A laminated heterostructure super-high strength and toughness magnesium alloy and a preparation method thereof

Abstract

This invention discloses a layered heterostructure ultra-high strength and toughness magnesium alloy and its preparation method. The ultra-high strength and toughness magnesium alloy comprises the following chemical composition by mass percentage: Gd: 9.0-11.0 wt%; Y: 1.5-2.5 wt%; Zn: 0.9-1.5 wt%; Zr: 0.3-0.8 wt%; with the balance being Mg and unavoidable impurities. Furthermore, the ultra-high strength and toughness magnesium alloy possesses a layered heterostructure. The ultra-high strength and toughness magnesium alloy obtained by this invention has a layered heterostructure, which can improve the strength of the magnesium alloy while retaining its excellent toughness, thus enabling the magnesium alloy to possess both high strength and high toughness.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and relates to magnesium alloys, and particularly to a layered heterostructure ultra-high strength and toughness magnesium alloy and its preparation method. Background Technology

[0002] Magnesium and magnesium alloys are currently the lightest engineering structural materials. Their low density, high specific strength, and excellent damping properties give them irreplaceable lightweight advantages in aerospace, new energy vehicles, and other fields. However, compared to traditional structural materials such as steel and aluminum alloys, magnesium alloys suffer from lower absolute strength and elastic modulus, poor plastic forming ability, low service temperature, and poor corrosion resistance, which severely limit their widespread application.

[0003] Rare earth magnesium alloys, especially Mg-Gd-Y alloys, can achieve long-period stacked structure phases (LPSO phases) and nano-precipitated phases. Under the synergistic strengthening effect of these two phases, Mg-Gd-Y alloys exhibit high strength, low density, and resistance to high-temperature creep, showing promising application prospects in the field of lightweight aerospace structural components. However, Mg-Gd-Y alloys are prone to elemental segregation during solidification, leading to uneven solute distribution. Solid solution strengthening, precipitation strengthening, and second-phase strengthening are usually affected by solute partitioning, making it difficult to simultaneously achieve high strength and high toughness. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide a layered heterostructure ultra-high strength and toughness magnesium alloy and its preparation method. The ultra-high strength and toughness magnesium alloy prepared by this invention has a layered heterostructure, which can improve the strength of the magnesium alloy while retaining its excellent toughness, so that the magnesium alloy has both high strength and high toughness.

[0005] The technical solution of this invention is implemented as follows:

[0006] A layered heterostructure ultra-high strength and toughness magnesium alloy, by mass percentage, comprises the following chemical composition: Gd: 9.0-11.0 wt%; Y: 1.5-2.5 wt%; Zn: 0.9-1.5 wt%; Zr: 0.3-0.8 wt%; the balance being Mg and unavoidable impurities; and the ultra-high strength and toughness magnesium alloy has a layered heterostructure.

[0007] Furthermore, the layered heterostructure is composed of alternating β´ nano-precipitates in the coarse-grained α-Mg region and LPSO phase in the fine-grained region.

[0008] The preparation method of the layered heterostructure ultra-high strength and toughness magnesium alloy described above specifically includes the following steps:

[0009] (1) The original ingot of Mg-Gd-Y-Zn-Zr alloy was obtained by a semi-continuous casting process. The original ingot has a layered heterostructure, which is composed of coarse α-Mg grains and fine LPSO phase, with Mg5Gd phase accompanying the LPSO phase.

[0010] (2) The original ingot is placed at 480-490℃ for 6-12 hours for solution treatment, and then cooled to room temperature by water cooling.

[0011] (3) The solution-treated magnesium alloy is aged at 190-200℃ for 12-24h, and then cooled to room temperature by air cooling to obtain the ultra-high strength and toughness magnesium alloy.

[0012] Furthermore, in step (1), the semi-continuous casting process is as follows:

[0013] Preparation of materials: Weigh magnesium ingots, magnesium-gadolinium master alloy, magnesium-zirconium master alloy, magnesium-yttrium master alloy and pure zinc.

[0014] Melting: Under a protective atmosphere of CO2 and SF6, set the temperature of the resistance furnace to 580-600℃. After the crucible is preheated to a dark red color, add magnesium ingots. Set the temperature to 650-670℃. After the magnesium ingots melt, raise the temperature to 700-720℃, and then add magnesium-gadolinium master alloy, magnesium-yttrium master alloy, and pure zinc to the crucible in sequence. After melting, raise the temperature to 740-760℃, and then add magnesium-zirconium master alloy. After the magnesium-zirconium master alloy melts, lower the temperature to 710-730℃, and continuously and evenly sprinkle RJ-6 flux into the crucible while stirring. After stirring, remove the surface slag, and then evenly sprinkle a layer of RJ-6 flux on the surface. Let it settle for 30 minutes to obtain the melt.

[0015] Semi-continuous casting: The inner wall of the crystallizer is polished and coated with boron nitride as a release agent. An ultrasonic vibration device is installed on the outside of the crystallizer. The ultrasonic vibration parameters can be adjusted according to the actual ingot size to ensure that the ultrasonic stress field can penetrate the crystallizer wall and act on the melt. The melt is quantitatively introduced into the crystallizer along the flow channel for casting, while cooling water is circulated through the outer wall of the crystallizer. The original ingot is then quickly pulled out. The casting temperature is 710-730℃, the water temperature is 20-30℃, the water flow rate is 100-120L / min, and the casting speed is 110-130mm / min.

[0016] Furthermore, in the CO2 and SF6 protective atmosphere, the volume ratio of CO2 to SF6 is 9:1.

[0017] Furthermore, during smelting, the total amount of RJ-6 flux used is 1-1.5% of the total amount of raw materials.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. This invention utilizes a semi-continuous casting process and controlled processes to obtain a magnesium alloy ingot with a layered heterostructure consisting of a small amount of LPSO fine-grained regions and a large amount of α-Mg coarse-grained regions. The fine-grained regions are filled with LPSO phase, retaining only a very small amount of Mg, while a small amount of Mg5Gd phase surrounds them. The LPSO phase in the fine-grained regions is a mixed LPSO structure composed of 18R-LPSO, 14H-LPSO, and 24R-LPSO, exhibiting good thermal stability. This ensures the stable existence of the layered heterostructure during heat treatment, guaranteeing heterogeneous deformation-induced (HDI) strengthening under different heat treatment conditions, resulting in excellent comprehensive mechanical properties.

[0020] Subsequent solution treatment dissolves the Mg5Gd phase and promotes the diffusion of solute elements into the α-Mg matrix; aging treatment promotes the precipitation of dispersed β' nano-precipitates in the coarse-grained region of α-Mg, thus obtaining a layered heterostructure with alternating β' nano-precipitates and fine-grained LPSO phases in the coarse-grained region of α-Mg. This achieves the synergistic effect of precipitation strengthening, fine-grain strengthening, and heterostructure strengthening, thereby effectively improving the mechanical properties of magnesium alloys.

[0021] 2. The ultra-high strength and toughness magnesium alloy obtained by this invention has a tensile strength greater than 440 MPa, a yield strength greater than 340 MPa, and an elongation of 10% or more, exhibiting excellent mechanical properties. Attached Figure Description

[0022] Figure 1 -Scanning electron microscope (SEM) images of magnesium alloy ingots obtained in Example 1 and Comparative Example 1.

[0023] Figure 2 -Scanning electron microscope (SEM) images of the ultra-high strength and toughness magnesium alloys obtained in Examples 1, 2 and Comparative Example 1.

[0024] Figure 3 - Stress-strain curves of ultra-high strength and toughness magnesium alloys obtained in Examples 1, 2 and 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0026] Example 1

[0027] A method for preparing a layered heterostructure ultra-high strength and toughness magnesium alloy:

[0028] (1) The preparation of magnesium alloy ingots using a semi-continuous casting process specifically includes the following steps:

[0029] (1.1) Material preparation: The raw materials for this alloy are magnesium ingots (Mg≥99.95%), zinc ingots (Zn≥99.95%), and MgGd30, MgZr30 and MgY30 master alloys.

[0030] (1.2) Smelting: Under the protective atmosphere of CO2 and SF6, the temperature of the resistance furnace was set to 600℃. After the crucible was preheated to a dark red color, magnesium ingots were added. The temperature was set to 660℃. After the magnesium ingots melted, the temperature was raised to 710℃. Magnesium gadolinium master alloy, magnesium yttrium master alloy and pure zinc were added to the crucible in sequence. After melting, the temperature was raised to 750℃ and magnesium zirconium master alloy was added. After the magnesium zirconium master alloy melted, the temperature was lowered to 720℃. While stirring, RJ-6 flux was continuously and evenly sprinkled into the crucible. After stirring, the surface slag was removed, and then a layer of RJ-6 flux was evenly sprinkled on the surface. After settling for 30 minutes, the melt was obtained. Under the protective atmosphere of CO2 and SF6, the volume ratio of CO2 to SF6 was 9:1. The total amount of RJ-6 flux was 1% of the total amount of materials fed.

[0031] (1.3) Semi-continuous casting: The inner wall of the crystallizer is polished and coated with boron nitride as a release agent. An ultrasonic vibration device is installed on the outside of the crystallizer. The ultrasonic vibration parameters can be adjusted according to the actual ingot size to ensure that the ultrasonic stress field can penetrate the crystallizer wall and act on the melt. The melt is quantitatively introduced into the crystallizer along the flow channel for casting, while cooling water is circulated through the outer wall of the crystallizer. The original ingot is quickly pulled out. The casting temperature is 720℃, the water temperature is 25℃, the water flow rate is 120L / min, and the casting speed is 130mm / min.

[0032] (2) Take a stretching bar of a certain size from the magnesium alloy ingot, and then treat the removed stretching bar at 480℃ for 10 hours and cool it to room temperature with water.

[0033] (3) The magnesium alloy after solution treatment is subjected to constant temperature aging treatment at 200℃ for 24h, and then air-cooled to room temperature to obtain the ultra-high strength and toughness magnesium alloy.

[0034] Example 2

[0035] A method for preparing a layered heterostructure ultra-high strength and toughness magnesium alloy includes the following steps:

[0036] (1) Take a stretching bar of a certain size from the magnesium alloy ingot prepared in Example 1, and then treat the stretching bar at 480°C for 6 hours and cool it to room temperature with water.

[0037] (2) The magnesium alloy after solution treatment is subjected to constant temperature aging treatment at 200℃ for 24h, and then air-cooled to room temperature to obtain the ultra-high strength and toughness magnesium alloy.

[0038] Comparative Example 1

[0039] A method for preparing a magnesium alloy:

[0040] (1) Take an ingot of a certain size from the magnesium alloy ingot obtained in Example 1, and then remelt and recast it using the traditional gravity casting process. The method is as follows: Under the protective atmosphere of CO2 and SF6, set the temperature of the resistance furnace to 600°C, preheat the crucible to a dark red color, add the ingot, and set the temperature to 750°C. After the ingot is completely melted, set the temperature to 720°C and let it settle for 30 minutes. In the protective atmosphere of CO2 and SF6, the volume ratio of CO2 to SF6 is 9:1. Then preheat the metal mold to 200°C, and pour the melt into the mold to obtain the ingot billet.

[0041] (2) Take a stretching bar of a certain size from the billet, and then treat the removed stretching bar at 480℃ for 10 hours and cool it to room temperature with water.

[0042] (3) The magnesium alloy after solution treatment is subjected to constant temperature aging treatment at 200℃ for 24h, and then air-cooled to room temperature to obtain the magnesium alloy.

[0043] 1. The main components of the magnesium alloy ingots obtained in Example 1 and Comparative Example 1 are shown in Table 1.

[0044] Table 1. Main component content (%) of magnesium alloy ingots

[0045] Gd Y Zn Zr Mg 10 1.9 1 0.5 margin

[0046] 2. Scanning electron microscope (SEM) images of the magnesium alloy ingots obtained in Example 1 and Comparative Example 1 are shown below. Figure 1 As shown, where Figure 1 (a) Corresponding to Example 1, Figure 1 (b) Response ratio 1. From Figure 1 It is known that the magnesium alloy ingot of Example 1 has a layered heterostructure, which is composed of a large number of coarse grains and a small number of fine grains, forming a layered heterostructure that provides heterostructure reinforcement. The coarse grains are α-Mg grains; the fine grains are filled with LPSO phase, retaining only a very small amount of Mg region, while a small amount of Mg5Gd phase accompanies the fine grain region. The magnesium alloy of Comparative Example 1 consists of a network of Mg3Gd phase, blocky Gd-Y phase, and α-Mg grains distributed along the grain boundaries.

[0047] 3. Scanning electron microscope (SEM) images of the magnesium alloys obtained in Examples 1, 2, and 1 are shown below. Figure 2 As shown, where Figure 2 (a) Corresponding to Example 1, Figure 2 (b) Corresponding to Example 2, Figure 2(c) As shown in the figure, the ultra-high strength and toughness magnesium alloys prepared in Examples 1 and 2 have a layered heterostructure, which consists of a coarse-grained region β´ nano-precipitate phase and a fine-grained region LPSO phase. In contrast, the magnesium alloy prepared in Comparative Example 1 precipitates a large number of lamellar LPSO phases and blocky Gd-Y phases.

[0048] 4. Tensile tests were performed on the magnesium alloys obtained in Examples 1, 2, and 1 (Comparative Example 1), and the stress-strain curves were obtained as follows: Figure 3 As shown in Table 2, the stretching data are as follows.

[0049] Table 2. Tensile test data of ultra-high strength and toughness magnesium alloys

[0050] Example Tensile strength / MPa Yield strength / MPa Elongation / % Example 1 447 354 10.0 Example 2 443 345 11.2 Comparative Example 1 340 219 3.2

[0051] As can be seen from the table above, the mechanical properties of the ultra-high strength and toughness magnesium alloy prepared by the present invention are significantly better than those of Comparative Example 1. The magnesium alloy of the present invention has a tensile strength greater than 440 MPa, a yield strength greater than 340 MPa, and an elongation that can be increased to 10% or more.

[0052] Finally, it should be noted that the above embodiments of the present invention are merely illustrative examples and not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A layered heterostructure ultrahigh strength-to-ductility magnesium alloy, characterized by, The ultra-high strength and toughness magnesium alloy comprises the following chemical composition by weight percentage: Gd: 9.0-11.0 wt%; Y: 1.5-2.5 wt%; Zn: 0.9-1.5 wt%; Zr: 0.3-0.8wt%; balance is Mg and unavoidable impurities; and the ultra-high strength and toughness magnesium alloy has a layered heterogeneous structure.

2. The layered heterostructure ultra-high strength-to-ductility magnesium alloy of claim 1, wherein, The layered heterostructure is composed of alternating β' nano-precipitated phases and LPSO phases.

3. The method for preparing a layered heterostructure ultrahigh strength and toughness magnesium alloy according to claim 1 or 2, characterized in that, Specifically, the following steps are included: (1) The original ingot of Mg-Gd-Y-Zn-Zr alloy was obtained by a semi-continuous casting process. The original ingot has a layered heterostructure, which is composed of coarse α-Mg grains and fine LPSO phase, with Mg5Gd phase accompanying the LPSO phase. (2) The original ingot is solution treated at 480-490℃ for 6-12 hours, and then cooled to room temperature; (3) The magnesium alloy after solution treatment is aged at 190-200℃ for 12-24h, and then cooled to room temperature to obtain the ultra-high strength and toughness magnesium alloy.

4. The method of claim 3, wherein the method further comprises the step of: In step (1), the semi-continuous casting process is as follows: Preparation of materials: Weigh magnesium ingots, magnesium-gadolinium master alloy, magnesium-zirconium master alloy, magnesium-yttrium master alloy, and pure zinc; Melting: Under a protective atmosphere of CO2 and SF6, set the resistance furnace temperature to 580-600℃. After the crucible is preheated to a dark red color, add magnesium ingots. Set the temperature to 650-670℃. After the magnesium ingots melt, raise the temperature to 700-720℃, and then add magnesium-gadolinium master alloy, magnesium-yttrium master alloy, and pure zinc to the crucible in sequence. After melting, raise the temperature to 740-760℃, and then add magnesium-zirconium master alloy. After the magnesium-zirconium master alloy melts, lower the temperature to 710-730℃, and continuously and evenly sprinkle RJ-6 flux into the crucible while stirring. After stirring, remove the surface slag, and then evenly sprinkle a layer of RJ-6 flux on the surface. Let it settle for 30 minutes to obtain the melt. Semi-continuous casting: The inner wall of the crystallizer is polished and coated with boron nitride as a release agent in advance, and an ultrasonic vibration device is installed on the outside of the crystallizer; then the melt is quantitatively introduced into the crystallizer along the flow channel to obtain the original ingot. Cooling water is circulated on the outer wall of the crystallizer during casting; the casting temperature is 710-730℃, the water temperature is 20-30℃, the water flow rate is 100-120L / min, and the casting speed is 110-130mm / min.

5. The method of claim 4, wherein the method further comprises the step of: In a protective atmosphere of CO2 and SF6, the volume ratio of CO2 to SF6 is 9:

1.

6. The method of claim 4, wherein the layered heterostructure ultrahigh strength and toughness magnesium alloy is prepared by the following steps of: During smelting, the total amount of RJ-6 flux used is 1-1.5% of the total amount of raw materials. ​

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