 s. During the pulping process, the rotation speed of the permanent magnet is dynamically adjusted according to the melt temperature through an online closed-loop control system, so that the melt temperature fluctuation is controlled within ±3℃. Pulping is stopped when the solid fraction reaches 40%.

[0051] Example 5: This example describes the preparation of a semi-solid 7075 aluminum alloy paste. The 7075 alloy material has the following weight percentage composition: Zn: 6.0%, Mg: 2.5%, Cu: 1.5%, Cr: 0.23%, Ti: 0.1%, with the remainder being Al. 20 kg of 7075 alloy melt was heated to 660℃ and held for 10 min, then transferred to a crucible preheated to 630℃. The gas supply system was turned on, and nitrogen gas was introduced through a porous graphite stirring rod at a flow rate of 12 L / min for 5 min of degassing. When the melt temperature dropped to 630℃, the porous graphite stirring rod was immersed in the melt. The eccentric composite stirring mechanism was activated: the stirring rod's rotation speed was 300 r / min; its revolution speed was 80 r / min; and its eccentric radius was 15 mm. Simultaneously, the three-dimensional rotating magnetic field mechanism was activated: the rotating permanent magnet's rotation speed was 600 r / min; its lifting stroke was 150 mm; and its lifting speed was 10 mm / s. During the pulping process, the rotation speed of the permanent magnet is dynamically adjusted according to the melt temperature through an online closed-loop control system, so that the melt temperature fluctuation is controlled within ±3℃. Pulping is stopped when the solid fraction reaches 25%.

[0052] Comparative Example 1 This comparative example demonstrates the preparation of semi-solid Al-7Si alloy slurry using the traditional mechanical stirring method. The composition of the Al-7Si alloy was the same as in Example 3. 25 kg of Al-7Si alloy melt was heated to 630°C and held for 10 min, then transferred to a crucible preheated to 600°C. No eccentric composite stirring mechanism or three-dimensional rotating magnetic field mechanism was used; only unidirectional mechanical stirring was employed at a stirring speed of 600 r / min. Nitrogen gas was introduced at a flow rate of 15 L / min, and the gas supply was stopped after 5 min of degassing. No magnetic field was applied during the stirring and pulping process, and no online closed-loop control was used. The pulping time was 120 s, and pulping was stopped when the solid fraction reached 30%.

[0053] Comparative Example 2 This comparative example demonstrates the preparation of semi-solid Al-7Si alloy slurry using the traditional two-dimensional electromagnetic stirring method. The composition of the Al-7Si alloy was the same as in Example 3. 25 kg of Al-7Si alloy melt was heated to 630°C and held for 10 min, then transferred to a crucible preheated to 600°C. A conventional fixed two-dimensional electromagnetic stirring device was used, with an electromagnetic coil frequency of 50 Hz, a current intensity of 10 A, and a stirring time of 120 s. Nitrogen gas was introduced at a flow rate of 15 L / min, and the gas supply was stopped after 5 min of degassing. An eccentric composite stirring mechanism and a three-dimensional rotating magnetic field mechanism were not used, nor was online closed-loop control employed. During the slurry preparation process, there was a significant temperature difference between the top and bottom of the melt, with the bottom temperature approximately 8°C higher than the top. Slurry preparation was stopped when the solid fraction reached 30%.

[0054] In summary, the parameter comparisons of Examples 4, 5, and 6 and Comparative Examples 1 and 2 are shown in Table 1 below:

[0055] Table 1 Comparison of slurries in each embodiment and comparative example The semi-solid aluminum alloy slurry prepared by the process of this invention can be directly used for die casting, extrusion casting, or semi-solid rolling forming. Tests showed that die casting using the Al-7Si semi-solid slurry prepared by the process of Example 3 of this invention resulted in castings with a tensile strength exceeding 320 MPa and an elongation exceeding 6%; while castings using the slurry prepared by the process of Comparative Example 1, subjected to the same forming process, had a tensile strength of only about 275 MPa and an elongation of approximately 4%.

[0056] Unless otherwise stated, if any of the technical solutions disclosed in this invention specify a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely one among many feasible numerical values ​​that has a more obvious or representative technical effect. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0057] If the terms "first" or "second" are used in this document to specify components, those skilled in the art should know that the use of "first" or "second" is merely for the purpose of distinguishing components in description, and unless otherwise stated, the above terms have no special meaning.

[0058] Meanwhile, if the present invention discloses or relates to mutually fixedly connected parts or structural components, then unless otherwise stated, fixed connection can be understood as: a fixed connection that can be detached (e.g., using bolts or screws), or a fixed connection that cannot be detached (e.g., riveting, welding). Of course, mutually fixed connections can also be replaced by an integral structure (e.g., manufactured by integral molding using a casting process) (except where it is obviously impossible to use an integral molding process).

[0059] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0060] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. An apparatus for preparing large-volume semi-solid aluminum alloy slurry, characterized in that, The device includes an eccentric composite stirring mechanism, a crucible, and a three-dimensional rotating magnetic field mechanism arranged sequentially from top to bottom. The eccentric composite stirring mechanism includes a porous graphite stirring rod extending into the crucible for stirring and an eccentric stirring drive assembly for driving the porous graphite stirring rod to rotate and revolve synchronously. The three-dimensional rotating magnetic field mechanism includes a rotating permanent magnet that can rotate around the crucible. While rotating, the rotating permanent magnet can move up and down along the axial direction of the crucible to reciprocate, so as to facilitate the formation of a three-dimensional rotating magnetic field.

2. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The eccentric stirring drive assembly includes a stirring motor, a planetary transmission structure, and a stirring shaft. The input end of the planetary transmission structure is connected to the stirring motor, the output end of the planetary transmission structure is connected to the stirring shaft, and the other end of the stirring shaft is connected to a porous graphite stirring rod.

3. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The three-dimensional rotating magnetic field mechanism also includes a screw lifting mechanism and a permanent magnet rotary motor for driving the rotating permanent magnet to rotate. The screw lifting mechanism includes a lifting slider, a lifting rail, a screw, and a support frame. The lifting rail is longitudinally arranged on the support frame. The rotating permanent magnet is rotatably mounted on the lifting slider. The two sides of the lifting slider are respectively slidably engaged with the lifting rail. The screw is threadedly engaged with the lifting slider. The screw is driven to rotate by the permanent magnet lifting motor to facilitate the synchronous up and down movement of the lifting slider, the permanent magnet rotary motor, and the rotating permanent magnet.

4. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The crucible is equipped with an insulated water circulation system, which includes an outer water-cooled shell and an inner heat-insulating ceramic layer arranged sequentially from the outside to the inside. The outer water-cooled shell is provided with a coolant circulation channel.

5. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The porous graphite stirring rod is externally connected to a gas supply system for introducing protective gas. The gas supply system includes a gas cylinder and a connecting gas pipe for connecting the gas cylinder and the porous graphite stirring rod. A gas flow control valve and a gas flow sensor are provided on the connecting gas pipe near the gas cylinder. The gas control valve is used to precisely control the flow of protective gas.

6. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The porous graphite stirring rod has a main air channel in the middle.

7. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The porous graphite stirring rod has a rotational speed of 200–1000 r / min, a revolution speed of 20–300 r / min, and an eccentric revolution radius of 10–50 mm.

8. The apparatus for preparing large-volume semi-solid aluminum alloy slurry according to claim 1, characterized in that, The rotating permanent magnet of the three-dimensional rotating magnetic field mechanism has a rotational speed of 200–1200 r / min, a lifting stroke of 50–300 mm, and a lifting speed of 5–50 mm / s.

9. A method for preparing large-volume semi-solid aluminum alloy slurry using the apparatus for preparing slurry according to any one of claims 1-8, characterized in that, The steps are as follows: (1) Melting and holding: Heat the aluminum alloy melt to 10-20°C above the liquidus and hold it at that temperature. Then transfer the alloy melt to a preheated crucible. (2) Degassing and purification: Cover the crucible with the lid, insert the porous graphite stirrer into the crucible, open the gas flow control valve, and blow the protective gas out from the porous graphite stirrer through the connecting gas pipe to perform degassing and purification of the melt. (3) Eccentric composite stirring: After a protective gas atmosphere is formed above the alloy melt, control the lifting motor. Immerse the graphite stirring rod into the alloy melt, continuously introduce protective gas, start the eccentric composite stirring mechanism, and make the porous graphite stirring rod rotate on its own axis while simultaneously revolving eccentrically; (4) Three-dimensional rotating magnetic field treatment: while starting the eccentric composite stirring mechanism, start the three-dimensional rotating magnetic field mechanism to form a rotating and axially moving three-dimensional rotating magnetic field, and the rotating permanent magnet insulated water circulation system runs synchronously; (5) Obtain semi-solid slurry: when the solid phase fraction of the melt reaches the target value, stop slurry making to obtain a large volume semi-solid aluminum alloy slurry.

10. The method for preparing a large-volume semi-solid aluminum alloy slurry according to claim 9, characterized in that, In step (5), when the solid fraction of the melt reaches 20-60%, the slurry preparation is stopped to obtain a semi-solid aluminum alloy slurry.

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