Multistage heterogeneous magnesium alloy and preparation method thereof

Abstract

The invention relates to the field of magnesium alloy material processing, in particular to a multistage heterogeneous magnesium alloy and a preparation method thereof.The preparation method comprises the steps that a magnesium alloy cast ingot is provided, and solution treatment and aging treatment are sequentially conducted on the magnesium alloy cast ingot; performing single-pass hot extrusion on the magnesium alloy subjected to aging treatment to obtain a magnesium alloy extruded plate, and setting the extrusion deformation to be 60-90%; compression deformation is conducted in 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 be 1%-9%. The magnesium alloy with a multilevel heterogeneous structure with grain size, precipitated phase and grain orientation can be prepared, and meanwhile the strength and plasticity of the magnesium alloy are improved.

Description

Technical Field

[0001] The present invention relates to the field of magnesium alloy material processing, and in particular to a multi-grade heterogeneous magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have low density, high specific strength, excellent shock absorption and electromagnetic shielding properties, and have great application prospects as lightweight materials and functional materials. Common magnesium alloys are close-packed hexagonal crystal structures, with fewer slip systems that can be activated at room temperature and poor plasticity. It is difficult to achieve high-strength and high-plasticity combination of magnesium alloys through conventional processes.

[0003] Heterogeneous materials are a new type of material that has emerged in the metal field in recent years. They are expected to significantly improve the strength and strain hardening of traditional metal materials at the same time to avoid the "inevitable" plastic loss. It is composed of hard and soft areas with flow stress differences greater than 100%. The mechanical incompatibility between adjacent heterogeneous regions during plastic deformation makes the strengthening mechanism and deformation behavior of heterogeneous structural materials different from those of homogeneous structural materials, such as significant heterogeneous deformation induced (HDI) strengthening and work hardening, strain transfer, diffuse strain bands, etc., thus achieving excellent strength-plasticity synergy.

[0004] In the related art, CN114635098A discloses a dual isomorphous magnesium alloy of grain size and precipitation phase and a preparation method thereof, which synergistically improves the strength and plasticity of the magnesium alloy plate by grain refinement and precipitation phase strengthening, which is a beneficial attempt in this field. Summary of the invention

[0005] The object of the present invention is to provide a multi-level heterogeneous magnesium alloy and a preparation method thereof, which can produce a magnesium alloy with a multi-level heterogeneous structure of grain size, precipitation phase and grain orientation, while improving the strength and plasticity of the magnesium alloy.

[0006] In order to achieve the above object, 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-grade heterogeneous magnesium alloy, which comprises: providing a magnesium alloy ingot, and sequentially performing a solution treatment and an aging treatment on the magnesium alloy ingot; performing a single-pass hot extrusion on the aging-treated magnesium alloy to obtain a magnesium alloy extruded plate, and the extrusion deformation amount is set to 60-90%; and performing compression deformation in the transverse and / or longitudinal direction of the magnesium alloy extruded plate, and the deformation amount of the compression deformation is set to 1-9%.

[0007] Furthermore, the solution temperature of the solution treatment is set to 400-450° C., and the solution time is set to 12-24 hours.

[0008] Furthermore, the aging temperature of the aging treatment is set to 150-200° C., and the aging time is set to 8-24 hours.

[0009] Furthermore, the single-pass hot extrusion comprises: placing the magnesium alloy after aging treatment in an extrusion die at a temperature of 220-280° C. for 6-8 minutes, and then extruding, with the extrusion speed set at 4-10 mm / s.

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

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

[0012] The present invention has the following unexpected beneficial effects: 1. The present invention first generates precipitation phases in magnesium alloy materials through solution treatment and aging treatment, and controls the distribution, size and quantity of precipitation phases in magnesium alloy materials by controlling the relevant process parameters of solution treatment and aging treatment, that is, a precipitation phase heterogeneous structure is obtained. After the aging treatment is completed, a single-pass large deformation hot extrusion treatment is performed. Since the distribution, size and quantity of precipitation phases in different regions of the magnesium alloy material after the aging treatment are different, the degree of grain boundary pinning is also different. Correspondingly, after the hot extrusion treatment, a two-level heterogeneous structure of fine grains with dense precipitation phases and coarse grains with sparse precipitation phases in different proportions is constructed, that is, a dual heterogeneous structure of grain size and precipitation phase is obtained. Furthermore, the magnesium alloy material is subjected to compression deformation treatment after hot extrusion, which activates a large number of tensile twins with different grain orientations from the magnesium alloy matrix. The dislocation slip range in the coarse grains is large, the stress concentration near the grain boundaries is severe, and twin nucleation is easy, so that the coarse grains with sparse precipitation phases introduce a higher proportion of tensile twins, while the fine grains with dense precipitation phases introduce a lower proportion of tensile twins, thereby obtaining a magnesium alloy material with a triple heterogeneous structure of grain size, precipitation phase and grain orientation.

[0013] 2. The present invention obtains a multi-level heterogeneous structure of a magnesium alloy with coarse-grained heterogeneous orientation coupled with fine-grained reinforcement phase through solution treatment, aging treatment, hot extrusion treatment and compression treatment. The coarse grains accommodate more dislocations and the heterogeneous orientation between the coarse grains is helpful for activating non-basal slip, which greatly improves the plasticity of the sheet. At the same time, the fine grain boundary strengthening is superimposed on the pinning effect of continuous and / or discontinuous precipitation of relatively fine grain high-density dislocations, which greatly improves the strength of the sheet, so that the material as a whole shows excellent synergistic improvement in strength and plasticity.

[0014] 3. The preparation method of the present invention has a simple process and low cost, which avoids the cost increase problem caused by the process of preparing composite materials and has the potential for large-scale industrial production.

[0015] 4. The present invention limits the aging temperature of the aging treatment to 150-200°C. If the aging temperature is too high, the nucleation driving force of the precipitate phase is large, and it is easy to produce coarse precipitate phases, which deteriorates the mechanical properties; if the aging temperature is too low, it is necessary to extend the aging time to ensure a sufficient amount of precipitates, which increases the cost.

[0016] 5. The present invention limits the hot extrusion process parameters. If the extrusion temperature is too high, the resistance of the precipitated phase to the movement of the grain boundary is lower than the growth rate of the grain boundary, making the heterogeneous structure of the grain unclear and causing some grains to be too coarse, which is not conducive to the improvement of the mechanical properties of the plate. If the extrusion temperature is too low, it is not conducive to the plastic forming of the extruded plate. Within the allowable range of the hydraulic press function parameters, the extrusion speed can be appropriately increased with the increase of the extrusion temperature. If the extrusion speed is too high, during the deformation process, the work hardening rate of the metal will exceed the softening rate of its dynamic recrystallization, thereby increasing the flow stress of the billet. In order to avoid internal defects in the ingot, the extrusion deformation is usually more than 60%, and the greater the extrusion deformation, the finer the grains of the plate, and the higher its strength. In summary, the extrusion temperature is limited to 220~280℃, the extrusion speed is 6~8mm / s, and the extrusion deformation is 60~90%.

[0017] 6. The present 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, the twin density introduced is small, making the heterogeneous orientation effect insignificant. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic diagram of the preparation process flow of the method for preparing the multi-grade heterogeneous magnesium alloy.

[0019] Figure 2 Schematic diagram of grain orientation and grain characteristics of magnesium alloy sheets under different processing conditions.

[0020] Figure 3 Schematic diagram of the precipitation phase characteristics of magnesium alloy sheets under different processing conditions.

[0021] Figure 4 Schematic diagram of the comparison of mechanical properties of magnesium alloy sheets under different processing conditions. DETAILED DESCRIPTION

[0022] The following will describe the embodiments of the present invention 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 contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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, 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-grade heterogeneous magnesium alloy, which comprises the following steps: Step 1: Provide a magnesium alloy ingot, and perform solution treatment and aging treatment on the magnesium alloy ingot in sequence; solution treatment is to allow the alloy elements to fully dissolve in the matrix at high temperature, and then during the aging treatment, the supersaturated alloy elements will precipitate from the matrix in the form of a precipitate phase, and the formation of the precipitate phase can be changed by adjusting process parameters such as treatment temperature and time.

[0024] Step 2: The magnesium alloy after aging treatment is subjected to single-pass hot extrusion to obtain a magnesium alloy extruded plate, and the extrusion deformation is set to 60-90%. The single-pass large deformation hot extrusion treatment after the aging treatment is performed in order to utilize the characteristics that the distribution, size, and quantity of precipitation phases in different regions of the magnesium alloy material after aging treatment are different, so that the degree of grain boundary pinning during the hot extrusion process is also different. During the hot extrusion process, the material flows with a large deformation under the action of the die. Due to the different precipitation phase conditions in different regions, the restriction effect on the grain boundary (grain boundary pinning) is different, resulting in different grain deformation and recrystallization conditions, thereby forming different proportions of fine grains and coarse grains and precipitation phases with different distribution densities, and then constructing a dual-level heterogeneous structure with different proportions of fine grains and dense precipitation phases and coarse grains and sparse precipitation phases, and finally obtaining a dual heterogeneous structure of grain size and precipitation phase.

[0025] Step 3: compress the magnesium alloy extruded plate in the transverse and / or longitudinal direction, and the amount of compression deformation is set to 1-9%. During compression deformation, due to the large slip range of dislocations in the coarse grains, severe stress concentration near the grain boundaries, and easy twin nucleation, the coarse grains with sparse precipitation phases can introduce a higher proportion of tensile twins, while the fine grains with dense precipitation phases introduce a lower proportion of tensile twins, thereby achieving isomerization of grain orientation.

[0026] In extruded sheet, the longitudinal direction refers to the main direction of material flow during the extrusion process, that is, the direction consistent with the extrusion axis. This direction is the direction in which the metal is squeezed out of the die cavity, similar to the direction of "stretching" the material. The transverse direction is perpendicular to the longitudinal direction, which is perpendicular to the extrusion axis and spans 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 the width of the paper.

[0027] The present invention first generates precipitation phases in the magnesium alloy material by solution treatment and aging treatment, and controls the distribution, size and quantity of the precipitation phases in the magnesium alloy material by controlling the relevant process parameters of the solution treatment and aging treatment, that is, a precipitation phase heterogeneous structure is obtained. After the aging treatment is completed, a single-pass large deformation hot extrusion treatment is performed. Since the distribution, size and quantity of precipitation phases in different regions of the magnesium alloy material after the aging treatment are different, the degree of grain boundary pinning is also different. Correspondingly, after the hot extrusion treatment, a dual-level heterogeneous structure of fine grains with denser precipitation phases and coarse grains with sparser precipitation phases in different proportions is constructed, that is, a dual heterogeneous structure of grain size and precipitation phase is obtained. Furthermore, the magnesium alloy material is subjected to compression deformation treatment after hot extrusion, which activates a large number of tensile twins with different grain orientations from the magnesium alloy matrix. The dislocation slip range in the coarse grains is large, the stress concentration near the grain boundaries is severe, and twin nucleation is easy, so that the coarse grains with sparse precipitation phases introduce a higher proportion of tensile twins, while the fine grains with dense precipitation phases introduce a lower proportion of tensile twins, thereby obtaining a magnesium alloy material with a triple heterogeneous structure of grain size, precipitation phase and grain orientation.

[0028] During the plastic deformation 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 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 slip systems to coordinate deformation. In view of the great advantages of multi-level heterogeneous materials with body-centered or face-centered cubic structures in improving mechanical properties, the combination of different heterogeneous structures and coupling with other conventional strengthening mechanisms provide a broad design space and mechanical property optimization space for multi-level heterogeneous structural materials. Constructing intrinsic crystallographic heterogeneous features in the heterogeneous grain size structure of close-packed hexagonal magnesium alloys and coupling with traditional fine grain strengthening mechanisms can induce multi-level strain hardening effects.

[0029] In a preferred embodiment, the solution temperature of the solution treatment is set to 400-450° C., and the solution time is set to 12-24 hours.

[0030] The solution temperature is in the range of 400~450℃, which comprehensively considers the dissolution characteristics of alloying elements in magnesium alloys and their influence on the subsequent microstructure formation. In this temperature range, the alloying elements can be dissolved into the magnesium matrix more fully. If the temperature is too low, the alloying elements are not fully dissolved, which will limit the formation of precipitate phases during subsequent aging treatment, and the regulation of the distribution, size and quantity of precipitate phases cannot be effectively achieved. For example, some key alloying elements may not reach a sufficiently supersaturated state, resulting in too few precipitate phases or uneven distribution during the aging process. If the temperature is too high, on the one hand, it may cause excessive melting of magnesium alloys or other thermal defects, such as coarse grains, which will have an adverse effect on the overall performance of magnesium alloys; on the other hand, too high a temperature may cause some alloying elements to react abnormally with the matrix or other elements, changing the originally expected alloying state, which is also not conducive to the reasonable formation of subsequent precipitate phases and the regulation of microstructures.

[0031] The solution time is set to 12~24h in order to give enough time for the alloy elements to fully dissolve at the appropriate solution temperature. When the solution time is too short, such as less than 12h, even if the solution temperature is in the appropriate range, some alloy elements may not have enough time to completely dissolve into the matrix, so that during the subsequent aging treatment, the formation of the precipitation phase does not meet expectations and the characteristics of the precipitation phase cannot be accurately controlled. If the solution time is too long, exceeding 24h, under the action of continuous high temperature, in addition to the above-mentioned problems caused by high temperature (such as coarse grains, etc.), it may also cause energy waste and reduce production efficiency, which is also disadvantageous from the perspective of production cost and production efficiency.

[0032] The parameter setting of the solution treatment is closely related to the subsequent aging treatment. Only when the alloying elements are fully dissolved during the solution treatment and the magnesium matrix reaches a suitable supersaturated state, after entering the aging treatment stage, can the supersaturated alloying elements form precipitation phases with appropriate distribution, size and quantity as expected, thereby laying the foundation for the subsequent construction of multi-level heterogeneous structures through hot extrusion and compression deformation. For example, if the temperature or time of the solution treatment is inappropriate, resulting in unsatisfactory precipitation phase formation, it will be difficult to construct a two-level heterogeneous structure of fine grains with denser precipitation phases and coarse grains with sparse precipitation phases based on different precipitation phase conditions during hot extrusion, and ultimately it will not be possible to successfully obtain a magnesium alloy material with a triple heterogeneous structure of grain size, precipitation phase and grain orientation.

[0033] In a preferred embodiment, the aging temperature of the aging treatment is set to 150-200° C., and the aging time is set to 8-24 hours.

[0034] In the aging temperature range of 150~200℃, for magnesium alloys, it is a more suitable temperature range for the formation and growth of precipitation phases. When the temperature is in this range, the alloying elements that are supersaturated and dissolved in the magnesium matrix after solution treatment can precipitate at a suitable rate to form fine and dispersed precipitation phases. If the aging temperature is lower than 150℃, the diffusion rate of atoms will become very slow, and it will be difficult for the supersaturated alloying elements to form a sufficient number of precipitation phases with ideal distribution within a reasonable time. This will lead to the inability to effectively control the size, number and distribution of the precipitation phase, thereby affecting the effect of constructing a multi-level heterogeneous structure through subsequent steps such as hot extrusion. It is necessary to extend the aging time to ensure a sufficient number of precipitation phases, which increases the cost. For example, it may not be possible to form enough precipitation phases to produce different degrees of pinning on the grain boundaries, affecting the formation of a two-level heterogeneous structure. On the contrary, if the aging temperature is higher than 200℃, the nucleation driving force of the precipitation phase is large, and the growth rate of the precipitation phase may be too fast, resulting in the production of coarse precipitation phases. Coarsened precipitates not only fail to play a good strengthening role, but may also reduce the mechanical properties of magnesium alloys because when the material is subjected to external forces, the coarsened precipitates cannot effectively hinder the movement of dislocations like fine dispersed precipitates, thus affecting the strength and toughness of the material.

[0035] The aging time is set at 8~24h in order to allow the precipitate phase to have enough time to complete the formation, growth and reach a relatively stable state at a given aging temperature. When the aging time is too short, such as less than 8 hours, the precipitate phase may not be fully formed or grown to a suitable degree at the aging temperature, resulting in insufficient amount and uneven distribution of the precipitate phase. It is also impossible to accurately control the characteristics of the precipitate phase, affecting the subsequent construction of multi-level heterogeneous structures. If the aging time is too long, more than 24 hours, at the aging temperature, the precipitate phase may continue to grow and overgrow or coarsen, which is similar to the adverse effects when the aging temperature is too high, which will reduce the mechanical properties of the magnesium alloy and is not conducive to obtaining an ideal multi-level heterogeneous structure.

[0036] The parameter setting of aging treatment is closely related to the previous solution treatment and the subsequent hot extrusion, compression deformation and other processing steps.

[0037] The connection with the solution treatment is that only the solution treatment can make the magnesium matrix reach a suitable supersaturated state, and combined with the aging temperature and time setting in this preferred embodiment, it can ensure that the precipitation phase with the expected distribution, size and quantity is accurately formed during the aging treatment process, laying the foundation for subsequent processing steps.

[0038] For the hot extrusion step, the distribution, size and quantity of the precipitates formed by the appropriate aging treatment will help to construct a two-level heterogeneous structure with different proportions of fine-grained dense precipitates and coarse-grained sparse precipitates due to 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 in different proportions during compression deformation, because different precipitation phase conditions will affect the dislocation slip and other behaviors within coarse grains and fine grains, thereby affecting the formation of tensile twins, and ultimately achieving the goal of obtaining a magnesium alloy material with a triple heterogeneous structure of grain size, precipitation phase and grain orientation.

[0040] In a preferred embodiment, the single-pass hot extrusion comprises: placing the magnesium alloy after aging treatment in an extrusion die at a temperature of 220-280° C. for 6-8 minutes, and then extruding, with the extrusion speed set to 4-10 mm / s.

[0041] The extrusion die temperature is set between 220°C and 280°C. This temperature range is crucial for the hot extrusion process of magnesium alloys. At this temperature, the plastic deformation ability of the magnesium alloy will be effectively improved, making it easier to flow and deform in the die. If the die temperature is too low, such as below 220°C, the plasticity of the magnesium alloy is insufficient, and it may face a large deformation resistance during the extrusion process, resulting in excessive extrusion pressure, which not only increases the energy consumption and burden of the equipment, but also may cause defects such as cracking in the magnesium alloy during the extrusion process, and it is impossible to successfully complete the extrusion molding to obtain the extruded plate. On the contrary, if the die temperature is too high, exceeding 280°C, on the one hand, it may cause excessive softening of the magnesium alloy, causing it to flow too fast and difficult to control in the die, affecting the dimensional accuracy and microstructural uniformity of the magnesium alloy extruded plate after extrusion; on the other hand, too high a temperature may accelerate the wear of the die, shorten the service life of the die, and increase production costs.

[0042] The holding time is set to 6 to 8 minutes, which gives the magnesium alloy enough time to reach a thermal equilibrium state at the above-mentioned appropriate mold temperature to ensure that its internal temperature is evenly distributed. When the holding time is too short, for example, less than 6 minutes, the interior of the magnesium alloy may not be fully and evenly heated, and the deformation resistance and flow characteristics of different parts may be different during extrusion, which will affect the quality of the extruded plate, such as uneven local deformation and uneven organization. If the holding time is too long, more than 8 minutes, while maintaining high temperature, in addition to the possibility of some unnecessary changes in the microstructure of the magnesium alloy (such as grain growth, etc.) due to long-term heating, it will also reduce production efficiency and increase production cycle and cost.

[0043] The extrusion speed is set between 4 and 10 mm / s. The appropriate extrusion speed has an important influence on controlling the flow of magnesium alloy in the die and the quality of the final extruded plate. When the extrusion speed is too slow, such as less than 4 mm / s, the residence time of the magnesium alloy in the die is too long, which may cause excessive heat exchange between it and the die, causing the local temperature of the magnesium alloy to decrease, affecting its plastic deformation ability, and thus affecting the smooth extrusion, while also reducing production efficiency. If the extrusion speed is too fast, exceeding 10 mm / s, the magnesium alloy flows too fast in the die, which may cause a sharp increase in extrusion pressure on the one hand, increasing the load and energy consumption of the equipment; on the other hand, too fast a flow rate is not conducive to the fine control of the microstructure of the magnesium alloy, and may cause uneven internal structure of the extruded plate, such as inconsistent degree of grain deformation, and other problems, affecting the effect of the subsequent construction of multi-level heterogeneous structure.

[0044] Relationship with aging treatment: The distribution, size and quantity of the precipitates formed in the magnesium alloy after aging treatment will play a role in the hot extrusion process due to the different degrees of grain boundary pinning in different regions. The setting of parameters such as die temperature, holding time and extrusion speed during hot extrusion should be based on the state of the magnesium alloy after aging treatment to ensure that the grain boundary pinning difference can be fully utilized, so as to construct a two-level heterogeneous structure with different proportions of fine grains and dense precipitation phases and coarse grains and sparse precipitation phases.

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

[0046] In a preferred embodiment, the amount of compression deformation is set to 3-7%, which 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%, a large number of tensile twins with different grain orientations from the magnesium alloy matrix can be activated in the magnesium alloy material. Within this range, the stress level is moderate, which can promote dislocation slip in the coarse grains. And because the dislocation slip range in the coarse grains is large, the stress concentration near the grain boundaries is serious, which is easy to nucleate twins. Coarse grains with sparse precipitation phases can introduce a higher proportion of tensile twins, while fine grains with dense precipitation phases introduce a lower proportion of tensile twins, thereby achieving effective control of grain orientation isomerism.

[0048] If the deformation is less than 3%, the stress generated may not be sufficient to activate a sufficient number of tensile twins, especially in the coarse-grained area, and the expected grain orientation adjustment effect cannot be achieved, which is not conducive to obtaining the triple heterogeneous structure of grain size, precipitation phase and grain orientation. If the deformation exceeds 7%, the stress inside the material may be too high. In this case, on the one hand, it may cause excessive growth of the already formed twins or destruction of the twin boundaries, and on the other hand, it may cause excessive plastic deformation of the material and even microcracks, which is not conducive to the performance improvement of magnesium alloy materials and the construction of heterogeneous structures.

[0049] Cooperation with hot extrusion: After hot extrusion, magnesium alloy materials have a specific two-level heterogeneous structure, including different proportions of fine grains with dense precipitation phases and coarse grains with sparse precipitation phases. The compression deformation in the range of 3-7% can play a better role based on the organizational morphology after hot extrusion. Through appropriate compression deformation, the grain orientation is further adjusted on the basis of not destroying the grain and precipitation phase structure constructed by hot extrusion to achieve a triple heterogeneous structure.

[0050] Solution and aging treatment regulate the distribution, size and quantity of precipitates in magnesium alloy materials. Within this range of compression deformation, the formation of tensile twins can be guided based on the heterogeneous structure of the precipitates that have been formed, according to the different conditions of the precipitates in coarse and fine grains, making the microstructure of the material more complex and heterogeneous, and cooperating with the previous treatment steps to jointly improve the performance of magnesium alloy materials.

[0051] In one embodiment, the present invention provides a multi-grade heterogeneous magnesium alloy, which is prepared by the above-mentioned preparation method of the multi-grade heterogeneous magnesium alloy.

[0052] The following is an analysis and explanation with specific examples.

[0053] Embodiment 1, a method for preparing a multi-grade heterogeneous magnesium alloy, comprising the following steps: Step 1: providing an AZ91 magnesium alloy ingot, and performing a solution treatment and an aging treatment on the magnesium alloy ingot in sequence.

[0054] The solution treatment specifically includes: subjecting the magnesium alloy ingot to a solution treatment at a temperature of 420° C. for 24 hours, and then cooling the ingot to room temperature with water to obtain a solid solution magnesium alloy.

[0055] The aging treatment is specifically as follows: the solid solution magnesium alloy is aged at a temperature of 200° C. for 16 hours, and then the surface is polished and degreased.

[0056] Step 2: The magnesium alloy after aging treatment is subjected to single-pass hot extrusion. After the temperature of the extrusion die and the extrusion barrel is stabilized at 220°C, the polished magnesium alloy is placed in the extrusion barrel and kept warm for 10 minutes before extrusion. Before extrusion, graphite is sprayed on the inner wall of the extrusion barrel 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 6mm / s. Finally, a magnesium alloy extrusion plate with a double-level heterogeneous structure of fine grains with dense precipitation phase and coarse grains with sparse precipitation phase is obtained, and its thickness is about 3mm.

[0057] Step three, a 3% compression deformation is performed in the transverse direction of the magnesium alloy extruded plate with a two-level heterogeneous structure, and the compression rate is set to 1 mm / min, so that a lower proportion of tensile twins are finally introduced into the two-level heterogeneous structure, and its thickness is about 3 mm.

[0058] The obtained multi-stage heterogeneous magnesium alloy plate was processed into a tensile sample for room temperature tensile test. The tensile sample specification complies with GB / T 16865-2013, and the tensile test method complies with GB / T228.1-2010. The yield strength of the multi-stage 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] In Example 2, the steps are the same as those in Example 1, except that step 3 in Example 1 is changed to subjecting the extruded plate of the dual-level heterogeneous structure to a 5% compression deformation along the transverse direction of the magnesium alloy extruded plate of the dual-level heterogeneous structure, and the compression rate is set to 1 mm / min, so that the dual-level heterogeneous structure finally introduces a medium proportion of tensile twins, and the thickness of the twins is about 3 mm.

[0060] The obtained multi-stage heterogeneous magnesium alloy plate was processed into a tensile sample for room temperature tensile test. The tensile sample specification complies with GB / T 16865-2013, and the tensile test method complies with GB / T228.1-2010. The yield strength of the multi-stage 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] Embodiment 3 has the same steps as Embodiment 1, except that step 3 in Embodiment 1 is changed to subjecting the extruded plate of the dual-level heterogeneous structure to a 7% compression deformation in the transverse direction of the magnesium alloy extruded plate of the dual-level heterogeneous structure, and the compression rate is set to 1 mm / min, so that a higher proportion of tensile twins are finally introduced into the dual-level heterogeneous structure, and the thickness thereof is about 3 mm.

[0062] The obtained multi-stage heterogeneous magnesium alloy plate was processed into a tensile sample for room temperature tensile test. The tensile sample specification complies with GB / T 16865-2013, and the tensile test method complies with GB / T228.1-2010. The yield strength of the multi-stage 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] In order to compare and analyze and illustrate the beneficial effects of the present invention, the following comparative examples are set up.

[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 a temperature of 420° C. for 24 hours, and then water-cooled to room temperature to obtain a solid solution magnesium alloy.

[0065] Step 2: The solid solution magnesium alloy is polished and degreased. After the temperature of the extrusion die and the extrusion barrel is stabilized at 220°C, the polished solid solution magnesium alloy is placed in the extrusion barrel for 10 minutes before extrusion. Before extrusion, graphite is sprayed on the inner wall of the extrusion barrel as a lubricant. The extrusion speed is set to 6mm / s, and finally a uniform structure of magnesium alloy extrusion plate is obtained, with a thickness of about 3mm.

[0066] The obtained uniform structure magnesium alloy extruded plate was processed into tensile samples for room temperature tensile test. 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 obtained 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 is a method for preparing a two-stage heterogeneous magnesium alloy based on grain size and precipitation phase. The steps are the same as those of Example 1, except that Step 3 in Example 1 is deleted, and a two-stage heterogeneous magnesium alloy plate is finally obtained.

[0068] The obtained two-stage heterogeneous magnesium alloy plate was processed into a tensile sample for room temperature tensile test. The tensile sample specification complies with GB / T 16865-2013, and the tensile test method complies with GB / T228.1-2010. The yield strength of the two-stage heterogeneous magnesium alloy plate obtained 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 also Figures 2 to 4Compared with the uniform structural organization in comparative example 1, after the pre-aging + extrusion process, due to the difference in the degree of hindrance of the unevenly distributed precipitation phases to the grain boundaries, comparative example 2 presents a two-level heterogeneous organization of grain size and precipitation phase, in which the coarse grains have a sparse distribution of precipitation phases, while the fine grains have a dense distribution of precipitation phases, and there is no obvious difference in grain orientation. The strength and plasticity of comparative example 2 are improved compared with comparative example 1. It can be seen that the difference in the strength of coarse and fine grains produces mechanical incompatibility behavior, resulting in the generation of strain gradients near the heterogeneous interface, inducing additional strengthening and work hardening effects; at the same time, the fine dispersed precipitates also induce precipitation strengthening and hardening effects.

[0070] In order to further optimize the mechanical properties of the two-stage heterogeneous tissue board, on the basis of comparative example 2, a 3% to 7% compression deformation was performed on it in the transverse direction, which were respectively recorded as example 1, example 2 and example 3, and the yield strength and tensile strength thereof were greatly increased.

[0071] In Example 1, when the compression deformation is 3%, a small number of tensile twins are introduced into the two-level heterogeneous structure, and the heterogeneity of the grain orientation is not significant; in Example 3, when the compression deformation is 7%, the coarse and fine grains are almost completely twinned, and most of the coarse and fine grains are deflected in the lateral direction; in Example 2, when the compression deformation is 5%, a large number of tensile twins are activated, especially in the coarse grain structure. At this time, on the basis of retaining the two-level heterogeneous structure, part of the mother crystals in the coarse grains maintain the original orientation, and the induced large number of tensile twins are deflected in the lateral direction. At the same time, as a densely distributed precipitation phase, it is mainly distributed in the fine grains as a reinforcement phase, presenting a multi-level heterogeneous structure of coarse grain heterogeneous orientation coupled with fine grain reinforcement phase. The use of coarse grains to accommodate more dislocations and the superposition of heterogeneous orientations between coarse grains is conducive to the activation of non-basal slip, which greatly improves the plasticity of the plate. At the same time, the fine grain boundary strengthening is superimposed on the pinning effect of continuous and / or discontinuous precipitation relative to the fine grain high-density dislocation, which greatly improves the strength of the plate, so that the material as a whole shows excellent synergistic improvement of strength and plasticity.

[0072] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A method for preparing a multi-grade heterogeneous magnesium alloy, characterized in that: include: Providing a magnesium alloy ingot, and sequentially performing a solution treatment and an aging treatment on the magnesium alloy ingot; The magnesium alloy after aging treatment is subjected to single-pass hot extrusion to obtain a magnesium alloy extruded sheet, and the extrusion deformation is set to 60-90%; The magnesium alloy extruded plate is subjected to compression deformation in the transverse direction and / or longitudinal direction, and the deformation amount of the compression deformation is set to 1-9%.

2. The method for preparing a multi-grade heterogeneous magnesium alloy according to claim 1, characterized in that: The solution temperature of the solution treatment is set to 400-450° C., and the solution time is set to 12-24 hours.

3. The method for preparing a multi-grade heterogeneous magnesium alloy according to claim 1, characterized in that: The aging temperature of the aging treatment is set at 150-200° C., and the aging time is set at 8-24 hours.

4. The method for preparing a multi-grade heterogeneous magnesium alloy according to claim 1, characterized in that: The single-pass hot extrusion comprises: placing the magnesium alloy after aging treatment in an extrusion die at a temperature of 220-280° C. and keeping the temperature for 6-8 minutes, and then extruding, and the extrusion speed is set to 4-10 mm / s.

5. The method for preparing a multi-grade heterogeneous magnesium alloy according to claim 1, characterized in that: The deformation amount of the compression deformation is set to 3-7%.

6. A multi-grade heterogeneous magnesium alloy, characterized in that: The multi-grade heterogeneous magnesium alloy is prepared by the preparation method of any one of claims 1 to 5.

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