Method and device for producing aluminum-alloy ingot

Abstract

To make it possible, in a process to produce an ingot, to reduce the macroscopic segregation of solute elements and inhibit casting cracks together with suppressing the occurrence of an abnormal texture with crystalline grain size micronized, by giving mechanical vibrations to a melt in a novel way.SOLUTION: A method of producing an aluminum-alloy ingot includes a casting process to rotate a predetermined stirrer 3 in a melt of aluminum alloy and solidify a melt while vibrating it. In the casting process, the stirrer is rotated to swing the melt such that a flow having a velocity component perpendicular to the solidification interface of 0.1 m / sec or greater acts upon the solidification interface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for producing an aluminum alloy ingot, and more particularly to a method and apparatus for producing an aluminum alloy ingot that reduces macroscopic segregation of solute elements, refines crystal grain size, suppresses the occurrence of abnormal structures, and suppresses casting cracks by mechanically vibrating the molten metal during the ingot production process. [Background technology]

[0002] For example, sputtering targets are required to have a chemical composition that contains few impurities, to be free of foreign matter such as nonmetallic inclusions, to have a low rate of defects such as voids, and to have uniform and fine crystal grain sizes across the entire sputtering surface, and similar properties are also required of the ingots that are the raw materials for such targets.

[0003] When manufacturing a sputtering target, the target metal is first melted, the composition is adjusted, the molten metal is purified, and the raw material is cast into an ingot. This ingot is then subjected to predetermined plastic working and heat treatment to obtain the sputtering target.

[0004] Furthermore, the crystal grains of the sputtering target are controlled in the processes of plastic working and heat treatment. The finer the crystal grain size of the ingot, the easier this control becomes, and simplifying the processes of plastic working and heat treatment also enables cost reduction.

[0005] In the chemical composition of ingots, which are the raw materials for sputtering targets, the impurity content is low and the frequency of solidification nuclei during the solidification process is low, so the crystal grain size tends to become coarse and abnormal structures such as feathery crystals occur frequently. Furthermore, the contained components are subject to strict regulations, and the addition of metals and their compounds called refiners, which are often used in general alloy ingots, is not permitted.

[0006] However, it is known that the coarse grain size and the presence of abnormal structures in the ingot, which is the material for the sputtering target, have adverse effects such as poor deformation and uneven structure during the plastic processing of the sputtering target, and that they cause solidification stress to concentrate during the solidification process of the ingot, which can lead to ingot cracking. Therefore, in order to improve the quality of sputtering targets, it is necessary to suppress the occurrence of abnormal structures and reduce the grain size.

[0007] In addition, in casting, when a molten metal containing solute elements is solidified, redistribution of the solute occurs, resulting in micro- and macro-segregation of the solute elements. Among these, macro-segregation of the solute elements in particular not only deteriorates the properties of the sputtering target, but can also cause cracking of the ingot. Therefore, reducing the macro-segregation of the solute elements can increase the success rate of the casting process.

[0008] It is already known that the above problems can be improved by mechanically or electromagnetically agitating the molten metal near the solidification interface during the casting process, and one such method has been proposed, for example, in Patent Document 1, entitled "Method for continuous casting of aluminum alloy."

[0009] This conventional "aluminum alloy continuous casting method" employs a combination of ultrasonic vibration and electromagnetic stirring, which applies a time-varying magnetic field to oscillate the molten metal. These methods are used to generate a molten metal flow with a vector parallel to the solidification interface, and processing is performed. Note that ultrasonic vibration is used in the hope of increasing the number of crystal nuclei (solidification nuclei) by applying impact and pressure, rather than generating a molten metal flow with a vector parallel to the solidification interface, as shown in Patent Document 2. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 8-238539 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-045558 Summary of the Invention [Problem to be solved by the invention]

[0011] However, when molten metal is stirred by electromagnetic stirring, even if a molten metal flow including a vector parallel to the solidification interface is generated, feathery crystals may actually occur, and the effect of reducing the crystal grain size to suppress the occurrence of abnormal structures or the effect of reducing the macroscopic segregation of solute elements to suppress casting cracks cannot be said to be sufficient, and sufficient quality of ingots cannot be consistently obtained.

[0012] Furthermore, compared to mechanical stirring, electromagnetic stirring requires expensive equipment and large amounts of electricity, resulting in high costs. Furthermore, a magnetic circuit must be built into the casting machine, and when multiple ingots are cast simultaneously, as is often the case when producing ingots for sputtering targets, sufficient clearance is required to prevent magnetic interference, resulting in a problem of large equipment size. For these reasons, it was also difficult to add molten metal shaking functionality to existing equipment.

[0013] The present invention has been devised in view of the above points, and aims to provide a method and apparatus for producing an aluminum alloy ingot, which reduces macroscopic segregation of solute elements, refines crystal grain size, suppresses the occurrence of abnormal structures, and suppresses casting cracks by mechanically vibrating the molten metal by a method not previously used in the ingot production process. [Means for solving the problem]

[0014] [1] In order to achieve the above object, the present invention provides a method for producing an aluminum alloy ingot, comprising a casting step of rotating a predetermined stirrer in molten aluminum alloy and solidifying the molten aluminum alloy while oscillating the molten aluminum alloy, wherein the casting step rotates the stirrer and oscillates the molten aluminum alloy so as to apply a flow having a velocity component of 0.1 m / sec or more in a direction perpendicular to the solidification interface to the solidification interface.

[0015] According to the method for producing an aluminum alloy ingot of the present invention, the rocking of the molten metal promotes the generation of crystal grains, thereby suppressing grain growth that causes coarsening of the crystal grain size and the growth of abnormal structures. That is, in the present invention, a predetermined stirrer is rotated in the molten aluminum alloy, and the molten aluminum alloy is solidified while being oscillated. As a result, the solidification interface is subjected to a predetermined pressure by the flow of the oscillating molten metal, and therefore, grain growth and the growth of abnormal structures that cause the above-mentioned crystal grain size to become coarse are suppressed.

[0016] Furthermore, by rotating the stirrer and oscillating the molten metal so that a flow with a velocity component of 0.1 m / sec or more in the direction perpendicular to the solidification interface acts on the solidification interface, the oscillating molten metal becomes a flow including a vector perpendicular to the solidification interface, rather than a flow consisting only of vectors parallel to the solidification interface, such as a swirling flow.

[0017] When the velocity of this flow is decomposed into a vector perpendicular to the solidification interface and another vector, the velocity of the former is set to 0.1 m / sec or more. In this case, the stirring effect of the flow also solves the problem of macroscopic segregation of the solute elements.

[0018] This rocking of the molten metal is effective in reducing the grain size, and reduces the grain size without adding a refiner (such as titanium or boron).

[0019] In this way, the present invention mechanically vibrates the molten metal to reduce macroscopic segregation of solute elements, and also applies pressure from the molten metal that includes a vector perpendicular to the solidification interface, thereby refining the crystal grain size and suppressing the occurrence of abnormal structures and casting cracks.

[0020] [2] In the method for producing an aluminum alloy ingot of the present invention, the flow of the molten metal can be applied to any position on the solidification interface.

[0021] In this case, the flow of the molten metal acts on any position on the solidification interface, so that the entire solidification interface of the entire ingot is exposed to a flow of the molten metal that includes a vector perpendicular to the solidification interface. This prevents adverse effects such as ingot cracking caused by the concentration of solidification stress due to coarsening of crystal grains and abnormal structure caused by the low frequency of solidification nuclei generation during the solidification process, as well as poor deformation and uneven structure when plastically deforming the ingot.

[0022] [3] In the method for producing an aluminum alloy ingot of the present invention, the stirring bar may be rotated non-steadily.

[0023] In this case, by rotating the stirrer unsteadily, the rotation direction of the molten metal near the molten metal surface is not constant, which makes it possible to slow the flow near the molten metal surface. Also, by rotating the stirrer unsteadily, the flow of the molten metal can expose the entire solidification interface.

[0024] For example, when the unsteady rotation is the forward / backward rotation of a stirrer that changes the direction of the molten metal flow, the flow directions change to opposite directions and cancel each other out, causing the flow to slow down near the molten metal surface. Also, when the unsteady rotation is the strong / weak rotation of a stirrer that changes the strength of the molten metal flow, the flow repeatedly changes strength, causing it to stagnate and move, making it unstable and likely to slow down the molten metal surface. Furthermore, when the unsteady rotation is the intermittent rotation of a stirrer that changes the timing or time of the molten metal flow, the flow also becomes unstable and likely to slow down the molten metal surface.

[0025] If a "depression on the molten metal surface" occurs due to the rotation of the stirring bar, the oxide film on the molten metal surface will be caught in the depression, causing the aluminum alloy ingot to contain foreign matter. Therefore, by slowing down the flow velocity near the molten metal surface and preventing the occurrence of "depressions on the molten metal surface," it is expected that high-quality aluminum alloy ingots can be obtained.

[0026] [4] In order to achieve the above object, the present invention provides a method for producing an aluminum alloy ingot, comprising a casting step of rotating a predetermined stirrer in molten aluminum alloy and solidifying the molten aluminum alloy while oscillating the molten aluminum alloy, wherein the casting step involves rotating the stirrer in an unsteady state, oscillating the molten aluminum alloy so as to apply a flow including a velocity component perpendicular to the solidification interface to the solidification interface.

[0027] According to the method for producing an aluminum alloy ingot of the present invention, the rocking of the molten metal promotes the generation of crystal grains, thereby suppressing grain growth that causes coarsening of the crystal grain size and the growth of abnormal structures. That is, in the present invention, a predetermined stirrer is rotated non-steadily in the molten aluminum alloy, and the molten aluminum is solidified while being oscillated. As a result, the solidification interface is subjected to a predetermined pressure flow due to the oscillating molten metal, and therefore, grain growth and the growth of abnormal structures that cause the above-mentioned crystal grain size to become coarse are suppressed.

[0028] Furthermore, by rotating the stirrer unsteadily and oscillating the molten metal so that a flow including a velocity component perpendicular to the solidification interface acts on the solidification interface, the oscillating molten metal becomes a flow including a vector perpendicular to the solidification interface, rather than a flow consisting only of vectors parallel to the solidification interface, such as a swirling flow.

[0029] This molten metal oscillation is effective in refining the crystal grain size, and can achieve this without adding refiners (such as titanium or boron). It can also reduce macroscopic segregation of solute elements.

[0030] In this way, the present invention mechanically vibrates the molten metal to reduce macroscopic segregation of solute elements, and also applies pressure from the molten metal that includes a vector perpendicular to the solidification interface, thereby refining the crystal grain size and suppressing the occurrence of abnormal structures and casting cracks.

[0031] Furthermore, according to the present invention, by rotating the stirring bar unsteadily, the rotation direction of the molten metal near the molten metal surface is not kept constant, thereby making it possible to slow the flow near the molten metal surface. Furthermore, by rotating the stirrer unsteadily, the flow of the molten metal can expose the entire solidification interface. As mentioned above, it is expected that a high-quality aluminum alloy ingot can be obtained by slowing down the flow velocity near the molten metal surface and preventing the occurrence of "depressions on the molten metal surface."

[0032] [5] In the method for producing an aluminum alloy ingot of the present invention, the stirring bar may be configured to switch rotation on and off, change the rotation speed, or switch the rotation direction in a cycle of 2 seconds or more and 30 seconds or less.

[0033] Here, if the cycle of switching the rotation on and off, changing the rotation speed, or switching the rotation direction (hereinafter referred to as the "switching cycle") is "less than 2 seconds," the flow caused by the rotation of the stirrer cannot be sufficiently imparted to the molten metal, and may only affect a part of the solidification interface.

[0034] On the other hand, when the switching period exceeds 30 seconds, the molten metal may become a steady flow and may only act on a part of the solidification interface. Therefore, in order to make the flow of the molten metal act on all positions of the solidification interface, it is preferable that the switching period be 2 seconds or more and 30 seconds or less.

[0035] [6] In the method for producing an aluminum alloy ingot of the present invention, the stirrer has a predetermined rotating shaft and a rotating blade attached to the rotating shaft and rotating with the rotation of the rotating shaft, and the casting step can also rotate the rotating shaft with a predetermined baffle positioned between the surface of the molten metal and the rotating blade.

[0036] In this case, a predetermined straightening plate is positioned between the surface of the molten metal and the rotating blades, which prevents the molten metal from being drawn in from above the stirrer, thereby preventing the molten metal surface from becoming depressed. Also, the flow of the molten metal generated by the stirrer can be concentrated between the stirrer and the solidification interface, improving the stirring efficiency near the solidification interface.

[0037] Furthermore, when a swirling flow is generated by the rotation of the stirrer, the flow is transmitted in the direction of the molten metal surface (upward) due to friction with the molten metal, causing the vortex to draw in the molten metal surface (resulting in a "depression in the molten metal surface"). However, if a baffle is positioned between the molten metal surface and the rotating blades, it is possible to prevent the generation of a molten metal drawing in flow from above the stirrer. Furthermore, since the transmission of the swirling flow in the direction of the molten metal surface due to the rotation of the stirrer is inhibited, it is also expected to have the effect of suppressing the generation of vortexes near the molten metal surface.

[0038] From these facts, it can be assumed that when a baffle is placed between the molten metal surface and the rotating blades, the effect of stirring above the stirrer will be reduced. In other words, it is expected that the majority of the energy used for stirring will be applied below the stirrer (near the solidification interface), thereby improving stirring efficiency.

[0039] [7] In the method for producing an aluminum alloy ingot of the present invention, the casting step may also include rotating the stirrer while a predetermined straightening plate is positioned on the surface of the molten metal.

[0040] In this case, a predetermined straightening plate is positioned on the surface of the molten metal, so that the drawing of the molten metal from above the stirrer is suppressed, thereby suppressing depressions in the molten metal surface.

[0041] Furthermore, when a swirling flow is generated by the rotation of the stirrer, the flow is transmitted toward the surface of the molten metal (upward) due to friction of the molten metal, causing the vortex to draw in the molten metal surface. However, if a specified straightening plate is positioned on the surface of the molten metal, the generation of a swirling flow of molten metal from above the stirrer can be prevented. Furthermore, since the transmission of the swirling flow toward the surface of the molten metal due to the rotation of the stirrer is inhibited, the generation of vortexes can also be expected to be suppressed.

[0042] From these facts, it can be assumed that when a specified straightening plate is positioned on the surface of the molten metal, the effect of stirring above the stirrer will be reduced. In other words, it is expected that the majority of the energy used for stirring will be applied below the stirrer (near the solidification interface), thereby improving stirring efficiency.

[0043] [8] In the method for producing an aluminum alloy ingot of the present invention, the stirrer may also have a predetermined rotation axis and a rotating blade that rotates around the rotation axis, is inclined at an angle of 20° to 70° with respect to a rotation plane perpendicular to the rotation axis, and rotates in conjunction with the rotation of the rotation axis.

[0044] Here, when the inclination of the rotating blades relative to the plane of rotation is "less than 20°" or "more than 70°," the area receiving the molten metal is extremely small, and it is not possible to generate a sufficient vertical flow (a flow with a velocity component perpendicular to the solidification interface). Therefore, in order to generate sufficient vertical flow and achieve even finer crystal grain size, it is preferable that the rotating blades are provided with an inclination of 20° or more and 70° or less with respect to the rotation plane.

[0045] [9] In the method for producing an aluminum alloy ingot of the present invention, the purity of the aluminum alloy can be 99.99 wt% or more.

[0046] In the case of high-purity aluminum alloys with a purity of 99.99 wt% or more, it is difficult to add a refiner (for example, titanium or boron). However, in the present invention, the crystal grain size can be refined without adding a refiner, and therefore, high-purity aluminum alloys can be refined.

[0047]

[10] In order to achieve the above object, the present invention provides an apparatus for producing aluminum alloy ingots, the apparatus comprising: a runner through which molten aluminum alloy is supplied; a molten metal receiving vessel having a basin for storing the molten metal fed through the runner; a vertical mold disposed below the molten metal receiving vessel; and a stirrer disposed within the molten metal receiving vessel and rotated to agitate the molten metal so as to apply a flow having a velocity component of 0.1 m / sec or more in a direction perpendicular to the solidification interface to the solidification interface.

[0048] According to the manufacturing apparatus for aluminum alloy ingots of the present invention, aluminum alloy is sequentially poured into the molten metal receiving vessel through the runner while forming a solidification interface on the upper surface of the ingot being cast, and the molten metal is filled into the basin so that the molten metal surface reaches a predetermined height.

[0049] In addition, by rotating the stirrer under specified conditions and applying a flow with a velocity component of 0.1 m / sec or more in the direction perpendicular to the solidification interface to the solidification interface, the generation of solidification nuclei can be promoted, and grain growth that causes coarsening of crystal grain size and the growth of abnormal structures can be suppressed. An aluminum alloy ingot is then produced and sent downward. [Effects of the Invention]

[0050] The present invention can provide a method and apparatus for producing an aluminum alloy ingot that can refine the crystal grain size of the ingot to suppress the occurrence of abnormal structures, reduce macroscopic segregation of solute elements, and suppress casting cracks. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of an aluminum alloy ingot manufacturing apparatus according to the present invention. [Figure 2] FIG. 10 is an explanatory diagram showing variations in the angle of the rotating blades of the stirring bar. [Figure 3] This is an explanatory diagram showing the flow of molten metal when the blade of the stirring bar is rotating in the forward direction and stirring the molten metal when the angle of the rotating blade of the stirring bar is 60° and 30°. [Figure 4] FIG. 1 is an explanatory diagram showing the flow of molten metal when a stirrer with rotating blades at 90° is rotated at the bottom of a casting mold in an aluminum alloy ingot manufacturing device. [Figure 5] FIG. 10 is an explanatory diagram showing the flow of molten metal when a stirrer is rotated forward at the bottom of a casting mold in the absence of a flow straightening plate. [Figure 6] FIG. 10 is an explanatory diagram showing the flow of molten metal when a stirrer is rotated forward at the bottom of a casting mold in the presence of a flow plate. [Figure 7] FIG. 1 is an explanatory diagram showing how the point at which the vertical flow velocity reaches a maximum on the solidification interface changes over time after stirring begins. [Figure 8] FIG. 10 is an explanatory diagram showing a variation of the form in which a current plate is provided near the stirring bar. [Figure 9] FIG. 1 is an explanatory diagram showing the flow of molten metal caused by the rotation of a stirrer with a rotating blade angle of 90° and no current plate provided. [Figure 10] FIG. 1 is an explanatory diagram showing the flow of molten metal caused by the rotation of a stirrer with a rotating blade angle of 45° and no current plate provided. [Figure 11] This is an explanatory diagram showing the flow of molten metal caused by the rotation of a stirrer with a rotating blade angle of 45° and a straightening plate attached. [Figure 12] FIG. 1 is an explanatory diagram showing the flow of molten metal during stirring when the height from the stirring blade to the molten metal surface is relatively high. [Figure 13] FIG. 1 is a diagram showing the state of crystal grains in a cut surface of an aluminum alloy ingot when the forward and reverse rotation speed of the stirring bar during continuous casting is 365 rpm. [Figure 14] FIG. 1 is a diagram showing the state of crystal grains in a cut surface of an aluminum alloy ingot when the forward and reverse rotation speed of the stirring bar during continuous casting is 350 rpm. DETAILED DESCRIPTION OF THE INVENTION

[0052] The embodiment of the present invention will be described in more detail with reference to FIGS. First, the HOTTOP casting method, which is one of the semi-continuous vertical casting methods, is mainly used in the manufacturing process of aluminum alloy ingots, which are materials for sputtering targets.

[0053] In this casting system, in order to agitate the molten metal near the solidification interface, it is necessary to insert a stirrer into the upper basin or mold and rotate the stirrer horizontally. Hereinafter, the structure of an apparatus M for producing an aluminum alloy ingot according to the present invention will be described with reference to FIG.

[0054] The ingot manufacturing apparatus M has a vertical jacketed mold 1. On top of the mold 1 is placed a molten metal receiving vessel 2 made of a heat insulating refractory material and having a molten metal reservoir 20 with a diameter smaller than that of the mold 1. A runner 21 for pouring molten aluminum alloy into the molten metal reservoir 20 is connected to the molten metal receiving vessel 2. While forming a solidification interface S on the upper surface of the ingot being cast, aluminum alloy is successively poured into the basin 20 of the molten metal receiving vessel 2 through the runner 21, filling the basin 20 so that the molten metal surface reaches a predetermined height.

[0055] A stirring bar 3 is placed inside the hot water reservoir 20. The stirring bar 3 has a rotating shaft 30 and a rotating blade 31c attached to the tip of the rotating shaft 30, and both the rotating shaft 30 and the rotating blade 31c are made of carbon or ceramic.

[0056] The rotating shaft 30 is provided so as to be rotatable forward and reverse by a motor (not shown), and the period of forward and reverse rotation is set to 5 seconds. Here, the cycle of forward and reverse rotation does not necessarily have to be 5 seconds, but may be in the range of 2 seconds to 30 seconds. Note that this cycle is preferably "2 seconds to 30 seconds" for total exposure of the solidification interface S, but does not have to be "2 seconds to 30 seconds" as long as total exposure is realized.

[0057] Furthermore, the inclination angle of the rotary vanes relative to the rotation plane perpendicular to the rotation axis 30 is appropriately set, and there are several variations. For example, rotating blade 31a shown in Figure 2(a) (90° relative to the plane of rotation), rotating blade 31b shown in Figure 2(b) (60° relative to the plane of rotation), rotating blade 31c shown in Figure 2(c) (45° relative to the plane of rotation), rotating blade 31d shown in Figure 2(d) (30° relative to the plane of rotation), and rotating blade 31e shown in Figure 2(e) (0° relative to the plane of rotation) can be mentioned, and although there are differences in stirring efficiency, in practice stirring is possible at a setting of 70° to 20°.

[0058] In addition, when tests were conducted with the rotating blades 31a to 31e shown in Figure 2, it was found that the rotating blade 31c, which is inclined at 45° with respect to the rotation plane perpendicular to the rotation axis 30, had a good balance between the area that receives the molten metal during forward rotation and the proportion of the molten metal that is discharged and flows downward, and was the most efficient rotating blade.

[0059] In contrast, in the case of the rotating blade 31b inclined at 60° (see FIG. 3(a)), although the area for receiving the molten metal (the area indicated by reference symbol 3A) is large, the “proportion of the molten metal that is discharged horizontally” indicated by reference symbol 3B is large, and therefore the “proportion of the molten metal that is discharged downward to cause it to flow” indicated by reference symbol 3C is small. 3(a), the symbol R indicates the direction of rotation of the rotary shaft 30. As shown in FIG.

[0060] Furthermore, in the case of the rotating blade 31d inclined at an angle of 30° (see FIG. 3(b)), the “proportion of molten metal discharged horizontally” indicated by the symbol 3E is small, and therefore the “proportion of molten metal discharged downward and flowing” indicated by the symbol 3F is large, but the area receiving the molten metal (the area indicated by the symbol 3D) is small. 3(b), the symbol R indicates the rotation direction of the rotary shaft 30. As shown in FIG.

[0061] It was also confirmed that, at the same rotation speed, the 45° rotating blade 31c had the greatest "downward flow velocity of the molten metal." Furthermore, it was also confirmed that even if there was an effect due to differences in the angle of the rotating blades, by adjusting the stirring speed, a sufficient perpendicular flow to the solidification interface could be obtained even when the inclination angle was between 70° and 20°.

[0062] In addition, in the case of the 90° rotating blade 31a (see Figure 4), a normal structure was obtained only directly below the stirrer 3 (region indicated by reference symbol 4A), and feathery crystals were generated around it (region indicated by reference symbol 4B). This is thought to be because an entrained flow (vertical flow) was generated only directly below the stirrer 3 and exerted its effect.

[0063] Here, in the case of the 90° rotating blade 31a (see Figure 4), it was confirmed that structural abnormalities occurred even though there was a flow parallel to the solidification interface S, so it was determined that the effect of the flow parallel to the solidification interface S was zero or almost zero. Note that the symbol 4X in FIG. 4 represents "discharge of the molten metal outward by centrifugal force," and the symbol 4Y in FIG. 4 represents "sucking up the amount of molten metal discharged outward (4X)."

[0064] Furthermore, with the rotary vanes 31e at 0°, the area that receives the molten metal is extremely small, making it difficult to generate a vertical flow.

[0065] The difference in the flow of the molten metal caused by the rotation of the stirrer 3 having several different shapes will now be described. First, as shown in Figure 10, when the 45° rotating blade 31c is rotated in both directions, with the rotation that generates a downward flow being the forward rotation (see Figure 10(a)) and the rotation that generates an upward flow being the reverse rotation (see Figure 10(b)), in the absence of a straightening vane, downward and upward flows alternate, resulting in an unsteady flow.

[0066] Furthermore, as shown in Figure 11, when a disk-shaped straightening plate 4 is attached on top of the 45° rotating blades 31c, weak suction occurs from below during forward rotation (see Figure 11(a)), and strong suction occurs during reverse rotation (see Figure 11(b)), resulting in an unsteady flow in the direction away from the solidification interface S.

[0067] Furthermore, even with the 90° rotating blades 31a as shown in Figure 9, a normal structure is obtained directly below the stirrer 3 as described above, which suggests that the cast structure is improved not only by the "pressure generated by the flow toward the solidification interface S" but also by the "pressure (negative pressure) generated by the flow away from the solidification interface S."

[0068] Here, the shape of the rotating blades may be a curved plate shape with the same angle (45°) as in this embodiment, or a curved plate shape with different angles, and the shape of the rotating blades is not particularly limited, and may be a plate body, a circular or elliptical straight plate, etc.

[0069] In addition, a straightening plate 4 that blocks or obstructs the flow of the molten metal is provided between the rotating blade 31c of the stirrer 3 of the ingot manufacturing device M and the surface of the molten metal (symbol omitted) (the straightening plate 4 is not shown in Figure 1). The straightening vane 4 is fixedly disposed on the rotary vane 31c, for example (see A to D in Fig. 8). The straightening vane 4 may be separated from the rotary shaft 30 or the rotary vane 31c and disposed by floating on the surface of the molten metal (see E in Fig. 8), or may not be disposed at all.

[0070] In the variations of FIG. 8, all of the rectifying plates 4 have a disk shape when viewed from above and below.

[0071] The function of the current plate 4 (in this embodiment, the current plate 4 indicated by A in FIG. 8) is to firstly suppress depression of the molten metal surface by suppressing the drawing in of the stirring bar 3 from above, and also to improve the stirring efficiency in the vicinity of the solidification interface S (see FIG. 6). On the other hand, if there is no straightening plate 4, for example, in the forward rotation, the stirrer 3 ejects the molten metal downward to make it flow, and then sucks in the corresponding molten metal from above (see Figure 5).

[0072] Furthermore, when a swirling flow is generated by the rotation of the stirrer 3, the flow is transmitted in the direction of the molten metal surface (upward) due to friction of the molten metal, causing the vortex to draw in the molten metal surface. If a straightening plate 4 is attached to the stirrer 3, the generation of a drawn-in flow from above the stirrer 3 can be prevented. Furthermore, since the transmission of the swirling flow in the direction of the molten metal surface due to the rotation of the stirrer 3 is inhibited, the generation of a vortex can also be expected to be suppressed.

[0073] From these facts, it can be considered that the straightening plate 4 in A of Figure 8 can reduce the influence of stirring above the stirrer 3 (the region indicated by reference symbol 6A in Figure 6). In other words, it is expected to have the effect of directing most of the energy used for stirring below the stirrer 3 (the region indicated by reference symbol 6B in Figure 6, near the solidification interface S) (see Figure 6). Note that reference symbol 6C in Figure 6 represents the "drawn flow from below."

[0074] On the other hand, when there is no straightening plate 4 (as in the case of FIG. 5), the influence of stirring extends to the entire molten metal (in other words, the stirring effect cannot be efficiently exerted on the solidification interface S). Note that the symbol 5A in FIG. 5 represents a "flow drawn in from above."

[0075] The rectifying plate 4 is not limited to the rectifying plate A in FIG. 8, but may be any of the rectifying plates B to E. Type B is positioned away from the rotating blades 31c (positioned vertically above the straightening plate of type A), types C and D have guides provided on the periphery of the lower surface to direct the horizontal discharge flow toward the solidification interface S, and type E is either floating on the molten metal surface or fixed from the outside, independent of the rotating shaft 30 or rotating blades 31c. Alternatively, it may be fixed to the inner surface (reference numeral omitted) of the molten metal receiving vessel 2 that faces the basin 20. The E type has a simple structure and is cost-effective (see FIG. 8).

[0076] Incidentally, depending on the structure of the ingot manufacturing apparatus M and the position of the stirrer 3, increasing the rotation speed of the stirrer 3 may increase the discharge flow rate in the horizontal direction, which may cause inconvenience. For example, in the HOTTOP casting method, a method of pressurizing the molten metal with gas (gas-pressurized HOTTOP casting method) is sometimes applied to improve the appearance of the ingot. However, when using a straightening plate A, if the position of the straightening plate A (position in the Z-axis direction) coincides with the gas-pressurized part (the gas pressurizing the molten metal), the increase in rotation speed will be limited to avoid damage to the gas-pressurized part due to an increase in the horizontal discharge flow rate.

[0077] In such a case (when the use of straightening vane A limits the increase in rotation speed), in the case of straightening vane B, the horizontal discharge flow rate increases as the rotation speed increases, but because the gas pressurization part is misaligned with the Z-axis direction, the horizontal discharge flow does not head toward the gas pressurization part, so the rotation speed can be increased.

[0078] In the case of straightening plates C and D, the horizontal discharge flow rate does not increase even if the rotation speed increases, so the rotation speed can be increased. Furthermore, the E straightening vane (floating type) is not in the hot water and does not produce a discharge flow, so the rotation speed can be increased, and the E straightening vane (external fixed type) is in the hot water but is misaligned in the Z-axis direction from the gas pressurization part, so the rotation speed can be increased. As an exception, if the rectifying plate 4 is not provided, the rotation speed can be increased since there is no effect on the rotation, just like the rectifying plate E.

[0079] Here, we will explain how the flow of the molten metal, which is caused by the unsteady rotation of the stirrer, acts on the solidification interface S. First, the time setting for exposing the solidification interface S to the flow of molten metal is set to a value that takes into consideration the time lag between when the stirring bar 3 starts to rotate, when the rotation starts to be transmitted to the molten metal, and when the molten metal reaches its maximum speed.

[0080] It is assumed that, in the oscillation of the molten metal caused by the unsteady rotation of the stirring bar 3, the point at which the vertical flow velocity on the solidification interface S becomes maximum after stirring starts changes over time, as shown in Figure 7, for example, and that if the maximum flow velocity at this time exceeds a reference value, an improvement in the ingot structure can be obtained.

[0081] Assuming that after stirring is started by the stirrer 3 operating at a constant rotation speed and intermittently at constant intervals, the position where the solidification interface S receives the maximum flow velocity moves from the center toward the edge, and it takes n seconds for it to move to the very edge, stirring must be continued for at least n seconds.

[0082] At this time, the maximum flow velocity hits a certain point X on the solidification interface S once every n seconds. Here, if the stirring time is increased, the flow becomes steady, and the vertical flow only acts on a part of the solidification interface S. Conversely, if the stirring time is decreased, the acceleration time of the molten metal required for the maximum flow velocity to reach the edge becomes insufficient. To satisfy these conditions, the forward / reverse rotation period of the motor must be between 2 and 30 seconds, and in this embodiment, the forward / reverse rotation period of the motor is set to 5 seconds.

[0083] By switching the rotation on and off, changing the rotation speed, or switching the rotation direction in this cycle, as described above, it is possible to cause the flow of the molten metal 9 to act on any position of the solidification interface S.

[0084] Here, an experiment was conducted to observe the flow of the molten metal 9 during stirring when the height from the stirring blade 31c to the molten metal surface 90 was relatively high, and this experiment will be described with reference to FIG.

[0085] The test conditions were: angle of the rotary vane 31c 45°, rotation speed 365 rpm, forward rotation 5 seconds → stop 1 second → reverse rotation 5 seconds → stop 1 second.

[0086] The case of forward rotation is shown in Figure 12(a). Below the stirrer 3, the downward flow caused by the rotating blade 31c bounces off the bottom surface (solidification interface S) directly below the stirrer 3, splitting into inner and outer flows, and a weak upward flow was observed in the center. Further outward, it was observed to collide vertically with the bottom surface S, and then change into a flow heading outward.

[0087] In the lateral direction of the stirring bar 3, no flow expelled in the horizontal direction due to centrifugal force could be observed, and it is thought that the force expelling from top to bottom is dominant.

[0088] Above the stirrer 3, the range (distance) of influence of the stirrer 3 is narrower than expected, and it is thought that there is almost no effect on the molten metal surface 90. It was also confirmed that the flows that have risen along the bottom surface S collide near the center, creating a vertical flow.

[0089] The case of reverse rotation is shown in Figure 12(b). Below the stirrer 3, a vortex caused by suction was generated directly below the stirrer 3, and it was possible to confirm that this vortex moved in a circular motion. Outside of that, there was almost no flow perpendicular to the bottom surface S, and the flow was along the bottom surface S.

[0090] As with forward rotation, no horizontal discharge was observed when the stirrer 3 was rotated sideways. Instead, it appeared as if the stirrer was sucking in the liquid from the side.

[0091] Above stirrer 3, it was observed that the flow discharged from stirrer 3 was not discharged straight up, but rather at an angle upwards. It was confirmed that the flow hit the wall and was split into upper and lower parts.

[0092] (Consideration) In the above test, it was found that the flow in the discharge direction (forward rotation: downward, reverse rotation: upward) was strong, and that the discharged flow was strongly affected by centrifugal force, so it hardly went straight in the discharge direction, but spread outward. From these results, it was found that there was almost no effect in suppressing the molten metal surface being drawn in by canceling out the flow from above caused by forward rotation with reverse rotation, and that most of the effect was due to canceling out the vortex flow (not shown in the figure) that rotates the entire molten metal in the rotation direction of the stirrer 3.

[0093] Furthermore, it was confirmed that flows perpendicular to the solidification interface S easily occur with forward rotation, but with reverse rotation they hardly occur anywhere except at the center, and it was found that most flows are parallel to the solidification interface S. Therefore, reverse rotation alone is only effective in canceling out the overall vortex flow, and it is highly likely that it will have almost no effect on improving the structure. However, by alternating between forward and reverse rotation, flows in opposite directions collide, and as a result, a perpendicular flow will occur even with reverse rotation, which is expected to have an effect on improving the structure.

[0094] (Example) An example will be described below. In the example, an aluminum alloy ingot was produced in the above-described ingot production apparatus M using a stirrer 3 having rotary blades 31c inclined at 45° without providing a straightening plate 4.

[0095] The rotation speed of the stirrer 3 is 365 rpm, the rotation direction is forward and reverse, with a cycle of 5 seconds of forward rotation, 1 second of stop, 5 seconds of reverse rotation, and 1 second of stop, and the installation height of the stirrer 3 is 122 mm from the top surface of the molten metal receiving vessel 2 to the top of the rotating blades 31c of the stirrer 3.

[0096] Here, by rotating the stirring bar 3 forward and backward under the above conditions, the molten metal around the stirring bar 3 becomes an unsteady flow, and alternates between downward and upward flow (see FIG. 10). It was confirmed by a water test that when the rotation speed of the stirring bar 3 was 365 rpm, the velocity component in the direction perpendicular to the solidification interface S was 0.1 m / sec or more.

[0097] Specifically, by rotating the stirrer 3 at 365 rpm in 10°C water containing beads (which can be evaluated as having a viscosity equivalent to that of molten aluminum at 700°C) and calculating the distance traveled by the beads per unit time, it was confirmed that the velocity component perpendicular to the solidification interface S was 0.1 m / sec or more.

[0098] Furthermore, as a comparative example, the rotation speed of the stirring bar 3 was set to 350 rpm, and an aluminum alloy ingot was produced under the same conditions as those of the example except for the rotation speed. Furthermore, it was confirmed by a water test that when the rotation speed of the stirring bar 3 was 350 rpm, there was a region where the velocity component in the direction perpendicular to the solidification interface S did not reach 0.1 m / sec.

[0099] Specifically, by rotating the stirring bar 3 at 350 rpm in water containing beads at 10°C and calculating the distance traveled by the beads per unit time, it was confirmed that there were regions where the velocity component perpendicular to the solidification interface S did not reach 0.1 m / sec.

[0100] The cross-sectional structure of the aluminum alloy ingot produced in the above-mentioned Example is shown in FIG. 13, and the cross-sectional structure of the aluminum alloy ingot produced in the above-mentioned Comparative Example is shown in FIG.

[0101] As shown in Figure 13, when the forward and reverse rotation speed of the stirring bar 3 is 365 rpm (i.e., when the velocity component in the direction perpendicular to the solidification interface S is 0.1 m / sec or more), the state of the crystal grains on the cut surface of the aluminum alloy ingot shows that the crystal grains are fine over almost the entire surface, there is no abnormal structure, and feathery crystals do not occur. In addition, macroscopic segregation of solute elements is reduced, and there are no casting cracks.

[0102] On the other hand, as shown in Figure 14, when the forward and reverse rotation speed of the stirring bar 3 was 350 rpm (i.e., when there was a region where the velocity component perpendicular to the solidification interface S did not reach 0.1 m / sec), the state of the crystal grains on the cut surface of the aluminum alloy ingot showed an area where feather-like crystals 5 had occurred around the center where the crystal grains were relatively fine.

[0103] The terms and expressions used in the present specification and claims are merely for explanatory purposes and are not limiting in any way, and are not intended to exclude terms and expressions equivalent to the features described in the present specification and claims or portions thereof. It goes without saying that various modifications are possible within the scope of the technical idea of ​​the present invention. [Explanation of symbols]

[0104] M Ingot manufacturing equipment 1. Mold 2. Molten metal receiving vessel 20 Hot Springs 21 Yudo 3 Stirring bar 30 Rotation axis 31a, 31b, 31c, 31d, 31e Rotating blades 4 Rectifier plate 5 Feathery crystals 9 Molten metal 90 Water surface S solidification interface

Claims

1. A method for producing an aluminum alloy ingot, comprising a casting step of rotating a predetermined stirrer in molten aluminum alloy and solidifying the molten aluminum alloy while shaking the molten aluminum alloy, The casting process includes: The stirrer is rotated to oscillate the molten metal so that a flow having a velocity component perpendicular to the solidification interface of 0.1 m / sec or more acts on the solidification interface. A method for manufacturing aluminum alloy ingots.

2. The flow of the molten metal is applied to any position on the solidification interface. The method for producing the aluminum alloy ingot according to claim 1.

3. The stirring bar is rotated non-steadily. The method for producing an aluminum alloy ingot according to claim 1 or 2.

4. A method for producing an aluminum alloy ingot, comprising a casting step of rotating a predetermined stirrer in molten aluminum alloy and solidifying the molten aluminum alloy while shaking the molten aluminum alloy, The casting process includes: The stirrer is rotated unsteadily to oscillate the molten metal so that a flow including a velocity component perpendicular to the solidification interface acts on the solidification interface. A method for manufacturing aluminum alloy ingots.

5. The stirring bar is Turning rotation on and off, changing rotation speed, or changing rotation direction every 2 seconds or more and 30 seconds or less The method for producing the aluminum alloy ingot according to claim 4.

6. The stirring bar has a predetermined rotation shaft and a rotary blade that is provided on the rotation shaft and rotates in accordance with the rotation of the rotation shaft, The casting process includes: The rotary shaft is rotated with a predetermined straightening plate positioned between the surface of the molten metal and the rotary blades. The method for producing an aluminum alloy ingot according to claim 1, claim 2 or claim 4.

7. The casting process includes: The stirrer is rotated with a predetermined straightening plate positioned on the surface of the molten metal. The method for producing an aluminum alloy ingot according to claim 1, claim 2 or claim 4.

8. The stirring bar is The rotor blades have a predetermined rotation axis and a rotation axis that rotates around the rotation axis, are inclined at an angle of 20° or more and 70° or less with respect to a rotation plane that is perpendicular to the rotation axis, and rotate in accordance with the rotation of the rotation axis. The method for producing an aluminum alloy ingot according to claim 1, claim 2 or claim 4.

9. The purity of the aluminum alloy is 99.99 wt% or more. The method for producing an aluminum alloy ingot according to claim 1, claim 2 or claim 4.

10. An apparatus for manufacturing aluminum alloy ingots, comprising: A runner through which the supplied molten aluminum alloy passes, a molten metal receiving vessel having a reservoir for storing the molten metal fed through the runner; a vertical mold disposed below the molten metal receiver; a stirrer disposed inside the molten metal receiving vessel and rotating to agitate the molten metal so as to apply a flow having a velocity component of 0.1 m / sec or more in a direction perpendicular to the solidification interface to the solidification interface; An apparatus for manufacturing aluminum alloy ingots comprising:

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