Cooperative inhibition method for hot crack defect of large-size rare earth magnesium alloy cast ingot

Abstract

The invention relates to the technical field of magnesium alloy large-size cast ingot preparation, in particular to a large-size rare earth magnesium alloy cast ingot hot crack defect synergistic inhibition method which comprises the following steps: S1, intermediate alloy pretreatment: placing an Mg-30Zr intermediate alloy blank in an equal-channel angular extrusion die, applying 70%-80% of deformation, and carrying out equal-channel angular extrusion on the Mg-30Zr intermediate alloy blank; the Zr clusters with the original size larger than or equal to 762 micrometers are crushed into discrete particles with the particle size ranging from 1 micrometer to 5 micrometers; s2, smelting and modification treatment: preparing materials according to a target alloy ZK61, and smelting industrial pure Mg and Zn and the Mg-30Zr intermediate alloy pretreated in the step S1 under a protective atmosphere; through electromagnetic oscillation and forced convection, the melt convection speed is increased, center melt heat dissipation is accelerated, temperature field / solute field homogenization is achieved, the structure component consistency is improved, casting stress generated in the solidification process is reduced, the generated axial circulation speed exceeds the rare earth sedimentation speed, and the bottom sedimentation phenomenon is effectively restrained; and the distribution uniformity and the yield of the rare earth are improved.

Description

Technical Field

[0001] This invention relates to the field of large-scale magnesium alloy ingot preparation technology, and more specifically, to a method for synergistic suppression of hot cracking defects in large-scale rare earth magnesium alloy ingots. Background Technology

[0002] Large-size magnesium alloy ingots are the basic material for large integrated components, with a diameter of ≥380mm. However, due to the long solidification time and large heat capacity, large-size ingots result in significant grain coarsening. At the same time, the difference in cooling rate of their cross sections can easily lead to defects such as compositional segregation, grain inhomogeneity, and even hot cracking.

[0003] The existing technology has the following limitations:

[0004] Semi-continuous casting, also known as direct water cooling, is the mainstream preparation process for large-size magnesium alloy ingots. However, its melt has weak natural convection, a significant temperature gradient exists during solidification, the solidification process is asynchronous, and the solidification shrinkage stress is large, which further aggravates the hot cracking defects of large-size ingots.

[0005] Patent publication number CN113462939B discloses a hot-cracking-resistant, high-strength, and high-ductility rare-earth magnesium alloy and its preparation method. This invention utilizes inexpensive light and heavy rare-earth elements such as Sm and Y, and non-rare-earth elements such as Zn, Sn, Ca, and Sr for multi-element micro-alloying. This improves the alloy's mechanical properties by generating thermally stable long-range ordered phases, precipitates, and dispersed phases, and by reducing the solidification range, thus reducing the alloy's hot-cracking tendency during casting. Furthermore, it can reduce the amount of rare-earth alloying elements used. However, its critical fracture diameter is ≤62mm, limiting its effectiveness in improving hot-cracking defects in large-size ingots.

[0006] Patent publication number CN115055653B discloses a method for preparing large-size rare-earth magnesium alloy ingots. While its vacuum solidification environment and zoned heating design contribute to simultaneous solidification, high-density rare-earth elements, such as...

[0007] Gd: 7.90 g / cm³ 3 Y: 4.47 g / cm 3 Gravity segregation is likely to occur in the melt, forming a bottom enriched deposit layer, which in turn induces fluctuations in composition gradient and mechanical properties. At the same time, zoned heating also increases the cost of casting process.

[0008] To optimize the solidification structure and casting defects of large-sized ingots, a common method is to introduce external fields, such as ultrasound and electromagnetic fields, during the metal solidification process.

[0009] Patent publication number CN107116194A discloses a magnesium alloy variable frequency ultrasonic semi-continuous casting equipment. Experiments have shown that variable frequency ultrasonic vibration can significantly refine the grain structure and achieve uniformity. However, existing ultrasonic technology faces three major limitations in its application to molten metals:

[0010] ①Sound waves exhibit significant attenuation and frequency drift during propagation, and the insufficient output power of the superimposed equipment limits the effective range of action;

[0011] ② The amplitude transformer needs to be in direct contact with the high-temperature molten metal, which presents challenges in terms of corrosion resistance and resistance to cavitation damage;

[0012] ③The above factors together hinder the industrialization of this technology.

[0013] Patent publication number CN218693706U discloses a semi-continuous aluminum alloy casting device. By adjusting the parameters such as the current, voltage, and frequency of each electromagnetic coil, the electromagnetic force generated by the electromagnetic coil acts on the molten cavity in the casting chamber, thereby driving the movement of the molten material in the cavity. On the one hand, it can redistribute the solute in the molten material in the cavity, reducing the compositional segregation in the cross-section of the ingot. On the other hand, it can allow the high-temperature molten material in the core of the cavity to permeate with the low-temperature molten material at the edge, making the temperature field in the cavity of the ingot more uniform, thereby improving the internal metallurgical quality of the ingot and meeting user requirements. However, the effect of a single electromagnetic field is limited by the skin effect. The field strength is significant in the edge region of the ingot and attenuates significantly in the center region, resulting in the shrinkage of the columnar crystal region at the edge and the coexistence of the coarse-grained region in the center. The improvement in the homogenization of the microstructure is limited, and the hot cracking defects of the ingot are still difficult to eliminate.

[0014] In summary, current methods for improving heterogeneity such as hot cracking in large-size magnesium alloy ingots using a single external field or rare earth additions are clearly insufficient. Furthermore, the traditional semi-continuous casting process suffers from weak melt convection, large temperature gradients, and concentrated shrinkage stress, which exacerbates hot cracking defects as the ingot size increases. Moreover, a single technical approach cannot simultaneously address the requirements for achieving microstructure homogenization and suppressing hot cracking.

[0015] Therefore, we propose a collaborative method for suppressing hot cracking defects in large-size rare earth magnesium alloy ingots to solve the above problems. Summary of the Invention

[0016] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide a method for synergistic suppression of hot cracking defects in large-size rare earth magnesium alloy ingots, so as to solve the problems mentioned in the background art.

[0017] To achieve the above objectives, the present invention provides the following technical solution: a method for synergistic suppression of hot cracking defects in large-size rare earth magnesium alloy ingots, comprising the following steps:

[0018] Step S1: Intermediate alloy pretreatment: Place the Mg-30Zr intermediate alloy billet in an equal channel angle extrusion die and apply 70%-80% deformation to break the Zr clusters with an original size ≥762μm into discrete particles of 1μm-5μm.

[0019] Step S2: Melting and Modification Treatment: According to the target alloy ZK61, industrial pure Mg, Zn and the Mg-30Zr master alloy pretreated in step S1 are melted under a protective atmosphere.

[0020] Then add Mg-30RE master alloy;

[0021] Then, a two-stage refining process is carried out, using rotary argon blowing for impurity removal and refining agent settling for slag removal;

[0022] Step S3: Semi-continuous casting: Preheat the crystallizer before pouring, and turn on the low-frequency differential electromagnetic stirring device after introducing the melt from step S2.

[0023] After the melt solidifies into a shell, the ingot jacking plate is moved downwards to pull out the formed ingot.

[0024] In a preferred embodiment, in step S1, the channel angle of the equal channel angle extrusion die is 90°±2°, the extrusion speed is 5mm / s-10mm / s, and the proportion of Zr in the dispersed 1μm-5μm discrete particles is ≥80%.

[0025] In a preferred embodiment, in step S2, the RE in the Mg-30RE master alloy is a La / Ce mixed rare earth element, wherein the La:Ce mass ratio is 1:1-1:2, and the RE addition amount in the alloy is 0.5wt.%-1.0wt.%.

[0026] In a preferred embodiment, during step S2, when adding the Mg-30Zr master alloy, the melting furnace needs to be continuously heated to ≥780℃. After the Mg-30Zr master alloy melts, it is mechanically stirred for 30-40 minutes, and the temperature is controlled at 780℃-800℃.

[0027] In a preferred embodiment, in step S2, the raw materials are industrial pure Mg, industrial pure Zn, Mg-30Zr and Mg-30RE master alloys, and the raw materials need to be preheated before being added to the gas furnace, with the preheating temperature controlled at 180℃-200℃.

[0028] In a preferred embodiment, in step S3, the current phase difference angle of the low-frequency differential phase electromagnetic stirring device is 90°-120°, the current intensity is 100A-300A, and the frequency is 10Hz-30Hz.

[0029] In a preferred embodiment, in step S3, the casting temperature of the magnesium alloy melt is 650℃-690℃.

[0030] In a preferred embodiment, in step S3, before casting, the crystallizer is preheated for the first time, and positive pressure is used to introduce the melt from the smelting furnace into the crystallizer.

[0031] In a preferred embodiment, in step S3, the downward movement rate of the derrick plate is 32 mm / min-36 mm / min.

[0032] The technical effects and advantages of this invention are as follows:

[0033] 1. This invention uses physical field crushing to break Zr clusters larger than 762μm into effective particles of 1μm-5μm, thereby increasing the number of effective nucleation cores in the melt, promoting nucleation, and refining the grain size.

[0034] 2. This invention uses a high-abundance rare earth element La:Ce ratio of 1:1 to 1:2 to form a low-melting-point Mg-(La,Ce) eutectic phase. The eutectic liquid phase penetrates and fills along the hot crack, healing the crack and inhibiting its initiation and propagation.

[0035] 3. This invention improves the melt convection speed through electromagnetic oscillation and forced convection, accelerates the heat dissipation of the central melt, achieves uniformity of temperature field / solute field, improves the consistency of microstructure composition, reduces casting stress generated during solidification, and the axial circulation velocity generated exceeds the rare earth settling rate, effectively suppressing the bottoming phenomenon and improving the uniformity of rare earth distribution and yield.

[0036] 4. The present invention has a wide range of applications and is suitable for the preparation of high-quality magnesium alloy large-scale ingots of various shapes and sizes. Attached Figure Description

[0037] Figure 1 SEM images of the traditional Mg-Zr master alloy in this invention (a) and dispersed Zr particles after composite pretreatment (b) are shown.

[0038] Figure 2 This is a photograph of the La / Ce eutectic phase healing crack at the hot crack location in this invention;

[0039] Figure 3 The images show the macroscopic morphology of the ingot in the embodiments of the present invention (a), the ingot in Comparative Example 1 (b), and the ingot in Comparative Example 2 (c). Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] (1) Pretreatment of intermediate alloy

[0042] The Mg-30Zr intermediate alloy billet is placed in an equal channel angle extrusion die, and a deformation of 70-80% is applied to disperse the Zr clusters with an original particle size ≥762μm into discrete particles of 1μm-5μm. The proportion of Zr in the 1μm-5μm discrete particles is ≥80%. The die channel angle is 90°±2°, and the extrusion speed is controlled at 5mm / s-10mm / s.

[0043] The formula for calculating deformation is as follows:

[0044] Deformation ε=(A0-A1) / A0×100%, where A0 and A1 are the cross-sectional areas of the billet before and after extrusion, respectively;

[0045] (2) Smelting and Deterioration Treatment

[0046] Batching and smelting: Batching is carried out according to the target alloy ZK61 (Mg-6Zn-0.6Zr). The raw materials are industrial pure Mg, industrial pure Zn, Mg-30Zr (wt.%) and Mg-30RE (wt.%) master alloy.

[0047] All furnace charge must be dried in a drying oven before being added, with the preheating temperature controlled at 180℃-200℃ to prevent moisture from entering. First, pure Mg is placed in a 3T gas furnace and heated to about 700℃-720℃. Pure Zn is then added. After the Zn is completely melted, the temperature is raised to 780℃-800℃. Subsequently, the Mg-Zr master alloy is added. It is particularly important to note that, to prevent severe cooling, the melting furnace must be continuously heated during the addition of the Mg-Zr master alloy. More specifically, the melting furnace must be continuously heated during the addition of the Mg-Zr master alloy to ensure that the temperature does not fall below 780℃. After the Mg-Zr master alloy is completely melted, mechanical stirring is applied for 30-40 minutes, with the temperature controlled at 780℃-800℃.

[0048] After the Mg-Zr master alloy is completely melted, mechanical stirring is applied to promote the dissolution of Zr. During the smelting process, the furnace charge is smelted in a gas furnace under the protection of a mixed atmosphere of CO2 and SF6 (volume ratio of 100:1).

[0049] Modification and refining: After the melt is completely melted, Mg-30RE (wt.%) master alloy is added. A sample is taken before the furnace for direct reading spectral analysis. The composition is dynamically adjusted to meet the requirements. The RE in the Mg-30RE (wt.%) master alloy is a La / Ce mixed rare earth, La:Ce = 1:1-1:2, and the RE addition amount in the alloy is 0.5wt.%-1.0wt.%.

[0050] Then, a two-stage refining process is carried out: the first stage is rotary argon blowing refining (200r / min×30min) to remove impurities;

[0051] After the secondary covering refining agent (RJ5 + fluorite powder) is left to stand for 10 minutes, the slag is removed, the composition is rechecked, and the melt is left to stand until the casting temperature is reached.

[0052] (3) Semi-continuous casting forming

[0053] Before casting, the crystallizer is preheated for the first time. Positive pressure is used to guide the molten metal from the furnace into the crystallizer. A low-frequency differential electromagnetic stirring device is activated. Once the molten metal in the cavity formed by the dummy plate and the crystallizer solidifies into a shell, the dummy plate is moved downwards to pull out the formed ingot. As the casting process progresses, the amount of molten metal in the furnace gradually decreases. Once all the molten metal has been poured, the entire casting process is complete.

[0054] The low-frequency differential phase electromagnetic stirring device has a current phase difference angle of 90°-120°, a current intensity of 100A-300A, and a current frequency of 10Hz-30Hz.

[0055] The casting temperature of the magnesium alloy melt is 650℃-690℃.

[0056] The downward movement speed of the magnesium alloy ingot guide plate is 32mm / min-36mm / min.

[0057] The purpose of this embodiment is to provide a homogeneous, crack-free large-size magnesium alloy ingot and its preparation method.

[0058] The alloy composition and its mass percentages are Zn: 5.6 wt.%, Zr: 5.7 wt.%, Mn: 0.08 wt.%, Si: 0.04 wt.%, Fe: 0.005 wt.%, RE: 0.74 wt.%, with the balance being Mg.

[0059] Specifically, the following steps are included:

[0060] (1) Pretreatment of intermediate alloy

[0061] The Mg-30Zr intermediate alloy billet is placed in an equal channel angular extrusion die with an included angle of 90°, and 70% deformation is applied during extrusion at a speed of 5 mm / s, so that the Zr clusters with original particle size ≥ 762 μm are dispersed into discrete particles of 1 μm-5 μm.

[0062] Statistical analysis of discrete Zr particles showed that 83.2% were within the 1μm-5μm range. Figure 1 As shown in (a).

[0063] (2) Smelting and Deterioration Treatment

[0064] Batching and smelting: Batching is carried out according to the target alloy ZK61 (Mg-6Zn-0.6Zr), and the raw materials are industrial pure Mg and industrial pure Zn.

[0065] Pretreated Mg-30Zr (wt.%) master alloy and Mg-30RE (wt.%) master alloy.

[0066] All furnace materials are dried in a 190°C drying oven before being added to prevent moisture from entering.

[0067] First, pure Mg is placed in a 3T gas furnace and heated. Pure Zn is added at 700℃. After the Zn has completely melted, the temperature is raised to 780℃.

[0068] Then, the pretreated Mg-Zr master alloy was added. To prevent severe cooling, the furnace temperature was continuously increased during the addition of the Mg-Zr master alloy, and the temperature was controlled to be above 780℃.

[0069] After the Mg-Zr master alloy has completely melted, mechanical stirring is applied for 30 minutes. During the smelting process, the furnace charge is smelted in a gas furnace under the protection of a mixed atmosphere of CO2 and SF6 (volume ratio of 100:1).

[0070] Deterioration and Refining:

[0071] After the melt is completely melted, Mg-30RE (wt.%) master alloy (La:Ce = 1:1.5) is added.

[0072] Before the furnace, a sample was taken for direct reading spectral analysis, and the composition was dynamically adjusted to meet the requirements. Then, a two-stage refining process was carried out: the first stage was rotary argon blowing refining (200r / min×30min) to remove impurities.

[0073] After the secondary covering refining agent (RJ5 + fluorite powder) has been left to stand for 10 minutes, the slag is removed.

[0074] After re-inspecting the composition, allow the melt to stand until it reaches the pouring temperature.

[0075] (3) Semi-continuous casting forming

[0076] Before casting, the crystallizer is preheated for the first time. Positive pressure is used to guide the molten metal from the melting furnace into the crystallizer. A low-frequency differential phase electromagnetic stirring device is activated. Once the molten metal in the cavity formed by the ingot guide plate and the crystallizer solidifies into a shell, the ingot guide plate is moved downwards to pull out the formed ingot. As the casting process progresses, the amount of molten metal in the melting furnace gradually decreases. The casting process is complete when all the molten metal has been poured. The pouring temperature is 690℃, the ingot guide speed is 32mm / min, and the current phase difference, intensity, and frequency are 90°, 200A, and 15Hz, respectively. Microstructural observation of the cross-section of the rare earth ZK61 magnesium alloy ingot from the example revealed no hot cracks. Figure 3 As shown in (a).

[0077] Comparative Example 1

[0078] The alloy composition and its mass percentages are Zn: 5.6 wt.%, Zr: 5.7 wt.%, Mn: 0.08 wt.%, Si: 0.04 wt.%, Fe: 0.005 wt.%, RE: 0.74 wt.%, with the balance being Mg.

[0079] Specifically, the following steps are included:

[0080] (1) Pretreatment of intermediate alloy

[0081] The Mg-30Zr intermediate alloy billet is placed in an equal channel angular extrusion die with an included angle of 90°, and 80% deformation is applied during extrusion at a speed of 5 mm / s, so that the Zr clusters with original particle size ≥762 μm are dispersed into discrete particles of 1-5 μm.

[0082] Statistical analysis of discrete Zr particles showed that 83.2% were within the 1μm-5μm range.

[0083] like Figure 1 As shown in (a).

[0084] (2) Smelting and Deterioration Treatment

[0085] Batching and smelting: Batching is performed according to the target alloy ZK61 (Mg-6Zn-0.6Zr). The raw materials are industrial pure Mg and industrial pure Zn.

[0086] Pretreated Mg-30Zr (wt.%) master alloy and Mg-30RE (wt.%) master alloy.

[0087] All furnace materials are dried in a 190°C drying oven before being added to prevent moisture from entering.

[0088] First, pure Mg was heated in a 3T gas-fired furnace, and pure Zn was added at 700℃. After the Zn was completely melted, the temperature was raised to 780℃. Then, pretreated Mg-Zr master alloy was added. To prevent severe cooling, the furnace temperature was continuously raised during the addition of the Mg-Zr master alloy, maintaining a temperature above 780℃. After the Mg-Zr master alloy was completely melted, mechanical stirring was applied for 30 minutes. Throughout the smelting process, the furnace charge was smelted in a gas-fired furnace under a mixed atmosphere of CO2 and SF6 (100:1 volume ratio).

[0089] Deterioration and Refining:

[0090] After the melt is completely melted, Mg-30RE (wt.%) master alloy (La:Ce = 1:1.5) is added.

[0091] Before taking samples from the furnace, perform direct-reading spectral analysis and dynamically adjust the composition until it meets the requirements.

[0092] Then, a two-stage refining process is carried out: the first stage is rotary argon blowing refining (200r / min×30min) to remove impurities;

[0093] After the secondary covering refining agent (RJ5 + fluorite powder) has been left to stand for 10 minutes, the slag is removed. After retesting the composition, the melt is left to stand until the casting temperature is reached.

[0094] (3) Semi-continuous casting forming

[0095] Before pouring, the crystallizer is preheated for the first time. Positive pressure is used to guide the molten metal from the melting furnace into the crystallizer. The low-frequency differential electromagnetic stirring device is not activated. Once the molten metal in the cavity formed by the dummy plate and the crystallizer solidifies into a shell, the dummy plate is moved downwards to pull out the formed ingot. As the casting process progresses, the amount of molten metal in the melting furnace gradually decreases. Once all the molten metal has been poured, the entire casting process is complete. The pouring temperature is 690℃, and the dummy plate speed is 32 mm / min.

[0096] Microstructural observation of the cross-section of the rare-earth-containing ZK61 magnesium alloy ingot in Comparative Example 1 revealed slight hot cracks, such as... Figure 3 As shown in (b), a La / Ce eutectic phase healed crack was observed at the hot crack location, as shown in [example image]. Figure 2 As shown.

[0097] Comparative Example 2

[0098] The alloy composition and its mass percentages are: Zn: 5.8 wt.%, Zr: 6.2 wt.%, Mn: 0.08 wt.%, Si: 0.04 wt.%, Fe: 0.005 wt.%, with the balance being Mg. The specific steps include:

[0099] (1) The intermediate alloy was not pretreated

[0100] (2) Large-area clusters of Zr appeared in the middle without pretreatment. According to the statistical measurement of Zr in discrete particles, the proportion in the 1μm-5μm range was only 35.8%.

[0101] like Figure 1 As shown in (b).

[0102] (2) Smelting and Deterioration Treatment

[0103] Batching and smelting: Batching is carried out according to the target alloy ZK61 (Mg-6Zn-0.6Zr). The raw materials are industrial pure Mg, industrial pure Zn, and untreated Mg-30Zr (wt.%) master alloy. All furnace charges are dried in a 190℃ drying oven before being added to prevent moisture from entering.

[0104] First, pure Mg is placed in a 3T gas furnace and heated. Pure Zn is added at 700℃. After the Zn has completely melted, the temperature is raised to 780℃.

[0105] Untreated Mg-Zr master alloy was then added. To prevent severe cooling, the furnace temperature was continuously increased during the addition of the Mg-Zr master alloy, and controlled above 780℃. After the Mg-Zr master alloy was completely melted, mechanical stirring was applied for 30 minutes. During the smelting process, the furnace charge was smelted in a gas-fired furnace under a mixed atmosphere of CO2 and SF6 (100:1 volume ratio).

[0106] Modification and refining: No Mg-30RE (wt.%) master alloy was used for modification. Direct-reading spectroscopic analysis was performed on samples taken before the furnace, and the composition was dynamically adjusted to meet the requirements.

[0107] Then, a two-stage refining process is carried out: the first stage is rotary argon blowing refining (200r / min×30min) to remove impurities;

[0108] After the secondary covering refining agent (RJ5 + fluorite powder) has been left to stand for 10 minutes, the slag is removed.

[0109] After re-inspecting the composition, allow the melt to stand until it reaches the pouring temperature.

[0110] (3) Semi-continuous casting forming

[0111] Before pouring, the crystallizer is preheated for the first time. Positive pressure is used to guide the molten metal from the melting furnace into the crystallizer. The low-frequency differential electromagnetic stirring device is not activated. Once the molten metal in the cavity formed by the dummy plate and the crystallizer solidifies into a shell, the dummy plate is moved downwards to pull out the formed ingot. As the casting process progresses, the amount of molten metal in the melting furnace gradually decreases. Once all the molten metal has been poured, the entire casting process is complete. The pouring temperature is 685℃, and the dummy plate speed is 32 mm / min.

[0112] Microstructural observation of the cross-section of the ZK61 magnesium alloy ingot without RE in Comparative Example 2 revealed coarse hot cracks, such as... Figure 3 As shown in (c).

[0113] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synergistic suppression of hot cracking defects in large-size rare earth magnesium alloy ingots, characterized in that; The method comprises the following steps: Step S1: intermediate alloy pretreatment: placing Mg-30Zr intermediate alloy billet in an equal-channel angular extrusion die, applying a deformation of 70%-80%, and breaking Zr clusters with an original size of ≥762 μm into discrete particles with a size of 1 μm-5 μm; Step S2: melting and modification treatment: according to the target alloy ZK61, melting industrial pure Mg, Zn, and the Mg-30Zr intermediate alloy pretreated in step S1 under a protective atmosphere; Then, Mg-30RE intermediate alloy is added; Then, two-stage refining is performed, and rotary argon blowing and a refining agent are used for slag removal; Step S3: semi-continuous casting: preheating the crystallizer before pouring, and starting low-frequency differential-phase electromagnetic stirring after the melt in step S2 is introduced; After the melt solidifies into a shell, the dummy bar is started to move downward, and the formed ingot is pulled out.

2. The method according to claim 1, wherein the method is characterized by: In step S1, the channel angle of the equal-channel angular extrusion die is 90°±2°, and the extrusion speed is 5 mm / s-10 mm / s, and the proportion of Zr dispersed into 1 μm-5 μm discrete particles is ≥80%.

3. The method according to claim 1, wherein the method is characterized by: In step S2, the RE in the Mg-30RE intermediate alloy is a mixed rare earth of La / Ce, the mass ratio of La:Ce is 1:1-1:2, and the RE addition in the alloy is 0.5wt.%-1.0wt.%.

4. The method according to claim 1, wherein the method is characterized by: In step S2, during the addition of the Mg-30Zr intermediate alloy, the melting furnace needs to be continuously heated to ≥780 ℃, mechanical stirring is performed for 30 min-40 min after the Mg-30Zr intermediate alloy is melted, and the temperature is controlled at 780 ℃-800 ℃.

5. The method according to claim 1, wherein the method is characterized by: In step S2, the raw materials are industrial pure Mg, industrial pure Zn, Mg-30Zr, and Mg-30RE intermediate alloy, and the raw materials need to be preheated before being added to the gas furnace, and the preheating temperature is controlled at 180 ℃-200 ℃.

6. The method according to claim 1, wherein the method is characterized by: In step S3, the current phase difference angle of the low-frequency differential-phase electromagnetic stirring device is 90°-120°, the current intensity is 100 A-300 A, and the frequency is 10 Hz-30 Hz.

7. The method according to claim 1, wherein the method is characterized by: In step S3, the pouring temperature of the magnesium alloy melt is 650 ℃-690 ℃.

8. The method according to claim 1, wherein the method is characterized by: In step S3, before pouring, the crystallizer is preheated for the first time, and the melt in the melting furnace is introduced into the crystallizer in a positive pressure manner.

9. The method according to claim 1, wherein the method is characterized by: In step S3, the downward moving speed of the dummy bar is 32 mm / min-36 mm / min.

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