A method for producing a rare earth magnesium alloy rod

Abstract

The application discloses a preparation method of a rare earth magnesium alloy rod, and the mass percentage composition of the rare earth magnesium alloy is as follows: Gd: 5.89-6.90%, Y: 3.41-3.90%, Zr: 0.42-0.46, and the rest is Mg. The preparation method comprises the following steps: A, extruding deformation is conducted on the rare earth magnesium alloy to obtain an extruded rod, the extrusion temperature is 430-450 DEG C, and the extrusion ratio is 40-55; B, rotary swaging deformation is conducted on the extruded rod to obtain a rotary swaged rod, the rotary swaging deformation temperature is 0-100 DEG C, and the total deformation amount of the rotary swaging deformation is 20-60%; C, first stage heat treatment is conducted on the rotary swaged rod, the first stage heat treatment temperature is 100-200 DEG C, and the heat preservation time is 24-360 h; and D, second stage heat treatment is conducted on the rotary swaged rod, the second stage heat treatment temperature is 260-340 DEG C, and the heat preservation time is 1-15 min. The application can induce a nano-crystal rare earth magnesium alloy rod to build a multi-scale structure through graded heat treatment, and meanwhile, the strength and plasticity of the rare earth magnesium alloy rod are improved.

Description

Technical Field

[0001] This invention belongs to the field of rare earth magnesium alloy rod preparation technology, specifically relating to a method for preparing rare earth magnesium alloy rods. Background Technology

[0002] Magnesium alloys, characterized by low density, high stiffness and specific strength, good damping properties, and ease of recycling, are hailed as "green engineering materials of the 21st century." They are currently the lightest metallic structural materials in the world, and their excellent weight-reduction characteristics offer promising applications in aerospace, transportation, and other fields. Existing nanocrystalline magnesium alloys typically possess high strength, but their relatively low ductility limits their applications. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing rare earth magnesium alloy rods, which improves their strength while ensuring good plasticity, thus expanding the application scenarios of magnesium alloys. The specific technical solution is as follows.

[0004] A method for preparing rare earth magnesium alloy rods, wherein the mass percentage composition of the rare earth magnesium alloy is Gd: 5.89-6.90%, Y: 3.41-3.90%, Zr: 0.42-0.46%, with the remainder being Mg, and the preparation method includes the following steps:

[0005] A. Extrusion deformation of rare earth magnesium alloy to obtain extruded bars, with an extrusion temperature of 430~450℃ and an extrusion ratio of 40~55;

[0006] B. The extruded bar is subjected to rotary forging to obtain rotary forged bar. The rotary forging temperature is 0~100℃, and the total deformation amount of rotary forging is 20~60%.

[0007] C. Perform the first stage heat treatment on the rotary forged bar stock. The first stage heat treatment temperature is 100~200℃ and the holding time is 24~360h.

[0008] D. Perform a second-stage heat treatment on the rotary forged bar stock. The second-stage heat treatment temperature is 260~340℃, and the holding time is 1~15min.

[0009] Preferably, the temperature of the first stage heat treatment is 125~175℃, and the holding time is 96~288h.

[0010] Preferably, the temperature of the second stage heat treatment is 280~320℃, and the holding time is 5~10min.

[0011] Preferably, the feed rate for the rotary forging deformation is 5~6 mm / min.

[0012] Preferably, the deformation amount per pass of the rotary forging is 10-20%.

[0013] Preferably, the average grain size of the rare earth magnesium alloy rod obtained in step C is 30~100nm.

[0014] Preferably, the average grain size of the rare earth magnesium alloy rod obtained in step D is 130~720nm.

[0015] Preferably, the rare earth magnesium alloy rod obtained in step D has a tensile strength ≥ 510 MPa, a yield strength ≥ 480 MPa, and an elongation after fracture ≥ 7%.

[0016] This invention provides a method for preparing rare-earth magnesium alloy rods. The obtained rare-earth magnesium alloy rods have a multi-scale nanocrystalline structure. The method includes the following steps: extruding and forging a rare-earth magnesium alloy ingot sequentially to obtain a nanocrystalline magnesium alloy rod; subjecting the nanocrystalline rare-earth magnesium alloy rod to a low-temperature heat treatment (first-stage heat treatment) and a high-temperature heat treatment (second-stage heat treatment) sequentially to obtain a nanocrystalline rare-earth magnesium alloy rod with a multi-scale structure. The low-temperature heat treatment temperature is 100-200℃, and the holding time is 24-360 h; the high-temperature heat treatment temperature is 260-340℃, and the holding time is 1-15 min. The nanocrystalline rare-earth magnesium alloy rod maintains a stable microstructure during low-temperature heat treatment, with no significant change in grain size. Furthermore, a large number of dispersed nanoscale precipitates can precipitate within the grains. These nanoscale precipitates can hinder dislocation movement and significantly improve the alloy strength. This invention first performs low-temperature heat treatment at 100-200℃, which can induce precipitate formation while preserving the nanocrystalline structure, thereby improving the alloy strength. Subsequently, a short-term high-temperature heat treatment at 260~340℃ was performed. A small amount of stable precipitates were precipitated at the grain boundaries in local areas of the alloy. These stable precipitates can act as Zener pins for the grain boundaries, preventing drastic grain growth. Therefore, only some grains grew after the high-temperature heat treatment. After low-temperature and high-temperature treatments, a multi-scale structure of "micron-sized grains + ultrafine grains + nano-sized grains + nano-sized precipitates" was formed inside the alloy. The average grain size of the multi-scale structure is 130~720nm (the average grain size was statistically analyzed using transmission electron microscopy images, which can be found in the academic paper "Application of XRD and TEM Techniques in Analyzing the Grain Size of Nanometals" (Southern Metals, Issue 150, June 2006)). It contains nano-sized grains with a grain size of 40~100nm, ultrafine grains with a grain size of 100~1000nm, and micron-sized grains with a grain size of 1~2μm. The average size of the nano-sized precipitates is 10~30nm. Micron-sized grains can coordinate plastic deformation, while the strong recovery during high-temperature heat treatment reduces dislocation density. The formation of micron-sized grains and the reduction in dislocation density improve the plasticity of the alloy; dispersed nano-sized precipitates can significantly improve the strength of the alloy. Therefore, this invention first constructs a nanocrystalline structure through extrusion and rotary forging deformation, and then induces the precipitation of strengthening phases in rare earth magnesium alloys through a graded heat treatment method of "low-temperature heat treatment + high-temperature heat treatment," causing some nanocrystalline grains to grow, constructing a multi-scale structure of "micron-sized grains + ultrafine grains + nanocrystalline grains + nano-sized precipitates." The construction of the multi-scale structure can simultaneously improve the strength and plasticity of the alloy. The results of the examples show that after graded heat treatment, the nanocrystalline rare earth magnesium alloy rods have a tensile strength ≥510MPa, a yield strength ≥480MPa, and an elongation after fracture ≥7%. Attached Figure Description

[0017] Figure 1 This is the microstructure of Example 1 after low-temperature heat treatment;

[0018] Figure 2 This is the microstructure after high-temperature heat treatment in Example 1;

[0019] Figure 3 The parameters of each embodiment and comparative example, as well as the properties of the prepared rare earth magnesium alloy rods, are described. Detailed Implementation

[0020] This invention provides a method for preparing rare earth magnesium alloy rods, comprising the following steps:

[0021] Rare earth magnesium alloy ingots are subjected to extrusion deformation and rotary forging deformation in sequence to obtain nanocrystalline magnesium alloy rods.

[0022] The nanocrystalline rare earth magnesium alloy rods were subjected to low-temperature heat treatment and high-temperature heat treatment in sequence to obtain nanocrystalline rare earth magnesium alloy rods with multi-scale structure.

[0023] The low-temperature heat treatment is performed at a temperature of 100~200℃ for 24~360h.

[0024] The high-temperature heat treatment is performed at a temperature of 260~340℃ and a holding time of 1~15min.

[0025] This invention involves subjecting rare earth magnesium alloy ingots to extrusion deformation and rotary forging deformation in sequence to obtain nanocrystalline magnesium alloy rods.

[0026] In one embodiment, the nanocrystalline rare earth magnesium alloy is a Mg-Gd-Y based magnesium alloy. In a specific embodiment, the composition of the nanocrystalline rare earth magnesium alloy is Mg-5.89Gd-3.41Y-0.42Zr (wt.%) or Mg-6.90Gd-3.90Y-0.46Zr (wt.%); the average grain size of the nanocrystalline rare earth magnesium alloy is 30~100 nm, and in a specific embodiment it is 80 nm or 85 nm.

[0027] In one embodiment, the Mg-5.89Gd-3.41Y-0.42Zr (wt.%) composition, by mass percentage, includes 5.89% Gd, 3.41% Y, and 0.42% Zr, with the balance being Mg; the Mg-6.90Gd-3.90Y-0.46Zr (wt.%) composition, by mass percentage, includes 6.90% Gd, 3.90% Y, and 0.46% Zr, with the balance being Mg.

[0028] In one embodiment, the extrusion deformation temperature is 430~450℃, specifically 450℃, and the extrusion ratio is 40~55, specifically 40~50.

[0029] In one implementation, the temperature of the rotary forging deformation is 0~100℃, specifically 35℃ in this embodiment; the deformation per pass is 5~20%, specifically 8% in this embodiment; the total deformation is 20~60%, specifically 30~50% in this embodiment; the feed rate is 2~6mm / min, specifically 5~6mm / min in this embodiment; the rotary forging deformation yields a rotary forged bar with a nanocrystalline structure, the average grain size of which is 30~100nm, specifically 80nm or 85nm in this embodiment. The deformation per pass is the cross-sectional area of ​​the bar after each pass of deformation divided by the cross-sectional area of ​​the bar before each pass of deformation; the total deformation is the cross-sectional area of ​​the bar after the rotary forging deformation is completed divided by the cross-sectional area of ​​the bar before the rotary forging deformation begins.

[0030] After obtaining the nanocrystalline magnesium alloy rod, the nanocrystalline rare earth magnesium alloy rod is subjected to low-temperature heat treatment and high-temperature heat treatment in sequence to obtain nanocrystalline rare earth magnesium alloy rod with multi-scale structure.

[0031] As one implementation method, the temperature of the low-temperature heat treatment is 100~200℃, and in a specific embodiment it is 125~175℃, and the holding time is 96~288h; the low-temperature heat treatment is carried out in an air atmosphere; after the low-temperature heat treatment, the method further includes: cooling the nanocrystalline rare earth magnesium alloy after the low-temperature heat treatment to room temperature; the cooling method is air cooling.

[0032] Nanocrystalline rare-earth magnesium alloys maintain stable microstructure and minimal grain size change during low-temperature heat treatment. Furthermore, a large number of dispersed nanoscale precipitates can form within the grains, which can hinder dislocation movement and significantly improve alloy strength. This invention first performs low-temperature heat treatment at 100-200℃, which induces precipitates while preserving the nanocrystalline structure, thereby increasing the alloy's strength. Below 100℃, the alloy cannot undergo a precipitation reaction and cannot form nanoscale precipitates; above 200℃, the precipitates tend to coarsen, reducing the alloy's strengthening effect. Simultaneously, stress concentration easily forms around the coarse second phase, leading to a sharp decrease in alloy plasticity.

[0033] In one implementation, the high-temperature heat treatment temperature is 260~340℃, specifically 280~320℃ in this embodiment, and the holding time is 5~10 minutes. If the high-temperature heat treatment time is too long, the grain size will be too large, reducing the alloy strength; if the high-temperature heat treatment time is too short, grain growth will be insufficient, making it difficult to form micron-sized grains, resulting in insufficient alloy plasticity. The high-temperature heat treatment is performed in an air atmosphere; after the high-temperature heat treatment, the process further includes cooling the heat-treated nanocrystalline rare-earth magnesium alloy to room temperature; the cooling method is air cooling.

[0034] After low-temperature heat treatment, this invention performs short-term high-temperature heat treatment at 260~340℃. A small amount of stable precipitates form at the grain boundaries in localized areas of the rare-earth magnesium alloy. These stable precipitates act as Zener pins, preventing drastic grain growth. Therefore, only some grains grow after the high-temperature heat treatment. When the temperature exceeds 340℃, stable precipitates cannot form, leading to rapid grain growth and coarse grains. When the temperature is below 260℃, the grain boundaries are stable, preventing the formation of a multi-scale structure.

[0035] After low-temperature and high-temperature treatments, the nanocrystalline rare-earth magnesium alloy rods exhibit a multi-scale microstructure consisting of "micron-sized grains + ultrafine grains + nanocrystalline grains + nanoscale precipitates". The micron-sized grains coordinate plastic deformation, while the strong recovery during high-temperature heat treatment reduces dislocation density. The formation of micron-sized grains and the reduction in dislocation density enhance the alloy's plasticity; the nanoscale dispersed precipitates significantly improve the alloy's strength.

[0036] As one implementation method, the average grain size of the multi-scale nanocrystalline rare earth magnesium alloy rod is 130~720nm, specifically 130nm, 150nm, 670nm or 720nm in the embodiments, the yield strength is ≥480MPa, specifically 483 MPa~543MPa in the embodiments, the tensile strength is ≥510MPa, specifically 512 MPa~585MPa in the embodiments, and the elongation after fracture is ≥7%, specifically 7.0%~7.5% in the embodiments.

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1

[0039] The alloy composition used was Mg-5.89Gd-3.41Y-0.42Zr (wt.%). The rare-earth magnesium alloy ingot was extruded at 450℃ with an extrusion ratio of 49. After extrusion, it underwent rotary forging at 35℃ with a total deformation of 39%. The resulting rotary-forged bar (average grain size 85nm) was then subjected to low-temperature heat treatment at 175℃ for 96 hours. The microstructure was as follows: Figure 1 As shown, it was then subjected to high-temperature heat treatment at 320℃ for 5 minutes, and the microstructure was as follows. Figure 2As shown, nanocrystalline rare-earth magnesium alloy rods with multi-scale structure were obtained, with an average precipitate size of 30 nm and an average grain size of 720 nm. Mechanical property tests were then conducted. The results showed that the yield strength of the nanocrystalline rare-earth magnesium alloy rods with multi-scale structure in Example 1 was 494 MPa, the tensile strength was 512 MPa, and the elongation after fracture was 7.1%.

[0040] Example 2

[0041] The alloy composition used was Mg-5.89Gd-3.41Y-0.42Zr (wt.%). The rare-earth magnesium alloy ingot was extruded at a temperature of 450℃ with an extrusion ratio of 49. After extrusion, it underwent rotary forging at a temperature of 35℃, with a total deformation of 39%. The resulting rotary-forged bar (average grain size 85nm) was first subjected to low-temperature heat treatment at 125℃ for 288h, followed by high-temperature heat treatment at 280℃ for 10min, yielding a nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure. The average size of the precipitated phase was 20nm, and the average grain size was 150nm. Mechanical properties were then tested. The results showed that the yield strength of the nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure in Example 2 was 483MPa, the tensile strength was 517MPa, and the elongation after fracture was 7.0%.

[0042] Example 3

[0043] The alloy composition used was Mg-6.90Gd-3.90Y-0.46Zr (wt.%). The rare-earth magnesium alloy ingot was extruded at 450℃ with an extrusion ratio of 49. After extrusion, it was rotary forged at 35℃ with a total deformation of 39%. The resulting rotary-forged bar (average grain size 80nm) was first heat-treated at 175℃ for 96 hours, followed by heat treatment at 320℃ for 5 minutes, yielding a nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure. The average size of the precipitated phase was 25nm, and the average grain size was 670nm. Mechanical properties were then tested. The results showed that the yield strength of the nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure in Example 3 was 536MPa, the tensile strength was 567MPa, and the elongation after fracture was 7.5%.

[0044] Example 4

[0045] The alloy composition used was Mg-6.90Gd-3.90Y-0.46Zr (wt.%). The rare-earth magnesium alloy ingot was extruded at 450℃ with an extrusion ratio of 49. After extrusion, it was rotary forged at 35℃ with a total deformation of 39%. The resulting rotary-forged bar (average grain size 80nm) was first heat-treated at 125℃ for 288h, followed by heat treatment at 280℃ for 10min, yielding a nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure. The average size of the precipitated phase was 20nm, and the average grain size was 130nm. Mechanical properties were then tested. The results showed that the yield strength of the nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure in Example 4 was 543MPa, the tensile strength was 585MPa, and the elongation after fracture was 7.0%.

[0046] Comparative Example 1

[0047] The alloy composition used was Mg-5.89Gd-3.41Y-0.42Zr (wt.%). The rare-earth magnesium alloy ingot was extruded at 450℃ with an extrusion ratio of 49. After extrusion, it underwent rotary forging at 35℃ with a total deformation of 39%. The resulting rotary-forged bar (average grain size 85nm) was first subjected to low-temperature heat treatment at 240℃ for 15 hours, followed by high-temperature heat treatment at 320℃ for 5 minutes. This yielded a nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure. The average size of the nanoscale precipitates was 35nm, and the average grain size was 690nm. Mechanical properties were then tested. The results showed that the yield strength of the nanocrystalline rare-earth magnesium alloy bar with a multi-scale microstructure in Comparative Example 1 was 433MPa, the tensile strength was 491MPa, and the elongation after fracture was 4.5%.

[0048] The difference from Example 1 is that the low-temperature heat treatment temperature is 240°C and the time is 15h. The rest is the same as Example 1. After the graded heat treatment, the average size of the nano-scale precipitates is 35nm, the average grain size is 690nm, the yield strength is 433MPa, the tensile strength is 491MPa, and the elongation after fracture is 4.5%.

[0049] Comparative Example 2

[0050] The difference from Example 1 is that the low-temperature heat treatment temperature is 95°C and the time is 280h. The rest is the same as Example 1. After the graded heat treatment, there are no nanoscale precipitates, the average grain size is 750nm, the yield strength is 397MPa, the tensile strength is 455MPa, and the elongation after fracture is 6.0%.

[0051] Comparative Example 3

[0052] The difference from Example 1 is that the high-temperature heat treatment temperature is 240℃ and the time is 15min. The rest is the same as Example 1. After the graded heat treatment, there are no micron-sized grains, the average size of the nano-sized precipitates is 20nm, the average grain size is 90nm, the yield strength is 575MPa, the tensile strength is 615MPa, and the elongation after fracture is 4.0%.

[0053] Comparative Example 4

[0054] The difference from Example 1 is that the high-temperature heat treatment temperature is 360°C and the time is 5 min. The rest is the same as Example 1. After graded heat treatment, all of them are micron-sized grains, the average size of the nano-sized precipitates is 50 nm, the average grain size is 1300 nm, the yield strength is 371 MPa, the tensile strength is 437 MPa, and the elongation after fracture is 7.5%.

[0055] Comparative Example 5

[0056] The difference from Example 3 is that the low-temperature heat treatment temperature is 240°C and the time is 15h. The rest is the same as Example 3. After the graded heat treatment, the average size of the nano-scale precipitates is 39nm, the average grain size is 630nm, the yield strength is 502MPa, the tensile strength is 535MPa, and the elongation after fracture is 4.9%.

[0057] Comparative Example 6

[0058] The difference from Example 3 is that the low-temperature heat treatment temperature is 95°C and the time is 280h. The rest is the same as Example 3. After the graded heat treatment, there are no nanoscale precipitates, the average grain size is 690nm, the yield strength is 416MPa, the tensile strength is 471MPa, and the elongation after fracture is 5.3%.

[0059] Comparative Example 7

[0060] The difference from Example 3 is that the high-temperature heat treatment temperature is 240℃ and the time is 15min. The rest is the same as Example 3. After the graded heat treatment, there are no micron-sized grains, the average size of the nano-sized precipitates is 21nm, the average grain size is 85nm, the yield strength is 577MPa, the tensile strength is 629MPa, and the elongation after fracture is 4.0%.

[0061] Comparative Example 8

[0062] The difference from Example 3 is that the high-temperature heat treatment temperature is 360°C and the time is 5 min. The rest is the same as Example 3. After the graded heat treatment, all of them are micron-sized grains, the average size of the nano-sized precipitates is 55 nm, the average grain size is 1160 nm, the yield strength is 394 MPa, the tensile strength is 441 MPa, and the elongation after fracture is 7%.

[0063] The parameters and properties of the prepared nanocrystalline rare-earth magnesium alloy rods with multi-scale structures in each embodiment and comparative example are as follows: Figure 3 As shown.

[0064] When the low-temperature heat treatment temperature is below 100℃, nano-sized precipitates cannot be generated, resulting in limited improvement in alloy strength and difficulty in achieving tensile strength exceeding 500MPa and yield strength exceeding 480MPa. When the low-temperature heat treatment temperature is above 200℃, the nano-sized precipitates coarsen (growing to more than 30nm), reducing alloy plasticity and resulting in elongation after fracture of less than 5%.

[0065] When the high-temperature heat treatment temperature is below 260℃, the grains cannot grow, and thus cannot form micron-sized grains that can coordinate plastic deformation. The alloy has low plasticity and it is difficult to achieve an elongation after fracture of more than 5%. When the high-temperature heat treatment temperature is above 340℃, the grains grow rapidly and cannot retain ultrafine grains. The nano-crystals in the original grains become micron-sized grains with a grain size of more than 1μm. The alloy strength drops sharply, with tensile strength below 450MPa and yield strength below 400MPa.

[0066] The embodiments of the present invention have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention is not limited to the specific embodiments described above; these embodiments are merely illustrative and not limiting. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing rare earth magnesium alloy rods, wherein the mass percentage composition of the rare earth magnesium alloy is Gd: 5.89-6.90%, Y: 3.41-3.90%, Zr: 0.42-0.46%, with the remainder being Mg, characterized in that, The preparation method includes the following steps: A. Extrusion deformation of rare earth magnesium alloy to obtain extruded bars, with an extrusion temperature of 430~450℃ and an extrusion ratio of 40~55; B. The extruded bar is subjected to rotary forging to obtain rotary forged bar. The rotary forging temperature is 0~100℃, and the total deformation is 20~60%. The deformation per pass of the rotary forging is 10~20%. C. Perform the first stage heat treatment on the rotary forged bar stock. The first stage heat treatment temperature is 100~200℃ and the holding time is 24~360h. D. Perform a second-stage heat treatment on the rotary forged bar stock. The second-stage heat treatment temperature is 260~340℃, and the holding time is 1~15min. The average grain size of the rare earth magnesium alloy rods obtained in step C is 30~100nm; The rare earth magnesium alloy rods obtained in step D have a tensile strength ≥ 510 MPa, a yield strength ≥ 480 MPa, and an elongation after fracture ≥ 7%; After the first and second stage heat treatments, the alloy forms a multi-scale structure consisting of micron-sized grains, ultrafine grains, nanocrystalline grains, and nanoscale precipitates. The average grain size of the multi-scale structure is 130–720 nm, containing nanoscale grains with a grain size of 40–100 nm, ultrafine grains with a grain size of 100–1000 nm, and micron-sized grains with a grain size of 1–2 μm. The average size of the nanoscale precipitates is 10–30 nm.

2. The method for preparing a rare earth magnesium alloy rod according to claim 1, characterized in that, The temperature of the first stage of heat treatment is 125~175℃, and the holding time is 96~288h.

3. The method for preparing a rare earth magnesium alloy rod according to claim 1, characterized in that, The second stage of heat treatment is carried out at a temperature of 280~320℃ and a holding time of 5~10 minutes.

4. The method for preparing a rare earth magnesium alloy rod according to claim 1, characterized in that, The feed rate for the rotary forging deformation is 5~6 mm / min.

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