Corrugated piece for degradable magnesium alloy bridge plug and rolling preparation method

Abstract

The present application belongs to the field of oil and gas field downhole tool manufacturing, and particularly relates to a corrugated piece for degradable magnesium alloy bridge plug and a rolling preparation method, which comprises the following steps: rolling equipment preparation and pretreatment, raw material pretreatment, special-shaped asynchronous hot rolling forming, stress relief annealing and finishing. The present application implements multi-pass asynchronous hole type rolling on the difficult-to-deform degradable magnesium alloy blank, utilizes the difference between the linear speeds of the lower and upper concave rollers to introduce a strong cross-shear field in the deformation zone, greatly improves the plastic flow capacity of the magnesium alloy, enables it to precisely fill the complex corrugated hole type, realizes near-net forming, effectively breaks the coarse second-phase particles while retaining the complete metal fiber flow lines of the compliant tooth profile distribution, induces non-basal plane slip and sufficient dynamic recrystallization, and thus weakens the basal plane texture. Finally, on the premise of greatly improving the material utilization rate, the shear strength, structural integrity and uniform degradation performance of the corrugated piece are synergistically improved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field downhole tool manufacturing, specifically relating to a biodegradable magnesium alloy bridge plug corrugated part and its rolling preparation method, particularly a method for preparing biodegradable magnesium alloy bridge plug corrugated parts through a non-circular asynchronous rolling forming process. Background Technology

[0002] In the development of unconventional oil and gas resources, especially in horizontal well fracturing operations for resources such as shale gas and tight oil, all-metal biodegradable bridge plugs are the core downhole tool for achieving segment isolation. With its characteristics of "controllable degradation after use and no need for drilling," this tool not only significantly improves operational efficiency but also effectively reduces well control risks, becoming one of the key technologies driving the efficient development of unconventional oil and gas.

[0003] Corrugated components (or corrugated anchor slips) are key components in bridge plug assemblies, responsible for anchoring and high-pressure sealing. They must withstand pressure differentials exceeding 70 MPa in high-temperature, high-mineralization fluids, making their service environment extremely harsh. This characteristic places extremely high demands on the materials used in the manufacture of corrugated components: the materials must not only possess excellent specific strength and a controllable degradation rate, but also maintain structural integrity and long-term reliability under the large deformation conditions generated during the setting process.

[0004] Currently, high-performance corrugated parts are mostly manufactured using biodegradable magnesium alloys. However, magnesium alloys are limited by their close-packed hexagonal crystal structure, resulting in a lack of room-temperature sliding systems and a narrow plastic processing window. Furthermore, to meet the dual requirements of pressure resistance and rapid melting, a large number of hard and brittle second phases are often dispersed in the alloy matrix. While these second phases strengthen the matrix, they also significantly increase the material's deformation resistance, leading to extremely high forming difficulty. Especially for the complex irregular structures of corrugated parts, existing mainstream forming processes—casting and extrusion—both have significant technical limitations. Casting suffers from loose microstructure and severe segregation, while extrusion exhibits significant anisotropy, mismatch between streamlines and stress, and high machining costs.

[0005] More importantly, regardless of whether the biodegradable magnesium alloy material is produced by casting or extrusion molding, it must be machined to finally produce the corrugated parts for bridge plugs. However, the machining process cuts off the metal flow lines, resulting in low material utilization and a series of problems such as insufficient shear resistance and uncontrollable degradation behavior, which seriously affect the performance stability and service life of the corrugated parts.

[0006] Therefore, there is an urgent need to develop a rolling forming method suitable for corrugated parts for biodegradable magnesium alloy bridge plugs, which can achieve high-performance forming and synergistic improvement of microstructure and properties of difficult-to-deform magnesium alloys. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a corrugated part for biodegradable magnesium alloy bridge plugs and a rolling preparation method. The aim is to provide a rolling forming method suitable for corrugated parts for biodegradable magnesium alloy bridge plugs, overcoming the limitations of traditional casting processes (loose microstructure, severe segregation) and extrusion processes (significant anisotropy, high subsequent machining costs, and damage to flow lines). Simultaneously, it solves a series of technical problems caused by machining, such as the interruption of metal flow lines, low material utilization, insufficient shear resistance, and uncontrollable degradation behavior. This achieves synergistic improvement in high-performance forming and microstructure properties of difficult-to-deform magnesium alloys, ultimately providing a biodegradable magnesium alloy corrugated part for bridge plugs with high material utilization and excellent toughness.

[0008] This invention employs multi-pass asynchronous die rolling on difficult-to-deform biodegradable magnesium alloy billets, utilizing the difference in linear velocity between the lower and upper concave rolls to introduce a strong cross-shear field (i.e., the rolling effect) in the deformation zone. This additional shear deformation not only significantly improves the plastic flowability of the magnesium alloy, enabling it to precisely fill complex corrugated dies and achieve near-net-shape forming, but also effectively breaks down coarse second-phase particles and induces non-basal slip and sufficient dynamic recrystallization while preserving the complete metal fiber flow lines conforming to the tooth distribution, thereby weakening the basal texture. Ultimately, while significantly improving material utilization, it achieves a synergistic improvement in the shear strength, structural integrity, and uniform degradation performance of corrugated parts.

[0009] The first aspect of this invention provides a rolling preparation method for corrugated parts for biodegradable magnesium alloy bridge plugs, comprising the following steps:

[0010] S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, and the corrugated rolls include upper concave rolls and lower concave rolls.

[0011] S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, then the surface of the homogenized heat-treated billet is mechanically ground until the oxide layer and surface defects are removed, and then it is cleaned and dried.

[0012] S3. Irregular asynchronous hot rolling forming: First, the corrugated roll and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is carried out to force the cross section of the billet to undergo rheological changes and roll it into a corrugated shape to obtain the rolled corrugated part. Then, the rolled corrugated part is water-cooled or air-cooled to room temperature. The temperature during the irregular asynchronous hot rolling forming process is 380~420℃.

[0013] S4. Stress-relief annealing: Annealing is performed on corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening caused by high-speed shearing and complex cross-sectional deformation.

[0014] S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug.

[0015] Preferably, the rolling mill is a two-roll reversible hot rolling mill, and the corrugated rolls are made of high-quality hot work die steel;

[0016] Furthermore, both the upper and lower concave rollers have irregularly shaped grooves on their surfaces that correspond to the corrugated parts, and these grooves have concentric circular arc-shaped cross-sectional profiles. The radius of curvature of the forming surface of the lower concave roller is equal to the outer radius of the central tube of the bridge plug to be assembled, and the radii of curvature of the forming surfaces of the upper and lower concave rollers and the target thickness of the corrugated parts satisfy the following relationship:

[0017] R2-R1=H

[0018] In the formula, R2 is the radius of curvature of the upper concave roller forming surface, R1 is the radius of curvature of the lower concave roller forming surface, and H is the target thickness of the corrugated part.

[0019] Preferably, the billet is a biodegradable magnesium alloy ingot, wherein the biodegradable magnesium alloy is a Mg-Al or Mg-Zn biodegradable magnesium alloy.

[0020] Preferably, the homogenization heat treatment process is as follows: the billet is heated to 380-420°C at a heating rate of 5-7 min / °C, held at that temperature for 18-24 h, and then water-cooled to room temperature;

[0021] The cleaning and drying process is as follows: Rinse the polished blank with room temperature water to remove the residual polishing dust on the surface, and then place the cleaned blank in a drying oven for hot air drying until the surface of the blank is dry and free of water stains.

[0022] The stress-relief annealing process is as follows: the corrugated parts after asynchronous hot rolling are placed into a heating furnace, heated to 200-300℃, held for 30-60 minutes, and then water-cooled to room temperature.

[0023] Finishing processes include straightening, cutting to length, and edge trimming.

[0024] Preferably, step S3 specifically includes:

[0025] S31. Heating and temperature control: Heat the pretreated billet to 380-420℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 160-200℃.

[0026] S32. Rough rolling: Set the linear speed of the upper concave roll / lower concave roll to 37-51 mm / s, then perform 3-4 passes of rolling, and perform annealing for 10 minutes after each pass. The speed ratio during rough rolling should meet the following condition: 1.2 ≤ speed ratio ≤ 1.3, where the speed ratio is the ratio of the linear speed of the lower concave roll to the linear speed of the upper concave roll; the single-pass reduction rate is 12.0%-20.6%, and the annealing temperature is 380-420℃.

[0027] S33. Finishing Rolling: Set the linear speed of the upper concave roll / lower concave roll to 22-36 mm / s, then perform 4-8 passes of rolling, and anneal for 10 minutes after each pass to obtain the rolled corrugated part. Then, water-cool or air-cool the rolled corrugated part to room temperature. During finishing rolling, the speed ratio must meet the following: 1.0 < speed ratio ≤ 1.1, where the speed ratio is the ratio of the linear speed of the lower concave roll to the linear speed of the upper concave roll; the single-pass reduction rate is 1.3%-5.4%, and the annealing temperature is 380-420℃.

[0028] Preferably, during the two-stage rolling process, the distribution of the single-pass reduction rate follows the principle of "rapid high-shear modification in rough rolling and slow micro-deformation control in finish rolling". Specifically, during rough rolling, a strategy of fewer passes and large deformation is adopted to break down the coarse second phase and induce dynamic recrystallization by utilizing the strong shear strain field introduced by the asynchronous rolling process; during finish rolling, a strategy of more passes and small deformation is adopted to correct the geometry and suppress springback by finely adjusting the deformation amount.

[0029] Based on the thickness of the pretreated billet, the total reduction rate after rough rolling is 40% to 50%; based on the thickness of the billet after rough rolling, the total reduction rate after finish rolling is 10% to 20%.

[0030] Preferably, during the non-linear asynchronous hot rolling forming process, under the synergistic effect of the strong shear rheology introduced by the non-linear rolling and the triaxial compressive stress of the corrugated hole, the original coarse casting grains with a size of 50-100μm in the billet undergo severe fragmentation, and high-density non-basal slip and continuous dynamic recrystallization are induced. The recrystallization volume fraction reaches more than 95%, and the microstructure after rolling is transformed into fine equiaxed grains with random orientation and uniform distribution, and the average grain size is refined to 5-15μm.

[0031] In addition, the second phase, which is distributed in a continuous / semi-continuous network or in a coarse skeletal / blocky form along the grain boundaries in the billet, is mechanically broken up during severe shear deformation. The broken second phase particles are eventually dispersed in a near-spherical or ellipsoidal shape within the grains and at the grain boundaries, with an average size refined to 0.5–2 μm and no obvious particle agglomeration occurs. The average network wall thickness of the second phase distributed in a continuous / semi-continuous network is 5–12 μm, and the diameter of the second phase in a coarse skeletal / blocky form is 20–50 μm.

[0032] Preferably, the manufactured biodegradable magnesium alloy corrugated plug has a tensile strength ≥250MPa, a yield strength ≥155MPa, an elongation ≥15%, and a base surface texture strength ≤15.

[0033] The second aspect of the present invention provides a corrugated part for a biodegradable magnesium alloy bridge plug, which is manufactured by a rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part.

[0034] Preferably, the biodegradable magnesium alloy corrugated bridge plug is used in shale gas extraction and oilfield development.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. This invention innovatively couples corrugated die design with asynchronous rolling forming process, constructing a complex stress field in the material deformation zone that combines strong shear and triaxial compressive stress. This stress state, by introducing significant additional shear strain, effectively overcomes the critical decomposition shear stress threshold for non-basal surface slip initiation, and extensively activates non-basal surface slip systems such as cylindrical and conical surfaces. This mechanism significantly broadens the plastic forming limit of magnesium alloys, fundamentally breaking through the processing bottleneck of poor intrinsic plasticity and easy edge cracking at room temperature and medium-low temperature environments.

[0037] 2. This invention proposes a multi-pass rheological microstructure control strategy of "large reduction rough rolling to induce strong shear microstructure modification and small reduction fine rolling to achieve precise dimensional control". This strategy effectively relaxes the residual stress induced by non-uniform deformation, significantly suppresses the elastic rebound behavior of complex corrugated surfaces, and ultimately endows the product with extremely high dimensional accuracy and assembly fit, realizing high-quality near-net-shape forming of magnesium alloy profiles.

[0038] 3. This invention utilizes the strong shear strain field unique to the asynchronous rolling forming process to introduce a violent rolling effect, breaking the coarse network second phase in the casting structure into submicron-sized dispersed particles, significantly improving the microstructure and degradation uniformity of the alloy. At the same time, this dispersed microstructure not only eliminates the risk of local pitting corrosion caused by large-sized second phases, enabling corrugated parts to exhibit uniform and controllable degradation behavior in chloride-containing downhole fluids, but also significantly improves the yield strength and hardness of the alloy through fine grain strengthening and precipitation strengthening mechanisms, solving the problem of difficulty in balancing strength and corrosion resistance in traditional processes.

[0039] 4. Compared to traditional extrusion molding processes, the corrugated parts prepared by this invention have a weakened basal texture and complete metal streamlines conforming to the tooth shape, resulting in superior mechanical properties. This invention successfully weakens the strong basal texture of magnesium alloys by inducing non-basal slip through asynchronous rolling, significantly reducing material anisotropy and improving lateral plasticity. This ensures that the corrugated parts maintain structural integrity and are less prone to cracking under large deformation conditions during sealing. Simultaneously, the production efficiency of the asynchronous rolling process is significantly higher than that of traditional extrusion molding. Its near-net-shape forming process not only greatly reduces material loss of expensive magnesium alloys but also ensures that the metal streamlines (fiber structure) strictly conform to the corrugated waveform distribution without being cut off, greatly enhancing the shear strength and anti-breakage capability of the tooth area. This effectively meets the stringent requirements for high tool reliability under high temperature and high pressure differential conditions in horizontal well fracturing operations for shale gas. Attached Figure Description

[0040] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A schematic diagram of the equipment model for traditional casting and molding processes;

[0042] Figure 2 Microstructure of a biodegradable magnesium alloy corrugated bridge plug manufactured using traditional casting processes;

[0043] Figure 3 A schematic diagram of the equipment model for a traditional extrusion molding process;

[0044] Figure 4 Microstructure of a biodegradable magnesium alloy bridge plug corrugated part manufactured using a traditional extrusion molding process;

[0045] Figure 5 A schematic diagram of the equipment model for the non-linear asynchronous rolling forming process provided by the present invention;

[0046] Figure 6 Microstructure of a biodegradable magnesium alloy bridge plug corrugated part manufactured using the non-circular asynchronous rolling forming process provided by the present invention;

[0047] Figure 7 A process flow diagram of a rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part provided by the present invention;

[0048] Figure 8 A schematic diagram of the structure of the corrugated component for the biodegradable magnesium alloy bridge plug provided by the present invention;

[0049] Figure 9 This is a schematic diagram illustrating the fitting of the corrugated roll profile provided by the present invention;

[0050] Figure 10 These are three views of the corrugated rolls provided by the present invention when they are in contact. Figure 10 'a' is the main view. Figure 10 In this context, 'b' represents the left view. Figure 10 In this context, 'c' represents the top view.

[0051] Figure 11 Microstructure diagram of the second phase with a continuous / semi-continuous network distribution provided by the present invention;

[0052] Figure 12 Microstructure diagram of the second phase with a coarse skeletal structure provided by the present invention;

[0053] Figure 13 Microstructure diagram of the coarse, blocky second phase provided by the present invention;

[0054] Figure 14 Microstructure diagram of the second phase, which is nearly spherical / ellipsoidal, provided by the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0056] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0057] While casting offers lower costs and the ability to form complex shapes, its microstructure often fails to meet the performance requirements of high-pressure corrugated components. Casting typically results in coarse grains and inevitably contains inherent defects such as dendritic segregation and micro-shrinkage. In chloride-containing downhole fluids, coarse grains and compositional segregation can induce severe localized corrosion (pitting), leading to uncontrolled degradation rates and premature failure of the corrugated components. Furthermore, the porous casting microstructure results in significantly lower yield strength and elongation compared to wrought magnesium alloys, making it difficult to withstand the high differential shear forces (up to 70 MPa) generated during bridge plug sealing, posing a significant risk of premature failure.

[0058] A schematic diagram of the equipment model for traditional casting molding process is shown below. Figure 1 As shown, the microstructure of a biodegradable magnesium alloy corrugated bridge plug manufactured using traditional casting processes is as follows. Figure 2 As shown. From Figure 2 It can be clearly seen that the dendritic structure of the biodegradable magnesium alloy bridge plug corrugated parts made by traditional casting molding process is coarse, and is accompanied by severe dendritic segregation and micro shrinkage porosity.

[0059] Extrusion molding is currently the mainstream industrial production process, capable of refining grains. However, it presents insurmountable challenges in the anisotropy of microstructure and properties when manufacturing corrugated components for biodegradable magnesium alloy bridge plugs. During hot extrusion, magnesium alloys develop a strong basal texture, with second-phase particles tending to be distributed in long strips or fibers along the extrusion direction. This singular longitudinal streamline structure leads to extreme mechanical anisotropy: while axial strength is high, transverse (radial) plasticity and shear resistance are significantly insufficient. For corrugated components, during downhole setting, they must withstand enormous radial expansion stress and axial interlocking shear force. The existing extrusion streamline direction is parallel to the main stress direction of the corrugated component (i.e., "parallel"), resulting in a lack of interwoven streamline support within the corrugated component. Under high-stress conditions, cracks easily initiate and propagate along the brittle second-phase strips, leading to intergranular brittle fracture or lamellar delamination in the corrugated component, causing bridge plug anchoring failure. Furthermore, the strip-shaped distribution of the second phase can lead to anisotropic degradation, making corrugated parts prone to deep-hole corrosion along the extrusion direction during degradation, thus compromising the integrity of the structure.

[0060] A schematic diagram of the equipment model for traditional extrusion molding process is shown below. Figure 3 As shown, the microstructure of a biodegradable magnesium alloy corrugated bridge plug manufactured using a conventional extrusion molding process is as follows. Figure 4 As shown. From Figure 4It is evident that the biodegradable magnesium alloy bridge plug corrugated parts manufactured using traditional extrusion molding processes exhibit banded microstructures in the deformation zone. Under high stress conditions, cracks readily initiate and propagate along the brittle second phase distributed in bands, leading to intergranular fracture or lamellar delamination. Simultaneously, the banded microstructure also forms corrosion pathways, accelerating non-uniform deep-hole corrosion along the extrusion direction.

[0061] Differential rolling (i.e., differential speed rolling) has unparalleled technical advantages in the preparation of corrugated parts for high-performance biodegradable magnesium alloy bridge plugs. It can achieve synergistic improvement in the forming and performance of difficult-to-deform magnesium alloys. The principle is as follows:

[0062] (1) Intense shear deformation and ultrafine second phase: Unlike the single compressive stress state of symmetrical rolling, asynchronous rolling of irregular shapes utilizes the difference in linear velocity between the lower concave roll 2 and the upper concave roll 1 to introduce a significant "cross shear field" and "rolling effect" in the deformation zone. This intense shear deformation can break up the coarse eutectic structure and hard and brittle second phase particles in magnesium alloy with extremely high efficiency, refining their size from the micrometer level to the submicrometer level and dispersing them. This not only greatly improves the strength of the material through precipitation strengthening and grain refinement, but more importantly, it eliminates the risk of local pitting corrosion caused by large-sized second phases, achieving uniform degradation of the alloy at the microscale.

[0063] (2) Weakening of basal texture and improvement of formability: Traditional rolling or extrusion easily forms a strong basal texture, leading to brittleness of the material. The shear strain introduced by non-basal asynchronous rolling can induce non-basal slip and dynamic recrystallization of crystals, significantly weakening or deflecting the strong basal texture. This not only effectively solves the problem of severe anisotropy in corrugated parts for biodegradable magnesium alloy bridge plugs, but also greatly reduces deformation resistance, making the metal more fluid and yielding a higher yield when filling complex surfaces such as corrugated crests.

[0064] (3) Streamline conformity and near-net-shape forming: Irregular asynchronous rolling is an advanced "near-net-shape forming" technology. Its metal streamlines strictly conform to the waveform profile distribution of the corrugation, and due to the improved metal fluidity, the streamlines are more dense and continuous at the transition between the crests and troughs, without being cut off. This highly dense streamline structure conforming to the corrugation geometry endows the gear teeth with extremely high shear strength and anti-chipping ability, perfectly adapting to the high pressure differential conditions downhole. At the same time, near-net-shape forming significantly reduces subsequent machining allowances, significantly reducing the consumption of expensive magnesium alloy materials and manufacturing costs.

[0065] In view of this, this application uses an asynchronous rolling process to prepare corrugated parts for biodegradable magnesium alloy bridge plugs, so as to achieve synergistic improvement of the forming and performance of difficult-to-deform magnesium alloys. At the same time, it overcomes the dual limitations of traditional casting forming process, such as loose structure and severe segregation, and extrusion forming process, such as significant anisotropy, high subsequent machining cost and damage to streamlines.

[0066] like Figure 5-10 As shown, the first aspect of the present invention provides a rolling preparation method for corrugated parts for biodegradable magnesium alloy bridge plugs, comprising the following steps:

[0067] S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, and the corrugated rolls include upper concave roll 1 and lower concave roll 2.

[0068] In this application, the rolling mill is a two-roll reversible hot rolling mill, and the corrugated rolls are made of high-quality hot work die steel.

[0069] In this embodiment of the application, the corrugated die roll is as follows: Figure 9-10 As shown.

[0070] In this application, by hardening and polishing the surface of the roll, a high-hardness wear-resistant layer can be formed on the surface of the roll to reduce the sticking and wear phenomena during high-temperature rolling.

[0071] In this application, the surfaces of the upper concave roller 1 and the lower concave roller 2 are both machined with irregular grooves corresponding to the corrugated parts, and the irregular grooves of the upper concave roller 1 and the lower concave roller 2 have concentric arc-shaped cross-sectional profiles.

[0072] Preferably, the radius of curvature of the forming surface of the lower concave roller 2 is equal to the outer radius of the central tube of the bridge plug to be assembled, and the radii of curvature of the forming surfaces of the upper concave roller 1 and the lower concave roller 2, as well as the target thickness of the corrugated part, satisfy the following relationship:

[0073] R2-R1=H

[0074] In the formula, R2 is the radius of curvature of the forming surface of the upper concave roller 1, R1 is the radius of curvature of the forming surface of the lower concave roller 2, and H is the target thickness of the corrugated part.

[0075] In this embodiment of the application, the radius of curvature R2 of the forming surface of the upper concave roller 1, the radius of curvature R1 of the forming surface of the lower concave roller 2, and the target thickness H of the corrugated part are as follows: Figure 8-9 As shown.

[0076] It should be noted that by strictly defining the relationship between the curvature radii of the forming surfaces of the upper concave roller 1 and the lower concave roller 2, this application can precisely constrain the direction of metal flow, prevent lateral extrusion and uneven wall thickness, and ensure the precise forming of corrugated parts.

[0077] S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, then the surface of the homogenized heat-treated billet is mechanically ground until the oxide layer and surface defects are removed, and then it is cleaned and dried.

[0078] In this application, the billet is a biodegradable magnesium alloy ingot, wherein the biodegradable magnesium alloy is a Mg-Al or Mg-Zn biodegradable magnesium alloy.

[0079] In this embodiment, the Mg-Al biodegradable magnesium alloy is Mg-6Al-2Cu biodegradable magnesium alloy, and the Mg-Zn biodegradable magnesium alloy is Mg-6Zn-2Cu biodegradable magnesium alloy or Mg-6Zn-0.5Zr-1Cu biodegradable magnesium alloy.

[0080] Preferably, the homogenization heat treatment process is as follows: the billet is heated to 380-420°C at a heating rate of 5-7 min / °C, held at that temperature for 18-24 h, and then water-cooled to room temperature.

[0081] In this application, by performing homogenization heat treatment on the billet, alloying elements can be fully diffused, eliminating compositional segregation.

[0082] In this embodiment, 200# to 600# sandpaper are used sequentially to mechanically polish the surface of the heat-treated billet. However, in actual applications, the grit of the sandpaper can be selected from coarse to fine as needed, and the billet can be polished until the oxide layer and surface defects are removed.

[0083] Preferably, the cleaning and drying process is as follows: the polished blank is rinsed with room temperature water to remove residual polishing dust from the surface, and then the cleaned blank is placed in a drying oven for hot air drying until the surface of the blank is dry and free of water stains.

[0084] In this embodiment of the application, when the cleaned blank is placed in a drying oven for hot air drying, the drying temperature is 50-70°C and the drying time is 10-30 minutes.

[0085] S3. Irregular Asynchronous Hot Rolling Forming: First, the corrugated rolls and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is performed to force the cross-section of the billet to undergo rheological changes and roll it into a corrugated shape, obtaining the rolled corrugated part. The rolled corrugated part is then water-cooled or air-cooled to room temperature. The temperature during the irregular asynchronous hot rolling forming process is 380-420℃, specifically:

[0086] S31. Heating and temperature control: Heat the pretreated billet to 380-420℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 160-200℃.

[0087] S32. Rough rolling: Set the linear speed of the upper concave roll 1 / lower concave roll 2 to 37-51 mm / s, then perform 3-4 passes of rolling, and perform annealing for 10 minutes after each pass. The speed ratio during rough rolling meets the following condition: 1.2 ≤ speed ratio ≤ 1.3. The speed ratio is the ratio of the linear speed of the lower concave roll 2 to the linear speed of the upper concave roll 1. The single pass reduction rate is 12.0%-20.6%, and the annealing temperature is 380-420℃.

[0088] In this application, the roughing stage introduces strong shear strain by increasing the linear speed, speed ratio and single-pass reduction rate of the upper concave roll 1 / lower concave roll 2, which effectively breaks up the coarse cast grains, significantly improves the basal texture of the magnesium alloy, and enhances the formability of the material.

[0089] S33. Finishing Rolling: Set the linear speed of the upper concave roll 1 / lower concave roll 2 to 22-36 mm / s, then perform 4-8 passes of rolling, and anneal for 10 minutes after each pass to obtain the rolled corrugated parts. Then, water-cool or air-cool the rolled corrugated parts to room temperature. The speed ratio during finishing rolling meets the following condition: 1.0 < speed ratio ≤ 1.1, where the speed ratio is the ratio of the linear speed of the lower concave roll 2 to the linear speed of the upper concave roll 1; the single-pass reduction rate is 1.3%-5.4%, and the annealing temperature is 380-420℃.

[0090] In this application, by reducing the linear speed, speed ratio and single-pass reduction rate of the upper concave roll 1 / lower concave roll 2 during the finishing rolling stage, the deformation heat effect and deformation resistance are reduced, ensuring the dimensional accuracy of corrugated parts (especially the thickness consistency of the crests and troughs) and surface finish.

[0091] In this application, the temperature is maintained within the range of 380 to 420°C during the asynchronous hot rolling process of the shaped alloy. This not only avoids uneven microstructure or cracking caused by temperature fluctuations, but also ensures the plastic deformation capacity of the magnesium alloy.

[0092] In this embodiment of the application, during the irregular asynchronous hot rolling forming process, the temperature of the rolling deformation zone is maintained stable by induction heating or resistance heat preservation device to prevent the billet from reducing plasticity or cracking due to excessive temperature drop.

[0093] In this application, by performing a short annealing treatment of 10 minutes after each rolling pass, work hardening can be eliminated in time, plasticity can be restored, and subsequent cracking can be prevented. At the same time, the fine grain structure is maintained due to the short time, thus realizing dynamic microstructure control of "deformation and recrystallization at the same time".

[0094] In this application, based on the thickness of the pretreated billet, the total reduction rate after rough rolling is 40% to 50%; based on the thickness of the billet after rough rolling, the total reduction rate after finish rolling is 10% to 20%.

[0095] In this embodiment, the formula for calculating the total reduction rate at each stage is as follows:

[0096]

[0097] In the formula, The total reduction rate at a certain stage. Let n be the single-pass reduction rate at a certain stage, and n be the total number of rolling passes at a certain stage.

[0098] In this application, during the two-stage rolling process, the distribution of the single-pass reduction rate follows the principle of "rapid strong shear modification in rough rolling and slow micro-deformation control in finish rolling". Specifically, during rough rolling, a strategy of fewer passes and large deformation is adopted to break up the coarse second phase and induce dynamic recrystallization by utilizing the strong shear strain field introduced by the asynchronous rolling of irregular shapes; during finish rolling, a strategy of more passes and small deformation is adopted to correct the geometry and suppress springback by finely adjusting the deformation amount.

[0099] In this application, during the asynchronous hot rolling forming process, under the synergistic effect of the strong shear rheology introduced by the differential speed rolling and the triaxial compressive stress of the corrugated hole, the original coarse casting grains with a size of 50-100 μm in the billet undergo severe fragmentation, inducing high-density non-basal slip and continuous dynamic recrystallization. The recrystallization volume fraction reaches over 95%, and the microstructure after rolling transforms into fine equiaxed grains with random orientation and uniform distribution, with the average grain size refined to 5-15 μm. In addition, the billet... The second phase, which is distributed in a continuous / semi-continuous network or in a coarse skeletal / massive form along the grain boundaries, is mechanically broken up during severe shear deformation. The broken second phase particles are eventually dispersed in a near-spherical or ellipsoidal shape within the grains and at the grain boundaries, with an average size refined to 0.5–2 μm and no obvious particle agglomeration. The average network wall thickness of the second phase distributed in a continuous / semi-continuous network is 5–12 μm, and the diameter of the second phase in a coarse skeletal / massive form is 20–50 μm.

[0100] It should be noted that this invention induces a very high proportion of continuous dynamic recrystallization through the high strain energy injected during heterogeneous rolling, transforming the original coarse casting structure into ultrafine equiaxed grains, fully leveraging the fine-grain strengthening effect. Simultaneously, the enormous mechanical shear force completely pulverizes the second phase, which was originally distributed in a continuous / semi-continuous network or coarse skeletal / blocky form, into near-spherical or ellipsoidal shapes, promoting its highly dispersed distribution within the grains and at grain boundaries. This not only eliminates stress concentration sources within the material but also brings about a significant second-phase dispersion strengthening effect. The extreme refinement and uniform dispersion of the second phase significantly reduces the local potential difference within the matrix, effectively suppressing localized galvanic corrosion. This results in corrugated parts exhibiting highly uniform and predictable rate-based overall corrosion degradation behavior after fracturing operations, completely avoiding fracturing failure caused by localized disintegration. This invention possesses extremely high engineering application and commercial promotion value.

[0101] In this application, the microstructure of the second phase, which exhibits a continuous / semi-continuous network distribution, is shown in the following diagram. Figure 11 As shown, the microstructure of the second phase, which appears as a coarse skeleton, is as follows. Figure 12 As shown, the microstructure of the coarse, blocky second phase is as follows. Figure 13 As shown, the microstructure of the second phase, which is nearly spherical / ellipsoidal, is as follows. Figure 14 As shown.

[0102] In addition, conventional rolling easily forms a strong base surface texture with a strength of 16 to 30, while this application effectively suppresses the formation of a strong base surface texture under strong shearing, so that the base surface texture strength of the final corrugated part is controlled below 15, which effectively improves the anisotropy of the material.

[0103] It is important to emphasize that conventional rolling easily forms a strong basal texture within magnesium alloys. This invention alters the grain rotation path through allometric shear rheology, promoting randomization of crystal orientation and effectively suppressing and weakening the formation of strong basal texture. This crucial microstructural evolution significantly improves the anisotropy of the material, resulting in superior mechanical properties in the final corrugated parts.

[0104] S4. Stress-relief annealing: Annealing is performed on corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening introduced by high-speed shearing and complex cross-sectional deformation.

[0105] In this application, the stress-relief annealing process specifically involves: loading the corrugated parts, which have been formed by asynchronous hot rolling, into a heating furnace, heating them to 200-300°C, holding them at that temperature for 30-60 minutes, and then water-cooling them to room temperature.

[0106] In this embodiment of the application, stress-relief annealing can effectively eliminate the macroscopic residual tensile stress introduced by irregular rolling without significantly reducing the material strength.

[0107] S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug.

[0108] In this application, finishing processes include straightening, cutting to length, and edge trimming.

[0109] In this embodiment, the corrugated part after stress-relief annealing is straightened to eliminate axial bending; the head and tail unsteady deformation areas are removed by length cutting and edge trimming, and finally a finished corrugated part with accurate geometric dimensions, smooth surface and meeting the assembly requirements of bridge plug sealing structure is produced.

[0110] Preferably, the manufactured biodegradable magnesium alloy corrugated plug has a tensile strength ≥250MPa, a yield strength ≥155MPa, an elongation ≥15%, and a base surface texture strength ≤15.

[0111] like Figure 8 As shown, the second aspect of the present invention provides a corrugated part for a biodegradable magnesium alloy bridge plug, which is manufactured by a rolling preparation method for a corrugated part for a biodegradable magnesium alloy bridge plug.

[0112] In this application, the biodegradable magnesium alloy bridge plug corrugated component is used in the fields of shale gas extraction and oilfield extraction.

[0113] In this application, the schematic diagram of the equipment model for the irregular asynchronous rolling forming process provided by the present invention is as follows: Figure 5 As shown, the microstructure of a biodegradable magnesium alloy corrugated bridge plug manufactured by an asynchronous rolling process is illustrated in the figure. Figure 6 As shown. From Figure 6 It is evident that the biodegradable magnesium alloy bridge plug corrugated parts manufactured by the irregular asynchronous rolling forming process have a dense and continuous structure. This dense and continuous structure not only significantly improves the shear strength of the corrugated parts but also effectively overcomes the inherent limitations of traditional processing methods.

[0114] Based on the aforementioned rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part, the present invention conducted the following series of experiments to prepare biodegradable magnesium alloy bridge plug corrugated parts, in order to test the performance of the biodegradable magnesium alloy bridge plug corrugated parts prepared by this method. It should be noted that the raw materials used in the following experiments were all commercially available.

[0115] Example 1

[0116] A method for rolling a biodegradable magnesium alloy bridge plug corrugated part includes the following steps:

[0117] S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, and the corrugated rolls include upper concave roll 1 and lower concave roll 2.

[0118] S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, and then the surface of the homogenized heat-treated billet is mechanically ground to remove the oxide layer and surface defects. Then, it is cleaned and dried. The billet is a Mg-6Al-2Cu biodegradable magnesium alloy ingot. The homogenization heat treatment process is as follows: the billet is heated to 420℃ at a heating rate of 7min / ℃, held for 24h, and then water-cooled to room temperature.

[0119] S3. Irregular Asynchronous Hot Rolling Forming: First, the corrugated rolls and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is performed to force the cross-section of the billet to undergo rheological changes and roll it into a corrugated shape to obtain the rolled corrugated part. The rolled corrugated part is then water-cooled to room temperature. Specifically:

[0120] S31. Heating and temperature control: Heat the pretreated billet to 420℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 200℃.

[0121] S32. Rough rolling: The linear speed of the upper concave roll 1 is set to 39.2 mm / s and the linear speed of the lower concave roll 2 is set to 51 mm / s. Then, three rolling passes are performed, and annealing is performed for 10 minutes after each rolling pass. The speed ratio during rough rolling is 1.3, the single-pass reduction rate is 20.6%, and the annealing temperature is 420℃.

[0122] S33. Finishing Rolling: The linear speed of the upper concave roll 1 is set to 32.7 mm / s and the linear speed of the lower concave roll 2 is set to 36 mm / s. Then, four rolling passes are performed, and annealing is carried out for 10 minutes after each rolling pass to obtain the rolled corrugated parts. The rolled corrugated parts are then water-cooled to room temperature. The speed ratio during finishing rolling is 1.1, the single-pass reduction rate is 5.4%, and the annealing temperature is 420℃.

[0123] S4. Stress-relief annealing: Annealing is performed on the corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening introduced by high-speed shearing and complex cross-sectional deformation. The stress-relief annealing process is as follows: the corrugated parts after asynchronous hot rolling are placed in a heating furnace, heated to 300°C, held for 60 minutes, and then water-cooled to room temperature.

[0124] S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug.

[0125] Example 2

[0126] A method for rolling a biodegradable magnesium alloy bridge plug corrugated part includes the following steps:

[0127] S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, and the corrugated rolls include upper concave roll 1 and lower concave roll 2.

[0128] S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, and then the surface of the homogenized heat-treated billet is mechanically ground to remove the oxide layer and surface defects. Then, it is cleaned and dried. The billet is a Mg-6Zn-2Cu biodegradable magnesium alloy ingot. The homogenization heat treatment process is as follows: the billet is heated to 380℃ at a heating rate of 5min / ℃, held for 18h, and then water-cooled to room temperature.

[0129] S3. Irregular Asynchronous Hot Rolling Forming: First, the corrugated rolls and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is performed to force the cross-section of the billet to undergo rheological changes and roll it into a corrugated shape to obtain the rolled corrugated part. The rolled corrugated part is then water-cooled to room temperature. Specifically:

[0130] S31. Heating and temperature control: Heat the pretreated billet to 380℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 160℃.

[0131] S32. Rough rolling: The linear speed of the upper concave roll 1 is set to 37 mm / s and the linear speed of the lower concave roll 2 is set to 44.4 mm / s. Then, four rolling passes are performed, and annealing is performed for 10 minutes after each rolling pass. The speed ratio during rough rolling is 1.2, the single-pass reduction rate is 12.0%, and the annealing temperature is 380℃.

[0132] S33. Finishing: The linear speed of the upper concave roll 1 is set to 22 mm / s and the linear speed of the lower concave roll 2 is set to 22.3 mm / s. Then, 8 passes of rolling are performed, and annealing is performed for 10 minutes after each pass to obtain the rolled corrugated part. The rolled corrugated part is then water-cooled to room temperature. The speed ratio during finishing is 1.01, the single-pass reduction rate is 1.3%, and the annealing temperature is 380℃.

[0133] S4. Stress-relief annealing: Annealing is performed on the corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening introduced by high-speed shearing and complex cross-sectional deformation. The stress-relief annealing process is as follows: the corrugated parts after asynchronous hot rolling are placed in a heating furnace, heated to 200°C, held for 30 minutes, and then water-cooled to room temperature.

[0134] S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug.

[0135] Example 3

[0136] A method for rolling a biodegradable magnesium alloy bridge plug corrugated part includes the following steps:

[0137] S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, and the corrugated rolls include upper concave roll 1 and lower concave roll 2.

[0138] S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, and then the surface of the homogenized heat-treated billet is mechanically ground to remove the oxide layer and surface defects. Then, it is cleaned and dried. The billet is a Mg-6Zn-0.5Zr-1Cu biodegradable magnesium alloy ingot. The homogenization heat treatment process is as follows: the billet is heated to 400℃ at a heating rate of 6min / ℃, held for 20h, and then water-cooled to room temperature.

[0139] S3. Irregular Asynchronous Hot Rolling Forming: First, the corrugated rolls and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is performed to force the cross-section of the billet to undergo rheological changes and roll it into a corrugated shape to obtain the rolled corrugated part. The rolled corrugated part is then water-cooled to room temperature. Specifically:

[0140] S31. Heating and temperature control: Heat the pretreated billet to 400℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 180℃.

[0141] S32. Rough rolling: The linear speed of the upper concave roll 1 is set to 35.2 mm / s and the linear speed of the lower concave roll 2 is set to 44 mm / s. Then, three passes of rolling are performed, and annealing is performed for 10 minutes after each pass. The speed ratio during rough rolling is 1.25, the single pass reduction rate is 18.1%, and the annealing temperature is 400℃.

[0142] S33. Finishing: The linear speed of the upper concave roll 1 is set to 27.6 mm / s and the linear speed of the lower concave roll 2 is set to 29 mm / s. Then, 6 passes of rolling are performed, and annealing is performed for 10 minutes after each pass to obtain the rolled corrugated part. The rolled corrugated part is then water-cooled to room temperature. The speed ratio during finishing is 1.05, the single-pass reduction rate is 2.7%, and the annealing temperature is 400℃.

[0143] S4. Stress-relief annealing: Annealing is performed on corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening introduced by high-speed shearing and complex cross-sectional deformation. The stress-relief annealing process is as follows: the corrugated parts after asynchronous hot rolling are placed in a heating furnace, heated to 250°C, held for 45 minutes, and then water-cooled to room temperature.

[0144] S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug.

[0145] Performance testing: Performance tests were conducted on the biodegradable magnesium alloy bridge plug corrugated parts and raw blanks prepared in Examples 1-3. The performance tests included room temperature tensile mechanical property testing and metallographic / microstructure testing. The test data of the biodegradable magnesium alloy bridge plug corrugated parts prepared in Examples 1-3 are recorded in Table 1, and the test data of the raw blanks used in Examples 1-3 are recorded in Table 2.

[0146] In this experiment, during the room temperature tensile mechanical property test, the tensile specimen had a rectangular cross-section with a total length of 45 mm. The length of the parallel deformation section in the middle of the specimen was 18 mm, the width was 4 mm, and the thickness was 2 mm. The original gauge length was 16 mm and was centrally located in the parallel deformation section. The parallel deformation section and the clamping sections at both ends were smoothly connected by a rounded transition zone with a radius R of 5 mm. The load-displacement curve was recorded throughout the test, and the tensile strength, yield strength, and elongation after fracture were calculated based on the curves after the test.

[0147] During the thermal tensile mechanical property testing in this laboratory, the machine was stretched at a speed of 1.0 mm / min until the sample broke.

[0148] In this experiment, metallographic / microstructure testing was used to detect the grain size, second phase morphology, and second phase size of the original billet and the degradable magnesium alloy bridge plug corrugated parts made from it.

[0149]

[0150]

[0151] As can be clearly seen from Tables 1 and 2, the biodegradable magnesium alloy corrugated bridge plugs prepared in Examples 1-3 exhibit significantly superior mechanical properties compared to the original blanks used, including tensile strength, yield strength, and elongation after fracture. Furthermore, the grain size is refined from approximately 71–86 μm to approximately 6–11 μm, and the second phase transforms from a network / semi-continuous network / blocky structure to fine granular particles with a significant reduction in size. Therefore, the preparation method provided by this invention demonstrates outstanding advantages in improving the mechanical properties of corrugated components. It not only ensures the high-pressure bearing capacity and fit of the bridge plug during setting under complex downhole conditions but also provides solid and reliable technical support for the high-performance fabrication of corrugated components.

[0152] Furthermore, Table 1 clearly shows that Example 1 exhibits high strength and low elongation, primarily due to the use of a magnesium alloy with a high aluminum content as the matrix material. Aluminum has a significant solid solution strengthening effect in magnesium alloys; it can integrate into the magnesium lattice structure, causing lattice distortion, thereby effectively hindering dislocation movement and significantly improving the material's strength. Simultaneously, in the asynchronous hot rolling process, Example 1 employed a single-pass high reduction rate and high speed ratio rolling method, subjecting the material to intense shear deformation during processing, leading to severe work hardening. During this process, the dislocation density within the material increases dramatically, and the entanglement and hindering effect between dislocations are further enhanced, significantly improving the material's yield strength and tensile strength. However, this intense work hardening also brings certain side effects; it inhibits grain slip and rotation within the material to some extent, reducing the material's plastic deformation capacity, ultimately resulting in Example 1 exhibiting a lower elongation.

[0153] Example 2 exhibits low strength and high elongation due to the use of a magnesium-zinc alloy, which inherently possesses relatively low strength characteristics. Furthermore, Example 2 employs an extremely mild processing method in its asynchronous hot rolling process, with minimal single-pass reduction and speed ratio. It also involves numerous finishing passes and frequent intermediate annealing during processing. This processing method provides ample time for dynamic recovery and recrystallization. During the dynamic recovery stage, dislocations within the material rearrange through slip and climb, releasing some residual stress. In the recrystallization stage, new, distortion-free equiaxed grains gradually form, further eliminating residual stress within the material. Therefore, Example 2 retains excellent plastic deformation capacity. However, due to the lack of strain hardening effects from strong deformation, the material's strength cannot be effectively improved, resulting in a lower strength level.

[0154] Example 3 achieves a good balance between strength and plasticity thanks to the introduction of zirconium. Zirconium plays a significant role in grain refinement in magnesium alloys, acting as a heterogeneous nucleation core to promote grain refinement and result in more uniform and smaller grain sizes within the material. These smaller grains not only improve the material's strength but also its plasticity. Furthermore, in the asynchronous hot rolling process for profiled materials, Example 3 selected a moderate reduction rate and velocity ratio. These process parameters ensure a certain degree of shear deformation and work hardening, allowing the material to maintain a high strength level, while also preventing excessive stress concentration within the material through a reasonable annealing rhythm. During annealing, residual stress within the material is appropriately released, the grain structure is further optimized, and ultimately a finished product with good comprehensive mechanical properties is obtained, achieving a perfect balance between strength and plasticity.

[0155] In summary, the graded and controlled asynchronous rolling forming process proposed in this invention achieves near-net-shape forming of corrugated parts through a "strong shear modification" and "near-net-shape forming" mechanism, resulting in high material utilization and excellent dimensional accuracy and surface quality. Furthermore, thanks to the combined effects of extremely refined grains, dispersed second-phase distribution, and weakened texture brought about by the preparation method proposed in this invention, the corrugated parts prepared by this invention successfully overcome the performance bottleneck of magnesium alloys being "strong but not tough," exhibiting excellent synergistic matching of strength and plasticity, and meeting the requirements for high-pressure differential bridge plug sealing and anchoring.

[0156] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for rolling and preparing a corrugated part for a biodegradable magnesium alloy bridge plug, characterized in that, Includes the following steps: S1. Preparation and pretreatment of rolling equipment: Prepare a rolling mill with variable speed rolling function in advance, and harden and polish the surface of the rolls. The rolls installed on the rolling mill are corrugated rolls, including upper concave rolls and lower concave rolls. The rolling mill is a two-roll reversible hot rolling mill, and the corrugated rolls are made of high-quality hot work die steel. Furthermore, both the upper and lower concave rollers have irregularly shaped grooves on their surfaces that correspond to the corrugated parts, and these grooves have concentric circular arc-shaped cross-sectional profiles. The radius of curvature of the forming surface of the lower concave roller is equal to the outer radius of the central tube of the bridge plug to be assembled, and the radii of curvature of the forming surfaces of the upper and lower concave rollers and the target thickness of the corrugated parts satisfy the following relationship: R2-R1=H, In the formula, R2 is the radius of curvature of the upper concave roller forming surface, R1 is the radius of curvature of the lower concave roller forming surface, and H is the target thickness of the corrugated part. S2. Raw material pretreatment: First, the billet is subjected to homogenization heat treatment, then the surface of the homogenized heat-treated billet is mechanically ground until the oxide layer and surface defects are removed, and then it is cleaned and dried. S3. Irregular Asynchronous Hot Rolling Forming: First, the corrugated rolls and the pretreated billet are heated and the temperature is controlled. Then, a two-stage rolling process is performed to force the cross-section of the billet to undergo rheological changes and roll it into a corrugated shape, obtaining the rolled corrugated part. The rolled corrugated part is then water-cooled or air-cooled to room temperature. The temperature during the irregular asynchronous hot rolling forming process is 380-420℃. During the two-stage rolling process, the distribution of the single-pass reduction rate follows the principle of "rapid strong shear modification in rough rolling and slow micro-deformation control in finish rolling". Specifically, during rough rolling, a strategy of fewer passes and larger deformation is adopted, utilizing the strong shear strain field introduced by asynchronous rolling to break up the coarse second phase and induce dynamic recrystallization; during finish rolling, a strategy of more passes and smaller deformation is adopted, correcting the geometry and suppressing springback by fine-tuning the deformation amount; based on the pre-treated billet thickness, the total reduction rate after rough rolling is 40%–50%; based on the billet thickness after rough rolling, the total reduction rate after finish rolling is 10%–20%; step S3 specifically includes: S31. Heating and temperature control: Heat the pretreated billet to 380-420℃ and hold for 30 minutes; before rolling, preheat the corrugated rolls to 160-200℃. S32. Rough rolling: Set the linear speed of the upper concave roll / lower concave roll to 37-51 mm / s, then perform 3-4 passes of rolling, and perform annealing for 10 minutes after each pass. The speed ratio during rough rolling should meet the following condition: 1.2 ≤ speed ratio ≤ 1.3, where the speed ratio is the ratio of the linear speed of the lower concave roll to the linear speed of the upper concave roll; the single-pass reduction rate is 12.0%-20.6%, and the annealing temperature is 380-420℃. S33. Finishing Rolling: Set the linear speed of the upper concave roll / lower concave roll to 22-36 mm / s, then perform 4-8 passes of rolling, and anneal for 10 minutes after each pass to obtain the rolled corrugated part. Then, water-cool or air-cool the rolled corrugated part to room temperature. The speed ratio during finishing rolling meets the following requirements: 1.0 < speed ratio ≤ 1.1, where the speed ratio is the ratio of the linear speed of the lower concave roll to the linear speed of the upper concave roll; the single-pass reduction rate is 1.3%-5.4%, and the annealing temperature is 380-420℃. S4. Stress-relief annealing: Annealing is performed on corrugated parts after asynchronous hot rolling to eliminate residual internal stress and work hardening introduced by high-speed shearing and complex cross-sectional deformation. S5. Finishing: The corrugated parts after stress-relief annealing are finished to obtain finished corrugated parts that meet the dimensional accuracy of the bridge plug. The biodegradable magnesium alloy bridge plug corrugated parts produced have a tensile strength ≥250MPa, a yield strength ≥155MPa, an elongation ≥15%, and a base surface texture strength ≤15.

2. The rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part according to claim 1, characterized in that, The billet is a biodegradable magnesium alloy ingot, wherein the biodegradable magnesium alloy is a Mg-Al or Mg-Zn biodegradable magnesium alloy.

3. The rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part according to claim 1, characterized in that, The homogenization heat treatment process is as follows: the billet is heated to 380-420℃ at a heating rate of 5-7 min / ℃, held for 18-24 h, and then water-cooled to room temperature; The cleaning and drying process is as follows: Rinse the polished blank with room temperature water to remove the residual polishing dust on the surface, and then place the cleaned blank in a drying oven for hot air drying until the surface of the blank is dry and free of water stains. The stress-relief annealing process is as follows: the corrugated parts after asynchronous hot rolling are placed into a heating furnace, heated to 200-300℃, held for 30-60 minutes, and then water-cooled to room temperature. Finishing processes include straightening, cutting to length, and edge trimming.

4. The rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part according to claim 1, characterized in that, During the asynchronous hot rolling process, under the combined effect of strong shear rheology introduced by the differential speed rolling and the triaxial compressive stress of the corrugated hole, the original coarse casting grains with a size of 50-100μm in the billet undergo severe fragmentation, and high-density non-basal slip and continuous dynamic recrystallization are induced. The recrystallization volume fraction reaches more than 95%. After rolling, the microstructure is transformed into fine equiaxed grains with random orientation and uniform distribution, and the average grain size is refined to 5-15μm. In addition, the second phase, which is distributed in a continuous / semi-continuous network or in a coarse skeletal / blocky form along the grain boundaries in the billet, is mechanically broken up during severe shear deformation. The broken second phase particles are eventually dispersed in a near-spherical or ellipsoidal shape within the grains and at the grain boundaries, with an average size refined to 0.5–2 μm and no obvious particle agglomeration occurs. The average network wall thickness of the second phase distributed in a continuous / semi-continuous network is 5–12 μm, and the diameter of the second phase in a coarse skeletal / blocky form is 20–50 μm.

5. A corrugated component for a biodegradable magnesium alloy bridge plug, characterized in that, It is manufactured using the rolling preparation method for a biodegradable magnesium alloy bridge plug corrugated part as described in any one of claims 1-4.

6. The corrugated component for a biodegradable magnesium alloy bridge plug according to claim 5, characterized in that, The biodegradable magnesium alloy corrugated bridge plug is used in shale gas extraction and oilfield development.

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