Method and device for controlling porosity defects of castings by ultrasonic and physical field cooperation

Abstract

The application discloses a kind of casting porosity defect control method and device of ultrasonic and physical field synergy, porosity defect is regarded as the control target independent from grain refinement, in different stages of the whole process of metal melt solidification, multi-mode ultrasonic wave (continuous ultrasonic, variable frequency ultrasonic, pulse ultrasonic) is used to assist physical field, from four dimensions of gas removal purification, refined structure prevents the blocking of feeding channel, acoustic flow feeding enhancement, resonance destroys bridge, the formation condition of porosity defect is actively intervened in whole process.The application also provides a special device for realizing the above method, including multi-station cooperative ultrasonic application system, auxiliary physical field system, ultrasonic assisted feeding assembly and intelligent control system.Compared with prior art, the application has the advantages of overall significant porosity control effect, no pollution, wide application range and low equipment cost.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, specifically a method and device for controlling porosity defects in castings through the synergistic effect of ultrasound and physical fields. Background Technology

[0002] Porosity refers to the tiny voids formed between dendrites in a casting due to obstruction of microscopic feeding channels during the casting process. Microscopically, it manifests as microscopic cavities between grain boundaries or grain arms, often accompanied by coarse dendritic structures. The formation mechanism of porosity defects involves multiple dimensions, including feeding channel blockage mechanisms, bridging phenomena, and gas precipitation mechanisms. The presence of porosity defects significantly reduces the mechanical properties, airtightness, and pressure resistance of castings, and in severe cases, leads to the scrapping of the casting.

[0003] Currently, the main technologies for preventing and controlling porosity defects include: optimizing mold design, adjusting alloy composition, introducing grain refiners, using heat-insulating risers to improve feeding efficiency, as well as electromagnetic stirring and light pressing technology at the end of solidification.

[0004] The above methods have the following shortcomings: (1) Adding grain refiners will introduce foreign elements, which will have an adverse effect on the purity of the material; (2) Optimizing the gating system and riser design is limited by the casting structure and has limited versatility; (3) Electromagnetic stirring equipment is expensive and has limited effect on deep parts due to the skin effect; (4) Light pressing technology has high requirements for process precision and improper operation will introduce new defects.

[0005] In recent years, ultrasonic technology has demonstrated significant advantages in the field of metal solidification, with its grain refinement mechanism primarily based on cavitation and acoustic flow effects. However, existing ultrasonic treatment technologies are mainly used for grain refinement, with porosity improvement mentioned only as a secondary effect, lacking a systematic ultrasonic process method for porosity control. More importantly, existing ultrasonic casting technologies mostly involve single ultrasonic field treatments, with limited scope of application, and are ineffective for controlling porosity in large castings or deep areas. For example, the ultrasonic resonance device for cast billets (CN205989042U) addresses the "bridging phenomenon" in continuously cast billets by using ultrasound to induce resonance in the two-phase regions within the billet, thus disrupting the bridging; however, it only solves the single problem of bridging.

[0006] Ultrasonic-assisted feeding riser structure (CN120190313A): It uses an ultrasonic receiver to transmit vibration to the riser sleeve to improve the feeding effect, but only focuses on the riser area.

[0007] A method for improving shrinkage porosity defects in die-cast steel ingots (CN121223020A): combining axial pressure pulses with multi-frequency ultrasonic vibration to simultaneously break dendrite bridging, refine grains, and enhance feeding. Its core innovation is "staged gradient deceleration casting and flow replenishment operation," with ultrasound serving only as an auxiliary means.

[0008] The apparatus and method for improving the quality of ingots cast by lower casting method using ultrasound (CN109692941A) mentions both cavitation effect and bridging failure, but the process is a single-stage continuous vibration and there is no multi-mode staged collaborative strategy.

[0009] There is a lack of systematic methods and devices in the current technology that take looseness elimination as the core objective and utilize the synergistic effect of multiple physical fields to achieve looseness control throughout the entire process from degassing, shrinkage enhancement, tissue refinement to destructive bridging. Summary of the Invention

[0010] To address the problems of existing technologies, this invention provides a method and apparatus for controlling porosity defects in castings through the synergistic effect of ultrasound and physical fields. Porosity defects are treated as a control target independent of grain refinement. At different stages of the entire solidification process of the molten metal, multi-mode ultrasound (continuous ultrasound, pulsed ultrasound, and frequency conversion ultrasound) is used in conjunction with physical fields (at least one of pulsed current, alternating magnetic field, and mechanical vibration). This proactively intervenes in the formation conditions of porosity defects throughout the entire process from four dimensions: degassing and purification, refining the microstructure to prevent channel blockage, acoustic flow compensation and enhancement, and resonance destruction bridging. The effect far surpasses the porosity control effect of a single ultrasonic field.

[0011] This invention provides a method for controlling porosity defects in castings through the synergistic effect of ultrasound and physical fields. During the solidification process of molten metal, a staged multi-mode ultrasonic treatment strategy is employed to actively intervene in the formation conditions of porosity defects throughout the entire process, from four dimensions: degassing and purification, microstructure refinement to prevent blockage of feeding channels, acoustic flow feeding enhancement, and resonance disruption bridging. Furthermore, an auxiliary physical field is simultaneously applied in at least one treatment stage. The staged multi-mode ultrasonic treatment strategy specifically includes: S1: Above the liquidus temperature, continuous ultrasonic waves are applied to the melt for degassing, purification, and homogenization. S2: In the solid-liquid two-phase region stage, variable frequency ultrasonic waves are applied to the melt to break up the growing dendrites and promote feeding. S3: During the final stage of solidification when the feeding channel is about to close, pulsed ultrasonic waves are applied to the casting to disrupt the formation of solidification bridges.

[0012] Further improvements include a frequency of 15–30 kHz for the variable frequency ultrasonic wave and a power of 200 W–5 kW for the power of the pulse ultrasonic wave; and a duty cycle of 30%–80% for the pulse ultrasonic wave.

[0013] In a further improvement, the auxiliary physical field is selected from at least one of pulsed current field, alternating magnetic field, and mechanical vibration field.

[0014] In a further improvement, at least one stage of steps S1 to S3 involves synchronously applying ultrasonic vibration in the riser or feed channel region.

[0015] The present invention also provides a casting porosity defect control device based on the synergistic effect of ultrasound and physical field, for implementing the above-mentioned casting porosity defect control method based on the synergistic effect of ultrasound and physical field, including an ultrasonic application system and a multi-station collaborative control system. The ultrasonic application system includes an amplitude transformer, a transducer, an ultrasonic generator and a tool head connected in sequence. The tool head is inserted into the molten metal. Auxiliary physical field application devices are provided on both sides of the mold containing the molten metal. The multi-station collaborative control system is connected to the amplitude transformer and the auxiliary physical field application devices respectively.

[0016] In a further improvement, the auxiliary physical field application system includes at least one of a pulse current application device, an alternating magnetic field generator, or a mechanical vibration generator.

[0017] In a further improvement, the riser or feeding channel area of ​​the mold is provided with an ultrasonic-assisted feeding component, which includes an ultrasonic receiver base and an absorption layer.

[0018] In a further improvement, the tool head end face is flat, and the amplitude is 10–40 μm.

[0019] In a further improvement, the metal material of the molten metal is selected from any one of aluminum alloy, magnesium alloy, copper alloy, steel, and nickel-based high-temperature alloy. When the molten metal being processed is aluminum alloy or magnesium alloy, the amplitude transformer is made of TC4 titanium alloy. When the molten metal being processed is steel or nickel-based high-temperature alloy, the ultrasonic application system adopts a non-contact electromagnetic ultrasonic excitation device. The non-contact electromagnetic ultrasonic excitation device includes an AC electromagnetic coil disposed above the free surface of the molten metal and a high-frequency AC power supply electrically connected thereto. It uses an alternating electromagnetic field to induce an alternating Lorentz force on the surface of the molten metal to excite ultrasonic waves in the molten metal in a non-contact manner.

[0020] In a further improvement, when the molten metal being processed is steel or a nickel-based superalloy and a contact-type solution is required, the tool head is made of Mo-Al2O3-ZrO2 cermet or SiAlON ceramic.

[0021] This invention achieves systematic control of looseness based on the following four-fold mechanism: The first layer: Cavitation effect refines the microstructure and prevents channel blockage. The collapse of cavitation bubbles generated by ultrasound in molten metal releases shock waves that break up growing dendrites, forming numerous new nucleation sites. This transforms the solidification microstructure from coarse dendrites to fine equiaxed crystals. Equiaxed crystals are less likely to form an interlocking network structure, thus preventing the feeding channels from being blocked. The direct purpose of this refinement is to ensure the unobstructed flow of feeding channels, not merely to improve mechanical properties.

[0022] The second effect: Acoustic flow promotes feeding and homogenization. The acoustic pressure gradient generated when ultrasound propagates in the melt drives macroscopic acoustic flow, promoting the replenishment of liquid metal to the solidification shrinkage area. Studies have shown that ultrasonic vibration can promote liquid feeding, and the feeding effect is most significant when the strong vibration point of the core is at the lower end of the feeding channel of the casting, indicating that precise application of feeding enhancement is required.

[0023] The third effect: Ultrasonic degassing reduces porosity. The cavitation effect induced by ultrasound promotes the precipitation of dissolved hydrogen and the rising of bubbles in the melt. Literature studies have shown that ultrasonic degassing plays a dominant role in suppressing micro-porosity, and this effect is independent of grain refinement—even if the microstructure is fine enough, if the hydrogen content in the melt is too high, hydrogen precipitation during solidification will still form porosity.

[0024] Fourthly: The resonance effect disrupts the bridging phenomenon. When ultrasound acts on the two-phase region inside the billet, it generates a resonance effect, which disrupts the solidification bridge formed by the preferential growth of columnar crystals during solidification. This ensures that the molten steel feeding channel in the liquid phase cavity is unobstructed, reducing the formation of central porosity and dendritic porosity.

[0025] The beneficial effects of this invention are as follows: 1. Comprehensive and significant control of porosity. The treatment systematically intervenes in the porosity formation conditions from four dimensions: degassing and purification, prevention of channel blockage, enhanced feeding, and disruption of bridging, achieving comprehensive control of various porosity defects. Experimental data shows that ultrasonic treatment can reduce the hydrogen content of aluminum alloy castings by more than 26.8%, reduce the porosity area ratio by more than 70%, and lower the ingot porosity rating from level 3 to level 1.

[0026] 2. Clearly defined objectives. Porosity elimination is taken as the core control objective, independent of grain refinement. A dedicated process and apparatus for porosity control have been designed, distinguishing it from existing technologies that prioritize grain refinement while treating porosity improvement as a secondary effect.

[0027] 3. Multi-stage, multi-mode synergistic multiplier effect. The four mechanisms of action are interdependent and progressive: refining the structure provides a smooth channel for feeding, feeding enhancement pushes the liquid metal to the required location, degassing and purification reduce the gas content in the feeding liquid, and disrupting bridging ensures the final unobstructed flow of the feeding channel—together achieving a loosening elimination effect far exceeding that of a single method or simple combination.

[0028] 4. Pollution-free and environmentally friendly. Ultrasonic treatment is a purely physical method that does not require the addition of any chemical refining agents or modifiers, and will not cause pollution to materials or the environment.

[0029] 5. Wide range of applications. Applicable to a variety of metal materials such as aluminum alloys, magnesium alloys, copper alloys, steel, and nickel-based high-temperature alloys, and can be applied to various casting processes such as gravity casting, low-pressure casting, differential pressure casting, continuous casting, and semi-continuous casting. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a process flow diagram of the method of the present invention; Figure 2 A timeline diagram of multi-mode ultrasound phased processing; Figure 3 This is a schematic diagram of the structure of the device of the present invention.

[0032] The numbers in the diagram are: 1-Ultrasonic generator; 2-Transducer; 3-Amplitude bar; 4-Tool head; 5-Mold; 6-Melted metal; 7-Multi-station collaborative control system; 8-Auxiliary physical field application device. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a multi-mode ultrasound staged processing strategy, such as... Figure 1 As shown, the details are as follows: Stage 1 (Liquid Phase): Continuous Ultrasonic Mode. Continuous ultrasonic treatment is used when the molten metal temperature is above the liquidus line. Main objectives: degassing, slag removal, and melt homogenization. Frequency range: 15–25 kHz; amplitude: 15–25 μm. This stage reduces the hydrogen content in the melt from the source, minimizing conditions for porosity.

[0035] The second stage (two-phase region): Variable frequency ultrasonic mode. In the solid-liquid two-phase region of the molten metal, a variable frequency ultrasonic mode is used, with the frequency varying within the range of 15–25 kHz according to a preset pattern. Frequency conversion prevents standing wave blind zones formed at a single frequency, resulting in more uniform ultrasonic coverage. The main objectives of this stage are: breaking up growing dendrites (preventing channel blockage) and promoting feeding. Optionally, an auxiliary physical field can be applied simultaneously to expand the effective range or enhance the feeding driving force.

[0036] The third stage (final stage of solidification): Pulsed ultrasonic mode. During the critical window period at the final stage of solidification when the feeding channel is about to close, a high-energy pulsed ultrasonic mode (pulse duty cycle 30%–80%) is used. The main objective is to disrupt any solidification bridges that may form, ensuring the feeding channel remains open in the final stage.

[0037] Figure 2 The timeline diagram for multi-mode ultrasound processing in stages illustrates the processing sequence and mode switching conditions for continuous ultrasound in the liquid phase region, frequency conversion ultrasound in the two-phase region, and pulse ultrasound at the end of solidification.

[0038] Process parameter scheme: The ultrasonic porosity control device of the present invention, such as Figure 3 As shown, it includes: (1) Ultrasonic application system: including ultrasonic generator 1, transducer 2, amplitude transformer 3 and tool head 4. The ultrasonic generator has an automatic frequency tracking function with a tracking accuracy of ±1 Hz. The end face of the tool head 4 is preferably flat—studies have shown that the axial sound intensity of the tool rod is the greatest, the acoustic flow phenomenon is the most significant, and the suppression of central microporousness is the best.

[0039] (2) Material Scheme for Amplifier Rod 3 (based on the melt temperature of the alloy being processed): For low-melting-point alloy melts such as aluminum alloys and magnesium alloys: the amplifier rod is made of TC4 titanium alloy (Ti-6Al-4V), which has good acoustic performance and corrosion resistance at melt temperatures of 700-800℃. For high-temperature melts such as steel and nickel-based high-temperature alloys: due to the fundamental failure problem of traditional metal amplifier rods in melts above 1500℃—studies have shown that ultrasonic vibrating rods melt once inserted into high-temperature molten steel and cannot work continuously—this device preferentially adopts the following alternative scheme: Scheme A (non-contact electromagnetic ultrasonic excitation device): a high-frequency AC electromagnetic coil is set above the free surface of the melt, and an alternating Lorentz force is induced in the skin layer of the melt surface by the alternating electromagnetic field, so as to excite ultrasonic waves in situ in the melt in a non-contact manner, while naturally having an electromagnetic stirring effect. This scheme fundamentally eliminates the material problems and melt contamination problems of contact amplifier rods. Option B (High-Temperature Contact Alternative Material): When a contact solution is required, the tool head is made of Mo-Al2O3-ZrO2 cermet or SiAlON ceramic, which can withstand ultrasonic vibration and resist erosion in melts above 1500°C.

[0040] (3) Auxiliary physical field application system 8 (optional configuration): including at least one of pulse current application device, alternating magnetic field generation device or mechanical vibration generation device, and disposed on both sides of the mold 5 containing the molten metal 6.

[0041] (4) Ultrasonic Assisted Feeding Assembly: An ultrasonic application device, including an ultrasonic receiver and an absorption layer, is installed in the riser or feeding channel area. The ultrasonic receiver transmits the vibration generated by the ultrasonic generator to the riser sleeve, generating ultrasonic action on the molten metal inside the riser sleeve and enhancing the feeding driving force. The absorption layer is used to prevent the ultrasonic from damaging the sand mold.

[0042] (5) Multi-station collaborative control system 7: For large castings or multi-point processing requirements, multiple ultrasonic transmitters and / or auxiliary physical field application devices are configured. The parameters of each device can be adjusted independently, and collaborative work is achieved through a central controller. The vibration position can be dynamically adjusted according to the solidification process to ensure that the ultrasonic energy is accurately projected onto the key area of ​​the feeding channel—studies have shown that the feeding enhancement effect of ultrasound is highly dependent on whether the vibration position is accurately located in the feeding channel area.

[0043] The present invention will be further illustrated by the following specific embodiments.

[0044] Example 1 (Ultrasonic porosity control of aluminum alloy gravity castings): Taking ZL205A aluminum alloy gravity castings as an example, at a pouring temperature of 720℃, an ultrasonic tool head was immediately inserted into the molten metal at the riser position of the casting for three-stage multi-mode ultrasonic treatment. Process parameters: First stage (liquid phase region, 710–650℃): continuous ultrasonic mode, frequency 20 kHz, power 160 W, amplitude 20 μm, treatment time 3 min; Second stage (two-phase region, 650–600℃): variable frequency ultrasonic mode, frequency scanning within the range of 18–22 kHz, power 200 W, amplitude 18 μm, treatment time 5 min; Third stage (before the feeding channel is closed): pulsed ultrasonic mode, frequency 20 kHz, power 300 W, pulse duty cycle 50%, pulse frequency 2 Hz, treatment time 2 min; Tool head insertion depth: 30 mm below the riser molten metal surface; Tool head end face was flat. Results: After ultrasonic treatment, the porosity defect area ratio of the hot spot of the casting is reduced by more than 70%, the grain size is refined to less than 50% of that of the untreated casting, and the mechanical properties (tensile strength and elongation) of the casting body are improved by more than 15%.

[0045] Example 2 (Ultrasonic porosity control of semi-continuous casting ingots of aluminum alloy): Using 7005 aluminum alloy semi-continuous water-cooled DC casting ingots as the subject, a three-stage multi-mode ultrasonic treatment was applied to the melt within the crystallizer. Process parameters: ultrasonic frequency 18 kHz, employing a continuous / variable frequency / pulse multi-mode strategy; power 1–1.5 kW; treatment time covering the entire casting process; tool head made of TC4 titanium alloy with a flat end face. Results: After ultrasonic treatment, the grain size at the ingot edge decreased from 200 μm to 100 μm; the grain size in the center decreased from 100 μm to 80 μm; hydrogen content decreased by 26.8%; the ingot porosity rating decreased from level 3 before treatment to level 1, and central porosity was essentially eliminated.

[0046] Example 3 (Ultrasonic porosity control of continuously cast steel billets): Using continuously cast steel billets as the target, a non-contact electromagnetic ultrasonic excitation device is arranged at the roller table of the continuous casting machine to apply multi-mode ultrasonic treatment to the billets in the two-phase region. Process parameters: The frequency of the electromagnetic ultrasonic excitation coil is precisely tuned to the acoustic resonance frequency of the billet-crystallizer system (approximately 15–18 kHz); input power is 2–4 kW, and the coil is forced water-cooled; the second stage uses a frequency conversion mode, and the third stage switches to pulse mode. Results: After ultrasonic treatment, the porosity rating of the billet center is reduced by 1–2 grades, center segregation is significantly reduced, and the incidence of centerline cracks after rolling is greatly reduced. The non-contact solution fundamentally avoids the erosion and contamination problems of traditional amplitude transformers in molten steel at 1500℃.

[0047] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, for the device embodiments, the above descriptions are merely preferred embodiments of the present invention. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple, and relevant parts can be referred to the descriptions of the method embodiments. The above descriptions are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, without departing from the principle of the present invention, should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for controlling porosity defects in castings through the synergistic effect of ultrasound and physical fields, characterized in that: During the solidification process of molten metal, a staged multi-mode ultrasonic treatment strategy is adopted to actively intervene in the formation conditions of porosity defects throughout the entire process from four dimensions: degassing and purification, refining the microstructure to prevent blockage of the feeding channels, enhancing acoustic flow feeding, and resonant destructive bridging. Furthermore, an auxiliary physical field is applied simultaneously in at least one treatment stage. Specifically, the staged multi-mode ultrasonic treatment strategy is as follows: S1: Above the liquidus temperature, continuous ultrasonic waves are applied to the melt for degassing, purification, and homogenization. S2: In the solid-liquid two-phase region stage, variable frequency ultrasonic waves are applied to the melt to break up the growing dendrites and promote feeding. S3: During the final stage of solidification when the feeding channel is about to close, pulsed ultrasonic waves are applied to the casting to disrupt the formation of solidification bridges.

2. The method for controlling casting porosity defects by synergistic effect of ultrasound and physical field according to claim 1, characterized in that: The frequency of the variable frequency ultrasonic wave is 15-30kHz, and the power is 200W-5kW; the duty cycle of the pulse ultrasonic wave is 30%-80%.

3. The method for controlling casting porosity defects by synergistic effect of ultrasound and physical field according to claim 1, characterized in that: The auxiliary physical field is selected from at least one of pulsed current field, alternating magnetic field, and mechanical vibration field.

4. The method for controlling casting porosity defects by synergistic effect of ultrasound and physical field according to claim 1, characterized in that: In at least one of steps S1 to S3, ultrasonic vibration is synchronously applied in the riser or feed channel region.

5. A device for controlling casting porosity defects through the synergistic effect of ultrasound and physical fields, used to implement the method for controlling casting porosity defects through the synergistic effect of ultrasound and physical fields as described in any one of claims 1-4, characterized in that: The system includes an ultrasonic application system and a multi-station collaborative control system. The ultrasonic application system includes an amplitude transformer, a transducer, an ultrasonic generator, and a tool head connected in sequence. The tool head is inserted into the molten metal. Auxiliary physical field application devices are provided on both sides of the mold containing the molten metal. The multi-station collaborative control system is connected to the amplitude transformer and the auxiliary physical field application devices respectively.

6. The casting porosity defect control device based on the synergistic effect of ultrasound and physical field according to claim 5, characterized in that: The auxiliary physical field application system includes at least one of a pulse current application device, an alternating magnetic field generator, or a mechanical vibration generator.

7. The casting porosity defect control device based on the synergistic effect of ultrasound and physical field as described in claim 5, characterized in that: The riser or feeding channel area of ​​the mold is provided with an ultrasonic-assisted feeding component, which includes an ultrasonic receiver base and an absorption layer.

8. The casting porosity defect control device based on the synergistic effect of ultrasound and physical field according to claim 5, characterized in that: The tool head has a flat end face and an amplitude of 10–40 μm.

9. The casting porosity defect control device based on the synergistic effect of ultrasound and physical field according to claim 5, characterized in that: The metal material of the molten metal is selected from any one of aluminum alloy, magnesium alloy, copper alloy, steel, and nickel-based high-temperature alloy. When the molten metal being processed is aluminum alloy or magnesium alloy, the amplitude transformer is made of TC4 titanium alloy. When the molten metal being processed is steel or nickel-based high-temperature alloy, the ultrasonic application system adopts a non-contact electromagnetic ultrasonic excitation device. The non-contact electromagnetic ultrasonic excitation device includes an AC electromagnetic coil set above the free surface of the molten metal and a high-frequency AC power supply electrically connected to it. It uses an alternating electromagnetic field to induce an alternating Lorentz force on the surface of the molten metal to excite ultrasonic waves in the molten metal in a non-contact manner.

10. The casting porosity defect control device based on the synergistic effect of ultrasound and physical field according to claim 5, characterized in that: When the molten metal being processed is steel or a nickel-based superalloy and a contact-type process is required, the tool head is made of Mo-Al2O3-ZrO2 cermet or SiAlON ceramic.

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