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

Abstract

The invention provides a high-strength and high-thermal-conductivity cast magnesium alloy material and a preparation method thereof. The high-strength and high-thermal-conductivity cast magnesium alloy material comprises the following elements in percentage by mass: 4.5-6.0% of Zn element, 0.55-1.65% of La element, 0.5-1.0% of Cu element, less than or equal to 0.2% of Ca element, 0.3-0.6% of Zr element, less than or equal to 0.15% of inevitable impurities and the balance of Mg element, according to the high-strength and high-thermal-conductivity cast magnesium alloy material, the thermal conductivity is 135-152 W / (mK), the tensile strength is 260-290 MPa, the yield strength is 130-155 MPa, and the ductility is 8-15%. The high-strength and high-thermal-conductivity cast magnesium alloy material has high thermal conductivity and mechanical properties, so that the performance requirements of different application fields on high-thermal-conductivity magnesium alloy heat dissipation parts are better met.

Description

Technical Field

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

[0002] With the continuous development of industries such as new energy vehicles, 3C products, satellite communications, and aerospace, the number and density of high-power electronic components are constantly increasing. This necessitates the timely release of heat generated during operation to ensure the reliability and stability of the equipment. Therefore, lightweight heat dissipation structures for electronic components place higher demands on the thermal conductivity and mechanical properties of the materials themselves. Magnesium alloys, as the lightest metallic structural materials currently available, possess advantages such as low density, high specific strength and specific stiffness, excellent electromagnetic radiation shielding and vibration damping performance, and ease of recyclability, making them widely used in the automotive, 3C, and aerospace industries. Currently, commonly used cast magnesium alloys such as AZ91, AM50, and AM60 have tensile strengths of around 220-240 MPa and room temperature thermal conductivity of only 50-60 W / (m²). Commercial rare-earth cast magnesium alloys such as WE43 and WE54 typically have a room temperature tensile strength as high as 350 MPa and a thermal conductivity of only 51 W / (m²). Therefore, the above magnesium alloy materials cannot simultaneously meet the requirement of thermal conductivity ≥130W / (m²) for high-power electronic heat sinks in fields such as new energy vehicles, 5G communications, and aerospace. K) and a tensile strength ≥ 250 MPa.

[0003] Chinese patent application CN114318097A discloses a method for preparing a Mg-Zn-La alloy with both high thermal conductivity and high strength. The alloy composition is: Zn content 6.18~6.43 wt.%, La content 0.32~0.55 wt.%, with the balance being Mg. However, the Zn content in this magnesium alloy composition is greater than 6 wt.%, resulting in poor resistance to hot cracking during casting. Furthermore, the Mg-Zn-La alloy prepared using this method employs an electric resistance furnace melting process. The addition of a Mg-17La master alloy increases the oxidizing activity of the magnesium alloy, leading to severe oxidation of the molten magnesium during casting and potentially causing a fire hazard.

[0004] Chinese patent application CN102719716A discloses a thermally conductive magnesium alloy and its preparation method. The alloy composition is as follows: Zn content 1-7 wt.%, Ca content 0.1-3 wt.%, La content 0.1-3 wt.%, Ce content 0.1-3 wt.%, with the balance being Mg. The drawback of this patent is that the Mg-Zn-Ca-La-Ce thermally conductive magnesium alloy has a wide composition range, resulting in relatively coarse grains after deformation (average grain size approximately 100 μm), and a thermal conductivity only reaching 125-128 W / (m²). In addition to the magnesium alloy smelting process, this preparation method requires a hot extrusion deformation process followed by an aging heat treatment process to obtain high thermal conductivity and mechanical properties. Furthermore, the preparation process is lengthy and cannot directly produce complex heat dissipation structural components.

[0005] Chinese patent application CN114351020A discloses a magnesium alloy casting, its preparation method, and its application. The alloy composition is as follows: Zr content 0.45-0.80% by mass, Zn content 0.40-0.90% by mass, RE content 0.45-1.0% by mass (RE is at least one of La and Ce), and Th content 0.05-0.20% by mass. The drawback of this patent is the presence of radioactive Th in the alloy composition. Due to its significant radioactivity and health risks, thorium-containing magnesium alloys have been strictly limited or completely phased out in modern industry. Currently, mainstream commercial magnesium alloys do not contain thorium. Furthermore, the casting requires smelting, secondary remelting, liquid forging extrusion deformation, solution treatment, and aging heat treatment, resulting in a long manufacturing process.

[0006] Therefore, developing a magnesium alloy material with both high thermal conductivity and high tensile strength has become a key research focus and challenge. Especially in cast magnesium alloys, how to improve thermal conductivity while ensuring high strength is a pressing issue. This requires not only innovation in composition design but also optimization of the manufacturing process to obtain a magnesium alloy that combines high strength and high thermal conductivity and is suitable for casting. Summary of the Invention

[0007] The main objective of this invention is to provide a high-strength, high-thermal-conductivity cast magnesium alloy material and its preparation method, so as to solve the problem that magnesium alloys in the prior art are difficult to balance high thermal conductivity and strength.

[0008] To achieve the above objectives, according to one aspect of the present invention, a high-strength, high-thermal-conductivity cast magnesium alloy material is provided, comprising, by mass percentage: 4.5-6.0% Zn, 0.55-1.65% La, 0.5-1.0% Cu, ≤0.2% Ca, 0.3-0.6% Zr, unavoidable total impurity content ≤0.15%, and the balance being Mg; the thermal conductivity of the high-strength, high-thermal-conductivity cast magnesium alloy material is 135-152 W / (m²). The tensile strength of high-strength, high-thermal-conductivity cast magnesium alloy is 260~290MPa, the yield strength is 130~155MPa, and the elongation is 8~15%.

[0009] Furthermore, by mass percentage, the high-strength, high-thermal-conductivity cast magnesium alloy material includes the following elements: 4.5~5.0% Zn, 0.55~0.8% La, 0.6~0.8% Cu, ≤0.2% Ca, 0.3~0.6% Zr, unavoidable total impurities ≤0.15%, and the balance being Mg.

[0010] Furthermore, the mass content of Ca is 0.1~0.2%; the mass content of Zr is 0.4~0.5%.

[0011] Furthermore, the mass ratio of Zn to La is 6~9:1; and / or the mass ratio of Zn to Cu is 6~8:1; and / or the average grain size of the high-strength, high-thermal-conductivity cast magnesium alloy is 32~58 μm.

[0012] According to another aspect of the present invention, a method for preparing a high-strength, high-thermal-conductivity cast magnesium alloy material is provided. The method includes: according to the composition of the high-strength, high-thermal-conductivity cast magnesium alloy material, batching raw materials including pure Mg ingots, pure Zn ingots, a first Mg-La master alloy, a Mg-Cu master alloy, a Mg-Ca master alloy, and a first Mg-Zr master alloy, and then sequentially performing melting, casting, T4 solution treatment, and T6 aging treatment to obtain the high-strength, high-thermal-conductivity cast magnesium alloy material; wherein the raw materials also include a second Mg-La master alloy and a second Mg-Zr master alloy; the second Mg-La master alloy is used to compensate for the compositional loss caused by the burning of La element; the second Mg-Zr master alloy is used to compensate for the compositional loss caused by the burning of Zr element; the melting includes sequentially performing a first heating and a second heating in a vacuum environment with a vacuum degree of 10. -3 ~10 -2Pa; the power of the second heating is greater than that of the first heating, and the power of the second heating is 35~40KW; the solution temperature of T4 solution treatment is 400~430℃; the temperature of T6 aging heat treatment is 180~200℃.

[0013] Furthermore, the power of the first heating is 10~15KW, the temperature of the first heating is 300~500℃, and the heating time is 10~15min; and / or, the temperature of the second heating is 770~790℃, the heating time of the second heating is 10~15min, and the holding time of the second heating is 3~5min; the atmosphere of the second heating is argon, and the pressure of the second heating is 0.04~0.06MPa.

[0014] Furthermore, the above preparation method further includes: surface treating the raw materials to obtain surface-treated raw materials; and / or, after melting, obtaining an alloy liquid; performing composition analysis on the alloy liquid, and casting the alloy liquid with the required composition; and / or, the mass ratio of the second Mg-La master alloy to the first Mg-La master alloy is 10~15:100; and / or, the mass percentage of the second Mg-Zr master alloy to the first Mg-Zr master alloy is 100~150:100.

[0015] Furthermore, the casting method is bottom casting with a side gating system; the casting process includes: pouring the molten alloy into a mold with a side gating system to obtain an ingot; wherein, the preheating temperature of the mold is 220~250℃; and the casting temperature is 720~740℃.

[0016] Furthermore, the T4 solution treatment process includes: under an argon atmosphere, the ingot is sequentially solution treated and quenched to obtain a solution-treated ingot; wherein, the solution temperature is 400~430℃, the solution holding time is 6~10h, the quenching temperature is 75~85℃, and the quenching medium is water.

[0017] Furthermore, the T6 aging treatment process includes: holding the solution-treated ingot at 180~200℃ for 10~20h under an argon atmosphere and then air-cooling it.

[0018] Applying the technical solution of this invention, this application, based on Mg-Zn thermally conductive magnesium alloy, optimizes the composition of the Mg-Zn-La-Cu-Ca-Zr multi-element alloy by controlling the elemental composition and mass content of the high-strength, high-thermal-conductivity cast magnesium alloy material within the aforementioned range, enabling it to possess both high thermal conductivity and high mechanical properties. After adding the aforementioned mass content of rare earth element La to the Mg-Zn alloy, a micron-sized granular strengthening phase is mainly formed in the as-cast state. τ 1. Dispersed on the grain boundaries, the Mg-Zn-La alloy, after solution treatment and aging, τPhase 1 promotes the formation of nanoscale rod-shaped β1'-Mg4Zn7 and disk-shaped β2'-MgZn2 precipitates, significantly improving the strength of magnesium alloys. Simultaneously, it reduces the solid solubility of Zn in the Mg matrix, facilitating Zn desolvation and minimizing the impact of lattice distortion on thermal conductivity, thus further enhancing the thermal conductivity of magnesium alloys. Adding Cu alloying element forms a highly thermally conductive dispersed Mg(ZnCu)2 (η' phase), simultaneously improving both the strength and thermal conductivity of magnesium alloys. Adding Ca and Zr elements acts as flame retardants and purifies impurities in the molten magnesium alloy, significantly refining the grain size, and has minimal impact on the thermal conductivity of magnesium alloys at low mass contents. Therefore, the high-strength, high-thermal-conductivity cast magnesium alloy material Mg-Zn-La-Cu-Ca-Zr developed in this application has high strength and high thermal conductivity. Its thermal conductivity, tensile strength, yield strength and elongation can reach the above range, thereby better meeting the performance requirements of high thermal conductivity magnesium alloy heat dissipation components in aerospace, satellite communication, new energy vehicles and 3C application fields. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 The SEM microstructure of the high-strength, high-thermal-conductivity cast magnesium alloy material in Embodiment 1 of this application is shown.

[0021] Figure 2 The TEM microstructure of the high-strength, high-thermal-conductivity cast magnesium alloy material in Embodiment 1 of this application is shown.

[0022] Figure 3 The room temperature tensile curve of the high-strength, high-thermal-conductivity cast magnesium alloy material in Example 1 of this application is shown. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] As analyzed in the background section of this application, existing magnesium alloys suffer from the problem of difficulty in achieving both high thermal conductivity and strength. To address these issues, this application provides a high-strength, high-thermal-conductivity cast magnesium alloy material and its preparation method.

[0025] In a typical embodiment of this application, a high-strength, high-thermal-conductivity cast magnesium alloy material is provided. By mass percentage, this high-strength, high-thermal-conductivity cast magnesium alloy material comprises the following elements: 4.5~6.0% Zn, 0.55~1.65% La, 0.5~1.0% Cu, ≤0.2% Ca, 0.3~0.6% Zr, unavoidable total impurity content ≤0.15%, and the balance being Mg. The thermal conductivity of the high-strength, high-thermal-conductivity cast magnesium alloy material is 135~152 W / (m²). The tensile strength of high-strength, high-thermal-conductivity cast magnesium alloy is 260~290MPa, the yield strength is 130~155MPa, and the elongation is 8~15%.

[0026] This application, based on Mg-Zn thermally conductive magnesium alloys, optimizes the composition of Mg-Zn-La-Cu-Ca-Zr multi-element alloying. By optimally controlling the elemental composition and mass content of the high-strength, high-thermal-conductivity cast magnesium alloy within the aforementioned range, it achieves both high thermal conductivity and high mechanical properties. After adding the aforementioned mass content of rare earth element La to the Mg-Zn alloy, a micron-sized granular strengthening phase is mainly formed in the as-cast state. τ 1. Dispersed on the grain boundaries, the Mg-Zn-La alloy, after solution treatment and aging, τ Phase 1 promotes the formation of nanoscale rod-shaped β1'-Mg4Zn7 and disk-shaped β2'-MgZn2 precipitates, significantly improving the strength of magnesium alloys. Simultaneously, it reduces the solid solubility of Zn in the Mg matrix, facilitating Zn desolvation and minimizing the impact of lattice distortion on thermal conductivity, thus further enhancing the thermal conductivity of magnesium alloys. Adding Cu alloying element forms a highly thermally conductive dispersed Mg(ZnCu)2 (η' phase), simultaneously improving both the strength and thermal conductivity of magnesium alloys. Adding Ca and Zr elements acts as flame retardants and purifies impurities in the molten magnesium alloy, significantly refining the grain size, and has minimal impact on the thermal conductivity of magnesium alloys at low mass contents. Therefore, the high-strength, high-thermal-conductivity cast magnesium alloy material Mg-Zn-La-Cu-Ca-Zr developed in this application has high strength and high thermal conductivity. Its thermal conductivity, tensile strength, yield strength and elongation can reach the above range, thereby better meeting the performance requirements of high thermal conductivity magnesium alloy heat dissipation components in aerospace, satellite communication, new energy vehicles and 3C application fields.

[0027] Specifically: 1) Zn can dissolve into the magnesium alloy matrix (the maximum solid solubility of Zn in the α-Mg matrix is ​​6.2 wt.%), playing a role in solid solution strengthening. Additionally, during the aging process of Mg-Zn alloys, Zn can form nanoscale precipitates of MgZn2 and Mg7Zn3 with Mg, thus achieving good age-strengthening. Furthermore, compared to metals such as Al, dissolved Zn has less impact on matrix lattice distortion, therefore, it has a smaller negative impact on the thermal conductivity of magnesium alloys. However, when the Zn content is too high, although it can increase the mechanical properties of magnesium alloys to some extent, it also produces excessive coarse MgZn phases, severely hindering electron or phonon conduction, leading to a significant decrease in the thermal conductivity of the magnesium alloy. When the Zn content is too low, although the thermal conductivity of the magnesium alloy is relatively high, Zn cannot fully exert its solid solution strengthening and age-strengthening effects, resulting in lower mechanical properties. Therefore, this application preferably controls the mass content of Zn element within the above range, which can achieve both high thermal conductivity and high mechanical properties.

[0028] 2) La can form Mg with Mg and Zn. 12 La Xiang, τ 1-La 0.08 (Mg, Zn) 0.92 Phase. Among them, the reinforcing phase in the as-cast state consists of micron-sized granular particles. τ Phase 1, dispersed along grain boundaries, can inhibit grain boundary migration. After solution treatment and aging, Mg-Zn-La alloys can promote the formation of nanoscale rod-shaped β1'-Mg4Zn7 and disk-shaped β2'-MgZn2 precipitates, which are distributed in the α-Mg matrix. These precipitates effectively hinder dislocation slip, thereby improving the yield strength and tensile strength of the magnesium alloy. At the same time, they reduce the solid solubility of Zn in the Mg matrix (after aging precipitation, the solid solubility of Zn in the α-Mg matrix decreases to 3.62~3.8 wt.%), thus achieving Zn desolvation, reducing the influence of lattice distortion on thermal conductivity, and further improving the thermal conductivity of the magnesium alloy. However, when the La content is too high, the excessive La phase is continuously distributed at the grain boundaries, hindering the heat conduction path and thus reducing the thermal conductivity of the magnesium alloy. Furthermore, the phase interface becomes a crack initiation point, leading to a decrease in the strength of the magnesium alloy. When the La content is too low, grain coarsening occurs, resulting in insufficient strength of the magnesium alloy, and incomplete impurity removal limits the improvement in thermal conductivity. Therefore, this application preferably controls the La content within the aforementioned range to further improve the thermal conductivity and strength of the magnesium alloy.

[0029] 3) Cu can lower the liquidus temperature of magnesium alloys, thereby improving the castability and fluidity of Mg-Zn alloys. Cu can also form nanoscale dispersed phases with high thermal conductivity with Mg and Zn. η The Cu content '-Mg(ZnCu)2' effectively enhances both the strength and thermal conductivity of magnesium alloys. However, when the Cu content is too low, precipitation strengthening is insufficient, resulting in limited strength improvement. Conversely, when the Cu content is too high, a continuous network of MgCu2 precipitates forms at grain boundaries, increasing electron scattering and reducing the thermal conductivity of the magnesium alloy. Therefore, this application preferably controls the Cu content within the aforementioned range to improve the casting performance of magnesium alloys while achieving a combination of high strength and high thermal conductivity.

[0030] 4) Ca (Ca) can act as a flame retardant, refine the microstructure, and inhibit hot cracking. It can form a CaO film on the surface of magnesium alloys, thus providing anti-oxidation and flame retardancy. Adding an appropriate amount of Ca, utilizing its segregation behavior at grain boundaries, can effectively achieve the dual effects of inhibiting high-temperature grain growth and reducing the susceptibility to solidification hot cracking. Adding ≤0.2 wt.% Ca can significantly improve the mechanical properties of magnesium alloys while having a relatively small impact on thermal conductivity. For every 0.5 wt.% increase in Ca, the thermal conductivity decreases by approximately 5~10 W / (m²). Therefore, this application preferably controls the mass content of Ca within the above range, which can achieve high mechanical properties while having little impact on thermal conductivity.

[0031] 5) Zr is a highly efficient grain refiner, serving as a nucleation site for α-Mg heterogeneous formation and purifying the melt by adsorbing impurities (Fe, Si), thus significantly improving the mechanical properties of magnesium alloys with minimal impact on thermal conductivity. When the Zr content is too low, grain coarsening occurs, leading to a decrease in both the strength and thermal conductivity of the magnesium alloy. When the Zr content is too high, Zr agglomerates to form large particles, causing stress concentration and reducing strength. Excessive solid solution slightly increases electron scattering, further reducing the thermal conductivity of the magnesium alloy. Each addition of 0.5 wt.% Zr only reduces thermal conductivity by <5 W / (m²). Zr can efficiently refine grains, thereby significantly improving the mechanical properties of magnesium alloys while having minimal impact on their thermal conductivity. Therefore, this application preferably controls the Zr content within the above-mentioned range to enable magnesium alloys to achieve high mechanical properties while having minimal impact on their thermal conductivity.

[0032] To further improve the thermal conductivity and mechanical properties of high-strength, high-thermal-conductivity cast magnesium alloy materials, in one embodiment of this application, the high-strength, high-thermal-conductivity cast magnesium alloy material comprises the following elements by mass percentage: 4.5~5.0% Zn, 0.55~0.8% La, 0.6~0.8% Cu, ≤0.2% Ca, 0.3~0.6% Zr, unavoidable total impurity content ≤0.15%, and the balance being Mg.

[0033] In one embodiment of this application, the mass content of Ca is 0.1~0.2% and the mass content of Zr is 0.4~0.5%.

[0034] Preferably controlling the mass content of Ca within the above-mentioned range helps improve the mechanical properties of magnesium alloys while reducing their negative impact on thermal conductivity. Similarly, preferably controlling the mass content of Zr within the above-mentioned range helps refine the grain size, thereby improving the mechanical properties of magnesium alloys while reducing their impact on thermal conductivity.

[0035] In one embodiment of this application, the mass ratio of Zn to La is 6~9:1, preferably 7~8:1; and / or, the mass ratio of Zn to Cu is 6~8:1, preferably 6~7:1; and / or, the average grain size of the high-strength, high-thermal-conductivity cast magnesium alloy material is 32~58μm.

[0036] Preferably controlling the mass ratio of Zn to La within the above-mentioned range helps to promote the formation of micron-sized particles. τ 1-La 0.08 (Mg, Zn) 0.92 This phase, dispersed near the grain boundaries, is beneficial for refining grains, optimizing the distribution of precipitated phases, and reducing impurity segregation and scattering at grain boundaries, thereby achieving simultaneous improvement in precipitation strengthening and thermal conductivity. Preferably, controlling the mass ratio of Zn to Cu within the aforementioned range helps in the formation of nanoscale particles. η The '-Mg(ZnCu)2 phase, dispersed within the grains, helps to further improve both the thermal conductivity and room-temperature mechanical properties of magnesium alloys. Preferably, the average grain size of the magnesium alloy is within the aforementioned range, which helps to further improve the strength and thermal conductivity of the magnesium alloy.

[0037] In another typical embodiment of this application, a method for preparing the above-mentioned magnesium alloy is provided. This method includes: according to the composition of a high-strength, high-thermal-conductivity cast magnesium alloy material, batching raw materials including pure Mg ingots, pure Zn ingots, a first Mg-La master alloy, a Mg-Cu master alloy, a Mg-Ca master alloy, and a first Mg-Zr master alloy, and then sequentially performing melting, casting, T4 solution treatment, and T6 aging treatment to obtain a high-strength, high-thermal-conductivity cast magnesium alloy material; wherein the raw materials also include a second Mg-La master alloy and a second Mg-Zr master alloy; the second Mg-La master alloy is used to compensate for the component loss caused by the burning off of La element; the second Mg-Zr master alloy is used to compensate for the component loss caused by the burning off of Zr element; the melting includes sequentially performing a first heating and a second heating in a vacuum environment with a vacuum degree of 10. -3 ~10 -2 Pa; the power of the second heating is greater than that of the first heating, and the power of the second heating is 35~40KW; the solution temperature of T4 solution treatment is 400~430℃; the temperature of T6 aging heat treatment is 180~200℃.

[0038] The high-strength, high-thermal-conductivity cast magnesium alloy material obtained by the preparation method of this application possesses both high mechanical and thermal conductivity properties. Specifically, regarding raw material preparation, based on the theoretical mass of the first Mg-La master alloy and the first Mg-Zr master alloy calculated according to elemental composition, this application performs compositional analysis on the alloy melt after melting. It was found that the La element loss rate during vacuum induction melting of the Mg-La master alloy is approximately 3-5%, and the Zr element exhibits sedimentation behavior during vacuum induction melting of the Mg-Zr master alloy, with an actual Zr element recovery rate of approximately 40-50%. Therefore, this application fully considers the burn-off of Zr and La elements, adding a second Mg-La master alloy and a second Mg-Zr master alloy to compensate for the compositional losses caused by the burn-off of La and Zr elements, obtaining their respective corresponding compensation masses. The theoretical mass of each alloy plus the compensation mass yields the actual mass of the Mg-La master alloy and the Mg-Zr master alloy that conforms to the elemental design, thereby improving the recovery rate of rare earth elements La and Zr. By sequentially subjecting the raw materials to first and second heating processes, the yields of rare earth elements (La) and Zr in the magnesium alloy can be improved. Before melting, a vacuum level of the aforementioned vacuum degree is applied, and by controlling the power of the first heating within the specified range, oxidation of the alloy during melting can be prevented. Controlling the power of the second heating within the specified range ensures complete melting of the alloy, reduces the loss of Zr and rare earth element (La), and guarantees the yield of other alloying elements. The aforementioned T4 solution treatment eliminates casting defects such as coarse eutectic structures and compositional segregation at grain boundaries in the as-cast microstructure, resulting in a more uniform microstructure and composition, and preparing the microstructure for aging treatment. Excessively high T4 solution treatment temperatures can cause grain growth and oxidation in the magnesium alloy, affecting its mechanical and thermal properties; conversely, excessively low T4 solution treatment temperatures can lead to incomplete dissolution of solute elements, failing to achieve the desired solution treatment effect. Therefore, this application preferably controls the solution temperature of the T4 solution treatment within the above-mentioned range, which can achieve a good solution treatment effect, thereby improving the mechanical and thermal conductivity of the magnesium alloy material. Preferably controlling the temperature of the T6 aging treatment within the above-mentioned range allows for the precipitation of more fine-grained second-phase precipitates from the magnesium alloy matrix. This reduces the Zn content in the magnesium alloy matrix, decreasing the lattice distortion caused by Zn and thus improving the thermal conductivity of the magnesium alloy material. Furthermore, the dispersed precipitation of the second phase strengthens the magnesium alloy, thereby improving its mechanical properties. In summary, the casting and heat treatment processes in this application are simple, easy to operate, and low in cost, making them suitable for large-scale production.

[0039] For industrial applications or large-volume magnesium alloys, the alloy liquid can be first melted sequentially through a small crucible using the above-mentioned melting process, and then the composition of the alloy liquid can be analyzed online using laser-induced breakdown spectroscopy (LIBS) non-contact method. After obtaining the required raw material ratio, the raw materials can be added in one go and prepared according to the preparation method of this application.

[0040] In one embodiment of this application, the power of the first heating is 10~15KW, the temperature of the first heating is 300~500℃, and the heating time is 10~15min; and / or, the temperature of the second heating is 770~790℃, the heating time of the second heating is 10~15min, and the holding time of the second heating is 3~5min; the atmosphere of the second heating is argon, and the pressure of the second heating is 0.04~0.06MPa.

[0041] Preferably controlling the power, temperature, and time of the first heating within the aforementioned range helps to further reduce the oxidation reaction of the alloy during the heating and melting process, thereby optimizing the melting effect of the first heating and improving the purity of the alloy. The second heating includes sequential heating and holding; preferably controlling the heating time and atmosphere of the second heating within the aforementioned range not only helps to achieve a uniform distribution of alloy components and reduce oxidation, thereby improving the purity and quality of the magnesium alloy material, but also helps to reduce the burn-off of rare earth element La and improve the yield of the aforementioned alloying elements. Introducing argon gas into the furnace to achieve the aforementioned pressure helps to improve the melting effect of the second heating. Controlling the temperature and holding time of the second heating within the aforementioned range helps to fully melt the alloy, promotes the uniform distribution of the components in the alloy, thereby providing a high-quality melt for the subsequent casting process.

[0042] Preferably, in a medium-frequency induction melting furnace, after loading the raw materials, the vacuum induction furnace cover is closed, and the vacuum is evacuated to the aforementioned vacuum level. Then, the first and second heating processes are carried out independently, which helps to further improve the melting efficiency.

[0043] In one embodiment of this application, the above preparation method further includes: surface treating the above raw materials to obtain surface-treated raw materials; and / or, after melting, obtaining alloy liquid; performing composition analysis on the alloy liquid, and casting the alloy liquid with the required composition; and / or, the mass ratio of the second Mg-La master alloy to the first Mg-La master alloy is 10~15:100; and / or, the mass percentage of the second Mg-Zr master alloy to the first Mg-Zr master alloy is 100~150:100.

[0044] Surface treatment of the above raw materials helps to remove oil stains and oxide layers from the surface of the alloy raw materials, thereby reducing oxides and other impurities caused by dirt on the surface of the raw materials.

[0045] The preferred Mg-La master alloy is Mg-La30 master alloy (La content 30% by mass), and the preferred Mg-Zr master alloy is Mg-Zr30 master alloy (Zr content 30% by mass). Compositional analysis of the molten alloy after melting revealed that the La loss rate of the Mg-La30 master alloy during vacuum induction melting was approximately 3-5%, and the Zr content of the Mg-Zr30 master alloy during vacuum induction melting exhibited sedimentation behavior, resulting in an actual Zr recovery rate of approximately 40-50%. Therefore, adding the aforementioned mass contents of the second Mg-La master alloy and the second Mg-Zr master alloy helps to improve the recovery rates of rare earth elements La and Zr. Controlling the mass ratios of the second Mg-La master alloy to the first Mg-La master alloy, and the second Mg-Zr master alloy to the first Mg-Zr master alloy, within the aforementioned ranges further helps to improve the recovery rates of rare earth elements La and Zr in the magnesium alloy.

[0046] In one embodiment of this application, the casting method is bottom casting with a side gating system; the casting process includes: casting the alloy liquid in a mold with a bottom gating system to obtain an ingot; wherein, the preheating temperature of the mold is 220~250℃; and the casting temperature is 720~740℃.

[0047] The heat-resistant steel mold with side runner bottom casting used in this application can serve as an intermediate buffer and slag remover. Preferably, controlling the preheating temperature of the mold within the above-mentioned range helps to control the cooling rate of the alloy liquid during casting, thereby reducing the occurrence of cracks or shrinkage cavities caused by rapid cooling of the alloy liquid after entering the mold, and thus helping to improve the uniformity of the internal structure of the ingot.

[0048] In one embodiment of this application, the T4 solution treatment process includes: under an argon atmosphere, the ingot is sequentially solution treated and quenched to obtain a solution-treated ingot; wherein the solution temperature is 400~430℃, the solution holding time is 6~10h, the quenching temperature is 75~85℃, and the quenching medium is water.

[0049] The preferred T4 solution treatment process helps to eliminate casting defects such as coarse eutectic structure and compositional segregation at grain boundaries in the as-cast structure, making the microstructure and composition of the alloy more uniform, which is beneficial for subsequent T6 aging treatment.

[0050] In one embodiment of this application, the T6 aging process includes: holding the solution-treated ingot at 180~200℃ for 10~20h under an argon atmosphere and then air-cooling it.

[0051] Excessive aging temperature or holding time in the T6 aging treatment can lead to over-aging, reducing the hardness and mechanical properties of the magnesium alloy. Conversely, insufficient aging temperature or holding time can result in inadequate second-phase precipitation and under-aging, limiting the improvement in thermal conductivity and mechanical properties, thus failing to achieve the goal of simultaneously improving the thermal conductivity and strength of the magnesium alloy through aging heat treatment. Therefore, this application employs the aforementioned T6 aging treatment process, controlling the aging temperature to 180-200℃ and the holding time to 10-20 hours, which helps to simultaneously improve the thermal conductivity and mechanical properties of the magnesium alloy. Air cooling to room temperature (20-25℃) is preferred.

[0052] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0053] Example 1

[0054] The raw materials, including 99.95% pure Mg ingots, 99.85% pure Zn ingots, the first Mg-La30 master alloy, Mg-Cu30 master alloy, Mg-Ca30 master alloy, and the first Mg-Zr30 master alloy, underwent surface treatment, i.e., surface grinding and polishing. Then, they were batched according to the composition of high-strength, high-thermal-conductivity cast magnesium alloy materials, using the mass percentages shown in Table 1. The second Mg-La30 master alloy and the second Mg-Zr30 master alloy were also added to the raw materials to compensate for the compositional loss caused by the burning of La and Zr elements. The mass ratio of the second Mg-La30 master alloy to the first Mg-La30 master alloy was 10:100, and the mass percentage of the second Mg-Zr30 master alloy to the first Mg-Zr30 master alloy was 1:1.

[0055] Melting: Place the prepared raw materials into a silicon carbide graphite crucible, then load it into a medium-frequency induction melting furnace. After loading, close the vacuum induction furnace cover and simultaneously evacuate to a vacuum degree of 10. -3 Pa, and simultaneously set the medium-frequency induction furnace to a power of 10KW for the first heating for 10 minutes. Continue evacuating until the vacuum degree reaches 10. -3 After Pa, argon gas is introduced to 0.06 MPa, and the medium-frequency induction furnace is set to a power of 35 KW for a second heating for 15 minutes until melting. Then, it is held at 770℃ for 4 minutes to obtain the alloy liquid.

[0056] The alloy melt was analyzed online using laser-induced breakdown spectroscopy (LIBS) non-contact method, and all the above elements were found to meet the composition design requirements.

[0057] The molten alloy was poured into a side-sprue bottom-cast metal mold at a temperature of 720°C. The mold was preheated to 220°C. The alloy was then produced using vacuum induction melting to achieve the specified dimensions. Ingots measuring 85mm × 320mm.

[0058] T4 Solution Treatment: Under argon gas protection, the ingot is heated at 400℃ for 6 hours, then quickly removed and quenched in hot water at 80℃ to obtain a solution-treated ingot.

[0059] T6 aging treatment: Under argon gas protection, the solution-treated ingot is held at 180℃ for 20 hours and then air-cooled to room temperature (25℃) to obtain a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0060] Example 2

[0061] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780°C, the casting temperature is 730°C, the mold preheating temperature is 230°C, the solution temperature of T4 solution treatment is 410°C, and the holding time of T6 aging treatment is 16h, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0062] Example 3

[0063] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780°C, the casting temperature is 730°C, the mold preheating temperature is 230°C, the T4 solution treatment temperature is 420°C, the T4 solution treatment holding time is 8h, the T6 aging treatment temperature is 190°C, and the T6 aging treatment holding time is 18h, finally obtaining a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0064] Example 4

[0065] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780°C, the casting temperature is 730°C, the mold preheating temperature is 230°C, the T4 solution treatment temperature is 420°C, the T4 solution treatment holding time is 8h, the T6 aging treatment temperature is 190°C, and the T6 aging treatment holding time is 18h, finally obtaining a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0066] Example 5

[0067] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 790°C, the casting temperature is 730°C, the mold preheating temperature is 250°C, the T4 solution treatment temperature is 430°C, the T4 solution treatment holding time is 10h, and the T6 aging treatment temperature is 200°C, finally obtaining a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0068] Example 6

[0069] The difference from Example 1 is that the elemental composition is shown in Table 1, and the holding time of T4 solution treatment is 8 hours, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0070] Example 7

[0071] The difference from Example 1 is that the elemental composition is shown in Table 1, the T6 aging treatment temperature is 10h, and a high-strength, high-thermal-conductivity cast magnesium alloy material is finally obtained.

[0072] Example 8

[0073] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780℃, the mold preheating temperature is 240℃, the T4 solution treatment temperature is 420℃, the T6 aging treatment temperature is 200℃, and the T6 aging treatment holding time is 16h, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0074] Example 9

[0075] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780°C, the casting temperature is 740°C, the mold preheating temperature is 240°C, the T4 solution treatment temperature is 430°C, the T6 aging treatment temperature is 200°C, and the T6 aging treatment time is 18h, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0076] Example 10

[0077] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 790°C, the casting temperature is 740°C, the mold preheating temperature is 250°C, the T4 solution treatment temperature is 430°C, the T4 solution treatment holding time is 10h, and the T6 aging treatment temperature is 200°C, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0078] Example 11

[0079] The difference from Example 1 is that the total mass content of Zn and La elements is 5.55%, and the mass ratio of Zn to La elements is 7:1, ultimately resulting in a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0080] Example 12

[0081] The difference from Example 1 is that the total mass content of Zn and La elements is 5.55%, and the mass ratio of Zn to La elements is 5:1, ultimately resulting in a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0082] Example 13

[0083] The difference from Example 1 is that the total mass content of Zn and Cu elements is 5.3%, and the mass ratio of Zn to Cu elements is 7.5:1, ultimately resulting in a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0084] Example 14

[0085] The difference from Example 1 is that the total mass content of Zn and Cu elements is 5.3%, and the mass ratio of Zn to Cu elements is 9:1, ultimately resulting in a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0086] Example 15

[0087] The difference from Example 1 is that the power of the first heating is 12KW, the power of the second heating is 36KW, and the vacuum degree of the vacuum environment for the first and second heating is 10. -2 Pa, ultimately yielding a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0088] Comparative Example 1

[0089] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 790°C, the casting temperature is 740°C, the mold preheating temperature is 250°C, the T4 solution treatment temperature is 430°C, the T4 solution treatment holding time is 10h, and the T6 aging treatment temperature is 200°C, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0090] Comparative Example 2

[0091] The difference from Example 1 is that the elemental composition is shown in Table 1, the second heating temperature is 780°C, the casting temperature is 740°C, the mold preheating temperature is 250°C, the T4 solution treatment temperature is 430°C, and the T4 solution treatment holding time is 10h, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0092] Comparative Example 3

[0093] The difference from Example 1 is that the elemental composition is shown in Table 1, the preheating temperature of the mold is 250℃, the holding time of T4 solution treatment is 10h, and finally a high-strength and high-thermal-conductivity cast magnesium alloy material is obtained.

[0094] Comparative Example 4

[0095] The difference from Example 1 is that the solution temperature of T4 solution treatment is 450°C and the temperature of T6 aging treatment is 220°C, ultimately yielding a high-strength, high-thermal-conductivity cast magnesium alloy material.

[0096] Comparative Example 5

[0097] The difference from Example 1 is that the solution temperature of T4 solution treatment is 380℃, the holding time of T4 solution treatment is 10h, and the temperature of T6 aging treatment is 160℃, finally obtaining a high-strength and high-thermal-conductivity cast magnesium alloy material.

[0098] Comparative Example 6

[0099] The difference from Example 1 is that the prepared raw materials are directly melted in a melting furnace at 770°C for 25 minutes to obtain an alloy liquid, and finally a high-strength and high-thermal-conductivity cast magnesium alloy material is obtained.

[0100] Test method:

[0101] Thermal conductivity test: laser flash method; Test standard: according to ASTM-E1461-13 (2022) "Standard Test Method for Determination of Thermal Diffusivity by Flash Method", the thermal diffusivity α of magnesium alloy samples at room temperature was tested. Sample dimensions: 10mm × 2.5mm. Based on the density ρ and specific heat capacity C of magnesium alloy at room temperature. p Finally, the thermal conductivity λ is obtained through the formula λ = ×ρ×C p The thermal conductivity of the magnesium alloy was calculated.

[0102] Tensile strength, yield strength, and elongation tests: Refer to national standard GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Tests at room temperature". Sample dimensions: parallel section diameter d = 5 ± 0.03 mm, gauge length L0 = 25 mm, total length L... t =71mm. Tensile testing equipment: Zwick / Roell Z100 electronic universal testing machine, extensometer is a fully automatic laser extensometer.

[0103] The test results are shown in Table 2.

[0104] Table 1

[0105]

[0106] Table 2

[0107]

[0108] As shown in Table 2, compared to the magnesium alloy in the comparative example, the high-strength, high-thermal-conductivity cast magnesium alloy material obtained in the embodiments of this application possesses both high thermal conductivity and high mechanical properties. The high-strength, high-thermal-conductivity cast magnesium alloy material in the embodiments not only has superior thermal conductivity but also higher mechanical strength than the comparative example. For example, the thermal conductivity of the high-strength, high-thermal-conductivity cast magnesium alloy material in Example 1 is increased by 34.5%, and the tensile strength is increased by 6.9% compared to Comparative Example 1.

[0109] in, Figure 1 This is a SEM microstructure image of the high-strength, high-thermal-conductivity cast magnesium alloy material in Example 1. Figure 1 It can be seen that the microstructure of magnesium alloy in the T6 state mainly consists of α - Mg matrix and micron-sized τ1-La particles dispersed near grain boundaries 0.08 (Mg, Zn) 0.92 This phase is beneficial for refining grains and can reduce the segregation and scattering of impurities at grain boundaries, thereby achieving simultaneous improvement in precipitation strengthening and thermal conductivity.

[0110] Figure 2 This is a TEM microstructure image of the high-strength, high-thermal-conductivity cast magnesium alloy material in Example 1. Figure 2 As can be seen, nanoscale rod-shaped β1'-Mg4Zn7 and disk-shaped β2'-MgZn2 precipitates are dispersed in the α-Mg matrix, and the size of the β1' and β2' phases is 20~50nm, and they are orderly dispersed in a certain direction. This structure of precipitates can effectively hinder dislocation slip, thereby improving the yield strength and tensile strength of magnesium alloy materials. At the same time, it reduces the solid solubility of Zn in the Mg matrix, thereby reducing the influence of lattice distortion on thermal conductivity, and thus improving the thermal conductivity of magnesium alloy materials.

[0111] Figure 3 This is the room temperature tensile curve of the high-strength, high-thermal-conductivity cast magnesium alloy material in Example 1, derived from... Figure 3 The true stress-true strain curves of the magnesium alloy obtained from the experiment were tested according to the test method of the national standard GB / T228.1-2021 for room temperature tensile testing of metallic materials. The results showed that the tensile strength of the magnesium alloy in Example 1 reached 278 MPa, the yield strength reached 133 MPa, and the elongation reached 14.6% at room temperature.

[0112] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0113] This application, based on Mg-Zn thermally conductive magnesium alloys, optimizes the composition of Mg-Zn-La-Cu-Ca-Zr multi-element alloying. By optimally controlling the elemental composition and mass content of the high-strength, high-thermal-conductivity cast magnesium alloy within the aforementioned range, it achieves both high thermal conductivity and high mechanical properties. After adding the aforementioned mass content of rare earth element La to the Mg-Zn alloy, a micron-sized granular strengthening phase is mainly formed in the as-cast state. τ 1. Dispersed on the grain boundaries, the Mg-Zn-La alloy, after solution treatment and aging, τPhase 1 promotes the formation of nanoscale rod-shaped β1'-Mg4Zn7 and disk-shaped β2'-MgZn2 precipitates, significantly improving the strength of magnesium alloys. Simultaneously, it reduces the solid solubility of Zn in the Mg matrix, facilitating Zn desolvation and minimizing the impact of lattice distortion on thermal conductivity, thus further enhancing the thermal conductivity of magnesium alloys. Adding Cu alloying element forms a highly thermally conductive dispersed Mg(ZnCu)2 (η' phase), simultaneously improving both the strength and thermal conductivity of magnesium alloys. Adding Ca and Zr elements acts as flame retardants and purifies impurities in the molten magnesium alloy, significantly refining the grain size, and has minimal impact on the thermal conductivity of magnesium alloys at low mass contents. Therefore, the high-strength, high-thermal-conductivity cast magnesium alloy material Mg-Zn-La-Cu-Ca-Zr developed in this application has high strength and high thermal conductivity. Its thermal conductivity, tensile strength, yield strength and elongation can reach the above range, thereby better meeting the performance requirements of high thermal conductivity magnesium alloy heat dissipation components in aerospace, satellite communication, new energy vehicles and 3C application fields.

[0114] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength, high-thermal-conductivity cast magnesium alloy material, characterized in that, The high-strength, high-thermal-conductivity cast magnesium alloy material comprises the following elements by weight percentage: 4.5~6.0% Zn element; 0.55~1.65% La element; 0.5~1.0% Cu; ≤0.2% Ca; 0.3~0.6% Zr, with unavoidable total impurities ≤0.15%, and the balance being Mg. The thermal conductivity of the high-strength, high-thermal-conductivity cast magnesium alloy material is 135~152 W / (m²). K); the high-strength, high-thermal-conductivity cast magnesium alloy material has a tensile strength of 260~290MPa, a yield strength of 130~155MPa, and an elongation of 8~15%.

2. The high-strength, high-thermal-conductivity cast magnesium alloy material according to claim 1, characterized in that, The high-strength, high-thermal-conductivity cast magnesium alloy material comprises the following elements by weight percentage: 4.5~5.0% of the Zn element; 0.55~0.8% of the La element; The Cu element is 0.6-0.8%; the Ca element is ≤0.2%; the Zr element is 0.3-0.6%; the total unavoidable impurity content is ≤0.15%; and the balance is Mg.

3. The high-strength, high-thermal-conductivity cast magnesium alloy material according to claim 1 or 2, characterized in that, The mass content of Ca is 0.1-0.2%; the mass content of Zr is 0.4-0.5%.

4. The high-strength, high-thermal-conductivity cast magnesium alloy material according to claim 1 or 2, characterized in that, The mass ratio of Zn to La is 6~9:1; and / or the mass ratio of Zn to Cu is 6~8:1; and / or the average grain size of the high-strength, high-thermal-conductivity cast magnesium alloy material is 32~58μm.

5. A method for preparing the high-strength, high-thermal-conductivity cast magnesium alloy material according to any one of claims 1 to 4, characterized in that, The preparation method includes: according to the composition of high-strength and high-thermal-conductivity cast magnesium alloy material, raw materials including pure Mg ingot, pure Zn ingot, first Mg-La master alloy, Mg-Cu master alloy, Mg-Ca master alloy and first Mg-Zr master alloy are batched and then subjected to melting, casting, T4 solution treatment and T6 aging treatment in sequence to obtain the high-strength and high-thermal-conductivity cast magnesium alloy material. The raw materials also include a second Mg-La master alloy and a second Mg-Zr master alloy; The second Mg-La master alloy is used to compensate for the composition loss caused by the burning off of La; the second Mg-Zr master alloy is used to compensate for the composition loss caused by the burning off of Zr. The melting process includes a first heating and a second heating performed sequentially in a vacuum environment with a vacuum degree of 10. -3 ~10 -2 Pa; the power of the second heating is greater than the power of the first heating, and the power of the second heating is 35~40KW; The solution temperature for the T4 solution treatment is 400~430℃; the temperature for the T6 aging heat treatment is 180~200℃.

6. The preparation method according to claim 5, characterized in that, The power of the first heating is 10~15KW, the temperature of the first heating is 300~500℃, and the heating time is 10~15min; And / or, the temperature of the second heating is 770~790℃, the heating time of the second heating is 10~15min, the holding time of the second heating is 3~5min; the atmosphere of the second heating is argon, and the pressure of the second heating is 0.04~0.06MPa.

7. The preparation method according to claim 6, characterized in that, The preparation method further includes: surface treating the raw material to obtain a surface-treated raw material; And / or, after the melting is completed, an alloy liquid is obtained; the alloy liquid is subjected to composition analysis, and the alloy liquid with the required composition is cast. And / or, the mass ratio of the second Mg-La master alloy to the first Mg-La master alloy is 10~15:100; And / or, the mass percentage of the second Mg-Zr master alloy and the first Mg-Zr master alloy is 100~150:

100.

8. The preparation method according to claim 7, characterized in that, The casting method is side-sprue bottom casting; the casting process includes: casting the alloy liquid in a mold with a side-sprue bottom casting to obtain an ingot; wherein, the preheating temperature of the mold is 220~250℃; the casting temperature is 720~740℃.

9. The preparation method according to claim 8, characterized in that, The T4 solution treatment process includes: under an argon atmosphere, the ingot is sequentially solution treated and quenched to obtain a solution-treated ingot; wherein, the solution temperature is 400~430℃, the solution holding time is 6~10h, the quenching temperature is 75~85℃, and the quenching medium is water.

10. The preparation method according to claim 9, characterized in that, The T6 aging treatment process includes: holding the solution-treated ingot at 180~200℃ for 10~20h under an argon atmosphere and then air-cooling it.

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