Magnesium alloy with high strength, plasticity and thermal conductivity and preparation method thereof

Abstract

The invention discloses a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy and a preparation method thereof.The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy is prepared from, by mass, 3%-6% of Al element, 0-0.2% of Mn element, 0.5%-3% of RE element and the balance Mg element; the RE element is any one of a Y element, a Gd element, an Er element and an Sm element; the grain of the high-strength high-plasticity high-thermal-conductivity magnesium alloy internally comprises an MgAl phase, the volume percentage of the MgAl phase is smaller than or equal to 20%, and the size is smaller than or equal to 300 nm. The high-strength high-plasticity high-thermal-conductivity magnesium alloy disclosed by the invention has the room-temperature yield strength of more than or equal to 200MPa, the tensile strength of more than or equal to 280MPa, the ductility of more than or equal to 20% and the thermal conductivity of more than or equal to 110W / (m.K), and can be applied to transportation tools such as new energy automobiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-ferrous metal materials and processing, and particularly relates to a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, magnesium alloy has outstanding advantages in energy conservation, emission reduction and improving fuel efficiency, making it an important lightweight material to replace steel. It has been planned and gradually applied to ground transportation tools, such as high-precision components and secondary load-bearing structural components like the body of new energy vehicles and the seats of high-speed trains. At present, rare-earth magnesium alloys prepared by adding 4% or more (mass percentage) of rare-earth (RE) elements such as Gd, Er, Y, La, Ce, and Sm have shown excellent strength and plasticity, but it is difficult to apply such rare-earth magnesium alloys to the preparation of new energy vehicles. Since these RE elements seriously affect the surface accuracy, performance uniformity and thermal conductivity of die-cast magnesium alloys, they cannot meet the requirements of components such as the body for good appearance and rapid heat dissipation. Moreover, the high cost of RE elements also restricts the cost performance and popularization of new energy vehicles. Therefore, existing commercial-grade cast magnesium alloys mainly added with non-rare-earth elements such as Al, Mn, Zn, and Sn, such as AM60 and AZ31, are still the preferred materials for vehicle lightweighting. Thus, how to prepare a die-cast magnesium alloy with high strength, high plasticity and high thermal conductivity has become the core of material development.

[0003] At present, existing cast magnesium alloys usually add RE elements with a total content higher than 9%, forming MgREAl or MgREZn massive precipitation phases at the grain boundary triple junctions as strengthening phases to obtain high-strength magnesium alloys. However, due to the addition of a large amount of rare earth elements, the fluidity of the melt during the casting process is poor, and the number of dendrites in the obtained ingot is too large to be completely eliminated by solution treatment, resulting in serious deficiencies in both plasticity and thermal conductivity. There are already relevant achievements, such as Chinese patent documents with application numbers CN201810223234.0, CN202011560459.9, and CN202310543366.2, which propose adding RE and Zn elements, or RE and Ca elements simultaneously to Mg-Al series die-cast magnesium alloys or AM60 magnesium alloys. Through high-pressure casting, massive precipitation phases such as MgREAl and / or MgREZn and / or AlRE and / or AlCa are formed at the grain boundaries, especially at the grain boundary triple junctions, thereby increasing the yield strength of the cast magnesium alloy to above 200 MPa. However, affected by the non-coherent relationship between the above four types of precipitation phases and the matrix, its elongation is difficult to exceed 15%, and the matching of strength and plasticity still needs to be optimized. For example, in Chinese patent documents with application numbers CN202110674574.7, CN202110743614.9, CN202111101948.2, and CN202311246312.6, a large amount of Cu elements are also added in combination to induce the precipitation of MgCu binary phases, further promoting precipitation strengthening. However, the above precipitation phases cannot coordinate the grain boundary strain and seriously damage the plasticity. In addition, as described in Chinese patent documents with application numbers CN201310728756.3, CN201810699719.7, CN202110201544.4, and CN202210785356.5, for high-plasticity Mg-Zn series magnesium alloys with a total RE element content lower than 4%, the precipitation response of the MgZn binary phase is fast, enabling the magnesium alloy to obtain high thermal conductivity characteristics simultaneously. However, the precipitation strengthening effect of the MgZn binary phase is significantly inferior to that of the rare earth phase. Therefore, how to balance and simultaneously improve strength, plasticity, and thermal conductivity remains a difficult problem for die-cast magnesium alloys. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy and its preparation method.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, by mass percentage, comprises the following components: 3% - 6% of Al element, 0 - 0.2% of Mn element, 0.5% - 3% of RE element, and the balance is Mg element; the RE element is any one of Y element, Gd element, Er element and Sm element; the interior of the grains of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contains MgAl phase, and the volume percentage of the MgAl phase ≤ 20%, and the size of the MgAl phase ≤ 300 nm.

[0007] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, further improved, the grain size of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy ≤ 40 μm; the grain boundaries of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contain RE element segregation.

[0008] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, further improved, the volume percentage of the MgAl phase ≤ 10%, and the size of the MgAl phase ≤ 100 nm;

[0009] The grain size of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy ≤ 30 μm;

[0010] When the content of Mn element is not 0, the interior of the grains of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy does not contain AlMn binary precipitation phase.

[0011] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, further improved, by mass percentage, it comprises the following components: 3% - 5% of Al element, 1% - 3% of RE element, and the balance is Mg element.

[0012] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, further improved, the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy further comprises 0 - 1% of Zn element and 0.2% - 0.5% of Cu element;

[0013] When the content of Zn element is not 0, the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contains Zn element segregation;

[0014] The interior of the grains of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contains MgRECu phase.

[0015] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, further improved, the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy further comprises 1% - 3% of Zn element and 0 - 0.2% of Cu element;

[0016] When the content of Cu element is not 0, the grain boundaries of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contain Cu element segregation;

[0017] The interior of the grains of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy contains MgZn phase.

[0018] For the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, which is further improved, the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy further comprises components of a), b) or c);

[0019] a) 0 to 0.5% of Ca element;

[0020] b) 0 to 0.5% of Zr element;

[0021] c) 0 to 0.5% of element A; the element A is one or both of La element and Ce element.

[0022] As a general technical concept, the present invention also provides a preparation method of the above-mentioned high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, and any one of the following methods is used to prepare the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy;

[0023] Method 1 includes the following steps:

[0024] S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, carry out melting and casting to obtain an ingot; the temperature of the melting and casting is 680°C to 750°C;

[0025] S2. Carry out solution treatment on the ingot; the temperature of the solution treatment is 400°C to 460°C and the time is 2h to 24h;

[0026] S3. Carry out aging treatment on the material after solution treatment to obtain the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy; the temperature of the aging treatment is 160°C to 240°C and the time is 6h to 48h;

[0027] Method 2 includes the following steps:

[0028] According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, carry out melting and casting to obtain the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy; the specific process of the melting and casting is: high-pressure casting at a temperature of 680°C to 750°C for 5s to 60s, then keep warm at 160°C to 240°C for 0 to 24h, and cool to room temperature.

[0029] For the above-mentioned preparation method, which is further improved, when preparing the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy by Method 1, when the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy further comprises 0 to 1% of Zn element and 0.2% to 0.5% of Cu element, in step S3, the temperature of the aging treatment is 200°C to 240°C and the time is 6h to 24h;

[0030] When the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy further comprises 1% to 3% of Zn element and 0 to 0.2% of Cu element, in step S3, the temperature of the aging treatment is 160°C to 200°C and the time is 24h to 48h.

[0031] In the above preparation method, for further improvement, when preparing the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy by Method 2, the pressure of the high-pressure casting is 20 MPa to 100 MPa; the specific process of the melting and casting is as follows: high-pressure casting for 5 s to 30 s at a temperature of 700 °C to 750 °C, then keeping warm at 200 °C to 240 °C for 0 to 6 h, and cooling to room temperature.

[0032] Compared with the prior art, the advantages of the present invention are as follows:

[0033] (1) For the existing die-cast Mg-Al series alloys (especially AM60 magnesium alloy), they contain a large number of MgAl precipitation phases that are incoherent with the matrix inside, and the size is usually greater than 500 nm or even close to the micron level, seriously damaging the plasticity, and the precipitation strengthening effect generated is extremely limited, resulting in the defects that both the strength and plasticity are difficult to meet the mechanical property requirements of transportation tools for magnesium alloys. The present invention creatively proposes a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy. By adding RE elements (one of Y, Gd, Er, and Sm elements) with a total content not exceeding 3%, it aggregates at the grain boundaries to form a segregation strengthening effect, and reduces the number of solute atoms in the grains, which is beneficial to thermal conductivity. At the same time, there are only a small number of MgAl precipitation phases in the grains that are incoherent with the matrix, with minimal damage to plasticity, so that the magnesium alloy has high strength, high plasticity and high thermal conductivity at room temperature. Specifically, the present invention adds RE elements with a total content not exceeding 3%, making the RE elements more inclined to segregate along the grain boundaries to form segregation strengthening. On the one hand, it can purify the Mg matrix, which is beneficial to the synchronous improvement of strength and thermal conductivity. On the other hand, it can refine the casting structure, that is, the segregation of RE elements along the grain boundaries will preferentially consume the internal energy and mechanical energy during the preparation process, successfully inhibiting the nucleation and coarsening of the MgAl phase, and not affecting the fluidity of the melt during the casting process, significantly improving the strength and plasticity of the magnesium alloy. In addition, for the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention, adding 0 to 0.2% of Mn elements can avoid the generation of irregularly shaped brittle AlMn phases and their damage to plasticity. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention has good melt fluidity and strong filling property, is suitable for high-pressure casting, and can be applied to transportation tools such as new energy vehicles; at the same time, the present invention reduces the total content of RE, not only saving rare earth resources, but also avoiding increasing the weight of the magnesium alloy, and can give full play to the lightweight advantage of the magnesium alloy. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention has a room-temperature yield strength ≥ 200 MPa, a tensile strength ≥ 280 MPa, an elongation ≥ 20%, and a thermal conductivity ≥ 110 W / (m·K).

[0034] (2) For the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention, by optimizing the volume percentage of the MgAl phase ≤ 10% and the size of the MgAl phase ≤ 100 nm, reducing the number and size of the MgAl phase can reduce the stress concentration of the basal plane dislocations at the incoherent precipitation phases, which is beneficial to improving the plasticity of the magnesium alloy.

[0035] (3) The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention further adds 0-1% of Zn element and 0.2%-0.5% of Cu element. Adding a low content of 0-1% of Zn element easily makes Zn and RE elements attract each other and co-segregate at the grain boundary, further enhancing grain boundary strengthening; adding 0.2%-0.5% of Cu element can promote the formation of MgRECu phase (bamboo-shaped ternary precipitation phase) by Cu and the remaining solute atoms in the crystal, purifying the matrix and improving the thermal conductivity. On the contrary, if the Cu content is continuously increased to more than 0.5%, it is easy to generate MgCu binary brittle phase, damaging plasticity.

[0036] (4) The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention further adds 1%-3% of Zn element and 0-0.2% of Cu element. Adding a low content of 0-0.2% of Cu element can attract each other with RE element and co-segregate at the grain boundary, further enhancing grain boundary strengthening; adding a moderate content of 1%-3% of Zn element can induce the formation of fine disk-shaped MgZn phase (binary precipitation phase). According to the Orowan mechanism, the smaller the size of the precipitation phase, the better the precipitation strengthening effect, and the limited damage to plasticity. At the same time, it can also purify the matrix and improve the thermal conductivity. On the contrary, if the Zn content is continuously increased to more than 3%, it is easy to generate long rod-shaped MgZn binary phase perpendicular to the basal plane, tangling with the basal plane dislocations and thus damaging plasticity.

[0037] (5) The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention further adds 0-0.5% of Ca element or 0-0.5% of Zr element. Adding a small amount of Ca or Zr can refine the casting structure, improve the strength, and have little influence on plasticity and thermal conductivity; on the contrary, if a large amount of Ca or Zr is added, it is extremely easy to reduce the melt fluidity during the casting process and form irregularly shaped AlCa phase or AlZr phase with Al element, seriously damaging plasticity.

[0038] (6) The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention further adds a total content of 0-0.5% of La element and / or Ce element. Adding a small amount of La or Ce can refine the casting structure, improve the strength, and have little influence on plasticity and thermal conductivity; on the contrary, if a large amount of La or Ce is added, it is extremely easy to reduce the melt fluidity during the casting process and form irregularly shaped AlLa phase or AlCe phase with Al element, seriously damaging plasticity.

[0039] (7) The present invention also correspondingly provides a preparation method of a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy. First, melting and casting are carried out at 680°C to 750°C, which can ensure that all raw materials are completely melted, evenly mixed and have a low burn-off rate, reducing the loss of raw materials and the deviation of components; then, high-temperature short-time solution treatment is carried out at 400°C to 460°C for 2h to 24h. The high-temperature solution treatment makes all the added elements exist in the form of solution atoms, reducing the impurities inside the magnesium alloy, and the short-time solution treatment can avoid grain coarsening and texture strengthening; then, aging treatment is carried out at 160°C to 240°C for 6h to 48h. Due to the relatively high aging temperature and short time, the precipitated phases will not rapidly coarsen during subsequent aging, and the plasticity of the magnesium alloy can be avoided from being damaged.

[0040] (8) In the preparation method of the present invention, when the magnesium alloy further contains 0 to 1% of Zn element and 0.2% to 0.5% of Cu element, the optimized aging treatment temperature is 200°C to 240°C and the time is 6h to 24h. The high-temperature short-time aging treatment can prevent the coarsening of the MgRECu ternary phase, and at the same time can save the preparation time and energy consumption; when the magnesium alloy further contains 1% to 3% of Zn element and 0 to 0.2% of Cu element, the optimized aging treatment temperature is 160°C to 200°C and the time is 24h to 48h. The low-temperature long-time aging treatment can make the moderately contained Zn element fully precipitate, which is more beneficial to improving the thermal conductivity.

[0041] (9) The present invention also correspondingly provides a preparation method of a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, adopting a "high-pressure casting + heat preservation" system. On the one hand, it can promote the more sufficient aggregation of RE elements at the grain boundaries, which is beneficial to simultaneously enhancing the segregation strengthening effect and improving the purity of the matrix, and realizing high strength and high thermal conductivity characteristics; on the other hand, it can improve the melt fluidity, the dimensional accuracy, the surface finish and the tissue compactness of the casting product during the casting process, and it is easier to obtain a magnesium alloy with both high strength, high plasticity and high thermal conductivity.

[0042] (10) In the preparation method of the present invention, by optimizing the melting and casting, that is, high-pressure casting is carried out at 700°C to 750°C for 5s to 30s, and then heat preservation is carried out at 200°C to 240°C for 0 to 6h. The high-temperature short-time heat preservation treatment can not only accelerate the nucleation of the precipitated phase, but also prevent the coarsening of the precipitated phase, especially inhibit the generation and growth of the MgAl phase, and at the same time can save the preparation time and energy consumption. Description of the Drawings

[0043] Figure 1 It is the grain size distribution diagram of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in Example 1 of the present invention.

[0044] Figure 2 It is the TEM dark field image of the precipitated phase of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in Example 1 of the present invention.

[0045] Figure 3 The TEM dark field image of the grain boundary of the high-strength, high-plasticity and high-thermal conductivity magnesium alloy prepared in Example 1 of the present invention.

[0046] Figure 4 The grain size distribution diagram of the magnesium alloy prepared in Comparative Example 1.

[0047] Figure 5 The TEM dark field image of the precipitation phase of the magnesium alloy prepared in Comparative Example 1.

[0048] Figure 6 The TEM dark field image of the grain boundary of the magnesium alloy prepared in Comparative Example 1. Detailed implementation mode

[0049] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0050] Example 1

[0051] A high-strength, high-plasticity and high-thermal conductivity magnesium alloy of the present invention contains the following components by mass percentage: 6% Al element, 3% Y element, 0.3% Zr element, and the balance is Mg element.

[0052] A preparation method of the high-strength, high-plasticity and high-thermal conductivity magnesium alloy of the present embodiment includes the following steps:

[0053] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0054] S2. Melting and casting: Mix the above raw materials evenly, first perform high-pressure casting, the temperature of high-pressure casting is 740°C to 750°C, the pressure is 80 MPa, and the pressure holding time is 60 s; then, cool down to 240°C and keep warm for 2 h, and finally cool to room temperature to obtain a high-strength, high-plasticity and high-thermal conductivity magnesium alloy, referred to as Mg-6Al-3Y-0.3Zr alloy, marked as Sample No. 1.

[0055] The high-strength, high-plasticity and high-thermal conductivity magnesium alloy prepared in this embodiment, as Figures 1 - 3 shown, its grain size is less than 30 μm, the grain boundary contains Y element segregation, and the volume percentage of MgAl phase in the grain is 10% and the size is less than 150 nm.

[0056] Example 2

[0057] A high-strength, high-plasticity and high-thermal conductivity magnesium alloy of the present invention contains the following components by mass percentage: 6% Al element, 0.2% Mn element, 3% Y element, 0.3% Zr element, and the balance is Mg element.

[0058] A preparation method of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy of this embodiment is basically the same as the preparation method of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy in Example 1, except that: the components of the magnesium alloy are different; the obtained high-strength, high-ductility and high-thermal-conductivity magnesium alloy is abbreviated as Mg-6Al-0.2Mn-3Y-0.3Zr alloy and marked as Sample No. 2.

[0059] For the high-strength, high-ductility and high-thermal-conductivity magnesium alloy obtained in this embodiment, its grain size is less than 40 μm, the grain boundary contains segregation of Y element, the volume percentage of MgAl phase in the grain is 14% and the size is less than 180 nm, and there is no AlMn phase in the grain.

[0060] Comparative Example 1

[0061] A magnesium alloy contains the following components by mass percentage: 8% Al element, 3% Y element, 0.3% Zr element, and the balance is Mg element.

[0062] The preparation method of this magnesium alloy is basically the same as the preparation method of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy in Example 1, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-8Al-3Y-0.3Zr alloy and marked as Sample No. 3.

[0063] The magnesium alloy obtained in Comparative Example 1, as Figures 4 - 6 shown, its grain size is less than 35 μm, the grain boundary contains segregation of Y element, and the volume percentage of MgAl phase in the grain is 45% and the size is greater than 700 nm.

[0064] Comparative Example 2

[0065] A magnesium alloy contains the following components by mass percentage: 6% Al element, 0.5% Mn element, 3% Y element, 0.3% Zr element, and the balance is Mg element.

[0066] The preparation method of this magnesium alloy is basically the same as the preparation method of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy in Example 1, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-6Al-0.5Mn-3Y-0.3Zr alloy and marked as Sample No. 4.

[0067] For the magnesium alloy obtained in Comparative Example 2, its grain size is less than 30 μm, the grain boundary contains segregation of Y element, the volume percentage of MgAl phase in the grain is 16% and some of the MgAl phases have a size greater than 600 nm, and the volume percentage of AlMn phase in the grain is 10%.

[0068] Comparative Example 3

[0069] A magnesium alloy contains the following components by mass percentage: 6% Al element, 0.2% Mn element, 5% Y element, 0.3% Zr element, and the balance is Mg element.

[0070] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 1, except that: the components of the magnesium alloy are different; the prepared magnesium alloy is abbreviated as Mg-6Al-0.2Mn-5Y-0.3Zr alloy and marked as Sample No. 5.

[0071] For the magnesium alloy prepared in Comparative Example 3, its grain size is less than 25 μm, there is no Y element segregation at the grain boundary, the volume percentage of MgAl phase in the grains is 9%, the size of some MgAl phases is greater than 500 nm, there is no AlMn phase in the grains, and the volume percentage of AlY phase in the grains is 15%.

[0072] The room-temperature uniaxial tensile mechanical properties and thermal conductivity of the 5 magnesium alloys obtained in Examples 1-2 and Comparative Examples 1-3 were tested respectively, and the results are shown in Table 1.

[0073] Table 1 Performance test results of magnesium alloys

[0074] Sample Thermal conductivity (W / (m·K)) Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 1 Sample No. 1 120 260 330 28 Example 2 Sample No. 2 115 250 310 22 Comparative Example 1 Sample No. 3 105 260 270 8 Comparative Example 2 Sample No. 4 110 235 250 9 Comparative Example 3 Sample No. 5 90 185 270 13

[0075] As can be seen from Table 1, Sample No. 1 has high strength, high plasticity and high thermal conductivity at the same time; for Sample No. 2, due to the relatively high quantity and large size of MgAl phases and the presence of AlMn phase, both the strength and plasticity and the thermal conductivity have decreased, but it still maintains relatively high strength, plasticity and thermal conductivity; for Sample No. 3, due to the too high Al content, the quantity and size of MgAl phases have both increased significantly, seriously damaging the plasticity and thermal conductivity; for Sample No. 4, due to the too high Mn content, which occupies the position of Al element as a solute atom, accelerating the precipitation of Al element, resulting in coarse MgAl phases and a large number of AlMn phases being generated at the same time, damaging the strength and plasticity; for Sample No. 5, due to the too high Y element content, the texture is weakened, the yield strength is reduced, and a large number of AlY phases are generated in the grains, resulting in the inability of Y element to form segregation strengthening at the grain boundary, damaging the tensile strength and plasticity, and the addition of Y element increases the degree of lattice distortion, and the thermal conductivity also decreases accordingly.

[0076] Example 3

[0077] A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 4% Al element, 1% Gd element, 3% Zn element, 0.1% Cu element, and the balance is Mg element.

[0078] A preparation method of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of this example includes the following steps:

[0079] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0080] S2. Melting and casting: Mix the above raw materials evenly and conduct melting and casting at a temperature of 700°C - 720°C to obtain an ingot.

[0081] S3. Solution treatment: Conduct solution treatment on the ingot at a temperature of 400°C for 24 hours.

[0082] S4. Aging treatment: Conduct aging treatment on the material after solution treatment at a temperature of 180°C for 36 hours to obtain a high-strength, high-ductility, and high-thermal-conductivity magnesium alloy, abbreviated as Mg-4Al-1Gd-3Zn-0.1Cu alloy, marked as Sample No. 6.

[0083] For the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy prepared in this example, its grain size is less than 25 μm, the grain boundary contains the segregation of both Gd and Cu elements, the volume percentage of MgAl phase in the grain is 6% and its size is less than 80 nm, and the volume percentage of MgZn phase in the grain is 10% and its size is less than 50 nm.

[0084] Example 4

[0085] A high-strength, high-ductility, and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 4% Al element, 1% Gd element, and the balance is Mg element.

[0086] A preparation method of the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy of this example is basically the same as that of the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy in Example 3, except that: the components of the magnesium alloy are different; the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy obtained is abbreviated as Mg-4Al-1Gd alloy and marked as Sample No. 7.

[0087] For the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy prepared in this example, its grain size is less than 35 μm, the grain boundary contains the segregation of Gd element, and the volume percentage of MgAl phase in the grain is 8% and its size is less than 100 nm.

[0088] Example 5

[0089] A high-strength, high-ductility, and high-thermal-conductivity magnesium alloy of the present invention has the same components as the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy in Example 3.

[0090] A preparation method of the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy of this example is basically the same as that of the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy in Example 3, except that: in step S4, the aging treatment temperature is 240°C; the high-strength, high-ductility, and high-thermal-conductivity magnesium alloy obtained is abbreviated as Mg-4Al-1Gd-3Zn-0.1Cu alloy and marked as Sample No. 8.

[0091] The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in this example has a grain size of less than 25 μm. The grain boundaries contain segregation of both Gd and Cu elements. The volume fraction of MgAl phase in the grains is 11% and the size is less than 150 nm. The volume fraction of MgZn phase in the grains is 13% and the size is less than 160 nm.

[0092] Comparative Example 4

[0093] A magnesium alloy contains the following components by mass percentage: 4% Al element, 1% Gd element, 6% Zn element, and the balance is Mg element.

[0094] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 3, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-4Al-1Gd-6Zn alloy and marked as Sample No. 9.

[0095] The magnesium alloy prepared in Comparative Example 4 has a grain size of less than 22 μm. The grain boundaries do not contain segregation of Gd element. The volume fraction of MgAl phase in the grains is 24% and some of the MgAl phase sizes are greater than 480 nm. The volume fraction of MgGdZn phase at the grain boundaries is 30% and the size is greater than 1 μm.

[0096] Comparative Example 5

[0097] A magnesium alloy has the same components as the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 3.

[0098] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 3, except that: in step S4, the aging treatment temperature is 240 °C and the time is 72 h; the obtained magnesium alloy is abbreviated as Mg-4Al-1Gd-3Zn-0.1Cu alloy and marked as Sample No. 10.

[0099] The magnesium alloy prepared in Comparative Example 5 has a grain size of less than 25 μm. The grain boundaries contain segregation of both Gd and Cu elements. The volume fraction of MgAl phase in the grains is 30% and the size is greater than 800 nm. The volume fraction of MgZn phase in the grains is 20% and the size is greater than 300 nm.

[0100] The room-temperature uniaxial tensile mechanical properties and thermal conductivities of the five magnesium alloys obtained in Examples 3-5 and Comparative Examples 4-5 were tested respectively, and the results are shown in Table 2.

[0101] Table 2 Performance test results of magnesium alloys

[0102] Sample Thermal conductivity (W / (m·K)) Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 3 Sample No. 6 125 260 310 27 Example 4 Sample No. 7 120 230 285 26 Example 5 Sample No. 8 115 240 285 22 Comparative Example 4 Sample No. 9 90 255 290 5 Comparative Example 5 Sample No. 10 95 180 220 14

[0103] As can be seen from Table 2, Sample No. 6 has high strength, high plasticity, and high thermal conductivity; the strength of Sample No. 7 decreases significantly because it lacks the strengthening effect of Cu element segregation and the precipitation strengthening of MgZn phase; for Sample No. 8, due to the relatively high aging temperature in Step S4, the quantity and size of MgAl phase both increase, resulting in a slight decrease in both strength and plasticity and impairing the thermal conductivity; for Sample No. 9, due to the excessive Zn content, massive brittle MgGdZn phase is formed at the grain boundaries, seriously damaging plasticity and thermal conductivity; for Sample No. 10, due to the excessive aging time, the MgAl phase coarsens rapidly, unable to form effective precipitation strengthening, and the large-sized MgAl phase also causes brittle fracture.

[0104] Example 6

[0105] A high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 3% Al element, 1% Er element, 0.2% Ca element, and the balance is Mg element.

[0106] A preparation method of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of this example includes the following steps:

[0107] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0108] S2. Melting and casting: Mix the above raw materials evenly, first perform high-pressure casting, the temperature of high-pressure casting is 680°C - 700°C, the pressure is 100 MPa, and the pressure holding time is 20 s; then, cool down to 210°C and keep it warm for 6 h, and finally cool to room temperature to obtain a high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy, abbreviated as Mg-3Al-1Er-0.2Ca alloy, marked as Sample No. 11.

[0109] The high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy prepared in this example has a grain size of less than 18 μm, the grain boundaries contain segregated Er element, and the volume percentage of MgAl phase in the grains is 4% and the size is less than 90 nm.

[0110] Example 7

[0111] A high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 3% Al element, 0.5% Er element, 0.2% Ca element, and the balance is Mg element.

[0112] A preparation method of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of this example is basically the same as that of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy in Example 6, the only difference being: the components of the magnesium alloy are different; the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy obtained is abbreviated as Mg-3Al-0.5Er-0.2Ca alloy, marked as Sample No. 12.

[0113] The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in this example has a grain size of less than 16 μm, with segregation of Er element in the grain boundary, and the volume percentage of MgAl phase in the grain is 7% and the size is less than 120 nm.

[0114] Comparative Example 6

[0115] A magnesium alloy contains the following components by mass percentage: 3% Al element, 1% Er element, 1% Ca element, and the balance is Mg element.

[0116] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 6, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-3Al-1Er-1Ca alloy and marked as Sample No. 13.

[0117] The magnesium alloy prepared in Comparative Example 6 has a grain size of less than 32 μm, with segregation of Er element in the grain boundary, the volume percentage of MgAl phase in the grain is 18% and some of the MgAl phases have a size greater than 520 nm, and the volume percentage of AlCa phase in the grain is 8% and the size is greater than 200 nm.

[0118] Comparative Example 7

[0119] A magnesium alloy has the same components as the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 6.

[0120] The preparation method of this magnesium alloy includes:

[0121] S1. Weigh the required raw materials according to the mass percentage of each component in the above magnesium alloy.

[0122] S2. Melting and casting: Mix the above raw materials evenly, first carry out high-pressure casting, the temperature of high-pressure casting is 680 °C - 700 °C, the pressure is 100 MPa, and the pressure holding time is 20 s; then, cool down to 210 °C and keep it warm for 48 h, and finally cool to room temperature to obtain the magnesium alloy, abbreviated as Mg-3Al-1Er-0.2Ca alloy and marked as Sample No. 14.

[0123] For the magnesium alloy prepared in Comparative Example 7, the size of some grains is greater than 43 μm, with segregation of Er element in the grain boundary, the volume percentage of MgAl phase in the grain is 33% and some of the MgAl phases have a size greater than 1.2 μm.

[0124] The room-temperature uniaxial tensile mechanical properties and thermal conductivity of the four magnesium alloys obtained in Examples 6 - 7 and Comparative Examples 6 - 7 were tested respectively, and the results are shown in Table 3.

[0125] Table 3 Performance test results of magnesium alloys

[0126]

[0127]

[0128] As can be seen from Table 3, Sample No. 11 has high strength, high plasticity and high thermal conductivity at the same time; for Sample No. 12, due to the low content of Er, the strengthening effect of grain boundary element segregation has decreased; for Sample No. 13, due to the excessive content of Ca, irregularly shaped AlCa brittle phases are formed in the grains, and the resulting lattice distortion further accelerates the precipitation and coarsening of the MgAl phase, ultimately causing the synchronous decline of strength and plasticity and impairing the thermal conductivity; for Sample No. 14, due to the too long holding time after high-pressure casting, grain coarsening and strength decline occur, and at the same time, the MgAl phase is more likely to precipitate and coarsen, damaging plasticity.

[0129] Example 8

[0130] A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 5% Al element, 2% Y element, 0.8% Zn element, 0.5% Cu element, and the balance is Mg element.

[0131] A preparation method of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of this example includes the following steps:

[0132] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy;

[0133] S2. Melting and casting: Mix the above raw materials evenly and perform high-pressure casting. The temperature of high-pressure casting is 730 °C to 740 °C, the pressure is 20 MPa, and the pressure holding time is 30 s to obtain a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, abbreviated as Mg-5Al-2Y-0.8Zn-0.5Cu alloy, marked as Sample No. 15.

[0134] The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in this example has a grain size of less than 15 μm. The grain boundaries contain segregation of both Y and Zn elements. The volume percentage of the MgAl phase in the grains is 7% and the size is less than 120 nm. The volume percentage of the MgYCu phase in the grains is 4% and the size is less than 200 nm.

[0135] Example 9

[0136] A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention has the same components as the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy in Example 8.

[0137] A preparation method of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of this example includes:

[0138] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy;

[0139] S2. Melting and Casting: Mix the above raw materials evenly, and then carry out melting and casting at a temperature of 710°C to 720°C to obtain an ingot.

[0140] S3. Solution Treatment: Carry out solution treatment on the ingot at a temperature of 460°C for 2 hours.

[0141] S4. Aging Treatment: Carry out aging treatment on the material after solution treatment at a temperature of 220°C for 12 hours to obtain a high-strength, high-ductility and high-thermal-conductivity magnesium alloy, abbreviated as Mg-5Al-2Y-0.8Zn-0.5Cu alloy, and marked as Sample No. 16.

[0142] For the high-strength, high-ductility and high-thermal-conductivity magnesium alloy prepared in this example, its grain size is less than 23 μm, the grain boundary contains segregation of both Y and Zn elements, the volume percentage of MgAl phase in the grain is 12% and the size is less than 220 nm, and the volume percentage of MgYCu phase in the grain is 7% and the size is less than 320 nm.

[0143] Comparative Example 8

[0144] A magnesium alloy contains the following components by mass percentage: 5% Al element, 2% Y element, 0.8% Zn element, 0.8% Cu element, and the balance is Mg element.

[0145] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy in Example 8, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-5Al-2Y-0.8Zn-0.8Cu alloy and marked as Sample No. 17.

[0146] For the magnesium alloy prepared in Comparative Example 8, the size of some grains is greater than 44 μm, the grain boundary contains segregation of both Y and Zn elements, the volume percentage of MgAl phase in the grain is 8% and the size is less than 150 nm, and the volume percentage of MgYCu phase in the grain is 15% and the size is greater than 1.5 μm.

[0147] Comparative Example 9

[0148] A magnesium alloy contains the following components by mass percentage: 5% Al element, 0.8% Zn element, 0.5% Cu element, and the balance is Mg element.

[0149] The preparation method of this magnesium alloy is basically the same as that of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy in Example 8, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-5Al-0.8Zn-0.8Cu alloy and marked as Sample No. 18.

[0150] For the magnesium alloy prepared in Comparative Example 9, the sizes of some grains are greater than 58 μm, the grain boundaries contain segregation of Zn element, the volume percentage of MgAl phase in the grains is 35%, the sizes of some MgAl phases are greater than 450 nm, the volume percentage of MgCu phase in the grains is 18%, and the sizes are all greater than 1.1 μm.

[0151] The room-temperature uniaxial tensile mechanical properties and thermal conductivities of the four magnesium alloys obtained in Examples 8-9 and Comparative Examples 8-9 were respectively tested, and the results are shown in Table 4.

[0152] Table 4 Test results of the properties of magnesium alloys

[0153] Sample Thermal conductivity (W / (m·K)) Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 8 Sample No. 15 135 255 315 28 Example 9 Sample No. 16 120 240 295 25 Comparative Example 8 Sample No. 17 123 265 275 3 Comparative Example 9 Sample No. 18 125 205 230 9

[0154] As can be seen from Table 4, Sample No. 15 has high strength, high plasticity and high thermal conductivity at the same time; for Sample No. 16, since the high-pressure casting method was not used, the grain size was coarsened, and the quantity and size of MgAl also increased, resulting in a decrease in both strength and plasticity and thermal conductivity; for Sample No. 17, since the Cu content was too high, the MgYCu phase was severely coarsened and the plasticity decreased sharply; for Sample No. 18, since the Y element was not added, the grain coarsening and strength decrease occurred, and at the same time, the brittle MgCu phase also damaged the plasticity.

[0155] Example 10

[0156] A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 5% Al element, 1.5% Y element, 0.2% La element, 0.3% Ce element, and the balance is Mg element.

[0157] A preparation method of the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy of this example includes the following steps:

[0158] S1. Weigh the required raw materials according to the mass percentages of the components in the above magnesium alloy.

[0159] S2. Melting and casting: Mix the above raw materials evenly and perform high-pressure casting. The temperature of high-pressure casting is 720 °C -730 °C, the pressure is 50 MPa, and the pressure holding time is 20 s to obtain a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, abbreviated as Mg-5Al-1.5Y-0.2La-0.3Ce alloy, marked as Sample No. 19.

[0160] For the high-strength, high-plasticity and high-thermal-conductivity magnesium alloy prepared in this example, the grain sizes are all less than 23 μm, the grain boundaries contain segregation of Y element, the volume percentage of MgAl phase in the grains is 8%, and the sizes are all less than 90 nm.

[0161] Example 11

[0162] A high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of the present invention contains the following components by mass percentage: 5% Al element, 1.5% Y element, and the balance is Mg element.

[0163] A preparation method of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy of this embodiment is basically the same as the preparation method of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy in Example 10, except that: the components of the magnesium alloy are different; the obtained high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy is abbreviated as Mg-5Al-1.5Y alloy and marked as Sample No. 20.

[0164] The high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy obtained in this embodiment has a grain size of less than 36 μm, the grain boundary contains Y element segregation, and the volume percentage of MgAl phase in the grain is 15% and the size is less than 150 nm.

[0165] Comparative Example 10

[0166] A magnesium alloy contains the following components by mass percentage: 5% Al element, 1.5% Y element, 0.2% La element, 0.8% Ce element, and the balance is Mg element.

[0167] The preparation method of this magnesium alloy is basically the same as the preparation method of the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy in Example 10, except that: the components of the magnesium alloy are different; the obtained magnesium alloy is abbreviated as Mg-5Al-1.5Y-0.2La-0.8Ce alloy and marked as Sample No. 21.

[0168] The magnesium alloy obtained in Comparative Example 10 has a grain size of less than 20 μm, the grain boundary contains Y element segregation, the volume percentage of MgAl phase in the grain is 26% and some of the MgAl phase sizes are greater than 330 nm, and the volume percentage of AlCe phase in the grain is 20% and the size is greater than 500 nm.

[0169] Comparative Example 11

[0170] A magnesium alloy has the same components as the high-strength, high-plasticity, and high-thermal-conductivity magnesium alloy in Example 10.

[0171] The preparation method of this magnesium alloy includes the following steps:

[0172] S1. Weigh the required raw materials according to the mass percentage of each component in the above magnesium alloy;

[0173] S2. Melting and casting: Mix the above raw materials evenly, carry out melting and casting, and the temperature of melting and casting is 720 °C to 730 °C to obtain an ingot;

[0174] S3. Solution treatment: Carry out solution treatment on the ingot, and the temperature of solution treatment is 460 °C and the time is 48 h;

[0175] S4. Aging treatment: The solution-treated material is subjected to aging treatment at a temperature of 180 °C for 48 h to obtain a magnesium alloy, abbreviated as Mg-5Al-1.5Y-0.2La-0.3Ce alloy, marked as Sample No. 22.

[0176] For the magnesium alloy prepared in Comparative Example 11, the sizes of some grains are larger than 76 μm, the grain boundaries contain segregation of Y element, the volume percentage of MgAl phase in the grains is 33%, and the sizes of some MgAl phases are larger than 1.3 μm.

[0177] The room-temperature uniaxial tensile mechanical properties and thermal conductivities of the four magnesium alloys obtained in Examples 10 - 11 and Comparative Examples 10 - 11 are tested respectively, and the results are shown in Table 5.

[0178] Table 5 Test results of the properties of magnesium alloys

[0179] Sample Thermal conductivity (W / (m·K)) Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) Example 10 Sample No. 19 130 260 305 28 Example 11 Sample No. 20 120 255 295 23 Comparative Example 10 Sample No. 21 125 255 270 10 Comparative Example 11 Sample No. 22 75 170 205 12

[0180] As can be seen from Table 5, Sample No. 19 has high strength, high plasticity and high thermal conductivity at the same time; for Sample No. 20, the absence of La and Ce leads to slightly coarser grains, and the precipitation and coarsening of MgAl phase also increase, resulting in a decrease in both strength and plasticity and thermal conductivity; for Sample No. 21, due to the relatively high total content of La and Ce, irregular brittle AlCe phases are formed, resulting in a serious decrease in plasticity and the tensile strength cannot reach the expected value; for Sample No. 22, the sample is overheated due to too long solution treatment time, and the grains are severely coarsened, severely damaging both strength and plasticity and thermal conductivity.

[0181] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes, without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of the protection of the technical solution of the present invention.

Claims

1. A high-strength, high-plasticity and high-thermal-conductivity magnesium alloy, characterized in that, By mass percentage, it contains the following components: 3% - 6% of Al element, 0 - 0.2% of Mn element, 0.5% - 3% of RE element, and the balance is Mg element; the RE element is any one of Y element, Gd element, Er element and Sm element; the interior of the grains of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contains MgAl phase, and the volume percentage of the MgAl phase ≤ 20%, and the size of the MgAl phase ≤ 300 nm.

2. The high-strength and high-thermal-conductivity magnesium alloy according to claim 1, wherein The grain size of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy ≤ 40 μm; the grain boundaries of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contain RE element segregation.

3. The high-strength and high-thermal-conductivity magnesium alloy according to claim 2, characterized in that, The volume percentage of the MgAl phase ≤ 10%, and the size of the MgAl phase ≤ 100 nm; The grain size of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy ≤ 30 μm; When the content of Mn element is not 0, the interior of the grains of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy does not contain AlMn binary precipitation phase.

4. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy according to any one of claims 1 to 3, characterized in that By mass percentage, it contains the following components: 3% - 5% of Al element, 1% - 3% of RE element, and the balance is Mg element.

5. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy according to any one of claims 1 to 3, characterized in that, The high-strength, high-ductility and high-thermal-conductivity magnesium alloy also contains 0 - 1% of Zn element and 0.2% - 0.5% of Cu element; When the content of Zn element is not 0, the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contains Zn element segregation; The interior of the grains of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contains MgRECu phase.

6. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy according to any one of claims 1 to 3, characterized in that, The high-strength, high-ductility and high-thermal-conductivity magnesium alloy also contains 1% - 3% of Zn element and 0 - 0.2% of Cu element; When the content of Cu element is not 0, the grain boundaries of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contain Cu element segregation; The interior of the grains of the high-strength, high-ductility and high-thermal-conductivity magnesium alloy contains MgZn phase.

7. The high-strength, high-plasticity and high-thermal-conductivity magnesium alloy according to any one of claims 1 to 3, characterized in that The high-strength, high-ductility and high-thermal-conductivity magnesium alloy also contains the components of a) or b) or c); a) 0 - 0.5% of Ca element; b) 0 - 0.5% of Zr element; c) 0 - 0.5% of A element; the A element is one or two of La element and Ce element.

8. A method for preparing a high-strength, high-plasticity and high-thermal-conductivity magnesium alloy according to any one of claims 1 to 7, characterized in that, The high-strength, high-ductility and high-thermal-conductivity magnesium alloy is prepared by any one of the following methods; Method 1 includes the following steps: S1. According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, carry out melting and casting to obtain an ingot; the temperature of the melting and casting is 680°C - 750°C; S2. Carry out solution treatment on the ingot; the temperature of the solution treatment is 400°C - 460°C and the time is 2 h - 24 h; S3. Carry out aging treatment on the material after solution treatment to obtain the high-strength, high-ductility and high-thermal-conductivity magnesium alloy; the temperature of the aging treatment is 160°C - 240°C and the time is 6 h - 48 h; Method 2 includes the following steps: According to the mass percentages of the components in the magnesium alloy, weigh the required raw materials, carry out melting and casting to obtain the high-strength, high-ductility and high-thermal-conductivity magnesium alloy; the specific process of the melting and casting is: high-pressure casting at a temperature of 680°C - 750°C for 5 s - 60 s, then keep warm at 160°C - 240°C for 0 - 24 h, and cool to room temperature.

9. The preparation method according to claim 8, characterized in that, When preparing the high-strength, high-ductility and high-thermal-conductivity magnesium alloy by Method 1, when the high-strength, high-ductility and high-thermal-conductivity magnesium alloy further contains 0-1% of Zn element and 0.2%-0.5% of Cu element, in step S3, the temperature of the aging treatment is 200°C-240°C and the time is 6h-24h; When the high-strength, high-ductility and high-thermal-conductivity magnesium alloy further contains 1%-3% of Zn element and 0-0.2% of Cu element, in step S3, the temperature of the aging treatment is 160°C-200°C and the time is 24h-48h.

10. The preparation method according to claim 8, wherein, When preparing the high-strength, high-ductility and high-thermal-conductivity magnesium alloy by Method 2, the pressure of the high-pressure casting is 20MPa-100MPa; the specific process of the melting and casting is: high-pressure casting at a temperature of 700°C-750°C for 5s-30s, then keeping warm at 200°C-240°C for 0-6h, and cooling to room temperature.

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