Comprehensive control method for fluorescent stripe defect of rare earth magnesium alloy casting

Abstract

The invention discloses a comprehensive control method for fluorescent stripe defects of a rare earth magnesium alloy casting, and belongs to the technical field of casting forming of metal parts. In order to solve the problems that in the mold filling process, rare earth magnesium alloy melt and air in a mold cavity are prone to oxidation reaction, the fluorescent stripe defect is generated on a casting, and the quality and the service life of the casting are affected. According to the method, the rare earth magnesium alloy casting is provided with a slag collecting unit, and the slag collecting unit is used for regulating and controlling a mold filling flow field of rare earth magnesium alloy melt so as to feed the rare earth magnesium alloy casting and collect slag; a chilling block is placed at a hot spot part in a cavity of the sand mold, and the chilling block is used for regulating and controlling a condensation sequence temperature field of the rare earth magnesium alloy melt so as to lead a metal oxide film to a slag collecting unit; and the concentration of oxidizing atmosphere in the cavity of the sand mold is reduced by enhancing exhaust and inhibiting gas generation, so that the generation of a metal oxide film is reduced.

Description

Technical Field

[0001] This invention relates to the field of metal parts casting technology, and in particular to a comprehensive control method for fluorescent stripe defects in rare earth magnesium alloy castings. Background Technology

[0002] Rare earth magnesium alloys (Mg-RE alloys) are considered the preferred material for lightweight structural components in aerospace due to their low density, excellent specific strength and stiffness, and high heat resistance. To meet the production demands of large, complex, thin-walled structural components for aerospace equipment, which are diverse in type and produced in small batches, sand casting / low-pressure casting processes are widely used. However, due to the high oxidizing properties of molten magnesium and rare earth elements, secondary oxidation easily occurs when exposed to the mold cavity atmosphere during the filling process, instantly forming a thin oxide film on the surface of the molten metal. Furthermore, the complex structure of the casing casting, with significant variations in wall thickness, necessitates the use of multi-gating systems for bottom-up filling. During this process, multiple streams of molten metal inevitably converge, and the oxide films at the leading edges of two streams come into contact, forming a double-layer oxide film defect without metallurgical bonding. This is equivalent to a pre-existing crack in the casting, severely impairing its mechanical properties. During the casting process of a certain type of large and complex magnesium rare-earth alloy casting, a double-layer oxide film defect with openings easily forms on the casting surface. In fluorescence inspection, this defect exhibits bright yellow-green fluorescent stripes. These defects are composed of rare-earth oxides such as Y₂O₃ / Gd₂O₃ and have the following characteristics: a double-layer film structure, approximately 1 μm thick, reaching depths of several millimeters, and no metallurgical bonding with the substrate. These fluorescent stripe defects are distributed in areas such as floats, bosses, and grooves of the casting, corresponding to the confluence locations in the casting filling flow field simulation analysis, and the defect distribution pattern is highly consistent with the confluence pattern. The fluorescent stripe defects cause the surface quality of the casting to fail to meet design requirements, necessitating repair through grinding and welding, and in severe cases, even scrapping. For areas that cannot be ground or welded, the only remaining option is to increase the patching allowance during the gating system design, which in turn increases weight. Traditional control methods (such as melt purification, pouring rate adjustment, and coating optimization) have limited effectiveness and fail to address the core issues: ① Secondary oxidation mechanism: During the filling process, the reaction between the melt and the cavity atmosphere (such as CO / CO2 generated by resin sand pyrolysis) inevitably generates an oxide film; ② Flow field-temperature field coupling effect: Converging turbulence promotes oxide film entrainment, and temperature gradients can drive the oxide film to migrate to harmful locations. Therefore, it is urgent to develop a multi-factor synergistic control process to control fluorescent stripe defects from three aspects: oxide film formation, movement trajectory, and final distribution. Summary of the Invention

[0003] In view of this, the present invention provides a comprehensive control method for fluorescent stripe defects in rare earth magnesium alloy castings. By synergistically regulating the filling flow field, solidification temperature field, and cavity atmosphere, it achieves directional guidance of the movement trajectory of the metal oxide film, harmless distribution of the metal oxide film, and inhibition of metal oxide film formation, thereby solving the problem of fluorescent stripe defects in rare earth magnesium alloy castings and improving the quality of rare earth magnesium alloy castings.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A comprehensive method for controlling fluorescent stripe defects in rare earth magnesium alloy castings, the method comprising the following steps:

[0006] (1) In the design of the rare earth magnesium alloy casting gating system, a slag collection unit is set at the casting float, boss, groove and other parts where the molten liquid flows during filling. The slag collection unit is used to regulate the filling flow field of the rare earth magnesium alloy molten liquid and plays the role of capturing and storing secondary oxide slag.

[0007] (2) During the process of arranging chills, chills are placed at the casting parts where the molten liquid converges and the numerical simulation shows a hot spot, in order to control the solidification sequence temperature field of the rare earth magnesium alloy molten liquid and to guide the metal oxide film to the slag collection unit.

[0008] (3) During the casting filling process, reduce the concentration of oxidizing atmosphere in the sand mold cavity to reduce the formation of metal oxide film.

[0009] Furthermore, the slag collection unit in step (1) includes a molten metal channel, a slag riser, and a slow-flow slag collection pit arranged in sequence.

[0010] Furthermore, the bottom of the molten metal channel is flush with the bottom of the slag riser, and the height of the molten metal channel is less than the height of the slag riser.

[0011] Furthermore, the height of the slow-flow slag collection pit is level with the height of the slag collection riser, and the bottom of the slow-flow slag collection pit is lower than the bottom of the slag collection riser.

[0012] Furthermore, the rare earth magnesium alloy casting described in step (1) includes a float structure, the molten metal channel is connected to the casting float, the bottom of the molten metal channel is flush with the bottom of the casting float, and the height of the molten metal channel is lower than the height of the casting float.

[0013] Furthermore, the casting parts where the molten flow converges and the numerical simulation shows a hot spot in step (2) are the casting parts where multiple streams of molten metal collide with each other during filling and the casting parts where the thickness changes abruptly and the solidification does not conform to the order.

[0014] Furthermore, the method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: the inner core adopts a hollow structure sand core, the inner core is a sand core surrounded by molten metal during the filling process, and the inner cavity of the hollow structure sand core needs to be filled with large-particle sand.

[0015] Further, the method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: applying a dense coating to the inner core surface, wherein the dense coating is a 256B enhanced alcohol-based coating.

[0016] Further, the method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: preparing a dry core by subjecting the sand core to a short-term high-temperature reheating treatment, wherein the reheating temperature of the reheating treatment is 200~250°C. o C, the warming time is 1~2 hours.

[0017] Furthermore, the method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: setting a main exhaust pipe at the filling end of the sand mold, and setting an exhaust plug at the opening of the main exhaust pipe; and adding an auxiliary exhaust hole at the sand core above where the molten metal in the sand mold converges.

[0018] The beneficial effects of this invention compared to the prior art are:

[0019] 1. This invention, through the scientific design of the molten metal channel, slag riser, and slow-flow slag collection pit, extends the flow path of the metal oxide film, facilitating its settling. Simultaneously, under the propulsion of the molten rare earth magnesium alloy and the guidance of the molten metal channel, slag riser, and slow-flow slag collection pit, the metal oxide film is ultimately pushed into the slow-flow slag collection pit, achieving collection and preventing the metal oxide film from existing inside the rare earth magnesium alloy casting, thus affecting its quality.

[0020] 2. In this invention, the height of the molten metal channel is lower than the height of the casting float. Under the influence of gravity and filling pressure, the molten rare earth magnesium alloy can flow directionally from the casting float into the molten metal channel. The bottom of the slag riser is flush with the bottom of the molten metal channel, and its height is higher than the molten metal channel. This allows a certain amount of molten rare earth magnesium alloy to be stored in the slag riser. When the molten rare earth magnesium alloy in the casting boss and casting float solidifies, based on the principle of thermal expansion and contraction, condensation may occur at the casting float. Shrinkage cavities and other issues affect the quality of metal castings. The molten rare earth magnesium alloy in the slag riser can compensate for the lack of molten rare earth magnesium alloy in the casting float, ensuring the quality of the casting float. The height of the slow-flow slag collecting nest is the same as the height of the slag riser, and the bottom of the slow-flow slag collecting nest is lower than the bottom of the slag riser. The design of the slow-flow slag collecting nest guides the flow of the molten rare earth magnesium alloy, which is more conducive to the accumulation of the sinking metal oxide film at the bottom of the slow-flow slag collecting nest, resulting in castings without fluorescent stripe defects.

[0021] 3. The present invention sets chills at the hot spot of the casting, which can accelerate the cooling rate of the rare earth magnesium alloy melt at the hot spot after the rare earth magnesium alloy melt is filled into the mold. This allows the rare earth magnesium alloy melt between the hot spot and the slow-flowing slag collection pit to form a sequential solidification temperature field, which not only facilitates the feeding of the rare earth magnesium alloy casting, but also, under the concentration difference between the rare earth magnesium alloy melt and the metal oxide film, can form a directional flow field in the mold cavity, guiding the metal oxide film to the slag riser and the slow-flowing slag collection pit, further improving the quality of the metal casting.

[0022] 4. This invention introduces a cavity structure sand core design. For the "water-encased core" surrounded by molten metal, its internal structure is designed with a cavity, and the cavity is filled with large sand particles. When pyrolysis gas begins to be generated inside the sand core and pressure is formed, the gas emitted due to the negative pressure will be discharged into the sand core cavity, avoiding the gas being forced to invade the molten metal due to having nowhere to go, thereby reducing the risk of oxidation defects.

[0023] 5. This invention forms a strong physical barrier with extremely low permeability by coating the inner core surface with a layer of reinforced alcohol-based dense coating. This barrier is formed after the inner core is baked. Its main functions are twofold: First, it effectively prevents gases (such as CO and CO2) generated by the pyrolysis of the internal resin and other binders from escaping into the melt when the sand core comes into contact with high-temperature molten metal, thus isolating most of the gas inside the sand core. Second, the coating itself possesses excellent high-temperature resistance, reducing the thermal shock and thermal impact range of the high-temperature melt on the sand core body, thereby reducing the gas generation rate and total amount generated per unit time from the source, achieving a "throttling" effect.

[0024] 6. The present invention performs a "high temperature and short time" reheating treatment on the sand core, and then assembles the sand core into a "dry core" before core assembly. This promotes the decomposition and volatilization of the binder and moisture in the sand core in a controlled environment. When the molten metal is filled, the amount of gas generated by the sand core will be greatly reduced, thereby reducing the tendency of rare earth magnesium alloy to undergo secondary oxidation during the filling process.

[0025] 7. The present invention, through the design of the main exhaust pipe and auxiliary exhaust hole, can reduce the concentration of oxidizing atmosphere in the cavity and reduce the amount of secondary metal oxide film generated by the reaction of oxidizing gas with rare earth magnesium alloy melt. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are provided to give a further understanding of the invention.

[0027] Figure 1 This is a schematic cross-sectional view of the rare earth magnesium alloy casting blank in Example 1.

[0028] Figure 2This is a schematic diagram showing the arrangement of the molten metal channel, slag riser, and slow-flow slag collection pit.

[0029] Figure 3 This is a schematic diagram of the filling flow field of the rare earth magnesium alloy melt during the casting filling process in Example 1.

[0030] Figure 4 This is a schematic diagram of the temperature field distribution of the rare earth magnesium alloy melt, where chills are arranged in front of the casting boss in Example 1.

[0031] Figure 5 This is a schematic diagram of the temperature field distribution of the rare earth magnesium alloy melt, where chills are arranged behind the casting boss in Example 1.

[0032] Figure 6 This is a schematic cross-sectional view of the rare earth magnesium alloy casting billet in Example 2. Figure 1 .

[0033] Figure 7 This is a schematic cross-sectional view of the rare earth magnesium alloy casting billet in Example 2. Figure 2 .

[0034] Explanation of reference numerals in the attached drawings: 1-Rare earth magnesium alloy casting, 2-Chill, 3-Molten metal channel, 4-Slag riser, 5-Slow-flow slag collection pit, 6-Casting boss, 7-Casting float, 8-Main exhaust pipe, 9-Sand core. Detailed Implementation

[0035] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Rare earth magnesium alloys are widely used in complex thin-walled components for aerospace applications due to their lightweight, high strength, and heat resistance. However, in sand casting / low-pressure casting, the molten alloy is prone to oxidation, forming an oxide film. When multiple streams of molten metal converge, a double-layer oxide film defect (fluorescent stripes) occurs, leading to cracks on the casting surface and severely affecting the metallurgical quality and casting yield of rare earth magnesium alloy sand castings. Traditional control methods have limited effectiveness. This invention solves the problem of fluorescent stripe defects by synergistically controlling the filling flow field, solidification temperature field, and cavity atmosphere to achieve directional guidance and suppression of the oxide film.

[0037] Flow field regulation during mold filling: A slag collection unit is installed at the end of the mold filling process for rare earth magnesium alloy castings. This slag collection unit includes a molten metal channel 3, a slag riser 4, and a slow-flow slag collection pit 5 arranged sequentially. During the filling process of the rare earth magnesium alloy molten metal, the design of the molten metal channel 3, the slag riser 4, and the slow-flow slag collection pit 5 extends the flow path of the metal oxide film, which is beneficial to the settling of the metal oxide film. At the same time, the metal oxide film is ultimately pushed into the slow-flow slag collection pit 5 by the molten rare earth magnesium alloy and guided by the molten metal channel 3, the slag riser 4, and the slow-flow slag collection pit 5, thus achieving the collection of the metal oxide film and preventing the metal oxide film from existing inside the rare earth magnesium alloy casting, which would affect the quality of the rare earth magnesium alloy casting.

[0038] Controlling the solidification temperature field: Chills are placed at the hot spots of the casting within the sand mold cavity. After the rare earth magnesium alloy molten metal fills the mold, the chills accelerate the solidification rate at the hot spots, creating a sequential solidification temperature field between the hot spots and the slow-flowing slag collection pit 5. This not only facilitates the feeding of the casting float 2 by the slag collection riser 4, but also, due to the concentration difference between the rare earth magnesium alloy molten metal and the metal oxide film, forms a directional flow field within the sand mold cavity. This guides the metal oxide film to the slag collection riser 4 and the slow-flowing slag collection pit 5, improving the quality of the metal casting.

[0039] Controlling the mold cavity atmosphere: During the filling process of rare earth magnesium alloy molten metal, the oxidizing atmosphere inside the sand mold cavity is discharged or its generation is inhibited, reducing the concentration of oxidizing atmosphere inside the sand mold cavity, thereby reducing the formation of metal oxide film from the source. A hollow core structure is adopted, and the emitted gas is discharged into the cavity through negative pressure; the surface of the sand core is coated with a reinforced alcohol-based dense coating to reduce the entry of pyrolysis gas from the sand core into the melt; at the same time, a heat-resistant coating reduces the thermal influence range of the melt on the sand core, reducing pyrolysis gas generation; a "high-temperature short-time" reheating treatment method is used to make the sand core into a dry core, releasing pyrolysis gas in advance and reducing pyrolysis gas generation during filling; the design of a main exhaust pipe and auxiliary exhaust holes effectively discharges the gas emitted from the sand mold cavity to the outside of the cavity.

[0040] Therefore, it can be seen that by controlling the filling flow field, solidification temperature field and cavity atmosphere, the present invention can reduce the generation of fluorescent stripe defects in rare earth magnesium alloy castings and improve the quality of rare earth magnesium alloy castings.

[0041] Example 1:

[0042] This embodiment uses Figure 1 The following detailed explanation uses a rare-earth magnesium alloy casting as an example to illustrate the control of the filling flow field and solidification temperature field. This rare-earth magnesium alloy casting includes a casting boss 6 and a casting float 7 connected in sequence. The comprehensive control method for fluorescent stripe defects in a rare-earth magnesium alloy casting according to this embodiment includes the following steps:

[0043] S1. In the design process of the rare earth magnesium alloy casting pouring system, a slag collection unit connected to the casting float 7 is designed. The slag collection unit includes a molten metal channel 3, a slag collection riser 4 and a slow-flow slag collection pit 5 connected in sequence.

[0044] S2. During the placement of chills, according to the numerical simulation results, magnesium alloy molten flow occurs at the casting boss 6 position. Moreover, the casting boss 6 has the highest temperature compared to the casting float 7 and the slag collection unit. Therefore, chills 2 are placed at the casting boss 6 position.

[0045] S3, rare earth magnesium alloy casting is performed by pouring a gating device located below and connected to a sand mold. Molten rare earth magnesium alloy is prepared and poured into the mold cavity through a riser pipe. During filling, the molten rare earth magnesium alloy flows upward through the riser pipe and is evenly distributed by the runner. Because the molten rare earth magnesium alloy is divided into multiple streams by the runner, each stream undergoes an oxidation reaction with the mold cavity atmosphere, forming a metallic oxide film at its leading edge. This film flows forward under the propulsion of subsequent streams. Each stream then flows vertically upward through two adjacent vertical runners. As the molten rare earth magnesium alloy exits the gate, the streams between adjacent gates converge. Due to the metallic oxide film at the leading edge of each stream, a double oxide film defect is formed. However, the rare earth magnesium alloy molten metal containing the double oxide film defect flows sequentially along the casting boss 6, casting float 7, molten metal channel 3, slag riser 4, and slow-flow slag collection pit 5 under the propulsion of the subsequent rare earth magnesium alloy molten metal, eventually converging into the slag riser 4 and slow-flow slag collection pit 5. Furthermore, since the density of the metal oxide film in the rare earth magnesium alloy molten metal is greater than that in the molten metal itself, and considering that the design of the molten metal channel 3, slag riser 4, and slow-flow slag collection pit 5 extends the flow path of the metal oxide film, it facilitates the settling of the metal oxide film and its downward flow to the lower-lying slow-flow slag collection pit 5, thus achieving the collection of the metal oxide film and preventing its presence at the casting boss 6 and casting float 7 from affecting the quality of the rare earth magnesium alloy casting.

[0046] S4. After the mold filling is completed, the rare earth magnesium alloy casting cools and solidifies in the mold. Due to the chilling effect of chill 2 (chill 2 has a higher thermal conductivity than sand core, which is conducive to the condensation of rare earth magnesium alloy melt), the cooling rate of rare earth magnesium alloy melt at the casting boss 6 will be accelerated. Figure 4 and Figure 5The diagrams show the temperature field distribution of the casting before and after placing the chill 2 on the casting boss 6. It can be seen that after placing the chill 2 on the casting boss 6, the temperature at the casting boss 6 is the lowest. The casting boss 6, casting float 7, molten metal channel 3, slag riser 4, and slow-flow slag collection pit 5 form a sequential solidification temperature field. The rapid cooling of the casting boss 6 can promote the faster flow of the rare earth magnesium alloy molten metal in the slag riser 4 towards the casting float 7, thereby achieving a more efficient feeding effect and helping to reduce defects such as shrinkage cavities and porosity caused by insufficient feeding on the casting float 7.

[0047] It should be noted that, in addition to forced convection during the filling process, the liquid metal is also subject to thermal convection caused by the temperature difference during solidification. Specifically, the liquid metal expands in areas of higher temperature, decreasing its density, while it contracts in areas of lower temperature, increasing its density. This creates a density difference between the high-temperature and low-temperature regions. In a gravitational field, the less dense liquid metal floats, and the more dense liquid metal sinks. Due to the existence of temperature and concentration differences, thermal convection occurs in the liquid metal, and the intensity of this convection can be expressed using the dimensionless Grashof number.

[0048] G T =gβ r L 3 △T / υ 2

[0049] G C =gβ r L 3 △C / υ 2

[0050] In the formula: g is the acceleration due to gravity; ΔT and ΔC are the temperature difference and concentration difference, respectively; L is half the distance between the hot and cold ends; υ is the kinematic viscosity; βr is the coefficient of volume expansion caused by temperature.

[0051] It is evident that the greater the temperature and concentration difference, the stronger the natural convection, which directly affects the trajectory of defects in the metal oxide film during solidification. Therefore, based on the method of controlling the forced convection of the melt, this embodiment sets a chill 2 at the casting boss 6 to create a directional temperature gradient in the unsolidified melt, causing the metal oxide film to migrate towards the high-temperature zone (in the direction of the slow-flowing slag collection pit 5), thereby controlling the trajectory of the metal oxide film and improving the capture of the metal oxide film by the slow-flowing slag collection pit 5. In other words, through the chill 2's quenching design, not only is the cooling sequence temperature field of the rare earth magnesium alloy melt adjusted, but the flow field of the metal oxide film is also adjusted, making it more conducive for the metal oxide film to enter the slag riser 4 and the slow-flowing slag collection pit 5, further improving the quality of the rare earth magnesium alloy casting.

[0052] S5. After solidification, open the sand mold, remove the chill 2, and obtain the billet. Cut off the slag riser 4, the slow-flow slag collection pit 5, and the molten metal channel 3 to obtain a rare earth magnesium alloy casting without fluorescent stripe defects.

[0053] See Figure 1 and Figure 2 In this embodiment, the height of the molten metal channel 3 is lower than the height of the casting float 2. Under the influence of gravity and filling pressure, the molten rare earth magnesium alloy can flow directionally from the casting float 7 into the molten metal channel 3. The bottom of the slag riser 4 is flush with the bottom of the molten metal channel 3, and the height of the slag riser 4 is higher than the height of the molten metal channel 3. This allows a certain amount of molten rare earth magnesium alloy to be stored in the slag riser 4. When the molten rare earth magnesium alloy at the casting boss 6 and the casting float 7 solidifies, shrinkage cavities and other problems will occur at the casting float 7 due to the principle of thermal expansion and contraction, affecting the quality of the metal casting. The molten rare earth magnesium alloy in the slag riser 4 can compensate for the lack of molten rare earth magnesium alloy in the casting float 7, ensuring the quality of the casting float 7. The height of the slow-flow slag collecting basin 5 is flush with the height of the slag collecting riser 4, while the bottom of the slow-flow slag collecting basin 5 is lower than the bottom of the slag collecting riser 4. The design of the slow-flow slag collecting basin 5 guides the flow of the rare earth magnesium alloy molten metal, making it easier to collect the sinking metal oxide film at the bottom of the basin 5, resulting in a casting without fluorescent stripe defects. Furthermore, the shape of the slow-flow slag collecting basin 5 can be adjusted according to the casting design. For example, when there is an oil hole at the float plate of the casting, the slow-flow slag collecting basin 5 needs to avoid this location and be designed as a fan shape or other shapes.

[0054] Among them, the height of the slag collection riser 4 is 50mm and the width is 30mm, the height of the slow-flow slag collection pit is 100mm and the width is 30mm, the width of the molten metal channel 3 is 60mm, and the thickness of the chill 2 is 1 to 1.5 times the thickness of the casting float 2.

[0055] Example 2:

[0056] See Figure 6 and Figure 7 This embodiment uses Figure 6 and Figure 7 The control of the cavity atmosphere is explained in detail using the rare earth magnesium alloy casting shown as an example. Figure 6 and Figure 7 The rare earth magnesium alloy casting is equipped with casting connecting ribs.

[0057] The method for controlling fluorescent stripe defects in rare earth magnesium alloy castings according to this embodiment includes the following steps:

[0058] S1, in the design of this rare earth magnesium alloy casting gating system, since molten metal flows together during the filling process of the top float 7, a slag collection unit connected to the casting float 7 is designed. The slag collection unit includes a molten metal channel 3 and a slag collection riser 4 connected in sequence. After adjustment, the leading edge of the flow will advance through the metal channel 3 to the slag collection riser 4 area, and the oxide film will migrate to the riser area and be captured by the slag collection riser 4.

[0059] S2, during the arrangement of chills, chills 2 are placed below the float plate 7. The casting float plate 7 and the slag riser 4 form a sequential solidification temperature field, which further discharges the converging oxide film inclusions from the float plate 7 and into the slag riser 4.

[0060] S3, during the casting filling process, the concentration of the oxidizing atmosphere in the sand mold cavity is reduced to decrease the formation of metal oxide film. The inner core 9 forms a "water-encased core" surrounded by molten metal, resulting in severe heat-affected zones. Gas generated from the sand core cannot escape, and the pyrolysis gas comes into full contact with the molten magnesium alloy. Here, the cavity atmosphere and the molten magnesium alloy undergo continuous oxidation, leading to severe oxide film thickening and a higher number of fluorescent stripe defects. During core preparation, the inner core 9 is designed with a cavity structure. When pyrolysis gas begins to be generated inside the sand core and pressure is created, the gas is expelled into the cavity due to negative pressure, preventing the gas from being forced into the molten metal due to lack of outlet, thus reducing the risk of oxidation defects. The inner core 9 is coated with a layer of reinforced alcohol-based dense coating, forming a strong physical barrier with extremely low permeability. This barrier serves two main purposes: first, it effectively prevents gases (such as CO and CO2) generated by the pyrolysis of the internal resin and other binders from escaping into the melt when the core comes into contact with high-temperature molten metal, effectively isolating most of the gas within the core; second, the coating itself possesses excellent high-temperature resistance, reducing the thermal shock and thermal impact range of the high-temperature melt on the core body, thereby reducing the gas generation rate and total amount generated per unit time from the source, achieving a "throttling" effect. The inner core 9 undergoes a "short-time high-temperature" reheating treatment at a temperature of 220°C. o C. The reheating time is 1.5 hours, which promotes the early decomposition and volatilization of the binder and moisture in the sand core. Multiple main exhaust pipes 8 are designed on the sand mold at the intersection of the connecting ribs of the casting. Exhaust plugs are installed at the openings of the exhaust pipes 8. The diameter of the main exhaust pipe 8 is 8 mm, and the distance between two adjacent main exhaust pipes is 30 mm.

[0061] S4. Rare earth magnesium alloy casting is performed by pouring. The pouring equipment is located below and connected to the sand mold. Molten rare earth magnesium alloy is prepared and poured into the cavity of the sand mold through the pouring equipment. Since the sand mold is mainly made of resin sand, it undergoes a pyrolysis reaction upon contact with the molten rare earth magnesium alloy, producing oxidizing gases such as CO / CO2. This makes the atmosphere inside the sand mold cavity prone to oxidation reaction with the molten rare earth magnesium alloy, which is the reason for the formation of a secondary metal oxide film during the filling process. In this embodiment, during the filling process, some of the oxidizing gases can be discharged from the cavity through the main exhaust pipe 8 and the auxiliary exhaust hole, reducing the concentration of oxidizing atmosphere inside the cavity and decreasing the amount of secondary metal oxide film formed by the reaction of oxidizing gases with the molten rare earth magnesium alloy, thus inhibiting the formation of the metal oxide film.

[0062] S5. After filling is completed, the rare earth magnesium alloy casting is cooled and solidified in the mold. After solidification, the sand mold is opened, the chill 2 is removed, and the billet is obtained. The metal pillar, metal channel 3 and slag riser 4 formed on the billet corresponding to the main exhaust pipe 8 are cut off to obtain a casting without fluorescent stripe defects.

[0063] The rare earth magnesium alloy castings obtained by the above method according to this invention showed no fluorescent stripe defects on the casting surface when subjected to fluorescence detection. This demonstrates that the design of slag collection units (slag riser 4 and molten metal channel 3), temperature field regulation using chills 2, venting of the ribs 8, dense coating on the sand core, and cavity structure sand cores 9 can solve the problem of oxidation-type fluorescent stripe defects in rare earth magnesium alloy castings, thereby improving the quality of rare earth magnesium alloy castings.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions created by the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions created by the present invention without departing from the essence and scope of the technical solutions created by the present invention.

Claims

1. A comprehensive control method for fluorescent stripe defects in rare earth magnesium alloy castings, characterized in that, The comprehensive control method for fluorescent stripe defects includes the following steps: (1) In the design of the rare earth magnesium alloy casting gating system, a slag collection unit is set at the casting float, boss, groove and other parts where the molten liquid flows during filling. The slag collection unit is used to regulate the filling flow field of the rare earth magnesium alloy molten liquid and plays the role of capturing and storing secondary oxide slag. (2) During the process of arranging chills, chills are placed at the casting parts where the molten liquid converges and the numerical simulation shows a hot spot, in order to control the solidification sequence temperature field of the rare earth magnesium alloy molten liquid and to guide the metal oxide film to the slag collection unit. (3) During the casting filling process, reduce the concentration of oxidizing atmosphere in the sand mold cavity to reduce the formation of metal oxide film.

2. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The slag collection unit in step (1) includes a molten metal channel, a slag riser, and a slow-flow slag collection pit arranged in sequence.

3. The method for comprehensive control of fluorescent stripe defects according to claim 2, characterized in that, The bottom of the molten metal channel is flush with the bottom of the slag riser, and the height of the molten metal channel is less than the height of the slag riser.

4. The method for comprehensive control of fluorescent stripe defects according to claim 2, characterized in that, The height of the slow-flow slag collection pit is the same as the height of the slag riser, and the bottom of the slow-flow slag collection pit is lower than the bottom of the slag riser.

5. The method for comprehensive control of fluorescent stripe defects according to claim 2, characterized in that, The rare earth magnesium alloy casting described in step (1) includes a float structure, a molten metal channel connected to the casting float, the bottom of the molten metal channel being flush with the bottom of the casting float, and the height of the molten metal channel being lower than the height of the casting float.

6. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The casting parts where the molten flow converges and the numerical simulation shows a hot spot in step (2) are the casting parts where multiple streams of molten metal collide with each other during filling and the casting parts where the thickness changes abruptly and solidification does not conform to the order.

7. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: using a hollow structure sand core, wherein the inner core is a sand core surrounded by molten metal during the filling process, and the inner cavity of the hollow structure sand core needs to be filled with large-particle sand.

8. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: applying a dense coating to the inner core surface, wherein the dense coating is a 256B enhanced alcohol-based coating.

9. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: preparing a dry core by subjecting the sand core to a high-temperature short-time reheating treatment, wherein the reheating temperature of the reheating treatment is 200~250°C. o C, the warming time is 1~2 hours.

10. The method for comprehensive control of fluorescent stripe defects according to claim 1, characterized in that, The method for reducing the concentration of oxidizing atmosphere in the sand mold cavity in step (3) includes: setting a main exhaust pipe at the filling end of the sand mold, and setting an exhaust plug at the opening of the main exhaust pipe; and adding an auxiliary exhaust hole at the sand core above where the molten metal in the sand mold converges.

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