Low-content high-formability fast-extrusion magnesium alloy and preparation method thereof

Abstract

This invention belongs to the field of metallic materials and provides a low-content, high-formability, fast-extrusion magnesium alloy and its preparation method. The alloy of this invention is composed of the following components by mass percentage: bismuth: 1.2-2%, manganese: 0.01-0.4%, zinc: 0.7-1%, calcium: 0.4-0.6%, aluminum: 0.01-0.05%, yttrium: 0.01-0.05%, unavoidable impurities ≤0.05%, and the balance being magnesium. The preparation method includes: melting, fast extrusion forming, rotary rolling, annealing, and aging treatment. This invention improves the alloy's ability to accommodate dislocations during plastic deformation by opening up a large amount of non-basal slip, effectively resisting crack propagation, resulting in an Eriksen cup convexity value ≥9.4mm in the annealed magnesium alloy; simultaneously improving the alloy's strength and plasticity, resulting in a yield strength ≥202MPa and an elongation ≥20.1%. This invention has a simple process, low cost, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, specifically to a low-content, high-formability, fast-extrusion magnesium alloy and its preparation method. Background Technology

[0002] Faced with increasingly severe environmental and global energy crises, magnesium alloys, as one of the most promising green structural materials, possess excellent specific strength, specific stiffness, and damping properties, as well as good recyclability, making them promising for applications in aerospace, transportation, and electronics manufacturing industries. However, slow extrusion rates, high production costs, and the difficulty in simultaneously improving mechanical properties and plasticity at room temperature remain pressing technical challenges that need to be addressed.

[0003] Related studies have found that magnesium alloys have poor plastic deformation capacity due to the asymmetry of their close-packed hexagonal structure. This means that only two independent slip systems can be activated at room temperature, resulting in anisotropic mechanical properties and poor room-temperature plasticity and formability. Existing technologies improve alloy formability (using Eriksen cup convexity as a representation) by adding high amounts of alloying elements or rare earth elements to weaken the texture. However, this leads to excessively slow extrusion speeds during the extrusion process, making it unsuitable for industrial production.

[0004] Therefore, how to simultaneously improve the high formability, fast extrusion, and strong plasticity of alloys by reducing the amount of alloy or rare earth elements added, increasing the extrusion speed, and simplifying the process is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical challenges, this invention provides a low-content, high-formability, fast-extrusion magnesium alloy. The alloy, by mass percentage, comprises the following components: bismuth: 1.2-2%, manganese: 0.01-0.4%, zinc: 0.7-1%, calcium: 0.4-0.6%, aluminum: 0.01-0.05%, yttrium: 0.01-0.05%, unavoidable impurities ≤0.05%, and the balance being magnesium; the total element content of this alloy is ≤4.1%. Its preparation method includes the following steps:

[0006] (1) Under the protection of a mixed gas of CO2 and SF6, the volume ratio of CO2 to SF6 is 95-80:5-20; pure magnesium is kept at 300-400℃ for 30-90 min, and then heated to 680-695℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Y, Mg-Ca, Mg-Mn, and Mg-Bi are selected as alloy materials. The alloy materials are preheated at 100-200℃ for 30-100 min and then added to the magnesium liquid. After the alloy materials are fully melted, they are stirred and kept at 700-720℃ for 5-10 min. Argon gas is blown in for refining and slag removal. After standing and holding again, the mixture is finally cast into a mold preheated to 220℃-240℃ and cooled to room temperature to obtain alloy ingots.

[0007] (2) After the alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment, it is water quenched to room temperature to obtain a homogenized alloy ingot. The multi-stage step homogenization treatment is a two-stage or three-stage step homogenization treatment. The two-stage step homogenization treatment is: holding at 300-420℃ for 4-6 hours, and then holding at 450-500℃ for 5-8 hours. The three-stage step homogenization treatment is: holding at 250-350℃ for 1-3 hours, then holding at 350-450℃ for 2-4 hours, and then holding at 450-550℃ for 4-6 hours.

[0008] (3) The homogenized alloy ingot obtained in step (2) is extruded and then air-cooled to room temperature. The extrusion process is as follows: extrusion temperature 200℃-400℃, extrusion ratio 20-45, extrusion speed 10-30m / min; then it is subjected to multi-pass rotary rolling followed by annealing. The multi-pass rotary rolling process is as follows: rolling temperature 50-200℃, the alloy needs to be held at 250-450℃ for 5-30min before each pass of rolling, and the alloy needs to be rotated 90° after each pass of rolling before entering the next pass of rolling. The multi-pass process is 2-10 passes, and each pass of rolling... The content is 5-40%; the annealing treatment is: holding at 300-400℃ for 5-30 minutes, then air-cooled to room temperature; after aging treatment, it is air-cooled to room temperature to obtain a low-content, high-formability, fast-extrusion magnesium alloy. The aging treatment is: holding at 150-250℃ for 30-120 minutes; after annealing, the Eriksen cup convexity of the alloy is ≥9.4mm, the yield strength of the low-content, high-formability, fast-extrusion magnesium alloy is ≥202MPa, the elongation is ≥20.1%, and the alloy sheet thickness is >1mm or 0 < alloy sheet thickness ≤1mm.

[0009] Further, the extrusion ratio in step (3) is 24-35, the extrusion speed is 20-30 m / min, and the rolling temperature is 80-150℃.

[0010] Furthermore, the Eriksen cupping value of the alloy after annealing in step (3) is 9.8-12 mm, the yield strength of the low-content, high-formability, fast-extruded magnesium alloy is 206-260 MPa, and the elongation is 25.1-30%.

[0011] Furthermore, the Eriksen cupping value of the alloy after annealing in step (3) is 10.8-11.5 mm, the yield strength of the low-content, high-formability, fast-extruded magnesium alloy is 221-250 MPa, and the elongation is 27-29%.

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

[0013] In existing technologies, adding a significant amount of rare earth elements (>0.05%) is typically used to weaken the texture, thereby improving alloy formability and increasing the Eriksen cup convexity. However, this reduces the extrusion speed of magnesium alloys, increasing production costs and hindering industrial production. In contrast, this invention, using a low-alloy, low-rare-earth composition design and control, significantly increases the extrusion speed. Through synergistic control of alloy composition, proportions, component interactions, and processes, it extensively activates non-basal plane slip, improving the alloy's dislocation tolerance and effectively resisting crack formation. Furthermore, it simultaneously precipitates a large number of nanoscale second phases and single-atom-layer GP regions, pinning dislocations and hindering dislocation slip, thus simultaneously improving the material's formability, strength, and plasticity. Moreover, without causing alloy cracking, this invention can process both thick and thin plates. Furthermore, according to existing technology reports, magnesium alloy sheets will crack when the rolling thickness is ≤1mm. However, this invention can not only process sheets with a thickness >1mm, but also process alloy sheets with a thickness ≤1mm without edge cracks. The cupping value of the annealed alloy can reach 9.4-11mm; the yield strength of the aged alloy is ≥202MPa and the elongation is ≥20.1%, which is suitable for industrial production. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to the embodiments.

[0015] Example 1

[0016] Taking the Mg-2Bi-0.4Mn-0.7Zn-0.6Ca-0.05Al-0.02Y alloy as an example (composed of the following components by mass percentage: bismuth: 2%, manganese: 0.4%, zinc: 0.7%, calcium: 0.6%, aluminum: 0.05%, yttrium: 0.02%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0017] (1) Under the protection of a mixed gas of CO2 and SF6 (CO2:SF6 volume ratio = 95:5), pure magnesium is kept at 300℃ for 90 min and then heated to 695℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Ca, Mg-Mn, Mg-Bi and Mg-Y intermediate alloys are selected as raw materials. The raw materials are preheated at 200℃ for 80 min and then added to the magnesium liquid in sequence. After the mixture is fully melted, it is stirred evenly and kept at 710℃ for 6 min. Argon gas is then blown in for refining and slag removal. After standing and holding at 200℃ again, it is finally cast into a mold at 220℃ and cooled to room temperature to obtain a refined alloy ingot.

[0018] (2) The alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment. The multi-stage step homogenization treatment is: heat treatment at 300℃ for 4 hours and then heat treatment at 500℃ for 6 hours, and then water quenched to room temperature to obtain homogenized alloy ingot.

[0019] (3) The homogenized alloy ingot from step (2) is extruded and then air-cooled to room temperature. The extrusion process is carried out at 300°C with an extrusion ratio of 24 and an extrusion speed of 20 m / min. Then, it is subjected to rotary rolling and annealing. The rotary rolling process is carried out at a rolling temperature of 100°C, with 4 passes and a reduction of 20% per pass. The alloy needs to be held at 350°C for 10 min before each pass. After each pass, the workpiece needs to be rotated 90° before entering the next pass. Finally, an alloy plate with a thickness of ≤1 mm is obtained. The annealing process is carried out at 350°C for 20 min and then air-cooled to room temperature. After aging treatment, it is air-cooled to room temperature to obtain a low-content, high-formability, fast-extruded magnesium alloy. The aging treatment is carried out at 200°C for 60 min and then air-cooled to room temperature.

[0020] Step (3) yielded an Eriksen cupping value of 9.4 mm for the annealed Mg-2Bi-0.4Mn-0.7Zn-0.6Ca-0.05Al-0.02Y alloy, and the yield strength of the alloy after aging treatment was 221 MPa and the elongation was 20.1%.

[0021] Example 2

[0022] Taking the Mg-1.5Bi-0.3Mn-0.7Zn-0.4Ca-0.04Al-0.03Y alloy as an example (composed of the following components by mass percentage: bismuth: 1.5%, manganese: 0.3%, zinc: 0.7%, calcium: 0.4%, aluminum: 0.04%, yttrium: 0.03%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0023] (1) Under the protection of a mixed gas of CO2 and SF6 (CO2:SF6 volume ratio = 80:20), pure magnesium is kept at 350℃ for 60 min and then heated to 690℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Ca, Mg-Mn, Mg-Bi and Mg-Y intermediate alloys are selected as raw materials. The raw materials are preheated at 180℃ for 90 min and then added to the magnesium liquid in sequence. After melting, the mixture is stirred evenly and kept at 720℃ for 5 min. Argon gas is then blown in for refining and slag removal. After standing and holding at 230℃ again, the mixture is finally cast into a mold at 230℃ and cooled to room temperature to obtain a refined alloy ingot.

[0024] (2) The alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment. The multi-stage step homogenization treatment is: heat treatment at 310℃ for 5 hours and then heat treatment at 490℃ for 7 hours, and then water quenched to room temperature to obtain homogenized alloy ingot.

[0025] (3) After extrusion treatment of the homogenized alloy ingot in step (2), it is air-cooled to room temperature. The extrusion treatment is performed at 320℃ with an extrusion ratio of 30 and an extrusion speed of 25m / min. Then, it is subjected to rotary rolling and annealing treatment. The rotary rolling is performed at a rolling temperature of 110℃, with 5 passes and a reduction of 15% per pass. The alloy needs to be held at 325℃ for 15 minutes before each pass of rolling. After each pass of rolling, the workpiece needs to be rotated 90° before entering the next pass of rolling. Finally, an alloy plate with a thickness of ≤1mm is obtained. The annealing treatment is performed at 375℃ for 10 minutes and then air-cooled to room temperature. After aging treatment, it is air-cooled to room temperature to obtain a low-content, high-formability, fast-extrusion magnesium alloy. The aging treatment is performed at 220℃ for 45 minutes and then air-cooled to room temperature.

[0026] Step (3) yields an Eriksen cupping value of 9.8 mm for the annealed Mg-1.5Bi-0.3Mn-0.7Zn-0.4Ca-0.04Al-0.03Y alloy, a yield strength of 206 MPa and an elongation of 25.1% after aging treatment.

[0027] Example 3

[0028] Taking the Mg-1.2Bi-0.4Mn-0.8Zn-0.5Ca-0.02Al-0.05Y alloy as an example (composed of the following components by mass percentage: bismuth: 1.2%, manganese: 0.4%, zinc: 0.8%, calcium: 0.5%, aluminum: 0.02%, yttrium: 0.05%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0029] (1) Under the protection of a mixed gas of CO2 and SF6 (CO2:SF6 volume ratio = 90:10), pure magnesium is kept at 400℃ for 30 min and then heated to 692℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Ca, Mg-Mn, Mg-Bi and Mg-Y intermediate alloys are selected as raw materials. The raw materials are preheated at 150℃ for 100 min and then added to the magnesium liquid in sequence. After it is fully melted, it is stirred evenly and kept at 715℃ for 10 min. Argon gas is blown in for refining and slag removal. After standing and holding again, it is finally cast into a mold at 240℃ and cooled to room temperature to obtain refined alloy ingots.

[0030] (2) The alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment. The multi-stage step homogenization treatment is: heat treatment at 320℃ for 6 hours and then heat treatment at 480℃ for 8 hours, and then water quenched to room temperature to obtain homogenized alloy ingot.

[0031] (3) The homogenized alloy ingot from step (2) is extruded and then air-cooled to room temperature. The extrusion process is carried out at 350°C with an extrusion ratio of 35 and an extrusion speed of 30 m / min. Then, it is subjected to rotary rolling and annealing. The rotary rolling process is carried out at a rolling temperature of 100°C, with 3 passes and a reduction of 25% per pass. The alloy needs to be held at 330°C for 20 min before each pass. After each pass, the workpiece needs to be rotated 90° before entering the next pass. Finally, an alloy plate with a thickness of ≤1 mm is obtained. The annealing process is carried out at 325°C for 30 min and then air-cooled to room temperature. After aging treatment, it is air-cooled to room temperature to obtain a low-content, high-formability, fast-extruded magnesium alloy. The aging treatment is carried out at 180°C for 60 min and then air-cooled to room temperature.

[0032] Step (3) yields an Eriksen cupping value of 10.8 mm for the annealed Mg-1.2Bi-0.4Mn-0.8Zn-0.5Ca-0.02Al-0.05Y alloy, a yield strength of 202 MPa and an elongation of 27%.

[0033] Example 4

[0034] Taking the Mg-1.4Bi-0.2Mn-0.7Zn-0.4Ca-0.02Al-0.02Y alloy as an example (composed of the following components by mass percentage: bismuth: 1.4%, manganese: 0.2%, zinc: 0.7%, calcium: 0.4%, aluminum: 0.02%, yttrium: 0.02%, unavoidable impurities ≤0.05%, balance magnesium), its preparation method includes the following steps:

[0035] (1) Under the protection of a mixed gas of CO2 and SF6 (CO2:SF6 volume ratio = 91:9), pure magnesium is kept at 350℃ for 50 min and then heated to 690℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Ca, Mg-Mn, Mg-Bi and Mg-Y intermediate alloys are selected as raw materials. The raw materials are preheated at 160℃ for 95 min and then added to the magnesium liquid in sequence. After it is fully melted, it is stirred evenly and kept at 710℃ for 9 min. Argon gas is blown in for refining and slag removal. After standing and holding again, it is finally cast into a mold at 235℃ and cooled to room temperature to obtain refined alloy ingots.

[0036] (2) The alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment. The multi-stage step homogenization treatment is: heat treatment at 300℃ for 5 hours, then heat treatment at 485℃ for 7 hours, and then water quenched to room temperature to obtain homogenized alloy ingot.

[0037] (3) After extrusion treatment of the homogenized alloy ingot in step (2), it is air-cooled to room temperature. The extrusion treatment is performed at 325°C with an extrusion ratio of 29 and an extrusion speed of 26 m / min. Then, it is subjected to rotary rolling and annealing treatment. The rotary rolling is performed at a rolling temperature of 100°C, with two passes and a reduction of 20% per pass. The alloy needs to be held at 335°C for 18 min before each pass of rolling. After each pass of rolling, the workpiece needs to be rotated 90° before entering the next pass of rolling. The annealing treatment is performed at 322°C for 28 min and then air-cooled to room temperature. After aging treatment, it is air-cooled to room temperature to obtain a low-content, high-formability, fast-extrusion magnesium alloy. The aging treatment is performed at 185°C for 55 min and then air-cooled to room temperature.

[0038] Step (3) yields an annealed Mg-1.4Bi-0.2Mn-0.7Zn-0.4Ca-0.02Al-0.02Y alloy with a thickness of 2-3 mm and no edge cracks;

[0039] Comparative Example 1

[0040] CN113444945A discloses a magnesium alloy sheet and its preparation method, wherein the weight percentage of its components is: Zn: 2%, Li: 2%, Gd: 0.9%, and the balance is magnesium. When the alloying elements and rare earth elements added in Comparative Example 1 are higher than the maximum addition amounts of alloying elements and rare earth elements in this invention, the Eriksen cupping value of the annealed alloy is 7.3 mm, which is less than the minimum Eriksen cupping value (~9.4 mm) of the alloy of this invention. Therefore, the alloy obtained by this invention has significantly better formability than the alloy obtained in Comparative Example 1 while reducing the alloy production cost.

[0041] Comparative Example 2

[0042] CN108300918B discloses a magnesium alloy sheet with high formability and its preparation method. The weight percentage of its components is: Al: 3%, Zn: 1%, Ca: 0.4%, Gd: 0.4%, Mn: 0.2%, with the balance being magnesium. The alloying elements and rare earth elements added in Comparative Example 2 are much higher than those in this invention. The Ericsson cupping value of the annealed alloy is 5 mm, which is less than the lowest Ericsson cupping value (~9.4 mm) of the alloy of this invention. Therefore, the alloy obtained by this invention has significantly better formability than the alloy obtained in Comparative Example 2 while reducing the alloy production cost.

[0043] Comparative Example 3

[0044] In the prior art, a published master's thesis entitled "Preparation and Plastic Deformation Mechanism Study of High Formability Mg-2Zn-xLi-yGd Alloy Sheets" (published by Yunnan University, May 2022, authors: Xue Guangjie et al.) mentions that the material used in the experimental materials is Mg-2Zn-3Li-1Gd. The alloy extrusion speed is 3 m / min. Through secondary rolling and annealing, the obtained alloy has an Eriksen cupping value of ~7.8 mm, which is less than the minimum cupping value (~9.4 mm) of the alloy of this invention. The total alloy content and rare earth element addition of this invention are not only less than those of Comparative Example 3, but the extrusion speed is also significantly better than that of Comparative Example 3. Therefore, while improving production efficiency and reducing production costs, the magnesium alloy obtained by this invention has significantly better processability than that of Comparative Example 3.

[0045] The beneficial effects of this invention are:

[0046] Compared with existing technologies, this invention, by employing a low-alloy, low-rare-earth composition design and significantly increasing the extrusion speed, simultaneously improves the formability, strength, and plasticity of the material through the coordinated control of alloy composition, proportion, component interaction, and process. Furthermore, according to existing technology reports, magnesium alloy sheets will crack when rolled to a thickness ≤1mm, while this invention can process not only sheets with a thickness >1mm but also alloy sheets with a thickness ≤1mm without edge cracks. The annealed alloy cupping value is 9.4-11mm; the aged alloy yield strength is ≥202MPa, and the elongation is ≥20.1%. Its formability and plasticity are far superior to alloys obtained by existing technologies, simultaneously improving the alloy's formability and plasticity, making it suitable for industrial production.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-content, high-formability, fast-extrusion magnesium alloy, characterized in that: The alloy, by mass percentage, consists of the following components: composition: Bismuth: 1.2-2%, Manganese: 0.01-0.4%, Zinc: 0.7-1%, Calcium: 0.4-0.6%, Aluminum: 0.01-0.05%, Yttrium: 0.01-0.05%, unavoidable impurities ≤0.05%, balance magnesium; the total content of this alloying element is ≤4.1%, and its preparation method includes the following steps: (1) Under the protection of a mixed gas of CO2 and SF6, the volume ratio of CO2 to SF6 is 95-80:5-20; pure magnesium is kept at 300-400℃ for 30-90 min, and then heated to 680-695℃ to obtain magnesium liquid. According to the designed alloy composition, pure Zn, pure Al, Mg-Y, Mg-Ca, Mg-Mn, and Mg-Bi are selected as alloy materials. The alloy materials are preheated at 100-200℃ for 30-100 min and then added to the magnesium liquid. After the alloy materials are fully melted, they are stirred and kept at 700-720℃ for 5-10 min. Argon gas is blown in for refining and slag removal. After standing and holding at 700-720℃, the alloy is finally cast into a mold preheated to 220℃-240℃ and cooled to room temperature to obtain alloy ingots. (2) After the alloy ingot obtained in step (1) is subjected to multi-stage step homogenization treatment, it is quenched in water to room temperature to obtain homogenized alloy ingot. The multi-stage step homogenization treatment is a two-stage step homogenization treatment. The two-stage step homogenization treatment is: heat treatment at 300-420℃ for 4-6h, and then heat treatment at 450-500℃ for 5-8h. (3) The homogenized alloy ingot obtained in step (2) is extruded and then air-cooled to room temperature. The extrusion process is as follows: extrusion temperature 200℃-400℃, extrusion ratio 20-45, extrusion speed 10-30 m / min; then it is subjected to multi-pass rotary rolling and annealing. The multi-pass rotary rolling process is as follows: rolling temperature 50-200℃, the alloy needs to be held at 250-450℃ for 5-30 min before each pass, and the alloy needs to be rotated 90° after each pass before entering the next pass. The multi-pass process is 2-10 passes, and the reduction in each pass is 5-40%. The annealing process is as follows: holding at 300-400℃ for 5-30 min, then air-cooled to room temperature; then subjected to aging treatment and air-cooled to room temperature to obtain a low-content, high-formability, fast-extrusion magnesium alloy. The aging treatment is as follows: holding at 150-250℃ for 30-120 min. min; the Eriksen cup convexity of the annealed alloy is 9.4-11 mm; the yield strength of the low-content high-formability fast extruded magnesium alloy after aging treatment is ≥202 MPa and the elongation is ≥20.1%; the low-content high-formability fast extruded magnesium alloy after aging treatment is a sheet with a processing thickness >1 mm or an alloy sheet with a processing thickness ≤1 mm without edge cracks.

2. The low-content, high-formability, fast-extrusion magnesium alloy according to claim 1, characterized in that: The extrusion ratio in step (3) is 24-35, the extrusion speed is 20-30 m / min, and the rolling temperature is 80-150℃.

3. A low-content, high-formability, fast-extrusion magnesium alloy according to claim 1 or 2, characterized in that, After annealing in step (3), the Eriksen cupping value of the alloy is 9.8-11 mm, the yield strength of the low-content, high-formability, fast-extruded magnesium alloy is 206-260 MPa, and the elongation is 25.1-30%.

4. A low-content, high-formability, fast-extrusion magnesium alloy according to claim 1 or 2, characterized in that, After annealing in step (3), the Eriksen cupping value of the alloy is 10.8-11 mm, the yield strength of the low-content, high-formability, fast-extruded magnesium alloy is 221-250 MPa, and the elongation is 27-29%.