Low pressure forming die for making ultra-fine grained magnesium alloys

Abstract

The application discloses a low-pressure forming die for preparing ultra-fine-grain magnesium alloy, which comprises a punch, a die, a feeding cylinder and a fixed base plate. One end of the punch is fixedly installed on a linear feeding mechanism, and the other end of the punch is placed into the die. The linear feeding mechanism drives the punch to move axially linearly. The die is provided with a cavity at one end close to the punch. The die is fixedly installed on a torsion mechanism at the other end away from the punch. The feeding cylinder and the fixed base plate are fixedly installed in the cavity. The feeding cylinder is provided with a upsetting cavity along the axial direction for placing a blank and the punch. The inner diameter of the front section of the upsetting cavity is smaller than that of the rear section to form a resistance flow belt for preventing the blank from overflowing. The fixed base plate is provided with a hollow torsion-extrusion cavity. The inner wall of the front section of the torsion-extrusion cavity is provided with a gradually inwardly tapered arc-shaped convex surface at the connecting position with the rear section of the upsetting cavity. The application can continuously apply a strong shearing stress to the magnesium alloy blank under a proper pressure condition to accumulate a high strain, shorten a technological process and realize the preparation of a weak anisotropy and uniform ultra-fine-grain magnesium alloy ingot.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic deformation technology, and in particular refers to a low-pressure forming mold for preparing ultrafine-grained magnesium alloys. Background Technology

[0002] With the increasing demands for lightweight high-end equipment in fields such as aerospace, the need for high-strength and high-ductility magnesium alloy components is becoming increasingly urgent. Against this backdrop, ultrafine-grained magnesium alloys, with their superior strength and ductility, have become key to solving the trade-off between strength and ductility in magnesium alloys. Compared to coarse-grained alloys, ultrafine-grained magnesium alloys achieve simultaneous improvements in strength and ductility through grain refinement technology.

[0003] During hot deformation, traditional large plastic deformation processes are limited by the finite strain and recrystallization grain growth, making it difficult to obtain ultrafine-grained structures to improve strength and toughness. The intense plastic deformation (SPD) method can produce ultrafine-grained materials through the synergistic effect of high strain accumulation and high hydrostatic pressure with almost no change in shape.

[0004] While high-strain rolling and constant-diameter angular extrusion (SPD) methods can reduce grain size and significantly improve the mechanical properties of alloys, their cumbersome and costly preparation processes greatly limit their widespread industrial application. On the other hand, although high-pressure torsional deformation can produce submicron-sized ultrafine-grained alloys in a shorter process, the requirement for forming force in large-scale equipment limits its application to the preparation of micron or submicron-sized ultrafine-grained billets in laboratory research, making it unsuitable for industrial use. Furthermore, the size of the ultrafine-grained alloys produced by this method is limited. Summary of the Invention

[0005] The purpose of this invention is to provide a low-pressure forming mold for preparing ultrafine-grained magnesium alloys, that is, to achieve high strain accumulation by continuously applying strong shear stress to magnesium alloy billets under appropriate pressure conditions, thereby shortening the process flow and realizing the preparation of weakly anisotropic, uniform ultrafine-grained magnesium alloy ingots.

[0006] To achieve the above objectives, the solution of the present invention is as follows: a low-pressure forming mold for preparing ultrafine crystalline magnesium alloy, comprising a punch, a die, a feeding cylinder, and a fixed pad. One end of the punch is fixedly mounted on a linear feed mechanism, and the other end of the punch is inserted into the die. The linear feed mechanism drives the punch to move linearly in the axial direction. The die has a cavity at the end near the punch and is fixedly mounted on a torsion mechanism at the end away from the punch. The feeding cylinder and the fixed pad are fixedly installed inside the cavity. The feeding cylinder has a hollow upsetting cavity along the axial direction for inserting the billet and the punch. The inner diameter of the front section of the upsetting cavity is smaller than that of the rear section to form a flow-blocking band to prevent the billet from overflowing. The rear section of the upsetting cavity is the upsetting working band. The fixed pad has a hollow torsion extrusion cavity. The front section of the torsion extrusion cavity has a gradually inwardly tapering arc-shaped boss surface at the connection between it and the rear section of the upsetting cavity, allowing the billet to flow in from the upsetting working band and contact it.

[0007] As a further improvement, the rear section of the twisting cavity is a square hole.

[0008] As a further improvement, the die is designed as two symmetrical segmented dies. After the two symmetrical segmented dies are closed, a nest is placed around their outer periphery, and the inner wall of the nest matches the outer wall of the die.

[0009] As a further improvement, the nested inner wall and the outer wall of the die have the same slope, and the nested inner wall and the outer wall of the die fit together.

[0010] As a further improvement, the feeding cylinder is designed as two symmetrical split feeding cylinders. The outer walls of the two symmetrical split feeding cylinders and the outer wall of the fixing pad are both provided with a straight groove along the axial direction. The inner wall of the cavity is provided with a straight rib at the position corresponding to the straight groove. The straight groove and the straight rib fit together tightly.

[0011] As a further improvement, the end of the punch is provided with a cross-shaped groove that contacts the blank.

[0012] As a further improvement, the slope of one side of the groove wall of the cross-shaped groove is greater than the slope of the other side.

[0013] As a further improvement, the interior of the punch, except for the part at the end that contacts the blank, is hollowed out.

[0014] As a further improvement, the cavity is provided with a relief cavity on the side of the fixed pad away from the feeding cylinder, and the relief cavity is located on the same axis as the upsetting cavity and the twisting cavity.

[0015] After adopting the above scheme, the gain effect of the present invention is as follows:

[0016] In this invention, the punch applies an appropriate axial force during forming. The rare earth magnesium alloy billet, placed in the unloading cylinder, first undergoes upsetting deformation in the upsetting cavity of the unloading cylinder and slight reverse extrusion deformation in the flow-blocking zone until the metal fills the upsetting cavity and its flow-blocking zone. Then, the die rotates under the drive of the torsion unit, causing the magnesium alloy billet to undergo torsion deformation in the torsion extrusion cavity of the fixed pad, thereby obtaining a submicron-level ultrafine-grained magnesium alloy ingot. This invention effectively improves the refinement degree of deformed alloys under constant strain conditions by increasing strong shear stress under high hydrostatic pressure, forming a submicron-level ultrafine-grained bulk magnesium alloy billet with good uniformity and weak anisotropy. In addition, this invention can simplify the preparation process and reduce the forming force requirements, laying a solid foundation for the engineering preparation of ultrafine-grained magnesium alloy billets. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the punch before it enters the die in this invention;

[0018] Figure 2 This is a schematic diagram of the structure of the punch entering the die of the present invention (without upsetting);

[0019] Figure 3 This is a schematic diagram of the structure of the punch extruding the blank according to the present invention;

[0020] Figure 4 This is a schematic diagram of the structure of the punch of the present invention;

[0021] Figure 5 This is a partial front view structural diagram of the cross-shaped groove of the present invention;

[0022] Figure 6 This is a partial side view of the cross-shaped groove of the present invention;

[0023] Figure 7 This is a schematic diagram of the structure of the concave mold of the present invention;

[0024] Figure 8 yes Figure 7 Schematic diagram of the structure of the middle die along direction A;

[0025] Figure 9 This is a schematic diagram of the nested structure of the present invention;

[0026] Figure 10 This is a schematic diagram of the material feeding cylinder of the present invention;

[0027] Figure 11 yes Figure 10 Schematic diagram of the structure of the feed cylinder from direction B;

[0028] Figure 12 This is a schematic diagram of the structure of the fixing pad of the present invention;

[0029] Figure 13 yes Figure 12 Schematic diagram of the structure of the fixed pad in direction C;

[0030] Figure 14 This invention relates to the microstructure of a low-pressure torsion forming alloy.

[0031] Label Explanation:

[0032] 1. Punch; 11. Hollowed-out structure; 12. Cross-shaped groove; 13. Annular flange; 2. Die; 21. Cavity; 22. Straight rib; 23. Relief cavity; 3. Feeding cylinder; 31. Straight groove; 32. Upsetting cavity; 33. Flow barrier; 4. Fixing pad; 41. Torque extrusion cavity; 42. Arc-shaped boss surface; 43. Square hole; 5. Nesting; 6. Blank. Detailed Implementation

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a low-pressure forming die for preparing ultrafine-grained magnesium alloys, such as... Figures 1 to 13 As shown, it includes a punch 1, a die 2, a feeding cylinder 3, and a fixing plate 4.

[0035] Figure 1 The diagram shown is a schematic representation of the overall structure of the mold of the present invention. One end of the punch 1 (specifically, it can be...) Figure 1 The annular flange shown is fixedly mounted on the linear feed mechanism (specifically, a hydraulic press) and secured with bolts to ensure the tightness of the connection between the mold and the linear feed mechanism. Figure 2 As shown, the other end of the punch 1 is inserted into the die 2 and contacts the blank 6. The linear feed mechanism drives the punch 1 to move axially in a linear motion. The die 2 has a cavity 21 at the end near the punch 1, and the end of the die 2 away from the punch 1 is fixedly mounted on the torsion mechanism (specifically, it can also be an annular flange 13 identical to one end of the punch 1). Except for the part of the punch 1 that contacts the blank 6 at the end, the other parts of the punch 1 have a hollowed-out structure 11. On the one hand, this makes it easier to ensure that the punch 1 maintains a relatively constant temperature during heating and heat preservation. On the other hand, it can also save production costs.

[0036] The material feeding cylinder 3 and the fixing pad 4 are fixedly installed inside the cavity 21. In one embodiment, both the material feeding cylinder 3 and the fixing pad 4 are cylindrical rotating bodies. Both the material feeding cylinder 3 and the fixing pad 4 can be designed as two symmetrical segmented structures. Designing them as segmented structures can facilitate mold installation, material feeding, and material unloading, etc. Figure 10 and Figure 11 As shown, the outer walls of the two symmetrical, segmented feeding cylinders 3 are provided with axially oriented grooves 31, such as... Figure 7 and Figure 8 As shown, the inner wall of the cavity 21 has a protruding I-shaped rib 22 at the position corresponding to the I-shaped groove 31, such as... Figure 1 The diagram shows the structure in which the feeding cylinder 3 and the fixing pad 4 are fixedly installed in the cavity 21. The straight groove 31 and the straight rib 22 fit tightly together to prevent the circumferential movement of the feeding cylinder 3 when it is torn and deformed.

[0037] Similarly, the cavity mold 2 can also be designed as two symmetrical segmented cavities 2. After the two symmetrical segmented cavities 2 are closed, a nesting 5 is placed around their outer periphery, such as... Figure 1 and Figure 9 As shown, the inner wall of the nest 5 mates with the outer wall of the die 2, so that the nest 5 can clamp the segmented die 2. Furthermore, the inner wall of the nest 5 and the outer wall of the die 2 have the same slope, and the inner wall of the nest 5 fits into the outer wall of the die 2, which helps the nest 5 to tightly fix the segmented die 2 and also facilitates the loading and unloading of the mold after twisting and forming.

[0038] like Figure 1 and Figure 2 As shown, the feeding cylinder 3 has a hollow upsetting cavity 32 along the axial direction for the blank 6 and the punch 1 to be placed. The inner diameter R1 of the front section of the upsetting cavity 32 is smaller than the inner diameter R1 of the rear section to form a flow-blocking band 33 to prevent the blank 6 from overflowing. The rear section of the upsetting cavity 32 is the upsetting working band, as shown in the figure. Figure 3 As shown, the flow-blocking band 33 can prevent the billet 6 from flowing towards the punch 1 in the feeding direction due to pressure during torsional deformation, that is, prevent the billet 6 from overflowing, which is conducive to controlling the orderly flow of metal. By simply changing the feeding cylinder 3 of different thicknesses, it is possible to form ultrafine-grained magnesium alloy billets of different sizes, and the preparation of ultrafine-grained bulk materials has good uniformity; such as Figure 1 , Figure 12 and Figure 13 As shown, the fixed pad 4 has a hollow extrusion cavity 41. The front section of the extrusion cavity 41 has a gradually tapering arc-shaped boss surface 42 on its inner circumference at the connection with the rear section of the upsetting cavity 32, allowing the billet 6 to flow in and contact from the upsetting working section. During operation, the billet 6 is torn and deformed. The rear section of the extrusion cavity 41 is a square hole 43. The transition from the arc-shaped boss surface 42 to the square hole 43 results in more significant grain refinement. The cavity 21 has a relief cavity 23 on the side of the fixed pad 4 away from the feeding cylinder 3. The relief cavity 23 is located on the same axis as the upsetting cavity 32 and the extrusion cavity 41. When the volume of the billet 6 is large, the required forming time is also long. The relief cavity 23 allows the billet 6 to enter from the extrusion cavity 41, thereby extending the overall forming process and making the forming more complete.

[0039] Before the torsion deformation, by controlling the magnitude of the axial compressive stress applied by the linear feed mechanism, the billet 6 can be fully upset into the required shape before entering the port of the arc-shaped boss surface 42. When the deformation temperature and other parameters are consistent, the forming force required for the upsetting of the billet 6 is relatively small, approximately 0.5 tons. However, the extrusion of the billet 6 into the port of the arc-shaped boss surface 42 is a typical positive extrusion. Furthermore, since the rear section of the torsion extrusion cavity 41 is a square hole 43, the forming force required for positive extrusion is greater, generally around 2 tons (the specific value is for a rod-shaped billet 6 with a diameter of 9m).

[0040] Finally, the extrusion into the twisting cavity is a deformation of the extrusion ratio. Its deformation is more difficult than that of upsetting. This can be achieved by using the equal volume method or simulation to determine the distance that needs to be extruded, so as to ensure that the billet is upset to a fixed shape without being squeezed into the twisting cavity.

[0041] like Figure 5 and Figure 6 As shown, the end of the punch 1 is provided with a cross-shaped groove 12 that contacts the blank 6. Furthermore, the slope of one side of the groove wall of the cross-shaped groove 12 is greater than that of the other side, so that the metal flows slowly from the larger slope of the cross-shaped groove 12 into the cross-shaped groove 12, thereby preventing the problem of fixation weakening caused by the continuous scraping of the contact end of the punch 1 of the blank 6. This provides a basis for large-turn torsional deformation, effectively solves the problem of the limitation of cumulative strain in traditional drastic plastic deformation, and creates conditions for the blank 6 not to slip during the torsion process after applying torque.

[0042] A low-pressure forming method for preparing ultrafine-grained magnesium alloys includes the following steps:

[0043] S1 Blanking: Take a section of magnesium alloy cylindrical billet 6;

[0044] S2 mold installation: (e.g.) Figure 1 As shown, the mold is assembled as described above. When assembling the mold, first, the fixing plate 4 and one of the feeding cylinders 3 are placed in the upsetting cavity 32 of one of the concave molds 2. The blank 6 wrapped with graphite paper is placed on the feeding cylinder 3. Then, the other feeding cylinder 3 and the other concave mold 2 are placed above the assembled mold so that the split feeding cylinder 3 and the split concave mold 2 are closed. Finally, the nest 5 is inserted axially from the end of the split concave mold 2 to complete the assembly of the mold.

[0045] Preparations before S3 forming: such as Figure 2 As shown, the tail ends of the punch 1 and the die 2 are respectively mounted on the linear feed mechanism and the torsion mechanism. Then the linear feed mechanism drives the punch 1 to feed axially. The punch 1 with the cross-shaped groove is placed into the feeding cylinder 3 and moves until the cross-shaped groove 12 of the punch 1 contacts the blank 6.

[0046] S4 Slight upsetting deformation: The linear feed mechanism drives the punch 1 to continue moving, and the blank 6 undergoes slight upsetting deformation until the blank 6 fills the rear section of the upsetting cavity 32 and the flow barrier 33.

[0047] S5 One-time torsional deformation: The die 2 rotates under the drive of the torsion mechanism, and the fixed pad 4 also rotates. The arc-shaped boss surface 42 in the torsion cavity 41 causes the end of the blank 6 in contact with it to undergo torsional deformation.

[0048] S6 Secondary Torsional Deformation: After the first torsional deformation is completed, the die 2 is removed, the deformed blank 6 is taken out of the die 2 and rotated 180°, and steps S2 and S4 are repeated to apply torsional deformation to the other end of the blank 6 that is not deformed through the die 2.

[0049] S7 Demolding: After the secondary torsional deformation is completed, the concave mold 2 is removed and the deformed blank 6 is taken out, thus completing the forming of an ultrafine crystalline magnesium alloy.

[0050] In step S7, the punch 1 is struck at its end to separate the punch 1 from the nest 5, which in turn causes the die 2, the split feeding cylinder 3, the fixed pad 4, and the deformed blank 6. Then, the unseparated parts are gently struck to separate the split die 2 and the split feeding cylinder 3 to facilitate the removal of the deformed blank 6.

[0051] The mold and blank 6 of the present invention can be heated simultaneously before and during forming. Specifically, the blank 6 and the mold are heated synchronously using a Gleeble-3500 (thermal simulation testing machine), and thermocouple wires are welded to the working end of the punch 1 near the die 2 to detect and control the deformation temperature in real time.

[0052] This invention optimizes low-pressure torsion process parameters based on the torsion unit of the Gleeble-3500 thermal simulation testing machine, which can lay the foundation for the preparation of large-scale ultrafine crystal ingots for industrial applications. Figure 14 The microstructure of the low-pressure torsion forming alloy of the present invention is shown in part (a) of the figure, which represents an optical microscope (OM) image and part (b) represents a transmission electron microscope (TEM) image. Both reflect the effect of the magnesium alloy billet 6 achieving high strain accumulation under continuous application of strong shear stress, resulting in a weakly anisotropic, uniform, ultrafine-grained magnesium alloy ingot billet.

[0053] During plastic deformation, magnesium alloys exhibit unique rotational dynamic recrystallization behavior under strong compressive shear stress, promoting grain refinement. The continuous formation and rotation of subgrains further enhances the refinement of the grains and second phase in the billet 6. The thickness of the prepared ultrafine grains depends on the orderly axial transmission of strong shear stress; that is, the preparation of ultrafine-grained billets 6 with different thicknesses depends on the port diameter of the arc-shaped bosses 42 with different areas. This technology enables the preparation of ultrafine-grained magnesium alloy ingots, overcoming the current dimensional limitations of ultrafine-grained bulk alloys. The introduction of strong shear stress activates conical slip, promoting the random orientation of dynamically recrystallized grains, significantly reducing basal texture, and effectively solving the problems of strong anisotropy and poor uniformity in traditional alloys subjected to severe plastic deformation.

[0054] Furthermore, when rare earth magnesium alloys are deformed on a Gleeble-3500 thermal simulation testing machine, the forming force required for different deformation methods varies while ensuring that the billet size and deformation temperature are consistent. Pure extrusion deformation requires approximately 2 tons, rotary extrusion deformation requires approximately 1.2 tons, while low-pressure torsion forming requires only 0.45 tons (these are the forming force values ​​at a deformation temperature of 420℃). Compared with large plastic deformations such as equal diameter angular extrusion and high-pressure torsion, the preparation method proposed in this invention is simple to implement and can reduce the forming load and equipment tonnage, i.e., low pressure, laying the foundation for the industrial mass production of large-size ultrafine crystal billets.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design features of this case shall fall within the protection scope of this case.

Claims

1. A low-pressure forming mold for preparing ultrafine-grained magnesium alloys, characterized in that: The assembly includes a punch, a die, a feed cylinder, and a fixed pad. One end of the punch is fixedly mounted on a linear feed mechanism, and the other end of the punch is inserted into the die. The linear feed mechanism drives the punch to move axially in a linear motion. The die has a cavity at the end near the punch, and the end away from the punch is fixedly mounted on a torsion mechanism. The feed cylinder and the fixed pad are fixedly installed inside the cavity. The feed cylinder has a hollow upsetting cavity along the axial direction for inserting the blank and the punch. The inner diameter of the front section of the upsetting cavity is smaller than that of the rear section to form a flow-blocking band to prevent the blank from overflowing. The rear section of the upsetting cavity is the upsetting working band. The fixed pad has a hollow torsion extrusion cavity. The front section of the torsion extrusion cavity has a gradually inward-curving arc-shaped boss surface at the connection between it and the rear section of the upsetting cavity, allowing the blank to flow in from the upsetting working section and contact it. The feed cylinder and the fixed pad are both segmented structures, and both are fixedly installed inside the die cavity.

2. The low-pressure forming mold for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: The rear section of the twisting cavity is a square hole.

3. The low-pressure forming mold for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: The die is designed as two symmetrical segmented dies. After the two symmetrical segmented dies are closed, a nest is placed around their outer periphery, and the inner wall of the nest matches the outer wall of the die.

4. The low-pressure forming mold for preparing ultrafine-grained magnesium alloy as described in claim 3, characterized in that: The nested inner wall and the outer wall of the die have the same slope, and the nested inner wall and the outer wall of the die fit together.

5. The low-pressure forming mold for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: The feeding cylinder is designed as two symmetrical split feeding cylinders. The outer walls of the two symmetrical split feeding cylinders and the outer wall of the fixed pad are both provided with a straight groove along the axial direction. The inner wall of the cavity is provided with a straight rib at the position corresponding to the straight groove. The straight groove and the straight rib fit together tightly.

6. The low-pressure forming mold for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: The end of the punch is provided with a cross-shaped groove that contacts the blank.

7. The low-pressure forming die for preparing ultrafine-grained magnesium alloy as described in claim 6, characterized in that: The slope of one side of the groove wall of the cross-shaped groove is greater than that of the other side.

8. The low-pressure forming die for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: Except for the part at the end that contacts the blank, the interior of the punch is hollowed out.

9. The low-pressure forming die for preparing ultrafine-grained magnesium alloy as described in claim 1, characterized in that: The cavity has a relief cavity on the side of the fixed pad away from the feeding cylinder, and the relief cavity is located on the same axis as the upsetting cavity and the twisting cavity.

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