Preparation method of high-strength and high-plasticity magnesium alloy with controllable stacking fault and substructure

Abstract

The invention discloses a preparation method of a high-strength and high-plasticity magnesium alloy with controllable stacking fault and substructure, and relates to the technical field of magnesium alloy processing. According to the high-strength and high-plasticity magnesium alloy material and the preparation method thereof, through combination design of components, fault energy and deformation, high-density faults and rich alloy structures with substructures, kink and recrystallized grains which are difficult to achieve through a conventional method are obtained, and then the high-strength and high-plasticity magnesium alloy material is obtained by regulating and controlling parameters such as the number, the size and the distribution of the faults, the substructures, the kink and the recrystallized grains.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium alloy processing, and in particular to a method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures. Background Art

[0002] As the lightest metal structural material, magnesium alloy has the advantages of high specific strength / specific stiffness, dimensional stability, easy processing and forming, good thermal conductivity and electrical conductivity, damping and vibration reduction, electromagnetic shielding and easy recycling. Therefore, it is known as the "21st century green engineering material" and is widely used in automobiles, aerospace, high-speed rail, rail transportation, electronic products and other fields. my country's magnesium-based new materials industry has great development potential. In recent years, with the rapid development of new energy vehicles, aerospace and other industries, the demand for magnesium metal has continued to increase, and it will continue to maintain a steady growth trend in the next few years. Magnesium metal is most widely used in the automotive industry, mainly used in body structural parts, engine parts, wheels, etc. According to data from the China Light Alloy Association, China's magnesium alloy automobile consumption in 2023 has exceeded 400,000 tons, accounting for about 25% of the global total. With the advancement of the "dual carbon" goal, electric vehicles and hybrid vehicles have developed rapidly. Magnesium metal has become a key material due to its excellent weight reduction performance, and it is expected to maintain a double-digit growth rate in the next five years. The demand for lightweight materials in the field of new energy vehicles continues to rise, especially in battery packs, motors, vehicle structures, etc., and the application prospects of magnesium metal are broader. In terms of rail transit, as long as the weight of the train body is reduced, the train can increase its effective load and run faster. Now a high-speed train consisting of eight carriages has a traction force of up to 5500 to 8800kW, and using magnesium alloy to reduce weight can greatly reduce power costs.

[0003] However, strength and plasticity are key factors that restrict magnesium alloys from fully replacing aluminum alloys, steel and other application fields. In 2021, the Ministry of Industry and Information Technology included magnesium alloy extruded bars with tensile strength ≥320MPa, yield strength ≥300MPa, and elongation ≥12% in the "Guidelines for the First Batch Application Demonstration of Key New Materials (2021 Edition)". Magnesium alloy materials with tensile strength ≥400MPa, yield strength ≥300MPa, and elongation greater than 7% will greatly broaden the application areas of magnesium alloys;

[0004] In terms of plasticity, close-packed hexagonal lattice Mg and its alloys have few slip systems, and both basal and prismatic slip are a dislocation slips, which cannot coordinate the strain along the c-axis, resulting in poor uniform plastic deformation capacity and greatly limiting their application.

[0005] Therefore, a new solution to the above problems needs to be proposed. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures, so as to solve the technical problems raised in the background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures, comprising at least the following steps:

[0008] S1: Material selection: select raw materials according to the Y / Zn atomic ratio that meets the condition Y / Zn ≥ 1.32, and divide the raw materials into master batches and sub-batch materials

[0009] S2: Smelting: First, heat the masterbatch to a certain temperature in a resistance crucible boiler, wait for the masterbatch to be completely melted, raise the temperature to a certain temperature for slag removal, then add the sub-material into the crucible, stir for a certain time after it is completely melted, and let it stand and keep warm after the composition is uniform;

[0010] S3: Casting, cooling the melt in S2 to 680°C-690°C and casting into an ingot under the protection of a mixed gas;

[0011] S4: machining: machining the ingot obtained in S3 to a size suitable for the extrusion barrel;

[0012] S5: hot extrusion treatment;

[0013] S6: air-cooling the rod obtained after S5 treatment to room temperature to obtain the material.

[0014] Furthermore, the master batch includes industrial pure magnesium ingots, and the sub-batch includes at least industrial pure zirconium, industrial pure zinc and Mg-40%Y master alloy.

[0015] Furthermore, in S2, the masterbatch is heated to 700°C to 720°C, and the slag removal temperature is 740°C to 750°C.

[0016] Furthermore, the stirring time in S2 is 3 minutes to 6 minutes, and the heat preservation time in S2 is 15 minutes to 18 minutes.

[0017] Furthermore, the mixed gas in S3 includes CO 2 and SF 6 .

[0018] Furthermore, the S5 at least includes the following steps:

[0019] First, the S4 ingot is heated to 460°C to 480°C and kept at this temperature for 10 to 12 hours for homogenization annealing;

[0020] Then the ingot is kept at 440℃~450℃ for 30min;

[0021] Finally the ingot is extruded into bars.

[0022] Furthermore, the extrusion ratio when the ingot is extruded into a rod is 11 and the extrusion speed is 2.0.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention obtains a rich alloy structure with high-density stacking faults and substructures, kinks, and recrystallized grains that coexist, which is difficult to achieve with conventional methods, through the combined design of composition, stacking fault energy, and deformation. Furthermore, a high-strength and high-plasticity magnesium alloy material is obtained by regulating parameters such as the number, size, and distribution of stacking faults, substructures, kinks, and recrystallized grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 The microstructure diagram of the as-cast Mg-3.67Y-2.03Zn-0.26Zr (wt%) alloy of the present invention;

[0027] Figure 2 TEM schematic diagram of the recrystallized grain (DRX-ed Grain), sub-grain and kink in the extruded Mg-3.67Y-2.03Zn-0.26Zr (wt%) alloy LPSO of the present invention;

[0028] Figure 3 It is a comparative schematic diagram of the extruded metallographic microstructure of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] A method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures comprises at least the following steps:

[0031] S1: Material selection: select raw materials according to the Y / Zn atomic ratio that meets the condition Y / Zn ≥ 1.32, and divide the raw materials into master batches and sub-batch materials

[0032] S2: Smelting: First, heat the masterbatch to a certain temperature in a resistance crucible boiler, wait for the masterbatch to be completely melted, raise the temperature to a certain temperature for slag removal, then add the sub-material into the crucible, stir for a certain time after it is completely melted, and let it stand and keep warm after the composition is uniform;

[0033] S3: Casting, cooling the melt in S2 to 680°C-690°C and casting into an ingot under the protection of a mixed gas;

[0034] S4: machining: machining the ingot obtained in S3 to a size suitable for the extrusion barrel;

[0035] S5: hot extrusion treatment;

[0036] S6: air-cooling the rod obtained after S5 treatment to room temperature to obtain the material.

[0037] The master batch includes industrial pure magnesium ingot, and the sub-batch includes at least industrial pure zirconium, industrial pure zinc and Mg-40%Y master alloy.

[0038] In S2, the masterbatch is heated to 700°C to 720°C, and the slag-breaking temperature is 740°C to 750°C.

[0039] The stirring time in S2 is 3 minutes to 6 minutes, and the heat preservation time in S2 is 15 minutes to 18 minutes.

[0040] The mixed gas in S3 includes CO 2 and SF 6 .

[0041] S5 at least includes the following steps:

[0042] First, the S4 ingot is heated to 460°C to 480°C and kept at this temperature for 10 to 12 hours for homogenization annealing;

[0043] Then the ingot is kept at 440℃~450℃ for 30min;

[0044] Finally the ingot is extruded into bars.

[0045] The extrusion ratio when the ingot was extruded into rods was 11 and the extrusion speed was 2.0.

[0046] A large number of studies have shown that reducing the stacking fault energy of magnesium alloys is conducive to activating the cone slip system, thereby coordinating the deformation in the c-axis direction and improving the plasticity or formability of magnesium alloys.

[0047] To this end, the present invention selects element Y which can significantly reduce the stacking fault energy of metal magnesium to regulate the stacking fault energy of the magnesium alloy, thereby obtaining a deformable magnesium alloy with significantly improved forming properties.

[0048] In terms of strength, the present invention, grain refinement and second phase strengthening are currently the most commonly used strengthening methods in magnesium alloys, so the element Zr is selected to refine the grains. In terms of second phase strengthening, among all the second phases containing Y, the long period stacking structure (LPSO) is completely coherent with the magnesium matrix and has low interface energy, so the interface between LPSO and the matrix is ​​a coherent interface, and the stability of the second phase is very high. When subjected to external forces, it can effectively pin dislocations, thereby increasing the strength of the alloy. At the same time, during the plastic deformation process, cracks are not easy to initiate at the interface, so the LPSO phase as the second phase improves the strength of the alloy without sacrificing plasticity. Studies have shown that when the Y / Zn atomic ratio meets the condition Y / Zn≥1.32, the second phase in the cast Mg-Y-Zn-Zr alloy is only a single LPSO phase.

[0049] In summary

[0050] Based on the above stacking fault energy and composition design, the present invention introduces rich microstructure morphology such as high-density stacking faults, substructures, kinks, and recrystallized grains through extrusion deformation, and obtains high-strength and high-plasticity magnesium alloy materials by regulating parameters such as the number, size, and distribution of stacking faults, substructures, kinks, and recrystallized grains.

[0051] Based on the above content, the following specific embodiments are proposed:

[0052] Embodiment 1:

[0053] 1) Material selection: select raw materials according to the condition that the Y / Zn atomic ratio satisfies the condition that Y / Zn is approximately equal to 1.32. The raw materials selected in this implementation are industrial pure magnesium ingot, industrial pure zirconium, industrial pure zinc, and Mg-40% Y master alloy;

[0054] 2) Smelting: First, heat industrial pure magnesium to 700℃ in a resistance crucible boiler. After the masterbatch is completely melted, heat it to 750℃ for slag removal. Then add zirconium ingot, zinc ingot and Mg-40%Y master alloy into the crucible. Stir for 3-6 minutes after all are melted. After the composition is uniform, let it stand and keep warm for 15-18 minutes.

[0055] 3) Casting: Cool the melt from step 2) to 690°C and heat in CO 2 and SF 6 Casting into ingots under the protection of mixed gas;

[0056] 4) Machining: The ingot obtained in step 3) of the car body is processed to a size suitable for the extrusion cylinder;

[0057] 5) Hot extrusion: firstly, the ingot of step 4) is heated to 460°C for 12 hours for homogenization annealing, then the ingot is kept at 450°C for 30 minutes, and finally the ingot is extruded into a rod; during extrusion, the extrusion ratio is 11 and the extrusion speed is 2.0;

[0058] 6) Air cooling step 5) to obtain the Mg-3.67Y-2.03Zn-0.26Zr (wt%) alloy rod to room temperature.

[0059] Embodiment 2:

[0060] 1) Material selection: select raw materials according to the condition that the Y / Zn atomic ratio satisfies Y / Zn≥1.32, and select Y / Zn=2.36. The raw materials selected in this implementation are industrial pure magnesium ingot, industrial pure zirconium, industrial pure zinc, and Mg-40%Y master alloy;

[0061] 2) Smelting: First, heat industrial pure magnesium to 700℃ in a resistance crucible boiler. After the masterbatch is completely melted, heat it to 750℃ for slag removal. Then add zirconium ingot, zinc ingot and Mg-40%Y master alloy into the crucible. Stir for 3-6 minutes after all are melted. After the composition is uniform, let it stand and keep warm for 15-18 minutes.

[0062] 3) Casting: Cool the melt from step 2) to 690°C and heat in CO 2 and SF 6 Casting into ingots under the protection of mixed gas;

[0063] 4) Machining: The ingot obtained in step 3) of the car body is processed to a size suitable for the extrusion cylinder;

[0064] 5) Hot extrusion: firstly, the ingot of step 4) is heated to 460°C for 12 hours for homogenization annealing, then the ingot is kept at 450°C for 30 minutes, and finally the ingot is extruded into a rod; during extrusion, the extrusion ratio is 11 and the extrusion speed is 2.0;

[0065] 6) Air cooling step 5) to obtain Mg-11.67Y-3.64Zn-0.23Zr (wt%) alloy rod to room temperature.

[0066] Based on the above two embodiments, the following experiment is proposed:

[0067] The extruded rods obtained in Examples 1 and 2 were tested for mechanical properties, and the results are shown in the following table:

[0068]

[0069] It can be seen from the table that the elongation of the magnesium alloys of Examples 1 and 2 is greater than 7%, and the tensile strength of Example 2 is greater than 400 MPa, and the yield strength is greater than 300 MPa. It is a magnesium alloy material with excellent strength and plasticity, rich microstructure and controllable structure.

[0070] See also Figure 1-Figure 3In this experiment, the metallographic structure of the deformed magnesium alloy was taken from the middle part of the extruded rod, and the direction was parallel to the extrusion direction. Before observing the metallographic structure, the sample needs to be coarsely ground, finely ground, eroded, etc. The sample was surface treated on 120#, 400#, 600#, 800#, 1000#, 1500# and 2000# water-abrasive sandpaper successively, and strive to have no obvious scratches on the surface. The corrosive agent used in this work is (2.7g picric acid + 2ml glacial acetic acid + 2ml water + 20ml ethanol). The corrosion time is about 20s (the corrosion time of alloys with higher alloying element content is shorter). Since magnesium alloys are easy to react with water, the surface of the corroded sample needs to be quickly cleaned with alcohol after corrosion, and blown dry with a hair dryer to avoid contact with water. Finally, the organization was observed and photographed under a Neophot30 metallographic microscope.

[0071] The TEM observation of this embodiment was observed under a Zeiss LIBRA200 FEI transmission electron microscope with an accelerating voltage of 200 kV. The preparation process of the transmission sample is as follows: 1) Slicing: Use wire cutting technology to cut a 0.5 mm thick slice from the metallographic sample; 2) Mechanical thinning: Fix the slice on 1500# sandpaper with an eraser and grind one side to a bright finish, stick it on glass with 502 glue, grind the other side, and thin it to 50-70 μm on sandpaper; 3) Electrolytic thinning: Use a punch to punch out a Φ3 mm disc, and perform double-jet electrolytic thinning. The electrolyte used is: (5.3g lithium chloride (LiCl), 11.16g magnesium perchlorate (Mg(ClO4)2), 500ml methanol and 100ml ethylene glycol butyl ether), the double spray process parameters are: voltage is 50-60V, current is 25-30mA, temperature is about -50℃; 4) Ion thinning: the sample after double spraying is thinned at a small angle on an ion thinning instrument to remove the oxide layer and contaminants on the surface of the sample; 5) Finally, the microstructure is observed under a transmission electron microscope.

[0072] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures, characterized in that: At least the following steps are included: S1: Material selection: select raw materials according to the Y / Zn atomic ratio that meets the condition Y / Zn≥1.32, and divide the raw materials into master batches and sub-batch materials; S2: Smelting: First, heat the masterbatch to a certain temperature in a resistance crucible boiler, wait for the masterbatch to be completely melted, raise the temperature to a certain temperature for slag removal, then add the sub-material into the crucible, stir for a certain time after it is completely melted, and let it stand and keep warm after the composition is uniform; S3: Casting, cooling the melt in S2 to 680°C-690°C and casting into an ingot under the protection of a mixed gas; S4: machining: machining the ingot obtained in S3 to a size suitable for the extrusion barrel; S5: hot extrusion treatment; S6: air-cooling the rod obtained after S5 treatment to room temperature to obtain the material.

2. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 1, characterized in that: The master batch includes industrial pure magnesium ingots, and the sub-batch includes at least industrial pure zirconium, industrial pure zinc and Mg-40%Y master alloy.

3. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 1, characterized in that: In the S2, the masterbatch is heated to 700°C to 720°C, and the slag removal temperature is 740°C to 750°C.

4. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 1, characterized in that: The stirring time in S2 is 3 minutes to 6 minutes, and the heat preservation time in S2 is 15 minutes to 18 minutes.

5. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 1, characterized in that: The mixed gas in S3 includes CO2 and SF6.

6. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 1, characterized in that: The S5 at least comprises the following steps: First, the S4 ingot is heated to 460°C to 480°C and kept at this temperature for 10 to 12 hours for homogenization annealing; Then the ingot is kept at 440℃~450℃ for 30min; Finally the ingot is extruded into bars.

7. The method for preparing a high-strength and high-plasticity magnesium alloy with controllable stacking faults and substructures according to claim 6, characterized in that: The extrusion ratio when the ingot is extruded into the rod is 11 and the extrusion speed is 2.0.

Images