Flame-retardant magnesium alloy and preparation method thereof

Abstract

The invention discloses a flame-retardant magnesium alloy and a preparation method thereof, and belongs to the technical field of flame-retardant magnesium alloys. The invention solves the problem of poor flame retardant property and casting property of the Mg-Al alloy. The flame-retardant magnesium alloy comprises the following chemical components in percentage by mass: 0.5-15% of Yb, 0.5-12% of Al, 0.03-0.5% of Mn, 0-5% of La, Ce, Sm, Zn or Si and the balance of Mg and inevitable impurities, Yb is used as a main flame-retardant element, and the flame retardance and casting performance of the magnesium alloy are effectively improved by introducing the elements such as Yb and Al into the magnesium alloy. The flame retardant point of the magnesium alloy developed by the invention is higher than 1050 DEG C, and the magnesium alloy does not contain Be and Ca, has excellent casting performance, can be applied to the fields of aerocars and aerospace, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant magnesium alloys, and particularly relates to a flame retardant magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest "green" metal structural material, magnesium alloy has many advantages, such as light density, high specific strength, good damping and shock absorption performance, excellent electromagnetic shielding performance, easy processing, recyclability, etc. Therefore, it has received great attention from many industries and is considered to be one of the most valuable lightweight structural materials.

[0003] With the rapid development of the aviation field, aircraft have also put forward an urgent demand for weight reduction. Manned spacecraft, such as large aircraft and flying cars, require lightweight materials to have high safety while achieving lightweight structure, especially commercial manned aircraft, which require lightweight materials to meet high flame retardant properties. Magnesium alloy is an effective way to achieve aircraft weight reduction. Among them, Mg-Al alloys are widely used, but Mg-Al alloys usually have very active physical properties. When the melt is directly exposed to the atmosphere, it will undergo violent oxidation combustion. The ignition point is usually lower than 680°C and the flame retardant performance is poor. Therefore, in order to improve the flame retardant properties of components prepared using Mg-Al alloys, it is often necessary to treat the surface of the components, such as surface coating technology and micro-arc oxidation technology, or add rare earth elements Gd and Y, alkaline earth elements Be and Ca, and refractory metal elements V, Ti, Ge, etc. to Mg-Al alloys. Surface treatment will increase the production cost of components, and the processing is complicated, and the durability of the coating is also problematic; the most effective metal elements added to Mg-Al magnesium alloys are Ca and Be elements. Be elements are harmful to the human body and are generally not recommended for industrial practical applications. Although adding Ca can significantly improve the flame retardant properties of Mg-Al alloys, the addition amount often needs to exceed 2wt% to have good flame retardant properties. This amount of Ca addition will cause Mg-Al alloys to have a serious tendency to thermal cracking, and it is impossible to prepare components with large sizes or complex structures, and it is also impossible to use the mainstream casting process on the market to prepare components, resulting in the magnesium alloys with Ca addition having no high practical application value. Therefore, the development of a Mg-Al alloy with excellent casting properties and high flame retardant properties can not only promote the development of magnesium alloys in the fields of aviation and low-altitude flying cars, but also has important significance for the development and application of magnesium alloys in the fields of new energy vehicles, electronic 3C (information home appliance industry that integrates the three major technology products of computers, communications, and consumer electronics). Summary of the invention

[0004] In order to solve the technical problem of poor flame retardancy and casting performance of Mg-Al alloys in the prior art, the present invention provides a flame retardant magnesium alloy and a preparation method thereof.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] One of the purposes of the present invention is to provide a flame retardant magnesium alloy, the chemical composition of the alloy includes, by weight percentage: Yb: 0.5-15%, Al: 0.5-12%, Mn: 0.03-0.5%, and the balance is magnesium and inevitable impurities.

[0007] A second object of the present invention is to provide a method for preparing the flame retardant magnesium alloy, comprising:

[0008] S1. Descaling and preheating magnesium ingots, aluminum ingots, Mg-Yb master alloys and Mg-Mn master alloys;

[0009] S2, putting magnesium ingot and Mg-Yb master alloy into a crucible furnace as charge, and passing protective gas;

[0010] S3, heating to a certain temperature, adding Mg-Mn master alloy after the charge is completely melted, and stirring;

[0011] S4, adjust the furnace temperature to a certain temperature, add aluminum ingots, and stir;

[0012] S5, adjusting the furnace temperature to a certain temperature, leaving the melt to stand, and obtaining a magnesium alloy melt;

[0013] S6. The magnesium alloy melt is subjected to gravity casting or high pressure die casting to obtain a flame retardant magnesium alloy.

[0014] It is further defined that the preheating temperature in S1 is 200-300° C. and the time is 20-40 minutes.

[0015] It is further defined that the protective gas in S2 is CO2 containing 1 to 10 vol% SF6.

[0016] It is further defined that the temperature in S3 is raised to 700-800°C.

[0017] It is further defined that the stirring time in S3 is 5 to 10 minutes.

[0018] It is further defined that in S4, the furnace temperature is adjusted to 700-710°C.

[0019] It is further defined that the stirring time in S4 is 5 to 7 minutes.

[0020] It is further defined that in S5, the furnace temperature is adjusted to 670-750°C.

[0021] It is further defined that the melt temperature during high pressure casting in S6 is 685-695°C.

[0022] It is further defined that the high pressure casting parameters of S6 are: injection pressure 110-130 MPa, injection rate 7.5-8.5 m / s, pressurization time 14-16 s, holding pressure 50-60 MPa, and holding time 11-12 s.

[0023] The third object of the present invention is to provide a flame retardant magnesium alloy, the chemical composition of the alloy, by weight percentage, includes: Yb: 0.5-15%, Al: 0.5-12%, Mn: 0.03-0.5%, M: 0-5%, the balance is magnesium and inevitable impurities; M is one of La, Ce, Sm, Zn, and Si.

[0024] A fourth object of the present invention is to provide a method for preparing the flame retardant magnesium alloy, comprising:

[0025] S1. Descaling and preheating magnesium ingots, aluminum ingots, zinc ingots, Mg-Yb master alloys, Mg-Mn master alloys, Mg-La master alloys, Mg-Ce master alloys, Mg-Sm master alloys and Mg-Si master alloys;

[0026] S2, putting a magnesium ingot, a Mg-Yb master alloy, and one of a Mg-La master alloy, a Mg-Ce master alloy, a Mg-Sm master alloy, and a Mg-Si master alloy into a crucible furnace as a charge, and passing a protective gas;

[0027] S3, heating to a certain temperature, adding Mg-Mn master alloy after the charge is completely melted, and stirring;

[0028] S4, adjust the furnace temperature to a certain temperature, add aluminum ingot and zinc ingot, and stir;

[0029] S5, adjusting the furnace temperature to a certain temperature, allowing the melt to stand, and obtaining a magnesium alloy melt;

[0030] S6. The magnesium alloy melt is subjected to gravity casting or high pressure die casting to obtain a flame retardant magnesium alloy.

[0031] It is further defined that the preheating temperature in S1 is 200-300° C. and the time is 20-40 minutes.

[0032] It is further defined that the protective gas in S2 is CO2 containing 1 to 10 vol% SF6.

[0033] It is further defined that the temperature in S3 is raised to 700-800°C.

[0034] It is further defined that the stirring time in S3 is 5 to 10 minutes.

[0035] It is further defined that in S4, the furnace temperature is adjusted to 700-710°C.

[0036] It is further defined that the stirring time in S4 is 5 to 10 minutes.

[0037] It is further defined that in S5, the furnace temperature is adjusted to 670-750°C.

[0038] It is further defined that the melt temperature during high pressure casting in S6 is 685-695°C.

[0039] It is further defined that the high pressure casting parameters of S6 are: injection pressure 110-130 MPa, injection rate 7.5-8.5 m / s, pressurization time 14-16 s, holding pressure 50-60 MPa, and holding time 11-12 s.

[0040] The beneficial effects achieved by the present invention are as follows:

[0041] (1) The flame retardant magnesium alloy provided by the present invention does not rely on traditional elements such as Ca, Be, Y, Sr, Nb, Gd, Y as the main flame retardant elements to achieve the purpose of flame retardancy, but uses Yb as the main flame retardant element. The affinity of Yb to oxygen is much greater than the affinity of magnesium to oxygen, so Yb will react with oxygen on the surface of the Mg-Al flame retardant magnesium alloy melt before Mg to form a dense ytterbium oxide film layer. Ytterbium oxide has a single structure and a high melting point, and has excellent high temperature resistance. At the same time, ytterbium oxide has a low thermal cracking tendency, so that the ytterbium oxide film layer will not crack at high temperatures. In addition, Yb diffuses faster in the magnesium melt and has a surface diffusion characteristic. Therefore, under high-temperature burning conditions, as time goes by, the ytterbium oxide film layer formed by Yb on the surface of the Mg-Al flame retardant magnesium alloy melt becomes thicker, thereby effectively isolating the contact between magnesium and oxygen, increasing the ignition temperature of the Mg-Al flame retardant magnesium alloy, and achieving a better flame retardant effect.

[0042] (2) In the flame-retardant magnesium alloy provided by the present invention, in addition to Yb, Al also has the characteristic of surface diffusion and can form an aluminum oxide film layer on the alloy surface. In addition, aluminum oxide has excellent high temperature resistance. Therefore, the addition of Al can further improve the thickness, density and heat resistance of the oxide film layer on the surface of the magnesium alloy melt; in addition, the addition of Al can also improve the casting performance of the alloy.

[0043] (3) In the flame-retardant magnesium alloy provided by the present invention, the addition of Mn effectively reduces the impurity elements in the magnesium alloy melt, such as Fe and Si, thereby reducing the cracking tendency of the ytterbium oxide and aluminum oxide film layers on the alloy surface, improving the protective effect of the film layer, and also improving the corrosion resistance of the Mg-Al flame-retardant magnesium alloy.

[0044] (4) The flame-retardant magnesium alloy provided by the present invention has good flame-retardant properties, and the flame-retardant point is higher than 1050°C. It also has excellent casting performance and can meet various casting process conditions such as conventional gravity casting, high-pressure casting, semi-continuous casting, etc. It is harmless to the human body and is suitable for large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1a This is a SEM image of the flame retardant magnesium alloy prepared in Example 1;

[0046] Figure 1b This is a SEM image of the flame retardant magnesium alloy prepared in Example 2;

[0047] Figure 1c This is a SEM image of the flame retardant magnesium alloy prepared in Example 3;

[0048] Figure 1d This is a SEM image of the flame retardant magnesium alloy prepared in Example 4;

[0049] Figure 1e This is a SEM image of the flame retardant magnesium alloy prepared in Example 5;

[0050] Figure 1f This is the SEM image of the flame retardant magnesium alloy prepared in Example 6. DETAILED DESCRIPTION

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in combination with the embodiments of the specification. In the following description, many specific details are elaborated to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0053] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0054] The purity of the magnesium ingot, aluminum ingot and zinc ingot used in the following examples is greater than 99.9%.

[0055] Example 1

[0056] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Yb: 4.5%, Al: 3.5%, Mn: 0.3%, and the balance is Mg and inevitable impurities. The magnesium ingot, Mg-30Yb master alloy, Mg-5Mn master alloy, and aluminum ingot are descaled and preheated at 250° C. for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and CO2 containing 2 vol% SF6 is introduced to raise the furnace temperature to 730° C. When the added furnace charge is completely melted, the Mg-5Mn master alloy is added, and the protective gas is continued to be introduced and stirred for 5 minutes. Then, the furnace temperature is adjusted to 710° C., the aluminum ingot is added, stirred for 10 minutes, and the furnace temperature is adjusted to 690° C. After the melt is allowed to stand for 30 minutes, gravity casting is performed to obtain a Mg-Yb-Al-Mn alloy.

[0057] Example 2

[0058] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Yb: 15%, Al: 0.5%, Mn: 0.5%, and the balance is Mg and inevitable impurities. The magnesium ingot, Mg-30Yb master alloy, Mg-5Mn master alloy and aluminum ingot are descaled and preheated at 250° C. for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and CO2 containing 2 vol% SF6 is introduced to raise the furnace temperature to 730° C. When the added charge is completely melted, the Mg-5Mn master alloy is added, and the protective gas is continued to be introduced and stirred for 10 minutes. Then, the furnace temperature is adjusted to 710° C., the aluminum ingot is added, stirred for 5 minutes, and the furnace temperature is adjusted to 690° C. After the melt is allowed to stand for 30 minutes, gravity casting is performed to obtain the Mg-Yb-Al-Mn alloy.

[0059] Example 3

[0060] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Yb: 1.5%, Al: 12%, Mn: 0.3%, and the balance is Mg and inevitable impurities. The magnesium ingot, Mg-30Yb master alloy, Mg-5Mn master alloy and aluminum ingot are descaled and preheated at 250° C. for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and CO2 containing 2 vol% SF6 is introduced to raise the furnace temperature to 730° C. When the added charge is completely melted, the Mg-5Mn master alloy is added, and the protective gas is continued to be introduced and stirred for 5 minutes. Then, the furnace temperature is adjusted to 710° C., the aluminum ingot is added, stirred for 10 minutes, and the furnace temperature is adjusted to 690° C. After the melt is allowed to stand for 30 minutes, gravity casting is performed to obtain a Mg-Yb-Al-Mn alloy.

[0061] Example 4

[0062] Weigh and prepare the ingredients according to the mass ratio of the alloy components, wherein Yb: 0.5%, Al: 5%, Mn: 0.3%, La: 4%, and the balance is Mg and inevitable impurities, descaling the magnesium ingot, Mg-30Yb master alloy, Mg-20La master alloy, Mg-5Mn master alloy and aluminum ingot, preheat at 250° C. for 30 min, then put the magnesium ingot, Mg-30Yb master alloy and Mg-20La master alloy into a crucible furnace, introduce CO2 containing 2 vol% SF6, raise the furnace temperature to 730° C., add the Mg-5Mn master alloy when the added charge is completely melted, continue to introduce the protective gas, stir for 5 min, then adjust the furnace temperature to 710° C., add the aluminum ingot, stir for 10 min, adjust the furnace temperature to 690° C., let the melt stand for 30 min, and obtain a Mg-Yb-Al-La-Mn alloy melt;

[0063] The Mg-Yb-Al-La-Mn alloy melt was subjected to high-pressure die casting, the melt temperature was maintained at 690°C, the injection pressure was 110 MPa, the injection rate was 7.5 m / s, the pressurization time was 15 ms, the holding pressure was 60 MPa, the holding time was 12 s, the die-casting mold was 60 mm × 80 mm × 2.6 mm, the mold temperature was 220°C, and the Mg-Yb-Al-La-Mn alloy was obtained by die casting.

[0064] Example 5

[0065] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Yb: 4.5%, Al: 6%, Mn: 0.3%, Zn: 0.8%, and the balance is Mg and inevitable impurities. The magnesium ingot, Mg-30Yb master alloy, Mg-5Mn master alloy, aluminum ingot and zinc ingot are descaled and preheated at 250° C. for 30 minutes. Then, the magnesium ingot and the Mg-30Yb master alloy are placed in a crucible furnace, and CO2 containing 2 vol% SF6 is introduced to raise the furnace temperature to 730° C. When the added charge is completely melted, the Mg-5Mn master alloy is added, and the protective gas is continued to be introduced and stirred for 5 minutes. Then, the furnace temperature is adjusted to 710° C., the aluminum ingot and the zinc ingot are added, and stirred for 10 minutes. The furnace temperature is adjusted to 690° C., and the melt is allowed to stand for 30 minutes for gravity casting to obtain a Mg-Yb-Al-Zn-Mn alloy.

[0066] Example 6

[0067] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Yb: 1.5%, Al: 0.5%, Mn: 0.3%, Sm: 5%, and the balance is Mg and inevitable impurities. The magnesium ingot, Mg-30Yb master alloy, Mg-20Sm master alloy, Mg-5Mn master alloy and aluminum ingot are descaled and preheated at 250° C. for 30 minutes. Then, the magnesium ingot, Mg-30Yb master alloy and Mg-20Sm master alloy are placed in a crucible furnace, CO2 containing 2 vol% SF6 is introduced, and the furnace temperature is raised to 730° C. When the added furnace charge is completely melted, the Mg-5Mn master alloy is added, and the protective gas is continued to be introduced and stirred for 8 minutes. Then, the furnace temperature is adjusted to 710° C., the aluminum ingot is added, stirred for 10 minutes, the furnace temperature is adjusted to 690° C., and the melt is allowed to stand for 30 minutes for casting to obtain a Mg-Yb-Al-Sm-Mn alloy.

[0068] Comparative Example 1

[0069] The ingredients are weighed and prepared according to the mass ratio of the alloy components, wherein Al: 9%, Zn: 0.5%, Mn: 0.3%, and the balance is Mg and inevitable impurities. The magnesium ingot, aluminum ingot, zinc ingot and Mg-5Mn master alloy are descaled and preheated at 250°C for 30 minutes. Then, the magnesium ingot and Mg-5Mn master alloy are placed in a crucible furnace, and CO2 containing 2 vol% SF6 is introduced. The furnace temperature is raised to 710°C. When the added charge is completely melted, the aluminum ingot and zinc ingot are added, stirred for 10 minutes, and then the furnace temperature is adjusted to 670°C. The melt is allowed to stand for 30 minutes and then gravity casting is performed to obtain a conventional AZ91D alloy.

[0070] Comparative Example 2

[0071] Weigh and prepare the ingredients according to the mass ratio of the alloy components, wherein La: 4%, Al: 4%, Mn: 0.3%, and the balance is Mg and inevitable impurities, descaling the magnesium ingot, Mg-20La master alloy, Mg-5Mn master alloy and aluminum ingot, preheat at 250° C. for 30 min, then put the magnesium ingot and Mg-20La master alloy into a crucible furnace, introduce CO2 containing 2% SF6, raise the furnace temperature to 730° C., add the Mg-5Mn master alloy when the added charge is completely melted, stir for 5 min, then adjust the furnace temperature to 710° C., add the aluminum ingot, stir for 10 min, adjust the furnace temperature to 690° C., let the melt stand for 30 min, and obtain a Mg-La-Al-Mn alloy melt;

[0072] The Mg-La-Al-Mn alloy melt was subjected to high-pressure die casting. The melt temperature was maintained at 690°C, the injection pressure was 110 MPa, the injection rate was 7.5 m / s, the pressurization time was 15 ms, the holding pressure was 60 MPa, the holding time was 12 s, the die-casting mold was 60 mm × 80 mm × 2.6 mm, the mold temperature was 220°C, and a conventional ALa44 (AE44 type) alloy sample was obtained by die casting.

[0073] The alloys in Examples 1 to 6 and Comparative Examples 1 to 2 were subjected to ignition point tests:

[0074] The magnesium alloys obtained in Examples 1 to 3, Examples 5 to 6 and Comparative Example 1 were machined to obtain 60 mm × 80 mm × 2.6 mm thin plates for ignition point testing. Thin plates for ignition point testing were prepared in the high pressure die casting process in Example 4 and Comparative Example 2. The ignition point test method was based on ASTM E659-17 "Standard Test Method for Autoignition Temperature of Liquid Chemicals". The test results are shown in Table 1.

[0075] Table 1 Ignition point test results of magnesium alloys prepared in Examples 1 to 6 and Comparative Examples 1 to 2

[0076]

[0077]

[0078] It can be seen from the data in Table 1 that the flame retardant magnesium alloys prepared in Examples 1 to 6 of the present invention did not burn at a high temperature of 1050°C, indicating excellent flame retardant properties. The magnesium alloys prepared in Comparative Examples 1 and 2 burned violently at temperatures of 700°C and 780°C, respectively, indicating poor flame retardant properties and a flame retardant point lower than the flame retardant magnesium alloy provided by the present invention.

[0079] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A flame retardant magnesium alloy, characterized in that: The chemical composition of the alloy includes, by weight percentage, 0.5-15% of Yb, 0.5-12% of Al, 0.03-0.5% of Mn, and the remainder is magnesium and inevitable impurities.

2. A method for preparing the flame retardant magnesium alloy according to claim 1, characterized in that: include: S1. Descaling and preheating magnesium ingots, aluminum ingots, Mg-Yb master alloys and Mg-Mn master alloys; S2, putting magnesium ingot and Mg-Yb master alloy into a crucible furnace as charge, and passing protective gas; S3, heating to a certain temperature, adding Mg-Mn master alloy after the charge is completely melted, and stirring; S4, adjust the furnace temperature to a certain temperature, add aluminum ingots, and stir; S5, adjusting the furnace temperature to a certain temperature, allowing the melt to stand, and obtaining a magnesium alloy melt; S6. The magnesium alloy melt is subjected to gravity casting or high pressure die casting to obtain a flame retardant magnesium alloy.

3. A flame retardant magnesium alloy, characterized in that: The chemical composition of the alloy, measured by weight percentage, includes: Yb: 0.5-15%, Al: 0.5-12%, Mn: 0.03-0.5%, M: 0-5%, and the balance is magnesium and unavoidable impurities; The M is one of La, Ce, Sm, Zn and Si.

4. A method for preparing the flame retardant magnesium alloy according to claim 3, characterized in that: include: S1. Descaling and preheating magnesium ingots, aluminum ingots, zinc ingots, Mg-Yb master alloys, Mg-Mn master alloys, Mg-La master alloys, Mg-Ce master alloys, Mg-Sm master alloys and Mg-Si master alloys; S2, putting a magnesium ingot, a Mg-Yb master alloy, and one of a Mg-La master alloy, a Mg-Ce master alloy, a Mg-Sm master alloy, and a Mg-Si master alloy into a crucible furnace as a charge, and passing a protective gas; S3, heating to a certain temperature, adding Mg-Mn master alloy after the charge is completely melted, and stirring; S4, adjust the furnace temperature to a certain temperature, add aluminum ingot and zinc ingot, and stir; S5, adjusting the furnace temperature to a certain temperature, allowing the melt to stand, and obtaining a magnesium alloy melt; S6. The magnesium alloy melt is subjected to gravity casting or high pressure die casting to obtain a flame retardant magnesium alloy.

5. The preparation method according to claim 2 or 4, characterized in that: The preheating temperature in S1 is 200-300°C and the time is 20-40 minutes.

6. The preparation method according to claim 2 or 4, characterized in that: The protective gas in S2 is CO2 containing 1 to 10 vol% SF6.

7. The preparation method according to claim 2 or 4, characterized in that: In S3, the temperature is raised to 700-800°C; the stirring time is 5-10 minutes.

8. The preparation method according to claim 2 or 4, characterized in that: In S4, the furnace temperature is adjusted to 700-710°C; the stirring time is 5-10 minutes.

9. The preparation method according to claim 2 or 4, characterized in that: In S5, the furnace temperature is adjusted to 670-750°C.

10. The preparation method according to claim 2 or 4, characterized in that: During the medium and high pressure die casting of S6, the melt temperature is 685-695°C; the high pressure die casting parameters are: injection pressure 110-130MPa, injection rate 7.5-8.5m / s, pressurization time 14-16s, holding pressure 50-60MPa, and holding time 11-12s.

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