A high-modulus and high-toughness dual-phase magnesium alloy and its preparation method

Abstract

The present invention belongs to the technical field of magnesium alloys, and relates to a high-modulus and high-toughness duplex magnesium alloy and a preparation method thereof. Aiming at the problem of the modulus-toughness mismatch in the field of magnesium alloys, the Mg-Y-Ni alloy system is selected. By setting the atomic ratio of Y to Ni to 1 and regulating the contents of Y and Ni in the magnesium alloy, the nucleation and growth of a large amount of 14H-LPSO phases are promoted, and a magnesium alloy containing only the α-Mg / 14H-LPSO duplex phase is prepared. Secondly, through extrusion deformation at a specific extrusion temperature and extrusion ratio, the proliferation and multiplication of the 14H-LPSO phases are promoted, and at the same time, fine recrystallized grains are obtained, so as to produce significant LPSO fiber strengthening and fine grain strengthening on the magnesium alloy matrix, and a high-modulus and high-toughness deformed magnesium alloy is prepared, with an elastic modulus ≥45 GPa, a tensile strength ≥350 MPa, a yield strength ≥300 MPa, and an elongation ≥7%.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and specifically to a high-modulus and high-toughness dual-phase magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys are widely used in major engineering fields such as rail transit, aerospace, and military industry. However, the elastic modulus of magnesium alloys is relatively low, only 40-45 GPa, far lower than that of aluminum alloys (70 GPa), titanium alloys (110 GPa), and steel (206 GPa). The ability to resist elastic deformation is poor, which limits their further practical engineering applications. Therefore, in order to meet the high-end requirements for the comprehensive performance of magnesium alloys in major engineering fields, the preparation of high-modulus magnesium alloys has become a major challenge in the development of high-performance magnesium alloys.

[0003] At present, the main methods for preparing high-modulus magnesium alloys are adding external reinforcements and in-situ self-generated reinforcements. The external reinforcement method is to add reinforcements with a relatively high elastic modulus in the magnesium alloy, such as TiB2, SiC, and Al2O3, etc., to prepare magnesium-based composites with a high elastic modulus. The in-situ self-generated reinforcement method is to add alloying elements such as Gd, Y, Al, Si, etc., to in-situ self-generate a second phase with a high elastic modulus in the magnesium alloy, such as Mg2Si, Gd5Si3, Y2Si, MgAg, Al2Y, etc., so as to improve the overall elastic modulus of the magnesium alloy. However, both the high-modulus reinforcements and the high-modulus second phases have high hardness and high brittleness. Introducing a large amount of them into the magnesium alloy seriously weakens the mechanical properties of the magnesium alloy, especially the toughness, resulting in a serious modulus-toughness mismatch problem in the field. In addition, in the prior art, through specific ultrasonic vibration compression processing, high and low deformation bands are formed in the AZ91 magnesium alloy, and while a large number of strengthening phases are precipitated, the lattice parameters of the magnesium matrix are reduced, so that the elastic modulus of the AZ91 magnesium alloy is increased to more than 52 GPa. The prior art also has methods such as melting, atomization, hot press sintering, extrusion molding, and aging treatment, etc., to prepare Mg-Zn-Zr-Sr-Sc alloys with a tensile strength greater than 400 MPa and an elastic modulus greater than 55 GPa by changing the morphology and distribution of the strengthening phases. It can be seen that through improving the preparation process, a series of high-modulus magnesium alloys can be obtained. However, the relatively complex preparation process and high cost make it difficult to achieve engineering applications. Therefore, it has become very urgent to develop high-modulus and high-toughness magnesium alloys and simplify the production process. In the prior art, the elastic modulus and ductility-brittle properties of some second phases in magnesium alloys are calculated by the first-principles method. Mg2Ni, MgCu2, MgZn2, etc. have both relatively high elastic modulus and good toughness. Introducing high-modulus and tough phases into magnesium alloys through multi-component alloying can improve the elastic modulus and toughness at the same time. However, the formation of the second phase in multi-component magnesium alloys is complex and difficult to control. Therefore, it is still necessary to develop high-modulus and high-toughness magnesium alloys with a simple system and easy control of the second phase to meet the applications in the engineering field. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to provide a high-modulus and high-toughness dual-phase magnesium alloy and a preparation method thereof.

[0005] According to one aspect of the present invention, the following technical solution is provided:

[0006] A preparation method of a high-modulus and high-toughness dual-phase magnesium alloy, comprising the following steps:

[0007] S1. Take raw materials according to the composition of the magnesium alloy for melting to obtain a magnesium alloy casting. The magnesium alloy is a Mg-Y-Ni alloy, and the atomic ratio of Y to Ni is 1. In the Mg-Y-Ni alloy system, the formation of the LPSO phase is closely related to the atomic ratio of Y to Ni. When the atomic ratio of Y to Ni is greater than 1, excessive Y atoms will dissolve into the magnesium matrix, and the alloy mainly consists of α-Mg, LPSO phase and Y-rich phase. When the atomic ratio of Y to Ni is less than 1, Ni element is excessive, and the alloy mainly consists of α-Mg, LPSO phase and Mg2Ni phase. When the atomic ratio of Y to Ni is equal to 1, the precipitation of the LPSO phase can be ensured.

[0008] S2. Perform solution treatment on the magnesium alloy casting;

[0009] S3. Perform extrusion deformation on the solution-treated magnesium alloy to obtain a high-modulus and high-toughness dual-phase magnesium alloy.

[0010] As a preferred embodiment of the preparation method of the high-modulus and high-toughness dual-phase magnesium alloy of the present invention, in step S1, the composition of the Mg-Y-Ni alloy is: Y 9.5-10.5 wt.%, Ni 6.0-7.0 wt.%, and the balance is Mg. Preferably, the composition of the Mg-Y-Ni alloy is: Y 10.0 wt.%, Ni 6.5 wt.%, and the balance is Mg.

[0011] As a preferred embodiment of the preparation method of the high-modulus and high-toughness dual-phase magnesium alloy of the present invention, in step S1, the composition of the Mg-Y-Ni alloy is: Y 12.1-13.1 wt.%, Ni 7.8-8.8 wt.%, and the balance is Mg. Preferably, the composition of the Mg-Y-Ni alloy is: Y 12.6 wt.%, Ni 8.3 wt.%, and the balance is Mg.

[0012] As a preferred embodiment of the preparation method of the high-modulus and high-toughness duplex magnesium alloy described in the present invention, wherein: in the step S1, the raw materials are high-purity magnesium ingots (Mg 99.99 wt.%), nickel sheets (Ni 99.99 wt.%), and magnesium-yttrium master alloy (Mg-30wt.%Y). At the same time, in order to obtain a high-quality magnesium alloy melt, the oxide layer on the surface of the raw materials needs to be removed before melting the alloy, and all the raw materials, as well as the covering agent, refining agent, slag skimming and stirring tools required for melting, are preheated in a drying oven at 200 °C.

[0013] As a preferred embodiment of the preparation method of the high-modulus and high-toughness duplex magnesium alloy described in the present invention, wherein: in the step S1, the melting is completed in a box-type resistance furnace under an argon atmosphere, and the specific steps are as follows:

[0014] S11. Melting magnesium ingots: Add the magnesium ingots into a steel crucible preheated to 500 °C in advance, cover its surface with a dried salt covering agent and introduce high-purity argon (99.999%) for protection; since pure magnesium is chemically active at high temperatures and reacts easily with oxygen and water vapor in the air, the present invention adopts double protection of flux protection (salt covering agent) + gas protection (high-purity argon). Raise the temperature of the resistance furnace to 720 °C and hold for 30 min to ensure that the magnesium ingots are completely melted;

[0015] S11. Adding magnesium-yttrium master alloy: Add the magnesium-yttrium master alloy preheated to 200 °C into the molten magnesium, cover the surface of the melt with a salt covering agent, close the furnace and raise the furnace temperature to 780 °C, and hold for 15 min;

[0016] S13. Adding nickel: After the holding is completed, open the furnace to remove slag, add the preheated nickel sheet and mechanically stir with a stirring rod for 3 - 5 min. After the stirring is completed, cover the surface of the melt with a covering agent, close the furnace and raise the furnace temperature back to 780 °C, and hold for 20 min;

[0017] S14. Refining: To ensure high-quality melting of the magnesium alloy, refining treatment is required; open the furnace to remove slag, add the salt refining agent into the alloy melt and stir for 3 min to make the magnesium melt fully contact with the refining agent. After the refining is completed, evenly sprinkle the covering agent on the surface of the melt, close the furnace and raise the furnace temperature back to 750 °C, and hold for 30 min;

[0018] S15. Casting: After the holding is completed, open the furnace to remove slag, and pour the alloy melt into a steel casting mold preheated to 200 °C in advance; use high-purity argon to remove the air in the mold before casting, and use argon for protection during the casting process. After cooling to room temperature, take out the magnesium alloy casting from the mold.

[0019] In the present invention, since the melting point of pure nickel (1452 °C) is much higher than that of pure magnesium (650 °C), and magnesium is extremely easy to evaporate at high temperatures. Therefore, to ensure that nickel melts while minimizing the loss of magnesium, a dual protection of solvent and gas is used during the smelting process. By means of a diffusion reaction at a lower smelting temperature, nickel is melted, effectively avoiding excessive loss of Mg element caused by smelting under high temperature conditions and affecting the accuracy of alloy composition.

[0020] As a preferred embodiment of the preparation method of a high modulus and high toughness dual-phase magnesium alloy according to the present invention, wherein: in the step S2, there is composition segregation during the solidification of the magnesium alloy, and high-temperature heat treatment can effectively eliminate the composition and structure segregation of the ingot. However, the characteristics that the magnesium alloy is easy to oxidize and burn out at high temperatures make the heat treatment of the magnesium alloy difficult. Therefore, the present invention adopts the method of powder embedding for the heat treatment of the magnesium alloy to ensure that the specimen will not be oxidized and burned out. The solution treatment of the magnesium alloy casting by the method of powder embedding includes the following steps:

[0021] S21. Use a lathe to machine the magnesium alloy casting into a cylindrical specimen with a diameter of Ø40×(25~35) mm.

[0022] S22. Prepare a sufficient amount of magnesium oxide powder and place it in a corundum crucible. Use a drying oven to dry the magnesium oxide powder at 200 °C for at least 30 min to remove the moisture in the magnesium oxide powder.

[0023] S23. Use tin foil and the dried magnesium oxide powder to wrap and compact the specimen, and then place the wrapped specimen in a preheated corundum crucible, and fill and compact the surrounding with dry magnesium oxide powder.

[0024] S24. Use a muffle furnace for solution treatment. The specimen is heated in the furnace to 500 °C and held for 12 h, and the heating rate is 10 °C / min; after the holding is completed, the specimen is taken out and quickly placed in water for cooling, and the surface oxide layer is removed with sandpaper to obtain a solution-treated magnesium alloy specimen.

[0025] As a preferred embodiment of the preparation method of a high modulus and high toughness dual-phase magnesium alloy according to the present invention, wherein: in the step S3, a vertical extrusion press is selected, and the extrusion method is forward extrusion. The extrusion die includes an extrusion female die, an extrusion gasket, an extrusion rod and an extrusion sleeve; the extrusion temperature is 400~420 °C, the extrusion ratio is 25 / 1~16 / 1, the extrusion speed is 0.4 mm / s, and the extrusion angle is 30°.

[0026] As a preferred embodiment of the preparation method of a high modulus and high toughness dual-phase magnesium alloy according to the present invention, wherein: in the step S3, the extrusion deformation includes the following steps:

[0027] S31. Place the extrusion die in a ring-shaped resistance furnace and heat it up to the temperature required for forward extrusion. To ensure uniform heating of all parts of the extrusion die, keep it at the extrusion temperature for at least 60 minutes after reaching the temperature.

[0028] S32. Use a heat treatment furnace to keep the specimen at the corresponding extrusion temperature for 60 minutes. This step is carried out simultaneously with step S31.

[0029] S33. After the heat preservation is completed, quickly put the specimen into the die and carry out uniform extrusion at an extrusion speed of 0.4 mm / s.

[0030] S34. After extrusion, take out the extruded part and cool it in the air to room temperature to obtain a magnesium alloy extrusion specimen, that is, a high-modulus and high-toughness duplex magnesium alloy.

[0031] According to another aspect of the present invention, the present invention provides the following technical solution:

[0032] A high-modulus and high-toughness duplex magnesium alloy is prepared by using the preparation method of the above high-modulus and high-toughness duplex magnesium alloy. The duplex magnesium alloy is an α-Mg / 14H-LPSO duplex magnesium alloy, and the volume fraction of the 14H-LPSO phase is ≥ 45%, and the size of the recrystallized grains is ≤ 3.2 μm. Preferably, the volume fraction of the 4H-LPSO phase is 45 - 65%, and the size of the recrystallized grains is 1.5 - 3.2 μm.

[0033] As a preferred embodiment of the high-modulus and high-toughness duplex magnesium alloy described in the present invention, among them: the elastic modulus of the high-modulus and high-toughness duplex magnesium alloy is ≥ 45 GPa, the tensile strength is ≥ 350 MPa, the yield strength is ≥ 300 MPa, and the elongation is ≥ 7%.

[0034] The beneficial effects of the present invention are as follows:

[0035] The present invention provides a high-modulus and high-toughness duplex magnesium alloy and its preparation method. Aiming at the problem of the modulus-toughness mismatch in the field of magnesium alloys, the Mg-Y-Ni alloy system is selected. By setting the atomic ratio of Y to Ni to 1 and regulating the contents of Y and Ni in the magnesium alloy, the nucleation and growth of a large number of 14H-LPSO phases are promoted, and a magnesium alloy containing only α-Mg / 14H-LPSO duplex phases is prepared. Secondly, through extrusion deformation at a specific extrusion temperature and extrusion ratio, the reproduction and proliferation of the 14H-LPSO phase are promoted, and at the same time, fine recrystallized grains are obtained, so as to produce significant LPSO fiber strengthening and fine grain strengthening on the magnesium alloy matrix, and a high-modulus and high-toughness deformed magnesium alloy is prepared, with an elastic modulus of ≥ 45 GPa, a tensile strength of ≥ 350 MPa, a yield strength of ≥ 300 MPa, and an elongation of ≥ 7%. Description of the Drawings

[0036] 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.

[0037] Figure 1 It is the processing map of the Mg-Y-Ni magnesium alloy prepared in the embodiment of the present invention;

[0038] Figure 2 It is the schematic diagram of the extrusion process and die in the embodiment of the present invention;

[0039] Figure 3 It is the extruded magnesium alloy specimen in the embodiment of the present invention;

[0040] Figure 4 It is the SEM photograph of the Mg-Y-Ni alloy under different extrusion conditions in the embodiment of the present invention;

[0041] Figure 5 It is the TEM photograph of the Mg-12.6Y-8.3Ni deformed alloy prepared in the embodiment of the present invention;

[0042] Figure 6 It is the elastic modulus at room temperature of the extruded Mg-Y-Ni alloy in the embodiment of the present invention;

[0043] Figure 7 It is the tensile stress-strain curve at room temperature of the extruded Mg-Y-Ni alloy in the embodiment of the present invention.

[0044] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the drawings. Detailed Embodiments

[0045] The following will clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. 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.

[0046] The present invention provides a high-modulus and high-toughness dual-phase magnesium alloy and its preparation method, which has the following advantages:

[0047] (1) By regulating the contents of Y and Ni in the magnesium alloy and setting the atomic ratio of Y to Ni as 1, the present invention prepares a high-modulus and high-toughness α-Mg / 14H-LPSO dual-phase magnesium alloy base material with a simple system and easy control of the second phase.

[0048] (2)Under the specific conditions of an extrusion temperature of 400 - 420 °C and an extrusion ratio of 25 / 1 - 16 / 1, a duplex structure of α-Mg / 14H-LPSO was obtained in the Mg-Y-Ni alloy, and the volume fraction of the 14H-LPSO phase reached over 45%. The 14H-LPSO phase itself has a relatively high elastic modulus (~66.7 GPa), and compared with the 18R-LPSO phase, the 14H-LPSO phase is more conducive to improving the toughness of the magnesium alloy. Introducing a large amount of 14H-LPSO into the magnesium alloy can improve both the elastic modulus and toughness simultaneously.

[0049] (3)Under the specific conditions of an extrusion temperature of 400 - 420 °C and an extrusion ratio of 25 / 1 - 16 / 1, recrystallized grains with a grain size of ≤3.2 μm were obtained in the Mg-Y-Ni alloy. Based on the Hall-Petch relationship, the fine recrystallized grains provide higher strength.

[0050] (4)Under the specific conditions of an extrusion temperature of 400 - 420 °C and an extrusion ratio of 25 / 1 - 16 / 1, a Mg-Y-Ni deformed alloy with both high modulus and high toughness was obtained. The obtained 14H-LPSO phase is completely coherent with the magnesium matrix, which can synergistically improve the elastic modulus and toughness of the magnesium alloy. Its elastic modulus is ≥45 GPa, the tensile strength is ≥350 MPa, the yield strength is ≥300 MPa, and the elongation is ≥7%.

[0051] (5)The Mg-Y-Ni deformed magnesium alloy with high modulus and high toughness prepared by the present invention has excellent comprehensive properties, and this alloy has a low production cost, a simple process, a simple die structure, without complex manufacturing processes and precision machinery and equipment, and is expected to be used in major engineering fields such as rail transit, aerospace, and military industry.

[0052] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0053] The present invention includes four groups of embodiments, and the conditions of each embodiment are as follows:

[0054] Example 1: The alloy composition is Mg-10Y-6.5Ni, the extrusion temperature is 420 °C, and the extrusion ratio is 25 / 1;

[0055] Example 2: The alloy composition is Mg-10Y-6.5Ni, the extrusion temperature is 400 °C, and the extrusion ratio is 25 / 1;

[0056] Example 3: The alloy composition is Mg-10Y-6.5Ni, the extrusion temperature is 400 °C, and the extrusion ratio is 16 / 1;

[0057] Example 4: The alloy composition is Mg-12.6Y-8.3Ni, the extrusion temperature is 400 °C, and the extrusion ratio is 16 / 1.

[0058] As Figure 1 shown, a method for preparing a high-modulus and high-toughness duplex magnesium alloy includes the following steps:

[0059] S1. Take raw materials according to the composition of the magnesium alloy and melt them to obtain a magnesium alloy casting; the raw materials are high-purity magnesium ingots (Mg 99.99 wt.%), nickel sheets (Ni 99.99 wt.%), and magnesium-yttrium master alloy (Mg-30 wt.% Y). At the same time, in order to obtain a high-quality magnesium alloy melt, the oxide layer on the surface of the raw materials needs to be removed before melting the alloy, and all raw materials, covering agents, refining agents, slag skimming and stirring tools required for melting are preheated in a 200 °C drying oven. Melting is completed in a box-type resistance furnace under an argon atmosphere. The specific steps are as follows:

[0060] S11. Melt the magnesium ingot: Add the magnesium ingot to a steel crucible preheated to 500 °C, cover its surface with a dried salt covering agent and introduce high-purity argon (99.999%) for protection; since pure magnesium is chemically active at high temperatures and easily reacts with oxygen and water vapor in the air, the present invention uses flux protection (salt covering agent) + gas protection (high-purity argon) for double protection. Raise the temperature of the resistance furnace to 720 °C and hold for 30 min to ensure that the magnesium ingot is completely melted;

[0061] S12. Add the magnesium-yttrium master alloy: Add the magnesium-yttrium master alloy preheated to 200 °C to the molten magnesium, cover the surface of the melt with a salt covering agent, close the furnace and raise the furnace temperature to 780 °C, and hold for 15 min;

[0062] S13. Add nickel: After the holding is completed, open the furnace to remove slag, add the preheated nickel sheet and mechanically stir for 3-5 min with a stirring rod. After the stirring is completed, cover the surface of the melt with a covering agent, close the furnace and raise the furnace temperature back to 780 °C, and hold for 20 min;

[0063] S14. Refining: To ensure the high-quality melting of the magnesium alloy, refining treatment is required; open the furnace to remove slag, add the salt refining agent to the alloy melt and stir for 3 min to make the magnesium melt fully contact with the refining agent. After the refining is completed, evenly sprinkle the covering agent on the surface of the melt, close the furnace and raise the furnace temperature back to 750 °C, and hold for 30 min;

[0064] S15. Casting: After the holding is completed, open the furnace to remove slag, pour the alloy melt into a steel casting mold preheated to 200 °C; use high-purity argon to remove the air in the mold before casting, use argon for protection during the casting process, and wait until it cools to room temperature, then take out the magnesium alloy casting from the mold.

[0065] S2. Solution treatment is carried out on the magnesium alloy casting; the magnesium alloy casting is subjected to solution treatment by means of powder embedding, including the following steps:

[0066] S21. Use a lathe to turn the magnesium alloy casting into a cylindrical specimen with a diameter of Ø40×(25 - 35) mm;

[0067] S22. Prepare a sufficient amount of magnesium oxide powder and place it in a corundum crucible. Use a drying oven to dry the magnesium oxide powder at 200°C for at least 30 minutes to remove the moisture in the magnesium oxide powder;

[0068] S23. Wrap and compact the specimen with tin foil and the dried magnesium oxide powder, then place the wrapped specimen in a preheated corundum crucible, and fill and compact the surrounding with dry magnesium oxide powder;

[0069] S24. Carry out solution treatment using a muffle furnace. The specimen is heated in the furnace to 500°C and held for 12 hours, with a heating rate of 10°C / min; after the holding is completed, take out the specimen and quickly place it in water for cooling. After removing the surface oxide layer with sandpaper, a solution-treated magnesium alloy specimen is obtained.

[0070] S3. Extrusion deformation is carried out on the solution-treated magnesium alloy. A vertical extrusion press is selected, and the forward extrusion method is used. The extrusion die includes an extrusion female die, an extrusion gasket, an extrusion rod, and an extrusion sleeve; the extrusion speed is 0.4 mm / s, and the extrusion angle is 30°. The schematic diagram of the extrusion process and the die is as Figure 2 shown. The extrusion deformation includes the following steps:

[0071] S31. Place the extrusion die in a ring resistance furnace and heat it to the required temperature for forward extrusion. To ensure uniform heating of each part of the extrusion die, hold for at least 60 minutes after reaching the extrusion temperature;

[0072] S32. Use a heat treatment furnace to hold the specimen at the corresponding extrusion temperature for 60 minutes. This step is carried out simultaneously with step S31;

[0073] S33. After the holding is completed, quickly put the specimen into the die and carry out uniform extrusion at an extrusion speed of 0.4 mm / s;

[0074] S34. After extrusion, take out the extruded part and cool it in the air to room temperature to obtain a magnesium alloy extrusion specimen, as Figure 3 shown.

[0075] The structures and properties of the specimens prepared in each embodiment of the present invention are tested, and the results are as Figures 4 to 7 shown.

[0076] Figure 4SEM photographs of Mg-Y-Ni alloys under different extrusion conditions in the embodiments of the present invention Figure 4 In (a), it is the microstructure of the alloy prepared in Example 1 Figure 4 In (b), it is the microstructure of the alloy prepared in Example 2 Figure 4 In (c), it is the microstructure of the alloy prepared in Example 3 Figure 4 In (d), it is the microstructure of the alloy prepared in Example 4. It can be seen that Figure 4 α-Mg / LPSO duplex microstructure is obtained in the Mg-Y-Ni deformed alloy. Among them, under the specific conditions of an extrusion temperature of 420 °C and an extrusion ratio of 25 / 1 in Example 1, the volume fraction of the LPSO phase in the Mg-10Y-6.5Ni alloy is 46.4% and the fine recrystallized grains are 3.12 μm. With the decrease of the extrusion temperature and extrusion ratio in Example 2 and Example 3, the volume fraction of the LPSO phase in the Mg-10Y-6.5Ni alloy is increased to 49.5% and 50.6% respectively, and the grain size is further reduced to 1.96 μm and 1.80 μm. On this basis, after increasing the proportion of alloying elements, under the specific conditions of an extrusion temperature of 400 °C and an extrusion ratio of 16 / 1 in Example 4, the Mg-12.6Y-8.3Ni alloy obtains an LPSO phase with a volume fraction as high as 60.6% and the recrystallized grains with the smallest grain size (1.62 μm).

[0077] Figure 5 TEM photographs of the Mg-12.6Y-8.3Ni deformed alloy prepared in Example 4 of the present invention Figure 5 In (a), it is the interfacial relationship between 14H-LPSO and the α-Mg matrix Figure 5 In (b), it is the diffraction spots of 14H-LPSO. It can be seen from Figure 5 (b) that there are 6 additional diffraction spots between two bright spots, indicating that the LPSO phase structure is of the 14H type and there are Figure 5 (a) It can be seen that the arrangement of atoms at the interface between 14H-LPSO and the α-Mg matrix is consistent, indicating that a coherent interface is formed between 14H-LPSO and the α-Mg matrix. The coherent interface generates very small or nearly zero lattice distortion and enables perfect load transfer between the matrix and the precipitate phase.

[0078] Figure 6 The elastic modulus at room temperature of the extruded Mg-Y-Ni alloy in the embodiments of the present invention. It can be seen from Figure 6It can be seen that under the specific conditions of an extrusion temperature of 420 °C and an extrusion ratio of 25 / 1 in Example 1, the elastic modulus of the Mg-10Y-6.5Ni alloy reached 48.85 GPa. Through the adjustment of the extrusion process, in Example 2 under the conditions of an extrusion temperature of 400 °C and an extrusion ratio of 25 / 1, and in Example 3 under the conditions of an extrusion temperature of 400 °C and an extrusion ratio of 16 / 1, the elastic modulus of the Mg-10Y-6.5Ni alloy was increased to 49.05 GPa and 49.35 GPa respectively. On this basis, by increasing the proportion of alloying elements, in Example 4 under the specific conditions of an extrusion temperature of 400 °C and an extrusion ratio of 16 / 1, the elastic modulus of the Mg-12.6Y-8.3Ni alloy at room temperature was as high as 50.85 GPa.

[0079] Figure 7 This is the tensile stress-strain curve of the extruded Mg-Y-Ni alloy at room temperature in the embodiment of the present invention. Figure 7 It can be seen that under the specific conditions of an extrusion temperature of 420 °C and an extrusion ratio of 25 / 1 in Example 1, the tensile strength, yield strength and elongation of the Mg-10Y-6.5Ni alloy reached 370 MPa, 305 MPa and 13% respectively. After the extrusion temperature in Example 2 decreased to 400 °C, the strength of the Mg-10Y-6.5Ni alloy increased while the elongation decreased, and its tensile strength, yield strength and elongation were 400 MPa, 365 MPa and 9% respectively. Compared with Example 2, in Example 3 the extrusion ratio was reduced to 16 / 1, and the tensile strength, yield strength and elongation of the Mg-10Y-6.5Ni alloy were all improved, being 425 MPa, 380 MPa and 12.2% respectively. On this basis, by increasing the proportion of alloying elements, in Example 4 under the specific conditions of an extrusion temperature of 400 °C and an extrusion ratio of 16 / 1, the tensile strength and yield strength of the Mg-12.6Y-8.3Ni alloy at room temperature were significantly improved, and its tensile strength and yield strength reached 483 MPa and 446 GPa respectively, and its elongation still remained above 8%.

[0080] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept 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 preparation method of a high-modulus and high-toughness dual-phase magnesium alloy, characterized in that, It includes the following steps: S1. Take raw materials according to the composition of the magnesium alloy for melting to obtain a magnesium alloy casting. The magnesium alloy is an Mg-Y-Ni alloy, and the atomic ratio of Y to Ni is 1. The composition of the Mg-Y-Ni alloy is: Y 9.5 - 10.5 wt.%, Ni 6.0 - 7.0 wt.%, and the rest is Mg; or the composition of the Mg-Y-Ni alloy is: Y 12.1 - 13.1 wt.%, Ni 7.8 - 8.8 wt.%, and the rest is Mg; S2. Perform solution treatment on the magnesium alloy casting; perform solution treatment on the magnesium alloy casting by means of powder embedding, including the following steps: S21. Process the magnesium alloy casting into a specimen; S22. Prepare magnesium oxide powder and dry it; S23. Wrap and compact the specimen with tin foil and the dried magnesium oxide powder, then place the wrapped and compacted specimen in a preheated corundum crucible, and fill and compact the surrounding with the dried magnesium oxide powder; S24. Perform solution treatment. The specimen is heated in the furnace to 500 °C and held for 12 h, and the heating rate is 10 °C / min; after the holding is completed, take out the specimen and quickly place it in water for cooling to obtain a solution-treated magnesium alloy specimen; S3. Perform extrusion deformation on the solution-treated magnesium alloy. The extrusion temperature is 400 - 420 °C, the extrusion ratio is 25 / 1 - 16 / 1, the extrusion speed is 0.4 mm / s, and the extrusion angle is 30°; obtain a high-modulus and high-toughness duplex magnesium alloy. The duplex magnesium alloy is an α-Mg / 14H-LPSO duplex magnesium alloy, and the volume fraction of the 14H-LPSO phase is ≥45%, and the size of the recrystallized grains is ≤3.2 μm.

2. The preparation method of the high-modulus and high-toughness duplex magnesium alloy according to claim 1, wherein In the step S1, the raw materials are high-purity magnesium ingots, nickel sheets, and magnesium-yttrium master alloys.

3. The preparation method of the high-modulus and high-toughness dual-phase magnesium alloy according to claim 1, wherein In the step S3, a vertical extrusion press is selected, and the extrusion method is forward extrusion. The extrusion die includes an extrusion female die, an extrusion gasket, an extrusion rod, and an extrusion sleeve.

4. The preparation method of the high modulus and high toughness dual-phase magnesium alloy according to claim 1, characterized in that, In the step S3, the extrusion deformation includes the following steps: S31. Place the extrusion die in a ring resistance furnace and heat it to the required temperature for forward extrusion; S32. Use a heat treatment furnace to hold the specimen at the corresponding extrusion temperature. This step is carried out simultaneously with step S31; S33. After the holding is completed, quickly put the specimen into the die for uniform extrusion; S34. After the extrusion is completed, take out the extruded part and cool it in the air to room temperature to obtain a magnesium alloy extrusion specimen.

5. A high modulus and high toughness dual-phase magnesium alloy, characterized in that It is prepared by using the preparation method of the high-modulus and high-toughness duplex magnesium alloy according to any one of claims 1 - 4.

6. The high-modulus and high-toughness dual-phase magnesium alloy according to claim 5, wherein The high-modulus and high-toughness duplex magnesium alloy has an elastic modulus ≥45 GPa, a tensile strength ≥350 MPa, a yield strength ≥300 MPa, and an elongation ≥7%.

Images