A die-cast magnesium alloy, a preparation method thereof, and an automobile structural part

Abstract

The present disclosure relates to a die-cast magnesium alloy, a preparation method thereof, and an automotive structural component. The die-cast magnesium alloy comprises 4.2-7.0 wt% Al, 0.15-0.5 wt% Mn, 0.20-2.50 wt% RE, 0.01-1.5 wt% Y, 0.03-0.80 wt% Ca, less than 0.01 wt% Fe+Ni+Cu, less than 0.20 wt% Zn, less than 0.05 wt% impurities, and the remainder Mg; wherein RE+Y≥0.5 wt%, and RE comprises one or both of La and Ce. The die-cast magnesium alloy disclosed herein has a relatively low rare earth addition content, and while ensuring good mechanical and casting properties of the alloy, the die-cast parts have excellent bending properties without heat treatment, making them more suitable for vehicle body structural components subjected to collision and compression conditions.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles, automakers are placing increasing emphasis on range and lightweighting requirements. Magnesium alloys are the lightest metal structural materials used in engineering applications. my country, with its abundant magnesium resources, can achieve complete material independence. With the continued decline in magnesium alloy prices in recent years, their use has become cost-effective, making their application in automobiles a current research hotspot.

[0003] Due to its unique close-packed hexagonal structure, magnesium alloys exhibit minimal slip systems and are difficult to deform at room temperature. Casting is the simplest and most feasible forming method. Traditional die-cast magnesium alloy applications in automobiles are primarily limited to interior parts with moderate alloy performance requirements, such as dashboard brackets and seat frames, or electrical housings with high thermal conductivity requirements. Currently, magnesium alloys have not found real application in vehicle body structural parts. However, with the increasing demand for lightweight vehicles, the demand for magnesium alloys in vehicle body structures, and even in large, one-piece die-cast parts, is becoming increasingly urgent.

[0004] Die-cast magnesium alloys used in vehicle body components, especially large, one-piece die-cast components, must not only offer low cost, excellent casting properties (such as fluidity and thermal cracking susceptibility), and good overall mechanical properties, but also possess excellent bending resistance to withstand the compressive bending deformation of structural components during collisions, ensuring optimal impact energy absorption. Traditional magnesium alloys such as the AZ, AM, and AS series fail to meet these requirements due to poor elongation, strength, or castability. Alloying with the addition of rare earth elements has become the mainstream solution. Related magnesium alloy technologies include: a high-plasticity Mg-Al-RE-Mn-Ca die-cast rare earth magnesium alloy and its preparation method, which achieves an alloy tensile strength of 240~270MPa, a yield strength of 160~180MPa, and an elongation of 9~12%. However, excessive addition of rare earth elements in the alloy (≥6 weight %) not only increases the alloy cost, but also makes the alloy difficult to smelt. At the same time, the excessive rare earth elements lead to severe alloy segregation and poor consistency in part performance, making it unsuitable for the production of large parts; a Mg-Al-RE alloy with a tensile strength of approximately 230MPa, a yield strength of 161MPa, and an elongation of 5.8%, which does not meet the connection performance requirements of vehicle body structural parts; a high-strength and toughness die-cast magnesium alloy and its preparation method, which has excellent mechanical properties after artificial heat treatment (T6), but artificial heat treatment is bound to increase the deformation of the parts and cannot be used for large-size die-cast parts. At the same time, the Al content in the alloy is low, which cannot meet the die-casting molding requirements of large-size parts. In particular, none of the existing patents mention the alloy's anti-bending performance, and subjectively equate the alloy's tensile elongation with the alloy's toughness. In fact, the stress states of the two are inconsistent. The anti-bending performance can better reflect the actual collision conditions of the parts, but it has not attracted attention. Summary of the Invention

[0005] The purpose of the present disclosure is to provide a die-cast magnesium alloy and its preparation method and automotive structural parts, which can have a relatively low rare earth addition, and the die-cast parts have excellent bending performance without heat treatment, and are better suitable for body structural parts under collision and compression conditions.

[0006] In order to solve the above technical problems, the first aspect of the present disclosure provides a die-cast magnesium alloy, which includes 4.2-7.0 wt% Al, 0.15-0.5 wt% Mn, 0.20-2.50 wt% RE, 0.01-1.5 wt% Y, 0.03-0.80 wt% Ca, less than 0.01 wt% Fe+Ni+Cu, less than 0.20 wt% Zn, less than 0.05 wt% impurities and the balance Mg; wherein RE+Y≥0.5 wt%, and RE includes one or both of La and Ce.

[0007] Through the above technical solution, the present disclosure provides a die-cast magnesium alloy. While strictly controlling the contents of Fe, Cu, Ni, Zn, etc., the die-cast magnesium alloy of the present disclosure, on the one hand, refines the size of α-Mg by introducing the element Ca; on the other hand, introduces low contents of rare earth elements RE and Y, thereby reducing the alloy use cost, avoiding segregation, and ensuring excellent casting performance, while making good use of the synergistic optimization effect of the two elements, ultimately obtaining a relatively ideal microstructure and achieving excellent comprehensive performance; the die-cast magnesium alloy provided by the present disclosure has excellent casting performance. After being cast in an S-shaped flow mold with a length exceeding 3.5m, not only are the parts fully filled and have excellent surface quality, but the alloy also has excellent alloy bending performance: it perfectly matches the extrusion conditions of structural parts under collision stress, better meets actual needs, ensures collision safety performance, and is particularly suitable for use in medium and large vehicle body structural parts.

[0008] In some embodiments, the die-cast magnesium alloy includes 4.5-6.5 wt% Al, 0.15-0.50 wt% Mn, 0.2-1.8 wt% RE, 0.01-1.2 wt% Y, 0.03-0.50 wt% Ca, less than 0.01 wt% Fe+Ni+Cu, less than 0.20 wt% Zn, less than 0.05 wt% impurities, and the balance Mg. This embodiment provides a die-cast magnesium alloy that, while strictly controlling the contents of Fe, Cu, Ni, and Zn, on the one hand, refines the size of α-Mg by introducing the element Ca; on the other hand, introduces low contents of the rare earth elements RE and Y. This reduces the alloy's cost, avoids segregation, and ensures excellent casting properties (fluidity, hot cracking sensitivity, etc.), while also making good use of the synergistic optimization effect of the two elements, ultimately achieving a relatively ideal microstructure and excellent overall performance.

[0009] In some preferred embodiments, in the die-cast magnesium alloy, 0.5 wt % ≤ RE + Y ≤ 2.0 wt %, which can further improve the performance of the die-cast magnesium alloy.

[0010] In some embodiments, in the die-cast magnesium alloy, 1 ≤ RE / Y ≤ 13, preferably 1 ≤ RE / Y ≤ 12. When the RE / Y content ratio in the die-cast magnesium alloy is within the range of this embodiment, especially within the preferred range, a better synergistic effect can be achieved in the die-cast magnesium alloy.

[0011] In some embodiments, the microstructure of the die-cast magnesium alloy includes an α-Mg matrix and Mg distributed in the α-Mg matrix. 17 Al 12 phase, long rod-shaped Al 11RE3 phase, fine dot-like Al3RE phase, and Al2Y phase; the α-Mg matrix is ​​spherical; in some preferred embodiments, the average grain size of the α-Mg matrix is ​​12 μm or less. The α-Mg matrix in the die-cast magnesium alloy provided by the present disclosure has a small and uniformly distributed grain size, which is more conducive to improving the bending performance of the magnesium alloy.

[0012] In some embodiments, the 2 mm equivalent bending angle of the die-cast magnesium alloy is greater than 50°, and the alloy has excellent bending performance.

[0013] A second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy, comprising the following steps:

[0014] S1. Smelting a magnesium alloy raw material to obtain a magnesium alloy melt; wherein the alloy raw material comprises: 4.2-7.0 wt % Al, 0.15-0.5 wt % Mn, 0.20-2.50 wt % RE, 0.01-1.5 wt % Y, 0.03-0.80 wt % Ca, 0.01 wt % or less of Fe+Ni+Cu, 0.20 wt % or less of Zn, 0.05 wt % or less of impurities, and the balance Mg; wherein RE+Y is ≥ 0.5 wt %, and RE comprises one or both of La and Ce;

[0015] S2, adding a refining agent to the magnesium alloy melt for refining treatment; adding a covering agent and then standing for cooling treatment to obtain an ingot material;

[0016] S3, placing the ingot material in a die-casting melting furnace for melting treatment and die-casting molding treatment.

[0017] Through the above technical solution, the present disclosure provides a method for preparing a die-cast magnesium alloy with a simple process. Under the premise of ensuring good casting properties (fluidity, resistance to thermal cracking sensitivity, etc.), it can have excellent bending performance without heat treatment, and is suitable for die-casting molding of large-size die-cast parts and the preparation of die-cast magnesium alloys with high bending performance.

[0018] In some embodiments, in step S2, the refining agent includes a first component and a second component; the first component includes one or more of magnesium chloride, potassium chloride, and sodium chloride; and the second component includes one or more of calcium chloride, calcium fluoride, and barium chloride. The refining agent composition provided in this embodiment is suitable for magnesium alloy refining.

[0019] In some embodiments, the covering agent includes one or more of magnesium chloride and potassium chloride; optionally, the covering agent covers the surface of the magnesium alloy melt to prevent the magnesium alloy liquid from burning during smelting and has a flame retardant effect.

[0020] In some embodiments, in step S2, the refining treatment includes stirring at a temperature of 740-760°C for 10-30 minutes, and adding the refining agent during the stirring process can have an excellent refining effect.

[0021] In some embodiments, the static cooling treatment includes: standing for 30 to 50 minutes to reduce the temperature of the magnesium alloy melt to 670 to 720° C., which is beneficial to improving the performance of the magnesium alloy.

[0022] In some embodiments, in step S3, the temperature of the melting treatment is 690-720° C., which is beneficial to improving the performance of the magnesium alloy.

[0023] In some embodiments, the die-casting processing conditions include: a die-casting speed of 3.0-7.5 m / s, a holding time of 3-15 s, and a mold temperature of 200-280° C., which is beneficial to improving the die-casting effect of the magnesium alloy.

[0024] A third aspect of the present disclosure provides a die-cast magnesium alloy prepared by the method described in the second aspect of the present disclosure.

[0025] A fourth aspect of the present disclosure provides an automotive structural part, comprising the die-cast magnesium alloy described in the first or third aspect of the present disclosure. The die-cast magnesium alloy provided by the present disclosure exhibits excellent casting properties. After casting through an S-shaped flow die exceeding 3.5 m in length, the part not only has complete mold filling and excellent surface quality, but also exhibits excellent bending properties, effectively matching the extrusion conditions of the structural part during collision stress, better meeting actual needs, and ensuring collision safety performance. The alloy is particularly suitable for use in medium- to large-sized vehicle body structural parts.

[0026] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0028] Figure 1 Schematic diagram of the S-mode used in the test examples disclosed herein to verify the flow properties of the alloy;

[0029] Figure 2a This is a SEM photograph of the die-cast magnesium alloy obtained in Example 3;

[0030] Figure 2b This is the SEM photograph of the die-cast magnesium alloy obtained in Comparative Example 7.

[0031] Reference numerals

[0032] a-Sampling location. DETAILED DESCRIPTION

[0033] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0034] This disclosure is based on the actual working conditions of magnesium alloy die-cast structural parts subjected to compression and bending deformation during collisions. While ensuring the alloy's certain mechanical and casting properties, it aims to maximize the bending resistance of the magnesium alloy, further enhancing vehicle body collision safety. The inventors of this disclosure, while analyzing the bending deformation mechanism of magnesium alloys, found that the bending deformation of magnesium alloys is strongly affected by the morphology and distribution of the secondary phase within them. During bending deformation, crack sources often originate from the coarse cast secondary phases and needle-shaped / rod-shaped secondary phases within the alloy, as stress concentration is easily generated at their tips. Furthermore, the morphology (uniformity and size) of α-Mg grains plays a significant role in the propagation of microcracks: the more uniform and smaller the α-Mg grains in the alloy, and the less secondary phases, especially needle-shaped / rod-shaped ones, are distributed, the better the alloy's bending performance.

[0035] Based on this discovery, the present invention improves the bending performance of the alloy in the existing AM alloy system mainly through the following aspects: first, strictly control the content of impurity elements containing Fe, Cu, Zn, and Ni, and strictly control the content of Al in the alloy while ensuring the casting performance of the alloy, to avoid the formation of a second phase with needle-like characteristics and to avoid the formation of excessive coarse Mg 17 Al 12 Casting the second phase reduces the number of crack sources; secondly, introducing trace Ca to refine the α-Mg grain size and control the average α-Mg grain size to be smaller (within 12μm); thirdly, the present disclosure introduces effective elements RE (one or both of La and Ce) and Y to synergistically optimize the performance: Element RE has extremely low solid solubility in the Mg matrix, and it mainly forms the second phase by combining with Al, making the alloy coarse and continuous eutectic Mg 17 Al 12 The phase transformation is small, independent island distribution, but its own improvement on the alloy strength is limited. Instead, it forms many long rod-shaped Al 11 RE3 phase deteriorates the bending performance (such as Figure 2b By adding the element Y with a high solid solubility to the Mg alloy, the solid solution strengthening can not only improve the strength of the alloy, but also form a high melting point and fine Al2Y phase with Al in the early solidification stage, which can also serve as a heterogeneous nucleation point to further refine the matrix and Al 11 RE3 phase (such as Figure 2a As shown in Figure 2), it can effectively improve the bending performance of magnesium alloy while taking into account the mechanical properties.

[0036] A first aspect of the present disclosure provides a die-cast magnesium alloy, comprising 4.2-7.0 wt % of Al, 0.15-0.5 wt % of Mn, 0.20-2.50 wt % of RE, 0.01-1.5 wt % of Y, 0.03-0.80 wt % of Ca, 0.01 wt % or less of Fe+Ni+Cu, 0.20 wt % or less of Zn, 0.05 wt % or less of impurities, and the balance Mg; wherein RE+Y≥0.5 wt %, and RE comprises one or both of La and Ce. This embodiment provides a die-cast magnesium alloy. While strictly controlling the contents of Fe, Cu, Ni, Zn, etc., on the one hand, by introducing the element Ca, the size of α-Mg is refined; on the other hand, low contents of rare earth elements RE and Y are introduced. While reducing the cost of alloy use, avoiding segregation and ensuring excellent casting properties (fluidity, thermal cracking sensitivity, etc.), the synergistic optimization effect of the two elements is well utilized, and ultimately a relatively ideal microstructure is obtained to achieve excellent comprehensive performance. The die-cast magnesium alloy provided by the present disclosure has excellent casting performance. After S-shaped flow mold casting with a length of more than 3.5m, not only are the parts fully filled and have excellent surface quality, but the alloy also has excellent alloy bending performance: it perfectly matches the extrusion conditions of structural parts under collision stress, better meets actual needs, ensures collision safety performance, and is particularly suitable for use in medium and large vehicle body structural parts.

[0037] In a preferred embodiment, the die-cast magnesium alloy includes 4.5-6.5 weight % of Al, 0.15-0.50 weight % of Mn, 0.2-1.8 weight % of RE, 0.01-1.2 weight % of Y, 0.03-0.50 weight % of Ca, less than 0.01 weight % of Fe+Ni+Cu, less than 0.20 weight % of Zn, less than 0.05 weight % of impurities and the remainder of Mg; when the component contents in the die-cast magnesium alloy are within the range of this embodiment, the die-cast magnesium alloy can have better bending performance and maintain good mechanical properties.

[0038] In a preferred embodiment, in the die-cast magnesium alloy, 0.5 wt % ≤ RE + Y ≤ 2.0 wt %. When the total content of RE + Y in the die-cast magnesium alloy is within the range of this embodiment, the performance of the material can be further improved.

[0039] In a preferred embodiment, in the die-cast magnesium alloy, 1 ≤ RE / Y ≤ 13, preferably 1 ≤ RE / Y ≤ 12, and more preferably 2 ≤ RE / Y ≤ 9. When the RE / Y content ratio in the die-cast magnesium alloy is within the range of this embodiment, especially within the preferred range, a better synergistic effect can be achieved in the die-cast magnesium alloy.

[0040] In a preferred embodiment, the microstructure of the die-cast magnesium alloy includes an α-Mg matrix and Mg distributed in the α-Mg matrix. 17 Al 12 phase, long rod-shaped Al 11 RE3 phase, small dot-shaped Al3RE phase and Al2Y phase; through the combination of the disclosed formula, a more reasonable organizational combination can be achieved, avoiding the long rod-shaped second phase and dominating, which is not conducive to improving the bending performance.

[0041] In a preferred embodiment, the α-Mg matrix is ​​spherical and has an average grain size of 12 μm or less. The α-Mg matrix in the die-cast magnesium alloy provided by the present disclosure has a small grain size and is evenly distributed, which is more conducive to improving the bending performance of the magnesium alloy.

[0042] In a specific embodiment, the 2 mm equivalent bending angle of the die-cast magnesium alloy is greater than 50°, and the alloy has excellent bending performance.

[0043] A second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy, comprising the following steps:

[0044] S1. Smelting a magnesium alloy raw material to obtain a magnesium alloy melt; wherein the alloy raw material comprises: 4.2-7.0 wt % Al, 0.15-0.5 wt % Mn, 0.20-2.50 wt % RE, 0.01-1.5 wt % Y, 0.03-0.80 wt % Ca, 0.01 wt % or less of Fe+Ni+Cu, 0.20 wt % or less of Zn, 0.05 wt % or less of impurities, and the balance Mg; wherein RE+Y is ≥ 0.5 wt %, and RE comprises one or both of La and Ce;

[0045] S2, adding a refining agent to the magnesium alloy melt for refining treatment; adding a covering agent and then standing for cooling treatment to obtain an ingot material;

[0046] S3, placing the ingot material in a die-casting melting furnace for melting treatment and die-casting molding treatment.

[0047] The present disclosure provides a method for preparing a die-cast magnesium alloy with a simple process. While ensuring good casting properties (fluidity, resistance to thermal cracking sensitivity, etc.), it can have excellent bending properties without heat treatment. The method is suitable for die-casting of large-sized die-cast parts and the preparation of die-cast magnesium alloys with high bending properties.

[0048] In a specific embodiment, in step S1, the magnesium alloy raw material is used in the form of pure Mg ingot, Mg-RE master alloy, Mg-Y master alloy, pure Al ingot, Mg-Mn master alloy, Mg-Ca master alloy or metallic Ca.

[0049] In a specific embodiment, step S1 includes: melting a pure Mg ingot at 730-760° C. under a protective atmosphere to obtain a pure magnesium melt; then adding a Mg-RE master alloy, a Mg-Y master alloy, a pure Al ingot, a Mg-Mn master alloy, a Mg-Ca master alloy or metallic Ca to the pure magnesium melt and melting the mixture to obtain the magnesium alloy melt; the protective atmosphere includes nitrogen or the like.

[0050] In a preferred embodiment, in step S2, the refining agent includes a first component and a second component; the first component includes one or more of magnesium chloride, potassium chloride and sodium chloride; the second component includes one or more of calcium chloride, calcium fluoride and barium chloride; the refining agent composition provided in this embodiment is suitable for magnesium alloy refining treatment and can be purchased through ordinary commercial channels or prepared by known methods.

[0051] In one embodiment, the covering agent includes one or more of magnesium chloride and potassium chloride, which can be purchased through ordinary commercial channels or prepared by known methods; optionally, the covering agent covers the surface of the magnesium alloy melt to prevent the magnesium alloy liquid from burning during smelting, and has a flame retardant effect.

[0052] In one embodiment, in step S2, the refining treatment includes: stirring at a temperature of 740-760° C. for 10-30 minutes, and adding the refining agent during the stirring process;

[0053] Optionally, the static cooling treatment includes: standing for 30 to 50 minutes to reduce the temperature of the magnesium alloy melt to 670 to 720°C.

[0054] In one embodiment, in step S3, the temperature of the melting treatment is 690-720°C;

[0055] The die-casting molding process includes: heating the die-casting mold to a required temperature and then keeping it warm under a protective atmosphere; and performing the die-casting molding process after the ingot material is melted. Optionally, the conditions of the die-casting molding process include: a die-casting speed of 3.0~7.5m / s, a holding time of 3~15s, and a mold temperature of 150~280℃.

[0056] A third aspect of the present disclosure provides a die-cast magnesium alloy prepared by the method described in the second aspect of the present disclosure.

[0057] A fourth aspect of the present disclosure provides an automotive structural component, comprising the die-cast magnesium alloy described in the first aspect or the third aspect of the present disclosure.

[0058] In a specific embodiment, the automobile structural parts include but are not limited to front and rear door left and right anti-collision bars (beams), front and rear bumpers, A-pillar reinforcement plates, B-pillar reinforcement plates, C-pillar reinforcement plates, center channels, roof reinforcement beams, integrated rear floors, integrated front cabins and other safety structural parts; they can also be used in the production of battery packs for new energy vehicles.

[0059] The present disclosure is further described in detail below through examples. The raw materials used in the examples can be obtained through commercial channels.

[0060] In the following examples and comparative examples, the die used in the die casting process is an S-shaped flow die (e.g. Figure 1 As shown), the thickness of the test piece is about 3mm; Figure 1 In the test, the mechanical properties of the alloy and the bending test pieces are sampled at the C1-D1 position, and the casting performance is judged by whether the flow mold can be completely formed and the surface quality of the part.

[0061] Example 1

[0062] (1) Preparation before smelting: According to the magnesium alloy component content listed in Table 1, pure Mg ingot, Mg-RE master alloy, Mg-Y master alloy, pure Al ingot, Mg-Mn master alloy, Mg-Ca or metallic Ca are used as raw materials for each element in the magnesium alloy. After properly considering the burnout, the corresponding raw materials are weighed according to the mass percentage of the components determined according to the above magnesium alloy component range. RE is one or both of La and Ce. All raw materials are dried.

[0063] (2) Alloy smelting: Put the metal magnesium ingot into the crucible and melt it at 745℃ under protective gas to form a pure magnesium melt; then add the required pure Al ingot, Mg-RE, Mg-Y, Mg-Mn and Mg-Ca (or metal Ca) master alloy in sequence to obtain a magnesium alloy melt;

[0064] (3) The magnesium alloy melt is stirred at a temperature of 750°C, and a special refining agent for magnesium alloy is added during the stirring process for refining; after refining, the flux and slag on the liquid surface are removed, and a layer of covering agent is lightly sprinkled; then it is allowed to stand, and the temperature of the magnesium alloy melt is lowered to 700°C for casting to obtain the ingot material.

[0065] The main components of magnesium alloy refining agents are magnesium chloride, potassium chloride, and sodium chloride, with the remainder being conventional reagents such as calcium chloride, calcium fluoride, and barium chloride. The content can be adjusted based on actual conditions. Covering agents are mixtures of magnesium chloride and chloride salts such as potassium chloride, and the dosage can be adjusted based on actual conditions.

[0066] (4) The obtained material ingot is placed into a die-casting melting furnace, and the furnace temperature is set to 700°C for melting. Protective gas is introduced into the furnace to protect the magnesium alloy melt. Simultaneously, the required die-casting mold is installed on the die-casting machine, and the mold oil temperature is raised to 240°C for insulation. After the material is melted, die-casting is performed to obtain a die-casting part in a non-heat-treated state.

[0067] Examples 2 to 9

[0068] Referring to the preparation method in Example 1, the difference from Example 1 is that the die-cast magnesium alloy is prepared according to the magnesium alloy composition in Table 1; the rest of the process is the same as that in Example 1.

[0069] Comparative Examples 1 to 8

[0070] Referring to the preparation method in Example 1, the difference from Example 1 is that the die-cast magnesium alloy is prepared according to the magnesium alloy composition in Table 1; the rest of the process is the same as that in Example 1.

[0071] Table 1

[0072]

[0073] In Table 1, the unit of each metal component data is "weight %"; the balance of the magnesium alloy in each embodiment and comparative example is Mg; a component content of "-" indicates that the component is not added.

[0074] Test Example 1

[0075] This test example is used to test the mechanical properties and bending properties of the die-cast magnesium alloys obtained in the above embodiments and comparative examples.

[0076] In this test case, the mechanical properties of the alloy and the bending test piece (refer to CN114487337A) are Figure 1 The sample is taken at the C1-D1 position on the "S"-shaped flow die shown in the figure. a represents the sample taken in the C1-D1 area. The bending specimen size is a 30×60mm long strip specimen. The test method refers to VDA238. The bending performance results are uniformly converted into a 2mm equivalent angle for evaluation. The conversion formula is shown in the following formula (1);

[0077] Formula (1);

[0078] In formula (1), α1 is the actual test bending angle of thickness , and α2 is the calculated angle of equivalent thickness (2 mm in this disclosure).

[0079] The casting performance of the alloy disclosed herein can be evaluated by the filling state and surface quality of the "S"-shaped flow die. The S-die forming and effect are marked "OK" if the cake thickness is stable, the S-die is completely filled, and there are no visible thermal cracks on the surface. Otherwise, it is marked "NOK".

[0080] The mechanical properties of the alloy material, including yield strength (YS), ultimate tensile strength (UTS), and elongation (EL), were tested in accordance with GB / T 228.1 standard, and the specimen size was based on the ASTM E8 small-size specimen.

[0081] The test results are listed in Table 2 below.

[0082] Table 2

[0083]

[0084] According to the data in Table 2, we can see that:

[0085] In Comparative Example 1, the Al content is lower than the range provided in the present disclosure. The magnesium alloy in Comparative Example 1 cannot be formed in the S-die forming test, the 2 mm equivalent bending angle is small, and the casting performance and bending performance are poor. On this basis, there is no need to further consider the mechanical properties of the magnesium alloy. In Comparative Example 3, the Al content is higher than the range provided in the present disclosure, the elongation is low, and the 2 mm equivalent bending angle is small, and the bending performance of the magnesium alloy is poor.

[0086] The magnesium alloy of Comparative Example 3 did not contain Ca, and the 2 mm equivalent bending angle of the magnesium alloy was small, resulting in poor bending performance. The magnesium alloy of Comparative Example 5 contained too much Ca, and the die-cast magnesium alloy obtained in Comparative Example 5 could not be formed in the S-mold forming test, resulting in poor casting performance.

[0087] The die-cast magnesium alloy of Comparative Example 4 has an excessively high RE content, and the weight ratio of RE / Y is also outside the optimized range provided by the present disclosure. The die-cast magnesium alloy obtained in Comparative Example 4 cannot be formed in an S-die forming test, and has poor casting performance.

[0088] The Zn content in the die-cast magnesium alloy of Comparative Example 6 is too high, the elongation of the die-cast magnesium alloy is low, and the 2mm equivalent bending angle is small, and the bending performance of the magnesium alloy is poor;

[0089] No Y was added to the die-cast magnesium alloy of Comparative Example 7, and no RE was added to the die-cast magnesium alloy of Comparative Example 8. The magnesium alloys obtained in Comparative Examples 7 and 8 had a small 2 mm equivalent bending angle and poor bending performance.

[0090] The die-cast magnesium alloys provided in Examples 1 to 6 of the present disclosure can have excellent S-die forming effects, and the 2mm equivalent bending angle is larger, and the magnesium alloy has better bending performance;

[0091] Comparing Examples 7 to 8 with Example 1, it can be seen that the RE and Y of the die-cast magnesium alloy in Example 1 are both within the preferred ranges provided in the present disclosure. The die-cast magnesium alloy in Example 1 can have an excellent S-die forming effect, and the 2mm equivalent bending angle is larger, and the magnesium alloy has better bending performance;

[0092] Comparing Example 1 with Example 9, it can be seen that the content of each component of the die-cast magnesium alloy in Example 1 is within the preferred range provided in the present disclosure. The die-cast magnesium alloy in Example 1 can have an excellent S-die forming effect, and the 2mm equivalent bending angle is larger, and the bending performance of the magnesium alloy is better.

[0093] Test Example 2

[0094] The die-cast magnesium alloys obtained in Example 3 and Comparative Example 7 were tested using a SEM electron microscope (Hitachi FlexSEM 1000PSU1000).

[0095] The SEM photograph of the die-cast magnesium alloy obtained in Example 3 is as follows: Figure 2a As shown by Figure 2a It can be seen that the size of each type of second phase in the die-cast magnesium alloy is small and dispersed; the average grain size of the α-Mg matrix is ​​about 10 μm; the SEM photo of the die-cast magnesium alloy obtained in Comparative Example 7 is as follows Figure 2b As shown by Figure 2b It can be seen that the die-cast magnesium alloy does not have Y added, lacks the coordination effect of Y and RE, and the second phase in the organization is coarse and the long rod-shaped second phase is obviously distributed. Figure 2a and Figure 2b By comparison, it can be seen that in Example 3, Y was added to the die-cast magnesium alloy, which played a coordinated role between Y and RE and could effectively refine the α-Mg matrix and Al 11 RE3 dimensions.

[0096] 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 of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0097] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0098] In addition, the 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, characterized in that: The die-cast magnesium alloy includes 4.5-6.5 weight percent of Al, 0.15-0.50 weight percent of Mn, 0.2-1.8 weight percent of RE, 0.01-1.2 weight percent of Y, 0.03-0.50 weight percent of Ca, less than 0.01 weight percent of Fe+Ni+Cu, less than 0.20 weight percent of Zn, less than 0.05 weight percent of impurities, and the balance Mg; wherein RE+Y is greater than or equal to 0.5 weight percent, and RE is one or both of La and Ce; the die-cast magnesium alloy includes an α-Mg matrix; the average grain size of the α-Mg matrix is ​​less than 12 μm; and the die-cast magnesium alloy has a 2 mm equivalent bending angle of greater than 50°.

2. The die-cast magnesium alloy according to claim 1, characterized in that In the die-cast magnesium alloy, 0.5 wt %≤RE+Y≤2.0 wt %.

3. The die-cast magnesium alloy according to claim 1, characterized in that In the die-cast magnesium alloy, 1≤RE / Y≤13.

4. The die-cast magnesium alloy according to claim 1, characterized in that The α-Mg matrix is ​​spherical.

5. A method for preparing the die-cast magnesium alloy as claimed in claim 1, characterized in that: The following steps are involved: S1. Smelting the magnesium alloy raw material to obtain a magnesium alloy melt; The alloy raw materials include: 4.5-6.5 wt% Al, 0.15-0.50 wt% Mn, 0.2-1.8 wt% RE, 0.01-1.2 wt% Y, 0.03-0.50 wt% Ca, less than 0.01 wt% Fe+Ni+Cu, less than 0.20 wt% Zn, less than 0.05 wt% impurities and the balance Mg; wherein RE+Y≥0.5 wt%, and RE is one or both of La and Ce; S2, adding a refining agent to the magnesium alloy melt for refining treatment; adding a covering agent and then standing for cooling treatment to obtain an ingot material; S3, placing the ingot material in a die-casting melting furnace for melting treatment and die-casting molding treatment.

6. The method according to claim 5, characterized in that In step S2, the refining agent includes a first component and a second component; the first component includes one or more of magnesium chloride, potassium chloride and sodium chloride; the second component includes one or more of calcium chloride, calcium fluoride and barium chloride; The covering agent includes one or more of magnesium chloride and potassium chloride.

7. The method according to claim 5, characterized in that In step S2, the refining treatment includes: stirring at a temperature of 740-760° C. for 10-30 minutes, and adding the refining agent during the stirring process; The static cooling treatment comprises: standing for 30 to 50 minutes to reduce the temperature of the magnesium alloy melt to 670 to 720° C.; In step S3, the temperature of the melting treatment is 690-720°C; The die-casting process conditions include: a die-casting speed of 3.0-7.5 m / s, a holding time of 3-15 s, and a mold temperature of 200-280° C.

8. An automobile structural part, characterized in that: The invention comprises the die-cast magnesium alloy according to any one of claims 1 to 4.

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