A device and method for preparing semi-solid gold slurry based on acousto-magnetic coupling serpentine channel

Abstract

A device and method for preparing semi-solid gold slurry based on an acoustic-magnetic coupled serpentine channel. The dual stirring force of the electromagnetic field and the serpentine channel can more effectively break up dendrites. When the melt flows into a mold under ultrasonic action, the grain size is improved and the degree of spheroidization is increased. The dual stirring force of the gradient spiral magnetic field and the serpentine channel can effectively promote the shedding of grains to varying degrees on the inner wall of the serpentine channel, producing more and more uniform free crystals. The strong stirring effect of the electromagnetic field on the melt can quickly generate strong convection in the melt in the channel, promoting uniform composition and structure. When the melt flows into the mold, the ultrasonic cavitation effect is utilized to further improve the quality of the semi-solid slurry. The present invention can also produce better semi-solid slurry when cast at a higher temperature, achieving a greater degree of supercooling and producing more free crystals. High-temperature casting can effectively reduce the hanging material in the serpentine channel. Under the action of ultrasound, the grain size is further improved, thereby improving the quality of the semi-solid slurry.

Description

Technical Field

[0001] The present invention belongs to the technical field of semi-solid metal forming, and in particular, is a device for preparing semi-solid gold slurry based on an acoustic-magnetic coupled serpentine channel. Technical Background

[0002] With the continuous development of industry, especially the development of automobile, aviation, aerospace, electronics and weapons industries, the demand for low-cost, lightweight, high-performance metal forming products is increasing. Aluminum alloys have the advantages of light weight, high strength, corrosion resistance and easy processing. They have rapidly developed into an extremely important structural material in modern industry and are widely used in the fields of automobiles, ships and aerospace. The traditional aluminum alloy processing technology mainly includes plastic forming and solidification forming, both of which have their advantages and disadvantages. In order to achieve the forming and manufacturing of high-performance complex components, semi-solid technology came into being. It is a very promising processing method.

[0003] Semi-solid forming technology was first proposed by Spencer et al. and Flemings in 1971. It primarily involves two forming methods: thixoforming and rheoforming. Products produced using semi-solid metal forming technology, because the forming temperature is in the solid-liquid two-phase region, reduce shrinkage during solidification, improve dimensional accuracy, and achieve excellent formability. This makes it suitable for the production of complex parts and allows for near-net-shape production. Furthermore, columnar crystals and coarse dendrites are eliminated from the microstructure, resulting in a dense and uniform casting structure with significantly fewer defects and macrosegregation. Furthermore, the reduced thermal shock to the forming mold increases the mold's service life, improving yield and product performance.

[0004] The key to semi-solid processing lies in the preparation of the semi-solid slurry. Numerous methods exist, including mechanical stirring, ultrasonic vibration, strain-induced melt activation (SIMA), rotating thermal equilibrium (SEED), and the low-superheat inclined plate method. Electromagnetic stirring is the predominant method for preparing semi-solid slurries. However, due to the skin effect, electromagnetic stirring results in uneven stirring forces on the alloy slurry. This results in a larger, unevenly distributed primary phase structure and non-rounded grain morphology, limiting the widespread application of electromagnetic stirring in industrial production. Ultrasonic vibration is also a commonly used method, but due to the attenuation of ultrasound in the melt, this results in varying stirring intensities, leading to non-uniform compositional fields and temperatures. Although over 30 rheological slurrying processes exist, each with its own unique characteristics, few are suitable for large-scale industrial application. Key to industrial application lies in efficient and controllable slurrying processes, cost-effectiveness, stability, and effective integration with forming equipment.

[0005] The serpentine channel method is an emerging semi-solid slurry preparation technology. During the pouring process of the slurry, this method enables the alloy melt to have the flow characteristics of "self-stirring" mixing inhibition and convection. Through the quenching effect of the inner wall of the channel, the "self-stirring" mixing inhibition and convection of the alloy melt, it greatly promotes heterogeneous nucleation and grain liberation, improves the survival rate of free crystals, destroys the conditions for dendrite growth under traditional solidification conditions, and makes the primary crystal nuclei gradually evolve into spherical or nearly spherical grains.

[0006] However, under low superheat pouring, due to the influence of the inner diameter and length of the serpentine channel, a lot of hanging materials will inevitably be produced, and even block the subsequent flow of molten aluminum. Under high-temperature pouring, although the hanging materials will be reduced, the size of the dendrites produced will be larger, which is not conducive to the breakage of the dendrites. Therefore, when using the serpentine channel, the inner diameter should not be too small and the number of bends should not be too many, which greatly limits the preparation of semi-solid state and makes it difficult to achieve slurry continuity.

[0007] Publication No. CN103691895A discloses a method and apparatus for preparing a vibrating serpentine channel for semi-solid metal. Molten metal with a certain degree of superheat is poured into the upper opening of a vertical or inclined serpentine channel with mechanical vibration characteristics. Under the action of mechanical vibration, the superheated molten metal flows downward along the inner wall of the serpentine channel until it reaches the lower outlet of the serpentine channel, producing semi-solid metal. The advantages of this method are that it utilizes an electrically stimulated mechanical vibration device to promote the cooling, nucleation, and grain liberation of the molten metal within the serpentine channel, reducing the amount of material hanging on the inner wall of the serpentine channel, making cleaning easier, and reducing the amount of metal remelted and the energy consumption of melting. However, this method does not consider the dendrite growth and breakage that occurs with the cooling gradient along the length of the serpentine channel. Furthermore, the attenuation of the locally acting mechanical vibration force makes it difficult to ensure the uniformity of the spheroidized grains in the semi-solid slurry. Furthermore, due to tooling limitations, it is difficult to change the vibration parameters in real time during the short flow period of pouring to control the entire semi-solid slurry forming process.

[0008] Publication No. CN205200471U discloses a device for rapidly preparing semi-solid alloy rheological slurries or billets using a composite external field treatment. Mechanical and electromagnetic stirring are combined to form a composite field. This combined electromagnetic and mechanical stirring allows the alloy melt to be intensely and uniformly stirred under the action of both electromagnetic and mechanical stirring forces. This, under conditions of more uniform temperature and solute fields within the alloy melt and a certain cooling rate, alters the growth pattern of the primary phase, resulting in fine, uniform spherical primary crystals. However, this method only applies the composite field to a fixed melt volume. The quality of the resulting semi-solid melt is affected by the crucible cooling gradient and crucible size, and it is not possible to achieve uniform, semi-solid spheroidized grains across a cross-section, as achieved by the serpentine channel method.

[0009] In summary, the present invention addresses the characteristics of the different forming stages of the semi-solid melt using serpentine channel technology by specifically introducing electromagnetic and ultrasonic fields for auxiliary control. This can effectively address the problems and application bottlenecks such as excessive material hanging in the serpentine channel, insufficient dendrite breakage during high-temperature casting, and uneven structure, thereby expanding the application range of semi-solid slurries and products. This new method for preparing semi-solid slurries with high uniformity, high degree of spheroidization, and controllable solid phase gradient using acoustic-magnetic coupling serpentine channels is expected to rapidly advance the application of semi-solid technology in various fields, such as aluminum alloy die casting. Summary of the Invention

[0010] In view of the shortcomings of the existing serpentine channel technology, the present invention provides an acoustic-magnetic coupling melt control device and method for preparing semi-solid metal under the conditions of a serpentine channel method. It is a new method for preparing aluminum alloy semi-solid slurry, which solves the problems of channel hanging material and poor structural uniformity.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] An acoustic-magnetic coupled serpentine channel for semi-solid metal, comprising: a melting crucible 1, a serpentine channel structure 2, a magnetic field regulator 3, an electromagnetic stirring device 4, a heat preservation device 5, a collecting crucible 6, an ultrasonic horn and probe 7, and an ultrasonic generating device 8.

[0013] The smelting crucible 1 is placed above the vertically placed serpentine channel structure 2 and is used to pour superheated molten metal into the serpentine channel structure 2.

[0014] The collecting crucible 6 is positioned below the outlet of the serpentine channel structure 2 and is used to collect the semi-solid molten metal flowing out of the serpentine channel structure 2. It is encased in a heating and heat-insulating device 5. The ultrasonic generator 8 is positioned below the collecting crucible 6. The ultrasonic horn and probe 7 above it are tightly connected to the bottom of the collecting crucible 6. The ultrasonic generator, horn, and collecting crucible are connected by threads to form an integrated structure.

[0015] The serpentine channel structure 2 is made of high-strength graphite and is a block structure with a serpentine channel arranged vertically within it. The channel has an inner diameter of 3-200mm and 1-15 bends, and is fixed in the electromagnetic field stirring area. The electromagnetic field stirring area is provided by the magnetic field regulator 3 and the electromagnetic stirring device 4, specifically:

[0016] The electromagnetic stirring device 4 is an annular structure and is placed outside the serpentine channel structure 2, and is used to generate an electromagnetic field stirring area in the serpentine channel structure 2; the electromagnetic stirring device 4 is coaxial with the serpentine channel structure 2, and a gap is left between the inner wall of the electromagnetic stirring device 4 and the outer wall of the serpentine channel structure 2.

[0017] The magnetic field regulator 3 is a gradient annular structure attached to the inner wall of the electromagnetic stirring device 4 and does not contact the outer wall of the serpentine channel structure 2. The magnetic field regulator 3 is used to effectively control the location of the electromagnetic field strength, so that the electromagnetic field reaches its maximum intensity at the collection crucible 6 and forms a composite field with the ultrasonic field provided by the ultrasonic generator 8.

[0018] Furthermore, the serpentine channel structure 2 is preferably a cylindrical structure.

[0019] Furthermore, the thickness of the magnetic field regulator 3 increases gradually from bottom to top.

[0020] Furthermore, the magnetic field regulator 3 is made of metal such as stainless steel, copper, and aluminum, and the shielding effect of the metal on the magnetic field is adjusted by changing the thickness gradient or the local magnetic permeability is increased by slits on the magnetic field regulator 3 to adjust the magnetic field strength at different positions in the serpentine channel (2) to meet the stirring requirements under different solid phase ratios.

[0021] Furthermore, the electromagnetic stirring device 4 can generate electromagnetic fields of the type including rotating magnetic field, traveling wave magnetic field or spiral magnetic field, or a combination of multiple magnetic fields. The alternation mode can be selected to be alternating or not.

[0022] Furthermore, the electromagnetic stirring frequency of the electromagnetic stirring device 4 is low, preferably 1-50 Hz, and the stirring current is 1-200A.

[0023] Furthermore, the ultrasonic vibration frequency of the ultrasonic generating device 8 is 1kHz-50kHz, and the power is 0-10kW.

[0024] Furthermore, the heating and heat preservation device 5 has a heating temperature range of 100-900°C and comprises, from the inside to the outside, a crucible, a resistance wire, and a heat preservation device. The collection crucible 6 is located in the carbon silicon rod or resistance wire heating area 5 and can keep the collected melt warm, allowing it to further inoculate and spheroidize.

[0025] Furthermore, the height and outer diameter of the serpentine channel structure 2 and the collecting crucible 6 are sufficient to allow them to be placed in an electromagnetic stirrer.

[0026] A method for preparing a semi-solid metal by using an acousto-magnetic coupling serpentine channel, comprising assembling the acousto-magnetic coupling serpentine channel, adjusting the magnetic field at different positions of the serpentine channel structure 2 using a magnetic field regulator 3, turning on the electromagnetic stirring device 4, and adjusting the frequency and power of the ultrasonic device 8. After starting, the superheated molten metal in the melting crucible 1 is poured into the serpentine channel structure 2 and flows downward until it reaches the lower outlet of the serpentine channel structure 2, and finally flows into the collecting crucible 6 to obtain a semi-solid metal. During the pouring process, the serpentine channel structure 2 and the collecting crucible 6 are constantly under the stirring action of the electromagnetic field, and the collecting crucible 6 is constantly under the action of the ultrasonic field. The ends of the ultrasonic horn and probe 7 are in close contact with the bottom of the collecting crucible 6 to ensure the transmission of ultrasonic waves.

[0027] The principle of the present invention is to utilize the electromagnetic force characteristics of the electromagnetic field to cover all stages of the entire semi-solid forming process without contact, and through gradient control of the magnetic field intensity, achieve targeted control of melts with different solid phase ratios, effectively solving the problem of material hanging in the serpentine channel. At the same time, an ultrasonic generator is used to generate high-energy ultrasonic waves, and an ultrasonic probe is used to apply high-frequency vibrations to the semi-solid slurry in the collection crucible, further refining and stabilizing the semi-solid melt by ultrasonic cavitation and acoustic streaming effects. To address the attenuation of ultrasound in the metal melt, the collection crucible is placed in the electromagnetic field to ensure convection of the semi-solid melt in the crucible, and to transport the unrefined melt to the ultrasonic action area.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention utilizes a gradient-controlled electromagnetic field to address the difficulty of achieving precise positioning and control during the short flow of serpentine channel semi-solid slurry during casting. This method addresses the problem of material accumulation in the serpentine channel by inhibiting dendrite growth and accelerating dendrite breakage, effectively producing a stable semi-solid slurry. The electromagnetic field is combined with serpentine channel technology to address the drawback of the traditional crucible method, where the quality of the semi-solid slurry varies gradually with the crucible size. Furthermore, an ultrasonic field is combined with the electromagnetic field to perform secondary refinement on the semi-solid slurry flowing out of the serpentine channel, ultimately producing a high-quality semi-solid slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the serpentine channel structure under the acoustomagnetic coupling control of the present invention.

[0031] In the figure: 1 melting crucible; 2 serpentine channel structure; 3 magnetic field regulator; 4 electromagnetic stirring device; 5 heating and heat preservation device; 6 collecting crucible; 7 ultrasonic amplitude transformer and probe; 8 ultrasonic generating device.

[0032] Figure 2 For comparative example, the following are microstructure comparison pictures of A356 alloy semi-solid slurry at different cross-sectional positions prepared by the serpentine channel method alone. Figure 2(a) is the core grain; Figure 2 (b) is the edge grain.

[0033] Figure 3 The following are microstructure comparison pictures of the A356 alloy solid slurry prepared by the embodiment of the present invention at different cross-sectional positions. Figure 3 (a) is the core grain; Figure 3 (b) is the edge grain. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] Example

[0036] The device and method provided by the present invention are used to prepare A356 aluminum alloy semi-solid slurry, and a cylindrical sample with a diameter of 100 mm is manufactured.

[0037] The serpentine channel 2 is selected to have 4 bends, an inner diameter of 25 mm, a length of 300 mm, and a temperature of room temperature; the collecting crucible 6 is preheated to 350°C; the stirring mode is set to spiral magnetic field stirring, the electromagnetic stirring frequency is 50 Hz, and the stirring current is 30 A. The magnetic field intensity is reduced from bottom to top to 50% of the maximum value by changing the gradient thickness of the magnetic field regulator 3, that is, the magnetic field intensity of the collecting crucible 6 is the largest and the smallest at the gate; the top thickness of the magnetic field regulator 3 is 20 mm, the bottom thickness is 5 mm, and its structure is as follows: Figure 1 As shown; ultrasonic frequency 20kHz, power 1.5kW.

[0038] After the alloy is melted, the melt temperature is controlled at 660°C, and the electromagnetic stirring device 4 and the ultrasonic generator 8 are turned on at the same time. The melt is poured into the serpentine channel 2 within the spiral magnetic field. During the flow of the serpentine channel 2, the magnetic field strengthens the stirring effect inside the melt, maximizing the formation and homogenization of spheroidal crystals. At the same time, the gradient-increasing electromagnetic force can significantly reduce the problem of material hanging caused by the gradual increase in the solid phase ratio in the serpentine channel 2 without affecting the control of the spheroidal crystal formation by the serpentine channel 2. When the melt completely flows into the mold, it is simultaneously subjected to the ultrasonic field and the electromagnetic field to ensure that the spheroidal crystal structure in different areas of the crucible is uniform. After 20 seconds, when the solid phase ratio reaches the required level, the collection crucible 6 containing the melt is water quenched. Samples are cut from the edge (within 10 mm of the edge) and the core (within 10 mm of the center point) of the semi-solid ingot to obtain the metallographic structure.

[0039] Comparative Example

[0040] The comparative experiment had no magnetic field or ultrasonic field, and other parameters were the same.

[0041] pass Figure 2When a semi-solid slurry is prepared using a single serpentine channel, the average grain size at the edge of the ingot is 97.8 μm, with a shape factor of 0.70, while the average grain size at the center is 72.6 μm, with a shape factor of 0.77. Localized coarse grains and even dendrites appear at the edge of the ingot, with grains as large as 267 μm.

[0042] pass Figure 3 It can be seen from the semi-solid slurry prepared by the inventive device shown that after the acousto-magnetic coupling field is applied, the dendritic characteristics of the grains disappear, most of them appear as spherical crystals, and a small part is cellular crystals. The grain size is relatively small, with an average grain size of 70 μm at 2 locations and a shape factor of 0.76. The average grain size at 1 location is 71.5 μm, with a shape factor of 0.81, and the structure in the cross section is very uniform.

[0043] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A device for preparing semi-solid gold slurry based on acousto-magnetic coupling serpentine channel, characterized in that: It comprises a smelting crucible (1), a serpentine channel structure (2), a magnetic field regulator (3), an electromagnetic stirring device (4), a heat preservation device (5), a collecting crucible (6), an ultrasonic horn and probe (7), and an ultrasonic generating device (8); The smelting crucible (1) is placed above the vertically placed serpentine channel structure (2) and is used to pour superheated molten metal into the serpentine channel structure (2); The collecting crucible (6) is placed below the outlet of the serpentine channel structure (2) and is used to collect the semi-solid metal liquid flowing out of the serpentine channel structure (2). The outer surface of the collecting crucible (6) is covered with a heating and heat preservation device (5); the ultrasonic generating device (8) is placed below the collecting crucible (6), and the ultrasonic amplitude rod and probe (7) above the collecting crucible (6) are closely connected; the ultrasonic generating device, the amplitude rod and the collecting crucible are connected by threads to form an integrated structure; The serpentine channel structure (2) is made of high-strength graphite and is a block structure. A serpentine channel is provided in the vertical direction thereof and is fixed in the electromagnetic field stirring area. The electromagnetic field stirring area is provided by a magnetic field regulator (3) and an electromagnetic stirring device (4). The electromagnetic field stirring region is provided by the magnetic field regulator (3) and the electromagnetic stirring device (4), specifically: The electromagnetic stirring device (4) is an annular structure, is placed outside the serpentine channel structure (2), and is used to generate an electromagnetic field stirring area in the serpentine channel structure (2); the electromagnetic stirring device (4) is coaxial with the serpentine channel structure (2), and a gap is left between the inner wall surface of the electromagnetic stirring device (4) and the outer wall surface of the serpentine channel structure (2); The magnetic field regulator (3) is a gradient ring structure, attached to the inner wall surface of the electromagnetic stirring device (4), and the magnetic field regulator (3) does not contact the outer wall surface of the serpentine channel structure (2); the magnetic field regulator (3) is used to effectively control the position of the electromagnetic field strength, so that the electromagnetic field reaches the maximum intensity at the collecting crucible (6) and forms a composite field with the ultrasonic field provided by the ultrasonic generating device (8).

2. The device according to claim 1, characterized in that The inner diameter of the serpentine channel is 3-200 mm, and the number of bends is 1-15.

3. The device according to claim 1, characterized in that The serpentine channel structure (2) is a cylindrical structure.

4. The device according to claim 1, characterized in that The magnetic field regulator (3) is made of stainless steel, copper, aluminum or other metals. The shielding effect of the metal on the magnetic field is adjusted by changing the thickness gradient or the local magnetic permeability is increased by slits on the magnetic field regulator (3) to adjust the magnetic field intensity at different positions in the serpentine channel structure (2) to meet the stirring requirements under different solid phase ratios.

5. The device according to claim 1, characterized in that The electromagnetic stirring device (4) can generate electromagnetic fields of the type including rotating magnetic field, traveling wave magnetic field or spiral magnetic field, or a combination of multiple magnetic fields.

6. The device according to claim 1, characterized in that The electromagnetic stirring frequency of the electromagnetic stirring device (4) is low frequency, and the stirring current is 1-200A; the ultrasonic vibration frequency of the ultrasonic generating device (8) is 1kHz-50kHz, and the power is selected to be 0-10kW.

7. The device according to claim 1, characterized in that The heating temperature range of the heating and heat preservation device (5) is 100-900°C.

8. A method for preparing semi-solid gold paste based on acousto-magnetic coupling serpentine channel, characterized in that: The device is implemented based on any one of claims 1-7, and the specific steps are as follows: first, assemble the above-mentioned acousto-magnetic coupling serpentine channel, use the magnetic field regulator (3) to adjust the magnetic field at different positions of the serpentine channel structure (2), turn on the electromagnetic stirring device (4), and adjust the frequency and power of the ultrasonic generating device (8) at the same time; secondly, after starting, pour the superheated metal liquid in the melting crucible (1) into the serpentine channel structure (2) and flow downward until it reaches the lower outlet of the serpentine channel structure (2), and finally flows into the collecting crucible (6) to obtain semi-solid metal; wherein, during the pouring process, the serpentine channel structure (2) and the collecting crucible (6) are always under the stirring action of the electromagnetic field, and the collecting crucible (6) is always under the action of the ultrasonic field, and the end of the ultrasonic amplitude rod and the probe (7) are in close contact with the bottom of the collecting crucible (6) to ensure the transmission of ultrasonic waves.

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