High-thermal-conductivity super-high-temperature-creep-resistant cast magnesium alloy and preparation method thereof

Abstract

The present application relates to high-thermal-conductivity super-high-temperature-creep-resistant cast magnesium alloy and its preparation method, the alloy contains 2-4.5 aluminum, 0.1-0.5 zinc, 0.1-0.5 manganese, 0.02-0.5 selenium, 0.02-0.5 copper, 2.5-6 lanthanum, 0.1-0.8 neodymium and 0.05-0.12 yttrium by mass percent, and the balance is magnesium and <0.2 impurities. The specific rare earth makes aluminum migrate to the grain boundary and form a heat stable, continuous but non-enclosed lamellar grain boundary second phase; the specific rare earth and non-rare earth compound in the grain induce the precipitation of a heat stable, super-anti-coarsening and creep-resistant precipitate phase; the grain boundary second phase has a micro-feeding channel; the bottleneck of synergistic improvement and control of the thermal conductivity, creep and casting performance of magnesium alloy is overcome, the thermal conductivity is matched with commercial aluminum alloy, the heat resistance temperature is greatly improved from 175 DEG C to 250 DEG C, the creep rate is reduced by an order of magnitude compared with the commercial benchmark magnesium alloy, and other breakthroughs are achieved, which is suitable for automobile, low-altitude economy, aerospace and other fields.

Description

Technical Field

[0001] This invention relates to the field of alloy casting technology, and in particular to a high thermal conductivity, high temperature creep resistant cast magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys, as lightweight metallic materials, have attracted widespread attention and are playing an increasingly important role in fields such as new energy vehicles, low-altitude economy, and aerospace. The urgent need for lightweight and high-performance in emerging complex castings operating at higher temperatures, such as electric drive components for new energy vehicles and drone engines, demands that next-generation die-cast magnesium alloys possess superior creep resistance at 250°C, significantly exceeding the 120-175°C heat resistance creep limit of traditional die-cast magnesium alloys to prevent early high-temperature creep failure. Simultaneously, they need to possess high thermal conductivity comparable to the widely used A380 / EN-AC 46000 die-cast aluminum alloy (~110 W / (m·K), 25°C) to achieve rapid heat dissipation in high-temperature operating environments. Furthermore, excellent casting properties are required to meet the forming requirements of complex castings.

[0003] Al is the element most beneficial to the casting properties of magnesium alloys. To ensure the castability of complex castings, a considerable amount of Al must be added to die-cast magnesium alloys. However, high Al content not only promotes Mg... 17 Al 12The formation of low-melting-point and thermally unstable phases significantly deteriorates the high-temperature creep properties of magnesium alloys. Furthermore, their high solid solubility (approximately 12.7 wt.% at 437℃) increases the solute atom content in the magnesium matrix, drastically reducing the thermal conductivity of magnesium alloys. Currently, the most widely used aluminum-rich die-cast magnesium alloys, including AZ91D, AM50, and AM60, have low creep temperatures of approximately 120℃ and room-temperature thermal conductivity of only 51-65 W / (m·K). To improve the creep resistance of aluminum-rich die-cast magnesium alloys, non-rare earth elements such as Sr, Ca, and Sn are introduced into these alloys. Representative alloys include Mg(5 / 6)Al2Sr (AJ52, AJ62), Mg8Al1CaZn (MRI153A), Mg8Al1CaSr (MRI153M), Mg6.5Al2Ca1SnSr (MRI230D), and Mg4.5Al3.5CaSr (AXJ530). However, the creep temperature of these magnesium alloys is typically below 175℃, and their room temperature thermal conductivity is only 60-77 W / (m·K). In addition, rare earth elements are also added to aluminum-rich die-cast magnesium alloys to improve their creep resistance; typical examples include Mg4Al1.2Ce0.6La (AE42) and Mg4Al2.5Ce1.2La (AE44). However, the creep temperature of AE42 and AE44 magnesium alloys still does not exceed 200℃, and their room temperature thermal conductivity is relatively low, only 78-92 W / (m·K). Overall, existing high-castability aluminum-rich die-cast magnesium alloys have significant problems with low high-temperature creep resistance and poor thermal conductivity, which cannot meet the stringent requirements of the aforementioned emerging complex lightweight components.

[0004] Furthermore, the synergistic regulation of thermal conductivity, creep resistance, and casting performance has been a challenge for decades. Creep resistance requires thermally stable, coarsening-resistant, and high-temperature creep-resistant intragranular precipitates induced by solute atoms in the alloy matrix to hinder the movement of creep dislocations in the matrix, and thermally stable and continuous grain boundary second phases to prevent creep dislocations from crossing grain boundaries and suppress grain boundary slip. However, excessive intragranular solute atoms increase hot carrier scattering and reduce thermal conductivity, while continuous and closed grain boundary second phases hinder solidification feeding and reduce casting performance. These factors pose a severe challenge to the synergistic regulation of high-temperature creep resistance and thermal conductivity in aluminum-rich die-cast magnesium alloys. Summary of the Invention

[0005] To address the comprehensive requirements of lightweight and complex structural components such as electric drive components for new energy vehicles and drone engines for high thermal conductivity, strong resistance to high-temperature creep, high corrosion resistance, and excellent casting performance, this invention provides a high thermal conductivity and ultra-high-temperature creep resistant cast magnesium alloy and its preparation method. This solves the bottleneck problems of low high-temperature creep resistance, poor thermal conductivity, and difficulty in synergistically improving and controlling thermal conductivity, creep performance, and casting performance in existing magnesium alloys.

[0006] To solve the above-mentioned technical problems, the present invention provides a high thermal conductivity, high-temperature creep resistant cast magnesium alloy, which comprises the following components by mass percentage: Non-rare earth elements: Al: 2.0-4.5%, Zn: 0.1-0.5%, Mn: 0.1-0.5%, Se: 0.02-0.5%, and Cu: 0.02-0.5%; and, Rare earth elements: La: 2.5-6.0%, Nd: 0.1-0.8% and Y: 0.05-0.12%; and, The balance consists of Mg and impurity elements with a content not exceeding 0.2%. The content ratio of rare earth elements (La, Nd, and Y) and Al in the magnesium alloy is between 1.2 and 2, and the content ratio of La to Nd and Y is between 5 and 11. The magnesium alloy contains Mn and Se in a ratio of 1 to 3.5, and Se and Cu in a ratio of 1 to 2.

[0007] Furthermore, the sum of the contents of Al and La is in the range of 6.0-9.0 wt%; Preferably, the Al content is selected from at least one range within the range of 2.0-4.0 wt%, including: 2.3-3.7 wt%, 2.5-3.5 wt%, 2.7-3.3 wt%, and 2.8-3.2 wt%. Preferably, the La content is selected from at least one range within the range of 3.2-5.8 wt%, including: 3.7-5.3 wt%, 3.9-5.1 wt%, 4.0-5.0 wt%, 4.1-4.9 wt%, and 4.2-4.8 wt%. Preferably, the Nd content is in the range of 0.3-0.6 wt%; Preferably, the content of Y is in the range of 0.08-0.1 wt%. Preferably, the Zn content is in the range of 0.2-0.4 wt%. Preferably, the Mn content is in the range of 0.2-0.4 wt%; Preferably, the content of Se is in the range of 0.2-0.4 wt%; Preferably, the Cu content is in the range of 0.1-0.3 wt%.

[0008] Furthermore, the content ratio of rare earth elements (La, Nd, and Y) and Al in the magnesium alloy is between 1.5 and 1.7, and the content ratio of La to Nd and Y is between 7 and 9. Preferably, the ratio of Mn to Se in the magnesium alloy is between 1 and 2, and the ratio of Se to Cu is between 1.3 and 1.7.

[0009] Furthermore, magnesium alloys may also include impurity elements, which can be alloying elements that have a negligible or insignificant effect on the properties of the magnesium alloy. Impurity elements include: Fe < 0.1 wt%, Si < 0.02 wt%, Sn < 0.02 wt%, Ni < 0.02 wt%, Ca < 0.02 wt%, and Sr < 0.02 wt%.

[0010] Furthermore, the rare earth elements La, Nd, and Y added to the magnesium alloy promote the migration of Al solute atoms to the grain boundaries during solidification and form a thermally stable, continuous but non-closed grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y), thereby reducing the content of Al solute atoms in the grains and improving the thermal conductivity of the magnesium alloy.

[0011] The grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) has a lamellar structure with micro-feeding channels between the lamellars. These micro-feeding channels optimize the solidification feeding of the alloy melt, reduce the alloy's sensitivity to shrinkage cavities, porosity, and hot cracking, and improve the alloy's casting performance.

[0012] The grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) remains stable after creeping for over 370 hours under harsh high temperature and stress conditions of 250℃ / 80MPa, exhibiting thermal stability and continuity. This hinders creep dislocations from crossing grain boundaries and suppresses grain boundary slip, thereby improving the high-temperature creep resistance of the alloy.

[0013] Furthermore, the magnesium alloy is modified by the composite addition and regulation of rare earth elements La, Nd and Y and non-rare earth elements Al, Mn, Se and Cu to induce the precipitation of thermally stable, ultra-resistant to coarsening and high-temperature creep precipitates Al8(Mn,Se,Cu)4RE(La,Nd,Y) within the crystal. The precipitated phase Al8(Mn,Se,Cu)4RE(La,Nd,Y) remains less than 10 nm after creeping for over 370 h under harsh high temperature and stress conditions of 250℃ / 80MPa. It exhibits thermal stability, superior resistance to coarsening, and high-temperature creep, effectively hindering the movement of intragranular creep dislocations and further enhancing the high-temperature creep resistance of the magnesium alloy.

[0014] On the other hand, the present invention also provides a method for preparing a high thermal conductivity, high temperature creep resistant cast magnesium alloy, which includes the following steps: S1. Preparation of alloy raw materials, and preheating and drying of the alloy raw materials, including industrial pure Mg, Mg-Al master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy, Mg-Cu master alloy, Mg-La master alloy, Mg-Nd master alloy and Mg-Y master alloy. S2. Melt industrial pure Mg at 700-760℃ in a protective atmosphere and perform alloying treatment to obtain a magnesium alloy melt with the target composition. S3. Heat the alloyed magnesium alloy melt to 760-800℃ and perform refining and degassing treatment 1-3 times, 5-15 min / time, and remove the slag. S4. The magnesium alloy melt after refining and degassing is subjected to high pressure die casting under the process conditions of injection speed of 2-6m / s, mold temperature of 180-280℃ and casting temperature of 680-780℃. S5. After high pressure die casting, the magnesium alloy casting is held under pressure of 60-120MPa for 10-60s to obtain a high thermal conductivity and high temperature creep resistant cast magnesium alloy casting. S6. Demold the high thermal conductivity and high temperature creep resistant cast magnesium alloy casting after pressure holding and solidification, and stabilize it at 180-250℃ for 0.5-10h.

[0015] Furthermore, the alloy is preheated and dried at a temperature of 80-200℃ for 1-4 hours; The smelting temperature of the industrial pure Mg is 700-760℃; The protective atmosphere is either SF6 / CO2 or Ar.

[0016] Furthermore, the alloying treatment is as follows: After industrial pure Mg is completely melted, Mg-Al master alloy, Mg-La master alloy, Mg-Nd master alloy, Mg-Y master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy and Mg-Cu master alloy are added in sequence, and mechanical stirring is carried out for 5-20 minutes and held at the temperature for 15-60 minutes. Preferably, the mechanical stirring time is 10-15 min; the heat preservation time is 25-35 min.

[0017] Furthermore, the refining and degassing treatment is as follows: After heating the magnesium alloy melt to 760-800℃, high-purity Ar gas is introduced into it for rotary degassing and slag removal; the rotary degassing time is 5-15 min / time, the rotary degassing is repeated 1-3 times, and the slag removal is performed after each rotary degassing.

[0018] Furthermore, the pressure holding and solidification pressure is 60-120 MPa; the pressure holding and solidification time is 10-60 s; Preferably, the pressure holding and solidification pressure is 80-100 MPa; the pressure holding and solidification time is 20-40 s.

[0019] Furthermore, the stabilization treatment temperature is 180-250℃, and the time is 0.5-10h.

[0020] Preferably, the stabilization treatment temperature is 200-220℃; and the stabilization treatment time is 1-6h.

[0021] By employing the above technical solution, the present invention provides a high thermal conductivity, high-temperature creep-resistant cast magnesium alloy and its preparation method, which has at least the following beneficial effects: (1) The high thermal conductivity and high temperature creep resistant aluminum-rich cast magnesium alloy provided by the present invention has a thermal conductivity exceeding 130 W / m·K at 250℃, and a steady-state creep rate of less than 2.2 × 10⁻⁶ under harsh high temperature and stress conditions of 250℃ / 80MPa. -9 s -1 Creep life exceeds 370 hours.

[0022] (2) This invention overcomes the bottleneck of synergistic improvement and control of thermal conductivity, high temperature creep resistance and casting performance of aluminum-rich cast magnesium alloys, and achieves breakthroughs in core indicators such as thermal conductivity comparable to commercial aluminum alloys, heat resistance temperature greatly increased from 120-175℃ to 250℃, and creep rate reduced by an order of magnitude compared with the existing commercial benchmark AE44 magnesium alloy. It can be widely used in automobiles, low-altitude economy, aerospace and other fields.

[0023] (3) The addition of La, Nd, and Y rare earth elements in this invention promotes the migration of Al solute atoms in the Mg matrix to the grain boundaries, forming a thermally stable, continuous but non-closed lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) with micro-feeding channels. This significantly reduces the Al solute atom content in the Mg matrix to below 0.3 wt.%, reducing lattice distortion and hot carrier scattering, and improving the thermal conductivity of the alloy. This allows for rapid conduction and diffusion of heat generated during the service of hot-end components such as electric drive components for new energy vehicles and drone engines, thus improving their heat dissipation performance. At the same time, the micro-feeding channels optimize the solidification feeding of the alloy melt, reducing the alloy's sensitivity to shrinkage cavities, porosity, and hot cracks, and improving the alloy's casting performance.

[0024] (4) The thermally stable and continuous grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) formed by the present invention remains stable after creeping for more than 370h under harsh high temperature and stress conditions of 250℃ / 80MPa, and effectively prevents creep dislocations from crossing grain boundaries and grain boundary slip, thereby improving the high temperature creep resistance of the alloy.

[0025] (5) This invention induces the precipitation of thermally stable, ultra-resistant to coarsening and high-temperature creep precipitates Al8(Mn,Se,Cu)4RE(La,Nd,Y) in the crystal by combining and regulating rare earth elements La, Nd and Y with non-rare earth elements Al, Mn, Se and Cu. The precipitates are less than 10 nm after creeping for more than 370 h under harsh high temperature and stress conditions of 250℃ / 80MPa, and effectively hinder the movement of creep dislocations in the crystal, further improving the high-temperature creep resistance of the alloy.

[0026] (6) The present invention controls the Al content at 2.0-4.5wt%, giving full play to the beneficial effect of Al on the casting performance of the alloy and ensuring the casting performance of the magnesium alloy. At the same time, by taking advantage of the low solid solubility of La and Nd in the Mg matrix and the ability to narrow the solidification temperature range, the fluidity and filling ability of the magnesium alloy melt are improved, which is conducive to obtaining high-quality complex castings with uniform structure and few defects.

[0027] (7) The Y element added in this invention has a high oxygen affinity, which can form a dense and stable Y-rich oxide film on the alloy surface, improving the flame retardancy, oxidation resistance and corrosion resistance of magnesium alloys, and enhancing the service safety and reliability of the material under high temperature conditions. At the same time, Y also improves the thermal stability of the microstructure and inhibits microstructure coarsening under high temperature conditions.

[0028] (8) The Mn element added in this invention also helps prevent castings from sticking to the mold and improves the strength of the alloy. At the same time, the Mn element also helps neutralize impurities in the alloy and changes the morphology of iron-containing compounds from needle-like to spherical to reduce the harmful effects of iron.

[0029] (9) The Zn element added in this invention promotes the nucleation and refinement of the precipitated phase, thereby improving the high-temperature creep resistance of magnesium alloys.

[0030] (10) The main body of the present invention uses low-cost Al element and low-cost rare earth element La, and the La, Nd and Y elements used are obtained in the form of low-cost mixed rare earth metals, which has the advantage of low cost, so as to produce cost-effective magnesium alloys with good mechanical properties and casting performance.

[0031] (11) This invention uses magnesium alloy to replace traditional aluminum alloy in the manufacture of castings for electric drive components of new energy vehicles, drone engines, chainsaw engines, aerospace engine parts, etc., which has a significant weight reduction effect. Compared with aluminum alloy materials, the weight of the castings is reduced by about 30%, which significantly improves the energy utilization efficiency and endurance of new energy vehicles, drones, tools, aerospace equipment, etc.

[0032] (12) The high thermal conductivity and high temperature creep resistance cast magnesium alloy provided by the present invention breaks through the key material bottleneck of high temperature service components of high-end equipment in key and strategic emerging fields such as new energy vehicles, low-altitude economy, and aerospace, and improves its lightweight level, thermal management capability, reliability, low-cost manufacturing and long service life, which has important strategic significance and engineering practical value. Attached Figure Description

[0033] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart of the preparation method of high thermal conductivity and high temperature creep resistant cast magnesium alloy in this invention; Figure 2 This is a comparison diagram of the flame retardant performance of Example 3, Comparative Example 1, and Comparative Example 2 in this invention; Figure 3 This is a comparison graph showing the thermal conductivity of Example 3 and Control Example 1 at 25-300°C in this invention. Figure 4 This is a comparison graph showing the yield strength of Example 3 and Control Example 1 at 25°C, 150°C, 250°C and 300°C. Figure 5 This is a comparison graph showing the tensile strength of Example 3 and Control Example 1 at 25°C, 150°C, 250°C, and 300°C. Figure 6 This is a comparison graph showing the elongation of Example 3 and Control Example 1 at 25°C, 150°C, 250°C and 300°C. Figure 7 This is a microstructure diagram of the as-cast state of Example 3 in this invention, showing a thermally stable, continuous but non-closed lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) containing micro-feeding channels; Figure 8 This is a comparison diagram of the Al solute atom content in the matrix of Example 3 and Control Example 1 in this invention; Figure 9 The image shows the microstructure of Example 3 of this invention after creeping for more than 370 hours at 250°C / 80MPa. It shows the precipitated phase Al8(Mn,Se,Cu)4RE(La,Nd,Y) which is thermally stable, highly resistant to coarsening and high-temperature creep, and its role in hindering the movement of creep dislocations within the crystal. Figure 10The images show the HAADF-STEM high-resolution images and EDS elemental scan results of the precipitated phase Al8(Mn,Se,Cu)4RE(La,Nd,Y) after creeping for more than 370 h at 250°C / 80MPa in Example 3 of this invention, which exhibits intragranular thermal stability, superior resistance to coarsening, and high-temperature creep. Figure 11 This is a microstructure diagram of the lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) in Example 3 of the present invention, which is thermally stable, continuous but not closed, and contains micro-compacting channels after creeping for more than 370 hours at 250°C / 80MPa. Figure 12 This diagram illustrates the hindering effect of the thermally stable, continuous but non-closed lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) with micro-compacted channels on creep dislocation crossing grain boundaries and grain boundary slip after creeping for more than 370 hours at 250°C / 80MPa in Example 3 of this invention. Figure 13 This is a schematic diagram illustrating the synergistic improvement and regulation mechanism of thermal conductivity, high-temperature creep resistance, and casting performance of the high thermal conductivity and ultra-high temperature creep resistant magnesium alloy in this invention. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This will allow for a full understanding of how the present application uses technical means to solve technical problems and achieve technical effects, and to facilitate its implementation.

[0035] This invention proposes a high thermal conductivity, high-temperature creep-resistant cast magnesium alloy and its preparation method. The high thermal conductivity, high-temperature creep-resistant cast magnesium alloy comprises the following components by mass percentage: Al: 2.0-4.5%, Zn: 0.1-0.5%, Mn: 0.1-0.5%, Se: 0.02-0.5%, Cu: 0.02-0.5%, La: 2.5-6.0%, Nd: 0.1-0.8%, Y: 0.05-0.12%; The balance consists of Mg and impurity elements, with the content of impurity elements not exceeding 0.2%.

[0036] In this invention, the high thermal conductivity, high-temperature creep resistant cast magnesium alloys corresponding to Examples 1 to 4 and the magnesium alloys corresponding to Comparative Examples 2 to 5 were all prepared using the following method. For example... Figure 1 As shown, the specific preparation method is as follows: First, weigh out industrial-grade pure Mg, Mg-Al master alloy, Mg-La master alloy, Mg-Nd master alloy, Mg-Y master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy, and Mg-Cu master alloy according to the designed composition. All raw materials are dried at 120°C for 2 hours to remove surface moisture and volatile impurities.

[0037] Industrial-grade pure Mg was then added to a resistance melting furnace and heated to 730°C under an SF6 / CO2 protective atmosphere until melted. After the industrial-grade pure Mg melted, Mg-Al master alloy, Mg-La master alloy, Mg-Nd master alloy, Mg-Y master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy, and Mg-Cu master alloy were added sequentially, and mechanically stirred for 12 minutes to ensure that each alloying element was fully dissolved. The mixture was then held at this temperature for 30 minutes to promote homogenization of the alloy composition.

[0038] After alloying, the magnesium alloy melt is heated to 780℃ and subjected to rotary degassing with high-purity Ar gas for 10 minutes to remove surface slag. This degassing process is repeated twice to reduce the gas content and inclusion content in the magnesium alloy melt and improve its purity.

[0039] The refined and degassed magnesium alloy melt is poured into the pressure chamber of a high-pressure die-casting equipment and die-cast at a mold temperature of 220℃ and a casting temperature of 730℃. The injection speed is controlled at 4m / s and the injection pressure is controlled at 100MPa.

[0040] After filling, the casting is held under 90 MPa pressure for 30 seconds to improve the density of the casting and reduce defects such as shrinkage porosity and shrinkage cavities.

[0041] After the casting has cooled, it is demolded and then stabilized at 220℃ for 2 hours to obtain a high thermal conductivity, high temperature creep resistant cast magnesium alloy casting.

[0042] Furthermore, the AE44 alloy corresponding to Comparative Example 1 was prepared using the same process.

[0043] Based on this, the composition of the alloys corresponding to Examples 1 to 4 and Comparative Examples 1 to 5 were determined according to ASTM standards. The test results of their thermal conductivity, tensile properties and high-temperature creep resistance are shown in Tables 1, 2 and 3, respectively.

[0044] Table 1. Thermal conductivity test results of the alloys corresponding to Examples 1-4 and Comparative Examples 1-5

[0045] Table 2 Tensile property test results of the alloys corresponding to Examples 1-4 and Comparative Examples 1-5

[0046] Table 3. Test results of high-temperature creep resistance of the alloys corresponding to Examples 1-4 and Comparative Examples 1-5

[0047] The flame retardant properties of some samples were tested during the smelting process. The combustion time of the alloy after the protective atmosphere was removed was used to describe the flame retardant properties. A comparison of the flame retardant properties of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3), AE44 alloy (Comparative Example 1), and Mg3.2Al4.4La0.4Nd0.3Zn0.4Mn0.3Se0.2Cu alloy (Comparative Example 2) was made. Figure 2 As shown.

[0048] The samples used for testing thermal conductivity, tensile properties, and high-temperature creep resistance had a casting wall thickness of 6 mm. The thermal conductivity of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3) and the AE44 alloy (Comparative Example 1) at 25-300°C was compared according to standard methods defined by ASTM. Figure 3 As shown.

[0049] A comparison of the yield strength of Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3) and AE44 alloy (Comparative Example 1) at 25°C, 150°C, 250°C, and 300°C. Figure 4 As shown.

[0050] A comparison of the tensile strength of Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3) and AE44 alloy (Comparative Example 1) at 25°C, 150°C, 250°C, and 300°C. Figure 5 As shown.

[0051] A comparison of the elongation of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3) and the AE44 alloy (Comparative Example 1) at 25°C, 150°C, 250°C, and 300°C. Figure 6 As shown.

[0052] Example 1: The high thermal conductivity and high-temperature creep resistant cast magnesium alloy prepared in this embodiment has the following elemental mass percentages: 2.8% Al, 4.2% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.3% Se, 0.2% Cu, and the balance Mg. The alloy exhibits an average thermal conductivity of 121 W / m·K at room temperature, an average yield strength of 137 MPa, an average tensile strength of 244 MPa, an average elongation of 9.3%, and an average steady-state creep rate of 2.09 × 10⁻⁶ at 250°C and 80 MPa. -9 s -1 .

[0053] Example 2: The high thermal conductivity and high-temperature creep resistant cast magnesium alloy prepared in this embodiment has the following elemental mass percentages: 3.0% Al, 4.4% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.2% Se, 0.1% Cu, and the balance Mg. The alloy has an average room temperature thermal conductivity of 119 W / m·K, an average yield strength of 140 MPa, an average tensile strength of 245 MPa, an average elongation of 8.9%, and an average steady-state creep rate of 2.11 × 10⁻⁶ at 250°C and 80 MPa. -9 s -1 .

[0054] Example 3: The high thermal conductivity and high-temperature creep resistant cast magnesium alloy prepared in this embodiment has the following elemental mass percentages: 3.2% Al, 4.4% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.3% Se, 0.2% Cu, and the balance Mg. The alloy has an average room temperature thermal conductivity of 114 W / m·K, an average yield strength of 142 MPa, an average tensile strength of 246 MPa, an average elongation of 9.0%, and an average steady-state creep rate of 1.99 × 10⁻⁶ at 250°C and 80 MPa. -9 s -1 The corrosion rate was reduced by more than 60% compared to alloy AE44 (Comparative Example 1). Furthermore, after the protective atmosphere was removed under smelting conditions, the alloy combusted after approximately 42 seconds.

[0055] Example 4: The high thermal conductivity and high-temperature creep resistant cast magnesium alloy prepared in this embodiment has the following elemental mass percentages: 3.2% Al, 4.8% La, 0.5% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.3% Se, 0.2% Cu, and the balance Mg. The alloy has an average room temperature thermal conductivity of 116 W / m·K, an average yield strength of 143 MPa, an average tensile strength of 248 MPa, an average elongation of 8.6%, and an average steady-state creep rate of 1.98 × 10⁻⁶ at 250°C and 80 MPa.-9 s -1 .

[0056] Compare with Example 1: The AE44 alloy has an average room temperature thermal conductivity of 86 W / m·K, an average yield strength of 132 MPa, an average tensile strength of 242 MPa, an average elongation of 12.3%, and an average steady-state creep rate of 1.51 × 10⁻⁶ at 250°C and 80 MPa. -8 s -1 The corrosion rate is approximately 2.55 mm / y. Furthermore, after the protective atmosphere is removed under smelting conditions, the alloy burns after approximately 18 seconds.

[0057] Compare with Example 2: The magnesium alloy prepared in this comparative example, with elemental mass percentages of 3.2% Al, 4.4% La, 0.4% Nd, 0.3% Zn, 0.4% Mn, 0.3% Se, 0.2% Cu, and the balance Mg, exhibited a corrosion rate 30-60% lower than that of the AE44 alloy (Comparative Example 1). Furthermore, after the protective atmosphere was removed under smelting conditions, this alloy combusted approximately 20 seconds later.

[0058] Compare with Example 3: The magnesium alloy prepared in this comparative example has the following elemental mass percentages: 3.2% Al, 4.4% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, and the balance Mg. The average steady-state creep rate of this alloy at 250°C / 80 MPa is 8.93 × 10⁻⁶. -9 s -1 .

[0059] Compare with Example 4: The magnesium alloy prepared in this comparative example has the following elemental mass percentages: 3.2% Al, 4.4% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.3% Se, and the balance Mg. The average steady-state creep rate of this alloy at 250°C / 80 MPa is 4.69 × 10⁻⁶. - 9 s -1 .

[0060] Compare with Example 5: The magnesium alloy prepared in this comparative example has the following elemental mass percentages: 3.2% Al, 4.4% La, 0.4% Nd, 0.1% Y, 0.3% Zn, 0.4% Mn, 0.2% Cu, and the balance Mg. The average steady-state creep rate of this alloy at 250°C / 80 MPa is 5.37 × 10⁻⁶. - 9 s -1 .

[0061] The microstructure of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy prepared in Example 3 was characterized in this invention.

[0062] In the as-cast state, the grain boundaries of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy consist of a thermally stable, continuous but unclosed lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) containing micro-feeding channels. These micro-feeding channels optimize solidification feeding and improve the alloy's casting properties. Figure 7 As shown. Furthermore, compared to the AE44 alloy in Comparative Example 1, the Al solute atom content in the Mg matrix of the alloy was significantly reduced from 0.7 wt.% to below 0.3 wt.%, reducing the scattering effect of solute atoms on hot carriers in the Mg matrix and improving the thermal conductivity of the alloy, such as... Figure 8 As shown.

[0063] Creep tests were conducted on the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy. After creeping for over 370 hours under harsh high temperature and stress conditions of 250°C / 80MPa, the microstructure of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy was characterized. The Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy contains a large number of thermally stable, highly resistant to coarsening and high-temperature creep precipitates, Al8(Mn,Se,Cu)4RE(La,Nd,Y). These precipitates exhibit excellent resistance to creep and high-temperature creep, remaining smaller than 10 nm even after creeping for over 370 hours under harsh conditions of 250°C / 80MPa. Furthermore, they have been observed to significantly impede the movement of intragranular creep dislocations, thus enhancing the alloy's resistance to high-temperature creep. The specific characteristics of these precipitates and their role in hindering intragranular creep dislocation movement are as follows: Figure 9 As shown; the HAADF-STEM image and EDS elemental scan results of the precipitated phase are as follows. Figure 10 As shown.

[0064] Meanwhile, the thermally stable and continuous grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) remained stable after creeping for over 370 h under harsh high temperature and stress conditions of 250°C / 80MPa. It was observed to hinder creep dislocations from crossing grain boundaries and suppress grain boundary slip, further enhancing the alloy's resistance to high-temperature creep. Figure 11 and Figure 12 As shown.

[0065] Compared with the AE44 alloy in Comparative Example 1, the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy showed a significantly reduced steady-state creep rate of 86.8% under high temperature and stress of 250°C / 80MPa; compared with the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn alloys and Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn alloys prepared in Comparative Examples 3, 4 and 5, the AE44 alloy showed a significantly reduced steady-state creep rate of 86.8%. Compared to the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se alloy, the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.2Cu alloy exhibits a steady-state creep rate reduced by at least 57.6% under harsh high-temperature and stress conditions of 250°C / 80MPa.

[0066] In summary, the synergistic improvement and regulation mechanism of the thermal conductivity, high-temperature creep resistance, and casting performance of the Mg3.2Al4.4La0.4Nd0.1Y0.3Zn0.4Mn0.3Se0.2Cu alloy (Example 3) is as follows: Figure 13 As shown, the thermally stable, continuous but non-closed lamellar grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) formed by the regulation of rare earth elements La, Nd, and Y significantly reduces the content of Al solute atoms in the Mg matrix to below 0.3 wt.%, reduces lattice distortion and hot carrier scattering, and improves the thermal conductivity of the alloy. This enables the heat generated during the service of hot-end components such as electric drive components of new energy vehicles and drone engines to be quickly conducted and diffused, thus improving their heat dissipation performance. The grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) has a lamellar structure with micro-feeding channels between the lamellars, which optimizes solidification feeding and improves the casting performance of the alloy. The grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) remains stable after creeping for more than 370 h under harsh high temperature and stress conditions of 250℃ / 80MPa. It has the characteristics of thermal stability and continuity, which hinders creep dislocations from crossing grain boundaries and inhibits grain boundary slip, thereby improving the high temperature creep resistance of the alloy. By combining and regulating rare earth elements La, Nd, and Y with non-rare earth elements Al, Mn, Se, and Cu, a thermally stable, ultra-resistant to coarsening and high-temperature creep precipitate Al8(Mn,Se,Cu)4RE(La,Nd,Y) was induced in the crystal. After creeping for more than 370 h under harsh high temperature and stress conditions of 250℃ / 80MPa, the precipitate was still less than 10 nm, and it effectively hindered the movement of creep dislocations in the crystal, further improving the high-temperature creep resistance of the alloy.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Since the above embodiments are substantially similar to the method embodiments, their descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0068] The above embodiments provide a detailed description of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A high thermal conductivity, high-temperature creep resistant cast magnesium alloy, characterized in that, This magnesium alloy comprises the following components by weight percentage: Non-rare earth elements: Al: 2.0-4.5%, Zn: 0.1-0.5%, Mn: 0.1-0.5%, Se: 0.02-0.5%, and Cu: 0.02-0.5%; and, Rare earth elements: La: 2.5-6.0%, Nd: 0.1-0.8% and Y: 0.05-0.12%; and, The balance consists of Mg and impurity elements with a content not exceeding 0.2%. The content ratio of rare earth elements and Al in the magnesium alloy is between 1.2 and 2, and the content ratio of La to Nd and Y is between 5 and 11. The magnesium alloy contains Mn and Se in a ratio of 1 to 3.5, and Se and Cu in a ratio of 1 to 2.

2. The high thermal conductivity, high-temperature creep resistant cast magnesium alloy according to claim 1, characterized in that, The sum of the contents of Al and La is in the range of 6.0-9.0 wt%. The Al content is selected from at least one range within the range of 2.0-4.0 wt%, including: 2.3-3.7 wt%, 2.5-3.5 wt%, 2.7-3.3 wt%, and 2.8-3.2 wt%. The La content is selected from at least one range within the range of 3.2-5.8 wt%, including: 3.7-5.3 wt%, 3.9-5.1 wt%, 4.0-5.0 wt%, 4.1-4.9 wt%, and 4.2-4.8 wt%. The Nd content is in the range of 0.3-0.6 wt%; The content of Y is in the range of 0.08-0.1 wt%. The Zn content is in the range of 0.2-0.4 wt%. The Mn content is in the range of 0.2-0.4 wt%; The content of Se is in the range of 0.2-0.4 wt%; The Cu content is in the range of 0.1-0.3 wt%.

3. The high thermal conductivity, high-temperature creep resistant cast magnesium alloy according to claim 1, characterized in that, The content ratio of rare earth elements and Al in the magnesium alloy is between 1.5 and 1.7, and the content ratio of La to Nd and Y is between 7 and 9. The content ratio of Mn to Se in the magnesium alloy is between 1 and 2, and the content ratio of Se to Cu is between 1.3 and 1.

7.

4. The high thermal conductivity, high-temperature creep resistant cast magnesium alloy according to claim 1, characterized in that, The impurity elements include Fe, Si, Sn, Ni, Ca, and Sr, with the following mass percentages for each element: Fe<0.1%; Si<0.02%; Sn<0.02%; Ni<0.02%; Ca<0.02%; Sr<0.02%.

5. The high thermal conductivity, high-temperature creep resistant cast magnesium alloy according to claim 1, characterized in that, The rare earth elements La, Nd, and Y added to the magnesium alloy are used to promote the migration of Al solute atoms to the grain boundaries during solidification and form a thermally stable, continuous but non-closed grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y), thereby reducing the content of Al solute atoms in the grains. The grain boundary second phase (Al,Mg,Cu)4RE(La,Nd,Y) has a lamellar structure and micro-compacting channels between the lamellars. The second phase also serves to prevent creep dislocations from crossing grain boundaries and to suppress grain boundary slip.

6. The high thermal conductivity, high-temperature creep resistant cast magnesium alloy according to claim 1, characterized in that, The magnesium alloy is modified by the composite addition and regulation of rare earth elements La, Nd and Y and non-rare earth elements Al, Mn, Se and Cu to induce the precipitation of thermally stable, ultra-resistant to coarsening and high-temperature creep precipitates Al8(Mn,Se,Cu)4RE(La,Nd,Y) within the crystal. The precipitated phase Al8(Mn,Se,Cu)4RE(La,Nd,Y) is used to hinder the movement of intracrystalline creep dislocations.

7. A method for preparing a high thermal conductivity, high-temperature creep-resistant cast magnesium alloy, used to prepare the high thermal conductivity, high-temperature creep-resistant cast magnesium alloy as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Preparation of alloy raw materials, and preheating and drying of the alloy raw materials, including industrial pure Mg, Mg-Al master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy, Mg-Cu master alloy, Mg-La master alloy, Mg-Nd master alloy and Mg-Y master alloy. S2. Melt industrial pure Mg at 700-760℃ in a protective atmosphere and perform alloying treatment to obtain a magnesium alloy melt with the target composition. S3. Heat the alloyed magnesium alloy melt to 760-800℃ and perform refining and degassing treatment 1-3 times, 5-15 min / time, and remove the slag. S4. The magnesium alloy melt after refining and degassing is subjected to high pressure die casting under the process conditions of injection speed of 2-6m / s, mold temperature of 180-280℃ and casting temperature of 680-780℃. S5. After high pressure die casting, the magnesium alloy casting is held under pressure of 60-120MPa for 10-60s to obtain a high thermal conductivity and high temperature creep resistant cast magnesium alloy casting. S6. Demold the high thermal conductivity and high temperature creep resistant cast magnesium alloy casting after pressure holding and solidification, and stabilize it at 180-250℃ for 0.5-10h.

8. The preparation method according to claim 7, characterized in that, The alloy is preheated and dried at a temperature of 80-200℃ for 1-4 hours. The smelting temperature of the industrial pure Mg is 700-760℃; The protective atmosphere is either SF6 / CO2 or Ar.

9. The preparation method according to claim 7, characterized in that, The alloying treatment is as follows: After industrial pure Mg is completely melted, Mg-Al master alloy, Mg-La master alloy, Mg-Nd master alloy, Mg-Y master alloy, Mg-Zn master alloy, Mg-Mn master alloy, Mg-Se master alloy and Mg-Cu master alloy are added in sequence, and mechanical stirring is carried out for 5-20 minutes and held at the temperature for 15-60 minutes. The refining and degassing process is as follows: After heating the magnesium alloy melt to 760-800℃, high-purity Ar gas is introduced into it for rotary degassing and slag removal; the rotary degassing time is 5-15 min / time, the rotary degassing is repeated 1-3 times, and the slag removal is performed after each rotary degassing.

10. The preparation method according to claim 7, characterized in that, The holding and solidification pressure is 60-120 MPa, and the time is 10-60 s; The stabilization treatment temperature is 180-250℃, and the time is 0.5-10h.

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