High-strength high-thermal-conductivity magnesium alloy and preparation method thereof

Abstract

The high-strength and high-thermal-conductivity magnesium alloy and a preparation method thereof have the following components by weight percentage: Zn: 5.0-8.0%; Al: 0.5-3.0%, Cu: 0.5-3.0%, Zr: 0.1-1%; Mn: 0-1%, Sr: 0-1%, La: 0.5-3%, Ce: 0.5-3%, and the rest contains Mg and inevitable impurities. The present application solves the problem that the existing magnesium alloy cannot simultaneously consider high thermal conductivity and high strength; the thermal conductivity of the magnesium alloy is 125-135 W / (m*K), the yield strength is 192-216 MPa, and the elongation is 7-10%, and the magnesium alloy product with complex structure that cannot be manufactured by a deformation process can be manufactured. The preparation method is low in cost, convenient for large-scale production, and can be widely used in the preparation of heat dissipation / heat conduction components in the fields of aerospace, 3C products and automobile parts.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy material forming technology, and in particular to a high-strength, high-thermal-conductivity magnesium alloy and its processing method. Background Technology

[0002] Magnesium is the lightest metallic material commonly used in engineering applications, with a density of 1.738 g / cm³. 3 Magnesium, with a strength approximately 2 / 3 that of aluminum and 1 / 4 that of steel, possesses the advantages of high specific strength and high specific stiffness characteristic of structural materials. Furthermore, magnesium and magnesium alloys also exhibit the characteristics of functional materials such as high electromagnetic shielding effectiveness, good damping performance, and excellent thermal conductivity. They are considered a highly promising structural-functional integrated material, making magnesium and magnesium alloys a preferred material for lightweighting in aerospace, rail transportation, automotive parts, and 3C products.

[0003] The thermal conductivity of pure magnesium at room temperature is approximately 154.5 W / (m·K). However, when alloyed for use as a structural material, the thermal conductivity decreases significantly. For example, the thermal conductivity of commonly used die-cast magnesium alloys Mg-9Al-1Zn (AZ91) and Mg-6Al-0.5Mn (AM60) is 51.2 W / (m·K) and 60.6 W / (m·K), respectively. Another example is the commercially available as-cast Mg-6Zn-1Zr (ZK61) magnesium alloy, which has a thermal conductivity of 115 W / (m·K). Furthermore, the yield strength of these materials is mostly between 150-180 MPa, making it impossible to simultaneously possess both high mechanical properties and high thermal conductivity, increasingly failing to meet the high-performance requirements of magnesium alloy products.

[0004] Chinese patent CN109136699B discloses "a high thermal conductivity magnesium alloy, an inverter housing, an inverter, and an automobile," which prepares a Mg-Al-Zn-Mn-La-Ce-Nd-Sr-Cu cast magnesium alloy. This alloy has a thermal conductivity greater than 110 W / (m·K), but a yield strength less than 160 MPa and an elongation of 5%. Chinese patent CN111286658A discloses "a die-castable high thermal conductivity flame-retardant magnesium alloy and its preparation method," which prepares a Mg-Al-RE-Ca die-cast magnesium alloy. This alloy has a thermal conductivity greater than 120 W / (m·K) and a yield strength of 140–180 MPa. Both of the above alloys have high thermal conductivity, but their yield strength is not significantly improved compared to the commercial die-cast AZ91D. Chinese patent CN110195180A discloses "A high thermal conductivity die-cast magnesium alloy and its preparation method," which produces a Mg-Al-La-Sr-Mn die-cast magnesium alloy with a thermal conductivity of 108–122 W / (m·K), a yield strength greater than 190–210 MPa, and an elongation greater than 6–12%. This alloy exhibits excellent thermal conductivity and mechanical properties, but the addition of a large amount of rare earth elements results in a higher alloy cost.

[0005] Magnesium alloy forming processes are broadly classified into two categories: wrought and casting. Wrought magnesium alloys offer superior performance, but the process is complex, costly, and unable to produce magnesium alloy products with complex shapes. Compared to wrought processes, casting technologies such as die casting offer advantages such as lower manufacturing costs and the ability to form complex structures. However, die-cast products have higher internal porosity, leading to decreased mechanical properties. Furthermore, die casting cannot precisely manufacture ultra-thin-walled magnesium alloy products. Semi-solid thixotropic injection molding is a more promising magnesium alloy casting technology than die casting. It involves uniformly mixing a semi-solid magnesium alloy slurry and then spraying it into a mold to form the product. Compared to traditional die-cast magnesium alloy products, semi-solid thixotropic injection molded magnesium alloys have fewer internal defects, a denser microstructure, and superior mechanical and thermal conductivity. Additionally, its lower linear shrinkage ratio allows for the production of magnesium alloy products with a wider range of wall thicknesses.

[0006] Chinese patent CN109136699B discloses a "high thermal conductivity magnesium alloy, inverter housing, inverter, and automobile," which prepares a Mg-Al-Zn-Mn-La-Ce-Nd-Sr-Cu cast magnesium alloy with the following chemical composition by mass percentage: Al: 2.0–4.0%, Mn: 0.1–0.3%, La: 1.0–2.0%, Ce: 2.0–4.0%, Nd: 0.1–1%, Zn: 0.5–2%, Ca: 0.1–0.5%, Sr: 0.1%, Cu≤0.1%, and the remainder being Mg. This alloy has a thermal conductivity greater than 110 W / (m·K), but a yield strength less than 160 MPa and an elongation of 5%. Although it has high thermal conductivity, its low yield strength cannot meet the high strength, toughness, and high thermal conductivity requirements of heat dissipation system structural materials in aerospace devices and transportation vehicles.

[0007] Chinese patent CN111286658A discloses "a die-castable high thermal conductivity and flame retardant magnesium alloy and its preparation method," which produces a Mg-Al-RE-Ca die-cast magnesium alloy with the following chemical composition by mass percentage: Al: 2.5–4.5%, La or Ce: 2.0–6.0%, Sm or Y: 0.05–0.5%, Ca: 0.01–0.45%, and the remainder being Mg. This alloy has a thermal conductivity greater than 120 W / (m·K) and a yield strength of 140–180 MPa. While this alloy exhibits excellent thermal conductivity, its mechanical properties are not significantly superior to those of the conventional die-cast magnesium alloy AZ91. Furthermore, the addition of a large amount of rare earth elements results in a high alloy cost.

[0008] Chinese patent CN110195180 A discloses "a high thermal conductivity die-cast magnesium alloy and its preparation method," which produces a Mg-Al-La-Sr-Mn die-cast magnesium alloy with the following chemical composition by mass percentage: Al: 5-7%, La: 5-8%, Sr: 0.3-1%, Mn: 0.2-0.5%, with the remainder being Mg and unavoidable impurity elements. This alloy exhibits a thermal conductivity of 108-122 W / (m·K), a yield strength greater than 190-210 MPa, and an elongation greater than 6-12%. While the alloy demonstrates excellent thermal conductivity and mechanical properties, the addition of a large amount of rare earth elements results in a high alloy cost.

[0009] Existing technology, as documented in the published paper "Study on the Microstructure and Process of Semi-Solid Thixotropic Injection Molding of AZ91D Magnesium Alloy," prepared a Mg-Al-Zn semi-solid thixotropic injection molding alloy. Its chemical composition is 8.3% Al, 0.54% Zn, 0.14% Mn, with the remainder being Mg. This alloy has a thermal conductivity of less than 60 W / (m·K), its yield strength is not mentioned, and its elongation is approximately 8%. This alloy cannot simultaneously achieve excellent mechanical properties and thermal conductivity, thus limiting its application areas.

[0010] In recent years, the need for high-strength, high-thermal-conductivity magnesium alloys has become increasingly urgent. Products such as laptop casings, mobile phone casings, and automotive central display screen back panels require materials that balance excellent thermal conductivity and mechanical properties to ensure high operational stability and service life. These products typically have complex shapes and structures, and considering cost factors, die casting is an ideal choice. However, currently commonly used commercial die-cast magnesium alloys, such as AZ91D and AM60B, have thermal conductivity less than 70 W / (m·K) and yield strength less than 160 MPa, thus failing to simultaneously achieve both thermal conductivity and mechanical properties. Therefore, there is an urgent need to conduct research on new magnesium alloy composition design and new forming technologies to develop high-strength, high-thermal-conductivity magnesium alloy products. Summary of the Invention

[0011] The purpose of this invention is to provide a high-strength, high-thermal-conductivity magnesium alloy and its preparation method, solving the problem that existing magnesium alloys cannot simultaneously achieve high thermal conductivity and high strength. The magnesium alloy has a thermal conductivity of 125-135 W / (m·K), a yield strength of 192-216 MPa, and an elongation of 7-10%. Moreover, it can manufacture magnesium alloy products with complex structures that cannot be manufactured by deformation processes. This process is low-cost, easy to scale up for mass production, and can be widely used in the preparation of heat dissipation / thermal conduction components in the fields of aerospace, 3C products, and automotive parts.

[0012] To achieve the above objectives, the technical solution of the present invention is as follows:

[0013] A high-strength, high-thermal-conductivity magnesium alloy has the following composition by weight percentage: Zn: 5.0–8.0%; Al: 0.5–3.0%; Mn: 0–1%; Sr: 0–1%; La: 0.5–3%; Ce: 0.5–3%; with the balance being Mg and unavoidable impurities.

[0014] A high-strength, high-thermal-conductivity magnesium alloy has the following composition by weight percentage: Zn: 5.0–8.0%; Cu: 0.5–3.0%; Zr: 0.1–1%; Mn: 0–1%; Sr: 0–1%; La: 0.5–3%; Ce: 0.5–3%; with the balance being Mg and unavoidable impurities.

[0015] The magnesium alloy described in this invention has a thermal conductivity of 125–135 W / (m·K), a yield strength of 192–216 MPa, and an elongation of 7–10%.

[0016] In the composition design of the high-strength, high-thermal-conductivity magnesium alloy described in this invention:

[0017] The strengthening mechanisms of the mechanical properties of magnesium alloys are mainly solid solution strengthening, second-phase strengthening, and grain refinement strengthening. Solid solution strengthening and second-phase strengthening improve mechanical properties by introducing dissimilar elements into the Mg matrix. However, the introduction of dissimilar elements reduces the thermal conductivity of magnesium alloys. Generally, the negative impact of dissimilar elements as solid-solution atoms on the thermal conductivity of magnesium alloys is much greater than their impact as second-phase elements. Furthermore, the effects of different dissimilar elements dissolved in the magnesium alloy matrix on its thermal conductivity vary.

[0018] The first compositional design of this invention employs a Mg-Zn-Al design. By adding Zn, a solid-solution element with minimal negative impact on thermal conductivity, the mechanical properties of the magnesium alloy are improved through solid-solution strengthening. The addition of Al reduces the tendency for hot cracking in semi-solid thixotropic injection-molded products. Simultaneously, Al forms a second phase with Mn, La, Ce, and Sr to further enhance the mechanical properties of the magnesium alloy, and the presence of this second phase significantly reduces its negative impact on the material's thermal conductivity. By controlling the types and contents of alloying elements, the material achieves both high strength and high thermal conductivity.

[0019] Zn exhibits solid solution strengthening in magnesium, and the Mg-Zn second phase formed with Mg also provides significant second-phase strengthening. Zn is also a weak grain refiner, resulting in a finer microstructure and thus improving the mechanical properties of magnesium alloys. When Zn exists in Mg as solid-solution atoms, its negative impact on the thermal conductivity of magnesium alloys is relatively small. Therefore, high thermal conductivity magnesium alloys can be developed based on the Mg-Zn system.

[0020] Furthermore, studies have found that when the Zn content is less than 3%, the semi-solid thixotropic injection-molded magnesium alloy exhibits a severe tendency for hot cracking and poor flowability of the semi-solid slurry, resulting in poor mechanical properties. Adding excessive Zn can easily form a coarse network-like second phase in the magnesium alloy, deteriorating the material's toughness and plasticity, while also reducing its thermal conductivity. Therefore, the Zn content in this invention is 5–8%.

[0021] Al also exhibits significant solid solution strengthening effects in Mg; however, Al existing in solid solution atomic form significantly reduces the thermal conductivity of magnesium alloys. This invention addresses this issue by controlling the content of each element to allow Al to form Al groups with La, Ce, Sr, and Mn. 11 La3, Al 11 The second phases Ce3, Al4Sr, and Al8Mn5 not only improve the mechanical properties of magnesium alloys but also have a relatively small negative impact on thermal conductivity when present as second phases. Furthermore, Al can reduce the two-phase temperature range of Mg-Zn alloys, improve the fluidity of semi-solid slurries, and reduce the tendency of magnesium alloys to hot crack. In this invention, the percentage content of Al is 0.5%–3%.

[0022] Mn can refine the microstructure of magnesium alloys, while controlling the Fe content can improve corrosion resistance. Furthermore, the appropriate amount of the second phase Al8Mn5 formed by Mn and Al can further improve the mechanical properties of magnesium alloys. A small amount of Mn has a minimal negative impact on the thermal conductivity of magnesium alloys and reduces the tendency for hot cracking in as-cast magnesium alloys; therefore, the percentage of Mn in this invention does not exceed 1%.

[0023] La and Ce are inexpensive rare earth elements that can refine the microstructure of magnesium alloys and purify the alloy melt. Especially beneficial is the rare earth second phase Al formed with Al. 11 La3, Al 11 Ce3 can significantly improve the mechanical properties of magnesium alloys. By controlling the formation of second phases of Al, La, and Ce in magnesium alloys, the negative impact of each element on thermal conductivity can be reduced, thus ensuring that the magnesium alloy possesses both excellent thermal conductivity and mechanical properties. Adding too much La and Ce will increase material costs and reduce thermal conductivity; therefore, the mass percentage of La and Ce in this invention is 0.5% to 3%.

[0024] A small amount of Sr can significantly refine the grain size of magnesium alloys, especially when the alloy contains Al. The formed Al-Sr second phase not only refines the grain size of the magnesium alloy but also acts as a second-phase strengthening agent. The Al-Sr second phase allows Al to exist in the magnesium alloy in a second-phase form, reducing the negative impact of Al on the thermal conductivity of the magnesium alloy. Therefore, the mass percentage of Sr in this invention does not exceed 1%.

[0025] The second composition design scheme of this invention adopts a Mg-Zn-Cu-Zr design. By adding Zn, a solid solution element with minimal negative impact on thermal conductivity, the mechanical properties of the magnesium alloy are improved through solid solution strengthening. Cu has minimal negative impact on thermal conductivity and reduces the hot cracking tendency of semi-solid thixotropic injection molded products. It also forms a Mg-Zn-Cu second phase with Mg and Zn to improve the mechanical properties of the material. Zr can significantly refine the grains and improve the mechanical properties of the magnesium alloy. By controlling the type and content of alloying elements, the material can possess both high strength and high thermal conductivity.

[0026] Zn exhibits solid solution strengthening in magnesium, and the Mg-Zn second phase formed with Mg also provides significant second-phase strengthening. Zn is also a weak grain refiner, resulting in a finer microstructure and thus improving the mechanical properties of magnesium alloys. When Zn exists in Mg as solid-solution atoms, its negative impact on the thermal conductivity of magnesium alloys is relatively small. Therefore, high thermal conductivity magnesium alloys can be developed based on the Mg-Zn system.

[0027] Furthermore, studies have found that when the Zn content is less than 3%, the semi-solid thixotropic injection-molded magnesium alloy exhibits a severe tendency for hot cracking and poor flowability of the semi-solid slurry, resulting in poor mechanical properties. Adding excessive Zn can easily form a coarse network-like second phase in the magnesium alloy, deteriorating the material's toughness and plasticity, while also reducing its thermal conductivity. Therefore, the Zn content in this invention is 5–8%.

[0028] When Cu is dissolved in Mg, its negative impact on thermal conductivity is relatively small. Simultaneously, it can reduce the hot cracking tendency of Mg-Zn alloys and improve the fluidity of semi-solid slurries. Furthermore, Cu forms a MgZnCu second phase with Mg and Zn, further improving the mechanical properties of magnesium alloys while maintaining thermal conductivity. Excessive Cu will reduce the corrosion resistance of magnesium alloys; therefore, the Cu content in this invention is 0–3%.

[0029] The addition of Zr significantly refines the grain size in Mg-Zn alloys, thereby improving the mechanical properties of magnesium alloys through grain refinement strengthening. A small amount of Zr added will not have a significant impact on the thermal conductivity of magnesium alloys. Therefore, the mass percentage of Zr in this invention does not exceed 1%.

[0030] Mn can refine the microstructure of magnesium alloys, while controlling the Fe content can improve corrosion resistance. Small amounts of Mn have a minimal negative impact on the thermal conductivity of magnesium alloys and reduce the tendency for hot cracking in as-cast magnesium alloys; therefore, the percentage of Mn in this invention does not exceed 1%.

[0031] La and Ce are inexpensive rare earth elements that can refine the microstructure of magnesium alloys and purify the alloy melt. The rare earth second phase Mg forms with Mg. 12 La, Mg12 Ce can significantly improve the mechanical properties of magnesium alloys. By controlling the formation of a second phase of La and Ce in magnesium alloys, their negative impact on thermal conductivity can be reduced, thus ensuring that the magnesium alloy possesses both excellent thermal conductivity and mechanical properties. Adding too much La and Ce will increase material costs and reduce thermal conductivity; therefore, the mass percentage of La and Ce in this invention is 0.5% to 3%.

[0032] A small amount of Sr can significantly refine the grain size of magnesium alloys, thereby playing a role in grain refinement and strengthening and optimizing the mechanical properties of magnesium alloys. A small amount of Sr has little negative impact on the thermal conductivity of magnesium alloys. Therefore, the mass percentage of Sr in this invention does not exceed 1%.

[0033] In this invention, controlling the Zn content to 5-8% results in good fluidity of the semi-solid slurry and a lower tendency for hot cracking. It also avoids the deterioration of material properties by the coarse network of Mg-Zn second phase. Al and Cu elements significantly improve the fluidity of the semi-solid slurry and reduce the tendency for hot cracking. By controlling the content of La, Ce, Sr, and Mn elements, they can form a second phase with Al, improving the mechanical properties of the material and reducing the negative impact on thermal conductivity. Zr significantly refines the grain size of the Mg-Zn alloy, improving the material's mechanical properties. Precise control of the content of each element in Mg improves the mechanical properties of the magnesium alloy while minimizing the negative impact of dissimilar elements on the thermal conductivity. Simultaneously, it ensures good compatibility between the alloy and semi-solid thixotropic injection molding technology, maximizing the advantages of semi-solid thixotropic injection molding, and ultimately producing a semi-solid thixotropic injection molded magnesium alloy product that balances thermal conductivity and mechanical properties.

[0034] This invention solves the problem of existing magnesium alloys being unable to simultaneously achieve high thermal conductivity and high strength without adding large amounts of expensive rare earth elements. The resulting magnesium alloy has a thermal conductivity of 125–135 W / (m·K), a yield strength of 192–216 MPa, and an elongation of 7–10%. Furthermore, this invention employs semi-solid thixotropic injection molding technology, resulting in products with significantly superior performance compared to die-cast magnesium alloys. It can also manufacture complex magnesium alloy products that cannot be produced by deformation processes. This process is low-cost, facilitates large-scale mass production, and can be widely used in the manufacture of heat dissipation / thermal conduction components for aerospace, 3C products, and automotive parts.

[0035] The method for preparing the high-strength, high-thermal-conductivity magnesium alloy of the present invention includes the following steps:

[0036] 1) Ingredients

[0037] The raw materials are pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-La, Mg-Ce and Mg-Sr master alloys, and are formulated according to the above composition.

[0038] 2) Smelting

[0039] Pure Mg ingots are placed in a crucible of a melting furnace and heated to 700–720°C. Under the protection of a mixed protective gas of CO2 and SF6, they are completely melted to form a melt. Then, the temperature is raised to 750–770°C, and one or more of the following are added to the melt in sequence: pure Zn ingots, pure Al ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-La, Mg-Ce, and Mg-Sr master alloys. After the alloys are completely melted, the mixture is stirred for 15–20 minutes, and then magnesium alloy flux is added for refining for 10–15 minutes to remove surface slag. Finally, the mixture is held at 720–760°C for 20–30 minutes and cast into a magnesium alloy ingot.

[0040] 3) Machining of magnesium alloy particles

[0041] Magnesium alloy ingots are placed in a granulator and processed into magnesium alloy particles.

[0042] 4) Semi-solid thixotropic injection molding

[0043] Magnesium alloy particles are placed in the barrel of a semi-solid thixotropic injection molding machine and heated to 560–620°C to form a semi-solid magnesium alloy slurry. Simultaneously, a screw shearing device is used to apply shearing force to the semi-solid slurry, and the screw speed is controlled at 200–250 r / min. After shearing, the semi-solid magnesium alloy slurry is injected into a mold to form a semi-solid metal part at an injection speed of 2–5 m / s. The mold temperature is 300–350°C, and the mold vacuum degree is 30–100 mbar.

[0044] Preferably, in step 2), the magnesium alloy flux is RJ-4 flux, RJ-5 flux, or RJ-6 flux, with RJ-5 flux being preferred.

[0045] Preferably, in step 3), the particle size of the magnesium alloy particles is 0.5 to 1.2 mm.

[0046] Preferably, in step 4), the solid fraction of the semi-solid slurry is controlled at 20%–60% by volume.

[0047] In the processing method of the high-strength, high-thermal-conductivity magnesium alloy described in this invention:

[0048] Compared with existing die-cast magnesium alloys, this invention employs a semi-solid thixotropic injection molding process, resulting in magnesium alloys with high density and low porosity. Therefore, their mechanical and thermal properties are significantly improved, and they can be used to produce magnesium alloy products with more complex shapes. The semi-solid thixotropic molding technology requires that the alloy semi-solid slurry have sufficient fluidity to fill complex mold cavities, while also having a low tendency for hot cracking to ensure that the material has a dense microstructure and excellent mechanical properties.

[0049] In this invention, the barrel temperature is set at 560–620°C and the solid fraction of the semi-solid slurry is 20–60%. At this solid fraction, the semi-solid slurry exhibits good fluidity and reduces the tendency for thermal cracking during alloy filling, resulting in high mechanical and thermal conductivity properties. Excessively high barrel temperature leads to a low solid fraction and poor alloy properties, while excessively low barrel temperature results in a high solid fraction, poor fluidity of the semi-solid slurry, and incomplete filling of the mold. The injection speed is 2–5 m / s. Too low an injection speed prevents complete filling, while too high an injection speed results in high porosity, reducing both mechanical and thermal conductivity properties.

[0050] Control the screw speed at 200-250 r / min to ensure uniform distribution of solid and liquid phases in the semi-solid slurry.

[0051] The mold temperature is set at 300-350℃. Within this temperature range, the alloy fills completely, and defects such as cracks and pores are greatly reduced, giving the alloy excellent properties.

[0052] The mold vacuum setting range is 30-100 mbar, which reduces defects in the filled products and improves product performance.

[0053] The beneficial effects of this invention are:

[0054] The high-strength, high-thermal-conductivity magnesium alloy of this invention uses conventional alloying elements Zn, Al or Cu and Zr as basic elements, with small amounts of La, Ce, Mn and Sr added. The mechanical properties of the material are improved through solid solution strengthening, second-phase strengthening, and grain refinement strengthening. Simultaneously, by adding solid solution elements Zn and Cu, which have minimal impact on the thermal conductivity of the magnesium alloy, or by precisely controlling the ratio of alloying elements Al, La, Ce, Mn and Sr to ensure their existence as a second phase within the magnesium matrix, the alloy ultimately maintains high thermal conductivity. Furthermore, the addition of small amounts of inexpensive rare earth elements La and Ce minimizes material costs while maintaining performance. The magnesium alloy obtained by this invention simultaneously achieves high thermal conductivity and high mechanical properties, with a thermal conductivity ≥125 W / (m·K), yield strength ≥190 MPa, and elongation ≥7%.

[0055] This invention controls the content of Zn, Al, and Cu elements in the composition design and selects to add elements such as Sr, Zr, Mn, La, and Ce for multi-element alloying. While ensuring that the magnesium alloy has high mechanical and thermal conductivity, it also makes the semi-solid slurry of the alloy have good fluidity. This ensures that it can fill complex mold cavities when using semi-solid thixotropic injection molding process to manufacture magnesium alloy products with complex structures. At the same time, the prepared material has fewer defects such as porosity and hot cracks, and can be used to manufacture complex structural components for heat dissipation / heat conduction systems in aerospace electronic devices, 3C products, and transportation vehicles.

[0056] This invention employs semi-solid thixotropic injection molding technology. By controlling the barrel temperature, injection speed, stirring speed, mold temperature, and mold vacuum, it reduces defects such as porosity and cracks in the material while ensuring good fluidity of the semi-solid slurry, thus producing high-performance magnesium alloy products. These products outperform traditional die-cast magnesium alloys and have low processing costs, making them suitable for large-scale mass production. Detailed Implementation

[0057] The technical solution of the present invention will be described in detail below through embodiments. These embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0058] The composition of the magnesium alloy in this embodiment is shown in Table 1, with the balance including Mg and unavoidable impurities. The preparation process parameters for the embodiments are shown in Table 2, and Table 3 shows the performance parameters of the magnesium alloys in the embodiments.

[0059] Example 1

[0060] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 5.2wt% Zn, 0.5wt% Al, 1.0wt% Sr, 0.5wt% La, 0.5wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the materials are prepared according to the weight percentage of the magnesium alloy composition designed.

[0061] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 705℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 750℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 15 minutes, then add RJ-6 flux to refine for 15 minutes to remove surface slag. Finally, hold at 750℃ for 20 minutes and cast into magnesium alloy ingots.

[0062] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.5mm×1mm×6mm;

[0063] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 570°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 230 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 2 m / s. The mold temperature is 300°C. The mold vacuum degree is 55 mbar.

[0064] Example 2

[0065] 1) The high-ductility thermally conductive magnesium alloy is designed with the following composition: 7.9wt% Zn, 2.5wt% Al, 0.3wt% Mn, 0.7wt% Sr, 1.5wt% La, 1.6wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0066] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 715℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 770℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted molten material. After the alloys are completely melted, stir thoroughly for 18 minutes, then add RJ-4 flux to refine for 13 minutes to remove surface slag. Finally, hold at 755℃ for 25 minutes and cast into magnesium alloy ingots.

[0067] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.8mm×0.9mm×5.1mm;

[0068] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 565°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 250 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 4.3 m / s. The mold temperature is 330°C and the mold vacuum degree is 85 mbar.

[0069] Example 3

[0070] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 6wt% Zn, 1.5wt% Al, 1.0wt% Mn, 0.5wt% Sr, 1.1wt% La, 0.9wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La and Mg-Ce master alloys are used as raw materials, and the materials are prepared according to the weight percentage of the magnesium alloy composition designed.

[0071] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 706℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 765℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 15 minutes, then add RJ-6 flux to refine for 12 minutes to remove surface slag. Finally, hold at 750℃ for 22 minutes and cast into magnesium alloy ingots.

[0072] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.7mm×1.2mm×6mm;

[0073] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 605°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 245 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 5 m / s. The mold temperature is 310°C. The mold vacuum degree is 60 mbar.

[0074] Example 4

[0075] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 7.1wt% Zn, 2.9wt% Al, 0.2wt% Mn, 0.3wt% Sr, 2wt% La, 1.2wt% Ce, and the remainder Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0076] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 708℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 770℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 16 minutes, then add RJ-6 flux to refine for 15 minutes to remove surface slag. Finally, hold at 745℃ for 23 minutes and cast into magnesium alloy ingots.

[0077] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 1.2mm×1.2mm×4.5mm;

[0078] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 590°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 200 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 3.1 m / s. The mold temperature is 307°C. The mold vacuum degree is 100 mbar.

[0079] Example 5

[0080] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 5.0wt% Zn, 2.1wt% Al, 0.5wt% Mn, 0.1wt% Sr, 2.9wt% La, 0.8wt% Ce, and the remainder Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0081] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 700℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 750℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 16 minutes, then add RJ-5 flux to refine for 12 minutes to remove surface slag. Finally, hold at 730℃ for 30 minutes and cast into magnesium alloy ingots.

[0082] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.7mm×1.2mm×5mm;

[0083] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 620°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 205 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 4.5 m / s. The mold temperature is 335°C and the mold vacuum degree is 95 mbar.

[0084] Example 6

[0085] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 6.3wt% Zn, 3wt% Al, 0.9wt% Mn, 0.9wt% La, 2.5wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Mn, Mg-La, and Mg-Ce master alloys are used as raw materials, and the materials are prepared according to the weight percentage of the magnesium alloy composition designed.

[0086] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 705℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 755℃ and add pure Zn ingots, pure Al ingots, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 18 minutes, then add RJ-5 flux to refine for 11 minutes to remove surface slag. Finally, hold at 740℃ for 20 minutes and cast into magnesium alloy ingots.

[0087] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.9mm×0.9mm×5.5mm;

[0088] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 585°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 220 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 2.5 m / s. The mold temperature is 305°C and the mold vacuum degree is 30 mbar.

[0089] Example 7

[0090] 1) The high-strength, high-thermal-conductivity magnesium alloy is designed with the following composition: 5.1wt% Zn, 1wt% Cu, 0.3wt% Zr, 0.6wt% Mn, 0.6wt% La, 1.5wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0091] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 720℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 760℃ and add pure Zn ingots, pure Al ingots, Mg-Zr, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 15 minutes, then add RJ-5 flux to refine for 15 minutes to remove surface slag. Finally, hold at 730℃ for 25 minutes and cast into magnesium alloy ingots.

[0092] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.5mm×1.1mm×5.2mm;

[0093] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 600°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 210 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 3.8 m / s. The mold temperature is 320°C and the mold vacuum degree is 35 mbar.

[0094] Example 8

[0095] 1) The high-ductility thermally conductive magnesium alloy is designed with the following composition: 6.2wt% Zn, 2wt% Cu, 0.6wt% Zr, 0.1wt% Mn, 0.8wt% Sr, 0.7wt% La, 0.6wt% Ce, and the remainder is Mg. Pure Mg ingots, pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0096] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 700℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 755℃ and add pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 20 minutes, then add RJ-5 flux to refine for 15 minutes to remove surface slag. Finally, hold at 750℃ for 25 minutes and cast into magnesium alloy ingots.

[0097] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.7mm×0.8mm×6mm;

[0098] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 610°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 246 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 4.2 m / s. The mold temperature is 350°C and the mold vacuum degree is 90 mbar.

[0099] Example 9

[0100] 1) The high-ductility thermally conductive magnesium alloy is designed with the following composition: 8wt% Zn, 3.0wt% Cu, 1.0wt% Zr, 0.6wt% Sr, 1.2wt% La, 0.7wt% Ce, and the remainder Mg. Pure Mg ingots, pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0101] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 710℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 760℃ and add pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 20 minutes, then add RJ-5 flux to refine for 11 minutes to remove surface slag. Finally, hold at 760℃ for 25 minutes and cast into magnesium alloy ingots.

[0102] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.9mm×1.0mm×4.1mm;

[0103] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 560°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 215 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 4.9 m / s. The mold temperature is 325°C and the mold vacuum degree is 75 mbar.

[0104] Example 10

[0105] 1) The high-ductility thermally conductive magnesium alloy is designed with the following composition: 6.9wt% Zn, 0.5wt% Cu, 0.7wt% Zr, 0.8wt% Mn, 0.2wt% Sr, 1wt% La, 2wt% Ce, and the remainder Mg. Pure Mg ingots, pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys are used as raw materials, and the alloy is prepared according to the weight percentage of the magnesium alloy composition designed.

[0106] 2) Place pure Mg ingots into the crucible of the melting furnace, heat to 720℃, and completely melt under the protection of a mixed protective gas of CO2 and SF6. Then heat to 750℃ and add pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-Sr, Mg-La, and Mg-Ce master alloys to the melted liquid in sequence. After the alloys are completely melted, stir thoroughly for 17 minutes, then add RJ-5 flux to refine for 13 minutes to remove surface slag. Finally, hold at 725℃ for 28 minutes and cast into magnesium alloy ingots.

[0107] 3) Place the magnesium alloy ingot in a granulator to process magnesium alloy particles with a size of 0.7mm×1.2mm×5.8mm;

[0108] 4) Place the magnesium alloy particles into the barrel of the semi-solid thixotropic injection molding equipment and heat it to 595°C to make it a semi-solid slurry. At the same time, use a screw shearing device to apply shearing force to the semi-solid slurry. The screw speed is 240 r / min. After shearing, inject the magnesium alloy semi-solid slurry into the mold to form a semi-solid part. The injection speed is 4.1 m / s. The mold temperature is 340°C and the mold vacuum degree is 40 mbar.

[0109] Comparative Example 1

[0110] The magnesium alloy composition was selected as follows: 9 wt% Al, 1 wt% Zn, and the remainder Mg;

[0111] Using pure Mg ingots, pure Al ingots, and pure Zn ingots as raw materials, an alloy was designed with the above-mentioned element mass percentages. Pure Mg ingots were added to a crucible furnace under CO2+SF6 gas protection and heated to 725℃ until completely melted. The temperature was then increased to 750℃, and pure Al ingots and pure Zn ingots were added sequentially. After the alloy was completely melted, it was stirred thoroughly for 12 minutes, then RJ-5 flux was added for refining for 16 minutes to remove surface slag. The mixture was held at 750℃ for 20 minutes and then transferred to a die-casting machine holding furnace. Die casting was performed on a magnesium alloy die-casting machine at a melt temperature of 650℃ and a mold temperature of 300℃ to obtain AZ91D die-cast parts.

[0112] Comparative Example 2

[0113] The magnesium alloy composition was selected as follows: 6 wt% Al, 0.5 wt% Mn, and the remainder Mg;

[0114] Using pure Mg ingots, pure Al ingots, and Mg-Mn master alloy as raw materials, an alloy was designed with the above-mentioned element mass percentages. Pure Mg ingots were added to a crucible furnace under CO2+SF6 gas protection, and the temperature was raised to 725℃ until completely melted. The temperature was then increased to 760℃, and pure Al ingots and Mg-Mn master alloy were added sequentially. After the alloy was completely melted, it was stirred thoroughly for 15 minutes, then RJ-5 was added for refining for 18 minutes to remove surface slag. The mixture was then held at 750℃ for 20 minutes and finally cast into a magnesium alloy ingot. This ingot was then transferred to a die-casting machine holding furnace; die-casting was performed on a magnesium alloy die-casting machine at a melt temperature of 660℃ and a mold temperature of 290℃ to obtain AM60B die-cast parts.

[0115] Comparative Examples 1 and 2 used commercial grades AZ91D and AM60, respectively, and the molding process for these two alloy grades was the traditional die casting process. However, this invention employs the design principle of a high-strength, high-thermal-conductivity magnesium alloy, and the molding process is a semi-solid injection molding process.

[0116] As shown in Table 3, the thermal conductivity of the magnesium alloy of the present invention is ≥125W / (m·K), and the yield strength is ≥190MPa.

[0117] The magnesium alloy obtained by this invention has significantly improved yield strength and tensile strength, as well as thermal conductivity, compared with traditional AZ91D and AM60B magnesium alloys.

[0118] Traditional die-cast AZ91D and AM60B magnesium alloys use Al as the main alloying element to achieve solid solution strengthening and second-phase (Mg17Al12) strengthening to improve the strength of the material. At the same time, a small amount of Zn and Mn are added to further improve the comprehensive mechanical properties of the material. However, this strengthening effect is limited, and when Al is dissolved in the magnesium matrix, it significantly reduces the thermal conductivity of the material.

[0119] Furthermore, die-cast magnesium alloys have poor overall mechanical properties due to their high porosity and low density. As can be seen from the comparative examples in Table 3, both die-cast AZ91D and die-cast AM60B magnesium alloys have thermal conductivity less than 65 W / (m·K) and yield strength less than 155 MPa.

[0120] Table 1. Alloy Chemical Composition (Unit: Weight Percentage %)

[0121]

[0122]

[0123] Table 2 Semi-solid injection molding process parameters

[0124]

[0125] Table 3 Mechanical and thermal properties of the alloy

[0126]

Claims

1. A high-strength, high-thermal-conductivity magnesium alloy, comprising the following components by weight percentage: Zn: 5.0~8.0%; Al: 0.5~3.0%; Mn: 0~1%; Sr: 0~1%; La: 0.5~3%; Ce: 0.5~3%; with the balance being Mg and unavoidable impurities; wherein the magnesium alloy has a thermal conductivity of 125~135 W / (m·K), a yield strength of 192~216 MPa, and an elongation of 7~10%.

2. A high-strength, high-thermal-conductivity magnesium alloy, comprising the following components by weight percentage: Zn: 5.0~8.0%; Cu: 0.5~3.0%; Zr: 0.1~1%; Mn: 0~1%; Sr: 0~1%; La: 0.5~3%; Ce: 0.5~3%; with the balance being Mg and unavoidable impurities; the magnesium alloy having a thermal conductivity of 125~135 W / (m·K), a yield strength of 192~216 MPa, and an elongation of 7~10%.

3. The method for preparing high-strength, high-thermal-conductivity magnesium alloy as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Ingredients The raw materials are pure Mg ingots, pure Zn ingots, pure Al ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-La, Mg-Ce and Mg-Sr master alloys, and are formulated according to the composition described in claim 1 or 2. 2) Smelting Pure Mg ingots are placed in a crucible of a melting furnace and heated to 700-720°C. Under the protection of a mixed protective gas of CO2 and SF6, they are completely melted to form a melt. The temperature is then raised to 750-770°C, and pure Zn ingots, pure Al ingots, Mg-Mn, Mg-La, Mg-Ce, and Mg-Sr master alloys are added to the melt in sequence. Alternatively, pure Zn ingots, Mg-Cu, Mg-Zr, Mg-Mn, Mg-La, Mg-Ce, and Mg-Sr master alloys are added to the melt in sequence. After the alloys are completely melted, the mixture is stirred for 15-20 minutes, and then magnesium alloy flux is added for refining for 10-15 minutes. The mixture is then held at 720-760°C for 20-30 minutes and cast into magnesium alloy ingots. 3) Machining of magnesium alloy particles Magnesium alloy ingots are placed in a granulator and processed into magnesium alloy particles; the particle size of the magnesium alloy particles is 0.5~1.2mm. 4) Semi-solid thixotropic injection molding Magnesium alloy particles are placed in the barrel of a semi-solid thixotropic injection molding machine and heated to 560~620℃ to form a magnesium alloy semi-solid slurry. The solid fraction of the semi-solid slurry is controlled at 20~60% by volume. At the same time, a screw shearing device is used to apply shearing force to the semi-solid slurry, and the screw speed is controlled at 200~250 r / min. After shearing, the magnesium alloy semi-solid slurry is injected into a mold to form a semi-solid metal part. The injection speed is 2~5m / s. The mold temperature is 300~350℃. The mold vacuum degree is 30~100mbar.

4. The method for preparing high-strength, high-thermal-conductivity magnesium alloy as described in claim 3, characterized in that, In step 2), the magnesium alloy flux is RJ-4 flux, RJ-5 flux, or RJ-6 flux.

5. The method for preparing high-strength, high-thermal-conductivity magnesium alloy as described in claim 3, characterized in that, In step 2), the magnesium alloy flux is RJ-5 flux.

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