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

Abstract

The invention relates to a die-casting magnesium alloy, a preparation method thereof and an automobile structural part. The die-casting magnesium alloy comprises 4.2%-7.0% by weight of Al, 0.15%-0.5% by weight of Mn, 0.20%-2.50% by weight of RE, 0.01%-1.5% by weight of Y, 0.03%-0.80% by weight of Ca, 0.01% by weight or less of Fe + Ni + Cu, 0.20% by weight or less of Zn, 0.05% by weight or less of impurities and the balance Mg. Wherein RE + Y is greater than or equal to 0.5 wt%, and RE comprises one or two of La and Ce. The die-casting magnesium alloy disclosed by the invention has relatively low rare earth addition amount, and on the premise of ensuring good mechanical property and casting property of the alloy, a die-casting piece has excellent bending property under the condition of not performing heat treatment, and is better suitable for a vehicle body structural member under a collision compression working condition.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles, automobile companies pay more and more attention to the cruising range requirement, and the lightweight requirement is getting higher and higher. As the lightest metal structural material in engineering applications, and with rich magnesium resources in China, complete material independence can be achieved. In recent years, with the continuous decline in the price of magnesium alloys, using magnesium alloys already has a certain cost advantage, which promotes the research focus on the application of magnesium alloys in automobiles.

[0003] Due to its unique close-packed hexagonal structure, magnesium alloys have few slip systems and are difficult to process and deform at room temperature. Casting is the simplest and feasible forming method. The application of traditional die-cast magnesium alloys in automobiles is mainly limited to interior parts with general alloy performance requirements, such as instrument panel brackets, seat skeletons, etc., or electrical housings with requirements for thermal conductivity. For body structural components, there is currently no real application. With the increasing requirement for automobile lightweight, the demand for the use of magnesium alloys in automobile body structures and even integral large die-cast parts is becoming more and more urgent.

[0004] As a die-casting magnesium alloy for vehicle body structural parts, especially for large integral die-cast structural parts, in addition to having low cost, excellent casting properties (fluidity, hot cracking sensitivity, etc.) and good comprehensive mechanical properties, it also needs to have excellent anti-bending performance to match the working condition of compression and bending deformation during the collision of structural parts and achieve better impact energy absorption. Traditional magnesium alloys such as AZ, AM, AS series, etc., do not meet the requirements respectively due to poor alloy elongation, alloy strength or alloy castability. Alloying by adding rare earths has become the mainstream solution. Related magnesium alloy technologies include: a Mg-Al-RE-Mn-Ca die-casting rare earth magnesium alloy with high plasticity and its preparation method, achieving an alloy tensile strength of 240-270 MPa, a yield strength of 160-180 MPa, and an elongation of 9-12%. However, too much rare earth element is added in the alloy (≥6 wt%), which not only increases the alloy cost but also causes difficulties in alloy melting. At the same time, due to too much rare earth element, the alloy segregation is serious and the part performance consistency is poor, which is not suitable for the production of large parts; a Mg-Al-RE alloy, with a tensile strength of about 230 MPa, a yield strength of 161 MPa, and an elongation of 5.8%, does not meet the requirements of vehicle body structural parts for connection performance; a high-strength and tough die-casting magnesium alloy and its preparation method, the alloy has excellent mechanical properties after artificial heat treatment (T6), but artificial heat treatment will inevitably increase the deformation of parts and cannot be applied to large-size die-cast parts. At the same time, the Al content in the alloy is relatively low and cannot meet the die-casting forming of large-size parts. In particular, the existing patents do not mention the anti-bending performance of the alloy, subjectively equating the alloy tensile elongation with the alloy toughness. In fact, the stress states of the two are inconsistent, and the anti-bending performance can better reflect the actual collision condition of parts, but it has not attracted attention. Summary of the Invention

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

[0006] To solve the above technical problems, in the first aspect of the present disclosure, a die-casting magnesium alloy is provided. The die-casting magnesium alloy includes 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, Fe+Ni+Cu below 0.01 wt%, Zn below 0.20 wt%, impurities below 0.05 wt% and the balance of 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., on the one hand, by introducing Ca element, the size of α-Mg is refined; on the other hand, introducing low contents of rare earth elements RE and Y, while reducing the alloy usage cost, avoiding segregation and ensuring excellent casting performance, the synergistic optimization effect of the two elements is well utilized, and finally an ideal microstructure is obtained, achieving excellent comprehensive performance; the die-cast magnesium alloy provided by the present disclosure has excellent casting performance. After being cast by an S-shaped flow die with a length exceeding 3.5 m, not only the parts are completely filled and the surface quality is excellent, but also the alloy has excellent alloy bending performance: it perfectly matches the extrusion working condition when the structural part is subjected to collision force, better meets the actual requirements, ensures the collision safety performance, and is especially suitable for use in medium and large-sized body structure parts.

[0008] In some embodiments, the die-cast magnesium alloy comprises 4.5 - 6.5 wt% of Al, 0.15 - 0.50 wt% of Mn, 0.2 - 1.8 wt% of RE, 0.01 - 1.2 wt% of Y, 0.03 - 0.50 wt% of Ca, Fe + Ni + Cu below 0.01 wt%, Zn below 0.20 wt%, impurities below 0.05 wt% and the balance of Mg. 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 Ca element, the size of α-Mg is refined; on the other hand, introducing low contents of rare earth elements RE and Y, while reducing the alloy usage cost, avoiding segregation and ensuring excellent casting performance (fluidity, hot cracking sensitivity, etc.), the synergistic optimization effect of the two elements is well utilized, and finally an ideal microstructure is obtained, achieving excellent comprehensive 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 content ratio of RE / Y in the die-cast magnesium alloy is within the range of this embodiment, especially within the preferred range, a better synergistic application effect can be exerted in the die-cast magnesium alloy.

[0011] In some embodiments, in the microstructure of the die-cast magnesium alloy, it includes an α-Mg matrix and Mg 17 Al 12 phase, long rod-shaped Al 11The α-Mg matrix is globular, and there are RE3 phase, fine and dot-like Al3RE phase and Al2Y phase; 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 grain size and is evenly distributed, 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 50° or more, and it has excellent alloy bending performance.

[0013] The second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy, including the following steps: S1. Melting the magnesium alloy raw materials to obtain a magnesium alloy melt; wherein the alloy raw materials include: 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, less than 0.01 wt% of Fe+Ni+Cu, less than 0.20 wt% of Zn, less than 0.05 wt% of impurities and the balance of Mg; wherein RE+Y≥0.5 wt%, and RE includes 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 performing a static cooling treatment to obtain an ingot material; S3. Placing the ingot material in a die-casting melting furnace for melting treatment and die-casting forming treatment.

[0014] Through the above technical solutions, the present disclosure provides a method for preparing a die-cast magnesium alloy, which has a simple process; without heat treatment, it can have excellent bending performance on the premise of ensuring good casting properties (fluidity, hot cracking sensitivity, etc.), and is suitable for die-casting forming of large-size die-cast parts and the preparation of die-cast magnesium alloys with high bending performance.

[0015] 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; the second component includes one or more of calcium chloride, calcium fluoride and barium chloride. The composition of the refining agent provided by this embodiment is suitable for the refining treatment of magnesium alloys.

[0016] 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 melting, and has a flame retardant effect.

[0017] In some embodiments, in step S2, the refining treatment includes: stirring at a temperature of 740 - 760°C for 10 - 30 min, and adding the refining agent during the stirring process, which can achieve excellent refining effects.

[0018] In some embodiments, the static cooling treatment includes: standing for 30 - 50 min and reducing the temperature of the magnesium alloy melt to 670 - 720°C, which is beneficial to improving the properties of the magnesium alloy.

[0019] In some embodiments, in step S3, the temperature of the melting treatment is 690 - 720°C, which is beneficial to improving the properties of the magnesium alloy.

[0020] In some embodiments, the conditions of the die-casting forming treatment include: a die-casting speed of 3.0 - 7.5 m / s, a holding pressure time of 3 - 15 s, and a die temperature of 200 - 280°C, which is beneficial to improving the die-casting forming effect of the magnesium alloy.

[0021] The third aspect of the present disclosure provides a die-cast magnesium alloy prepared by the method according to the second aspect of the present disclosure.

[0022] The fourth aspect of the present disclosure provides an automotive structural part, including the die-cast magnesium alloy according to the first aspect or the third aspect of the present disclosure. The die-cast magnesium alloy provided by the present disclosure has excellent casting performance. After being cast by an S-shaped flow die with a length exceeding 3.5 m, not only the parts are completely filled but also the surface quality is excellent. At the same time, the alloy has excellent alloy bending performance: it perfectly matches the extrusion working condition of the structural part during collision, better meets the actual requirements, ensures the collision safety performance, and is particularly suitable for use in medium and large-sized body structure parts.

[0023] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific implementation, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings: Figure 1 Schematic diagram of the S die for verifying the alloy flow performance used in the test example of the present disclosure; Figure 2a SEM photograph of the die-cast magnesium alloy obtained in Example 3; Figure 2b SEM photograph of the die-cast magnesium alloy obtained in Comparative Example 7.

[0025] REFERENCE NUMERALS a - Sampling position. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will describe in detail the specific embodiments of the present disclosure with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present disclosure, and are not intended to limit the present disclosure.

[0027] Based on the actual working conditions of the magnesium alloy die-cast structural parts under collision, compression, and bending deformation, on the premise of ensuring certain mechanical properties and casting properties of the alloy, the bending resistance of the magnesium alloy is improved as much as possible to further enhance the vehicle body collision safety. When the inventors of the present disclosure analyzed the bending deformation mechanism of magnesium alloys, it was found that the bending deformation of magnesium alloys is strongly affected by the morphology and distribution of the second phase inside. When the alloy is bent, the crack source often occurs at the coarse cast second phase and the second phase in the needle / long rod shape in the alloy, because stress concentration is likely to occur at its tip; and the morphology of α-Mg grains (uniformity and size) plays an important role in the propagation of microcracks: when the α-Mg grains in the alloy are more uniform and smaller in size, and at the same time the distribution of the second phase, especially the needle / long rod-shaped second phase, in the alloy is less, the bending performance of the alloy is better.

[0028] Based on this discovery, on the existing AM series alloy system, the present disclosure mainly improves the bending performance of the alloy in the following aspects: First, strictly control the content of impurity elements such as Fe, Cu, Zn, and Ni, and strictly control the content of Al in the alloy on the premise of ensuring the casting performance of the alloy, to avoid forming a second phase with a needle-like feature and avoid forming too many coarse Mg 17 Al 12 cast second phases, reducing the number of crack sources; Second, introduce a small amount of Ca to refine the α-Mg grain size and control the average α-Mg grain size to be relatively small (within 12 μm); Third, the present disclosure introduces effective elements RE (one or both of La and Ce) and Y to synergistically optimize the performance: Since the solubility of element RE in the Mg matrix is extremely low, it mainly combines with Al to form a second phase, making the eutectic Mg 17 Al 12 phase in the alloy change from thick and continuous to small and independent island-like distribution, but its own improvement of the alloy strength is limited. Instead, because of the numerous long rod-shaped Al 11 RE3 phases formed with Al deteriorate the bending performance (as Figure 2b shown); and by adding element Y with a relatively high solubility in the Mg alloy, since solid solution strengthening can not only improve the strength of the alloy, but also the high melting point and fine Al2Y phase formed by it and Al at the initial stage of solidification can further refine the matrix and Al 11 RE3 phase (as Figure 2a shown), the bending performance of the magnesium alloy can be effectively improved while taking into account the mechanical properties.

[0029] A first aspect of the present disclosure provides a die-cast magnesium alloy, which includes 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, less than 0.01 wt % of Fe+Ni+Cu, less than 0.20 wt % of Zn, less than 0.05 wt % of impurities and the balance Mg; wherein RE+Y≥0.5 wt %, and RE includes one or both of La and Ce. The present 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 Ca element, the size of α-Mg is refined; on the other hand, by introducing low contents of rare earth elements RE and Y, while reducing the use cost of the alloy, avoiding segregation and ensuring excellent casting properties (fluidity, resistance to thermal cracking sensitivity, etc.), the synergistic optimization effect of the two elements is well utilized, and finally 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 the structural parts when subjected to collision stress, better meets actual needs, and ensures collision safety performance, and is particularly suitable for use in medium and large vehicle body structural parts.

[0030] In a preferred embodiment, the die-cast magnesium alloy includes 4.5~6.5 weight % Al, 0.15~0.50 weight % Mn, 0.2~1.8 weight % RE, 0.01~1.2 weight % Y, 0.03~0.50 weight % Ca, less than 0.01 weight % Fe+Ni+Cu, less than 0.20 weight % Zn, less than 0.05 weight % impurities and the remainder 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.

[0031] 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.

[0032] 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 content ratio of RE / Y in the die-cast magnesium alloy is within the range of this embodiment, especially within the preferred range, a better synergistic application effect can be exerted in the die-cast magnesium alloy.

[0033] In a preferred embodiment, the microstructure of the die-cast magnesium alloy includes an α-Mg matrix and Mg 17 Al 12 phases, long rod-shaped Al 11 RE3 phases, fine dot-shaped Al3RE phases and Al2Y phases; through the formula combination of the present disclosure, a more reasonable tissue combination can be achieved, avoiding the dominance of long rod-shaped second phases, which is not conducive to improving the bending performance.

[0034] In a preferred embodiment, the α-Mg matrix is spheroid-like, and the average grain size of the α-Mg matrix is below 12 μm. The grain size of the α-Mg matrix in the die-cast magnesium alloy provided by the present disclosure is small and evenly distributed, which is more conducive to improving the bending performance of the magnesium alloy.

[0035] In a specific embodiment, the equivalent bending angle of 2 mm of the die-cast magnesium alloy is above 50°, and it has excellent alloy bending performance.

[0036] The second aspect of the present disclosure provides a method for preparing a die-cast magnesium alloy, including the following steps: S1. Melting the magnesium alloy raw materials to obtain a magnesium alloy melt; wherein the alloy raw materials include: 4.2-7.0% by weight of Al, 0.15-0.5% by weight of Mn, 0.20-2.50% by weight of RE, 0.01-1.5% by weight of Y, 0.03-0.80% by weight of Ca, Fe+Ni+Cu below 0.01% by weight, Zn below 0.20% by weight, impurities below 0.05% by weight and the balance of Mg; wherein RE+Y≥0.5% by weight, and RE includes 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 performing a static cooling treatment to obtain an ingot material; S3. Placing the ingot material in a die-casting melting furnace for melting treatment and die-casting forming treatment.

[0037] The present disclosure provides a method for preparing a die-cast magnesium alloy, with a simple process; without heat treatment, it can have excellent bending performance on the premise of ensuring good casting performance (fluidity, hot cracking sensitivity, etc.), and is suitable for die-casting forming of large-size die-cast parts and the preparation of die-cast magnesium alloys with high bending performance.

[0038] In a specific embodiment, in step S1, the forms of use of the magnesium alloy raw materials include pure Mg ingots, Mg-RE master alloys, Mg-Y master alloys, pure Al ingots, Mg-Mn master alloys, Mg-Ca master alloys or metallic Ca.

[0039] In a specific embodiment, step S1 includes: melting pure Mg ingots at 730 - 760 °C under a protective atmosphere to obtain a pure magnesium melt; then adding Mg-RE master alloy, Mg-Y intermediate, pure Al ingots, Mg-Mn master alloy, Mg-Ca master alloy or metallic Ca to the pure magnesium melt and melting them to obtain the magnesium alloy melt; the protective atmosphere includes nitrogen, etc.

[0040] 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 composition of the refining agent provided in this embodiment is suitable for the refining treatment of magnesium alloys and can be obtained through ordinary commercial channels or prepared by known methods.

[0041] In one embodiment, the covering agent includes one or more of magnesium chloride and potassium chloride and can be obtained 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 melting and has a flame retardant effect.

[0042] In one embodiment, in step S2, the refining treatment includes: stirring at a temperature of 740 - 760 °C for 10 - 30 min, and adding the refining agent during the stirring process; Optionally, the static cooling treatment includes: standing for 30 - 50 min and reducing the temperature of the magnesium alloy melt to 670 - 720 °C.

[0043] In one embodiment, in step S3, the temperature of the melting treatment is 690 - 720 °C; The die-casting forming treatment includes: heating a die-casting mold to a required temperature and keeping it warm under a protective atmosphere; performing die-casting forming treatment after the ingot material melts; optionally, the conditions of the die-casting forming treatment include: a die-casting speed of 3.0 - 7.5 m / s, a holding pressure time of 3 - 15 s, and a mold temperature of 150 - 280 °C.

[0044] The third aspect of the present disclosure provides a die-cast magnesium alloy prepared by the method according to the second aspect of the present disclosure.

[0045] The fourth aspect of the present disclosure provides an automotive structural part including the die-cast magnesium alloy according to the first aspect or the third aspect of the present disclosure.

[0046] In a specific embodiment, the automotive structural components 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 tunnels, roof reinforcement beams, integrated rear floors, integrated front compartments and other safety structural components; it can also be applied to the production of battery packs for new energy vehicles.

[0047] The present disclosure will be further described in detail below through examples. The raw materials used in the examples can all be obtained through commercial channels.

[0048] In the following examples and comparative examples, the mold used for die-casting forming treatment is an S-shaped flow mold (as Figure 1 shown), and the thickness of the test piece is about 3 mm; Figure 1 In, the mechanical properties of the alloy and the samples are taken at the C1-D1 positions of the bent test pieces, and the casting performance is judged by whether the flow mold can be completely formed and the surface quality of the parts.

[0049] Example 1 (1) Preparation before melting: According to the magnesium alloy component contents listed in Table 1, using pure Mg ingots, Mg-RE master alloys, Mg-Y intermediates, pure Al ingots, Mg-Mn master alloys, Mg-Ca or metallic Ca as the raw materials for each element in the magnesium alloy, after appropriately considering the burn-off, the mass percentages of the components are determined according to the above magnesium alloy composition range, and the corresponding raw materials are weighed; RE is one or two of La or Ce; all the raw materials are dried; (2) Alloy melting: Put the metallic magnesium ingot into the crucible and melt it at 745 °C under a protective gas to form a pure magnesium melt; then successively add the required pure Al ingots, Mg-RE, Mg-Y, Mg-Mn and Mg-Ca (or metallic Ca) master alloys to obtain a magnesium alloy melt; (3) Stir the magnesium alloy melt at a temperature of 750 °C, and add a special refining agent for magnesium alloy during the stirring process for refining; after refining, remove the flux and scum on the liquid surface, and then gently sprinkle a layer of covering agent; then let it stand, and when the temperature of the magnesium alloy melt drops to 700 °C, carry out casting to obtain the ingot material.

[0050] Among them, the main components of the magnesium alloy refining agent are magnesium chloride, potassium chloride, sodium chloride, and the rest are conventional reagents such as calcium chloride, calcium fluoride, barium chloride, etc., and the content can be adjusted according to the actual situation. The covering agent is a mixture mainly composed of chloride salts such as magnesium chloride and potassium chloride, and the dosage can be adjusted according to the actual situation.

[0051] (4) Put the obtained ingot material into a die-casting melting furnace, set the furnace temperature at 700 °C for melting, introduce a protective gas into the furnace to protect the magnesium alloy melt, synchronously install the required die-casting mold on the die-casting machine, raise the mold oil temperature to 240 °C for heat preservation, and carry out die-casting forming after the material melting is completed to obtain a die-cast part in a non-heat-treated state.

[0052] Examples 2 - 9 Referring to the preparation method in Example 1, the difference from Example 1 is that die-cast magnesium alloy is prepared according to the magnesium alloy composition in Table 1; the remaining processes are the same as those in Example 1.

[0053] Comparative Examples 1 - 8 Referring to the preparation method in Example 1, the difference from Example 1 is that die-cast magnesium alloy is prepared according to the magnesium alloy composition in Table 1; the remaining processes are the same as those in Example 1.

[0054] Table 1

[0055] In Table 1, the unit of each metal component data is "wt%"; the balance of the magnesium alloy in each example and comparative example is Mg; the component content of "-" means that this component is not added.

[0056] Test Example 1 This test example is used to test the mechanical properties and bending properties of the die-cast magnesium alloys obtained in the above examples and comparative examples.

[0057] In this test example, the mechanical properties of the alloy and the bending test piece (refer to CN114487337A) are sampled from the C1 - D1 position on the "S"-shaped flow die shown, a represents the sampling in the C1 - D1 area, the bending specimen is a long strip specimen with dimensions of 30×60 mm, the test method refers to VDA238, and the bending property results are uniformly converted into an equivalent angle of 2 mm for evaluation. The conversion formula is shown in the following formula (1); Figure 1 In formula (1); Formula (1); In formula (1), α1 is the actual measured bending angle with a certain thickness, and α2 is the calculated angle with an equivalent thickness (2 mm in this disclosure).

[0058] In this disclosure, the casting performance of the alloy can be evaluated by the filling state and surface quality of the "S"-shaped flow die. The stable thickness of the sprue in the S die forming and effect, the complete filling of the S die, and the absence of visible hot cracks on the surface indicate "OK", otherwise it is "NOK".

[0059] The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the mechanical properties of the alloy material are obtained by testing according to the GB / T 228.1 standard, and the specimen size refers to the small-size specimen of ASTM E8.

[0060] The test results are listed in Table 2 below.

[0061] Table 2

[0062] It can be seen from the data in Table 2 that: In Comparative Example 1, the Al content is lower than the range provided by the present disclosure. In the S die forming test of the magnesium alloy in Comparative Example 1, forming cannot be achieved, the equivalent bending angle of 2 mm is small, and the casting performance and bending performance are poor. On this basis, it is not necessary to further consider the mechanical properties of this magnesium alloy. In Comparative Example 3, the Al content is higher than the range provided by the present disclosure, the elongation rate is low and the equivalent bending angle of 2 mm is small, and the bending performance of this magnesium alloy is poor. Ca is not added to the magnesium alloy of Comparative Example 3, the equivalent bending angle of 2 mm of this magnesium alloy is small, and the bending performance is poor. The Ca content in the magnesium alloy of Comparative Example 5 is too high, and forming cannot be achieved in the S die forming test of the die-cast magnesium alloy obtained in Comparative Example 5, and the casting performance is poor. The RE content in the die-cast magnesium alloy of Comparative Example 4 is too high, and the weight ratio of RE / Y is also not within the optimized range provided by the present disclosure. Forming cannot be achieved in the S die forming test of the die-cast magnesium alloy obtained in Comparative Example 4, and the casting performance is poor. The Zn content in the die-cast magnesium alloy of Comparative Example 6 is too high, the elongation rate of this die-cast magnesium alloy is low and the equivalent bending angle of 2 mm is small, and the bending performance of this magnesium alloy is poor. Y is not added to the die-cast magnesium alloy of Comparative Example 7, and RE is not added to the die-cast magnesium alloy of Comparative Example 8. The equivalent bending angle of 2 mm of the magnesium alloys obtained in Comparative Examples 7-8 is small, and the bending performance is poor. The die-cast magnesium alloys provided in Examples 1-6 of the present disclosure can have excellent S die forming effects, and the equivalent bending angle of 2 mm is larger, and the bending performance of the magnesium alloy is better. Comparing Examples 7-8 with Example 1, it can be seen that in Example 1, both RE and Y in the die-cast magnesium alloy are within the preferred ranges provided by the present disclosure. The die-cast magnesium alloy in Example 1 can have excellent S die forming effects, and the equivalent bending angle of 2 mm is larger, and the bending performance of the magnesium alloy is better. Comparing Example 1 with Example 9, it can be seen that in Example 1, the contents of each component in the die-cast magnesium alloy are within the preferred ranges provided by the present disclosure. The die-cast magnesium alloy in Example 1 can have excellent S die forming effects, and the equivalent bending angle of 2 mm is larger, and the bending performance of the magnesium alloy is better.

[0063] Test Example 2 Perform SEM electron microscopy (Hitachi FlexSEM 1000PSU1000) tests on the die-cast magnesium alloys obtained in Example 3 and Comparative Example 7.

[0064] The SEM photograph of the die-cast magnesium alloy obtained in Example 3 is as Figure 2a shown, by Figure 2aIt can be seen that the sizes of various types of secondary phases in the die-cast magnesium alloy are small and are dispersedly distributed; the average grain size of the α-Mg matrix is about 10 μm; the SEM photograph of the die-cast magnesium alloy obtained in Comparative Example 7 is as Figure 2b shown, and it can be seen from Figure 2b that Y is not added to this die-cast magnesium alloy, lacking the synergistic effect of Y and RE, and the secondary phases in the microstructure are coarse and the distribution of the long rod-shaped secondary phases is obvious. Comparing Figure 2a with Figure 2b it can be known that adding Y to the die-cast magnesium alloy in Example 3 plays the synergistic effect of Y and RE, and can effectively refine the α-Mg matrix and the size of Al 11 RE3.

[0065] The preferred embodiments of the present disclosure have been 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 scope of 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 belong to the protection scope of the present disclosure.

[0066] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination methods.

[0067] Furthermore, any combination can be made between various different embodiments of the present disclosure, as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A die-cast magnesium alloy, characterized in that, The die-cast magnesium alloy comprises 4.2 to 7.0 wt% of Al, 0.15 to 0.5 wt% of Mn, 0.20 to 2.50 wt% of RE, 0.01 to 1.5 wt% of Y, 0.03 to 0.80 wt% of Ca, Fe + Ni + Cu below 0.01 wt%, Zn below 0.20 wt%, impurities below 0.05 wt% and the balance of Mg; wherein RE + Y ≥ 0.5 wt%, and RE includes one or both of La and Ce.

2. The die-cast magnesium alloy according to claim 1, characterized in that, The die-cast magnesium alloy comprises 4.5 to 6.5 wt% of Al, 0.15 to 0.50 wt% of Mn, 0.2 to 1.8 wt% of RE, 0.01 to 1.2 wt% of Y, 0.03 to 0.50 wt% of Ca, Fe + Ni + Cu below 0.01 wt%, Zn below 0.20 wt%, impurities below 0.05 wt% and the balance of Mg.

3. 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%.

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

5. The die-cast magnesium alloy according to claim 1, characterized in that, The die-cast magnesium alloy comprises an α-Mg matrix; the α-Mg matrix is spheroid-like.

6. The die-cast magnesium alloy according to claim 5, characterized in that, The average grain size of the α-Mg matrix is 12 μm or less.

7. The die-cast magnesium alloy according to claim 1, characterized in that, The 2-mm equivalent bending angle of the die-cast magnesium alloy is 50° or more.

8. A method for preparing a die-cast magnesium alloy, characterized in that, Comprising the following steps: S1. Melting the magnesium alloy raw materials to obtain a magnesium alloy melt; wherein the alloy raw materials include: 4.2 to 7.0 wt% of Al, 0.15 to 0.5 wt% of Mn, 0.20 to 2.50 wt% of RE, 0.01 to 1.5 wt% of Y, 0.03 to 0.80 wt% of Ca, Fe + Ni + Cu below 0.01 wt%, Zn below 0.20 wt%, impurities below 0.05 wt% and the balance of Mg; wherein RE + Y ≥ 0.5 wt%, and RE includes one or both of La and Ce; S2. Adding a refining agent to the magnesium alloy melt for refining; adding a covering agent and then carrying out a standing and cooling treatment to obtain an ingot material; S3. Placing the ingot material in a die-casting melting furnace for melting treatment and die-casting forming treatment.

9. The method according to claim 8, 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.

10. The method according to claim 8, characterized in that, In step S2, the refining treatment includes: stirring at a temperature of 740 to 760 °C for 10 to 30 min, and adding the refining agent during the stirring process; The standing and cooling treatment includes: standing for 30 to 50 min, and reducing the temperature of the magnesium alloy melt to 670 to 720 °C; In step S3, the temperature of the melting treatment is 690 to 720 °C; The conditions of the die-casting forming treatment include: a die-casting speed of 3.0 to 7.5 m / s, a holding pressure time of 3 to 15 s, and a mold temperature of 200 to 280 °C.

11. A die-cast magnesium alloy prepared by the method according to any one of claims 8 to 10.

12. An automotive structural component, characterized in that, Comprising the die-cast magnesium alloy according to any one of claims 1 to 7 and 11.

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