High-toughness and high-thermal-conductivity die-cast magnesium alloy and preparation method therefor

Abstract

A high-toughness and high-thermal-conductivity die-cast magnesium alloy and a preparation method therefor. The high-toughness and high-thermal-conductivity die-cast magnesium alloy comprises the following components in percentage by weight: Al: 2.5-4.0%, RE: 3.5-5.5%, Mn: 0.1-0.3%, Be: 0.002-0.003%, Ca: 0.1-1.0%, Gd: 0.05-0.3%, Re being one or two of La or Ce, and the balance comprising Mg and other inevitable impurities. The described elements need to simultaneously satisfy: 0.7≤Al / RE≤0.8. Introduction of a new acicular Al3RE second phase enables the mechanical properties of the material to be improved with a better second phase strengthening effect. Formation of the second phase reduces the adverse impact of the Al element on the thermal conductivity of a magnesium alloy, and also inhibits generation of brittle phase Mg17Al12 and prevents the thermal conductivity from being significantly reduced, thereby obtaining a magnesium alloy having both high thermal conductivity and high room-temperature mechanical properties. The obtained magnesium alloy has a room-temperature yield strength of 140-150 MPa, an elongation rate of 8-12%, and a thermal conductivity of 100-110 W / (m·K).

Description

A high-strength, high-toughness, high-thermal-conductivity die-cast magnesium alloy and its preparation method Technical Field

[0001] The present invention relates to the technical field of magnesium alloy materials, and in particular to a high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy and a preparation method thereof. Background Art

[0002] Cooling system structures for mobile phone midplanes, laptop computer cases, 5G base station housings, automotive headlight bases, and mobile energy storage devices require materials with not only low density and high strength, but also excellent thermal conductivity and heat dissipation properties. Magnesium alloys are the lowest-density metals currently used in engineering structures. They also possess excellent thermal conductivity, damping, and electromagnetic properties, making them considered highly promising materials for structural-functional integration. Due to their combination of lightweight features and excellent physical properties, magnesium alloys hold broad application prospects in the aforementioned 3C products and automotive parts sectors.

[0003] The thermal conductivity of pure magnesium at room temperature is about 154.5W / (m·K), but its yield strength is too low to be used as an engineering material. Deformed magnesium alloys have excellent mechanical properties, but conventional extrusion, rolling, and forging of magnesium alloys are expensive, and it is impossible to produce magnesium alloy products with complex structures and shapes. Therefore, more than 80% of magnesium alloy products are formed by die casting. Die casting is the most widely used magnesium alloy casting process. It has the advantages of low manufacturing cost and the ability to form complex structural products. Products such as 3C product housings, 5G base station housings, car headlight bases, mobile energy storage equipment, etc. require their materials to have excellent thermal conductivity / heat dissipation and mechanical properties while being lightweight to ensure high working stability and service life of the product. In addition, such products usually have complex external structures. Considering the cost factor, the die casting process is an ideal choice. The most commonly used die-cast magnesium alloy AZ91D (Mg-9Al-1Zn) is made by adding a certain amount of Al, Zn and other elements to pure magnesium to improve its mechanical properties. However, its thermal conductivity is significantly reduced, with a thermal conductivity of only 51.2W / (m·K), which is increasingly unable to meet the demand for magnesium alloy products. Therefore, there is an urgent need to carry out research on the composition design and forming technology of new magnesium alloys to develop high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy products.

[0004] Chinese patent CN105463280A discloses "a magnesium alloy with high thermal conductivity and its preparation method," producing a Mg-Al-RE-Mn die-cast magnesium alloy with the following chemical composition by weight: Al: 3.0-6.8%, Mn: 0.3-0.8%, mixed rare earth elements (La, Ce, Pr, and Nd): 2.8-4.8%, and the remainder Mg. The alloy has a thermal conductivity greater than 100 W / (m·K), but the patent does not mention the mechanical properties of the magnesium alloy.

[0005] Chinese patent CN107604228A discloses "High Thermal Conductivity and Corrosion-Resistant Die-Casting Magnesium Alloy and Preparation Method Thereof," producing a Mg-Al-Ce-Mn-Be die-cast magnesium alloy with the following chemical composition by weight: Ce: 3.5-5.0%, Al: 2.5-3.5%, Mn: 0.5%, Be: 0.05%, and the remainder Mg. The alloy has a thermal conductivity greater than 100 W / (m·K) and a tensile strength of 250-260 MPa. Key mechanical properties such as yield strength and elongation are not mentioned.

[0006] Chinese patent CN114351022A discloses "A high thermal conductivity magnesium alloy containing a high solid solubility rare earth element and its preparation method." The invention prepares a Mg-RE-Al cast magnesium alloy with the following chemical composition: RE: 4-16% (mass percent), Al: the atomic ratio of Al to RE is 0.3-4%, and the remainder is Mg. The alloy has a thermal conductivity of ≥100 W / (m·K). However, the alloy contains a large amount of the precious rare earth element Sm, which increases the cost, and the mechanical properties are not mentioned.

[0007] The die-cast magnesium alloy materials reported in the existing technology cannot simultaneously take into account high strength and toughness, high thermal conductivity and processing costs. Therefore, it is urgently necessary to carry out research on the composition design of new die-cast magnesium alloys and new forming technologies to develop new high-strength, toughness and high-thermal conductivity die-cast magnesium alloys to expand the application of magnesium alloys.

[0008] Summary of the Invention

[0009] The present invention aims to provide a high-strength, high-toughness, and high-thermal-conductivity die-cast magnesium alloy and a preparation method thereof. Without adding expensive rare earth elements or other alloying elements, a low-cost alloy formula is adopted to ensure that the alloy has good casting properties, thereby solving the problem that existing magnesium alloys cannot simultaneously achieve high mechanical properties and high thermal conductivity. The room-temperature thermal conductivity of the magnesium alloy is 100-110 W / (m·K), the room-temperature yield strength is 140-150 MPa, and the room-temperature elongation is 8-12%. The magnesium alloy can also be used to manufacture magnesium alloy products with complex structures. The process is low-cost and easy to scale up for mass production. The alloy can be widely used in heat dissipation / heat-conducting components in the fields of 3C products and automotive parts.

[0010] To achieve the above object, the technical solution of the present invention is:

[0011] A high-strength, high-toughness, and high-thermal-conductivity die-cast magnesium alloy, comprising the following components by weight: Al: 2.5-4.0%, RE: 3.5-5.5%, Mn: 0.1-0.3%, Be: 0.002-0.003%, Ca: 0.1-1.0%, Gd: 0.05-0.3%, RE being one or both of La and Ce, and the balance comprising Mg and other unavoidable impurities; and the above elements also need to meet the following requirements:

[0012] 0.7≤Al / RE≤0.8.

[0013] Preferably, the balance is Mg and other inevitable impurities.

[0014] The die-cast magnesium alloy matrix of the present invention is uniformly distributed with Al 11 RE3, Al2RE, Al2Ca, (Mg,Al)2Ca, Al2Gd and needle-shaped Al3RE second phase.

[0015] The room temperature yield strength of the die-cast magnesium alloy of the present invention is 140-150 MPa, the elongation is 8-12%, and the thermal conductivity is 100-110 W / (m·K).

[0016] Al is the most commonly used alloying element in magnesium alloys, and Mg-Al alloys have good casting properties. However, the atomic volume of Al is smaller than that of Mg. As Al atoms dissolve in Mg, the lattice volume gradually decreases. The smaller the lattice volume, the greater the possibility of free electron scattering, and the more obvious the negative effect on thermal conductivity. In addition, the difference in valence electrons between Al atoms and Mg atoms also leads to a significant reduction in the thermal conductivity of magnesium alloys when Al dissolves in Mg. For example, the thermal conductivity of the commercial die-cast magnesium alloy AZ91D is only 51.2W / (m·K).

[0017] In the present invention, elements such as La, Ce, Ca and Gd having strong affinity with Al are added to form Al 11 RE3, Al2RE, Al2Ca, (Mg,Al)2Ca, Al2Gd second phase, and introduced a new needle-shaped Al3RE second phase, which is slightly larger than Al 11 The smaller RE3 second phase exhibits a superior second-phase strengthening effect, significantly improving the material's mechanical properties. These second phases not only enhance the material's mechanical properties but also consume the Al element in the Mg matrix, increasing the lattice volume and reducing the likelihood of free electron scattering. This prevents the decrease in thermal conductivity caused by Al solid solution in the magnesium alloy. This allows the magnesium alloy to achieve both high mechanical and thermal conductivity.

[0018] In Mg-Al alloys, when the Al content is less than 2.5%, the die-casting performance is affected and the fluidity of the magnesium melt is poor; when the Al content is higher than 4%, the thermal conductivity is significantly reduced. Therefore, in the present invention, the Al content is controlled at 2.5-4.0%.

[0019] La and Ce form a large amount of Al with Al 11RE3 second phase and a small amount of Al2RE second phase, wherein the added Al and RE elements are controlled to meet 0.7≤Al / RE≤0.8, so that Al and RE are in the form of fine lamellar Al 11 RE3, very fine needle-like Al3RE second phase and granular Al2RE second phase exist in the original Al 11 On the basis of the existence of RE3 and Al2RE second phases, the introduction of the new second phase Al3RE has a more excellent second phase strengthening effect and significantly improves the mechanical properties of the material. 11 The formation of RE3, Al3RE and Al2RE second phases largely avoids the presence of Al in the magnesium alloy in the form of solid solution atoms, reduces the negative impact of Al on the thermal conductivity of the magnesium alloy, and thus does not lead to a decrease in the thermal conductivity of the material, ensuring that the magnesium alloy has both excellent thermal conductivity and mechanical properties. The cheap rare earth elements La and Ce also have the function of purifying the magnesium alloy melt. Too little La and Ce elements cannot form enough Al-RE second phases to improve material properties. When La and Ce are added in excess of 5.5%, the die-casting performance of the magnesium alloy is significantly reduced, the melt fluidity deteriorates, and too much RE will also increase the material cost. Therefore, in the present invention, the amount of RE (La and Ce) is controlled at 3.5 to 5.5%.

[0020] The fine dispersed Al2Ca second phase and (Mg,Al)2Ca second phase formed by the Ca element and Al in the Mg-Al alloy can significantly improve the room temperature mechanical properties of the magnesium alloy, while ensuring that the material has excellent plasticity and toughness. In addition, the presence of the second phase Al2Ca in the magnesium alloy does not significantly reduce the thermal conductivity of the material. In addition, Ca also has the effect of anti-oxidation and flame retardancy in the magnesium alloy, which inhibits the oxidation of the surface of the magnesium alloy melt during die casting and greatly reduces the inclusions in the die-cast magnesium alloy. However, too much Ca element will reduce the fluidity of the magnesium solution during die casting, increase the tendency to hot cracking and brittleness, and reduce the mechanical properties of the material. Therefore, in the present invention, the Ca element content is controlled at 0.1 to 1.0%.

[0021] Mn has an extremely low solid solubility in magnesium alloys, effectively reducing the content of harmful elements such as Fe, Cu, and Ni in magnesium alloys, thereby improving their corrosion resistance. Furthermore, an appropriate amount of Mn refines the as-cast structure of magnesium alloys, improving the material's plasticity and toughness while also having a minimal negative impact on thermal conductivity. However, adding more than 0.3% Mn in the present invention reduces the grain refinement effect. Therefore, the Mn content is controlled within a range of 0.1 to 0.3%.

[0022] Be has a greater affinity for oxygen than Mg. A very small amount of Be can form a dense oxide film on the surface of a magnesium alloy melt, preventing oxidation. When the Be content is less than 0.002%, the degree of oxidation of the magnesium alloy solution significantly increases. When the Be content exceeds 0.003%, the material's microstructure becomes significantly coarser, and mechanical properties degrade. Therefore, in the present invention, the Be content is controlled between 0.002 and 0.003%, reducing slag and inclusions in the magnesium alloy solution, improving the material's mechanical properties while preventing inclusions and oxides from reducing the material's thermal conductivity.

[0023] When Gd is added to Mg-Al alloy, a large amount of network Mg is precipitated at the grain boundaries of conventional Mg-Al alloy during solidification. 17 Al 12 The second phase distributed at the grain boundary seriously destroys the periodic arrangement of the magnesium matrix lattice and scatters the free electrons, thereby reducing the thermal conductivity of the material. The addition of Gd element in the present invention can form Al2Gd second phase with Al element, thereby inhibiting the brittle phase Mg 17 Al 12 The formation of Gd can avoid a significant decrease in thermal conductivity. The Al2Gd phase formed at the same time has a significant strengthening effect, which improves the strength of the magnesium alloy without significantly reducing the plasticity of the material. In addition, the Al2Gd phase can also promote the heterogeneous nucleation process, increase the nucleation rate during die casting solidification, and refine the grain size and microstructure. Too little Gd element in magnesium alloy cannot play a strengthening effect and inhibit the growth of Mg. 17 Al 12 Too much Gd addition will reduce the die casting performance of magnesium alloy. Therefore, in the present invention, the Gd content is controlled at 0.05-0.3%.

[0024] Therefore, the present invention obtains a die-cast magnesium alloy with both high strength and high toughness by controlling the composition while ensuring that the magnesium alloy has excellent casting properties.

[0025] The method for preparing the high-strength, toughness and high-thermal-conductivity die-cast magnesium alloy of the present invention comprises the following steps:

[0026] 1) Ingredients

[0027] Pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder and Mg-Ca, Mg-Gd, Al-Be master alloys are used as raw materials and the ingredients are prepared according to the above magnesium alloy composition;

[0028] 2) Melting

[0029] A pure Mg ingot is placed in a crucible, heated to 680-710°C, and completely melted under protective gas protection. Then, a pure Al ingot and pure Mn powder are added, and stirred under a protective atmosphere until the alloy is completely melted. Then, the temperature is raised to 740-750°C, and a pure La ingot and a pure Ce ingot are added in sequence. The alloy is stirred under a protective atmosphere until it is completely melted. Then, the temperature is lowered to 690-710°C, and Al-Be, Mg-Ca and Mg-Gd master alloys are added to the melt. After the master alloy is completely melted, the mixture is stirred for 5-10 minutes to obtain a magnesium alloy melt.

[0030] 3) Refining

[0031] Adding magnesium alloy flux to the obtained magnesium alloy melt, refining for 5 to 10 minutes, removing surface scum, and then heating to 700 to 720° C. and keeping the temperature for 10 to 15 minutes;

[0032] 4) Molding

[0033] The refined magnesium alloy melt is cast into an ingot, which is then placed in a die-casting machine furnace and melted at 680-700°C. The melt enters the mold through an injection system for filling, wherein the mold temperature is 200-250°C, the casting pressure is 100-110 MPa, and the injection speed is 3-5 m / s.

[0034] Preferably, in step 3), the magnesium alloy flux is RJ-2 flux and RJ-3 flux.

[0035] Preferably, in step 2), the protective gas is a mixed gas of CO2+SF6.

[0036] Preferably, in step 4), the pouring temperature is 680-700°C.

[0037] In the die-casting process of the present invention, the furnace temperature is controlled at 680-700°C, ensuring that the magnesium alloy solution has good fluidity and filling properties while avoiding the formation of coarse dendrites in the material that affect the mechanical properties of the material. When the temperature is lower than 680°C, the fluidity of the magnesium alloy solution deteriorates and defects appear on the surface of the filled product. When the temperature is higher than 700°C, coarse dendrites appear in the microstructure of the filled product, and the mechanical properties of the material are reduced.

[0038] The mold temperature is controlled between 200 and 250°C. Within this temperature range, the alloy fills completely, defects such as cracks and pores are significantly reduced, and the material has excellent mechanical properties. When the temperature is below 200°C, the large temperature difference between the high-temperature melt and the mold temperature causes surface defects in the filled product and reduces the plasticity of the product. When the mold temperature exceeds 250°C, the fine grain area on the product surface decreases, and the mechanical properties are reduced.

[0039] The casting pressure is 100-110 MPa to ensure normal filling of the product, making the material's microstructure dense, and having excellent mechanical properties and thermal conductivity.

[0040] The injection speed is controlled at 3-5m / s. If the injection speed is too low, the material cannot be completely filled into the mold. If the injection speed is too high, the porosity of the material is high, and the mechanical properties and thermal conductivity will be reduced.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The high strength, toughness and thermal conductivity magnesium alloy of the present invention is added with Al, La, Ce, Ca and Gd elements in the magnesium matrix to form Al 11 RE3, Al2RE, Al2Ca, (Mg,Al)2Ca, Al2Gd second phases. At the same time, the added Al and RE elements are controlled to meet 0.7≤Al / RE≤0.8, and a new needle-shaped Al3RE second phase is introduced to improve the mechanical properties of the material with a more excellent second phase strengthening effect. Moreover, the formation of these second phases greatly avoids the existence of Al in the form of solid solution atoms in the magnesium alloy, reducing the negative impact of the Al element on the thermal conductivity of the magnesium alloy, thereby not causing a decrease in the thermal conductivity of the material. Combined with the addition of the Gd element and the Al element to form the Al2Gd second phase, thereby suppressing the brittle phase Mg 17 Al 12 The formation of MgO avoids a significant decrease in thermal conductivity, thereby obtaining a magnesium alloy with both high thermal conductivity and high room temperature mechanical properties.

[0043] The alloying elements added in this invention ensure both material performance and die-casting manufacturability. Based on the compositional design, the appropriate furnace temperature, mold temperature, casting pressure, and injection speed are matched simultaneously, resulting in excellent fluidity and mold filling during die-casting of the magnesium alloy. The resulting product has a dense, defect-free microstructure and a low process cost, enabling large-scale production of complex structural components such as 3C housings and automotive parts.

[0044] The room temperature thermal conductivity of the magnesium alloy obtained by the invention is 100-110 W / (m·K), the room temperature yield strength is 140-150 MPa, and the room temperature elongation is 8-12%. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is described in detail below through examples. This example is implemented under the premise of the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following examples.

[0046] The composition of the magnesium alloy in the embodiment of the present invention is shown in Table 1, and the rest is Mg and other inevitable impurities.

[0047] Example 1

[0048] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0049] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 700°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 740°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 710°C, and adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 5 minutes, then adding a magnesium alloy flux RJ-2 and refining for 10 minutes to remove surface scum, and finally holding the temperature at 700°C for 15 minutes to cast it into a magnesium alloy ingot;

[0050] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 680°C. The melt entered the mold through the injection system for filling. The mold temperature was 216°C, the casting pressure was 105 MPa, and the injection speed was 3.5 m / s.

[0051] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0052] Example 2

[0053] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0054] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 690°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt. Subsequently, pure Al ingots and pure Mn powder were added and stirred under a protective atmosphere until the alloy was completely melted. The temperature was then raised to 741°C, and pure La ingots and pure Ce ingots were added in sequence under a protective atmosphere and stirred until the alloy was completely melted. The mixture was allowed to stand and cool to 700°C before adding Al-Be, Mg-Ca, and Mg-Gd master alloys to the melt. After the alloy was completely melted, the mixture was stirred for 6 minutes, and then magnesium alloy flux RJ-3 was added and refined for 7 minutes to remove surface scum. Finally, the mixture was kept at 710°C for 12 minutes and cast into a magnesium alloy ingot.

[0055] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 692°C. The melt entered the mold through the injection system for filling. The mold temperature was 220°C, the casting pressure was 100 MPa, and the injection speed was 3 m / s.

[0056] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0057] Example 3

[0058] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0059] 2) placing a pure Mg ingot into a crucible of a smelting furnace, heating it to 710°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 750°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 705°C, and then adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 10 minutes, then adding a magnesium alloy flux RJ-2 and refining for 10 minutes to remove surface scum, and finally holding the temperature at 705°C for 11 minutes to cast it into a magnesium alloy ingot;

[0060] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 700°C. The melt entered the mold through the injection system for filling. The mold temperature was 239°C, the casting pressure was 101 MPa, and the injection speed was 4 m / s.

[0061] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0062] Example 4

[0063] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0064] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 695°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt. Subsequently, adding a pure Al ingot and pure Mn powder, stirring under the protective atmosphere until the alloy is completely melted, then heating it to 749°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under the protective atmosphere until the alloy is completely melted. After standing and cooling to 708°C, Al-Be, Mg-Ca, and Mg-Gd master alloys are added to the melt. After the alloy is completely melted, stirring is performed for 10 minutes, and then magnesium alloy flux RJ-3 is added and refined for 9 minutes to remove surface scum. Finally, the melt is kept at 710°C for 15 minutes and cast into a magnesium alloy ingot;

[0065] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 695°C. The melt entered the mold through the injection system for filling. The mold temperature was 250°C, the casting pressure was 110 MPa, and the injection speed was 3.3 m / s.

[0066] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0067] Example 5

[0068] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0069] 2) placing a pure Mg ingot into a crucible of a smelting furnace, heating it to 705°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 748°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 706°C, and adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 10 minutes, then adding a magnesium alloy flux RJ-2 and refining for 10 minutes to remove surface scum, and finally holding the temperature at 720°C for 10 minutes to cast it into a magnesium alloy ingot;

[0070] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 688°C. The melt entered the mold through the injection system for filling. The mold temperature was 208°C, the casting pressure was 108 MPa, and the injection speed was 4.3 m / s.

[0071] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0072] Example 6

[0073] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0074] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 680°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 745°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 690°C, and adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 5 minutes, then adding a magnesium alloy flux RJ-2 and refining for 5 minutes to remove surface scum, and finally holding the temperature at 705°C for 11 minutes to cast it into a magnesium alloy ingot;

[0075] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 690°C. The melt entered the mold through the injection system for filling. The mold temperature was 200°C, the casting pressure was 109 MPa, and the injection speed was 5 m / s.

[0076] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0077] Example 7

[0078] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0079] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 700°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 743°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 695°C, and adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 8 minutes, then adding a magnesium alloy flux RJ-2 and refining for 8 minutes to remove surface scum, and finally holding the temperature at 713°C for 11 minutes to cast it into a magnesium alloy ingot;

[0080] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 695°C. The melt entered the mold through the injection system for filling. The mold temperature was 226°C, the casting pressure was 102 MPa, and the injection speed was 4.6 m / s.

[0081] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0082] Example 8

[0083] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0084] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 690°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 744°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 705°C, and then adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 7 minutes, then adding a magnesium alloy flux RJ-2 and refining for 7 minutes to remove surface scum, and finally holding the temperature at 720°C for 15 minutes to cast it into a magnesium alloy ingot;

[0085] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 698°C. The melt entered the mold through the injection system for filling. The mold temperature was 239°C, the casting pressure was 103 MPa, and the injection speed was 3.1 m / s.

[0086] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0087] Example 9

[0088] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0089] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 710°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 746°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 694°C, and then adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 7 minutes, then adding a magnesium alloy flux RJ-2 and refining for 6 minutes to remove surface scum, and finally holding the temperature at 715°C for 11 minutes to cast it into a magnesium alloy ingot;

[0090] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 685°C. The melt entered the mold through the injection system for filling. The mold temperature was 203°C, the casting pressure was 104 MPa, and the injection speed was 3.9 m / s.

[0091] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0092] Example 10

[0093] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0094] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 705°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 747°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 698°C, and then adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 5 minutes, then adding a magnesium alloy flux RJ-2 and refining for 5 minutes to remove surface scum, and finally holding the temperature at 718°C for 15 minutes to cast it into a magnesium alloy ingot;

[0095] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 689°C. The melt entered the mold through the injection system for filling. The mold temperature was 245°C, the casting pressure was 106 MPa, and the injection speed was 4.8 m / s.

[0096] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0097] Comparative Examples 1 and 2 respectively use commercial grades AZ91D and AM60, which are formed by conventional die-casting. The present invention, on the other hand, adopts the design principle of high-strength, high-toughness, and high-thermal-conductivity magnesium alloys and uses die-casting as the forming process.

[0098] Comparative Example 1

[0099] The percentage content of the magnesium alloy composition is selected as follows: 9wt% Al, 1wt% Zn, and the rest is Mg;

[0100] A pure Mg ingot is placed in a crucible of a melting furnace, heated to 695°C, and completely melted to form a melt under the protection of a mixed protective gas of CO2 and SF6. Subsequently, a pure Al ingot and a pure Zn ingot are added and stirred in the mixed protective atmosphere for 8 minutes. After the alloy is completely melted, a magnesium alloy flux RJ-2 is added and refined for 7 minutes to remove surface scum. Finally, the alloy is kept at 720°C for 15 minutes and cast into a magnesium alloy ingot. The magnesium alloy ingot is placed in a 650T die-casting machine furnace and melted at 680°C. The melt enters the mold through the injection system for filling. The mold temperature is 206°C, the casting pressure is 105MPa, and the injection speed is 3.5m / s.

[0101] Comparative Example 2

[0102] The composition percentage of the magnesium alloy is selected as follows: 6wt% Al, 0.5wt% Mn, and the rest is Mg;

[0103] A pure Mg ingot was placed in a crucible of a melting furnace, heated to 710°C, and completely melted to form a melt under the protection of a mixed protective gas of CO2 and SF6. Subsequently, pure Al ingots and pure Mn powder were added and stirred in the mixed protective atmosphere for 10 minutes. After the alloy was completely melted, magnesium alloy flux RJ-2 was added and refined for 10 minutes to remove surface slag. Finally, the alloy was kept at 720°C for 10 minutes and cast into a magnesium alloy ingot. The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 700°C. The melt entered the mold through the injection system for filling. The mold temperature was 209°C, the casting pressure was 105MPa, and the injection speed was 3.9m / s.

[0104] Comparative Example 3

[0105] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0106] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 703°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 747°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 695°C, and adding Al-Be, Mg-Ca and Mg-Gd master alloys to the melt. After the alloy is completely melted, stirring for 5 minutes, then adding a magnesium alloy flux RJ-2 and refining for 5 minutes to remove surface scum, and finally holding the temperature at 718°C for 15 minutes to cast it into a magnesium alloy ingot;

[0107] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 695°C. The melt entered the mold through the injection system for filling. The mold temperature was 220°C, the casting pressure was 100 MPa, and the injection speed was 3.5 m / s.

[0108] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0109] Comparative Example 4

[0110] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be, Mg-Ca, and Mg-Gd master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0111] 2) A pure Mg ingot was placed in a crucible of a melting furnace, heated to 705°C, and completely melted under a protective gas mixture of CO2 and SF6 to form a melt. Subsequently, a pure Al ingot and pure Mn powder were added and stirred under a protective atmosphere until the alloy was completely melted. The temperature was then raised to 740°C, and pure La ingots and pure Ce ingots were added in sequence under a protective atmosphere and stirred until the alloy was completely melted. The melt was allowed to cool to 700°C, and Al-Be, Mg-Ca, and Mg-Gd master alloys were added to the melt. After the alloy was completely melted, the melt was stirred for 5 minutes, and then magnesium alloy flux RJ-2 was added and refined for 5 minutes to remove surface scum. Finally, the melt was kept at 718°C for 15 minutes and cast into a magnesium alloy ingot.

[0112] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 700°C. The melt entered the mold through the injection system for filling. The mold temperature was 230°C, the casting pressure was 103 MPa, and the injection speed was 3 m / s.

[0113] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0114] Comparative Example 5

[0115] 1) Using pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder, and Al-Be and Mg-Ca master alloys as raw materials, the ingredients are prepared according to the weight percentages of the designed magnesium alloy components;

[0116] 2) placing a pure Mg ingot into a crucible of a melting furnace, heating it to 709°C, and completely melting it under the protection of a mixed protective gas of CO2 and SF6 to form a melt, then adding a pure Al ingot and pure Mn powder, stirring under a protective atmosphere until the alloy is completely melted, then heating it to 739°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring them under a protective atmosphere until the alloy is completely melted, standing and cooling to 698°C, and then adding Al-Be and Mg-Ca master alloys to the melt. After the alloy is completely melted, stirring for 5 minutes, then adding a magnesium alloy flux RJ-2 and refining for 5 minutes to remove surface scum, and finally holding the temperature at 718°C for 15 minutes to cast it into a magnesium alloy ingot;

[0117] 3) The magnesium alloy ingot was placed in a 650T die-casting machine furnace and melted at 710°C. The melt entered the mold through the injection system for filling. The mold temperature was 215°C, the casting pressure was 101 MPa, and the injection speed was 3.6 m / s.

[0118] The properties of the obtained die-cast magnesium alloy parts are shown in Table 3.

[0119] As shown in Table 3, the room-temperature thermal conductivity of the magnesium alloy of the present invention is 100-110 W / (m·K), the room-temperature yield strength is 140-150 MPa, and the room-temperature elongation is 8-12%. The magnesium alloy obtained by the present invention exhibits significantly improved room-temperature mechanical properties and thermal conductivity compared to conventional AZ91D and AM60B magnesium alloys.

[0120] The traditional die-cast AZ91D magnesium alloy and die-cast AM60B magnesium alloy use Al as the main alloying element, which plays the role of solid solution strengthening and secondary phase (Mg 17 Al 12 ) strengthening effect to improve the room temperature yield strength of the material, and adding a small amount of Zn and Mn to further improve the comprehensive mechanical properties of the material; however, this strengthening effect is limited, and when more Al elements are dissolved in the magnesium matrix, the thermal conductivity of the material is significantly reduced.

[0121] It can be seen from the comparative examples in Table 3 that the thermal conductivity of the die-cast AZ91D magnesium alloy in Comparative Example 1 and the die-cast AM60B magnesium alloy in Comparative Example 2 are both less than 65 W / (m·K), the room temperature yield strength is less than 150 MPa, and the elongation is less than 10%, that is, they cannot have both excellent mechanical properties and thermal conductivity.

[0122] In Comparative Example 3, the Al content and RE content are low, and the second phase strengthening effect is weak, so the material yield strength is only 131 MPa, the elongation is 10%, and the thermal conductivity is 95 W / (m·K).

[0123] In Comparative Example 4, the Al / RE mass ratio is 1, and more Al elements are dissolved in the Mg matrix or form more Mg 17 Al 12 Phase, alloying elements have a more obvious negative impact on thermal conductivity, so the material yield strength is 138MPa, elongation is 11%, and thermal conductivity is 90W / (m·K).

[0124] In Comparative Example 5, Gd was not added, and Al formed more Mg at the grain boundaries. 17 Al 12 phase, so the material has a yield strength of 139 MPa, an elongation of 10.6%, and a thermal conductivity of 91 W / (m·K).

[0125] Table 1 Unit: Weight percentage

[0126] Table 2

[0127] Table 3

Claims

1. A high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy, whose components by weight percentage are: Al: 2.5-4.0%, RE: 3.5-5.5%, Mn: 0.1-0.3%, Be: 0.002-0.003%, Ca: 0.1-1.0%, Gd: 0.05-0.3%, RE is one or both of La or Ce, and the balance includes Mg and other inevitable impurities; and the above elements also need to satisfy the following conditions at the same time: 0.7≤Al / RE≤0.

8.

2. The high-strength, toughness and high-thermal-conductivity die-cast magnesium alloy according to claim 1, characterized in that: The balance is Mg and other inevitable impurities.

3. The high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy according to claim 1 or 2, characterized in that: The die-cast magnesium alloy matrix is ​​uniformly distributed with Al 11 RE3, Al2RE, Al2Ca, (Mg,Al)2Ca, Al2Gd and needle-shaped Al3RE second phase.

4. The high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy according to claim 1, 2 or 3, characterized in that: The room temperature yield strength of the die-cast magnesium alloy is 140-150 MPa, the elongation is 8-12%, and the thermal conductivity is 100-110 W / (m·K).

5. The method for preparing a high-strength, high-toughness and high-thermal-conductivity die-cast magnesium alloy according to any one of claims 1 to 4, characterized in that: The following steps are involved: 1) Ingredients Pure Mg ingots, pure Al ingots, pure La ingots, pure Ce ingots, pure Mn powder and Mg-Ca, Mg-Gd, Al-Be master alloys are used as raw materials and the magnesium alloy composition according to claim 1 or 2 is prepared; 2) Melting Putting a pure Mg ingot into a crucible, heating it to 680-710°C, and completely melting it under the protection of a protective gas, then adding a pure Al ingot and a pure Mn powder, stirring it under the protective atmosphere until the alloy is completely melted, then heating it to 740-750°C, and then sequentially adding a pure La ingot and a pure Ce ingot, stirring it under the protective atmosphere until the alloy is completely melted, then cooling it to 690-710°C, adding Al-Be, Mg-Ca and Mg-Gd master alloys into the melt, and stirring it for 5-10 minutes after the master alloy is completely melted to obtain a magnesium alloy melt; 3) Refining Adding magnesium alloy flux to the obtained magnesium alloy melt, refining for 5 to 10 minutes, removing surface scum, and then heating to 700 to 720° C. and keeping the temperature for 10 to 15 minutes; 4) Die casting The refined magnesium alloy melt is cast into an ingot, which is then placed in a die-casting machine furnace to melt at 680-700°C. The melt enters the mold through an injection system for filling, wherein the mold temperature is 200-250°C, the casting pressure is 100-110 MPa, and the injection speed is 3-5 m / s.

6. The preparation method according to claim 5, characterized in that: In step 3), the magnesium alloy flux is RJ-2 flux and RJ-3 flux.

7. The preparation method according to claim 5, characterized in that: In step 2), the protective gas is a mixed gas of CO2+SF6.

8. The preparation method according to claim 5, characterized in that: In step 4), the pouring temperature is 680-700°C.

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