A high-efficiency extruded low-content high-strength plastic magnesium alloy and its preparation method

Abstract

This invention belongs to the field of metallic materials and provides a high-efficiency extrusion low-content high-strength ductile magnesium alloy and its preparation method. The alloy is composed of the following components by mass percentage: bismuth: 0.1-1%, manganese: 0.5-1%, zinc: 0.1-0.6%, calcium: 0.1-0.3%, unavoidable impurities ≤0.05%, and the balance being magnesium. The preparation method includes: melting, ultrasonic treatment, gravity casting, homogenization, extrusion, and aging treatment. The resulting magnesium alloy has a bimodal microstructure with both deformed grains and fine recrystallized grains. The elemental segregation at grain boundaries effectively inhibits further grain growth and generates a large number of nanoscale second phases, simultaneously improving the alloy's strength and ductility, with a yield strength ≥280MPa and an elongation ≥18.6%.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, specifically relating to a high-efficiency extrusion low-content high-strength PVC-Mg alloy and its preparation method. Background Technology

[0002] Magnesium alloys, as one of the most promising green structural materials, possess excellent specific strength, specific stiffness, and damping properties, and are recyclable, making them widely applicable in aerospace, transportation, and electronics manufacturing industries. Promoting the widespread use of magnesium alloys, especially wrought magnesium alloys, is crucial for alleviating environmental and energy crises. However, compared to commercial aluminum alloys, commonly used commercial magnesium alloys AZ80 and ZK60 can only achieve extrusion speeds of 0.5-2.5 m / min at high temperatures, only one-tenth the extrusion speed of aluminum alloys. Therefore, poor machinability, low yield, high manufacturing costs, and the difficulty in simultaneously improving strength and plasticity are among the main problems limiting the application of extruded magnesium alloys.

[0003] Current technologies improve the strength and ductility of magnesium alloys by increasing the content of alloying elements or adding high amounts of rare earth elements. However, this leads to increased production costs and reduces extrusion speed, limiting the large-scale production of high-performance extruded magnesium alloys. Commercial magnesium alloys contain a large number of easily molten, low-melting-point unstable eutectic phases, which readily melt back into the matrix during extrusion. Furthermore, magnesium alloys have a relatively small number of nailing phases that inhibit grain growth, leading to crack formation and ultimately negatively impacting the alloy's mechanical properties. Therefore, improving magnesium alloy yield, extrusion speed, and reducing costs to simultaneously enhance strength and ductility is a pressing technical challenge. Summary of the Invention

[0004] To address the aforementioned technical challenges, this invention provides a high-efficiency extruded, low-content, high-strength ductile magnesium alloy. The alloy, by mass percentage, comprises the following components: bismuth: 0.1-1%, manganese: 0.5-1%, zinc: 0.1-0.6%, calcium: 0.1-0.3%, unavoidable impurities ≤0.05%, and the balance being magnesium; the total element content of the alloy is <3%. Its preparation method includes the following steps:

[0005] (1) According to the alloy composition ratio, under the protection of a mixed gas of carbon dioxide and sulfur hexafluoride, the volume ratio of carbon dioxide to sulfur hexafluoride is 90-99:10-1; pure magnesium is held at 300-400℃ for 30-90 min, and then heated to 680-695℃ to obtain magnesium liquid. Pure zinc, magnesium-bismuth, magnesium-manganese and magnesium-calcium intermediate alloys are selected as alloy materials. The alloy materials are preheated at 100-200℃ for 30-100 min. Add the magnesium liquid sequentially, then heat to 720-740℃ to melt it; add anhydrous calcium fluoride refining agent and let it stand for 5-10 minutes, then stir it evenly at 660-710℃ and keep it at that temperature for 10-20 minutes. Blow in argon gas for refining and remove slag to obtain magnesium alloy melt. Then insert an ultrasonic probe into the magnesium alloy melt at 1 / 3-2 / 3 of the distance to ultrasonic treatment, and then pour it into a mold at 150-250℃ by gravity casting to obtain alloy ingots.

[0006] (2) The alloy ingot obtained in step (1) is homogenized and quenched, then held at 150-450℃ for 60-120 min and then extruded, air-cooled to room temperature, and then aged and cooled to room temperature to obtain a high-efficiency extruded low-content high-strength ductile magnesium alloy; the magnesium alloy has a yield strength ≥280MPa and an elongation ≥18.6%.

[0007] The ultrasonic treatment described in step (1) is as follows: ultrasonic treatment at a power of 1200-2200W for 1-20 minutes;

[0008] The homogenization process in step (2) is: heat preservation at 400-550℃ for 4-10 hours; the extrusion process is: extrusion at 150-450℃ with an extrusion ratio of 20-40:1 and an extrusion speed of 9-28 m / min; the aging process is: heat preservation at 100-300℃ for 10-48 hours.

[0009] Further, the ultrasonic treatment in step (1) is: ultrasonic treatment at 1500-2000W power for 5-20 minutes; the homogenization treatment in step (2) is: heat treatment at 450-500℃ for 6-8 hours; the extrusion treatment is: extrusion at 200-400℃ with an extrusion ratio of 25-35:1 and an extrusion speed of 9-25m / min; the aging treatment is: heat treatment at 150-250℃ for 12-24 hours.

[0010] Furthermore, the magnesium alloy obtained in step (2) has a yield strength of 305.7-360 MPa and an elongation of 20.5-30%.

[0011] Furthermore, the magnesium alloy obtained in step (2) has a yield strength of 320-350 MPa and an elongation of 25-26%.

[0012] Compared with the prior art, the present invention has the following characteristics:

[0013] Existing technologies improve the mechanical properties of magnesium alloys by adding high-content alloying elements or rare earth elements, which results in slower extrusion speeds and increased production costs. This invention improves the microstructure of low-content magnesium alloys by controlling the interactions between alloy components (types and proportions) and synergistic regulation of process parameters, while reducing the alloy addition amount (<3%), omitting rare earth elements, and operating under rapid extrusion conditions. Compared to existing technologies that disclose the formation of numerous low-melting-point phases within extruded magnesium alloys, this invention forms more high-melting-point phases (which are more difficult to remelt back into the matrix), thus suppressing the formation of voids and hot cracks. Compared to the microstructure of alloys disclosed in existing technologies, the β-phase precipitated in this invention and the element segregation at grain boundaries can effectively… This invention effectively pins grain boundaries and dislocations, delaying the dynamic recrystallization of deformed grains and hindering the abnormal growth of already dynamically recrystallized grains. Furthermore, compared with existing technologies, this invention obtains a larger number of pinned phases that prevent grain growth. At the same time, it achieves a bimodal structure with finer dynamically recrystallized grains and elongated deformed grains coexisting, as well as a uniformly dispersed nanoscale second phase. Under the combined strengthening effects of high-melting-point phases, a large number of pinned phases, bimodal structure, grain boundary segregation, and nanoscale phase precipitation, the alloy's strength and plasticity are simultaneously improved, with a yield strength ≥280MPa and an elongation ≥18.6%. Attached Figure Description

[0014] Figure 1 This is a curve showing the room temperature mechanical properties of the Mg-1Bi-0.8Mn-0.6Zn-0.3Ca alloy from Example 1. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to the embodiments.

[0016] Example 1

[0017] Taking the Mg-1Bi-0.8Mn-0.6Zn-0.3Ca alloy as an example (composed of the following components by mass percentage: bismuth: 1%, manganese: 0.8%, zinc: 0.6%, calcium: 0.3%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0018] (1) According to the alloy composition ratio, pure magnesium is kept at 300℃ for 90 min under the protection of a mixed gas of carbon dioxide and sulfur hexafluoride (the volume ratio of carbon dioxide and sulfur hexafluoride is 90:10), and then heated to 690℃ to melt the pure magnesium to obtain magnesium liquid. Pure zinc, magnesium-manganese, magnesium-calcium, and magnesium-bismuth intermediate alloys are selected as alloy materials. The alloy materials are preheated at 200℃ for 90 min and then added to the magnesium liquid. The temperature is then raised to 720℃, anhydrous calcium fluoride refining agent is added and left to stand for 5 min. Then, the mixture is stirred evenly at 700℃ and kept at 20 min. Argon gas is blown in for refining and slag removal to obtain magnesium alloy melt. Then, an ultrasonic probe is inserted 1 / 3 of the distance from the magnesium alloy melt for ultrasonic treatment (ultrasonic power is 2000W, time is 5 min). Finally, the alloy ingot is obtained by gravity casting into a mold at 250℃.

[0019] (2) The alloy ingot obtained in step (1) is homogenized and then immediately quenched. The homogenization treatment is held at 500℃ for 6 hours, and the quenching is water quenching at room temperature to room temperature. The ingot is held at 300℃ for 120 minutes, and then extruded at 300℃. The extrusion ratio is 25:1 and the extrusion speed is 9 m / min. After aging treatment, the ingot is air-cooled to room temperature to obtain Mg-1Bi-0.8Mn-0.6Zn-0.3Ca alloy. The aging treatment is held at 220℃ for 12 hours.

[0020] The Mg-1Bi-0.8Mn-0.6Zn-0.3Ca alloy obtained in step (2) has a yield strength of 320 MPa and an elongation of 18.6%.

[0021] Example 2

[0022] Taking the Mg-0.7Bi-0.6Mn-0.5Zn-0.2Ca alloy as an example (composed of the following components by mass percentage: bismuth: 0.7%, manganese: 0.6%, zinc: 0.5%, calcium: 0.2%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0023] (1) According to the alloy composition ratio, pure magnesium is kept at 320°C for 60 min under the protection of a mixed gas of carbon dioxide and sulfur hexafluoride (the volume ratio of carbon dioxide and sulfur hexafluoride is 95:5), and then heated to 695°C to melt the pure magnesium to obtain magnesium liquid. Pure zinc, magnesium-manganese, magnesium-calcium, and magnesium-bismuth intermediate alloys are selected as alloy materials. The alloy materials are preheated at 180°C for 100 min and then added to the magnesium liquid in sequence. The temperature is then raised to 730°C, anhydrous calcium fluoride refining agent is added and left to stand for 8 min. Then, the mixture is stirred evenly at 690°C and kept at 18 min. Argon gas is blown in for refining and slag removal to obtain magnesium alloy melt. An ultrasonic probe is inserted at 1 / 2 distance from the magnesium alloy melt for ultrasonic treatment (ultrasonic power is 1800W, time is 8 min). The alloy ingot is then cast into a mold at 200°C by gravity casting to obtain alloy ingot.

[0024] (2) The alloy ingot obtained in step (1) is homogenized and then immediately quenched. The homogenization treatment is held at 480℃ for 8 hours, and the quenching is water quenching at room temperature to room temperature. The ingot is held at 320℃ for 100 minutes, and then extruded at 320℃. The extrusion ratio is 30:1 and the extrusion speed is 20 m / min. After aging treatment, the ingot is air-cooled to room temperature to obtain Mg-0.7Bi-0.6Mn-0.5Zn-0.2Ca alloy. The aging treatment is held at 200℃ for 20 hours.

[0025] The Mg-0.7Bi-0.6Mn-0.5Zn-0.2Ca alloy obtained in step (2) has a yield strength of 305.7 MPa and an elongation of 20.5%.

[0026] Example 3

[0027] Taking the Mg-0.5Bi-1Mn-0.5Zn-0.15Ca alloy as an example (composed of the following components by mass percentage: bismuth: 0.5%, manganese: 1%, zinc: 0.5%, calcium: 0.15%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0028] (1) According to the alloy composition ratio, pure magnesium is kept at 350°C for 50 min under the protection of a mixed gas of carbon dioxide and sulfur hexafluoride (the volume ratio of carbon dioxide and sulfur hexafluoride is 93:7), and then heated to 685°C to melt the pure magnesium to obtain magnesium liquid. Pure zinc, magnesium-manganese, magnesium-calcium, and magnesium-bismuth intermediate alloys are selected as alloy materials. The alloy materials are preheated at 190°C for 100 min and then added to the magnesium liquid. The temperature is then raised to 735°C, anhydrous calcium fluoride refining agent is added and left to stand for 10 min. Then, the mixture is stirred evenly at 710°C and kept at 15 min. Argon gas is blown in for refining and slag removal to obtain magnesium alloy melt. Then, an ultrasonic probe is inserted 1 / 3 of the distance from the magnesium alloy melt for ultrasonic treatment (ultrasonic power is 1500W, time is 20 min). Finally, the alloy ingot is obtained by gravity casting into a mold at 245°C.

[0029] (2) The alloy ingot obtained in step (1) is homogenized and then immediately quenched. The homogenization treatment is held at 490℃ for 5 hours, and the quenching is water quenching at room temperature to room temperature. The ingot is held at 350℃ for 60 minutes, and then extruded at 350℃. The extrusion ratio is 35:1 and the extrusion speed is 25 m / min. After aging treatment, the ingot is air-cooled to room temperature to obtain Mg-0.5Bi-1Mn-0.5Zn-0.15Ca alloy. The aging treatment is held at 180℃ for 24 hours.

[0030] The yield strength of the aged Mg-0.5Bi-1Mn-0.5Zn-0.15Ca alloy obtained in step (2) is 280.

[0031] MPa, elongation of 25%.

[0032] Comparative Example 1

[0033] The master's thesis, titled "Influence of Hot Extrusion and Rolling Processes on the Microstructure and Properties of AE44 Magnesium Alloy" (published November 2018, affiliation: Xi'an University of Technology, author: Ai Xiangle), mentions in the experimental materials section that the selected materials had the following weight percentages: Al: 3.99%, RE(Ce+La): 4.34%, Mn: 0.36%, Zn: 0.02%, Fe: 0.002%, with the balance being Mg. The highest extrusion speed involved was 2 m / min, and the obtained alloy yield strength was 180.7 MPa, with an elongation of 9.5%. Compared to the present invention, Comparative Example 1 contains three times the maximum amount of alloying elements added (2.9%), and includes a large amount of expensive rare earth elements (Ce+La), while the present invention does not contain any rare earth elements. Therefore, Comparative Example 1 is significantly more advantageous for industrial production than the present invention. Furthermore, the extrusion speed of Comparative Example 1 (2 m / min) is much lower than the minimum extrusion speed (9 m / min) used in the processing of the alloy in the present invention. In addition, the yield strength and plasticity of the alloy obtained in Comparative Example 1 are lower than the minimum yield strength and plasticity of the alloy obtained in the present invention. In summary, compared to Comparative Example 1, the present invention significantly improves the extrusion speed of magnesium alloys while reducing the amount of alloying elements added and omitting rare earth elements, achieving higher strength and plasticity than Comparative Example 1, thus realizing a simultaneous improvement in the strength and plasticity of the alloy.

[0034] Comparative Example 2

[0035] The journal article titled "Effects of extrusion parameters on the microstructure and mechanical properties of Mg–Zn–(Mn)–Ce / Gd alloys" (published in Materials Science & Engineering A, Volume 598, March 2014, authors: Sung Hyuk Park et al.) mentions in its experimental materials that the selected materials had a weight percentage of Zn: 2%, Gd: 1.5%, and the balance being Mg. The comparative alloy Mg–2Zn–1.5Gd (with an alloy element content higher than the maximum alloy element content of this invention (2.9%), and a large amount of rare earth elements added, while this invention did not include rare earth elements) had a maximum extrusion speed of 4 m / min (significantly lower than the minimum extrusion speed of this invention (9 m / min)), a yield strength of 215 MPa, and an elongation of 11.7%. The strength and plasticity of the alloy obtained in the comparative example are lower than the minimum strength and plasticity of the alloy obtained in this invention, respectively. Compared with the comparative example, the present invention has a faster extrusion speed, less alloy element content, and no rare earth elements are added. Compared with the comparative example, the present invention improves the strength and plasticity of the alloy simultaneously.

[0036] In summary, compared with existing technologies, this invention achieves higher strength and plasticity of the alloy obtained at high extrusion speeds by reducing the amount of alloy added and without using rare earth elements. This invention achieves rapid extrusion forming of magnesium alloys through the interaction between alloy components and the synergistic control of process parameters, using low-content alloying and without the addition of rare earth elements. Under the combined strengthening effects of high-melting-point phases, abundant pinned phases, bimodal microstructure, grain boundary segregation, and nanophase precipitation, a high-strength and plastic magnesium alloy is obtained, suitable for industrial production, improving production efficiency, simplifying the production process, reducing energy consumption and production costs, and solving the technical challenges of simultaneously improving the strength and plasticity of magnesium alloys and achieving efficient industrial production.

Claims

1. A high-efficiency extruded low-content high-strength ductile magnesium alloy, characterized in that, The alloy, by mass percentage, consists of the following components: composition: Bismuth: 0.1-1%, Manganese: 0.5-1%, Zinc: 0.1-0.6%, Calcium: 0.1-0.3%, unavoidable impurities ≤0.05%, balance magnesium; total content of alloying elements <3%, its preparation method includes the following steps: (1) According to the alloy composition ratio, under the protection of a mixed gas of carbon dioxide and sulfur hexafluoride, the volume ratio of carbon dioxide to sulfur hexafluoride is 90-99:10-1; pure magnesium is kept at 300-400 ℃ for 30-90 min, and then heated to 680-695 ℃ to obtain magnesium liquid. Pure zinc, magnesium-bismuth, magnesium-manganese and magnesium-calcium intermediate alloys are selected as alloy materials. The alloy materials are preheated at 100-200 ℃ for 30-100 min and then added to the magnesium liquid. The temperature is then raised to 720-740 ℃ for heating and melting. After adding anhydrous calcium fluoride refining agent, it is allowed to stand for 5-10 min, and then stirred evenly at 660-710 ℃ and kept at 10-20 min. Argon gas is blown in for refining and slag removal to obtain magnesium alloy melt. Then, an ultrasonic probe is inserted into the magnesium alloy melt at 1 / 3-2 / 3 of the distance to the magnesium alloy melt for ultrasonic treatment. After that, it is poured into the melt by gravity casting to 150-250 ℃. Alloy ingots are obtained in a mold at ℃; (2) The alloy ingot obtained in step (1) is homogenized and quenched, then held at 150-450 ℃ for 60-120 min and extruded, then air-cooled to room temperature, and then aged and air-cooled to room temperature to obtain a high-efficiency extruded low-content high-strength ductile magnesium alloy; the magnesium alloy has a yield strength ≥280MPa and an elongation ≥18.6%; The ultrasonic treatment described in step (1) is: ultrasonic treatment at a power of 1200-2200 W for 1-20 min; The homogenization treatment in step (2) is to keep the temperature at 400-550 ℃ for 4-10 h; the extrusion treatment is to extrude at 150-450 ℃ with an extrusion ratio of 20-40:1 and an extrusion speed of 9-28 m / min; the aging treatment is to keep the temperature at 100-300 ℃ for 10-48 h.

2. The high-efficiency extruded low-content high-strength ductile magnesium alloy according to claim 1, characterized in that, The ultrasonic treatment in step (1) is performed by ultrasonication at a power of 1500-2000 W for 5-20 min; the homogenization treatment in step (2) is performed by heat preservation at 450-500 ℃ for 6-8 h; the extrusion treatment is performed by extrusion at 200-400 ℃ with an extrusion ratio of 25-35:1 and an extrusion speed of 9-25 m / min; the aging treatment is performed by heat preservation at 150-250 ℃ for 12-24 h.

3. The high-efficiency extruded low-content high-strength ductile magnesium alloy according to claim 1, characterized in that, The magnesium alloy obtained in step (2) has a yield strength of 305.7-360 MPa and an elongation of 20.5-30%.

4. The high-efficiency extruded low-content high-strength ductile magnesium alloy according to claim 1, characterized in that, The magnesium alloy obtained in step (2) has a yield strength of 320-350 MPa and an elongation of 25-26%.

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