Die-casting magnesium alloy material, preparation method thereof and automobile structural part

Abstract

The invention relates to a die-casting magnesium alloy material, a preparation method of the die-casting magnesium alloy material and an automobile structural part. The die-casting magnesium alloy material comprises, by weight, 5%-10% of Al, 0.4%-1.0% of Zn, 0.15%-0.6% of Mn, 0.01%-1.0% of Ca, 5 ppm-30 ppm of Be, 0.08% or less of Si, 0.004% or less of Fe, 0.02% or less of Cu, 0.001% or less of Ni, 0.001%-0.1% of Hf, 0.01% or less of impurities and the balance Mg. The die-casting magnesium alloy material provided by the invention can give consideration to cost, high strength and corrosion resistance at the same time; and the body performance requirements of the automobile structural component can be met.

Description

Technical Field

[0001] The present disclosure relates to the technical field of die-cast magnesium alloys, and in particular to a die-cast magnesium alloy material and a preparation method thereof, and an automobile structural part. Background Art

[0002] With the widespread adoption of lightweight automotive parts, magnesium alloys are used in many areas of the automotive industry. Currently, most magnesium alloys are formed by die casting. The most widely used traditional die-cast magnesium alloys are AZ series (such as AZ91D) and AM series (such as AM50, AM60) alloys, but the Mg content of AZ and AM alloys is 17 Al 12 The eutectic phase has a low melting point and is easily softened at high temperatures, which leads to poor high-temperature mechanical properties and creep resistance of AZ and AM alloys. Among traditional die-cast magnesium alloys, AX alloys (such as AX53 and AXJ530) with good heat resistance have a large tendency to hot cracking and poor part formability. Therefore, it is difficult for traditional die-cast magnesium alloys to take into account both high strength and heat resistance and good formability, which makes the application of magnesium alloys in high-strength and heat-resistant parts poor. Therefore, the existing die-cast magnesium alloy materials cannot take into account the technical difficulties of cost, high strength, and corrosion resistance at the same time, making die-cast magnesium alloys unable to meet the needs of new energy vehicle motor housings for parts with high strength and heat resistance requirements. It is urgent to develop new high-strength and high-heat-resistant die-cast magnesium alloys to expand the application of die-cast magnesium alloys in high-strength and heat-resistant parts.

[0003] In addition, more attention should be paid to the bulk properties that magnesium alloy materials can achieve in structural parts, but the performance requirements currently met by die-cast magnesium alloy materials are not based on bulk sampling. Summary of the invention

[0004] The purpose of the present disclosure is to provide a die-cast magnesium alloy material and a preparation method thereof, and an automobile structural part, which can take into account cost, high strength and corrosion resistance at the same time; and can meet the body performance requirements of automobile structural parts.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides a die-cast magnesium alloy material. Based on the total weight of the die-cast magnesium alloy material, the die-cast magnesium alloy includes: 5-10 wt% Al, 0.4-1.0 wt% Zn, 0.15-0.6 wt% Mn, 0.01-1.0 wt% Ca, 5-30 ppm Be, less than 0.08 wt% Si, less than 0.004 wt% Fe, less than 0.02 wt% Cu, less than 0.001 wt% Ni, 0.001-0.1 wt% Hf, less than 0.01 wt% impurities and the remainder Mg.

[0006] Optionally, the die-cast magnesium alloy includes: 8.5-9.5 weight % Al, 0.5-0.8 weight % Zn, 0.15-0.6 weight % Mn, 0.3-0.7 weight % Ca, 5-30 ppm Be, less than 0.08 weight % Si, less than 0.004 weight % Fe, less than 0.02 weight % Cu, less than 0.001 weight % Ni, 0.04-0.08 weight % Hf, less than 0.01 weight % impurities and the balance Mg.

[0007] Optionally, in the die-cast magnesium alloy material, a content ratio of Hf / Al is ≥45 / 10000.

[0008] Optionally, the bulk properties of the die-cast magnesium alloy material include: a yield strength of 140 MPa or more, a tensile strength of 230 MPa or more, and an elongation of 1.5% or more.

[0009] A second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy material, comprising the following steps: S1. Under a protective atmosphere, melting an alloy raw material mixture in a melting furnace to obtain a first alloy melt; based on the total weight of the alloy raw material mixture, the alloy raw material mixture comprises: 5-10 wt % Al, 0.4-1.0 wt % Zn, 0.15-0.6 wt % Mn, 0.01-1.0 wt % Ca, 5-30 ppm Be, 0.08 wt % or less Si, 0.004 wt % or less Fe, 0.02 wt % or less Cu, 0.001 wt % or less Ni, 0.001-0.1 wt % Hf, 0.01 wt % or less impurities and the remainder Mg; S2, refining and deslagging the first alloy melt to obtain a second alloy melt; S3, subjecting the second alloy melt to die casting.

[0010] Optionally, in step S1, Mg, Al, and Zn in the alloy raw material mixture are prepared in the form of pure magnesium, pure aluminum, and pure zinc; Mn and Ca are prepared in the form of Mg-containing Mn master alloys and Mg-containing Ca master alloys; and Hf is prepared in the form of Al-10.45Hf master alloy; Step S1 includes: Under a protective atmosphere, pure magnesium in the alloy raw material mixture is placed in a melting furnace for melting to obtain a magnesium melt; other alloy raw materials except pure magnesium are added to the magnesium melt, and the mixture is kept warm and melted to obtain the first alloy melt.

[0011] Optionally, the conditions for melting the pure magnesium include: a temperature of 680-745° C. and a time of 1-2 h; The heat preservation and melting conditions include: a temperature of 740°C or higher and a time of 30 minutes or higher; The protective atmosphere includes N 2 , CO 2 and SF 6 One or more of the .

[0012] Optionally, in step S2, the refining treatment conditions include: temperature of 720-740°C, standing time of 10-15 min; In step S3, the die-casting treatment conditions include: a die-casting temperature of 700-730° C., an injection speed of 2-5 m / s, and a casting pressure of 80-160 MPa.

[0013] A third aspect of the present disclosure provides a die-cast magnesium alloy material prepared according to the method described in the second aspect of the present disclosure.

[0014] A fourth aspect of the present disclosure provides an automobile structural part, comprising the die-cast magnesium alloy material according to the first aspect or the third aspect of the present disclosure.

[0015] Through the above technical scheme, the present disclosure provides a die-cast magnesium alloy material and a preparation method thereof, and an automotive structural part. The die-cast magnesium alloy achieves the effects of metamorphism and fine grain strengthening through alloying control and AI model iteration, by exploring the content range of Al, Zn, and Mn, as well as the addition of Hf and Ca, and the ratio of Hf and Al elements, so as to obtain a material suitable for a motor housing with the best comprehensive strength and elongation; and the performance of the die-cast magnesium alloy disclosed in the present disclosure has been fully verified on a motor housing mold, and body sampling can be achieved and body performance requirements can be met at the motor barrel wall position, that is, the place where the motor requires the highest strength; the die-cast magnesium alloy does not require heat treatment, and can achieve the performance of other conventional alloys after heat treatment. The absence of heat treatment can save costs and reduce carbon emissions, and also has great benefits for the dimensional accuracy of parts; the corrosion resistance of the die-cast magnesium alloy material is also improved to a certain extent (the corrosion resistance can reach a level equivalent to that of ADC12), and it is more suitable for the application environment where the electric drive is located in the chassis.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings: Figure 1 A process flow chart of a method for preparing a die-cast magnesium alloy material provided by the present disclosure is shown; Figure 2An electron microscope photograph of the cast magnesium alloy material prepared in Example 1 of the present disclosure is shown; Figure 3 The motor housing and sampling position for body sampling of the die-cast magnesium alloy material provided by the present disclosure are shown.

[0018] Description of Reference Numerals a-eutectic phase, b-Hf strengthened phase, c-α-Mg phase, 1-bulk sampling position. DETAILED DESCRIPTION

[0019] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0020] The inventors of the present disclosure have found that the magnesium-gold material currently developed is based on the performance development of tensile test bars. This performance index has no reference significance for the actual product development process. It does not represent the performance requirements required for real application conditions, and the test bar performance / flat die sample will be further attenuated in the actual product body sampling performance. As for how much attenuation will also vary due to different shell sampling positions and different process parameters, so this performance cannot be used as an input for product development. Therefore, in view of the problem that the current die-cast magnesium alloy cannot meet the needs of automotive motor housing parts with high strength and heat resistance requirements, and there is no corresponding body performance data, the present disclosure has developed a high-strength die-cast magnesium alloy by controlling the content of each element in the alloy, which can achieve high strength and elongation in the performance of the electric drive housing body without heat treatment, so as to expand the application of die-cast magnesium alloys in high-strength and heat-resistant parts.

[0021] A first aspect of the present disclosure provides a die-cast magnesium alloy material. Based on the total weight of the die-cast magnesium alloy material, the die-cast magnesium alloy includes: 5-10 wt % of Al (aluminum), 0.4-1.0 wt % of Zn (zinc), 0.15-0.6 wt % of Mn (manganese), 0.01-1.0 wt % of Ca (calcium), 5-30 ppm of Be (beryllium), 0.08 wt % or less of Si (silicon), 0.004 wt % or less of Fe (iron), 0.02 wt % or less of Cu (copper), 0.001 wt % or less of Ni (nickel), 0.001-0.1 wt % of Hf (hafnium), 0.01 wt % or less of impurities and the remainder of Mg (magnesium).

[0022] The present disclosure provides a die-cast magnesium alloy material, which achieves the effects of modification and fine grain strengthening through alloying control and AI model iteration, by exploring the content range of Al, Zn, and Mn, the addition of Hf and Ca, and the ratio of Hf and Al elements, and has a significant impact on the microstructure and mechanical properties of the alloy, thereby obtaining a material suitable for a motor housing with the best comprehensive strength and elongation; and the performance of the die-cast magnesium alloy disclosed in the present disclosure has been fully verified on a motor housing mold, and body sampling can be achieved and body performance requirements can be met at the motor barrel wall, i.e., the place where the motor requires the highest strength; the corrosion resistance of the die-cast magnesium alloy material has also been improved to a certain extent (the corrosion resistance can reach a level equivalent to that of ADC12), and it is more suitable for the application environment where the electric drive is located in the chassis.

[0023] According to the present disclosure, the Ca element in the die-cast magnesium alloy is solid dissolved in the Mg 17 Al 12 Phase, increased Mg 17 Al 12 The strength, hardness, melting point and thermal stability of the phase can improve the strength and heat resistance of the magnesium alloy, thereby improving the high temperature heat resistance of the alloy.

[0024] According to the present disclosure, Hf in the die-cast magnesium alloy mainly exists in the form of undissolved particles and dissolved Hf solute. The strong component supercooling caused by the Hf solute will prevent the continuous growth of α-Mg dendrites and achieve grain refinement. At the same time, the undissolved Hf particles can serve as heterogeneous nucleation sites, promote nucleation, and thus limit grain growth.

[0025] In a preferred embodiment, based on the total weight of the die-cast magnesium alloy material, the die-cast magnesium alloy includes: 8.5-9.5 wt% Al, 0.5-0.8 wt% Zn, 0.15-0.6 wt% Mn, 0.3-0.7 wt% Ca, 5-30 ppm Be, 0.08 wt% or less Si, 0.004 wt% or less Fe, 0.02 wt% or less Cu, 0.001 wt% or less Ni, 0.04-0.08 wt% Hf, 0.01 wt% or less impurities and the remainder Mg. The die-cast magnesium alloy having the component contents provided in this embodiment can have better strength and elongation.

[0026] The inventors of the present disclosure have also found that the Hf / Al content ratio in the die-cast magnesium alloy material also has an influence on the properties of the die-cast magnesium alloy.

[0027] In a preferred embodiment, in the die-cast magnesium alloy material, the Hf / Al content ratio is ≥45 / 10000, preferably the Hf / Al content ratio is ≥50 / 10000. When the Hf / Al content ratio is within the range of this embodiment, especially within the preferred range, the bulk properties of the die-cast magnesium alloy material can be further improved.

[0028] In a specific embodiment, the bulk properties of the die-cast magnesium alloy material include: a yield strength of 140MPa or more, a tensile strength of 230MPa or more, and an elongation of 1.5% or more; preferably, the yield strength is 150MPa or more, the tensile strength is 250MPa or more, and the elongation is 1.5% or more. In the present disclosure, the bulk properties of the die-cast magnesium alloy material refer to: taking out a tensile specimen that meets the requirements from the part in actual application, and performing a tensile test to obtain the strength properties of the part body. The bulk sampling can be performed by the following method: first, the part body is obtained by a die-casting process, and the area that meets the tensile test is marked out, and then the sample block marked out is obtained by cutting, and a standard tensile test specimen is obtained from the above sample block by wire cutting.

[0029] A second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy material, comprising the following steps: S1. Under a protective atmosphere, melting an alloy raw material mixture in a melting furnace to obtain a first alloy melt; based on the total weight of the alloy raw material mixture, the alloy raw material mixture comprises: 5-10 wt % Al, 0.4-1.0 wt % Zn, 0.15-0.6 wt % Mn, 0.01-1.0 wt % Ca, 5-30 ppm Be, 0.08 wt % or less Si, 0.004 wt % or less Fe, 0.02 wt % or less Cu, 0.001 wt % or less Ni, 0.001-0.1 wt % Hf, 0.01 wt % or less impurities and the remainder Mg; S2, refining and deslagging the first alloy melt to obtain a second alloy melt; S3, subjecting the second alloy melt to die casting.

[0030] The present disclosure provides a method for preparing a die-cast magnesium alloy material, which can achieve the performance of other conventional alloys after heat treatment without heat treatment; not requiring heat treatment can save costs and reduce carbon emissions, and also has great benefits for the dimensional accuracy of parts.

[0031] In a preferred embodiment, based on the total weight of the alloy raw material mixture, the alloy raw material mixture includes: 8.5-9.5 wt% Al, 0.5-0.8 wt% Zn, 0.15-0.6 wt% Mn, 0.3-0.7 wt% Ca, 5-30 ppm Be, 0.08 wt% or less Si, 0.004 wt% or less Fe, 0.02 wt% or less Cu, 0.001 wt% or less Ni, 0.04-0.08 wt% Hf, 0.01 wt% or less impurities and the remainder Mg. Using the alloy raw material mixture with the component contents provided in this embodiment, a die-casting magnesium alloy material with better strength and elongation can be prepared.

[0032] In a preferred embodiment, in the alloy raw material mixture, the Hf / Al content ratio is ≥45 / 10000, preferably the Hf / Al content ratio is ≥50 / 10000. Controlling the Hf / Al content ratio of the alloy raw material mixture within the scope of this embodiment, especially within the preferred range, can further improve the bulk properties of the obtained die-cast magnesium alloy material.

[0033] In a specific embodiment, in step S1, Mg, Al, and Zn in the alloy raw material mixture are prepared in the form of pure magnesium, pure aluminum, and pure zinc; Mn and Ca are prepared in the form of Mg-containing Mn master alloy and Mg-containing Ca master alloy; and Hf is prepared in the form of Al-10.45Hf master alloy; Step S1 includes: Under a protective atmosphere, pure magnesium in the alloy raw material mixture is placed in a melting furnace for melting to obtain a magnesium melt; other alloy raw materials except pure magnesium are added to the magnesium melt, and the mixture is kept warm and melted to obtain the first alloy melt.

[0034] In a preferred embodiment, the conditions for melting the pure magnesium include: a temperature of 680-745° C. and a time of 1-2 hours; preferably, a temperature of 690-745° C. and a time of 1-1.5 hours; The heat preservation and melting conditions include: a temperature of 740°C or above and a time of 30 minutes or above; preferably, a temperature of 740-750°C and a time of 40-60 minutes; The protective atmosphere includes N 2 , CO 2 and SF 6 One or more of the .

[0035] In one embodiment, the refining treatment conditions include: a temperature of 720-740°C and a standing time of 10-15 minutes; preferably, a temperature of 730-740°C and a standing time of 12-15 minutes; specifically, the refining treatment includes: adding a refining agent to the first alloy melt under stirring, and then standing; the refining agent can be a conventionally selected type in the field and can be obtained through ordinary commercial channels. Refining treatment according to the conditions in this embodiment, especially according to the preferred process conditions, has a better purification effect; The deslagging process includes removing scum using a deslagging tool.

[0036] In one embodiment, in step S3, the die-casting process conditions include: a die-casting temperature of 700-730°C, an injection speed of 2-5 m / s, and a casting pressure of 80-160 MPa. According to the process conditions in this embodiment, especially according to the preferred process conditions, a die-casting magnesium alloy material with better bulk properties can be obtained.

[0037] A third aspect of the present disclosure provides a die-cast magnesium alloy material prepared according to the method described in the second aspect of the present disclosure.

[0038] A fourth aspect of the present disclosure provides an automobile structural part, comprising the die-cast magnesium alloy material according to the first aspect or the third aspect of the present disclosure.

[0039] Furthermore, the automotive structural parts include parts that are formed by die casting and have high strength and high yield requirements for the parts themselves, including but not limited to motor housings, motor end covers, intermediate housings, balancing discs, reducer housings and other electric drive parts. Figure 3 As shown, Figure 3 The motor housing of the structure shown in , wherein the body sampling position 1 is on the motor housing.

[0040] The present disclosure is further described in detail by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0041] The electron microscope photographs of the die-cast magnesium alloys obtained in the following examples were obtained using a PHENOM XL scanning electron microscope.

[0042] Example 1 This embodiment prepares a die-cast magnesium alloy according to the alloy raw material composition listed in Table 1, including the following steps: (1) Prepare materials according to the formula ingredients; wherein Mg, Al, and Zn are prepared in the form of pure magnesium, pure aluminum, and pure zinc; Mn and Ca are prepared in the form of Mn and Ca master alloys containing Mg; and Hf is prepared in the form of Al-10.45Hf master alloy; (2) First, place pure magnesium in a melting furnace and introduce protective gas (CO 2+SF 6 Protective gas, mixed gas, CO 2 The volume content of magnesium is in the range of 5 to 8 volume %), and the temperature is 745° C., and the time is 1 hour; then, the materials of the other components except pure magnesium are added, and the materials are kept warm and melted at a temperature of 750° C., and the time is 50 minutes. After melting, the molten metal is stirred evenly to obtain a first alloy melt; (3) adding a refining agent powder to the first alloy melt for refining treatment, and performing slag removal to obtain a second alloy melt; wherein the refining treatment conditions include: adding the refining agent for refining at 730° C. while stirring; after the addition of the refining agent is completed, standing for 15 minutes; (4) The second alloy melt is die-casted. The die-casting conditions include: a die-casting temperature of 720° C., an injection speed of 4 m / s, and a casting pressure of 90 MPa.

[0043] The electron microscope photo of the die-cast magnesium alloy material prepared in this example is as follows Figure 2 As shown by Figure 2 It can be seen that the structure of the die-cast magnesium alloy material is mainly composed of α-Mg, eutectic phase and trace Hf strengthening precipitates, and the α-Mg and eutectic phase are fine and evenly distributed; Figure 1 In the figure, a represents the eutectic phase (white), b represents the Hf strengthening phase (white granular), and c represents α-Mg (black).

[0044] Embodiment 2~7 Referring to the preparation method in Example 1, the difference from Example 1 is that the magnesium alloy material is prepared according to the magnesium alloy raw material composition listed in Table 1, and the rest of the process is the same as Example 1.

[0045] Comparative Examples 1 to 3 Referring to the preparation method in Example 1, the difference from Example 1 is that the magnesium alloy material is prepared according to the magnesium alloy raw material composition listed in Table 1, and the rest of the process is the same as Example 1.

[0046] Table 1

[0047] In Table 1, the unit of the contents of Al, Zn, Mn, Ca, Si, Fe, Cu, Ni and Hf is "weight %"; the unit of the content of Be is ppm.

[0048] Test Example 1 This test example is used to take body samples of the products prepared in the above embodiments and comparative examples and to perform mechanical property tests.

[0049] The method for body sampling is: first, the part body is obtained through the die-casting process, the area that meets the tensile test specimen is marked, and then the sample block marked above is obtained by cutting, and the standard tensile test specimen is obtained from the above sample block by wire cutting. The sample specification is a small-size test according to ASTM E8, and the thickness is the actual thickness of the body, about 4~6mm, and the tensile test specimen is taken.

[0050] The test methods for yield strength, tensile strength and elongation of the bulk specimen refer to standard GB / T228.1. The test results are listed in Table 2 below.

[0051] Table 2

[0052] According to the data in Table 2 above, we can see that: In Comparative Example 1, Hf is replaced by metal Y (yttrium) in the die-cast magnesium alloy material, and the content of Ca is not within the range provided in the present disclosure; in Comparative Example 2, Hf is not added to the die-cast magnesium alloy, and the component content is not within the range provided in the present disclosure; in Comparative Example 3, Hf is replaced by metal Ce (cerium), and the contents of the remaining components are the same as those in Example 1; the die-cast magnesium alloy materials obtained in Comparative Examples 1 to 3 cannot simultaneously take into account high yield strength, high tensile strength and high elongation; compared with the die-cast magnesium alloys obtained in Comparative Examples 1 to 3, the die-cast magnesium alloys in Examples 1 to 7 having the component contents provided in the present disclosure can simultaneously have high yield strength, tensile strength and elongation, and have better comprehensive performance; Comparing Example 1 with Examples 2 to 7, it can be seen that the composition of the die-cast magnesium alloy material obtained in Example 1 is within the preferred range provided in the present disclosure, and the die-cast magnesium alloy material in Example 1 has higher yield strength and tensile strength, and also has high elongation, and has better comprehensive performance; Among them, by comparing Example 1 with Examples 2~3 and 7, it can be seen that the Hf / Al content ratio of the die-cast magnesium alloy material in Example 1 is within the optimization range provided by the present disclosure (Hf / Al≥45 / 10000), and the die-cast magnesium alloy material obtained in Example 1 has higher yield strength and tensile strength, and takes into account high elongation, and has better comprehensive performance.

[0053] Test Example 2 This test example is used to test the corrosion resistance of the die-cast magnesium alloys obtained in some embodiments and comparative examples.

[0054] The test method is based on GB / T10125. The test results are listed in Table 3 below.

[0055] Table 3

[0056] From the data in Table 3 above, we can see that: The corrosion rate of the die-cast magnesium alloy obtained in Example 1 and Comparative Example 1 is lower and the corrosion resistance is better; and the die-cast magnesium alloy obtained in Example 1 can achieve corrosion resistance equivalent to that of ADC12.

[0057] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0058] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0059] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A die-cast magnesium alloy material, characterized in that: Based on the total weight of the die-casting magnesium alloy material, the die-casting magnesium alloy includes: 5-10 weight % of Al, 0.4-1.0 weight % of Zn, 0.15-0.6 weight % of Mn, 0.01-1.0 weight % of Ca, 5-30 ppm of Be, less than 0.08 weight % of Si, less than 0.004 weight % of Fe, less than 0.02 weight % of Cu, less than 0.001 weight % of Ni, 0.001-0.1 weight % of Hf, less than 0.01 weight % of impurities and the balance of Mg.

2. The die-cast magnesium alloy material according to claim 1, characterized in that: The die-casting magnesium alloy includes: 8.5-9.5 weight % of Al, 0.5-0.8 weight % of Zn, 0.15-0.6 weight % of Mn, 0.3-0.7 weight % of Ca, 5-30 ppm of Be, less than 0.08 weight % of Si, less than 0.004 weight % of Fe, less than 0.02 weight % of Cu, less than 0.001 weight % of Ni, 0.04-0.08 weight % of Hf, less than 0.01 weight % of impurities and the balance of Mg.

3. The die-cast magnesium alloy material according to claim 1, characterized in that: In the die-cast magnesium alloy material, the content ratio of Hf / Al is ≥45 / 10000.

4. The die-cast magnesium alloy material according to claim 1, characterized in that: The bulk properties of the die-cast magnesium alloy material include: a yield strength of more than 140 MPa, a tensile strength of more than 230 MPa, and an elongation of more than 1.5%.

5. A method for preparing a die-cast magnesium alloy material, characterized in that: The following steps are involved: S1. Under a protective atmosphere, melting an alloy raw material mixture in a melting furnace to obtain a first alloy melt; based on the total weight of the alloy raw material mixture, the alloy raw material mixture comprises: 5-10 wt % Al, 0.4-1.0 wt % Zn, 0.15-0.6 wt % Mn, 0.01-1.0 wt % Ca, 5-30 ppm Be, 0.08 wt % or less Si, 0.004 wt % or less Fe, 0.02 wt % or less Cu, 0.001 wt % or less Ni, 0.001-0.1 wt % Hf, 0.01 wt % or less impurities and the remainder Mg; S2, refining and deslagging the first alloy melt to obtain a second alloy melt; S3, subjecting the second alloy melt to die casting.

6. The method according to claim 5, characterized in that In step S1, Mg, Al, and Zn in the alloy raw material mixture are prepared in the form of pure magnesium, pure aluminum, and pure zinc; Mn and Ca are prepared in the form of Mg-containing Mn master alloy and Mg-containing Ca master alloy; and Hf is prepared in the form of Al-10.45Hf master alloy; Step S1 includes: Under a protective atmosphere, pure magnesium in the alloy raw material mixture is placed in a melting furnace for melting to obtain a magnesium melt; other alloy raw materials except pure magnesium are added to the magnesium melt, and the mixture is kept warm and melted to obtain the first alloy melt.

7. The method according to claim 6, characterized in that The conditions for melting the pure magnesium include: a temperature of 680-745° C. and a time of 1-2 hours; The heat preservation and melting conditions include: a temperature of 740°C or higher and a time of 30 minutes or higher; The protective atmosphere includes one or more of N2, CO2 and SF6.

8. The method according to claim 5, characterized in that In step S2, the refining treatment conditions include: temperature of 720-740°C and standing time of 10-15 minutes; In step S3, the die-casting treatment conditions include: a die-casting temperature of 700-730° C., an injection speed of 2-5 m / s, and a casting pressure of 80-160 MPa.

9. The die-casting magnesium alloy material prepared according to the method according to any one of claims 5 to 8.

10. An automobile structural part, characterized in that: The invention comprises the die-cast magnesium alloy material as described in any one of claims 1 to 4 and 9.

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