High-strength large-specification extruded magnesium alloy and preparation method thereof

Abstract

The invention provides a high-strength large-specification extruded magnesium alloy and a preparation method thereof, and belongs to the field of metal material processing, the high-strength large-specification extruded magnesium alloy comprises the following alloy components in percentage by mass: 3.5-4.0 wt.% of Y, 1.5-2.0 wt.% of Nd, 0.5-1.0 wt.% of Gd, 0.1-0.2 wt.% of Ce, 0.1-0.2 wt.% of La, 0.4-0.5 wt.% of Zr, and the balance of magnesium and inevitable impurities, and the content of the inevitable impurities is less than or equal to 0.05 wt.%. The preparation method mainly comprises the steps of smelting, semi-continuous casting, hot extrusion and aging treatment.The high-strength large-specification extruded magnesium alloy obtained through the method has a high-density nanometer precipitated phase, the number density is 800-2000 / micron < 2 >, the size is 15-30 nm, the precipitated phase has a large pinning effect on dislocation, and the obtained magnesium alloy is high in strength and large in specification and can be used for manufacturing the magnesium alloy. And the yield strength of the magnesium alloy at room temperature is 320-349 MPa.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, specifically relating to a high-strength, large-size extruded magnesium alloy and its preparation method. Background Technology

[0002] Magnesium and magnesium alloys are the lightest commercially available structural metals. They hold great promise for achieving strategic goals of "carbon neutrality" and "emissions peaking," and for alleviating the energy crisis. Magnesium alloys possess high specific strength and specific stiffness, excellent damping performance, good biocompatibility, large theoretical hydrogen storage capacity, and high theoretical battery specific capacity. Therefore, magnesium and magnesium alloys have high application potential in aerospace, automotive, and 3C (computer, communication, and consumer electronics) fields. Traditional casting of magnesium alloys typically requires high temperatures to obtain a fluid alloy melt, which exacerbates grain coarsening and element loss, directly leading to strength loss. While subsequent plastic deformation processing can improve strength by refining the grains, it requires massive equipment tonnage and more complex mold designs for large workpieces. Furthermore, magnesium alloys have poor room temperature plasticity and a narrow deformation window, making them highly susceptible to cracking during processing, significantly reducing the feasibility of the process. Even with heat treatment methods such as solution treatment, aging, and annealing, large-sized components often suffer from significant differences in properties between the core and surface due to their large cross-sectional thickness and uneven temperature field, making it difficult to achieve uniform and sufficient phase transformation strengthening. Currently, industrially produced large-sized magnesium alloys are typically manufactured using multi-pass rolling processes, resulting in low yield strengths (100-200 MPa). For structural components, this low yield strength limits the application of magnesium alloys. These complex processes increase alloy processing costs, reduce production efficiency, and produce small alloy samples, which is not conducive to large-scale engineering applications.

[0003] Therefore, how to simplify the process and avoid cracking, while simultaneously improving the size and strength of magnesium alloys, and realizing the industrial production of large-scale magnesium alloy materials with high strength has become an urgent technical problem to be solved. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a high-strength, large-size extruded magnesium alloy, which, by mass percentage, comprises the following components: Y: 3.5-4.0 wt.%, Nd: 1.5-2.0 wt.%, Gd: 0.5-1.0 wt.%, Ce: 0.1-0.2 wt.%, La: 0.1-0.2 wt.%, Zr: 0.4-0.5 wt.%, unavoidable impurities ≤ 0.05 wt.%, and the remainder being Mg;

[0005] Its preparation method includes the following steps:

[0006] (1) Prepare raw materials according to the alloy composition ratio. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95-97:5-3, pure Mg, Mg-Y master alloy, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Ce master alloy, Mg-La master alloy, and Mg-Zr master alloy are held at 200-250℃. After melting at 680-720℃, the alloy melt is obtained by stirring, removing slag, and holding at a constant temperature for 15-30 minutes. The alloy melt is then cast using semi-continuous casting to obtain magnesium alloy ingots.

[0007] (2) The magnesium alloy ingot obtained in step (1) is subjected to machining to remove oxide scale, hot extrusion treatment, and artificial aging treatment to obtain a high-strength, large-size extruded magnesium alloy; the magnesium alloy has the following dimensions: length > 200 mm, width > 100 mm, and thickness > 3 mm. The alloy has high-density nano-precipitates, in which the precipitates exert a significant pinning effect on dislocations. The precipitate size is 15-30 nm, and the number density is 800-2000 / μm. 2 The yield strength at room temperature is 320-349 MPa; the hot extrusion treatment in step (2) is: extrusion temperature is 380-420℃, extrusion speed is 4-5 mm / s, and extrusion ratio is 8-12:1; the artificial aging treatment is: heat treatment at 175-225℃ for 80-120 hours.

[0008] Further, by mass percentage, Y: 3.6-3.8 wt.%, Nd: 1.7-1.9 wt.%, Gd: 0.6-0.9 wt.%, Ce: 0.12-0.16 wt.%, La: 0.12-0.16 wt.%, Zr: 0.42-0.48 wt.%.

[0009] Furthermore, the extrusion temperature in step (2) is 390-410℃, the extrusion speed is 4.2-4.6mm / s, and the extrusion ratio is 9-11:1.

[0010] The artificial aging treatment in step (2) is to keep the temperature at 185-215℃ for 90-100 hours.

[0011] Further, the magnesium alloy dimensions described in step (2) are: length: 500-5000mm, width: 120-300mm, and thickness: 4-30mm.

[0012] Compared with existing technologies, the present invention achieves the following beneficial effects through the synergistic regulation of component interactions, proportions, processes, and process parameters:

[0013] (1) Existing technologies mainly produce magnesium alloy materials by combining multiple-pass deformation after casting and multi-stage long-term high-temperature heat treatment to refine grains and regulate strengthening phases, which is a complex process. Under existing technologies, the strength of magnesium alloys produced on a large scale is low (yield strength 100-200MPa), and they are prone to cracking during multi-pass deformation, which limits their application range. In addition, to achieve large sizes, the prepared magnesium alloys require complex processes and equipment, making mass production difficult. In contrast, this invention adopts a single-pass extrusion combined with a single aging treatment after casting, which is a simple process and simultaneously achieves large sizes and effectively suppresses cracking, making it suitable for industrial production.

[0014] (2) Compared with the prior art, the present invention simultaneously controls the size and density of the precipitated phase, and the prepared alloy has a high-density nano-precipitated phase with a precipitated phase size of 15-30 nm and a number density of 800-2000 / μm. 2 The magnesium alloy obtained by this invention has a yield strength of 320-349 MPa. The magnesium alloy is uniformly dispersed in the matrix and has a good pinning effect on the relative dislocations. Detailed Implementation

[0015] Example 1

[0016] The alloy consists of the following components by mass percentage: Y: 3.7 wt.%, Nd: 1.7 wt.%, Gd: 0.6 wt.%, Ce: 0.13 wt.%, La: 0.16 wt.%, Zr: 0.47 wt.%, unavoidable impurities ≤ 0.05 wt.%, and the remainder is Mg.

[0017] Its preparation method includes the following steps:

[0018] (1) Prepare raw materials according to the alloy composition ratio. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95:5, pure Mg, Mg-Y master alloy, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Ce master alloy, Mg-La master alloy and Mg-Zr master alloy are held at 200℃. After melting at 710℃, the alloy melt is obtained by stirring, removing slag and holding at a constant temperature for 20 minutes. Then, the alloy melt is obtained by casting using semi-continuous casting to obtain magnesium alloy ingots.

[0019] (2) The magnesium alloy ingot obtained in step (1) is machined to remove oxide scale, hot extruded and artificially aged to obtain a high-strength large-size extruded magnesium alloy.

[0020] The extrusion process in step (2) is as follows: extrusion temperature is 400℃, extrusion speed is 4.5mm / s, and extrusion ratio is 9:1; artificial aging treatment is performed by holding at 210℃ for 100 hours. The dimensions of the obtained extruded magnesium alloy are: length: 5000mm, width: 300mm, thickness: 30mm; the size of the precipitated phase inside the alloy is 25-28nm, and the number density is 800-850 / μm. 2 The yield strength at room temperature is 320 MPa.

[0021] Example 2

[0022] The alloy consists of the following components by mass percentage: Y: 3.8 wt.%, Nd: 1.8 wt.%, Gd: 0.9 wt.%, Ce: 0.15 wt.%, La: 0.14 wt.%, Zr: 0.45 wt.%, unavoidable impurities ≤ 0.05 wt.%, and the remainder is Mg.

[0023] Its preparation method includes the following steps:

[0024] (1) Prepare raw materials according to the alloy composition ratio. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 97:3, pure Mg, Mg-Y master alloy, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Ce master alloy, Mg-La master alloy and Mg-Zr master alloy are held at 220℃. After melting at 700℃, the alloy melt is obtained by stirring, removing slag and holding at a constant temperature for 25 minutes. Then, the alloy melt is obtained by casting using semi-continuous casting to obtain magnesium alloy ingots.

[0025] (2) The magnesium alloy ingot obtained in step (1) is machined to remove oxide scale, hot extruded and artificially aged to obtain a high-strength large-size extruded magnesium alloy.

[0026] The extrusion process in step (2) is as follows: extrusion temperature is 410℃, extrusion speed is 4.2mm / s, and extrusion ratio is 11:1; the artificial aging process is as follows: holding at 195℃ for 90 hours. The dimensions of the obtained extruded magnesium alloy are: length: 3000mm, width: 240mm, thickness: 20mm; the size of the precipitated phase inside the alloy is 15-17nm, and the number density is 1800-1850 / μm. 2 The yield strength at room temperature is 338 MPa.

[0027] Example 3

[0028] The alloy consists of the following components by mass percentage: Y: 3.6 wt.%, Nd: 1.9 wt.%, Gd: 0.7 wt.%, Ce: 0.12 wt.%, La: 0.13 wt.%, Zr: 0.46 wt.%, unavoidable impurities ≤ 0.05 wt.%, and the remainder is Mg.

[0029] Its preparation method includes the following steps:

[0030] (1) Prepare raw materials according to the alloy composition ratio. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 96:4, pure Mg, Mg-Y master alloy, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Ce master alloy, Mg-La master alloy and Mg-Zr master alloy are held at 250℃. After melting at 720℃, the alloy melt is obtained by stirring, removing slag and holding at a constant temperature for 30 minutes. Then, the alloy melt is obtained by casting using semi-continuous casting to obtain magnesium alloy ingots.

[0031] (2) The magnesium alloy ingot obtained in step (1) is machined to remove oxide scale, hot extruded and artificially aged to obtain a high-strength extruded magnesium alloy.

[0032] The extrusion process in step (2) is as follows: extrusion temperature is 405℃, extrusion speed is 4.3mm / s, and extrusion ratio is 10:1; artificial aging treatment is performed by holding at 200℃ for 95 hours. The dimensions of the obtained extruded magnesium alloy are: length: 500mm, width: 120mm, thickness: 5mm; the size of the precipitated phase inside the alloy is 20-23nm, and the number density is 1200-1250 / μm. 2 The yield strength at room temperature is 349 MPa.

[0033] Comparative Example 1

[0034] The publicly published LA143 alloy (Su, et al, “Effect of mix-rolling process on microstructure and mechanical properties of Mg-14Li-3Al alloy”, Materials Characterization, 2025, ISSN 1044-5803) has the following composition by mass percentage: Li: 14.16 wt.%, Al: 2.98 wt.%, with the balance being Mg. The optimal alloy preparation process includes the following steps: melting and casting into ingots at approximately 690-710℃, homogenizing the ingots at 260℃ for 4 hours, solution treating at 350℃ for 3 hours, hot rolling at 260℃, and then room temperature rolling. The resulting LA143 alloy has dimensions of 120mm×20mm×2.5mm. The hybrid rolling process introduces a large number of dislocations and refines the grains through dynamic recrystallization, reducing dislocation slip paths. The interaction between grain boundaries and dislocations improves the strength of the alloy. The yield strength of the LA143 alloy at room temperature is 307MPa.

[0035] Compared with Comparative Example 1, the present invention has the following advantages: In terms of cost, the total content of alloying elements in the present invention (≤8.0 wt.%) is lower than that in Comparative Example 1 (17.14 wt.%), reducing production costs; in terms of process, the present invention adopts a semi-continuous casting followed by single-pass extrusion, and then a single aging treatment, optimizing the complex process of "casting + homogenization treatment + solution treatment + hot rolling + room temperature rolling" used in Comparative Example 1. In comparison, the process is simpler, has lower energy consumption, and higher efficiency, making it suitable for continuous industrial production of large-size profiles; in terms of alloy size, the LA143 alloy prepared in Comparative Example 1 has a size of 120 mm × 20 mm × 2.5 mm, and the small size limits the application scenarios of the alloy. The extruded magnesium alloy prepared in the present invention has a significantly larger size than the alloy obtained in Comparative Example 1; in terms of performance, the alloy obtained in the present invention has a high density (800-2000 / μm). 2 The nanoscale precipitates (15-30 nm) exhibit a stronger pinning effect on dislocations, and the highest yield strength of the alloy obtained in Comparative Example 1 is lower than the lowest yield strength of the alloy of this invention. This invention simultaneously satisfies the requirements of both high strength and large size, demonstrating excellent prospects for industrial application.

[0036] In summary, this invention employs a semi-continuous casting followed by direct extrusion and then a single aging treatment, eliminating the need for multiple deformation stages and multi-stage heat treatments. This simplifies the process, saves energy, and is suitable for large-scale production. All embodiments of this invention have different compositions, proportions, and process parameters, resulting in varying alloy properties. This demonstrates that the superior effects achieved by this invention are not determined by any single element, proportion, or process parameter, but rather by the synergistic regulation of interactions between components, proportions, processes, and process parameters. Furthermore, the optimal technical effects can only be achieved within the scope of the claims of this invention. This invention utilizes semi-continuous casting, extrusion, and a single aging treatment to obtain a microstructure with uniform precipitates, simultaneously controlling the size and density of the precipitates to achieve the optimal combination. This results in a significant improvement in the strength and size of the magnesium alloy, with a yield strength of 320-349 MPa at room temperature. This breakthrough overcomes the existing strength-size bottleneck in magnesium alloys, enabling the production of high-strength, large-size extruded magnesium alloys.

Claims

1. A high-strength, large-size extruded magnesium alloy, characterized in that: The alloy consists of the following components by weight percentage: composition: Y: 3.5-4.0 wt.%, Nd: 1.5-2.0 wt.%, Gd: 0.5-1.0 wt.%, Ce: 0.1-0.2 wt.%, La: 0.1-0.2 wt.%, Zr: 0.4-0.5 wt.%, unavoidable impurities ≤0.05 wt.%, the remainder is Mg; Its preparation method includes the following steps: (1) Prepare raw materials according to the alloy composition ratio. Under the protection of a mixed gas of CO2 and SF6 with a volume ratio of 95-97:5-3, pure Mg, Mg-Y master alloy, Mg-Nd master alloy, Mg-Gd master alloy, Mg-Ce master alloy, Mg-La master alloy, and Mg-Zr master alloy are held at 200-250℃. After melting at 680-720℃, the alloy melt is obtained by stirring, removing slag, and holding at a constant temperature for 15-30 minutes. The alloy melt is then cast using semi-continuous casting to obtain magnesium alloy ingots. (2) The magnesium alloy ingot obtained in step (1) is subjected to machining to remove oxide scale, hot extrusion treatment, and artificial aging treatment to obtain a high-strength, large-size extruded magnesium alloy; the magnesium alloy has the following dimensions: length > 200 mm, width > 100 mm, thickness > 3 mm, and the alloy has high-density nano-precipitates with a precipitate size of 15-30 nm and a number density of 800-2000 / μm. 2 The yield strength at room temperature is 320-349 MPa; the hot extrusion treatment in step (2) is: extrusion temperature is 380-420℃, extrusion speed is 4-5 mm / s, and extrusion ratio is 8-12:1; the artificial aging treatment is: heat treatment at 175-225℃ for 80-120 hours.

2. The high-strength, large-size extruded magnesium alloy according to claim 1, characterized in that: By mass percentage, Y: 3.6-3.8 wt.%, Nd: 1.7-1.9 wt.%, Gd: 0.6-0.9 wt.%, Ce: 0.12-0.16 wt.%, La: 0.12-0.16 wt.%, Zr: 0.42-0.48 wt.%.

3. The high-strength, large-size extruded magnesium alloy according to claim 1, characterized in that: The extrusion temperature in step (2) is 390-410℃, the extrusion speed is 4.2-4.6mm / s, and the extrusion ratio is 9-11:

1.

4. The high-strength, large-size extruded magnesium alloy according to claim 1, characterized in that: The artificial aging treatment described in step (2) is to keep the temperature at 185-215℃ for 90-100 hours.

5. A high-strength, large-size extruded magnesium alloy according to claim 1, characterized in that: The magnesium alloy dimensions described in step (2) are: length: 500-5000mm, width: 120-300mm, and thickness: 4-30mm.