Rare earth magnesium alloy creep age forming method and application

Abstract

The invention provides a rare earth magnesium alloy creep age forming method and application, and the method comprises the following steps: (1) rare earth magnesium alloy is heated until the creep temperature is reached; (2) the rare earth magnesium alloy reaching the creep temperature is subjected to creep forming under first tensile stress; (3) carrying out aging treatment on the rare earth magnesium alloy under the conditions of creep temperature and first tensile stress; wherein in the step (1), the rare earth magnesium alloy is selected from any one of an Mg-9Gd rare earth magnesium alloy, an Mg-7. 5Gd <-1.5 > Y <-0.4 > Zr rare earth magnesium alloy and an Mg-7. 3Y <-2.9 > Nd <-1.0 > Gd <-0.5 > Zr rare earth magnesium alloy, and the creep temperature ranges from 200 DEG C to 240 DEG C; in the step (2), the first tensile stress ranges from 150 MPa to 250 MPa. According to the method, the formability of the rare earth magnesium alloy can be improved, the microstructure and the mechanical property of the alloy are optimized, and the strength and the plasticity of the alloy can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of forming and strengthening of metal materials, and particularly relates to a creep aging forming method and application of a rare earth magnesium alloy. Background Art

[0002] With the rapid development of high-end manufacturing industries such as aerospace, automotive, and electronics, the demand for high-performance magnesium alloy materials is increasing day by day. Magnesium alloys are widely used in lightweight structural materials due to their low density, high specific strength, good damping performance, and good machinability. However, the strength and creep resistance of traditional magnesium alloys are insufficient in high-temperature environments, which limits their application under higher temperatures and more complex working conditions. To meet the requirements of modern industries for high-performance magnesium alloys, it is particularly important to develop a magnesium alloy and its forming process that can maintain high strength and good creep resistance at high temperatures.

[0003] In recent years, rare earth elements have been widely used in magnesium alloys to improve their properties due to their unique physical and chemical properties. Adding rare earth elements (such as Gd, Y, Nd, etc.) to magnesium alloys can significantly improve their mechanical properties, corrosion resistance, and high-temperature stability. However, the forming process of rare earth magnesium alloys still faces challenges. Traditional forming methods (such as casting, forging, and extrusion) often have difficulty in simultaneously optimizing the microstructure and mechanical properties of the alloy, especially in high-temperature environments. In addition, traditional processes may result in higher residual stresses and non-uniform microstructures, thus affecting the final properties of the alloy.

[0004] Calcium can form intermetallic compounds with magnesium in magnesium alloys, such as Mg2Ca, etc. These compounds can play a role in precipitation strengthening, thereby improving the strength of the alloy. For example, in some rare earth magnesium alloys, after adding an appropriate amount of calcium, both the tensile strength and yield strength are significantly improved. CN117987708A discloses a magnesium gadolinium neodymium calcium zirconium alloy, which, by mass percentage, includes the following elemental components: gadolinium 3-6%, neodymium 0.5-2%, calcium 0.1-1.5%, zirconium 0.2-0.8%, and the balance is magnesium. In the present invention, by reducing the content of the heavy rare earth element gadolinium to less than 6 wt%, adding a small amount of lighter rare earth elements (neodymium) with lower density and inexpensive alkaline earth metal elements (calcium), and utilizing the synergistic effect of foreign elements, it is beneficial to reduce the solid solubility of each element in magnesium. Combining forward extrusion at a lower temperature and short-time creep aging treatment, it promotes the precipitation of nano-scale second phases, enables a large number of nano-scale second phases to be uniformly distributed in the magnesium matrix, promotes dynamic recrystallization, makes the structure more refined, enhances the mechanical properties of the magnesium alloy, and enables the magnesium gadolinium neodymium calcium zirconium alloy to have both high strength and high plasticity.

[0005] The aforementioned method is mainly aimed at rare earth magnesium alloys containing calcium, through the synergistic effect of two alien elements, namely rare earth elements and calcium, combined with forward extrusion at a relatively low temperature and short-time creep aging treatment. However, for rare earth magnesium alloys without calcium, how to significantly improve their formability while maintaining high strength remains an urgent problem to be solved. Summary of the Invention

[0006] The main object of the present invention is to provide a creep aging forming method and application for rare earth magnesium alloys, so as to solve the problems of poor formability and difficult processing of rare earth magnesium alloys without calcium under high strength conditions; the method of the present invention can simultaneously achieve creep flow and aging strengthening of magnesium alloys during the forming process, improve their plasticity and mechanical properties, and improve the forming accuracy and mechanical stability of components.

[0007] To achieve the above object, the present invention provides a creep aging forming method for rare earth magnesium alloys, comprising the following steps:

[0008] (1) Heat-treat the rare earth magnesium alloy until the creep temperature is reached;

[0009] (2) Perform creep forming on the rare earth magnesium alloy at the creep temperature under a first tensile stress;

[0010] (3) Under the creep temperature and the first tensile stress conditions, perform aging treatment on the rare earth magnesium alloy;

[0011] Wherein, in step (1), the rare earth magnesium alloy is selected from any one of Mg-9Gd rare earth magnesium alloy, Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and Mg-4.3Y-2.9Nd-1.0Gd-0.5Zr rare earth magnesium alloy, and the creep temperature is 200 - 240 °C;

[0012] In step (2), the first tensile stress is 150 - 250 MPa;

[0013] In step (3), the aging treatment time is 6 - 24 hours.

[0014] Further, in step (1), the conditions of the heat treatment further include: the heating rate is 1 - 10 °C / min.

[0015] Further, in step (2), the first tensile stress is 200 - 250 MPa.

[0016] Preferably, in step (2), the conditions of the creep forming further include: the loading rate of the first tensile stress is 10 - 20 N / s.

[0017] Further, in step (3), the aging treatment time is 10 - 24 hours.

[0018] Further, in step (3), the method further includes: after the aging treatment of the rare earth magnesium alloy is completed, unloading the first tensile stress.

[0019] Further, in step (3), the unloading rate of the first tensile stress is 50 - 200 N / s.

[0020] Further, the rare earth magnesium alloy is a Mg-9Gd rare earth magnesium alloy, the creep temperature is 220 - 230 °C, the first tensile stress is 200 - 225 MPa, and the aging treatment time is 6 - 12 hours.

[0021] Further, the rare earth magnesium alloy is a Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and the creep temperature is 200 - 205 °C, the first tensile stress is 240 - 250 MPa, and the aging treatment time is 20 - 22 hours.

[0022] The present invention also provides an application of the above-mentioned creep age forming method of rare earth magnesium alloy in the casting forming process, forging forming process or extrusion forming process of magnesium alloy.

[0023] The beneficial effects of the present invention are as follows:

[0024] The creep age forming method of rare earth magnesium alloy provided by the present invention is directed to several specific calcium-free rare earth magnesium alloys. During the creep process, by combining creep forming and aging strengthening treatment, optimizing and adjusting the process parameters of creep forming and aging treatment, the synergistic effect between the dynamic softening and aging strengthening of the alloy is realized. The creep forming stage promotes the grain boundary or dislocation strengthening of the alloy, while the aging treatment stage enhances the strength and hardness of the alloy by precipitating strengthening phases (such as Mg5Gd, Mg7Gd, Mg 24 Y5, Mg 12 Nd, etc.). It can be seen that the method of the present invention can not only improve the formability of calcium-free rare earth magnesium alloy, optimize the microstructure and mechanical properties of the alloy, but also significantly improve its strength and plasticity.

[0025] Compared with the traditional process, the method of the present invention can effectively improve the formability of the alloy, while maintaining high strength and good plasticity. In addition, the method of the present invention can also simplify the heat treatment process without reducing the performance. Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0027] Figure 1 This is the process route diagram of the creep age forming method of the rare earth magnesium alloy provided by the present invention.

[0028] Figure 2 These are the microstructure morphology diagrams of the rare earth magnesium alloy before and after creep age treatment in Example 2 and Comparative Example 2. Among them, (a1) is the crystal orientation distribution diagram of the sample before creep age in Example 2, (b1) is the crystal orientation distribution of the sample after creep age in Example 2, (a2) is the morphology diagram of the artificial aging precipitation phase in Comparative Example 2, and (b2) is the morphology diagram of the creep age precipitation phase in Comparative Example 2.

[0029] The realization of the object, functional characteristics, and advantages of the present invention will be further described with reference to the drawings in combination with the embodiments. Specific Embodiments

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] In addition, in the present invention, descriptions such as "first" and "second" are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] As described above, the present invention provides a creep age forming method for a rare earth magnesium alloy, including the following steps:

[0033] (1) Heat the rare earth magnesium alloy until the creep temperature is reached;

[0034] (2) Creep form the rare earth magnesium alloy that has reached the creep temperature under the first tensile stress;

[0035] (3) Under the conditions of the creep temperature and the first tensile stress, perform aging treatment on the rare earth magnesium alloy;

[0036] Wherein, in step (1), the rare earth magnesium alloy is selected from any one of Mg-9Gd rare earth magnesium alloy, Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and Mg-4.3Y-2.9Nd-1.0Gd-0.5Zr rare earth magnesium alloy, and the creep temperature is 200-240°C;

[0037] In step (2), the first tensile stress is 150-250 MPa;

[0038] In step (3), the aging treatment time is 6-24 hours.

[0039] When the creep temperature is too high, the nucleation and growth rates of the precipitation phases increase, which easily leads to coarsening of the precipitation phases, resulting in a decrease in the strength or plasticity of the alloy after creep aging; in addition, when the creep temperature is too high, the surface of the calcium-free rare earth magnesium alloy may be oxidized, reducing the surface quality of the component after creep aging; while when the creep temperature is too low, on the one hand, the nucleation rate of the precipitation phases decreases, and the precipitation of the precipitation phases is insufficient; on the other hand, dislocation movement is difficult, which may lead to dislocation pile-up, forming a large internal stress, and it is difficult to meet the requirements of the strength and toughness of the component; in addition, too low a temperature will reduce the actual creep amount of the component, greatly increasing the time cost of creep aging. In the present invention, the creep temperature can be, for example, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C or any value between 200-240°C. The inventors of the present invention have found through research that, combined with the performance characteristics of the calcium-free rare earth magnesium alloy, setting its creep temperature in the range of 200-240°C can better promote grain boundary or dislocation strengthening of the alloy, thereby significantly improving the mechanical properties such as the tensile strength and yield strength of the rare earth magnesium alloy, as well as improving the ductility and formability of the rare earth magnesium alloy.

[0040] Under different temperature and stress conditions, the creep mechanism of magnesium alloys will change. Through the synergistic effect of creep temperature and creep stress, the creep mechanism of rare earth magnesium alloys in this invention mainly focuses on dislocation slip. When the creep stress is too high, a large number of dislocations will proliferate and move inside the alloy, accelerating creep deformation and even leading to creep fracture, thus damaging the integrity of the component structure and performance; while when the creep stress is too low, the dislocation movement is insufficient, and the alloy mainly creeps through the diffusion mechanism, with relatively slow creep deformation, enabling the component to maintain good dimensional stability. However, long-term low-stress creep may cause the aggregation of vacancies inside the alloy, triggering crack initiation and propagation, thereby reducing the strength and toughness of the alloy after creep forming. The inventors of this invention found through research that setting the creep forming stress of several specific rare earth magnesium alloys selected in this invention within the range of 150 - 250 MPa and matching the creep temperature of 200 - 240 °C can obtain rare earth magnesium alloys with excellent mechanical properties such as tensile strength and yield strength.

[0041] The method of this invention is aimed at several specific calcium-free rare earth magnesium alloys. Through the synergistic effect of creep forming and aging treatment, the grain boundary or dislocation strengthening effect of rare earth magnesium alloys is enhanced. At the same time, by utilizing the precipitation orientation effect, the strength of the alloy is significantly improved. When the aging treatment time is too long, the precipitates coarsen and even undergo a structural transformation, changing from a metastable strengthening phase to a stable phase, thus resulting in a decrease in the strength and toughness of the alloy after creep aging; while when the aging treatment time is too short, the precipitates do not precipitate sufficiently, and the volume fraction and spatial distribution characteristics of the precipitates are difficult to meet the strength and toughness requirements of the alloy. The inventors of this application found through research that subjecting the specific rare earth magnesium alloys adopted in this invention to aging treatment under the action of a creep stress of 150 - 250 MPa at a creep temperature of 200 - 240 °C and controlling the aging treatment time within 6 - 24 hours can simultaneously achieve creep flow and aging strengthening of the magnesium alloy, further improving its plasticity and mechanical properties, thereby enhancing the forming accuracy and mechanical stability of magnesium alloy components.

[0042] In the process of creep forming of the method of this invention, through optimizing and adjusting the creep temperature, stress, and aging time, the synergistic effect between the dynamic softening and aging strengthening of the alloy is achieved. The creep stage promotes the grain boundary or dislocation strengthening of the alloy, while the aging stage enhances the strength and hardness of the alloy through the precipitation of strengthening phases (such as Mg5Gd, Mg7Gd, Mg 24 Y5, Mg 12 Nd, etc.).

[0043] In some specific embodiments, the rare earth element in the rare earth magnesium alloy is selected from at least one of Gd, Y, and Nd.

[0044] It should be noted that the three rare earth elements, Gd, Y, and Nd, all have significant effects on refining the grain size, improving the mechanical properties, and enhancing the microstructure of magnesium alloys. They significantly improve the comprehensive properties of magnesium alloys through mechanisms such as solid solution strengthening, precipitation strengthening, and inhibiting the formation of harmful phases. The specific effects of the aforementioned three rare earth elements on rare earth magnesium alloys are as follows:

[0045] The element Gd (gadolinium) is a rare earth element, silver-white in color, with strong magnetism and superconductivity at low temperatures. Adding the Gd element to magnesium alloys can have the following effects: (1) It can significantly refine the grain size of magnesium alloys and improve the microstructure of the alloys; (2) The addition of the Gd element can significantly increase the tensile strength and elongation of magnesium alloys; (3) The stable phases formed by the Gd element (such as the Al2Gd phase) can significantly improve the creep resistance of the alloys; (4) In Mg-Gd series alloys, the addition of Gd can promote the formation of age-precipitation phases (such as the β” phase), further increasing the strength of the alloys.

[0046] The element Y (yttrium) is a rare earth element, silver-gray in color, and is often used to make alloys, special glasses, electronics, and optical devices. The Y element can serve as the core of heterogeneous nucleation, significantly refining the grain size of magnesium alloys, thereby increasing the strength and toughness of the alloys. Adding the Y element to magnesium alloys can also significantly increase the tensile strength and yield strength of magnesium alloys; at the same time, the Y element can reduce the formation of coarse discontinuous phases (such as the Mg5(Gd, Y, Zn) phase) and promote the formation of beneficial LPSO (long-period stacking ordered) phases, further improving the high-temperature performance of the alloys. Moreover, the addition of the Y element can improve the thermal stability of the alloys, enabling them to exhibit better performance in high-temperature environments.

[0047] The element Nd (neodymium) is a rare earth element, silver-white in color, and is prone to oxidation in air. The Nd element can significantly refine the grain size of magnesium alloys, thereby increasing the strength and toughness of the alloys; adding the Nd element to magnesium alloys can significantly increase the tensile strength and yield strength of magnesium alloys and can also promote the formation of precipitation phases (such as the Mg 12 (Nd, Zn) phase), further increasing the strength of the alloys. At the same time, the Nd element can also transform the coarse continuous phase (such as the Mg 17 Al 12 phase) into fine discontinuous distributed phases, thereby improving the microstructure of the alloys.

[0048] It should be noted that the present invention does not particularly limit the types of rare earth magnesium alloys, and rare earth magnesium alloys well-known to those skilled in the art can be used. According to a particularly preferred specific embodiment, the rare earth magnesium alloy is selected from Mg-Gd series alloys, Mg-Y series alloys, Mg-Nd series alloys, or rare earth magnesium alloys composed of at least two of the rare earth elements Gd, Y, and Nd and Mg.

[0049] According to a particularly preferred specific embodiment, the rare earth magnesium alloy is selected from at least one of Mg-9Gd rare earth magnesium alloy, Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and Mg-4.3Y-2.9Nd-1.0Gd-0.5Zr rare earth magnesium alloy.

[0050] It should be noted that the above rare earth magnesium alloy used in the present invention can be obtained by purchasing from the market or can be prepared by conventional methods. Exemplarily, the preparation method of the rare earth magnesium alloy includes the following steps: adding pure magnesium ingot blanks into an electric resistance furnace, waiting for the magnesium ingots to completely melt and the furnace temperature to rise to 700-800 °C, and adding intermediate alloys such as Mg-30Gd, Mg-30Y, Mg-30Nd, and Mg-30Zr into the melt in turn under the protection of SF6 / CO2 mixed gas (volume ratio of 1:99) and MgCl2 flux; then introducing argon gas into the furnace body for refining and slag skimming, and starting to pour out the magnesium alloy ingot blanks after standing for about 1 h. After homogenization treatment, the magnesium alloy ingots can be directly subjected to creep aging forming; or after homogenization treatment, the billets are extruded and rolled into magnesium alloy plates and then subjected to creep aging.

[0051] According to a particularly preferred specific embodiment, in step (1), the conditions of the heat treatment further include: the heating rate is 1-10 °C / min. The heating rate can be, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min or any value between 1-10 °C / min.

[0052] According to a particularly preferred specific embodiment, in step (2), the first tensile stress is 200-250 MPa. Preferably, in step (3), the aging treatment time is 10-24 hours. The first tensile stress can be, for example, 200 MPa, 205 MPa, 210 MPa, 215 MPa, 220 MPa, 225 MPa, 230 MPa, 235 MPa, 240 MPa, 245 MPa, 250 MPa or any value between 200-250 MPa; the aging treatment time can be, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours or any value between 10-24 hours. The inventors found that by adopting the specific embodiment of this preferred case, a rare earth magnesium alloy with more excellent mechanical properties such as tensile strength and yield strength can be obtained.

[0053] According to a particularly preferred specific embodiment of the present invention, the rare earth magnesium alloy is a Mg-9Gd rare earth magnesium alloy, the creep temperature is 220-230°C, the first tensile stress is 200-225 MPa, and the aging treatment time is 6-12 hours. The inventors have found that in this preferred case, after creep aging forming of the Mg-9Gd rare earth magnesium alloy, not only can the elongation be improved, but also the mechanical properties such as the tensile strength and yield strength of the alloy can be greatly improved.

[0054] According to another particularly preferred specific embodiment of the present invention, the rare earth magnesium alloy is a Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, the creep temperature is 200-205°C, the first tensile stress is 240-250 MPa, and the aging treatment time is 20-22 hours. The inventors have found through research that by adopting the specific embodiment of this preferred case, compared with artificial aging, the strength and toughness of the alloy are synergistically improved.

[0055] In some specific embodiments, in step (2), the conditions for creep forming further include: the loading rate of the first tensile stress is 10-20 N / s. The loading rate can be, for example, 10 N / s, 11 N / s, 12 N / s, 13 N / s, 14 N / s, 15 N / s, 16 N / s, 17 N / s, 18 N / s, 19 N / s, 20 N / s or any value between 10-20.

[0056] According to a particularly preferred specific embodiment, in step (3), the method further includes: after the aging treatment of the rare earth magnesium alloy is completed, unloading the first tensile stress.

[0057] According to a particularly preferred specific embodiment, in step (3), the unloading rate of the first tensile stress is 50-200 N / s.

[0058] In some specific embodiments, in step (3), the method further includes: after the unloading of the first tensile stress is completed, cooling the rare earth magnesium alloy.

[0059] The present invention does not have a particular limitation on the cooling method, and the cooling methods well-known to those skilled in the art can be adopted, as long as the purpose of cooling to room temperature can be achieved. Exemplarily, in step (3), the method further includes: after the unloading of the first tensile stress is completed, air-cooling or water-cooling the rare earth magnesium alloy until it reaches room temperature.

[0060] The creep aging process route diagram of the rare earth magnesium alloy provided by the present invention is as Figure 1As shown, the creep temperature is controlled at 200 - 240 °C, and by controlling the stress during creep to be 150 - 250 MPa and the aging treatment time to be 6 - 24 hours, the collaborative preparation of the formability of rare earth magnesium alloy components is achieved. The method of the present invention can improve the comprehensive properties of rare earth magnesium alloys, including enhancing the ductility and formability of the alloy. Compared with conventional artificial aging, creep aging can achieve a higher strengthening effect for rare earth magnesium alloys.

[0061] The present invention also provides an application of the above-mentioned creep aging forming method of rare earth magnesium alloy in the casting forming process, forging forming process or extrusion forming process of magnesium alloy.

[0062] The present invention will be described in detail below through examples. In the following examples, without special instructions, various raw materials and instruments used are commercially available products.

[0063] Example 1

[0064] This example provides a creep aging forming method for rare earth magnesium alloy, wherein the type of rare earth magnesium alloy is Mg - 9Gd rare earth magnesium alloy; specifically includes the following steps:

[0065] At a heating rate of 5 °C / min, the Mg - 9Gd rare earth magnesium alloy is heated to 225 °C, and then a first tensile stress of 225 MPa is applied at a loading rate of 10 N / s for creep forming; under the conditions of a temperature of 225 °C and a first tensile stress of 225 MPa, the Mg - 9Gd rare earth magnesium alloy is subjected to aging treatment for 10 hours. After the aging treatment is completed, the first tensile stress is unloaded at an unloading rate of 50 N / s, and the Mg - 9Gd rare earth magnesium alloy sample is naturally cooled to room temperature.

[0066] Comparative Example 1

[0067] This comparative example is carried out according to the method of Example 1, the difference being that: no first tensile stress is applied, that is, artificial aging treatment is adopted; specifically includes the following steps:

[0068] At a heating rate of 5 °C / min, the Mg - 9Gd rare earth magnesium alloy is heated to 225 °C, and under the condition of a temperature of 225 °C, the Mg - 9Gd rare earth magnesium alloy is subjected to aging treatment for 10 hours. After the aging treatment is completed, the Mg - 9Gd rare earth magnesium alloy sample is naturally cooled to room temperature.

[0069] Example 2

[0070] This example provides a creep aging forming method for rare earth magnesium alloy, wherein the type of rare earth magnesium alloy is Mg - 7.5Gd - 1.5Y - 0.4Zr; specifically includes the following steps:

[0071] The Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy was heated to 200°C at a heating rate of 10°C / min, and then a first tensile stress of 250 MPa was applied at a loading rate of 15 N / s for creep forming; under the conditions of a temperature of 200°C and a first tensile stress of 250 MPa, the Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy was subjected to aging treatment for 21 hours. After the aging treatment was completed, the first tensile stress was unloaded at an unloading rate of 70 N / s, and the Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy sample was naturally cooled to room temperature.

[0072] Comparative Example 2

[0073] This comparative example was carried out according to the method of Example 2, the difference being that: no first tensile stress was applied, that is, artificial aging treatment was used; it specifically included the following steps:

[0074] The Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy was heated to 200°C at a heating rate of 10°C / min. Under the condition of a temperature of 200°C, the Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy was subjected to aging treatment for 21 hours. After the aging treatment was completed, the Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy sample was naturally cooled to room temperature.

[0075] Example 3

[0076] This example provides a creep aging forming method for a rare earth magnesium alloy, which was carried out according to the method of Example 1, the difference being that: the aging treatment time was 12 hours.

[0077] Example 4

[0078] This example provides a creep aging forming method for a rare earth magnesium alloy, which was carried out according to the method of Example 1, the difference being that: the aging treatment time was 7.5 hours.

[0079] Example 5

[0080] This example provides a creep aging forming method for a rare earth magnesium alloy, which was carried out according to the method of Example 1, the difference being that: the first tensile stress was 150 MPa.

[0081] Comparative Example 3

[0082] This comparative example provides a creep aging forming method for a rare earth magnesium alloy, which was carried out according to the method of Example 1, the difference being that: the aging treatment time was 5 hours.

[0083] Comparative Example 4

[0084] This comparative example provides a creep age forming method for rare earth magnesium alloy, which is carried out with reference to the method of Example 1, except that: the first tensile stress is 75 MPa.

[0085] Comparative Example 5

[0086] This comparative example provides a creep age forming method for rare earth magnesium alloy, which is carried out with reference to the method of Example 1, except that: the type of rare earth magnesium alloy is the extrusion specimen obtained in Example 1 of CN117987708A.

[0087] Analysis Example 1

[0088] The rare earth magnesium alloy samples obtained after creep age forming in the examples and comparative examples are subjected to performance testing. The untreated Mg-9Gd rare earth magnesium alloy in Example 1 is used as the control group. The performance testing includes performance testing such as tensile strength, yield strength and elongation rate. The specific test results are shown in Table 1.

[0089] Among them, the test method for tensile strength is: GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature";

[0090] The test method for yield strength is: GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature";

[0091] The test method for elongation rate is: GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0092] Table 1

[0093]

[0094]

[0095] By comparing the control group, Example 1 and Comparative Example 1, it can be seen that the rare earth magnesium alloy after aging treatment has obvious improvements in both strength and plasticity; specifically, by comparing Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, it can be seen that compared with conventional artificial aging, the properties such as tensile strength, yield strength and elongation rate of the rare earth magnesium alloy after creep forming have obvious improvements. It can be seen that the calcium-free rare earth magnesium alloy treated by the method of the present invention shows higher strength and plasticity.

[0096] By comparing Example 1, Examples 3 - 5, and Comparative Examples 3 - 4, it can be seen that the method of the present invention synchronously realizes creep flow and age hardening of magnesium alloys during the forming process by specifically adjusting the creep temperature, stress, and aging time. Through the synergistic effect between the dynamic softening and age hardening of the alloy, the strengthening effect of grain boundaries or dislocations of rare earth magnesium alloys is enhanced. At the same time, by utilizing the precipitation orientation effect, the strength and toughness of the alloy are significantly improved.

[0097] By comparing Example 1 and Comparative Example 5, it can be seen that the present invention combines creep forming and age hardening treatment, and optimizes and adjusts the process parameters of creep forming and age treatment during the creep process, which is very beneficial to improving the formability of calcium-free rare earth magnesium alloys and can also significantly enhance their strength and plasticity. When the method of the present invention is used to treat the magnesium gadolinium neodymium calcium alloy containing calcium, it may promote the precipitation and aggregation of the second phase (such as calcium compounds) in the alloy, and also cause a large number of dislocations to be generated inside the alloy, increasing the dislocation density, thereby triggering plastic deformation and crack initiation, and also affecting the mechanical properties of the alloy.

[0098] Analysis Example 2

[0099] Observe the microstructure morphology diagrams of rare earth magnesium alloys before and after creep aging treatment in Example 2 and Comparative Example 2. The specific results are shown in Figure 2 。

[0100] In Figure 2 , (a1) is the crystal orientation distribution diagram of the sample before creep aging in Example 2, (b1) is the crystal orientation distribution of the sample after creep aging in Example 2, (a2) is the morphology diagram of the artificial aging precipitation phase in Comparative Example 2, and (b2) is the morphology diagram of the creep aging precipitation phase in Comparative Example 2.

[0101] By comparing the crystal orientation evolution of rare earth magnesium alloys before and after creep aging and the morphological differences of precipitation phases between artificial aging and creep aging, it can be seen that after the rare earth magnesium alloy is treated by the creep aging process of the present invention, there is indeed a precipitation orientation effect, thereby effectively improving the ductility and strength of the rare earth magnesium alloy.

[0102] It should be noted that in this article, the terms "including", "comprising", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article, or device.

[0103] In the above technical solution of the present invention, the above is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A creep age forming method for rare earth magnesium alloy, characterized in that It includes the following steps: (1) Heat the rare earth magnesium alloy until it reaches the creep temperature; (2) Perform creep forming on the rare earth magnesium alloy that has reached the creep temperature under a first tensile stress; (3) Under the conditions of the creep temperature and the first tensile stress, perform aging treatment on the rare earth magnesium alloy; Wherein, in step (1), the rare earth magnesium alloy is selected from any one of Mg-9Gd rare earth magnesium alloy, Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and Mg-4.3Y-2.9Nd-1.0Gd-0.5Zr rare earth magnesium alloy, and the creep temperature is 200-240 °C; In step (2), the first tensile stress is 150-250 MPa; In step (3), the aging treatment time is 6-24 hours.

2. The creep age forming method of rare earth magnesium alloy according to claim 1, characterized in that, In step (1), the conditions of the heat treatment further include: the heating rate is 1-10 °C / min.

3. The creep age forming method of rare earth magnesium alloy according to claim 1, characterized in that In step (2), the first tensile stress is 200-250 MPa.

4. The creep age forming method of the rare earth magnesium alloy according to claim 3, characterized in that In step (2), the conditions of the creep forming further include: the loading rate of the first tensile stress is 10-20 N / s.

5. The creep age forming method of rare earth magnesium alloy according to claim 1, characterized in that In step (3), the aging treatment time is 10-24 hours.

6. The creep age forming method of the rare earth magnesium alloy according to claim 1, characterized in that, In step (3), the method further includes: after the aging treatment of the rare earth magnesium alloy is completed, unload the first tensile stress.

7. The creep age forming method of rare earth magnesium alloy according to claim 6, characterized in that, In step (3), the unloading rate of the first tensile stress is 50-200 N / s.

8. The creep age forming method of rare earth magnesium alloy according to any one of claims 1-7, characterized in that, The rare earth magnesium alloy is Mg-9Gd rare earth magnesium alloy, the creep temperature is 220-230 °C, the first tensile stress is 200-225 MPa, and the aging treatment time is 6-12 hours.

9. The creep age forming method of rare earth magnesium alloy according to any one of claims 1-7, characterized in that, The rare earth magnesium alloy is Mg-7.5Gd-1.5Y-0.4Zr rare earth magnesium alloy, and the creep temperature is 200-205 °C, the first tensile stress is 240-250 MPa, and the aging treatment time is 20-22 hours.

10. Application of the creep aging forming method of the rare earth magnesium alloy according to any one of claims 1-9 in the casting forming process, forging forming process or extrusion forming process of magnesium alloys.

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