A method of weakening the texture of a wrought magnesium alloy

Abstract

The application discloses a method for weakening texture of deformed magnesium alloy, comprising the following steps: 1) pre-stretching magnesium alloy sheet along the extrusion direction by 2% to 5%; 2) compressing the pre-stretched sheet along the transverse direction by 10% to 16%; and 3) finally annealing the pre-deformed sheet, wherein the annealing temperature is 200 DEG C to 250 DEG C, and the annealing time is 10 min to 120 min. The pre-stretching-re-compressing-post-annealing process is adopted to treat the magnesium alloy sheet, so that the strong basal texture of the magnesium alloy sheet is effectively weakened, and the maximum texture intensity is reduced from 20 mud to 11 mud. The application provides a new method for weakening the texture of deformed magnesium alloy, and lays a solid foundation for producing high-plasticity magnesium alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium alloy processing, and particularly relates to a method for weakening the texture of deformed magnesium alloy. BACKGROUND

[0002] Magnesium alloys are widely used in the automobile, electronic, medical and other industries due to their light weight, high specific strength, good biocompatibility and other advantages. However, pure magnesium, AZ31, ZK60 and other traditional deformed magnesium alloys have limited grains for coordinated deformation due to strong basal plane texture, and often exhibit low room temperature plasticity, thereby limiting their more extensive application. For example, Zhaoxuan Wu reported in the academic paper "Mechanistic origin and prediction of enhanced ductility in magnesium alloys" published in Science that the plasticity of pure magnesium with a maximum texture intensity of 15 mud is only 3.5%. C.M. Cepeda-Jime'nez reported in the paper "Effect of grain size on slip activity in pure magnesium polycrystals" published in Acta Materialia that the plasticity of pure magnesium is 10% when the maximum intensity of the basal plane texture is 10 mud. It can be seen that texture weakening is an important means to improve the room temperature plasticity of magnesium alloys.

[0003] Currently, the main method to weaken the texture of wrought magnesium alloys is rare earth alloying. After adding rare earth elements, the stacking fault energy can be reduced, thereby promoting the generation of <c+a> dislocations in magnesium alloys during deformation processing. The activation of <c+a> dislocations can promote the nucleation of non-basal oriented grains during subsequent annealing. For example, JP. Hadorn in the paper "Role of solute in the texture modification during hot deformation of Mg-Rare Earth Alloys" published in METALLURGICAL AND MATERIALS TRANSACTIONS A pointed out that the activation of <c+a> dislocations can lead to more uniform strain distribution, thereby promoting the nucleation of non-basal oriented grains. At the same time, the segregation of rare earth atoms at grain boundaries can inhibit the preferred growth of basal oriented grains, thereby promoting the uniform growth of basal and non-basal oriented grains, so that the non-basal oriented nuclei are not excessively consumed during the recrystallization and growth process. For example, Dikai Guan in the paper "Individual effect of recrystallisation nucleation sites on texture weakening in a magnesium alloy: Part 2- shear bands" published in Acta Materialia reported that during the recrystallization and grain growth stage of WE43 magnesium alloy, due to the segregation of rare earth atoms at grain boundaries, the uniform growth of grains of various orientations was promoted. The above two factors together lead to the fact that magnesium rare earth alloys often have weak basal texture. A. Kula in the research paper "Flow stress and work hardening of Mg-Y alloys" published in International Journal of Plasticity pointed out that a small amount of yttrium (Y) can significantly weaken the strong basal texture of pure magnesium. Mg-1Y (mass ratio 1%) and Mg-3Y both exhibit weak basal texture, and the maximum strength of basal texture is only 3mud and 2mud, respectively.

[0004] Although rare earth alloying can weaken the texture of magnesium alloys, there are still some problems: rare earth elements are expensive due to their low content and complex refining process, and the complex metallurgical smelting process increases the processing cost; at the same time, the addition of alloying elements is not conducive to the recycling of magnesium alloys. Therefore, it is urgent to explore a low-cost method to weaken the texture of wrought magnesium alloys without adding rare earth elements. SUMMARY

[0005] In view of the above-mentioned deficiencies of the prior art, the present application aims to provide a method for weakening the texture of deformed magnesium alloy, and solve the problems of the prior art, i.e., the texture of the deformed magnesium alloy is too strong, and the traditional process for weakening the texture of rare earth magnesium alloy is complex and has high production cost.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A method for weakening the texture of deformed magnesium alloy, comprising the following steps:

[0008] 1) pre-stretching the magnesium alloy plate along the extrusion direction, and the deformation amount is 2% to 5%;

[0009] 2) compressing the pre-stretched plate along the transverse direction, and the deformation amount is 10% to 16%;

[0010] 3) finally annealing the pre-deformed plate, the annealing temperature is 200 DEG C to 250 DEG C, and the annealing time is 10 min to 120 min.

[0011] The present application first pre-stretches along the extrusion direction, which can introduce basal plane dislocations, and by re-compression of the pre-stretched sheet along the transverse direction (perpendicular to the extrusion direction) to introduce tensile twins, the basal plane The dislocation is transformed into a pyramidal <c+a> dislocation, thereby promoting the nucleation of non-basal plane oriented grains in the recrystallization process and achieving the purpose of weakening the texture.

[0012] Further, the magnesium alloy plate is prepared by the following method: a magnesium alloy ingot is hot extruded into a plate, the die temperature is 300 DEG C, the preheating time is 2-3 hours, the extrusion temperature is 300 DEG C, and the extrusion ratio is 18.3-45.7.

[0013] Further, the magnesium alloy plate is sequentially subjected to coarse grinding by No. 400, No. 600 and No. 800 sandpaper and then subjected to fine grinding by No. 1000, No. 1200 and No. 2000 sandpaper before pre-stretching deformation. In this way, stress concentration at surface defects during pre-deformation can be prevented, so that abnormal grain growth during subsequent annealing can be prevented.

[0014] Further, the pre-stretching temperature is 25 DEG C, the pre-stretching strain rate is 1*10 -3 s -1 . In this way, abundant basal planes can be introduced. Dislocations.

[0015] Further, the compression temperature is 25°C, and the compression strain rate is 1*10 -3 s -1 . In this way, a large number of tensile twins can be introduced, which can change the preset basal plane Dislocations are effectively converted to non-basal planes<c+a> dislocation.

[0016] Furthermore, after pre-deformation, before annealing the sheet, the pre-deformed sheet is first covered with aluminum foil to prevent the formation of a surface oxide layer during annealing.

[0017] Furthermore, the magnesium alloy is pure magnesium, AZ31 or ZK60. The magnesium alloy used in the present invention does not contain rare earth elements, which can effectively simplify the process and has low production costs.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention significantly weakens the texture of the magnesium alloy sheet through a pre-stretching-recompression-post-annealing process. The texture strength is reduced from 20mud to 11mud, a relative reduction of 45%. This greatly solves the problem of excessively high texture strength of the basal surface of deformed magnesium alloys that do not contain rare earth elements.

[0020] 2. Magnesium alloy texture weakening processes with similar effects to the present invention generally require the addition of rare earth elements, which increases raw material costs, processing costs, and recycling costs. The present method does not require the addition of rare earth elements, has a simple process flow, low production costs, and high practical industrial application value and excellent economic efficiency.

[0021] 3. The present invention introduces the base surface by pre-stretching dislocations, and by re-compression of the pre-stretched sheet along the transverse direction (perpendicular to the extrusion direction) to introduce tensile twins, the basal plane The dislocations are effectively converted into pyramidal <c+a> dislocations, so as to promote the nucleation of non-basal plane oriented grains in the recrystallization process, and achieve the purpose of weakening the texture. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A schematic diagram of the pre-stretching-re-compressing-post annealing process for the pure magnesium plate of the present application;

[0023] Figure 2 A diagram of the internal dislocation configuration of the pre-stretched and re-compressed sample;

[0024] Figure 3 Microstructure diagrams and (0002) pole figures of different embodiments, (a, b) are for embodiment 1, (c, d) are for embodiment 2, and (e, f) are for embodiment 3. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application will be further described in detail below in combination with specific embodiments.

[0026] The numerical range in the present application should be understood as also specifically disclosing each intermediate value between the upper limit and the lower limit of the range. Each smaller range within any stated value or stated range, as well as any other stated value or stated range, is also included within the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0027] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which this application pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All publications mentioned in this specification are herein incorporated by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The citation of any reference herein should not be construed as an admission that it is at odds with any portion of the present specification. With respect to the use of "comprising", "containing", "having", "including", "carrying", "composed of", "made of", "composed of", "made of", "consisting of", "consisting essentially of" and the like, there is no difference between the positive and negative forms of these terms. That is, reference to a composition or method comprising one or more elements or steps means that the composition or method can further include other elements or steps.

[0028] The experimental methods used in the present application are conventional methods unless otherwise specified.

[0029] The materials, reagents and the like used in the present application can be purchased or synthesized by known methods unless otherwise specified.

[0030] The quantitative test in the present application is set up with three repeated experiments, and the average value is taken.

[0031] Reference Figure 1 A method for weakening the texture of a wrought magnesium alloy, comprising the following steps:

[0032] The magnesium alloy ingot is hot extruded into a plate, the plate is pre-stretched along the extrusion direction, the pre-stretched plate is then compressed transversely (perpendicular to the extrusion direction), the pre-deformed plate is then annealed, and finally the texture is tested. The thickness of the plate is less than 20 mm to facilitate pre-deformation.

[0033] Example 1

[0034] The present embodiment provides a method for preparing a pure magnesium plate, comprising the following steps:

[0035] A pure magnesium ingot with a diameter of 80 mm and a mass percentage of magnesium of 99.95% is hot extruded into a plate. The thickness of the plate after hot extrusion is 5 mm, the mold temperature is 300°C, the preheating time is 2-3 hours, the extrusion temperature is 300°C, and the extrusion ratio is 18.3.

[0036] Texture test:

[0037] The obtained pure magnesium plate is sampled on the extrusion surface (the plane formed by the extrusion direction and the transverse direction), and the texture is tested by electron backscatter diffraction (EBSD). The results are as follows: Figure 3As shown in (a, b), the extruded pure magnesium sheet without pre-deformation and annealing treatment shows a strong basal texture, the grains are equiaxed, the basal poles are concentrated near the normal direction, the c-axis of most grains is parallel to the plate normal, and the maximum texture strength is 20 mud.

[0038] Example 2

[0039] This embodiment provides a method for weakening the texture of a deformed magnesium alloy, comprising the following steps:

[0040] (1) Preparation of pure magnesium plate: The preparation process is the same as that in Example 1.

[0041] (2) The pure magnesium sheet was subjected to compression pre-deformation and annealing treatment along the normal direction (perpendicular to the extrusion surface). Before the normal compression pre-deformation, the pure magnesium sheet was coarsely ground with sandpaper No. 400, No. 600, and No. 800, and then finely ground with sandpaper No. 1000, No. 1200, and No. 2000. Then, it was subjected to normal pre-compression deformation under a CMT5105 universal testing machine. The compression deformation was 11%, the compression temperature was 25°C, and the compression strain rate was 1*10 -3 s -1 In order to ensure that the plate does not buckle during the compression process, the plate is fixed with a clamp for compression test. After pre-compression deformation, the plate is wrapped with aluminum foil and annealed at 250℃ for 30 minutes, followed by air cooling.

[0042] The pure magnesium sample obtained in Example 2 was subjected to texture testing. The results are as follows Figure 3 (c, d) show that the pure magnesium plate pre-deformed and annealed by normal compression still exhibits basal texture. Compared with the untreated initial plate in Example 1, the maximum texture strength is reduced to 15 mud, a relative decrease of 25%. The basal extremes are more diffusely distributed, and the strong basal texture is weakened to a certain extent. However, some grains grow abnormally, and the final microstructure exhibits a mixed crystal structure combining coarse grains and fine grains.

[0043] Example 3

[0044] This embodiment provides a method for weakening the texture of a deformed magnesium alloy, comprising the following steps:

[0045] (1) Preparation of pure magnesium plate: The preparation process is the same as that in Example 1.

[0046] (2) The pure magnesium sheet was subjected to pre-stretching-recompression-post-annealing treatment. Before the pre-stretching deformation in the extrusion direction, the pure magnesium sheet was coarsely ground with sandpaper No. 400, No. 600, and No. 800, and then finely ground with sandpaper No. 1000, No. 1200, and No. 2000. Then, it was pre-stretched on an MTS 809 fatigue machine. The pre-stretching temperature was 25 °C, the pre-stretching deformation was 3%, and the pre-stretching strain rate was 1*10-3 s -1 The internal dislocation configuration of the pre-stretched plate is as follows: Figure 2 (a, b) shows that after pre-stretching, the rich base surface Dislocations are introduced into the pure magnesium sheet.

[0047] The pre-stretched sheet is then compressed in the transverse direction on a CMT5105 universal testing machine, with a compression deformation of 14%, a compression temperature of 25°C, and a compression strain rate of 1*10 -3 s -1 To ensure that the sheet does not buckle during compression, the sheet is fixed by a clamp for compression testing. The dislocation configuration in the compressed sheet is as follows Figure 2 As shown in (c, d), after recompression, the twins effectively move the pre-set basal planes The dislocations are transformed into conical <c+a> dislocations.

[0048] After pre-stretching and re-compression deformation, the sheet was covered by aluminum foil and annealed at 250 °C for 10 minutes. After annealing, the sheet was air-cooled.

[0049] The pure magnesium sample obtained in Example 3 was subjected to texture testing. The results are shown in Table 2. Figure 3 (e, f) show that the pure magnesium plate after pre-stretching-recompression-post-annealing treatment exhibits a weak basal texture, the basal extremes are diffusely distributed, and the maximum texture strength is only 11mud, which is 45% lower than the untreated initial plate in Example 1. The strong basal texture is significantly weakened. At the same time, the microstructure exhibits an equiaxed crystal structure, and there is no obvious abnormally grown grain.

[0050] Example 4

[0051] This embodiment provides a method for weakening the texture of a deformed magnesium alloy. The preparation process is the same as that of Example 3, except that the pre-stretching deformation is 2% and the compressive deformation is 10%.

[0052] The texture test results show that the pure magnesium plate after deformation treatment in this embodiment exhibits a weak basal texture, with basal extremes diffusely distributed and a maximum texture strength of only 14mud, which is 30% lower than that of the untreated initial plate in Example 1. The strong basal texture is significantly weakened, and the microstructure exhibits an equiaxed crystal structure without obvious abnormally grown grains.

[0053] Example 5

[0054] This embodiment provides a method for weakening the texture of a deformed magnesium alloy. The preparation process is the same as that of Example 3, except that the pre-stretching deformation is 5% and the compressive deformation is 16%.

[0055] The texture test results show that the pure magnesium plate after deformation treatment in this embodiment exhibits a weak basal texture, with basal extremes diffusely distributed and a maximum texture strength of only 12mud, which is 40% lower than that of the untreated initial plate in Example 1. The strong basal texture is significantly weakened, and the microstructure exhibits an equiaxed crystal structure without obvious abnormally grown grains.

[0056] In summary, after the pre-stretching-recompression-post-annealing process of the present invention is applied to the deformed magnesium alloy with strong basal texture, its strong basal texture is significantly weakened, and the maximum texture strength is reduced from 20mud to 11mud. Pre-stretching along the extrusion direction can introduce rich basal texture. dislocations, and by re-compression of the pre-stretched sheet along the transverse direction (perpendicular to the extrusion direction) to introduce tensile twins, the basal plane The dislocation is effectively converted into <c+a> dislocation, and the <c+a> dislocation can promote the nucleation of non-basal plane oriented grains, which is the main reason for the texture weakening. Meanwhile, the application does not need the addition of rare earth elements, avoids the expensive and complex metallurgical smelting treatment, has a simple process flow, is easy for industrial batch production, and has high industrial practical application value.

[0057] The application only takes the typical pure magnesium extruded plate with strong basal plane texture as the implementation object, compares the materials and processes, proves that the application has obvious effect on weakening the texture, but does not exclude that the process method of the application is also applicable to the texture weakening of other strong basal plane texture deformed magnesium alloys, such as AZ31, ZK60, etc. And the above is only the preferred implementation mode of the application, and the deformation amount of the pre-stretching deformation of the application is not limited to the numerical value of the embodiment, for example, 2%, 4%, 5%; the deformation amount of the re-compression deformation is also not limited to the numerical value of the embodiment, for example, 10%, 12%, 16%; the annealing temperature and the annealing time of the annealing treatment are also not limited to the numerical value of the embodiment, for example, 200℃-120 minutes, 220℃-60 minutes, 240℃-20 minutes. It should be pointed out that, for the ordinary skilled in the art, some improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements should also be regarded as the protection scope of the application.

Claims

1. A method for weakening the texture of a deformed magnesium alloy, characterized in that: The steps include: 1) Pre-stretch the magnesium alloy sheet along the extrusion direction with a deformation of 2% to 5%; 2) The pre-stretched plate is then compressed in the transverse direction with a deformation of 10% to 16%; 3) Finally, the pre-deformed sheet is annealed at a temperature of 200°C to 250°C for 10 minutes to 120 minutes; Introduction of the base surface by pre-stretching dislocation, and then the twins introduced by compression will Dislocations are effectively converted into cones<c+a> Dislocations promote the nucleation of non-basal-plane oriented grains during recrystallization, thereby weakening the texture.

2. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: The magnesium alloy plate is prepared by the following method: a magnesium alloy ingot is cast and hot-extruded into a plate, the mold temperature is 300° C., the preheating time is 2 to 3 hours, the extrusion temperature is 300° C., and the extrusion ratio is 18.3 to 45.

7.

3. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: Before the pre-stretching deformation, the magnesium alloy plate is firstly coarsely ground with sandpapers of No. 400, No. 600 and No. 800 in sequence; and then finely ground with sandpapers of No. 1000, No. 1200 and No. 2000 in sequence.

4. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: The pre-stretching temperature is 25℃ and the pre-stretching strain rate is 1*10 -3 s -1 .

5. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: The compression temperature is 25℃ and the compression strain rate is 1*10 -3 s -1 .

6. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: After pre-deformation, the pre-deformed sheet is wrapped with aluminum foil before annealing.

7. The method for weakening the texture of a deformed magnesium alloy according to claim 1, wherein: The magnesium alloy is pure magnesium, AZ31 or ZK60.

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