Method for improving performance of double-phase magnesium-lithium alloy through extrusion deformation

Abstract

The invention relates to the field of alloy materials, and discloses a method for improving the performance of a double-phase magnesium-lithium alloy through extrusion deformation, which comprises the following steps: S1, ingot smelting: weighing raw materials for smelting according to the proportion of chemical components in the magnesium-lithium alloy, and then casting to obtain a magnesium-lithium alloy ingot; step S2, homogenizing heat treatment: cutting a cylindrical sample from the magnesium-lithium alloy ingot, carrying out heat treatment, and immediately putting the cylindrical sample into water for quenching after heat treatment is completed; and S3, extrusion: putting the sample subjected to heat treatment and the extrusion die into a heat treatment furnace for preheating, coating a graphite lubricant after preheating is completed, putting the sample and the extrusion die on an extruder, extruding a magnesium-lithium alloy bar, and immediately putting the extruded bar into water at the temperature of 15-25 DEG C for quenching. And moreover, the method is simple and easy to operate, the efficiency can be improved, and the production cost can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of alloy materials, and in particular to a method for improving the performance of a dual-phase magnesium-lithium alloy through extrusion deformation. Background Art

[0002] In response to the requirements of the era of environmental protection and energy conservation, industrial production applications have begun to focus on lightweight materials, with an eye on the development of lightweight materials to replace steel. Magnesium alloy, as one of the representatives of lightweight materials, has become a research hotspot at this stage. The density of magnesium alloy is 1.738g / cm 3 , about 2 / 3 of aluminum, 2 / 5 of titanium, and 1 / 4 of steel. At the same time, magnesium alloys have the advantages of high specific strength, high specific stiffness, good damping and shock absorption, and easy processing. It is mainly used in aerospace, 3C electronic products, automotive components, etc. However, magnesium alloys have a close-packed hexagonal structure and poor plasticity at room temperature. Studies have found that adding Li to magnesium alloys can further reduce the density of magnesium alloys, and Li has a body-centered hexagonal structure, which can activate more slip systems at room temperature. In addition, the crystal structure of magnesium-lithium alloys also changes significantly after adding different amounts of Li. When the Li content is lower than 5.7wt.%, the alloy maintains the hcp structure, and the matrix at this time is called α-Mg; when the Li addition amount is 5.7-10.3wt.%, the eutectic structure of α-Mg+β-Li appears in the cast alloy after solidification, and the structure of β-Li is bcc. In this composition range, the volume fraction of β-Li increases with the increase of Li content. The plasticity of the alloy increases with the increase of the volume fraction of β-Li, but the strength shows a downward trend; when the Li content is greater than 10.3wt.%, β-Li completely replaces α-Mg in the solidified cast alloy, and the volume fraction of β-Li remains at 100% with the increase of Li content. At this time, the density of the alloy is further reduced, and the plasticity is also improved [Peng Xiang, Liu Wencai, Wu Guohua. Alloying and Application of Magnesium-Lithium Alloys [J]. Journal of the Chinese Society of Nonferrous Metals. 2021, 31(11): 3024-3043]. While magnesium-lithium alloys have excellent properties such as ultra-lightweight, high specific strength and room temperature plastic processing capabilities, they also have problems such as insufficient strength, poor corrosion resistance and wear resistance, and face a series of challenges in practical applications. The current ways to improve these problems mainly include alloying, heat treatment, and plastic processing.

[0003] Among them, plastic deformation processing methods are widely used to improve and enhance the mechanical properties of materials, mainly because: alloying needs to rely on element addition to achieve strengthening effects, which may increase the density of the alloy due to the addition of elements, and also increase the complexity of the preparation process; heat treatment has high energy consumption and complex processes; in comparison, plastic processing does not change the alloy composition, can ensure lightweight requirements, and the process is simple, suitable for large-scale applications, and can be combined with alloying and heat treatment to achieve multi-scale strengthening. At present, the main plastic processing methods are extrusion, forging, rolling, etc., among which extrusion has been widely used as the most traditional processing method. For example, the article "Microstructure and strengthening mechanism of hot-extruded ultralight Mg-Li-Al-Sn alloys with high strength" published in Volume 103 of Journal of Materials Science & Technology in 2022 pointed out that the Mg-7Li-2Al-1.5Sn alloy was extruded at an extrusion temperature of 533K, so that the yield strength, tensile strength and elongation of the alloy reached 250MPa, 324MPa and 11.9% respectively. [Zhou G., Yang Y., Zhang HZ, Hu FP, et al., Microstructure and strengthening mechanism of hot-extruded ultralight Mg-Li-Al-Sn alloys with high strength [J]. Journal of Materials Science & Technology, 2022, 103: 186-196]. In the patent "An ultralight high-strength microalloyed magnesium-lithium alloy and its low-temperature extrusion forming process" (publication number CN117965981A), an ultralight high-strength microalloyed magnesium-lithium alloy and its low-temperature extrusion forming process are disclosed. Through low-temperature extrusion, the further growth of dynamic recrystallization grains is avoided, the extrusion forming performance of the alloy is improved, and high-strength and tough magnesium extrusion parts with tensile strength ≥ 303MPa and elongation ≥ 8% are successfully prepared. The patent "A lightweight and high-strength magnesium-lithium alloy plate and its preparation method" (publication number CN118563188A) discloses a lightweight and high-strength magnesium-lithium alloy plate and its preparation method. After large deformation by extrusion or forging, the alloy is deformed by online heating and rolling to improve the plasticity and strength of the alloy. A lightweight and high-strength magnesium-lithium alloy plate is prepared, with a yield strength of 200-240MPa, a tensile strength of 220-270Mpa, and an elongation of 20-40%.The patent "A method for preparing an ultra-light and highly plastic magnesium-lithium alloy rod" (publication number CN118957330A) discloses a method for preparing an ultra-light and highly plastic magnesium-lithium alloy rod, which is composed of the following components: Li: 8%-14%, Zn: 4%-8%, Y: 0.5%-2.5%, and the balance is Mg. The patent synergistically improves the mechanical properties of the magnesium-lithium alloy by extrusion and forging, and obtains a density of no more than 1.70g / cm. 2 , ultra-light and high-plastic magnesium-lithium alloy bars with a yield strength of not less than 154MPa, a tensile strength of not less than 194MPa, and an elongation of not less than 51.5%.

[0004] Among the existing technologies for improving the mechanical properties of magnesium-lithium alloys through extrusion deformation, some technologies cannot effectively improve the comprehensive mechanical properties of the alloys. Even if some technologies can synergistically improve the strength and plasticity of magnesium-lithium alloys, most of them use composite technologies, such as extrusion and rolling, extrusion and forging, extrusion, forging and rolling, etc. These technologies generally have problems such as complex processes, long processing time, and high production costs. In comparison, it is of great practical value to develop a processing technology that is simple and easy to operate and synergistically improves the strength and plasticity of magnesium-lithium alloys. Based on this, the present invention proposes a method for improving the performance of dual-phase magnesium-lithium alloys through extrusion deformation. Summary of the invention

[0005] The object of the present invention is to provide a method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation, comprising the following steps:

[0007] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy, lithium strip, industrial pure magnesium, aluminum ingot, magnesium-yttrium master alloy, and magnesium-gadolinium alloy are weighed respectively, stacked in sequence and placed in an electric arc furnace, and smelted under the protection of high-purity argon gas. The smelting process is repeated at least 3 times, and finally a magnesium-lithium alloy ingot is cast;

[0008] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot, the cylindrical sample is wrapped with tin foil, and buried in sand for heat treatment. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0009] Step S3, extrusion: the heat-treated sample and the extrusion die are placed in a heat treatment furnace for preheating. After the preheating is completed, the sample and the die are immediately taken out from the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started to extrude a magnesium-lithium alloy rod with a diameter of 11.5 mm. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching.

[0010] Preferably, the purity of the magnesium ingot, lithium ingot and aluminum ingot in step S1 is 99.95-99.99%.

[0011] Preferably, in step S1, the mass percentages of the elements in the magnesium-lithium alloy are: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.% and the balance Mg, and the total amount of each component is 100%.

[0012] Preferably, the heat treatment process in step S2 is performed at 300° C. for 4 hours.

[0013] As a preferred embodiment, in the preferred extrusion deformation process in step S3, the preheating temperature is set to 200-400° C., and the holding time is 30 minutes.

[0014] Preferably, the extrusion speed used for the extrusion deformation in S3 is 10 mm / s, and the extrusion ratio is 11.5:1.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1) The extrusion deformation technology proposed in the present invention can eliminate defects such as pores and shrinkage generated during the casting process. In addition, the extrusion deformation can improve the composition uniformity of the alloy through uniform plastic flow;

[0017] 2) The present invention adopts extrusion deformation technology to break up the Al2(Gd, Y) second phase originally distributed at the phase boundary, so that it is dispersed at the phase boundary. Al2(Y, Gd) is distributed at the phase boundary as a hard phase, which not only acts on the matrix of the phase boundary, but also hinders the movement of dislocations at the phase boundary, thereby producing a strengthening effect and greatly improving the comprehensive mechanical properties of the magnesium-lithium alloy.

[0018] 3) The present invention uses extrusion deformation technology to make the alloy undergo a large degree of plastic deformation. During the deformation, the second phase is refined, the α-Mg phase is elongated, and dynamic recrystallization occurs in the β-Li phase. In addition, as the extrusion temperature changes, the dynamic recrystallization grains are gradually refined. Grain refinement strengthens the plasticity and strength of the magnesium alloy to a certain extent;

[0019] 4) The comprehensive mechanical properties of the magnesium-lithium alloy obtained by the present invention are significantly improved, with a yield strength of 250Mpa-320Mpa, a tensile strength of 280Mpa-350Mpa, and an elongation of 18%-25%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention;

[0021] Figure 2 It is the OM diagram of magnesium-lithium alloy without extrusion treatment and after extrusion deformation treatment at different temperatures;

[0022] Figure 3 It is the XRD diagram of magnesium-lithium alloy without extrusion treatment and after extrusion deformation treatment at different temperatures;

[0023] Figure 4 These are the tensile stress-strain curves of magnesium-lithium alloy specimens without extrusion treatment and after extrusion deformation treatment at different temperatures. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0025] Example

[0026] See also Figure 1 , a method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation as shown in the figure comprises the following steps:

[0027] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy (the mass percentage of each element is: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.%, the balance is Mg, and the total amount of each component is 100%), lithium strip (purity is 99.99%), industrial pure magnesium (purity is 99.95%), aluminum ingot (purity is 99.99%), magnesium-yttrium master alloy, magnesium-gadolinium alloy are weighed respectively and stacked in sequence into an electric arc furnace, and smelted under the protection of high-purity argon gas. To ensure the uniformity of the alloy, the smelting process is repeated for no less than 3 times, and finally cast to obtain a magnesium-lithium alloy ingot;

[0028] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot obtained in step S1, the sample is wrapped with tin foil, and buried in sand for heat treatment at a temperature of 300° C. for 4 hours. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0029] Step S3, extrusion: the sample and the extrusion die after the heat treatment in step S2 are placed in a heat treatment furnace for preheating to avoid cracks in the sample during extrusion. The preheating temperature is 200°C-400°C, and the preheating time is 30 minutes. After the preheating is completed, the sample and the die are immediately taken out from the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started. The extrusion speed is 10 mm / s, the extrusion ratio is 11.5:1, and the magnesium alloy rod with a diameter of 11.5 mm is extruded. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching.

[0030] The magnesium-lithium alloy after extrusion deformation obtained by the above method of the present invention is subjected to mechanical property testing, and the testing method is as follows:

[0031] The magnesium-lithium alloy without extrusion treatment and after extrusion deformation treatment was subjected to electric spark cutting to obtain tensile specimens. The specimens were subjected to tensile testing using a universal mechanical testing machine to obtain the tensile stress-strain curve of the specimens, and then the mechanical properties such as yield strength, tensile strength and elongation of the specimens were obtained. During all tensile tests, an extensometer (Epsilon 3442) with a gauge length of 10 mm was used, the maximum experimental load was 100 kN, and the tensile rate was 0.5 mm / min.

[0032] The present invention is described below by means of specific examples. It will be understood by those skilled in the art that the following specific examples are only for the purpose of illustration and do not limit the scope of the present invention in any way. In addition, in the following examples, unless otherwise specified, the reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained commercially. The units used in this specification are all international standard units, and the numerical values ​​and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production. If the specific processing conditions and processing methods are not clearly described in the following examples, the conditions and methods known in the art can be used for processing.

[0033] Comparative Example

[0034] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy (the mass percentage of each element is: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.%, the balance is Mg, and the total amount of each component is 100%), lithium strip (purity is 99.99%), industrial pure magnesium (purity is 99.95%), aluminum ingot (purity is 99.99%), magnesium-yttrium master alloy, magnesium-gadolinium alloy are weighed respectively and stacked in sequence into an electric arc furnace, and smelted under the protection of high-purity argon gas. To ensure the uniformity of the alloy, the smelting process is repeated for no less than 3 times, and finally cast to obtain a magnesium-lithium alloy ingot;

[0035] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot obtained in step S1, the sample is wrapped with tin foil, and buried in sand for heat treatment at a temperature of 300° C. for 4 hours. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0036] Step S3, the sample after homogenization heat treatment in step S2 is subjected to electric spark cutting to obtain a tensile sample, and the sample is subjected to a tensile test by a universal mechanical testing machine. During all tensile tests, an extensometer (Epsilon3442) with a gauge length of 10 mm is used, the maximum experimental load is 100 kN, and the tensile rate is 0.5 mm / min.

[0037] The tensile stress-strain curves of the corresponding specimens are shown in the attached figure. Figure 4 As shown (marked as-homogeneous), the tensile strength of the sample is 296 MPa, the yield strength is 256 MPa, and the elongation is 22% obtained from the tensile stress-strain curve.

[0038] Example 1

[0039] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy (the mass percentage of each element is: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.%, the balance is Mg, and the total amount of each component is 100%), lithium strip (purity is 99.99%), industrial pure magnesium (purity is 99.95%), aluminum ingot (purity is 99.99%), magnesium-yttrium master alloy, magnesium-gadolinium alloy are weighed respectively and stacked in sequence into an electric arc furnace, and smelted under the protection of high-purity argon gas. To ensure the uniformity of the alloy, the smelting process is repeated for no less than 3 times, and finally cast to obtain a magnesium-lithium alloy ingot;

[0040] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot obtained in step S1, the sample is wrapped with tin foil, and buried in sand for heat treatment at a temperature of 300° C. for 4 hours. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0041] Step S3, extrusion: the sample and the extrusion die after the heat treatment in step S2 are placed in a heat treatment furnace for preheating to avoid cracks in the sample during extrusion. The preheating temperature is set to 250°C and the preheating time is 30 minutes. After the preheating is completed, the sample and the die are immediately taken out of the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started. The extrusion speed is 10 mm / s, the extrusion ratio is 11.5:1, and the magnesium alloy rod with a diameter of 11.5 mm is extruded. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching;

[0042] Step S4, the magnesium-lithium alloy rod after extrusion deformation in step S3 is subjected to electric spark cutting to obtain a tensile specimen, and the specimen is subjected to a tensile test by a universal mechanical testing machine. During all tensile tests, an extensometer (Epsilon3442) with a gauge length of 10 mm is used, the maximum experimental load is 100 kN, and the tensile rate is 0.5 mm / min.

[0043] The tensile stress-strain curves of the corresponding specimens are shown in the attached figure. Figure 4 As shown (marked as-extruded-250°C), the tensile strength of the sample is 303 MPa, the yield strength is 266 MPa, and the elongation is 25% obtained from the tensile stress-strain curve.

[0044] Example 2

[0045] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy (the mass percentage of each element is: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.%, the balance is Mg, and the total amount of each component is 100%), lithium strip (purity is 99.99%), industrial pure magnesium (purity is 99.95%), aluminum ingot (purity is 99.99%), magnesium-yttrium master alloy, magnesium-gadolinium alloy are weighed respectively and stacked in sequence into an electric arc furnace, and smelted under the protection of high-purity argon gas. To ensure the uniformity of the alloy, the smelting process is repeated for no less than 3 times, and finally cast to obtain a magnesium-lithium alloy ingot;

[0046] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot obtained in step S1, the sample is wrapped with tin foil, and buried in sand for heat treatment at a temperature of 300° C. for 4 hours. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0047] Step S3, extrusion: the sample and the extrusion die after the heat treatment in step S2 are placed in a heat treatment furnace for preheating to avoid cracks in the sample during extrusion. The preheating temperature is set to 300°C and the preheating time is 30 minutes. After the preheating is completed, the sample and the die are immediately taken out of the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started. The extrusion speed is 10 mm / s, the extrusion ratio is 11.5:1, and the magnesium alloy rod with a diameter of 11.5 mm is extruded. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching;

[0048] Step S4, the magnesium-lithium alloy rod after extrusion deformation in step S3 is subjected to electric spark cutting to obtain a tensile specimen, and the specimen is subjected to a tensile test by a universal mechanical testing machine. During all tensile tests, an extensometer (Epsilon3442) with a gauge length of 10 mm is used, the maximum experimental load is 100 kN, and the tensile rate is 0.5 mm / min.

[0049] The tensile stress-strain curves of the corresponding specimens are shown in the attached figure. Figure 4 As shown (marked as-extruded-300°C), the tensile strength of the sample is 312 MPa, the yield strength is 274 MPa, and the elongation is 22% obtained from the tensile stress-strain curve.

[0050] Example 3

[0051] Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy (the mass percentage of each element is: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.%, the balance is Mg, and the total amount of each component is 100%), lithium strip (purity is 99.99%), industrial pure magnesium (purity is 99.95%), aluminum ingot (purity is 99.99%), magnesium-yttrium master alloy, magnesium-gadolinium alloy are weighed respectively and stacked in sequence into an electric arc furnace, and smelted under the protection of high-purity argon gas. To ensure the uniformity of the alloy, the smelting process is repeated for no less than 3 times, and finally cast to obtain a magnesium-lithium alloy ingot;

[0052] Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot obtained in step S1, the sample is wrapped with tin foil, and buried in sand for heat treatment at a temperature of 300° C. for 4 hours. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching;

[0053] Step S3, extrusion: the sample and the extrusion die after the heat treatment in step S2 are placed in a heat treatment furnace for preheating to avoid cracks in the sample during extrusion. The preheating temperature is set to 350°C and the preheating time is 30 minutes. After the preheating is completed, the sample and the die are immediately taken out of the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started. The extrusion speed is 10 mm / s, the extrusion ratio is 11.5:1, and the magnesium alloy rod with a diameter of 11.5 mm is extruded. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching;

[0054] Step S4, the magnesium-lithium alloy rod after extrusion deformation in step S3 is subjected to electric spark cutting to obtain a tensile specimen, and the specimen is subjected to a tensile test by a universal mechanical testing machine. During all tensile tests, an extensometer (Epsilon3442) with a gauge length of 10 mm is used, the maximum experimental load is 100 kN, and the tensile rate is 0.5 mm / min.

[0055] The tensile stress-strain curves of the corresponding specimens are shown in the attached figure. Figure 4 As shown (marked as-extruded-350°C), the tensile strength of the sample is 355 MPa, the yield strength is 325 MPa, and the elongation is 18% obtained from the tensile stress-strain curve.

[0056] It can be clearly seen that compared with the magnesium-lithium alloy without extrusion deformation, the magnesium-lithium alloy deformed by hot extrusion has significantly increased yield strength and tensile strength while maintaining high elongation, and as the extrusion temperature increases from 250°C to 350°C, the yield strength and tensile strength of the alloy gradually increase. When the extrusion temperature is 350°C, the strength of the magnesium-lithium alloy obtained is the highest. The extrusion deformation method proposed in the present invention significantly improves the comprehensive mechanical properties of the magnesium-lithium alloy.

[0057] The reasons for the improvement of mechanical properties of magnesium-lithium alloy after extrusion deformation can be combined with Figure 2 OM diagram of magnesium-lithium alloy without extrusion and after extrusion deformation treatment, and Figure 3 The XRD spectrum shown is further analyzed. Figure 2 It can be observed that the alloy is mainly composed of two matrix phases, α-Mg phase, β-Li phase and black granular second phase Al 2 (Gd, Y) composition, combined Figure 3It can be inferred that the phase composition of the alloy did not change significantly after extrusion deformation. Figure 2 It can also be clearly seen that with the increase of extrusion temperature, the α-Mg phase gradually elongates along the extrusion direction, the second phase breaks and is more evenly distributed in the phase boundary, and the dynamic recrystallization grains in the β-Li phase gradually become smaller. The second phase Al2 (Gd, Y) is a hard phase, which is evenly distributed in the phase boundary and can hinder the movement of dislocations during deformation, thereby playing a role in second phase strengthening. On the other hand, during the deformation process, dynamic recrystallization occurs in the β-Li phase of the alloy, and the dynamic recrystallization grains gradually become smaller as the deformation temperature increases. According to the Hall-Petch formula, the strength increases with the decrease of grain size, and the smaller the grain, the more grain boundaries there are. During deformation, multiple grains participate in sliding synergistically, which can reduce local stress concentration and improve plasticity. Therefore, under the combined effect of second phase strengthening and fine grain strengthening, the comprehensive mechanical properties of the alloy are improved. When the extrusion deformation temperature is 350℃, the room temperature tensile properties of the deformed alloy obtained are the best, with a tensile strength of 355Mpa, a yield strength of 325Mpa, and an elongation of 18%.

[0058] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation, characterized in that: The steps include: Step S1, ingot smelting: according to the chemical composition ratio of the magnesium-lithium alloy, lithium strip, industrial pure magnesium, aluminum ingot, magnesium-yttrium master alloy, and magnesium-gadolinium alloy are weighed respectively, stacked in sequence and placed in an electric arc furnace, and smelted under the protection of high-purity argon gas. The smelting process is repeated at least 3 times, and finally a magnesium-lithium alloy ingot is cast; Step S2, homogenization heat treatment: a cylindrical sample with a diameter of 39 mm and a height of 23 mm is cut from the magnesium-lithium alloy ingot, the cylindrical sample is wrapped with tin foil, and buried in sand for heat treatment. After the heat treatment is completed, the sample is immediately placed in water at a temperature of 15-25° C. for quenching; Step S3, extrusion: the heat-treated sample and the extrusion die are placed in a heat treatment furnace for preheating. After the preheating is completed, the sample and the die are immediately taken out from the heat treatment furnace, coated with graphite lubricant and placed on the extruder, and then the extruder is started to extrude a magnesium-lithium alloy rod with a diameter of 11.5 mm. The extruded rod is immediately placed in water at a temperature of 15-25°C for quenching.

2. The method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation according to claim 1, characterized in that: In step S1, the purity of the magnesium ingot, lithium ingot and aluminum ingot is 99.95-99.99%.

3. The method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation according to claim 2, characterized in that: In the step S1, the mass percentages of the elements in the magnesium-lithium alloy are: Li: 6-10wt.%, Al: 0.05-6wt.%, Y: 0.05-5wt.%, Gd: 0.05-5wt.% and the balance Mg, and the total amount of each component is 100%.

4. The method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation according to claim 3, characterized in that: The heat treatment process in step S2 is performed at 300° C. for 4 hours.

5. The method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation according to claim 4, characterized in that: In the preferred extrusion deformation process in step S3, the preheating temperature is set to 200-400° C. and the holding time is 30 minutes.

6. The method for improving the performance of a dual-phase magnesium-lithium alloy by extrusion deformation according to claim 5, characterized in that: The extrusion speed used for the extrusion deformation in S3 is 10 mm / s, and the extrusion ratio is 11.5:1.

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