A high modulus high strength high toughness Mg 90 Method for preparing Y4Zn2Ni4 wrought magnesium alloy

Abstract

The application discloses a high-modulus high-strength high-toughness Mg 90 The application discloses a preparation method of Y4Zn2Ni4 wrought magnesium alloy and belongs to the technical field of magnesium alloy preparation. The method comprises alloy smelting: according to the component proportion of a magnesium alloy to be prepared, raw material metals of Mg, Y, Zn and Ni are mixed and smelted through a flux covering protection smelting method to pour into a cast alloy; then, the cast alloy is subjected to solid solution treatment; finally, the cast alloy after the solid solution treatment is subjected to extrusion at an extrusion temperature of 400-420 DEG C, an extrusion speed of 0.4 mm / s, an extrusion ratio of 25:1 and an extrusion angle of 30 DEG. The method introduces a large amount of Ni elements into a Mg-Y-Zn alloy for alloy modification treatment, obtains a large amount of layered and blocky LPSO phases, further improves the volume fraction of the LPSO phases through a solid solution treatment technology, finally obtains the LPSO phases arranged in a fibrous shape through hot extrusion deformation, and a Mg-Y-Zn-Ni alloy with high modulus, high strength and high toughness is prepared.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy preparation technology, and relates to a high-modulus, high-strength, and high-toughness Mg alloy. 90 Preparation method of Y4Zn2Ni4 wrought magnesium alloy. Background Technology

[0002] In recent years, aerospace weaponry has placed higher demands on the dimensional stability of magnesium alloy load-bearing structural components. While the room temperature tensile strength of deformed magnesium alloys can reach over 400 MPa, their elongation is generally less than 10%, and their elastic modulus is only about 45 GPa. This exhibits a significant mismatch between strength, toughness, and modulus, leading to significant elastic deformation of magnesium alloy parts under high-stress service conditions, which seriously affects their service performance. Therefore, developing magnesium alloys with high strength, high toughness, and high elastic modulus is of great significance for the upgrading and replacement of aerospace weaponry.

[0003] In Mg-Gd / Y-Zn magnesium alloys, long-period stacking ordered (LPSO) strengthening phases can form, effectively improving the alloy's strength and toughness. Common LPSO types include 6H, 10H, 14H, 18R, and 24R, with 14H and 18R being the most prevalent. The diverse LPSO phase structures result in significant differences in the properties of magnesium alloys containing LPSO phases, drawing widespread attention from materials scientists. Controlling the volume fraction and structural morphology of LPSO phases to regulate the overall mechanical properties (strength, ductility, and elastic modulus) of the alloy has become a research hotspot in the strengthening and toughening of magnesium alloys.

[0004] Alloying and hot extrusion deformation are effective methods to modify the properties of LPSO phases. Studies have shown that Ni has a greater potential than Zn in participating in and promoting LPSO phase formation; given a fixed solute content, Ni atoms are more conducive to LPSO phase formation. For example, Zhang Jinshan et al. from Taiyuan University of Technology induced the formation of a large amount of LPSO phase by replacing Zn with a small amount of Ni in Mg-Gd-Zn alloys. Ni not only participated in the formation of LPSO phases itself but also stimulated Zn to participate in LPSO phase formation. Jiang Bin et al. from Chongqing University studied the extrusion of Mg... 96In Y2Zn2 alloys, with Ni replacing Zn, the volume fraction of the LPSO phase increases from 32.2% to 42.5%, and some LPSO phases transform from blocky to lamellar form. Furthermore, the extruded alloy exhibits increased strength but decreased ductility. The lamellar LPSO phase possesses higher elastic modulus and hardness, improving alloy strength, while the blocky LPSO phase enhances ductility, a fact confirmed by previous studies. In addition, the LPSO phase undergoes kinking and bending during hot extrusion deformation, increasing dislocation density and providing further strengthening. During extrusion, the LPSO phase is elongated along the extrusion direction, acting as a short-fiber phase, which further improves the overall mechanical properties of the alloy. Therefore, Ni alloying can effectively increase the volume fraction of the LPSO phase and alter its morphology, while hot extrusion deformation can further enhance the strengthening effect of the LPSO phase.

[0005] Although researchers have made some progress in studying the effects of Ni substitution for Zn on the LPSO phase and mechanical properties of Mg-Re-Zn alloys, previous studies have only involved small amounts of Ni (≤1%). The effects of directly adding higher Ni contents on the LPSO phase and mechanical properties of Mg-Re-Zn alloys remain unclear. Summary of the Invention

[0006] This invention overcomes the shortcomings of existing technologies and proposes a high-modulus, high-strength, and high-toughness Mg 90 Preparation method of Y4Zn2Ni4 wrought magnesium alloy.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] A high-modulus, high-strength, and high-toughness Mg 90 The preparation method of Y4Zn2Ni4 wrought magnesium alloy includes the following steps:

[0009] 1) Alloy smelting: According to the composition ratio of the magnesium alloy to be prepared, the raw material metals of Mg, Y, Zn and Ni are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy.

[0010] 2) Solution treatment: The as-cast alloy is subjected to solution treatment;

[0011] 3) Hot extrusion deformation: The solution-treated cast alloy is extruded at an extrusion temperature of 400-420℃, an extrusion speed of 0.4mm / s, an extrusion ratio of 25:1, and an extrusion angle of 30°.

[0012] Preferably, the alloy smelting process involves first melting magnesium ingots, then adding Mg-30Y master alloy and zinc, melting them, and then adding nickel and refining them.

[0013] Even better, the alloy system is prepared under protective gas conditions using magnesium ingots, pure zinc blocks, nickel sheets and Mg-30wt.%Y master alloy as raw materials.

[0014] Even better, melting magnesium ingots: Place the crucible in a pit-type resistance furnace, heat it to 500°C, put the preheated pure Mg into the crucible, and evenly sprinkle the ground and preheated covering agent on its surface. At the same time, introduce high-purity Ar2 into the furnace as a protective gas; raise the temperature of the resistance furnace to 710°C and hold for 10 minutes, then raise it to 720°C and hold for 10 minutes to completely melt the magnesium ingot.

[0015] More preferably, after the magnesium ingots are completely melted, the furnace is opened and the scum on the surface of the solution is skimmed off. Then, the preheated Mg-30Y master alloy and pure zinc blocks are added. After the covering agent is evenly sprinkled on the surface of the solution, the furnace is closed and the temperature is raised. When the furnace temperature reaches 750℃, it is held for 10 minutes and then the temperature is raised again. When the temperature reaches 780℃, the furnace is opened again and the scum on the surface of the solution is skimmed off. The preheated nickel sheets are added and stirred for 2-3 minutes. After stirring, the covering agent is evenly sprinkled on the surface of the solution and the furnace is closed and the temperature is raised. When the furnace temperature returns to 780℃, it is held for 10 minutes. Then, when the furnace temperature drops to 740℃, the furnace is opened for the third time and the scum on the surface of the solution is skimmed off. A refining agent is added and refined for 2-3 minutes. After refining, the covering agent is evenly sprinkled on the surface of the solution and the furnace is closed and the temperature is raised. When the furnace temperature reaches 780℃, it is held for 20 minutes.

[0016] Even better, after refining, the furnace temperature is lowered to 740°C, the furnace is opened and the slag on the surface of the solution is skimmed off, the molten metal is poured into a water-cooled steel mold, cooled to room temperature, and then the cast alloy is taken out and cooled to room temperature.

[0017] Preferably, in the solution treatment, the as-cast alloy is embedded with dry magnesium oxide powder.

[0018] Even better, the solution treatment temperature is >450℃.

[0019] Even better, the solution treatment temperature is 500℃.

[0020] Preferably, the hot extrusion deformation involves mounting the extrusion die on a vertical extruder, heating the die to the required extrusion temperature using an electric resistance furnace and holding it at that temperature for ≥30 minutes to ensure uniform heating inside the die; while the die is being heated, the heat treatment furnace is heated to the required extrusion temperature, and once the temperature is reached, the solution-treated casting is placed in the furnace and held at that temperature for 1 hour; then, hot extrusion deformation is performed.

[0021] The beneficial effects of this invention compared to the prior art are as follows:

[0022] This invention introduces a large amount of Ni element into a Mg-Y-Zn alloy for alloy modification treatment, obtaining a large number of layered and blocky LPSO phases. The volume fraction of the LPSO phase is further increased through solution treatment, and finally, fibrous LPSO phases are obtained through hot extrusion deformation. A high-modulus, high-strength, and high-toughness synergistic Mg-Y-Zn-Ni alloy is prepared, with an elastic modulus of up to 51.32 GPa, a tensile strength of up to 457.3 MPa, an elongation of up to 27.9%, and a strength-ductility product of 12.75 GPa%, the highest among current high-strength and high-toughness magnesium alloys. Specifically:

[0023] (1) To address the significant differences in physical properties between the alloying elements Mg and Ni, this invention employs a flux-covered protective melting method to ensure the accuracy of the alloy composition. Furthermore, during the alloy melting process, small-sized thin nickel sheets are added, and subsequent stirring ensures that the added Ni melts more uniformly into the magnesium alloy, guaranteeing a uniform distribution of Ni in the α-Mg matrix. During solution treatment, magnesium oxide powder is used to embed the magnesium alloy sample, preventing oxidation and ensuring the integrity of the sample after solution treatment. In addition, with the addition of a high content of rare earth Y (12.23 wt.%), lower extrusion temperatures (400℃ and 420℃) and higher extrusion ratios (25:1) are used to obtain a higher recrystallization ratio and more uniform fine grains, achieving a synergistic improvement in strength and plasticity.

[0024] (2) In this invention, Ni alloying modification treatment was applied to Mg-Y-Zn magnesium alloy to increase the volume fraction of LPSO phase. Layered LPSO phase and blocky LPSO phase were formed and formed a continuous network structure along the grain boundaries. Through solid solution treatment (temperature and time), some eutectic phases dissolved, and Y, Zn, and Ni atoms dissolved in the matrix reacted with Mg atoms to further generate more Long Period Stacking Ordered (LPSO) phases. After hot extrusion deformation, the network LPSO phases were broken up during the extrusion process and rearranged along the extrusion direction to form a ribbon-like fibrous structure. In addition, a small amount of nano-14H LPSO phase precipitated inside the recrystallized grains, further strengthening the magnesium matrix and improving the comprehensive mechanical properties of the magnesium alloy together with a large amount of fibrous LPSO phase.

[0025] Ni on Mg 94 The influence of Ni on the microstructure and properties of Y4Zn2 alloy, as well as the effect of Ni on the volume fraction and structural morphology of the LPSO phase, combined with the changes in the microstructure and properties of the extruded alloy, reveals the strengthening and toughening mechanism of the extruded alloy, thus preparing a high-modulus, high-strength, and high-toughness extruded Mg alloy. 90 Y4Ni4Zn2 alloy. Attached Figure Description

[0026] Figure 1 The Mg prepared in the examples 90 SEM microstructure of Y4Zn2Ni4 alloy; where (a) is the as-cast state, (c) is a magnified view of (a); (b) is the solution-treated state, and (d) is a magnified view of (b).

[0027] Figure 2 yes Figure 1 EDS spectra at positions A, B, C, and D; where (a) is position A, (b) is position B, (c) is position C, and (d) is position D.

[0028] Figure 3 The extruded Mg in the example 90 SEM microstructure of Y4Zn2Ni4 alloy at different extrusion temperatures; where (a) is at 400℃, (b) is a magnified view of (a), (c) is at 420℃, and (d) is a magnified view of (c).

[0029] Figure 4 The Mg in the example was extruded at 400℃ 90 EDS energy dispersive spectroscopy of Y4Zn2Ni4 alloy;

[0030] Figure 5 yes Figure 4 Enlarged EDS energy dispersive spectra of Mg, Y, Zn, and Ni;

[0031] Figure 6 The extruded Mg in the example 90 Room temperature mechanical properties of Y4Zn2Ni4 alloy under different extrusion parameters. Detailed Implementation

[0032] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0033] This embodiment proposes a high-modulus, high-strength, and high-toughness Mg 90 The preparation method of Y4Zn2Ni4 wrought magnesium alloy specifically includes the following steps:

[0034] Step 1: Alloy Melting

[0035] Pure magnesium ingots, pure aluminum, and yttrium magnesium master alloy (Mg-30wt.%Y) were cut using a band saw, and the surface oxide layer was removed by grinding with an angle grinder before being preheated in a drying oven. 0.015mm thick nickel sheets were cut into 10×10mm pieces, cleaned with alcohol, dried, and then preheated in a drying oven. In this embodiment, an alloy system was prepared using magnesium ingots, zinc ingots, nickel sheets, and yttrium magnesium master alloy (Mg-30wt.%Y) as raw materials in a box-type resistance furnace under a protective gas (Ar2) atmosphere. The specific steps are as follows:

[0036] (1) Melt the magnesium ingot. Place the crucible in a pit-type resistance furnace and heat it to 500°C. Then, put the pure Mg, which has been preheated to 200°C, into the crucible and evenly sprinkle the ground and preheated covering agent on its surface. At the same time, introduce high-purity Ar2 (99.999%) into the furnace as a protective gas. In addition, because magnesium is chemically active, it is very easy to react with water vapor and oxygen in the air at high temperatures. Therefore, this embodiment uses a salt covering agent + Ar2 protection method for protection. Raise the resistance furnace temperature to 710°C and hold for 10 minutes, then raise the temperature again to 720°C and hold for 10 minutes to ensure that the magnesium ingot is completely melted.

[0037] (2) Add Mg-30Y master alloy and zinc. After the magnesium ingot is completely melted, open the furnace and skim off the slag on the surface of the solution. Then add the preheated Mg-30Y master alloy and pure zinc. Sprinkle the covering agent evenly on the surface of the solution and then close the furnace and raise the temperature. After the furnace temperature reaches 750℃ and is kept at 750℃ for 10 minutes, raise the temperature.

[0038] (3) Add nickel. When the temperature rises to 780℃, open the furnace again to skim off the scum on the surface of the solution. Add the preheated nickel sheet according to the test requirements and stir for 2-3 minutes. After stirring, evenly sprinkle the covering agent on the surface of the solution and close the furnace to raise the temperature. After the furnace temperature rises back to 780℃, keep it at that temperature for 10 minutes.

[0039] (4) Refining: When the furnace temperature drops to 740 ℃, the furnace is opened for the third time to skim off the scum on the surface of the solution, and refining agent is added for 2-3 minutes. After refining, a covering agent is evenly sprinkled on the surface of the solution, and the furnace is closed and the temperature is raised. After the furnace temperature reaches 780 ℃, it is kept at that temperature for 20 minutes.

[0040] (5) Casting: After the heat preservation period, the furnace temperature is lowered to 740°C. After skimming off the slag from the surface of the solution, the molten metal is poured into a water-cooled steel mold. After cooling to room temperature, the as-cast alloy is removed. During the casting process, the flow rate is kept uniform. After the mold cools naturally to room temperature, the sample is removed from the mold to obtain the as-cast alloy casting rod. The as-cast SEM microstructure is as follows: Figure 1 As shown in (a).

[0041] Mg has a melting point of 650°C, while Ni has a melting point of 1450°C, and their vapor pressures differ significantly. To address this large difference in melting point and vapor pressure between the alloying elements Mg and Ni, a flux-covered protective melting method is chosen. This method fuses elements with significantly different properties through diffusion reactions at lower melting temperatures, effectively avoiding the loss of elements with lower melting points and higher vapor pressures caused by high-temperature melting, which would affect the accuracy of the alloy composition. In this invention, nickel is added using a thin nickel sheet with a thickness of 0.15 mm and dimensions of 10 × 10 mm. After addition, the sheet is stirred for 2-3 minutes to ensure uniform melting of the nickel in the molten magnesium alloy, allowing the Ni element to diffuse evenly throughout the magnesium alloy.

[0042] Step 2: Solution treatment

[0043] (1) The casting obtained by casting is machined into a cylinder with a diameter of Ø40×25mm by lathe;

[0044] (2) Place the magnesium oxide powder in a drying oven at 200°C for at least two hours to prevent the moisture in the magnesium oxide powder from reacting with the alloy during the subsequent heat treatment process and affecting the performance of the casting.

[0045] (3) After the magnesium oxide powder is dried, wrap the casting with tin foil and press it firmly. Then place the wrapped sample in an iron can with a small amount of magnesium oxide powder at the bottom, fill the gaps around the sample with magnesium oxide powder and press it firmly. Then cover the mouth of the iron can with tin foil and make several small holes evenly on the tin foil. The purpose is to allow air to pass through.

[0046] (4) Place the iron can containing the casting and magnesium oxide powder into a heat treatment furnace with an initial temperature of room temperature. Heat the furnace to 500°C and hold for 10 hours. After holding, remove the casting and water-cool it. Clean the surface oxide layer with sandpaper. After solution treatment, the SEM microstructure is as follows: Figure 1 As shown in (b).

[0047] Magnesium alloys oxidize rapidly at temperatures above 450°C, readily reacting with oxygen and water vapor in the air. To prevent burn-off due to oxidation during solution treatment, this invention embeds the sample in dry magnesium oxide powder to protect it from burn-off.

[0048] Step 3: Hot extrusion deformation

[0049] (1) Install the mold required for extrusion on the vertical extruder, heat the mold to the required extrusion temperature with an electric resistance furnace and keep it at the temperature for at least 30 minutes to ensure that the mold is heated evenly inside.

[0050] (2) While the mold is being heated, the heat treatment furnace is heated to the required extrusion temperature. After the temperature is reached, the solution-treated casting is placed in the furnace and kept at that temperature for 1 hour.

[0051] (3) After the mold and casting have been kept warm, quickly put the casting into the mold and extrude it at an extrusion speed of 0.4 mm / s, an extrusion ratio of 25:1 and an extrusion angle of 30°.

[0052] (4) After extrusion, the extruded part is removed and water-cooled to obtain a slender extrusion rod with a diameter of Ø8mm. The extruded SEM microstructure is shown below. Figure 3 As shown, Mg in extruded state at 400℃ 90 EDS energy spectrum of Y4Zn2Ni4 alloy as follows Figure 4 and Figure 5 As shown.

[0053] This embodiment employs two extrusion temperatures. Both methods utilize the melting and solution treatment processes described above, differing only in the extrusion temperature. This invention uses extrusion temperatures of 400°C and 420°C, with an extrusion speed of 0.4 mm / s and an extrusion angle of 30°C for both. o The extrusion ratio was 25:1 for both alloys. At 400°C, the tensile strength was 457.3 MPa, elongation was 27.9%, and elastic modulus was 51.32 GPa. At 420°C, the tensile strength was 415.9 MPa, elongation was 23.5%, and elastic modulus was 50.57 GPa. The room temperature tensile stress-strain curves and tensile strength / elongation of the alloy are shown below. Figure 6 See Table 1.

[0054] Table 1 Extruded Mg 90 Room temperature mechanical properties of Y4Zn2Ni4 alloy under different extrusion parameters

[0055]

[0056] The hot extrusion temperature is closely related to the amount of rare earth elements added to the magnesium alloy; a higher amount of rare earth elements requires a higher temperature. In this embodiment, after alloying with a high content of rare earth Y (12.23 wt.%), a lower extrusion temperature (400℃ and 420℃) and a high extrusion ratio (25:1) were used for hot extrusion deformation. The lower extrusion temperature is beneficial to the refinement of the grain structure, thereby achieving a good strength improvement, while the high extrusion ratio is beneficial to the increase of the alloy recrystallization ratio and can promote the improvement of elongation. Therefore, the Mg alloy prepared in this embodiment... 90 Y4Zn2Ni4 wrought magnesium alloys exhibit a good balance between strength and plasticity.

[0057] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A high-modulus, high-strength, and high-toughness Mg 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, Includes the following steps: 1) Alloy smelting: According to the composition ratio of the magnesium alloy to be prepared, the raw material metals of Mg, Y, Zn and Ni are mixed and smelted by flux covering and protected smelting method and then cast into as-cast alloy. 2) Solution treatment: The as-cast alloy is subjected to solution treatment; the solution treatment is to embed the as-cast alloy with dry magnesium oxide powder, and the solution treatment temperature is >450℃. 3) Hot extrusion deformation: The solution-treated cast alloy is extruded at an extrusion temperature of 400-420℃, an extrusion speed of 0.4mm / s, an extrusion ratio of 25:1, and an extrusion angle of 30°.

2. The high-modulus, high-strength, and high-toughness Mg according to claim 1 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, The alloy smelting process involves first melting magnesium ingots, then adding Mg-30Y master alloy and zinc, melting them, and then adding nickel and refining them.

3. The high-modulus, high-strength, and high-toughness Mg according to claim 2 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, An alloy system was prepared using magnesium ingots, pure zinc blocks, nickel sheets, and Mg-30wt.%Y master alloy as raw materials under protective gas conditions.

4. The high-modulus, high-strength, and high-toughness Mg according to claim 3 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, Melting magnesium ingots: Place the crucible in a pit-type resistance furnace, heat it to 500℃, put the preheated pure Mg into the crucible, and evenly sprinkle the ground and preheated covering agent on its surface. At the same time, introduce high-purity Ar2 into the furnace as a protective gas. Raise the temperature of the resistance furnace to 710℃ and hold for 10 minutes, then raise the temperature again to 720℃ and hold for 10 minutes to completely melt the magnesium ingots.

5. A high-modulus, high-strength, and high-toughness Mg alloy according to claim 4. 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, After the magnesium ingots are completely melted, the furnace is opened and the slag on the surface of the solution is skimmed off. Then, the preheated Mg-30Y master alloy and pure zinc blocks are added. After the covering agent is evenly sprinkled on the surface of the solution, the furnace is closed and the temperature is raised. After the furnace temperature reaches 750℃ and is held for 10 minutes, the temperature is raised again. When the temperature reaches 780℃, the furnace is opened again to skim off the scum on the surface of the solution. The preheated nickel sheet is added and stirred for 2-3 minutes. After stirring, a covering agent is evenly sprinkled on the surface of the solution and the furnace is closed and the temperature is raised. After the furnace temperature rises back to 780℃, it is held for 10 minutes. Then, when the furnace temperature drops to 740℃, the furnace is opened for the third time to skim off the scum on the surface of the solution and a refining agent is added for 2-3 minutes of refining. After refining, a covering agent is evenly sprinkled on the surface of the solution and the furnace is closed and the temperature is raised. After the furnace temperature rises to 780℃, it is held for 20 minutes.

6. The high-modulus, high-strength, and high-toughness Mg according to claim 5 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, After refining, the furnace temperature is lowered to 740°C. After skimming off the slag on the surface of the solution, the molten metal is poured into a water-cooled steel mold. After cooling to room temperature, the cast alloy is removed and cooled to room temperature.

7. The high-modulus, high-strength, and high-toughness Mg according to claim 1 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, The solution treatment temperature is 500℃.

8. The high-modulus, high-strength, and high-toughness Mg according to claim 1 90 The method for preparing Y4Zn2Ni4 wrought magnesium alloy is characterized by, The hot extrusion deformation involves mounting the required die on a vertical extruder, heating the die to the required extrusion temperature using an electric resistance furnace, and holding it at that temperature for ≥30 minutes to ensure uniform heating inside the die. While the mold is being heated, the heat treatment furnace is heated to the required extrusion temperature. Once the temperature is reached, the solution-treated casting is placed in the furnace and kept at that temperature for 1 hour. Then, hot extrusion deformation is performed.

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