Weak-texture high-strength and ductility fine-grained magnesium alloy and preparation method thereof

Abstract

This invention belongs to the field of metal material processing, specifically relating to a weak-textured, high-strength, fine-grained magnesium alloy and its preparation method. The magnesium alloy composition, by mass percentage, is: zinc: 0.5-1.0%, calcium: 0.05-0.45%, manganese: 0.1-0.5%, additives: 0.05-1.0%, unavoidable impurities ≤0.05%, with the balance being magnesium. The total content of alloying elements is <3%, and the additives are one or any combination of gadolinium, yttrium, cerium, and zirconium. The preparation method includes: smelting, casting, solution treatment, extrusion, rolling, and heat treatment to obtain the weak-textured, high-strength, fine-grained magnesium alloy. The magnesium alloy obtained by this invention has advantages such as low cost, weak texture, fine grains, high strength and plasticity at room temperature, and formability. Furthermore, the preparation process is reliable, efficient, and easy to promote and apply.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, and in particular relates to a weakly textured, high-strength, fine-grained magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest of practical metals, possess advantages such as low density, high specific strength, high damping properties, good electromagnetic shielding, and easy recyclability, making them promising for applications in electronics, communications, transportation, and aerospace. However, magnesium has a close-packed hexagonal structure, resulting in fewer easily activated slip systems at room temperature and poor plastic deformation capabilities. Hot rolling, one of the most common methods for producing commercial magnesium alloy sheets, is prone to cracking during the rolling process, severely impacting the yield of magnesium alloy sheets. Furthermore, magnesium alloys tend to form strong basal textures during rolling, leading to high anisotropy, low room-temperature plasticity, and insufficient secondary plastic forming capabilities, making it difficult to meet industrial production requirements.

[0003] Studies have shown that adding a large amount of rare earth elements to magnesium alloys can refine recrystallized grains, improve the strength of magnesium alloys, activate non-basal slip, and improve the basal texture of magnesium alloys, thereby improving the room temperature ductility and anisotropy of the alloy. However, higher alloy additions will lead to increased alloy costs, which is not conducive to large-scale production by enterprises, and will also reduce the alloy's deformation processing capability. Therefore, it is difficult for existing technologies to simultaneously improve strength and formability. For example, patent 202110179888.X discloses "a high-strength and high-plasticity Mg-Al-Ce(Nd) wrought magnesium alloy and its preparation method." This alloy is processed by reverse extrusion of Mg-Al-Ce(Nd). This process is costly and time-consuming. Although it improves the strength of the alloy, it reduces the plasticity of the alloy (the elongation is only 8-15.6%), making it difficult to achieve simultaneous improvement of strength and plasticity. Therefore, how to reduce the amount of alloy additions, simplify the process, and reduce costs to obtain magnesium alloys with weak texture, high formability, and high strength and plasticity is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] To address the aforementioned technical challenges, this invention provides a low-texture, high-strength, fine-grained magnesium alloy. By mass percentage, the alloy composition comprises: zinc: 0.5-1.0%, calcium: 0.05-0.45%, manganese: 0.1-0.5%, additives: 0.05-1.0%, total unavoidable impurities ≤ 0.05%, and the balance being magnesium. The additives are one or any combination of gadolinium, yttrium, cerium, and zirconium. Its preparation method includes the following steps:

[0005] Step 1: Mix CO2 and SF6 as a protective gas at a volume ratio of 95.5-99:4.5-1, then add pure magnesium, pure zinc, magnesium-manganese, magnesium-calcium master alloy, and additive element master alloy in sequence, and heat to melt at 690-710℃; then stir evenly, refine, degas and remove slag to obtain alloy melt. The additive element master alloy is one or any combination of magnesium-yttrium, magnesium-cerium, magnesium-gadolinium, and magnesium-zirconium master alloys.

[0006] Step Two: The alloy molten liquid obtained in Step One is poured into a mold to obtain an ingot, which is then subjected to solution treatment at a temperature of 430-550℃ for 2-24 hours. Afterward, it is air-cooled to room temperature and then held at 350-450℃ for 2-4 hours before extrusion. The extrusion process is as follows: extrusion temperature 340-450℃, extrusion ratio 20:1-50:1, extrusion speed 0.1-2.0 m / min; after holding at 430-550℃ for 1-3 hours, it is water-cooled and then subjected to multiple passes. The multi-pass rolling process consists of 5-10 passes, with a reduction of 10%-50% per pass, a rolling temperature of 250-350℃, and a holding time of 200-350℃ for 2-25 minutes before each pass; after rolling, a holding time of 250-380℃ for 5-30 minutes is performed to obtain a weakly textured, high-strength, fine-grained magnesium alloy; the obtained alloy has an average grain size of <3μm, a texture strength of ≤5, a tensile strength of ≥280MPa, a yield strength of ≥265MPa, and an elongation of ≥19%.

[0007] Furthermore, the zinc content is 0.6-0.8%, the manganese content is 0.15-0.4%, and the calcium content is 0.2-0.3%.

[0008] Furthermore, the content of the added element is 0.1-0.8%.

[0009] Furthermore, the extrusion temperature in step two is 360-430℃, and the extrusion ratio is 30:1-45:1.

[0010] Furthermore, the multi-pass rolling described in step two consists of 3-9 passes, with a reduction of 15%-40% per pass, and a rolling temperature of 280-300℃.

[0011] Furthermore, in step two, the temperature is maintained at 240-340℃ for 5-20 minutes before each rolling pass.

[0012] Compared with the existing technology, the present invention has the following characteristics:

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] This invention achieves the following superior effects through the interaction between alloy components, their proportions, and the synergistic control of processes and process parameters:

[0015] 1) The total mass percentage of alloying elements added in this invention is <3wt.%, which is a low-alloy content alloy, and has the advantages of low alloy content and low cost;

[0016] 2) This invention, through alloy composition design and processing technology optimization, firstly, effectively controls the type, size, distribution, and quantity density of magnesium alloy microstructure and second phase; secondly, it can effectively change the stacking fault energy of basal and non-basal planes by pinning grain boundaries and changing the axial ratio, thereby weakening the recrystallization texture and improving the alloy formability; thirdly, it can promote the interaction of solid solution elements, further weaken the texture, achieve co-segregation of related elements at grain boundaries, delay recrystallization, and inhibit crystal nucleus growth, effectively refine recrystallized grains, and improve the strength and plasticity of the alloy. In addition, by forming a high-density, nanoscale second phase, a second phase strengthening effect is produced.

[0017] 3) Compared with the prior art, the alloy obtained by the present invention achieves simultaneous grain refinement and texture weakening, as well as simultaneous improvement of alloy strength, plasticity and formability: wherein the obtained alloy has an average grain size of <3μm, texture strength ≤5, tensile strength ≥280MPa, yield strength ≥265MPa and elongation ≥19%. Detailed Implementation

[0018] Example 1

[0019] Taking the Mg-1Zn-1Gd-0.2Ca-0.2Mn alloy as an example (by mass percentage: Zn: 1.0%, Gd: 1.0%, Ca: 0.2%, Mn: 0.2%; total unavoidable impurities ≤ 0.05%, balance being magnesium), its preparation method is as follows:

[0020] Step 1: Under the protection of a mixed gas of CO2 + SF6 (CO2 and SF6 volume fraction ratio 99:1), pure magnesium, pure zinc, magnesium-gadolinium master alloy, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and heated to 710℃ to melt; then stirred evenly, refined, degassed and slag-removed to obtain alloy liquid.

[0021] Step 2: The alloy liquid obtained in Step 1 is poured into a mold to obtain an ingot, and then solution-treated at 450℃ for 4 hours. After air cooling to room temperature, it is held at 430℃ for 2 hours and then extruded. The extrusion process is as follows: extrusion temperature 445℃, extrusion ratio ~35:1, extrusion speed 0.2m / min. After holding at 450℃ for 3 hours, it is water-cooled to room temperature and then rolled in multiple passes. The rolling process is as follows: 5 passes, each pass with a reduction of 30%, rolling temperature of 300℃, and holding at 325℃ for 15 minutes before each pass. Finally, after heat treatment at 310℃ for 15 minutes, the Mg-1Zn-1Gd-0.2Ca-0.2Mn alloy is obtained.

[0022] The Mg-1Zn-1Gd-0.2Ca-0.2Mn alloy obtained in step two of this embodiment has a weakly textured fine-grained structure with an average grain size of ~2.1μm, a texture strength of ~4.8, a yield strength of ~270MPa, a tensile strength of ~300MPa, and an elongation of up to 20%.

[0023] Example 2

[0024] Taking the Mg-0.8Zn-0.4Gd-0.3Ca-0.15Mn alloy as an example (Zn: 1.0%, Gd: 0.5%, Ca: 0.3%, Mn: 0.15%; total unavoidable impurities ≤ 0.05%, balance magnesium), its preparation method is as follows:

[0025] Step 1: Under the protection of a mixed gas of CO2 and SF6 (CO2 and SF6 volume fraction ratio of 95.5:4.5), pure magnesium, pure zinc, magnesium-manganese master alloy, magnesium-calcium master alloy and magnesium-gadolinium master alloy are added in sequence and heated to 705℃ to melt; then stirred evenly, refined, degassed and slag-removed to obtain alloy liquid;

[0026] Step 2: The alloy liquid obtained in Step 1 is poured into a mold to obtain an ingot, and then solution-treated at 460℃ for 2.5 hours. After air cooling to room temperature, it is held at 425℃ for 2 hours and then extruded. The extrusion process is as follows: extrusion temperature 440℃, extrusion ratio ~30:1, extrusion speed 0.5m / min, and the extrusion is to form a sheet. After holding at 460℃ for 2.5 hours, it is water-cooled to room temperature and then subjected to multi-pass rolling. The rolling process is as follows: 10 passes, each pass with a reduction of 15%, rolling temperature of 280℃, and holding at 320℃ for 10 minutes before each pass. Finally, after heat treatment at 305℃ for 20 minutes, the Mg-0.8Zn-0.4Gd-0.3Ca-0.15Mn alloy is obtained.

[0027] The Mg-0.8Zn-0.4Gd-0.3Ca-0.15Mn alloy obtained in step two of this embodiment has a weakly textured fine-grained structure with an average grain size of ~2.5μm, a texture strength of ~5, a yield strength of ~265MPa, a tensile strength of ~290MPa, and an elongation of ~22%.

[0028] Example 3

[0029] Taking the Mg-1Zn-0.5Y-0.25Ca-0.2Mn alloy as an example (Zn: 1.0%, Y: 0.5%, Ca: 0.25%, Mn: 0.2%; total unavoidable impurities ≤ 0.05%, balance magnesium), its preparation method is as follows:

[0030] Step 1: Under the protection of a mixed gas of CO2 + SF6 (CO2 and SF6 volume fraction ratio 98:2), pure magnesium, pure zinc, magnesium-manganese master alloy, magnesium-calcium master alloy and magnesium-yttrium master alloy are added in sequence and heated to 690℃ to melt; then stirred evenly, refined, degassed and slag-removed to obtain alloy liquid;

[0031] Step 2: The alloy liquid obtained in Step 1 is poured into a mold to obtain an ingot, and then solution-treated at 440℃ for 2 hours. After air cooling to room temperature, it is held at 440℃ for 1 hour and then extruded. The extrusion process is as follows: extrusion temperature 430℃, extrusion ratio ~50:1, extrusion speed 2m / min, and extrusion into a sheet. After holding at 430℃ for 2 hours, it is water-cooled to room temperature and then subjected to multi-pass rolling. The rolling process is as follows: 5 passes, each pass with a reduction of 30%, rolling temperature of 290℃, and holding at 300℃ for 10 minutes before each pass. Finally, after heat treatment at 290℃ for 10 minutes, the Mg-1Zn-0.5Y-0.25Ca-0.2Mn alloy is obtained.

[0032] The Mg-1Zn-0.5Y-0.25Ca-0.2Mn alloy obtained in step two of this embodiment has a weakly textured fine-grained structure with an average grain size of ~2.6μm, a texture strength of ~4.1, a tensile strength of ~280MPa, and an elongation of up to 23%.

[0033] Example 4

[0034] Taking the Mg-0.9Zn-0.45Y-0.3Zr-0.2Ca-0.2Mn alloy as an example (based on the following composition by mass percentage: Zn: 1.0%, Y: 0.5%, Zr: 0.3%, Ca: 0.2%, Mn: 0.3%; total unavoidable impurities ≤ 0.05%, balance being magnesium), its preparation method is as follows:

[0035] Step 1: Under the protection of a mixed gas of CO2 + SF6 (CO2 and SF6 volume fraction ratio 96:4), pure magnesium, pure zinc, magnesium-manganese master alloy, magnesium-calcium master alloy, magnesium-zirconium master alloy and magnesium-yttrium master alloy are added in sequence and heated to 700℃ to melt; then stirred evenly, refined, degassed and slag-removed to obtain alloy liquid.

[0036] Step Two: The alloy liquid obtained in Step One is poured into a mold to obtain an ingot, and then solution-treated at 445℃ for 8 hours. After air cooling to room temperature, it is held at 420℃ for 3 hours and then extruded. The extrusion process is as follows: extrusion temperature 430℃, extrusion ratio ~40:1, extrusion speed 1.5m / min, and the extrusion is into a sheet. After holding at 445℃ for 2 hours, it is water-cooled to room temperature and then rolled in multiple passes. The rolling process is as follows: 3 passes, each pass with a reduction of 40%, rolling temperature of 300℃, and holding at 320℃ for 15 minutes between passes. Finally, after heat treatment at 310℃ for 15 minutes, the Mg-0.9Zn-0.45Y-0.3Zr-0.2Ca-0.2Mn alloy is obtained.

[0037] The Mg-0.9Zn-0.45Y-0.3Zr-0.2Ca-0.2Mn alloy obtained in step two of this embodiment has a weakly textured fine-grained structure with an average grain size of ~2.3μm, a texture strength of ~4.3, a tensile strength of ~295MPa, and an elongation of up to 19%.

[0038] Comparative Example 1

[0039] Zhai et al. published a journal article: The Influence of Rolling Deformation on the Microstructure and Properties of Mg-Zn-Y Alloy [J]. Heat Treatment of Metals, 2022, 47(06) 39-45. In this paper, a small deformation process was used to roll the Mg-4Zn-2Y alloy from 10 mm thickness to 6, 4, and 2 mm respectively, with a deformation amount of 0.5 mm each time, a deformation temperature of 400℃, and a holding time of 15 min. The optimal mechanical properties were: tensile strength of 277 MPa and elongation of 14%.

[0040] As can be seen from all embodiments of the present invention, the alloy composition of Example 3 (Mg-1Zn-0.5Y-0.25Ca-0.2Mn) is most similar to the composition disclosed in Comparative Example 1. The total alloy and rare earth contents of Example 3 are 1.95% and 0.5%, respectively, with a tensile strength of ~280MPa and an elongation of up to 23%. In contrast, the total alloy and rare earth contents of the Mg-4Zn-2Y alloy disclosed in Comparative Example 1 are 6% and 2%, respectively, with a tensile strength of 277MPa and an elongation of 14%. Compared with Comparative Example 1, Example 3 of the present invention reduces the total alloy addition and rare earth addition, thereby reducing costs. Furthermore, the process used in the present invention is significantly different from that disclosed in Comparative Example 1. Compared with Comparative Example 1, the present invention simultaneously improves the strength and plasticity of the alloy. In addition, Comparative Example 1 does not provide a technical solution for the weak texture of Mg-4Zn-2Y.

[0041] Comparative Example 2

[0042] The journal article published by Lin et al., Xia Lin et al, Deformation mechanism, orientation evolution and mechanical properties of annealed cross-rolled Mg-Zn-Zr-Y-Gd sheet during tension, Journal of Magnesium and Alloys, 2023, 11(7) 2340-2350, reported that Mg-6.75Zn-0.57Zr-0.4Y-0.18Gd (wt.%) alloy was preheated at 425℃ for 30 min and then rolled at 425℃ with a total reduction of 90%. Before each rolling pass, the alloy was held at 425℃ for 15 min. After each rolling pass, the sample was rotated 90° before the next rolling pass. The rolled alloy was annealed at 400℃ for 1 h and then water quenched to room temperature. The obtained alloy yield strength was ~211MPa, elongation was ~14.7%, and texture strength was ~11.74.

[0043] The total alloy content of Comparative Example 2, which discloses a Mg-6.75Zn-0.57Zr-0.4Y-0.18Gd (wt.%) alloy, is 7.9%, with a rare earth content of 0.58%. Compared to Example 4 of the present invention (Mg-0.9Zn-0.45Y-0.3Zr-0.2Ca-0.2Mn alloy with a total alloy content of 2.05% and a rare earth content of 0.45%), the total alloy content and rare earth content of Comparative Example 2 are higher than those of the alloy obtained in Example 4 of the present invention, and the two examples use different processes. In this invention, while reducing the cost of alloy raw materials, the alloy texture strength (4.3) of Example 4 is weaker than that of the alloy texture strength (11.74) obtained in Comparative Example 2. Therefore, the alloy formability of this invention is better than that of Comparative Example 2. Furthermore, the yield strength (295 MPa) and elongation (19%) of the alloy of Example 4 of this invention are higher than those of the alloy obtained in Comparative Example 2 (yield strength 211 MPa) and elongation (14.7%), respectively. In summary, compared with Comparative Example 2, this invention improves the strength, plasticity and formability of the alloy simultaneously while saving costs.

[0044] In summary, this invention, using lower alloy and rare earth content than existing technologies, employs different processes and parameters. Compared to existing technologies, it simultaneously weakens texture and refines grains, thereby simultaneously improving the alloy's strength, plasticity, and formability. This demonstrates that the superior performance of the alloy obtained by this invention is achieved through the synergistic control of the interactions between alloy components, their proportions, the process, and process parameters.

Claims

1. A low-texture, high-strength, fine-grained magnesium alloy, characterized in that: The alloy composition, by mass percentage, includes: zinc: 0.6-1.0%, calcium: 0.05-0.45%, manganese: 0.1-0.5%, additives: 0.05-1.0%, total unavoidable impurities ≤0.05%, and the balance being magnesium. The additives are any combination of gadolinium, yttrium, and zirconium. Its preparation method includes the following steps: Step 1: Mix CO2 and SF6 as a protective gas at a volume ratio of 95.5-99:4.5-1. Under the protective atmosphere, add pure magnesium, pure zinc, magnesium-manganese, magnesium-calcium master alloy, and additive element master alloy in sequence, and heat to melt at 690-710℃. Then stir evenly, refine, degas, and remove slag to obtain the alloy melt. The additive element master alloy is any combination of magnesium-yttrium, magnesium-gadolinium, and magnesium-zirconium master alloys. Step Two: The alloy molten liquid obtained in Step One is poured into a mold to obtain an ingot, which is then subjected to solution treatment. The solution treatment is performed at a temperature of 430-550℃ for 2-24 hours, followed by air cooling to room temperature, and then holding at 350-450℃ for 2-4 hours before extrusion. The extrusion treatment is performed at a temperature of 340-450℃, an extrusion ratio of 20:1-50:1, and an extrusion speed of 0.1-2.

0. m / min; then hold at 430-550℃ for 1-3 hours and water cool, then perform multi-pass rolling treatment, the multi-pass rolling is: 5-10 passes, each pass reduction of 10%-40%, rolling temperature 250-350℃, and holding at 200-350℃ for 2-25 minutes before each pass; after rolling, perform heat treatment at 250-380℃ for 5-30 minutes to obtain a weakly textured high-strength ductile fine-grained magnesium alloy; the obtained alloy has an average grain size <3μm, texture strength ≤5, tensile strength ≥280MPa, yield strength ≥265MPa, and elongation ≥19%.

2. The weakly textured, high-strength, fine-grained magnesium alloy according to claim 1, characterized in that: The zinc content is 0.6-0.8%, manganese content is 0.15-0.4%, and calcium content is 0.2-0.3% by mass percentage.

3. The weakly textured, high-strength, fine-grained magnesium alloy according to claim 1, characterized in that: The added element, by weight percentage, is 0.1-0.8%.

4. A low-texture, high-strength, fine-grained magnesium alloy according to any one of claims 1-3, characterized in that: The extrusion temperature in step two is 360-430℃, and the extrusion ratio is 30:1-45:

1.

5. A low-texture, high-strength, fine-grained magnesium alloy according to claim 4, characterized in that: The multi-pass rolling process described in step two consists of 5-9 passes, with a reduction of 15%-40% per pass, and a rolling temperature of 280-300℃.

6. A low-texture, high-strength, fine-grained magnesium alloy according to claim 4, characterized in that: In step two, the temperature is maintained at 240-340℃ for 5-20 minutes before each rolling pass.