A method for preparing a light alloy based on rare earth fractionation and multi-element solid solution synergistic strengthening

Abstract

This invention relates to a method for preparing lightweight alloys based on rare earth grading and multi-element solid solution synergistic strengthening, belonging to the technical field of lightweight alloy materials. The lightweight alloy is a magnesium alloy, and its components, by mass percentage, include: Zr: 0.3-0.8%, Mn: 0.3-0.8%, rare earth element Sm: 0.5-3.5%, with the balance being Mg and unavoidable impurities. By grading the addition of rare earth Sm, a multi-element solid solution synergistic effect is achieved with the inherent Zr and Mn elements in the alloy. After homogenization heat treatment, a supersaturated solid solution is formed, thereby changing the deformation mechanism of the alloy from basal slip-dominated to multi-system slip synergistic. Compared with the baseline alloy without added Sm, the alloy of this invention achieves significant improvements in yield strength and tensile strength, while also increasing elongation after fracture. This successfully solves the industry problem of balancing strength and plasticity in lightweight rare earth magnesium alloys, providing a new approach for the design of high-performance lightweight structural materials.

Description

Technical Field

[0001] This invention relates to the field of lightweight alloy materials technology, specifically a method for preparing lightweight alloys based on rare earth grading and multi-element solid solution synergistic strengthening. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, have great application potential in aerospace, transportation, and portable electronic products due to their high specific strength, high specific stiffness, good damping properties, and electromagnetic shielding performance. However, their inherent drawbacks, such as low absolute strength, poor room temperature plasticity, and poor processability, severely limit their widespread commercial application.

[0003] Solid solution strengthening is one of the most fundamental and effective methods to improve the properties of magnesium alloys. Common solid solution elements such as Al and Zn, while providing some strengthening effect, often lead to the formation of coarse and brittle second phases, resulting in a sharp decrease in plasticity. Rare earth (RE) elements are widely recognized as key elements for improving the overall properties of magnesium alloys. Among them, samarium (Sm), as a light rare earth element, has high solid solubility in magnesium and can cause strong lattice distortion, producing a significant solid solution strengthening effect. However, current technologies mostly focus on adding a single, high dose of a rare earth element. While this approach can improve strength, it often leads to loss of plasticity and increased costs, and fails to fully explore the synergistic potential between rare earth elements and other elements.

[0004] Furthermore, in lightweight alloys like the Mg-Zr-Mn system, which possess excellent basic properties, how to further break through their performance ceiling through innovative composition design and process control is a key research focus in this field. Current technologies lack a systematic approach for the graded and quantitative addition of rare earth element Sm, and for utilizing its synergistic effect with elements such as Zr and Mn to simultaneously achieve strengthening and toughening. Summary of the Invention

[0005] In order to solve the problems of the prior art, the present invention provides a method for preparing lightweight alloys based on rare earth grading and multi-element solid solution synergistic strengthening.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: Firstly, a method for preparing a lightweight alloy based on rare earth grading and multi-element solid solution synergistic strengthening, wherein the lightweight alloy is a magnesium alloy, and is composed of the following components by mass percentage: Zr: 0.3-0.8%, Mn: 0.3-0.8%, rare earth element Sm: 0.5-3.5%, with the balance being Mg and unavoidable impurities; The preparation method includes the following steps: S1: Raw material smelting: Using magnesium ingots, Mg-Zr master alloy, Mg-Mn master alloy and Mg-Sm master alloy as raw materials, heat to 720-750℃ under a protective atmosphere to completely melt them into a melt. S2: Refining and settling: The melt is refined and purified, and then settling at 710-730℃ for 20-40 minutes to allow the alloying elements to fully pre-diffuse. S3: Casting: The molten material after standing is poured into a preheated mold to obtain an ingot; S4: Homogenization heat treatment: The ingot is held at 500-530℃ for 8-24 hours to promote the uniform solid solution of Sm, Zr and Mn elements in the magnesium matrix and achieve synergistic control of solid solution, followed by rapid cooling. S5: Hot deformation processing: The homogenized ingot is hot-extruded or hot-rolled at 300-450℃ to obtain the final material.

[0007] Ingredient design and synergistic mechanism: Rare Earth Sm (Graded Addition Core): This invention selects Sm as the key alloying rare earth element. Its innovation lies in the graded addition strategy: (1): 0.5%-1.0%: This is the effective strengthening threshold. At this stage, Sm begins to dissolve in the Mg matrix in large quantities, producing a significant strengthening effect, and its performance begins to surpass that of the benchmark alloy.

[0008] (2): 1.0%-3.0% (preferred): This is the synergistic strengthening peak region. In this range, sufficient Sm atoms work together with Zr and Mn to produce strong synergistic solid solution strengthening and grain refinement strengthening, resulting in a simultaneous leap in strength and plasticity.

[0009] (3): >3.0%: This is the diminishing returns zone. Excessive addition weakens the improvement effect on plasticity and reduces cost-effectiveness.

[0010] Zr and Mn (synergistic regulatory elements): Zr is a highly efficient grain refiner, providing a fine-grained "base" for Sm solid solution; Mn purifies the melt and improves thermal stability. Together, they create a uniform, clean, and fine microstructure, which, together with the graded addition of Sm, promotes the formation of a multi-dimensional synergistic strengthening pattern of "grain refinement + strong solid solution," which is the key to achieving high strength and high plasticity.

[0011] In one specific embodiment of the first aspect, the mass percentage of the rare earth element Sm is 1.0-3.0%.

[0012] In one specific embodiment of the first aspect, the mass percentage of the rare earth element Sm is 1.5-2.5%.

[0013] In one specific embodiment of the first aspect, the mass percentage of the rare earth element Sm is 0.5-1.0%.

[0014] In one specific embodiment of the first aspect, the homogenization heat treatment process in step S4 is: holding at 520°C for 12 hours.

[0015] In one specific embodiment of the first aspect, the rapid cooling described in step S4 is water quenching.

[0016] In one specific embodiment of the first aspect, the protective atmosphere described in step S1 is a mixture of CO2 and SF6.

[0017] In one specific embodiment of the first aspect, the hot deformation process described in step S5 is hot extrusion, with an extrusion temperature of 380-420°C and an extrusion ratio of 15:1 to 25:1.

[0018] In one specific embodiment of the first aspect, the hot deformation process described in step S5 is hot rolling.

[0019] The second aspect is a lightweight alloy prepared according to a method for preparing lightweight alloys based on rare earth classification and multi-element solid solution synergistic strengthening.

[0020] The beneficial effects of this invention are as follows: 1. By designing the addition amount of rare earth element Sm in a graded manner, and forming a multi-element solid solution synergistic strengthening mechanism with the inherent Zr and Mn elements in the alloy, a significant simultaneous improvement in the strength and plasticity of lightweight magnesium alloys was achieved. Specifically, Sm produces a strong lattice distortion effect in the magnesium matrix, Zr provides a fine-grained substrate, and Mn plays a role in melt purification and thermal stability regulation. After homogenization heat treatment, the three elements form a homogeneous supersaturated solid solution. Under this synergistic effect, the dislocation motion mode of the alloy undergoes a fundamental transformation: from a single deformation mechanism dominated by basal plane slip in traditional magnesium alloys to a uniform deformation mode involving multiple slip systems (basal plane, cylindrical plane, and conical plane). This change in microscopic mechanism effectively suppresses local strain concentration, allowing the alloy to more fully activate different slip systems when subjected to external loads. This achieves high strength while maintaining or even improving plastic deformation capacity, breaking through the long-standing technical bottleneck in the field of lightweight rare earth magnesium alloys where strength and plasticity are difficult to balance.

[0021] 2. This invention employs a graded addition strategy, dividing the Sm content into different effective ranges, each of which effectively activates the synergistic strengthening effect with Zr and Mn. Through a process path of "pre-diffusion and static setting - high-temperature homogenization and solution treatment - rapid cooling," the uniform distribution and maximum solubility of Sm, Zr, and Mn elements in the magnesium matrix are ensured, avoiding the precipitation of harmful coarse second phases. Based on this, combined with subsequent hot deformation processing, a fine and uniform grain structure and dispersed precipitates are formed within the alloy, further enhancing the grain boundary and dislocation pinning effects. Experimental results show that the alloy prepared by this invention achieves comprehensive improvements in yield strength, tensile strength, and elongation after fracture, exhibiting excellent strength-ductility matching, providing a reliable technical solution for the design and industrial production of high-performance lightweight structural materials. Attached Figure Description

[0022] Figure 1 These are schematic diagrams of four magnesium alloy KAMs according to the present invention.

[0023] Figure 2 This is a schematic diagram of the average orientation difference of the cores of four magnesium alloys with different Sm contents according to the present invention.

[0024] Figure 3 These are schematic diagrams of tensile stress and strain of four magnesium alloy specimens according to the present invention.

[0025] Figure 4 This is a line graph showing the comparison of tensile data of four magnesium alloy samples according to the present invention.

[0026] Figure 5 This is a schematic diagram illustrating the identification of activated slip modes under different strain conditions in two magnesium alloys according to the present invention.

[0027] Figure 6 This is a statistical schematic diagram of the slip modes activated under different tensile strains of two magnesium alloys according to the present invention. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figures 1 to 6 This paper presents a method for preparing lightweight alloys based on rare earth grading and multi-element solid solution synergistic strengthening. Example 1

[0030] The four alloys were prepared, and their specific components (wt.%) are shown in Table 1 below. Table 1: Alloy composition design (wt.%) Preparation process: 1. Melting: High-purity magnesium ingots, Mg-30Zr, Mg-10Mn and Mg-20Sm master alloys are used and melted at 730℃ under the protection of CO2+SF6 mixed gas and stirred thoroughly.

[0031] 2. Processing and casting: After refining, the melt is allowed to stand at 720°C for 30 minutes, and then poured into a metal mold preheated to 350°C.

[0032] 3. Homogenization heat treatment: The ingot is held at 520℃ for 12 hours, followed by water quenching, to maximize the uniform distribution of solid solution atoms (Sm, Zr, Mn).

[0033] Tests and Results: The KAM diagrams and nucleus-average orientation difference diagrams of four magnesium alloy samples obtained from EBSD testing are as follows: Figure 1 , 2 As shown.

[0034] The magnesium alloy samples prepared above were subjected to room temperature tensile tests, and the test results are as follows: Figure 3 and Figure 4 The results are recorded in Table 2 below.

[0035] To investigate the deformation mechanism of Sm-containing magnesium alloy samples, EBSD and EBSD combined with SEM-assisted slip trace analysis were used to identify the slip system activation modes of the two magnesium alloys under different strains. The results are as follows: Figure 5 , Figure 6 .

[0036] in Figure 5 (a) SEM and EBSD images of 0Sm magnesium alloy with 5% tensile strain; (bd) SEM and EBSD images of 2Sm magnesium alloy with 5%, 10%, and 15% tensile strain.

[0037] Table 2. Comparison of mechanical properties at room temperature Results analysis: Combination Figure 1 KAM topographic map and Figure 2The KAM numerical distribution curves show that Sm content has a significant regulatory effect on the microstructure lattice distortion and strain distribution of the Mg-0.5Zr-0.5Mn alloy. Without Sm addition (0Sm), the KAM distribution curve shows the highest peak value with a significant rightward shift, corresponding to coarse, inhomogeneous grains and high-strain concentration regions continuously distributed along grain boundaries in the morphology diagram, indicating a high dislocation density and micro-stress accumulation within the alloy. After adding 1% Sm, the KAM peak value significantly decreases and shifts to the left, and the high-KAM region in the morphology diagram decreases and becomes more dispersed, indicating that the pinning effect of Sm-based precipitation on grain boundaries and dislocations is initially apparent, effectively alleviating strain concentration. When the Sm content is increased to 2%, the KAM curve peak value drops to its lowest point and is positioned furthest to the left, indicating a significant reduction in the strain region. This demonstrates optimal grain refinement and strain homogenization. However, with excessive Sm addition (4Sm), the KAM peak value rises again and shifts to the right, corresponding to the reappearance of localized strain concentration areas in the morphology diagram. This is because excessive Sm may slightly coarsen the precipitated phases, thereby exacerbating micro-stress accumulation and deteriorating the internal strain distribution of the material. Therefore, an appropriate amount of Sm (1%-2%) can synergistically regulate the micro-strain distribution of the alloy through grain refinement and dispersion strengthening, with 2% Sm being the optimal addition amount. Excessive Sm, on the other hand, will disrupt strain homogenization and adversely affect mechanical properties.

[0038] The data in Table 2 clearly demonstrates the effectiveness of this invention, leading to the following conclusions: (1) Leap in performance: The mechanical properties of all alloys in the examples are superior to those of Comparative Example 1. In particular, Example 2 (2% Sm) has a yield strength and tensile strength that are increased by about 65% and 50% respectively compared to Example 1, while the elongation after fracture is also increased by about 27%. This fully demonstrates the effect of "synergistic strengthening and toughening".

[0039] (2) Manifestation of the graded effect: As the Sm content increases, the strength shows a trend of first rising rapidly and then leveling off, while the plasticity reaches its peak at an Sm content of 2%. This verifies the scientific nature and necessity of the graded addition strategy of Sm described in this invention, that is, there is an optimal composition window (1.0-3.0%, especially around 2.0%), within which the best balance of performance can be achieved.

[0040] To obtain statistical results, the slip traces of 0Sm and 2Sm magnesium alloys under different strains were analyzed, with more than 300 grains analyzed for each strain. For example... Figure 5 The activation frequencies of slip modes in two magnesium alloys under different tensile strains were quantitatively analyzed, and the promoting effect of Sm element on non-basal plane slip activation can be clearly seen: such as Figure 6In the 0Sm-5% sample, the activation frequency of basal slip reached as high as 55%, cylindrical slip was only 33%, and conical slip was less than 10%, indicating that deformation was highly dependent on basal slip, while the activation of non-basal slip was limited. In the 2Sm alloy, as the strain increased from 5% to 15%, the slip mode changed significantly: at 5% strain, the basal slip frequency was still the highest (approximately 58%); when the strain increased to 10%, the cylindrical slip frequency jumped to approximately 47%, and the conical slip also increased to approximately 23%; at 15% strain, the cylindrical slip frequency further increased to approximately 51%, the conical slip stabilized at approximately 30%, while the basal slip frequency decreased to approximately 19%. It is evident that the introduction of Sm fundamentally altered the deformation mechanism of magnesium alloys—from "basal slip dominance and highly concentrated deformation" to "multi-system slip synergy and uniform and controllable deformation."

[0041] In summary, this invention, through the innovative design of "rare earth grading" and "multi-element solid solution synergy," has successfully prepared a high-strength, high-plasticity lightweight rare earth magnesium alloy, solving the industry problem of the difficulty in coexisting Mn and Sm elements. The results are significant, and it has great practical value and promising prospects for promotion.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lightweight alloys based on rare earth classification and multi-element solid solution synergistic strengthening, characterized in that, The lightweight alloy is a magnesium alloy, composed of the following components by mass percentage: Zr: 0.3-0.8%, Mn: 0.3-0.8%, rare earth element Sm: 0.5-3.5%, with the balance being Mg and unavoidable impurities; The preparation method includes the following steps: S1: Raw material smelting: Using magnesium ingots, Mg-Zr master alloy, Mg-Mn master alloy and Mg-Sm master alloy as raw materials, heat to 720-750℃ under a protective atmosphere to completely melt them into a melt. S2: Refining and settling: The melt is refined and purified, and then settling at 710-730℃ for 20-40 minutes to allow the alloying elements to fully pre-diffuse. S3: Casting: The molten material after standing is poured into a preheated mold to obtain an ingot; S4: Homogenization heat treatment: The ingot is held at 500-530℃ for 8-24 hours to promote the uniform solid solution of Sm, Zr and Mn elements in the magnesium matrix and achieve synergistic control of solid solution, followed by rapid cooling. S5: Hot deformation processing: The homogenized ingot is hot-extruded or hot-rolled at 300-450℃ to obtain the final material.

2. The method according to claim 1, characterized in that, The mass percentage of the rare earth element Sm is 1.0-3.0%.

3. The method according to claim 1, characterized in that, The mass percentage of the rare earth element Sm is 1.5-2.5%.

4. The method according to claim 1, characterized in that, The mass percentage of the rare earth element Sm is 0.5-1.0%.

5. The method according to claim 1, characterized in that, The homogenization heat treatment process described in step S4 is as follows: holding at 520°C for 12 hours.

6. The method according to claim 1, characterized in that, The rapid cooling described in step S4 is water quenching.

7. The method according to claim 1, characterized in that, The protective atmosphere described in step S1 is a mixture of CO2 and SF6.

8. The method according to claim 1, characterized in that, The hot deformation process described in step S5 is hot extrusion, with an extrusion temperature of 380-420℃ and an extrusion ratio of 15:1 to 25:

1.

9. The method according to claim 1, characterized in that, The hot deformation process described in step S5 is hot rolling.

10. A lightweight alloy prepared by the method according to any one of claims 1 to 9.

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