Method for restraining rolling edge cracks of magnesium alloy plate through edge flow blocking complex lining plate and magnesium alloy plate

Abstract

The invention belongs to the technical field of magnesium alloy rolling, and particularly relates to a method for restraining rolling edge cracks of a magnesium alloy plate through an edge flow blocking complex lining plate and the magnesium alloy plate. Preparing a complex lining plate, wherein one surface of the complex lining plate is a lining plate clamping surface; the magnesium alloy blank is clamped between the two complex lining plates to form a combined blank, and the two sides of the magnesium alloy blank make contact with the lining plate clamping faces of the two complex lining plates correspondingly; binding the combined blank by using a high-temperature-resistant metal wire; the bundled combined blank is fed into a heating furnace to be preheated and subjected to heat preservation; the preheated combined blank is rolled through a multi-pass accumulative rolling technology, and a magnesium alloy plate clamped between the two complex lining plates is obtained; the magnesium alloy plate is separated from the two complex lining plates, and a magnesium alloy plate finished product without macroscopic cracks on the edge is obtained; and the rolling success rate of the magnesium alloy plate is increased through the complex lining plate and the multi-pass accumulative rolling process.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy rolling technology, specifically relating to a method for suppressing edge cracking during the rolling of magnesium alloy sheets using edge-blocking composite liners, and the magnesium alloy sheets themselves. Background Technology

[0002] In the flat rolling process of magnesium alloy sheets, following the law of constant volume, as the metal thickness decreases, it inevitably extends along the rolling direction and widens along the width direction. For magnesium alloys, which are difficult to deform, the edges of the sheet are under uniaxial or biaxial tensile stress. When the tangential tensile stress caused by the widening exceeds the material's fracture limit, cracks will immediately appear and propagate towards the center. Furthermore, the high-temperature oxidation characteristics of magnesium alloys further exacerbate the damage sensitivity of the edge surface. Therefore, improving the edge stress state during the rolling process is crucial for producing high-quality magnesium alloy sheets.

[0003] Existing technologies employ methods such as liner-wrapped rolling, warm rolling, and edge induction heating to prevent magnesium alloy sheets from cracking due to excessive tangential tensile stress caused by widening during rolling, which could exceed the material's fracture limit. Conventional liner rolling, which uses a hard metal plate to wrap the magnesium alloy, reduces heat loss and improves surface friction to some extent. However, existing liners are mostly flat and smooth, relying solely on Coulomb friction at the interlayer interface for lateral restraint. Under conditions of large reductions or complex deformations, this limited friction is insufficient to overcome the lateral flow tendency of the magnesium alloy, making it difficult to effectively suppress the free widening of the sheet edges. Consequently, the edges remain dominated by tensile stress, and the risk of edge cracking remains. On the other hand, while auxiliary processes such as edge heating can improve local plasticity, the equipment is complex, energy-intensive, and prone to causing uneven microstructure throughout the sheet, making it difficult to meet the demands of continuous, low-cost production. Summary of the Invention

[0004] The purpose of this invention is to provide a method and a magnesium alloy sheet for suppressing edge cracking during the rolling process using an edge-blocking composite liner, thereby reducing the occurrence of edge cracking in magnesium alloy sheets during rolling and improving the success rate of magnesium alloy sheet rolling.

[0005] The technical solution of the present invention is: a method for suppressing edge cracks in magnesium alloy sheet rolling using an edge-blocking composite liner, comprising the following steps:

[0006] S1: Select the magnesium alloy billet to be rolled and perform surface pretreatment to ensure the consistency of the initial state of the magnesium alloy billet;

[0007] S2: Prepare two composite liners. The high-temperature yield strength of the composite liners is higher than that of the magnesium alloy billet to be rolled. Each composite liner has fixed L-shaped lugs symmetrically arranged at both ends. One surface of each composite liner is a liner clamping surface. The liner clamping surface is divided into a smooth rheological zone and a wave-shaped flow-blocking zone along its width direction. The smooth rheological zone is located in the middle of the liner clamping surface, and the wave-shaped flow-blocking zone is located on both sides of the smooth rheological zone. The wave-shaped flow-blocking zone has a wave-shaped texture. Among them, the wave-shaped flow-blocking zone of any one of the two composite liners has several upward-protruding wave-shaped textures, and the wave-shaped flow-blocking zone of the other composite liner has several downward-recessed wave-shaped textures.

[0008] S3: A composite billet with a sandwich structure is formed by clamping a magnesium alloy billet between two composite liners, with both sides of the magnesium alloy billet in contact with the clamping surfaces of the two composite liners; the position of the magnesium alloy billet is adjusted so that its upper and lower sides correspond to the smooth rheological zones of the two composite liners, and the edge of the magnesium alloy billet in the width direction is in contact with the corrugated flow-blocking zone of the two composite liners; high-temperature resistant metal wire is wrapped around the fixed L-shaped lugs at both ends of the two composite liners to bind the composite billet;

[0009] S4: Send the bundled composite billet into the heating furnace and heat it to 360-420℃ for overall preheating, and keep it at that temperature for 30-50 minutes;

[0010] S5: The preheated composite billet is rolled using a multi-pass cumulative rolling process to obtain a magnesium alloy sheet sandwiched between two composite liners; during the rolling process, the wave-shaped flow-blocking zone of the two composite liners is used to apply lateral constraints to the edges of the magnesium alloy billet in the width direction.

[0011] S6: After rolling, the magnesium alloy sheet is separated from the two composite backing plates to obtain a finished magnesium alloy sheet with no macroscopic cracks at the edges.

[0012] Preferably, in step S1, the magnesium alloy billet belongs to the Mg-Al-Zn-Mn alloy system, and its chemical composition by mass percentage includes: Al: 2.4~3.6%, Zn: 0.5~1.5%, Mn: 0.05~1.0%, with the balance being Mg and impurities; the magnesium alloy billet to be rolled is subjected to surface pretreatment by sanding with sandpaper and cleaning with anhydrous ethanol in sequence.

[0013] Preferably, in step S2, the composite liner is made of stainless steel or hot work die steel, and the high temperature yield strength of the composite liner is more than three times the high temperature yield strength of the magnesium alloy billet to be rolled.

[0014] Preferably, in the composite liner, the width of each wave-shaped flow-blocking zone accounts for 20%-30% of the total width of the composite liner. Several wave-shaped textures in the wave-shaped flow-blocking zone together form a microchannel array structure. The extension direction of each wave-shaped texture in the microchannel array structure is perpendicular to the rolling direction of the magnesium alloy billet. The cross-sectional profile of the microchannel array structure in the width direction is a continuous sine wave, and the corrugation height of the microchannel array structure is 0.5-1.0 mm. The corrugation height refers to the vertical distance between the highest point of the corrugation ridge or the lowest point of the corrugation groove and the reference reference plane. Taking the liner clamping surface as the reference reference plane, the distance between the peaks of two adjacent corrugation ridges is 0.5-1.0 mm. The sine function relationship of the waveform curve of each wave-shaped texture in the microchannel array structure is:

[0015]

[0016] In this equation, the origin O is taken as the vertex of one corner of the complex liner. In the equation, x is the x-axis extending along the short side of the complex liner, perpendicular to the rolling direction, and the unit is mm; y is the y-axis extending along the long side of the complex liner, in the same direction as the rolling direction, and the unit is mm; a is the wave frequency coefficient of each wavy texture in the microchannel array structure, ranging from 2 to 10, and the unit is dimensionless; A is the amplitude coefficient of each wavy texture in the microchannel array structure, and the unit is mm.

[0017] Preferably, in step S3, the width of the magnesium alloy billet to be rolled is... Width of the smooth rheological region in the complex liner The same applies to the total width of the composite liner. The width of the smooth rheological region With the width of the two wave-blocking zones The total width of the composite lining plate was jointly determined. .

[0018] Preferably, the multi-pass cumulative rolling process is a multi-pass low-reduction, low-speed cumulative rolling process. This process decomposes the total deformation of the composite billet into multiple passes. Each pass uses a low reduction rate of 6.3%-9.4% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes. Only after annealing is the next rolling pass performed. The thickness of the combined billet is gradually reduced through multiple rolling passes. After the final rolling pass, a magnesium alloy sheet is obtained sandwiched between two composite liners. The magnesium alloy sheet is then separated from the two composite liners and air-cooled to room temperature, finally yielding a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process is divided into the following stages: the initial rolling stage from the first to the fourth pass, the intermediate cumulative stage from the fifth to the ninth pass, and the late forming stage from the tenth to the fourteenth pass.

[0019] Preferably, during the four-pass rolling process in the initial rolling stage, the composite billet is in a high-temperature environment of 360-420℃, and each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the initial rolling stage is 23.1%-32.7%.

[0020] During the five-pass rolling process in the intermediate cumulative stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the intermediate cumulative stage is 27.9%-39.1%.

[0021] During the five-pass rolling process in the later forming stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the later forming stage is 27.9%-39.1%.

[0022] Through multiple rolling passes in the initial rolling stage, the intermediate accumulation stage, and the late forming stage, the total reduction rate of the composite billet reaches 60%-75%.

[0023] Furthermore, the multi-pass cumulative rolling process is a micro-speed ratio multi-pass variable parameter cumulative rolling process. This process decomposes the total deformation of the composite billet into multiple rolling passes. Each pass uses a reduction rate of 5%-12% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes. Only after annealing is the next rolling pass performed. The thickness of the combined billet is gradually reduced through multiple rolling passes. After the final rolling pass, a magnesium alloy sheet is obtained sandwiched between two composite liners. The magnesium alloy sheet is then separated from the two composite liners and air-cooled to room temperature, finally yielding a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process in the micro-variable speed ratio multi-pass variable parameter cumulative rolling process is divided into: the initial rolling stage of the first to fourth passes, the intermediate cumulative stage of the fifth to ninth passes, and the late forming stage of the tenth to fourteenth passes.

[0024] Furthermore, during the four-pass rolling process in the initial rolling stage, the combined billet is placed in a high-temperature environment of 360-420℃. Each pass uses a low-speed rolling with a small reduction rate of 10%-12% and a rolling speed of 30-36mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.09-1.1, and the total reduction rate in the initial rolling stage is 34.4%-40.0%.

[0025] During the five-pass rolling process in the intermediate cumulative stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 7%-9% and a rolling speed of 24-30mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.07-1.09. The total reduction rate in the intermediate cumulative stage is 30.4%-37.6%.

[0026] During the five-pass rolling process in the later forming stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass uses a small reduction rate of 5%-6% and a rolling speed of 18-24mm / s for low-speed rolling. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in rolling is 1.05-1.06. The total reduction rate of the later forming stage is 22.6%-26.6%.

[0027] Through multiple rolling passes in the initial rolling stage, the intermediate accumulation stage, and the late forming stage, the total reduction rate of the composite billet reaches 60%-75%.

[0028] The present invention also provides a magnesium alloy sheet, which is manufactured by the above-mentioned method of using an edge-blocking composite liner to suppress edge cracking during rolling of magnesium alloy sheet. The magnesium alloy sheet has a tensile strength ≥270MPa, a yield strength ≥190MPa, and an elongation ≥6%. The microstructure of the magnesium alloy sheet is a fully dynamic recrystallized structure, and the average grain size of the magnesium alloy sheet is 3-10μm.

[0029] The beneficial effects of this invention are as follows: By applying lateral constraint force to the edge position of the magnesium alloy billet in the width direction through the wave-shaped flow-blocking zone of the composite liner edge, the free transverse rheology of the magnesium alloy billet edge during conventional rolling is transformed into controlled longitudinal extension, thereby suppressing edge cracking caused by excessive widening of the magnesium alloy billet during rolling and significantly improving the yield of magnesium alloy sheet; During the rolling process, the high frictional resistance generated by the wave-shaped flow-blocking structure of the composite liner and the magnesium alloy billet prevents the magnesium alloy billet from completely filling the interior of the microchannel array structure, forcing the edge of the magnesium alloy billet to undergo severe local plastic deformation in the wave-shaped flow-blocking zone, thereby inducing dynamic recrystallization inside the magnesium alloy billet, refining the grains of the magnesium alloy sheet, and improving the plasticity and toughness of the edge of the magnesium alloy sheet from the microstructure level.

[0030] The multi-pass low-speed cumulative rolling process decomposes the total deformation of the composite billet into multiple passes for rolling. In the initial rolling stage of the multi-pass low-speed cumulative rolling process, the edge of the magnesium alloy billet in the width direction comes into contact with the wave-shaped flow-blocking zone in the composite liner. The microchannel array structure in the wave-shaped flow-blocking zone physically blocks the lateral expansion of the magnesium alloy billet, forcing the magnesium alloy billet to expand in the rolling direction. In the intermediate cumulative stage of the multi-pass low-speed cumulative rolling process, the microchannel array structure in the wave-shaped flow-blocking zone causes severe shear deformation at the edge of the magnesium alloy billet in the width direction, further promoting local recrystallization at the edge of the magnesium alloy billet in the width direction, thereby achieving grain refinement, dynamic softening and homogenization of the microstructure at the edge of the magnesium alloy billet in the width direction.

[0031] The micro-velocity ratio multi-pass variable parameter cumulative rolling process decomposes the total deformation of the composite billet into multiple rolling passes. In the initial rolling stage, the wave-shaped flow-blocking zones of two composite liners jointly provide transverse extrusion to the magnesium alloy billet. Through the synergistic effect of longitudinal shearing and transverse extrusion, the coarse original grains in the magnesium alloy billet are destroyed, suppressing the initiation of macroscopic cracks at the width-direction edges of the magnesium alloy billet in the initial rolling stage. In the intermediate cumulative stage, the wave-shaped flow-blocking zones of the two composite liners jointly apply periodic alternating shear strain to the width-direction edges of the magnesium alloy billet. Under thermal activation at 360-420℃, this induces cracks at the edges and center of the magnesium alloy billet. The process involves comprehensive and uniform dynamic recrystallization in the parts, achieving dynamic softening of the magnesium alloy billet structure. In the later forming stage of the micro-asynchronous speed ratio multi-pass variable parameter cumulative rolling process, the combination of micro-asynchronous speed ratio and low speed and small reduction rate, along with the continuous lateral binding constraint of the magnesium alloy billet by the composite liner, not only further weakens the residual basal texture on the magnesium alloy billet, but also effectively closes and heals the internal micropores of the magnesium alloy billet that may have been induced by the large deformation in the early stage through the kneading effect of the wave flow blocking zone on the magnesium alloy billet extrusion and micro-shearing, completely releasing residual stress. Ultimately, this ensures that the rolled magnesium alloy sheet achieves the set total reduction rate while effectively suppressing the generation of rolling edge crack defects, achieving high integrity of the magnesium alloy sheet edge and surface flatness control.

[0032] Furthermore, in both the multi-pass low-pressure, low-speed cumulative rolling process and the micro-variable speed ratio multi-pass variable parameter cumulative rolling process, intermediate annealing is performed after each rolling pass until the final rolling pass is completed to obtain the magnesium alloy sheet, which is then air-cooled to room temperature. By performing intermediate annealing after each rolling pass, static recrystallization of the magnesium alloy billet is promoted, avoiding residual "work hardening" and ensuring that subsequent passes are dominated by dynamic recrystallization, rather than a mixture of "cold deformation and hot deformation". This allows the deformed microstructure inside the magnesium alloy billet to be further refined through static recrystallization. By adjusting the annealing temperature and annealing time, excessive grain growth in the rolled magnesium alloy sheet is suppressed, thereby improving the yield strength of the rolled magnesium alloy sheet. Attached Figure Description

[0033] 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.

[0034] Figure 1 This is a flowchart of the magnesium alloy sheet rolling process in this invention;

[0035] Figure 2 This is a schematic diagram of the structure of the combined billet during the rolling process in this invention;

[0036] Figure 3 This is a schematic diagram of the structure of a composite liner in this invention;

[0037] Figure 4 This is a schematic diagram of the structure of another composite liner plate in this invention;

[0038] Figure 5 This is a coordinate system definition diagram for any compound liner plate in this invention.

[0039] In the figure: 1. Magnesium alloy billet; 2. Compound liner; 21. Smooth rheological zone; 22. Wave-shaped flow-blocking zone; 23. Fixed L-shaped lug; 24. High-temperature resistant metal wire. Detailed Implementation

[0040] 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.

[0041] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" 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 communication 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.

[0042] Example 1

[0043] like Figure 1-5 As shown, a method for suppressing edge cracks in magnesium alloy sheet rolling using an edge-blocking composite liner includes the following steps:

[0044] S1: Select the magnesium alloy billet 1 to be rolled and perform surface pretreatment to ensure the consistency of the initial state of the magnesium alloy billet 1.

[0045] The selected magnesium alloy billet 1 belongs to the Mg-Al-Zn-Mn alloy system. Its chemical composition by mass percentage includes: Al: 2.4~3.6%, Zn: 0.5~1.5%, Mn: 0.05~1.0%, with the balance being Mg and impurities. The magnesium alloy billet 1 to be rolled is subjected to surface pretreatment by sanding and cleaning with anhydrous ethanol to ensure the consistency of the initial state of the magnesium alloy billet material, and at the same time to ensure that the surface of the magnesium alloy billet 1 is clean and free of oil stains to prevent the introduction of impurities during the rolling process.

[0046] Specifically, in this embodiment, an AZ31B magnesium alloy rolled sheet with a length of 100mm, a width of 40mm, and a thickness of 5mm is selected as the magnesium alloy billet 1 to be rolled. The specific chemical composition of the magnesium alloy billet 1 is shown in Table 1.

[0047]

[0048] AZ31B is currently the most widely used, most technologically mature, and cost-effective wrought magnesium alloy in industry. Its composition and microstructure give it good deformation potential under warm conditions. Therefore, in this embodiment, AZ31B magnesium alloy rolled sheet is selected as magnesium alloy billet 1.

[0049] S2: Prepare two composite liner plates 2. The high-temperature yield strength of the composite liner plates 2 is higher than that of the magnesium alloy billet 1 to be rolled. Each composite liner plate 2 has symmetrically fixed L-shaped lugs 23 at both ends. One surface of each composite liner plate 2 is the liner clamping surface. The liner clamping surface is divided into a smooth rheological zone 21 and a wave-shaped flow-blocking zone 22 along its width direction. The smooth rheological zone 21 is located in the middle of the liner clamping surface, and the wave-shaped flow-blocking zone 22 is located on both sides of the smooth rheological zone 21. The wave-shaped flow-blocking zone 22 has a wave-shaped texture. Among them, the wave-shaped flow-blocking zone 22 of any one of the two composite liner plates 2 has several upward-protruding wave-shaped textures, and the wave-shaped flow-blocking zone 22 of the other composite liner plate 2 has several downward-recessed wave-shaped textures, as shown in the figure. Figure 3 and Figure 4 As shown, Figure 3 The wave-resistant flow zone 22 in the middle has several upward-convex wave-shaped textures. Figure 4 The wave-resistant zone 22 in the middle has several downward-recessed wave-shaped textures.

[0050] In this embodiment, the composite liner 2 is made of stainless steel or hot work die steel, and the high temperature yield strength of the composite liner 2 is more than three times the high temperature yield strength of the magnesium alloy sheet to be rolled.

[0051] Specifically, such as Figure 2-5 As shown, in the composite liner 2, the width of each wave-shaped flow-blocking zone 22 accounts for 20%-30% of the total width of the composite liner 2. Several wave-shaped textures in the wave-shaped flow-blocking zone 22 together form a microchannel array structure. The extension direction of each wave-shaped texture in the microchannel array structure is perpendicular to the rolling direction of the magnesium alloy billet. Figure 2 The arrow in the figure represents the rolling direction of magnesium alloy billet 1; the cross-sectional profile of the microchannel array structure in the width direction is a continuous sine wave, that is, the profile of each wave-shaped texture in the wave choking zone 22 is a continuous sine wave; the corrugation height of the microchannel array structure is 0.5-1.0 mm, and the corrugation height refers to the vertical distance between the highest point of the corrugation ridge or the lowest point of the corrugation groove and the reference datum plane. Among them, taking the liner clamping surface as the reference datum plane, the distance between the peaks of two adjacent corrugation ridges is 0.5-1.0 mm, that is, the corrugation spacing is 0.5-1.0 mm; the sine function relationship of the waveform curve of each wave-shaped texture in the microchannel array structure is:

[0052] (Formula 1)

[0053] Among them, such as Figure 5 As shown, the origin O of the coordinate system is the vertex of one corner of the complex liner 2. In the formula, x is the x-axis extending along the short side of the complex liner 2, which is perpendicular to the rolling direction and is in mm; y is the y-axis extending along the long side of the complex liner 2, which is in the same direction as the rolling direction and is in mm; a is the wave frequency coefficient of each wavy texture in the microchannel array structure, which is used to adjust the density of each wavy texture and has a value range of 2-10 and is dimensionless; A is the amplitude coefficient of each wavy texture in the microchannel array structure. A determines the undulation of each wavy texture in the microchannel array structure and limits the swing range of each wavy texture in the height direction and is in mm.

[0054] Specifically, in this embodiment, the ripple height of the microchannel array structure is 0.5 mm, representing the undulation amplitude of each wavy texture in the thickness direction; the ripple spacing is 0.5 mm, representing the arrangement density of each wavy texture in the width direction of the composite backing plate 2; the sine function relationship of the waveform curve of each wavy texture is:

[0055] (Formula 2)

[0056] In this embodiment, a is selected as 2. The ripple period of the wave pattern is adjusted by the wave frequency coefficient a to achieve a high-density and compact arrangement of microchannels. The amplitude coefficient A of the wave pattern is set to 0.5. The amplitude coefficient A precisely anchors the ripple feature height of the wave pattern to 0.5mm, thereby strictly limiting the undulation amplitude of the wave pattern in the height direction.

[0057] S3: A composite billet with a sandwich structure is formed by sandwiching the magnesium alloy billet 1 between two composite liner plates 2, with both sides of the magnesium alloy billet in contact with the clamping surfaces of the two composite liner plates 2. It should be noted that the two composite liner plates 2 do not have a distinction between upper and lower positions; that is, if one composite liner plate 2 is placed below the magnesium alloy billet 1, the other composite liner plate is placed above the magnesium alloy billet 1. The position of the magnesium alloy billet 1 is adjusted so that its upper and lower sides correspond to the surfaces of the two composite liner plates 2 respectively. The flow-changing zone 21 is formed, and the edge portion of the magnesium alloy billet 1 in the width direction is connected to the wave-blocking zone 22 of the two composite liner plates 2, that is, the left and right sides of the magnesium alloy billet 1 are connected to the wave-blocking zone 22 corresponding to them respectively; a high-temperature resistant metal wire 24 is wound around the fixed L-shaped lugs 23 at both ends of the two composite liner plates 2, and the composite billet is bound by the high-temperature resistant metal wire 24. The high-temperature resistant metal wire can be made of high-temperature resistant metal materials such as iron and chromium, and there is no limitation in this application.

[0058] Based on the above embodiments, each composite liner 2 has symmetrically provided fixed L-shaped lugs 23 at both ends, that is, each composite liner 2 has four fixed L-shaped lugs 23; when the magnesium alloy billet 1 is clamped between two composite liner 2 to form a combined billet, the positions of the two composite liner 2 correspond to each other, and each fixed L-shaped lug 23 located above the magnesium alloy billet 1 has a fixed L-shaped lug 23 located below it. The two corresponding fixed L-shaped lugs 23 are wound together with high-temperature resistant metal wire 24 to complete the binding of the combined billet, specifically as follows. Figure 2 As shown.

[0059] In addition, such as Figure 5 As shown, the width of the magnesium alloy billet 1 to be rolled is... Width of the smooth rheological region 21 in the complex liner 2 Similarly, the total width of the composite liner 2 The width of the smooth rheological region 21 Width of the two wave-blocking zones 22 The total width of the composite liner 2 was jointly determined. .

[0060] Based on the above embodiments, such as Figure 2 and Figure 5As shown, the clamping surfaces of the two composite liners 2 are respectively in contact with the upper and lower sides of the magnesium alloy billet 1, ensuring that the magnesium alloy billet 1 is completely placed between the two corrugated flow-blocking zones 22 on the single composite liner 2. The composite billet 1 and the combined billet formed by the two composite liners 2 are bound together with wire to ensure that there is no relative misalignment between the composite liners 2 and the magnesium alloy billet 1 before subsequent preheating and before entering the bite zone of the rolls. It should be noted that the width direction of the magnesium alloy billet 1, the composite liners 2, and the combined billet is the same, all aligned with... Figure 5 The x-axis directions shown are consistent.

[0061] S4: The bundled composite billets are sent into the heating furnace and heated to 360-420℃ for overall preheating. The temperature is held for 30-50 minutes to ensure that the magnesium alloy billet 1 has sufficient plastic rheological capacity.

[0062] In this embodiment, the heating temperature is set to 400℃ and the holding time is 40min. This process fully softens the AZ31B magnesium alloy sheet, which is the magnesium alloy blank 1, so that its internal structure becomes uniform and it has excellent plastic rheological ability.

[0063] S5: The preheated composite billet is rolled using a multi-pass cumulative rolling process to obtain a magnesium alloy sheet sandwiched between two composite liners 2. During the rolling process, the wave-blocking zone 22 of the two composite liners 2 is used to apply lateral constraints to the edge of the magnesium alloy sheet in the width direction.

[0064] Furthermore, since the width of the magnesium alloy billet 1 is exactly the same as the width of the smooth rheological zone 21 in the composite liner 2, during the rolling of the combined billet, the magnesium alloy billet 1 is extended in both length and width directions to ensure that the edge of the magnesium alloy billet 1 in the width direction covers the wave-resistant zone 22 of the composite liner 2. At the same time, the microchannel array structure in the wave-resistant zone 22 will gradually press into the softened edge of the magnesium alloy billet 1. The two composite liners 2 together form a mechanical interlock for the magnesium alloy billet 1, preventing the magnesium alloy billet 1 from completely filling the interior of the microchannel array structure through high frictional resistance. This forces the edge material of the magnesium alloy billet 1 in the width direction to undergo severe local shear deformation in the wave-resistant zone 22, inducing the magnesium alloy billet 1 to undergo dynamic recrystallization, refining the edge grains in the width direction of the rolled magnesium alloy sheet, and suppressing the propagation of edge cracks in the width direction of the magnesium alloy sheet.

[0065] S6: After rolling, the magnesium alloy sheet is separated from the two composite liner plates 2 to obtain the finished magnesium alloy sheet with no macroscopic cracks at the edges.

[0066] Specifically, the multi-pass cumulative rolling process is a multi-pass low-reduction, low-speed cumulative rolling process. This process decomposes the total deformation of the composite billet into multiple passes. Each pass uses a low reduction rate of 6.3%-9.4% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes. Only after annealing is the next rolling pass performed. Rolling is performed to cumulatively reduce the thickness of the combined billet. After the last rolling pass is completed, a magnesium alloy sheet is obtained sandwiched between two composite liners 2. The magnesium alloy sheet is then separated from the two composite liners 2 and air-cooled to room temperature to finally obtain a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process in the multi-pass low-speed cumulative rolling process is divided into the initial rolling stage from the first to the fourth pass, the intermediate cumulative stage from the fifth to the ninth pass, and the late forming stage from the tenth to the fourteenth pass.

[0067] It should be noted that, in this embodiment, the edges of the magnesium alloy billet 1 or the magnesium alloy sheet are all located at the edges in the width direction of the magnesium alloy billet 1 or the magnesium alloy sheet, and the width direction of the magnesium alloy sheet or the magnesium alloy billet 1 is perpendicular to the rolling direction of the magnesium alloy billet 1. Although this embodiment is a combined billet being rolled, in the combined billet composed of the magnesium alloy billet 1 and two composite liners 2, the high-temperature yield strength of the composite liners 2 is more than three times that of the high-temperature yield strength of the magnesium alloy billet 1. Therefore, during the rolling process, the main change is the reduction in the thickness of the magnesium alloy billet 1.

[0068] During the four-pass rolling process in the initial rolling stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate in the initial rolling stage is 23.1%-32.7%, meaning that the thickness of the magnesium alloy billet 1 is reduced by 23.1%-32.7% in the initial rolling stage. During this process, the edge of the magnesium alloy billet 1 in the width direction comes into contact with the wave-resistant flow-blocking zone 22 in the composite liner 2. Due to the high frictional resistance between the magnesium alloy billet 1 and the wave-resistant flow-blocking zone 22, the microchannel array structure in the wave-resistant flow-blocking zone 22 is in a non-completely filled state. The microchannel array structure in the wave-resistant flow-blocking zone 22 physically blocks the lateral expansion of the magnesium alloy billet 1, forcing the magnesium alloy billet 1 to expand in the rolling direction.

[0069] During the intermediate accumulation stage, as the accumulated strain increases, dynamic recrystallization and microstructure reconstruction become dominant in the magnesium alloy billet 1. During the five rolling passes of the intermediate accumulation stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass uses a low reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s for low-speed rolling. The microchannel array structure in the wave choke zone 22 causes severe shear deformation at the edge of the magnesium alloy billet 1 in the width direction, further promoting local recrystallization at the edge of the magnesium alloy billet 1 in the width direction. This achieves grain refinement, dynamic softening and homogenization of the microstructure at the edge of the magnesium alloy billet 1 in the width direction. The total reduction rate of the intermediate accumulation stage is 27.9%-39.1%, meaning that the thickness of the magnesium alloy billet 1 is reduced by 27.9%-39.1% during the intermediate accumulation stage.

[0070] During the five-pass rolling process in the later forming stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate in the later forming stage is 27.9%-39.1%, meaning that the thickness of the magnesium alloy billet 1 is reduced by 27.9%-39.1% in the later forming stage. After multiple passes of rolling in the initial rolling stage, the intermediate cumulative stage, and the later forming stage, the total reduction rate of the magnesium alloy billet 1 reaches 60%-70%. At the same time, the edge position of the magnesium alloy billet 1 in the width direction is constrained by the wave-blocking zone 22 of the composite liner 2.

[0071] In this embodiment, an AZ31B magnesium alloy rolled sheet with a length of 100mm, a width of 40mm, and a thickness of 5mm is used as the magnesium alloy billet 1 to be rolled. Taking low-speed rolling with a small reduction rate of 8% per pass and a rolling speed of 25mm / s as an example, after four passes in the initial rolling stage, the thickness of the magnesium alloy billet 1 is reduced from the original 5mm to approximately 3.58mm, that is, the total reduction rate in the initial rolling stage is approximately 28.4%, specifically: After the five rolling passes in the intermediate cumulative stage, the thickness of magnesium alloy billet 1 decreased from 3.58 mm to approximately 2.36 mm, meaning the total reduction rate in the intermediate cumulative stage was approximately 34%, specifically: After five rolling passes in the later forming stage, the thickness of magnesium alloy billet 1 decreased from 2.36 mm to approximately 1.56 mm, meaning the total reduction rate in the later forming stage was approximately 34%, specifically: After multiple rolling passes through the initial rolling stage, the intermediate accumulation stage, and the final forming stage, the thickness of the magnesium alloy billet 1 was reduced from the original 5 mm to a total of 1.56 mm, with a total reduction rate of approximately 69%. .

[0072] Based on the above embodiment, the mechanical flow obstruction effect of the wave obstruction zone 22 in the composite liner 2 transforms the "free transverse expansion" of the edge position in the width direction of the magnesium alloy billet 1 in conventional rolling into "controlled longitudinal extension," and transforms the tangential tensile stress that is prone to cracking at the edge into a triaxial compressive stress state that is conducive to forming. At the same time, the mechanical flow obstruction effect of the wave obstruction zone 22 induces dynamic recrystallization at the edge in the width direction of the magnesium alloy billet 1, which significantly suppresses the generation of edge cracks caused by excessive expansion of the magnesium alloy billet during rolling, and improves the yield and processing efficiency of magnesium alloy sheets.

[0073] A magnesium alloy sheet was prepared using a method in this embodiment that utilizes an edge-damping composite liner to suppress edge cracking during rolling. Performance tests were conducted on the magnesium alloy sheet with no macroscopic edge cracks prepared in this embodiment and on the original magnesium alloy billet 1. The performance tests included room temperature tensile mechanical properties and metallographic / microstructure testing. The test results are shown in Table 2.

[0074]

[0075] In this embodiment, AZ31B magnesium alloy rolled sheet is used as magnesium alloy billet 1 and is rolled by a multi-pass low-speed cumulative rolling process to obtain magnesium alloy sheet. The tensile strength of the magnesium alloy sheet is ≥270MPa, the yield strength is ≥190MPa, and the elongation is ≥6%. The microstructure of the magnesium alloy sheet is a fully dynamic recrystallized structure, and the average grain size of the magnesium alloy sheet is 3-10μm.

[0076] Example 2

[0077] The difference between this embodiment and Embodiment 1 is that:

[0078] The multi-pass cumulative rolling process is a low-speed-ratio multi-pass variable-parameter cumulative rolling process. This process decomposes the total deformation of the composite billet into multiple passes. Each pass uses a reduction rate of 5%-12% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes before the next pass. The thickness of the composite billet is gradually reduced. After the last rolling pass, a magnesium alloy sheet is obtained between two composite liners 2. The magnesium alloy sheet is then separated from the two composite liners 2 and air-cooled to room temperature to obtain a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process of micro-variable speed ratio multi-pass variable parameter cumulative rolling is divided into the initial rolling stage of the first to fourth passes, the intermediate cumulative stage of the fifth to ninth passes, and the late forming stage of the tenth to fourteenth passes.

[0079] It should be noted that in this embodiment, the same AZ31B magnesium alloy rolled sheet as in Example 1 is used as magnesium alloy billet 1, the heating temperature is set to 400℃, and the holding time is 40min. That is, the only difference between this embodiment and the multi-pass variable parameter cumulative rolling process with micro-speed ratio used in Example 1 is the multi-pass low-speed cumulative rolling process with small reduction used in Example 1. All other steps are the same as in Example 1.

[0080] During the four-pass rolling process in the initial rolling stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 10%-12% and a rolling speed of 30-36mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.09-1.1. The total reduction rate of the initial rolling stage is 34.4%-40.0%.

[0081] Specifically, in this embodiment, the single-pass reduction rate in the initial rolling stage is set to 11%, the rolling speed is controlled at 33 mm / s, and the micro-asynchronous rolling speed ratio between the upper and lower rolls is set to 1.1, that is, the rotational speed of the upper roll is greater than that of the lower roll, so that the flow velocity of the metal on the upper surface of the magnesium alloy billet 1 along the rolling direction is faster than that on the lower surface of the magnesium alloy billet 1 along the rolling direction; during the four-pass rolling process in the initial rolling stage, cross-shear strain is introduced by using the micro-asynchronous rolling speed of 1.1, and at the same time, the compound liner plates 2 on the upper and lower sides of the magnesium alloy billet 1 prevent the lateral widening of the magnesium alloy billet 1 in the width direction; in general, in the initial During the initial rolling stage, the edge of the magnesium alloy billet 1 in the width direction comes into contact with the wave-blocking zone 22 in the upper and lower composite liners 2. Due to the high frictional resistance between the magnesium alloy billet 1 and the composite liners 2, the microchannel array structure of the two composite liners 2 is in a non-fully filled state. The upper and lower rolls provide longitudinal shearing to the magnesium alloy billet 1 in the combined billet, and the wave-blocking zone 22 of the two composite liners 2 jointly provide transverse extrusion to the magnesium alloy billet 1. Through the synergistic effect of longitudinal shearing and transverse extrusion, the coarse original grains in the magnesium alloy billet 1 are destroyed, and the initiation of macroscopic cracks in the width direction edge of the magnesium alloy billet 1 is suppressed in the initial stage of rolling.

[0082] During the five-pass rolling process in the mid-term cumulative stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 7%-9% and a rolling speed of 24-30mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.07-1.09. The total reduction rate in the mid-term cumulative stage is 30.4%-37.6%. In this stage, the internal structure of magnesium alloy billet 1 is dominated by dynamic recrystallization and microstructure reconstruction.

[0083] Specifically, in this embodiment, the single-pass reduction rate in the intermediate accumulation stage is set to 8%, the rolling speed is controlled at 28 mm / s, and the micro-asynchronous rolling speed ratio between the upper and lower rolls is set to 1.08. The single-pass reduction rate and speed ratio in the initial rolling stage are steadily reduced so that the rolling of the composite billet enters the intermediate accumulation stage. The steadily reduced micro-asynchronous speed ratio continuously causes the base surface texture of the magnesium alloy billet 1 to deflect in the thickness direction. In general, during the five-pass rolling process in the intermediate accumulation stage, the wave-blocking zones 22 of the two composite liners 2 jointly apply periodic alternating shear strain to the edge of the magnesium alloy billet 1 in the width direction. Under the thermal activation at 400°C, comprehensive and uniform dynamic recrystallization is induced in the edge and center of the magnesium alloy billet 1, realizing the dynamic softening of the magnesium alloy billet 1 structure.

[0084] During the five-pass rolling process in the later forming stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 5%-6% and a rolling speed of 18-24mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.05-1.06. The total reduction rate of the later forming stage is 22.6%-26.6%.

[0085] Specifically, in this embodiment, the single-pass reduction rate in the later forming stage is set to 5%, the rolling speed is controlled at 20 mm / s, and the micro-asynchronous rolling speed ratio between the upper and lower rolls is set to 1.05. By using the micro-asynchronous rolling speed ratio of 1.05 in conjunction with the low speed and small reduction rate, and by using the compound liner 2 to continuously laterally adhere and constrain the magnesium alloy billet 1, not only can the residual base texture on the magnesium alloy billet 1 be further weakened, but also the squeezing and micro-shearing kneading effect of the wave flow blocking zone 22 on the magnesium alloy billet 1 can effectively close and heal the internal micropores of the magnesium alloy billet 1 that may be induced in the early large deformation, and completely release the residual stress. Ultimately, this ensures that the rolled magnesium alloy sheet achieves the set total reduction rate while effectively suppressing the generation of edge crack defects in the magnesium alloy sheet, and realizing high integrity of the edge and surface flatness control of the magnesium alloy sheet.

[0086] Through multiple rolling passes in the initial rolling stage, the intermediate accumulation stage, and the late forming stage, the total reduction rate of the composite billet reaches 60%-75%.

[0087] Specifically, in this embodiment, after rolling with a reduction rate of 11% per pass in the initial rolling stage, 8% per pass in the intermediate cumulative stage, and 5% per pass in the later forming stage, the final magnesium alloy sheet has an actual total reduction rate of 68% compared to the initial magnesium alloy billet 1.

[0088] In the specific implementation process, the scientific rationality of the single-pass parameter range and the final total reduction rate target of the fourteen-pass micro-speed ratio multi-pass variable parameter cumulative rolling process in this embodiment can be verified by the multi-pass cumulative deformation formula.

[0089] The magnesium alloy billet 1 selected in this embodiment is the same material as the magnesium alloy billet 1 selected in Embodiment 1, both being AZ31B magnesium alloy rolled sheet. To clearly illustrate the deformation accumulation process at each stage, the initial thickness of the magnesium alloy billet 1 is set to H0; after the initial rolling stage, the thickness of the magnesium alloy billet 1 is set to H1; after the intermediate accumulation stage, the thickness of the magnesium alloy billet 1 is set to H2; after the final forming stage, a magnesium alloy sheet is obtained sandwiched between two compound liner plates 2, and the thickness of the magnesium alloy sheet is set to H3; the final total reduction rate is set to R, the single-pass reduction rate in the initial rolling stage is set to r1, and the number of passes is set to n1; the single-pass reduction rate in the intermediate accumulation stage is set to r2, and the number of passes is set to n2; and the single-pass reduction rate in the final forming stage is set to r3, and the number of passes is set to n3.

[0090] Based on the principle of constant plastic volume in metals and the characteristics of multi-pass rolling, the specific calculation formulas for the theoretical stage reduction rate and total reduction rate at each stage are derived as follows:

[0091] (1) Stage reduction ratio R1 in the initial rolling stage:

[0092] In this stage, the thickness of magnesium alloy billet 1 is reduced from H0 to H1, and the formula for calculating the cumulative stage reduction rate R1 in this stage is:

[0093] (Formula 3)

[0094] (Formula 4)

[0095] In this embodiment, an AZ31B magnesium alloy rolled sheet with a length of 100mm, a width of 40mm, and a thickness of 5mm is used as the magnesium alloy billet 1 to be rolled. In the initial rolling stage, the reduction rate is 11% per pass. After four passes of rolling in the initial rolling stage, the thickness of the magnesium alloy billet 1 is reduced from 5mm to about 3.14mm. The stage reduction rate in the initial rolling stage is about 37.2%.

[0096] (2) Phase reduction rate R2 in the intermediate cumulative phase:

[0097] In the intermediate cumulative stage, before rolling, the initial thickness of magnesium alloy billet 1 is H1. In this stage, the thickness of magnesium alloy billet 1 is further reduced from H1 to H2. The formula for calculating the cumulative stage reduction rate R2 in this stage is:

[0098] (Formula 5)

[0099] (Formula 6)

[0100] In this embodiment, the reduction rate per pass in the intermediate cumulative stage is 8%. Before rolling, the initial thickness of the magnesium alloy billet 1 is about 3.14 mm. After five passes of rolling in the intermediate cumulative stage, the thickness of the magnesium alloy billet 1 is reduced from 3.14 mm to about 2.07 mm. The stage reduction rate in the intermediate cumulative stage is about 34%.

[0101] (3) Stage reduction ratio R3 in the later forming stage:

[0102] In the later forming stage, before rolling, the initial thickness of magnesium alloy billet 1 is H2. In this stage, the thickness of magnesium alloy billet 1 is eventually reduced from H2 to H3. The formula for calculating the cumulative stage reduction rate R3 in this stage is:

[0103] (Formula 7)

[0104] (Formula 8)

[0105] In this embodiment, the reduction rate per pass in the later forming stage is 5%. Before rolling, the initial thickness of the magnesium alloy billet 1 is about 2.07 mm. After five rolling passes in the later forming stage, the thickness of the magnesium alloy billet 1 is reduced from 2.07 mm to about 1.6 mm, resulting in a magnesium alloy sheet with a thickness of about 1.6 mm. The stage reduction rate in the later forming stage is about 23%.

[0106] (4) The total reduction R of magnesium alloy billet 1 after fourteen rolling passes:

[0107] Combining the three stages of continuous rolling deformation mentioned above, the total reduction rate R of magnesium alloy billet 1 from the initial thickness H0 to the final thickness H3 of the finished magnesium alloy sheet can be accurately expressed as a product of the single-pass parameters of each stage:

[0108] (Formula 9)

[0109] (Formula 10)

[0110] Furthermore, the total reduction rate R also satisfies the following coupling geometric relationship with the stage reduction rate R1 in the initial rolling stage, the stage reduction rate R2 in the intermediate cumulative stage, and the stage reduction rate R3 in the later forming stage:

[0111] (Formula 11)

[0112] After fourteen rolling passes in this embodiment, the magnesium alloy billet 1 is gradually reduced from an initial thickness of 5 mm to a thickness of 1.6 mm to form a magnesium alloy sheet. The total reduction rate of the magnesium alloy billet 1 rolled by the micro-speed ratio multi-pass variable parameter cumulative rolling process in this embodiment is 68%.

[0113] A magnesium alloy sheet was produced using a method described in this embodiment that utilizes an edge-damping composite liner to suppress edge cracking during the rolling process. In this embodiment, AZ31B magnesium alloy rolled sheet was used as magnesium alloy billet 1 and rolled using a multi-pass variable parameter cumulative rolling process with a micro-speed ratio. Performance tests were conducted on the magnesium alloy sheet with no macroscopic edge cracks produced in this embodiment and the original magnesium alloy billet 1. The test results are shown in Table 3.

[0114]

[0115] The magnesium alloy sheet has a tensile strength ≥270MPa, a yield strength ≥190MPa, and an elongation ≥6%; and the microstructure of the magnesium alloy sheet is a fully dynamic recrystallized structure with an average grain size of 3-10μm.

[0116] It is particularly important to note that the total deformation of the magnesium alloy billet 1 in this application is strictly limited and decomposed into fourteen rolling passes. This is based on the optimal engineering parameters derived from the thermodynamic and kinetic evolution of magnesium alloys, rather than a design that can be arbitrarily increased or decreased by those skilled in the art based on conventional experience. Through the precise division of fourteen passes, this application has found a perfect balance between the accumulation rate of deformation distortion energy and the grain growth tendency caused by high-temperature exposure. Under the premise of ensuring that the plate does not crack at the edge, it preserves the fine grain structure to the maximum extent. If the number of rolling passes is reduced, the single-pass reduction rate will inevitably surge, exceeding the inherent plastic limit of the magnesium alloy billet 1, causing the stress to be unable to be released in time through dynamic recrystallization, thereby inducing severe macroscopic edge cracks. If the number of passes is blindly increased, the single-pass reduction will be too small in the later stages, which will not provide the critical distortion energy required for the magnesium alloy billet 1 to break through the dynamic recrystallization nucleation barrier. More fatally, too many rolling passes will result in the magnesium alloy plate experiencing too long an intermediate annealing time, which is very likely to cause secondary coarsening of the newly formed fine grains inside the magnesium alloy plate and severe surface oxidation, completely destroying the fine grain strengthening effect.

[0117] Furthermore, based on the multi-pass low-reduction low-speed cumulative rolling process and the micro-variable speed ratio multi-pass variable parameter cumulative rolling process proposed in Embodiments 1 and 2 of this application, after each rolling pass from the first to the thirteenth pass of these two rolling processes, an intermediate annealing treatment of 360-420℃ for 10 minutes is performed before the next rolling pass. This provides sufficient thermal activation time for the magnesium alloy billet 1, thereby inducing dynamic recrystallization inside the magnesium alloy billet 1 and effectively counteracting work hardening. This continues until the fourteenth rolling pass, at which point a magnesium alloy sheet is obtained sandwiched between two composite liner plates 2. This magnesium alloy sheet is then placed between the two composite liner plates... The liner plate 2 is separated, and the magnesium alloy sheet is placed in the air to cool naturally to room temperature. Through the intermediate annealing process after each rolling pass, the residual "cold work hardening" of the magnesium alloy billet 1 is avoided, ensuring that subsequent passes are still mainly dynamic recrystallization, rather than a mixed mode of "cold deformation and hot deformation". At the same time, the intermediate annealing process after each rolling pass promotes the static recrystallization of the magnesium alloy billet 1, so that the deformed structure inside the magnesium alloy billet 1 can be further refined through static recrystallization. By adjusting the annealing temperature and annealing time, excessive grain growth in the rolled magnesium alloy sheet is suppressed, and the yield strength of the rolled magnesium alloy sheet is improved.

[0118] 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 suppressing edge cracking during the rolling of magnesium alloy sheets using edge-damping composite liners, characterized in that, Includes the following steps: S1: Select the magnesium alloy billet to be rolled and perform surface pretreatment to ensure the consistency of the initial state of the magnesium alloy billet; S2: Prepare two composite liners. The high-temperature yield strength of the composite liners is higher than that of the magnesium alloy billet to be rolled. Each composite liner has fixed L-shaped lugs symmetrically arranged at both ends. One surface of each composite liner is a liner clamping surface. The liner clamping surface is divided into a smooth rheological zone and a wave-shaped flow-blocking zone along its width direction. The smooth rheological zone is located in the middle of the liner clamping surface, and the wave-shaped flow-blocking zone is located on both sides of the smooth rheological zone. The wave-shaped flow-blocking zone has a wave-shaped texture. Among them, the wave-shaped flow-blocking zone of any one of the two composite liners has several upward-protruding wave-shaped textures, and the wave-shaped flow-blocking zone of the other composite liner has several downward-recessed wave-shaped textures. S3: A composite billet with a sandwich structure is formed by clamping a magnesium alloy billet between two composite liners, with both sides of the magnesium alloy billet in contact with the clamping surfaces of the two composite liners; the position of the magnesium alloy billet is adjusted so that its upper and lower sides correspond to the smooth rheological zones of the two composite liners, and the edge of the magnesium alloy billet in the width direction is in contact with the corrugated flow-blocking zone of the two composite liners; high-temperature resistant metal wire is wrapped around the fixed L-shaped lugs at both ends of the two composite liners to bind the composite billet; S4: Send the bundled composite billet into the heating furnace and heat it to 360-420℃ for overall preheating, and keep it at that temperature for 30-50 minutes; S5: The preheated composite billet is rolled using a multi-pass cumulative rolling process to obtain a magnesium alloy sheet sandwiched between two composite liners; during the rolling process, the wave-shaped flow-blocking zone of the two composite liners is used to apply lateral constraints to the edges of the magnesium alloy billet in the width direction. S6: After rolling, the magnesium alloy sheet is separated from the two composite backing plates to obtain a finished magnesium alloy sheet with no macroscopic cracks at the edges.

2. The method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 1, characterized in that, In step S1, the magnesium alloy billet belongs to the Mg-Al-Zn-Mn alloy system, and its chemical composition by mass percentage is as follows: Includes: Al: 2.4~3.6%, Zn: 0.5~1.5%, Mn: 0.05~1.0%, with the balance being Mg and impurities; The magnesium alloy billet to be rolled is pretreated by sanding with sandpaper and cleaning with anhydrous ethanol.

3. The method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 2, characterized in that, In step S2, the composite liner is made of stainless steel or hot work die steel, and the high temperature yield strength of the composite liner is more than three times the high temperature yield strength of the magnesium alloy billet to be rolled.

4. The method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 3, characterized in that, In the complex liner, the width of each wave-shaped flow-blocking zone accounts for 20%-30% of the total width of the complex liner. Several wave-shaped textures in the wave-shaped flow-blocking zone together form a microchannel array structure. The extension direction of each wave-shaped texture in the microchannel array structure is perpendicular to the rolling direction of the magnesium alloy billet. The cross-sectional profile of the microchannel array structure in the width direction is a continuous sine wave, and the corrugation height of the microchannel array structure is 0.5-1.0 mm. The corrugation height refers to the vertical distance between the highest point of the corrugation ridge or the lowest point of the corrugation groove and the reference datum plane. Taking the liner clamping surface as the reference datum plane, the distance between the peaks of two adjacent corrugation ridges is 0.5-1.0 mm. The sine function relationship of the waveform curve of each wave-shaped texture in the microchannel array structure is: ； In this equation, the origin O is taken as the vertex of one corner of the complex liner. In the equation, x is the x-axis extending along the short side of the complex liner, perpendicular to the rolling direction, and the unit is mm; y is the y-axis extending along the long side of the complex liner, in the same direction as the rolling direction, and the unit is mm; a is the wave frequency coefficient of each wavy texture in the microchannel array structure, ranging from 2 to 10, and the unit is dimensionless; A is the amplitude coefficient of each wavy texture in the microchannel array structure, and the unit is mm.

5. A method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 4, characterized in that, In step S3, the width of the magnesium alloy billet to be rolled Width of the smooth rheological region in the complex liner The same applies to the total width of the composite liner. The width of the smooth rheological region With the width of the two wave-blocking zones The total width of the composite lining plate was jointly determined. .

6. A method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 5, characterized in that, Multi-pass cumulative rolling is a multi-pass low-reduction, low-speed cumulative rolling process. In this process, the total deformation of the composite billet is decomposed into multiple passes. Each pass uses a low reduction rate of 6.3%-9.4% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes before the next pass. The thickness of the composite billet is gradually reduced. After the last rolling pass, a magnesium alloy sheet is obtained sandwiched between two composite liners. The magnesium alloy sheet is then separated from the two composite liners and air-cooled to room temperature to finally obtain a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process is divided into the following stages: the initial rolling stage from the first to the fourth pass, the intermediate accumulation stage from the fifth to the ninth pass, and the late forming stage from the tenth to the fourteenth pass.

7. A method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner as described in claim 6, characterized in that, During the four-pass rolling process in the initial rolling stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the initial rolling stage is 23.1%-32.7%. During the five-pass rolling process in the intermediate cumulative stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the intermediate cumulative stage is 27.9%-39.1%. During the five-pass rolling process in the later forming stage, the composite billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 6.3%-9.4% and a rolling speed of 18-36mm / s. The total reduction rate of the later forming stage is 27.9%-39.1%. Through multiple rolling passes in the initial rolling stage, the intermediate accumulation stage, and the late forming stage, the total reduction rate of the composite billet reaches 60%-75%.

8. A method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner according to claim 5, characterized in that, The multi-pass cumulative rolling process is a low-speed-ratio multi-pass variable-parameter cumulative rolling process. This process decomposes the total deformation of the composite billet into multiple rolling passes. Each pass uses a reduction rate of 5%-12% and a rolling speed of 18-36 mm / s. After each pass, the composite billet undergoes intermediate annealing at 360-420℃ for 10 minutes before the next rolling pass. The thickness of the composite billet is gradually reduced. After the last rolling pass, a magnesium alloy sheet is obtained sandwiched between two composite liners. The magnesium alloy sheet is then separated from the two composite liners and air-cooled to room temperature, finally yielding a finished magnesium alloy sheet with no macroscopic cracks at the edges. The multi-pass rolling process in the micro-speed ratio multi-pass variable parameter cumulative rolling process is divided into: the initial rolling stage of the first to fourth passes, the intermediate cumulative stage of the fifth to ninth passes, and the late forming stage of the tenth to fourteenth passes.

9. A method for suppressing edge cracking during rolling of magnesium alloy sheets using an edge-blocking composite liner as described in claim 8, characterized in that, During the four-pass rolling process in the initial rolling stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass uses a low-speed rolling with a small reduction rate of 10%-12% and a rolling speed of 30-36mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.09-1.

1. The total reduction rate of the initial rolling stage is 34.4%-40.0%. During the five-pass rolling process in the intermediate cumulative stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass is rolled at a low speed with a small reduction rate of 7%-9% and a rolling speed of 24-30mm / s. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in the rolling is 1.07-1.

09. The total reduction rate in the intermediate cumulative stage is 30.4%-37.6%. During the five-pass rolling process in the later forming stage, the combined billet is in a high-temperature environment of 360-420℃. Each pass uses a small reduction rate of 5%-6% and a rolling speed of 18-24mm / s for low-speed rolling. The micro-asynchronous rolling speed ratio between the upper and lower rolls used in rolling is 1.05-1.

06. The total reduction rate of the later forming stage is 22.6%-26.6%. Through multiple rolling passes in the initial rolling stage, the intermediate accumulation stage, and the late forming stage, the total reduction rate of the composite billet reaches 60%-75%.

10. A magnesium alloy sheet, characterized in that, The magnesium alloy sheet is manufactured using any one of the methods described in claims 1-9 for suppressing edge cracking during rolling with an edge-blocking composite liner. The magnesium alloy sheet has a tensile strength ≥270MPa, a yield strength ≥190MPa, and an elongation ≥6%. The microstructure of the magnesium alloy sheet is a fully dynamic recrystallized structure, and the average grain size of the magnesium alloy sheet is 3-10μm.

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