A method for preparing a high-strength low-cost magnesium alloy bar

Abstract

The application discloses a preparation method of high-strength low-cost magnesium alloy rod, and the magnesium alloy comprises the following raw materials in percentage by mass: Y 3~7%, Zn 1~2%, Mn 0.5~1.5%, and the balance is magnesium and inevitable impurities; the application combines the accurate control of the content of each element of the alloy and the solid solution aging treatment process, and changes the original LPSO phase structure before extrusion through the solid solution aging treatment, and then the gamma prime phase is precipitated; then the LPSO phase and the gamma prime phase influence the dynamic recrystallization process in the extrusion process, the bimodal grain structure is regulated, the strength of the deformed magnesium alloy is significantly improved, and the high plasticity is maintained, and a new idea is provided for the research on the preparation of high-performance magnesium alloy. The equipment used in the application is simple, the content of alloy elements is low, the cost is low, the processing technology operation is simple and convenient, and the large-scale industrial production is easy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium alloy casting preparation, and particularly relates to a preparation method of high-strength low-cost magnesium alloy rod. BACKGROUND

[0002] Magnesium alloy is one of the most potential lightweight materials, which has the advantages of high specific strength, high specific stiffness, good damping and vibration reduction performance, electromagnetic shielding performance and the like, has great development and application potential in the fields of aerospace, national defense and military industry, rail transportation and the like, and has been paid more and more attention. However, compared with traditional steel materials or aluminum alloys, the magnesium alloy has low strength and poor processing formability, which limits its development and application in the industrial field. Generally, the increase of the strength of the traditional magnesium alloy is often accompanied by the decrease of the plasticity, so it is difficult to obtain the magnesium alloy with high strength and high plasticity at the same time. The main reason is that the magnesium alloy has limited slip system, and it is difficult to activate the non-basal slip at room temperature. In addition, the existence of the second phase particles in the alloy aggravates the dislocation accumulation, improves the alloy strength, and also promotes the crack initiation, and reduces the alloy plasticity. Therefore, the development of the magnesium alloy with high plasticity and high strength will become the focus of the research work of the magnesium alloy.

[0003] Extrusion casting is an effective forming technology for high-performance magnesium alloy parts, while the alloys deformed by traditional extrusion and rolling often have a strong basal texture orientation, which can lead to mechanical property anisotropy and reduce ductility. Therefore, large plastic deformation technology is proposed, which promotes the widespread use of magnesium alloys in practical production and application activities. For example, equal channel angular extrusion and high-pressure torsion can significantly refine the grains and weaken the basal texture, but the small sample size and high equipment requirements make it difficult to apply to industrial production. At present, the heat treatment methods of deformed magnesium alloys mainly include traditional aging treatment, deformation aging treatment and double aging treatment. For example, the invention patent CN113755734B discloses a preparation method of a high-strength high-plasticity heat-resistant magnesium alloy with LPSO phase and SFs structure, which comprises the following components in weight percentage: Er 6.0%-7.0%, Y 6.0%-7.0%, Cu 0.3%-0.4%, Zr 0.1%-0.2%, and the balance is Mg; the preparation process includes: material selection, melting, solid solution treatment, extrusion deformation and aging heat treatment. The invention patent CN109182864B discloses a high-strength magnesium alloy profile and its preparation process and application, which is mainly obtained by temperature treatment, extrusion and aging treatment of magnesium alloy ingot. The invention patent CN101191168B discloses a magnesium alloy and its preparation method, which comprises the following components and contents: Gd 7-11 wt%, Y2-5 wt%, Zr 0.3-0.6 wt%, Zn 0.5-1.0 wt%, and the balance is Mg. The preparation method of the alloy includes alloy melting, refining, casting, solid solution, extrusion deformation and two artificial aging methods to produce high-strength and high-toughness heat-resistant magnesium alloy extruded rod. However, the above aging treatments are based on the microstructure after original deformation, and the strengthening effect is achieved through the precipitated phase after aging. These methods can only improve the strength on one side, but reduce the plasticity of the alloy. In addition, in order to ensure the stability of the size in industrial production, a certain amount of excess is generally reserved after extrusion production, and then rough machining is carried out before aging treatment, and finally fine machining is carried out. At the same time, the above-mentioned patents have high content of rare earth elements and rare metal zirconium, which greatly increases the production cost. SUMMARY

[0004] In view of the above problems of the prior art, the technical problem to be solved by the present application is to provide a preparation method of high-strength low-cost magnesium alloy rod, which solves the problems of poor strength and plasticity and high cost of existing extrusion casting magnesium alloy.

[0005] In order to solve the above technical problems, the application adopts the following technical scheme: a preparation method of high-strength and low-cost magnesium alloy rod, the magnesium alloy comprises the following raw materials in mass percentage: Y 3~7%, Zn 1~2%, Mn 0.5~1.5%, and the balance is magnesium and inevitable impurities; in this way, the alloy content is relatively low, and good plasticity is achieved.

[0006] The magnesium alloy is prepared by the following steps:

[0007] 1) according to the composition of the magnesium alloy, the raw materials are subjected to melting and casting to obtain an alloy casting;

[0008] 2) after the alloy ingot obtained in step 1) is subjected to solid solution treatment in a heat treatment furnace, it is water-cooled to room temperature;

[0009] 3) after the sample subjected to the solid solution treatment in step 2) is subjected to aging treatment, it is air-cooled to room temperature;

[0010] 4) the sample obtained in step 3) is subjected to hot extrusion treatment to obtain a magnesium alloy with a bimodal grain structure, i.e. a high-strength and low-cost magnesium alloy rod.

[0011] Preferably, the raw materials are industrial pure magnesium, industrial pure zinc, Mg-Mn intermediate alloy and Mg-Y intermediate alloy.

[0012] Preferably, the solid solution treatment is performed at a temperature of 520~530℃ for 12~18 h.

[0013] Preferably, the aging treatment is performed at a temperature of 170~180℃ for 20~24 h.

[0014] Preferably, in the hot extrusion treatment, the temperature is 420~450℃, the extrusion speed is 10~20 mm / min, and the extrusion ratio is 16~25:1.

[0015] Preferably, the magnesium alloy rod contains γ' phase and LPSO phase; the LPSO phase includes lamellar LPSO phase, bulk LPSO phase and granular LPSO phase.

[0016] Preferably, the bimodal grain structure is a combination of coarse deformed grains and fine dynamic recrystallized grains. The deformed grains and the dynamic recrystallized grains are mainly distinguished by the average misorientation angle and the shape in the grains. Generally, the average misorientation angle in the deformed grains is between 1° and 7.5°, and the dynamic recrystallized grains are less than 1°; as for the shape, the deformed grains are elongated grains, and the dynamic recrystallized grains are equiaxed grains.

[0017] Another object of the application is to provide a high-strength and low-cost magnesium alloy rod prepared by the above method.

[0018] 1、The present application changes the original LPSO phase structure before extrusion by adopting the way of combining the accurate control of alloy element content and solid solution aging treatment process, precipitates γ' phase, and the microstructure morphology of coexisting 18R-LPSO phase and γ' precipitated phase appears; then part of the 18R-LPSO phase is crushed into block or granular in the hot extrusion process, provides dynamic recrystallization grain nucleation points, promotes the nucleation of dynamic recrystallization grains, and refines the grains. At the same time, the γ' precipitated phase and the fine lamellar 14H-LPSO phase dynamically precipitated in the extrusion process will inhibit the dynamic recrystallization process, forming coarse deformed grains. Therefore, the bimodal grain structure can significantly improve the strength of the magnesium alloy and maintain high plasticity, expand the engineering field of practical application of magnesium alloy, and also provide a new idea for the research of high-performance magnesium alloy, which has great significance.

[0019] 2、The equipment used in the present application is simple, and the alloy element content is low; the processing technology is simple and convenient, and no aging treatment is needed after extrusion, which can omit the rough machining step, optimize the production process, effectively reduce the production cost, and is easy to industrialize large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The microstructure morphology of the sample after different pre-treatment in the present application: (a) as-cast sample, (b) solid solution sample, (c) solid solution and aging sample.

[0021] Figure 2 The EBSD data of the extruded sample (a) Comparative Example 1, (b) Comparative Example 2, (c) Example 1.

[0022] Figure 3 Engineering stress-strain diagram of the sample in the present application. IMPLEMENTATION

[0023] The present application will be further described in detail below in conjunction with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0024] I. A method for preparing high-strength low-cost magnesium alloy rod Example 1

[0025] 1) Magnesium alloy material, wherein the content of Y element is about 6.70 wt.%, the content of Zn element is about 1.89 wt.%, the content of Mn element is about 1.5 wt.%, the rest is Mg and inevitable impurity elements, the raw materials are weighed after being prepared according to the above composition and polished to a metallic luster, and the raw materials used are high-purity Mg (99.99 wt.%), pure Zn (99.99 wt.%), Mg-30 wt.% Y intermediate alloy and Mg-30 wt.% Mn intermediate alloy.

[0026] 2) The weighed raw materials are respectively preheated in a heat treatment furnace at a preheating temperature of 250 ℃, then the preheated pure magnesium is placed in a resistance furnace, the melting temperature is set to 730 ℃, heated under a dynamic protective atmosphere of mixed gas of CO2 and SF6 (ratio of 99:1), after melting, the other raw materials are placed, and the alloy melt is formed after holding for 15 ~ 20 min. The magnesium alloy melt is stirred for 2 min at 730 ℃, and held for 10 min, after removing the slag on the surface of the melt, the alloy melt is poured into a low-carbon steel mold preheated at 250 ℃, cooled to room temperature, and the magnesium alloy ingot is obtained after demolding.

[0027] 3) The as-cast magnesium alloy sample obtained in step 2) is placed in a heat treatment furnace (KRJ3-4-600 high-temperature resistance furnace) and held at 520 ~ 530 ℃ for 12 h, and then water-cooled to room temperature to obtain a solid solution state magnesium alloy sample.

[0028] 4) The solid solution state magnesium alloy sample obtained in step 3) is held at 170 ~ 180 ℃ for 24 h, and then air-cooled to room temperature to obtain a solid solution aging state magnesium alloy sample.

[0029] 5) The solid solution aging state magnesium alloy sample obtained in step 4) is subjected to hot extrusion (JX-3600 horizontal extruder) at 450 ℃, the extrusion speed is 20 mm / s, and the extrusion ratio is 16:1, to obtain a magnesium alloy with a bimodal grain structure, i.e. a high-strength low-cost magnesium alloy rod.

[0030] Comparative Example 1

[0031] No solid solution treatment and aging treatment are performed, and the other raw materials and steps are the same as in Example 1.

[0032] Comparative Example 2

[0033] No aging treatment is performed, and the other raw materials and steps are the same as in Example 1.

[0034] II. Performance verification

[0035] 1) The magnesium alloy samples prepared in Example 1 after different heat treatments are observed under a scanning microscope, and the results are shown in Figure 1 .

[0036] As shown in Figure 1 a, the microstructure of the as-cast alloy is mainly composed of Mg matrix and 18R-LPSO phase, at the same time, a lot of nano-sized α-Mn particles also exist in the alloy, but cannot be observed under SEM. The 18R-LPSO phase distributed on the grain boundary of the solution-treated alloy gradually becomes continuous, and the lamellar LPSO phase precipitates Figure 1 b). After the sample after solution treatment continues to be aged, γ' phase precipitates in the intracrystalline, and the lamellar LPSO phase increases Figure 1 c).

[0037] 2, the magnesium alloy rod prepared in example 1 and comparative examples 1~2 is analyzed by electron backscatter diffraction (EBSD) under scanning electron microscope, and the results are shown in Figure 2 .

[0038] It can be seen from Figure 2 that comparative example 1 and comparative example 2 are composed of a large number of dynamic recrystallization grains, and the microstructure of example 1 exhibits a bimodal grain structure composed of coarse deformed grains and fine dynamic recrystallization grains. This is because the blocky and granular 18R-LPSO phase in the sample of example 1 will promote the dynamic recrystallization process by particle stimulated nucleation or discontinuous dynamic recrystallization, forming fine dynamic recrystallization grains. After aging, a large number of γ' phase precipitates in the matrix and fine lamellar 14H-LPSO phase dynamically precipitates during extrusion will significantly inhibit the dynamic recrystallization process of the alloy during hot working, thereby forming coarse deformed grains. Therefore, the inhibition effect of fine lamellar 14H-LPSO phase and γ' phase on dynamic recrystallization and the promotion effect of 18R-LPSO phase on dynamic recrystallization occur at the same time, so that the bimodal grain structure appears in the alloy. The existence of bimodal grain structure will produce back stress strengthening effect, which can significantly improve the strength of WZM721 magnesium alloy. Through EBSD determination, solution and aging treatment before extrusion can effectively refine the dynamic recrystallization grains, thereby obtaining effective fine grain strengthening effect. Due to the existence of LPSO phase and γ' phase, the dislocation movement will be hindered, and the effect of second phase strengthening will be achieved.

[0039] 3, the magnesium alloy rod prepared in example 1 and comparative examples 1~2 is subjected to mechanical property test, and the yield strength, tensile strength and elongation test results are shown in table 1 and Figure 3 .

[0040] Table 1

[0041] YS / MPa UTS / MPa SEL / % Example 1 314 396 9.7 Comparative Example 1 242 348 10.8 Comparative Example 2 280 369 11.8

[0042] From table 1 and Figure 1It can be seen that, compared with the comparative example, the yield strength and tensile strength of the magnesium alloy rod prepared by the application are obviously improved without affecting the plasticity of the alloy.

[0043] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of producing a high-strength low-cost magnesium alloy rod material, characterized by, The magnesium alloy comprises raw materials with the following mass percentage contents: Y 3~7%, Zn 1~2%, Mn 0.5~1.5%, and the balance being magnesium and inevitable impurities; The magnesium alloy is prepared by the following steps: 1) According to the composition of the magnesium alloy, the raw materials are subjected to melting and casting to obtain an alloy casting; 2) After the alloy ingot obtained in step 1) is placed in a heat treatment furnace for solid solution treatment, it is water-cooled to room temperature; the temperature of the solid solution treatment is 520~530℃, and the time is 12~18 h; 3) After the sample subjected to the solid solution treatment in step 2) is subjected to aging treatment, it is air-cooled to room temperature; the temperature of the aging treatment is 170~180℃, and the time is 20~24 h; 4) The sample obtained in step 3) is subjected to hot extrusion treatment to obtain a magnesium alloy with a bimodal grain structure, i.e. a high-strength low-cost magnesium alloy rod; in the hot extrusion treatment process, the temperature is 420~450℃, the extrusion speed is 10~20 mm / min, and the extrusion ratio is 16~25:

1.

2. The method of producing a high-strength low-cost magnesium alloy rod material according to claim 1, characterized by, The raw materials are industrial pure magnesium, industrial pure zinc, Mg-Mn intermediate alloy and Mg-Y intermediate alloy.

3. The method of claim 1, wherein the high-strength low-cost magnesium alloy rod is prepared by the steps of: preparing a magnesium alloy ingot by a casting method; and hot extruding the magnesium alloy ingot at a temperature of 300 to 400°C. The magnesium alloy rod contains γ' phase and LPSO phase.

4. The method of claim 1, wherein the high-strength low-cost magnesium alloy rod is prepared by the steps of: preparing a magnesium alloy ingot by a casting method; and hot extruding the magnesium alloy ingot at a temperature of 300 to 400°C. The bimodal grain structure is a combination of coarse deformed grains and fine dynamic recrystallized grains.

5. A high-strength low-cost magnesium alloy rod prepared by the method of any one of claims 1~4.

Images