A method for semi-continuous casting of light alloy rods by multi-field coupling assisted hot top

Abstract

The present invention relates to the field of metal material preparation, and specifically to a method for multi-field coupling assisted hot top semi-continuous casting of light alloy casting rods. A method for multi-field coupling assisted hot top semi-continuous casting of light alloy casting rods, the system used includes an ultrasonic interference head, a melt flow channel, a crystallizer, a directional electromagnetic homogenizer, a screw traction system, a melt furnace and a temperature field adjustment system, the crystallizer is installed below the end of the melt flow channel; the directional electromagnetic homogenizer is installed on the periphery of the crystallizer. The present invention solves the problems of segregation, coarse grains, and uneven composition during the solidification process of light alloy casting billets, while increasing the central equiaxed crystal ratio, effectively eliminating intermediate cracks, and improving the problem of micro-loose defects in the solidification structure of light alloy casting billets; it can effectively improve the processing performance of subsequent products, improve material utilization, and significantly reduce production costs. At the same time, the product quality is high, and the performance can meet the design requirements of aerospace and military fields for high performance and lightweight.

Description

Technical Field

[0001] The invention relates to the field of metal material preparation, and in particular to a method for multi-field coupling assisted hot top semi-continuous casting of light alloy casting rods. Background Art

[0002] The hot top casting process is currently the main way to prepare large-sized metal billets in the industry. In the traditional process, the molten metal is melted into a light alloy melt in the smelting furnace and quickly transferred to the diversion trough. When the temperature reaches the pouring temperature, the molten metal flows into the crystallizer. The liquid metal melt contacts the bottom ingot head and the graphite ring on the inner wall of the crystallizer to form a solidified shell. Due to solidification shrinkage, the metal gradually separates from the graphite ring on the inner wall of the crystallizer to form a gap. The traction system is started, and the traction ingot head moves downward at a certain speed and contacts the cooling water sprayed from the lower end of the crystallizer. Under the secondary cooling effect of the cooling water, the entire ingot gradually solidifies and the alloy test rod is stretched out.

[0003] The patent document with the publication number of "CN 100534669C" discloses "Vertical semi-continuous casting method and equipment for light alloy ingots with synergistic effect of power ultrasound and low-frequency electromagnetic". In this method, it is believed that the electromagnetic field or ultrasound acts on a limited area respectively, the electromagnetic field mainly acts on the surface area, and the ultrasonic field mainly acts on the central area. The single application of the two external fields cannot achieve the full volume effect of the melt, and it is difficult to completely eliminate the coarse product area and dendrite area of ​​the ingot. Therefore, in this method, a low-frequency electromagnetic field and a power ultrasonic field or a low-frequency electromagnetic oscillation field and a power ultrasonic field are applied simultaneously during the casting process, and the synergistic effect is achieved by adjusting the parameters of the two external fields, so that the full volume external field effect is achieved during the solidification process of the crystallizer melt for casting.

[0004] The applied ultrasonic frequency was 18kHz to 28kHz, and the ultrasonic intensity was 3W / cm 2 ~50W / cm 2 The effective time of ultrasound is 5s to 180s, and the high-power ultrasonic field acts on the axis of the crystallizer through the ultrasonic rod.

[0005] The applied low-frequency electromagnetic frequency ranges from 1 Hz to 90 Hz, the intensity is from 2000AT to 40000AT, the static magnetic field intensity is from 1500AT to 30000AT, and the electromagnetic field mainly acts near the surface of the metal melt due to the skin effect.

[0006] The melt temperature in the casting tundish is controlled at 50°C to 100°C higher than the liquidus temperature, and the casting speed is 20mm / min to 300mm / min.

[0007] However, the study found that the problems with this method are: 1. For light alloys with a wide crystallization range, thick dendrites are easily formed during solidification, which affects the shrinkage compensation of the light alloy solution. In addition, when preparing large-sized cast rods, deep liquid pockets are easily generated, resulting in central cracks in the cast rods, and the overall cracking tendency of the cast rods is stronger. 2. Since the electromagnetic field of this method only acts on the surface area of ​​the molten metal, such electromagnetic influence on the melt is small, the shape of the liquid pocket does not change significantly, it is difficult to inhibit the formation of dendrites, the solidification structure of the ingot is uneven, and the internal quality of large ingots is not ideal. 3. The ultrasonic field, electromagnetic field and temperature field mentioned in this method act on the molten metal separately, and the improvement of the alloy composition, structure and internal quality is limited, making it difficult to achieve the production of high-quality large-diameter cast rods. Summary of the invention

[0008] The present invention provides a method for semi-continuous casting of light alloy rods by multi-field coupling assisted hot top, so as to solve the problems in the prior art that the shape of liquid cavity is not obviously changed, the formation of dendrites is difficult to inhibit and the casting of large diameter rods is difficult to realize.

[0009] In order to achieve the above-mentioned object, the technical scheme of the present invention is as follows: a method for semi-continuous casting of light alloy casting rods by multi-field coupling auxiliary hot top, the system used includes an ultrasonic interference head, a melt flow channel, a crystallizer, a directional electromagnetic homogenizer, a screw traction system, a melt furnace and a temperature field adjustment system, the crystallizer is installed below the end of the melt flow channel; the directional electromagnetic homogenizer is installed on the periphery of the crystallizer;

[0010] The method comprises the following steps:

[0011] Step 1: prepare a light alloy according to the alloy composition ratio, obtain a light alloy melt in a smelting furnace, and pour it in a melting furnace at 700-720°C;

[0012] Step 2: The light alloy melt flows into the crystallizer and the directional electromagnetic homogenizer is turned on;

[0013] Step 3: The ultrasonic interference head is inserted into the liquid-solid area in the melt flow channel, and the ultrasonic interference head is turned on. The power of the ultrasonic interference head is 1000-2500W, and the temperature of the light alloy melt in the melt flow channel is adjusted to 660-690°C through the temperature field adjustment system;

[0014] Step 4: Start the lead screw traction system and start to stretch the alloy test rod downward at a speed of 70-100 mm / min to obtain a light alloy casting rod; turn off the ultrasonic interference head and the electromagnetic homogenizer.

[0015] Furthermore, in the above step 2, when the temperature of the molten metal in the melt flow channel is between 680°C and 690°C, a low-frequency electromagnetic is used, namely, 3 to 5 Hz, and the current is 3 to 10A.

[0016] Furthermore, in the above step 2, when the temperature of the molten metal in the melt flow channel is between 660 and 680° C., an electromagnetic frequency of 5 to 10 Hz and a current of 10 to 15 A are used.

[0017] Furthermore, in the above step three, at the beginning of continuous casting, the casting is carried out at a speed of 70 to 80 mm / min. When the continuous casting length is 5 to 10 mm, the pulling speed is slowly increased to 90 to 100 mm / min until the continuous casting is completed.

[0018] Furthermore, the electromagnetic homogenizer is a three-phase six-pole circuit phase electromagnetic stirrer.

[0019] Furthermore, the melt flow channel of the electromagnetic homogenizer is divided into two parts by a vertical partition, and the two parts are connected by a screen arranged at the bottom of the partition, and the screen is made of an alumina foam ceramic filter sheet with a PPI of 30 to 40.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] 1. The casting method provided by the present invention is to simultaneously apply an ultrasonic field, an electromagnetic field and a temperature field during the casting process. The ultrasonic field breaks up the dendrites to form more equiaxed grains. The electromagnetic field acts on the entire volume of the molten metal to reduce component segregation, alleviate or eliminate central porosity and central shrinkage. The temperature field realizes directional rapid solidification of the alloy. The coupling effect is achieved by the coordination of the three external field parameters to realize hot top semi-continuous casting of light alloy casting rods.

[0022] One of the core points: the ultrasonic effect of the ultrasonic interference head adopted in the present invention runs through the whole continuous casting process, and is effective from the beginning of the continuous casting production of cast rods to the end of the continuous casting production, ensuring that all dendrites are broken into small dendrites or equiaxed crystals, and the broken small dendrites will not grow into large dendrites again.

[0023] The second core: The present invention selects electromagnetic equipment with stirring function, and optimizes the electromagnetic AC frequency. When the temperature of the molten metal in the melt flow channel is 680-690℃, a low-frequency electromagnetic is used, that is, 3-5Hz, and the current is 3-10A; when the temperature in the melt flow channel decreases to 660-680℃, the electromagnetic frequency can be increased, that is, 5-10Hz, and the current is 10-15A. By increasing the electromagnetic frequency, the electromagnetic heats the melt, ensuring the smooth continuous casting. Under the above frequency, the electromagnetic force generated by the electromagnetic equipment produces radial forced convection on the melt, dispersing the detached crystal nuclei into the melt and forming the nucleation center; promoting the uniformity of the temperature distribution at the front of the solid-liquid interface. The electromagnetic action of the present invention has the dual effects of electromagnetic stirring and electromagnetic oscillation, so it can significantly refine the grains of the solidified structure and significantly improve the uniformity of the composition of high-alloy ingots. Since it can act on the entire volume of the metal melt, it can fully reduce the component segregation, reduce or eliminate the central looseness and central shrinkage.

[0024] The third core: The screen installed at the bottom of the melt flow channel allows the molten metal to flow through the screen part, which can make the liquid level of the metal in the flow channel stable, filter out the tiny oxide inclusions in the molten metal, ensure the cleanliness of the melt, and give full play to the role of the subsequent three fields. The ultrasonic wave will completely break up the dendrites, and the electromagnetic force will ensure the uniformity of the temperature distribution at the front of the solid-liquid interface. The temperature field quickly transfers heat to ensure rapid cooling and promote grain refinement.

[0025] The above core points are combined and work synergistically. While the ultrasonic field acts on the entire area before the metal melt solidifies, the electromagnetic field acts on the entire field, stirring the entire area. After the stretching begins, the continuously rotating light alloy melt needs to be coordinated with a suitable stretching speed to ensure the smooth progress of continuous casting. Under the method of the present invention, when the metal melt solidifies, the liquid cavity depth becomes shallower, and the solidification structure grains are more refined and cut evenly, which solves the problems of segregation, coarse grains, and uneven composition during the solidification process of the light alloy ingot. At the same time, the central equiaxed crystal ratio is increased, the middle cracks are effectively eliminated, and the problem of microscopic loose defects in the solidification structure of the light alloy ingot is improved. .

[0026] 2. The diameter of the cast rod of the present invention is large, which can reach 200 mm, and the length can reach 1500-2000 mm. If the space size of the hot top semi-continuous casting cast rod stretching equipment allows, the cast rod length can be longer. The products cast by the method of the present invention can effectively improve the processing performance of subsequent products, increase material utilization, and significantly reduce production costs. At the same time, the product quality is high, and the performance can meet the design requirements of aerospace and military fields for high performance and lightweight. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a hot top semi-continuous casting device;

[0028] Figure 2 Casting of alloys;

[0029] Figure 3 The metallographic organization diagram of ZL205A, wherein a is the conventional casting, and b is the casting of the present invention;

[0030] Figure 4 : It is a comparison diagram of liquid cavity under different working conditions, wherein a is the liquid cavity state at the beginning of continuous casting by the traditional process, and b is the liquid cavity state at the beginning of continuous casting by the present invention.

[0031] In the figure: 1-ultrasonic interference head, 2-melt flow channel, 3-casting crystallizer, 4-directional electromagnetic homogenizer, 5-hydraulic traction system, 6-melt furnace, 7-temperature field adjustment system, 8-screen. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments and drawings.

[0033] like Figure 1 As shown, a hot top semi-continuous casting device for light alloy casting rods under the multi-field coupling action of ultrasonic field, electromagnetic field and temperature field comprises: an ultrasonic interference head (1), a melt flow channel (2), a crystallizer (3), a directional electromagnetic homogenizer (4), a hydraulic traction system (5), a melt furnace (6) and a temperature field adjustment system (7).

[0034] The directional electromagnetic homogenizer (4) is a three-phase six-pole circuit phase electromagnetic stirrer, which is evenly installed on the periphery of the crystallizer and can act on the entire volume of the light alloy melt to stir the melt.

[0035] The ultrasonic interference head (1) is a high-power ultrasonic device equipped with a high-strength titanium alloy probe. The titanium alloy probe can ensure the cleanliness of the molten metal, and the high-power ultrasonic wave of up to 2500W ensures that all dendrites in the molten metal are broken.

[0036] The electromagnetic homogenizer melt flow channel (2) is divided into two parts by a vertical partition, and the two parts are connected by a screen (8) arranged at the bottom of the partition, and the screen is made of a 30-40PPI aluminum oxide foam ceramic filter.

[0037] Embodiment: A method for semi-continuous casting of light alloy rods by multi-field coupling assisted hot top casting comprises the following steps:

[0038] Step 1: prepare a light alloy in accordance with the alloy composition ratio, obtain a light alloy melt in a smelting furnace (6), and pour the light alloy melt in a melting furnace at 700-720° C.;

[0039] Step 2: The light alloy melt flows into the crystallizer (3), and the directional electromagnetic homogenizer (4) is turned on. When the temperature of the molten metal in the melt flow channel (2) is measured to be 680-690°C, a low-frequency electromagnetic, i.e., 3-5 Hz, and a current of 3-10A are used; when the temperature of the molten metal in the melt flow channel (2) drops to 660-680°C, an electromagnetic frequency of 5-10 Hz and a current of 10-15A are used to increase the electromagnetic frequency, so that the electromagnetic heats the melt, thereby ensuring smooth continuous casting.

[0040] Step 3, the ultrasonic interference head (1) extends into the liquid-solid area in the melt flow channel (2), the power of the ultrasonic interference head (1) is 1000-2500W, and at the same time, the temperature of the light alloy melt in the melt flow channel (2) is adjusted to be maintained at 660-690°C through the temperature field adjustment system (7);

[0041] Step 4: Start the lead screw traction system (5). When continuous casting begins, the speed is 70-80 mm / min. When the continuous casting length is 5-10 mm, the pulling speed is slowly increased to 90-100 mm / min until the continuous casting is completed to obtain the light alloy cast rod. Turn off the ultrasonic interference head (1) and the electromagnetic homogenizer (4). Figure 2 As shown, the diameter is 200mm and the length is 2000mm. Its metallographic structure is as follows Figure 3 As shown by Figure 3 It can be seen that the cast rods produced by continuous casting according to the present invention have finer grains and no obvious defects in the structure. Figure 4 This is a comparison diagram of liquid pockets under different working conditions. It can be seen that after adding ultrasound and electromagnetic, the alloy liquid pockets become shallower, that is, the solid-liquid interface tends to be horizontal, ensuring the uniformity of composition and structure of the same cross-section of the cast rod.

[0042] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes to the concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for semi-continuous casting of light alloy rods by multi-field coupling assisted hot top casting, characterized in that: The system used comprises an ultrasonic interference head (1), a melt flow channel (2), a crystallizer (3), a directional electromagnetic homogenizer (4), a screw traction system (5), a melt furnace (6) and a temperature field adjustment system (7). The crystallizer (3) is installed below the end of the melt flow channel (2); the directional electromagnetic homogenizer (4) is installed on the periphery of the crystallizer (3); The method comprises the following steps: Step 1: prepare a light alloy in accordance with the alloy composition ratio, obtain a light alloy melt in a melting furnace (6), and pour the melt in the melting furnace (6) at 700-720° C.; Step 2: The light alloy melt flows into the crystallizer (3), and the directional electromagnetic homogenizer (4) is turned on; Step 3, the ultrasonic interference head (1) is extended into the liquid-solid zone in the melt flow channel (2), and the ultrasonic interference head (1) is turned on. The power of the ultrasonic interference head (1) is 1000-2500W, and at the same time, the temperature of the light alloy melt in the melt flow channel (2) is adjusted to be maintained at 660-690°C through the temperature field adjustment system (7); Step 4: Start the lead screw traction system (5) and start to pull the alloy test rod downward at a speed of 70-100 mm / min to obtain a light alloy casting rod; turn off the ultrasonic interference head (1) and the electromagnetic homogenizer (4); In the step 2, when the temperature of the molten metal in the melt flow channel (2) is between 680°C and 690°C, a low-frequency electromagnetic wave, i.e., 3 to 5 Hz, is used, and the current is 3 to 10 A; In the step 2, when the temperature of the molten metal in the melt flow channel (2) is between 660 and 680° C., an electromagnetic frequency of 5 to 10 Hz and a current of 10 to 15 A are used; In the step 3, at the beginning of continuous casting, the casting is carried out at a speed of 70-80 mm / min. When the continuous casting length is 5-10 mm, the casting speed is slowly increased to 90-100 mm / min until the continuous casting is completed. The electromagnetic homogenizer (4) is an electromagnetic stirrer with a three-phase six-pole circuit phase.

2. The method for semi-continuous casting of light alloy rods by multi-field coupling assisted hot top casting according to claim 1, characterized in that: The electromagnetic homogenizer melt flow channel (2) is divided into two parts by a vertical partition, and the two parts are connected by a screen (8) arranged at the bottom of the partition, and the screen (8) is made of a 30-40 PPI aluminum oxide foam ceramic filter.

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