Semi-solid metal slurry preparation method based on equal channel angular pressing

Abstract

The invention discloses a semi-solid metal slurry preparation method based on equal channel angular pressing, and belongs to the technical field of metal semi-solid forming. The method comprises the following steps: (1) carrying out homogenizing annealing treatment on a metal as-cast blank to obtain an annealed blank; (2) cutting a bar, putting the bar into an equal channel angular extrusion die channel, and carrying out graded speed regulation equal channel angular extrusion on the bar; (3) rotating the extruded blank by taking the axis of the blank as a rotating shaft, and repeating the step of graded speed regulation equal channel angular extrusion until the total rotating angle of the blank reaches 360 degrees, so as to obtain a deformed blank; and (4) the deformed blank is subjected to semi-solid isothermal treatment, and semi-solid slurry is obtained after water cooling. According to the method, by optimizing the corner angle of the equal channel angular extrusion die channel and combining graded speed regulation control in the extrusion process, stress concentration and severe plastic deformation of the as-cast blank can be well generated, and crystal grains are broken and fine, so that element segregation of the semi-solid slurry is improved, and the slurry with uniform solid and liquid and fine crystal grains is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal semi-solid forming, and relates to a semi-solid slurry preparation method based on equal-channel angular pressing. BACKGROUND

[0002] Semi-solid metal slurry is a solid-liquid mixed state material formed by controlling the solidification process of a metal melt in a solid-liquid temperature range. The semi-solid metal slurry has rheological properties such as low viscosity and high flowability, can significantly improve the mechanical properties of magnesium / aluminum alloy parts, and can reduce the forming temperature, and therefore has attracted widespread attention.

[0003] Severe plastic deformation (SPD) is a kind of plastic processing method that can introduce a true strain greater than 1 during deformation, thereby effectively refining the metal to a sub-micron or nanometer level and preparing a complete large-size block sample. This technology can simultaneously achieve the synergistic improvement of high strength and large plasticity of the material. Equal-channel angular pressing (ECAP) is a typical representative of severe plastic deformation technology and is widely used.

[0004] Strain-Induced Melt Activation (SIMA) is a semi-solid billet preparation method developed by Young and developed by the Kirkwood team. This method forms a rod with tensile deformation structure by cold deformation, warm deformation or hot deformation of conventional ingots through extrusion, rolling and other deformation processes, and obtains a non-dendritic structure billet after solid-liquid two-phase zone heat preservation and rapid cooling.

[0005] Since the extrusion deformation process is involved in SIMA, ECAP can be introduced into SIMA for semi-solid metal slurry preparation. However, at present, the process flow of semi-solid metal slurry prepared by combining ECAP and SIMA is relatively rough, without considering the fine optimization of the process flow combined with the properties of the metal itself, and without paying attention to the key influence of the equal-channel angular pressing die structure on the semi-solid metal properties, resulting in poor applicability of the process flow in the process of preparing semi-solid metal slurry by ECAP+SIMA. This causes the process flow to fail to fully play its role, resulting in poor grain refinement effect in the semi-solid metal slurry, serious element segregation, large solid-liquid segregation area and other problems, which ultimately affects the performance of the semi-solid metal slurry itself, cannot fully reflect its performance advantages, and limits its actual application.

[0006] Therefore, it is necessary to provide a method for preparing semi-solid metal paste based on equal diameter angular extrusion, which can effectively improve the problems of element segregation and large solid-liquid agglomeration regions in semi-solid metal paste, and improve the grain refinement effect of semi-solid metal paste, so that the advantages of semi-solid metal paste can be fully reflected and its application limitations can be overcome. Summary of the Invention

[0007] To overcome the problems in the prior art, this invention refines and optimizes the process flow by combining the properties of the metal itself, making the process flow more targeted. At the same time, the structure of the equal diameter angular extrusion die is optimized. Through the synergistic effect of die structure optimization and process flow refinement and targeted optimization, the grain size of the semi-solid metal slurry is effectively improved, its elemental segregation is reduced, the uniformity of element distribution in the semi-solid metal slurry is improved, and the solid-liquid agglomeration area is reduced. Thus, a semi-solid metal slurry with excellent comprehensive performance is prepared, and its superior performance is more fully reflected.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention proposes a method for preparing semi-solid metal slurry based on constant diameter angular extrusion, the method comprising the following steps: (1) The metal casting billet is subjected to homogenization annealing treatment to obtain annealed metal billet.

[0009] (2) Cut the annealed metal billet from step (1) into bars and place them into the channel of the equal diameter angular extrusion die. Start the hydraulic press, and the hydraulic press punch will... It moves toward the bar at a speed.

[0010] (3) When the hydraulic press punch does not exert pressure on the bar in step (2), by Calculate the continuing moving speed of the hydraulic press punch. ,in, For room temperature elongation of bars, The length of the bar stock is given in mm, and Φ is the interior angle of the equal diameter angular extrusion die in degrees. The calculation yields... Then, set the hydraulic press punch movement speed to... Hydraulic press punch The moving speed continues downwards, applying pressure to the bar stock, causing the bottom end of the bar stock to move towards the corner position of the channel of the equal-diameter angular extrusion die. At any stage where the hydraulic press punch is not applying pressure to the bar stock, the speed can be adjusted to... ,so, Can be with Equal, of course, in order to shorten the time it takes for the hydraulic press punch to move to the position of the bar, A higher speed can also be used.

[0011] (4) When the rod material of the total length 1 / 10 begins to enter the corner of the equal-diameter angle extrusion die channel, the moving speed of the hydraulic press punch is calculated by the moving speed of the hydraulic press punch , wherein is the yield strength of the annealed metal blank, in MPa, is the yield strength of the as-cast metal blank, in MPa, is the gap distance between the rod material surface and the inner wall of the equal-diameter angle extrusion die channel, in mm, D is the diameter of the rod material, in mm, and is calculated by , the moving speed of the hydraulic press punch is set to , and the hydraulic press punch continues to move downward at the moving speed of and applies pressure to the rod material, until the entire rod material is pressed into and through the corner position of the equal-diameter angle extrusion die, and the first pass equal-diameter angle extrusion is completed. During the equal-diameter angle extrusion process, if a hydraulic press with a stepless speed function is used, the speed parameters can be pre-calculated and input into the hydraulic press control system, and the hydraulic press can automatically control the speed transformation during the equal-diameter angle extrusion process according to the pre-set parameters. Moreover, if a hydraulic press with a stepless speed function is used, there is no need to stop the machine for parameter setting and hydraulic press speed change during the process.

[0012] (5) After the blank after the first pass equal-diameter angle extrusion in step (4) is rotated by a certain angle with its axis as the rotation axis, it is again placed into the channel of the equal-diameter angle extrusion die, and steps (2), (3), and (4) are repeated to complete the second pass equal-diameter angle extrusion. Then, after the blank is rotated by the same angle, steps (2), (3), and (4) are continuously repeated. After each pass of equal-diameter angle extrusion, the blank is rotated by the same angle and steps (2), (3), and (4) are repeated to complete the equal-diameter angle extrusion, until the total rotation angle of the blank reaches 360°, and steps (2), (3), and (4) are repeated to complete the last pass of equal-diameter angle extrusion. The forming pressure of each pass of equal-diameter angle extrusion is increased by 5% to 10% compared to that of the previous pass of equal-diameter angle extrusion, and a deformed blank is obtained. Equal-diameter angle extrusion itself is a conventional processing technology. The forming pressure of the first pass of equal-diameter angle extrusion can be obtained by using conventional numerical values. For example, for a typical semi-solid metal slurry preparation raw material ZCuSn10P1 alloy, which has low plasticity (usually elongation < 10%), the first pass forming pressure is usually controlled within 800 to 1200 MPa. For magnesium and aluminum alloys, which have high plasticity (usually elongation ≥ 10%), the first pass forming pressure is usually controlled within 300 to 600 MPa.

[0013] (6) the semi-solid isothermal heat treatment of the deformed billet obtained in step (5) is carried out, and then water cooling is carried out to obtain a semi-solid metal slurry. The semi-solid isothermal heat treatment can be carried out in a conventional manner, i.e. the deformed billet is heated to the solid-liquid temperature range of the alloy and is kept for a period of time, for example, the solid-liquid temperature range of the typical semi-solid metal slurry preparation raw material ZCuSn10P1 alloy is 867.3-1035.6℃, the deformed billet prepared by the ZCuSn10P1 alloy raw material is heated to 867.3-1035.6℃, and is kept for 1-60min, so that the semi-solid slurry is formed; the semi-solid temperature range of the AZ91D magnesium alloy is 470-595℃, the deformed billet prepared by the AZ91D magnesium alloy raw material is heated to 470-595℃, and is kept for 1-60min, so that the semi-solid slurry is formed; the semi-solid temperature range of the 6061 aluminum alloy is 579.3-658.8℃, the deformed billet prepared by the 6061 aluminum alloy raw material is heated to 579.3-658.8℃, and is kept for 1-60min, so that the semi-solid slurry is formed.

[0014] Preferably, in step (2), the inner angle of the corner of the channel of the equal-diameter angular extrusion die is Φ=110°, and the outer angle is Ψ=38°.

[0015] Preferably, according to the preparation method of claim 1, characterized in that: in step (2), the corner angle of the channel of the equal-diameter angular extrusion die is calculated by the formula , wherein, k is a safety factor, k =1, is the rated maximum speed of the hydraulic machine, in mm / s, is the distance between the bottom end of the hydraulic punch and the top end of the channel of the equal-diameter angular extrusion die before the hydraulic machine is started, in mm, is the critical deceleration distance of the hydraulic punch, =10mm. After calculating , the hydraulic punch can better avoid violent impact with the die and the bar, and the hydraulic punch can move to the bar at the maximum speed, thereby saving the semi-solid metal slurry preparation time.

[0016] Preferably, in step (5), the billet with an elongation of ≥10% is rotated by an angle of 90° each time, and the billet with an elongation of <10% is rotated by an angle of 180° each time.

[0017] The beneficial effects of the present application are: ​1. This invention comprehensively considers factors such as the properties of the mold and the metal itself, and optimizes the design of the equal diameter angular extrusion deformation process, making the process more targeted and refined, and making the process more adaptable to different types of alloy raw materials, thereby preparing a semi-solid metal slurry with excellent comprehensive performance.

[0018] 2. The plastic deformation process of metals is mainly achieved through dislocation slip and twinning. Dislocations encounter obstacles during slip, requiring a thermal activation process to accumulate energy so that the dislocations can "cut through" or "bypass" these obstacles. This invention, by comprehensively considering the properties of the material itself... The hydraulic press punch begins to extrude the bar at a more reasonable rate. At this time, the dislocations have enough accumulated thermal activation energy and break through the potential barrier through energy fluctuations, thereby reducing the critical shear stress of dislocation movement. This makes the metal more prone to severe plastic deformation, which in turn causes the original grains of the metal material to be severely broken and obtain finer and more uniformly distributed grains. This is beneficial for obtaining excellent semi-solid microstructure after isothermal treatment.

[0019] 3. When 1 / 10 of the total length of the bar begins to enter the corner of the equal-diameter angle extrusion die, the stress uniformity of the remaining metal bar that has not yet entered the corner of the equal-diameter angle extrusion die will increase. At this time, the extrusion speed can be calculated by combining the yield strength and other properties of the metal itself. It can promote the dynamic recovery and recrystallization process of metal materials, and make the metal deform uniformly, reducing the probability of crack formation while maintaining a high speed in the extrusion process, which helps to improve its comprehensive mechanical properties and saves the preparation time of semi-solid metal slurry.

[0020] 4. Ben Setting the inner angle of the equal diameter angular extrusion die to 110° and the outer angle to 38° can effectively improve the uniformity of metal deformation, provide better adaptability to multi-pass cumulative deformation, further reduce the probability of metal cracking, reduce the flow resistance at the channel exit of the equal diameter angular extrusion die, and improve the surface quality of the deformed billet.

[0021] 5. The present invention achieves uniform deformation by rotating the deformed billet and performing multiple passes of equal diameter angular extrusion, thereby improving the uniformity of the structure of the deformed billet and thus improving the uniformity of the structure of the semi-solid metal slurry.

[0022] 6. The process flow of this invention is easy to automate, has low actual control difficulty, and is suitable for industrial promotion and application. Attached Figure Description Figure 1 This is a schematic diagram of the channel angle of the equal diameter angular extrusion die of the present invention; Figure 2 This is a schematic diagram of the equal diameter angular extrusion process of the present invention; Figure 3 This is a microstructure diagram of the semi-solid slurry prepared in Example 1 of the present invention; Figure 4 This is a microstructure diagram of the semi-solid slurry prepared in Comparative Example 1 of the present invention. Figure 5 This is a microstructure diagram of the semi-solid slurry prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0024] Example 1 In this embodiment, ZCuSn10P1 alloy plate is used as raw material, and a semi-solid slurry is prepared according to the following steps: (1) Under the condition of 660℃, the ZCuSn10P1 alloy plate was kept at the temperature for 8 hours for homogenization annealing treatment. Then, a bar with a diameter of 30mm and a height of 80mm was cut from the plate after homogenization annealing. After applying graphite lubricant to the surface of the bar and the inner wall of the channel of the equal diameter angle extrusion die, the bar was placed into the channel of the equal diameter angle extrusion die.

[0025] (2) Through Calculate the moving speed of the hydraulic press punch, where k =1, =150mm / s, =300mm, =10mm, calculated Set the hydraulic press punch speed to 129.2 mm / s, then start the hydraulic press. The hydraulic press punch will move towards the bar at a speed of 129.2 mm / s.

[0026] (3) When the hydraulic press punch does not exert pressure on the bar in step (2), by Calculate the continuing speed of the hydraulic press punch, where, =0.08, =80mm, =110°, calculated as follows The hydraulic press punch is set to move at a speed of 3.7 mm / s, and the hydraulic press forming pressure is set to 800 MPa. The hydraulic press punch continues to move downward at a speed of 3.7 mm / s and applies pressure to the bar, causing the bottom end of the bar to move towards the corner position of the channel of the equal diameter angular extrusion die.

[0027] (4) When 1 / 10 of the total length of the bar begins to enter the corner of the equal diameter angular extrusion die channel, through Calculate the continuing speed of the hydraulic press punch, where... =51MPa, =65MPa, =1mm, D =30mm, calculated Set the hydraulic press punch speed to 6.3 mm / s, then start the hydraulic press. The hydraulic press punch continues to move downward at a speed of 6.3 mm / s and applies pressure to the bar until the entire bar is pressed into the corner position of the equal diameter angular extrusion die, thus obtaining the deformed blank I.

[0028] (5) Rotate the deformed blank I by 180° with its axis as the rotation axis and put it back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed blank II. The forming pressure of this equal diameter angle extrusion process is 10% higher than the forming pressure of the previous one.

[0029] (6) After rotating the deformed billet II by 180° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain that the forming pressure of the deformed billet in this equal diameter angle extrusion process is 10% higher than the forming pressure of the previous one.

[0030] (7) The deformed billet was kept at 920℃ for 20 minutes, and then the billet was cooled with water to obtain a semi-solid slurry.

[0031] Example 2 In this embodiment, 6061 aluminum alloy cast round ingots are used as raw materials, and a semi-solid slurry is prepared according to the following steps: (1) Under the condition of 650℃, the cast round ingot of 6061 aluminum alloy was kept at 6h for homogenization annealing treatment. Then, a bar with a diameter of 30mm and a height of 80mm was cut from the round ingot after homogenization annealing. After applying graphite lubricant to the surface of the bar and the inner wall of the channel of the equal diameter angle extrusion die, the bar was placed into the channel of the equal diameter angle extrusion die.

[0032] (2) Through Calculate the moving speed of the hydraulic press punch, where k =1, =150mm / s, =300mm, =10mm, calculated Set the hydraulic press punch speed to 129.2 mm / s, then start the hydraulic press. The hydraulic press punch will move towards the bar at a speed of 129.2 mm / s.

[0033] (3) When the hydraulic press punch contacts the top of the bar, pause the hydraulic press and proceed through... Calculate the continuing speed of the hydraulic press punch, where, =0.20, =80mm, =110°, calculated as follows Set the hydraulic press punch speed to 9.3 mm / s and the hydraulic press forming pressure to 350 MPa. Then start the hydraulic press. The hydraulic press punch continues to move downward at a speed of 9.3 mm / s and applies pressure to the bar, causing the bottom end of the bar to move towards the corner position of the channel of the equal diameter angle extrusion die.

[0034] (4) When 1 / 10 of the total length of the bar begins to enter the corner of the equal diameter angular extrusion die channel, through Calculate the continuing speed of the hydraulic press punch, where... =83MPa =195MPa, =1mm, D =30mm, calculated Set the hydraulic press punch speed to 15.5 mm / s, then start the hydraulic press. The hydraulic press punch continues to move downward at a speed of 15.5 mm / s and apply pressure to the bar until the entire bar is pressed into the corner position of the equal diameter angular extrusion die, thus obtaining the deformed blank I.

[0035] (5) Rotate the deformed blank I by 90° with its axis as the rotation axis and put it back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed blank II. The forming pressure of this equal diameter angle extrusion process is increased by 5% compared with the previous forming pressure.

[0036] (6) After rotating the deformed billet II by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed billet III. The forming pressure of this equal diameter angle extrusion process is increased by 5% compared with the previous forming pressure.

[0037] (8) After rotating the deformed billet III by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed billet IV. The forming pressure of this equal diameter angle extrusion process is increased by 5% compared with the previous forming pressure.

[0038] (9) After rotating the deformed blank IV by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed blank. The forming pressure of this equal diameter angle extrusion process is increased by 5% compared with the previous forming pressure.

[0039] (10) The deformed billet was kept at 610℃ for 15 minutes, and then the billet was cooled with water to obtain a semi-solid slurry.

[0040] Example 3 In this embodiment, AZ91D magnesium alloy cast round ingots were used as raw materials, and a semi-solid slurry was prepared according to the following steps: (1) At 470℃, the AZ91D magnesium alloy cast round ingot was kept at 470℃ for 8 hours for homogenization annealing treatment. Then, a bar with a diameter of 25mm and a height of 80mm was cut from the round ingot after homogenization annealing. After applying graphite lubricant to the surface of the bar and the inner wall of the channel of the equal diameter angle extrusion die, the bar was placed into the channel of the equal diameter angle extrusion die.

[0041] (2) Through Calculate the moving speed of the hydraulic press punch, where k =1, =150mm / s, =300mm, =10mm, calculated Set the hydraulic press punch speed to 129.2 mm / s, then start the hydraulic press. The hydraulic press punch will move towards the bar at a speed of 129.2 mm / s.

[0042] (3) When the hydraulic press punch contacts the top of the bar, pause the hydraulic press and proceed through... Calculate the continuing speed of the hydraulic press punch, where, =0.15, =80mm, =110°, calculated as follows Set the hydraulic press punch speed to 7mm / s and the hydraulic press forming pressure to 450MPa. Then start the hydraulic press. The hydraulic press punch continues to move downward at a speed of 7mm / s and applies pressure to the bar, causing the bottom end of the bar to move towards the corner position of the channel of the equal diameter angular extrusion die.

[0043] (4) When 1 / 10 of the total length of the bar begins to enter the corner of the equal diameter angular extrusion die channel, through Calculate the continuing speed of the hydraulic press punch, where... =130MPa =160MPa, =3.5mm, D =25mm, calculated Set the hydraulic press punch speed to 22mm / s, then start the hydraulic press. The hydraulic press punch continues to move downwards at a speed of 22mm / s and applies pressure to the bar until the entire bar is pressed into the corner position of the equal diameter angular extrusion die, thus obtaining the deformed blank I.

[0044] (5) After rotating the deformed billet I by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed billet II. The forming pressure of this equal diameter angle extrusion process is 8% higher than the forming pressure of the previous one.

[0045] (6) After rotating the deformed blank II by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed blank III. The forming pressure of this equal diameter angle extrusion process is 8% higher than the forming pressure of the previous one.

[0046] (8) After rotating the deformed billet III by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed billet IV. The forming pressure of this equal diameter angle extrusion process is 8% higher than the forming pressure of the previous one.

[0047] (9) After rotating the deformed blank IV by 90° with its axis as the rotation axis, it is placed back into the channel of the equal diameter angle extrusion die. Repeat steps (2), (3), and (4) to obtain the deformed blank. The forming pressure of this equal diameter angle extrusion process is 8% higher than the forming pressure of the previous one.

[0048] (10) The deformed billet was kept at 550℃ for 18 minutes, and then the billet was cooled with water to obtain a semi-solid slurry.

[0049] Comparative Example 1 This comparative example uses the same raw materials and equal diameter angular extrusion die as Example 1, and the same method to prepare ZCuSn10P1 alloy semi-solid slurry. The difference is that this comparative example does not use a graded speed regulation method for extrusion. During the extrusion process, the hydraulic press speed is 10 mm / s throughout.

[0050] Comparative Example 2 This comparative example uses the same raw materials and equal diameter angular extrusion die as Example 1, and the same method to prepare ZCuSn10P1 alloy semi-solid slurry. The difference is that the bar is not rotated during each extrusion pass in this comparative example.

[0051] Comparative Example 3 This comparative example uses the same raw materials, equal diameter angular extrusion die, and the same method to prepare ZCuSn10P1 alloy semi-solid slurry as Example 1. The difference is that the outer angle of the channel of the equal diameter angular extrusion die in this comparative example is 30° and the inner angle is 90°.

[0052] The microstructure of the semi-solid slurries prepared in Example 1, Comparative Example 1, and Comparative Example 2 was observed using a Nikon ECLIPSE M500 optical microscope. The results are as follows: Figures 3-5 As shown in Table 1, the average grain size, shape factor, and liquid fraction of the semi-solid slurries prepared in Examples 1-3, Comparative Example 1, and Comparative Example 2 were statistically analyzed using Image-Pro Plus software.

[0053] Table 1 As shown in Table 1, compared with Comparative Example 1, the average grain size of the semi-solid slurry prepared in Example 1 was refined by 28.7%, the shape factor was increased by 24.6%, and the liquid phase ratio was increased by 33%. This is because the optimal constant diameter angular extrusion rate was calculated and graded by the method of the present invention, which improved the extrusion efficiency and made the plastic deformation of the billet easier, resulting in a more obvious grain refinement effect.

[0054] Compared with Comparative Example 2, Example 1 shows that the average grain size of the semi-solid slurry prepared by Example 1 is 36.8% finer, the shape factor is increased by 35.7%, and the liquid phase ratio is increased by 67.3%. This is because the rotation at a certain angle in each pass during the extrusion process makes the structure more uniform, thereby greatly improving the liquid phase ratio.

[0055] The shape factor indicates the degree of deviation between the grain geometry parameters and the ideal unit cell parameters. The closer it is to "1", the closer the grain is to a perfect circle, the more uniform the element distribution, and the smaller the degree of element segregation. The liquid phase ratio refers to the proportion of liquid phase in a semi-solid structure. For semi-solid molding, an increase in the liquid phase ratio indicates that the thickness of the liquid film between grains is increasing, which promotes a gradual reduction in solid-liquid segregation.

[0056] In the preparation process of Comparative Example 3, a small number of microcracks appeared in the metal rod during the constant diameter angular extrusion process. Because the shear strain is large when the inner angle of the die is 90°, the uniformity of metal flow is reduced, stress concentration is generated, and microcracks are easily generated. In contrast, no cracks were generated in the rod during the preparation process of Example 1.

[0057] In summary, this invention, by optimizing the channel angle of the equal-diameter angular extrusion die and combining it with staged speed control during the extrusion process, effectively induces stress concentration and large plastic deformation in the cast billet, resulting in finer, more fragmented grains. This improves elemental segregation in the semi-solid slurry, yielding a slurry with uniform solid-liquid structure and fine grains. The semi-solid slurry prepared using the method and die of this invention effectively reduces elemental segregation, minimizes solid-liquid aggregation regions, and produces fine, dense, and uniform semi-solid grains, resulting in superior performance and expanding the applicability of semi-solid slurries.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a semi-solid metal slurry based on constant diameter angular extrusion, characterized in that: The preparation method includes the following steps: (1) The metal casting billet is subjected to homogenization annealing treatment to obtain annealed metal billet; (2) Cut the annealed metal billet from step (1) into bars and place them into the channel of the equal diameter angular extrusion die. Start the hydraulic press, and the hydraulic press punch will... The speed at which it moves toward the bar; (3) When the hydraulic press punch does not exert pressure on the bar in step (2), by Calculate the continuing moving speed of the hydraulic press punch. ,in, For room temperature elongation of bars, The length of the bar stock is given in mm, and Φ is the interior angle of the equal diameter angular extrusion die in degrees. The calculation yields... Then, set the hydraulic press punch moving speed to... Hydraulic press punch The moving speed continues to move downward and apply pressure to the bar, causing the bottom end of the bar to move towards the corner position of the channel of the equal diameter angular extrusion die; (4) When 1 / 10 of the total length of the bar begins to enter the corner of the equal diameter angular extrusion die channel, through Calculate the continuing moving speed of the hydraulic press punch. ,in The yield strength of the annealed metal billet is expressed in MPa. The yield strength of the cast metallic billet is expressed in MPa. This refers to the clearance distance between the surface of the bar stock and the inner wall of the channel of the equal diameter angular extrusion die, expressed in mm. D The diameter of the bar is in mm, calculated as follows: Set the hydraulic press punch movement speed to Hydraulic press punch The moving speed continues to move downward and apply pressure to the bar until the entire bar is pressed into and passes through the corner position of the equal diameter angle extrusion die, thus completing the first pass of equal diameter angle extrusion. (5) After the billet after the first pass of equal diameter angle extrusion in step (4) is rotated by a certain angle with its axis as the rotation axis, it is put into the channel of the equal diameter angle extrusion die again. Steps (2), (3), and (4) are repeated to complete the second pass of equal diameter angle extrusion. Then, the billet is rotated by the same angle and steps (2), (3), and (4) are repeated. After each pass of equal diameter angle extrusion is completed, the billet is rotated by the same angle and steps (2), (3), and (4) are repeated to complete the equal diameter angle extrusion. When the total rotation angle of the billet reaches 360°, steps (2), (3), and (4) are repeated to complete the last equal diameter angle extrusion. The forming pressure of each pass of equal diameter angle extrusion is increased by 5% to 10% compared with the forming pressure of the previous pass of equal diameter angle extrusion to obtain a deformed billet. (6) The deformed billet obtained in step (5) is subjected to semi-solid isothermal heat treatment and then water cooling to obtain semi-solid metal slurry.

2. The preparation method according to claim 1, characterized in that: In step (2), the inner angle Φ of the channel of the equal diameter angular extrusion die is 110° and the outer angle Ψ is 38°.

3. The preparation method according to claim 1, characterized in that: In step (2), the formula is used. Calculated ,in, k For safety reasons, k =1, The rated maximum speed of the hydraulic press is expressed in mm / s. This refers to the distance in mm between the bottom of the hydraulic press punch and the top of the channel of the equal diameter angular extrusion die before the hydraulic press is started. This is the critical deceleration distance of the hydraulic press punch. =10mm.

4. The preparation method according to claim 1, characterized in that: In step (5), the billet with an elongation of ≥10% is rotated at an angle of 90° each time, and the billet with an elongation of <10% is rotated at an angle of 180° each time.

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