Mn-containing ultralight high-toughness weak-texture magnesium-lithium alloy sheet and preparation method thereof

Abstract

The invention discloses a Mn-containing ultralight high-toughness weak-texture magnesium-lithium alloy sheet and a preparation method thereof, and belongs to the technical field of metal materials. The preparation method comprises the following steps: preparing materials (containing at least one of a pure magnesium ingot, a pure zinc ingot, a magnesium-lithium intermediate alloy, a magnesium-calcium intermediate alloy and a magnesium-erbium / magnesium-manganese intermediate alloy), smelting under argon protection, casting at 720-750 DEG C, cooling, carrying out linear cutting to obtain a cast ingot, preheating at 200-300 DEG C, extruding into a plate blank, and carrying out small-pass (2-4 passes) large-deformation rolling at 25-200 DEG C. According to the invention, the comprehensive mechanical properties of the alloy are improved, the basal texture is weakened and the room-temperature formability is improved by adding a light Ca element, a grain refined Mn element or a rare earth Er element through a novel short-distance efficient deformation process of extrusion pre-deformation and small-pass large-deformation online heating rolling, so that the unification of ultra-light weight, high toughness and high formability is realized, and the production cost is reduced. The method is simple in process, low in cost, efficient and suitable for the fields of aerospace, 3C electronics and the like.

Description

Technical Field

[0001] This invention relates to the field of metallic materials technology, and in particular to a thin sheet of magnesium-lithium alloy containing Mn that is ultralight, high-strength, tough, and has a weak texture, and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, possess a series of advantages such as high specific strength and specific stiffness, good damping and vibration reduction properties, excellent electromagnetic shielding performance, and easy recyclability, showing great application potential in aerospace, defense, 3C electronics, and transportation. However, traditional magnesium alloys (such as AZ31 and ZK60) have poor plastic processing ability and low formability due to their close-packed hexagonal crystal structure and few independent slip systems at room temperature. This severely restricts their large-scale commercial application, especially in fields requiring the stamping of complex-shaped thin sheets.

[0003] Magnesium-lithium alloys have the lowest density among existing alloy systems, due to the addition of metallic lithium, which has a density of only 0.543 g / cm³. 3 Therefore, the density of magnesium-lithium alloys decreases with increasing lithium content, reaching only 2 / 3 to 3 / 4 that of typical magnesium alloys and 1 / 3 to 1 / 2 lighter than most aluminum alloys. Thus, magnesium-lithium alloys are also known as ultralight alloys. When the lithium content exceeds approximately 5.7 wt.%, the alloy's crystal structure transforms from a close-packed six-way body-centered cubic structure. The body-centered cubic structure possesses more slip systems, significantly improving the room-temperature plasticity, toughness, and cold-forming ability of magnesium-lithium alloys, making it possible to prepare ultralight, highly formable magnesium-lithium alloy sheets. However, magnesium-lithium alloys also suffer from poor thermal stability, low absolute strength, and insufficient formability, thus preventing large-scale industrial application.

[0004] Alloying is one of the effective methods to improve the mechanical properties of magnesium-lithium alloy materials. Zn and Ca are the main alloying elements in magnesium-lithium alloys, and alloy systems such as Mg-Li-Zn or Mg-Li-Zn-Ca have been formed. However, the solid solubility of these elements in magnesium-lithium alloys is limited, which has a limited effect on improving the strength of the alloy and can easily lead to poor stability of the mechanical properties of the alloy, which is not conducive to the production of ultra-lightweight and high-performance magnesium-lithium alloy thin plates.

[0005] Furthermore, current research on the preparation of magnesium-lithium alloy thin plates mostly adopts a process route of "multi-pass repeated hot rolling + intermediate annealing + post-rolling annealing". This process suffers from problems such as long path, high cost, and low production efficiency. Moreover, during the repeated heating and rolling processes, it is difficult to maintain uniform and stable microstructure and properties, easily generating anisotropy and strong texture, further reducing the forming limit of the thin plate. Therefore, there is an urgent need to develop a novel alloying design and short-path, high-efficiency preparation process to achieve a balance between ultra-lightweight, high-strength, high-toughness, and high formability of magnesium-lithium alloy thin plates. Summary of the Invention

[0006] The purpose of this invention is to provide a lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet containing Mn and its preparation method. This is achieved by refining the grain size with metallic Mn, weakening the basal texture with Ca, followed by extrusion pre-deformation into a slab, and then employing a novel short-path, high-efficiency deformation process with few passes and large deformation in online heated rolling. This process improves the strength and plasticity of the alloy, resulting in a lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet. This invention achieves a perfect combination of ultralightness, high strength and toughness, and high formability in the magnesium-lithium alloy sheet, while simplifying the process flow, improving production efficiency, enhancing product quality stability, and significantly reducing production costs, thereby solving the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing a thin sheet of ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn, comprising the following steps: S1. Material preparation: Prepare at least one of pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, magnesium-erbium master alloy, and magnesium-manganese master alloy. S2. Melting: Melting the raw materials under argon protection to obtain an alloy melt; S3. Casting: The melt is kept at 720-750℃, slag is removed and then poured into a mold. After cooling, the ingot is obtained by wire cutting. S4. Extrusion Pre-deformation: After the ingot is preheated to 200-300℃, it is extruded into a slab at an extrusion ratio of 20-30:1, an extrusion speed of 0.1-2mm / s, and a temperature of 200-300℃, and then air-cooled to room temperature. S5. Online heating rolling: The slab is rolled at 25-200℃ with a small number of passes and a large deformation, with 2-4 passes, a single pass reduction of 15-25%, and a total reduction of 80-90%, to obtain the target thin plate.

[0008] Preferably, in step S4, the preheating temperature is 210-260℃ and the preheating time is 1-2 hours.

[0009] Preferably, in step S4, the extrusion ratio is (24-28):1, the extrusion speed is 0.1-1 mm / s, and the extrusion temperature is 210-260℃.

[0010] Preferably, in step S5, the temperature of the online heating and rolling is 60-150℃.

[0011] The present invention also provides a thin sheet of ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn prepared by the above method.

[0012] Preferably, the chemical element composition of the magnesium-lithium alloy sheet, by mass fraction, includes: Li: 5-13 wt.%, Zn: 0.1-4 wt.%, Ca: 0.1-3 wt.%, Er: 0-3 wt.%, Mn: 0-3 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%; and the Er and Mn contents are not both 0.

[0013] Preferably, the chemical element composition of the magnesium-lithium alloy sheet, by mass fraction, includes: Li: 6-12 wt.%, Zn: 1-3 wt.%, Ca: 0.1-2 wt.%, Er: 0-2 wt.%, Mn: 0-2 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%; and the Er and Mn contents are not both 0.

[0014] Preferably, the thickness of the magnesium-lithium alloy sheet is 0.1-0.4 mm.

[0015] Preferably, the magnesium-lithium alloy sheet has a yield strength of 200-260 MPa, a tensile strength of 224-295 MPa, an elongation of 8-26%, and a density of 1.489-1.546 g / cm³. 3 The cylindrical drawing depth is 9.1-13.6mm.

[0016] Therefore, the Mn-containing ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy thin plate and its preparation method provided by the present invention have the following beneficial effects: (1) The present invention adds calcium (Ca) to the Mg-Li-Zn alloy system to weaken the basal texture, erbium (Er) to the Mg-Li-Zn alloy system to the erbium (Er) alloy system to the erbium (Mn ...

[0017] (2) The present invention optimizes the microstructure of magnesium-lithium alloy slab by pre-deformation by extrusion. Dynamic recrystallization occurs during hot extrusion, generating a large number of fine recrystallized grains. The size of the second phase particles can also be refined, making the as-cast structure more uniform and improving the mechanical properties of magnesium-lithium alloy slab.

[0018] (3) This invention further deforms the extruded alloy slab by employing a method of online hot rolling with a small number of passes and large deformation, further breaking down the initially refined second-phase particles in the extruded alloy, making them dispersed within the grains and at the grain boundaries. This provides sufficient second-phase strengthening effect for the magnesium-lithium alloy, greatly improving the comprehensive mechanical properties of the magnesium-lithium alloy sheet. At the same time, the internal structure becomes more uniform during the hot rolling process, reducing the basal texture, ultimately obtaining an ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet with a yield strength of 200-260 MPa, a tensile strength of 224-295 MPa, an elongation of 8-26%, and a density of 1.489-1.546 g / cm³. 3 In the formability test, the drawing depth of the cylinder was 9.1-13.6 mm.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 The metallographic structure of the magnesium-lithium alloy produced by online heating rolling process in Example 1; Figure 2 The metallographic structure of the magnesium-lithium alloy produced by online heating rolling process in Example 2; Figure 3 The metallographic structure of the magnesium-lithium alloy produced by online heating rolling process in Example 3; Figure 4 SEM image of magnesium-lithium alloy produced by online heating rolling process in Example 1; Figure 5 SEM image of magnesium-lithium alloy produced by online heating rolling process in Example 2; Figure 6 SEM image of magnesium-lithium alloy produced by online heating rolling process in Example 3; Figure 7 The stress-strain curve of the magnesium-lithium alloy produced by online heating rolling process in Example 1 is shown. Figure 8 The stress-strain curve of the magnesium-lithium alloy produced by online heating rolling process in Example 2 is shown. Figure 9 The stress-strain curve of the magnesium-lithium alloy produced by online heating rolling process in Example 3 is shown. Detailed Implementation

[0021] This invention provides a thin sheet of ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn. The chemical element composition of the thin sheet of magnesium-lithium alloy, by mass fraction, includes: Li: 5-13 wt.%, Zn: 0.1-4 wt.%, Ca: 0.1-3 wt.%, Er: 0-3 wt.%, Mn: 0-3 wt.%, with the remainder being magnesium and unavoidable impurities, the total content of which is less than or equal to 0.3%; and the contents of Er and Mn are not both 0.

[0022] In this invention, the chemical element composition of the magnesium-lithium alloy sheet, by mass fraction, includes: Li: 6-12 wt.%, Zn: 1-3 wt.%, Ca: 0.1-2 wt.%, Er: 0-2 wt.%, Mn: 0-2 wt.%, with the remainder being magnesium and unavoidable impurities, the total content of which is less than or equal to 0.3%; and the contents of Er and Mn are not both 0.

[0023] This invention also provides the above-mentioned Mn-containing ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy thin plate and its preparation method, comprising the following steps: S1. Material preparation: Prepare at least one of the following: pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, magnesium-erbium master alloy, and magnesium-manganese master alloy.

[0024] S2, Melting: Place the raw materials obtained in step S1 into a vacuum melting furnace, and evacuate the furnace to a vacuum level of 2.5 × 10⁻⁶. - 1 Pa, then argon gas is added as a protective gas until the entire vacuum furnace is in a protective gas atmosphere for melting.

[0025] S3. Casting: After removing the slag and stirring the alloy melt obtained in step S2 at a temperature of 720-750℃, let it stand for 10-15 minutes and then pour it into a stainless steel mold with a diameter of Φ90 and a length of 300mm. After naturally cooling in a vacuum melting furnace, the oxide scale or contamination layer on the surface is removed by wire cutting to obtain an ingot with a diameter of Φ80.

[0026] S4. Extrusion Pre-deformation: The wire-cut ingot obtained in step S3 is placed in a heating furnace for preheating. Then, the preheated alloy ingot is selected using a 110mm extrusion furnace. After the 2mm slab die is extruded in the extruder, it is cooled to room temperature by a fan to obtain an extruded slab of magnesium-lithium alloy.

[0027] In this invention, the preheating temperature is 200-300℃ and the preheating time is 0-3h; the extrusion molding conditions are: extrusion ratio of (20-30):1; extrusion speed of 0.1-2mm / s; and extrusion temperature of 200-300℃.

[0028] In this invention, the preferred preheating temperature is 210-260℃, and the preheating time is 1-2h; the extrusion molding conditions are: extrusion ratio (24-28):1; extrusion speed is 0.1-1mm / s; and extrusion temperature is 210-260℃.

[0029] S5. Online heating and rolling: The extruded slab obtained in step S4 is subjected to online heating and rolling deformation treatment with a small number of passes and a large deformation amount at a temperature of 25-200℃, and finally a thin sheet of magnesium-lithium alloy containing Mn, which is ultra-light, high-strength, tough and weakly textured, is obtained, and the complete stamping of complex frame structure is successfully realized.

[0030] In this invention, the rolling temperature is 60-150℃, the rolling passes are 2-4, the single-pass rolling reduction is 15-25%, and the rolling is carried out with a total rolling reduction of 80%-90%, finally obtaining an ultra-lightweight, high-strength, tough, weakly textured magnesium-lithium alloy sheet with a thickness of 0.1-0.4mm.

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0032] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0033] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0034] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that this is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range. Unless otherwise stated, all percentages, parts, ratios, etc., herein are by weight. Unless otherwise specified, the reagents, instruments, and equipment used in this invention are those commonly used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, which will not be further elaborated here.

[0035] In the following embodiments of the present invention, the pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloys, magnesium-calcium master alloys, magnesium-erbium master alloys, and magnesium-manganese master alloys used are all commercially available products. The purity of the pure magnesium ingots is ≥99.95%, and the purity of the pure zinc ingots is ≥99.99%. The magnesium-lithium master alloys, magnesium-calcium master alloys, magnesium-erbium master alloys, and magnesium-manganese master alloys are collectively referred to as magnesium master alloys, and lithium, calcium, erbium, and manganese in the magnesium master alloys each account for 10-20% of the total mass of the magnesium master alloy.

[0036] The tensile testing machine used in the following embodiments of the present invention is a UTM4104; the metallurgical microscope is an OLYMPUS PMG3; the scanning electron microscope is a FEINOVA400; and the heat treatment vacuum drying oven is a DZF-6050BZ.

[0037] Example 1 This embodiment provides an ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet provided by the present invention, which has the following chemical element composition by mass fraction: Li: 10%, Zn: 3%, Ca: 1%, Er: 2%, with the remainder being magnesium and unavoidable impurities, the total content of which is less than or equal to 0.3%.

[0038] The preparation method of the above-mentioned ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy thin sheet includes three stages: vacuum melting and casting, hot extrusion pre-deformation, and online heating rolling. The specific steps are as follows: S1. Materials preparation: pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, magnesium-erbium master alloy.

[0039] S2. Melting: Under the protection of argon gas, pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-erbium master alloy are placed in a crucible according to the above mass fraction ratio and heated in a melting furnace to 750°C until all materials are completely melted to obtain an alloy melt.

[0040] S3. Casting: The alloy melt obtained in step S2 is stirred at a temperature of 740℃ until all raw materials are mixed evenly. The slag on the surface of the alloy melt is removed. After standing for 12 minutes, it is poured into a stainless steel mold with a diameter of Φ90 and a length of 300mm. After natural cooling in a vacuum furnace, the oxide scale or contamination layer on the surface is removed by wire cutting to obtain an ingot with a diameter of Φ80.

[0041] S4. Extrusion Pre-deformation: After removing the oxide scale or contamination layer from the surface of the ingot obtained in step S3, place it in a heating furnace for preheating at 250°C for 1 hour. Then, extrude the preheated alloy ingot on an extrusion press with an extrusion temperature of 250°C, an extrusion ratio of 28:1, and an extrusion speed of 0.6 mm / s. After extrusion, the ingot is cooled to room temperature by a blower to obtain an extruded slab with a thickness of 2 mm.

[0042] S5. Online heating and rolling: The extruded slab obtained in step S4 is subjected to online heating and rolling deformation treatment at a temperature of 100℃ with a small number of passes and a large deformation amount. The rolling passes are 3, the single pass rolling reduction is 25%, and the total rolling reduction is 85%, finally obtaining an ultra-lightweight, high-strength, tough, weakly textured magnesium-lithium alloy sheet with a thickness of 0.3mm.

[0043] This embodiment tests the mechanical and forming properties of the extruded slab prepared by the extrusion process in step S4 and the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process with small number of passes and large deformation in step S5. The results are as follows: the performance indicators of the extruded slab prepared by the extrusion process are: yield strength of 142 MPa, tensile strength of 157 MPa, elongation of 33%, and density of 1.504 g / cm³. 3 The cylindrical drawing depth is 9.1 mm. Figure 7 It can be seen that the performance indicators of the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process are: yield strength of 181 MPa, tensile strength of 205 MPa, elongation of 30%; and density of 1.504 g / cm³. 3 The cylindrical drawing depth is 11.3 mm.

[0044] Example 2 This embodiment provides an ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet provided by the present invention, which has the following chemical element composition by mass fraction: Li: 10%, Zn: 3%, Ca: 1%, Mn: 0.5%, with the remainder being magnesium and unavoidable impurities, the total content of which is less than or equal to 0.3%.

[0045] The preparation method of the above-mentioned ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy thin sheet includes three stages: vacuum melting and casting, hot extrusion pre-deformation, and online heating rolling. The specific steps are as follows: S1. Material preparation: Prepare pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-manganese master alloy.

[0046] S2. Melting: Under the protection of argon gas, pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-manganese master alloy are placed in a crucible according to the above mass fraction ratio and heated in a melting furnace to 750°C until all materials are completely melted to obtain an alloy melt.

[0047] S3. Casting: The alloy melt obtained in step S2 is stirred at a temperature of 740℃ until all raw materials are mixed evenly. The slag on the surface of the alloy melt is removed. After standing for 12 minutes, it is poured into a stainless steel mold with a diameter of Φ90 and a length of 300mm. After natural cooling in a vacuum furnace, the oxide scale or contamination layer on the surface is removed by wire cutting to obtain an ingot with a diameter of Φ80.

[0048] S4. Extrusion Pre-deformation: After removing the oxide scale or contamination layer from the surface of the ingot obtained in step S3, place it in a heating furnace for preheating at 250°C for 1 hour. Then, extrude the preheated alloy ingot on an extrusion press at an extrusion temperature of 250°C, an extrusion ratio of 28:1, and an extrusion speed of 0.7 mm / s. After extrusion, the ingot is cooled to room temperature by a blower to obtain an extruded slab with a thickness of 2 mm.

[0049] S5. Online heating and rolling: The extruded slab obtained in step S4 is subjected to online heating and rolling deformation treatment at a temperature of 120°C with a small number of passes and a large deformation amount. The rolling passes are 3, the single pass rolling reduction is 25%, and the total rolling reduction is 85%, finally obtaining an ultra-lightweight, high-strength, tough, weakly textured magnesium-lithium alloy sheet with a thickness of 0.3mm.

[0050] This embodiment tests the mechanical and forming properties of the extruded slab prepared by the extrusion process in step S4 and the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process with small number of passes and large deformation in step S5. The results are as follows: the performance indicators of the extruded slab prepared by the extrusion process are: yield strength of 161 MPa, tensile strength of 172 MPa, elongation of 32%, and density of 1.489 g / cm³. 3 The cylindrical drawing depth is 11.7 mm. Figure 8 It can be seen that the performance indicators of the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process are: yield strength of 219 MPa, tensile strength of 232 MPa, elongation of 27%; and density of 1.489 g / cm³. 3 The cylindrical drawing depth is 12.9 mm.

[0051] Example 3 This embodiment provides an ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy sheet provided by the present invention, which has the following chemical element composition by mass fraction: Li: 8%, Zn: 3%, Ca: 1%, Mn: 0.5%, with the remainder being magnesium and unavoidable impurities, the total content of which is less than or equal to 0.3%.

[0052] The preparation method of the above-mentioned ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy thin sheet includes three stages: vacuum melting and casting, hot extrusion pre-deformation, and online heating rolling. The specific steps are as follows: S1. Material preparation: Prepare pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-manganese master alloy.

[0053] S2. Melting: Under the protection of argon gas, pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, and magnesium-manganese master alloy are placed in a crucible according to the above mass fraction ratio and heated in a melting furnace to 750°C until all materials are completely melted to obtain an alloy melt.

[0054] S3. Casting: The alloy melt obtained in step S2 is stirred at a temperature of 740℃ until all raw materials are mixed evenly. The slag on the surface of the alloy melt is removed. After standing for 12 minutes, it is poured into a stainless steel mold with a diameter of Φ90 and a length of 300mm. After natural cooling in a vacuum furnace, the oxide scale or contamination layer on the surface is removed by wire cutting to obtain an ingot with a diameter of Φ80.

[0055] S4. Extrusion Pre-deformation: After removing the oxide scale or contamination layer from the surface of the ingot obtained in step S3, place it in a heating furnace for preheating at 280℃ for 1 hour. Then, extrude the preheated alloy ingot on an extrusion press with an extrusion temperature of 280℃, an extrusion ratio of 28:1, and an extrusion speed of 0.6 mm / s. After extrusion, the ingot is cooled to room temperature by a blower to obtain an extruded slab with a thickness of 2 mm.

[0056] S5. Online heating and rolling: The extruded slab obtained in step S4 is subjected to online heating and rolling deformation treatment at a temperature of 150°C with a small number of passes and a large deformation amount. The rolling passes are 3, the single pass rolling reduction is 25%, and the total rolling reduction is 85%, finally obtaining an ultra-lightweight, high-strength, tough, weakly textured magnesium-lithium alloy sheet with a thickness of 0.3mm.

[0057] This embodiment tests the mechanical and forming properties of the extruded slab prepared by the extrusion process in step S4 and the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process with small number of passes and large deformation in step S5. The results are as follows: the performance indicators of the extruded slab prepared by the extrusion process are: yield strength of 184 MPa, tensile strength of 196 MPa, elongation of 15%, and density of 1.546 g / cm³. 3The cylindrical drawing depth is 9.2 mm. Figure 9 It can be seen that the performance indicators of the magnesium-lithium alloy rolled sheet prepared by the online heating rolling process are: yield strength of 263 MPa, tensile strength of 295 MPa, elongation of 9%; and density of 1.546 g / cm³. 3 The cylindrical drawing depth is 10.6 mm.

[0058] Comparative Example 1 This comparative example relates to an ultralight high-performance magnesium-lithium alloy sheet. The composition of the magnesium-lithium alloy is the same as that in Example 1, except that it does not contain Er element. The preparation method of the magnesium-lithium alloy sheet is the same as that in Example 1.

[0059] This comparative example tests the properties of the extruded slab prepared by the extrusion process in step S4 and the plate-shaped magnesium-lithium alloy material prepared by the online heating rolling process in step S5. The results are as follows: The performance indicators of the extruded slab prepared by the extrusion process are: yield strength 121 MPa, tensile strength 140 MPa, elongation 22%, and density 1.485 g / cm³. 3 The cylindrical drawing depth is 6.2 mm. The performance indicators of the magnesium-lithium alloy material prepared by hot rolling process are: yield strength of 163 MPa, tensile strength of 174 MPa, elongation of 16%, and density of 1.485 g / cm³. 3 The cylindrical drawing depth is 7.8mm.

[0060] Compared with Example 1, Comparative Example 1 showed a significant improvement in mechanical and forming properties. This is likely because the absence of a second phase containing rare earth Er elements to improve the microstructure of the magnesium-lithium alloy matrix resulted in no grain refinement or texture weakening. This suggests that the magnesium-lithium alloy matrix requires effective alloying elements to introduce second-phase particles to enhance the matrix.

[0061] Comparative Example 2 This comparative example relates to an ultralight high-performance magnesium-lithium alloy sheet. The composition of the magnesium-lithium alloy is the same as that in Example 2, except that it does not contain Mn. The preparation method of the magnesium-lithium alloy sheet is the same as that in Example 2.

[0062] This comparative example tests the properties of the extruded slab prepared by the extrusion process in step S4 and the plate-shaped magnesium-lithium alloy material prepared by the online heating rolling process in step S5. The results are as follows: The performance indicators of the extruded slab prepared by the extrusion process are: yield strength 132 MPa, tensile strength 159 MPa, elongation 24%, and density 1.490 g / cm³. 3The cylindrical drawing depth is 6.5 mm. The performance indicators of the magnesium alloy material prepared by hot rolling are: yield strength of 180 MPa, tensile strength of 195 MPa, elongation of 20%, and density of 1.490 g / cm³. 3 The cylindrical drawing depth is 8.2mm.

[0063] Compared with Example 2, Comparative Example 2 shows a significant improvement in mechanical and forming properties. This is likely because the absence of a second phase containing Mn to improve the microstructure of the magnesium-lithium alloy matrix means that it does not produce grain refinement or texture weakening effects. This suggests that the magnesium-lithium alloy matrix requires effective alloying elements to introduce second-phase particles to enhance the matrix.

[0064] Comparative Example 3 This comparative example relates to an ultralight high-performance magnesium-lithium alloy sheet. The composition of the magnesium-lithium alloy is the same as that in Example 3, except that it does not contain Ca or Mn elements. The preparation method of the magnesium-lithium alloy sheet is the same as that in Example 3.

[0065] This comparative example tests the properties of the extruded slab prepared by the extrusion process in step S4 and the plate-shaped magnesium-lithium alloy material prepared by the online heating rolling process in step S5. The results are as follows: The performance indicators of the extruded slab prepared by the extrusion process are: yield strength 154 MPa, tensile strength 168 MPa, elongation 17%, and density 1.543 g / cm³. 3 The cylindrical drawing depth is 5.9 mm. The performance indicators of the magnesium alloy material prepared by hot rolling are: yield strength of 198 MPa, tensile strength of 210 MPa, elongation of 12%, and density of 1.543 g / cm³. 3 The cylindrical drawing depth is 6.5mm.

[0066] Compared with Example 3, Comparative Example 3 showed a significant improvement in mechanical and forming properties. This is likely because the absence of a second phase containing Ca and Mn elements to improve the microstructure of the magnesium-lithium alloy matrix resulted in no grain refinement or texture weakening. This suggests that the magnesium-lithium alloy matrix requires effective alloying elements to introduce second-phase particles to enhance the matrix.

[0067] Comparative Example 4 This comparative example relates to an ultralight high-performance magnesium-lithium alloy sheet. The composition of the magnesium-lithium alloy is the same as that in Example 3. The difference is in step S5, which involves hot rolling deformation treatment of the extruded slab obtained in step S4 at a temperature of 160°C, with 6 rolling passes, a single-pass rolling reduction of 7%, and a total rolling reduction of 40%, to finally obtain a magnesium-lithium alloy sheet with a thickness of 0.9 mm.

[0068] This comparative example tests the properties of the extruded slab prepared by the extrusion process in step S4 and the plate-shaped magnesium-lithium alloy material prepared by the hot rolling process in step S5. The results are as follows: The performance indicators of the extruded slab prepared by the extrusion process are: yield strength 184 MPa, tensile strength 196 MPa, elongation 15%, and density 1.546 g / cm³. 3 The cylindrical drawing depth is 9.2 mm. The performance indicators of the magnesium-lithium alloy material prepared by hot rolling process are: yield strength of 221 MPa, tensile strength of 247 MPa, elongation of 11%, and density of 1.546 g / cm³. 3 The cylindrical drawing depth is 9.4 mm.

[0069] Compared with Example 3, Comparative Example 4 shows improved mechanical properties and forming properties in the rolled state. Considering that the rolling process parameters such as rolling temperature, single-pass rolling reduction and total rolling reduction are different, the microstructure of the magnesium-lithium alloy matrix is ​​also different, resulting in different effects such as grain refinement and texture weakening. This shows that the magnesium-lithium alloy matrix needs appropriate rolling deformation process parameters to introduce a strengthening effect to enhance the matrix.

[0070] The ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy sheets obtained in Examples 1-3 of this invention were subjected to microstructure analysis using a metallographic microscope and a scanning electron microscope. The metallographic structures of the ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy sheets prepared by a few-pass, large-deformation online heating rolling process in Examples 1, 2, and 3 are as follows: Figure 1 , Figure 2 and Figure 3 As shown, SEMs are respectively as follows Figure 4 , Figure 5 and Figure 6 As shown in the figure, after extrusion pre-deformation and a novel short-path, high-efficiency online heated rolling process with few passes and large deformation amounts, the magnesium-lithium alloy material exhibits fine recrystallized grains, resulting in a more uniform microstructure. The second phase in the material transforms into fine, spherical, and dispersed particles, which are smaller in size and more evenly distributed. This novel short-path, high-efficiency extrusion pre-deformation and short-path, high-deformation online heated rolling process achieves extreme grain refinement through dynamic recrystallization, thus providing a powerful fine-grain strengthening effect. Furthermore, it transforms the coarse and harmful second phase into a fine and dispersed strengthening phase, significantly improving the efficiency of second-phase strengthening. This provides a reliable process path for manufacturing ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy thin-plate structural components.

[0071] The tensile tests conducted on the extruded slabs prepared by the extrusion process in Examples 1-3 and Comparative Examples 1-4 of this invention, as well as the ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy sheets after online heating and rolling, were performed on standard tensile specimens according to the national standard GB228-2000. The tensile specimens were sheet-like, and the axial direction of the specimen was the same as the rolling flow line direction of the material. As can be seen from the data of the above-disclosed examples and comparative examples, the magnesium-lithium alloy material prepared in the embodiments of this invention has high comprehensive performance at room temperature. The addition of Li to the magnesium alloy can change the c / a ratio of the α-Mg matrix, promoting the activation of non-basal slip systems and increasing the material's coordination ability during deformation, further enhancing the material's plasticity.

[0072] In summary, this invention aims to improve the mechanical and formability properties of magnesium-lithium alloys by fully utilizing their excellent plasticity. It employs a novel short-path, high-efficiency deformation process—extrusion pre-deformation and in-situ heated rolling with a small number of passes and large deformation amounts—to prepare magnesium-lithium alloy thin sheets. The resulting sheets have a smooth and flat surface, eliminating the need for post-rolling annealing. This ultimately yields a Mn-containing, ultra-lightweight, high-strength, tough, and weakly textured magnesium-lithium alloy thin sheet, successfully enabling the complete stamping of complex frame structures. Furthermore, this invention enhances the strength of the magnesium-lithium alloy thin sheet while maintaining high plasticity through alloying and the novel short-path, high-efficiency deformation process, meeting the needs of subsequent forming processes and applications. Moreover, the use of extrusion pre-deformation and in-situ heated rolling with a small number of passes and large deformation amounts reduces the low production efficiency and high costs associated with intermediate and post-rolling annealing, shortening several intermediate steps in the existing magnesium-lithium alloy thin sheet processing, making it more environmentally friendly, lower-cost, and more controllable.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a thin sheet of ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn, characterized in that, Includes the following steps: S1. Material preparation: Prepare at least one of pure magnesium ingots, pure zinc ingots, magnesium-lithium master alloy, magnesium-calcium master alloy, magnesium-erbium master alloy, and magnesium-manganese master alloy. S2. Melting: Melting the raw materials under argon protection to obtain an alloy melt; S3. Casting: The melt is kept at 720-750℃, slag is removed and then poured into a mold. After cooling, the ingot is obtained by wire cutting. S4. Extrusion Pre-deformation: After the ingot is preheated to 200-300℃, it is extruded into a slab at an extrusion ratio of 20-30:1, an extrusion speed of 0.1-2mm / s, and a temperature of 200-300℃, and then air-cooled to room temperature. S5. Online heating rolling: The slab is rolled at 25-200℃ with a small number of passes and a large deformation, with 2-4 passes, a single pass reduction of 15-25%, and a total reduction of 80-90%, to obtain the target thin plate.

2. The method for preparing a thin sheet of Mn-containing ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy, as described in claim 1, is characterized in that: In step S4, the preheating temperature is 210-260℃ and the preheating time is 1-2 hours.

3. The method for preparing a thin sheet of ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn according to claim 1, characterized in that: In step S4, the extrusion ratio is (24-28):1, the extrusion speed is 0.1-1 mm / s, and the extrusion temperature is 210-260℃.

4. The method for preparing a thin sheet of ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn according to claim 1, characterized in that: In step S5, the online heating rolling temperature is 60-150℃.

5. A thin sheet of ultralight, high-strength, tough, and weakly textured magnesium-lithium alloy containing Mn, characterized in that: The magnesium-lithium alloy sheet is prepared by any one of the preparation methods of claims 1-4.

6. The Mn-containing ultralight, high-strength, tough, weakly textured magnesium-lithium alloy sheet according to claim 5, characterized in that: The chemical element composition of the magnesium-lithium alloy sheet, by mass fraction, includes: Li: 5-13 wt.%, Zn: 0.1-4 wt.%, Ca: 0.1-3 wt.%, Er: 0-3 wt.%, Mn: 0-3 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%; and the Er and Mn contents are not both 0.

7. The Mn-containing ultralight, high-strength, tough, weakly textured magnesium-lithium alloy sheet according to claim 6, characterized in that: The chemical element composition of the magnesium-lithium alloy sheet, by mass fraction, includes: Li: 6-12 wt.%, Zn: 1-3 wt.%, Ca: 0.1-2 wt.%, Er: 0-2 wt.%, Mn: 0-2 wt.%, with the remainder being magnesium and unavoidable impurities, the total impurity content being ≤0.3%; and the Er and Mn contents are not both 0.

8. The Mn-containing ultralight, high-strength, tough, weakly textured magnesium-lithium alloy sheet according to claim 5, characterized in that: The thickness of the magnesium-lithium alloy sheet is 0.1-0.4 mm.

9. The Mn-containing ultralight, high-strength, tough, weakly textured magnesium-lithium alloy sheet according to claim 5, characterized in that: The magnesium-lithium alloy sheet has a yield strength of 200-260 MPa, a tensile strength of 224-295 MPa, an elongation of 8-26%, and a density of 1.489-1.546 g / cm³. 3 The cylindrical drawing depth is 9.1-13.6mm.

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