Preparation method of magnesium alloy plate

Abstract

The invention belongs to the technical field of metal processing, and particularly relates to a preparation method of a magnesium alloy plate which comprises a first rare earth magnesium alloy layer, a magnesium-aluminum-zinc alloy layer and a second rare earth magnesium alloy layer which are sequentially stacked. The preparation method comprises the following steps that a first rare earth magnesium alloy block, a magnesium-aluminum-zinc alloy block and a second rare earth magnesium alloy block are sequentially stacked, rolled and annealed after being extruded, the magnesium alloy plate is prepared, and the rolling direction in the rolling process is perpendicular to the extrusion direction in the extrusion process. According to the method, in the extrusion process, the plate is in a three-dimensional stress state, plastic deformation and solid welding are facilitated, after extrusion forming, rolling is conducted, the rolling direction in the rolling process is controlled to be perpendicular to the extrusion direction in the extrusion process, the texture strength can be weakened, anisotropy can be reduced, and then the forming performance of the magnesium alloy plate is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal processing, and particularly relates to a method for preparing a magnesium alloy plate. Background Art

[0002] Magnesium is the lightest metal in engineering applications, but the mechanical properties and corrosion resistance of pure magnesium are relatively low. In the existing technology, the mechanical properties and corrosion resistance of magnesium are usually improved by adding a certain amount of alloying elements. Magnesium alloys have the advantages of low density, high strength, good rigidity, strong toughness, strong shock absorption, strong electromagnetic shielding ability, good castability, machinability, thermal conductivity, damping, and easy recycling, making them an ideal material to replace aluminum alloys, steel, and engineering plastics. In recent years, with the increasing awareness of energy conservation and environmental protection, the use of magnesium alloys has continued to expand, and they are widely used in aviation, aerospace, national defense, automobiles, communications electronics, computers, home appliances, power tools, medical equipment, sports equipment, leisure products and other fields.

[0003] However, magnesium alloys have a hexagonal close-packed (HCP) crystal structure, which results in an insufficient number of slip / twin systems during plastic deformation at room temperature. Furthermore, due to the low symmetry of the HCP crystal structure and the large differences in critical resolved shear stress (CRSS) values ​​between slip / twin systems, which span several orders of magnitude, it is difficult for magnesium alloys to initiate slip at room temperature, resulting in poor plasticity.

[0004] Research has shown that adding rare earth elements can effectively improve the formability of magnesium alloy sheets, but rare earth elements are relatively expensive. Furthermore, during secondary forming, magnesium alloy sheets are subjected to compressive stress on the inside and tensile stress on the outside. The different stress conditions inside and outside the sheet make it more susceptible to cracking and failure on the outside during deformation. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a magnesium alloy sheet to improve the forming performance of the magnesium alloy sheet.

[0006] To achieve the above solution, the technical solution of the present invention is as follows: The present application provides a method for preparing a magnesium alloy plate, wherein the magnesium alloy plate comprises a first rare earth magnesium alloy layer, a magnesium-aluminum-zinc alloy layer, and a second rare earth magnesium alloy layer stacked in sequence. The method for preparing the magnesium alloy plate comprises the following steps: The first rare earth magnesium alloy block, the magnesium aluminum zinc alloy block and the second rare earth magnesium alloy block are stacked in sequence, extruded and then rolled, and annealed to obtain the magnesium alloy sheet, wherein the rolling direction during the rolling process is perpendicular to the extrusion direction during the extrusion process.

[0007] In this application, during the extrusion process, the plate is in a triaxial stress state, which is conducive to plastic deformation and solid-state welding. After extrusion forming, it is rolled, and the rolling direction during the rolling process is controlled to be perpendicular to the extrusion direction during the extrusion process, which can weaken the texture strength and reduce anisotropy, thereby improving the forming performance of the magnesium alloy plate.

[0008] In the present application, the first rare earth magnesium alloy layer and the second rare earth magnesium alloy layer are made of the same material.

[0009] Optionally, the rare earth element contained in the first rare earth magnesium alloy block or the second rare earth magnesium alloy block is selected from at least one of Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc.

[0010] In the present application, rare earth elements such as Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc can form rare earth texture by inducing random orientation of dynamically recrystallized grains, reduce anisotropy, and improve the formability of magnesium alloy sheets.

[0011] In the present application, the mass percentage of the rare earth element in the first rare earth magnesium alloy block or the second rare earth magnesium alloy block is 0.5wt%-1.5wt%.

[0012] Rare earth elements can refine the casting structure of magnesium alloys and hinder grain growth. In this application, if the mass percentage of rare earth elements is lower than 0.5wt%, it will lead to grain coarsening, reduced grain boundaries, weakened resistance to dislocation movement and deformation, and negatively affect the formability of magnesium alloy sheets; if the mass percentage of rare earth elements is higher than 1.5wt%, it will lead to increased viscosity and reduced fluidity of the magnesium alloy melt, which will adversely affect the formability of the magnesium alloy sheet.

[0013] In the present application, in the magnesium-aluminum-zinc alloy block, the mass percentage of aluminum element is 2.5wt%-3.5wt%, and the mass percentage of zinc element is 0.6wt%-1.4wt%.

[0014] Optionally, the extrusion temperature is 350-400°C, preferably 360-400°C.

[0015] In this application, if the extrusion temperature is lower than 350°C, the diffusion ability of metal atoms is weak, dislocation movement is hindered, deformation resistance is increased, and extrusion forming is difficult; if the extrusion temperature is higher than 400°C, the diffusion ability of atoms inside the metal is enhanced, the grain boundary migration speed is accelerated, adjacent grains are quickly merged to form coarse grains, the grains are coarsened, and the forming performance of the magnesium alloy sheet is deteriorated.

[0016] Optionally, the extrusion speed is 0.2-0.5 mm / s.

[0017] In this application, if the extrusion speed is less than 0.2 mm / s, the magnesium alloy stays in the mold cavity for too long, and the surface metal atoms cool and shrink rapidly due to contact with the mold, while the internal metal atoms continue to flow in a high temperature state, forming an internal and external shrinkage difference to produce a bending moment. After extrusion, the plate is prone to bending and cannot be subsequently rolled; if the extrusion speed is greater than 0.5 mm / s, the friction between the mold and the magnesium alloy contact surface is intensified, the local heating rate is too fast, exceeding the recrystallization temperature of the magnesium alloy, forming a softening layer, and the surface of the plate is prone to scratches after extrusion.

[0018] Optionally, during the extrusion process, the extrusion ratio is 10-12, preferably 10-11.

[0019] In this application, if the extrusion ratio is less than 10, the basal texture orientation cannot be effectively dispersed, the anisotropy is aggravated, and the formability of the magnesium alloy sheet is deteriorated; if the extrusion ratio is greater than 12, the texture will be too concentrated, the anisotropy will be aggravated, and the formability of the magnesium alloy sheet will be deteriorated.

[0020] Optionally, the rolling temperature is 355-365°C, preferably 358-365°C.

[0021] In this application, if the rolling temperature is lower than 355°C, the diffusion ability of metal atoms will be inhibited, the dislocation slip resistance will be increased, the elongation of the magnesium alloy will be reduced, and brittle fracture will be easily caused when the local deformation exceeds the critical value; if the rolling temperature is higher than 365°C, the migration ability of metal atoms will be increased, the grain boundary migration will be accelerated, and the austenite grains will grow at an exponential rate, resulting in obvious coarsening of the grains.

[0022] Optionally, the rolling passes are 2-4 passes.

[0023] In this application, if the number of rolling passes is less than 2, the base surface texture will be strengthened, the anisotropy will be aggravated, and the formability of the magnesium alloy sheet will be deteriorated; if the number of rolling passes is greater than 4, the recrystallized grain size will be too small, causing a tendency to brittle fracture. At the same time, the residual shear band will reduce the formability of the magnesium alloy sheet.

[0024] Optionally, during the rolling process, the reduction in a single pass is 15%-20%.

[0025] In this application, during the rolling process, if the single-pass reduction is less than 15%, the deformation capacity of the magnesium alloy is insufficient, the dynamic recrystallization process is hindered, resulting in uneven grain size distribution, local stress concentration and uneven deformation during the forming process, and the resulting finished product is prone to wrinkles, cracks, etc.; during the rolling process, if the single-pass reduction is greater than 20%, the grain refinement effect will be limited due to the excessively fast strain rate, the local grain size difference will be significant, the basal texture will be strengthened, the non-uniform deformation will be aggravated, and the forming performance of the magnesium alloy sheet will be reduced.

[0026] Optionally, the annealing includes: keeping the temperature at 370-400° C. for 20-40 minutes.

[0027] In this application, if the annealing temperature is lower than 370°C, the basal texture formed by rolling cannot be effectively weakened, resulting in difficulty in activating the non-basal slip system at room temperature, and the forming performance of the magnesium alloy sheet cannot be effectively improved; if the annealing temperature is higher than 400°C, the dynamic recrystallization grains grow too fast, the grain size distribution is uneven, local stress concentration and uneven deformation are likely to occur during the forming process, and the finished product is prone to wrinkles, cracks, etc.

[0028] In the present application, a pre-annealing step is also included between adjacent rolling passes.

[0029] In the present application, by adding a pre-annealing step between adjacent rolling passes, the base surface texture strength can be reduced, the non-slip system can be activated, the anisotropy can be reduced, and the formability of the magnesium alloy sheet can be improved.

[0030] In the present application, the pre-annealing temperature is 370-400° C., and the pre-annealing time is 10-20 minutes.

[0031] In this application, if the pre-annealing temperature is lower than 370°C, the basal texture formed by rolling cannot be effectively weakened, resulting in difficulty in activating the non-basal slip system at room temperature and inability to improve the forming performance of the magnesium alloy sheet; if the pre-annealing temperature is higher than 400°C, the dynamic recrystallization grains grow too fast, the grain size distribution is uneven, local stress concentration and uneven deformation occur during the forming process, and the finished product is prone to wrinkles, cracks, etc.

[0032] Optionally, before the stacking, the method for preparing the magnesium alloy plate further comprises the following step: performing homogenization heat treatment on the first rare earth magnesium alloy block, the magnesium-aluminum-zinc alloy block, and the second rare earth magnesium alloy block, respectively.

[0033] In the present application, by adding a homogenization heat treatment step before stacking, stress concentration points can be reduced, a homogenized matrix can be provided for subsequent extrusion, and the forming performance of the magnesium alloy sheet can be further improved.

[0034] In the present application, the temperature of the homogenization heat treatment is 450-550° C., and the duration of the homogenization heat treatment is 10-15 hours.

[0035] In this application, if the temperature of the homogenization heat treatment is lower than 450°C, it will lead to insufficient diffusion of alloy elements, reduce the homogeneity of the structure, and be detrimental to the improvement of the formability of the magnesium alloy sheet; if the temperature of the homogenization heat treatment is higher than 550°C, it will lead to excessive dynamic recrystallization of the magnesium alloy, increase the recrystallized grain size, produce local coarse-grained areas, induce stress concentration, and be detrimental to the improvement of the formability of the magnesium alloy sheet.

[0036] In this application, the magnesium alloy sheet can be used in automobiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the stacking order in this application; Figure 2 This is an SEM image of the magnesium alloy plate obtained in Example 1. The upper and lower light-colored areas are Mg-Gd layers, and the middle area is the AZ31 layer. Figure 3 : is the crystal phase diagram of the magnesium alloy plate obtained in Example 1; Figure 4 : is the crystal phase diagram of the magnesium alloy plate prepared in Comparative Example 3; Figure 5 This is a physical picture of the plate after extrusion in comparative example 4; Figure 6 This is a physical picture of the plate after extrusion in comparative example 5; Figure 7 : is the crystal phase diagram of the magnesium alloy plate prepared in Comparative Example 6; Figure 8 This is a physical picture of the magnesium alloy plate prepared in Comparative Example 7; Figure 9 Graph showing the texture distribution characteristics of the magnesium alloy plates prepared in Example 1 and Comparative Examples 8-9. DETAILED DESCRIPTION

[0038] The present invention is further illustrated below through specific examples. However, it should be noted that the specific material ratios, process conditions and results described in the embodiments of the present invention are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention should be included in the scope of protection of the present invention.

[0039] One embodiment of the present application provides a method for preparing a magnesium alloy plate, the magnesium alloy plate comprising a first rare earth magnesium alloy layer, a magnesium-aluminum-zinc alloy layer, and a second rare earth magnesium alloy layer stacked in sequence, the method comprising the following steps: homogenizing the first rare earth magnesium alloy block, the magnesium aluminum zinc alloy block, and the second rare earth magnesium alloy block at 450-550° C. for 10-15 hours; The first rare earth magnesium alloy block, the magnesium aluminum zinc alloy block and the second rare earth magnesium alloy block after homogenization heat treatment are stacked in sequence, and then rolled after extrusion and annealed to obtain a magnesium alloy sheet, wherein the rolling direction during the rolling process is perpendicular to the extrusion direction during the extrusion process; The rare earth element contained in the first rare earth magnesium alloy block or the second rare earth magnesium alloy block is at least one selected from the group consisting of Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc; The extrusion temperature is 350-400°C, the extrusion speed is 0.2-0.5 mm / s, and the extrusion ratio is 10-12; The rolling temperature is 355-365℃, the rolling passes are 2-4, and the reduction in a single pass is 15%-20%; Annealing includes: keeping the temperature at 370-400°C for 20-40 minutes.

[0040] Between adjacent rolling passes, a pre-annealing step is also included. The pre-annealing temperature is 370-400°C and the pre-annealing time is 10-20 minutes.

[0041] The present invention is described in detail below by way of specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, and those skilled in the art can make selections within a suitable range through the description herein, and are not to be limited to the specific numerical values ​​exemplified below.

[0042] Example 1 A method for preparing a magnesium alloy plate, comprising the following specific steps: S1. Melting: Melt the Mg-30Gd alloy (the mass percentage of the Gd element in the alloy is 30wt%) and pure magnesium separately. The specific steps are as follows: 1) Pure magnesium (99.99 wt% purity) and the master alloy Mg-30Gd alloy were cut into blocks using a saw. The master alloy surface was then polished with an angle grinder to remove surface oxide films and impurities. Considering a 10% burnout of alloying elements during the smelting process, the weight of pure magnesium and master alloy required to cast a 3 kg ingot was calculated to obtain a Mg-1Gd ingot containing 1 wt% Gd. After preparing the required materials, a boron nitride-alcohol suspension was applied to the inner walls of the crucible and the casting mold to prevent impurities on the inner walls from mixing into the magnesium alloy ingot. 2) Preheating: Place the casting mold and crucible in a 300°C heat treatment furnace for preheating, and set the resistance furnace temperature to 500°C. After the resistance furnace temperature rises to 500°C, disconnect the resistance furnace power supply. 3) Melting: Place a pre-weighed pure magnesium-aluminum-zinc alloy block in the crucible, then clamp the crucible into the resistance furnace, turn the resistance furnace power back on, set the temperature to 750°C, and simultaneously introduce a shielding gas (composed of CO2 and SF6 in a ratio of 99:1 by volume) through the shielding gas inlet pipe to begin melting the pure magnesium-aluminum-zinc alloy block. After the pure magnesium-aluminum-zinc alloy block is melted, disconnect the power supply again in the same manner and add the pre-weighed master alloy Mg-30Gd master alloy block to melt the Mg-30Gd master alloy block. 4) Standing: After the master alloy is melted, place the magnesium alloy melt in a resistance furnace and keep it still for 15 minutes, then remove impurities on the melt surface; 5) Casting: Pour the magnesium alloy melt into a preheated casting mold under the protection of a protective gas (composed of CO2 and SF6 in a volume ratio of 99:1). After the melt cools and solidifies, take out a magnesium alloy ingot (i.e., Mg-1Gd alloy ingot) with a diameter of 85 mm; S2. Homogenization heat treatment: The smelting magnesium alloy ingot and the commercially available AZ31 magnesium alloy ingot (ie, magnesium-aluminum-zinc alloy ingot) were placed in a 500°C heating furnace for 12 hours, then removed and rapidly cooled in cold water to complete the homogenization heat treatment; S3 Extrusion: The magnesium alloy ingot after homogenization heat treatment was cut into 50mm×10mm×30mm blocks using a wire cutter. The AZ31 magnesium alloy ingot was cut into 50mm×30mm×30mm blocks using a wire cutter. The surface oxide film and impurities of the cut blocks were polished off with an angle grinder, placed in a preheated extrusion die, and extrusion was started. The cut AZ31 magnesium alloy blocks and magnesium alloy ingot blocks are stacked in the order of magnesium alloy ingot block, AZ31 magnesium alloy block, magnesium alloy ingot block (eg Figure 1 As shown, the upper and lower layers are magnesium alloy ingots, and the middle layer is AZ31 magnesium alloy blocks. The extrusion is performed vertically at 380°C using a 200-ton hydraulic press with an extrusion speed of 0.3 mm / s and an extrusion ratio of 11, resulting in an extruded plate with a width of 45 mm and a thickness of 3 mm. S4. Rolling: The extruded sheet was cut into 100 mm long segments and hot rolled on a two-roll mill at 360°C in three passes, with the rolling direction perpendicular to the extrusion direction. The reduction per pass was 15%. Between passes, the sheet was pre-annealed in a 380°C furnace for 15 minutes to obtain a 1 mm thick sheet. S5. Annealing: The obtained 1 mm thick sheet was placed in a heating furnace at 380°C for 30 minutes and then air-cooled to room temperature to obtain a magnesium alloy sheet.

[0043] The magnesium alloy sheet obtained in this embodiment was subjected to electron microscope scanning (i.e. SEM scanning) to observe the interface delamination state of the magnesium alloy sheet. The results are as follows: Figure 2 shown.

[0044] Depend on Figure 2 It can be seen that the interface bonding state of the magnesium alloy plate prepared in the present application is good.

[0045] The crystal phase of the magnesium alloy sheet prepared in this embodiment was observed using an optical microscope (OM). Figure 3 shown.

[0046] Depend on Figure 3 It can be seen that the magnesium alloy sheet produced in the present application has a low dislocation density, basically achieves complete recrystallization, forms a good metallurgical bonding interface between the composite layers, and thus improves the forming performance of the magnesium alloy sheet.

[0047] Example 2 A method for preparing a magnesium alloy plate, comprising the following specific steps: S1. Melting: Melt the Mg-30Gd alloy (the mass percentage of the Gd element in the alloy is 30wt%) and pure magnesium separately. The specific steps are as follows: 1) Pure magnesium (99.99 wt% purity) and the master alloy Mg-30Gd alloy were cut into blocks using a saw. The master alloy surface was then polished with an angle grinder to remove surface oxide films and impurities. Considering a 10% burnout of alloying elements during the smelting process, the weight of pure magnesium and master alloy required to cast a 3 kg ingot was calculated to obtain a Mg-1Gd ingot containing 1 wt% Gd. After preparing the required materials, a boron nitride-alcohol suspension was applied to the inner walls of the crucible and the casting mold to prevent impurities on the inner walls from mixing into the magnesium alloy ingot. 2) Preheating: Place the casting mold and crucible in a 300°C heat treatment furnace for preheating, set the resistance furnace temperature to 500°C, and after the resistance furnace temperature rises to 500°C, disconnect the resistance furnace power supply; 3) Melting: Place a pre-weighed pure magnesium-aluminum-zinc alloy block in the crucible, then clamp the crucible into the resistance furnace, turn on the resistance furnace power supply again, set the temperature to 750°C, and simultaneously introduce a protective gas (composed of CO2 and SF6 in a ratio of 99:1 by volume) from the protective gas inlet pipe to start melting the pure magnesium-aluminum-zinc alloy block. After the pure magnesium-aluminum-zinc alloy block is melted, disconnect the power supply again in the same manner and add a pre-weighed master alloy Mg-30Gd master alloy block to melt the Mg-30Gd master alloy block; 4) Standing: After the master alloy is melted, place the magnesium alloy melt in a resistance furnace and keep it still for 15 minutes, then remove impurities on the melt surface; 5) Casting: Pour the magnesium alloy melt into a preheated casting mold under the protection of a protective gas (composed of CO2 and SF6 in a volume ratio of 99:1). After the melt cools and solidifies, take out a magnesium alloy ingot (i.e., Mg-1Gd alloy ingot) with a diameter of 85 mm; S2. Homogenization heat treatment: The smelting magnesium alloy ingot and the commercially available AZ31 magnesium alloy ingot (ie, magnesium-aluminum-zinc alloy ingot) were placed in a 500°C heating furnace for 12 hours, then removed and rapidly cooled in cold water to complete the homogenization heat treatment; S3 Extrusion: The magnesium alloy ingot after homogenization heat treatment was cut into 50mm×10mm×30mm blocks using a wire cutter. The AZ31 magnesium alloy ingot was cut into 50mm×30mm×30mm blocks using a wire cutter. The surface oxide film and impurities of the cut blocks were polished off with an angle grinder, placed in a preheated extrusion die, and extrusion was started. The cut AZ31 magnesium alloy blocks and magnesium alloy ingot blocks are stacked in the order of magnesium alloy ingot block, AZ31 magnesium alloy block, magnesium alloy ingot block (eg Figure 1 As shown, the uppermost and lowermost layers are magnesium alloy ingots, and the middle layer is AZ31 magnesium alloy blocks), and the extrusion is performed at 350°C using a 200-ton hydraulic press in a vertical extrusion method with an extrusion speed of 0.2 mm / s and an extrusion ratio of 10 to obtain an extruded plate; S4. Rolling: The extruded sheet was cut into 100 mm long segments and hot rolled on a two-roll mill at 365°C in two passes, with the rolling direction perpendicular to the extrusion direction. The reduction per pass was 20%. Between passes, the sheet was pre-annealed in a 370°C furnace for 20 minutes to obtain thin sheets. S5. Annealing: The obtained thin plate is placed in a heating furnace at 400°C for 20 minutes, and then air-cooled to room temperature to obtain a magnesium alloy plate.

[0048] Example 3 A method for preparing a magnesium alloy plate, comprising the following specific steps: S1. Melting: Melt the Mg-30Gd alloy (the mass percentage of the Gd element in the alloy is 30wt%) and pure magnesium separately. The specific steps are as follows: 1) Pure magnesium (99.99 wt% purity) and the master alloy Mg-30Gd alloy were cut into blocks using a saw. The master alloy surface was then polished with an angle grinder to remove surface oxide films and impurities. Considering a 10% burnout of alloying elements during the smelting process, the weight of pure magnesium and master alloy required to cast a 3 kg ingot was calculated to obtain a Mg-1Gd ingot containing 1 wt% Gd. After preparing the required materials, a boron nitride-alcohol suspension was applied to the inner walls of the crucible and the casting mold to prevent impurities on the inner walls from mixing into the magnesium alloy ingot. 2) Preheating: Place the casting mold and crucible in a 300°C heat treatment furnace for preheating, set the resistance furnace temperature to 500°C, and after the resistance furnace temperature rises to 500°C, disconnect the resistance furnace power supply; 3) Melting: Place a pre-weighed pure magnesium-aluminum-zinc alloy block in the crucible, then clamp the crucible into the resistance furnace, turn on the resistance furnace power supply again, set the temperature to 750°C, and simultaneously introduce a protective gas (composed of CO2 and SF6 in a ratio of 99:1 by volume) from the protective gas inlet pipe to start melting the pure magnesium-aluminum-zinc alloy block. After the pure magnesium-aluminum-zinc alloy block is melted, disconnect the power supply again in the same manner and add a pre-weighed master alloy Mg-30Gd master alloy block to melt the Mg-30Gd master alloy block; 4) Standing: After the master alloy is melted, place the magnesium alloy melt in a resistance furnace and keep it still for 15 minutes, then remove impurities on the melt surface; 5) Casting: Pour the magnesium alloy melt into a preheated casting mold under the protection of a protective gas (composed of CO2 and SF6 in a volume ratio of 99:1). After the melt cools and solidifies, take out a magnesium alloy ingot (i.e., Mg-1Gd alloy ingot) with a diameter of 85 mm; S2. Homogenization heat treatment: The smelting magnesium alloy ingot and the commercially available AZ31 magnesium alloy ingot (ie, magnesium-aluminum-zinc alloy ingot) were placed in a 500°C heating furnace for 12 hours, then removed and rapidly cooled in cold water to complete the homogenization heat treatment; S3 Extrusion: The magnesium alloy ingot after homogenization heat treatment was cut into 50mm×10mm×30mm blocks using a wire cutter. The AZ31 magnesium alloy ingot was cut into 50mm×30mm×30mm blocks using a wire cutter. The surface oxide film and impurities of the cut blocks were polished off with an angle grinder, placed in a preheated extrusion die, and extrusion was started. The cut AZ31 magnesium alloy blocks and magnesium alloy ingot blocks are stacked in the order of magnesium alloy ingot block, AZ31 magnesium alloy block, magnesium alloy ingot block (eg Figure 1As shown, the uppermost and lowermost layers are magnesium alloy ingots, and the middle layer is AZ31 magnesium alloy blocks), and are extruded at 400°C using a 200-ton hydraulic press in a vertical extrusion method with an extrusion speed of 0.5 mm / s and an extrusion ratio of 10 to obtain an extruded plate; S4. Rolling: The extruded sheet was cut into 100 mm long segments and hot rolled on a two-roll mill at 355°C in four passes, with the rolling direction perpendicular to the extrusion direction. The reduction per pass was 10%. Between passes, the sheet was pre-annealed in a 400°C furnace for 10 minutes to obtain thin sheets. S5. Annealing: The obtained thin plate is placed in a heating furnace at 370°C for 40 minutes, and then air-cooled to room temperature to obtain a magnesium alloy plate.

[0049] Comparative Example 1 The difference between this comparative example and Example 1 is that the rolling direction is parallel to the extrusion direction.

[0050] Comparative Example 2 The difference between this comparative example and Example 1 is that the extrusion temperature is 250°C.

[0051] During the production process, magnesium alloys are difficult to extrude due to their high resistance to deformation.

[0052] Comparative Example 3 The difference between this comparative example and Example 1 is that the extrusion temperature is 500°C.

[0053] The crystal phase of the magnesium alloy plate prepared in this comparative example was observed using an optical microscope (OM). Figure 4 shown.

[0054] Depend on Figure 4 It can be seen that in the magnesium alloy sheet prepared in this comparative example, the grains of Mg-Gd and AZ31 are obviously coarsened.

[0055] Comparative Example 4 The difference between this comparative example and Example 1 is that the extrusion speed is 0.1 mm / s.

[0056] During the production process, after extrusion, the plate is obviously bent and cannot be rolled later (e.g. Figure 5 shown).

[0057] Comparative Example 5 The difference between this comparative example and Example 1 is that the extrusion speed is 0.8 mm / s.

[0058] During the production process, after extrusion, the plate will be obviously scratched and have surface defects (such as Figure 6 shown).

[0059] Comparative Example 6 The difference between this comparative example and Example 1 is that the rolling temperature is 450°C.

[0060] The crystal phase of the magnesium alloy plate prepared in this comparative example was observed using an optical microscope (OM). Figure 7 shown.

[0061] Depend on Figure 7 It can be seen that in the magnesium alloy plate prepared in this comparative example, the grains of Mg-Gd and AZ31 are obviously coarsened.

[0062] Comparative Example 7 The difference between this comparative example and Example 1 is that the rolling temperature is 250°C.

[0063] The magnesium alloy sheet prepared in this comparative example is Figure 8 As shown, the left picture is Mg-Gd plate and the right picture is AZ31 plate.

[0064] like Figure 8 As shown, the magnesium alloy plate prepared in this comparative example exhibits cracking.

[0065] Comparative Example 8 The difference between this comparative example and Example 1 is that three cut AZ31 magnesium alloy blocks are stacked.

[0066] Comparative Example 9 The difference between this comparative example and Example 1 is that three cut magnesium alloy ingots are stacked.

[0067] test The texture distribution characteristics of the magnesium alloy plates prepared in Example 1 and Comparative Examples 8-9 were observed using electron backscatter diffraction (EBSD) technology. The results are as follows: Figure 9 As shown, from left to right are the texture distribution characteristic diagrams of the magnesium alloy plates prepared in Comparative Example 8, Comparative Example 9 and Example 1.

[0068] Depend on Figure 9 It can be seen that, compared with Comparative Examples 8 and 9, the texture strength of the magnesium alloy sheet prepared in Example 1 is significantly reduced.

[0069] The magnesium alloy sheets prepared in Example 1 and Comparative Examples 8-9 were tested for yield ratio, work hardening index, and plastic strain ratio at room temperature, 150°C, and 250°C. Specifically, uniaxial tension creep tests were conducted in accordance with GB / T 2039-2024 Metallic Materials - Uniaxial Tension Creep Test Method to obtain a stress-extension curve. The stress value corresponding to the fluctuation platform in the curve is the yield strength, the stress value corresponding to the highest point in the curve is the tensile strength, and the ratio of the yield strength to the tensile strength is the yield ratio. The plastic deformation stage in the curve was logarithmically transformed and linearly fitted to obtain a straight line. The slope of the straight line is the work hardening index. The ratio of the strain in the width direction of the sheet to the strain in the thickness direction of the sheet corresponding to a tensile deformation of 20% in the curve is the plastic strain ratio. The results are shown in Tables 1 to 3.

[0070] Table 1 Test results of yield ratio, work hardening index and plastic strain ratio at room temperature

[0071] Table 2 Test results of yield strength ratio, work hardening index and plastic strain ratio at 150℃

[0072] Table 3 Test results of yield strength ratio, work hardening index and plastic strain ratio at 250℃

[0073] The ultimate tensile height (LDH) of the magnesium alloy plates prepared in Example 1 and Comparative Examples 8-9 was tested at room temperature, 150°C and 250°C. Specifically, the temperature was increased by a heating coil embedded in the blank holder. During the temperature increase, the temperature was controlled by a thermocouple and a temperature control system. The sample to be tested was placed under the blank holder, and the hydraulic press was started to move the punch downward to draw the blank. The punch contacted the sheet material and applied pressure to the sheet material, causing it to gradually deform and flow into the gap between the punch and the die to form a cylindrical shape. The test was stopped when the sheet material cracked, a stress mutation occurred, or the sheet material was completely drawn to form a complete cylindrical specimen. During the stretching process, the maximum drawing depth that can be achieved without the sheet material breaking is the ultimate tensile height. The results are shown in Table 4.

[0074] Table 4 Limiting tensile height (LDH) test results

[0075] As shown in Table 4, the ultimate tensile strength (LDH) of the magnesium alloy sheet produced in Example 1 is significantly improved compared to Comparative Example 8. The ultimate tensile strength (LDH) (150°C) of the magnesium alloy sheet produced in Example 1 is significantly improved compared to Comparative Examples 8 and 9. The ultimate tensile strength (LDH) (250°C) of the magnesium alloy sheet produced in Example 1 is significantly improved compared to Comparative Example 8. These results demonstrate that the formability of the magnesium alloy sheet produced by the method of the present application is significantly improved.

[0076] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing a magnesium alloy sheet, wherein the magnesium alloy sheet comprises a first rare earth magnesium alloy layer, a magnesium aluminum zinc alloy layer, and a second rare earth magnesium alloy layer stacked in sequence, characterized in that: The method for preparing the magnesium alloy sheet comprises the following steps: The first rare earth magnesium alloy block, the magnesium aluminum zinc alloy block and the second rare earth magnesium alloy block are stacked in sequence, extruded and then rolled, and annealed to obtain the magnesium alloy sheet, wherein the rolling direction during the rolling process is perpendicular to the extrusion direction during the extrusion process.

2. The method for preparing a magnesium alloy sheet according to claim 1, wherein: The rare earth element contained in the first rare earth magnesium alloy block or the second rare earth magnesium alloy block is at least one selected from Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc.

3. The method for preparing a magnesium alloy sheet according to claim 1, wherein: The extrusion temperature is 350-400°C.

4. The method for preparing a magnesium alloy sheet according to claim 3, wherein: The extrusion speed is 0.2-0.5 mm / s.

5. The method for preparing a magnesium alloy sheet according to claim 3, wherein: During the extrusion process, the extrusion ratio is 10-12.

6. The method for preparing a magnesium alloy sheet according to claim 1, wherein: The rolling temperature is 355-365°C.

7. The method for preparing a magnesium alloy sheet according to claim 6, wherein: The rolling passes are 2-4 passes.

8. The method for preparing a magnesium alloy sheet according to claim 6, wherein: During the rolling process, the reduction in a single pass is 15%-20%.

9. The method for preparing a magnesium alloy sheet according to claim 1, wherein: The annealing comprises: keeping the temperature at 370-400° C. for 20-40 minutes.

10. The method for preparing a magnesium alloy sheet according to claim 1, wherein: Before the stacking, the method for preparing the magnesium alloy plate further includes the following steps: performing homogenization heat treatment on the first rare earth magnesium alloy block, the magnesium-aluminum-zinc alloy block, and the second rare earth magnesium alloy block, respectively.

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