Magnesium alloy with high strength and plasticity and high creep property in wide temperature range and preparation method

Abstract

The invention belongs to the field of material science and engineering, and particularly relates to a magnesium alloy with high strength and plasticity and high creep property in a wide temperature range and a preparation method. According to the method, the requirements of the magnesium alloy for high-strength plasticity and high creep property in a wide temperature range of-180 DEG C to 200 DEG C can be met; the magnesium alloy prepared by the method comprises a multi-scale mixed crystal structure of micron grains and stable ultra-fine grains; the material provided by the method (in a stress interval within 200MPa and a temperature interval below 200DEG C) shows creep resistance far higher than that of magnesium alloys in a common as-cast state, a heat treatment state and a common deformation treatment state, so that the application of the magnesium alloy in a creep-resistant structural member is expanded, and the creep-resistant performance of the magnesium alloy is improved. And meanwhile, the instant mechanical properties at room low temperature (-180 DEG C to room temperature) show good strength and plasticity.

Description

Technical Field

[0001] The present invention belongs to the field of material science and engineering, and specifically relates to a magnesium alloy with high strength, plasticity and high creep performance in a wide temperature range and a preparation method thereof. Background Art

[0002] Magnesium alloys are widely used in aerospace, automotive and defense fields due to their lightweight characteristics, but they face the problems of low-temperature embrittlement, high-temperature strength reduction and insufficient comprehensive mechanical properties caused by temperature cycles in a wide temperature range service environment. Under low temperature conditions, the plasticity and toughness of the material decrease, and brittle fracture is prone to occur; under high temperature environments, grain boundary sliding and creep effects lead to a decrease in strength and dimensional stability; and frequent temperature cycles cause thermal stress accumulation and thermal fatigue, accelerating the initiation and expansion of microcracks. Although microstructure refinement can significantly improve the room temperature strength of magnesium alloys through the fine grain strengthening mechanism, under high temperature environments, the refined grain boundaries are prone to grain boundary sliding and stress concentration due to high interfacial energy and low thermal stability, becoming weak areas for creep deformation, thereby reducing high temperature service performance. Therefore, while pursuing microstructure refinement to improve strength, how to stabilize the grain boundary structure and inhibit grain boundary sliding through process means, and balance the wide temperature range strength and high temperature creep performance, is an effective way to ensure the high strength, plasticity and high creep performance of magnesium alloys under a wide temperature range.

[0003] At present, WE43 alloy has become one of the most common commercial magnesium alloys of Mg-Y-RE-Zr alloy system. Its composition contains 4wt% Y, 3.3wt% RE (Nd, Gd) and 0.5wt% Zr. It has excellent castability and high strength, especially excellent creep resistance, and is considered to be one of the most promising magnesium alloy series. However, most of the current research on creep resistance of WE43 alloy is aimed at its cast structure or solid solution structure, and there are few studies on its creep resistance in deformed form and effective processing and preparation technology. However, because the instantaneous mechanical properties of cast structure and solid solution structure are poor, according to literature records, its yield strength is usually between 140MPa-230MPa at room temperature, and usually only 100MPa-140MPa at 200℃, which leads to it only being able to withstand creep environment with lower stress. The yield strength of the deformed WE43 alloy will increase significantly, reaching 300MPa at room temperature and maintaining 160-200MPa at 200°C, allowing it to serve in higher stress creep environments. However, compared with the cast structure, the deformed form has obvious grain recrystallization and refinement, resulting in the grain size being refined from 200 microns in the cast state to less than 10 microns after deformation. Too many fine grains greatly accelerate the speed of grain boundary sliding at high temperatures, which will significantly reduce the creep resistance of the material. Therefore, in order to expand the application range of deformed WE43, there is an urgent need for a preparation process that can ensure the high yield strength of the deformed WE43 magnesium alloy while ensuring good creep resistance at high temperatures. A large number of previous literature studies have confirmed that the addition of Y element and other rare earth elements such as gadolinium (Gd) and neodymium (Nd) in Mg-RE alloys similar to WE43 alloys maintains the high-temperature microstructural stability of the alloy and has obvious precipitation and solid solution hardening. Therefore, adding solid solution treatment to the WE43 alloy before deformation can improve the creep resistance to a certain extent.

[0004] With the widespread use of magnesium alloys and the increasingly complex service environment, low temperature environments have attracted much attention. The brittleness caused by low temperature is also a factor that must be considered and affects the service reliability of alloy components. At high or room temperature, metal materials have enough slip systems or twins to coordinate deformation, but after the temperature drops, the strength of the interaction between interstitial impurity atoms and dislocations and grain boundaries increases, hindering the movement of dislocations and blocking the movement of slip, resulting in a decrease in the plasticity of metal materials at low temperatures. Compared with body-centered cubic iron, chromium, tungsten and other alloys, hexagonal close-packed magnesium alloys show a trend of decreasing plasticity, but no obvious low-temperature brittleness. Existing research focuses on the mechanical or creep properties of magnesium alloys at room temperature or above medium and high temperatures, while there is less research on mechanical properties below room temperature (e.g., -180℃ to room temperature), and there are few reports on the research of high-performance magnesium alloys with a wide temperature range of room temperature, low temperature transient mechanical properties and high temperature creep properties.

[0005] Therefore, there is no magnesium alloy production and preparation process that can simultaneously improve the high and low temperature transient mechanical properties and high temperature creep properties of magnesium alloys at room temperature to meet the needs of high strength plasticity and high creep properties in a wide temperature range of -180°C to 200°C. The research and development idea of ​​this patent is: to use a gradient extrusion process to prepare a mixed crystal structure with alternating coarse and fine grains, and introduce a phase structure with high temperature deformation resistance at the grain boundary. Through the fine grain strengthening and precipitation strengthening of fine grains and nanophases, the strength and plasticity of the alloy under high temperature conditions are ensured, and some coarse grains can effectively hinder grain boundary sliding under high temperature creep conditions, thereby improving the creep resistance of the alloy. At the same time, the deformation coordination between coarse and fine grains produces a back stress strengthening effect, inhibits local instability, and improves the uniform ductility of the material. The synergistic effect of the mixed crystal structure can achieve low temperature strength and toughness integration, which can provide new design ideas for the contradiction that strength and toughness are difficult to achieve in traditional uniform grain materials. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing a magnesium alloy with high strength, plasticity and high creep performance in a wide temperature range, comprising the following steps:

[0007] S1: homogenizing annealing the WE43 magnesium alloy, keeping the alloy warm during the homogenizing annealing process, pre-adding ferrous sulfide powder during the keeping process, taking the alloy out after keeping the alloy warm for 24 hours, and air cooling the alloy to obtain a homogenizing annealed material;

[0008] S2: pre-treating the homogenized annealed material obtained in S1 to obtain a processed material, and performing a solid solution treatment in a holding furnace. During the solid solution treatment, ferrous sulfide powder is pre-placed in the holding furnace, and after the solid solution treatment, the material is taken out for quenching to obtain a solid solution treated material;

[0009] S3: drying the material obtained in S2, placing it in a heat preservation furnace for heat preservation and preheating, and then performing gradient extrusion to obtain a material after gradient extrusion;

[0010] S4: The material after gradient extrusion is quenched, dried, cyclically heated, and then kept warm to obtain a magnesium alloy with high strength, plasticity, and high creep properties in a wide temperature range.

[0011] Furthermore, the temperature in the homogenization annealing described in S1 is 400° C., and the holding time is 24 h.

[0012] Furthermore, the solution treated material described in S2 is cylindrical, and the height of the solution treated material is 30 mm and the diameter is 30 mm.

[0013] Furthermore, the insulation time described in S2 is 10 hours.

[0014] Furthermore, the insulation temperature described in S3 is 400° C., and the insulation time is 25 h.

[0015] Furthermore, in the gradient extrusion process described in S3, the extrusion temperature is 400° C., the extrusion speed is 2 mm / s, the extrusion gradient is T2, the extrusion ratio is 9:1, and the diameter of the cylindrical sample is 10 mm.

[0016] Furthermore, the heating temperature described in S4 is 250° C., the insulation time is 8 hours, and the number of cycle heating is 3 times.

[0017] A magnesium alloy with high strength, plasticity and creep performance in a wide temperature range. The components and their mass percentages of the magnesium alloy material with high strength, plasticity and creep performance in a wide temperature range are 3.8% wt.Y, 2.1% wt.Nd, 0.61% wt.Gd, 0.5% wt.Zr and 0.089% wt.Zn, and the rest is Mg.

[0018] Beneficial Effects

[0019] The variable gradient extrusion WE43 alloy (SET process) prepared by the present invention has a distinct heterogeneous structure - a coarse and long crystal region with a fine crystal region with fine grains. While ensuring that fine grain strengthening significantly improves the yield strength of the material, so that the material can accept creep stress below a higher yield strength, the coarse and long crystals can effectively reduce the grain boundary sliding in the creep stage and improve the creep resistance. In addition, the focus of the SET process is the phase structure and grain structure changes caused by the variable gradient extrusion process after solid solution. Different from the previous solid solution extrusion process, the precipitated phase distribution of the WE43 alloy of the present invention after solid solution and variable gradient extrusion presents a distinct Y-rich block phase and a linear precipitated phase arranged along the extrusion direction and around the grain boundary, and the variable gradient extrusion of the process provides a distinct heterogeneous structure of coarse and long crystals with fine equiaxed crystals in the plastic deformation stage. The entire microstructure after extrusion is changed by means of the variable gradient extrusion process, resulting in the formation of fine particle phases that precipitate and completely break during the extrusion process after the variable gradient extrusion (SET process). Compared with the SE process alloy fracture precipitation phase, which is only distributed in the fine equiaxed crystal structure, the extrusion fracture phase after the variable gradient extrusion (SET process) has a greater distribution difference. One part of the precipitated phase is distributed around the coarse long crystal, and the other part is distributed around the fine equiaxed crystal, so that it is better dispersed in the mixed crystal heterogeneous matrix. This fine particle phase is conducive to becoming a nucleation source during the process of deformation and recrystallization to hinder the growth of grains during growth and promote the formation of fine equiaxed crystals. The variable gradient extrusion changes the extrusion ratio during the continuous deformation stage of the extrusion. The extrusion ratio is an important factor affecting dynamic recrystallization. As the extrusion gradient value increases, the extrusion ratio in the initial stage will become smaller, and the deformation heat generated will be less, thereby affecting and reducing the proportion of DRX in the initial stage. This leads to the formation of heterogeneous microstructures. The subsequent multiple cycle heating method is mainly to promote the dynamic precipitation of rare earth elements. When the temperature is kept at 250℃ for 8h, the Y, Gd, and Nd elements that were not completely precipitated during the extrusion process continue to precipitate, and the Mg 12 Nd phase has significant low-temperature aging strengthening effect. At the same time, the formed Mg5Gd phase has excellent high-temperature stability. Multiple cycles of heating have obtained a rich and widely distributed rare earth second phase, which forms a stable organizational structure with heterogeneous organization. The heterogeneous organization has significant fine grains and coarse grains, which not only hinders dislocation movement and improves yield strength, so that it can accept stress under higher creep conditions, but also effectively reduces the number of grain boundaries, reduces the possibility of grain boundary sliding, and improves creep resistance. When the creep resistance test is carried out for 100 hours under creep conditions of 200℃ and less than 200MPa, taking the SE process material with the same composition as an example, the creep deformation of the SET process alloy at 200℃ is about 0.089%, and the steady-state creep rate is about 3.1069E -10 S -1Compared with the creep deformation of SE process under the same conditions, the creep rate is 0.159% and the steady-state creep rate is 1.0831E -9 S -1 The creep deformation of the SET alloy is 2 times less than that of the control group, and the steady-state creep rate is one order of magnitude (10 times) lower than that of the control group. On the basis of only changing the low-cost extrusion gradient process, the creep resistance of the deformed WE43 material at 200MPa and 200℃ is significantly improved.

[0020] For low-temperature environments, the magnesium alloy obtained by this technology not only has good strength but also has good plasticity retention at low temperatures. This technology expands the application scenarios of deformed magnesium alloys and provides a technical support for the application of magnesium alloys at low temperatures. The mixed crystal structure obtained by variable gradient extrusion (SET process), that is, a part of the fine particle phase is distributed around the coarse grains. This large grain size distribution makes the alloy have excellent strength and plasticity at low temperatures. The heterogeneous mixed crystal structure reduces the sensitivity of brittle fracture between grains, especially under low temperature conditions. The presence of fine grain areas and soft phases can alleviate the low-temperature embrittlement behavior of the material. When the temperature drops sharply, the deformation mechanism of the metal is often suppressed, for example, dislocation slip is difficult to proceed, but the mixed crystal structure can promote the synergistic effect of multiple deformation mechanisms through the interaction between grain boundaries and phase boundaries, such as dislocation slip, twin deformation, phase transformation, etc. This multiple deformation mechanism helps to improve the plastic deformation ability of the material and delay the fracture behavior at low temperatures. The grain boundaries, phase boundaries and interface regions in the mixed crystal can effectively passivate the crack tip and prevent the rapid expansion of the crack. And through the alternating distribution of soft and hard areas, the deformation coordination of the material can be improved. This coordination is particularly important in low-temperature environments, because materials are more likely to fracture and fail at low temperatures. This also explains why the alloy obtained by extrusion through this process has good strength and plasticity retention at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0022] Figure 1 This is the backscattered scanning electron microscope image of the microstructure of WE43 alloy in solid solution extrusion state;

[0023] Figure 2 (a) is the creep deformation-creep time curve corresponding to the 100h creep test of SE process alloy and SET process alloy of WE43 alloy. Figure 2(b) The corresponding steady-state creep rate-creep time curve.

[0024] Figure 3 The schematic diagram of the gradient change in the process step diagram used for SE process alloy and SET process alloy of WE43 alloy;

[0025] Figure 4 To prepare the IPFZ images of EBSD of SE process alloy and SET process alloy before creep test;

[0026] Figure 5 The microstructure diagram of SE and SET alloys after solid solution and before extrusion;

[0027] Figure 6 Engineering stress-strain curves of SET process alloys at room temperature (RT), -100℃ and -180℃.

[0028] Figure 7 Engineering stress-strain curves of SET process alloy at room temperature (RT) and high temperature 200℃. DETAILED DESCRIPTION

[0029] The following will be combined with embodiments 1 to 6 of the present invention and the attached Figures 1 to 7 , clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The purpose of the present invention is to provide a preparation method that can significantly improve the creep resistance of deformed WE43 alloy, so that the alloy exhibits creep resistance much higher than that of WE43 alloy in ordinary cast state, heat treatment and ordinary deformation treatment in the stress range within 200MPa and the temperature range below 200°C, thereby expanding the application of magnesium alloys in creep-resistant structural parts.

[0031] In the further optimized scheme, in order to reflect the superiority of the present invention, two different processes were compared. The main processes used in the process of the present invention include: solution treatment, variable gradient extrusion and cyclic heating method after rapid cooling. The process of the present invention is defined as SET process. The other group of comparison processes are solution treatment and non-gradient extrusion followed by cyclic heating method, which is defined as SE process.

[0032] Example 1

[0033] S1: placing the commercial WE43 magnesium alloy melted by vacuum in a holding furnace at 400°C for homogenization annealing, pre-placing ferrous sulfide powder in the furnace during the annealing process, taking it out for air cooling after holding it for 24 hours, and obtaining the homogenized material;

[0034] S2: The homogenized material of S1 was polished with a steel brush to remove the surface oxide scale, and then cut into a cylindrical sample with a height of 30 mm and a diameter of 30 mm; the processed cylindrical sample was placed in a 525°C insulation furnace for solid solution treatment, during which ferrous sulfide powder was still pre-placed in the furnace, and after insulation for 10 hours, it was taken out and immediately quenched with distilled water at room temperature to obtain the material after solid solution treatment;

[0035] S3: After the solution treated material of S2 is dried, it is placed in a 400°C holding furnace for preheating and holding for 25 minutes for gradient extrusion. The extrusion temperature is controlled to be 400°C, the extrusion speed is 2mm / s, the extrusion gradient is T2, the extrusion ratio is 9:1, and a cylindrical sample with a diameter of 10mm is obtained;

[0036] S4; the sample obtained after S3 gradient extrusion is quickly water quenched, then taken out for drying, and then heated three times again, the heating temperature is 250°C, and the insulation time is 8h; finally, a magnesium alloy with high strength, plasticity and high creep properties in a wide temperature range is obtained.

[0037] from Figure 1 It can be seen that Figure 1 (a) (c) are SE process alloys obtained by gradient extrusion according to preparation step T1. Figure 1 (b)(d) are SET process alloys obtained by gradient extrusion in full accordance with the preparation step T2. Figure 1 In (b), we can see that the SET alloy has dispersed precipitates, some of which are distributed around fine equiaxed crystals, and some of which are distributed around coarse elongated crystals. Figure 1 The precipitation phase of WE43 alloy produced by SE process in (a) is completely dispersed along the fine equiaxed grains.

[0038] from Figure 2 It can be seen that Figure 2 (a) is the creep deformation-creep time curve corresponding to the 100h creep test of SE process alloy and SET process alloy of WE43 alloy. Figure 2 (b) The corresponding steady-state creep rate-creep time curve.

[0039] Figure 3 The T1 gradient corresponds to the SE process, and the T2 gradient corresponds to the SET process. Figure 4 It can be seen that Figure 4 (a) is the IPFZ diagram of SE process alloy. Figure 4 (b) IPFZ diagram of SET process alloy.

[0040] from Figure 4 In the EBSD IPFZ image of (b), it can be clearly observed that the SET process alloy has a heterogeneous structure, with coarse elongated crystals and fine equiaxed crystals. The grain size of the fine equiaxed crystals is less than 3μm, while the size of the coarse elongated crystals is greater than 100μm.

[0041] from Figure 5 It can be seen that Figure 5 This is a comparison of the organization diagrams of SE process and SET process alloys before extrusion. Before extrusion, the solid solution alloy of WE43 alloy did not have dispersed fine phases, only the larger Y-rich block phase produced in the casting stage and a small amount of undissolved second phase completely near the grain boundary were retained. The solution treatment provided the supersaturated solid solution required for the precipitation and fragmentation of the second phase in the extrusion deformation stage. After the solution treatment, setting different extrusion gradients changed the conditions required for the extrusion precipitation of the second phase and the occurrence of dynamic recrystallization of the supersaturated solid solution, because the variable gradient extrusion changed the extrusion ratio during the continuous deformation stage of the extrusion. The extrusion ratio is an important factor affecting dynamic recrystallization. As the extrusion gradient value increases, the extrusion ratio in the initial stage will become smaller, and the deformation heat generated will be less, thereby affecting and reducing the proportion of DRX in the initial stage. At the same time, a large amount of deformation heat is generated in the extrusion process after the gradient is increased, resulting in a high actual temperature in the deformation zone. The increased temperature accelerates the diffusion of grain boundary atoms, leading to grain growth. However, in addition to the effect of the extrusion gradient change on the recrystallization ratio and grain size of the alloy by changing the temperature, the change of the extrusion gradient also affects the uneven distribution of the broken second phase along the extrusion direction, which may also be one of the reasons for the appearance of different grain structures. Due to the particle-stimulated nucleation (PSN) mechanism, a large number of micron-sized second phases can induce dynamic recrystallization in the alloy and promote the nucleation of fine equiaxed grains. In short, the combined factors such as deformation temperature and precipitate phase distribution affected by changing the extrusion gradient lead to the trend of forming a bimodal grain structure.

[0042] from Figure 6 It can be seen that combined Figure 6 It can be clearly seen from the engineering stress curves at low temperature and room temperature and the data in Table 3 that as the temperature drops from room temperature to -180°C, the strength of the alloy gradually increases, and the plasticity of the alloy decreases at -100°C compared with room temperature, but relatively speaking, the plasticity decreases less, only 3.83%. When the temperature drops to -180°C, the plasticity of the alloy decreases by 11.81% compared with room temperature. In summary, the alloy material prepared by the SET process has a high low-temperature plasticity retention.

[0043] from Figure 7 It can be seen that combined Figure 7It can be clearly seen from the data of the engineering stress curve at high temperature of 200℃ and room temperature that as the temperature rises from room temperature to 200℃, the plasticity of the alloy at 200℃ increases significantly compared to room temperature, but relatively speaking, the strength decreases less, only decreasing by 25MPa. The plasticity of the alloy increases by 3.65% compared to room temperature. Overall, the alloy material prepared by the SET process has good high-temperature strength and plasticity.

[0044] The creep resistance of the alloy in Example 1 and the alloy after the SE process was tested. The creep temperature of the extruded alloy in Example 1 and the alloy after the SE process was set at 200°C and three sets of stresses of 200MPa, 150MPa and 100MPa were maintained for 100 hours to test the creep resistance. The creep deformation (%) and steady-state creep rate (S -1 ), the test results are shown in Table 1.

[0045] Table 1 Data results obtained when SE and SET process alloys were subjected to multiple sets of variable stress creep performance tests at 200°C.

[0046]

[0047] From the statistical results in Table 1, it can be seen that the WE43 alloy of the SET process shows less creep deformation and smaller steady-state creep rate under the three creep conditions of 200MPa, 150MPa and 100MPa set at 200℃. This is because compared with the SE process alloy, the coarse grain and fine grain regions in the mixed crystal structure of the SET process alloy have different degrees of accumulated dislocations during the deformation process. Under creep conditions, the two have different hindering effects on dislocation movement. The presence of fine grains effectively hinders dislocation movement and increases the yield strength, so that it can accept stress under higher creep conditions while reducing dislocation movement during creep, thereby improving creep resistance. However, too many fine grains will also promote the possibility of grain boundary sliding at high temperature, greatly reducing creep resistance. The presence of coarse grains can effectively reduce the number of grain boundaries, reduce the possibility of grain boundary sliding, and improve creep resistance. At the same time, the precipitated phase of the SET alloy is full of fine grains and coarse long grains, which can effectively hinder dislocation movement. When the creep mechanism is controlled by dislocation movement, its creep resistance is determined by the speed-limiting process of dislocations bypassing obstacles. When the dislocation line encounters a tiny second phase particle, it cannot continue to slide on the slip plane until the energy accumulates to a certain level, and the dislocation will climb to overcome the obstacle, resulting in creep deformation. At the same time, a large number of precipitated phases are distributed along the grain boundaries of coarse grains and fine grains, which will also pin the grain boundaries to a certain extent, making it more difficult to slide at the grain boundaries, increasing the energy required for creep, and improving creep resistance.

[0048] Table 2 shows the final average data results obtained after the SET process alloy was tested for creep resistance at 200 MPa and 200°C for 100 hours.

[0049]

[0050] The extruded alloy obtained in Example 1 was tested for instantaneous tensile properties at RT, -100°C and -180°C, and the corresponding stress-strain curves of the SET alloy from instantaneous tensile deformation to fracture under the three sets of temperature conditions were determined, and the yield strength, tensile strength and elongation data under the three sets of temperature conditions were obtained.

[0051] The results and characterization of three sets of low-temperature tensile properties tests, such as Figure 6 As shown in Table 3, the performance of SET alloy at room temperature RT is 248MPa of yield strength YS, 286MPa of ultimate tensile strength UTS, and 19.55% of elongation EL. When the temperature is lowered to -100℃, the performance is 300MPa of yield strength YS, 347MPa of ultimate tensile strength UTS, and 15.72% of elongation EL. When the temperature is lowered to -180℃, the performance is 340MPa of yield strength YS, 374MPa of ultimate tensile strength UTS, and 7.74% of elongation EL. The strength increases from room temperature to -100℃ and then to -180℃: YS increases by 55MPa and 92MPa, and UTS increases by 61MPa and 88MPa. The strength increases significantly at low temperatures. The plasticity retention rates from room temperature to -100℃ and then to -180℃ are 80.41% and 39.60% respectively. Within the range of -100℃, the plasticity decreases less and the plasticity retention is more obvious. When in the extreme low temperature environment of -180℃, the plasticity retention rate is still 39.60%, showing obvious toughness. Therefore, the alloy still retains good toughness and high strength in the extreme low temperature environment of -180℃.

[0052] Table 3 The final average data results of strength and plasticity corresponding to the engineering stress-strain curves of SET process alloys at room temperature (RT), -100°C, -180°C and 200°C.

[0053]

[0054] The present invention provides a magnesium alloy with high strength, plasticity and high creep performance in a wide temperature range and a preparation method. Through a unique variable gradient extrusion process (SET process), a heterogeneous microstructure is formed after solid solution extrusion, showing a significant technical effect. The heterogeneous distribution of coarse and long grains and fine grains not only significantly improves the yield strength of the material, enabling it to withstand creep stress at a higher yield strength, but also significantly improves the creep resistance by reducing grain boundary sliding. At the same time, the rare earth element-rich precipitate phase formed by the SET process, such as Mg 12 The Nd and Mg5Gd phases show excellent stability in low and high temperature environments, respectively, further enhancing the comprehensive performance of the material. Through multiple cycles of heating process, the distribution of the rare earth second phase is more uniform, and in combination with the heterogeneous microstructure, a stable matrix structure of a mixture of fine grains and coarse and long grains is constructed. The creep resistance of this type of alloy at 200°C and 200MPa is far superior to that of traditional process materials, and its steady-state creep rate is reduced by more than an order of magnitude. In addition, this process also expands the application scenarios of deformed magnesium alloys in low temperature environments, significantly improves the strength and plasticity retention rate of the alloy at low temperatures, and provides technical support for the widespread application of magnesium alloys in extreme environments.

Claims

1. A method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range, characterized in that: The following steps are involved: S1: homogenizing annealing the WE43 magnesium alloy, keeping the alloy warm during the homogenizing annealing process, pre-adding ferrous sulfide powder during the keeping process, taking the alloy out after keeping the alloy warm for 24 hours, and air cooling the alloy to obtain a homogenizing annealed material; S2: pre-treating the homogenized annealed material obtained in S1 to obtain a processed material, and performing a solid solution treatment in a holding furnace. During the solid solution treatment, ferrous sulfide powder is pre-placed in the holding furnace, and after the solid solution treatment, the material is taken out for quenching to obtain a solid solution treated material; S3: drying the material obtained in S2, placing it in a heat preservation furnace for heat preservation and preheating, and then performing gradient extrusion to obtain a material after gradient extrusion; S4: The material after gradient extrusion is quenched, dried, cyclically heated, and then kept warm to obtain a magnesium alloy with high strength, plasticity, and high creep properties in a wide temperature range.

2. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The temperature in the homogenization annealing described in S1 is 400° C. and the holding time is 24 h.

3. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The cylindrical sample described in S2 has a height of 30 mm and a diameter of 30 mm.

4. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The holding time described in S2 is 10 h.

5. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The holding temperature described in S3 is 400° C. and the holding time is 25 h.

6. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The extrusion temperature in the gradient extrusion process described in S3 is 400° C., the extrusion speed is 2 mm / s, the extrusion gradient is T2, the extrusion ratio is 9:1, and the diameter of the cylindrical sample is 10 mm.

7. The method for preparing a magnesium alloy with high strength, plasticity and creep performance in a wide temperature range according to claim 1, characterized in that: The heating temperature described in S4 is 250° C., the insulation time is 8 hours, and the number of cycle heating is 3 times.

8. A magnesium alloy with high strength, plasticity and creep properties in a wide temperature range obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The components and their mass percentages of the magnesium alloy material with high strength, plasticity and creep performance in a wide temperature range are 3.8% wt.Y, 2.1% wt.Nd, 0.61% wt.Gd, 0.5% wt.Zr and 0.089% wt.Zn, and the rest is Mg.

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