A multi-stage heterogeneous magnesium alloy and a preparation method thereof

Abstract

The application relates to the field of magnesium alloy material processing, in particular to a multi-stage heterogeneous magnesium alloy and a preparation method thereof, which comprises the following steps: providing a magnesium alloy ingot, and sequentially performing solid solution treatment and aging treatment on the magnesium alloy ingot; performing single-pass hot extrusion on the magnesium alloy after the aging treatment to obtain a magnesium alloy extrusion plate, and the extrusion deformation amount is set to 60-90%; and performing compression deformation along the transverse direction and / or the longitudinal direction of the magnesium alloy extrusion plate, and the deformation amount of the compression deformation is set to 1-9%. The magnesium alloy with the multi-stage heterogeneous structure of grain size, precipitated phase and grain orientation can be prepared, and the strength and plasticity of the magnesium alloy are improved.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy material processing, specifically to a multi-level heterogeneous magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys have low density, high specific strength, and excellent damping and electromagnetic shielding properties, making them promising candidates for lightweight and functional materials. Commonly used magnesium alloys have a close-packed hexagonal crystal structure, resulting in fewer activating slip systems at room temperature and poor plasticity. Achieving a high-strength, high-plasticity bond in magnesium alloys using conventional processes is therefore quite difficult.

[0003] Heterogeneous materials are a new type of material that has emerged in the field of metals in recent years. They are expected to significantly improve the strength and strain hardening of traditional metallic materials simultaneously, thus avoiding the "inevitable" loss of plasticity. They consist of hard and soft regions with a flow stress difference greater than 100%. The mechanical incompatibility between adjacent heterogeneous regions during plastic deformation makes the strengthening mechanism and deformation behavior of heterogeneous materials different from those of homogeneous materials. These include significant heterogeneous deformation-induced (HDI) strengthening and work hardening, strain transfer, and diffuse strain bands, thereby achieving excellent strength-plasticity synergy.

[0004] In related technologies, CN114635098A discloses a magnesium alloy with dual heterogeneity in grain size and precipitates and its preparation method. By synergistically improving the strength and plasticity of magnesium alloy plates through grain refinement and precipitate strengthening, it is a beneficial attempt in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-level heterogeneous magnesium alloy and its preparation method, which can produce magnesium alloys with multi-level heterogeneous structures of different grain sizes, precipitates, and grain orientations, while improving the strength and plasticity of the magnesium alloy.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a multi-level heterogeneous magnesium alloy, comprising: providing a magnesium alloy ingot, and subjecting the magnesium alloy ingot to solution treatment and aging treatment in sequence; subjecting the aging magnesium alloy to single-pass hot extrusion to obtain a magnesium alloy extrusion plate, wherein the extrusion deformation amount is set to 60~90%; and performing compression deformation along the transverse and / or longitudinal direction of the magnesium alloy extrusion plate, wherein the compression deformation amount is set to 1~9%.

[0007] Furthermore, the solution temperature for the solution treatment is set to 400~450℃, and the solution time is set to 12~24h.

[0008] Furthermore, the aging temperature for the aging process is set to 150~200℃, and the aging time is set to 8~24h.

[0009] Furthermore, the single-pass hot extrusion includes: placing the aged magnesium alloy in an extrusion die at a temperature of 220~280℃ and holding it for 6~8 minutes, then extruding it, with the extrusion speed set to 4~10mm / s.

[0010] Furthermore, the amount of compression deformation is set to 3-7%.

[0011] Secondly, the present invention provides a multi-level heterogeneous magnesium alloy, which is prepared by the above-mentioned method for preparing multi-level heterogeneous magnesium alloy.

[0012] The present invention has the following unexpected beneficial effects: 1. This invention first generates precipitates in magnesium alloy materials through solution treatment and aging treatment. By controlling the relevant process parameters of solution treatment and aging treatment, the distribution, size, and quantity of precipitates in the magnesium alloy materials are controlled, thus obtaining a precipitate heterogeneous structure. After aging treatment, a single-pass large deformation hot extrusion treatment is performed. Because the distribution, size, and quantity of precipitates in different regions of the magnesium alloy material are different after aging treatment, the degree of grain boundary pinning is also different. Accordingly, after hot extrusion treatment, a bi-level heterogeneous structure with different proportions of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates is constructed, thus obtaining a dual heterogeneous structure of grain size and precipitate phases. Furthermore, after hot extrusion, the magnesium alloy material is subjected to compression deformation treatment, which activates a large number of tensile twins with different grain orientations from the magnesium alloy matrix. Moreover, the dislocation slip path in the coarse grains is large, and the stress concentration near the grain boundaries is severe, which facilitates twin nucleation. This results in a higher proportion of tensile twins being introduced into the coarse grains with sparse precipitates, while a lower proportion of tensile twins are introduced into the fine grains with dense precipitates. In this way, a magnesium alloy material with a triple heterogeneous structure of grain size, precipitates, and grain orientation is obtained.

[0013] 2. This invention utilizes a combination of solution treatment, aging treatment, hot extrusion treatment, and compression treatment to obtain a multi-level heterogeneous microstructure of magnesium alloy with coarse-grained hetero-oriented and fine-grained reinforcing phases. The coarse grains accommodate more dislocations, and the heterogeneous orientation between coarse grains facilitates non-basal plane slip activation, significantly improving the plasticity of the sheet. Simultaneously, the fine grain boundary reinforcement utilizes the pinning effect of continuous and / or discontinuous precipitates relative to the high density of dislocations in the fine grains, greatly improving the strength of the sheet. Therefore, the material as a whole exhibits excellent synergistic improvement in strength and plasticity.

[0014] 3. The preparation method described in this invention has a simple process and low cost, avoiding the cost increase problem brought about by the preparation of composite materials, and has the potential for large-scale industrial production.

[0015] 4. The present invention limits the aging temperature to 150~200℃. If the aging temperature is too high, the nucleation driving force of the precipitated phase is large, which easily produces coarse precipitated phase and deteriorates the mechanical properties. If the aging temperature is too low, it is necessary to extend the aging time to ensure a sufficient number of precipitated phases, which increases the cost.

[0016] 5. This invention limits the hot extrusion process parameters. If the extrusion temperature is too high, the resistance to grain boundary movement caused by precipitated phases will be lower than the grain boundary growth rate, resulting in an indistinct grain heterogeneous structure and excessively coarse grains, which is detrimental to improving the mechanical properties of the sheet. If the extrusion temperature is too low, it will be detrimental to the plastic forming of the extruded sheet. Within the allowable range of the hydraulic press's functional parameters, the extrusion speed can be appropriately increased with the increase of the extrusion temperature. If the extrusion speed is too high, the work hardening rate of the metal will exceed its dynamic recrystallization softening rate during deformation, thereby increasing the flow stress of the billet. To avoid internal defects in the cast billet, the extrusion deformation amount is usually above 60%, and the greater the extrusion deformation amount, the finer the grains of the sheet and the higher its strength. In summary, the extrusion temperature is limited to 220~280℃, the extrusion speed to 6~8mm / s, and the extrusion deformation amount to 60~90%.

[0017] 6. This invention limits the amount of compression deformation to 1-9%. If the amount of compression deformation is too large, it is easy to cause large residual stress and microcracks inside the plate. If the amount of compression deformation is too small, it will introduce low twin density, making the hetero-orientation effect insignificant. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process of the multi-level heterogeneous magnesium alloy described in this invention.

[0019] Figure 2 This is a schematic diagram showing the grain orientation and grain characteristics of magnesium alloy sheets under different processing conditions.

[0020] Figure 3 This is a schematic diagram showing the precipitated phase characteristics of magnesium alloy sheets under different processing conditions.

[0021] Figure 4 This is a schematic diagram comparing the mechanical properties of magnesium alloy sheets under different processing conditions. Detailed Implementation

[0022] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0023] In one embodiment, see Figure 1 As shown, the present invention provides a method for preparing a multi-level heterogeneous magnesium alloy, which includes the following steps: Step 1: Provide magnesium alloy ingots and perform solution treatment and aging treatment on the magnesium alloy ingots in sequence. Solution treatment allows the alloying elements to fully dissolve in the matrix at high temperature. Then, during the aging treatment, the supersaturated alloying elements will precipitate from the matrix in the form of precipitates. The formation of precipitates can be changed by adjusting process parameters such as treatment temperature and time.

[0024] Step two involves single-pass hot extrusion of the aged magnesium alloy to obtain an extruded magnesium alloy plate, with the extrusion deformation set at 60-90%. Performing single-pass hot extrusion with large deformation after aging is to utilize the differences in the distribution, size, and quantity of precipitates in different regions of the aged magnesium alloy material, resulting in varying degrees of grain boundary pinning during hot extrusion. During hot extrusion, the material undergoes large deformation under the action of the die. Due to the different precipitate conditions in different regions, the binding effect on grain boundaries (grain boundary pinning) varies, leading to differences in grain deformation and recrystallization. This results in different proportions of fine and coarse grains, as well as different precipitate densities, thus constructing a bi-level isomorphic structure with varying proportions of denser fine-grained precipitates and sparser coarse-grained precipitates, ultimately obtaining a dual isomorphic structure in terms of grain size and precipitate distribution.

[0025] Step 3: Perform compression deformation along the transverse and / or longitudinal direction of the magnesium alloy extrusion plate, with the deformation amount set to 1-9%. During compression deformation, due to the large dislocation slip path in coarse grains and severe stress concentration near grain boundaries, twin nucleation is easily achieved. This allows coarse grains with sparse precipitates to introduce a higher proportion of tensile twins, while fine grains with dense precipitates introduce a lower proportion of tensile twins, thereby achieving grain orientation isomerization.

[0026] In sheet metal extrusion, the longitudinal direction refers to the main direction of material flow during the extrusion process, which is the direction consistent with the extrusion axis. This direction is where the metal is extruded in the die cavity, similar to the direction of "stretching" the material. The transverse direction is perpendicular to the longitudinal direction, running across the width of the sheet. If you imagine the extruded sheet as a piece of paper, the longitudinal direction is like the length of the paper, and the transverse direction is like the width of the paper.

[0027] This invention first generates precipitates in magnesium alloy materials through solution treatment and aging treatment. By controlling the relevant process parameters of solution treatment and aging treatment, the distribution, size, and quantity of precipitates in the magnesium alloy materials can be regulated, thus obtaining a precipitate heterogeneous structure. After aging treatment, a single-pass large deformation hot extrusion treatment is performed. Because the distribution, size, and quantity of precipitates in different regions of the magnesium alloy material are different after aging treatment, the degree of grain boundary pinning is also different. Accordingly, after hot extrusion treatment, a bi-level heterogeneous structure with different proportions of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates is constructed, thus obtaining a dual heterogeneous structure of grain size and precipitate phases. Furthermore, after hot extrusion, the magnesium alloy material is subjected to compression deformation treatment, which activates a large number of tensile twins with different grain orientations from the magnesium alloy matrix. Moreover, the dislocation slip path in the coarse grains is large, and the stress concentration near the grain boundaries is severe, which facilitates twin nucleation. This results in a higher proportion of tensile twins being introduced into the coarse grains with sparse precipitates, while a lower proportion of tensile twins are introduced into the fine grains with dense precipitates. In this way, a magnesium alloy material with a triple heterogeneous structure of grain size, precipitates, and grain orientation is obtained.

[0028] In the plastic deformation process of magnesium alloys, the orientation difference between adjacent grains is a key factor affecting the slip mode; the larger the orientation difference angle, the more non-basal plane slip systems are activated. From a crystallographic perspective, increasing the orientation difference between adjacent grains can greatly enhance the deformation incompatibility between grains, thereby promoting the activation of more difficult-to-slip systems to coordinate deformation. Given the significant advantages of hierarchical heterogeneous materials with body-centered or face-centered cubic structures in improving mechanical properties, the combination of different heterostructures and coupling with other conventional strengthening mechanisms provides a broad design space and mechanical property optimization space for hierarchical heterostructure materials. Constructing intrinsic crystallographic heterogeneous features and coupling them with traditional fine-grain strengthening mechanisms in the grain size heterogeneous microstructure of close-packed hexagonal magnesium alloys can induce a hierarchical strain hardening effect.

[0029] In a preferred embodiment, the solution temperature of the solution treatment is set to 400~450℃, and the solution time is set to 12~24h.

[0030] The solution treatment temperature range of 400-450℃ is chosen to comprehensively consider the solubility characteristics of alloying elements in magnesium alloys and their impact on subsequent microstructure formation. Within this temperature range, alloying elements can be sufficiently dissolved into the magnesium matrix. If the temperature is too low, insufficient dissolution of alloying elements will limit the formation of precipitates during subsequent aging treatment, making it impossible to effectively control the distribution, size, and quantity of precipitates. For example, some key alloying elements may not reach a sufficiently supersaturated state, resulting in too few or unevenly distributed precipitates during aging. If the temperature is too high, it may cause over-melting of the magnesium alloy or other thermal defects, such as coarse grains, which will adversely affect the overall performance of the magnesium alloy. Furthermore, excessively high temperatures may cause some alloying elements to undergo abnormal chemical reactions with the matrix or other elements, altering the originally expected alloying state, which is also detrimental to the rational formation of subsequent precipitates and the control of microstructure.

[0031] The solution treatment time is set to 12-24 hours to allow sufficient time for the alloying elements to fully dissolve at a suitable solution temperature. If the solution treatment time is too short, such as less than 12 hours, even if the solution temperature is within the appropriate range, some alloying elements may not have enough time to completely dissolve into the matrix. This can lead to undesirable precipitate formation during subsequent aging treatment, making it impossible to precisely control the characteristics of the precipitates. On the other hand, if the solution treatment time is too long, exceeding 24 hours, the continuous high temperature can cause problems such as coarse grains, as well as energy waste and reduced production efficiency, which is also detrimental from the perspective of production costs and benefits.

[0032] The parameter settings for the solution treatment are closely related to the subsequent aging treatment. Only when the alloying elements are fully dissolved during the solution treatment, allowing the magnesium matrix to reach a suitable supersaturation state, can the supersaturated alloying elements form precipitates with appropriate distribution, size, and quantity during the aging treatment stage. This lays the foundation for constructing a multi-level heterogeneous structure through subsequent steps such as hot extrusion and compression deformation. For example, if the temperature or time of the solution treatment is inappropriate, resulting in unsatisfactory precipitate formation, it will be difficult to construct a bi-level heterogeneous structure with fine-grained, denser precipitates and coarser, sparser precipitates during hot extrusion, ultimately failing to obtain a magnesium alloy material with a triple heterogeneous structure in terms of grain size, precipitates, and grain orientation.

[0033] In a preferred embodiment, the aging temperature is set to 150~200℃ and the aging time is set to 8~24h.

[0034] For magnesium alloys, the aging temperature range of 150–200℃ is a suitable range for promoting the formation and growth of precipitates. Within this range, alloying elements supersaturated and dissolved in the magnesium matrix after solution treatment can precipitate at a suitable rate, forming fine and dispersed precipitates. If the aging temperature is below 150℃, the atomic diffusion rate becomes very slow, making it difficult for supersaturated alloying elements to form a sufficient number and ideal distribution of precipitates within a reasonable time. This results in an inability to effectively control the size, quantity, and distribution of precipitates, thus affecting the effectiveness of subsequent steps such as hot extrusion in constructing hierarchical heterogeneous structures. Extending the aging time is necessary to ensure a sufficient number of precipitates, increasing costs. For example, it may be impossible to form enough precipitates to create varying degrees of pinning effect on grain boundaries, affecting the formation of bi-hierarchical heterogeneous structures. Conversely, if the aging temperature is above 200℃, the nucleation driving force of the precipitates is high, and the growth rate of the precipitates may be too fast, resulting in coarse precipitates. Coarsened precipitates not only fail to provide effective strengthening, but may also reduce the mechanical properties of magnesium alloys. This is because coarsened precipitates, when subjected to external forces, cannot effectively hinder dislocation movement as fine, dispersed precipitates can, thus affecting the material's strength and toughness.

[0035] The aging time is set between 8 and 24 hours to allow sufficient time for the precipitates to form, grow, and reach a relatively stable state at a given aging temperature. If the aging time is too short, such as less than 8 hours, the precipitates may not have formed or grown to the appropriate extent at the aging temperature, resulting in insufficient quantity and uneven distribution of precipitates. This also makes it impossible to precisely control the characteristics of the precipitates, affecting the subsequent construction of hierarchical heterogeneous structures. Conversely, if the aging time is too long, exceeding 24 hours, the precipitates may continue to grow at the aging temperature, leading to overgrowth or coarsening. This is similar to the adverse effects of excessively high aging temperatures, reducing the mechanical properties of magnesium alloys and hindering the acquisition of ideal hierarchical heterogeneous structures.

[0036] The parameter settings for aging treatment are closely related to the preceding solution treatment and subsequent hot extrusion, compression deformation, and other treatment steps.

[0037] The connection with solution treatment is that only when the solution treatment brings the magnesium matrix to a suitable supersaturated state, combined with the aging temperature and time settings in this preferred embodiment, can it be ensured that precipitates with the expected distribution, size and quantity are accurately formed during the aging process, laying the foundation for subsequent processing steps.

[0038] For the hot extrusion step, the distribution, size and quantity of precipitates formed by appropriate aging treatment will help to construct a bipolar structure with different proportions of fine-grained, denser precipitates and coarse-grained, sparser precipitates due to the different degrees of grain boundary pinning during hot extrusion.

[0039] The connection with the compression deformation step is that accurate aging treatment results can provide conditions for activating tensile twins of different proportions during compression deformation. This is because different precipitate conditions will affect the behavior of dislocation slip in coarse and fine grains, thereby affecting the formation of tensile twins, and ultimately achieving the goal of obtaining magnesium alloy materials with a triple heterogeneous structure of grain size, precipitate phase and grain orientation.

[0040] In a preferred embodiment, the single-pass hot extrusion includes: placing the aged magnesium alloy in an extrusion die at a temperature of 220~280℃ and holding it for 6~8 minutes, then extruding it, with the extrusion speed set to 4~10mm / s.

[0041] Setting the extrusion die temperature between 220℃ and 280℃ is crucial for the hot extrusion process of magnesium alloys. At this temperature, the plastic deformation capacity of the magnesium alloy is effectively enhanced, making it easier to flow and deform within the die. If the die temperature is too low, such as below 220℃, the magnesium alloy lacks plasticity and may face greater deformation resistance during extrusion, leading to excessively high extrusion pressure. This not only increases the energy consumption and burden on the equipment but may also cause defects such as cracking during extrusion, preventing successful extrusion forming of the extruded sheet. Conversely, if the die temperature is too high, exceeding 280℃, it may cause excessive softening of the magnesium alloy, resulting in excessively rapid and uncontrollable flow within the die, affecting the dimensional accuracy and microstructure uniformity of the extruded magnesium alloy sheet. Furthermore, excessively high temperatures may accelerate die wear, shorten die life, and increase production costs.

[0042] The holding time is set to 6 to 8 minutes to allow the magnesium alloy sufficient time to reach thermal equilibrium under the appropriate mold temperature, ensuring a uniform internal temperature distribution. If the holding time is too short, such as less than 6 minutes, the magnesium alloy may not be sufficiently and uniformly heated internally. This can lead to differences in deformation resistance and flow characteristics at different locations during extrusion, affecting the quality of the extruded sheet and potentially causing problems such as uneven local deformation and microstructure. Conversely, if the holding time is too long, exceeding 8 minutes, maintaining high temperatures may cause unnecessary changes in the magnesium alloy's microstructure (such as grain growth) due to prolonged heating, and it will also reduce production efficiency, increase production cycle time, and increase costs.

[0043] The extrusion speed is set between 4 and 10 mm / s. A suitable extrusion speed has a significant impact on controlling the flow of magnesium alloy in the die and the quality of the final extruded plate. If the extrusion speed is too slow, such as less than 4 mm / s, the magnesium alloy will remain in the die for too long, potentially leading to excessive heat exchange between the alloy and the die. This can cause localized temperature drops in the magnesium alloy, affecting its plastic deformation capacity and hindering the smooth progress of extrusion, while also reducing production efficiency. If the extrusion speed is too fast, exceeding 10 mm / s, the magnesium alloy will flow too quickly in the die. This can lead to a sharp increase in extrusion pressure, increasing equipment load and energy consumption. Furthermore, excessively fast flow rates are detrimental to the precise control of the magnesium alloy's microstructure, potentially causing uneven internal structure within the extruded plate, such as inconsistent grain deformation, which can affect the subsequent construction of multi-level heterogeneous structures.

[0044] The relationship with aging treatment: The distribution, size, and quantity of precipitates formed in magnesium alloys after aging treatment will play a role during hot extrusion due to the different degrees of grain boundary pinning in different regions. The settings of parameters such as die temperature, holding time, and extrusion speed during hot extrusion must be based on the state of the magnesium alloy after aging treatment to ensure that this difference in grain boundary pinning can be fully utilized, thereby constructing a bi-level heterogeneous structure with different proportions of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates.

[0045] Relationship with compression deformation: The microstructure (including grain size, precipitate distribution, etc.) of magnesium alloy extruded sheets obtained by hot extrusion is the basis for compression deformation. Appropriate hot extrusion parameter settings ensure that the extruded sheet has a specific microstructure. Only on this basis can compression deformation be carried out to activate different proportions of tensile twins as expected, thereby achieving the goal of obtaining magnesium alloy materials with a triple heterogeneous microstructure of grain size, crystalline phase, and grain orientation.

[0046] In a preferred embodiment, the amount of compression deformation is set to 3-7%. This amount of deformation is neither too small to effectively activate tensile twins, nor too large to cause excessive deformation of the material or even defects such as cracks.

[0047] When the deformation is between 3% and 7%, tensile twins with different grain orientations than the magnesium alloy matrix can be activated in large quantities in magnesium alloy materials. Within this range, the stress level is moderate, which can promote dislocation slip within coarse grains. Due to the large dislocation slip path within coarse grains, stress concentration is severe near grain boundaries, which facilitates twin nucleation. Coarse grains with sparse precipitates can introduce a higher proportion of tensile twins, while fine grains with dense precipitates introduce a lower proportion of tensile twins, thereby achieving effective control over grain orientation heterogeneity.

[0048] If the deformation is less than 3%, the resulting stress may be insufficient to activate a sufficient number of tensile twins, especially in coarse-grained regions, failing to achieve the desired grain orientation adjustment effect and hindering the acquisition of a triple heterogeneous structure in terms of grain size, precipitates, and grain orientation. If the deformation exceeds 7%, the internal stress of the material may become excessively high. In this case, on the one hand, it may lead to overgrowth of existing twins or destruction of twin boundaries; on the other hand, it may cause excessive plastic deformation of the material, or even microcracks, which is detrimental to the performance improvement of magnesium alloy materials and the construction of heterogeneous structures.

[0049] Combination with hot extrusion: Hot-extruded magnesium alloys exhibit a specific bilevel heterogeneous structure, comprising varying proportions of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates. Compression deformation within the range of 3-7% can better leverage this post-hot-extruded microstructure. Through appropriate compression deformation, without damaging the grain and precipitate structure established by hot extrusion, the grain orientation can be further adjusted to achieve a triple heterogeneous structure.

[0050] Solution treatment and aging treatment regulate the distribution, size, and quantity of precipitates in magnesium alloys. Within this range of compressive deformation, based on the already formed isomorphic precipitate structure, the formation of tensile twins can be guided according to the different precipitate conditions in coarse and fine grains, making the microstructure of the material more complex and isomorphic. This, combined with the previous treatment steps, jointly improves the performance of magnesium alloys.

[0051] In one embodiment, the present invention provides a multi-level heterogeneous magnesium alloy, which is prepared by the above-described method for preparing multi-level heterogeneous magnesium alloys.

[0052] The following analysis and explanation will be based on specific examples.

[0053] Example 1: A method for preparing a multi-level heterogeneous magnesium alloy, comprising the following steps: Step 1: Provide AZ91 magnesium alloy ingots and perform solution treatment and aging treatment on the magnesium alloy ingots in sequence.

[0054] The solution treatment is specifically performed by solution treating the magnesium alloy ingot at a temperature of 420℃ for 24 hours, followed by water cooling to room temperature to obtain a solution-treated magnesium alloy.

[0055] The aging treatment is as follows: the solution-treated magnesium alloy is aged at 200℃ for 16 hours, followed by surface polishing and degreasing.

[0056] Step two involves hot extruding the aged magnesium alloy in a single pass. After the extrusion die and extrusion cylinder temperatures stabilize at 220℃, the polished magnesium alloy is placed into the extrusion cylinder and held at that temperature for 10 minutes before extrusion. Before extrusion, graphite ink is sprayed onto the inner wall of the extrusion cylinder as a lubricant. The extrusion ratio is 6.5, the single-pass extrusion deformation is set to 80%, and the extrusion speed is set to 6 mm / s. The final product is a magnesium alloy extruded plate with a bipolar heterogeneous structure consisting of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates, with a thickness of approximately 3 mm.

[0057] Step 3: Perform 3% compression deformation along the transverse direction of the magnesium alloy extrusion plate with a bipolar isomer structure. The compression rate is set to 1 mm / min. This will eventually introduce a low proportion of tensile twins into the bipolar isomer structure, with a thickness of approximately 3 mm.

[0058] The obtained multi-level heterogeneous magnesium alloy plate was processed into tensile samples for room temperature tensile testing. The specifications of the tensile samples conformed to GB / T 16865-2013, and the tensile testing method conformed to GB / T228.1-2010. The yield strength of the multi-level heterogeneous magnesium alloy plate prepared in Example 1 was measured to be 278.2 MPa, the tensile strength was 412.9 MPa, and the elongation was 10.7%.

[0059] Example 2 follows the same steps as Example 1, except that step 3 in Example 1 is replaced by performing a 5% compression deformation on the extrusion plate of the bipolar isomorphic structure along the transverse direction of the magnesium alloy extrusion plate of the bipolar isomorphic structure. The compression rate is set to 1 mm / min, which ultimately introduces a moderate proportion of tensile twins into the bipolar isomorphic structure, with a thickness of approximately 3 mm.

[0060] The obtained multi-level heterogeneous magnesium alloy plate was processed into tensile samples for room temperature tensile testing. The specifications of the tensile samples conformed to GB / T 16865-2013, and the tensile testing method conformed to GB / T228.1-2010. The yield strength of the multi-level heterogeneous magnesium alloy plate prepared in Example 2 was measured to be 307.1 MPa, the tensile strength was 427.7 MPa, and the elongation was 11.0%.

[0061] Example 3 follows the same steps as Example 1, except that step 3 in Example 1 is replaced by performing a 7% compression deformation on the extrusion plate of the bipolar isomorphic structure along the transverse direction of the magnesium alloy extrusion plate of the bipolar isomorphic structure. The compression rate is set to 1 mm / min, which ultimately introduces a higher proportion of tensile twins into the bipolar isomorphic structure, with a thickness of approximately 3 mm.

[0062] The obtained multi-level heterogeneous magnesium alloy plate was processed into tensile samples for room temperature tensile testing. The specifications of the tensile samples conformed to GB / T 16865-2013, and the tensile testing method conformed to GB / T228.1-2010. The yield strength of the multi-level heterogeneous magnesium alloy plate prepared in Example 3 was measured to be 345.0 MPa, the tensile strength was 434.5 MPa, and the elongation was 8.1%.

[0063] To illustrate the beneficial effects of the present invention through comparative analysis, the following comparative examples have been provided.

[0064] Comparative Example 1: A method for preparing a uniformly structured magnesium alloy, comprising the following steps: Step 1: Solution treatment. The AZ91 magnesium alloy ingot with high aging potential is solution treated at 420℃ for 24 hours and then water-cooled to room temperature to obtain a solution-treated magnesium alloy.

[0065] Step two involves surface polishing and degreasing of the solution-treated magnesium alloy. After the extrusion die and extrusion cylinder temperatures stabilize at 220℃, the polished solution-treated magnesium alloy is placed in the extrusion cylinder and held at that temperature for 10 minutes before extrusion. Before extrusion, graphite ink is sprayed onto the inner wall of the extrusion cylinder as a lubricant. The extrusion speed is set to 6 mm / s, ultimately yielding a magnesium alloy extruded plate with a uniform structure and a thickness of approximately 3 mm.

[0066] The obtained uniform structure magnesium alloy extruded plate was processed into tensile samples for room temperature tensile testing. The tensile sample specifications conformed to GB / T 16865-2013, and the tensile test method conformed to GB / T228.1-2010. The yield strength of the uniform structure magnesium alloy extruded plate prepared in Comparative Example 1 was measured to be 210.2 MPa, the tensile strength was 350.8 MPa, and the elongation was 10.1%.

[0067] Comparative Example 2: A method for preparing a bipolar heterogeneous magnesium alloy based on grain size and precipitated phases. The steps are the same as in Example 1, except that step 3 in Example 1 is deleted, resulting in a bipolar heterogeneous magnesium alloy plate.

[0068] The obtained bipolar heterogeneous magnesium alloy plate was processed into tensile samples for room temperature tensile testing. The specifications of the tensile samples conformed to GB / T 16865-2013, and the tensile testing method conformed to GB / T228.1-2010. The yield strength of the bipolar heterogeneous magnesium alloy plate prepared in Comparative Example 2 was measured to be 232.1 MPa, the tensile strength was 403.2 MPa, and the elongation was 13.6%.

[0069] See Figures 2 to 4Compared to the uniform structure in Comparative Example 1, Comparative Example 2, after pre-aging and extrusion, exhibits a bilevel heterogeneous structure in terms of grain size and precipitated phases due to the difference in the degree of obstruction between the unevenly distributed precipitates and grain boundaries. The coarse grains have a sparse distribution of precipitates, while the fine grains have a dense distribution, with no significant difference in grain orientation. Comparative Example 2 shows improved strength and plasticity compared to Comparative Example 1. This demonstrates that the difference in strength between coarse and fine grains leads to mechanical incompatibility, resulting in a strain gradient near the heterogeneous interface, inducing additional strengthening and work hardening effects. Simultaneously, the fine, dispersed precipitates also induce precipitation strengthening and hardening effects.

[0070] To further optimize the mechanical properties of the bipolar heterostructured plate, based on Comparative Example 2, it was subjected to transverse compression deformation of 3% to 7%, referred to as Example 1, Example 2 and Example 3, respectively. Its yield strength and tensile strength were significantly increased.

[0071] In Example 1, at 3% compression deformation, a small number of tensile twins are introduced into the bipolar isomer, and its grain orientation heterogeneity is not significant. In Example 3, at 7% compression deformation, the coarse and fine grains are almost completely twinned, with most of the coarse and fine grains deflecting laterally. In Example 2, at 5% compression deformation, a large number of tensile twins are activated, especially in the coarse grain structure. At this point, while retaining the bipolar isomer, some parent crystals in the coarse grains maintain their original orientation, and the induced large number of tensile twins deflect laterally. Meanwhile, the densely distributed precipitates act as reinforcing phases, mainly distributed in the fine grains, exhibiting a multipolar isomer structure with coarse grain heterogeneous orientation coupled to fine grain reinforcing phases. The coarse grains accommodate more dislocations, and the heterogeneous orientation between coarse grains helps to activate non-basal plane slip, significantly improving the plasticity of the sheet. At the same time, the reinforcement of the fine grain boundaries strengthens the pinning effect of continuous and / or discontinuous precipitates relative to the high-density dislocations in the fine grains, significantly improving the strength of the sheet. Thus, the material as a whole exhibits excellent synergistic improvement in strength and plasticity.

[0072] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-level heterogeneous magnesium alloy, characterized in that, include: A magnesium alloy ingot is provided, and the magnesium alloy ingot is subjected to solution treatment and aging treatment in sequence; the solution treatment temperature is set to 400~450℃ and the solution treatment time is set to 12~24h; the aging treatment temperature is set to 150~200℃ and the aging time is set to 8~24h; by controlling the relevant process parameters of solution treatment and aging treatment, the distribution, size and quantity of precipitates in magnesium alloy material can be controlled to obtain a precipitate heterogeneous structure; Aging-treated magnesium alloy is subjected to single-pass hot extrusion to obtain magnesium alloy extruded plates, with the extrusion deformation set to 60-90%. The single-pass hot extrusion includes: placing the aging-treated magnesium alloy in an extrusion die at a temperature of 220-280℃ and holding it for 6-8 minutes, then extruding it at an extrusion speed of 4-10 mm / s. The hot extrusion process constructs a bi-level heterogeneous structure with different proportions of fine-grained, densely packed precipitates and coarse-grained, sparsely packed precipitates, thus obtaining a dual heterogeneous structure in terms of grain size and precipitate composition. The magnesium alloy extrusion plate is subjected to compression deformation in the transverse direction, and the deformation amount of the compression deformation is set to 3~7%; this allows the coarse grains with sparse precipitates to introduce a higher proportion of tensile twins, while the fine grains with dense precipitates introduce a lower proportion of tensile twins, thereby obtaining a magnesium alloy material with a triple heterogeneous structure of grain size, precipitates and grain orientation.

2. A multi-level heterogeneous magnesium alloy, characterized in that: The alloy was prepared using the method described in claim 1 for preparing multi-stage heterogeneous magnesium alloys.

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