Manufacturing method and device for aluminum alloy ingot

Abstract

In the ingot manufacturing process, the molten metal is mechanically rocked by an unprecedented method, which makes it possible to refine the crystal grain size and suppress the occurrence of abnormal structures, while also reducing the macroscopic segregation of solute elements and suppressing casting cracks. [Solution] A manufacturing method for aluminum alloy ingots includes a casting process in which a designated stirrer 3 is rotated in molten aluminum alloy and the molten metal is solidified while being oscillated. In the casting process, the stirrer is rotated to oscillate the molten metal so as to apply a flow to the solidification interface with a velocity component of 0.1 m / sec or more in the direction perpendicular to the solidification interface.

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, which reduces macroscopic segregation of solute elements, refines crystal grain size, suppresses the occurrence of abnormal structures, and suppresses casting cracks by mechanically vibrating a molten metal in the ingot production process. [Background technology]

[0002] For example, a sputtering target is required to have a chemical composition that contains few impurities, to be free of foreign matter such as non-metallic inclusions, to have a low rate of defects such as voids, and to have uniform and fine crystal grain sizes over the entire sputtering surface, and the ingot from which the target is made is also required to have similar characteristics.

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

[0004] In addition, the crystal grains of the sputtering target are controlled in the processes of plastic processing and heat treatment. The finer the crystal grain size of the ingot, the easier this control is. Also, by simplifying the processes of plastic processing and heat treatment, costs can be reduced.

[0005] In addition, the chemical composition of the ingot, which is the material for the sputtering target, contains few impurities and the frequency of solidification nuclei during the solidification process is low, so the crystal grain size is likely to become coarse and abnormal structures such as feathery crystals are likely to occur. Furthermore, there are strict regulations on the ingredients, and the addition of metals and their compounds, which are often used in general alloy ingots as grain refiners, 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 non-uniform structure in the plastic processing process of the sputtering target, and that they cause solidification stress to concentrate during the solidification process of the ingot, resulting in cracking of the ingot. 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, the macro-segregation of the solute elements 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 in the casting process. One such method is proposed in, for example, Patent Document 1, entitled "Method for continuous casting of aluminum alloy."

[0009] In this conventional "aluminum alloy continuous casting method", ultrasonic vibration and electromagnetic stirring, which oscillates the molten metal by applying a magnetic field that changes over time, are combined and used. These means are used to generate a flow of the molten metal that includes 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, as shown in Patent Document 2, rather than generating a flow of the molten metal that includes a vector parallel to the solidification interface. [Prior art documents] [Patent documents]

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

[0011] However, when the 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 miniaturizing the crystal grain size to suppress the occurrence of abnormal structures and the effect of reducing the macroscopic segregation of solute elements to suppress casting cracks cannot be said to be sufficient, and sufficient quality of the ingot could not be consistently obtained.

[0012] In addition, electromagnetic stirring requires expensive equipment and large amounts of electricity compared to mechanical stirring, resulting in high costs. Furthermore, a magnetic circuit needs to be built into the casting machine, and when performing simultaneous casting of multiple pieces, which is often done in the production of ingots for sputtering targets, sufficient clearance is required to prevent interference from the magnetic forces, which creates a problem of large equipment. For this reason, it was also difficult to add a molten metal shaking function to existing equipment.

[0013] The present invention has been devised in view of the above points, and has an object 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 in a non-conventional manner during 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 rocking the molten aluminum alloy to solidify it, wherein the casting step rotates the stirrer and rocks the molten aluminum so as to apply a flow having a velocity component of 0.1 m / sec or more 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 specified 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 specified pressure by the flow of the oscillating molten metal, and thus grain growth and growth of abnormal structures that cause the above-mentioned crystal grain size to become coarse are suppressed.

[0016] In addition, by rotating the stirrer and oscillating the molten metal so that a flow with a velocity component perpendicular to the solidification interface of 0.1 m / sec or more 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 refining the crystal grain size, and the refining of the crystal grain size can be achieved without adding a refining material (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 including a vector perpendicular to the solidification interface from the molten metal, thereby making it possible to refine the crystal grain size and suppress the occurrence of abnormal structures and to suppress 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 of the solidification interface.

[0021] In this case, the flow of the molten metal acts on any position of 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 makes it possible to prevent adverse effects such as ingot cracking caused by concentration of solidification stress resulting from coarsening of crystal grains and abnormal structure due to 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 stirrer 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, and the flow velocity near the molten metal surface can be reduced. 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 forward and reverse rotation of the stirrer that changes the direction of the molten metal flow, the flow directions change to the opposite directions and cancel each other out, causing the flow to slow down near the molten metal surface. When the unsteady rotation is strong and weak rotation of the stirrer that changes the strength of the molten metal flow, the flow repeatedly changes strength and weakness, causing it to stagnate and move, making it unstable and likely to cause the molten metal surface to slow down. Furthermore, when the unsteady rotation is intermittent rotation of the stirrer that changes the timing or time of the molten metal flow, the flow also becomes unstable and the molten metal surface is likely to slow down.

[0025] If a "depression on the molten metal surface" occurs due to the rotation of the stirrer, the oxide film on the molten metal surface will be drawn in, causing the aluminum alloy ingot to contain foreign matter. Therefore, by slowing down the flow speed near the molten metal surface and preventing the occurrence of "depressions on the molten metal surface," it is expected that a high-quality aluminum alloy ingot 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 rocking the molten aluminum alloy to solidify it, wherein the casting step comprises rotating the stirrer in a non-steady state, and rocking 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 specified stirrer is rotated in a non-steady state in the molten aluminum alloy, and the molten aluminum is solidified while being oscillated. As a result, the solidification interface is subjected to a specified pressure flow due to the oscillating molten metal, and thus grain growth and growth of abnormal structures that cause the above-mentioned crystal grain size to become coarse are suppressed.

[0028] In addition, 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 motion of the molten metal becomes a flow including a vector perpendicular to the solidification interface, rather than a flow consisting of only vectors parallel to the solidification interface, such as a swirling flow.

[0029] This rocking of the molten metal is effective in refining the crystal grain size, and can achieve this without adding refinement materials (such as titanium or boron). It can also reduce the 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 including a vector perpendicular to the solidification interface from the molten metal, thereby making it possible to refine the crystal grain size and suppress the occurrence of abnormal structures and to suppress casting cracks.

[0031] Furthermore, according to the present invention, by rotating the stirrer unsteadily, the rotation direction of the molten metal near the molten metal surface is not kept constant, thereby making it possible to slow down the flow speed near the molten metal surface. Furthermore, by rotating the stirrer unsteadily, the flow of the molten metal can expose the entire solidification interface. As described above, 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 a high-quality aluminum alloy ingot can be obtained.

[0032] [5] In the method for producing an aluminum alloy ingot of the present invention, the stirrer may be configured to turn 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 period for switching the rotation on and off, changing the rotation speed, or switching the rotation direction (hereinafter referred to as the "switching period") 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 cycle exceeds 30 seconds, the molten metal may become a steady flow and may only affect a part of the solidification interface. Therefore, in order to allow the flow of the molten metal to affect any position of the solidification interface, it is preferable that the switching cycle is 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 designated rotating shaft and a rotating blade provided on the rotating shaft and rotating with the rotation of the rotating shaft, and the casting process can also rotate the rotating shaft with a designated baffle positioned between the surface of the molten metal and the rotating blade.

[0036] In this case, a certain baffle plate is positioned between the surface of the molten metal and the rotor blades, so that the drawing of the molten metal from above the stirrer is suppressed, thereby suppressing the formation of a depression on the molten metal surface. 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 occurs due to the rotation of the stirrer, the flow is transmitted in the direction of the molten metal surface (upward) due to friction of the molten metal, and the vortex causes the molten metal surface to be pulled in (when the molten metal surface is pulled in, a "depression in the molten metal surface" occurs as a result). However, if a baffle plate is positioned between the molten metal surface and the rotating blades, it is possible to prevent the molten metal from being pulled in from above the stirrer. In addition, because 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 considered that the influence of stirring above the stirrer is reduced when the baffle is located between the molten metal surface and the rotor blades. In other words, it is expected that the effect of increasing the stirring efficiency will be achieved by applying most of the energy used for stirring below the stirrer (near the solidification interface).

[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 positioning a predetermined baffle plate on the surface of the molten metal.

[0040] In this case, a predetermined baffle 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 occurs due to the rotation of the stirrer, the flow is transmitted toward the surface of the molten metal (upward) due to friction of the molten metal, and the swirling flow draws in the molten metal surface. However, if a specific baffle plate is positioned on the surface of the molten metal, it is possible to prevent the generation of a swirling flow of molten metal from above the stirrer. In addition, because the transmission of the swirling flow toward the surface of the molten metal due to the rotation of the stirrer is inhibited, it is also expected to have an effect of suppressing the generation of swirling flow.

[0042] From these facts, it can be considered that when a certain baffle plate is placed on the surface of the molten metal, the influence of stirring above the stirrer is 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), which will increase the 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° or more and 70° or less 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 blade with respect 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 having 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 for the rotating blades to be 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 may be 99.99 wt % or more.

[0046] In the case of high-purity aluminum alloys having a purity of 99.99 wt% or more, it is difficult to add a refiner (e.g., titanium or boron). However, in the present invention, the crystal grain size can be refined without adding a refiner, making it possible to refine high-purity aluminum alloys.

[0047]

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

[0048] According to the apparatus for manufacturing an aluminum alloy ingot of the present invention, while a solidification interface is formed on the upper surface of the ingot being cast, aluminum alloy is successively poured into the interior of a molten metal receiving vessel through a runner, filling the basin so that the molten metal surface is at a predetermined height.

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

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

[0051] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of an aluminum alloy ingot manufacturing apparatus according to the present invention. [Diagram 2] FIG. 13 is an explanatory diagram showing variations in the angle of the rotating blades of the stirrer. [Diagram 3] FIG. 1 is an explanatory diagram showing the flow of molten metal when the stirring blade is rotating in the forward direction and stirring is performed with the blade at angles of 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° of an aluminum alloy ingot manufacturing device is rotated at the bottom of a casting mold. [Diagram 5] FIG. 1 is an explanatory diagram showing the flow of molten metal when a stirrer is rotated in the forward direction at the bottom of a casting mold in the absence of a baffle. [Figure 6] FIG. 1 is an explanatory diagram showing the flow of molten metal when a stirrer is rotated in the forward direction at the bottom of a casting mold in the presence of a baffle. [Figure 7] FIG. 1 is an explanatory diagram showing how the point at which the vertical flow velocity becomes maximum on the solidification interface changes over time after stirring is started. [Figure 8] FIG. 11 is an explanatory diagram showing a variation of the form in which a baffle plate is provided near the stirrer. [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 baffle plate. [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 baffle plate. [Figure 11] 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 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 stirrer 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 stirrer during continuous casting is 350 rpm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 the raw material for sputtering targets.

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

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

[0055] A stirring bar 3 is disposed inside the basin 20. The stirrer 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 in both directions by a motor (not shown), and the period of the forward and reverse rotation is set to 5 seconds. Here, the period of forward and reverse rotation does not necessarily have to be 5 seconds, but may be in the range of 2 to 30 seconds. Note that, for the total exposure of the solidification interface S, this period is preferably "2 to 30 seconds", but it does not have to be "2 to 30 seconds" as long as the total exposure is realized.

[0057] Furthermore, the inclination angle of the rotating blades with respect 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] When tests were conducted with the rotor blades 31a to 31e shown in FIG. 2, it was found that the rotor 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 rotor 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 discharged horizontally" indicated by reference symbol 3B is large, and therefore the "proportion of the molten metal discharged downward and caused to flow" indicated by reference symbol 3C is small. 3(a), the symbol R indicates the rotation direction of the rotating shaft 30. As shown in FIG.

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

[0061] It was also confirmed that, for the same rotation speed, the 45° rotor blade 31c had the greatest "downward flow velocity of the molten metal." 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 with an inclination angle of 70° to 20°.

[0062] In the case of the 90° rotating blade 31a (see FIG. 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 the entrainment flow (vertical flow) was generated only directly below the stirrer 3 and had an effect.

[0063] Here, in the case of the 90° rotor 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 is negligible or almost negligible. In addition, the symbol 4X in FIG. 4 indicates "discharge of the molten metal to the outside by centrifugal force", and the symbol 4Y in FIG. 4 indicates "suction up of the molten metal discharged to the outside (4X)".

[0064] Furthermore, with the rotary vanes 31e at 0°, the area receiving 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° rotor blades 31c are rotated in forward and reverse directions, with the rotation generating a downward flow being the forward rotation (see Figure 10(a)) and the rotation generating an upward flow being the reverse rotation (see Figure 10(b)), in the absence of a baffle vane, the downward and upward flows alternate, resulting in an unsteady flow.

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

[0067] Incidentally, even with the 90° rotating blades 31a as shown in FIG. 9, a normal structure is obtained directly below the stirrer 3 as described above. This 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 curved plate shapes with the same angle (45°) as in this embodiment, or curved plate shapes with different angles.The shape of the rotating blades is not particularly limited, and may be a plate body or a straight plate with a circular or elliptical shape.

[0069] In addition, a baffle plate 4 that blocks or impedes the flow of the molten metal is provided between the rotating blade 31c of the stirrer 3 of the ingot manufacturing equipment M and the surface of the molten metal (reference number omitted) (the baffle plate 4 is not shown in Figure 1). The straightening plate 4 is fixedly disposed on the rotary vane 31c, for example (see A to D in FIG. 8). The straightening plate 4 may be disposed separately from the rotary shaft 30 or the rotary vane 31c, for example, 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, each of the straightening plates 4 has a disk shape when viewed from above and below.

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

[0072] Furthermore, when a swirling flow occurs due to 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, and the swirling flow draws in the molten metal surface. If a baffle plate 4 is attached to the stirrer 3, the generation of the drawn-in flow from above the stirrer 3 can be prevented. In addition, 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 the swirling flow can also be suppressed.

[0073] From these facts, it can be considered that the baffle plate 4 in A of Fig. 8 can reduce the influence of stirring above the stirrer 3 (the region indicated by reference symbol 6A in Fig. 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 Fig. 6, near the solidification interface S) (see Fig. 6). Note that reference symbol 6C in Fig. 6 represents the "drawn-in flow from below."

[0074] On the other hand, when there is no baffle 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). In addition, the reference symbol 5A in FIG. 5 represents a "flow drawn in from above."

[0075] The current plate 4 is not limited to the current plate A in FIG. 8, but may be any of the current plates B to E. Type B is positioned away from the rotating blades 31c (positioned vertically above the baffle plate A), types C and D have a guide provided on the periphery of the lower surface to direct the horizontal discharge flow toward the solidification interface S, and type E is independent of the rotating shaft 30 or rotating blades 31c and floats on the molten metal surface or is fixed from the outside. Also, it may be fixed to the inner surface (reference numeral omitted) of the molten metal receiving vessel 2 that faces the molten metal reservoir 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 horizontal discharge flow rate, 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 in order 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 the rotation speed is restricted in order 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 baffle plate A limits the increase in rotation speed), in the case of baffle plate B, the horizontal discharge flow rate increases as the rotation speed increases, but because the gas pressurized part is misaligned with the Z-axis direction, the horizontal discharge flow does not head toward the gas pressurized part, making it possible to increase the rotation speed.

[0078] In the case of the 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 baffle 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 baffle 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 baffle plate 4 is not provided, the rotation is not affected, just like the baffle plate E, so the rotation speed can be increased.

[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 based on 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] In the oscillation of the molten metal caused by the unsteady rotation of the stirring bar 3, for example as shown in FIG. 7, it is assumed that the point at which the vertical flow velocity on the solidification interface S becomes maximum after stirring starts changes over time, and when the maximum flow velocity at this time exceeds a reference value, the effect of improving the ingot structure is 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 acts only 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 period of forward and reverse rotation of the motor needs to be 2 seconds or more and 30 seconds or less, and in this embodiment, the period of forward and reverse rotation 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 such a cycle, it is possible to affect the flow of the molten metal 9 at any position of the solidification interface S, as described above.

[0084] Here, with reference to FIG. 12, an experiment was carried out 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.

[0085] The test conditions were: angle of the rotor blades 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 blades 31c bounced off the bottom surface (solidification interface S) directly below the stirrer 3 and separated into inner and outer flows, and a weak upward flow was observed in the center. Further outside, it was observed to collide vertically with the bottom surface S, and then changed into a flow heading outward.

[0087] In the lateral direction of the stirrer 3, no horizontal flow due to centrifugal force could be observed, and it is believed 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 considered that there is almost no effect on the molten metal surface 90. In addition, it was confirmed that the flows coming up along the bottom surface S collide near the center, generating 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 confirmed that the 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 the forward rotation, no horizontal discharge was observed in the lateral direction of the stirrer 3. 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 upwards, but was discharged diagonally upwards. It was confirmed that the flow hit the wall and was divided 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, and spread outward almost without proceeding in a straight line in the discharge direction. From this result, it was found that there was almost no effect in suppressing the molten metal surface drawing in by canceling the flow from above to below caused by forward rotation with reverse rotation, and that most of the effect was due to canceling 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 perpendicular flows 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. For this reason, reverse rotation alone is only effective in canceling out the overall vortex flow, and it is highly likely that it has almost no effect on improving the structure. However, by alternating between forward and reverse rotation, flows in opposite directions collide, and as a result, perpendicular flows are generated even with reverse rotation, which is expected to have an effect on improving the structure.

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

[0095] In addition, the rotation speed of the stirrer 3 is 365 rpm, the rotation direction is forward and reverse, with a cycle of forward rotation for 5 seconds, stop for 1 second, reverse rotation for 5 seconds, and stop for 1 second, 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 stirrer 3 forward and backward under the above conditions, the molten metal around the stirrer 3 becomes an unsteady flow, repeating downward and upward flows (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 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 (whose viscosity can be evaluated as 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. 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 stirrer 3 at 350 rpm in water at 10°C containing beads 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 Fig. 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 no feathery crystals are generated. In addition, the 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 in which the velocity component in the direction 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 was such that a region in which feather-like crystals 5 had occurred around the center where the crystal grains were relatively fine was confirmed.

[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 parts thereof. In addition, 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 Spring Pool 21 Yudo 3 Stirring bar 30 Rotational 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 stirrer having a rotating shaft and a rotor blade attached to the rotating shaft and rotating with the rotation of the rotating shaft in a molten aluminum alloy, and solidifying the molten aluminum alloy while agitating the molten aluminum alloy, The casting process includes: With a predetermined baffle plate positioned between the surface of the molten metal and the rotor blade, the stirrer is rotated to oscillate 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; A guide is provided on the lower peripheral edge of the straightening plate to direct the horizontal discharge flow toward the solidification interface. A method for manufacturing aluminum alloy ingots.

2. The guide is located outside the rotor blades in a plan view. A method for producing the aluminum alloy ingot according to claim 1.

3. The baffle plate is provided on the rotating shaft and rotates with the rotation of the rotating shaft. The method for producing an aluminum alloy ingot according to claim 1 or 2.

4. The aluminum alloy has a purity of 99.99 wt% or more. The method for producing an aluminum alloy ingot according to claim 1 or 2.

5. A runner through which molten aluminum alloy is supplied; 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 receiving vessel; a stirrer having a predetermined rotating shaft and a rotating blade provided on the rotating shaft and rotating with the rotation of the rotating shaft, the stirrer being disposed inside the molten metal receiving vessel and rotating with a predetermined baffle plate positioned between the surface of the molten metal and the rotating blade, to rock 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 producing an aluminum alloy ingot, comprising: A guide is provided on the lower peripheral edge of the straightening plate to direct the horizontal discharge flow toward the solidification interface. Manufacturing equipment for aluminum alloy ingots.

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