A core roller structure and a rare earth magnesium alloy ring piece roll forming method

Abstract

The present application belongs to the technical field of rolling forming, and discloses a core roller structure, characterized by comprising a core roller body and trapezoidal protrusions arranged along the outer wall of the core roller body in an axial direction. A rare earth magnesium alloy ring piece rolling forming method using the core roller structure is also disclosed. Each time the core roller feeds, the blank is compressed and deformed, and at the same time, a dislocation constraint shearing effect is generated along the thickness direction of the blank. The design of the present application can strengthen the refinement ability of the structure and improve the isotropic ability of the rare earth magnesium alloy ring piece. The present application changes the profile characteristics of the core roller, adds trapezoidal protrusion structures, forms a sawtooth structure, increases the shearing strain of the ring piece along the thickness direction by using the dislocation deformation principle, and is more conducive to refining the grains during the ring rolling process.

Description

Technical Field

[0001] This invention belongs to the field of rolling forming technology, and more specifically relates to a core roller structure and a rolling forming method for rare earth magnesium alloy rings. Background Technology

[0002] Magnesium alloys have a close-packed hexagonal structure, a large c / a axis ratio, and lack sufficient slip systems, relying mainly on basal plane slip. This results in excessively strong basal texture, small single-pass deformation, severe anisotropy, low plasticity, and relatively poor formability. Therefore, weakening the basal texture of magnesium alloys, eliminating or reducing low-melting-point and coarse compounds, improving the plasticity of magnesium alloys, and developing high-formability processing technologies for magnesium alloys are the main technical challenges currently facing the large-scale application of magnesium alloys. In recent years, teams led by Academician Pan Fusheng of Chongqing University and Academician Ding Wenjiang of Shanghai Jiao Tong University have successfully developed a batch of high-plasticity rare-earth magnesium alloy materials using new alloy design approaches such as solid solution strengthening and plasticization. Currently, magnesium rare-earth alloy castings have been applied as non-load-bearing components in engine casings, new missile hulls, and aerospace vehicles, achieving a 20% weight reduction and significantly improving the combat and technical indicators of strategic and tactical weapons and equipment, thus receiving high attention.

[0003] In order to further improve the key performance indicators such as carrying capacity, speed and range of the new generation of strategic and tactical missiles and other weapons and equipment, the main load-bearing structure is planned to adopt heat-resistant rare earth magnesium alloy thin-walled ring forgings. Its integral forming technology has received high attention. However, due to the poor plasticity of magnesium alloy and the strong constraint on material flow by roll forming, its integral forming is difficult. Specifically, it is difficult to control the structural dimensions stably, the mechanical properties are highly discrete (the radial strength, circumferential strength and axial strength are quite different), and the quality stability is poor, which directly affects the delivery cycle of the new generation of products.

[0004] The material flow patterns in the traditional rolling forming processes of aluminum alloys, titanium alloys, and nickel-based alloys lead to a strong tendency for magnesium alloys to form textures along the circumference of the ring forging during deformation. This strong texture is difficult to control through subsequent deformation or heat treatment, ultimately resulting in significant differences in the mechanical properties of the ring forging in different directions and substandard product performance. Furthermore, the existing cylindrical mandrel only generates compressive strain along the thickness direction of the ring blank and cannot generate shear deformation along the thickness direction of the ring forging, resulting in a very weak grain refinement effect.

[0005] Therefore, researching a mandrel structure that can improve the microstructure refinement capability, eliminate texture tendency, and enhance the isotropic properties of rare earth magnesium alloy ring forgings, as well as developing an integral rolling forming technology for heat-resistant rare earth magnesium alloy ring forgings that meets shape / property control requirements, are key technological challenges facing lightweight manufacturing of aerospace equipment. Summary of the Invention

[0006] In view of this, the present invention provides a mandrel structure and a method for rolling and expanding rare earth magnesium alloy rings using the mandrel structure. On the one hand, it can significantly improve the ability to refine the microstructure of magnesium alloy materials; on the other hand, it can achieve three-dimensional control of the grain orientation of magnesium alloy materials, so that the grain orientation is not parallel to the circumferential direction of the ring forging, which can greatly eliminate the strong texture of magnesium alloy formed during deformation, while improving the grain refinement ability of rolling and expanding and the overall mechanical properties of the ring forging.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A core roller structure, characterized in that it comprises: a core roller body, and trapezoidal protrusions arranged axially at intervals along the outer wall of the core roller body.

[0009] The technical effects achieved by adopting the above technical solution include at least the following: each feed of the core roller structure causes the billet to undergo compression deformation, while simultaneously generating a misaligned constraint shearing effect along the thickness direction of the billet, thereby enhancing the grain refinement effect; moreover, this non-uniform stress field rolling deformation can significantly weaken the basal texture of rare earth magnesium alloys, significantly improve formability, and significantly improve anisotropy.

[0010] Furthermore, the angle θ between the inclined side of the trapezoidal protrusion and the tangent at the connection between the inclined side and the outer wall of the core roller body satisfies 30° to 60°.

[0011] Furthermore, the distance between the two sides of the top of the trapezoidal protrusion and the vertical projection distance corresponding to the hypotenuse of the trapezoidal protrusion are both a, and a satisfies 0.75mm~1.5mm.

[0012] Furthermore, the trapezoidal protrusions are evenly distributed along the axial direction of the outer wall of the core roller body, and the spacing b between the trapezoidal protrusions is 0.75mm to 1.5mm.

[0013] The technical effects achieved by adopting the above-mentioned technical solution include at least the following: Some current technologies for rolling irregularly shaped cross-section materials use upper and lower rolls with grooves of very small depth and width on the roll surface, thus only suppressing elongation in the length direction and reducing the fluctuation of the rolled part. However, this invention strictly limits the angle and size of the trapezoidal protrusion, using values ​​far greater than those in existing technologies. Within this limited range, the trapezoidal protrusion generates a shearing effect, capable of penetrating the deformed material, thereby enabling the grain orientation of the deformed ring forging to achieve a three-dimensional spatial distribution, avoiding the formation of a strong texture distribution along the circumference of the ring forging, and thus suppressing or eliminating anisotropy. Furthermore, within the scope of this invention, by changing the angle and width of the trapezoidal protrusion on the mandrel, the orientation of the rare earth magnesium alloy grains can be adjusted according to actual conditions, thereby optimizing the mechanical properties of the ring forging, resulting in good consistency of mechanical properties and meeting practical application requirements.

[0014] The present invention also provides a method for rolling and expanding a rare earth magnesium alloy ring using the above-described mandrel structure, comprising the following steps:

[0015] S1: First, perform multi-directional forging on rare earth magnesium alloy (Mg-Gd-Y-Zn-Zr can be selected) ingots. The initial forging temperature should not exceed 450℃. The cumulative strain of multi-directional forging should reach 2.5 to 3.5. Ensure that each deformation reaches the critical deformation amount for dynamic recrystallization of rare earth magnesium alloy, and the cumulative deformation amount of multi-directional forging reaches the critical deformation amount for geometric recrystallization of material.

[0016] S2: After the billet is opened, the rare earth magnesium alloy forging is subjected to homogenization heat treatment at a temperature range of 420~450℃ for ≥20h. The billet after homogenization treatment is then subjected to two upsetting and drawing processes to prepare a round cake-shaped billet, and punched to prepare a thick-walled ring billet. The two upsetting and drawing processes ensure that there are no coarse grains and mixed grains inside the forging, the uniformity of grains is ≥95%, and there are no obvious pore-type defects.

[0017] S3: Before rolling and forming, the main roll and core roll structure are preheated at 340-360℃, and the thick-walled ring billet is heated to 380-390℃. Both are kept at the temperature for ≥2h to ensure that the temperature of the rare earth magnesium alloy ring forging plate is uniformly distributed along the thickness direction.

[0018] S4: The entire core roller is a shearing zone. Let the circumference of the core roller be x, the size of the shearing unit be a, and the inner circumference of the blank be y. Then, when y = nx + (2n + 1) × a (n is an integer), the area that is sheared during the first deformation will be flattened during the second deformation. Correspondingly, the area that is flattened in the first deformation will be sheared in the second deformation, and so on in an alternating cycle.

[0019] S5: The core roller is fed linearly along the direction close to the main roller at a speed of 0.5 mm / s to 1.2 mm / s. The trapezoidal protrusions of the core roller act as shearing units to shear the blank. The core roller shearing unit dimensions are a = 0.75 mm to 1.5 mm, angle θ = 30 to 60°, and b = 0.75 mm to 1.5 mm, ensuring that the shear strain along the thickness direction can penetrate the central region of the deformed material during each deformation process.

[0020] S6: When the total feed amount of the mandrel in linear motion reaches the required reduction in ring blank thickness, that is, when the total feed amount of the mandrel in linear motion is equal to the reduction in ring blank thickness, the rare earth magnesium alloy ring is then subjected to multi-stage quenching treatment to reduce the tendency to crack. The deformed thin-walled rare earth magnesium alloy ring is first placed in water at 50-80℃ and kept at that temperature for 20-30 minutes, and then transferred to room temperature water for cooling.

[0021] Rare earth magnesium alloy rings are aged at 210–220°C for ≥20 hours; after aging, the rings are subjected to cold expansion forming, with deformation controlled within 1%, to eliminate internal stress in the rings.

[0022] According to GJB, samples were taken every 90 degrees on the upper and lower end faces of rare earth magnesium alloy rings to determine their microstructure, mechanical properties, and limiting hardness under high and low magnification.

[0023] The beneficial effects of adopting the above technical solution include at least the following:

[0024] In existing technologies, the grain orientation of formed ring parts is always parallel to the circumferential direction, and the mechanical properties differ by about 50 MPa in each direction, resulting in anisotropy of the ring parts and poor stability and safety in practical applications. The rare earth magnesium alloy ring forging rolling forming process with constrained shear effect proposed in this invention has each step working together. Multi-directional forging blanking ensures that the cumulative deformation reaches the critical deformation amount for geometric recrystallization of the material. Homogenized heat treatment and upsetting and drawing effectively improve the uniformity of grains and avoid internal defects. Preheating of the mandrel ensures uniform temperature distribution. The mandrel generates a misaligned constrained shear effect along the thickness direction of the blank, and the grain orientation is no longer parallel to the circumferential direction of the ring forging. This greatly reduces the strong texture of magnesium alloy formed during deformation and realizes three-dimensional control of the grain orientation of magnesium alloy materials.

[0025] As can be seen from the above technical solution, compared with the prior art, the present invention provides a core roller structure and a method for rolling and expanding rare earth magnesium alloy rings, which has the following technical effects and advantages:

[0026] This invention proposes a rolling and expanding process for rare earth magnesium alloy ring forgings with constrained shear effect. On the one hand, it can significantly improve the ability to refine the microstructure of magnesium alloy materials, with an initial microstructure ≥80μm and a fine-grained microstructure ≤8μm after rolling and expanding. On the other hand, it can achieve three-dimensional control of the grain orientation of magnesium alloy materials. The deformation with shear effect can greatly weaken the basal texture and improve the mechanical properties of rare earth magnesium alloy ring forgings. Even if the grain orientation is not parallel to the circumferential direction of the ring forging, it can greatly eliminate the strong texture of magnesium alloy formed during deformation, while improving the grain refinement ability of rolling and expanding and the overall mechanical properties of the ring forging.

[0027] The core roller structure designed according to this invention changes the surface features of the core roller, adds a trapezoidal protrusion structure to form a sawtooth structure, and increases the shear strain of the ring along the thickness direction by utilizing the principle of misalignment deformation, which is more conducive to refining the grains during the ring rolling process. Moreover, the core roller designed by this invention is mainly used in the ring rolling of rare earth magnesium alloys, that is, the deformation of composite metals, i.e., bimetallic rings. The misalignment effect formed by the trapezoidal protrusion structure on the surface of the core roller is an asymmetric deformation, which is conducive to eliminating the tendency of the base surface texture and improving the mechanical properties of magnesium alloy rings. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of the magnesium alloy ring rolled according to the present invention;

[0030] Figure 2 This is a top view of the magnesium alloy ring rolling process of the present invention;

[0031] Figure 3 This is a schematic diagram of the surface structure of the core roller structure of the present invention;

[0032] Figure 4 for Figure 3 AA section diagram;

[0033] Figure 5 This is a schematic diagram of the trapezoidal protrusion structure of the core roller structure of the present invention;

[0034] Figure 6 This is a schematic diagram illustrating the principle of the first shear deformation due to misalignment during the annular rolling forming process of magnesium alloy in this invention, with the right side being an enlarged view of region C.

[0035] Figure 7 This is a schematic diagram of the second shear deformation principle of the magnesium alloy annular rolling forming process of the present invention; wherein, the right side is an enlarged view of region C, and from left to right are the misalignment effect, deformation effect, and final effect;

[0036] Figure 8 This is a schematic diagram illustrating the principle of geometric recrystallization triggered by cumulative deformation during the multi-directional forging process of magnesium alloys in this invention; from left to right, it shows geometric recrystallization as strain increases.

[0037] Figure 9 The strain distribution diagram is shown in the rolling and forming process of the heat-resistant rare earth magnesium alloy ring of the present invention. In the diagram, a is a traditional smooth cylindrical core roller, b is rolling and forming with a core roller with a half-circumferential shear surface feature, and c is rolling and forming with a core roller with a full-circumferential shear surface feature.

[0038] Figure 10 This is a schematic diagram of the initial fine-grained structure of a magnesium alloy.

[0039] Figure 11 This is a schematic diagram of the fine-grained structure of a magnesium alloy after rolling and expanding.

[0040] Figure 12This is a schematic diagram of the sampling of the ring component, where d is the sampling range;

[0041] Among them, 1 is a thick-walled ring blank; 2 is the core roller body; 3 is the main roller; and 4 is a trapezoidal protrusion. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] As attached Figure 3-5 As shown, the present invention proposes a core roller structure, characterized in that it includes: a core roller body 2, and trapezoidal protrusions 4 arranged axially at intervals along the outer wall of the core roller body 2.

[0044] The mandrel structure of this invention causes compression deformation of the billet with each feed, while simultaneously generating a misaligned constraint shearing effect along the thickness direction of the billet, enhancing the grain refinement effect. At the same time, the shearing effect brought about by the trapezoidal protrusions of the mandrel structure can penetrate the deformed material, thereby enabling the grain orientation of the deformed ring forging to achieve a three-dimensional distribution in space, avoiding the formation of a strong texture distribution along the circumference of the ring forging, and thus suppressing or eliminating anisotropy. Moreover, this non-uniform stress field rolling deformation can significantly weaken the basal texture of rare earth magnesium alloys, significantly improve formability, and significantly improve anisotropy.

[0045] In this invention, the bottom surface of the trapezoidal protrusion 4 is arc-shaped and consistent with the surface of the core roller body 2. It extends obliquely upward along both sides of the bottom surface parallel to the longitudinal direction of the core roller to form a platform.

[0046] In this invention, the angle θ between the inclined side of the trapezoidal protrusion 4 and the tangent at the connection between the inclined side and the outer wall of the core roller body 2 satisfies 30° to 60°.

[0047] In this invention, the distance between the two sides of the top of the trapezoidal protrusion 4 and the vertical projection distance corresponding to the hypotenuse of the trapezoidal protrusion 4 are both a, and a satisfies 0.75mm~1.5mm.

[0048] In this invention, the trapezoidal protrusions 4 are uniformly distributed along the outer wall of the core roller body 2, and the spacing b between the trapezoidal protrusions 4 is 0.75mm to 1.5mm.

[0049] The technical effects achieved by adopting the above technical solution include at least the following: by changing the angle θ, width a, and distance b of the trapezoidal protrusion 4 of the core roller, the orientation of the rare earth magnesium alloy grains can be adjusted according to the actual situation, thereby optimizing the mechanical properties of the ring forging and meeting the actual application requirements.

[0050] like Figure 1-2 As shown, the present invention provides a method for rolling and expanding a rare earth magnesium alloy ring using the above-described mandrel structure, comprising the following steps:

[0051] S1: First, perform multi-directional forging on rare earth magnesium alloy (Mg-Gd-Y-Zn-Zr can be selected) ingots. The initial forging temperature should not exceed 450℃. The cumulative strain of multi-directional forging should reach 2.5 to 3.5. Ensure that each deformation reaches the critical deformation amount for dynamic recrystallization of rare earth magnesium alloy, and the cumulative deformation amount of multi-directional forging reaches the critical deformation amount for geometric recrystallization of material.

[0052] S2: After the billet is opened, the rare earth magnesium alloy forging is subjected to homogenization heat treatment at a temperature range of 420~450℃ for ≥20h. The billet after homogenization treatment is then subjected to two upsetting and drawing processes to prepare a round cake-shaped billet, and punched to prepare a thick-walled ring billet. The two upsetting and drawing processes ensure that there are no coarse grains and mixed grains inside the forging, the uniformity of grains is ≥95%, and there are no obvious pore-type defects.

[0053] S3: Before rolling and forming, the main roll and core roll structure are preheated at a temperature of 340-360℃. The thick-walled ring billet is heated to 380-390℃ and held for ≥2 hours to ensure that the temperature of the rare earth magnesium alloy ring forging plate is uniformly distributed along the thickness direction.

[0054] S4: The entire core roller is a shearing zone. Let the core roller circumference be x, the shearing unit size be a, and the inner circumference of the blank be y. Then, when y = nx + (2n + 1) × a (n is an integer), the area sheared during the first deformation will be flattened during the second deformation, and correspondingly, the area flattened in the first deformation will be sheared in the second deformation, and so on in an alternating cycle. The specific deformation misalignment principle is as follows: Figures 6-7 As shown, the magnesium alloy ring forging is guaranteed to produce a full-range shearing effect along the thickness direction of the deformation zone every 2 rotations. With the same strain as the cylindrical mandrel, the shear deformation refinement effect is 5 to 10 times that of the general compressive strain grain refinement effect.

[0055] S5: The core roller is fed linearly along the direction close to the main roller at a speed of 0.5 mm / s to 1.2 mm / s. The trapezoidal protrusions of the core roller act as shearing units to shear the blank. The core roller shearing unit dimensions are a = 0.75 mm to 1.5 mm, angle θ = 30 to 60 degrees, and b = 0.75 mm to 1.5 mm, ensuring that the shear strain along the thickness direction can penetrate the central region of the deformed material during each deformation process.

[0056] S6: When the total feed amount of the mandrel in linear motion reaches the process requirements, that is, the required reduction in ring blank thickness is achieved, that is, the total feed amount of the mandrel in linear motion is equal to the reduction in ring blank thickness. Then, the rare earth magnesium alloy ring is subjected to multi-stage quenching treatment to reduce the tendency to crack. Specifically, the deformed thin-walled rare earth magnesium alloy ring is first placed in hot water at 50-80℃ and kept at that temperature for 20-30 minutes, and then transferred to room temperature water for cooling.

[0057] Rare earth magnesium alloy rings are aged at 210–220°C for ≥20 hours; after aging, the rings are subjected to cold expansion forming, with deformation controlled within 1%, to eliminate internal stress in the rings.

[0058] like Figure 12 As shown, according to GJB, samples were taken every 90 degrees on the upper and lower end faces of the rare earth magnesium alloy ring to determine its microstructure, mechanical properties, and limiting hardness under high and low magnification.

[0059] The specific working process of the mandrel and main roll for rare earth magnesium alloy ring blanks is as follows: The uniformly heated ring blank is placed on a horizontal ring rolling machine with a rolling force of ≥250 tons. The main roll rotates clockwise at a constant speed of 30-35 rpm. The ring blank is placed on the base so that the ring blank and the mandrel are basically concentric. Then, the centering roll, measuring roller and axial frame approach the ring blank. When the rolling forming begins, the mandrel gradually approaches the main roll through radial linear feed motion. The friction between the mandrel and the blank will cause the mandrel to rotate passively, and the ring will continuously deform and the diameter will gradually increase.

[0060] The present invention relates to a rolling and expanding process for rare earth magnesium alloy ring forgings with constrained shear effect. In step S1, after multi-directional forging, the grain size of the forging is ≤34μm and the hardness is ≥60HV.

[0061] In the embodiment, after homogenization treatment in step S2, the average diameter of the nano-precipitated phase on the cylindrical surface of the forging billet is ≤29nm and the hardness is ≥80HV.

[0062] In the embodiment, after the billet undergoes two upsetting and drawing processes in step S2, the grain size of the rare earth magnesium alloy forging billet is ≤22μm.

[0063] In this embodiment, the main roller is made of H13 hot work die steel, and the core roller is made of 5CrNiMo hot work die steel.

[0064] In the embodiment, the deformed ring forging has a global grain size ≤8μm and a hardness ≥90HV after step S5.

[0065] In the embodiment, the rare earth magnesium alloy ring obtained in step S6 has a hardness ≥110HV.

[0066] In the embodiment, in step S8, the circumferential, axial and radial yield strength of the ring forging is ≥410MPa, and the difference between the yield strengths in the three directions is ≤10MPa; the circumferential, axial and radial elongation of the ring forging is ≥11%, and the difference between the elongation in the three directions is ≤0.5%.

[0067] In this embodiment, the initial rare-earth magnesium alloy ring blank has an inner diameter of 200 mm, an outer diameter of 280 mm, and a height of 150 mm; after rolling and forming, the resulting ring forging has an inner diameter of 385 mm, an outer diameter of 432 mm, and a height of 150 mm. Dimensions are not a constraint, provided the equipment allows.

[0068] Example 1

[0069] S1: First, the rare earth magnesium alloy (Mg-Gd-Y-Zn-Zr) ingot is forged in multiple directions. The initial forging temperature is 450℃, and the cumulative strain of the multiple forging reaches 2.5.

[0070] S2: After the billet is opened, the rare earth magnesium alloy forging is subjected to homogenization heat treatment at 420℃ for 20 hours. The billet after homogenization treatment is then uptaken and drawn twice to prepare a round cake-shaped billet, and punched to prepare a thick-walled ring billet.

[0071] S3: Before rolling and forming, the main roll and core roll are preheated at 340℃, and the thick-walled ring blank is heated to 390℃ and held for 2 hours.

[0072] S4: The entire core roller is a shearing zone. Let the circumference of the core roller be x, the size of the shearing unit be a, and the inner circumference of the blank be y. Then, when y = nx + (2n + 1) × a (n is an integer), the area that is sheared during the first deformation will be flattened during the second deformation. Correspondingly, the area that is flattened in the first deformation will be sheared in the second deformation, and so on in an alternating cycle.

[0073] S5: The core roller moves in a straight line along the direction close to the main roller at a speed of 0.5 mm / s, with a total feed of 16.5 mm. The core roller shearing unit size is a = 0.75 mm, the angle θ = 30 degrees, and the distance b = 0.75 mm.

[0074] S6: The total feed amount of the core roller in linear motion reaches the process requirements, that is, the required reduction in ring blank thickness is 16.5mm. First, immerse the deformed thin-walled rare earth magnesium alloy ring in water at 50℃ and keep it warm for 20 minutes, then transfer it to room temperature water for cooling.

[0075] The rare earth magnesium alloy ring was aged at 220℃ for 20 hours, and then the aged ring was subjected to cold expansion forming.

[0076] According to GJB, samples were taken every 90 degrees on the upper and lower end faces of rare earth magnesium alloy rings to determine their microstructure, mechanical properties, and limiting hardness under high and low magnification.

[0077] In this embodiment, the rare earth magnesium alloy ring forging process with constrained shear effect is rolled and expanded. After multi-directional forging in step S1, the grain size of the forging is 34μm and the hardness is 60HV.

[0078] In this embodiment, after homogenization treatment in step S2, the average diameter of the nano-precipitated phase on the cylindrical surface of the forging billet is 29 nm, and the hardness is 80 HV.

[0079] In this embodiment, after the billet undergoes two upsetting and drawing processes in step S2, a rare earth magnesium alloy forging billet with a grain size of 22 μm is obtained.

[0080] In this embodiment, the main roller is made of H13 hot work die steel, and the core roller is made of 5CrNiMo hot work die steel.

[0081] In this embodiment, the deformed ring forging has a global grain size of 8μm and a hardness of 90HV in step S5.

[0082] In this embodiment, the rare earth magnesium alloy ring obtained in step S6 has a hardness of 110HV.

[0083] In this embodiment, in step S8, the circumferential, axial, and radial yield strengths of the ring forging are all greater than 410 MPa, and the yield strengths in the three directions differ by less than 10 MPa; the circumferential, axial, and radial elongations of the ring forging are 11%, 11.2%, and 11.5%, respectively, and the elongations in the three directions differ by 0.5%.

[0084] Example 2

[0085] S1: First, perform multi-directional forging on rare earth magnesium alloy (Mg-Gd-Y-Zn-Zr can be selected) ingots, with an initial forging temperature of 450℃ and a cumulative strain of 3.5 during multi-directional forging.

[0086] S2: After the billet is opened, the rare earth magnesium alloy forging is subjected to homogenization heat treatment at 450℃ for 20 hours. The billet after homogenization is then uptaken and drawn twice to prepare a round cake-shaped billet, and punched to prepare a thick-walled ring billet.

[0087] S3: Before rolling and forming, the main roll and core roll are preheated at 360°C, and the thick-walled ring blank is heated to 390°C and held for 2 hours.

[0088] S4: The entire core roller is a shearing zone. Let the circumference of the core roller be x, the size of the shearing unit be a, and the inner circumference of the blank be y. Then, when y = nx + (2n + 1) × a (n is an integer), the area that is sheared during the first deformation will be flattened during the second deformation. Correspondingly, the area that is flattened in the first deformation will be sheared in the second deformation, and so on in an alternating cycle.

[0089] S5: The core roller moves in a straight line along the direction close to the main roller at a speed of 1.2 mm / s. The core roller shearing unit size is a = 1.5 mm, the bottom angle θ = 45 degrees, and the distance b = 1.5 mm.

[0090] S6: The total feed amount of the core roller in linear motion reaches the process requirements, that is, the required reduction in ring blank thickness is 16.5mm. First, the deformed thin-walled rare earth magnesium alloy ring is placed in water at 80℃ and kept at that temperature for 20 minutes, and then transferred to room temperature water for cooling.

[0091] The rare earth magnesium alloy ring was aged at 220℃ for 20 hours; the aged ring was then subjected to cold expansion forming.

[0092] According to GJB, samples were taken every 90 degrees on the upper and lower end faces of rare earth magnesium alloy rings to determine their microstructure, mechanical properties, and limiting hardness under high and low magnification.

[0093] In this embodiment, the rare earth magnesium alloy ring forging process with constrained shear effect is rolled and expanded. After multi-directional forging in step S1, the grain size of the forging is 29μm and the hardness is 65HV.

[0094] In this embodiment, after homogenization treatment in step S2, the average diameter of the nano-precipitated phase on the cylindrical surface of the forging billet is 22 nm, and the hardness is 82 HV.

[0095] In this embodiment, after the billet undergoes two upsetting and drawing processes in step S2, a rare earth magnesium alloy forging billet with a grain size of 18 μm is obtained.

[0096] In this embodiment, the main roller is made of H13 hot work die steel, and the core roller is made of 5CrNiMo hot work die steel.

[0097] In this embodiment, the deformed ring forging has a global grain size of 5μm and a hardness of 95HV in step S5.

[0098] In this embodiment, the rare earth magnesium alloy ring obtained in step S6 has a hardness of 120HV.

[0099] In this embodiment, the circumferential, axial, and radial yield strengths of the ring forging obtained in step S8 are all around 420 MPa; the circumferential, axial, and radial elongations of the ring forging are 11.5%, 11.7%, and 11.2%, respectively, with a difference of 0.5% in the elongations of the three directions.

[0100] Comparative analysis with rare earth magnesium alloy rings formed by traditional cylindrical mandrel rolling:

[0101] (1) Finite element analysis calculations were carried out on the rare earth magnesium alloy Mg-Gd-Y-Zn-Zr rolling forming process using both the traditional cylindrical core roller and the strip-shaped core roller with misalignment constraint shear effect proposed in this invention.

[0102] (2) The finite element calculation uses the Hansel Spittel constitutive model, and the specific formula is as follows:

[0103]

[0104] In the formula, A = 632.61, m1 = -5.07 × 10 -3 m2 = -4.36 × 10 -2 m3 = 7.50 × 10 -2 m4 = -9.49 × 10 -3 .

[0105] (3) Set the main roller speed to 30 rpm, the core roller speed to 0.5-0.7 mm / s, the total feed to 16.5 mm (initial wall thickness 40 mm), and no lubrication (friction coefficient 0.4-0.8).

[0106] (4) Trapezoidal protrusion feature dimensions of the core roller profile: a = 1 mm, θ = 45 degrees, such as Figure 5 As shown.

[0107] (5) The specific simulation of strain distribution in the formed ring forging is as follows: Figure 9 As shown in the figure, the core roller with misalignment constraint shear characteristics generates greater tangential strain during the rolling forming process, which is more conducive to grain refinement and elimination of rare earth magnesium alloy texture tendency, thereby improving the comprehensive mechanical properties of rare earth magnesium alloy rings.

[0108] Experimental verification:

[0109] A heat-resistant rare-earth magnesium alloy ring was formed using the above-mentioned mandrel mold with surface features and hot-rolling aluminum alloy forming process parameters. The final mechanical properties of the ring in the circumference, axial direction, and radial direction are compared with those of a ring formed using a conventional cylindrical mandrel forming process, as shown in Table 1. The size and material of the ring formed using the conventional process are the same as those in Example 2.

[0110] Table 1

[0111]

[0112] As shown in Table 1, rare earth magnesium alloy rings formed using core rollers with periodic trapezoidal protrusions exhibit better mechanical properties, particularly with an approximately 20% increase in axial and radial yield strength. Furthermore, the consistency of circumferential, axial, and radial mechanical properties is better, with deviations within 10 MPa. In contrast, the mechanical properties of rings formed using traditional methods differ by approximately 50 MPa in each direction, leading to anisotropy in the rings and hindering the improvement of stability and safety during the flight of rare earth magnesium alloy projectiles.

[0113] The core roller structure designed according to this invention changes the surface features of the core roller, adds a trapezoidal protrusion structure to form a sawtooth structure, and increases the shear strain of the ring along the thickness direction by utilizing the principle of misalignment deformation, which is more conducive to refining the grains during the ring rolling process. Moreover, the core roller designed by this invention is mainly used in the ring rolling of rare earth magnesium alloys, that is, the deformation of composite metals, i.e., bimetallic rings. The misalignment effect formed by the trapezoidal protrusion structure on the surface of the core roller is an asymmetric deformation, which is conducive to eliminating the tendency of the base surface texture and improving the mechanical properties of magnesium alloy rings.

[0114] The parts of this invention not described in detail in the embodiments can be implemented using existing technologies, and will not be elaborated here.

[0115] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0116] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for rolling and expanding a rare earth magnesium alloy ring, characterized in that, Includes the following steps: S1: Multi-directional forging of rare earth magnesium alloy ingots; S2: After the rare earth magnesium alloy forging is opened, it is subjected to homogenization heat treatment, upsetting and drawing to form a round cake-shaped billet, and then punching to prepare a thick-walled ring billet. S3: Before rolling and forming, the main roll and the core roll are preheated to heat the thick-walled ring blank, ensuring that the temperature of the rare earth magnesium alloy ring forging slab is uniformly distributed along the thickness direction; the core roll includes: a core roll body, and trapezoidal protrusions arranged circumferentially along the outer wall of the core roll body; the distance between the two sides of the top of the trapezoidal protrusion and the radial projection length corresponding to the hypotenuse of the trapezoidal protrusion are both a; the trapezoidal protrusions are uniformly distributed circumferentially along the outer wall of the core roll body, and the distance between the trapezoidal protrusions is b. S4: The entire core roller is a shearing zone. Let the core roller circumference be x, the shearing unit size be a, and the inner circumference of the blank be y. When y = nx + (2n + 1) × a, n is an integer. The area that is sheared during the first deformation will be flattened during the second deformation. Correspondingly, the area that is flattened in the first deformation will be sheared in the second deformation, and so on in an alternating cycle. S5: The core roller is fed linearly at a speed of 0.5 mm / s to 1.2 mm / s along the direction close to the main roller. The trapezoidal protrusions of the core roller act as shearing units to shear the blank. S6: When the total feed amount of the core roller in linear motion reaches the process requirements, the magnesium alloy ring is then subjected to multi-stage quenching, aging treatment, and sampling performance testing.

2. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, The angle θ between the inclined side of the trapezoidal protrusion and the tangent at the connection between the inclined side and the outer wall of the core roller body satisfies 30° to 60°.

3. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, a satisfies 0.75mm~1.5mm.

4. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, b satisfies 0.75mm~1.5mm.

5. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, In step S1, the initial forging temperature of the multi-directional forging billet does not exceed 450℃, and the cumulative strain of the multi-directional forging reaches 2.5 to 3.

5.

6. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, In step S2, homogenization heat treatment refers to heat treating the rare earth magnesium alloy forging at 420-450℃ for ≥20 hours, and performing two upsetting and drawing operations on the billet.

7. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, In step S3, the preheating temperature for the main roll and core roll is 340-360℃, and the heating temperature for the thick-walled ring blank is 380-390℃, with both temperatures maintained for ≥2 hours.

8. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, The main roller is made of H13 hot work die steel, and the core roller is made of 5CrNiMo hot work die steel.

9. The method for rolling and expanding a rare earth magnesium alloy ring according to claim 1, characterized in that, The multi-stage quenching process in step S6 involves first immersing the deformed thin-walled rare-earth magnesium alloy ring in water at 50-80°C for 20-30 minutes, and then transferring it to room temperature water for cooling. The aging process involves holding the rare earth magnesium alloy ring at 210–220°C for ≥20 hours. The sampling performance testing method is to take samples at 90 degrees on the upper and lower end faces of the rare earth magnesium alloy ring according to GJB, and to measure the microstructure, mechanical properties and microhardness at high and low magnification.

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