High-temperature-resistant high-strength high-thermal-conductivity cast magnesium alloy material and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant high-strength high-thermal-conductivity casting magnesium alloy material which comprises Al, La, Ca, Mn, Mg and inevitable impurities. Wherein the mass ratio of the Al to the La to the Ca to the Mn to the Mg is (3.6 to 4.4) to (3.6 to 4.4) to (0.3 to 1.3) to (0.1 to 0.5) to 1; compared with the prior art, through reasonable component regulation and control, elements of the alloy material can be mutually promoted to be separated out, alloy elements in a matrix are mutually consumed, the purpose of synergistically improving the mechanical property and the heat-conducting property is achieved, the inversion relation between the strength and the heat conductivity is overcome, and the performance of the alloy material is far higher than that of most Mg-Al series alloys in the prior art.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy technology, specifically to a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material and its preparation method. Background Technology

[0002] With the rapid development of information technology, the integration and power density of electronic components on integrated circuits are constantly increasing, leading to a sharp increase in the heat released per unit time and unit area. Overheating has become a key bottleneck restricting the further improvement of the performance and the miniaturization and lightweighting of 3C (computer, communication, and consumer electronics) products. Therefore, efficient heat dissipation components play an increasingly important role in this field.

[0003] Currently, the market requirements for 3C heat dissipation components have gone beyond simply high thermal conductivity. Driven by both energy conservation, environmental protection, and user experience, heat dissipation components must ensure excellent heat dissipation capabilities while also possessing low density and lightweight characteristics. Magnesium (Mg), as the lightest metallic structural material, has inherently good thermal conductivity, making it an ideal candidate material for manufacturing lightweight heat dissipation components and possessing enormous application potential.

[0004] However, the practical dilemma faced by those skilled in the art is that current research and development of thermally conductive magnesium alloys largely focuses on achieving extremely high thermal conductivity without fully considering their mechanical properties, particularly the balance between strength and thermal conductivity. Many existing high thermal conductivity magnesium alloys often lack the strength to withstand the mechanical stress and impacts that actual heat dissipation components must withstand during processing, assembly, and use, severely limiting their engineering applications. For example, excessively reducing the content of alloying elements in pursuit of high thermal conductivity, while improving conductivity, severely sacrifices the material's strength, making it difficult to achieve both high strength and high thermal conductivity simultaneously.

[0005] Therefore, there is an urgent need in the existing technology to develop a new type of magnesium alloy material that can break the traditional "seesaw" effect between thermal conductivity and mechanical properties, while maintaining the advantages of magnesium alloys in terms of lightness and high thermal conductivity, and at the same time possessing sufficiently high strength to meet the stringent requirements of modern 3C heat dissipation components for the comprehensive performance of materials. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material and its preparation method, so as to solve the problem that the existing technology cannot simultaneously possess excellent high strength and high thermal conductivity.

[0007] To achieve the above objectives, the first aspect of the present invention adopts the following technical solution: a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material, comprising Al, La, Ca, Mn, Mg, and unavoidable impurities; wherein the mass ratio of Al, La, Ca, Mn, and Mg is 3.6-4.4:3.6-4.4:0.3~1.3:0.1~0.5:1.

[0008] Furthermore, its microstructure includes an α-Mg matrix, an Al8Mn5 phase, Mg2Ca, and an Al2Ca phase. Specifically, by controlling the Ca content and regulating the partial molar Gibbs free energy of Al, the concentration of Al atoms in the matrix is ​​reduced. This allows the microstructure of this high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material to include an α-Mg matrix, an Al8Mn5 phase, Mg2Ca, and an Al2Ca phase, thus overcoming the inverse relationship between strength and thermal conductivity.

[0009] The second aspect of this invention adopts the following technical solution: a method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material as described in the first aspect of this invention, comprising the following steps: Step S1: Prepare the raw materials and refining agents according to the specified proportions; Step S2: Melt the prepared raw materials in a certain order and let them stand, then mix them with the refining agent and cast them in the first temperature range, using CO2 and SF6 as a protective atmosphere during this process; Step S3: Pour the melt into a metal mold that has cooled to room temperature. After solidification, immediately remove it and slowly immerse it in water to obtain an ingot. Step S4: Wrap the ingot with carbon powder and keep it at a temperature within the second temperature range for a period of time, then slowly cool it with water to obtain the ingot in the T4 state. Step S5: Hold the T4 state ingot at a third temperature range for a period of time, then air cool it to obtain the T4 state ingot.

[0010] Furthermore, the raw materials include pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca, and Mg-5 wt.% Mn ingots.

[0011] Furthermore, the first temperature range is 720-750℃.

[0012] Furthermore, in step S3, the temperature of the melt needs to be reduced to the fourth temperature range before casting.

[0013] Furthermore, the fourth temperature range is 670-690℃.

[0014] Furthermore, in step S4, the second temperature range is 470-520℃; and when 0.3≤Ca / Mg mass ratio≤0.8, the holding time is 10-12 h; when 0.8<Ca / Mg mass ratio≤1.1, the holding time is 5-7 h; and when 1.1<Ca / Mg mass ratio≤1.3, the holding time is 4-6 h.

[0015] Furthermore, in step S5, the third temperature range is 150-250℃; and when 0.3≤Ca / Mg mass ratio≤1.1, the holding time is 8-10h; when 1.1<Ca / Mg mass ratio≤1.3, the holding time is 6-8h.

[0016] Furthermore, the amount of the refining agent is 1 wt.% of the total amount of raw materials, and the components of the refining agent include MgCl2, KCl, BaCl2, CaF2, NaCl, CaCl2 and MgO.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention regulates the partial molar Gibbs free energy of Al in the matrix by adding Ca, and designs the alloy composition at the key nodes of the change of the partial molar Gibbs free energy of Al, so that the resulting alloy material has better comprehensive thermal conductivity and mechanical properties: through reasonable composition control, the elements in the alloy material will promote each other's precipitation, and the alloy elements in the matrix will consume each other, so as to achieve the purpose of synergistic improvement of mechanical properties and thermal conductivity, overcome the inverse relationship between strength and thermal conductivity, and far exceed the performance of most Mg-Al alloys in the prior art.

[0018] 2. The alloy material prepared by this invention has an ultimate tensile strength, tensile yield strength, and elongation of at least 155 MPa, 87 MPa, and 7.9% at 150°C, respectively, and its thermal conductivity is at least 92.5 W·K. -1 ·m -1 .

[0019] 3. The present invention uses common metal elements, which have the advantage of low cost and are easy to mass-produce. At the same time, the preparation method of the present invention adopts a combination of metal mold gravity casting and heat treatment, which is simple and easy to implement and suitable for industrial production. Detailed Implementation

[0020] The present invention will be further described in detail below through specific embodiments: A method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material includes the following steps: (1) Five raw materials are used: pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca and Mg-5 wt.% Mn. The raw materials and refining agent are prepared according to the ratio. The five raw materials are placed in a forced-air drying oven at 200℃ for more than 30 minutes. At the same time, the carbon steel crucible is polished with sandpaper, the surface welding slag is removed and then rinsed with alcohol. The crucible is placed in a forced-air drying oven at 200℃ together with the raw materials for heat preservation.

[0021] (2) Weigh out pure Mg, pure Al and Mg-5 wt.% Mn and add them into a carbon steel crucible and place it in a pit-type resistance furnace preheated to 400℃. Keep it at that temperature for more than 30 minutes. No gas protection is required during this period.

[0022] (3) Set the well-type resistance furnace to 720℃, and after the raw materials are completely melted, continue to keep it at the temperature for 20-40 minutes. During the entire heating and holding process, use a mixed gas of CO2:SF6=99:1 (mass ratio) as the protective gas, and the flow rate of the mixed gas is 2L / min.

[0023] (4) Add the preheated Mg-30 wt.% La and Mg-25 wt.% Ca to the molten Mg melt and stir continuously for 1-3 min to ensure that the melt composition is uniform. Take care not to damage the film on the surface of the melt. Then keep the Mg melt at 720-750℃ for 30 min.

[0024] (5) Weigh out the refining agent (composition: MgCl2:KCl:BaCl2:CaF2:NaCl:CaCl2:MgO=85:72:14:10:8:8:3, the amount of which is 1% of the mass of the Mg melt) that has been kept at 200℃ for more than 30 min, add it directly to the Mg alloy melt, and stir continuously for 1-3 min. Be careful not to damage the film on the surface of the melt, and then keep it at 20℃ for 30 min.

[0025] (6) Lower the temperature of the pit-type resistance furnace to 700-720℃, and after the furnace temperature reaches the set temperature, lower the temperature again to 670-690℃. During this period, in order to accurately control the melt temperature, a dried handheld thermocouple needs to be inserted into the Mg melt.

[0026] (7) When the temperature of the Mg melt drops to 670-690 ℃, the Mg melt is quickly poured into a metal mold that has been held at 200℃ for more than 30 minutes and has been cooled to room temperature in the air. Before pouring, the mold needs to be filled with protective gas, and the Mg melt is continuously purged with protective gas throughout the pouring process.

[0027] (8) After the Mg melt solidifies, immediately remove the ingot from the mold and immerse it in water at room temperature. To prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled, remove it from the water and let it dry.

[0028] (9) As a solution heat treatment (T4) for the alloy, the cast ingot is held in a box-type resistance furnace preheated to 470-520℃ for 4-12 hours. During this period, carbon powder needs to be wrapped around the surface of the ingot. After the heat treatment is completed, the ingot is taken out and immediately immersed in room temperature water for a short period of time. In order to prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled down, it is taken out of the water and dried to form an alloy ingot in the T4 state.

[0029] (10) As an aging heat treatment (T6) for the alloy, the alloy ingot in the T4 state is kept in a preheated drying oven at 150-250℃ for 6-10 hours, and then slowly cooled to room temperature in the air.

[0030] The high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy materials prepared above, by mass percentage, include: 3.6-4.4% Al; 3.6-4.4% La; 0-1.3% Ca; 0.1-0.5% Mn; with the balance being Mg and unavoidable impurities. All of these high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy materials exhibit mechanical properties and thermal conductivity exceeding those of the AE44 matrix alloy, indicating a successful breakthrough in overcoming the inverse relationship between mechanical and thermal conductivity.

[0031] The following examples illustrate this point.

[0032] Example 1 A high-temperature resistant, high-strength, and high-thermal-conductivity Mg-4.0Al-3.9La-0.5Mn-0.3Ca alloy material was prepared (wherein the mass ratio of Mg:Al:La:Mn:Ca is 1:4.0:3.9:0.5:0.3). (1) Five raw materials are used: pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca and Mg-5 wt.% Mn. Weigh the required raw materials according to the proportions and place the five raw materials in a 200℃ forced-air drying oven for more than 30 minutes to remove the moisture from the raw materials. At the same time, the carbon steel crucible is polished clean with sandpaper, the surface welding slag is removed and then rinsed clean with alcohol. It is then placed in a 200℃ forced-air drying oven together with the raw materials for heat preservation.

[0033] (2) Weigh out pure Mg, pure Al and Mg-5 wt.% Mn and add them into a carbon steel crucible and place it in a pit-type resistance furnace preheated to 400℃. Keep it at that temperature for more than 30 minutes. No gas protection is required during this period.

[0034] (3) Set the well-type resistance furnace to 720℃, observe from time to time whether the raw material has melted, and continue to keep it warm for 40 min after the raw material has completely melted. During the entire heating and holding process, use a mixed gas of CO2:SF6=99:1 (mass ratio) as the protective gas, and the flow rate of the mixed gas is 2 L / min.

[0035] (4) Add the preheated Mg-30 wt.% La and Mg-25 wt.% Ca to the molten Mg melt and stir continuously for 3 min to ensure that the melt composition is uniform. Take care not to damage the film on the surface of the melt. Then keep the Mg melt at 750℃ for 30 min.

[0036] (5) Weigh out the refining agent (composition: MgCl2:KCl:BaCl2:CaF2:NaCl:CaCl2:MgO=85:72:14:10:8:8:3, and its amount is 1% of the mass of Mg melt) that has been kept at 200℃ for more than 30 min, add it directly to the Mg melt, and stir continuously for 3 min. Be careful not to damage the film on the surface of the melt, and then keep it at 20℃ for 30 min.

[0037] (6) Lower the temperature of the pit-type resistance furnace to 700°C, and after the furnace temperature reaches the set temperature, lower the temperature again to 670°C. During this period, in order to accurately control the melt temperature, a dried handheld thermocouple needs to be inserted into the Mg melt.

[0038] (7) When the temperature of the Mg melt drops to 670°C, the Mg melt is quickly poured into a metal mold that has been held at 200°C for more than 30 minutes and has been cooled to room temperature in the air. Before pouring, the mold needs to be filled with protective gas, and the Mg melt is continuously purged with protective gas throughout the pouring process.

[0039] (8) After the Mg melt solidifies, immediately remove the ingot from the mold and immerse it in water at room temperature. To prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled, remove it from the water and let it dry.

[0040] (9) As a solution heat treatment (T4) for the alloy, the cast ingot is held in a box-type resistance furnace preheated to 520°C for 12 hours. During this period, carbon powder needs to be wrapped around the surface of the ingot. After the heat treatment is completed, the ingot is taken out and immediately immersed in water at room temperature for a short period of time. In order to prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled down, it is taken out of the water and dried to form an alloy ingot in the T4 state.

[0041] (10) As an aging heat treatment (T6) for the alloy, the alloy ingot in the T4 state is kept in a preheated drying oven at 180°C for 10 h, and then slowly cooled to room temperature in the air.

[0042] The Mg-4.0Al-3.9La-0.5Mn-0.3Ca alloy material prepared in this embodiment has an ultimate tensile strength of 169 MPa, a tensile yield strength of 98 MPa, an elongation of 9.7% at 150℃, and a thermal conductivity of 106.6 W·K. -1 ·m -1 .

[0043] Example 2 Prepare a high-temperature resistant, high-strength, and high-thermal-conductivity Mg-4.4Al-3.6La-0.1Mn-0.8Ca alloy material (wherein the mass ratio of Mg:Al:La:Mn:Ca is 1:4.4:3.6:0.1:0.8). (1) Five raw materials are used: pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca and Mg-5 wt.% Mn. Weigh the required raw materials according to the proportions and place the five raw materials in a 200℃ forced-air drying oven for more than 30 minutes to remove the moisture from the raw materials. At the same time, the carbon steel crucible is polished clean with sandpaper, the surface welding slag is removed and then rinsed clean with alcohol. It is then placed in a 200℃ forced-air drying oven together with the raw materials for heat preservation.

[0044] (2) Weigh out pure Mg, pure Al and Mg-5 wt.% Mn and add them into a carbon steel crucible and place it in a pit-type resistance furnace preheated to 400℃. Keep it at that temperature for more than 30 minutes. No gas protection is required during this period.

[0045] (3) Set the well-type resistance furnace to 720℃, observe from time to time whether the raw material has melted, and continue to keep it warm for 40 min after the raw material has completely melted. During the entire heating and holding process, use a mixed gas of CO2:SF6=99:1 (mass ratio) as the protective gas, and the flow rate of the mixed gas is 2 L / min.

[0046] (4) Add the preheated Mg-30 wt.% La and Mg-25 wt.% Ca to the molten Mg melt and stir continuously for 3 min to ensure that the melt composition is uniform. Take care not to damage the film on the surface of the melt. Then keep the Mg melt at 750℃ for 30 min.

[0047] (5) Weigh out the refining agent (composition: MgCl2:KCl:BaCl2:CaF2:NaCl:CaCl2:MgO=85:72:14:10:8:8:3, and its amount is 1% of the mass of Mg melt) that has been kept at 200℃ for more than 30 min, add it directly to the Mg melt, and stir continuously for 3 min. Be careful not to damage the film on the surface of the melt, and then keep it at 20℃ for 30 min.

[0048] (6) Lower the temperature of the pit-type resistance furnace to 720°C, and after the furnace temperature reaches the set temperature, lower the temperature again to 690°C. During this period, in order to accurately control the melt temperature, a dried handheld thermocouple needs to be inserted into the Mg melt.

[0049] (7) When the temperature of the Mg melt drops to 670°C, the Mg melt is quickly poured into a metal mold that has been held at 200°C for more than 30 minutes and has been cooled to room temperature in the air. Before pouring, the mold needs to be filled with protective gas, and the Mg melt is continuously purged with protective gas throughout the pouring process.

[0050] (8) After the Mg melt solidifies, immediately remove the ingot from the mold and immerse it in water at room temperature. To prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled, remove it from the water and let it dry.

[0051] (9) As a solution heat treatment (T4) for the alloy, the cast ingot is held in a box-type resistance furnace preheated to 520°C for 10 hours. During this period, carbon powder needs to be wrapped around the surface of the ingot. After the heat treatment is completed, the ingot is taken out and immediately immersed in water at room temperature for a short period of time. In order to prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled down, it is taken out of the water and dried to form an alloy ingot in the T4 state.

[0052] (10) As an aging heat treatment (T6) for the alloy, the alloy ingot in the T4 state is kept in a preheated drying oven at 250°C for 8 hours, and then slowly cooled to room temperature in the air.

[0053] The Mg-4.0Al-3.9La-0.5Mn-0.3Ca alloy material prepared in this embodiment has an ultimate tensile strength of 184 MPa, a tensile yield strength of 110 MPa, an elongation of 14.4% at 150℃, and a thermal conductivity of 112 W·K. -1 ·m -1 .

[0054] Example 3 A high-temperature resistant, high-strength, and high-thermal-conductivity Mg-4.2Al-3.8La-0.4Mn-1.3Ca alloy material was prepared (wherein the mass ratio of Mg:Al:La:Mn:Ca is 1:4.2:3.8:0.4:1.3). (1) Five raw materials are used: pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca and Mg-5 wt.% Mn. Weigh the required raw materials according to the proportions and place the five raw materials in a 200℃ forced-air drying oven for more than 30 minutes to remove the moisture from the raw materials. At the same time, the carbon steel crucible is polished clean with sandpaper, the surface welding slag is removed and then rinsed clean with alcohol. It is then placed in a 200℃ forced-air drying oven together with the raw materials for heat preservation.

[0055] (2) Weigh out pure Mg, pure Al and Mg-5 wt.% Mn and add them into a carbon steel crucible and place it in a pit-type resistance furnace preheated to 400℃. Keep it at that temperature for more than 30 minutes. No gas protection is required during this period.

[0056] (3) Set the well-type resistance furnace to 720℃, observe from time to time whether the raw material has melted, and continue to keep it warm for 30 min after the raw material has completely melted. During the entire heating and holding process, use a mixed gas of CO2:SF6=99:1 (mass ratio) as the protective gas, and the flow rate of the mixed gas is 2 L / min.

[0057] (4) Add the preheated Mg-30 wt.% La and Mg-25 wt.% Ca to the molten Mg melt and stir continuously for 1 min to ensure that the melt composition is uniform. Take care not to damage the film on the surface of the melt. Then keep the Mg melt at 720℃ for 30 min.

[0058] (5) Weigh out the refining agent (composition: MgCl2:KCl:BaCl2:CaF2:NaCl:CaCl2:MgO=85:72:14:10:8:8:3, and its amount is 1% of the mass of Mg melt) that has been kept at 200℃ for more than 30 min, add it directly to the Mg melt, and stir continuously for 1 min. Be careful not to damage the film on the surface of the melt, and then keep it at 20℃ for 30 min.

[0059] (6) Lower the temperature of the pit-type resistance furnace to 700°C, and after the furnace temperature reaches the set temperature, lower the temperature again to 670°C. During this period, in order to accurately control the melt temperature, a dried handheld thermocouple needs to be inserted into the Mg melt.

[0060] (7) When the temperature of the Mg melt drops to 670°C, the Mg melt is quickly poured into a metal mold that has been held at 200°C for more than 30 minutes and has been cooled to room temperature in the air. Before pouring, the mold needs to be filled with protective gas, and the Mg melt is continuously purged with protective gas throughout the pouring process.

[0061] (8) After the Mg melt solidifies, immediately remove the ingot from the mold and immerse it in water at room temperature. To prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled, remove it from the water and let it dry.

[0062] (9) As a solution heat treatment (T4) for the alloy, the cast ingot is held in a box-type resistance furnace preheated to 470°C for 4 hours. During this period, carbon powder needs to be wrapped around the surface of the ingot. After the heat treatment is completed, the ingot is taken out and immediately immersed in water at room temperature for a short period of time. In order to prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled down, it is taken out of the water and dried to form an alloy ingot in the T4 state.

[0063] (10) As an aging heat treatment (T6) for the alloy, the alloy ingot in the T4 state is kept in a preheated drying oven at 150°C for 8 hours, and then slowly cooled to room temperature in the air.

[0064] The Mg-4.0Al-3.9La-0.5Mn-0.3Ca alloy material prepared in this embodiment has an ultimate tensile strength of 169 MPa, a tensile yield strength of 98 MPa, an elongation of 9.7% at 150℃, and a thermal conductivity of 111.2 W·K. -1 ·m -1 .

[0065] Example 4 A high-temperature resistant, high-strength, and high-thermal-conductivity Mg-3.6Al-4.4La-0.3Mn-0.9Ca alloy material was prepared (wherein the mass ratio of Mg:Al:La:Mn:Ca is 1:3.6:4.4:0.3:1.9). (1) Five raw materials are used: pure Mg, pure Al, Mg-30 wt.% La, Mg-25 wt.% Ca and Mg-5 wt.% Mn. Weigh the required raw materials according to the proportions and place the five raw materials in a 200℃ forced-air drying oven for more than 30 minutes to remove the moisture from the raw materials. At the same time, the carbon steel crucible is polished clean with sandpaper, the surface welding slag is removed and then rinsed clean with alcohol. It is then placed in a 200℃ forced-air drying oven together with the raw materials for heat preservation.

[0066] (2) Weigh out pure Mg, pure Al and Mg-5 wt.% Mn and add them into a carbon steel crucible and place it in a pit-type resistance furnace preheated to 400℃. Keep it at that temperature for more than 30 minutes. No gas protection is required during this period.

[0067] (3) Set the well-type resistance furnace to 720℃, observe from time to time whether the raw material has melted, and continue to keep it warm for 20 minutes after the raw material has completely melted. During the entire heating and holding process, use a mixed gas of CO2:SF6=99:1 (mass ratio) as the protective gas, and the flow rate of the mixed gas is 2 L / min.

[0068] (4) Add the preheated Mg-30 wt.% La and Mg-25 wt.% Ca to the molten Mg melt and stir continuously for 2 min to ensure that the melt composition is uniform. Take care not to damage the film on the surface of the melt. Then keep the Mg melt at 735℃ for 30 min.

[0069] (5) Weigh out the refining agent (composition: MgCl2:KCl:BaCl2:CaF2:NaCl:CaCl2:MgO=85:72:14:10:8:8:3, and its amount is 1% of the mass of Mg melt) that has been kept at 200℃ for more than 30 min, add it directly to the Mg melt, and stir continuously for 2 min. Be careful not to damage the film on the surface of the melt, and then keep it at 20℃ for 30 min.

[0070] (6) Lower the temperature of the pit-type resistance furnace to 710°C, and after the furnace temperature reaches the set temperature, lower the temperature again to 680°C. During this period, in order to accurately control the melt temperature, a dried handheld thermocouple needs to be inserted into the Mg melt.

[0071] (7) When the temperature of the Mg melt drops to 670°C, the Mg melt is quickly poured into a metal mold that has been held at 200°C for more than 30 minutes and has been cooled to room temperature in the air. Before pouring, the mold needs to be filled with protective gas, and the Mg melt is continuously purged with protective gas throughout the pouring process.

[0072] (8) After the Mg melt solidifies, immediately remove the ingot from the mold and immerse it in water at room temperature. To prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled, remove it from the water and let it dry.

[0073] (9) As a solution heat treatment (T4) for the alloy, the cast ingot is held in a box-type resistance furnace preheated to 490°C for 6 hours. During this period, carbon powder needs to be wrapped around the surface of the ingot. After the heat treatment is completed, the ingot is taken out and immediately immersed in water at room temperature for a short period of time. In order to prevent the ingot from cracking due to uneven local heat distribution, this process should not be too fast. After the ingot has completely cooled down, it is taken out of the water and dried to form an alloy ingot in the T4 state.

[0074] (10) As an aging heat treatment (T6) for the alloy, the alloy ingot in the T4 state is kept in a preheated drying oven at 180°C for 9 h, and then slowly cooled to room temperature in the air.

[0075] The Mg-4.0Al-3.9La-0.5Mn-0.3Ca alloy material prepared in this embodiment has an ultimate tensile strength of 190 MPa, a tensile yield strength of 121 MPa, an elongation of 18.6% at 150℃, and a thermal conductivity of 113.6 W·K. -1 ·m -1 .

[0076] Comparative Example 1 The difference from Example 1 is that Ca is not added (i.e., Mg-25 wt. % Ca is not added, so that the amount of Mg that is insufficient in the alloy material is supplemented by pure Mg), otherwise the same.

[0077] Comparative Example 2 It uses AZ91 alloy.

[0078] Comparative Example 3 Compared to Example 1, Mg-5 wt.% Mn was replaced with pure Zn in equal amounts, and the amount of Mg that was insufficient in the alloy material was supplemented by pure Mg, while the rest remained the same.

[0079] Comparative Example 4 The only difference from Example 1 is that the subsequent operations (9) and (10) are not performed.

[0080] Comparative Example 5 The only difference from Example 2 is that the subsequent operations (9) and (10) are not performed.

[0081] Comparative Example 6 The only difference from Example 3 is that the subsequent operations (9) and (10) are not performed.

[0082] Comparative Example 7 The only difference from Example 4 is that the subsequent operations (9) and (10) are not performed.

[0083] In the preparation process of Examples 1-4, it should be noted that during the mixing of Mg melt and refining agent, a dense protective film will be generated on the surface of Mg melt by the mixed gas of CO2:SF6=99:1, which can effectively prevent Mg evaporation. Therefore, during the stirring process, care should be taken not to damage the protective film on the surface of the melt to prevent Mg evaporation, which would make it difficult to control the composition of Mg alloy melt. At the same time, the damaged protective film should be avoided from becoming inclusions, so as to reduce the performance of the final Mg alloy material.

[0084] The purpose of the two cooling cycles is that when the temperature of the pit-type resistance furnace is reduced, the resistance wire immediately stops working. The various gases inside the pit-type resistance furnace have very low heat capacity, so the temperature of the carbon steel crucible drops rapidly. However, the heat capacity of Mg melt is very high, so the temperature of Mg melt drops slowly, resulting in a large temperature difference between the surface and the center of Mg melt. When the internal temperature of Mg melt reaches the predetermined value, its surface temperature will be lower than the predetermined value, and it may even solidify to some extent, affecting the casting process.

[0085] The ultimate tensile strength (UTS), tensile yield strength (TYS), elongation (EL), and thermal conductivity at 150°C for Examples 1-4 and Comparative Examples 1-7 are shown in Table 1.

[0086] Table 1 As can be seen from Table 1, the magnesium alloy materials prepared in Examples 1-4 can better balance mechanical properties and thermal conductivity compared with the magnesium alloy materials prepared in Comparative Examples 1-7.

[0087] As can be seen from Comparative Examples 1-3, although only one or two components were changed compared to the corresponding embodiments, and the final magnesium alloy materials showed some reduction in mechanical or thermal conductivity, Therefore, the magnesium alloy materials prepared in Comparative Examples 1-3 cannot simultaneously achieve good thermal conductivity and mechanical properties.

[0088] As for Comparative Examples 4-7, the two heat treatment steps of solution treatment and aging were reduced. Although the thermal conductivity did not change significantly, the mechanical properties were severely reduced compared to Examples 1-4. Therefore, magnesium alloy materials prepared by a single casting method also could not achieve good mechanical and thermal properties.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature-resistant, high-strength, high-thermal-conductivity cast magnesium alloy material, characterized in that, The Al, La, Ca, Mn and Mg have a mass ratio of 3.6-4.4:3.6-4.4:0.3-1.3:0.1-0.5:

1.

2. The high-temperature-resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material according to claim 1, characterized in that, The microstructure includes an α-Mg matrix, Al8Mn5 phase, Mg2Ca and Al2Ca phase.

3. A method for preparing a high-temperature-resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material as claimed in claim 1 or 2, characterized in that, The method comprises the following steps: Step S1, preparing raw materials and refining agents in proportion; Step S2, melting the prepared raw materials in a certain order and standing, then mixing with the refining agents and casting in a first temperature range, and using CO2 and SF6 as protective atmosphere in the process; Step S3, pouring the melt into a metal mold cooled to room temperature, taking out immediately after solidification and slowly immersing in water to obtain an ingot; Step S4, wrapping the ingot with carbon powder and heat treating in a second temperature range for a period of time, then slowly water cooling to obtain a T4 state ingot; Step S5, heat treating the T4 state ingot in a third temperature range for a period of time, then air cooling to obtain a T4 state ingot.

4. The preparation method of the high-temperature-resistant, high-strength and high-thermal-conductivity cast magnesium alloy material according to claim 3, characterized in that, The raw materials include pure Mg, pure Al, Mg-30 wt. % La, Mg-25 wt. % Ca and Mg-5 wt. % Mn ingots.

5. The method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material according to claim 3, characterized in that, The first temperature range is 720-750℃.

6. The method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material according to claim 3, characterized in that, In the step S3, the temperature of the melt needs to be lowered to a fourth temperature range before casting.

7. The method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material according to claim 6, characterized in that, The fourth temperature range is 670-690℃.

8. The preparation method of the high-temperature-resistant, high-strength and high-thermal-conductivity cast magnesium alloy material according to claim 3, characterized in that, In the step S4, the second temperature range is 470-520℃; and when 0.3≤Ca / Mg mass ratio≤0.8, the heat treatment time is 10-12 h; when 0.8 9. The method for preparing a high-temperature resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material according to claim 3, characterized in that, In the step S5, the third temperature range is 150-250℃; and when 0.3≤Ca / Mg mass ratio≤1.1, the heat treatment time is 8-10 h; when 1.1 10. The method according to claim 3, wherein the high-temperature-resistant, high-strength, and high-thermal-conductivity cast magnesium alloy material is prepared by the following steps. The amount of the refining agent is 1 wt. % of the total amount of raw materials, and the components of the refining agent include MgCl2, KCl, BaCl2, CaF2, NaCl, CaCl2 and MgO.

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