A high thixotropic magnesium-based metal material and preparation method thereof

Abstract

The present application relates to the field of semi-solid alloy manufacturing, and specifically to a magnesium-based metal material with high thixotropy and a preparation method thereof. The present application provides a preparation method of a magnesium-based metal material with high thixotropy, which combines a gas induction method with a high-energy ultrasonic treatment. The semi-solid slurry with a high solid content prepared by the gas induction method has a large number of dendrites distributed in the porous graphite rod area. At this time, an ultrasonic probe is set to perform high-power and high-frequency ultrasonic treatment. The high-energy ultrasonic treatment can provide a strong shear force on the one hand to promote the violent movement of dendrites near the porous graphite rod, thereby promoting the fracture of the latter crystal dendrites. On the other hand, it provides a higher energy to generate a local high-temperature area to promote the dissolution of the crystal dendrites, thereby significantly reducing the proportion of dendrites near the porous graphite rod, making the overall particles of the slurry more uniform, and enhancing the thixotropy.

Description

Technical Field

[0001] The present application relates to the field of semi-solid alloy manufacturing, and in particular to a highly thixotropic magnesium-based metal material and a preparation method thereof. Background Art

[0002] Semi-solid alloy is a metal material processed in the solid-liquid two-phase region. It uses the special microstructure and forming properties of metal in the semi-solid temperature range to achieve efficient near-net forming of complex components under low forming loads. This technology plays an important role in improving the quality utilization and performance utilization of metal materials, extending the life of molds, and saving energy and reducing emissions.

[0003] In the field of magnesium alloys, the application of semi-solid forming technology is particularly important. Magnesium alloys have broad application prospects in areas such as automobile lightweighting due to their light weight, high strength, and easy recycling. The introduction of semi-solid forming technology can improve the product quality and production efficiency of magnesium alloys.

[0004] When using gas induction to prepare semi-solid alloys in traditional technology, gas is injected into the melt to form bubbles to achieve cooling and mixing of the melt, thereby further increasing the contact between the heat exchange bubbles and the melt during the rising process, increasing the heat exchange area between the melt and the environment, and facilitating the rapid dissipation of heat. It also forms a convection effect. The rising of the bubbles causes the melt to flow and form convection, which can accelerate the transfer of heat and thus improve the cooling efficiency.

[0005] However, due to the small shear force provided by the bubbles, the morphology of the grains is unevenly distributed. Along the radius of the crucible, the grains become more rounded as the distance from the center of the crucible increases, while the grains near the center of the crucible are mainly dendrites. If the slurry is directly used for casting, the thixotropy of the slurry is poor and pores are easily generated. If the gas method and composite stirring method are used to prepare the slurry, although the problem of uneven distribution of grain morphology can be solved, more bubbles will be introduced into the slurry, resulting in more pores.

[0006] Therefore, the magnesium-based metal materials prepared by the conventional gas induction method have low thixotropy, which is not conducive to further forming the desired shape and structure. Summary of the invention

[0007] Based on this, an embodiment of the present application provides a method for preparing a magnesium-based metal material with high thixotropy. The magnesium-based metal material prepared by the method has strong thixotropy.

[0008] On the one hand, the present application provides a method for preparing a magnesium-based metal material with high thixotropy, comprising the following steps:

[0009] Metal raw materials are provided according to the composition of magnesium-based metal materials, and after mixing the metal raw materials, they are heated to 10°C to 20°C above the liquidus to form a melt.

[0010] Placing a porous graphite rod in the melt, cooling the melt by a gas induction method, and when the solid content in the melt reaches 20% to 50%, removing the porous graphite rod and recording the position of the porous graphite rod, placing an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, and preparing a magnesium-based metal material;

[0011] The parameters of the ultrasonic treatment include: power of 0.4kw~1kw, frequency of 80kHz~100kHz.

[0012] In one embodiment, the parameters of the ultrasonic treatment include: power of 0.8 kW and frequency of 100 kHz.

[0013] In one embodiment, the ultrasonic treatment time is 3s~8s.

[0014] In one embodiment, the gas induction method includes injecting bubbles of an inert gas into the melt.

[0015] In one embodiment, the inert gas includes argon and helium.

[0016] In one embodiment, the flow rate of the argon gas is 2L / min~4L / min.

[0017] In one embodiment, when the solid content in the melt reaches 30%, ultrasonic treatment is performed near the porous graphite rod.

[0018] In one embodiment, the magnesium-based metal material includes one or a mixture of Fe, Si, Mn, Ni, Cu, Al and Zn.

[0019] In one embodiment, the magnesium-based metal material is AM60B alloy.

[0020] On the other hand, the present application provides a magnesium-based metal material with high thixotropy, and the magnesium-based metal material with high thixotropy is prepared by the above-mentioned preparation method.

[0021] The present application provides a method for preparing a magnesium-based metal material with high thixotropy, which combines a gas induction method with a high-energy ultrasonic treatment. The semi-solid slurry with a high solid content prepared by the gas induction method has a large number of dendrites distributed in the porous graphite rod area. At this time, the porous graphite rod is removed and an ultrasonic probe is set at the position of the porous graphite rod for high-power and high-frequency ultrasonic treatment. The high-energy ultrasonic treatment can provide a strong shear force to promote the violent movement of dendrites near the ultrasonic probe, thereby promoting the breakage of the latter dendrites. On the other hand, it provides a higher energy to generate a local high-temperature area to promote the melting of the dendrites, thereby significantly reducing the proportion of dendrites near the ultrasonic probe, and making the overall particles of the slurry more uniform, and the thixotropy is enhanced. The present application generates a high-temperature and high-shear force area at the position of the porous graphite rod. The high-temperature and high-shear force conditions are not conducive to the production of refined grains, but are conducive to the melting of existing dendrites, thereby reducing the proportion of dendrites.

[0022] Furthermore, by using high-frequency ultrasonic waves with poor penetration, the ultrasonic action is concentrated on the spherical grains in other areas of the melt near the ultrasonic probe, and the morphology will not change due to the ultrasonic action. Therefore, a magnesium-based metal material with higher thixotropy can be obtained by the above method.

[0023] On the other hand, the present application provides a magnesium-based metal material with high thixotropy, and the magnesium-based metal material with high thixotropy is prepared by the above-mentioned preparation method.

[0024] The magnesium-based metal material has strong thixotropy, which is conducive to further forming a desired shape and structure.

[0025] The details of one or more embodiments of the present application are set forth in the description which follows, and other features, objects, and advantages of the present application will be apparent from the description and its claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0027] Figure 1 The metallographic image of the die-cast product of the magnesium-based metal material prepared in Example 1;

[0028] Figure 2 This is the metallographic phase diagram of the die-cast product of the magnesium-based metal material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0029] Below in conjunction with embodiment and example, the application is further described in detail.It should be understood that these embodiments and examples are only used to illustrate the application and are not used to limit the scope of the application, and the purpose of providing these embodiments and examples is to make the understanding of the disclosure of the application more thorough and comprehensive.It should also be understood that the application can be implemented in many different forms, is not limited to the embodiment and example described herein, and those skilled in the art can make various changes or modifications without violating the connotation of the application, and the equivalent form obtained also falls within the protection scope of the application.In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the application, and it should be understood that the application can be implemented without one or more of these details.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0031] the term

[0032] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0033] The terms "and / or", "or / and", and "and / or" used in this article include any one of two or more related listed items, and also include any and all combinations of related listed items, and the arbitrary and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution that is all connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the combination of four of A, B, C, and D (that is, the technical solution that is all connected by "logical AND").

[0034] In the present application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0035] As used herein, "combination thereof", "any combination thereof", "any combination thereof" etc. include all suitable combinations of any two or more of the listed items.

[0036] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc., shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0037] In the present application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present application.

[0038] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0039] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0040] In the present application, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the integer group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0041] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0042] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0043] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the invention purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0044] In order to solve the problem of poor thixotropy caused by uneven morphology distribution of semi-solid slurry grains prepared by gas induction method, it is necessary to provide a magnesium-based metal material with high thixotropy and a preparation method thereof.

[0045] On one hand, the present application provides a method for preparing a magnesium-based metal material with high thixotropy, providing metal raw materials according to the composition of the magnesium-based metal material, mixing the metal raw materials and heating them to 10°C to 20°C above the liquidus to form a melt;

[0046] A porous graphite rod is placed in the melt, and the melt is cooled by gas induction. When the solid content in the melt reaches 20% to 50%, the porous graphite rod is removed and the position of the porous graphite rod is recorded. An ultrasonic probe is placed at the position of the porous graphite rod for ultrasonic treatment to obtain a magnesium-based metal material. For example, the solid content can reach 20%, 30%, 40%, or 50%. It is understood that after removing the porous graphite rod, the ultrasonic probe is placed at the position of the porous graphite rod or the previous position with a center diameter of about 1 cm to 2 cm for in-situ ultrasonic treatment.

[0047] The parameters of the ultrasonic treatment include: power of 0.4 kw to 1 kw, and frequency of 80 kHz to 100 kHz. For example, the power is 0.4 kw, 0.5 kw, 0.6 kw, 0.7 kw, 0.8 kw, 0.9 kw, 1.0 kw, and the frequency is 80 kHz, 85 kHz, 90 kHz, 95 kHz, 100 kHz.

[0048] The present application adopts ultra-high power and ultra-high frequency ultrasonic parameters. On the one hand, high-energy ultrasonic treatment provides a strong shear force to promote the violent movement of dendrites near the porous graphite rods, thereby promoting the breakage of the latter dendrites. On the other hand, it increases the higher energy to produce a local high-temperature area to promote the melting of the dendrites, thereby significantly reducing the proportion of dendrites near the porous graphite rods, thereby making the overall particles of the slurry more uniform and the thixotropy enhanced.

[0049] Furthermore, the effects of ultrasound in molten metal include gas removal, particle dispersion, grain refinement, dissolution of solid solution, surface activity improvement, and improved temperature uniformity.

[0050] In a specific example, the ultrasonic parameters include: power of 0.8 kW and frequency of 100 kHz.

[0051] Optionally, the ultrasound duration is 3s to 8s, for example 3s, 4s, 5s, 6s, 7s, or 8s.

[0052] Further optionally, the gas induction method includes injecting bubbles of an inert gas into the melt.

[0053] In a specific example, the inert gas includes argon and helium.

[0054] In a specific example, the flow rate of the argon gas is 2 L / min to 4 L / min. For example, 2 L / min, 3 L / min, 4 L / min. In a specific example, when the solid content in the melt reaches 30%, an ultrasonic probe is placed at the position of the porous graphite rod for ultrasonic treatment.

[0055] Optionally, the magnesium-based metal material includes one or a mixture of Fe, Si, Mn, Ni, Cu, Al and Zn.

[0056] In a specific example, the magnesium-based metal material is AM60B alloy.

[0057] The present application provides a method for preparing a magnesium-based metal material with high thixotropy, which combines a gas induction method with a high-energy ultrasonic treatment. A semi-solid slurry with a high solid content prepared by the gas induction method is subjected to a high-power and high-frequency ultrasonic treatment. The high-energy ultrasonic treatment can, on the one hand, provide a strong shear force to promote the violent movement of dendrites near the position of a porous graphite rod, thereby promoting the breakage of the latter's dendrites. On the other hand, it increases the energy to generate a local high-temperature area to promote the melting of the dendrites, thereby significantly reducing the proportion of dendrites near the position of the porous graphite rod, making the overall particles of the slurry more uniform, and enhancing the thixotropy.

[0058] Furthermore, high-frequency ultrasonic waves have poor penetration, and the ultrasonic effect is concentrated near the ultrasonic probe, that is, near the location of the porous graphite rod, and the spherical grains in other areas of the melt will not change their morphology due to the ultrasonic effect. Therefore, a magnesium-based metal slurry with higher thixotropy can be obtained by the above method.

[0059] On the other hand, the present application provides a magnesium-based metal material with high thixotropy. The magnesium-based metal material with high thixotropy is prepared by the above-mentioned preparation method. The magnesium-based metal material has strong thixotropy, which is conducive to further forming a desired shape and structure.

[0060] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0061] In the following specific embodiments, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument test accuracy or operation accuracy are allowed.

[0062] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0063] Embodiment 1: This embodiment provides a method for preparing a magnesium-based metal material with high thixotropy, which specifically includes:

[0064] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0065] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, remove the porous graphite rod and record the position of the porous graphite rod, place an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, and ultrasonicate for 3 seconds with a power of 400 W and a frequency of 80 kHz.

[0066] 3. Take part of the semi-solid slurry to test its thixotropy, transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 m / s. The mold is a plate forming mold, and the other embodiments and comparative examples use the same mold.

[0067] Embodiment 2: This embodiment provides a method for preparing a magnesium-based metal material with high thixotropy, which specifically includes:

[0068] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0069] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, remove the porous graphite rod and record the position of the porous graphite rod, place an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, and ultrasonicate for 3 seconds with a power of 0.8 kW and a frequency of 100 kHz.

[0070] 3. Take part of the semi-solid slurry to test its thixotropy, and transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 / s.

[0071] Embodiment 3: This embodiment provides a method for preparing a magnesium-based metal material with high thixotropy, which specifically includes:

[0072] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0073] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, remove the porous graphite rod and record the position of the porous graphite rod, place an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, and ultrasonicate for 8 s with a power of 400 W and a frequency of 80 kHz.

[0074] 3. Take part of the semi-solid slurry to test its thixotropy, and transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 m / s.

[0075] Comparative Example 1: This comparative example provides a method for preparing a common magnesium-based metal material. Compared with Example 1, this comparative example does not perform ultrasonic treatment, and specifically includes:

[0076] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0077] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, remove the porous graphite rod and let it stand for 3 seconds.

[0078] 3. Take part of the semi-solid slurry to test its thixotropy, and transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 / s.

[0079] Comparative Example 2: This comparative example provides a method for preparing a common magnesium-based metal material. Compared with Example 1, this comparative example uses conventional low-frequency ultrasonic treatment, specifically comprising:

[0080] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0081] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, remove the porous graphite rod and record the position of the porous graphite rod, place an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, and ultrasonicate for 3 seconds with a power of 400 W and a frequency of 10 kHz.

[0082] 3. Take part of the semi-solid slurry to test its thixotropy, and transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 m / s.

[0083] Comparative Example 3: This comparative example provides a method for preparing a common magnesium-based metal material. Compared with Example 1, this comparative example uses conventional low-power ultrasonic treatment and specifically includes:

[0084] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0085] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt until the solid content in the melt reaches 30%, and then perform ultrasound at a power of 100 W and a frequency of 80 kHz for 3 seconds.

[0086] 3. Take part of the semi-solid slurry to test its thixotropy, and transfer the remaining semi-solid slurry to the mold for die casting at a strain rate of 2 / s.

[0087] Comparative Example 4: This comparative example provides a method for preparing a magnesium-based metal alloy by simultaneously performing an ultrasonic and a bubble method, specifically comprising:

[0088] 1. Various pure metals were weighed according to the components required for preparing 9.7 kg of AM60B alloy and added into a resistance furnace for smelting, among which magnesium accounted for 95%, aluminum accounted for 6.0%, zinc accounted for 0.40%, manganese accounted for 0.42%, and rare earth elements accounted for 0.50%, and a melt with a temperature of 20°C above the liquidus was obtained.

[0089] 2. Place a porous graphite rod in the melt, introduce argon at 4 L / min to cool the melt, and place an ultrasonic probe around the porous graphite rod for ultrasonic treatment at a power of 400 W and a frequency of 80 kHz until the solid content in the melt reaches 30%, then stop the ultrasound and remove the porous graphite rod.

[0090] Third, a portion of the semi-solid slurry was taken to test its thixotropy, and the remaining semi-solid slurry was transferred to a mold for die casting at a strain rate of 2 m / s.

[0091] (1) Thixotropy related performance testing:

[0092] A Brookfield rotary viscometer was used to measure the viscosity at rotor speeds of 5 r / min and 50 r / min, and the thixotropic index of Examples 1 to 3 and Comparative Examples 1 to 3 was calculated according to the following formula.

[0093] The formula is It: It=η5 / η50. Where: It-thixotropic index; η5-viscosity measured at a rotor speed of 5r / min; η50-viscosity measured at a rotor speed of 50r / min.

[0094] (2) Tensile strength test: measured in accordance with the national standard GB / T 23301-2009.

[0095] The test results are shown in Table 1:

[0096] Table 1

[0097] The results show that compared with comparative examples 1-4, examples 1-3 of the present application use high-energy ultrasonic treatment to provide strong shear force to promote the violent movement of dendrites near the porous graphite rods, further promote the fracture of the dendrites, and generate local high-temperature areas with higher energy to promote the melting of the dendrites, so that the proportion of dendrites near the porous graphite rods is significantly reduced, thereby making the overall particles of the slurry more uniform and the thixotropy is enhanced. The metallographic image of the product of the magnesium-based metal slurry die-casting prepared in example 1 is as follows: Figure 1 As shown by Figure 1 It can be seen that there are no obvious crystal dendrites, the overall sphericity of the slurry particles is good, and the thixotropy is enhanced.

[0098] In Comparative Example 1, since ultrasonic treatment was not used and only gas induction was used to prepare the semi-solid alloy, the shear force provided by the bubbles was small, the morphology of the grains was unevenly distributed, and the additional grains in the central area were mainly dendrites. The thixotropy of the slurry was poor. The metallographic image of the product of the magnesium-based metal slurry die-casting prepared in Comparative Example 1 is as follows: Figure 2 As shown by Figure 2 It can be seen that there are many crystal dendrites, the overall sphericity of the slurry particles is poor, and the thixotropy is also poor.

[0099] Comparative Example 2 uses ultrasonic treatment at a lower frequency. The penetration of low-frequency ultrasound is too strong, which will affect the melt at a position far away from the porous graphite rod, and affect the uniformity of spherical particles in other areas, resulting in a decrease in thixotropy. Therefore, it is necessary to strictly control the frequency of ultrasound and the position of ultrasonic treatment. It is understandable that if the ultrasonic probe is placed in other areas for ultrasonic treatment, it will further affect the uniformity of spherical particles in other areas, further leading to a decrease in thixotropy.

[0100] Comparative Example 3 uses relatively low-power ultrasonic treatment. Low-power ultrasonic treatment cannot provide strong shear force and local high-temperature environment, thereby failing to cause the dendrites near the porous graphite rod to move violently and break and promote the melting of the dendrites. Although Comparative Example 3 is also slightly better than Comparative Example 1 without ultrasonic treatment, there are still a large number of unevenly distributed grains, and similarly, good thixotropy cannot be formed.

[0101] Comparative Example 4 uses the bubble method and ultrasonic treatment at the same time. Although the ultrasonic treatment provides a strong shear force for the slurry around the porous graphite rod, which helps to refine the slurry, the use of ultrasonic treatment at low solid content is easy to introduce more bubbles, thereby forming pores in the casting and ultimately leading to a decrease in tensile strength; on the other hand, the ultrasonic wave is severely attenuated when propagating in the slurry, especially the high-frequency and high-power ultrasonic waves mentioned above will provide more energy to the slurry near the porous graphite rod, but reduce the cooling rate and supercooling of the slurry near the porous graphite rod, so that the grains tend to grow rather than nucleate, thus eventually leading to grain coarsening, thereby reducing the thixotropic index. In Example 1, after preparing the slurry by the bubble method, ultrasonic treatment is performed to form a high-temperature and high-shear force area near the porous graphite rod, thereby further reducing the proportion of dendrites.

[0102] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as a limitation on the scope of protection of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several deformations and improvements can be made, which all belong to the protection scope of the present application. In addition, it should be understood that after reading the above-mentioned teaching content of the present application, the technicians in this field can make various changes or modifications to the present application, and the equivalent forms obtained also fall within the protection scope of the present application. It should also be understood that the technical solutions obtained by the technicians in this field through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the claims attached to the present application. Therefore, the protection scope of the patent of the present application shall be based on the content of the attached claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A method for preparing a highly thixotropic magnesium-based metal material, characterized in that: The following steps are involved: Provide metal raw materials according to the composition of magnesium-based metal materials, mix the metal raw materials and heat them to 10°C to 20°C above the liquidus to form a melt; Placing a porous graphite rod in the melt, cooling the melt by a gas induction method, and when the solid content in the melt reaches 20% to 50%, removing the porous graphite rod and recording the position of the porous graphite rod, placing an ultrasonic probe at the position of the porous graphite rod for ultrasonic treatment, wherein the ultrasonic treatment time is 3s to 8s, to obtain the magnesium-based metal material; The parameters of the ultrasonic treatment include: power of 0.4kw~1kw, frequency of 80kHz~100kHz.

2. The method for preparing a magnesium-based metal material with high thixotropy according to claim 1, characterized in that: The parameters of the ultrasonic treatment include: power of 0.8 kW and frequency of 100 kHz.

3. The method for preparing a magnesium-based metal material with high thixotropy according to claim 1, characterized in that: The gas induction method involves injecting bubbles of an inert gas into the melt.

4. The method for preparing a magnesium-based metal material with high thixotropy according to claim 3, characterized in that: The inert gas includes argon and helium.

5. The method for preparing a magnesium-based metal material with high thixotropy according to claim 4, characterized in that: The flow rate of the argon gas is 2L / min~4L / min.

6. The method for preparing a magnesium-based metal material with high thixotropy according to any one of claims 1 to 5, characterized in that: When the solid content in the melt reaches 30%, the ultrasonic probe is placed at the position of the porous graphite rod for ultrasonic treatment.

7. The method for preparing a magnesium-based metal material with high thixotropy according to any one of claims 1 to 5, characterized in that: The magnesium-based metal material includes one or more of Fe, Si, Mn, Ni, Cu, Al and Zn.

8. The method for preparing a magnesium-based metal material with high thixotropy according to claim 6, characterized in that: The magnesium-based metal material is AM60B alloy.

Images