An ultra-high strength magnesium alloy and its preparation method

Abstract

This invention discloses an ultra-high strength magnesium alloy and its preparation method. The ultra-high strength magnesium alloy comprises, by mass percentage: Gd: 8~13 wt%; Y: 1~3 wt%; Zn: 0.5~1.5 wt%; Zr: 0.2~0.8 wt%; Fe≤0.003 wt%; Cu≤0.002 wt%; Si≤0.005 wt%; Ni≤0.0012 wt%; the remainder being Mg and unavoidable impurities. The preparation method is as follows: Preheat the crucible, add magnesium ingots to the crucible and melt the ingots; then raise the temperature to 770-790℃, add magnesium-gadolinium master alloy, magnesium-zirconium master alloy, magnesium-yttrium master alloy and zinc granules to the crucible for homogenization treatment; then refine; after refining, remove surface slag, cover with a covering agent, and then sequentially undergo high-temperature and low-temperature settling; during casting, ensure the crystallizer is dry and brush the inner wall with lubricating oil, and under the protection of sulfur hexafluoride and argon, the casting temperature is 710-730℃, and the water temperature is room temperature, to obtain a magnesium alloy ingot; then heat treat to obtain the ultra-high strength magnesium alloy. The ultra-high strength magnesium alloy of this invention has excellent mechanical properties and has wide application potential.

Description

Technical Field

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

[0002] Magnesium alloys are among the lightest metallic structural materials used in engineering applications. The density of pure magnesium is only 1.74 g / cm³. 3 It is about 2 / 3 the weight of aluminum and 1 / 4 the weight of iron. At the same time, magnesium alloys have become the most promising new structural materials after steel and aluminum alloys due to their advantages such as weight reduction, high specific strength and specific stiffness.

[0003] Magnesium alloys are widely used in many fields such as automobiles, aerospace, and 3C products due to their low density, excellent comprehensive mechanical properties, and abundant reserves in the Earth's crust. However, their relatively low strength and ductility are one of the most important factors hindering their widespread application. Therefore, the preparation of ultra-high-strength magnesium alloys with superior properties is particularly important.

[0004] In recent years, to develop high-strength magnesium alloys, high-performance rare-earth magnesium alloys, represented by Mg-Gd, Mg-Y, and Mg-Nd, have been developed. For example, the VW103Z cast magnesium alloy developed by Shanghai Jiao Tong University has a tensile strength of 328 MPa, a yield strength of 248 MPa, and an elongation of 1.1% in the T6 state. The Mg-Y-Nd-Zn-Zr alloy developed by Central South University has a tensile strength, yield strength, and elongation of 330 MPa, 265 MPa, and 6.5%, respectively. How to further improve the mechanical properties (tensile strength, yield strength, and elongation) of magnesium alloys remains a technical problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to provide an ultra-high strength magnesium alloy and its preparation method. The ultra-high strength magnesium alloy of this invention has good mechanical properties and has the potential for wide application.

[0006] The technical solution of this invention is implemented as follows:

[0007] An ultra-high strength magnesium alloy, comprising the following chemical composition by mass percentage: Gd: 8–13 wt%; Y: 1–3 wt%; Zn: 0.5–1.5 wt%; Zr: 0.2–0.8 wt%; Fe ≤ 0.003 wt%; Cu ≤ 0.002 wt%; Si ≤ 0.005 wt%; Ni ≤ 0.0012 wt%; the remainder being Mg and unavoidable impurities.

[0008] The first method for preparing the aforementioned ultra-high strength magnesium alloy specifically includes the following steps:

[0009] (1) Semi-continuous casting of magnesium alloy ingots: Preheating the crucible: Set the temperature of the electric melting furnace to 550-600℃; Loading the furnace: First add magnesium ingots, and after each layer is added, sprinkle a layer of RJ-6 flux on the surface; Homogenization treatment: Raise the temperature of the electric furnace to 770-790℃, remove the slag on the surface of the liquid, and add magnesium gadolinium master alloy, magnesium zirconium master alloy, magnesium yttrium master alloy and pure zinc into the crucible. Stir manually and continuously sprinkle RJ-6 flux evenly. After stirring, remove the slag from the bottom and surface of the crucible and let it settle for 5-10 minutes; Refining: Insert the argon tube 80-100m above the bottom of the crucible. Argon gas is introduced in all directions at a flow rate of 0.03–0.08 MPa. Refining is carried out for 10–20 minutes. After refining, the surface slag is removed, and a layer of RJ-6 flux is sprinkled on top to cover it. Then, high-temperature settling and low-temperature settling are carried out in sequence. Semi-continuous casting: During semi-continuous casting, under the protection of sulfur hexafluoride and argon gas, the crystallizer is kept dry and the inner wall is brushed with lubricating oil. The casting temperature is 710–730℃, the water temperature is room temperature, the casting speed is 110–130 mm / min, the water flow rate is 100–120 L / min, and the water pressure is 0.15–0.25 MPa.

[0010] (2) Aging treatment: The magnesium alloy ingot is kept at 190-210℃ for 36-64 hours and then air-cooled to room temperature to obtain the ultra-high strength magnesium alloy.

[0011] The second method for preparing the aforementioned ultra-high strength magnesium alloy specifically includes the following steps:

[0012] (1) Semi-continuous casting of magnesium alloy ingots: Preheating the crucible: Set the temperature of the electric melting furnace to 550-600℃; Loading the furnace: First add magnesium ingots, and after each layer is added, sprinkle a layer of RJ-6 flux on the surface; Homogenization treatment: Raise the temperature of the electric furnace to 770-790℃, remove the slag on the surface of the liquid, and add magnesium gadolinium master alloy, magnesium zirconium master alloy, magnesium yttrium master alloy and pure zinc into the crucible. Stir manually and continuously sprinkle RJ-6 flux evenly. After stirring, remove the slag from the bottom and surface of the crucible and let it settle for 5-10 minutes; Refining: Insert the argon tube 80-100m above the bottom of the crucible. Argon gas is introduced in all directions at a flow rate of 0.03–0.08 MPa. Refining is carried out for 10–20 minutes. After refining, the surface slag is removed, and a layer of RJ-6 flux is sprinkled on top to cover it. Then, high-temperature settling and low-temperature settling are carried out in sequence. Semi-continuous casting: During semi-continuous casting, under the protection of sulfur hexafluoride and argon gas, the crystallizer is kept dry and the inner wall is brushed with lubricating oil. The casting temperature is 710–730℃, the water temperature is room temperature, the casting speed is 110–130 mm / min, the water flow rate is 100–120 L / min, and the water pressure is 0.15–0.25 MPa.

[0013] (2) Solution treatment: The magnesium alloy ingot is kept at 480-500℃ for 8-12 hours and then cooled to room temperature by water.

[0014] (3) Aging treatment: The magnesium alloy after solution treatment is kept at 190-210℃ for 36-64 hours and then air-cooled to room temperature to obtain the ultra-high strength magnesium alloy.

[0015] Furthermore, in the two preparation methods mentioned above, the high-temperature standing time is 10-20 minutes at 780-810°C.

[0016] Furthermore, in the two preparation methods mentioned above, during the low-temperature standing process, the temperature is set at 670–700°C for 10–20 minutes.

[0017] Furthermore, in the two preparation methods mentioned above, in step (1), the total amount of RJ-6 flux is 1% of the total amount of raw materials.

[0018] Furthermore, in the two preparation methods described above, in step (1), during refining, a first refining and a second refining are performed sequentially:

[0019] First refining: Insert the argon tube 80-100mm above the bottom of the crucible and pull it upwards. Adjust the argon flow rate to 0.03-0.08MPa in eight directions equal to the crucible diameter. Refine for 5-10 minutes, and continuously and evenly sprinkle refining agent onto the wave crest during the refining process.

[0020] Secondary refining: Argon gas is used for stirring for 5-10 minutes at a flow rate of 0.03-0.08 MPa. During the refining process, refining agent is continuously and evenly sprinkled onto the wave crests until the surface of the magnesium melt is mirror-like, at which point the refining is stopped.

[0021] The total amount of refining agent used in primary and secondary refining is 2-3% of the total feed.

[0022] Furthermore, the refining agent is a mixture of RJ-6 flux and magnesium fluoride, wherein the mass ratio of RJ-6 flux to magnesium fluoride is 4:1.

[0023] Furthermore, in the two preparation methods mentioned above, in step (1), the volume ratio of sulfur hexafluoride to argon is 1:5.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention obtains magnesium alloy ingots through a semi-continuous casting process. During the casting process, the ingots undergo high-temperature and low-temperature settling, which effectively reduces impurity elements in the melt, resulting in Fe≤0.003wt%, Cu≤0.002wt%, Si≤0.005wt%, and Ni≤0.0012wt%, thereby improving the mechanical properties of magnesium alloy products.

[0026] 2. After heat treatment, the magnesium alloy material of this invention exhibits a large amount of blocky second phase and a small amount of lamellar long-period stacked ordered (LPSO) phase, a significant amount of precipitated phase, and a small amount of cubic (Gd-Y) phase in the matrix. The blocky second phase is distributed along the grain boundaries, while the lamellar long-period stacked ordered (LPSO) phase grows into the grains along the grain boundaries. The cubic (Gd-Y) phase is mainly distributed at the grain boundaries, with a small amount distributed inside the grains. The synergistic effect of the abundant diffusely distributed second phase and precipitated phase provides the alloy with excellent mechanical properties. After solution treatment and aging, the tensile strength of the alloy reaches 420 MPa, and after direct aging without solution treatment, the tensile strength of the alloy reaches 404 MPa. Attached Figure Description

[0027] Figure 1 - Stress-strain curves of magnesium alloys in the as-cast state.

[0028] Figure 2 - OM image of the as-cast metallographic microstructure of magnesium alloy.

[0029] Figure 3 - SEM image of a magnesium alloy in its as-cast state.

[0030] Figure 4 - Stress-strain curves of ultra-high strength magnesium alloys obtained in Examples 1 to 4.

[0031] Figure 5 Example 1: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment.

[0032] Figure 6 Example 1: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment and aging treatment.

[0033] Figure 7 Example 2: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment.

[0034] Figure 8 Example 2: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment and aging treatment.

[0035] Figure 9 Example 3: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment.

[0036] Figure 10 Example 3: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after solution treatment and aging treatment.

[0037] Figure 11 Example 4: Local high-magnification scanning electron microscope (SEM) image of a magnesium alloy ingot after direct aging treatment. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0039] The preparation of magnesium alloy ingots using a semi-continuous casting process specifically includes the following steps:

[0040] (1) Material preparation: The raw materials for this alloy are magnesium ingots (Mg≥99.95%), zinc ingots (Zn≥99.95%), and MgGd40, MgZr30 and MgY30 master alloys.

[0041] Prepare the following raw materials by weight percentage:

[0042] Gd (%) Y(％) Zn(%) Zr(％) Mg (%) Ingredient Value 10.3 2.2 1.1 0.5 margin

[0043] (2) Preheating the crucible: During production, the temperature of the electric furnace is set to 600℃, and the crucible is preheated to a dark red color.

[0044] (3) Charging: First add magnesium ingots, and after each addition, sprinkle a layer of RJ-6 flux on the surface to prevent oxidation of the melt surface.

[0045] (4) Homogenization: Heat to 780℃, remove slag, and then add Mg-Gd master alloy, Mg-Y master alloy, Mg-Zr master alloy, and Zn particles to the crucible. Stir manually for 5 minutes, continuously and evenly sprinkling RJ-6 flux onto the peaks of the liquid during stirring. After stirring, use a slag-removing spoon to remove the slag from the bottom and surface of the pot. Finally, evenly sprinkle a thin layer of RJ-6 flux on the surface and allow it to settle for 10 minutes.

[0046] (5) Refining

[0047] First refining: Insert the argon tube 100mm above the bottom of the crucible and pull it upwards. Adjust the argon flow rate to 0.04MPa in eight directions equal to the crucible diameter. Refine for 5 minutes. During the refining process, continuously and evenly sprinkle refining agent onto the peak of the liquid.

[0048] Secondary refining: Argon gas stirring is also used for 5 minutes at a flow rate of 0.04 MPa. During the refining process, refining agent is continuously and evenly sprinkled onto the wave crest until the surface of the magnesium melt is mirror-like, at which point the refining is stopped.

[0049] The refining agent is a mixture of RJ-6 flux and magnesium fluoride. The total amount of refining agent used in primary and secondary refining is 2-3% of the total feed.

[0050] (6) Let stand

[0051] High-temperature settling: After refining, remove the surface scum, sprinkle a layer of RJ-6 flux to cover it, and then transfer to high-temperature settling at 800℃ for 10 minutes.

[0052] Low-temperature settling: After the high-temperature settling is completed, the furnace is closed and the temperature is lowered to 690℃ to reduce the iron content; then the furnace is opened and the temperature is raised to 720℃ for casting.

[0053] The total amount of RJ-6 flux used in the charging step (3), homogenization step (4) and settling step (6) is 1% of the total amount of material fed.

[0054] (7) Use a crane to hoist the pre-packed lid onto the crucible and align it with the crucible flange; heat the casting tube until it glows red, then slowly lower it into the crucible and secure it. Dry the crystallizer with dry compressed air, brush the inner wall with lubricating oil, raise the casting base 40mm into the crystallizer and plug it with asbestos rope, and clean and fully preheat the tools used in the casting process. The ratio of sulfur hexafluoride to argon is 1:5 during casting, the casting temperature is 710~730℃, the water temperature is room temperature, the casting speed is 110-130mm / min, the water flow rate is 100-120L / min, and the water pressure is 0.15-0.25Mpa. Finally, a magnesium alloy ingot is obtained by casting.

[0055] 1. The main components of the obtained magnesium alloy ingot were tested, and the test results are shown in Table 1.

[0056] Table 1. Main component content (%) of magnesium alloy ingots

[0057] Gd Y Zn Zr Fe Cu Si Ni Mg 10.2 2.04 1.04 0.45 0.0015 0.0019 0.0002 0.0012 margin

[0058] 2. Tensile tests were performed on the as-cast magnesium alloy, and the resulting stress-strain curves are shown below. Figure 1 As shown, the tensile test data are shown in Table 2.

[0059] Table 2. As-cast tensile test data of magnesium alloys

[0060]

[0061]

[0062] 3. The as-cast metallographic microstructure (OM) image and scanning electron microscope (SEM) image of the magnesium alloy are shown below. Figure 2 and Figure 3 As shown, by Figure 3 It can be seen that the alloy phase consists of a second phase distributed in a network along the grain boundaries, dot-shaped Zn-Zr phases distributed in a dispersed form in the grains, blocky Gd-Y phases, and lamellar structure in the grains.

[0063] Example 1

[0064] A drawing bar of a certain size is taken from the above magnesium alloy ingot. The drawing bar is then subjected to constant temperature solution treatment at 480℃ for 10 hours, followed by water cooling to room temperature. Finally, the solution is aged at constant temperature at 200℃ for 48 hours and then air-cooled to room temperature to obtain an ultra-high strength magnesium alloy.

[0065] Example 2

[0066] A drawing bar of a certain size is taken from the above magnesium alloy ingot. The drawing bar is then subjected to constant temperature solution treatment at 480℃ for 10 hours, followed by water cooling to room temperature. Finally, the solution is aged at constant temperature at 200℃ for 36 hours and then air-cooled to room temperature to obtain an ultra-high strength magnesium alloy.

[0067] Example 3

[0068] A drawing bar of a certain size is taken from the above magnesium alloy ingot. The drawing bar is then subjected to constant temperature solution treatment at 480℃ for 12 hours, followed by water cooling to room temperature. Finally, the solution is aged at constant temperature at 200℃ for 48 hours and then air-cooled to room temperature to obtain an ultra-high strength magnesium alloy.

[0069] Example 4

[0070] A drawing bar of a certain size is taken from the above-mentioned magnesium alloy ingot. Without solution treatment, the drawing bar is directly aged at 200℃ for 48 hours and then air-cooled to room temperature to obtain an ultra-high strength magnesium alloy.

[0071] 1. Tensile tests were conducted on the ultra-high strength magnesium alloys obtained in Examples 1 to 4. The tensile test data are shown in Table 3, and the stress-strain curves obtained are as follows: Figure 4 As shown.

[0072] Table 3. Tensile test data of ultra-high strength magnesium alloys obtained in Examples 1 to 4

[0073] Example Tensile strength / MPa Yield strength / MPa Elongation / % Example 1 420 352 5.9 Example 2 419 351 5.0 Example 3 416 283 5.1 Example 4 404 314 4.5

[0074] As can be seen from the table above, the mechanical properties of the magnesium alloy after the optimal solution treatment and aging process reach 420 MPa, and the mechanical properties after direct aging treatment without solution treatment also reach 404 MPa, which is a significant improvement in mechanical properties compared to magnesium alloy materials.

[0075] 3. The high-magnification scanning electron microscope (SEM) images of the magnesium alloy ingots after solution treatment and solution treatment + aging treatment in Example 1 are shown below. Figure 5 and Figure 6 As shown; the high-magnification scanning electron microscope (SEM) images of the magnesium alloy ingots after solution treatment and solution treatment + aging treatment in Example 2 are shown below. Figure 7 and Figure 8As shown; the high-magnification scanning electron microscope (SEM) images of the magnesium alloy ingots after solution treatment and solution treatment + aging treatment in Example 3 are shown below. Figure 9 and Figure 10 As shown; the local high-magnification scanning electron microscope (SEM) images of the magnesium alloy ingot after direct aging treatment in Example 4 are shown below. Figure 11 As shown.

[0076] Depend on Figure 5 , Figure 7 and Figure 9 It is evident that after solution treatment, the lamellar structure within the alloy grains has completely dissolved into the matrix. The Zn-Zr phase and the second phase distributed along the grain boundaries have also partially dissolved into the matrix. The rare-earth-rich (Gd-Y) phase shows no signs of dissolution. Figure 9 It can be seen that after a longer solid solution treatment in Example 3, more of the second phase in the alloy dissolved into the matrix, and the number density of each microstructure was reduced compared with Example 1 and Example 2.

[0077] Depend on Figure 6 , Figure 8 and Figure 10 It is evident that after aging treatment, the number density of the second phase distributed along the grain boundaries did not change significantly, relative to... Figure 3 The second phase has changed from a continuous network distribution to a discontinuous distribution, and at the same time, more precipitated phases have formed in the matrix.

[0078] contrast Figure 11 and Figure 3 In Example 4, without solution treatment and after direct aging, the distribution of the second phase and its as-cast state showed no significant difference. However, compared to Examples 1-3, the second phase dispersibility in Example 4 was poor, and the number density of precipitated phases in the matrix was also lower, resulting in relatively weaker mechanical properties. Finally, it should be noted that the above embodiments of the present invention are merely examples for illustrating the invention and are not intended to limit the implementation of the invention. For those skilled in the art, other variations and modifications can be made based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing an ultra-high strength magnesium alloy, characterized in that, The ultra-high strength magnesium alloy comprises the following chemical components by weight percentage: Gd: 8~13 wt%; Y: 1~3 wt%; Zn: 0.5~1.5 wt%; Zr: 0.2~0.8 wt%; Fe ≤0.003 wt%; Cu ≤0.002 wt%; Si ≤0.005 wt%; Ni ≤0.0012 wt%; the remainder is Mg and unavoidable impurities; the preparation method specifically includes the following steps: (1) Semi-continuous casting of magnesium alloy ingots: Preheating crucible: Set the temperature of the electric melting furnace to 550~600 ℃; Loading furnace: First add magnesium ingots, and after each layer is added, sprinkle a layer of RJ-6 flux on the surface; Homogenization treatment: Raise the temperature of the electric furnace to 770~790 ℃, remove the slag on the surface of the liquid, add magnesium gadolinium master alloy, magnesium zirconium master alloy, magnesium yttrium master alloy and pure zinc into the crucible, stir manually and continuously sprinkle RJ-6 flux evenly, after stirring, remove the bottom and surface slag, and let it settle for 5~10 min; Refining: Insert the argon tube 80~100mm above the bottom of the crucible and pass argon gas in all directions at a pressure of 0.03~0.08 MPa, refine for 10~20 min, after refining remove the surface slag, sprinkle a layer of RJ-6 flux to cover, and then perform high temperature settling and low temperature settling in sequence. During high temperature settling, settling at 780~810 ℃ for 10~20 min. min; When standing at low temperature, stand at 670~700 ℃ for 10~20 min; Semi-continuous casting: During semi-continuous casting, under the protection of sulfur hexafluoride and argon, ensure that the crystallizer is dry and brush the inner wall with lubricating oil, the casting temperature is 710~730 ℃, the water temperature is room temperature, the casting speed is 110~130 mm / min, the water flow rate is 100~120 L / min, and the water pressure is 0.15~0.25 MPa; (2) Aging treatment: The magnesium alloy ingot is kept at 190~210℃ for 36~64 h and then air-cooled to room temperature to obtain the ultra-high strength magnesium alloy.

2. A method for preparing an ultra-high strength magnesium alloy, characterized in that, The ultra-high strength magnesium alloy comprises the following chemical components by weight percentage: Gd: 8~13 wt%; Y: 1~3 wt%; Zn: 0.5~1.5 wt%; Zr: 0.2~0.8 wt%; Fe ≤0.003 wt%; Cu ≤0.002 wt%; Si ≤0.005 wt%; Ni ≤0.0012 wt%; the remainder is Mg and unavoidable impurities; the preparation method specifically includes the following steps: (1) Semi-continuous casting of magnesium alloy ingots: Preheating crucible: Set the temperature of the electric melting furnace to 550~600 ℃; Loading furnace: First add magnesium ingots, and after each layer is added, sprinkle a layer of RJ-6 flux on the surface; Homogenization treatment: Raise the temperature of the electric furnace to 770~790 ℃, remove the slag on the surface of the liquid, add magnesium gadolinium master alloy, magnesium zirconium master alloy, magnesium yttrium master alloy and pure zinc into the crucible, stir manually and continuously sprinkle RJ-6 flux evenly, after stirring, remove the bottom and surface slag, and let it settle for 5~10 min; Refining: Insert the argon tube 80~100mm above the bottom of the crucible and pass argon gas in all directions at a pressure of 0.03~0.08 MPa, refine for 10~20 min, after refining remove the surface slag, sprinkle a layer of RJ-6 flux to cover, and then perform high temperature settling and low temperature settling in sequence. During high temperature settling, settling at 780~810 ℃ for 10~20 min. min; When standing at low temperature, stand at 670~700 ℃ for 10~20 min; Semi-continuous casting: During semi-continuous casting, under the protection of sulfur hexafluoride and argon, ensure that the crystallizer is dry and brush the inner wall with lubricating oil, the casting temperature is 710~730 ℃, the water temperature is room temperature, the casting speed is 110~130 mm / min, the water flow rate is 100~120 L / min, and the water pressure is 0.15~0.25 MPa; (2) Solution treatment: The magnesium alloy ingot is kept at 480~500 ℃ for 8~12 h and then cooled to room temperature by water; (3) Aging treatment: The magnesium alloy after solution treatment is kept at 190~210 ℃ for 36~64 h and then air-cooled to room temperature to obtain the ultra-high strength magnesium alloy.

3. The method for preparing an ultra-high strength magnesium alloy according to claim 1 or 2, characterized in that, In step (1), the total amount of RJ-6 flux is 1% of the total amount of material fed.

4. A method for preparing an ultra-high strength magnesium alloy according to claim 1 or 2, characterized in that, In step (1), the volume ratio of sulfur hexafluoride to argon is 1:

5.

5. An ultra-high strength magnesium alloy, characterized in that, It is prepared by the preparation method of any one of claims 1 to 4 for an ultra-high strength magnesium alloy.

Images