Device and method for improving macrosegregation of discontinuous gradient aluminum alloy

Abstract

The invention belongs to the field of metal casting, and particularly relates to a device and method for improving macrosegregation of a discontinuous gradient aluminum alloy. According to the technical scheme, the device for improving the macrosegregation of the discontinuous gradient aluminum alloy comprises a smelting furnace, a discontinuous gradient mold, a copper base and a low-frequency electromagnetic mechanism, the smelting furnace is used for smelting aluminum alloy melt, the discontinuous gradient mold is provided with a plurality of step-shaped mold cavities with symmetrical longitudinal sections, and the low-frequency electromagnetic mechanism is arranged in the mold cavities; the discontinuous gradient mold is placed on the copper base, the copper base and the low-frequency electromagnetic mechanism are both fixedly arranged on the casting platform, the copper base is located in the middle of the low-frequency electromagnetic mechanism, and the low-frequency electromagnetic mechanism is located below the discontinuous gradient mold and used for providing a low-frequency electromagnetic field. According to the device and method for improving the macrosegregation of the discontinuous gradient aluminum alloy, the macrosegregation problem in the solidification process of the complex aluminum alloy of multiple sizes can be solved through a low-frequency electromagnetic mechanism which is simple in structure and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of metal casting, and specifically relates to an apparatus and method for improving macroscopic segregation in discontinuous gradient aluminum alloys. Background Technology

[0002] In traditional gravity casting, after the high-temperature molten metal is poured into a low-temperature mold, a significant temperature gradient decreases from the mold wall towards the ingot center. This thermal field condition dominates the solidification evolution of the ingot. More importantly, this temperature gradient induces the redistribution and macroscopic migration of solute atoms: for solute elements with an equilibrium partition coefficient k < 1, they are continuously expelled from the solid / liquid interface front, resulting in continuous solute enrichment in the liquid phase at the interface front. Due to the density difference caused by changes in composition and temperature, this enriched liquid phase triggers natural convection in the gravitational field, continuously transporting the enriched solute to the ingot center or the final solidification region. This amplifies the microscopic solute redistribution into macroscopic compositional inhomogeneity in the ingot, i.e., macroscopic segregation.

[0003] In aerospace, high-end equipment and other fields, gravity casting is often used to form large and complex structural parts and thin-walled components. To address the problem of macroscopic segregation, existing research mainly focuses on two aspects: process parameter control and external field assistance. The former includes optimizing pouring temperature and mold temperature; the latter covers methods such as centrifugal force fields, gravity-directed solidification, and composite mold motion. The core idea is to control the solidification process and suppress the flow of solute-rich liquid driven by composition and temperature inhomogeneity.

[0004] However, existing improvement technologies all have certain limitations. Taking patent CN112828250A as an example, it employs a combination of toroidal and directional magnetic fields to induce shear flow in the unsolidified melt, thereby refining grains and suppressing segregation. While this method is effective and allows for non-contact processing, it suffers from problems such as complex equipment, high cost, and difficulty in process control, making it difficult to promote in conventional industries. Other methods also have their shortcomings: for example, process parameter optimization has limited effectiveness for complex castings; electromagnetic stirring can easily cause new defects such as "bright white bands"; gravity / centrifugal casting is limited by the shape of the casting; ultrasonic treatment carries the risk of probe contamination; and gravity-directed solidification requires significant equipment modification. Therefore, in actual production, a comprehensive balance must be struck based on specific casting requirements, cost, and equipment conditions; a universally applicable solution has not yet been formed. Summary of the Invention

[0005] This invention provides an apparatus and method for improving macrosegregation in discontinuous gradient aluminum alloys. It can improve the macrosegregation problem in the solidification process of complex aluminum alloys of multiple sizes by using a low-frequency electromagnetic mechanism with simple structure and low cost.

[0006] The technical solution of the present invention is as follows: An apparatus for improving macroscopic segregation in discontinuous gradient aluminum alloys includes a melting furnace, a discontinuous gradient mold, a copper base, and a low-frequency electromagnetic mechanism. The melting furnace is used to melt the aluminum alloy. The discontinuous gradient mold has multiple stepped cavities with symmetrical longitudinal sections. The discontinuous gradient mold is placed on the copper base. The copper base and the low-frequency electromagnetic mechanism are both fixedly mounted on a casting platform. The copper base is located in the middle of the low-frequency electromagnetic mechanism, which is located below the discontinuous gradient mold to provide a low-frequency electromagnetic field.

[0007] Furthermore, in the aforementioned device for improving macroscopic segregation of discontinuous gradient aluminum alloys, the low-frequency electromagnetic device includes a housing and a coil. The coil is arranged in two parallel winding states inside the housing. The coil is formed by connecting hollow copper tubes in series to form a circuit. The copper tubes are provided with an inlet and an outlet. Cooling water flows in the copper tubes to cool the coil during the energization process.

[0008] A method for improving macrosegregation in discontinuous gradient aluminum alloys, utilizing the aforementioned apparatus for improving macrosegregation in discontinuous gradient aluminum alloys, includes the following steps: 1) Preheating of discontinuous gradient mold; 2) Preparation of the smelting furnace; 3) The materials for preparing the aluminum alloy are smelted in a melting furnace to obtain molten aluminum alloy; 4) Turn on the power to the low-frequency electromagnetic mechanism to generate an induced magnetic field symmetrical about the axis of the discontinuous gradient mold. 5) Pour the molten aluminum alloy into the cavity of a discontinuous gradient mold, cool for 10-15 minutes, and then air-cool to room temperature to obtain an aluminum alloy ingot with a discontinuous gradient structure.

[0009] Furthermore, in the method for improving macrosegregation of discontinuous gradient aluminum alloys, in step 1), the discontinuous gradient mold is heated and kept at a temperature of 300~400°C in a drying oven for 1~2 hours.

[0010] Furthermore, in the method for improving macrosegregation of discontinuous gradient aluminum alloys, in step 2), the smelting furnace is cleaned; firstly, it is kept at a high temperature of 600℃~700℃ for 30~60 minutes; then it is lowered to a low temperature of 200℃~300℃; and finally, boron nitride coating is sprayed on.

[0011] Furthermore, in the method for improving macrosegregation in discontinuous gradient aluminum alloys, in step 3), the composition of the aluminum alloy by mass percentage includes: 4.6–4.65% Zn, 1.2–1.25% Mg, 0.49–0.51% Mn, 0.1–0.12% Cu, 0.1–0.13% Zr, with the balance being Al and unavoidable impurities. The total mass percentage of unavoidable impurities is ≤0.1%, and the mass percentage of a single impurity is ≤0.03%.

[0012] Furthermore, in the method for improving macrosegregation of discontinuous gradient aluminum alloys, step 3) involves preparing aluminum alloys using materials including pure aluminum, pure zinc, pure magnesium, electrolytic copper plate, manganese agent, and Al-5Zr master alloy.

[0013] Furthermore, in the method for improving macroscopic segregation of discontinuous gradient aluminum alloys, in step 3), pure aluminum is smelted in a melting furnace to obtain molten metal, and pure zinc, pure magnesium, electrolytic copper plate, manganese agent and Al-5Zr master alloy are added. After degassing and slag removal, the mixture is kept at a constant temperature and allowed to stand. The process of adding pure zinc, pure magnesium, electrolytic copper plate, manganese agent and Al-5Zr master alloy is as follows: temperature 740℃~750℃, time 5~10min; degassing temperature 730~740℃, time 10~15min; standing time 15min.

[0014] Furthermore, in the method for improving macrosegregation of discontinuous gradient aluminum alloys, in step 4), the electromagnetic parameters of the low-frequency electromagnetic mechanism are: frequency of 20Hz, current intensity of 0~400A, and time of 10~15min.

[0015] The beneficial effects of this invention are as follows: 1. This invention designs a low-frequency electromagnetic mechanism, which is applied to a discontinuous gradient mold to ensure that multi-sized ingots are subjected to a magnetic field during solidification. It provides a novel device and method that is cost-controllable, easy to operate, applicable to complex multi-sized configurations, and does not contaminate the melt.

[0016] 2. The magnetic field generated by the low-frequency electromagnetic mechanism of the present invention induces forced flow, which on the one hand homogenizes the temperature and solute field of the melt and removes the solute enriched at the solidification front; on the other hand, it violently washes away the growing dendrites, breaking them down and making them new nucleation points, ultimately significantly refining the grains, promoting the formation of equiaxed crystals, improving the uniformity of the structure, and greatly reducing macroscopic segregation.

[0017] 3. This invention achieves the goal of controlling discontinuous gradient aluminum alloy materials, solving the problem of poor microstructure and property uniformity in complex multi-sized ingots and subsequent processed products in gravity casting, making it suitable for industrial applications. Compared with existing technologies, the equipment used is all conventional and general-purpose, the process design is reasonable, the operation is simple, and it is easy to promote and apply, greatly saving experimental costs and test cycles. Under the same casting conditions, aluminum alloy materials of different ingot sizes were obtained on a single mold, ensuring the scientific, reliable, and reasonable comparison of the microstructure and properties of the alloy materials, resulting in a significant reduction in experimental costs and test cycles, and possessing important theoretical significance and practical application value. Attached Figure Description

[0018] Figure 1 A schematic diagram of an apparatus for improving macrosegregation in discontinuous gradient aluminum alloys; Figure 2 A schematic diagram showing the induced magnetic field generated by a low-frequency electromagnetic mechanism acting on the molten aluminum alloy in a discontinuous gradient mold. Figure 3 This is a macroscopic photograph of the aluminum alloy ingot cast without electricity in Example 1, showing the low-frequency electromagnetic mechanism. Figure 4 This is a macroscopic microstructure photograph of the aluminum alloy ingot cast with a current intensity of 60A for the low-frequency electromagnetic mechanism in Example 2. Figure 5 This is a macroscopic microstructure photograph of the aluminum alloy ingot cast with a current intensity of 90A for the low-frequency electromagnetic mechanism in Example 3. Figure 6 This is a schematic diagram showing the locations for measuring macroscopic segregation of components in aluminum alloy ingots; where 7 is location 1, 8 is location 2, 9 is location 3, and 10 is location 4. Figure 7 for Figure 6 Macroscopic segregation diagram of the composition at position 1 of each aluminum alloy ingot; Figure 8 for Figure 6 Macroscopic segregation diagram of the components at position 2 of each aluminum alloy ingot; Figure 9 for Figure 6 Macroscopic segregation diagram of the components at position 3 of each aluminum alloy ingot; Figure 10 for Figure 6 Macroscopic segregation diagram of the components at position 4 of each aluminum alloy ingot. Detailed Implementation

[0019] like Figure 1 , 2As shown, an apparatus for improving macroscopic segregation in discontinuous gradient aluminum alloys includes a melting furnace 2, a discontinuous gradient mold 3, a copper base 4, and a low-frequency electromagnetic mechanism. The melting furnace 2 is used to melt the aluminum alloy molten liquid 1. The discontinuous gradient mold 3 has multiple stepped cavities with symmetrical longitudinal sections. The discontinuous gradient mold 3 is placed on the copper base 4. Both the copper base 4 and the low-frequency electromagnetic mechanism are fixedly mounted on a casting platform. The copper base 4 is located in the middle of the low-frequency electromagnetic mechanism, which is located below the discontinuous gradient mold 3 to provide a low-frequency electromagnetic field. The low-frequency electromagnetic device includes a housing 5 and coils 6. The coils 6 are arranged in two parallel wound configurations inside the housing 5. The coils 6 are formed by connecting hollow copper tubes in series to form a circuit. The copper tubes have inlet and outlet ports, and cooling water flows in the copper tubes to cool the coils 6 during energization. The low-frequency electromagnetic mechanism generates an induced magnetic field symmetrical about the ingot axis. The direction of the magnetic field lines of the low-frequency electromagnetic mechanism is determined according to the coils 6 and the winding configuration. Example 1

[0020] A method for improving macrosegregation in discontinuous gradient aluminum alloys includes the following steps: 1) Clean the surface of the discontinuous gradient mold 3, and then heat the discontinuous gradient mold 3 in a drying oven at a temperature of 280℃ for 1 hour. 2) Clean the smelting furnace 2, then heat it to 650℃ and hold it for 60 minutes; then lower it to a low temperature of 200℃~300℃, and finally spray it with boron nitride coating. 3) The aluminum alloy composition by mass percentage is: 4.6% Zn, 1.2% Mg, 0.5% Mn, 0.1% Cu, 0.1% Zr, with the remainder being Al. Pure aluminum is smelted in melting furnace 2 to obtain molten liquid 1. Pure zinc, pure magnesium, electrolytic copper plate, manganese agent, and Al-5Zr master alloy are added. The process of adding pure zinc, pure magnesium, electrolytic copper plate, manganese agent, and Al-5Zr master alloy is as follows: temperature 740℃~750℃, holding time 10min; hexachloroethane is added for degassing and refining, degassing temperature 730~740℃, holding time 15min; slag is removed, and the mixture is held at the same temperature for 15min. 4) The power supply to the low-frequency electromagnetic mechanism is not connected; 5) Pour the molten aluminum alloy 1 into the cavity of the discontinuous gradient mold 3, cool for 10 minutes, and then remove and air-cool to room temperature to obtain an aluminum alloy ingot with a discontinuous gradient structure.

[0021] The macroscopic microstructure variation of the aluminum alloy ingot prepared in this embodiment is as follows: Figure 3 As shown; by Figure 3It can be seen that, under the condition of a certain casting process, when the aluminum alloy ingot size is the same, that is, at the position of the aluminum alloy ingot corresponding to the inner cavity of the same mold section, the microstructure change pattern from the edge to the center of the aluminum alloy ingot at this position is basically the same; when the aluminum alloy ingot size is different, that is, at the position of the aluminum alloy ingot corresponding to the inner cavity of different mold sections, the grain size of the edge and the center of the aluminum alloy ingot at these different positions is inconsistent, and the orientation of columnar crystals is more obvious in the mold section with smaller ingot size. Example 2

[0022] The difference from Example 1 is that the aluminum alloy composition by mass percentage is: 4.63% Zn, 1.25% Mg, 0.51% Mn, 0.11% Cu, 0.13% Zr, with the remainder being Al and unavoidable impurities; before casting, the power supply of the low-frequency electromagnetic mechanism is turned on with a current intensity of 60A to generate an induced magnetic field symmetrical about the ingot axis, and casting is carried out after the magnetic field stabilizes.

[0023] The macroscopic microstructure of the aluminum alloy ingot obtained in this embodiment is shown in the photograph. Figure 4 As shown; by Figure 4 It can be seen that the organizational change pattern is consistent with that of Example 1. Compared with Example 1, for ingots of the same size, the size of the equiaxed crystals in the core of large ingots is smaller and the area is larger, while the columnar crystals have a certain directionality for small ingots. Example 3

[0024] The difference from Example 2 is that the aluminum alloy composition by mass percentage is: 4.64% Zn, 1.22% Mg, 0.49% Mn, 0.12% Cu, 0.11% Zr, with the remainder being Al and unavoidable impurities; before casting, the power supply of the low-frequency electromagnetic mechanism is turned on with a current intensity of 90A to generate an induced magnetic field symmetrical about the ingot axis, and casting is carried out after the magnetic field stabilizes.

[0025] The macroscopic microstructure of the aluminum alloy ingot obtained in this embodiment is shown in the photograph. Figure 5 As shown; by Figure 5 As can be seen, consistent with the organizational change pattern of Example 2, compared with Example 2, at locations with consistent ingot size, the boundary between columnar crystals and equiaxed crystals is more obvious for large-sized ingots, while the directionality of columnar crystals is more obvious for small-sized ingots, and the area of ​​equiaxed crystals is reduced.

[0026] like Figure 6 As shown, samples were taken from the aluminum alloy ingots obtained in Examples 1-3 at positions 7, 8, 9, and 10 for macroscopic component segregation measurement.

[0027] like Figure 7As shown, as the current intensity increases from 0A to 60A, the variation range of Zn content from the edge to the center of the ingot, ΔC, decreases significantly from 0.251 to 0.185. This indicates that the forced melt convection under the action of the electromagnetic field effectively breaks up the dendrite arms and homogenizes the solute field, thereby greatly improving macroscopic segregation. When the current continues to increase to 90A, ΔC is 0.184, and the improvement effect tends to saturate. This is mainly because the central region of the ingot is far from the source of the magnetic field, and the influence of the electromagnetic force has reached a stable state. Further increasing the current intensity has a limited effect on homogenizing the composition in this region.

[0028] like Figure 8 As shown, with the current intensity increasing from 0A to 60A and 90A, the variation range ΔC of Zn content from the edge to the center of the ingot decreased from 0.255 to 0.180 and 0.124, respectively, indicating that the degree of macroscopic segregation continuously decreased with increasing current, with the improvement effect of the 90A process being the most significant. This is mainly attributed to the enhanced electromagnetic stirring effect with increasing current: the stronger Lorentz force drives more intense melt convection, which not only further refines the grains but also more effectively promotes the uniform distribution of solute elements. It is particularly noteworthy that, because the No. 2 position of the ingot is closer to the magnetic field source, it is more directly and strongly affected by electromagnetic stirring, so the improvement effect of increasing the current intensity on the compositional homogenization in this region is particularly significant.

[0029] like Figure 9 As shown, with the current intensity increasing from 0A to 60A and 90A, the variation range ΔC of Zn content from the edge to the center of the ingot significantly decreased from 0.246 to 0.146 and 0.115, respectively. This indicates that the degree of macroscopic segregation continuously decreases with increasing current intensity, and the improvement effect of the 90A process is the most significant. This phenomenon is mainly attributed to the effect of the low-frequency electromagnetic field: the increase in current strengthens the Lorentz force induced by the electromagnetic field, thereby driving the melt to form more intense forced convection. Since position 3 of the ingot is closer to the magnetic field source, the electromagnetic force felt in this region is significantly enhanced, and the melt flow is more significant. Therefore, the effect of increasing the current intensity on improving the compositional homogenization in this region is also more obvious.

[0030] like Figure 10 As shown, with the current intensity increasing from 0A to 60A and 90A, the variation range ΔC of Zn content from the edge to the center of the ingot gradually decreased from 0.178 to 0.143 and 0.122, indicating that the degree of macroscopic segregation continuously decreases with increasing current, and the improvement effect of the 90A process is the best. This phenomenon is mainly attributed to the enhancement of electromagnetic stirring: the increase in current strengthens the Lorentz force, and the forced convection of the melt is more intense, thereby more effectively breaking up dendrites and homogenizing the solute field. In particular, since position 4 of the ingot is closest to the magnetic field source, the melt in this region is subjected to the strongest electromagnetic stirring, and therefore the improvement effect of increasing the current intensity on its compositional homogenization is also the most significant.

Claims

1. An apparatus for improving macroscopic segregation in discontinuous gradient aluminum alloys, characterized in that, The device includes a smelting furnace, a discontinuous gradient mold, a copper base, and a low-frequency electromagnetic mechanism. The smelting furnace is used to melt aluminum alloy. The discontinuous gradient mold has multiple stepped cavities with symmetrical longitudinal sections. The discontinuous gradient mold is placed on the copper base. The copper base and the low-frequency electromagnetic mechanism are both fixedly mounted on a casting platform. The copper base is located in the middle of the low-frequency electromagnetic mechanism, which is located below the discontinuous gradient mold to provide a low-frequency electromagnetic field.

2. The apparatus for improving macroscopic segregation in discontinuous gradient aluminum alloys according to claim 1, characterized in that, The low-frequency electromagnetic device includes a housing and a coil. The coil is arranged inside the housing in two parallel windings. The coil is formed by connecting hollow copper tubes in series to form a circuit. The copper tubes are provided with an inlet and an outlet. Cooling water flows in the copper tubes to cool the coil during the energization process.

3. A method for improving macroscopic segregation in discontinuous gradient aluminum alloys, characterized in that, The apparatus for improving macroscopic segregation in discontinuous gradient aluminum alloys as described in claim 1 or 2 includes the following steps: 1) Preheating of discontinuous gradient mold; 2) Preparation of the smelting furnace; 3) The materials for preparing the aluminum alloy are smelted in a melting furnace to obtain molten aluminum alloy; 4) Turn on the power to the low-frequency electromagnetic mechanism to generate an induced magnetic field symmetrical about the axis of the discontinuous gradient mold. 5) Pour the molten aluminum alloy into the cavity of a discontinuous gradient mold, cool for 10-15 minutes, and then air-cool to room temperature to obtain an aluminum alloy ingot with a discontinuous gradient structure.

4. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 3, characterized in that, In step 1), the discontinuous gradient mold is heated and kept warm in a drying oven at a temperature of 300~400°C for 1~2 hours.

5. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 3, characterized in that, In step 2), the smelting furnace is cleaned; first, it is kept at a high temperature of 600℃~700℃ for 30~60 minutes; then it is lowered to a low temperature of 200℃~300℃; and then boron nitride coating is sprayed on.

6. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 3, characterized in that, In step 3), the aluminum alloy composition by mass percentage includes: 4.6–4.65% Zn, 1.2–1.25% Mg, 0.49–0.51% Mn, 0.1–0.12% Cu, 0.1–0.13% Zr, with the balance being Al and unavoidable impurities. The total mass percentage of unavoidable impurities is ≤0.1%, and the mass percentage of a single impurity is ≤0.03%.

7. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 6, characterized in that, In step 3), the materials used to prepare the aluminum alloy include pure aluminum, pure zinc, pure magnesium, electrolytic copper plate, manganese agent, and Al-5Zr master alloy.

8. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 7, characterized in that, In step 3), pure aluminum is smelted in a smelting furnace to obtain molten liquid, and pure zinc, pure magnesium, electrolytic copper plate, manganese agent and Al-5Zr master alloy are added. The liquid is degassed and slag is removed, and it is kept warm and allowed to stand. The process of adding pure zinc, pure magnesium, electrolytic copper plate, manganese agent and Al-5Zr master alloy is as follows: temperature 740℃~750℃, time 5~10min; degassing temperature 730~740℃, time 10~15min; standing time 15min.

9. The method for improving macrosegregation in discontinuous gradient aluminum alloys according to claim 3, characterized in that, In step 4), the electromagnetic parameters of the low-frequency electromagnetic mechanism are: frequency of 20Hz, current intensity of 0~400A, and time of 10~15min.

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