High-thermal-conductivity Mg-Zn series magnesium alloy suitable for rheoforming and preparation and processing method of high-thermal-conductivity Mg-Zn series magnesium alloy

Abstract

The invention discloses a high-thermal-conductivity Mg-Zn magnesium alloy suitable for rheoforming and a preparation and processing method of the high-thermal-conductivity Mg-Zn magnesium alloy. The alloy comprises the following components in percentage by weight: 1-8% of Zn, 0.5-5% of Cu, 0.2-2% of Sn, 0.2-1% of Sc and the balance of Mg and inevitable impurities. The preparation and processing method comprises the following steps: (1) preparing raw materials according to the composition of the alloy components, and smelting by adopting a medium-frequency induction furnace and taking mixed gas of tetrafluoroethane and argon as a protective atmosphere; (2) mechanical stirring and ultrasonic synergistic stirring are combined to form a uniform melt; (3) preparing semi-solid slurry with a solid phase ratio of 35-50%; (4) forming; (5) cooling and opening the mold; (6) the obtained rheoforming blank is heated to 340-430 DEG C, heat preservation is conducted for 2-12 h, and after heat preservation is finished, quenching is conducted immediately, and cooling is conducted to the room temperature; (7) pre-aging; and (8) aging. By reasonably designing alloy components and optimizing rheoforming parameters, the defects of shrinkage, hot cracking and segregation of a conventional cast Mg-Zn alloy are overcome, and meanwhile, high heat conductivity and mechanical properties are guaranteed.

Description

Technical Field

[0001] This invention relates to a high thermal conductivity Mg-Zn magnesium alloy suitable for rheological processing and its preparation and processing method, belonging to the field of industrial light metal structural materials. Background Technology

[0002] With the rapid development of miniaturization of electronic devices, automotive electrification, and new energy technologies, efficient heat dissipation has become a core requirement for ensuring equipment reliability and extending service life. Magnesium alloys, as the lowest density metallic structural material currently used in engineering applications, possess both thermal conductivity and mechanical properties. They have irreplaceable application value in fields such as heat dissipation substrates for electronic chips, automotive motor housings, LED heat sinks, and 5G base station heat dissipation modules. They can reduce equipment energy consumption and structural load, and their thermal conductivity can quickly dissipate heat generated by core components, which is of great significance for promoting the industrial upgrading of "energy conservation and consumption reduction" and "high performance".

[0003] Currently available high thermal conductivity magnesium alloys are mainly divided into two categories: cast and wrought. Wrought thermal conductivity magnesium alloys require plastic processing processes such as rolling, extrusion, and forging. Although high mechanical properties can be achieved by refining grains and controlling texture, the processing procedures are complex, the production cycle is long, and the cost is high. They are mostly used in high-end fields such as aerospace and military equipment with stringent performance requirements, and it is difficult to meet the needs of large-scale, low-cost applications in the civilian market. Cast high thermal conductivity magnesium alloys do not require complex plastic processing and can be formed through processes such as sand casting and metal mold casting. They have low production costs and high production efficiency, and have greater advantages in the civilian heat dissipation field. This is the core direction for the current civilian application development of high thermal conductivity magnesium alloys.

[0004] Conventional cast high thermal conductivity magnesium alloys are mainly Mg-Al based. To balance mechanical and casting properties, the industry often modifies them by adding rare earth elements (Nd, Gd, Y) or alkaline earth elements (Ca, Sr). However, in Mg-Al alloys, Al readily reacts with Mg to form MgO. 17 Al 12 The second phase has a much lower thermal conductivity than the magnesium matrix, making it unsuitable for the high heat dissipation requirements of high-power electronic chips and high-efficiency motors. Additionally, there are Mg-RE and Mg-Si systems, whose thermal conductivity is also not ideal.

[0005] In comparison, Mg-Zn alloys exhibit superior thermal conductivity: the thermal conductivity of the MgZn2 second phase formed by Zn and Mg is higher than that of Mg. 17 Al 12Furthermore, Zn can enhance the mechanical properties of the magnesium matrix through solid solution strengthening, giving Mg-Zn alloys the natural advantage of both high thermal conductivity and high mechanical properties. However, Mg-Zn alloys are currently mostly used in wrought alloy form. If prepared using conventional casting processes, they will face a series of intractable defects: ① Wide solidification range (approximately 120-150℃), with a solidification shrinkage rate as high as 4.5%-5.0%, easily resulting in shrinkage cavities, porosity, and low density; ② Severe tendency to hot cracking, especially when the Zn content is >3%, the grain boundaries are prone to precipitating low-melting-point MgZn2 eutectic phase (melting point approximately 340℃), which easily leads to intergranular cracking under thermal stress in the later stages of solidification; ③ Obvious macroscopic segregation of Zn element, resulting in thermal conductivity differences of more than 15% in different regions of the alloy, and poor heat dissipation uniformity; ④ Coarse grains, enhanced grain boundary scattering effect, which not only reduces mechanical properties but also decreases thermal conductivity. These defects make it difficult to achieve industrial application of conventionally cast Mg-Zn alloys.

[0006] Rheology forming, as a core process in semi-solid metal processing, provides a key path to solving the aforementioned problems. By controlling the melt cooling rate and stirring conditions, it pre-prepares a semi-solid slurry with a solid phase ratio of 30%-60%, which is then die-cast or forged. This process offers multiple advantages: it significantly reduces porosity and looseness, increases alloy density, suppresses solidification shrinkage, and reduces the tendency for hot cracking. It is particularly well-suited to the wide solidification range of Mg-Zn alloys. The forming process can break up grains, refining grain size, improving microstructure uniformity, and reducing Zn segregation. However, current industry practices using rheology forming directly on Mg-Zn alloys still face challenges such as difficulty in controlling Zn segregation and uneven dispersion of solid particles, failing to fully leverage the technological advantages of rheology forming and the material advantages of Mg-Zn alloys. Summary of the Invention

[0007] The purpose of this invention is to provide a high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming and its preparation and processing method. By rationally designing the alloy composition and optimizing the rheological forming parameters, the shrinkage, hot cracking, and segregation defects of conventional cast Mg-Zn magnesium alloys are solved, while ensuring high thermal conductivity and mechanical properties.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming has the following composition by mass percentage: Zn: 1~8%, Cu: 0.5~5%, Sn: 0.2~2%, Sc: 0.2~1%, with the balance being Mg and unavoidable impurities.

[0009] Preferably, the total content of Zn and Cu is 2-12%, the content ratio of Zn to Cu is 1.5-6, and the content ratio of Sn to Sc is 1-3.

[0010] Preferably, among unavoidable impurities, the content of a single impurity is ≤0.05%, and the total impurity content is ≤0.15%.

[0011] A method for preparing and processing a high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming includes the following steps: (1) Prepare raw materials according to the alloy composition, and use a medium frequency induction furnace with a protective atmosphere of a mixture of tetrafluoroethane and argon to carry out smelting; (2) Mechanical stirring combined with ultrasonic synergistic stirring is used to form a homogeneous melt; (3) Cool the temperature to 570-600℃ at a rate of 5-8℃ / min, adjust the mechanical stirring speed to 200-300r / min, turn off the ultrasonic stirring, keep the temperature for 20-25min, and prepare a semi-solid slurry with a solid phase ratio of 35-50%. (4) Preheat the mold to 300~350℃, press 50~60% of the slurry into the cavity at a low speed of 0.5~1m / s to expel the air in the cavity; press the remaining slurry into the cavity at a high speed of 2~3m / s, with an injection pressure of 80~120MPa and a holding time of 10~15s. (5) After the pressure holding is completed, cool to below 200°C at a rate of 15~20°C / min, open the mold and take out the molded part to obtain the rheoformed magnesium alloy blank; (6) Place the rheoformed billet into a box-type resistance furnace and heat it to 340-430℃ at a rate of 10-15℃ / min. Hold it for 2-12 hours. After holding, immediately immerse the billet in hot water at 80-90℃ for quenching and cool it to room temperature. (7) Place the quenched blank into a low-temperature aging furnace, heat it to 90~120℃, hold it for 2~10h, and air cool it to room temperature; (8) Place the pre-aged billet back into the aging furnace, heat it to 165~220℃, keep it at that temperature for 10~72h, and then air cool it to room temperature.

[0012] Furthermore, in step (1), Zn, Cu, and Sn are added in the form of pure metal particles, and Sc is added in the form of Mg-20Sc master alloy.

[0013] Further, in step (1), pure magnesium ingots are first added to a crucible and heated to 680~720℃ to completely melt them, and kept at that temperature for 10~15min; pure Zn particles and pure Cu particles are added in sequence, with an interval of 5~8min between the two additions, and the stirring rate is 300~400r / min, and kept at that temperature for 20~25min until completely dissolved; the temperature is lowered to 700~710℃, pure Sn particles are added, and the mixture is stirred for 15~20min; then Mg-20Sc master alloy is added and stirred for 25~30min; the temperature is raised to 720~750℃, C2Cl6 degassing agent is added, with the addition amount being 0.1~0.3% of the total mass of the alloy, and the mixture is stirred for 10~15min and then allowed to stand for 15~20min to remove the surface slag.

[0014] Furthermore, in step (1), the power of the medium-frequency induction furnace is 5~10kW, and the volume ratio of tetrafluoroethane to argon is 1:99.

[0015] Further, in step (2), a certain amount of magnesium melt is taken out as needed and placed into a special material cup. Under the protection of a mixed gas of "tetrafluoroethane + argon", the temperature is reduced to 650~680℃ and kept at that temperature for 10~15min. Then, "mechanical stirring + ultrasonic synergistic stirring" is turned on. The mechanical stirring rate is 500~600r / min, the stirring paddle is spiral, the material is H13 steel, and the surface is coated with Al2O3 coating for corrosion protection. The ultrasonic power is 300~400W, the ultrasonic frequency is 20~25kHz, and it is continued for 15~20min to break the initial grains and form a uniform melt.

[0016] Furthermore, in step (4), the mold cavity is coated with graphite lubricant with a thickness of 5~10μm.

[0017] The beneficial effects of this invention are: The magnesium alloy of this invention has a room temperature thermal conductivity ≥140W / (m•K), tensile strength ≥210MPa, elongation ≥5%, density ≥90%, and hot cracking rate <0.5%, which can meet the demand for high thermal conductivity, high mechanical properties, and low cost magnesium alloys in civilian fields such as heat dissipation substrates for electronic chips and automotive motor housings.

[0018] The preparation and processing method of this invention optimizes rheological molding parameters, which can solve the shrinkage, hot cracking and segregation defects of conventional cast Mg-Zn magnesium alloys, while ensuring high thermal conductivity and mechanical properties. It has important practical significance and economic value for filling the gap in existing technology, meeting the high heat dissipation requirements in the civilian field and promoting the large-scale application of high thermal conductivity magnesium alloys. Detailed Implementation

[0019] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the solution of the present invention.

[0020] The present invention relates to a high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming. The alloy composition, by mass percentage, is as follows: Zn: 1~8%, Cu: 0.5~5%, Sn: 0.2~2%, Sc: 0.2~1%, with the balance being Mg and unavoidable impurities, wherein the individual impurity is ≤0.05% and the total impurities are ≤0.15%.

[0021] In the high thermal conductivity Mg-Zn magnesium alloy of this invention, the roles of each element are as follows: (1) Zn: The main strengthening element, which can be dissolved in the Mg matrix to form a solid solution, and at the same time precipitate second phases such as Mg7Zn3 and MgZn2 to improve the strength of the alloy; (2) Cu: The second phase composition is optimized in conjunction with Zn, and its thermal and electrical conductivity is higher than that of the pure Mg-Zn phase. At the same time, it reduces the solidification range of the alloy and improves its rheological properties. (3) Sn: refines grains, inhibits Sc agglomeration, and improves the corrosion resistance of the alloy (forming a dense SnO2 oxide film on the alloy surface). (4)Sc: A powerful grain refiner that can control the grain size of the alloy after rheoforming to 8~20μm, reduce the obstacle of grain boundaries to heat conduction, and improve the high-temperature stability of the alloy.

[0022] The high thermal conductivity Mg-Zn magnesium alloy of this invention is further preferably designed to meet the following synergistic compositional constraints: Total Zn and Cu content control: Zn + Cu = 2~12%; Zn to Cu ratio limit: Zn / Cu = 1.5~6; Sn to Sc ratio limit: Sn / Sc = 1~3. Analyzing from the principle: (1) Total Zn and Cu content control (2~12%): As alloying elements, if the total amount of Zn and Cu is too low, there will be insufficient solid solution atoms, which will not effectively strengthen the material; if the total amount is too high, it will exceed the solid solution limit of the matrix, and the precipitation of coarse second phase will lead to increased brittleness. In terms of effect, it can balance the strength and toughness of the material, both by hindering dislocation movement through solid solution atoms to improve strength, and by avoiding the decrease in plasticity caused by excessive second phase. At the same time, it is compatible with the solid solution ability of most matrix metals, reduces compositional segregation, and ensures the uniformity of the microstructure.

[0023] (2) Control of Zn to Cu ratio (Zn / Cu=1.5~6): Zn and Cu have different atomic radii and electronic structures. When the ratio is lower than 1.5, Cu is prone to forming too much hard and brittle MgZnCu phase, which has no heat treatment strengthening ability. When the ratio is higher than 6, Zn is prone to agglomerate to form a low melting point phase. Under a reasonable ratio, the two can form an appropriate microstructure, which can simultaneously improve the material hardness and elongation, and achieve synergistic mechanical properties.

[0024] (3) Sn to Sc ratio control (Sn / Sc=1~3): Sc can form heterogeneous nucleation cores to refine grains but is prone to agglomeration. Sn can prevent Sc agglomeration by filling interatomic gaps and improve processability. When the ratio is less than 1, Sc agglomeration leads to grain refinement failure. When it is more than 3, Sn excess forms a low-hardness phase. In terms of effect, it can achieve uniform distribution of Sc, improve the grain refinement effect, improve the balance of strength and plasticity, and also improve the strength retention rate of the material at 200~300℃, reduce deformation resistance, and make the alloy easier to form.

[0025] (4) Overall synergistic effect: The matrix regulation of Zn-Cu (which determines the basic mechanical properties) provides a stable matrix for the micro-optimization of Sn-Sc (such as grain refinement), and the optimization of Sn-Sc compensates for the possible decrease in plasticity due to high Zn-Cu content. In effect, it achieves a three-dimensional improvement in the material's mechanical properties (strength and toughness), environmental adaptability (corrosion resistance, high temperature stability), and processability, avoiding the performance shortcomings caused by single-element regulation.

[0026] The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to the present invention includes the following steps: 1. Use a medium-frequency induction furnace (power 5~10kW) with a protective atmosphere of tetrafluoroethane + argon gas mixture (volume ratio 1:99) to prevent Mg oxidation and combustion. First, add pure magnesium ingots to the crucible and heat to 680~720℃ to completely melt them, and hold for 10~15min. Then, add pure Zn particles and pure Cu particles in sequence (adding them 5~8min apart to avoid local overheating), stirring at 300~400r / min, and hold for 20~25min until completely dissolved. Cool down to 700~710℃, add pure Sn particles, and stir for 15~20min. Then, add Mg-20Sc master alloy and stir for 25~30min. Heat to 720~750℃, add C2Cl6 degassing agent (addition amount is 0.1~0.3% of the total alloy mass), stir for 10~15min, and let stand for 15~20min to remove surface slag.

[0027] 2. Take out a certain amount of magnesium melt as needed and put it into a special material cup. Under the protection of a mixture of tetrafluoroethane and argon, cool it to 650~680℃ and hold it for 10~15 minutes. Turn on the mechanical stirring and ultrasonic synergistic stirring. The mechanical stirring rate is 500~600r / min (the stirring paddle is a spiral type, made of H13 steel, and coated with Al2O3 coating for corrosion protection). The ultrasonic power is 300~400W and the ultrasonic frequency is 20~25kHz. Continue for 15~20 minutes to break up the initial grains and form a uniform melt.

[0028] 3. Cool the material to 570-600℃ at a gradient rate of 5-8℃ / min, adjust the mechanical stirring rate to 200-300r / min, turn off the ultrasonic stirring, and keep it at this temperature for 20-25min to prepare a semi-solid slurry with a solid phase ratio of 35-50%.

[0029] 4. Preheat the mold to 300~350℃, and coat the mold cavity with graphite lubricant (thickness 5~10μm); press 50~60% of the slurry into the cavity at a low speed of 0.5~1m / s to expel air from the cavity and avoid air entrapment; press the remaining slurry into the cavity at a high speed of 2~3m / s, with an injection pressure of 80~120MPa and a holding time of 10~15s.

[0030] 5. After the pressure holding period, cool the mold to below 200°C at a rate of 15~20°C / min, open the mold and remove the molded part to obtain the rheologically formed magnesium alloy blank.

[0031] 6. Place the rheoformed blank into a box-type resistance furnace and heat it to 340-430℃ at a rate of 10-15℃ / min. Hold it at this temperature for 2-12 hours. After holding, immediately immerse the blank in hot water at 80-90℃ for quenching and cool it to room temperature.

[0032] 7. Place the quenched blank into a low-temperature aging furnace, heat it to 90~120℃, hold it for 2~10 hours, and then air cool it to room temperature.

[0033] 8. Place the pre-aged billet back into the aging furnace, heat it to 165~220℃, hold it for 10~72 hours, and air cool it to room temperature.

[0034] In the following embodiments, the test methods for each performance parameter: thermal conductivity, tensile strength, elongation, density, and hot cracking rate are as follows: Thermal conductivity: Laser flash method. The front side of the sample is rapidly heated with a laser pulse, and the temperature rise curve of the back side over time is measured. The thermal diffusivity is calculated, and then combined with the specific heat capacity and density to convert it into thermal conductivity.

[0035] Tensile strength and elongation: National standard GB 228.1.

[0036] Density: Archimedes' displacement method. First, weigh the mass of the sample in air, then weigh the mass of the sample completely submerged in water. Calculate the actual volume based on the principle of buoyancy, and thus obtain the actual density. The theoretical density is calculated from the material composition and the density of each component. The final density = (actual density ÷ theoretical density) × 100%.

[0037] Hot cracking rate: A certain number of samples are placed in a muffle furnace, heated, held, and cooled according to a set program. After repeated cycles, the samples are taken out and the number of cracked samples is counted. Hot cracking rate = (number of cracked samples ÷ total number of samples) × 100%.

[0038] Example 1 Alloy composition: Zn=1.5%, Cu=1% (Zn+Cu=2.5%, Zn / Cu=1.5), Sn=0.2%, Sc=0.2% (Sn / Sc=1), balance Mg (purity 99.95%), impurities: Si=0.03%, Fe=0.02%, total impurities=0.05%.

[0039] The medium-frequency induction furnace has a power of 5kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 680℃ and melted, and held for 10 minutes. Pure Zn particles (purity 99.9%) are added, and the stirring speed is 300r / min. The temperature is held for 20 minutes. Pure Cu particles (purity 99.9%) are added every 5 minutes, and the stirring continues for 20 minutes. The temperature is lowered to 700℃ and pure Sn particles (purity 99.9%) are added, and the stirring continues for 15 minutes. Mg-20Sc master alloy is added and the stirring continues for 25 minutes. The temperature is raised to 720℃ and C2Cl6 (0.1%) is added. The mixture is stirred for 10 minutes and then allowed to stand for 15 minutes. Surface slag is removed.

[0040] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 650℃ and hold it for 10 minutes. Turn on "mechanical stirring 500r / min + ultrasonic 300W / 20kHz" for 15 minutes to break up the initial grains and form a uniform melt.

[0041] The temperature was gradually reduced to 570℃ at a rate of 5℃ / min, the mechanical stirring rate was adjusted to 200r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 20min to prepare a semi-solid slurry with a solid phase ratio of 35%.

[0042] Preheat the mold to 300℃ and apply graphite lubricant (5μm thickness) to the cavity; inject 50% of the slurry into the cavity at a low speed of 0.5m / s; inject the remaining slurry into the cavity at a high speed of 2m / s, with an injection pressure of 80MPa and a holding time of 10s.

[0043] After the pressure holding period, the temperature is cooled to 190°C at a rate of 15°C / min. The mold is then opened and the molded part is removed to obtain a rheologically formed magnesium alloy blank.

[0044] The blank is placed in a box-type resistance furnace and heated to 340℃ at a rate of 10℃ / min, and held for 2 hours. After the holding period, it is immediately quenched in 80℃ hot water and cooled to room temperature.

[0045] After quenching, the blank is placed in a low-temperature aging furnace, heated to 90°C, held for 2 hours, and then air-cooled to room temperature.

[0046] The pre-aged billet is placed back into the aging furnace, heated to 165℃, held for 10 hours, and then air-cooled to room temperature.

[0047] Final properties: thermal conductivity = 140 W / (m•K), tensile strength = 210 MPa, elongation = 5%, density = 92%, hot cracking rate = 0.1%.

[0048] Example 2 Alloy composition: Zn=8%, Cu=4% (Zn+Cu=12%, Zn / Cu=2), Sn=2%, Sc=0.7% (Sn / Sc≈2.86), balance Mg (purity 99.95%), impurities: Mn=0.04%, Ni=0.01%, total impurities=0.05%.

[0049] The medium-frequency induction furnace has a power of 10kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 720℃ and melted, and held for 15 minutes. Pure Zn particles are added, and the stirring speed is 400r / min. The temperature is held for 25 minutes. Pure Cu particles are added at 8-minute intervals, and stirring is continued for 25 minutes. The temperature is lowered to 710℃ and pure Sn particles are added. The stirring is continued for 20 minutes. Mg-20Sc master alloy is added and stirred for 30 minutes. The temperature is raised to 750℃ and C2Cl6 (0.3%) is added. The mixture is stirred for 15 minutes and then allowed to stand for 20 minutes. Surface slag is removed.

[0050] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 680℃ and hold it for 15 minutes. Turn on "mechanical stirring at 600r / min + ultrasonication at 400W / 25kHz" for 20 minutes to break up the initial grains and form a uniform melt.

[0051] The temperature was gradually reduced to 600℃ at a rate of 8℃ / min, the mechanical stirring rate was adjusted to 300r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 25min to prepare a semi-solid slurry with a solid phase ratio of 50%.

[0052] Preheat the mold to 350℃ and apply graphite lubricant (10μm thickness) to the cavity; inject 60% of the slurry into the cavity at a low speed of 1m / s; inject the remaining slurry into the cavity at a high speed of 3m / s, with an injection pressure of 120MPa and a holding time of 15s.

[0053] After the pressure holding period, the temperature is cooled to 180°C at a rate of 20°C / min. The mold is then opened and the molded part is removed to obtain a rheologically formed magnesium alloy blank.

[0054] The blank is placed in a box-type resistance furnace and heated to 430℃ at a rate of 15℃ / min, and held for 12 hours. After the holding period, it is immediately quenched in 90℃ hot water and cooled to room temperature.

[0055] After quenching, the blank is placed in a low-temperature aging furnace, heated to 120°C, held for 10 hours, and then air-cooled to room temperature.

[0056] The pre-aged blanks were placed back into the aging furnace, heated to 220°C, held for 72 hours, and then air-cooled to room temperature.

[0057] Final properties: thermal conductivity = 145 W / (m•K), tensile strength = 270 MPa, elongation = 5.0%, density = 93%, hot cracking rate = 0.1%.

[0058] Example 3 Alloy composition: Zn=3%, Cu=0.5% (Zn+Cu=3.5%, Zn / Cu=6), Sn=0.3%, Sc=0.2% (Sn / Sc=1.5), balance Mg (purity 99.95%), impurities: Al=0.03%, Si=0.02%, total impurities=0.05%.

[0059] The medium-frequency induction furnace has a power of 7kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 700℃ and melted, and held for 12 minutes. Pure Zn particles are added, and the stirring speed is 350r / min. The temperature is held for 22 minutes. Pure Cu particles are added at 6-minute intervals, and stirring is continued for 22 minutes. The temperature is lowered to 705℃ and pure Sn particles are added. The stirring is continued for 17 minutes. Mg-20Sc master alloy is added and stirred for 28 minutes. The temperature is raised to 730℃ and C2Cl6 (0.2%) is added. The stirring is continued for 12 minutes and then allowed to stand for 17 minutes. Surface slag is removed.

[0060] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 660℃ and hold it for 12 minutes. Turn on "mechanical stirring 550r / min + ultrasonic 350W / 22kHz" for 17 minutes to break up the initial grains and form a uniform melt.

[0061] The temperature was gradually reduced to 580℃ at a rate of 6℃ / min, the mechanical stirring rate was adjusted to 250r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 22min to prepare a semi-solid slurry with a solid phase ratio of 40%.

[0062] Preheat the mold to 320℃ and apply graphite lubricant (7μm thickness) to the cavity; inject 55% of the slurry into the cavity at a low speed of 0.7m / s; inject the remaining slurry into the cavity at a high speed of 2.5m / s, with an injection pressure of 100MPa and a holding time of 12s.

[0063] After the pressure holding period, the temperature is cooled to 195°C at a rate of 17°C / min. The mold is then opened and the molded part is removed to obtain the rheologically formed magnesium alloy blank.

[0064] The blank is placed in a box-type resistance furnace and heated to 380°C at a rate of 12°C / min, and held for 6 hours. After the holding period, it is immediately immersed in 85°C hot water for quenching and then cooled to room temperature.

[0065] After quenching, the blank is placed in a low-temperature aging furnace, heated to 100℃, held for 5 hours, and then air-cooled to room temperature.

[0066] The pre-aged billet is placed back into the aging furnace, heated to 180℃, held for 30 hours, and then air-cooled to room temperature.

[0067] Final properties: thermal conductivity = 142 W / (m•K), tensile strength = 225 MPa, elongation = 5.0%, density = 95%, hot cracking rate = 0.1%.

[0068] Example 4 (Comparative Example) Alloy composition: Zn=7%, Cu=5% (Zn+Cu=12%, Zn / Cu=1.4), Sn=1.5%, Sc=1% (Sn / Sc=1.5), balance Mg (purity 99.95%), impurities: Fe=0.04%, Mn=0.01%, total impurities=0.05%.

[0069] The medium-frequency induction furnace has a power of 9kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 710℃ and melted, and held for 14min. Pure Zn particles are added, and the stirring speed is 380r / min, and the temperature is held for 24min. Pure Cu particles are added at 7min intervals, and stirring is continued for 24min. The temperature is lowered to 708℃ and pure Sn particles are added, and stirring is carried out for 19min. Mg-20Sc master alloy is added and stirred for 29min. The temperature is raised to 740℃ and C2Cl6 (0.25%) is added. After stirring for 14min, the mixture is allowed to stand for 19min, and the surface slag is removed.

[0070] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 670℃ and hold it for 14 minutes. Turn on "mechanical stirring 580r / min + ultrasonic 380W / 24kHz" for 19 minutes to break up the initial grains and form a uniform melt.

[0071] The temperature was gradually reduced to 590℃ at a rate of 7℃ / min, the mechanical stirring rate was adjusted to 280r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 24min to prepare a semi-solid slurry with a solid phase ratio of 48%.

[0072] Preheat the mold to 340℃ and apply graphite lubricant (9μm thickness) to the cavity; inject 58% of the slurry into the cavity at a low speed of 0.9m / s; inject the remaining slurry into the cavity at a high speed of 2.8m / s, with an injection pressure of 110MPa and a holding time of 14s.

[0073] After the pressure holding period, the temperature is cooled to 185°C at a rate of 19°C / min. The mold is then opened and the molded part is removed to obtain a rheologically formed magnesium alloy blank.

[0074] The blank is placed in a box-type resistance furnace and heated to 420°C at a rate of 14°C / min, and held for 10 hours. After the holding period, it is immediately quenched in 88°C hot water and cooled to room temperature.

[0075] The quenched blank is placed in a low-temperature aging furnace, heated to 115℃, held for 9 hours, and then air-cooled to room temperature.

[0076] The pre-aged billet is placed back into the aging furnace, heated to 210℃, held for 60 hours, and then air-cooled to room temperature.

[0077] Final properties: thermal conductivity = 140 W / (m•K), tensile strength = 265 MPa, elongation = 2.0%, density = 93%, hot cracking rate = 0.2%.

[0078] Example 5 Alloy composition: Zn=4%, Cu=2% (Zn+Cu=6%, Zn / Cu=2), Sn=0.2%, Sc=0.2% (Sn / Sc=1), balance Mg (purity 99.95%), impurities: Ni=0.02%, Al=0.03%, total impurities=0.05%.

[0079] The medium-frequency induction furnace has a power of 6kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 685℃ and melted, and held for 11 minutes. Pure Zn particles are added, and the stirring speed is 320r / min. The temperature is held for 21 minutes. Pure Cu particles are added at 5-minute intervals, and stirring is continued for 21 minutes. The temperature is lowered to 702℃ and pure Sn particles are added. The temperature is stirred for 16 minutes. Mg-20Sc master alloy is added and stirred for 26 minutes. The temperature is raised to 725℃ and C2Cl6 (0.15%) is added. The temperature is stirred for 11 minutes and then allowed to stand for 16 minutes. Surface slag is removed.

[0080] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 655℃ and hold it for 11 minutes. Turn on "mechanical stirring 520r / min + ultrasonic 320W / 21kHz" for 16 minutes to break up the initial grains and form a uniform melt.

[0081] The temperature was gradually reduced to 575℃ at a rate of 5.5℃ / min, the mechanical stirring rate was adjusted to 220r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 21min to prepare a semi-solid slurry with a solid phase ratio of 37%.

[0082] Preheat the mold to 310℃, apply graphite lubricant (6μm thickness) to the cavity; inject 52% of the slurry into the cavity at a low speed of 0.6m / s; inject the remaining slurry into the cavity at a high speed of 2.2m / s, with an injection pressure of 85MPa and a holding time of 11s.

[0083] After the pressure holding period, the temperature is cooled to 192°C at a rate of 16°C / min. The mold is then opened and the molded part is removed to obtain the rheologically formed magnesium alloy blank.

[0084] The blank is placed in a box-type resistance furnace and heated to 360°C at a rate of 11°C / min, and held for 4 hours. After the holding period, it is immediately quenched in 82°C hot water and cooled to room temperature.

[0085] After quenching, the blank is placed in a low-temperature aging furnace, heated to 95°C, held for 3 hours, and then air-cooled to room temperature.

[0086] The pre-aged blank is placed back into the aging furnace, heated to 170℃, held for 50 hours, and then air-cooled to room temperature.

[0087] Final properties: thermal conductivity = 141 W / (m•K), tensile strength = 220 MPa, elongation = 6.0%, density = 99%, hot cracking rate = 0.1%.

[0088] Example 6 Alloy composition: Zn=6%, Cu=3% (Zn+Cu=9%, Zn / Cu=2), Sn=2%, Sc=0.7% (Sn / Sc≈2.86), balance Mg (purity 99.95%), impurities: Si=0.04%, Fe=0.01%, total impurities=0.05%.

[0089] The medium-frequency induction furnace has a power of 8kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 715℃ and melted, and held for 13 minutes. Pure Zn particles are added, and the stirring speed is 360r / min. The temperature is held for 23 minutes. Pure Cu particles are added at 7-minute intervals, and stirring is continued for 23 minutes. The temperature is lowered to 706℃ and pure Sn particles are added. The stirring is continued for 18 minutes. Mg-20Sc master alloy is added and stirred for 27 minutes. The temperature is raised to 735℃ and C2Cl6 (0.22%) is added. The stirring is continued for 13 minutes and then allowed to stand for 18 minutes. Surface slag is removed.

[0090] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 665℃ and hold it for 13 minutes. Turn on "mechanical stirring 560r / min + ultrasonic 360W / 23kHz" for 18 minutes to break up the initial grains and form a uniform melt.

[0091] The temperature was gradually reduced to 585℃ at a rate of 6.5℃ / min, the mechanical stirring rate was adjusted to 260r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 23min to prepare a semi-solid slurry with a solid phase ratio of 45%.

[0092] Preheat the mold to 330℃ and apply graphite lubricant (8μm thickness) to the cavity; inject 56% of the slurry into the cavity at a low speed of 0.8m / s; inject the remaining slurry into the cavity at a high speed of 2.6m / s, with an injection pressure of 95MPa and a holding time of 13s.

[0093] After the pressure holding period, the temperature is cooled to 188°C at a rate of 18°C / min. The mold is then opened and the molded part is removed to obtain the rheologically formed magnesium alloy blank.

[0094] The blank is placed in a box-type resistance furnace and heated to 400℃ at a rate of 13℃ / min, and held for 3 hours. After the holding period, it is immediately quenched in 86℃ hot water and cooled to room temperature.

[0095] After quenching, the blank is placed in a low-temperature aging furnace, heated to 105℃, held for 7 hours, and then air-cooled to room temperature.

[0096] The pre-aged billet is placed back into the aging furnace, heated to 195℃, held for 20 hours, and then air-cooled to room temperature.

[0097] Final properties: thermal conductivity = 143 W / (m•K), tensile strength = 245 MPa, elongation = 6.0%, density = 99%, hot cracking rate = 0.1%.

[0098] Example 7 Alloy composition: Zn=1.5%, Cu=1% (Zn+Cu=2.5%, Zn / Cu=1.5), Sn=2%, Sc=1% (Sn / Sc=2), balance Mg (purity 99.95%), impurities: Mn=0.03%, Ni=0.02%, total impurities=0.05%.

[0099] The medium-frequency induction furnace has a power of 5.5kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 690℃ and melted, and held for 11.5min. Pure Zn particles are added, and the stirring speed is 310r / min. The temperature is held for 20.5min. Pure Cu particles are added at 5.5min intervals and the stirring continues for 20.5min. The temperature is lowered to 703℃ and pure Sn particles are added and stirred for 15.5min. Mg-20Sc master alloy is added and stirred for 25.5min. The temperature is raised to 722℃ and C2Cl6 (0.12%) is added. After stirring for 10.5min, the mixture is allowed to stand for 15.5min, and the surface slag is removed.

[0100] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 652℃ and hold it for 10.5 min. Turn on "mechanical stirring 510r / min + ultrasonic 400W / 20kHz" for 15.5 min to break up the initial grains and form a uniform melt.

[0101] The temperature was gradually reduced to 572℃ at a rate of 5.2℃ / min, the mechanical stirring rate was adjusted to 210r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 20.5min to prepare a semi-solid slurry with a solid phase ratio of 36%.

[0102] Preheat the mold to 305℃ and apply graphite lubricant (5.5μm thickness) to the cavity; inject 51% of the slurry into the cavity at a low speed of 0.55m / s; inject the remaining slurry into the cavity at a high speed of 2.1m / s, with an injection pressure of 82MPa and a holding time of 10.5s.

[0103] After the pressure holding period, the temperature is cooled to 193°C at a rate of 15.5°C / min. The mold is then opened and the molded part is removed to obtain a rheologically formed magnesium alloy blank.

[0104] The blank is placed in a box-type resistance furnace and heated to 350℃ at a rate of 10.5℃ / min, and held for 2.5 hours. After the holding period, it is immediately quenched in 81℃ hot water and cooled to room temperature.

[0105] The quenched blank is placed in a low-temperature aging furnace, heated to 92°C, held for 2.5 hours, and then air-cooled to room temperature.

[0106] The pre-aged billet is placed back into the aging furnace, heated to 168℃, held for 15 hours, and then air-cooled to room temperature.

[0107] Final properties: thermal conductivity = 149 W / (m•K), tensile strength = 215 MPa, elongation = 7.0%, density = 100%, hot cracking rate = 0%.

[0108] Example 8 (Comparative Example) Alloy composition: Zn=7%, Cu=5% (Zn+Cu=12%, Zn / Cu=1.4), Sn=0.3%, Sc=0.2% (Sn / Sc=1.5), balance Mg (purity 99.95%), impurities: Al=0.04%, Si=0.01%, total impurities=0.05%.

[0109] The medium-frequency induction furnace has a power of 9.5kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 718℃ and melted, and held for 14.5min. Pure Zn particles are added, and the stirring speed is 390r / min, and the temperature is held for 24.5min. Pure Cu particles are added at 7.5min intervals, and stirring is continued for 24.5min. The temperature is lowered to 709℃ and pure Sn particles are added, and stirring is carried out for 19.5min. Mg-20Sc master alloy is added and stirred for 29.5min. The temperature is raised to 745℃ and C2Cl6 (0.28%) is added. After stirring for 14.5min, the mixture is allowed to stand for 19.5min, and the surface slag is removed.

[0110] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 675℃ and hold it for 14.5 minutes. Turn on "mechanical stirring 600r / min + ultrasonic 390W / 25kHz" for 19.5 minutes to break up the initial grains and form a uniform melt.

[0111] The temperature was gradually reduced to 595℃ at a rate of 7.5℃ / min, the mechanical stirring rate was adjusted to 290r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 24.5min to prepare a semi-solid slurry with a solid phase ratio of 49%.

[0112] Preheat the mold to 345℃ and apply graphite lubricant (9.5μm thickness) to the cavity; inject 59% of the slurry into the cavity at a low speed of 0.95m / s; inject the remaining slurry into the cavity at a high speed of 2.9m / s, with an injection pressure of 115MPa and a holding time of 14.5s.

[0113] After the pressure holding period, the molded part is cooled to 182°C at a rate of 19.5°C / min, and then removed from the mold to obtain a rheoformed magnesium alloy blank. The blank is placed in a box-type resistance furnace and heated to 420℃ at a rate of 14.5℃ / min, and held for 11 hours. After the holding period, it is immediately quenched in 89℃ hot water and cooled to room temperature.

[0114] The quenched blank is placed in a low-temperature aging furnace, heated to 118℃, held for 9.5 hours, and then air-cooled to room temperature.

[0115] The pre-aged billet is placed back into the aging furnace, heated to 215℃, held for 65 hours, and then air-cooled to room temperature.

[0116] Final properties: thermal conductivity = 142 W / (m•K), tensile strength = 230 MPa, elongation = 2.0%, density = 99%, hot cracking rate = 0.1%.

[0117] Example 9 Alloy composition: Zn=5%, Cu=2.5% (Zn+Cu=7.5%, Zn / Cu=2), Sn=1%, Sc=0.5% (Sn / Sc=2), balance Mg (purity 99.95%), impurities: Fe=0.03%, Mn=0.02%, total impurities=0.05%.

[0118] The medium-frequency induction furnace has a power of 7.5kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 705℃ and melted, and held for 12.5min. Pure Zn particles are added, and the stirring speed is 340r / min, and the temperature is held for 22.5min. Pure Cu particles are added at 6.5min intervals, and stirring is continued for 22.5min. The temperature is lowered to 704℃ and pure Sn particles are added, and stirring is carried out for 17.5min. Mg-20Sc master alloy is added and stirred for 27.5min. The temperature is raised to 732℃ and C2Cl6 (0.18%) is added. After stirring for 12.5min, the mixture is allowed to stand for 17.5min, and the surface slag is removed.

[0119] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 662℃ and hold it for 12.5 minutes. Turn on "mechanical stirring 540r / min + ultrasonic 340W / 22.5kHz" for 17.5 minutes to break up the initial grains and form a uniform melt.

[0120] The temperature was gradually reduced to 582℃ at a rate of 6.2℃ / min, the mechanical stirring rate was adjusted to 240r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 22.5min to prepare a semi-solid slurry with a solid phase ratio of 39%.

[0121] Preheat the mold to 325℃ and apply graphite lubricant (7.5μm thickness) to the cavity; inject 54% of the slurry into the cavity at a low speed of 0.75m / s; inject the remaining slurry into the cavity at a high speed of 2.4m / s, with an injection pressure of 90MPa and a holding time of 12.5s.

[0122] After the pressure holding period, the temperature is cooled to 190°C at a rate of 17.5°C / min. The mold is then opened and the molded part is removed to obtain a rheologically formed magnesium alloy blank.

[0123] The blank is placed in a box-type resistance furnace and heated to 390℃ at a rate of 12.5℃ / min, and held for 5.5 hours. After the holding period, it is immediately quenched in 84℃ hot water and cooled to room temperature.

[0124] The quenched blank is placed in a low-temperature aging furnace, heated to 102℃, held for 4.5 hours, and then air-cooled to room temperature.

[0125] The pre-aged billet is placed back into the aging furnace, heated to 185℃, held for 18 hours, and then air-cooled to room temperature.

[0126] Final properties: thermal conductivity = 149 W / (m•K), tensile strength = 238 MPa, elongation = 7.0%, density = 99%, hot cracking rate = 0%.

[0127] Example 10 Alloy composition: Zn=2.5%, Cu=1.5% (Zn+Cu=4%, Zn / Cu≈1.67), Sn=0.6%, Sc=0.3% (Sn / Sc=2), balance Mg (purity 99.95%), impurities: Ni=0.02%, Al=0.03%, total impurities=0.05%.

[0128] The medium-frequency induction furnace has a power of 6.5kW and a protective atmosphere of "tetrafluoroethane + argon = 1:99". Pure magnesium ingots are heated to 695℃ and melted, and held for 13.5min. Pure Zn particles are added, and the stirring speed is 330r / min, and the temperature is held for 23.5min. Pure Cu particles are added at 6min intervals, and stirring is continued for 23.5min. The temperature is lowered to 707℃ and pure Sn particles are added, and stirring is carried out for 18.5min. Mg-20Sc master alloy is added and stirred for 28.5min. The temperature is raised to 738℃ and C2Cl6 (0.23%) is added. After stirring for 13.5min, the mixture is allowed to stand for 18.5min, and the surface slag is removed.

[0129] Take out the magnesium melt as needed and put it into a special material cup. Under the protection of "tetrafluoroethane + argon", cool it to 668℃ and hold it for 13.5 minutes. Turn on "mechanical stirring 570r / min + ultrasonic 370W / 23.5kHz" for 18.5 minutes to break up the initial grains and form a uniform melt.

[0130] The temperature was gradually reduced to 588℃ at a rate of 6.8℃ / min, the mechanical stirring rate was adjusted to 270r / min, the ultrasonic stirring was turned off, and the temperature was maintained for 23.5min to prepare a semi-solid slurry with a solid phase ratio of 46%.

[0131] Preheat the mold to 335℃ and apply graphite lubricant (8.5μm thickness) to the cavity; inject 57% of the slurry into the cavity at a low speed of 0.85m / s; inject the remaining slurry into the cavity at a high speed of 2.7m / s, with an injection pressure of 105MPa and a holding time of 13.5s.

[0132] After the pressure holding period, the temperature is cooled to 186°C at a rate of 18.5°C / min. The mold is then opened and the molded part is removed to obtain the rheologically formed magnesium alloy blank.

[0133] The blank is placed in a box-type resistance furnace and heated to 410℃ at a rate of 13.5℃ / min, and held for 9 hours. After the holding period, it is immediately quenched in 87℃ hot water and cooled to room temperature.

[0134] The quenched blank is placed in a low-temperature aging furnace, heated to 110℃, held for 8 hours, and then air-cooled to room temperature.

[0135] The pre-aged blank is placed back into the aging furnace, heated to 200℃, held for 45 hours, and then air-cooled to room temperature.

[0136] Final properties: thermal conductivity = 148.3 W / (m•K), tensile strength = 232 MPa, elongation = 6.0%, density = 99%, hot cracking rate = 0.2%.

Claims

1. A high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming, characterized in that, The alloy composition by mass percentage is: Zn: 1~8%, Cu: 0.5~5%, Sn: 0.2~2%, Sc: 0.2~1%, with the balance being Mg and unavoidable impurities.

2. The high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming according to claim 1, characterized in that, The total content of Zn and Cu is 2-12%, the content ratio of Zn to Cu is 1.5-6, and the content ratio of Sn to Sc is 1-3.

3. The high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming according to claim 1 or 2, characterized in that, Among unavoidable impurities, the content of a single impurity is ≤0.05%, and the total impurity content is ≤0.15%.

4. A method for preparing and processing a high thermal conductivity Mg-Zn magnesium alloy suitable for rheological forming, as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Prepare raw materials according to the alloy composition, and use a medium frequency induction furnace with a protective atmosphere of a mixture of tetrafluoroethane and argon to carry out smelting; (2) Mechanical stirring combined with ultrasonic synergistic stirring is used to form a homogeneous melt; (3) Cool the temperature to 570-600℃ at a rate of 5-8℃ / min, adjust the mechanical stirring speed to 200-300r / min, turn off the ultrasonic stirring, keep the temperature for 20-25min, and prepare a semi-solid slurry with a solid phase ratio of 35-50%. (4) Preheat the mold to 300~350℃, press 50~60% of the slurry into the cavity at a low speed of 0.5~1m / s to expel the air in the cavity; press the remaining slurry into the cavity at a high speed of 2~3m / s, with an injection pressure of 80~120MPa and a holding time of 10~15s. (5) After the pressure holding is completed, cool to below 200°C at a rate of 15~20°C / min, open the mold and take out the molded part to obtain the rheoformed magnesium alloy blank; (6) Place the rheoformed billet into a box-type resistance furnace and heat it to 340-430℃ at a rate of 10-15℃ / min. Hold it for 2-12 hours. After holding, immediately immerse the billet in hot water at 80-90℃ for quenching and cool it to room temperature. (7) Place the quenched blank into a low-temperature aging furnace, heat it to 90~120℃, hold it for 2~10h, and air cool it to room temperature; (8) Place the pre-aged billet back into the aging furnace, heat it to 165~220℃, keep it at that temperature for 10~72h, and then air cool it to room temperature.

5. The preparation and processing method for high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 4, characterized in that, In step (1), Zn, Cu, and Sn are added in the form of pure metal particles, and Sc is added in the form of Mg-20Sc master alloy.

6. The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 4, characterized in that, In step (1), pure magnesium ingots are first added to a crucible and heated to 680-720℃ to completely melt them. The temperature is maintained for 10-15 minutes. Pure Zn particles and pure Cu particles are added sequentially, with an interval of 5-8 minutes between the two additions. The stirring rate is 300-400 r / min, and the temperature is maintained for 20-25 minutes until completely dissolved. The temperature is lowered to 700-710℃, pure Sn particles are added, and the mixture is stirred for 15-20 minutes. Then, Mg-20Sc master alloy is added and stirred for 25-30 minutes. The temperature is raised to 720-750℃, C2Cl6 degassing agent is added, with an addition amount of 0.1-0.3% of the total alloy mass. The mixture is stirred for 10-15 minutes and then allowed to stand for 15-20 minutes to remove surface slag.

7. The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 4 or 6, characterized in that, In step (1), the power of the medium-frequency induction furnace is 5~10kW, and the volume ratio of tetrafluoroethane to argon is 1:

99.

8. The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 4, characterized in that, In step (2), a certain amount of magnesium melt is taken out as needed and placed into a special material cup. Under the protection of a mixture of tetrafluoroethane and argon, the temperature is lowered to 650~680℃ and kept at that temperature for 10~15 minutes. Then, mechanical stirring and ultrasonic synergistic stirring are turned on. The mechanical stirring rate is 500~600r / min, the ultrasonic power is 300~400W, the ultrasonic frequency is 20~25kHz, and the stirring is continued for 15~20 minutes to break up the initial grains and form a uniform melt.

9. The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 8, characterized in that, The mechanical agitator has a spiral impeller made of H13 steel with an Al2O3 coating for corrosion protection.

10. The method for preparing and processing high thermal conductivity Mg-Zn magnesium alloys suitable for rheological forming according to claim 4, characterized in that, In step (4), the mold cavity is coated with graphite lubricant with a thickness of 5~10μm.