Multi-morphology LPSO phase magnesium rare earth alloy and preparation method thereof

Abstract

The invention provides a multi-morphology LPSO phase magnesium rare earth alloy and a preparation method thereof.The preparation method comprises the following steps that (1) after pure magnesium, pure zinc and magnesium alloy are mixed according to the proportion, a refining agent is added for mixed smelting, then the mixture is added into a mold to be cooled, and as-cast alloy is obtained; wherein the magnesium alloy comprises a magnesium-gadolinium alloy, a magnesium-yttrium alloy and a magnesium-zirconium alloy; and (2) the as-cast alloy is sequentially subjected to homogenization treatment and water cooling treatment, then the alloy subjected to water cooling treatment is subjected to multi-pass rolling, and the multi-morphology LPSO phase magnesium rare earth alloy is obtained, wherein in the rolling process, the pressing rate of each pass is gradually increased along with the increase of the rolling passes. According to the method, more efficient and more uniform control over the morphology and distribution of the LPSO phase is achieved, the complex heat treatment procedure of the rolled alloy is omitted, meanwhile, the formability, strength and plasticity matching far better than that of a traditional technology is obtained, and meanwhile the overall production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of magnesium rare earth alloy technology, and in particular to a multimorphic LPSO phase magnesium rare earth alloy and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, have broad application prospects in aerospace, transportation, and 3C products. However, their poor absolute strength and ductility limit their large-scale industrial applications. Among various magnesium alloy systems, Mg-RE (rare earth)-Zn alloys have attracted much attention because they can form long-period packed ordered (LPSO) phases. This phase structure can simultaneously improve the strength and ductility of the alloy, which is the key to breaking through the performance bottleneck of magnesium alloys.

[0003] Currently, the main process for controlling the LPSO phase involves prolonged heat treatment to form it. However, this method tends to result in coarse LPSO phases with uncontrollable content and distribution, which is detrimental to subsequent plastic processing. Furthermore, in rolled alloys prepared by conventional hot rolling processes, the LPSO phase often coarsens or dissolves during deformation, making it difficult to achieve fine microstructure control across multiple scales and morphologies. Consequently, the overall mechanical properties of the alloy, especially the balance between strength and plasticity, fail to reach an ideal state, limiting its application potential in high-performance components.

[0004] Therefore, there is an urgent need to provide a multimorphic LPSO phase magnesium rare earth alloy and its preparation method. Summary of the Invention

[0005] This invention provides a magnesium rare earth alloy with multimorphic LPSO phase and its preparation method, which can solve the problem that the LPSO phase in magnesium rare earth alloys prepared by existing hot rolling processes is coarse and cannot guarantee good comprehensive mechanical properties, especially strong plasticity.

[0006] In a first aspect, the present invention provides a method for preparing a multi-morphology LPSO phase magnesium rare earth alloy, the preparation method comprising the following steps: (1) Pure magnesium, pure zinc and magnesium alloy are mixed in proportion, and then a refining agent is added for mixing and melting. The mixture is then placed in a mold and cooled to obtain a cast alloy. The magnesium alloy includes magnesium-gadolinium alloy, magnesium-yttrium alloy and magnesium-zirconium alloy. (2) The as-cast alloy is subjected to homogenization treatment and water cooling treatment in sequence, and then the water-cooled alloy is rolled in multiple passes to obtain the multi-morphology LPSO phase magnesium rare earth alloy; wherein, during the rolling process, the reduction ratio of each pass increases with the increase of the rolling passes.

[0007] Preferably, before step (1), a step of designing the composition of the magnesium rare earth alloy is included; wherein, in the magnesium rare earth alloy, the total amount of rare earth elements gadolinium and yttrium is 4.0-9.5 wt.%, the content of zinc is 1.0-3.5 wt.%, and the content of zirconium is 0.3-0.5 wt.%.

[0008] More preferably, the ratio of rare earth elements to zinc is 2.1 to 2.3, and the ratio of gadolinium to yttrium is 3.3 to 3.5.

[0009] More preferably, in the magnesium rare earth alloy, the content of gadolinium is 5.1 wt.%, the content of yttrium is 1.5 wt.%, the content of zinc is 2.3 wt.%, the content of zirconium is 0.3 wt.%, and the remainder is magnesium or other unavoidable impurities.

[0010] Preferably, in step (1), the temperature of the mixed melting is 740-780℃ and the melting time is 30-50min; the refining agent is hexachloroethane and the amount of refining agent added is 0.3-0.5wt. of the total alloy.

[0011] Preferably, in step (1), the temperature of the mold is 290-310℃.

[0012] Preferably, in step (2), the homogenization treatment is carried out at a temperature of 500-510℃ for 12-14 hours.

[0013] Preferably, the water cooling temperature is 25-30°C, and the water cooling process further includes a step of polishing the alloy surface.

[0014] Preferably, in step (2), the rolling temperature is 470-480℃ and the rolling speed is 18-22m / min.

[0015] Preferably, the alloy is held at the rolling temperature for 30-40 minutes before rolling, and held at the rolling temperature for 10-15 minutes after each rolling pass.

[0016] Preferably, in step (2), during the rolling process, the ratio of the absolute reduction amount of each pass to the initial thickness of the alloy is a fixed value, preferably 5%, and after multiple rolling passes, the ratio of the total reduction amount of the alloy to the initial thickness of the alloy is 75-85%.

[0017] Secondly, embodiments of the present invention also provide a multimorphic LPSO phase magnesium rare earth alloy, which is prepared by any of the preparation methods described in the first aspect above.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: In this invention, the composition of magnesium rare earth alloy is first optimized. Based on the reasonable composition design, a multi-pass rolling process with progressively increasing pressure ratio is innovatively adopted. Combined with the inter-pass annealing phase process, the dissolution and precipitation kinetics of W phase and LPSO phase are cleverly controlled by utilizing the synergistic effect of deformation strain energy and thermal activation energy. This multi-pass rolling with progressively increasing pressure ratio ensures that strain energy is continuously and effectively input during the rolling process, promoting the non-equilibrium precipitation and transformation of LPSO phase in different microscopic positions and morphologies. As a result, various morphologies of LPSO phase, such as blocky, coarse lamellar, and fine lamellar, are directly induced in the alloy. The resulting multi-morphological LPSO phases construct a multi-scale synergistic strengthening system within the deformed microstructure. Specifically, the blocky LPSO phase can bear stress and pin grain boundaries, promoting grain refinement through the PSN mechanism during rolling. The intragranular lamellar LPSO phase can inhibit grain recrystallization, bear stress, and induce a bimodal microstructure, improving the alloy's strength and plasticity. The fine lamellar LPSO phase strengthens the matrix and delays matrix deformation and cracking. Compared to traditional rolling processes, this invention achieves more efficient and uniform control over the morphology and distribution of LPSO phases, and enables the rolled alloy to achieve far superior formability, strength, and plasticity matching compared to traditional processes while eliminating complex heat treatment steps, thus improving overall production efficiency. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The types and distribution of the second phase in the initial microstructure of the alloy in Example 2 of the present invention are shown; wherein, (a) is the cast alloy and (b) is the alloy after homogenization treatment; Figure 2 The types and distribution of the second phase in the initial microstructure of the alloy in Example 1 of the present invention are shown; wherein, (c) is the cast alloy and (d) is the alloy after homogenization treatment; Figure 3 The types and distribution of the second phase in the initial microstructure of the alloy in Example 3 of the present invention are shown; wherein, (e) is the cast alloy and (f) is the alloy after homogenization treatment; Figure 4 These are optical microscope (OM) images of the three alloys in the rolled state in Examples 1 to 3 of the present invention; wherein, (a) is Example 2, (b) is Example 1, and (c) is Example 3; Figure 5SEM images of the three alloys in the rolled state in Examples 1 to 3 of the present invention are shown; wherein, (a) is Example 2, (b) is Example 1, and (c) is Example 3. Figure 6 The images show the types of second phases and the characteristic morphology of different second phases in the three rolled alloys of Examples 1 to 3 of the present invention. Figure 7 The diagrams show the inverse polarity (IPF) of the three rolled alloys in Examples 1 to 3 of the present invention; where (a) is Example 2, (b) is Example 1, and (c) is Example 3. Figure 8 The figures show the tensile stress-strain curves of the three rolled alloys in Examples 1 to 3 of this invention; where the horizontal axis represents elongation and the vertical axis represents tensile stress intensity. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a method for preparing a multi-morphology LPSO phase magnesium rare earth alloy, the method comprising the following steps: (1) Pure magnesium, pure zinc and magnesium alloy are mixed in proportion, and then a refining agent is added for mixing and melting. The mixture is then placed in a mold and cooled to obtain a cast alloy. The magnesium alloy includes magnesium-gadolinium alloy, magnesium-yttrium alloy and magnesium-zirconium alloy. (2) The as-cast alloy is subjected to homogenization treatment and water cooling treatment in sequence, and then the water-cooled alloy is rolled in multiple passes to obtain the multi-morphology LPSO phase magnesium rare earth alloy; wherein, during the rolling process, the reduction ratio of each pass increases with the increase of the rolling passes.

[0023] In this embodiment of the invention, the composition of the magnesium rare earth alloy is first optimized. Based on the reasonable composition design, a multi-pass rolling process with progressively increasing pressure ratio is innovatively adopted. Combined with the inter-pass annealing phase process, the dissolution and precipitation kinetics of the W phase and LPSO phase are cleverly controlled by utilizing the synergistic effect of deformation strain energy and thermal activation energy. This multi-pass rolling with progressively increasing pressure ratio ensures that strain energy is continuously and effectively input during the rolling process, promoting the non-equilibrium precipitation and transformation of the LPSO phase in different microscopic positions and morphologies. As a result, various morphologies of LPSO phase, such as blocky, coarse lamellar, and fine lamellar, are directly induced in the alloy. The various morphologies of LPSO phases constructed in this way form a multi-scale synergistic strengthening system in the deformed microstructure. Among them, the blocky LPSO phase can bear stress and pin grain boundaries, promoting grain refinement through the PSN mechanism during rolling; the intragranular lamellar LPSO phase can inhibit grain recrystallization, bear stress, and promote the formation of a bimodal microstructure in the alloy, improving the alloy's strength and plasticity; the fine lamellar LPSO phase can strengthen the matrix and delay matrix deformation and cracking. Compared with traditional rolling processes, the embodiments of this invention achieve more efficient and uniform control over the morphology and distribution of LPSO phases, and enable the rolled alloy to achieve formability, strength, and plasticity matching far superior to traditional processes while eliminating complex heat treatment procedures, and improving overall production efficiency.

[0024] According to some preferred embodiments, before step (1), a step of designing the composition of the magnesium rare earth alloy is included; wherein, in the magnesium rare earth alloy, the total amount of rare earth elements gadolinium and yttrium is 4.0-9.5 wt.% (for example, it can be 4.0 wt.%, 4.5 wt.%, 5 wt.%, 6.6 wt.%, 7 wt.%, 8 wt.%, 9.2 wt.%, or 9.5 wt.%), the content of zinc is 1.0-3.5 wt.% (for example, it can be 1.0 wt.%, 1.4 wt.%, 2.3 wt.%, 3.2 wt.%, or 3.5 wt.%), and the content of zirconium is 0.3-0.5 wt.% (for example, it can be 0.3 wt.%, 0.35 wt.%, 0.4 wt.%, 0.45 wt.%, or 0.5 wt.%); the ratio of gadolinium to zinc content is 2.1-2.3, and the ratio of gadolinium to yttrium content is 3.3-3.5.

[0025] In this embodiment of the invention, a magnesium rare earth alloy with both high performance and low cost was designed through Pandat phase diagram calculations and in-depth composition optimization. Compared with traditional magnesium rare earth alloys, by appropriately increasing the content of low-cost zinc and reducing the content of high-cost rare earth elements, and by precisely controlling the content of each key element, the magnesium rare earth alloy system is more accurately located at the critical transition point between the W phase and the LPSO phase. This system is more conducive to promoting the synergistic precipitation of LPSO phases with various morphologies. Furthermore, this composition design is more sensitive to subsequent multi-pass rolling and inter-pass annealing processes. Thus, while ensuring the alloy performance, the cost of raw materials is significantly reduced, achieving a balance between cost reduction and efficiency improvement.

[0026] According to some preferred embodiments, the magnesium rare earth alloy contains 5.1 wt.% gadolinium, 1.5 wt.% yttrium, 2.3 wt.% zinc, 0.3 wt.% zirconium, and the remainder is magnesium or other unavoidable impurities.

[0027] In this embodiment of the invention, extensive experimental verification revealed that when the content of each component in the magnesium rare earth alloy is optimized to the above-mentioned content, it is at the critical point of competition between the W phase and the LPSO phase in the phase diagram. Thus, through subsequent multi-pass rolling and inter-pass annealing processes, three morphologies of LPSO phase—blocky, fine lamellar, and coarse lamellar within the grains—can be synchronously and stably induced. These three morphologies of LPSO phase constitute a multi-scale synergistic strengthening system, which is conducive to achieving the best match between strength and plasticity in its mechanical properties. Experimental verification showed that the alloy with this composition exhibits the best comprehensive mechanical properties (yield strength 317 MPa, tensile strength 339 MPa, elongation 10.3%), and its strength is much higher than that of other alloy compositions, successfully solving the contradiction that traditional high-strength magnesium alloys are usually accompanied by low plasticity.

[0028] According to some preferred embodiments, in step (1), the temperature of the mixing and melting is 740-780℃ (e.g., 740℃, 750℃, 760℃, 770℃ or 780℃), and the melting time is 30-50min (e.g., 30min, 40min or 50min); the refining agent is hexachloroethane, and the amount of refining agent added is 0.3-0.5wt.% of the total alloy (e.g., 0.3wt.%, 0.4wt.% or 0.5wt.%); the temperature of the mold is 290-310℃ (e.g., 290℃, 300℃ or 310℃).

[0029] In this embodiment of the invention, during the mixed smelting, the oxide scale on the surface of each raw material is first removed. Then, the components are added to the smelting furnace in batches in the order of magnesium-gadolinium alloy, magnesium-yttrium alloy, magnesium-zirconium alloy, pure magnesium, and pure zinc for melting. A mixed atmosphere of CO2 and SF6 is introduced into the smelting furnace, and the smelting temperature is controlled at 740-760°C. After each batch of raw materials is added, wait 15-20 minutes before adding the next batch. After all the raw materials are added, add hexachloroethane refining agent, let stand, and stir for 10 minutes. Raise the smelting temperature to 770-780°C and let stand for 30 minutes. This not only ensures that the components are fully mixed but also ensures good fluidity, which is beneficial for subsequent mold casting. It should be noted that in the above magnesium-rolled alloy, magnesium-yttrium alloy, and magnesium-zirconium alloy, the mass percentage of gadolinium, yttrium, and zirconium is 30%.

[0030] According to some preferred embodiments, in step (2), the homogenization treatment temperature is 500-510℃ (for example, it can be 500℃, 505℃ or 510℃), and the time is 12-14h (for example, it can be 12h, 13h or 14h); the water cooling treatment temperature is 25-30℃ (for example, it can be 25℃, 28℃ or 30℃), and the water cooling treatment further includes a step of polishing the alloy surface.

[0031] In this embodiment of the invention, before rolling deformation, the obtained as-cast alloy is first homogenized at a certain temperature. This effectively promotes the dissolution of the blocky second phase, which is distributed at the grain boundaries in a network or irregular shape, into the magnesium matrix. It also effectively eliminates the segregation of alloying elements at the grain boundaries, leaving only a small amount of spherical or square second phase. This not only ensures that the subsequent rolling-annealing process can accurately and efficiently induce multi-morphological LPSO phases, thereby guaranteeing good comprehensive mechanical properties of the final alloy material, but also avoids the risk of cracking during subsequent rolling.

[0032] Meanwhile, in this embodiment of the invention, the homogenization treatment temperature is set within the aforementioned range. This effectively promotes the re-dissolution of harmful second phases and the homogenization of composition without causing overheating. Experiments of this invention have confirmed that if the homogenization treatment temperature is too low, the network and irregularly shaped blocky second phases in the as-cast structure cannot be effectively dissolved in the magnesium matrix, and the segregation of alloying elements cannot be effectively eliminated, which is not conducive to the subsequent accurate and efficient induction of multimorphic LPSO phases. If the homogenization treatment temperature is too high, the local temperature at the grain boundaries may exceed their tolerance temperature, causing local melting or overheating of the grain boundaries.

[0033] According to some preferred embodiments, in step (2), the rolling temperature is 470-480℃ (e.g., 470℃, 475℃ or 480℃), and the rolling speed is 18-22m / min (e.g., 18m / min, 20m / min or 22m / min); before rolling, the alloy is held at the rolling temperature for 30-40min (e.g., 30min, 35min or 40min), and after each rolling pass, it is held at the rolling temperature for 10-15min (e.g., 10min, 12min or 15min).

[0034] According to some preferred embodiments, in step (2), during the rolling process, the ratio of the absolute reduction amount of each pass to the initial thickness of the alloy is a fixed value, preferably 5%, and after multiple passes of rolling, the ratio of the total reduction amount of the alloy to the initial thickness of the alloy is 75-85% (for example, it can be 75%, 80% or 85%).

[0035] Unlike traditional rolling methods with a constant reduction rate, this invention sets the ratio of the reduction rate to the initial thickness of the alloy in each pass to a fixed value. This allows the reduction rate to gradually increase with each rolling pass, ensuring a continuous and effective input of strain energy throughout the rolling process. This directly induces the formation of various LPSO phase morphologies within the alloy, including blocky, coarse lamellar, and fine lamellar phases. Specifically, in the early stages of rolling, a smaller reduction rate is used for deformation to avoid cracking due to excessive initial deformation, ensuring good formability of the magnesium rare earth alloy billet. This also facilitates the simultaneous dissolution and reprecipitation of both the LPSO and W phases, thus initially constructing a multiphase microstructure conducive to strengthening and toughening. As the rolling process progresses into the middle and later stages, the reduction rate of each pass is gradually increased, injecting higher strain energy into the alloy material. This provides a nucleation driving force for subsequent recrystallization and ultimately enhances grain refinement through recrystallization.

[0036] It should be noted that, in the embodiments of the present invention, during the rolling process, the reduction rate of each pass is specifically (thickness of the alloy workpiece before rolling in this pass - thickness of the alloy workpiece after rolling in this pass) / thickness of the alloy workpiece before rolling in this pass × 100%; the initial thickness of the alloy workpiece is specifically the original thickness of the alloy before rolling; the absolute reduction amount of the pass is specifically the physical thickness of the alloy workpiece that is reduced in the i-th pass, that is, the difference between the thickness of the alloy workpiece before rolling in this pass and the thickness of the alloy workpiece after rolling in this pass; the total reduction amount of the alloy workpiece is the cumulative reduction thickness of the alloy workpiece throughout the entire rolling process, that is, the difference between the initial thickness of the alloy workpiece and the final thickness of the alloy workpiece after rolling.

[0037] This invention also provides a multimorphic LPSO phase magnesium rare earth alloy obtained by any of the above preparation methods.

[0038] To more clearly illustrate the technical solution and advantages of the present invention, the following detailed description of a multimorphic LPSO phase magnesium rare earth alloy and its preparation method is provided through several embodiments.

[0039] Example 1: The composition of the magnesium rare earth alloy is designed as follows: gadolinium content is 5.1 wt.%, yttrium content is 1.5 wt.%, zinc content is 2.3 wt.%, zirconium content is 0.3 wt.%, and the remainder is magnesium or other unavoidable impurities; denoted as Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr; (1) After removing the oxide scale from the surface of the alloy raw materials, magnesium-gadolinium alloy (30 wt.% gadolinium), magnesium-yttrium alloy (30 wt.% yttrium), magnesium-zirconium alloy (30 wt.% zirconium), pure magnesium (99.9%), and pure zinc (99.9%) are added in batches according to the above proportions to a melting furnace (with a CO2 / SF6 mixed protective atmosphere) and mixed and melted at 760°C. After each batch of raw materials is added, wait 15 minutes before adding the next batch. After all the raw materials are added, add a refining agent (hexachloroethane), mix and let stand for 10 minutes, then heat to 780°C and let stand for 30 minutes. Then, put it into a mold preheated to 300°C and cool to obtain the cast alloy. The refining agent is 0.3 wt.% of the total amount of alloy raw materials. (2) The as-cast alloy was placed in a muffle furnace and held at 500℃ for 12 hours, and then water-cooled at 25℃. After water cooling, the alloy plate was polished until the surface had a metallic luster and no other impurities. The treated alloy plate (75 mm × 60 mm × 8 mm) was first held at 480℃ for 30 minutes, and then rolled in multiple passes at 480℃. During the rolling process, the ratio of the absolute reduction of each pass to the initial thickness of the alloy was 5%, and after multiple passes of rolling, the ratio of the total reduction of the alloy to the initial thickness of the alloy was 75%, thus obtaining a multi-morphology LPSO phase magnesium rare earth alloy. During the rolling process, the rolling speed was 20 m / min, and after each pass of rolling, it was held at 480℃ for 10 minutes.

[0040] Example 2: The composition of the magnesium rare earth alloy is designed as follows: gadolinium content is 3.1 wt.%, yttrium content is 0.9 wt.%, zinc content is 1.4 wt.%, zirconium content is 0.3 wt.%, and the remainder is magnesium or other unavoidable impurities; denoted as Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr; (1) After removing the oxide scale from the surface of the alloy raw materials, magnesium-gadolinium alloy (30 wt.% gadolinium), magnesium-yttrium alloy (30 wt.% yttrium), magnesium-zirconium alloy (30 wt.% zirconium), pure magnesium (99.9%), and pure zinc (99.9%) are added in batches according to the above proportions to a melting furnace (with a CO2 / SF6 mixed protective atmosphere) and mixed and melted at 760°C. After each batch of raw materials is added, wait 15 minutes before adding the next batch. After all the raw materials are added, add a refining agent (hexachloroethane), mix and let stand for 10 minutes, then heat to 780°C and let stand for 30 minutes. Then, put it into a mold preheated to 300°C and cool to obtain the cast alloy. The refining agent is 0.3 wt.% of the total amount of alloy raw materials. (2) The as-cast alloy was placed in a muffle furnace and held at 500℃ for 12 hours, and then water-cooled at 25℃. After water cooling, the alloy plate was polished until the surface had a metallic luster and no other impurities. The treated alloy plate (75 mm × 60 mm × 8 mm) was first held at 480℃ for 30 minutes, and then rolled in multiple passes at 480℃. During the rolling process, the ratio of the absolute reduction of each pass to the initial thickness of the alloy was 5%, and after multiple passes of rolling, the ratio of the total reduction of the alloy to the initial thickness of the alloy was 75%, thus obtaining a multi-morphology LPSO phase magnesium rare earth alloy. During the rolling process, the rolling speed was 20 m / min, and after each pass of rolling, it was held at 480℃ for 10 minutes.

[0041] Example 3: The composition of the magnesium rare earth alloy is designed as follows: gadolinium content is 7.1 wt.%, yttrium content is 2.1 wt.%, zinc content is 3.2 wt.%, zirconium content is 0.3 wt.%, and the remainder is magnesium or other unavoidable impurities; Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr; (1) After removing the oxide scale from the surface of the alloy raw materials, magnesium-rolled alloy (30 wt.% rolled), magnesium-yttrium alloy (30 wt.% yttrium), magnesium-zirconium alloy (30 wt.% zirconium), pure magnesium (99.9%), and pure zinc (99.9%) are added in batches according to the above proportions to a melting furnace (with a CO2 / SF6 mixed protective atmosphere) and mixed and melted at 760°C. After each batch of raw materials is added, wait 15 minutes before adding the next batch. After all the raw materials are added, add a refining agent (hexachloroethane), mix and let stand for 10 minutes, then heat to 780°C and let stand for 30 minutes. Then, put it into a mold preheated to 300°C and cool to obtain the cast alloy; wherein, the refining agent is 0.3 wt.% of the total amount of alloy raw materials. (2) The as-cast alloy was placed in a muffle furnace and held at 500℃ for 12 hours, and then water-cooled at 25℃. After water cooling, the alloy plate was polished until the surface had a metallic luster and no other impurities. The treated alloy plate (75 mm × 60 mm × 8 mm) was first held at 480℃ for 30 minutes, and then rolled in multiple passes at 480℃. During the rolling process, the ratio of the absolute reduction of each pass to the initial thickness of the alloy was 5%, and after multiple passes of rolling, the ratio of the total reduction of the alloy to the initial thickness of the alloy was 75%, thus obtaining a multi-morphology LPSO phase magnesium rare earth alloy. During the rolling process, the rolling speed was 20 m / min, and after each pass of rolling, it was held at 480℃ for 10 minutes.

[0042] Figures 1 to 3 The types and distribution of the second phase in the initial microstructure of the three alloys in Examples 1 to 3 are shown. In the as-cast Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr alloy, for example... Figure 1 As shown in (a), the second phase mainly consists of network and irregularly shaped blocky phases, distributed at grain boundaries, and contains a small amount of alloying element segregation; after homogenization treatment, as shown in... Figure 1 (b), by Figure 1 As shown in (b), the second phase is basically dissolved back into the matrix, with only a small amount of spherical and square second phases remaining. With the increase of alloying element content, the as-cast Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy is mainly composed of irregular blocky second phases, and there is also segregation of alloying elements at the grain boundaries (such as...). Figure 2 (c) shows that after homogenization, as shown in the figure Figure 2 (d) As shown in the figure, most of the bulky second phase dissolves back, with only a small amount of bulky and spherical second phases precipitating, and a small amount of square second phase is found in the second phase enrichment region; such as Figure 3 In (e), the blocky second phase in the as-cast Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr alloy is larger in size and significantly more numerous, with a small number of spherical second phases embedded within the blocky second phases. After homogenization treatment, as shown... Figure 3 (f) The blocky second phase almost completely re-dissolves, leaving only a small amount of smaller blocky second phase, which coexists with the precipitated spherical second phase, and a small amount of square second phase can still be seen in the enrichment area.

[0043] Figure 4 These are optical microscope (OM) images of the rolled alloys from Examples 1 to 3. Figure 4As shown in (a), the rolled Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr alloy has equiaxed grains and coarse grains. This is because the second phase content of the alloy is low during rolling, and abnormal grain growth occurs during the holding stage between each rolling pass. The deformation amount in subsequent rolling is insufficient to elongate the grains along the RD direction and form a basal orientation, and recrystallization is difficult to occur, thus preserving the original microstructure. Figure 4 As shown in (b), the rolled Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy consists of large grains elongated along the RD direction and small equiaxed grains in other regions. The gray area in the figure represents the second phase, which also exhibits three forms: blocky, coarse lamellar within the grains, and fine dispersed lamellar. The difference in grain size is related to the morphology and distribution of the second phase. Figure 4 As shown in (c), in the rolled alloy of Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr, there are a large number of gray second phases that are elongated into strips along the RD direction, and the grains are distributed between the second phases. They tend to elongate along the RD direction, but are limited by the boundaries of the second phases.

[0044] Figure 5 SEM images of the rolled alloys from Examples 1 to 3 are shown. Microscopic observation of the rolled alloys with different compositions clearly reveals the decisive influence of alloying element content on the morphology and composition of the second phase. In the Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr alloy ( Figure 5 a) Due to the low total amount of alloying elements and the multiple rolling passes, the elements are almost completely dissolved in the matrix, with only a small amount of spherical W phase and fine lamellar LPSO phase precipitated; therefore, this alloy can serve as an ideal control group to evaluate the strengthening effect of the LPSO phase. When the alloying element content is increased to Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr ( Figure 5 (b) A multi-morphological LPSO phase synergistic structure emerged, including blocky LPSO phases elongated along the rolling direction, dispersed fine lamellar LPSO phases, and coarse lamellar LPSO phases within the grains. When the composition further increased to Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr ( Figure 5 c) The morphology of the LPSO phase is mainly characterized by fragmented and more densely distributed blocky LPSO phases along the rolling direction, accompanied by a small amount of spherical W phase. It can be seen that by precisely controlling the alloy composition (especially the contents of Gd, Y and Zn), the formation of various morphologies of LPSO phases in the rolled alloy can be effectively guided.

[0045] Figure 6 The types and morphologies of the second phase in the three rolled alloys in Examples 1 to 3 are shown. Figure 6(a) is a spherical W phase (the second phase in Example 2), with a size on the submicron scale, and is diffusely distributed in the matrix; Figure 6 (b) is a fine lamellar LPSO phase (L-LPSO, the second phase in Example 1), with a size on the micrometer scale, dispersed in the magnesium matrix, and exhibiting a gray lamellar structure; Figure 6 (c) is a coarse lamellar LPSO phase within the crystal (I-LPSO, the second phase in Example 1), which is relatively large in size, ranging from tens of micrometers to hundreds of micrometers, and is distributed in the magnesium matrix region, elongated along the RD direction; Figure 6 (d) is a bulk LPSO phase (B-LPSO, the second phase in Examples 1 and 3), with a size ranging from tens to hundreds of micrometers, arranged in a fibrous manner along the RD direction.

[0046] Figure 7 The figures show the inverse pole figures (IPF) of the three rolled alloys in Examples 1 to 3. The figures reveal that the alloy element content and the resulting LPSO phase morphology have a decisive influence on the grain structure and orientation distribution. Figure 7 As shown in (a), in the Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr alloy, the grain shape distribution is relatively random, and the color distribution shows that most grains are basal-oriented, but there are also a small number of randomly oriented grains, and the grain size varies significantly. Figure 7 As shown in (b), in the Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy, the large grains elongated along the rolling direction (RD) contain a large number of coarse lamellar LPSO phases with strong basal orientation; around the bulk LPSO phases (unidentified white areas), a large number of fine crystalline grains with random orientations are formed, while the distribution area of ​​the fine lamellar LPSO phases is mainly composed of small grains with basal orientation. Figure 7 As shown in (c), in the Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr alloy, the unidentified region of the blocky LPSO phase mainly consists of fine basal-oriented grains, accompanied by a small number of randomly oriented grains, while large grains have essentially disappeared. This indicates that by controlling the alloy composition to change the morphology and distribution of the LPSO phase, different recrystallization behaviors can be precisely induced, thereby achieving microstructure design from weak texture and bimodal structure to uniform fine grains.

[0047] Figure 8 The figures show the tensile stress-strain curves of the three rolled alloys in Examples 1 to 3. Figure 8As can be seen, the Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy exhibits the best strength-ductility balance, with a yield strength (TYS) of 317 MPa, a tensile strength (UTS) of 339 MPa, and an elongation (EL) of 10.3%. In contrast, the Mg-3.1Gd-0.9Y-1.4Zn-0.3Zr alloy has lower strength but higher elongation due to the limited strengthening effect of the second phase. A surprising finding is that higher content of alloying elements and second phases does not necessarily mean better performance: however, in this embodiment, the Mg-7.1Gd-2.1Y-3.2Zn-0.3Zr alloy, despite containing higher content of alloying elements and second phases, has lower TYS, UTS, and EL than the Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy. Microstructural comparison revealed the presence of three LPSO phase morphologies in the Mg-5.1Gd-1.5Y-2.3Zn-0.3Zr alloy: blocky, fine lamellar, and coarse lamellar within the grains. These synergistic effects induce a strong and tough bimodal grain structure. This demonstrates that the synergistic strengthening system constructed from multiple LPSO phase morphologies contributes significantly more to performance than the simple superposition of single or two LPSO phase morphologies.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a multi-morphology LPSO phase magnesium rare earth alloy, characterized in that, The preparation method includes the following steps: (1) Pure magnesium, pure zinc and magnesium alloy are mixed in proportion, and then a refining agent is added for mixing and melting. The mixture is then placed in a mold and cooled to obtain a cast alloy. The magnesium alloy includes magnesium-gadolinium alloy, magnesium-yttrium alloy and magnesium-zirconium alloy. (2) The as-cast alloy is subjected to homogenization treatment and water cooling treatment in sequence, and then the water-cooled alloy is rolled in multiple passes to obtain the multi-morphology LPSO phase magnesium rare earth alloy; wherein, during the rolling process, the reduction ratio of each pass increases with the increase of the rolling passes.

2. The preparation method according to claim 1, characterized in that, Before step (1), the magnesium rare earth alloy is further designed with a composition; wherein, in the magnesium rare earth alloy, the total amount of rare earth elements gadolinium and yttrium is 4.0-9.5 wt.%, the content of zinc is 1.0-3.5 wt.%, and the content of zirconium is 0.3-0.5 wt.%.

3. The preparation method according to claim 2, characterized in that, The ratio of rare earth elements to zinc is 2.1 to 2.3, and the ratio of gadolinium to yttrium is 3.3 to 3.

5.

4. The preparation method according to claim 3, characterized in that, In the magnesium rare earth alloy, the content of gadolinium is 5.1 wt.%, the content of yttrium is 1.5 wt.%, the content of zinc is 2.3 wt.%, the content of zirconium is 0.3 wt.%, and the remainder is magnesium or other unavoidable impurities.

5. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the mixing and melting is 740-780℃, and the melting time is 30-50min; The refining agent is hexachloroethane, and the amount of refining agent added is 0.3-0.5 wt.% of the total alloy.

6. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the mold is 290-310℃.

7. The preparation method according to claim 1, characterized in that, In step (2), the homogenization treatment is carried out at a temperature of 500-510℃ for 12-14 hours. The water cooling temperature is 25-30℃. Preferably, the water cooling process further includes a step of polishing the alloy surface.

8. The preparation method according to claim 1, characterized in that, In step (2), the rolling temperature is 470-480℃ and the rolling speed is 18-22m / min; Preferably, the alloy is held at the rolling temperature for 30-40 minutes before rolling, and held at the rolling temperature for 10-15 minutes after each rolling pass.

9. The preparation method according to any one of claims 1 to 8, characterized in that, In step (2), during the rolling process, the ratio of the absolute reduction amount of each pass to the initial thickness of the alloy is a fixed value, preferably 5%, and after multiple passes of rolling, the ratio of the total reduction amount of the alloy to the initial thickness of the alloy is 75-85%.

10. A multi-morphology LPSO phase magnesium rare earth alloy, characterized in that, It is prepared by any one of claims 1 to 9.

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