Semi-solid thixotropic die casting forming method of narrow solid-liquid two-phase region alloy
By combining melting and casting, extrusion deformation, recrystallization heat treatment, solid-liquid two-phase heat treatment, and die casting, the problem of preparing semi-solid billets of alloys with narrow solid-liquid two-phase regions was solved, realizing the preparation of high-quality billets and efficient forming, reducing costs, and improving the mechanical properties and forming accuracy of metallic materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGSU LONGCHENG PREC FORGING CO LTD
- Filing Date
- 2023-03-14
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies make it difficult to prepare high-quality semi-solid billets of alloys with narrow solid-liquid two-phase regions, and traditional equipment is costly and suffers from problems such as gas entrapment, slag inclusion, shrinkage porosity, and cold shuts.
A method combining melting and casting, extrusion deformation, recrystallization heat treatment, solid-liquid two-phase heat treatment, and die casting is adopted. Through two isothermal heat treatments and cold extrusion, a narrow solid-liquid two-phase alloy semi-solid billet is prepared to obtain a high-density dislocation and lattice distortion structure, ensuring that the recrystallized grains are fine and uniform.
It improves the utilization rate and yield of metal materials, significantly enhances the mechanical properties and forming accuracy of semi-solid billets, reduces processing costs, simplifies the operation process, and is suitable for mass production.
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Figure CN116475374B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of die casting technology, specifically relating to a semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions. Background Technology
[0002] Semi-solid forming technology is widely used in the forming of materials such as steel, aluminum alloys, magnesium alloys, and titanium alloys. Semi-solid forming technology includes sub-technologies such as semi-solid casting, semi-solid forging, and semi-solid rolling. Among these, semi-solid casting technology is widely disclosed for two different processes: semi-solid rheo-die casting and semi-solid thixotropic die casting.
[0003] Semi-solid rheostat die casting is a continuous process that saves time and costs, aligning with my country's green manufacturing requirements. Semi-solid thixostat die casting involves directly heating a semi-solid thixostat billet to its semi-solid temperature range and then die-casting it, a simpler process. Semi-solid thixostat die casting generally consists of several steps: rheostat slurry preparation, cooling to form a billet, quantitative division, secondary heating, and forming. Representative rheostat slurry preparation methods include mechanical stirring and electromagnetic stirring. Their common characteristic is the need to melt the alloy into a liquid state, cool it to a semi-solid temperature, and simultaneously perform intense mechanical or electromagnetic stirring to obtain the desired semi-solid slurry with spherical solid phases and surrounding liquid phases. Rheostat forming requires specialized slurry preparation equipment, resulting in higher costs. Furthermore, traditional semi-solid forming technologies require a wide temperature range in the solid-liquid two-phase region of the material, necessitating sufficient nucleation time for spheroidization of the primary solid phase. Therefore, alloys suitable for semi-solid forming should inherently possess a wide liquid-solid two-phase range.
[0004] The solid-liquid two-phase temperature range of narrow solid-liquid two-phase alloys is usually within 50℃. When the temperature range of the solid-liquid two-phase region of the material is relatively narrow, the temperature change range during the crystallization process of the metal is small, the cooling rate is fast, the temperature control requirements are extremely high, and it is difficult to form a stable semi-solid slurry. According to the existing publicly available semi-solid forming technology, it is impossible to prepare high-quality semi-solid alloy materials that meet the requirements of use.
[0005] In summary, the preparation of high-quality semi-solid alloy billets with narrow solid-liquid two-phase regions can promote the development of semi-solid forming methods and broaden the application range of semi-solid technology. The preparation of semi-solid forming billets with narrow solid-liquid two-phase regions is the key to the application of forming technology. Summary of the Invention
[0006] The present invention aims to solve at least one of the technical problems existing in the prior art.
[0007] Therefore, this invention proposes a semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions. This method has the advantage of producing castings with excellent physical properties when semi-solid thixotropic die casting of alloys with narrow solid-liquid two-phase regions.
[0008] The semi-solid thixotropic die casting method for a narrow solid-liquid two-phase region alloy according to an embodiment of the present invention includes the following steps: Step 1: Adding a narrow solid-liquid two-phase region alloy with a solid-liquid two-phase region of less than 50°C to a heating device and heating it to a superheated temperature, allowing it to cool for a certain period of time after complete melting, to obtain an alloy billet with a cast structure; Step 2: Adding the alloy billet to an extrusion device and holding it under a certain pressure for a certain period of time to complete cold extrusion, to obtain an alloy billet containing a high-density dislocation and lattice distortion structure; Step 3: Placing the alloy billet in a heating device for a first heating, with the heating temperature set between the recrystallization temperature and the solidus temperature of the alloy, and performing isothermal heat treatment to obtain fine and uniform recrystallized grains; Step 4: Placing the alloy billet in a heating device for a second heating, with the heating temperature set above the solidus temperature of the narrow solid-liquid two-phase region alloy, and performing isothermal heat treatment to obtain a semi-solid billet; Step 5: Quickly transferring the obtained semi-solid billet into a die casting mold for die casting.
[0009] According to one embodiment of the present invention, the narrow solid-liquid two-phase region alloy is one of aluminum alloy, magnesium alloy, steel, titanium alloy and high-temperature alloy.
[0010] According to one embodiment of the present invention, in step one, the overheating temperature is 100-200°C higher than the liquidus temperature of the narrow solid-liquid two-phase alloy, and the static cooling time is 5-10 minutes.
[0011] According to one embodiment of the present invention, in step two, the extrusion pressure of the extrusion equipment is 2000-3500kN, the holding time is 30-60min, and the extrusion deformation is greater than 50%.
[0012] According to one embodiment of the present invention, in step three, the holding time of the isothermal heat treatment is 30-120 min, and the recrystallization temperature of the narrow solid-liquid two-phase region alloy is 0.55-0.8 times the melting point of the narrow solid-liquid two-phase region alloy.
[0013] According to one embodiment of the present invention, in step four, the holding time for isothermal heat treatment is 5-60 minutes.
[0014] According to one embodiment of the present invention, the heating rate of the first heating is higher than the heating rate of the second heating.
[0015] According to one embodiment of the present invention, the heating current of the heating device is 25-35A and the heating voltage is 220-350V.
[0016] According to one embodiment of the present invention, in step five, during die casting, the forming temperature of the semi-solid billet is between the solidus temperature and the liquidus temperature of the alloy in the narrow solid-liquid two-phase region, and the injection speed is 1-6 m / s.
[0017] According to one embodiment of the present invention, in step four, the roundness of the recrystallized grains of the semi-solid billet is greater than 0.9, and the grain size can reach 1-20 μm.
[0018] The beneficial effects of this invention are:
[0019] (1) The thixotropic die casting method for forming narrow solid-liquid two-phase metal materials proposed in this invention, which combines melting and casting, extrusion deformation, recrystallization heat treatment, solid-liquid two-phase heat treatment, and die casting, does not need to consider the solid-liquid two-phase region of the alloy compared with the traditional semi-solid forming process. It not only solves the problem that traditional equipment is difficult to prepare semi-solid billets of narrow solid-liquid two-phase alloys, but also avoids problems such as gas entrapment, slag inclusion, shrinkage porosity, cold shut and secondary remelting, which can greatly improve the utilization rate and yield of metal materials.
[0020] (2) This invention obtains a modified microstructure containing high-density dislocations and lattice distortion by directly cold extruding the alloy billet in the narrow solid-liquid two-phase region. By performing two isothermal heatings on the alloy in the narrow solid-liquid two-phase region, the first isothermal heat treatment fully utilizes the high distortion characteristics of the cold-extruded billet, ensuring the nucleation driving force for recrystallization, resulting in small, uniform, and highly rounded recrystallized grains. The second isothermal heat treatment ensures precise control of the temperature and time during the heating process. Parameters such as the size, roundness, grain coarsening rate, and solid fraction of the primary solid phase can be reasonably adjusted according to the process, thereby obtaining a semi-solid billet with good fluidity and high quality. The two isothermal heat treatments improve the quality of the semi-solid billet of the alloy in the narrow solid-liquid two-phase region, which helps to significantly improve the mechanical properties of the metal material.
[0021] (3) The present invention achieves high distortion and high density of material structure after cold extrusion deformation. The first isothermal treatment between recrystallization temperature and solidus temperature results in fine recrystallized grains with a grain size of 1-20 μm. The second isothermal treatment above solidus temperature causes the grain boundaries of recrystallized grains to melt rapidly, resulting in a semi-solid billet with a grain roundness greater than 0.9 and recrystallized grains suspended in the molten grain boundary liquid phase. This semi-solid billet has extremely high deformability, which significantly reduces the tonnage of the die casting machine in the die casting process. It is very beneficial to achieve die casting. There is almost no air entrapment problem in die casting, which can fill the cavity well and improve the forming accuracy and mechanical properties.
[0022] (4) The present invention can complete the preparation of semi-solid billets using traditional extrusion equipment and heating equipment. It does not require mechanical stirring or electromagnetic stirring equipment for rheological or thixotropic die casting. The operation process is simple, the processing cost is low, and it is easy to mass-produce. The operation method is simple and can significantly reduce energy consumption and save costs.
[0023] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.
[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, wherein:
[0026] Figure 1 This is a schematic diagram of a semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to the present invention.
[0027] Figure 2 This is a metallographic diagram of the 4032 aluminum alloy extrusion casting billet prepared according to the present invention;
[0028] Figure 3 This is a metallographic diagram of a 4032 aluminum alloy extrusion casting billet prepared using traditional die casting technology.
[0029] Figure 4 This is a metallographic diagram of the C70250 copper alloy extrusion casting billet prepared according to the present invention; Detailed Implementation
[0030] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.
[0031] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, features defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0033] The semi-solid thixotropic die casting method for narrow solid-liquid two-phase alloys according to embodiments of the present invention is described in detail below with reference to the accompanying drawings.
[0034] like Figure 1 As shown, the semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to an embodiment of the present invention includes the following steps:
[0035] Step 1: Add the alloy with a narrow solid-liquid two-phase region of less than 50°C into the heating equipment and heat it to 100°C above the liquidus line of the alloy. After it is completely melted, let it stand and cool for 5-10 minutes, and then cast it to obtain an alloy billet with a cast structure.
[0036] Step 2: Add the alloy billet to the extrusion equipment and hold it under a pressure of 2000-3500kN for 30-60 minutes to obtain an alloy billet containing high-density dislocations and lattice distortion structures; wherein the extrusion deformation is greater than 50%.
[0037] Step 3: Place the alloy billet in a heating device for the first heating. The heating temperature of the heating device is set between the recrystallization temperature and the solidus temperature of the alloy, and isothermal heat treatment is performed for 30-120 minutes to obtain fine and uniform recrystallized grains. In this embodiment, the recrystallization temperature of the narrow solid-liquid two-phase region alloy is 0.55-0.8 times the melting point of the narrow solid-liquid two-phase region alloy.
[0038] Step 4: Place the alloy billet in a heating device for a second heating. The heating device heats the billet to above the solidus line of the narrow solid-liquid two-phase region alloy and performs isothermal heat treatment for 5-30 minutes to obtain a semi-solid billet with recrystallized grains suspended in the molten grain boundary liquid phase, grain roundness greater than 0.9, and grain size reaching 1-20μm.
[0039] Step 5: Quickly transfer the obtained semi-solid billet into the die-casting mold for die casting, with a transfer time of less than 15 seconds. During die casting, the forming temperature of the semi-solid billet is between the solidus temperature and liquidus temperature of the alloy in the narrow solid-liquid two-phase region, and the injection speed is 2-6 m / s.
[0040] In this embodiment, the narrow solid-liquid two-phase region alloy is one of aluminum alloy, magnesium alloy, steel, titanium alloy and high-temperature alloy.
[0041] According to one embodiment of the present invention, the heating rate of the first heating is higher than that of the second heating. In this embodiment, the heating current of the heating device is 25-35A, and the heating voltage is 220-350V. The present invention controls the heating rate by controlling the heating current and heating voltage of the heating device. By reducing the second heating rate, uneven heating is avoided, ensuring the stability of the semi-solid billet.
[0042] Example 1
[0043] 4032 aluminum alloy castings were prepared using the semi-solid thixotropic die casting method for alloys with a narrow solid-liquid two-phase region described above. DSC testing showed that the solidus temperature of the 4032 aluminum alloy was 518℃ and the liquidus temperature was 565℃. The process included the following steps:
[0044] Step 1: Place the aluminum alloy ingot into the melting furnace for induction heating, introduce the protective gas argon, heat to 750℃ and melt for 3 hours. At this time, the aluminum alloy ingot is completely melted into aluminum alloy liquid. Then let it stand and cool for 5-10 minutes, and cast to obtain an aluminum alloy billet with a cast structure.
[0045] Step 2: Place the aluminum alloy billet in a cold extrusion press and apply a force of 2000-3500kN for extrusion. Then hold the pressure for 30-60 minutes until the aluminum alloy billet obtains a deformed microstructure containing high-density dislocations and lattice distortion. The extrusion deformation is 60%.
[0046] Step 3: Place the aluminum alloy billet in a heating furnace for the first heating. Set the heating temperature of the furnace to 400℃ and perform isothermal heat treatment for 120 minutes.
[0047] Step 4: Place the recrystallized aluminum alloy billet in a heating furnace for a second heating. The heating temperature of the furnace is set at 530℃, and isothermal heat treatment is performed for 10 minutes. 530℃ is between the solidus and liquidus of 4032 aluminum alloy.
[0048] Step 5: Quickly transfer the obtained semi-solid aluminum alloy billet to the mold cavity of the die-casting mold, set the pouring temperature to 530℃, the injection speed to 2m / s, and the injection pressure to 160MPa, and form it using the die-casting process.
[0049] The mechanical properties of the prepared castings were tested by changing the extrusion pressure in this embodiment, and the results are shown in Table 1.
[0050] Table 1. Mechanical property tests of 4032 aluminum alloy castings prepared under different extrusion pressures in Example 1.
[0051]
[0052] Comparative Example 1
[0053] 4032 aluminum alloy castings were die-cast using traditional aluminum alloy casting methods. The mechanical properties of the 4032 aluminum alloy castings prepared by the traditional aluminum alloy casting methods are shown in Table 2.
[0054] Table 2 Mechanical property tests of aluminum alloy castings prepared using conventional methods
[0055]
[0056] From Table 1, Table 2, Figure 2 and Figure 3 It can be seen that the hardness, yield strength, and tensile strength of each casting in Example 1 increase linearly and then decrease with increasing extrusion pressure, while the extrusion pressure of 2000-3500kN is the optimal extrusion pressure. Therefore, compared with the traditional aluminum alloy die casting method, the microstructure obtained after extrusion in this invention contains high-density dislocations and lattice distortion. By performing two isothermal heatings on the alloy in the narrow solid-liquid two-phase region, the first isothermal heat treatment fully utilizes the high distortion characteristics of the cold-extruded billet, ensuring the nucleation driving force for recrystallization, resulting in fine, uniform, and highly rounded recrystallized grains. The second isothermal heat treatment ensures precise control of temperature and time during the heating process. Finally, the hardness, yield strength, and tensile strength of the castings prepared by this method are significantly improved.
[0057] Example 2
[0058] C70250 copper alloy castings were prepared using the semi-solid thixotropic die casting method for alloys with a narrow solid-liquid two-phase region described above. DSC testing showed that the solidus temperature of the C70250 copper alloy was 1052℃ and the solidus temperature was 1079℃. The process included the following steps:
[0059] Step 1: Place the C70250 copper alloy ingot into a melting furnace for induction heating, introduce protective argon gas, heat to 1200℃ and melt for 3 hours. At this time, the copper alloy ingot will be completely melted into copper alloy liquid. Then let it stand and cool for 5-10 minutes, and cast to obtain a copper alloy billet with as-cast structure.
[0060] Step 2: Place the copper alloy billet in a cold extrusion press and apply a force of 3500kN for extrusion. Then hold the pressure for 30-60 minutes until the copper alloy billet obtains a deformed morphological structure containing high-density dislocations and lattice distortion. The extrusion deformation is 95%. Different extrusion forces have different effects.
[0061] Step 3: Place the copper alloy billet in a heating furnace for the first heating. Set the heating temperature of the furnace to 600℃ and perform isothermal heat treatment for 60 minutes.
[0062] Step 4: Place the recrystallized copper alloy billet in a heating furnace for a second heating. The heating temperature of the furnace is set at 1055℃, and isothermal heat treatment is performed for 10 minutes. 1055℃ is between the solidus and liquidus of C70250 copper alloy.
[0063] Step 5: Quickly transfer the obtained semi-solid copper alloy billet to the mold cavity of the die-casting mold, set the pouring temperature to 1055℃, the injection speed to 1m / s, and the injection pressure to 160MPa, and form it using the die-casting process.
[0064] The mechanical properties of the prepared castings were tested by changing the extrusion pressure in this embodiment, and the results are shown in Table 3.
[0065] Table 3. Mechanical property tests of 4032 aluminum alloy castings prepared under different extrusion pressures in Example 2.
[0066]
[0067] From Table 3, Figure 4It can be seen that the hardness, yield strength, and tensile strength of each casting in Example 2 increase linearly and then decrease with increasing extrusion pressure, while the extrusion pressure of 2000-3500kN is the optimal extrusion pressure. Therefore, compared with the traditional aluminum alloy die casting method, the microstructure obtained after extrusion in this invention contains high-density dislocations and lattice distortion. By performing two isothermal heatings on the alloy in the narrow solid-liquid two-phase region, the first isothermal heat treatment fully utilizes the high distortion characteristics of the cold-extruded billet, ensuring the nucleation driving force for recrystallization, resulting in fine, uniform, and highly rounded recrystallized grains. The second isothermal heat treatment ensures precise control of temperature and time during the heating process. Finally, the hardness, yield strength, and tensile strength of the castings prepared by this method are significantly improved.
[0068] In summary, the beneficial effects of this invention are:
[0069] The thixotropic die casting method for forming narrow solid-liquid two-phase region metallic materials proposed in this invention combines melting and casting, extrusion deformation, recrystallization heat treatment, solid-liquid two-phase region heat treatment, and die casting. Compared with traditional semi-solid forming processes, it does not require consideration of the solid-liquid two-phase region range of the alloy. It not only solves the problem that traditional equipment is difficult to prepare semi-solid billets of narrow solid-liquid two-phase region alloys, but also avoids problems such as gas entrapment, slag inclusion, shrinkage porosity, cold shuts, and secondary remelting. It can greatly improve the utilization rate and yield of metallic materials.
[0070] This invention obtains a modified microstructure containing high-density dislocations and lattice distortion by directly cold-extruded alloy billets in a narrow solid-liquid two-phase region. The alloy undergoes two isothermal heating processes. The first isothermal heat treatment fully utilizes the high distortion characteristics of the cold-extruded billet, ensuring the nucleation driving force for recrystallization, resulting in fine, uniform, and highly rounded recrystallized grains. The second isothermal heat treatment ensures precise control of temperature and time during the heating process. Parameters such as the size, roundness, grain coarsening rate, and solidity of the primary solid phase can be rationally adjusted according to the process, thereby obtaining a semi-solid billet with good fluidity and high quality. The two isothermal heat treatments improve the quality of the semi-solid billet in the narrow solid-liquid two-phase region alloy, contributing to a significant improvement in the mechanical properties of metallic materials.
[0071] This invention achieves high distortion and high density of material structure after cold extrusion deformation. The first isothermal treatment between the recrystallization temperature and the solidus temperature yields fine recrystallized grains with an average grain size of 1-20 μm. The second isothermal treatment above the solidus temperature causes the grain boundaries of the recrystallized grains to melt rapidly, resulting in a semi-solid billet with a grain sphericity greater than 0.9, where the recrystallized grains are suspended in the molten grain boundary liquid phase. This semi-solid billet has extremely high deformability, significantly reducing the tonnage of the die-casting machine during the die-casting process, which is very beneficial for die-casting. Die-casting almost eliminates the problem of air entrapment, can fill the cavity well, and is conducive to improving forming accuracy and mechanical properties.
[0072] This invention can complete the preparation of semi-solid billets using traditional extrusion and heating equipment, without the need for mechanical or electromagnetic stirring equipment required for rheological or thixotropic die casting. The operation process is simple, the processing cost is low, and it is easy to mass-produce. The simple operation method can significantly reduce energy consumption and save costs.
[0073] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0074] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims
1. A semi-solid thixotropic die casting method for alloys with a narrow solid-liquid two-phase region, characterized in that, Includes the following steps, Step 1: Add the alloy with a narrow solid-liquid two-phase region of less than 50°C into the heating equipment and heat it to the superheat temperature. After it is completely melted, let it stand and cool for a certain period of time to obtain an alloy billet with a cast structure. Step 2: Add the alloy billet to the extrusion equipment and hold it under a certain pressure for a certain time to complete the cold extrusion, so as to obtain an alloy billet containing high-density dislocations and lattice distortion structure; Step 3: Place the alloy billet into a heating device for the first heating. The heating temperature of the heating device is set between the recrystallization temperature and the solidus temperature of the alloy, and isothermal heat treatment is performed to obtain fine and uniform recrystallized grains. Step 4: Place the alloy billet into a heating device for a second heating. Set the temperature of the heating device above the solidus line of the alloy in the narrow solid-liquid two-phase region, and perform isothermal heat treatment to obtain a semi-solid billet. Step 5: Quickly transfer the obtained semi-solid blank into the die-casting mold for die casting.
2. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, The narrow solid-liquid two-phase region alloy is one of aluminum alloy, magnesium alloy, steel, titanium alloy, and high-temperature alloy.
3. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step one, the overheating temperature is 100-200°C higher than the liquidus temperature of the alloy in the narrow solid-liquid two-phase region, and the static cooling time is 5-10 minutes.
4. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step two, the extrusion pressure of the extrusion equipment is 2000-3500kN, the holding time is 30-60min, and the extrusion deformation is greater than 50%.
5. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step three, the holding time for isothermal heat treatment is 30-120 min, and the recrystallization temperature of the narrow solid-liquid two-phase region alloy is 0.55-0.8 times the melting point of the narrow solid-liquid two-phase region alloy.
6. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step four, the holding time for isothermal heat treatment is 5-60 minutes.
7. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, The heating rate of the first heating is higher than that of the second heating.
8. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 7, characterized in that, The heating current of the heating equipment is 25-35A, and the heating voltage is 220-350V.
9. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step five, during die casting, the forming temperature of the semi-solid billet is between the solidus temperature and the liquidus temperature of the alloy in the narrow solid-liquid two-phase region, and the injection speed is 1-6 m / s.
10. The semi-solid thixotropic die casting method for alloys with narrow solid-liquid two-phase regions according to claim 1, characterized in that, In step four, the roundness of the recrystallized grains of the semi-solid billet is greater than 0.9, and the grain size can reach 1-20μm.