High-toughness wrought rare-earth magnesium alloy and preparation method thereof

Abstract

The application discloses a high-strength and high-toughness deformed rare earth magnesium alloy and a preparation method thereof. The magnesium alloy comprises the following chemical components in percentage by mass: Gd: 9-12 wt%; Y: 1-3 wt%; Zn: 0.5-1.5 wt%; Mn: 0.5-0.8 wt%; Fe: less than or equal to 0.003 wt%; Cu: less than or equal to 0.002 wt%; Si: less than or equal to 0.005 wt%; Ni: less than or equal to 0.0012 wt%; and the rest is Mg and inevitable impurities. In the preparation, firstly, a magnesium alloy ingot with qualified components is obtained through casting; then the magnesium alloy ingot is solid-solved at 480-500 DEG C for 6-10 hours, and then is heated to 520-540 DEG C and solid-solved for 10-14 hours, and is air-cooled to room temperature to obtain an ingot after solid-solution; the ingot after solid-solution is extruded at 400-440 DEG C to obtain an extruded rod, wherein the extrusion ratio is 14-16; and the extruded rod is heat-treated at 180-220 DEG C for 40-60 hours and is air-cooled to room temperature, so that the high-strength and high-toughness deformed rare earth magnesium alloy is obtained. The deformed rare earth magnesium alloy prepared by the application has good mechanical strength and plasticity.

Description

Technical Field

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

[0002] Magnesium alloys, due to their light weight, high specific strength, and excellent recyclability, have broad application prospects in the automotive industry, 3C products, aerospace, and other fields. In recent years, although the application rate of extruded magnesium alloys in the market has steadily increased, its commercial application rate still lags significantly behind that of extruded aluminum alloys. This is mainly because problems such as poor extrusion, asymmetric tensile-compression yield, and low absolute strength limit their commercial development. Improving the strength and extrusion efficiency of magnesium alloys can effectively expand their commercial applications. Among these factors, alloy composition and hot extrusion process parameters are the decisive factors affecting the microstructure and properties of extruded alloys.

[0003] Among wrought magnesium alloys, Mg-RE alloys exhibit high strength and toughness, making them a popular high-performance rare-earth magnesium alloy research topic in recent years. Meanwhile, Zr, as the most effective grain refiner, makes Mg-RE-Zn-Zr a preferred choice for wrought magnesium alloys, achieving room-temperature tensile strengths as high as 500 MPa. However, their plasticity is relatively low, with elongation mostly between 5% and 10%. Therefore, how to improve the plasticity of wrought rare-earth magnesium alloys while ensuring their mechanical strength is a technical problem that needs to be solved by those skilled in the art. 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 high-strength and high-toughness wrought rare earth magnesium alloy and its preparation method. The wrought rare earth magnesium alloy prepared by this invention has good mechanical strength and plasticity.

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

[0006] A high-strength and high-toughness wrought rare-earth magnesium alloy comprises the following chemical composition by mass percentage: Gd: 9-12 wt%; Y: 1-3 wt%; Zn: 0.5-1.5 wt%; Mn: 0.5-0.8 wt%; Fe ≤ 0.003 wt%; Cu ≤ 0.002 wt%; Si ≤ 0.005 wt%; Ni ≤ 0.0012 wt%; the remainder being Mg and unavoidable impurities.

[0007] Furthermore, by mass percentage, Gd: 10.55 wt%; Y: 1.68 wt%; Zn: 1.00 wt%; Mn: 0.64 wt%.

[0008] The aforementioned method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy includes the following steps:

[0009] (1) The magnesium alloy ingot obtained by casting has the following chemical composition by mass percentage: Gd: 9-12 wt%; Y: 1-3 wt%; Zn: 0.5-1.5 wt%; Mn: 0.5-0.8 wt%; Fe≤0.003 wt%; Cu≤0.002 wt%; Si≤0.005 wt%; Ni≤0.0012 wt%; the remainder is Mg and unavoidable impurities;

[0010] (2) The magnesium alloy ingot is dissolved at 480-500℃ for 6-10 hours, then heated to 520-540℃ and dissolved for 10-14 hours, and then air-cooled to room temperature to obtain the dissolved ingot.

[0011] (3) The solution-treated ingot is extruded at 400-440°C to obtain an extrusion rod, wherein the extrusion ratio is 14-16;

[0012] (4) The extrusion bar is heat-treated at 180-220°C for 40-60 hours and then air-cooled to room temperature to obtain the high-strength and tough deformable rare earth magnesium alloy.

[0013] Further, in step (1), the magnesium alloy ingot is cast using the following method:

[0014] S1: Prepare pure magnesium, pure zinc, Mg-Gd master alloy, Mg-Y master alloy and Mg-Mn master alloy;

[0015] S2: Place pure magnesium in a crucible and put it in a melting furnace. Set the temperature of the melting furnace to 650-670℃ and introduce a mixture of CO2 and SF6 for protection. After the pure magnesium melts, raise the temperature to 680-720℃ and add pure zinc, Mg-Gd master alloy, Mg-Y master alloy and Mg-Mn master alloy into the crucible. After all the alloy has melted, stir the melt to make the alloy composition uniform.

[0016] S3: Heat the melt to 730-750℃, remove the slag on the surface of the melt, add the refining agent to the melt, and then stir and refine for 3-5 minutes;

[0017] S4: After refining, let it stand at 730-750℃ for 30-40 minutes, and then water cool to obtain the magnesium alloy ingot.

[0018] Furthermore, in S2, the inner wall of the steel crucible is first coated with hexagonal boron nitride, and the smelting furnace is preheated and dried at 100-300°C. Then, pure magnesium is placed into the crucible, and the crucible containing pure magnesium is placed in the smelting furnace.

[0019] Furthermore, the refining agent is C2Cl6, and its addition amount is 0.5% to 1% of the melt mass.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention uses Mn as a grain refiner. Through a two-stage solution treatment + extrusion + aging treatment, it can effectively improve the plasticity of wrought rare earth magnesium alloys, giving them good mechanical strength and plasticity. Specifically, the two-stage solution treatment promotes the precipitation of Mg5(GdY) that can be precipitated at low temperatures during the low-temperature solution stage, thereby increasing the solubility of each element during the high-temperature solution stage. This can more effectively eliminate dendritic microstructures in the alloy, improve the degree of solid solution in the matrix and the distribution of Mn. Then, extrusion further promotes continuous dynamic recrystallization of the alloy structure and more dispersed dynamic precipitation of the second phase, thus improving the alloy performance.

[0022] 2. Compared with Zr, which is commonly used in existing technologies, the use of Mn as a grain refiner in this invention can effectively reduce production costs, reduce alloy grain size, and significantly improve alloy performance.

[0023] 3. The deformed rare earth magnesium alloy obtained by this invention has a tensile strength of 445 MPa, a yield strength of 402 MPa, and an elongation of 13%, exhibiting good mechanical strength and plasticity. Attached Figure Description

[0024] Figure 1 - Stress-strain curves of magnesium alloys obtained in Example 1, Comparative Example 1, and Comparative Example 2.

[0025] Figure 2 -Metallographic microstructure (OM) of magnesium alloy ingot extrusion deformation perpendicular to the extrusion direction in Example 1.

[0026] Figure 3 - A high-magnification scanning electron microscope (SEM) image of a local area perpendicular to the extrusion direction of a magnesium alloy ingot after extrusion deformation in Example 1.

[0027] Figure 4 - Metallographic microstructure (OM) of magnesium alloy ingots in Comparative Example 1, with the extrusion deformation perpendicular to the extrusion direction.

[0028] Figure 5 - Metallographic microstructure (OM) of magnesium alloy ingots in Comparative Example 2, with the extrusion deformation perpendicular to the extrusion direction.

[0029] Figure 6 - A high-magnification scanning electron microscope (SEM) image of a local area perpendicular to the extrusion direction of a magnesium alloy ingot after extrusion deformation in Comparative Example 2.

[0030] Figure 7 -SEM image of the tensile fracture surface of magnesium alloy obtained in Example 1. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] (1) Batching: Pure Mg (99wt%), pure Zn (99wt%), Mg-25Gd (99wt%), Mg-20Y (99wt%) and Mg-10Mn (99wt%) are used to batch the target alloy;

[0034] (2) Melting: The inner wall of the steel crucible is coated with hexagonal boron nitride. At the same time, the melting furnace is preheated and dried at 200°C. Then, pure Mg is placed in the crucible and placed in the melting furnace. The temperature of the melting furnace is set to 670°C, and a mixture of CO2 and SF6 is introduced for protection. After the pure Mg melts, the temperature is raised to 720°C, and pure Zn, Mg-25Gd, Mg-20Y and Mg-30Mn master alloys are added to the crucible. After all the alloys have melted, the melt is stirred to make the alloy composition uniform.

[0035] (3) Refining: Heat the melt to 740°C, remove the slag on the surface of the melt, add refining agent C2Cl6 to the melt (the amount added is 0.8% of the mass of the melt), and then stir thoroughly.

[0036] (4) Standing: After the melt temperature is raised to 740℃, it is left to stand for 30 minutes and then water-cooled to obtain magnesium alloy ingots;

[0037] (5) Solution treatment: Obtained from the above-mentioned magnesium alloy ingot. The spindle with H=100mm was then removed and dissolved at a constant temperature of 500℃ for 8 hours. The temperature was then raised to 520℃ and dissolved at a constant temperature for 12 hours. The spindle was then air-cooled to room temperature.

[0038] (6) Extrusion: The ingot obtained after solution treatment is extruded at a high temperature of 420°C and an extrusion ratio of 16 / 1. Extruded magnesium alloys (extruded state);

[0039] (7) Heat treatment: The extruded magnesium alloy is heat-treated at 200°C for 48 hours and then air-cooled to room temperature to obtain the high-strength and tough wrought rare earth magnesium alloy (extruded + heat-treated state).

[0040] Comparative Example 1

[0041] (1) Solution treatment: obtained from the magnesium alloy ingot of Example 1 The spindle with H=100mm was then removed and dissolved at a constant temperature of 500℃ for 8 hours. The temperature was then raised to 520℃ and dissolved at a constant temperature for 12 hours. The spindle was then air-cooled to room temperature.

[0042] (2) Extrusion: The ingot obtained after solution treatment is extruded at a high temperature of 420°C and an extrusion ratio of 10 / 1. Extruded magnesium alloys (extruded state);

[0043] (3) Heat treatment: The extruded magnesium alloy is heat-treated at 200℃ for 48h and then air-cooled to room temperature to obtain the high strength and toughness wrought rare earth magnesium alloy (extruded + heat-treated state).

[0044] Comparative Example 2

[0045] This embodiment is the same as Embodiment 1, except that Mg-25Zr (99wt%) is used instead of Mg-10Mn (99wt%).

[0046] 1. The actual composition of the VW92 as-cast alloys prepared in Example 1 and Comparative Example 2 is shown in Table 1.

[0047] Table 1. Actual composition (wt.%) of VW92 as-cast alloys produced by different smelting processes

[0048]

[0049] 2. Tensile tests were conducted on the extruded and extruded + heat-treated samples obtained in Example 1, Comparative Example 1, and Comparative Example 2. The tensile test data are shown in Table 2, and the obtained stress-strain curves are as follows: Figure 1 As shown.

[0050] Table 2. Tensile test data

[0051]

[0052] As can be seen from the table above, (1) compared with Comparative Example 1 (extrusion ratio of 10 / 1), the mechanical properties of the extruded state and the extruded state + heat-treated state samples in Example 1 (extrusion ratio of 16 / 1) are better, indicating that in this cast alloy, a larger extrusion ratio has a greater effect on improving the mechanical properties of the alloy.

[0053] (2) The mechanical properties of the extruded sample in Example 1 are similar to those of the extruded sample in Comparative Example 2. However, after heat treatment, the tensile strength of the magnesium alloy in Example 1 reached 445 MPa, the yield strength reached 402 MPa, and the elongation was 13%. Compared with Comparative Example 2, its tensile strength was 38 MPa higher and its yield strength was 125 MPa higher. This shows that when the deformed magnesium alloy is prepared by the preparation method described in this invention, adding Mn is more effective than adding Zr in improving the mechanical strength of the magnesium alloy.

[0054] 2. (1) According to Figure 2 , Figure 4 , Figure 5 The grain size of the magnesium alloy can be observed and calculated using the truncation method. The grain size of the magnesium alloy obtained in Example 1 is approximately 4.7 μm, the grain size of the magnesium alloy obtained in Comparative Example 1 is 4.3 μm, and the grain size of the magnesium alloy obtained in Comparative Example 2 is approximately 6.3 μm. The sample in Comparative Example 1 with a smaller extrusion ratio has a smaller average grain size in the recrystallization region, but a smaller degree of recrystallization. In contrast, a larger extrusion ratio provides higher strain energy for recrystallization, thus making the alloy more prone to recrystallization. Furthermore, combined with metallographic comparison, the LPSO phase in the microstructure with a larger extrusion ratio exhibits greater fragmentation, with finer fragments and a more dispersed distribution. Compared with the wrought magnesium alloy with added Mn, the addition of Zr in Comparative Example 2 significantly refined the grain size of the cast magnesium alloy by forming a nucleating agent. However, it could not restrict grain growth during solution treatment and had no limiting effect on the grain size of the extruded alloy. Mn had little effect on the grain size of the cast magnesium alloy, but the α-Mn particles precipitated during solution treatment restricted the growth of recrystallized grains during extrusion, which was beneficial for refining the grain size of the extruded alloy.

[0055] (2) By Figure 3 , Figure 6 It is evident that after extrusion, nucleation and growth occur at grain boundaries and the phase interface between α-Mg and the bulk LPSO phase, forming recrystallized grains. The broken LPSO phase is distributed at the grain boundaries, which further promotes recrystallization through the particle-induced mechanism while also pinning the grain boundaries and inhibiting the growth of recrystallized grains. In the alloy with added Mn, the α-Mn particles at the grain boundaries further restrict the precipitation of LPSO. It can be seen that the LPSO phase distribution in Example 1 is more dispersed.

[0056] (3) The SEM image of the tensile fracture surface of the magnesium alloy obtained in Example 1 is shown below. Figure 7 As shown, 7(a) is a macroscopic morphological view of the fracture surface; 7(b) is a magnified view of a portion of (a), from... Figure 7 As can be seen, the deformed magnesium alloy after extrusion and heat treatment in Example 1 contains a large number of dimples and a small number of cleavage surfaces, which confirms the large plasticity of the deformed magnesium alloy.

[0057] 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 the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy, characterized in that, Includes the following steps: (1) The magnesium alloy ingot obtained by casting has the following chemical composition by mass percentage: Gd: 9~12 wt%; Y: 1~3 wt%; Zn: 0.5~1.5 wt%; Mn: 0.5~0.8 wt%; Fe ≤0.003wt%; Cu ≤0.002wt%; Si ≤0.005 wt%; Ni ≤0.0012 wt%; the remainder is Mg and unavoidable impurities; (2) The magnesium alloy ingot is dissolved at 480~500℃ for 6~10h, then heated to 520~540℃ and dissolved for 10~14h, and then air-cooled to room temperature to obtain the dissolved ingot; (3) The solution-treated ingot is extruded at 400~440 ℃ to obtain an extrusion rod, wherein the extrusion ratio is 14~16; (4) The extruded rod is heat-treated at 180~220℃ for 40~60 h and then air-cooled to room temperature to obtain the high-strength and tough deformable rare earth magnesium alloy.

2. The method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy according to claim 1, characterized in that, In step (1), the magnesium alloy ingot is cast using the following method: S1: Prepare pure magnesium, pure zinc, Mg-Gd master alloy, Mg-Y master alloy and Mg-Mn master alloy; S2: Place pure magnesium in a crucible and put it in a melting furnace. Set the temperature of the melting furnace to 650~670 ℃ and introduce a mixture of CO2 and SF6 for protection. After the pure magnesium melts, raise the temperature to 680~720 ℃ and add pure zinc, Mg-Gd master alloy, Mg-Y master alloy and Mg-Mn master alloy into the crucible. After it has completely melted, stir the melt to make the alloy composition uniform; S3: Heat the melt to 730~750 ℃, remove the slag on the surface of the melt, add refining agent to the melt, and then stir and refine for 3~5 min; S4: After refining, let it stand at 730~750 ℃ ​​for 30~40 min, and then water cool to obtain the magnesium alloy ingot.

3. The method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy according to claim 2, characterized in that, In S2, the inner wall of the steel crucible is first coated with hexagonal boron nitride, and the smelting furnace is preheated and dried at 100~300 ℃. Then, pure magnesium is placed into the crucible, and the crucible containing pure magnesium is placed in the smelting furnace.

4. The method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy according to claim 2, characterized in that, The refining agent is C2Cl6, and its addition amount is 0.5~1% of the melt mass.

5. The method for preparing a high-strength, high-toughness, deformable rare-earth magnesium alloy according to claim 1, characterized in that, In step (1), the magnesium alloy ingot, by mass percentage, has Gd: 10.55 wt%; Y: 1.68 wt%; Zn: 1.00 wt%; Mn: 0.64wt%.

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