Asymmetric extrusion preparation method for heterogeneous magnesium alloy composite board with adjustable layer thickness ratio

Abstract

The invention discloses an asymmetric extrusion preparation method for a heterogeneous magnesium alloy composite board with an adjustable layer thickness ratio. The method comprises the steps that an asymmetric extrusion die with an extrusion outlet deviating from the center is designed, and an extrusion deformation section is of a triangular section in the thickness direction and of an isosceles trapezoid section in the width direction; a VK41 magnesium alloy, a ZK61 alloy and pure magnesium are machined into blanks with the thicknesses of A, B and C, the blanks are combined according to the EZP sequence after homogenization treatment, the blanks are heated to 350-400 DEG C, heat preservation is conducted, and the extrusion speed is 1-2 mm / s; extruding by adopting an asymmetric die, and placing pure magnesium on the alpha angle side to obtain a three-layer composite board; and carrying out folding or V-shaped bending test on the processed sample. By regulating and controlling the ratio of A: B: C and the extrusion shrinkage angle, accurately controlling the layer thickness ratio, introducing shear strain to improve the texture, coordinating the tension and compression asymmetry and remarkably improving the bending performance, the process is simple, and the method is suitable for industrial production and is suitable for the fields of aerospace, automobiles and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy material processing, and relates to a heterogeneous magnesium alloy composite plate asymmetric extrusion preparation method with adjustable layer thickness ratio. BACKGROUND

[0002] Magnesium alloys have significant lightweight application prospects in the fields of aerospace, automobiles and high-speed rail due to their high specific strength, specific stiffness, excellent damping performance and recyclability. However, the limited slip system at room temperature due to the hexagonal close-packed (HCP) crystal structure leads to poor ductility and formability, especially in processes such as drawing, stamping and bending. The magnesium alloy plate prepared by traditional extrusion or rolling process forms strong basal texture (c-axis parallel to the plate surface normal), resulting in significant tensile-compressive asymmetry in the extrusion direction (ED). During bending forming, the stress state of the outside being in tension and the inside being in compression causes uneven thickness direction strain, the neutral layer migrates inward, and the outside strain increases, leading to cracking.

[0003] To improve the forming performance, researchers have explored heterogeneous structure design by introducing composite layers (such as combinations of magnesium rare earth alloys, commercial alloys and pure magnesium) in the thickness direction to coordinate strain distribution. Magnesium rare earth alloys can refine grains and weaken texture by adding yttrium (Y) and gadolinium (Gd), but the cost is high; ZK61 alloy (containing zinc and zirconium) has moderate strength and plasticity; pure magnesium has good ductility but low strength. The EZP structure (magnesium rare earth alloy / ZK61 / pure magnesium) can reduce the amount of rare earth elements and optimize the performance by proper arrangement. However, the existing symmetric extrusion method cannot accurately control the thickness ratio of each layer, and the flow stress difference leads to uneven layer thickness, affecting the stability of performance.

[0004] Asymmetric extrusion forms an asymmetric structure by shifting the extrusion outlet, introduces shear strain, disperses texture and controls material flow path. Existing asymmetric extrusion researches mainly focus on single-phase alloys, and the mechanism of layer thickness ratio control for heterogeneous magnesium alloy composite plates is not clear, especially lacking a systematic method of joint control of die angle and initial material thickness ratio. In addition, traditional methods such as laminated rolling or explosive welding have problems such as complex process, low interfacial bonding strength or high cost, which are difficult to meet the industrialization demand. SUMMARY

[0005] Therefore, the purpose of the present application is to solve the above problems and provide a heterogeneous magnesium alloy composite plate asymmetric extrusion preparation method with adjustable layer thickness ratio.

[0006] To achieve the above purpose, the present application provides the following technical scheme:

[0007] A heterogeneous magnesium alloy composite plate asymmetric extrusion preparation method with adjustable layer thickness ratio, comprising the following steps:

[0008] a. design an asymmetric extrusion die, the extrusion outlet of which deviates from the center of the extrusion cavity, and the bottom of the extrusion cavity is connected with the extrusion outlet through an extrusion deformation section; the cross section of the extrusion deformation section in the thickness direction of the plate is triangular, and the shrinkage angles of the thicknesses of the two sides are α and β, respectively, and α < β;

[0009] b. homogenize the magnesium-rare earth alloy and the commercial ZK61 magnesium alloy ingot, and do not homogenize the pure magnesium; process the magnesium-rare earth alloy, the commercial ZK61 alloy and the pure magnesium into cuboid billets with thicknesses of A, B and C, respectively, and polish the surfaces to remove the oxide film;

[0010] c. combine the billets in the order of magnesium-rare earth alloy / commercial ZK61 alloy / pure magnesium to form a complete cuboid billet matching the size of the extrusion cavity, and heat the complete cuboid billet to the extrusion temperature and keep it at the temperature;

[0011] d. use the asymmetric extrusion die to extrude the complete cuboid billet to obtain an EZP three-layer composite plate; during the extrusion, the pure magnesium is placed close to the side of the α angle.

[0012] Further, by adjusting the initial thickness ratio A:B:C of the raw materials and the α and β angles, the layer thickness ratio is controlled, the texture is weakened, and the tensile-compressive asymmetry is coordinated.

[0013] Further, the thickness of the complete cuboid billet formed by the combination of the magnesium-rare earth alloy, the commercial ZK61 alloy and the pure magnesium is T, A is B is C is

[0014] Further, the homogenization treatment parameters of the commercial ZK61 alloy in step b are 440-460 ℃ for 10-14 h, and water quenching at room temperature; the magnesium-rare earth alloy is homogenized according to its characteristics.

[0015] Further, the cross section of the extrusion deformation section in the width direction of the plate is symmetrical along the center of the extrusion cavity and is isosceles trapezoidal, and the shrinkage angles of the widths of the two sides are γ.

[0016] Further, the range of α is 30-45°, the range of β is 50-60°, and the range of γ is 0-10°.

[0017] Further, the extrusion temperature in the extrusion process is 350-400 ℃, and the extrusion speed is 1-2 mm / s.

[0018] Optionally, the method further comprises step e: processing the composite plate into a bending sample to perform bending test, and the bending test comprises a folding test or a three-point bending test to verify the forming performance of the composite plate.

[0019] The beneficial effects of the present application are as follows:

[0020] This invention discloses an asymmetric extrusion method for preparing heterogeneous magnesium alloy composite sheets with adjustable layer thickness ratios. This method primarily leverages the unique design of the asymmetric extrusion die and the synergistic effect of the EZP heterostructure to achieve precise control over the flow behavior, microtexture, and macroscopic stress distribution of the magnesium alloy material. Specifically, the asymmetric extrusion die, through its design of the extrusion outlet being offset from the center of the extrusion cavity, forms a triangular cross-section (contraction angle α < β) in the thickness direction and an isosceles trapezoidal cross-section (contraction angle γ) in the width direction of the extrusion deformation section, introducing a non-uniform shear strain field. This asymmetric strain field alters the material flow path during extrusion: the material flow velocity is slower on the side closer to angle α (smaller angle) and faster on the side closer to angle β (larger angle), resulting in the amplification or harmonization of flow stress differences. By adjusting the initial billet thickness ratio A:B:C and the die angles α, β, and γ, the deformation amount of each layer and the final layer thickness distribution can be dynamically controlled. For example, when C (pure magnesium thickness) is increased and the α angle is decreased, the pure magnesium layer (placed on the α angle side) widens due to enhanced shear strain. The layer thickness ratio is adjusted from 1:1:1 to a variable ratio, thereby optimizing the heterostructure.

[0021] At the microscopic level, the EZP heterostructure utilizes the differences in mechanical properties among three alloys: the high strength and grain refinement of magnesium rare-earth alloys, the moderate plasticity and strengthening phase distribution of ZK61 alloy, and the high ductility and low flow stress of pure magnesium. The interfacial shear strain introduced by asymmetric extrusion promotes grain rotation and recrystallization, dispersing the basal texture (the c-axis shifts from being parallel to the plate surface normal to a random distribution), thereby weakening the texture strength. Studies show that texture weakening can activate more slip systems (such as conical slip), improving room temperature ductility by approximately 20%–30%. Simultaneously, during bending deformation, the inward migration of the neutral layer in traditional magnesium alloys leads to an increase in tensile strain on the outer side (up to 10% or more), making it prone to cracking. This invention coordinates the tension-compression asymmetry through EZP arrangement: when the outer pure magnesium layer is subjected to tensile stress, the texture dispersion caused by its shear promotes uniform plastic rheology, effectively eliminating local stress concentration and thus preventing the initiation of outer cracks; the middle ZK61 alloy buffers stress transmission; and the inner magnesium rare earth alloy absorbs compressive stress and promotes uniform deformation, reducing the migration of the neutral layer by about 50%, reducing the strain on the outer side, and significantly improving the bending limit.

[0022] Overall, this invention, based on the principles of flow dynamics, micrometallurgy, and macromechanics, solves the bottlenecks in traditional magnesium alloy processing, provides an efficient and economical preparation path, and promotes the application of magnesium alloys in the field of lightweighting.

[0023] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0025] Figure 1 This is a schematic cross-sectional view of the asymmetric extrusion die in the thickness direction of the sheet metal in this invention.

[0026] Figure 2 This is a schematic cross-sectional view of the asymmetric extrusion die in the width direction of the sheet metal in this invention.

[0027] Figure 3 This is a schematic diagram of the complete cuboid billet formed by the combination of VK41 magnesium alloy / ZK61 alloy / pure magnesium in Embodiment 1 of the present invention.

[0028] Figure 4 The figures show the pole diagrams of the pure magnesium layer and the VK41 layer of the composite plate prepared in Example 1.

[0029] Figure 5 The dimensions are those of the mold used in Embodiment 1 of this invention.

[0030] Figure 6 Microscopic morphology image of the magnesium alloy composite plate prepared in Example 1

[0031] Figure 7 The results are from the bending and folding tests in Example 1 of this invention.

[0032] Figure 8 The results are from the bending test in Example 2 of this invention. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0034] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0035] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0036] Example 1

[0037] A method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio by asymmetric extrusion includes the following steps:

[0038] a. Design an asymmetric extrusion die: Design an asymmetric extrusion die with the extrusion outlet offset from the center of the extrusion chamber. The bottom of the extrusion chamber and the extrusion outlet are connected through an extrusion deformation section. The cross-section of the extrusion deformation section in the thickness direction of the sheet metal is triangular, such as... Figure 1 , 5 As shown, the contraction angles of the thickness on both sides are α = 37° and β = 58°, respectively; the cross-section in the width direction is symmetrical along the center of the extrusion cavity and has an isosceles trapezoidal shape, as shown. Figure 2 As shown, the contraction angle γ on both sides is 6°.

[0039] b. Billet Preparation and Homogenization: VK41 magnesium alloy (magnesium rare earth alloy) and commercial ZK61 magnesium alloy ingots are homogenized at 450℃ for 12 hours, followed by water quenching at 20℃; pure magnesium is not heat-treated. The three alloys are processed into rectangular billets with thicknesses A (VK41 magnesium alloy), B (ZK61 alloy), and C (pure magnesium), respectively. The A:B:C ratio is determined based on the extrusion cavity dimensions (a complete rectangular billet is shown in the image). Figure 3 As shown in the figure, the surface of the blank is mechanically polished to remove the oxide film and enhance the interfacial bonding.

[0040] c. Billet Assembly and Heating: The billets are assembled in the order of VK41 magnesium alloy / ZK61 alloy / pure magnesium (EZP) to form a complete cuboid billet that matches the size of the extrusion chamber. Figure 3The billet is heated to the extrusion temperature of 400℃ and held for 5 minutes to ensure uniform heating. The thickness of the complete rectangular billet is T, then A is... B is C is

[0041] d. Asymmetric extrusion: Extrusion is performed using the asymmetric extrusion die designed in step a. During extrusion, pure magnesium is placed on the side closer to angle α (37°), and the extrusion speed is 1 mm / s to obtain EZP three-layer heterogeneous magnesium alloy composite sheet.

[0042] e. Bending performance test: The composite board is processed into a bending sample with the pure magnesium layer on the outside. A folding test is conducted using a 5mm folding pad (folding radius r = board thickness t) to verify the forming performance.

[0043] Results: The microstructure of the composite board is as follows Figure 6 As shown, a uniform interface bonding and refined grain structure are evident. (Pole diagram of pure magnesium layer) Figure 4 This indicates that the shear strain introduced by asymmetric compression effectively disperses the basal texture, resulting in a more random c-axis distribution. (VK41 solitopic plot) Figure 4 This indicates that the shear deformation introduced by asymmetric extrusion transforms the rare-earth texture into one that is more conducive to providing thickness-direction deformation on the inner side of the bend, further improving the tension-compression asymmetry. In the folding test, the sheet was successfully formed without cracking. Figure 7 The EZP structure harmonizes the tension-compression asymmetry, reduces neutral layer migration, lowers outer strain, and significantly improves bending performance.

[0044] Example 2 (Comparative Example)

[0045] This embodiment uses traditional molds to process magnesium alloy composite sheets, and the steps are as follows:

[0046] a. Billet preparation and homogenization: The VK41 magnesium alloy ingot was homogenized by holding at 450℃ for 12 hours and then water-quenching at room temperature. It was then processed into a single-layer cuboid billet with the same dimensions as the complete cuboid billet in Example 1, and the oxide film was removed by surface grinding.

[0047] b. Billet heating: Heat the billet to 400℃ and hold for 5 minutes.

[0048] c. Traditional extrusion: Extrusion is performed using a traditional symmetrical extrusion die (the extrusion outlet is located in the center of the extrusion chamber, without a triangular or trapezoidal cross-section design) at an extrusion speed of 1 mm / s to obtain a single-layer VK41 magnesium alloy sheet.

[0049] d. Bending performance test: The sheet material is processed into bending specimens and tested using a 150° three-point bending mold.

[0050] Result: Cracks appeared at the bottom of the sheet during the 150° bending test. Figure 8 The forming performance is poor. Compared with Example 1, traditional symmetrical extrusion cannot effectively weaken the texture or coordinate the tension-compression asymmetry, resulting in significant performance degradation.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. 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 be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio by asymmetric extrusion, characterized in that, Includes the following steps: a. Design an asymmetric extrusion die, wherein the extrusion outlet of the die is offset from the center of the extrusion chamber, and the bottom of the extrusion chamber is connected to the extrusion outlet by an extrusion deformation section; the cross-section of the extrusion deformation section in the thickness direction of the sheet is triangular, and the shrinkage angles of the thickness on both sides are α and β, respectively, and α < β; b. Homogenize the magnesium rare earth alloy and commercial ZK61 magnesium alloy ingots, but do not treat the pure magnesium. Process the magnesium rare earth alloy, commercial ZK61 alloy and pure magnesium into cuboid blanks with thicknesses A, B and C respectively, and grind the surface to remove the oxide film. c. Combine the billets in the order of magnesium rare earth alloy / commercial ZK61 alloy / pure magnesium to form a complete cuboid billet that matches the size of the extrusion cavity, and heat it to the extrusion temperature and hold it at that temperature; d. The complete rectangular blank is extruded using the asymmetric extrusion die to obtain EZP three-layer composite sheet; during extrusion, pure magnesium is placed on the side closer to the α angle.

2. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 1, characterized in that: By adjusting the initial thickness ratio A:B:C of the raw materials and the α and β angles, the layer thickness ratio can be controlled, the texture can be improved, and the tension-compression asymmetry can be coordinated.

3. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 2, characterized in that: If the thickness of the complete cuboid billet formed by the combination of magnesium rare earth alloy, commercial ZK61 alloy, and pure magnesium is T, then A is... B is C is 4. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 1, characterized in that: In step b, the homogenization treatment parameters for commercial ZK61 alloy are 440℃~460℃ for 10~14h, followed by room temperature water quenching; the magnesium rare earth alloy is homogenized according to its characteristics.

5. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 1, characterized in that: The cross-section of the extrusion deformation section is symmetrical along the center of the extrusion cavity in the width direction of the plate, and is in the shape of an isosceles trapezoid, with a contraction angle of γ on both sides.

6. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 5, characterized in that: The range of α is 30–45°, the range of β is 50–60°, and the range of γ is 0–10°.

7. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 1, characterized in that: The extrusion temperature during the extrusion process is 350–400℃, and the extrusion speed is 1–2 mm / s.

8. The method for preparing heterogeneous magnesium alloy composite plates with adjustable layer thickness ratio according to claim 1, characterized in that: It also includes step e, which involves processing the composite board into a bending specimen and conducting a bending test, including a folding test or a three-point bending test, to verify the forming performance of the composite board.

Images