Magnesium alloy plate with gradient twin crystal structure as well as preparation method and application of magnesium alloy plate

Abstract

The invention discloses a preparation method of a magnesium alloy plate with a gradient twin structure, and belongs to the technical field of heterostructure material preparation. According to the method, firstly, a magnesium alloy plate serves as a base plate, magnesium alloy wires of the same mark are adopted for double-heat-source auxiliary heating stirring friction solid-phase additive manufacturing, and a deposition plate with crystal grains preferentially oriented in the thickness direction is obtained by regulating and controlling the heating temperature and deposition head process parameters; keeping the heating state of the substrate, performing heat source-assisted ultrasonic rolling on the deposited plate, and enabling crystal grains in the thickness direction of the plate to generate twinning deformation of different degrees by regulating and controlling rolling parameters; and finally, separating the substrate from the deposition plate to obtain the magnesium alloy plate with the gradient twin structure. Heterogeneous particles are not introduced, the material is pure, the technological process is short, the production efficiency is high, the cost is low, the prepared plate is small in grain, the gradient twin crystal structure penetrates through the thickness, the comprehensive performance is excellent, and the method is suitable for industrial production and can be applied to the fields of automobiles, aerospace, medical instruments and the like.

Description

Technical Field

[0001] This invention belongs to the field of heterostructure materials technology, and relates to a magnesium alloy plate with a gradient twin structure, its preparation method and application. Background Technology

[0002] Heterogeneous metals refer to metallic materials with two or more microstructures and different properties. The different microstructures within heterogeneous metals interact synergistically, typically significantly improving their overall mechanical and service performance. Types of heterostructures include gradient heterostructures, multiphase heterostructures, lamellar heterostructures, defect heterostructures, reinforcing phase heterostructures, and hierarchical heterostructures. Among these, gradient heterostructures (also known as gradient structures) are a typical type, characterized by a gradient distribution of the material's internal microstructure, such as gradient distribution of grain size, phase volume fraction, or twinning.

[0003] Magnesium alloys, due to their low density, high specific strength, and good recyclability, are widely used in the automotive, aerospace, and medical device industries, and are hailed as green engineering materials of the 21st century. With the increasing demand for high-performance materials, the need for preparing gradient structure magnesium alloys is becoming increasingly urgent. Existing methods for preparing gradient structure materials are mainly divided into two categories: heteroparticle-induced gradient structures and special deformation-induced gradient structures.

[0004] Introducing heterogeneous particles into gradient structures has inherent drawbacks: firstly, it alters the original composition of the material, leading to a significant reduction in material purity; secondly, during subsequent service, the heterogeneous particles and the metal matrix are prone to stress concentration, drastically reducing the material's ductility and toughness. Special deformation-induced gradient structures suffer from long processing flows, low production efficiency, and high costs. Furthermore, the prepared gradient materials are large in scale, exhibiting a gradient structure macroscopically but with uniform microstructure, failing to meet the application requirements of gradient magnesium alloy thin plates. Summary of the Invention

[0005] In view of the defects and deficiencies in the existing technology, the purpose of this invention is to provide a magnesium alloy sheet with a gradient twin structure, its preparation method and application, so as to achieve high-quality, high-efficiency and low-cost preparation of the gradient twin structure magnesium alloy sheet, while ensuring the purity of the material composition, and meeting the application needs of gradient magnesium alloy thin sheets in related fields.

[0006] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: A method for preparing a magnesium alloy sheet with a gradient twinning structure includes the following steps: S1. Select a magnesium alloy sheet as the metal substrate and fix it on the worktable of the friction stir additive manufacturing equipment; select a magnesium alloy wire of the same grade as the metal substrate as the additive raw material; heat the magnesium alloy wire and magnesium alloy sheet respectively and perform friction stir solid-state additive manufacturing to obtain a heated magnesium alloy deposited sheet with different preferred orientations of grains along the thickness direction. S2, keeping the heating temperature of the magnesium alloy substrate constant, ultrasonically roll the magnesium alloy deposition plate to cause twinning deformation of grains with different orientations along the thickness direction of the plate, and obtain the ultrasonically rolled magnesium alloy deposition plate. S3, the magnesium alloy deposited plate after ultrasonic rolling is separated from the metal substrate to obtain a gradient twinned magnesium alloy plate.

[0007] 2. The method for preparing magnesium alloy sheet with gradient twin structure as described in claim 1, characterized in that the magnesium alloy sheet and magnesium alloy wire in S1 are of the AZ series or ZK series.

[0008] Preferably, the thickness of the magnesium alloy substrate in S1 is ≤5mm, and the diameter of the magnesium alloy wire is 2~3mm.

[0009] Preferably, in S1, a dual heat source using resistance wire is used to heat the magnesium alloy wire and the magnesium alloy plate respectively; the heating temperature of the magnesium alloy wire... The unit is ℃, where This is an empirical coefficient, with a value ranging from 0.8 to 0.9. The melting point of magnesium alloy wire; the heating temperature of the upper surface of magnesium alloy sheet. The unit is ℃, where This is an empirical coefficient, with a value ranging from 0.6 to 0.8.

[0010] Preferably, in S1, the downward pressure load of the deposition head manufactured by friction stir solid-phase additive manufacturing is 3~6KN, the rotation speed of the deposition head is 1000~3800r / min, and the forward speed of the deposition head is 50~300mm / min.

[0011] Preferably, the thickness of the single-layer magnesium alloy sheet is achieved by adjusting the distance between the shoulder of the deposition head and the upper surface of the metal substrate, and the deposition layer thickness is... , where L is the distance between the shoulder of the deposition head and the upper surface of the magnesium alloy plate, with a value of 1 to 3, in mm.

[0012] Preferably, the ultrasonic rolling pressure in S2 is 300~800N, amplitude is 5~9μm, and speed is 50~80mm / min.

[0013] Preferably, ultrasonic rolling is used to ultrasonically roll the magnesium alloy deposited plate in a "snake-like" trajectory.

[0014] A magnesium alloy sheet with a gradient twinned structure is prepared by the method for preparing a magnesium alloy sheet with a gradient twinned structure disclosed in this application.

[0015] An application of a magnesium alloy sheet with a gradient twin structure prepared by the method disclosed in this application.

[0016] The above technical solution has the following beneficial effects: (1) High material purity: This invention achieves a gradient twin structure by heat source-assisted ultrasonic rolling without introducing any heterogeneous particles, thus maintaining the original composition of the magnesium alloy and avoiding stress concentration problems caused by heterogeneous particles. The material has significantly better plasticity and toughness than the gradient materials prepared by the existing heterogeneous particle induction method, and has extremely high potential application value in the field of high-purity gradient magnesium alloy demand.

[0017] (2) Short process flow and high production efficiency: The present invention can complete the preparation through only three core processes: "dual heat source assisted stirring friction solid phase additive manufacturing + heat source assisted ultrasonic rolling + separation". It does not require multiple deformations or complex post-processing, resulting in high production efficiency and low production cost. It can also realize the one-time forming of gradient magnesium alloy thin plates, solving the problem that traditional special deformation induction methods cannot prepare thin plates.

[0018] (3) Wide process window and good forming quality: The dual heat source auxiliary heating design greatly improves the plasticity of magnesium alloy, effectively expands the process window of friction stir solid phase additive manufacturing, avoids the problems of defects and forming difficulties that are easy to occur when manufacturing magnesium alloys by traditional friction stir solid phase additive manufacturing, and the prepared magnesium alloy deposition plate has good density and fine grains (<5μm).

[0019] (4) Controllable gradient twin structure with through thickness: During the heat source assisted ultrasonic rolling process, the heat decreases gradually along the substrate to the surface of the deposited plate. Combined with the high frequency vibration and pressure transmission of ultrasonic rolling, twinning occurs at different positions in the thickness direction of the plate to form a through gradient twin layer of 1~3mm thickness, which significantly improves the comprehensive mechanical properties of magnesium alloy plates and solves the defect that traditional ultrasonic rolling can only form a thin surface twin layer (<500μm).

[0020] (5) Low production cost and strong environmental adaptability: The friction stir solid phase additive manufacturing process does not require material melting, avoiding the solidification defects of high energy beam additive manufacturing. It can be carried out in an atmospheric environment. The raw material is metal wire, which has a high material utilization rate and greatly reduces production energy consumption and cost. It can be applied to automobiles, aerospace, medical devices and other fields. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method of the present invention; Figure 2This is a schematic diagram of a typical gradient structure magnesium alloy prepared by the method of this invention; Figure 3 This is the macroscopic morphology of the surface of the magnesium alloy sheet prepared in Example 1; Figure 4 The microstructure morphology of the magnesium alloy sheet prepared in Example 1; Figure 5 This is the microstructure morphology of the bottom surface of the magnesium alloy plate prepared in Example 1; Figure 6 The macroscopic morphology of the surface of the solid-phase additive magnesium alloy sheet produced by friction stirring without dual heat source auxiliary heating in Comparative Example 1 is shown. Figure 7 This is a comparison of the surface microstructure of the magnesium alloy sheet without heat source-assisted ultrasonic rolling in Comparative Example 2.

[0022] The specific content of the present invention will be further explained in detail below with reference to comparative examples. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] This invention discloses a magnesium alloy sheet with a gradient twinning structure and its preparation method. The method includes using a magnesium alloy sheet as a substrate, firstly using magnesium alloy wire of the same grade as the substrate for stir friction solid-state additive manufacturing, in which resistance wire is used to heat both the magnesium alloy wire and the magnesium alloy substrate with dual heat sources. The resulting magnesium alloy deposited sheet has grains with different preferred orientations along the thickness direction. Subsequently, the surface of the deposited magnesium alloy sheet is subjected to heat-assisted ultrasonic rolling. By controlling the pressure, amplitude, and rolling speed under ultrasonic rolling, different degrees of twinning deformation of grains with different orientations along the thickness direction of the sheet are achieved. Finally, the deposited magnesium alloy sheet is separated from the metal substrate to obtain a magnesium alloy sheet with a gradient distribution of twinning structure along the thickness direction of the sheet.

[0025] The main principle of the friction stir solid-state additive manufacturing technology in this invention is to use a rotating friction deposition head to rub, extrude, and deposit magnesium alloy wire, thereby achieving personalized component manufacturing. In traditional friction stir solid-state additive manufacturing of magnesium alloys, the poor plasticity of magnesium alloys results in an extremely narrow solid-state additive manufacturing process window, making defects easily generated and even preventing effective forming during actual production. To address this problem, this invention proposes a dual-heat-source assisted heating friction stir solid-state additive manufacturing method for magnesium alloy sheets. The core of this method is to preheat the wire to rapidly soften it, thereby improving the plasticity of the magnesium alloy during friction, extrusion, and deposition. Simultaneously, preheating the magnesium alloy substrate allows for effective bonding between the magnesium alloy wire and the substrate during deposition, accelerating the deposition process. This dual-heat-source assisted heating process enables effective magnesium alloy deposition and effectively expands the friction stir solid-state additive manufacturing process window, improving production efficiency. This method is one of the core innovations of this invention.

[0026] Because magnesium alloys have a close-packed hexagonal structure, they rotate during friction, extrusion, and deposition, resulting in a distinct preferred orientation along the thickness direction of the deposited magnesium alloy sheet, where the c-axis of the grains is parallel to the normal direction of the sheet. Traditional ultrasonic rolling for surface treatment of magnesium alloy sheets manufactured by friction stir solid-state additive manufacturing fails to initiate basal plane slip due to the parallel c-axis, only promoting twinning in a small number of grains. Consequently, the surface of the magnesium alloy sheet exhibits only a gradient twin layer of less than 500 μm. Because this gradient twin layer is so thin, its impact on the overall performance of the magnesium alloy sheet is minimal. To obtain a gradient twin structure characteristic that extends throughout the thickness direction of the sheet, this invention proposes using heat-assisted ultrasonic rolling for surface treatment of magnesium alloy sheets manufactured by friction stir solid-state additive manufacturing. During the heat-assisted process, heat is transferred from the substrate to the surface of the deposited magnesium alloy sheet. The heat distribution exhibits a gradient distribution characteristic, meaning that the heat gradually decreases from the bottom to the surface of the deposited magnesium alloy sheet. This results in different softening characteristics between the bottom and surface of the deposited magnesium alloy sheet. During ultrasonic rolling, high-frequency vibration and high ultrasonic rolling pressure can be transferred to different thickness positions of the deposited magnesium alloy sheet, which helps to induce twinning of varying degrees along the thickness direction of the deposited magnesium alloy sheet. This can significantly increase the twinning ratio of grains along the thickness direction of the magnesium alloy sheet, thus achieving a gradient twinned layer of 1-3 mm thickness. Figure 2 This method is another core innovation of the present invention.

[0027] This invention not only produces gradient magnesium alloy materials with pure microstructures, but also offers high production efficiency. Furthermore, compared to traditional additive manufacturing techniques using high-energy beams as heat sources, this method avoids material melting during friction-stirred solidification additive manufacturing, effectively preventing solidification defects caused by melting in traditional high-energy beam-heat-source additive manufacturing, thus significantly improving overall service performance. Simultaneously, this method allows for friction-stirred solidification additive manufacturing to be carried out in an atmospheric environment, using metal wire as the initial deposition material, resulting in a substantial reduction in overall production costs. Based on the inherent advantages of friction-stirred solidification additive manufacturing, combined with the heat-assisted ultrasonic rolling technique proposed in this invention, gradient twin structures in magnesium alloy sheets are fabricated.

[0028] Example 1: According to this invention, gradient AZ31 magnesium alloy plates are prepared using AZ31 magnesium alloy as an example: (1) Dual heat source assisted heating stirring friction solid phase additive manufacturing: AZ31 magnesium alloy plate with a thickness of 5 mm is selected as the metal substrate and fixed on the worktable of the stirring friction additive manufacturing equipment. AZ31 magnesium alloy wire with a diameter of 2 mm is selected for additive manufacturing. During the additive manufacturing process, the heating temperature of the magnesium alloy wire is T1=550℃ (empirical coefficient K=0.84), and the heating temperature of the upper surface of the magnesium alloy substrate is T2=400℃ (empirical coefficient K=0.61). As shown in the figure, the heating is from the bottom, so that the upper surface temperature reaches T2. The pressure load of the deposition head is 4 KN, the rotation speed is 3800 r / min, the forward speed is 50 mm / min, and the distance between the shoulder of the deposition head and the upper surface of the metal substrate is 2.2 mm. (2) Ultrasonic rolling: After the friction stir solid-phase additive manufacturing is completed, the surface of the deposited magnesium alloy plate is rolled by an ultrasonic rolling head. The ultrasonic rolling pressure is 600 N, the ultrasonic rolling amplitude is 9 μm, and the ultrasonic rolling speed is 50 mm / min. During the ultrasonic rolling process, the heating temperature of the upper surface of the magnesium alloy substrate is T2=400℃ (empirical coefficient K=0.61). The ultrasonic rolling head rolls the entire surface of the magnesium alloy plate in a "snake" trajectory. (3) After ultrasonic rolling is completed, the magnesium alloy substrate is separated from the metal substrate, thus obtaining a twinned magnesium alloy plate with a gradient distribution along the thickness direction of the plate.

[0029] This embodiment utilizes optimized friction stir solid-phase additive manufacturing parameters and optimized heat source-assisted ultrasonic rolling to prepare a 2 mm thick AZ31 magnesium alloy gradient material sheet, and the sheet has good forming properties. Figure 3 The heat source-assisted ultrasonic rolling of the sheet metal resulted in a higher surface twin integral number. Figure 4 The twin integral number on the bottom surface of the plate is relatively low. Figure 5Furthermore, the integral number of the twin crystal decreases along the surface of the plate to the bottom surface.

[0030] Comparative Example 1 The method used in this comparative example is the same as that in Example 1. The difference is that this comparative example 1 did not use dual heat source assisted heating for stirring friction solid-state additive manufacturing. Magnesium alloys have extremely poor plastic deformation ability during the stirring friction solid-state additive manufacturing process, resulting in many surface forming defects, or even failure to form. Figure 6 ).

[0031] Comparative Example 2 The method used in this comparative example is the same as that in Example 1. The difference is that no heat-assisted ultrasonic rolling process was performed in Comparative Example 2. The AZ31 magnesium alloy sheet prepared in this example has a uniform microstructure, with fine, uniform, and equiaxed grains, and no gradient twinning structure is generated. Figure 7 ).

[0032] Comparative Example 3 Chinese patent CN118563303A employs a method of cold spraying aluminum powder and Al2O3 particles of varying amounts onto a metal substrate surface, followed by friction stir processing. In this method, the proportion of aluminum powder used in subsequent cold spraying stages is greater than that in previous stages, and the particle size of the aluminum powder used in the subsequent cold spraying stages is smaller than that in the previous stages. This method can achieve the preparation of materials with a gradient structure. However, the gradient structure material prepared in this comparative example introduces Al2O3 particles, which cannot be eliminated from the prepared gradient structure. Compared to Example 1, the gradient structure prepared in Example 1 clearly does not introduce heterogeneous particles, and its composition is purer.

[0033] Comparative Example 4 The published paper "Microstructure and mechanical properties of Mg-15Gd-1Zn-0.4Zr alloys treated by ultrasonic surface rolling process" describes the treatment of magnesium alloys using conventional ultrasonic rolling, and the thickness of the gradient twin layer is less than 500 μm, which is much lower than the 1-3 mm thickness of the gradient twin layer in this invention.

[0034] The embodiments described above are merely preferred embodiments of the present invention and are not limited to the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention that do not depart from the technology of the present invention, and applied to any field, constitute an infringement of the protection scope of the present invention and are included within the protection scope of the present invention.

Claims

1. A method for preparing a magnesium alloy sheet with a gradient twinning structure, characterized in that, Includes the following steps: S1. Select a magnesium alloy sheet as the metal substrate and fix it on the worktable of the friction stir additive manufacturing equipment; select magnesium alloy wire of the same grade as the metal substrate as the additive raw material. Magnesium alloy wire and magnesium alloy sheet were heated separately and subjected to friction stir solid-state additive manufacturing to obtain heated magnesium alloy deposited sheets with different preferred orientations of grains along the thickness direction. S2, keeping the heating temperature of the magnesium alloy substrate constant, ultrasonically roll the magnesium alloy deposition plate to cause twinning deformation of grains with different orientations along the thickness direction of the plate, and obtain the ultrasonically rolled magnesium alloy deposition plate. S3, the magnesium alloy deposited plate after ultrasonic rolling is separated from the metal substrate to obtain a gradient twinned magnesium alloy plate.

2. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 1, characterized in that, The magnesium alloy sheet and magnesium alloy wire mentioned in S1 are of the AZ series or ZK series.

3. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 1, characterized in that, The thickness of the magnesium alloy substrate in S1 is ≤5mm, and the diameter of the magnesium alloy wire is 2~3mm.

4. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 1, characterized in that, S1 specifically uses a dual heat source of resistance wire to heat the magnesium alloy wire and the magnesium alloy plate respectively; Heating temperature of the magnesium alloy wire The unit is ℃, where This is an empirical coefficient, with a value ranging from 0.8 to 0.

9. The melting point of magnesium alloy wire; Heating temperature of the upper surface of the magnesium alloy plate The unit is ℃, where This is an empirical coefficient, with a value ranging from 0.6 to 0.

8.

5. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 4, characterized in that, The deposition head manufactured by friction stir solid-phase additive manufacturing as described in S1 has a pressure load of 3~6KN, a rotation speed of 1000~3800r / min, and a forward speed of 50~300mm / min.

6. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 5, characterized in that, The thickness of the single-layer magnesium alloy sheet is achieved by adjusting the distance between the shoulder of the deposition head and the upper surface of the metal substrate, thus controlling the thickness of the deposited layer. , where L is the distance between the shoulder of the deposition head and the upper surface of the magnesium alloy plate, with a value of 1~3, in mm.

7. The method for preparing magnesium alloy sheet with a gradient twinning structure as described in any one of claims 1 to 6, characterized in that, The ultrasonic rolling pressure in S2 is 300~800N, amplitude is 5~9μm, and speed is 50~80mm / min.

8. The method for preparing magnesium alloy sheet with gradient twinning structure as described in claim 7, characterized in that, The magnesium alloy deposition plate was ultrasonically rolled in a "snake-like" trajectory.

9. A magnesium alloy sheet with a gradient twinning structure, characterized in that, It is prepared by the method for preparing magnesium alloy sheet with gradient twin structure as described in any one of claims 1 to 8.

10. An application of a magnesium alloy sheet with a gradient twin structure prepared by the preparation method of magnesium alloy sheet with gradient twin structure according to any one of claims 1 to 8.

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