Method for manufacturing magnesium alloy castings and magnesium alloy castings

Abstract

The application relates to the field of metal casting, in particular to a magnesium alloy casting manufacturing method and a magnesium alloy casting. The magnesium alloy casting manufacturing method comprises the following steps: injecting a liquid magnesium alloy into a casting mold, controlling a magnetic field generating device to apply a continuous three-phase rotating magnetic field to the melt; acquiring the temperature of the melt in the mold in real time; based on the temperature of the melt being less than or equal to the second phase precipitation temperature of the magnesium alloy, controlling the magnetic field generating device to stop applying the continuous three-phase rotating magnetic field, and controlling the magnetic field generating device to apply an intermittent three-phase rotating magnetic field with a first duty ratio to the melt; when the melt cools to the solidus temperature of the magnesium alloy, controlling the magnetic field generating device to stop applying the intermittent three-phase rotating magnetic field; by intermittently applying the three-phase rotating magnetic field after reaching the second phase precipitation temperature, the problem that, in the solidification process of the magnesium alloy, although the continuous application of the three-phase rotating magnetic field can significantly reduce the hot crack sensitivity of the alloy, the problem of eutectic phase segregation near the hot crack caused by the sharp rise of the feeding driving force is avoided.

Description

Technical Field

[0001] This invention relates to the field of metal casting, and more specifically, to a method for manufacturing magnesium alloy castings and magnesium alloy castings. Background Technology

[0002] Currently, magnesium alloys, as the lightest metallic structural materials, possess advantages such as high specific strength, excellent biocompatibility, and great alloying potential, and have been widely used in the automotive industry, 3C electronics, aerospace, and biomedical fields in recent years. However, the wide solidification range and large volumetric shrinkage of magnesium alloys make them highly susceptible to hot cracking, thus limiting their development.

[0003] In related technologies, electromagnetic fields are applied during the casting process of magnesium alloys to reduce their susceptibility to hot cracking. These fields, applied to the molten magnesium alloy, have shown good results in reducing hot cracking susceptibility by refining grains, improving feeding channels, increasing feeding driving force, and enhancing alloy feeding efficiency. However, while applying an external electromagnetic field during the solidification process can significantly reduce the alloy's hot cracking susceptibility, it also leads to a marked increase in the amount of eutectic phase near the crack, causing severe segregation and consequently weakening the local mechanical properties and corrosion resistance of the casting. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0005] Therefore, the first aspect of the present invention provides a method for manufacturing magnesium alloy castings.

[0006] A second aspect of the present invention provides a magnesium alloy casting.

[0007] In view of this, a first aspect of the present invention provides a method for manufacturing a magnesium alloy casting, comprising: placing a magnesium alloy ingot in a melting crucible within the furnace chamber of a melting furnace; introducing a protective gas into the melting furnace; controlling the melting furnace to heat to a first temperature to melt the magnesium alloy ingot into a liquid magnesium alloy; refining the liquid magnesium alloy for a first duration; injecting the liquid magnesium alloy into a casting mold while simultaneously controlling a magnetic field generating device to apply a continuous three-phase rotating magnetic field to the molten metal in the casting mold; acquiring the temperature of the molten metal in the casting mold in real time; based on the fact that the temperature of the molten metal in the casting mold is less than or equal to the second phase precipitation temperature of the magnesium alloy, controlling the magnetic field generating device to stop applying the continuous three-phase rotating magnetic field, and controlling the magnetic field generating device to apply an intermittent three-phase rotating magnetic field with a first duty cycle to the molten metal in the casting mold; when the molten metal in the casting mold cools to the solidus temperature of the magnesium alloy, controlling the magnetic field generating device to stop applying the intermittent three-phase rotating magnetic field; and allowing the casting mold to cool naturally to room temperature.

[0008] In this technical solution, the continuous application of a three-phase rotating magnetic field during the early stage of solidification optimizes the alloy microstructure and improves its hot cracking resistance. After reaching the second-phase precipitation temperature, the three-phase rotating magnetic field is applied intermittently to reduce the cooling gradient at the solid / liquid interface front, increase compositional supercooling, and improve the distribution of solute elements within the liquid film at the solid-liquid interface front. Furthermore, by intermittently applying the three-phase rotating magnetic field after reaching the second-phase precipitation temperature, the problem of eutectic phase segregation near hot cracks caused by the sharp increase in feeding driving force, which is present in the case of continuous application of a three-phase rotating magnetic field during magnesium alloy solidification, although it significantly reduces the alloy's hot cracking sensitivity, is avoided. This reduces segregation and improves the mechanical properties and corrosion resistance of specific locations in the casting. The manufacturing method provided in this application fully considers the characteristics and practical requirements of magnesium alloys at different solidification stages, achieving precise control of the magnesium alloy solidification process and solving the random electromagnetic effects of single and composite magnetic fields applied in previous studies on alloy flow behavior, solidification process, and solidification shrinkage compensation.

[0009] A second aspect of the present invention provides a magnesium alloy casting, which is manufactured by the method for manufacturing magnesium alloy castings as described in any of the above-described technical solutions. Since the magnesium alloy casting is manufactured by the method for manufacturing magnesium alloy castings as described in any of the above-described technical solutions, it possesses all the beneficial effects of the method for manufacturing magnesium alloy castings as described in any of the above-described technical solutions.

[0010] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0011] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 A flowchart illustrating a method for manufacturing a magnesium alloy casting according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the changes in current and temperature over time during the magnesium alloy casting process according to an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the precise application of phase-separation region magnetization in a method for manufacturing magnesium alloy castings according to an embodiment of the present invention. Figure 4 One of the cross-sectional microstructure diagrams of a magnesium alloy casting according to an embodiment of the present invention; Figure 5 This is a second cross-sectional microstructure diagram of a magnesium alloy casting according to an embodiment of the present invention; Figure 6 This is the third cross-sectional microstructure diagram of a magnesium alloy casting according to an embodiment of the present invention; Figure 7 This is the fourth cross-sectional microstructure diagram of a magnesium alloy casting according to an embodiment of the present invention. Detailed Implementation

[0012] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0013] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0014] The following reference Figures 1 to 7 A method for manufacturing magnesium alloy castings and magnesium alloy castings according to some embodiments of the present invention are described.

[0015] In one embodiment of the present invention, such as Figure 1 As shown, a method for manufacturing a magnesium alloy casting is provided, comprising: Step 102: Place the magnesium alloy ingot in the melting crucible inside the furnace of the melting furnace; Step 104: Introduce protective gas into the smelting furnace; Step 106: Control the furnace temperature to the first temperature so that the magnesium alloy ingot melts into liquid magnesium alloy; Step 108: Refine the liquid magnesium alloy for the first time. Step 110: Inject liquid magnesium alloy into the casting mold, and at the same time control the magnetic field generator to apply a continuous three-phase rotating magnetic field to the molten metal in the casting mold. Step 112: Real-time acquisition of the temperature of the molten metal in the casting mold; Step 114: Based on the fact that the temperature of the molten metal in the casting mold is less than or equal to the second phase precipitation temperature of the magnesium alloy, the magnetic field generating device is controlled to stop applying the continuous three-phase rotating magnetic field, and the magnetic field generating device is controlled to apply an intermittent three-phase rotating magnetic field with a first duty cycle to the molten metal in the casting mold. Step 116: When the temperature of the molten metal in the casting mold cools down to the solidus temperature of the magnesium alloy, the control magnetic field generator stops applying the intermittent three-phase rotating magnetic field. Step 118: Allow the casting mold to cool naturally to room temperature.

[0016] In this embodiment, the continuous application of a three-phase rotating magnetic field during the early stage of solidification optimizes the alloy microstructure and improves its hot cracking resistance. After reaching the second-phase precipitation temperature, the three-phase rotating magnetic field is applied intermittently to reduce the cooling gradient at the solid / liquid interface front, increase compositional supercooling, and improve the distribution of solute elements within the liquid film at the solid-liquid interface front. Furthermore, by intermittently applying the three-phase rotating magnetic field after reaching the second-phase precipitation temperature, the problem of eutectic phase segregation near hot cracks caused by the sharp increase in feeding driving force, which is present in the case of continuous application of a three-phase rotating magnetic field during magnesium alloy solidification, although it significantly reduces the alloy's hot cracking sensitivity, is avoided. This reduces segregation and improves the mechanical properties and corrosion resistance of specific locations in the casting. The manufacturing method provided in this application fully considers the characteristics and actual needs of magnesium alloys at different solidification stages, achieving precise control of the magnesium alloy solidification process and solving the random electromagnetic effects of single and composite magnetic fields applied in previous studies on alloy flow behavior, solidification process, and solidification shrinkage compensation.

[0017] Specifically, the molten metal in the casting mold mentioned in step 110 includes liquid magnesium alloy injected into the casting mold.

[0018] Specifically, taking the Mg-4Zn-1.5Ca-0.3Zr alloy as the casting raw material as an example, a melting crucible is placed inside the furnace of a melting furnace, which is used to heat and melt the magnesium alloy ingot placed in the crucible. A protective gas supply pipeline is connected to the inside of the furnace and is used to fill the furnace with a mixed gas composed of SF6 and N2 to prevent oxidation and combustion of the magnesium alloy during melting and refining. After the magnesium alloy ingot is placed in the melting crucible, the melting furnace starts the heating program to raise the temperature inside the furnace to a first temperature, which is set at 720°C. After the magnesium alloy ingot is completely melted into liquid magnesium alloy, a settling and refining agent accounting for 1.5% of the total mass of the melt is added to the liquid magnesium alloy, and stirring is continued for 5 minutes to refine the liquid magnesium alloy.

[0019] The casting mold is located inside the coil of the magnetic field generator, which surrounds the outer periphery of the mold, maintaining a non-contact gap between the coil and the mold. The casting mold contains the molten magnesium alloy injected into it and allows it to solidify. The magnetic field generator applies a rotating magnetic field to the inside of the mold to influence the solidification process of the molten magnesium alloy. After refining, the magnetic field generator is energized and applies a continuous three-phase rotating magnetic field to the molten metal in the mold. The excitation current intensity of this continuous three-phase rotating magnetic field is set to 150A, and the current frequency is set to 15Hz. Simultaneously with the application of the continuous three-phase rotating magnetic field, the refined molten magnesium alloy is poured into the cavity of the casting mold.

[0020] The hot spot area of ​​the casting mold is pre-set with thermocouple mounting holes. The temperature measuring end of the thermocouple is inserted into the thermocouple mounting hole, and the signal output end of the thermocouple is electrically connected to the signal input end of the temperature recorder. The temperature recorder is used to collect and record the temperature data of the melt in the hot spot area of ​​the casting mold in real time. After the liquid magnesium alloy is poured, the temperature recorder continuously monitors the temperature change of the molten metal in the casting mold. When the temperature recorder shows that the temperature of the molten metal in the casting mold drops to less than or equal to the second phase precipitation temperature of the alloy, the magnetic field generator stops applying the continuous three-phase rotating magnetic field. The second phase precipitation temperature is obtained in advance through a dual thermocouple differential thermal analysis experiment. Subsequently, the magnetic field generator switches its working mode and applies an intermittent three-phase rotating magnetic field with a first duty cycle to the molten metal in the casting mold. The first duty cycle is set to 33.3%, the excitation current intensity of the intermittent three-phase rotating magnetic field is maintained at 150A, and the current frequency is maintained at 15Hz. During the application of the intermittent three-phase rotating magnetic field, the coil of the magnetic field generator generates a rotating magnetic field during the energizing cycle and stops generating the magnetic field during the de-energizing cycle, thus alternating in a cycle.

[0021] When the temperature recorder shows that the temperature of the molten metal in the casting mold drops to the solidus temperature of the magnesium alloy, the magnetic field generator stops applying the intermittent three-phase rotating magnetic field. Subsequently, the casting mold is allowed to cool naturally in the air until its temperature drops to room temperature, after which the casting is removed from the casting mold.

[0022] The Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting prepared in this embodiment was cut along the centerline, and the cross-sectional microstructure at the location prone to hot crack initiation was observed. The observation results showed that the microstructure was uniform at the location prone to hot crack initiation, and no hot crack defects or linear segregation defects were observed.

[0023] Based on the above, it can be seen that by continuously applying a three-phase rotating magnetic field in the early stage of solidification, the microstructure of the alloy was optimized and the unobstructed flow of the feeding channels was improved. After reaching the second-phase precipitation temperature, the three-phase rotating magnetic field was switched to an intermittent one, which reduced the cooling gradient at the solid-liquid interface front and increased the compositional supercooling, thus improving the distribution of solute elements in the liquid film at the solid-liquid interface front. At the same time, it avoided the excessive feeding driving force caused by the continuous magnetic field, which would lead to the segregation of the eutectic phase near the hot crack. This embodiment successfully prepared a magnesium alloy casting without hot cracks and without linear macrosegregation defects, thereby achieving synergistic suppression of hot cracking and linear segregation behavior during the solidification process of magnesium alloy.

[0024] Specifically, such as Figure 2 As shown, with the cooling of the magnesium alloy, before the temperature of the magnesium alloy reaches the second phase precipitation temperature T... ssp At that time, a continuous three-phase rotating magnetic field is turned on, and the magnesium alloy is cooled to the second phase precipitation temperature T. ssp At that time, the intermittent three-phase rotating magnetic field is activated.

[0025] Specifically, such as Figure 4 As shown, when a magnesium alloy casting is cut under its natural solidification state, severe hot cracking and segregation can be observed.

[0026] like Figure 5 As shown, during the cooling process of the magnesium alloy casting, an intermittent three-phase rotating magnetic field with a certain duty cycle is applied throughout the process. After the magnesium alloy casting solidifies, cutting the magnesium alloy casting reveals that the segregation of the magnesium alloy casting is reduced, but hot cracks still exist.

[0027] like Figure 6 As shown, a continuous three-phase rotating magnetic field is applied throughout the cooling process of the magnesium alloy casting. After the magnesium alloy casting solidifies, cutting the magnesium alloy casting reveals that the hot cracking is reduced, but the segregation is more severe.

[0028] like Figure 7 As shown, during the cooling process of magnesium alloy castings, magnesium alloy castings are cast using the manufacturing method of magnesium alloy castings provided by this invention. After the magnesium alloy castings solidify, cutting the magnesium alloy castings reveals that the grains are significantly refined, and hot cracking and segregation are effectively suppressed.

[0029] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0030] Methods for manufacturing magnesium alloy castings also include: Thermal analysis was performed on the magnesium alloy castings to obtain their cooling profiles. The first and second derivative curves were obtained based on the cooling curve of the magnesium alloy casting. The liquidus temperature, second phase precipitation temperature, and solidus temperature of magnesium alloys are obtained based on the first and second derivative curves.

[0031] In this embodiment, by combining dual thermocouple differential thermal analysis experiments with first and second derivative analysis of the cooling curves, the location of the exothermic peak corresponding to the precipitation of the second phase can be accurately identified, thereby accurately obtaining the precipitation temperature of the second phase. This temperature data provides a quantitative basis for the switching time between continuous and intermittent magnetic fields, ensuring the accuracy and repeatability of the magnetic field switching time in the "phase separation region variable magnetic control" method, and solving the problem of inaccurate matching between the applied external magnetic field and the alloy solidification stage. Furthermore, based on the first and second derivative curves, the liquidus temperature and solidus temperature can also be obtained more accurately.

[0032] Specifically, taking Mg-4Zn-1.5Ca-0.3Zr alloy as an example.

[0033] The method for manufacturing magnesium alloy castings provided by this invention, such as... Figure 3 As shown, a dual thermocouple differential thermal analysis (DTA) system was used to collect and record temperature changes in the alloy during solidification. Two K-type sheathed thermocouples were placed at the center and edge of the melt, respectively, to measure and record the temperature changes (T0) at the corresponding locations during solidification. c and T e To ensure radial solidification of the molten metal in the graphite crucible, thickened asbestos material is placed at the top and bottom of the crucible for thermal insulation. Because the cooling rate at the crucible edges is significantly higher than that at the center during melt cooling, a temperature difference (ΔT = T) will exist between the two locations before dendrite overlap. c -T e Meanwhile, since the thermal conductivity of the solid phase is better than that of the liquid phase, the ΔT value will continuously increase as solidification proceeds. However, when the dendrites in the melt begin to overlap, heat from the melt edges and center is rapidly conducted through the solid dendrites, causing the ΔT value to immediately and continuously decrease. Therefore, in this study, the melt temperature value collected by the central thermocouple when ΔT begins to decrease is defined as the dendrite overlap temperature of the alloy (T). coh Furthermore, during the solidification process of the alloy, the melt temperature continuously decreases over time. When a solid phase precipitates in the melt, the latent heat of solidification released by the phase precipitation reaction changes the slope of the cooling curve. Therefore, the change in the first derivative curve of the cooling curve (the temperature change curve of the central thermocouple) can directly reflect the heat change of the alloy during solidification. The peak value in the first derivative curve corresponds to the phase precipitation reaction at the corresponding moment during the alloy solidification process, and the starting point of the exothermic peak is the precipitation temperature of the second phase (T). ssp Similarly, the first and last moments when the second derivative of the cooling curve is zero correspond to the start and end points of the alloy solidification process, i.e., the liquidus temperature (T) of the alloy. L ) and solidus temperature (T) S ).

[0034] In the subsequent casting process, when casting begins and the temperature recorder shows that the temperature of the casting mold has not dropped to less than or equal to 340°C (t1), a continuous three-phase rotating magnetic field is applied. When the temperature recorder shows that the temperature of the casting mold has dropped to less than or equal to 340°C (t2), the magnetic field generator stops applying the continuous three-phase rotating magnetic field and switches to applying an intermittent three-phase rotating magnetic field with a first duty cycle.

[0035] Figure 3 China T 0.9 This indicates a solid fraction of 0.9, T 0.99 This indicates a solid fraction of 0.99.

[0036] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0037] The manufacturing process also includes the following steps before injecting the liquid magnesium alloy into the casting mold: The casting mold is preheated to a second temperature, wherein the second temperature is greater than or equal to 200°C and less than or equal to 300°C.

[0038] In this embodiment, by preheating the casting mold to 200°C to 300°C before pouring, the temperature gradient between the liquid magnesium alloy and the mold cavity wall is reduced. This avoids excessive solidification shrinkage stress in the liquid magnesium alloy due to rapid cooling during the initial pouring stage, and provides a stable temperature environment for the subsequent continuous three-phase rotating magnetic field to fully stir the melt and refine the grains. Combined with the subsequent phase separation zone magnetic field switching step, this embodiment effectively reduces the risk of hot cracking in the casting during the initial solidification stage, thereby improving the forming quality of the magnesium alloy casting.

[0039] Specifically, the second temperature is 200℃.

[0040] The second temperature is 220℃.

[0041] The second temperature is 250℃.

[0042] The second temperature is 270℃.

[0043] The second temperature is 300℃.

[0044] Specifically, a melting crucible is placed inside the furnace chamber of a melting furnace, which is used to heat and melt the magnesium alloy ingot placed inside the crucible. A casting mold is housed inside the coil of a magnetic field generator, with the coil surrounding the outer periphery of the mold. Resistance heating elements are embedded inside the sidewalls or bottom of the casting mold, and their power input terminals are electrically connected to the power output terminals of a temperature control cabinet. The temperature control cabinet controls the energizing and de-energizing of the resistance heating elements, thereby controlling the preheating temperature of the casting mold. The thermocouple's measuring end is inserted inside the cavity of the casting mold or into a measuring hole on the mold wall, and its signal output terminal is electrically connected to the temperature signal input terminal of the temperature control cabinet. The temperature control cabinet contains a temperature comparison unit, which compares the actual temperature value fed back by the thermocouple with a preset target temperature value.

[0045] Before the liquid magnesium alloy is poured into the casting mold, the temperature control cabinet outputs current to the resistance heating element. The energized resistance heating element generates Joule heat, which is conducted through the mold wall to the entire mold. Thermocouples continuously monitor the actual temperature of the casting mold and feed the temperature signal back to the temperature control cabinet in real time. When the temperature comparison unit determines that the actual temperature is lower than the preset target temperature, the temperature control cabinet maintains the energization of the resistance heating element. When the actual temperature reaches the preset target temperature, the temperature control cabinet cuts off the current to the resistance heating element, keeping the casting mold within the target temperature range. In this embodiment, the preheating target temperature of the casting mold is set to 250°C. During preheating, the temperature of the casting mold gradually rises from room temperature. When the temperature value fed back by the thermocouple reaches 250°C, the temperature control cabinet automatically cuts off the power supply to the resistance heating element, maintaining the temperature of the casting mold within the range of 250°C ± 10°C.

[0046] While the casting mold is preheated to 250°C, the magnesium alloy ingot in the melting furnace is melted into liquid magnesium alloy at 720°C and then refined. The refined liquid magnesium alloy is removed from the melting crucible and poured into the cavity of the casting mold, which is preheated to 250°C. Subsequently, a magnetic field generator is activated, applying a continuous three-phase rotating magnetic field to the molten metal in the casting mold. The magnetic field parameters are an excitation current intensity of 150A and a current frequency of 15Hz. During the application of the magnetic field...

[0047] When liquid magnesium alloy is poured into a preheated casting mold, the temperature of the mold cavity wall is much higher than room temperature. This reduces the temperature difference between the liquid magnesium alloy and the cavity wall, thereby decreasing the cooling rate of the liquid magnesium alloy upon contact with the cavity wall. A temperature recorder continuously monitors the temperature change in the hot spot region of the casting mold after pouring. When the temperature drops to the second-phase precipitation temperature of the alloy (340°C), the magnetic field generator stops applying the continuous three-phase rotating magnetic field and switches to applying an intermittent three-phase rotating magnetic field with a duty cycle of 33.3%.

[0048] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0049] The excitation current intensity of the continuous three-phase rotating magnetic field is greater than or equal to 100A and less than or equal to 200A.

[0050] The current frequency of a continuous three-phase rotating magnetic field is greater than or equal to 10Hz and less than or equal to 30Hz.

[0051] In this embodiment, the excitation current intensity of the continuous three-phase rotating magnetic field is 100A to 200A, and the current frequency of the continuous three-phase rotating magnetic field is 10Hz to 30Hz, so that the continuous three-phase rotating magnetic field can effectively refine the grains of magnesium alloy, improve the feeding channel, increase the feeding driving force, and improve the feeding efficiency of magnesium alloy.

[0052] Specifically, the excitation current intensity of the continuous three-phase rotating magnetic field is 100A.

[0053] The excitation current intensity of the continuous three-phase rotating magnetic field is 120A.

[0054] The excitation current intensity of the continuous three-phase rotating magnetic field is 150A.

[0055] The excitation current intensity of the continuous three-phase rotating magnetic field is 170A.

[0056] The excitation current intensity of the continuous three-phase rotating magnetic field is 200A.

[0057] The current frequency of the continuous three-phase rotating magnetic field is 10Hz.

[0058] The current frequency of the continuous three-phase rotating magnetic field is 20Hz.

[0059] The current frequency of the continuous three-phase rotating magnetic field is 30Hz.

[0060] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0061] The excitation current intensity of the intermittent three-phase rotating magnetic field is greater than or equal to 100A and less than or equal to 200A.

[0062] The current frequency of the intermittent three-phase rotating magnetic field is greater than or equal to 10Hz and less than or equal to 30Hz.

[0063] In this embodiment, the excitation current intensity of the intermittent three-phase rotating magnetic field is 100A to 200A, and the current frequency of the intermittent three-phase rotating magnetic field is 10Hz to 30Hz, so that the intermittent three-phase rotating magnetic field can effectively refine the grains of magnesium alloy, improve the feeding channel, increase the feeding driving force, and improve the feeding efficiency of magnesium alloy.

[0064] Specifically, the excitation current intensity of the intermittent three-phase rotating magnetic field is 100A.

[0065] The excitation current intensity of the intermittent three-phase rotating magnetic field is 120A.

[0066] The excitation current intensity of the intermittent three-phase rotating magnetic field is 150A.

[0067] The excitation current intensity of the intermittent three-phase rotating magnetic field is 170A.

[0068] The excitation current intensity of the intermittent three-phase rotating magnetic field is 200A.

[0069] The current frequency of the intermittent three-phase rotating magnetic field is 10 Hz.

[0070] The current frequency of the intermittent three-phase rotating magnetic field is 20Hz.

[0071] The current frequency of the intermittent three-phase rotating magnetic field is 30Hz.

[0072] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0073] The first duty cycle of the intermittent three-phase rotating magnetic field is greater than or equal to 20% and less than or equal to 40%.

[0074] In this embodiment, the first duty cycle of the intermittent three-phase rotating magnetic field is set to 20% to 40%, which reduces the cooling gradient at the solid-liquid interface front, increases compositional supercooling, and improves the distribution of solute elements in the liquid film at the solid-liquid interface front. At the same time, it provides an appropriate feeding driving force to avoid the occurrence of "burst feeding behavior", thereby achieving synergistic suppression of hot cracking and linear segregation behavior during the solidification process of magnesium alloy.

[0075] Specifically, the first duty cycle of the intermittent three-phase rotating magnetic field is 20%.

[0076] The first duty cycle of the intermittent three-phase rotating magnetic field is 30%.

[0077] The first duty cycle of the intermittent three-phase rotating magnetic field is 40%.

[0078] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0079] The first temperature is greater than or equal to 700℃ and less than or equal to 730℃.

[0080] In this embodiment, setting the melting temperature within the range of 700°C to 730°C enables the magnesium alloy ingot to melt fully and obtain good melt fluidity, while avoiding increased oxidation and burning loss and increased gas solubility due to excessively high temperature.

[0081] Specifically, the first temperature is 700℃.

[0082] The first temperature is 710℃.

[0083] The first temperature is 720℃.

[0084] The first temperature is 730℃.

[0085] Specifically, within this temperature range, a melting temperature of 710℃ can balance the fluidity and purity of the melt, providing a high-quality melt state for the subsequent coordinated control of continuous and intermittent three-phase rotating magnetic fields. Thus, under the combined effect of phase separation region magnetic field regulation, magnesium alloy castings without hot cracks or linear segregation defects can be obtained.

[0086] The melting temperature is set to 710℃ using a temperature control cabinet. After the magnesium alloy ingot is added to the melting crucible, the temperature control cabinet controls the heating element to heat the crucible. The first thermocouple continuously monitors the actual temperature of the liquid magnesium alloy and feeds the temperature signal back to the temperature control cabinet in real time. When the temperature comparison unit determines that the actual temperature is below 710℃, the temperature control cabinet maintains the heating element energized. When the actual temperature reaches 710℃, the temperature control cabinet cuts off part of the current to the heating element, maintaining the temperature of the liquid magnesium alloy within the range of 710℃ ± 5℃. After the magnesium alloy ingot is completely melted into liquid magnesium alloy at 710℃, a settling refining agent accounting for 1.5% of the total melt mass is added to the liquid magnesium alloy, and the mixture is continuously stirred for 5 minutes for refining.

[0087] Furthermore, under the same alloy raw materials and other process conditions (continuous magnetic field 150A, 15Hz, intermittent magnetic field duty cycle 33.3%, mold preheating 250℃) unchanged, comparative experiments were conducted by adjusting the melting temperature to 700℃ and 730℃ respectively. When the melting temperature was set to 700℃, the time required for the magnesium alloy ingot to completely melt was longer, the viscosity of the liquid magnesium alloy was higher, the fluidity decreased, and the ability of the melt to fill the mold cavity during casting was weakened. When the melting temperature was set to 730℃, the fluidity of the liquid magnesium alloy was good, but the higher melting temperature increased the degree of oxidation and burn-off of the magnesium alloy, the oxide film on the melt surface thickened, and the solubility of gases in the melt increased. Comparing the castings prepared under 700℃ and 730℃ conditions with the casting prepared under 710℃ conditions, the casting obtained under 710℃ conditions achieved the best suppression effect on hot cracking and linear segregation defects.

[0088] This embodiment provides a method for manufacturing magnesium alloy castings. In addition to the technical features of the above embodiments, this embodiment further includes the following technical features.

[0089] The first refining time for liquid magnesium alloys includes: A settling refining agent is added to the liquid magnesium alloy, wherein the ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is greater than or equal to 1% and less than or equal to 2%. The first stirring time for the liquid magnesium alloy with added settling refining agent is greater than or equal to 5 minutes and less than or equal to 10 minutes.

[0090] In this embodiment, the mass ratio of the settling refining agent is set within the range of 1% to 2%, and the stirring time is set within the range of 5 min to 10 min. This ensures that non-metallic inclusions in the liquid magnesium alloy are fully adsorbed and settled out, resulting in a high-purity melt. The pure melt reduces the number of inclusions that could act as initiation sites for hot cracks during subsequent solidification, while also improving the feeding fluidity of the liquid magnesium alloy. Thus, under the combined effect of phase separation region magnetic modulation, the uniformity and integrity of the casting's internal quality are further guaranteed, achieving stable preparation of magnesium alloy castings without hot cracks or linear segregation defects.

[0091] Specifically, the ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is 1%.

[0092] The ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is 1.2%.

[0093] The ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is 1.4%.

[0094] The ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is 1.6%.

[0095] The ratio of the mass of the settling refining agent to the mass of the liquid magnesium alloy is 2%.

[0096] The first duration is 5 minutes.

[0097] The first duration is 7 minutes.

[0098] The first duration is 8 minutes.

[0099] The first duration is 10 minutes.

[0100] Specifically, taking the alloy raw material Mg-4Zn-1.5Ca-0.3Zr alloy as an example.

[0101] The operator first calculates the total mass of the liquid magnesium alloy based on the capacity of the melting crucible and the density of the liquid magnesium alloy. Then, the operator weighs out the corresponding mass of settling refining agent according to a ratio of 1.5% of the liquid magnesium alloy mass. The weighed settling refining agent is added to the liquid magnesium alloy in the melting crucible. A stirrer is positioned above the melting crucible, with its stirring rod extending into the liquid magnesium alloy. The stirrer's drive motor is electrically connected to the signal output of a speed controller, which controls the stirrer's rotation speed. The operator starts the stirrer and continuously stirs the liquid magnesium alloy containing the settling refining agent. The stirrer's rotation speed is set to 120 rpm. The operator sets the stirring time to 8 minutes using a timer. During stirring, the settling refining agent is uniformly dispersed in the liquid magnesium alloy and undergoes adsorption and chemical reactions with oxide inclusions and gases in the liquid magnesium alloy. After stirring, the liquid magnesium alloy is left to stand in the melting crucible for 5 minutes, allowing the settling refining agent that has adsorbed inclusions to settle to the bottom of the melting crucible under gravity.

[0102] Furthermore, under the same alloy raw materials and other unchanged process conditions, comparative experiments were conducted by adjusting the mass ratio of the settling refining agent to less than 1% and greater than 2%, and adjusting the stirring time to less than 5 min and greater than 10 min, respectively. When the mass ratio of the settling refining agent was less than 1%, the refining agent's adsorption of inclusions in the melt was insufficient, and some oxide inclusions remained in the liquid magnesium alloy. When the mass ratio of the settling refining agent was greater than 2%, the amount of refining agent added was sufficient, but excessive refining agent would increase the risk of melt contamination. When the stirring time was less than 5 min, the dispersion uniformity of the refining agent in the liquid magnesium alloy was insufficient, and the adsorption reaction of inclusions was incomplete. When the stirring time was greater than 10 min, the dispersion and reaction of the refining agent in the liquid magnesium alloy were sufficient. Comparing the castings obtained under different refining agent ratios and stirring times, the highest melt purity was achieved when the refining agent ratio was 1.5% and the stirring time was 8 min, and no inclusion-induced crack initiation was found inside the casting.

[0103] In one embodiment of the present invention, a magnesium alloy casting is provided, which is cast by the manufacturing method of magnesium alloy casting as described in any of the above embodiments. Since the magnesium alloy casting is cast by the manufacturing method of magnesium alloy casting as described in any of the above embodiments, it possesses all the beneficial effects of the manufacturing method of magnesium alloy casting as described in any of the above embodiments.

[0104] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0105] Example 1: The manufacturing method of Mg-4Zn-1.5Ca-0.3Zr alloy castings includes: The Mg-4Zn-1.5Ca-0.3Zr alloy ingot is placed in a melting crucible inside the furnace of the melting furnace; A protective gas is introduced into the melting furnace; The melting furnace is heated to the first temperature so that the Mg-4Zn-1.5Ca-0.3Zr alloy ingot is melted into liquid Mg-4Zn-1.5Ca-0.3Zr alloy; The first refining time for the liquid Mg-4Zn-1.5Ca-0.3Zr alloy; Liquid Mg-4Zn-1.5Ca-0.3Zr alloy is injected into a casting mold, while a magnetic field generator is controlled to apply a continuous three-phase rotating magnetic field to the molten metal in the casting mold. Real-time acquisition of the temperature of the molten metal in the casting mold; Based on the fact that the temperature of the molten metal in the casting mold is less than or equal to the second phase precipitation temperature of the Mg-4Zn-1.5Ca-0.3Zr alloy, the magnetic field generator is controlled to stop applying the continuous three-phase rotating magnetic field, and the magnetic field generator is controlled to apply an intermittent three-phase rotating magnetic field with magnetic field parameters of 120A, 15Hz and duty cycle of 33.3% to the molten metal in the casting mold. When the molten metal in the casting mold cools to the solidus temperature of the Mg-4Zn-1.5Ca-0.3Zr alloy, the control magnetic field generator stops applying the intermittent three-phase rotating magnetic field; The casting mold was allowed to cool naturally to room temperature.

[0106] Upon observation of the Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting manufactured using the method of Example 1, it was found that hot cracks and linear segregation defects existed at locations prone to hot crack initiation, with the hot crack volume being 24 mm. 3 The length of the linear macrosegregation is 700 μm.

[0107] Example 2: Based on Example 1, the excitation current intensity was increased from 120A to 150A. That is, after cooling to the second phase precipitation temperature, a rotating magnetic field with magnetic field parameters of 150A, 15Hz and duty cycle of 33.3% was applied to prepare a Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting. The casting was then cut along the center line to observe hot cracks and linear segregation defects at the locations where hot cracks are likely to occur.

[0108] After observing the Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting manufactured by the manufacturing method of Example 2, it was found that the microstructure at the location of easy-to-initiate hot cracks was uniform and there were no hot cracks or linear segregation defects.

[0109] Example 3: Based on Example 2, the material of the casting was changed from "Mg-4Zn-1.5Ca-0.3Zr alloy" to "AXJ530 (Mg-5Al-3Ca-0.17Sr) alloy". Specifically, after cooling to the second phase precipitation temperature, a rotating magnetic field with parameters of 150A, 15Hz, and a duty cycle of 33.3% was applied to prepare an AXJ530 alloy "T-shaped" casting. The casting was then cut along its centerline, and hot cracks and linear segregation defects at locations prone to hot crack initiation were observed. Observation of the AXJ530 alloy "T-shaped" casting manufactured using the method of Example 3 revealed that the microstructure at locations prone to hot crack initiation was uniform, with no hot cracks or linear segregation defects.

[0110] Example 4: Based on Example 2, the duty cycle is adjusted from 33.3% to 20%.

[0111] The excitation current intensity of the continuous three-phase rotating magnetic field of the magnetic field generator is set to 150A, and the current frequency is set to 15Hz. The excitation current intensity of the intermittent three-phase rotating magnetic field of the magnetic field generator is also set to 150A, the current frequency is set to 15Hz, and the duty cycle of the intermittent three-phase rotating magnetic field is set to 20%. After the liquid magnesium alloy is refined, the liquid magnesium alloy is poured into the cavity of the casting mold. Simultaneously, the magnetic field generator is activated, applying a continuous three-phase rotating magnetic field with an excitation current intensity of 150A and a current frequency of 15Hz to the melt in the casting mold.

[0112] A temperature recorder continuously monitors the temperature change of the melt in the hot spot region of the casting mold. When the temperature drops to the second-phase precipitation temperature of the alloy (340°C), the magnetic field generator stops applying the continuous three-phase rotating magnetic field. Subsequently, the magnetic field generator switches to applying an intermittent three-phase rotating magnetic field with a 20% duty cycle. During the application of the intermittent magnetic field with a 20% duty cycle, the coil of the magnetic field generator generates a rotating magnetic field during the energizing cycle and stops generating the magnetic field during the de-energizing cycle, with an energizing time to de-energizing time ratio of 1:4. When the temperature of the casting mold drops to the solidus temperature of the alloy, the magnetic field generator stops applying the intermittent three-phase rotating magnetic field. The casting mold is then allowed to cool naturally to room temperature in air.

[0113] The Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting prepared in this embodiment was cut along the centerline, and the cross-sectional microstructure at the location prone to hot crack initiation was observed. The observation results showed the presence of hot cracks and linear segregation defects at the location of the hot crack initiation. Quantitative measurements of the cross-section were performed using image analysis software; the hot crack volume was 28 mm². 3 The length of the linear macrosegregation defect is 800 μm.

[0114] The measurement results of 20% duty cycle in this embodiment were compared with those of 33.3% duty cycle in Example 2. Under the 20% duty cycle condition, the intermittent magnetic field had a shorter energizing time and a longer de-energizing time, resulting in a lower frequency of intermittent stirring of the melt. This led to insufficient improvement in the distribution of solute elements at the solid-liquid interface front, and insufficient feeding driving force. Therefore, it failed to completely suppress the formation of hot cracks and the local segregation of the eutectic phase. Under the 33.3% duty cycle condition, the ratio of energizing to de-energizing time of the intermittent magnetic field was more balanced. This ensured both the periodic improvement effect of the magnetic field on the solute distribution at the solid-liquid interface front and provided sufficient feeding driving force, while avoiding the problem of eutectic phase segregation caused by excessive feeding driving force under continuous magnetic field action.

[0115] Therefore, when the duty cycle of the intermittent three-phase rotating magnetic field is set to 20%, the magnetic field's interaction time with the melt is insufficient due to the low proportion of energization time, resulting in the continued existence of hot cracks and linear segregation defects. When the duty cycle is increased to 33.3%, the intensity and time ratio of the intermittent magnetic field reach the optimal balance point, thus obtaining a defect-free casting. This verifies the rationality of setting the first duty cycle within the range of 20% to 40%, and shows that selecting a duty cycle of 33.3% within this range can achieve the optimal control effect of the intermittent three-phase rotating magnetic field on the solidification process of magnesium alloys, thereby realizing the synergistic suppression of hot cracks and linear segregation.

[0116] Comparative Example 1: The difference between Comparative Example 1 and Examples 1 to 4 is that, before cooling to the second phase precipitation temperature, the scheme of Comparative Example 1 did not control the magnetic field generating device to apply a continuous three-phase rotating magnetic field to the molten metal in the casting mold. After cooling to the second phase precipitation temperature, the scheme of Comparative Example 1 also did not apply an intermittent three-phase rotating magnetic field.

[0117] That is, in Comparative Example 1, the casting method for the Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting includes: The Mg-4Zn-1.5Ca-0.3Zr alloy ingot is placed in a melting crucible inside the furnace of the melting furnace; A protective gas is introduced into the smelting furnace; The melting furnace is heated to a first temperature so that the Mg-4Zn-1.5Ca-0.3Zr alloy ingot is melted into liquid Mg-4Zn-1.5Ca-0.3Zr alloy; The liquid Mg-4Zn-1.5Ca-0.3Zr alloy was refined for a first time. The liquid Mg-4Zn-1.5Ca-0.3Zr alloy was injected into a casting mold; The molten metal in the casting mold cooled naturally to room temperature.

[0118] The Mg-4Zn-1.5Ca-0.3Zr alloy "T-shaped" casting produced by the above casting method solidified naturally (without applying a magnetic field during cooling). The casting was then cut along its centerline to observe hot cracks and linear segregation defects at locations prone to hot crack initiation. Comparative Example 1 was observed to contain hot cracks and linear macroscopic segregation defects, with a hot crack volume of 60 mm². 3 The length of the linear macrosegregation is 4000 μm.

[0119] Table 1 shows the test results of one comparative example and four implementation cases. Table 1 presents the measurement results of hot crack volume and linear segregation defect length. As can be seen from Table 1, the manufacturing method of magnesium alloy castings provided in this application can effectively reduce the occurrence of hot cracks and linear macrosegregation defects in magnesium alloy castings, and can produce magnesium alloy castings without hot cracks and linear macrosegregation defects.

[0120] Table 1

[0121] In the claims, description, and accompanying drawings of this invention, the term "plural" refers to two or more. Unless otherwise explicitly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and simplifying the descriptive process, and are not intended to indicate or imply that the device or element referred to must have the described specific orientation, or be constructed and operated in a specific orientation. Therefore, these descriptions should not be construed as limiting the invention. The terms "connect," "install," "fix," etc., should be interpreted broadly. For example, "connect" can be a fixed connection between multiple objects, a detachable connection between multiple objects, or an integral connection; it can be a direct connection between multiple objects or an indirect connection between multiple objects through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this invention can be understood based on the specific circumstances of the above data.

[0122] In the claims, description, and accompanying drawings of this invention, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In the claims, description, and accompanying drawings of this invention, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0123] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 method for manufacturing a magnesium alloy casting, characterized in that, include: Magnesium alloy ingots are placed in a melting crucible inside the furnace of a melting furnace; A protective gas is introduced into the smelting furnace; The melting furnace is heated to a first temperature so that the magnesium alloy ingot is melted into liquid magnesium alloy. The liquid magnesium alloy is refined for a first time; The liquid magnesium alloy is injected into a casting mold, and at the same time, a magnetic field generating device is controlled to apply a continuous three-phase rotating magnetic field to the molten metal in the casting mold. The temperature of the molten metal in the casting mold is acquired in real time. Based on the fact that the temperature of the molten metal in the casting mold is less than or equal to the second phase precipitation temperature of the magnesium alloy, the magnetic field generating device is controlled to stop applying the continuous three-phase rotating magnetic field, and the magnetic field generating device is controlled to apply an intermittent three-phase rotating magnetic field with a first duty cycle to the molten metal in the casting mold. When the molten metal in the casting mold cools to the solidus temperature of the magnesium alloy, the magnetic field generating device is controlled to stop applying the intermittent three-phase rotating magnetic field; The casting mold cooled naturally to room temperature.

2. The method for manufacturing magnesium alloy castings according to claim 1, characterized in that, Also includes: Thermal analysis was performed on the magnesium alloy casting to obtain its cooling profile. The first and second derivative curves were obtained based on the cooling curve of the magnesium alloy casting. The liquidus temperature, the second phase precipitation temperature, and the solidus temperature of the magnesium alloy are obtained based on the first and second derivative curves.

3. The method for manufacturing magnesium alloy castings according to claim 1, characterized in that, Prior to injecting the liquid magnesium alloy into the casting mold, the manufacturing method further includes: The casting mold is preheated to a second temperature, wherein the second temperature is greater than or equal to 200°C and less than or equal to 300°C.

4. The method for manufacturing magnesium alloy castings according to claim 1, characterized in that, The excitation current intensity of the intermittent three-phase rotating magnetic field is greater than or equal to 100A and less than or equal to 200A; The current frequency of the intermittent three-phase rotating magnetic field is greater than or equal to 10Hz and less than or equal to 30Hz.

5. The method for manufacturing magnesium alloy castings according to claim 1, characterized in that, The first duty cycle of the intermittent three-phase rotating magnetic field is greater than or equal to 20% and less than or equal to 40%.

6. The method for manufacturing magnesium alloy castings according to claim 1, characterized in that, The first temperature is greater than or equal to 700°C and less than or equal to 730°C.

7. The method for manufacturing magnesium alloy castings according to any one of claims 1 to 6, characterized in that, The first refining time of the liquid magnesium alloy includes: A settling refining agent is added to the liquid magnesium alloy, wherein the mass ratio of the settling refining agent to the mass of the liquid magnesium alloy is greater than or equal to 1% and less than or equal to 2%. The liquid magnesium alloy is stirred and added with the settling refining agent for a first time, the first time being greater than or equal to 5 minutes and less than or equal to 10 minutes.

8. A magnesium alloy casting, characterized in that, The magnesium alloy casting is produced by the method for manufacturing magnesium alloy castings as described in any one of claims 1 to 6.

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