Heterogeneous magnesium alloy multilayer composite board with high bending formability and preparation method thereof

Abstract

The 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, and comprises a middle AZ31 alloy layer and magnesium rare earth alloy layers on the two sides of the middle AZ31 alloy layer. The preparation method comprises the following steps: (1) carrying out homogenization treatment on AZ31 alloy and magnesium rare earth alloy cast ingots, processing the cast ingots into cuboid blanks with preset sizes, and removing surface oxidation films at the same time; (2) the blanks are stacked according to the mode of magnesium rare earth, AZ31 and magnesium rare earth, and the blanks are heated to 330-370 DEG C; and (3) extruding by using a symmetric extrusion die to obtain the plate with a three-layer composite structure. A channel of the extrusion die is composed of an inlet section, a conical transition section and an outlet section, and the included angle of the conical transition section ranges from 70 degrees to 110 degrees. The tension and compression asymmetry in the bending process of the plate is weakened through the multi-layer heterostructure, and therefore the forming performance of the plate is remarkably improved. The prepared composite board is subjected to a bending performance test, and the result shows that the formability of the composite board is superior to that of a single alloy board.

Description

Technical Field

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

[0002] As the lightest metal structural material, magnesium alloy has the advantages of high specific strength, specific stiffness, good damping and good recyclability, and has great application prospects in lightweight manufacturing in the fields of aerospace, automobiles and high-speed rail. However, magnesium alloy has a hexagonal close-packed (HCP) crystal structure, and the number of slip systems that can be opened at room temperature is limited, resulting in poor ductility and formability at room temperature, which limits the widespread application of deformable magnesium alloys.

[0003] The magnesium alloy sheet produced by the traditional extrusion or rolling process has a strong basal texture, that is, the c-axis of most grains is parallel to the plate surface normal (ND), resulting in the sheet having strong anisotropy and tensile-compressive asymmetry, and low forming performance. 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 greatly improving its bending forming performance. Therefore, the present invention will provide a multi-layer heterogeneous magnesium alloy composite plate with high bending forming performance and a preparation method thereof, to promote 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 the magnesium alloy plate has poor bending formability and is 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 intermediate AZ31 alloy layer and magnesium rare earth alloy layers composited on both sides of the AZ31 alloy layer.

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

[0008] S1, respectively homogenizing the magnesium rare earth alloy and the AZ31 alloy ingots, processing them into rectangular blanks of predetermined sizes, and mechanically grinding the surfaces of the blanks to remove the surface oxide film;

[0009] S2, stacking the magnesium rare earth alloy and AZ31 alloy rectangular blanks in the manner of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded blank of EAE composite structure, heating to an extrusion temperature of 330-370° C., and the holding time depends on the size of the blank;

[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 die includes a die body, an extrusion channel is provided in the die body, and the extrusion channel is sequentially composed of: an inlet section, a tapered transition section and an outlet section from the feed port to the discharge port, and 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.

[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 14h, and after homogenization treatment, the ingot is water quenched at room temperature. The rare earth magnesium alloy is homogenized according to the alloy characteristics.

[0014] Further, 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, the thickness of the AZ31 alloy rectangular blank is B, and 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 a bending specimen for bending forming performance testing.

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

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

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

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

[0020] 3. The dispersion of grain orientation improves the bending performance. Twin coordinated strain is more likely to occur on the inside, reducing the inner compressive stress, thereby weakening the tension-compression asymmetry. When a traditional sheet is bent, the neutral layer migrates 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 strain on the outside becomes smaller, the strain distribution in the thickness direction is improved, and the bending performance is greatly improved. At the same time, the EAE three-layer composite layered structure effectively reduces the stress concentration on the outside of the sheet, further improving the bending performance.

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

[0022] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can 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 in conjunction with the accompanying drawings, wherein:

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

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

[0026] Figure 3 It 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 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 only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

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

[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 the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position 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 respectively, processed into rectangular blanks of predetermined sizes, and the surface of the blanks is mechanically polished to remove the surface oxide film; wherein, 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, and the rare earth magnesium alloy is homogenized according to the alloy characteristics.

[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, the thickness of the AZ31 alloy rectangular blank is B, and the value of A / (2A+B) is controlled to be 0.25-0.4.

[0038] S2, stacking the magnesium rare earth alloy and AZ31 alloy rectangular blanks in the manner of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded blank of EAE composite structure, heating to an extrusion temperature of 330-370° C., and the holding time depends on the size of the blank;

[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 comprises a die body, an extrusion channel is arranged in the die body, and the extrusion channel is sequentially composed of an inlet section, a tapered transition section and an outlet section from an inlet to an outlet, and 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, and the value range of the angle α of the tapered transition section is 70 to 110°.

[0041] Specific:

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

[0044] S3, using a symmetrical extrusion die for extrusion 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 sheet 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 microstructure and texture components of each layer 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, the plate can be successfully formed in the 30° bending test and the folding test without any cracks.

[0047] Comparative Example

[0048] S1. The commercial AZ31 ingot is homogenized and processed into a rectangular blank of a certain size after quenching; the homogenization parameters of the AZ31 ingot are 450°C / 12h, and the quenching is 20°C water quenching. The blank is the size of the EAE combination in Example 1.

[0049] S2, heating the blank to the extrusion temperature and keeping it warm; the keeping 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 for bending forming performance test. The three-point bending die used in the test is 60°. The test results are as follows: Figure 6 As shown, the extruded AZ31 magnesium alloy sheet was not successfully formed in the 60° bending forming 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 coordination 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, and the outer strain becomes smaller, which improves the strain distribution of the plate in the thickness direction and 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 and further improves the bending performance.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A high bending formability heterogeneous magnesium alloy multilayer composite plate, characterized in that: It includes an AZ31 alloy layer in the middle and magnesium rare earth alloy layers compounded on both sides of the AZ31 alloy layer.

2. A method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability as claimed in claim 1, characterized in that: The following steps are involved: S1, respectively homogenizing the magnesium rare earth alloy and the AZ31 alloy ingots, processing them into rectangular blanks of predetermined sizes, and mechanically grinding the surfaces of the blanks to remove the surface oxide film; S2, stacking the magnesium rare earth alloy and AZ31 alloy rectangular blanks in the manner of magnesium rare earth-AZ31-magnesium rare earth to form a rectangular extruded blank of EAE composite structure, heating to an extrusion temperature of 330-370° C., and the holding time depends on the size of the blank; 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.

3. The method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability according to claim 2, characterized in that: In step S3, the symmetrical extrusion die includes a die body, an extrusion channel is provided in the die body, and the extrusion channel is sequentially composed of: an inlet section, a tapered transition section and an outlet section from the feed port to the discharge port, and 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.

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

5. The method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability according to claim 2, characterized in that: In step S1, the parameters for homogenization treatment of the AZ31 alloy ingot are 440°C-460°C / 10-14h, and the ingot is quenched in water at room temperature after homogenization treatment. The rare earth magnesium alloy is homogenized according to the alloy characteristics.

6. The method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability according to claim 2, 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, the thickness of the AZ31 alloy rectangular blank is B, and the value of A / (2A+B) is controlled to be 0.25-0.

4.

7. The method for preparing a heterogeneous magnesium alloy multilayer composite plate with high bending formability according to claim 2, characterized in that: The obtained magnesium alloy composite sheets were processed into bending specimens for bending forming performance testing.

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