High-flame-retardant high-thermal-conductivity magnesium alloy and preparation method thereof
By adding trace amounts of Sn and Y to magnesium alloys, controlling the Al/Ca ratio, and employing stepwise refining and high-strain hot extrusion processes, a microstructure with high flame retardancy and high thermal conductivity was constructed, solving the performance problem of magnesium alloys in highly integrated electronic devices and realizing the low-cost preparation of high-performance magnesium alloys.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 山西银光华盛镁业股份有限公司
- Filing Date
- 2026-05-15
- Publication Date
- 2026-06-16
AI Technical Summary
Existing magnesium alloys are difficult to balance high flame retardancy, high thermal conductivity, and good mechanical properties in highly integrated electronic devices. Furthermore, the addition of rare earth elements leads to increased costs and decreased thermal conductivity.
By adding trace amounts of Sn and Y to the Mg-Al-Zn system and controlling the Al/Ca ratio, combined with stepwise refining, composite modification, two-stage solid solution and large strain hot extrusion processes, a microstructure of granular Al2Ca phase and nanoscale Mg2Sn phase was constructed, reducing the amount of rare earth elements used.
It achieves comprehensive performance with an ignition point of not less than 780℃, a room temperature thermal conductivity of not less than 125W/(m·K), a tensile strength of not less than 300MPa, a yield strength of not less than 220MPa, and an elongation of not less than 10%, reducing raw material costs and making it suitable for high-end heat dissipation structures in 5G communication and new energy vehicles.
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Figure CN122214727A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metallic materials technology, and in particular to a high flame-retardant and high thermal conductivity magnesium alloy and its preparation method. Background Technology
[0002] Magnesium alloys, as one of the lightest metallic structural materials, have broad application prospects in aerospace, automotive electronics, and 3C products. However, magnesium's high chemical reactivity makes it highly susceptible to oxidation and combustion during smelting and processing; simultaneously, most magnesium alloys have low thermal conductivity, making it difficult to meet the heat dissipation requirements of highly integrated electronic devices. Therefore, developing magnesium alloys that combine high flame retardancy and high thermal conductivity has become a research hotspot in the industry.
[0003] Currently, the most widely used commercial magnesium alloys, such as the AZ series (Mg-Al-Zn system), possess good strength and casting properties, but their flame retardant temperature is typically below 600℃, and their room temperature thermal conductivity is only 50~80 W / (m·K), making them unsuitable for high-end heat dissipation structural components. To improve the flame retardancy of magnesium alloys, existing research often involves adding elements such as Ca and rare earth (RE) to form high-melting-point oxide films or stabilize the second phase. However, the rare earth element content added in existing studies is usually high, leading to a significant increase in raw material costs, and the coarse second phase in the microstructure can adversely affect thermal conductivity.
[0004] Therefore, there is an urgent need to develop a magnesium alloy with high flame retardancy, high thermal conductivity and good mechanical properties, and a low preparation cost, as well as its preparation method. Summary of the Invention
[0005] To address some or all of the technical problems existing in the prior art, this invention provides a high flame-retardant and high thermal conductivity magnesium alloy and its preparation method. Based on a low-cost Mg-Al-Zn system, it achieves high flame retardancy, high thermal conductivity, and good mechanical properties through micro-alloying and synergistic processes.
[0006] The technical solution of the present invention is as follows: In a first aspect, a high flame-retardant and high thermal conductivity magnesium alloy is provided, comprising the following components by weight percentage: Al: 7.0~10.0%, Zn: 0.8~2.2%, Ca: 1.0~1.8%, Mn: 0.4~0.9%, Sn: 0.1~0.8%, Y: 0.05~0.25%, with the balance being Mg and unavoidable impurity elements, and the Al content [Al], Ca content [Ca], Sn content [Sn], and Y content [Y] meet the following requirements: 5.0≤[Al] / [Ca]≤9.0; [Sn]+[Y]≤0.85%.
[0007] Furthermore, in some embodiments, the microstructure of the high flame retardant and high thermal conductivity magnesium alloy includes: a fine equiaxed α-Mg grain matrix, granular Al2Ca phase dispersed within the grains and grain boundaries, and nanoscale Mg2Sn phase and Y-containing precipitates.
[0008] Furthermore, in some embodiments, the Y-containing precipitate comprises an Al2Y phase, and the Mg2Sn phase and the Y-containing precipitate preferentially precipitate at grain boundaries or Al2Ca phase interfaces.
[0009] Furthermore, in some embodiments, the high flame-retardant and high thermal conductivity magnesium alloy has an ignition point ≥780℃, a room temperature thermal conductivity ≥125W / (m·K), a tensile strength ≥300MPa, a yield strength ≥220MPa, and an elongation ≥10%.
[0010] Secondly, a method for preparing the aforementioned high flame-retardant and high thermal conductivity magnesium alloy is also provided, comprising the following steps: Raw material smelting and primary alloying: Under a protective atmosphere, pure magnesium ingots are melted and heated to 730~750℃. Preheated Al ingots, pure Zn ingots, and Al-Mn master alloys are added in sequence and stirred until completely melted. Then, the temperature is adjusted to 740~750℃, Al-Ca master alloys are added, and the mixture is stirred thoroughly until clear to obtain the basic melt. Trace element addition and refining: Reduce the temperature of the base melt to 720~735℃, add Al-Sn master alloy and Mg-Y master alloy in sequence, stir and introduce inert gas for refining; Composite modification and casting: A composite modifier consisting of SrCO3 and nano AlN powder is added to the refined melt. After stirring, settling, and slag removal, electromagnetic semi-continuous casting is carried out. The casting cooling rate is controlled at 15~40℃ / s to obtain ingots. Two-stage solution treatment: First, the ingot is held at 410~430℃ for 6~12 hours, then the temperature is raised to 450~470℃ and held for 4~8 hours, followed by water quenching; Large strain hot extrusion and online quenching: The solution-treated ingot is heated to 340~380℃ and held for 1~2 hours, followed by hot extrusion with an extrusion ratio of 30:1 to 60:1 and an extrusion speed of 2~6m / min. The extruded magnesium alloy profile is then rapidly cooled online at the extrusion outlet.
[0011] Furthermore, in some embodiments, the protective atmosphere is a mixture of CO2 and SF6 in the raw material smelting and primary alloying steps.
[0012] Furthermore, in some embodiments, in the trace element addition and refining step, the stirring and inert gas introduction for refining further includes: During the addition of Al-Sn master alloy and Mg-Y master alloy, mechanical stirring and argon bottom blowing are performed. After the master alloy is added, rotary argon refining is carried out at 720~730℃ for 10~15 minutes.
[0013] Furthermore, in some embodiments, in the composite modification and casting steps, the amount of the composite modifier added is 0.1 to 0.3% of the total mass of the melt, and the mass ratio of SrCO3 to nano-AlN powder in the composite modifier is 1:0.2 to 1:1.
[0014] Furthermore, in some embodiments, during the high-strain hot extrusion and online quenching steps, the online rapid cooling method is high-power air cooling or water mist cooling.
[0015] Furthermore, in some embodiments, after the high-strain hot extrusion and online quenching steps, the following steps are also included: Low-temperature aging treatment: Magnesium alloy profiles are subjected to low-temperature aging treatment at 150~220℃ for 4~24 hours.
[0016] The main advantages of the technical solution of this invention are as follows: This invention discloses a high flame-retardant and high thermal conductivity magnesium alloy and its preparation method. By precisely controlling the Al / Ca ratio in the Mg-Al-Zn-Ca-Mn alloy system and adding trace amounts of Sn and Y, a microstructure is constructed with granular Al2Ca phase as the thermally conductive framework, nano-sized Mg2Sn, and Y-containing precipitates as reinforcing embellishments. Simultaneously, combined with stepwise refining, composite modification refinement, two-stage solid solution, and a synergistic process of large-strain hot extrusion and online quenching, this invention solves the problem of existing magnesium alloys failing to simultaneously achieve high flame retardancy, high thermal conductivity, and high strength. Compared with existing technologies, this invention can reduce the amount of rare earth elements to below 0.25%, significantly saving raw material costs. It achieves excellent comprehensive performance with an ignition point of not less than 780℃, a room temperature thermal conductivity of not less than 125 W / (m·K), a tensile strength of not less than 300 MPa, a yield strength of not less than 220 MPa, and an elongation of not less than 10%. This provides key material support for the large-scale application of magnesium alloys in high-end heat dissipation structures such as 5G communications and new energy vehicles. Attached Figure Description
[0017] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic flowchart illustrating a method for preparing a high flame-retardant and high thermal conductivity magnesium alloy, as provided in an embodiment of the present invention. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0019] The technical solutions provided by the embodiments of the present invention are described in detail below.
[0020] In a first aspect, embodiments of the present invention provide a high flame-retardant and high thermal conductivity magnesium alloy, comprising the following chemical composition by weight percentage: Al: 7.0~10.0%, Zn: 0.8~2.2%, Ca: 1.0~1.8%, Mn: 0.4~0.9%, Sn: 0.1~0.8%, Y: 0.05~0.25%, with the balance being Mg and unavoidable impurity elements, and the Al content [Al], Ca content [Ca], Sn content [Sn], and Y content [Y] meet the following requirements: 5.0≤[Al] / [Ca]≤9.0; [Sn]+[Y]≤0.85%.
[0021] In this embodiment of the invention, controlling the chemical composition and content within the above-mentioned range is one of the key factors in achieving high flame retardancy, high thermal conductivity, and good mechanical properties of magnesium alloys. The specific mechanism of action is as follows: By adding 0.1–0.8% Sn and 0.05–0.25% Y to the Mg-Al-Zn system, and controlling the sum of Sn and Y contents to be less than or equal to 0.85%, observable nanoscale Mg2Sn phases can be formed using Sn to provide significant precipitation strengthening while ensuring minimal impact on the thermal conductivity of the matrix; continuous Y2O3 films can be formed using Y to increase the ignition point and improve flame retardancy; nanoscale Y-containing precipitates can be formed using Y, which interacts with the added Sn to enhance the thermal stability of the precipitates; Y can combine with some impurity elements to purify grain boundaries; and the low addition amount of rare earth element Y can reduce the preparation cost of magnesium alloys.
[0022] By adding 7.0~10.0% Al and 1.0~1.8% Ca to the Mg-Al-Zn system, and controlling the Al content [Al] and Ca content [Ca] to meet the condition 5.0≤[Al] / [Ca]≤9.0, it is possible to promote the formation of a fine-grained, thermally stable Al2Ca phase, rather than a coarse or continuous network phase, thus avoiding obstruction of the heat conduction path and preventing excessive Ca solid solution, thereby improving the flame retardant and thermal conductivity properties of magnesium alloys.
[0023] Furthermore, in this embodiment of the invention, the content of each impurity element is controlled as follows by mass percentage: Fe≤0.003%, Si≤0.01%, Cu≤0.002%, Ni≤0.001%, other individual impurity elements≤0.05%, and the total amount of impurity elements≤0.15%.
[0024] Furthermore, in the embodiments of the present invention, the microstructure of the high flame retardant and high thermal conductivity magnesium alloy includes: a fine equiaxed α-Mg grain matrix, granular Al2Ca phase dispersed within the grains and grain boundaries, and nanoscale Mg2Sn phase and Y-containing precipitates.
[0025] Among them, the Y-containing precipitates include Al2Y phase, Mg2Sn phase, and Y-containing precipitates preferentially precipitate at grain boundaries or Al2Ca phase interfaces.
[0026] In this embodiment of the invention, the microstructure of the high flame retardant and high thermal conductivity magnesium alloy is obtained based on the above-defined chemical composition and in combination with the preparation method provided in this embodiment of the invention.
[0027] refer to Figure 1 Secondly, embodiments of the present invention also provide a method for preparing a high flame-retardant and high thermal conductivity magnesium alloy as described above, comprising the following steps: Raw material smelting and primary alloying: Under a protective atmosphere, pure magnesium ingots are melted and heated to 730~750℃. Preheated Al ingots, pure Zn ingots, and Al-Mn master alloys are added in sequence and stirred until completely melted. Then, the temperature is adjusted to 740~750℃, Al-Ca master alloys are added, and the mixture is stirred thoroughly until clear to obtain the basic melt. Trace element addition and refining: Reduce the temperature of the base melt to 720~735℃, add Al-Sn master alloy and Mg-Y master alloy in sequence, stir and introduce inert gas for refining; Composite modification and casting: A composite modifier consisting of SrCO3 and nano AlN powder is added to the refined melt. After stirring, settling, and slag removal, electromagnetic semi-continuous casting is carried out. The casting cooling rate is controlled at 15~40℃ / s to obtain ingots. Two-stage solution treatment: First, the ingot is held at 410~430℃ for 6~12 hours, then the temperature is raised to 450~470℃ and held for 4~8 hours, followed by water quenching; Large strain hot extrusion and online quenching: The solution-treated ingot is heated to 340~380℃ and held for 1~2 hours, followed by hot extrusion with an extrusion ratio of 30:1 to 60:1 and an extrusion speed of 2~6m / min. The extruded magnesium alloy profile is then rapidly cooled online at the extrusion outlet.
[0028] In this embodiment of the invention, during the raw material smelting and primary alloying steps, the protective atmosphere is a mixture of CO2 and SF6, which can effectively suppress the oxidation and combustion of the magnesium alloy melt, prevent the melt from absorbing gas and forming inclusions, thereby ensuring the purity and stability of the alloy composition.
[0029] In this embodiment of the invention, in the trace element addition and refining step, the Al-Sn master alloy and Mg-Y master alloy are added sequentially by lowering the temperature of the base melt to 720~735℃. During the addition of the Al-Sn master alloy and Mg-Y master alloy, mechanical stirring and argon bottom blowing are performed to ensure that Sn and Y elements dissolve quickly and uniformly and reduce burn-off. After the master alloy is added, rotary argon refining is performed at 720~730℃ for 10~15 minutes.
[0030] In this embodiment of the invention, during the composite modification and casting steps, a composite modifier consisting of SrCO3 and nano-AlN powder is added. Combined with electromagnetic semi-continuous casting and precisely controlled casting cooling rate, this achieves significant refinement of α-Mg grains, improvement of the Al2Ca phase morphology, and high uniformity of ingot composition, providing an excellent microstructure foundation for subsequent heat treatment and extrusion processing. Specifically, the Sr element produced by the decomposition of SrCO3 effectively refines the α-Mg grains and improves the Al2Ca phase morphology, while nano-AlN acts as a highly efficient heterogeneous nucleation core, further strongly refining the grains. Together, they lay the foundation for the final ultrafine-grained microstructure.
[0031] Preferably, the amount of composite modifier added is 0.1 to 0.3% of the total mass of the melt, and the mass ratio of SrCO3 to nano AlN powder in the composite modifier is 1:0.2 to 1:1.
[0032] Preferably, in the composite modification and casting step, a composite modifier composed of SrCO3 and nano AlN powder is added to the refined melt. After thorough stirring, the melt is allowed to stand for 5 to 8 minutes, and then the slag is removed. The melt is then transferred to a holding furnace and subjected to low-frequency electromagnetic semi-continuous casting at 710 to 720°C. The casting cooling rate is controlled at 15 to 40°C / s to obtain an ingot with uniform composition and fine structure.
[0033] In this embodiment of the invention, the two-stage solution treatment step, which involves first performing a low-temperature solution treatment followed by a high-temperature solution treatment, can achieve component homogenization and sufficient dissolution of elements such as Sn and Y.
[0034] In this embodiment of the invention, in the high-strain hot extrusion and online quenching steps, by subjecting the ingot to high-strain hot extrusion with an ultra-high extrusion ratio, complete dynamic recrystallization and ultrafine grain formation can be ensured. By performing online rapid cooling after hot extrusion, the ideal metastable structure after hot extrusion can be instantly "frozen" to prevent grain growth and precipitation of undesirable phases, thereby simultaneously improving the strength and thermal conductivity of the magnesium alloy.
[0035] In this embodiment of the invention, the online rapid cooling method is strong air cooling or water mist cooling. Specifically, a strong air cooling device or a water mist cooling device is set at the extrusion outlet of the extruder to strongly cool or cool the extruded magnesium alloy profile, thereby maximizing the preservation of fine grains formed by dynamic recrystallization and the supersaturated solid solution state of elements such as Sn and Y.
[0036] Furthermore, in the preparation method provided in this embodiment of the invention, after the high-strain hot extrusion and online quenching steps, the following steps are also included: Low-temperature aging treatment: Magnesium alloy profiles are subjected to low-temperature aging treatment at 150~220℃ for 4~24 hours.
[0037] In this embodiment of the invention, by subjecting the magnesium alloy profile after large strain hot extrusion and online quenching to low-temperature aging treatment at 150~220℃ for 4~24 hours, the dispersion precipitation of nano-sized Mg2Sn phase and Y-containing precipitate phase can be further promoted, thereby further improving the strength of the magnesium alloy without compromising its thermal conductivity.
[0038] In this embodiment of the invention, the high flame-retardant and high thermal conductivity magnesium alloy prepared based on the above-defined chemical composition and preparation method has an ignition point ≥780℃, a room temperature thermal conductivity ≥125W / (m·K), a tensile strength ≥300MPa, a yield strength ≥220MPa, and an elongation ≥10%.
[0039] To make the above technical solutions of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0040] (I) Alloy composition design of the examples and comparative examples The alloys for each example and comparative example were prepared according to the mass percentages shown in Table 1. The raw materials used were industrial pure magnesium ingots (purity ≥99.9%), pure Al ingots (purity ≥99.7%), pure Zn ingots (purity ≥99.9%), Al-Mn master alloy, Al-Ca master alloy, Al-Sn master alloy, and Mg-Y master alloy. All master alloys were pre-dried for use.
[0041] Table 1. Alloy chemical composition (wt.%) of the examples and comparative examples ; Among them, by mass percentage, the impurity elements in each alloy are controlled as follows: Fe≤0.003%, Si≤0.01%, Cu≤0.002%, Ni≤0.001%, other individual impurity elements≤0.05%, and the total amount of impurity elements≤0.15%.
[0042] (II) Preparation method Based on the alloy chemical compositions of Examples 1-3 and Comparative Examples 1-3 above, the corresponding magnesium alloys were prepared using the same preparation process, as follows: Raw material smelting and primary alloying: Under a protective atmosphere with a CO2 to SF6 volume ratio of 100:1, pure magnesium ingots are placed in a resistance crucible furnace for melting and heated to 740°C. After the magnesium ingots are completely melted, pure Al ingots, pure Zn ingots, and Al-Mn master alloys preheated to 200°C are added in sequence and stirred until completely melted. The melt temperature is stabilized at 745°C, and Al-Ca master alloys are added and stirred thoroughly until the melt is clear to obtain the basic melt.
[0043] Trace element addition and refining: The base melt was cooled to 728℃, and Al-Sn master alloy and Mg-Y master alloy were added in sequence. The mixture was stirred for 10 minutes by mechanical stirring at 150 rpm and bottom blowing of argon gas at a flow rate of 2 L / min to ensure that Sn and Y elements were uniformly dissolved. After the addition was completed, the mixture was refined at 725℃ by rotary jetting of argon gas for 12 minutes. The jetting rotor speed was 300 rpm and the argon gas flow rate was 3 L / min.
[0044] Composite Modification and Casting: After refining, surface slag is removed, and a composite modifier is added. The composite modifier is a mixture of SrCO3 and nano AlN powder at a mass ratio of 1:0.5, and the amount added is 0.2% of the total mass of the melt. After adding, the mixture is stirred for 3 minutes, allowed to stand for 6 minutes, and slag is removed again. Then, the melt is transferred to a holding furnace and subjected to low-frequency electromagnetic semi-continuous casting at 715℃. The casting speed is 80mm / min, and the cooling water flow rate is controlled to achieve a casting cooling rate of 25℃ / s, resulting in a round ingot with a diameter of 200mm.
[0045] Two-stage solution treatment: The ingot is placed in a box-type resistance furnace for two-stage solution treatment. First, it is held at 425℃ for 10 hours, and then the temperature is raised to 460℃ and held for 6 hours. After the holding is completed, the ingot is immediately immersed in hot water at 60~80℃ for rapid quenching.
[0046] Large strain hot extrusion and online quenching: After solution treatment, the ingot is machined and peeled to remove the surface oxide layer. Then, it is preheated at 370℃ for 1.5 hours for homogenization. Hot extrusion is carried out using an extruder. The die preheating temperature is 360℃, the extrusion barrel temperature is 380℃, the extrusion ratio is 45:1, and the extrusion speed is 4m / min. A water mist cooling device is installed at the extrusion outlet to rapidly cool the extruded profile online. The cooling rate is controlled to be above 50℃ / s, and the profile outlet temperature drops to below 100℃.
[0047] Low-temperature aging treatment: The profiles after large strain hot extrusion and online quenching are aged at 180℃ for 12 hours, and then air-cooled to room temperature.
[0048] (III) Performance Testing The performance of each prepared magnesium alloy was tested, and the performance test results are shown in Table 2.
[0049] Table 2 Performance Test Results
[0050] As shown in Table 2, the room temperature thermal conductivity of Examples 1-3 of this invention all reached over 128 W / (m·K), which is more than 70% higher than that of commercial AZ80 alloy (Comparative Example 3) and more than 8 W / (m·K higher than that of Comparative Example 2 without Sn and Y addition. This indicates that the composition design (high Al / Ca ratio combined with trace amounts of Sn and Y) and preparation process control of this invention can effectively reduce the scattering of thermally conductive electrons by solid solution atoms. At the same time, the particulate Al2Ca phase and nanoscale precipitation have less obstruction to the thermal conductivity path, thus achieving excellent thermal conductivity. Among them, although Comparative Example 1 has a high ignition point, its thermal conductivity is only 108 W / (m·K), indicating that its low Al / Ca ratio leads to a large amount of Ca solid solution or the formation of a continuous network phase, which has an adverse effect on thermal conductivity. This confirms the necessity of limiting the Al / Ca ratio to 5.0-9.0 in this invention.
[0051] As shown in Table 2, the ignition points of Examples 1-3 of this invention are all above 785℃, far exceeding the 630℃ of the commercial AZ80 alloy (Comparative Example 3), and also higher than the 710℃ of Comparative Example 2 without Sn and Y additions. This indicates that the trace synergistic addition of Sn and Y significantly improves the flame retardancy of the alloy. The mechanism of action may include: Y forming a dense Y2O3 oxide film on the melt surface, and Sn refining the grain boundary precipitates, thereby hindering the oxygen diffusion channels. Among them, although Comparative Example 1 has a high ignition point of 860℃, this is achieved at the cost of sacrificing thermal conductivity and increasing the amount of rare earth elements, which does not meet the design goal of low cost and high thermal conductivity.
[0052] As shown in Table 2, the tensile strength of Examples 1-3 of the present invention all reached above 315 MPa, the yield strength all reached above 228 MPa, and the elongation all reached above 10%, demonstrating a good balance between strength and plasticity. Compared with Comparative Example 1, Examples 1-3 of the present invention achieved better plasticity and thermal conductivity while maintaining comparable strength; compared with Comparative Example 2, the yield strength of Examples 1-3 of the present invention increased by more than 23 MPa, and the tensile strength increased by more than 30 MPa, fully demonstrating the strengthening effect of the nano-sized Mg2Sn phase and the Y-containing precipitate phase.
[0053] (iv) Microstructural characterization Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations of the magnesium alloy profile from Example 1 revealed the following: the matrix consists of fine equiaxed α-Mg grains; granular Al2Ca phases are dispersed within the grains and at grain boundaries; a large number of nanoscale Mg2Sn phases and Y-containing precipitates (Al2Y phase) exist at grain boundaries and Al2Ca phase interfaces; there is no continuous network eutectic structure, and the precipitates are uniformly distributed. This composite multi-scale structure is the structural basis for achieving a synergistic improvement in high flame retardancy, high thermal conductivity, and high strength in magnesium alloys.
[0054] (v) Verification test of process parameters To verify the impact of key process parameters, a comparative process experiment was conducted based on the composition of Example 1 of this invention: Composite modifier addition test: When the amount of composite modifier added is less than 0.1%, the grain refinement effect is insufficient; when the amount of composite modifier added is greater than 0.3%, inclusions and agglomeration occur; the structure is most uniform when the amount of addition is 0.2%.
[0055] Extrusion ratio test: When the extrusion ratio is lower than 30:1, recrystallization is incomplete; when the extrusion ratio is higher than 60:1, the equipment load is too large and the profile surface is prone to cracking; the overall performance is best at 45:1.
[0056] Online quenching comparison: Profiles without online rapid cooling showed grain coarsening, and both thermal conductivity and strength decreased.
[0057] The high flame-retardant and high thermal conductivity magnesium alloy and its preparation method provided in this invention achieve a microstructure with granular Al2Ca phase as the thermally conductive framework, nano-sized Mg2Sn and Y-containing precipitates as reinforcing embellishments by precisely controlling the Al / Ca ratio in the Mg-Al-Zn-Ca-Mn alloy system and adding trace amounts of Sn and Y. At the same time, the combined process of stepwise refining, composite modification refinement, two-stage solid solution, and large strain hot extrusion and online quenching can solve the problem that existing magnesium alloys cannot simultaneously achieve high flame retardancy, high thermal conductivity and high strength. Compared with existing technologies, this invention can reduce the amount of rare earth elements to below 0.25%, significantly saving raw material costs. It can achieve excellent comprehensive performance with an ignition point of not less than 780℃, a room temperature thermal conductivity of not less than 125W / (m·K), a tensile strength of not less than 300MPa, a yield strength of not less than 220MPa, and an elongation of not less than 10%. It can provide key material support for the large-scale application of magnesium alloys in high-end heat dissipation structures such as 5G communication and new energy vehicles.
[0058] It should be noted that, in this document, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.
[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A high flame-retardant and high thermal conductivity magnesium alloy, characterized in that, Includes the following chemical components by weight percentage: Al: 7.0~10.0%, Zn: 0.8~2.2%, Ca: 1.0~1.8%, Mn: 0.4~0.9%, Sn: 0.1~0.8%, Y: 0.05~0.25%, with the balance being Mg and unavoidable impurity elements, and the Al content [Al], Ca content [Ca], Sn content [Sn], and Y content [Y] meet the following requirements: 5.0≤[Al] / [Ca]≤9.0; [Sn]+[Y]≤0.85%.
2. The high flame-retardant and high thermal conductivity magnesium alloy according to claim 1, characterized in that, The microstructure of the high flame retardant and high thermal conductivity magnesium alloy includes: a fine equiaxed α-Mg grain matrix, granular Al2Ca phase dispersed within the grains and grain boundaries, and nanoscale Mg2Sn phase and Y-containing precipitates.
3. The high flame-retardant and high thermal conductivity magnesium alloy according to claim 2, characterized in that, The Y-containing precipitate includes the Al2Y phase, and the Mg2Sn phase and the Y-containing precipitate preferentially precipitate at grain boundaries or Al2Ca phase interfaces.
4. The high flame-retardant and high thermal conductivity magnesium alloy according to any one of claims 1-3, characterized in that, The high flame-retardant and high thermal conductivity magnesium alloy has an ignition point ≥780℃, a room temperature thermal conductivity ≥125W / (m·K), a tensile strength ≥300MPa, a yield strength ≥220MPa, and an elongation ≥10%.
5. A method for preparing a high flame-retardant and high thermal conductivity magnesium alloy as described in any one of claims 1-4, characterized in that, Includes the following steps: Raw material smelting and primary alloying: Under a protective atmosphere, pure magnesium ingots are melted and heated to 730~750℃. Preheated Al ingots, pure Zn ingots, and Al-Mn master alloys are added in sequence and stirred until completely melted. Then, the temperature is adjusted to 740~750℃, Al-Ca master alloys are added, and the mixture is stirred thoroughly until clear to obtain the basic melt. Trace element addition and refining: Reduce the temperature of the base melt to 720~735℃, add Al-Sn master alloy and Mg-Y master alloy in sequence, stir and introduce inert gas for refining; Composite modification and casting: A composite modifier consisting of SrCO3 and nano AlN powder is added to the refined melt. After stirring, settling, and slag removal, electromagnetic semi-continuous casting is carried out. The casting cooling rate is controlled at 15~40℃ / s to obtain ingots. Two-stage solution treatment: First, the ingot is held at 410~430℃ for 6~12 hours, then the temperature is raised to 450~470℃ and held for 4~8 hours, followed by water quenching; Large strain hot extrusion and online quenching: The solution-treated ingot is heated to 340~380℃ and held for 1~2 hours, followed by hot extrusion with an extrusion ratio of 30:1 to 60:1 and an extrusion speed of 2~6m / min. The extruded magnesium alloy profile is then rapidly cooled online at the extrusion outlet.
6. The method for preparing a high flame-retardant and high thermal conductivity magnesium alloy according to claim 5, characterized in that, In the raw material smelting and primary alloying steps, the protective atmosphere is a mixture of CO2 and SF6.
7. The method for preparing a high flame-retardant and high thermal conductivity magnesium alloy according to claim 5, characterized in that, In the trace element addition and refining step, the stirring and inert gas introduction for refining further includes: During the addition of Al-Sn master alloy and Mg-Y master alloy, mechanical stirring and argon bottom blowing are performed. After the master alloy is added, rotary argon refining is carried out at 720~730℃ for 10~15 minutes.
8. The method for preparing a high flame-retardant and high thermal conductivity magnesium alloy according to claim 5, characterized in that, In the composite modification and casting steps, the amount of composite modifier added is 0.1~0.3% of the total mass of the melt, and the mass ratio of SrCO3 to nano AlN powder in the composite modifier is 1:0.2 to 1:
1.
9. The method for preparing a high flame-retardant and high thermal conductivity magnesium alloy according to claim 5, characterized in that, In the high-strain hot extrusion and online quenching process, the online rapid cooling method is either high-power air cooling or water mist cooling.
10. The method for preparing a high flame-retardant and high thermal conductivity magnesium alloy according to claim 5, characterized in that, Following the high-strain hot extrusion and online quenching steps, the following steps are also included: Low-temperature aging treatment: Magnesium alloy profiles are subjected to low-temperature aging treatment at 150~220℃ for 4~24 hours.