Composite process method for synergistically improving flame retardant property and mechanical property of AM50 magnesium alloy

Abstract

The invention belongs to the field of metal forming processes, and particularly relates to a composite process method for synergistically improving the flame retardant property and the mechanical property of an AM50-series magnesium alloy. A technical breakthrough is formed through the synergistic effect of Ca element flame retardant modification and ultrasonic treatment in the smelting process. And through general parameter regulation and control (non-customized equipment), the mixture is poured into a metal mold when the solid fraction is 10%. Under the condition that the alloy is not subjected to subsequent deformation processing, the alloy shows the strength and plasticity matching performance superior to those of AM50-1. 2Ca matrix alloy and superior to those of AM50 base metal without Ca, and the flame retardance and the mechanical performance (especially plasticity) are synchronously improved.

Description

Technical Field

[0001] This invention belongs to the field of metal forming technology, specifically relating to a composite process method for synergistically improving the flame retardant and mechanical properties of AM50 series magnesium alloys. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials currently used in industrial applications, have shown broad application prospects in the automotive, aerospace, and electronic device fields due to their low density, high specific strength, good casting properties, and recyclability. Especially against the backdrop of the rapid development of the global new energy vehicle industry, lightweighting has become a key approach to improving vehicle range and energy efficiency, making the demand for magnesium alloys increasingly urgent.

[0003] AM-series magnesium alloys (such as AM50 alloy) have become a key candidate material for automotive parts manufacturing due to their high strength, good casting properties, and cost advantages. However, the inherent defects of AM50 alloy in terms of strength, ductility, and high-temperature performance severely limit its widespread application in key components such as powertrain systems and chassis structures of new energy vehicles. Specifically, under high-temperature service environments, the Mg content in AM50 alloy... 17 Al 12 The material is prone to coarsening and softening, which leads to a significant decrease in its mechanical properties. At the same time, its low ignition point (usually below 600℃) also poses serious safety hazards and makes it difficult to meet the stringent requirements of new energy vehicles for the flame retardant properties of materials.

[0004] To address these issues, researchers have conducted extensive studies using alloying and forming process optimization techniques. Among these, adding non-rare earth elements (such as Ca) to the AM50 alloy has proven to be an economical and effective improvement method. The introduction of Ca not only significantly increases the alloy's ignition point (up to over 800°C) and enhances its flame-retardant properties, but also inhibits the growth of magnesium (Mg). 17 Al 12 The formation of the phase and grain refinement improve the high-temperature stability of the alloy. However, the addition of Ca also brings new problems: it easily forms a continuously distributed second phase (such as a network or lamellar structure) with other elements in the alloy, which destroys the uniformity of the alloy structure, weakens the grain boundary bonding force, and leads to a significant decrease in the plasticity of the material. It is prone to brittle fracture during load-bearing, which in turn restricts the engineering application of the alloy.

[0005] For the problem of plasticity deterioration caused by calcium (Ca), external field control technology is considered a potential solution, among which ultrasonic treatment technology has attracted attention due to its ability to effectively improve the microstructure of alloys. The cavitation and acoustic flow effects generated by ultrasound in molten metal can refine grains by increasing the number of crystal nuclei, breaking up coarse second phases, and promoting microstructure homogenization, theoretically offsetting the adverse effects of Ca on plasticity. However, current research on ultrasound in the field of magnesium alloys has significant limitations: on the one hand, existing studies are mostly limited to applying ultrasound at a single fixed temperature, with almost no exploration of continuous ultrasonic treatment during cooling, making it difficult to fully utilize the regulatory role of ultrasound throughout the solidification process; on the other hand, there are few reports on ultrasonic treatment of AM-based magnesium alloys, especially AM50 alloys, and traditional ultrasonic process parameters (such as power, time, and application method) lack systematic optimization, resulting in unstable effects on the breaking and dispersion of the second phase, and failing to effectively coordinate the flame-retardant advantages of Ca with the need for plasticity improvement.

[0006] In summary, how to improve the flame retardant properties of AM50 series magnesium alloys by utilizing Ca while overcoming the bottleneck of decreased plasticity through optimized ultrasonic treatment processes, and achieving a synergistic improvement in flame retardant properties and mechanical properties (especially plasticity), has become a key technical problem that urgently needs to be solved in the application of AM50 series magnesium alloys in fields such as new energy vehicles. Summary of the Invention

[0007] The purpose of this invention is to provide a composite process method for synergistically improving the flame retardant and mechanical properties of AM50 series magnesium alloys. This method achieves a technological breakthrough through the synergistic effect of Ca element flame retardant modification and ultrasonic treatment during the smelting process, realizing the simultaneous improvement of flame retardancy and mechanical properties (especially plasticity).

[0008] The objective of this invention is achieved through the following technical solution: This invention provides a composite process method for synergistically improving the flame retardant and mechanical properties of AM50 series magnesium alloys, comprising the following steps: (1) Raw material selection: Pure magnesium with a purity of ≥99.9%, pure aluminum with a purity of 99.7%, Mg-30Ca master alloy and pure manganese with a purity of 99.5% are used; (2) Smelting process: The raw materials are put into the resistance furnace, heated to 720℃ and held for 30 minutes. A CO2 / SF6 mixed gas with a volume ratio of 99:1 is introduced for protection. After holding, the slag is removed to obtain an alloy with the composition of Mg-4.89Al-1.19Ca-0.28Mn. (3) Ultrasonic treatment: The alloy obtained in step (2) is remelted to 720°C, protected by CO2 / SF6 mixed gas and kept at the temperature for 30 minutes, and the slag is removed until the slag layer thickness is ≤0.5mm; using Hangzhou Jinghao Machinery JHR2000W-20 ultrasonic melt treatment equipment, the TC4 titanium alloy amplitude rod preheated to 200°C is vertically inserted into the bottom 1 / 2 of the melt, and ultrasonic treatment is applied in the temperature range of 720°C to 630°C. After treatment, it is poured into the bottom pouring mold. (4) Sample preparation and performance characterization: The cast alloy was processed and its performance was tested.

[0009] Furthermore, the resistance furnace described in step (2) is equipped with a bottom-pouring gravity casting square mold.

[0010] Furthermore, the ultrasonic melt processing equipment described in step (3) is equipped with a 20kHz high-frequency transducer.

[0011] Furthermore, the power range of the ultrasonic treatment in step (3) is 500-2000W.

[0012] Furthermore, the time range of the ultrasonic treatment in step (3) is 5-25 min.

[0013] Furthermore, the bottom-injection mold described in step (3) needs to be preheated to 200°C.

[0014] Furthermore, the sample processing in step (4) includes: the tensile sample is processed into a dumbbell shape with a total length of 64 mm and a gauge length of 22.5 mm, the gauge length section has a cross-sectional size of 5 mm × 3 mm, and the surface is polished with 400-800 grit sandpaper; the metallographic sample is cut into a 5 mm × 5 mm × 7 mm square, polished with 200 grit → 3000 grit sandpaper, and then etched with 4% nitric acid alcohol solution for 10-15 s. Furthermore, the performance tests described in step (4) include: room temperature tensile test, observation of microstructure using a ZEISS EVO18 scanning electron microscope, determination of ignition point and recording of combustion rate using vertical combustion method.

[0015] Furthermore, the optimal power range for the ultrasonic treatment is 1.5-2kW.

[0016] Furthermore, the optimal time range for the ultrasonic treatment is 15-20 minutes.

[0017] The beneficial effects of this invention are as follows: Compared to traditional methods such as extrusion deformation to improve the room-temperature mechanical properties of magnesium alloys, although these methods can increase strength through work hardening, the improvement in plasticity is limited by process parameters such as hot extrusion temperature and recrystallization ratio. Furthermore, the deformed alloy, due to its fixed size and shape, is difficult to directly apply to complex structural parts. This invention achieves a technological breakthrough through the synergistic effect of Ca element flame-retardant modification and ultrasonic treatment during the melting process: ultrasound is applied during the alloy's liquid stage, and through generalized parameter control (non-customized equipment), it is poured into a metal mold at a solid fraction of 10%. Without subsequent deformation processing, it exhibits strength and plasticity matching performance superior to AM50-1.2Ca matrix alloys, and even surpasses that of uncalcified AM50 base material, achieving a simultaneous improvement in flame retardancy and mechanical properties (especially plasticity).

[0018] The significant advantages of this invention are also reflected in its process feasibility and economy: ultrasonic treatment is carried out continuously after the alloy melts, and the equipment is a commercially available general-purpose type, requiring no customized investment; the core raw materials (Ca element, AM50 alloy, ultrasonic probe) are readily available and relatively inexpensive, significantly reducing energy consumption and process complexity compared to other alloy modification technologies, and achieving performance optimization without additional deformation processing. After ultrasonic parameter treatment with controlled parameters, the mechanical properties of the sample at room temperature are stable, indicating that the process possesses the quality reliability and process repeatability required for industrial application. Attached Figure Description

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic diagram of the ultrasonic processing device in this invention, wherein 1 is a forklift, 2 is a thermocouple, 3 is an ultrasonic transducer, 4 is a wire, 5 is an ultrasonic generator, 6 is an amplitude transformer, 7 is an ultrasonic probe, 8 is a resistance furnace, 9 is a crucible, and 10 is a magnesium alloy melt. Figure 2 This is a comparison of the room temperature mechanical properties of AM50-1.2Ca alloy before and after ultrasonication in this invention; Figure 3 This is a comparison diagram of alloy grain size before and after ultrasonication in this invention; Figure 4 This is a comparison diagram of the room temperature mechanical properties of the alloy before and after ultrasonication in Example 1 of the present invention; Figure 5 This is a comparison image of the alloy microstructure before and after ultrasonication in Example 1 of the present invention; Figure 6This is a comparison diagram of the mechanical properties before and after ultrasound in Embodiment 2 of the present invention; Figure 7 This is a comparison image of the second phase morphology before and after ultrasound in Embodiment 2 of the present invention. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0024] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0025] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0026] The specific operation flow of the composite process for synergistically improving the flame retardant and mechanical properties of AM50 series magnesium alloys in this invention is as follows: I. Raw Material Selection The raw materials used in this invention include: pure magnesium with a purity of ≥99.9%, pure aluminum with a purity of 99.7%, Mg-30Ca master alloy (wherein the Ca element content is 30±2%), and pure manganese with a purity of 99.5%. All of the above raw materials are commercially available conventional materials, easy to procure, and cost-effective.

[0027] II. Smelting Process Melting Equipment and Environmental Control: An electric resistance furnace is used as the melting equipment, equipped with a bottom-pouring gravity casting square mold (this mold has a low defect rate and can ensure molding quality). During the melting process, a CO2 / SF6 mixed gas with a volume ratio of 99:1 is introduced for protection to prevent oxidation of the alloy melt.

[0028] Melting and Composition Control: The above raw materials were added to a resistance furnace according to the target composition, heated to 720℃ and held for 30 minutes. After holding, the surface of the melt was slag-removed. ICP (Inductively Coupled Plasma) analysis revealed that the final alloy composition was Mg-4.89Al-1.19Ca-0.28Mn (mass percentage). The Ca content was controlled below 2 wt.%, ensuring the alloy's ignition point reached above 800℃ while avoiding the severe decrease in plasticity caused by excessive Ca addition.

[0029] III. Ultrasonic Processing System and Parameter Control Equipment Configuration: The Hangzhou Jinghao Machinery JHR2000W-20 ultrasonic melt processing equipment is selected. This equipment is equipped with a 20kHz high-frequency transducer and a TC4 titanium alloy amplitude transformer (diameter 16mm, length 200mm). Ultrasonic waves work through periodic positive and negative pressure effects. The cavitation effect generates microbubbles in the melt, causing them to periodically expand and collapse, thus breaking up the continuous second phase. The acoustic flow effect drives forced convection in the melt, promoting compositional homogenization and crystal shedding. Key Operational Details: Melt pretreatment: The AM50-1.2Ca alloy prepared above was reheated and melted to 720℃, and a CO2 / SF6 mixed gas was introduced for protection (gas flow rate of 5L / min). After holding at this temperature for 30 minutes, mechanical slag removal was performed to ensure that the slag layer thickness was ≤0.5mm.

[0030] Ultrasonic application: Insert the preheated 200℃ amplitude transformer vertically into the bottom half of the melt (15-20mm from the bottom of the crucible), apply ultrasonic power ranging from 500-2000W, and process for 5-25 minutes.

[0031] Ultrasonic temperature range: Ultrasonic treatment begins at 720℃ and ends at 630℃ (thermodynamic calculations show that the alloy solid fraction is 10% at 630℃). After ultrasonic treatment, the melt is poured into a bottom-pouring mold preheated to 200℃.

[0032] IV. Sample Preparation and Performance Characterization Sample preparation: Tensile test specimens: The cast alloy was machined into dumbbell-shaped specimens with a total length of 64 mm and a gauge length of 22.5 mm using wire cutting. The gauge length section had a cross-sectional dimension of 5 mm × 3 mm. The specimen surface was polished in stages with 400-800 grit sandpaper to remove the surface oxide layer.

[0033] Metallographic specimens: Cut the alloy into 5mm×5mm×7mm squares, first polish them with sandpaper in the order of 200 mesh → 3000 mesh, and then etch them with 4% nitric acid alcohol solution for 10-15s.

[0034] Performance testing: Mechanical properties: A room temperature tensile test was conducted at a displacement rate of 2 mm / min. The average value of three parallel specimens under each test condition was taken as the result.

[0035] Microstructure: The distribution of the second phase of the alloy was observed using a ZEISS EVO18 scanning electron microscope with an accelerating voltage of 20 kV.

[0036] Flame retardancy test: The ignition point of the alloy was determined by the vertical burning method (heating rate of 10℃ / min), and the burning rate was recorded (unit: mm / min).

[0037] V. Optimization Range of Process Parameters Through orthogonal experiments (experimental factors included ultrasonic power and processing time, where power was set to 0.5 / 1.0 / 1.5 / 2.0 kW and time was set to 5 / 10 / 15 / 20 / 25 min), the optimal process window for this invention was determined as follows: Ultrasonic power: 0-2kW, with the optimal power range being 1.5-2kW; Processing time: 0-25 min, with the optimal time range being 15-20 min.

[0038] Within the above-mentioned optimal process parameters, it can be ensured that the ultrasonic waves can break up the dendrites as soon as they begin to form, thereby fully utilizing the flame-retardant effect of Ca while effectively improving the mechanical properties of the alloy, especially its plasticity.

[0039] The schematic diagram of the ultrasonic processing device is shown below. Figure 1 As shown, the room temperature mechanical properties of AM50-1.2Ca alloy before and after ultrasonication are compared. Figure 2 As shown, the comparison of alloy grain size before and after ultrasound is as follows: Figure 3 As shown.

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings: Example 1: Ultrasonic treatment of AM50-1.2Ca alloy (1) Process parameters According to the composite process method described above in this invention, AM50-1.2Ca alloy (composition: Mg-4.89Al-1.19Ca-0.28Mn, mass percentage) is processed. The ultrasonic stirring power is controlled at 1.5kW, the ultrasonic time is 20 minutes, and other process parameters (such as melting temperature 720℃, holding time 30 minutes, ultrasonic temperature range 720℃ to 630℃, mold preheating 200℃, etc.) strictly follow the aforementioned technical solution.

[0041] (2) Performance results After the above process, the room temperature mechanical properties of the obtained alloy are: yield strength (YS) = 83.7 MPa, tensile strength (UTS) = 188.6 MPa, and elongation (EL) = 9.2%. Compared with AM50-1.2Ca matrix alloy without ultrasonic treatment, YS is increased by 27%, UTS by 27%, and EL by 74%; Compared with AM50 base material without Ca addition, YS increased by 70%, UTS increased by 5%, and plasticity remained at the standard level of AM50 alloy (all data are results after taking into account the error of the as-cast test).

[0042] (3) Organization and performance correlation The final comparison of the room temperature mechanical properties of the alloy before and after ultrasound is as follows: Figure 4 As shown, the microstructure of the alloy before and after ultrasound is compared. Figure 5 As shown in the figure above, the second phase of the alloy is significantly refined after ultrasonic treatment, and the continuity of the originally continuously distributed second phase is disrupted. This is the main reason for the improvement in mechanical properties (especially plasticity).

[0043] Example 2: Ultrasonic treatment of AM50-2Ca alloy (1) Process parameters Drawing on the experience of ultrasonic process control for the AM50-1.2Ca system, the AM50-2Ca alloy was processed using the same method. The melting and ultrasonic application methods were the same as in Example 1, with the ultrasonic parameters remaining at 1.5kW power and 20 minutes.

[0044] (2) Performance results The properties of the AM50-2Ca matrix alloy without ultrasonic treatment are: YS=89MPa, UTS=119.7MPa, EL=0.9%; After ultrasonic treatment, the alloy properties are improved as follows: YS=89.5MPa UTS = 156.9 MPa (31% improvement) EL=3.7% (an increase of 311%).

[0045] (3) Organization and performance correlation The final comparison of mechanical properties before and after ultrasound is as follows: Figure 6 As shown, the morphology comparison of the second phase before and after ultrasound is as follows: Figure 7 As shown in the figure above, the second phase of the AM50-2Ca alloy is not only finer after ultrasonic treatment, but the continuity of the continuously distributed second phase is also significantly disrupted. This directly leads to a substantial increase in its tensile strength and plasticity. Meanwhile, the alloy's ignition point remains around 900℃, and its flame-retardant properties are unaffected.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A composite process for synergistically improving the flame retardant and mechanical properties of AM50 series magnesium alloys, characterized in that, Includes the following steps: (1) Raw material selection: Pure magnesium with a purity of ≥99.9%, pure aluminum with a purity of 99.7%, Mg-30Ca master alloy and pure manganese with a purity of 99.5% are used; (2) Smelting process: The raw materials are put into the resistance furnace, heated to 720℃ and held for 30 minutes. A CO2 / SF6 mixed gas with a volume ratio of 99:1 is introduced for protection. After holding, the slag is removed to obtain an alloy with the composition of Mg-4.89Al-1.19Ca-0.28Mn. (3) Ultrasonic treatment: The alloy obtained in step (2) is remelted to 720°C, protected by CO2 / SF6 mixed gas and kept at the temperature for 30 minutes, and the slag is removed until the slag layer thickness is ≤0.5mm; using Hangzhou Jinghao Machinery JHR2000W-20 ultrasonic melt treatment equipment, the TC4 titanium alloy amplitude rod preheated to 200°C is vertically inserted into the bottom 1 / 2 of the melt, and ultrasonic treatment is applied in the temperature range of 720°C to 630°C. After treatment, it is poured into the bottom pouring mold. (4) Sample preparation and performance characterization: The cast alloy was processed and its performance was tested.

2. The method according to claim 1, characterized in that, The resistance furnace described in step (2) is equipped with a bottom-pouring gravity casting square mold.

3. The method according to claim 1, characterized in that, The ultrasonic melt processing equipment described in step (3) is equipped with a 20kHz high-frequency transducer.

4. The method according to claim 1, characterized in that, The power range of the ultrasonic treatment in step (3) is 500-2000W.

5. The method according to claim 1, wherein The time range for ultrasonic treatment in step (3) is 5-25 min.

6. The method according to claim 1, characterized in that, The bottom-injection mold described in step (3) also needs to be preheated to 200°C.

7. The method according to claim 1, characterized in that, The sample processing described in step (4) includes: the tensile sample is processed into a dumbbell shape with a total length of 64 mm and a gauge length of 22.5 mm, the gauge length section has a cross-sectional size of 5 mm × 3 mm, and the surface is polished with 400-800 grit sandpaper; the metallographic sample is cut into a 5 mm × 5 mm × 7 mm square, polished with 200 grit → 3000 grit sandpaper, and then etched with 4% nitric acid alcohol solution for 10-15 s.

8. The method according to claim 1, characterized in that The performance tests described in step (4) include: room temperature tensile test, observation of microstructure using a ZEISS EVO18 scanning electron microscope, determination of ignition point and recording of burning rate using vertical burning method.

9. The method according to claim 4, characterized in that, The optimal power range for the ultrasonic treatment is 1.5-2kW.

10. The method according to claim 5, characterized in that, The optimal time range for ultrasonic treatment is 15-20 minutes.

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