Preparation method of high-strength and high-plasticity gradient nanostructure AZ31 magnesium alloy sheet

Abstract

The invention provides a preparation method of a high-strength and high-plasticity AZ31 magnesium alloy sheet with a gradient nanostructure to solve the problem that an existing magnesium alloy sheet is insufficient in strength and plasticity. Commercial as-cast AZ31 magnesium alloy is used as a raw material, a magnesium alloy plate is obtained through rolling, extrusion and other deformation processes firstly, then the plate is further treated through an ultrasonic surface deep rolling technology, and the AZ31 magnesium alloy sheet with the gradient nano structure is prepared, and the strength and plasticity of the AZ31 magnesium alloy sheet are greatly improved compared with as-cast alloy; the comprehensive mechanical property of the magnesium alloy plate is superior to that of a commercial AZ31 magnesium alloy plate, and a high-performance and low-cost lightweight material is provided for intelligent equipment, 3C products and the like.

Description

Technical Field

[0001] The invention relates to the field of magnesium alloys, and in particular to a novel preparation method of a high-strength and high-plasticity magnesium alloy thin plate. Background Art

[0002] With the increasing requirements for lightweight metal materials in smart devices, 3C electronics, rail transit, etc., the research and development of lightweight and high-strength metal materials is of great significance to the advancement of science and technology, the improvement of social productivity and the enhancement of national strategic status. Magnesium and its alloys have attracted much attention due to their advantages such as light weight, high specific strength and biocompatibility. With a density of only 1.74g / cm, it is one of the lightest metals among industrial structural metal materials, which makes magnesium alloys have far-reaching application potential in industrial manufacturing fields such as aerospace, automobile manufacturing, electronic products and medical equipment. However, limited by the special properties of the close-packed hexagonal lattice structure, magnesium alloys have low strength, poor room temperature plastic deformation ability, and a more prominent inverse relationship between strength and plasticity.

[0003] In response to the above problems, relevant studies have proposed methods to improve the strength and plasticity of magnesium alloys. Patent CN201910463907.4 introduces a method for preparing a structure with multiple twin variants, by repeatedly compressing and stretching the AZ31 magnesium alloy sheet along the thickness direction to make a magnesium alloy sheet to improve the strength and forming performance of the magnesium alloy sheet. Patent CN201310568800.9 introduces a method for improving the forming performance of AZ31 magnesium alloy by homogenization, hot rolling and other processes. Patent CN202111197985.8 introduces a method for preparing a magnesium alloy sheet and strip with a gradient isomerization structure, by repeatedly cold rolling the magnesium alloy sheet and strip obtained by solution treatment of the AZ31 magnesium alloy ingot until the thickness of the magnesium alloy sheet and strip reaches the use requirements to improve the metal strength and plasticity. However, the large amount of plastic deformation in the preparation process, while promoting the improvement of strength, sacrifices plasticity to a large extent, and the strength-plasticity contradiction still exists. Summary of the invention

[0004] The present invention provides a method for preparing a high-strength and high-plasticity gradient nanostructured AZ31 magnesium alloy sheet. Specifically, an AZ31 magnesium alloy with a gradient nanostructure is prepared by a combination of traditional plastic processing and ultrasonic surface deep rolling process, thereby achieving a synergistic improvement in strength and plasticity. The gradient nanostructure is the source of the high strength and high plasticity of the AZ31 magnesium alloy: the gradient-changing grains, on the one hand, improve the material strength through the grain refinement mechanism; on the other hand, the larger grains in the core can accommodate more dislocations, thereby providing high plasticity; furthermore, the gradient of the microstructure promotes deformation incompatibility, induces more geometrically necessary dislocations and heterogeneous deformation-induced strengthening and hardening mechanisms, and further improves strength and plasticity.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention provides a method for preparing a high-strength and high-plasticity gradient nanostructured AZ31 magnesium alloy sheet, comprising the following steps:

[0007] S1. Use commercial AZ31 magnesium alloy ingot.

[0008] S2. Obtain AZ31 magnesium alloy thin plate by conventional plastic deformation methods such as hot rolling, hot extrusion or mechanical processing methods.

[0009] Furthermore, the thickness of the thin plate is 1 to 4 mm.

[0010] S3. Fix the AZ31 magnesium alloy thin plate sample on a processing base and further process it by ultrasonic surface deep rolling to obtain a thin plate with a gradient nanostructure.

[0011] Furthermore, the processing head for ultrasonic surface deep rolling is a cemented carbide or ceramic ball with a diameter of 14 mm.

[0012] Furthermore, the processing parameters of the ultrasonic surface deep rolling are: ultrasonic signal frequency is 23kHz, amplitude is 5μm, S-shaped route is used for scanning processing, scanning interval is 0.1mm, and linear speed is 0.8m / min.

[0013] Furthermore, cutting oil is used for cooling and lubrication during the rolling process to obtain a high-quality surface.

[0014] Furthermore, the static pressure during the rolling process is 100-2000N. By changing the pressure, the thickness of the gradient layer can be regulated, and then the strong plasticity can be regulated.

[0015] Furthermore, one or both sides of the thin plate can be rolled, and an asymmetric gradient nanostructure is obtained by single-sided processing, and a symmetric gradient nanostructure is obtained by double-sided processing.

[0016] Furthermore, the magnesium alloy is pretreated before ultrasonic surface deep rolling, and the pretreatment specifically comprises: grinding the magnesium alloy and ultrasonically cleaning it.

[0017] Furthermore, the above rolling process can be performed multiple times to obtain thin plates with different thicknesses and different strength-plasticity combinations.

[0018] S4. Through the above steps, an AZ31 magnesium alloy sheet with a gradient nanostructure is prepared.

[0019] The present invention discloses the following technical effects:

[0020] The present invention proposes a method for preparing a gradient nanostructured AZ31 magnesium alloy sheet, and obtains an asymmetric gradient nanostructure and a symmetric gradient nanostructure respectively through single-sided and double-sided ultrasonic surface deep rolling treatment. The static pressure of ultrasonic surface deep rolling is regulated to achieve precise regulation of the thickness of the surface gradient layer and the strong plasticity: as the static pressure increases, the thickness of the gradient layer increases, the strength increases, and the elongation decreases slightly. This method significantly improves the strength of the magnesium alloy while maintaining good plasticity, and the prepared magnesium alloy sheet has high surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings to be used in the embodiments are briefly introduced. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Attached Figure 1 This is a metallographic photograph of the sample of Comparative Example 1.

[0023] Attached Figure 2 This is a TEM image of the sample surface in Example 1.

[0024] Attached Figure 3 It is a comparison chart of the tensile properties of the samples of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0026] Embodiment 1:

[0027] S1. A commercial AZ31 magnesium alloy ingot with a diameter of 90 mm is hot extruded into a rod with a diameter of 16 mm by hot extrusion. The extrusion temperature is 350°C and the extrusion speed is 0.5 mm / min.

[0028] S2. Cut a 3 mm thick sheet using wire cutting, with the sheet surface parallel to the axis of the extruded rod. Then grind it with #400 and #800 silicon carbide sandpapers in turn, then ultrasonically clean it in anhydrous ethanol for 3 minutes and blow dry.

[0029] Ultrasonic deep surface rolling processing was performed on S3 and AZ31 magnesium alloy sheets: the processing head was a carbide ball with a diameter of 14 mm, ultrasonic, frequency was 23 kHz, amplitude was 5 μm, interval was 0.1 mm, rolling line speed was 0.8 m / min, static pressure was 1200 N, processing path was "S" type, double-sided processing, and each surface was rolled once.

[0030] Figure 1TEM image of the sample surface of Example 1. A large number of nano-sized layered structures and equiaxed nanocrystals can be observed, indicating the formation of a gradient nanostructure.

[0031] Comparative Example 1:

[0032] The AZ31 magnesium alloy ingot was directly used as comparative example 1. Figure 2 It can be seen that the as-cast sample has a coarse grain structure.

[0033] Figure 3 The uniaxial tensile stress-strain curves of the samples of Example 1 and Comparative Example 1 are given. The tensile yield strength of the sample of Comparative Example 1 is 70 MPa, the ultimate tensile strength is 179 MPa, and the elongation is 13%. In the sample of Example 1, the yield strength and the ultimate tensile strength are increased to 276 MPa and 348 MPa, which are 2.9 times and 0.9 times higher than those of the sample of Comparative Example 1, respectively, while retaining the original elongation.

[0034] The embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements and modifications made by those skilled in the art without departing from the essence of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength and high-plasticity gradient nanostructured AZ31 magnesium alloy sheet, characterized in that: The following steps are involved: S1, using commercial AZ31 magnesium alloy ingot; S2. Obtaining an AZ31 magnesium alloy sheet by a plastic deformation method or a mechanical processing method; S3. The sheet is further processed by ultrasonic surface deep rolling to obtain a gradient nanostructure.

2. According to claim 1, the plastic deformation method used in step S2 includes but is not limited to extrusion, rolling, forging, etc. The thickness of the thin plate is 1 to 4 mm.

3. According to claim 1, in step S3, the processing parameters of the ultrasonic surface deep rolling technology are: frequency of 23kHz, amplitude of 5μm, rolling speed of 0.8m / min, scanning interval of 0.1mm, ball diameter of 14mm, and rolling once.

4. According to claim 1, in said step S3, the processing head used in the ultrasonic surface deep rolling technology is a cemented carbide or ceramic ball with a diameter of 14 mm.

5. According to claim 1, in step S3, the static pressure used in the ultrasonic surface deep rolling technology is 100-2000N. Increasing static pressure increases strength and slightly decreases elongation.

6. According to claim 1, in the ultrasonic surface deep rolling process of step S3, cutting oil is used for cooling and lubrication to obtain a high-quality surface.

7. According to claim 1, in step S3, the ultrasonic surface deep rolling is performed at room temperature.

8. According to claim 1, in step S3, the ultrasonic deep surface rolling can be applied to one side or both sides of the thin plate.

9. The high-strength and high-plasticity gradient nanostructured AZ31 magnesium alloy sheet prepared by the preparation method according to claims 1-7, characterized in that: The thin plate has a gradient nanostructure, and the surface grains are refined to a nanometer scale.

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