High bending formability heterogeneous magnesium alloy multilayer composite plate and preparation method thereof

Abstract

The present invention relates to a high-bending formability heterogeneous magnesium alloy multilayer composite plate and a preparation method thereof. The composite plate adopts a three-layer structure, including an AZ31 alloy layer in the middle and magnesium rare earth alloy layers on both sides thereof. The preparation method comprises: (1) homogenizing AZ31 alloy and magnesium rare earth alloy ingots and processing them into rectangular blanks of predetermined size, while removing the surface oxide film; (2) stacking the blanks in the manner of magnesium rare earth-AZ31-magnesium rare earth and heating them to 330°C to 370°C; (3) using a symmetrical extrusion die for extrusion to obtain a plate with a three-layer composite structure. The channel of the extrusion die consists of an inlet section, a tapered transition section and an outlet section, and the angle of the tapered transition section ranges from 70° to 110°. The present invention reduces the tensile and compressive asymmetry of the plate during bending through the multilayer heterogeneous structure, thereby significantly improving its forming performance. The prepared composite plate is subjected to a bending performance test, and the results show that its formability is better than that of a single alloy plate.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy plate preparation, and relates to a high-bending-formability heterogeneous magnesium alloy multilayer composite plate and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloys offer advantages such as high specific strength, specific stiffness, good damping, and good recyclability, and hold great promise for lightweight manufacturing in aerospace, automotive, and high-speed rail applications. However, magnesium alloys have a hexagonal close-packed (HCP) crystal structure and a limited number of slip systems that can be activated at room temperature, resulting in poor ductility and formability at room temperature, limiting the widespread application of wrought magnesium alloys.

[0003] Magnesium alloy sheets produced by traditional extrusion or rolling processes have a strong basal texture, that is, the c-axis of most grains is parallel to the plate surface normal (ND), resulting in strong anisotropy and tensile-compressive asymmetry in the sheet, and low formability. Studies have shown that arranging heterogeneous structures in the thickness direction of the sheet, such as heterogeneous composite layers, can weaken the tensile-compressive asymmetry of the magnesium alloy sheet during bending deformation, thereby significantly improving its bending formability. Therefore, the present invention will provide a multi-layer heterogeneous magnesium alloy composite sheet with high bending formability and a preparation method thereof, promoting the development and application of high-formability magnesium alloy sheets. Summary of the Invention

[0004] In view of this, the purpose of the present application is to provide a highly bendable heterogeneous magnesium alloy multilayer composite plate and a preparation method thereof, so as to solve the problem that magnesium alloy plates have poor bending formability and are prone to cracking during the bending process.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A high-bending-formability heterogeneous magnesium alloy multilayer composite plate comprises an AZ31 alloy layer in the middle and magnesium-rare earth alloy layers composited on both sides of the AZ31 alloy layer.

[0007] A method for preparing the above-mentioned high bending formability heterogeneous magnesium alloy multilayer composite plate comprises the following steps:

[0008] S1. The magnesium rare earth alloy and AZ31 alloy ingots are homogenized and processed into rectangular blanks of predetermined sizes, and the surfaces of the blanks are mechanically polished to remove the surface oxide film;

[0009] S2. Stacking magnesium rare earth alloy and AZ31 alloy rectangular billets in the form of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded billet with an EAE composite structure, heating the billet to an extrusion temperature of 330-370° C., and holding the billet for a time determined by the billet size;

[0010] S3. Extrusion is performed using a symmetrical extrusion die at an extrusion speed of 1 to 2 mm / s to obtain a magnesium alloy composite plate having an EAE three-layer composite structure.

[0011] Further, in step S3, the symmetrical extrusion mold includes a mold body, and an extrusion channel is provided in the mold body. The extrusion channel is composed of an inlet section, a tapered transition section and an outlet section from the feed port to the discharge port. The inlet section, the tapered transition section and the outlet section are symmetrical relative to the center line of the mold body; the large diameter end of the tapered transition section is connected to the inlet section, and the small diameter end of the tapered transition section is connected to the outlet section.

[0012] Furthermore, the angle α of the tapered transition section ranges from 70° to 110°.

[0013] Furthermore, in step S1, the parameters for homogenization treatment of the AZ31 alloy ingot are 440°C to 460°C / 10 to 14 hours, and room temperature water quenching is performed after homogenization treatment. The rare earth magnesium alloy is homogenized according to the alloy properties.

[0014] Furthermore, in step S1, the size of the rectangular blank is determined according to the size of the extrusion chamber used and the properties of the magnesium rare earth alloy. The thickness of the magnesium rare earth alloy rectangular blank is A, and the thickness of the AZ31 alloy rectangular blank is B. The value of A / (2A+B) is controlled to be 0.25~0.4.

[0015] Furthermore, the obtained magnesium alloy composite sheet was processed into bending specimens for bending forming performance testing.

[0016] The beneficial effects of the present invention are:

[0017] The present invention uses the EAE arrangement to prepare a composite board with a three-layer heterogeneous structure:

[0018] 1. Texture changes caused by materials: The texture (0001) extreme density points of rare earth magnesium alloy are more dispersed after extrusion.

[0019] 2. The alloy interface shearing caused by the arrangement makes the texture dispersion of each layer of the plate more obvious.

[0020] 3. The dispersion of grain orientation improves bending performance. Twin coordinated strain is more likely to occur on the inside, reducing the internal compressive stress and thus weakening the tension-compression asymmetry. When traditional plates are bent, the neutral layer migrates inward, resulting in relatively large strain on the outside. However, after the tension-compression asymmetry is improved, the inward migration of the neutral layer becomes smaller, the strain on the outside becomes smaller, the through-thickness strain distribution is improved, and the bending performance is greatly improved. At the same time, the EAE three-layer composite layered structure effectively reduces stress concentration on the outside of the plate, further improving the bending performance.

[0021] 4. The present invention reduces the use of rare earth magnesium alloy and reduces costs on the basis of improving bending forming performance.

[0022] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0024] Figure 1 It is a structural schematic diagram of the symmetrical extrusion die in the present invention.

[0025] Figure 2 The rectangular extruded billet is formed by laminating the magnesium rare earth alloy and AZ31 alloy rectangular billets in the present invention.

[0026] Figure 3 This is the mold size used in Example 1 of the present invention.

[0027] Figure 4 The microstructure and texture components of each layer of the composite plate in Example 1.

[0028] Figure 5 These are the bending and folding test results in Example 1 of the present invention.

[0029] Figure 6 The bending test results in the comparative example are shown in FIG. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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 illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0031] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0032] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships 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 direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] Example 1

[0034] A high-bending-formability heterogeneous magnesium alloy multilayer composite plate comprises an AZ31 alloy layer in the middle and magnesium-rare earth alloy layers composited on both sides of the AZ31 alloy layer.

[0035] A method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability comprises the following steps:

[0036] S1. The magnesium rare earth alloy and AZ31 alloy ingots are homogenized separately and processed into rectangular blanks of predetermined sizes. The surfaces of the blanks are mechanically polished to remove the surface oxide film. The parameters for the homogenization treatment of the AZ31 alloy ingot are 440℃~460℃ / 10~14h, and the ingots are quenched in water at room temperature after the homogenization treatment. The rare earth magnesium alloy is homogenized according to the alloy properties.

[0037] See also Figure 2 The size of the rectangular blank is determined by the size of the extrusion chamber used and the properties of the magnesium rare earth alloy. The thickness of the magnesium rare earth alloy rectangular blank is A, and the thickness of the AZ31 alloy rectangular blank is B. The value of A / (2A+B) is controlled to be 0.25~0.4.

[0038] S2. Stacking magnesium rare earth alloy and AZ31 alloy rectangular billets in the form of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded billet with an EAE composite structure, heating the billet to an extrusion temperature of 330-370° C., and holding the billet for a time determined by the billet size;

[0039] S3. Extrusion is performed using a symmetrical extrusion die at an extrusion speed of 1 to 2 mm / s to obtain a magnesium alloy composite plate having an EAE three-layer composite structure.

[0040] See also Figure 1 The symmetrical extrusion die includes a die body, an extrusion channel is provided in the die body, and the extrusion channel is composed of an inlet section, a tapered transition section and an outlet section from the feed port to the discharge port. The inlet section, the tapered transition section and the outlet section are symmetrical relative to the center line of the die body; the large diameter end of the tapered transition section is connected to the inlet section, and the small diameter end of the tapered transition section is connected to the outlet section. The angle α of the tapered transition section is in the range of 70 to 110°.

[0041] Specifically:

[0042] S1. The Mg-1.5Gd magnesium alloy and the commercial AZ31 alloy ingots are homogenized and processed into rectangular blanks of a certain size. The size of the rectangular blanks is determined by the size of the extrusion chamber used and the properties of the magnesium rare earth alloy ( Figure 2 ), in this example, A / (2A+B)=1 / 3 is selected, and the surface of the billet is mechanically polished to remove the surface oxide film; the homogenization treatment parameters for Mg-1.5Gd and AZ31 ingots are 450℃ / 12h, and the quenching is 20℃ water quenching.

[0043] S2. Combine the Mg-1.5Gd magnesium alloy and the commercial AZ31 alloy rectangular billets in the manner of Mg-1.5Gd magnesium alloy-commercial AZ31-Mg-1.5Gd magnesium alloy (EAE) to form a complete rectangular extruded billet, heat it to an extrusion temperature of 350°C, and keep it warm for 5 minutes.

[0044] S3, using a symmetrical extrusion die to extrude at a speed of 1 mm / s to obtain an EAE three-layer magnesium alloy composite sheet; the die size is selected as follows Figure 3 As shown, α=90°.

[0045] S4. Process the plate into a bending specimen for bending forming performance test. The three-point bending mold used in the test is 30°, and the thickness of the folding mold pad is 5.8mm.

[0046] In this embodiment, the micromorphology and texture components of the Mg-1.5Gd-AZ31-Mg-1.5Gd composite plate extruded by the die are as follows: Figure 4 As shown, the bending performance test is as follows Figure 5 As shown in the figure, the plate can be successfully formed in the 30° bending test and the folding test without any cracks.

[0047] Comparative Example

[0048] S1. Homogenize the commercial AZ31 ingot, quench it, and process it into a rectangular blank of a certain size. The homogenization parameters of the AZ31 ingot are 450°C / 12h, and the quenching is water quenching at 20°C. The blank has the size of the EAE combination in Example 1.

[0049] S2. Heat the billet to the extrusion temperature and keep it warm; the holding temperature is 350°C;

[0050] S3. After the heat preservation is completed, the symmetrical extrusion die in Example 1 is used for extrusion at an extrusion speed of 1 mm / s to obtain an AZ31 plate.

[0051] S4. Process the plate into a bending specimen and test its bending performance. The three-point bending die used in the test is 60°. The test results are as follows: Figure 6 As shown in Figure 3, the extruded AZ31 magnesium alloy sheet was not successfully formed in the 60° bending test, and cracks were observed at the bottom.

[0052] It can be seen from the test results of Example 1 and the comparative example that the alloy interface shear brought about by the arrangement of the composite plate in the present invention makes the texture dispersion of each layer of the plate more obvious. In addition, the dispersion of grain orientation brings about the improvement of bending performance. The inner side is more likely to produce twin coordinated strain, reducing the inner compressive stress, thereby weakening the tension-compression asymmetry. When the traditional plate is bent, the neutral layer will migrate inward, resulting in a relatively large strain on the outside. After the tension-compression asymmetry is improved, the inward migration of the neutral layer becomes smaller, the outer strain becomes smaller, and the strain distribution of the plate in the thickness direction is improved, which greatly improves the bending performance. At the same time, the layered structure of the EAE three-layer composite effectively reduces the stress concentration on the outside of the plate, further improving the bending performance.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability, characterized in that: The high bending formability heterogeneous magnesium alloy multilayer composite plate includes an AZ31 alloy layer in the middle and magnesium rare earth alloy layers composited on both sides of the AZ31 alloy layer, wherein the magnesium rare earth alloy layer is a Mg-1.5Gd magnesium alloy layer. The preparation method includes the following steps: S1. The magnesium rare earth alloy and AZ31 alloy ingots are homogenized and processed into rectangular blanks of predetermined sizes, and the surfaces of the blanks are mechanically polished to remove the surface oxide film; S2. stacking magnesium rare earth alloy and AZ31 alloy rectangular billets in the form of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded billet with an EAE composite structure, heating the billet to an extrusion temperature of 330-370° C., and holding the billet for a time determined by the billet size; S3. Extrusion is performed using a symmetrical extrusion die at an extrusion speed of 1-2 mm / s to obtain a magnesium alloy composite plate having an EAE three-layer composite structure.

2. The method for preparing a heterogeneous magnesium alloy multi-layer composite plate with high bending formability according to claim 1, characterized in that: In step S3, the symmetrical extrusion mold includes a mold body, and an extrusion channel is provided in the mold body. The extrusion channel is composed of an inlet section, a tapered transition section and an outlet section from the feed port to the discharge port. The inlet section, the tapered transition section and the outlet section are symmetrical relative to the center line of the mold body; the large diameter end of the tapered transition section is connected to the inlet section, and the small diameter end of the tapered transition section is connected to the outlet section.

3. The method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability according to claim 2, characterized in that: The angle α of the tapered transition section ranges from 70° to 110°.

4. The method for preparing a heterogeneous magnesium alloy multi-layer composite plate with high bending formability according to claim 1, characterized in that: In step S1, the AZ31 alloy ingot is homogenized at a temperature of 440°C to 460°C for 10 to 14 hours, and then water quenched at room temperature. The rare earth magnesium alloy is homogenized according to the alloy properties.

5. The method for preparing a heterogeneous magnesium alloy multi-layer composite plate with high bending formability according to claim 1, characterized in that: In step S1, the size of the rectangular blank is determined according to the size of the extrusion chamber used and the properties of the magnesium rare earth alloy. The thickness of the magnesium rare earth alloy rectangular blank is A, and the thickness of the AZ31 alloy rectangular blank is B. The value of A / (2A+B) is controlled to be 0.25~0.

4.

6. The method for preparing a heterogeneous magnesium alloy multi-layer composite plate with high bending formability according to claim 1, characterized in that: The obtained magnesium alloy composite sheets were processed into bending specimens for bending forming performance testing.

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