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

Abstract

This disclosure relates to a die-cast magnesium alloy, its preparation method, and automotive structural components. Based on the total weight of the die-cast magnesium alloy, it comprises: 5-7 wt% Al, 7-12 wt% La, 0.2-0.4 wt% Mn, less than 0.3 wt% impurities, and the balance Mg; wherein the Al to La content ratio is 0.50-0.75. This disclosure provides a magnesium alloy that simultaneously achieves cost-effectiveness, high strength, and heat resistance and creep resistance, expanding the application of die-cast magnesium alloys in high-strength, heat-resistant components.

Description

Technical Field

[0001] This disclosure relates to the field of die-cast magnesium alloy technology, specifically to a die-cast magnesium alloy and its preparation method, and automotive structural components. Background Technology

[0002] Magnesium alloys possess advantages such as low density, high specific strength and stiffness, and good damping performance. With the widespread adoption of lightweight automotive components, magnesium alloys are being used to replace aluminum alloys, steel, and other metal materials in many areas of the automotive industry, making them one of the most promising lightweight materials. However, gravity casting suffers from slow filling, low production efficiency, low density, numerous internal porosity defects, and poor strength in magnesium alloy castings. Therefore, die casting is currently the most common method for producing magnesium alloys.

[0003] The most widely used traditional die-cast magnesium alloys are AZ-based (such as AZ91D) and AM-based (such as AM50 and AM60) alloys. However, the Mg17Al12 eutectic phase in AZ-based and AM-based alloys has a low melting point and is prone to softening at high temperatures, resulting in poor high-temperature mechanical properties and creep resistance. Meanwhile, AX-based alloys (such as AX53 and AXJ530), which have better heat resistance among traditional die-cast magnesium alloys, have a high tendency for hot cracking and poor part formability.

[0004] The existing die-cast magnesium alloy materials cannot simultaneously achieve the technical challenges of cost, high strength, and heat resistance and creep resistance, making them unable to meet the high strength and heat resistance requirements of components such as motor housings in new energy vehicles. Summary of the Invention

[0005] The purpose of this disclosure is to provide a die-cast magnesium alloy and its preparation method, as well as automotive structural parts, to provide a magnesium alloy that simultaneously considers cost, high strength, and heat resistance and creep resistance, thereby expanding the application of die-cast magnesium alloys in high-strength and heat-resistant components.

[0006] To achieve the above objectives, the first aspect of this disclosure provides a die-cast magnesium alloy, wherein, based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-7% by weight of Al, 7-12% by weight of La, 0.2-0.4% by weight of Mn, less than 0.3% by weight of impurities, and the balance of Mg; wherein the ratio of Al to La content is 0.50-0.75.

[0007] Preferably, based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-6% by weight of Al, 8-11% by weight of La, 0.3-0.4% by weight of Mn, less than 0.2% by weight of impurities, and the balance of Mg.

[0008] Preferably, in the die-cast magnesium alloy, the content of Al and La satisfies: 80≤11Al+3La≤100.

[0009] Preferably, the die-cast magnesium alloy has a yield strength of 190~200 MPa and a tensile strength of 240~260 MPa; the die-cast magnesium alloy produces a creep strain of 0.009~0.02% under creep conditions of 120℃, 100MPa and 100h.

[0010] A second aspect of this disclosure provides a method for preparing die-cast magnesium alloys, comprising the following steps:

[0011] S1. Under a protective atmosphere, Mg raw material is subjected to a first melting treatment; then Al raw material, La raw material and Mn raw material are added for a second melting treatment to obtain a first alloy melt; based on the total weight of the first alloy melt, the first alloy melt includes 5-7% by weight of Al, 7-12% by weight of La, 0.2-0.4% by weight of Mn, less than 0.3% by weight of impurities and the balance of Mg; wherein the ratio of Al to La content is 0.50-0.75;

[0012] S2. The first alloy melt is refined and slag is removed to obtain the second alloy melt.

[0013] S3. The second alloy melt is die-cast.

[0014] Optionally, in step S1, the conditions for the first melting treatment include: a melting temperature of 680~720℃; and the conditions for the second melting treatment include: a melting temperature of 740~760℃ and a melting time of 1~2h.

[0015] The protective atmosphere is selected from one or more of N2, CO2 and SF6 gases;

[0016] Optionally, the Mg raw material includes pure magnesium, the Al raw material includes pure aluminum, the La raw material includes pure lanthanum, and the Mn raw material includes one or more of pure manganese, manganese-magnesium master alloy, or manganese-aluminum master alloy.

[0017] Optionally, in step S2, the refining conditions include: adding a refining agent at 720~740℃ for refining, while stirring, and letting it stand for 10~15 minutes.

[0018] The slag removal process includes using slag removal tools to remove floating slag.

[0019] Optionally, in step S3, the conditions for the die-casting process include:

[0020] The die-casting pressure is 50~100MPa, the vacuum degree is 50~100mbar, and the temperature of the second alloy melt is 700~730℃.

[0021] A third aspect of this disclosure provides a die-cast magnesium alloy prepared according to the method described in the second aspect of this disclosure.

[0022] This disclosure provides a fourth aspect of an automotive structural component, comprising the die-cast magnesium alloy described in the first or third aspect of this disclosure.

[0023] Through the above technical solution, this disclosure provides a die-cast magnesium alloy and its preparation method, as well as automotive structural parts. The die-cast magnesium alloy provided by this disclosure precisely controls the content of Al and La elements and their ratio, so as to form an Al content of appropriate value. 11 The La3 eutectic phase ensures the strength, heat resistance, and formability of the magnesium alloy; the die-cast magnesium alloy provided in this disclosure possesses comprehensive properties of high strength and high heat resistance. The die-cast aluminum alloy provided in this disclosure can be applied to components with high strength and high heat resistance requirements, and can meet the performance requirements of high-performance, high-torque motor housing parts in current new energy vehicles.

[0024] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 A process flow diagram of the method for preparing die-cast magnesium alloys provided in this disclosure is shown;

[0027] Figure 2 Here is a SEM image of the die-cast magnesium alloy obtained in Example 1 of this disclosure;

[0028] Figure 3 SEM microstructure of the die-cast magnesium alloy obtained in Comparative Example 2 of this disclosure;

[0029] Figure 4 This is a SEM image of the die-cast magnesium alloy obtained in Comparative Example 3 of this disclosure. Detailed Implementation

[0030] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0031] The first aspect of this disclosure provides a die-cast magnesium alloy, wherein, based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-7% by weight Al (aluminum), 7-12% by weight La (lanthanum), 0.2-0.4% by weight Mn (manganese), less than 0.3% by weight of impurities, and the balance Mg (magnesium); wherein the ratio of Al to La content is 0.50-0.75.

[0032] This disclosure provides a die-cast magnesium alloy in which the contents of Al and La are precisely controlled to form an alloy with an appropriate Al content. 11 The La3 eutectic phase ensures the strength, heat resistance, and formability of the magnesium alloy; the die-cast magnesium alloy provided in this disclosure possesses comprehensive properties of high strength and high heat resistance. The die-cast aluminum alloy provided in this disclosure can be applied to components with high strength and high heat resistance requirements, meeting the performance requirements of high-performance, high-torque motor housing parts in current new energy vehicles. The inventors of this disclosure have also discovered that the Al to La content ratio in the magnesium alloy has a significant impact on the alloy's properties. When the Al to La content ratio is within the range provided in this embodiment, the magnesium alloy exhibits superior performance; however, when the La content exceeds this ratio, the Al element is insufficient to bind all the La elements, and the excess La elements will combine with Mg elements, forming a MgLa phase that increases the alloy's hot cracking tendency, which is detrimental to alloy forming; if the Al content exceeds this ratio, the La element is insufficient to bind all the Al elements, and the excess Al elements will combine with Mg elements to form low-melting-point Mg. 17 Al 12 This phase reduces the heat resistance of the alloy.

[0033] According to this disclosure, controlling the Al content in die-cast magnesium alloys to 5-7% by weight and the La content to 7-12% by weight can achieve the synergistic effect of the two elements and form an Al content that is suitable for the desired alloy composition. 11 The La3 eutectic phase avoids the problem that excessive hard eutectic phase significantly reduces the alloy's plasticity and formability, while insufficient hard eutectic phase cannot guarantee the alloy's strength and heat resistance.

[0034] According to this disclosure, adding a small amount of Mn element to die-cast magnesium alloy, with the Mn element content controlled in the range of 0.2~0.4% by weight, can reduce the harm of impurity elements such as Fe and Ni, improve the corrosion resistance of the alloy, and reduce the burn-off of the alloy during the smelting process.

[0035] In a preferred embodiment, based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-6% by weight Al, 8-11% by weight La, 0.3-0.4% by weight Mn, less than 0.2% by weight of impurities, and the balance Mg. The die-cast magnesium alloy with the component content provided in this embodiment can possess superior overall properties such as strength and heat resistance.

[0036] In a preferred embodiment, the Al to La content ratio in the die-cast magnesium alloy is 0.5 to 0.6. When the Al to La content ratio in the die-cast magnesium alloy is within the preferred range provided in this embodiment, the magnesium alloy can have higher yield strength and better heat resistance.

[0037] In a more preferred embodiment, the Al and La contents in the die-cast magnesium alloy satisfy the following: 80 ≤ 11Al + 3La ≤ 100, preferably 82 ≤ 11Al + 3La ≤ 95. When the Al and La contents in the die-cast magnesium alloy are within the range provided in this embodiment, especially within the preferred range, the magnesium alloy can have higher tensile strength.

[0038] In one specific embodiment, the die-cast magnesium alloy has a yield strength of 190-200 MPa, preferably 195-200 MPa; a tensile strength of 240-260 MPa, preferably 250-260 MPa; and a creep strain of 0.009-0.02%, preferably 0.009-0.015%, under creep conditions of 120℃, 100MPa, and 100h. The die-cast magnesium alloy provided in this disclosure possesses comprehensive properties of ultra-high strength and ultra-high heat resistance, and exhibits significantly lower creep strain, an order of magnitude lower than that of the traditional die-cast aluminum alloy ADC12 under the same test conditions (ADC12 is approximately 0.125%).

[0039] A second aspect of this disclosure provides a method for preparing die-cast magnesium alloys, comprising the following steps:

[0040] S1. Under a protective atmosphere, Mg raw material is subjected to a first melting treatment; then Al raw material, La raw material and Mn raw material are added for a second melting treatment to obtain a first alloy melt; based on the total weight of the first alloy melt, the first alloy melt includes 5-7% by weight of Al, 7-12% by weight of La, 0.2-0.4% by weight of Mn, less than 0.3% by weight of impurities and the balance of Mg, wherein the ratio of Al to La content is 0.50-0.75;

[0041] S2. The first alloy melt is refined and slag is removed to obtain the second alloy melt.

[0042] S3. The second alloy melt is die-cast.

[0043] The method for preparing die-cast magnesium alloys disclosed herein is simple, has high production efficiency, and the resulting magnesium alloys possess comprehensive properties such as ultra-high strength and ultra-high heat resistance.

[0044] In one embodiment, in step S1, the conditions for the first melting treatment include: a melting temperature of 680~720℃; the conditions for the second melting treatment include: a melting temperature of 740~760℃ and a melting time of 1~2h.

[0045] The protective atmosphere is selected from one or more of N2, CO2, and SF6 gases. According to the conditions provided in this embodiment, the alloy solution can be made homogeneous in composition, with minimal element loss and few oxide inclusions. In this disclosure, the apparatus for the first and second melting treatments can be a conventional magnesium alloy melting furnace.

[0046] In one specific embodiment, the Mg raw material includes pure magnesium, the Al raw material includes pure aluminum, the La raw material includes pure lanthanum, and the Mn raw material includes one or more of pure manganese, manganese-magnesium master alloy, or manganese-aluminum master alloy.

[0047] In one embodiment, in step S2, the refining conditions include: adding a refining agent at 720~740°C for refining, while stirring, and letting it stand for 10~15 minutes; wherein the refining agent is a type conventionally selected in the art and can be obtained through ordinary commercial channels;

[0048] The slag removal process includes using slag removal tools to remove floating slag.

[0049] In one embodiment, in step S3, the conditions for the die-casting process include:

[0050] The die-casting pressure is 50~100MPa, the vacuum degree is 50~100mbar, and the temperature of the second alloy melt is 700~730℃; preferably, the die-casting pressure is 80~100MPa and the vacuum degree is 50~70mbar. Magnesium alloys obtained by die-casting according to the die-casting conditions of this embodiment, especially the preferred die-casting conditions, have the effects of high density, good mechanical properties, and good surface quality.

[0051] This disclosure provides a third aspect of providing a die-cast magnesium alloy prepared according to the method described in the second aspect of this disclosure.

[0052] This disclosure provides a fourth aspect of an automotive structural component, comprising the die-cast magnesium alloy described in the first or third aspect of this disclosure.

[0053] Furthermore, the automotive structural components include parts formed by die casting that require high strength, high yield strength, and high heat resistance, including but not limited to electric drive components such as motor housings, motor end covers, and reducer housings.

[0054] The present disclosure is further described in detail below through examples. All raw materials used in the examples are commercially available.

[0055] SEM analysis of the die-cast alloy samples was performed using a PHENOM XL scanning electron microscope.

[0056] Example 1

[0057] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 6 wt%; La: 8.8 wt%; Mn: 0.3 wt%; total amount of other impurities ≤ 0.2 wt%, balance being Mg.

[0058] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy includes the following steps:

[0059] (1) Prepare materials according to the formula composition; among them, Mg, Al and La are prepared in the form of pure magnesium, pure aluminum and pure lanthanum, and Mn is prepared in the form of Al-10Mn master alloy (i.e. Mn content is 10% by weight);

[0060] (2) First, pure magnesium is placed in a melting furnace and CO2 + SF6 protective gas (of which the volume fraction of CO2 is 99% by volume) is introduced for the first melting treatment at a melting temperature of 700℃; then pure aluminum, pure lanthanum, and Al-10Mn master alloy are added and kept at 750℃ for 2 hours (second melting treatment). After melting, the molten metal is stirred evenly to obtain the first alloy melt.

[0061] (3) At 730°C, refining agent powder was added to the melt (first alloy melt) for refining treatment, and the melt was allowed to stand for 15 minutes and the slag was removed to obtain the second alloy melt.

[0062] (4) After the melt (second alloy melt) reaches 720°C, die casting is carried out to obtain die casting parts, wherein the die casting pressure is 90MPa and the vacuum degree is 60mbar.

[0063] The SEM microstructure of the die-cast magnesium alloy part prepared in this embodiment is shown in the image below. Figure 2 As shown in the figure, the alloy microstructure obtained in this embodiment is basically all Al. 11 The La3 eutectic phase contains only a small amount of α-Mg.

[0064] Example 2

[0065] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 5.5 wt%; La: 11 wt%; Mn: 0.35 wt%; total amount of other impurities ≤ 0.2 wt%, balance being Mg.

[0066] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy includes the following steps:

[0067] (1) Prepare materials according to the formula composition; among them, Mg, Al and La are prepared in the form of pure magnesium, pure aluminum and pure lanthanum, and Mn is prepared in the form of Mg-5Mn master alloy (i.e. Mn content is 5% by weight);

[0068] (2) First, pure magnesium is placed in a melting furnace and N2+SF6 protective gas (where the volume fraction of N2 is 99% by volume) is introduced for the first melting at a melting temperature of 710℃; then pure aluminum, pure lanthanum, and Mg-5Mn master alloy are added and the mixture is kept at 745℃ for 1 hour (second melting treatment). After melting, the molten metal is stirred evenly to obtain the first alloy melt.

[0069] (3) At 725°C, refining agent powder was added to the melt (first alloy melt) for refining treatment, and the melt was allowed to stand for 10 minutes. The slag was removed to obtain the second alloy melt.

[0070] (4) After the melt (second alloy melt) reaches 710°C, die casting is carried out to obtain die casting parts, wherein the die casting pressure is 70MPa and the vacuum degree is 70mbar.

[0071] Example 3

[0072] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy, with the following weight percentages for each component:

[0073] Al: 5 wt%; La: 9.2 wt%; Mn: 0.38 wt%; other impurities total ≤0.2 wt%, balance Mg.

[0074] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy includes the following steps:

[0075] (1) Prepare materials according to the formula composition; among them, Mg, Al and La are prepared in the form of pure magnesium, pure aluminum and pure lanthanum, and Mn is prepared in the form of pure manganese master alloy.

[0076] (2) First, pure magnesium is placed in a melting furnace and CO2 protective gas is introduced for the first melting. The melting temperature is 690℃. Then, pure aluminum, pure lanthanum and pure manganese are added and kept at 760℃ for 1.5h. After melting, the metal liquid is stirred evenly to obtain the first alloy melt.

[0077] (3) At 735°C, refining agent powder was added to the melt (first alloy melt) for refining treatment, and the melt was allowed to stand for 12 minutes and the slag was removed to obtain the second alloy melt.

[0078] (4) After the melt (second alloy melt) reaches 730°C, die casting is carried out to obtain die casting parts, wherein the die casting pressure is 50MPa and the vacuum degree is 50mbar.

[0079] Example 4

[0080] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 7 wt%; La: 10 wt%; Mn: 0.24 wt%; total amount of other impurities ≤ 0.3 wt%, balance being Mg.

[0081] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy is the same as that in Example 1.

[0082] Example 5

[0083] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 5.2 wt%; La: 7 wt%; Mn: 0.4 wt%; total amount of other impurities ≤ 0.3 wt%, balance being Mg.

[0084] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy is the same as that in Example 1.

[0085] Example 6

[0086] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 6.8 wt%; La: 11.1 wt%; Mn: 0.2 wt%; total amount of other impurities ≤0.3 wt%, balance being Mg.

[0087] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy is the same as that in Example 1.

[0088] Example 7

[0089] This embodiment provides an ultra-high strength heat-resistant die-cast magnesium alloy with the following weight percentages: Al: 6.5 wt%; La: 12 wt%; Mn: 0.28 wt%; total amount of other impurities ≤ 0.3 wt%, balance being Mg.

[0090] The preparation method of this ultra-high strength heat-resistant die-cast magnesium alloy is the same as that in Example 1.

[0091] Comparative Example 1

[0092] This comparative example provides a conventional ADC12 die-cast aluminum alloy with the following weight percentages of components: Si: 10.8 wt%; Fe: 0.9 wt%; Cu: 1.6 wt%; Mn: 0.21 wt%; Mg: 0.13 wt%; Zn: 0.65 wt%; Ni: 0.24 wt%; and other impurities totaling ≤0.3 wt%, with the balance being Al.

[0093] In this comparative example, the ADC12 die-casting aluminum alloy was directly melted using commercially available ADC12 die-casting aluminum alloy ingots, and then refined and slag-removed. After the melt reached 660 °C, it was die-cast to obtain die-cast parts.

[0094] Comparative Example 2

[0095] This comparative example provides a die-cast magnesium alloy with the following component weight percentages: Al: 4.9 wt%; La: 8.8 wt%; Mn: 0.3 wt%; total other impurities ≤ 0.2 wt%, balance being Mg.

[0096] The preparation and die-casting process of the die-cast magnesium alloy provided in this comparative example are the same as those in Example 1.

[0097] The SEM microstructure of the die-cast magnesium alloy part prepared in this comparative example is shown below. Figure 3 As shown, from Figure 3 As can be seen from this, the microstructure of the alloy obtained in this comparative example consists of α-Mg and Al 11 The alloy consists of a La3 eutectic phase, and the α-Mg content is significantly higher than that in Example 1. This indicates that the die-cast magnesium alloy in Example 1, with the alloy composition of this disclosure, has a higher Al content. 11 La3 eutectic phase.

[0098] Comparative Example 3

[0099] This comparative example provides a die-cast magnesium alloy with the following component weight percentages: Al: 5.4 wt%; La: 11 wt%; Mn: 0.35 wt%; total other impurities ≤ 0.2 wt%, balance being Mg.

[0100] The preparation and die-casting process of the die-cast magnesium alloy provided in this comparative example are the same as those in Example 2.

[0101] The SEM microstructure of the die-cast magnesium alloy part prepared in this comparative example is shown below. Figure 4 As shown, from Figure 4 As can be seen from this, the alloy microstructure obtained in this comparative example, except for α-Mg and Al 11 In addition to the La3 eutectic phase, a MgLa second phase was also formed.

[0102] Comparative Example 4

[0103] This comparative example provides a die-cast magnesium alloy with the following component weight percentages: Al: 7.6 wt%; La: 10 wt%; Mn: 0.24 wt%; total other impurities ≤ 0.3 wt%, balance being Mg.

[0104] The preparation and die-casting process of the die-cast magnesium alloy provided in this comparative example are the same as those in Example 1.

[0105] The compositions of the die-cast magnesium alloys obtained in the above embodiments and comparative examples are listed in Table 1 below.

[0106] Table 1

[0107]

[0108] Test case

[0109] The die-cast alloy products prepared in the above examples and comparative examples were subjected to room temperature tensile mechanical property tests and creep performance tests. The creep test conditions were: creep temperature 120℃, creep stress 100 MPa, and creep time 100 h. The creep performance of the alloy was evaluated by creep strain. Under the same conditions, the smaller the creep strain, the better the creep performance. The alloy performance test results are listed in Table 2 below.

[0110] The room temperature tensile mechanical properties test refers to GB / T 228.1-2021 standard; the creep properties test refers to GB / T2039-2012 standard.

[0111] Table 2

[0112]

[0113] The data in Table 2 shows that:

[0114] Comparative Example 1 provides an ADC12 aluminum alloy. Compared with the aluminum alloy of Comparative Example 1, the die-cast magnesium alloys provided in Examples 1-7 have higher yield strength and elongation, and the creep strain of the die-cast magnesium alloys in Examples 1-7 is significantly lower than that of the aluminum alloy of Comparative Example 1.

[0115] In Comparative Example 2, the Al element is too low and is not within the composition range of the die-cast magnesium alloy provided in this disclosure. The tensile and creep properties of the die-cast magnesium alloy obtained in Comparative Example 2 are low. The strength and creep properties of the die-cast magnesium alloys with the alloy composition provided in this disclosure in Examples 1 to 7 are significantly improved.

[0116] In Comparative Example 3, the Al / La content ratio is outside the range provided in this disclosure, resulting in the formation of a MgLa phase with a high tendency for hot cracking in its alloy microstructure. This leads to poor alloy formability and a significant reduction in various properties. This demonstrates that the die-cast magnesium alloys with the alloy composition provided in this disclosure in Examples 1-7 exhibit significantly improved strength and creep properties.

[0117] The addition of excessive Al in Comparative Example 4 is outside the composition range of the die-cast magnesium alloys disclosed in this publication, and its Al / La content ratio is also outside the range of this publication. As a result, low-melting-point Mg was generated in the alloy microstructure of the magnesium alloy obtained in Comparative Example 4. 17 Al 12 The creep properties of the alloy are significantly reduced. This indicates that the die-cast magnesium alloys with the alloy composition provided in this disclosure in Examples 1-7 have better strength and creep properties.

[0118] Comparing Examples 1, 4-6 with Examples 2-3, 7, the Al / La content ratio in the die-cast magnesium alloys obtained in Examples 2-3 and 7 is within the preferred range provided in this disclosure. The die-cast magnesium alloys obtained in Examples 2-3 and 7 have higher yield strength, lower creep strain, and better creep performance.

[0119] Comparing Examples 1-3 with Examples 4-7, it can be seen that the component content and the value of 11Al+3La in the die-cast magnesium alloys in Examples 1-3 are within the preferred range provided in this disclosure, and the die-cast magnesium alloys obtained in Examples 1-3 have higher tensile strength.

[0120] Comparing Examples 2-3 with Examples 1 and 4-7, it can be seen that the component content, Al / La content ratio, and 11Al+3La value of the die-cast magnesium alloy in Examples 2-3 are all within the preferred range provided in this disclosure. The die-cast magnesium alloy in Examples 2-3 has higher yield strength and tensile strength, and lower creep strain.

[0121] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0122] 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, this disclosure will not describe the various possible combinations separately.

[0123] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A die-cast magnesium alloy, characterized in that, Based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-7% by weight Al, 7-12% by weight La, 0.2-0.4% by weight Mn, less than 0.3% by weight impurities and the balance Mg; wherein the ratio of Al to La content is 0.50-0.75, and the Al to La content satisfies: 80≤11Al+3La≤100.

2. The die-cast magnesium alloy according to claim 1, characterized in that, Based on the total weight of the die-cast magnesium alloy, the die-cast magnesium alloy comprises: 5-6% by weight Al, 8-11% by weight La, 0.3-0.4% by weight Mn, less than 0.2% by weight of impurities and the balance Mg.

3. The die-cast magnesium alloy according to claim 1, characterized in that, The die-cast magnesium alloy has a yield strength of 190~200 MPa and a tensile strength of 240~260 MPa; the die-cast magnesium alloy exhibits a creep strain of 0.009~0.02% under creep conditions of 120℃, 100MPa, and 100h.

4. A method for preparing die-cast magnesium alloy, characterized in that, Includes the following steps: S1. Under a protective atmosphere, Mg raw material is subjected to a first melting treatment; then Al raw material, La raw material and Mn raw material are added for a second melting treatment to obtain a first alloy melt; based on the total weight of the first alloy melt, the first alloy melt includes 5-7% by weight of Al, 7-12% by weight of La, 0.2-0.4% by weight of Mn, less than 0.3% by weight of impurities and the balance of Mg, wherein the ratio of Al to La content is 0.50-0.75, and the Al to La content satisfies: 80≤11Al+3La≤100; S2. The first alloy melt is refined and slag is removed to obtain the second alloy melt. S3. The second alloy melt is die-cast.

5. The method according to claim 4, characterized in that, In step S1, the conditions for the first melting treatment include: a melting temperature of 680~720℃; the conditions for the second melting treatment include: a melting temperature of 740~760℃ and a melting time of 1~2h. The protective atmosphere is selected from one or more of N2, CO2 and SF6 gases.

6. The method according to claim 5, characterized in that, The Mg raw material includes pure magnesium, the Al raw material includes pure aluminum, the La raw material includes pure lanthanum, and the Mn raw material includes one or more of pure manganese, manganese-magnesium master alloy, or manganese-aluminum master alloy.

7. The method according to claim 4, characterized in that, In step S2, the refining conditions include: adding a refining agent at 720~740℃ for refining, while stirring, and letting it stand for 10~15 minutes. The slag removal process includes using slag removal tools to remove floating slag.

8. The method according to claim 4, characterized in that, In step S3, the conditions for the die-casting process include: The die-casting pressure is 50~100MPa, the vacuum degree is 50~100mbar, and the temperature of the second alloy melt is 700~730℃.

9. The die-cast magnesium alloy prepared by the method according to any one of claims 4 to 8.

10. An automotive structural component, characterized in that, Includes the die-cast magnesium alloy as described in any one of claims 1 to 3 and 9.

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