Large-size high-strength heat-resistant magnesium alloy pipe and preparation method thereof

Abstract

The invention discloses a large-size high-strength heat-resistant magnesium alloy pipe and a preparation method thereof, and belongs to the technical field of magnesium alloy. The magnesium alloy pipe is composed of Mg, Er, Co, Zr and other elements, and comprises, by mass, 8.0%-12.0% of Er, 2.0%-3.0% of Co, 0.2%-0.5% of Zr and the balance Mg and other inevitable impurity elements. The heavy rare earth element Er is added, the heavy rare earth element Er has large solid solubility in an Mg matrix, the heavy rare earth element Er and the added Co element can form a long-period ordered structure phase Mg12CoEr phase, namely an LPSO phase, the LPSO phase can be coherent with the magnesium matrix to improve the plasticity of the magnesium alloy, and the LPSO phase distributed at the grain boundary can hinder grain growth, so that the comprehensive mechanical property of the magnesium alloy is optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy materials and relates to a large-size high-strength heat-resistant magnesium alloy pipe and a preparation method thereof. Background Art

[0002] With the vigorous promotion of "lightweight" and "energy conservation and emission reduction", magnesium alloys have broad application prospects in various fields due to their light weight, high specific strength and specific stiffness. However, traditional magnesium alloys have low strength and can only be used for non-load-bearing parts, and their poor plasticity makes it difficult to further process. Therefore, the development of magnesium alloys with better comprehensive mechanical properties is one of the current research hotspots of magnesium alloys. By adding rare earth elements with a large solid solubility in magnesium, the alloy microstructure can be effectively improved and the room temperature and high temperature mechanical behavior of magnesium alloys can be improved.

[0003] At present, most of the research on high-strength and heat-resistant magnesium alloys is to strengthen their properties through aging precipitation, but most of these precipitated phases are unstable at high temperatures and easily coarsen, thereby significantly reducing the strength. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a large-size high-strength heat-resistant magnesium alloy pipe and a preparation method thereof, so as to solve the problem that most of the precipitated phases in the magnesium alloy in the prior art are unstable at high temperatures and easily coarsened, thereby greatly reducing the strength.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A large-size high-strength heat-resistant magnesium alloy, comprising, by mass percentage: Er: 8.0~12.0%; Co: 2.0~3.0%; Zr: 0.2~0.5%; The balance is Mg and other unavoidable impurity elements; The large-size high-strength heat-resistant magnesium alloy contains Mg 12 CoEr phase.

[0006] A further improvement of the present invention is: Preferably, the large-size high-strength heat-resistant magnesium alloy is in the form of a tube, with a maximum room temperature tensile strength of 360 MPa and a maximum elongation of 23%; the tensile strength of the tube at 200°C is 330 MPa, and the elongation is greater than 30%.

[0007] A method for preparing a large-size high-strength heat-resistant magnesium alloy comprises the following steps: Step 1, according to the composition of the large-size high-strength heat-resistant magnesium alloy, the raw materials are mixed and melted, and then cast to obtain a casting; Step 2, homogenizing the casting to achieve structural transformation of the LPSO phase; Step 3, extruding the homogenized casting through a five-hole die to obtain an extruded tube, which is the large-size high-strength and heat-resistant magnesium alloy.

[0008] Preferably, in step 1, during the smelting process, the raw materials added include pure magnesium ingot, Mg-30Er master alloy, Mg-10Co master alloy and Mg-30Zr master alloy; After the pure magnesium ingot is completely dissolved, Mg-30Er master alloy, Mg-10Co master alloy and Mg-30Zr master alloy are added.

[0009] Preferably, in step 1, the melting temperature is 760°C and the pouring temperature is 720°C.

[0010] Preferably, in step 1, during the smelting process, a protective gas is introduced into the smelting furnace, and the protective gas is CO 2 and SF 6 of mixed gases.

[0011] Preferably, in step 2, the homogenization temperature is 505-525° C., and the homogenization time is 10-12 h.

[0012] Preferably, in step 2, the homogenization treatment is followed by quenching in 70° C. water, and the quenching is followed by cooling to room temperature.

[0013] Preferably, in step 3, the extrusion temperature is 350-380°C.

[0014] Preferably, in step 3, the extrusion ratio is 25:1, the extrusion speed is 0.2 mm / s, and the extrusion process.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a large-size high-strength heat-resistant magnesium alloy pipe, which is composed of elements such as Mg, Er, Co, and Zr, with the mass percentages being: Er: 8.0-12.0%, Co: 2.0-3.0%, Zr: 0.2-0.5%, and the remainder being Mg and other inevitable impurity elements. The present invention adds a heavy rare earth element Er, which has a large solid solubility in the Mg matrix and can form a variety of strengthening phases with the added Co element. At the same time, the heavy rare earth element Er also has the effect of refining the grains; Co can form a long-period ordered structure phase Mg with the rare earth element Er through a proportioning process. 12The CoEr phase is a LPSO phase (Long-Period Stacking Order). The addition of Zr can significantly refine the grains, optimize the microstructure, and synergistically improve the strength and plasticity of magnesium alloys. At the same time, Er, as a rare earth element, has a good solid solubility in the Mg matrix and can play a role in solid solution strengthening of magnesium alloys.

[0016] Furthermore, in the Er- and Co-containing high-strength and heat-resistant magnesium alloy tube of the present invention, the amount and distribution of the long-period ordered structure phase LPSO phase at the grain boundary and within the crystal are regulated by controlling the content of Er atoms and Co atoms as well as the deformation processing and heat treatment process. This LPSO phase is co-lattice with the magnesium matrix to improve the plasticity of the magnesium alloy, and the LPSO phase distributed at the grain boundary can hinder the growth of grains, thereby optimizing the comprehensive mechanical properties of the magnesium alloy. The appropriate LPSO phase ratio within the grain boundary can jointly play the role of hindering relative dislocations within the crystal and at the grain boundary, thereby improving the strength of the alloy. In addition, these LPSO phases can promote the initiation of more slip systems, thereby improving the plasticity of the alloy, thereby enabling the alloy to obtain higher strength and plasticity, thereby avoiding the deficiency of only optimizing the mechanical properties of the grain boundary LPSO phase. In addition, the alloy has a certain proportion of LPSO phases at the grain boundary and within the crystal. In addition, the magnesium alloy after extrusion will also form some fine dispersed Mg 24 RE 5 Phase, these fine dispersed second phases can hinder dislocation slip and improve the strength of magnesium alloys.

[0017] The present invention discloses a method for preparing a large-size high-strength and heat-resistant magnesium alloy tube, which comprises material selection, smelting, solution treatment and extrusion treatment. The strength, plasticity and heat resistance of the alloy of the present invention are improved by regulating the content of Er and Co and thereby regulating the distribution and quantity of the long-period stacking ordered phase (LPSO phase) at the grain boundary and within the grain, and the alloy can be widely used in high-strength and heat-resistant fields such as aerospace.

[0018] The present invention also realizes the structural transformation of the stacking sequence in the LPSO phase through a suitable homogenization heat treatment process, making the organization more uniform and the formability better, avoiding the problem of deterioration of the mechanical properties due to the coarsening of the precipitated phase in the traditional aging precipitation strengthening, and at the same time regulating the distribution of the LPSO phase at the grain boundary and in the grain to regulate the comprehensive mechanical properties and high temperature properties of the magnesium alloy. The Er-containing and Co-containing high-strength heat-resistant magnesium alloy of the present invention has good strength, plasticity and heat resistance, and can be applied to automotive parts, aerospace and other fields.

[0019] Furthermore, the conventional large-size magnesium alloy tubes have poor formability. Considering the poor fluidity of rare earth elements in magnesium, the present invention uses a five-hole die for extrusion molding to increase its fluidity and finally extrude it into a whole. The high-strength heat-resistant magnesium alloy tube obtained by this method is a seamed tube with good formability and large size. The diameter can reach 120mm and the thickness can reach 10mm. The room temperature tensile strength of the tube can reach ~360MPa and the elongation can reach ~23%. The tensile strength of the tube at a high temperature of 200°C is about 330MPa and the elongation can exceed 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the five-hole die extrusion of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings: In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0022] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0023] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0024] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0025] The first aspect of the present invention discloses a large-size high-strength heat-resistant magnesium alloy pipe, the large size is for a magnesium alloy pipe, the diameter of the magnesium alloy pipe can reach 120mm, the wall thickness can reach 10mm. In terms of mass percentage, it includes the following components: Er: 8.0~12.0%; Co: 2.0~3.0%; Zr: 0.2~0.5%; The balance is Mg and other unavoidable impurity elements; magnesium alloy contains Mg 12 The CoEr phase contains the LPSO phase.

[0026] In the method of the present invention, Er is a heavy rare earth element. By controlling the Er element within this range, the strength of the magnesium alloy can be enhanced, and at the same time, the generation of Mg can be ensured. 12 CoEr phase; Co element is the main influencing element for the formation of LPSO phase. Controlling this content can generate LPSO phase. Zr is a grain refiner to optimize the microstructure.

[0027] The high-strength heat-resistant magnesium alloy is in the form of a tube. The maximum room temperature tensile strength of the heat-resistant magnesium alloy is 360 MPa, and the maximum elongation is 23%. The tensile strength of the tube at 200° C. is 330 MPa, and the elongation is greater than 30%.

[0028] The second aspect of the present invention discloses a method for preparing a high-strength heat-resistant magnesium alloy, comprising the following steps: Step 1: Prepare raw materials and smelt Prepare raw materials: The required raw materials are industrial pure magnesium ingots, Mg-30Er master alloy, Mg-10Co master alloy and Mg-30Zr master alloy, which are weighed according to the above target composition and placed in a heating furnace. The content of pure magnesium ingot is greater than 99.85%, and the purity of Mg-30Er master alloy and Mg-10Co master alloy is greater than 99%.

[0029] Melting: Introduce CO with a volume ratio of 99:1 into the melting furnace. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2, isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760°C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720°C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0030] Because the melting point of the intermediate alloy is lower than that of pure magnesium ingots and the alloy composition is more stable, the alloy yield can be improved by controlling the order of adding magnesium ingots and other alloys.

[0031] Step 2, homogenization solution treatment: homogenize the obtained casting at 505-525°C for 10-12h, then quench with 70°C warm water and cool to room temperature. The homogenization treatment is completed. The warm water treatment can prevent the casting from stress concentration cracking.

[0032] Step 3, extrusion: the homogenized casting is extruded at a temperature of 350-380°C, an extrusion ratio of 25:1, an extrusion speed of 0.2 mm / s, through a five-hole die, and air-cooled after extrusion to obtain a large-sized seam extruded pipe to obtain the high-strength rare earth heat-resistant magnesium alloy.

[0033] The Er- and Co-containing high-strength heat-resistant magnesium alloy of the present invention has good strength, plasticity and heat resistance, and can be applied to the fields of automobile parts, aerospace, etc.

[0034] The following is further described in conjunction with specific embodiments.

[0035] Example 1 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 8.5% Er, 2.0% Co, 0.2% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0036] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2, isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760°C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720°C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0037] The ingot was homogenized at 505°C for 12 h and then quenched in 70°C warm water.

[0038] The homogenized ingot was extruded at a temperature of 350°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-sized seamed extruded tube.

[0039] Example 2 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 10.2% Er, 2.1% Co, 0.2% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0040] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2 , isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0041] The ingot was homogenized at 520°C for 10 h and then quenched in 70°C warm water.

[0042] The homogenized ingot was extruded at a temperature of 360°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-size seamed extruded tube.

[0043] Example 3 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 11.5% Er, 2.4% Co, 0.3% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0044] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2 , isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0045] The ingot was homogenized at 525°C for 12 h and then quenched in 70°C warm water.

[0046] The homogenized ingot was extruded at a temperature of 370°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-sized seamed magnesium alloy tube.

[0047] Example 4 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 9.7% Er, 2.1% Co, 0.2% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0048] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2 , isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0049] The ingot was homogenized at 510°C for 11 h and then quenched in 70°C warm water.

[0050] The homogenized ingot was extruded at a temperature of 350°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-sized seamed extruded tube.

[0051] Example 5 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 9.0% Er, 2.2% Co, 0.3% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0052] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2 , isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0053] The ingot was homogenized at 515°C for 10 h and then quenched in 70°C warm water.

[0054] The homogenized ingot was extruded at a temperature of 360°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-size seamed extruded tube.

[0055] Example 6 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 8.0% Er, 3% Co, 0.5% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0056] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2, isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0057] The ingot was homogenized at 520°C for 11 h and then quenched in 70°C warm water.

[0058] The homogenized ingot was extruded at a temperature of 380°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-size seamed extruded tube.

[0059] Example 7 The high-strength and heat-resistant rare earth magnesium alloy containing Er and Co in this embodiment has a composition ratio of 12.0% Er, 2.8% Co, 0.4% Zr by weight, and the rest is Mg and other inevitable impurity elements.

[0060] The volume ratio of CO2 to the smelting furnace is 99:1. 2 and SF 6 Mix the protective gas and add a low melting point covering agent, which is BaCl mixed in a specific ratio. 2 , CaCl 2 and MgCl 2 , isolate the air to prevent the magnesium alloy from being oxidized, and then add a refining agent to dissolve and absorb excess oxides and gases. Add magnesium ingots, wait for the magnesium ingots to melt completely, and then add Mg-30Er master alloy, Mg-10Co master alloy, and Mg-30Zr master alloy in sequence. After the melting furnace is heated to 760 ° C, a molten metal can be obtained. After removing the impurities on the surface, the molten metal is cooled to 720 ° C and kept warm for 15 minutes, and then the molten metal is cast into a mold to obtain a semi-continuous casting.

[0061] The ingot was homogenized at 520°C for 11 h and then quenched in 70°C warm water.

[0062] The homogenized ingot was extruded at a temperature of 360°C, an extrusion ratio of 25:1, and an extrusion speed of 0.2 mm / s. It was extruded through a five-hole die and air-cooled after extrusion to obtain a large-size seamed extruded tube.

[0063] The magnesium alloy tubes of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Example 7 were tested for mechanical properties at room temperature and 200° C. The results are shown in the following table: Table 1 Mechanical properties test of the examples

[0064] As shown in Table 1, the room temperature yield strength of the magnesium alloys of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Example 7 is 302.3-318.4MPa, and the tensile strength is 347.1-360.9MPa, which is good in strength, and the elongation exceeds 22%, which has good plastic deformation ability while having high strength. At 200°C, the elongation of the alloy can reach 32.6-34.8%, the yield strength is 261.8-270.3MPa, and the tensile strength is 327.4-335.6MPa, which shows that the alloy has good high temperature resistance, and this magnesium alloy pipe can be used for large-scale industrial production.

[0065] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A large-size high-strength heat-resistant magnesium alloy, characterized in that: In terms of mass percentage, it includes: Er：8.0~12.0%； Co: 2.0~3.0%; Zr：0.2~0.5%； The balance is Mg and other unavoidable impurity elements; The large-size high-strength heat-resistant magnesium alloy contains Mg 12 CoEr phase.

2. A large-size high-strength heat-resistant magnesium alloy according to claim 1, characterized in that: The large-size high-strength heat-resistant magnesium alloy is in the form of a tube, with a maximum room temperature tensile strength of 360 MPa and a maximum elongation of 23%; the tensile strength of the tube at 200°C is 330 MPa, and the elongation is greater than 30%.

3. A method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 1, characterized in that: The following steps are involved: Step 1, according to the composition of the large-size high-strength heat-resistant magnesium alloy, the raw materials are mixed and melted, and then cast to obtain a casting; Step 2, homogenizing the casting to achieve structural transformation of the LPSO phase; Step 3, extruding the homogenized casting through a five-hole die to obtain an extruded tube, which is the large-size high-strength and heat-resistant magnesium alloy.

4. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 1, during the smelting process, the raw materials added include pure magnesium ingot, Mg-30Er master alloy, Mg-10Co master alloy and Mg-30Zr master alloy; After the pure magnesium ingot is completely dissolved, Mg-30Er master alloy, Mg-10Co master alloy and Mg-30Zr master alloy are added.

5. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 1, the melting temperature is 760°C and the pouring temperature is 720°C.

6. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 1, during the smelting process, a protective gas is introduced into the smelting furnace, and the protective gas is a mixed gas of CO2 and SF6.

7. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 2, the homogenization temperature is 505-525° C., and the homogenization time is 10-12 h.

8. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 2, the homogenization treatment is followed by quenching with 70° C. water, followed by cooling to room temperature.

9. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 3, the extrusion temperature is 350-380°C.

10. The method for preparing a large-size high-strength heat-resistant magnesium alloy according to claim 3, characterized in that: In step 3, the extrusion ratio is 25:1, the extrusion speed is 0.2 mm / s, and the extrusion process.

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