Aluminum alloy ingot and manufacturing method thereof

Abstract

To provide an aluminum alloy ingot that is made fine and uniform in metal texture by providing a high cooling rate and inhibited from becoming non-uniform in metal texture internal of the ingot, and a method of producing the same.SOLUTION: An aluminum alloy ingot comprises 0.15 mass%-1.0 mass% of Cu, 0.6 mass%-1.2 mass% of Mg, 0.95 mass%-1.35 mass% of Si, 0.4 mass%-0.6 mass% of Mn, 0.15 mass%-0.70 mass% of Fe, 0.09 mass%-0.25 mass% of Cr, 0.012 mass%-0.035 mass% of Ti, and the balance consisting of Al and inevitable impurities. A difference between the maximum value and the minimum value of a secondary dendrite arm spacing in a cross section orthogonal to a casting direction of the aluminum alloy ingot falls within a range of 5 μm-20 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy ingot and a method for producing an aluminum alloy ingot using a horizontal continuous casting machine. [Background technology]

[0002] When producing high-quality aluminum alloy ingots with excellent strength and durability, it is important to form a fine and uniform metal structure in order to obtain excellent mechanical properties and stable quality. If the metal structure becomes coarse or non-uniform, the mechanical properties will be reduced compared to when the metal structure is uniform, and there is a concern that this will lead to a decrease in the reliability of final products produced using such aluminum alloy ingots.

[0003] The metallographic structure of these aluminum alloy ingots is determined during the casting process, and this structure is maintained throughout the final product. In other words, controlling the metallographic structure during the casting process is extremely important in order to create a fine and uniform metallographic structure.

[0004] In the past, in the casting process of aluminum alloy ingots, it has been considered effective to apply a high cooling rate to the molten aluminum alloy (hereinafter referred to as "molten metal") and to cool and solidify the molten metal in a short time in order to obtain a fine and uniform cast structure. For example, in the continuous casting method, which is often used in the production of wrought alloys, the molten metal is cooled by cooling the mold that comes into contact with the molten metal, and therefore, there are limitations on increasing the cooling rate due to the heat storage in the mold itself.

[0005] To increase the cooling rate of the molten metal, it is necessary to thin the ingot itself to cool and solidify the entire body more quickly. However, if the ingot itself is too thin, it becomes difficult to mold it into medium- to large-sized products, which limits the freedom of the shape of the final product.

[0006] Furthermore, simply increasing the cooling rate can produce a fine and uniform metal structure in a portion of the ingot, particularly near the surface, but the difference in cooling rate between the surface and central portions of the ingot results in a large non-uniformity in the metal structure. Specifically, there is concern that this will result in biases in the distribution of crystal grain size and second-phase particles, which will have a negative impact on the properties of the final product. BACKGROUND ART There are known conventional casting devices and casting methods that can produce ingots with uniform metal structure by improving the casting conditions and the configuration of the casting device (see, for example, Patent Documents 1 to 4). Also known is a method for casting a thin plate material that suppresses the non-uniformity of the metal structure while applying a high cooling rate (see, for example, Non-Patent Document 1).Furthermore, a method for obtaining a wire rod having a uniform metal structure by performing a drawing process on the cast wire rod is also known (see, for example, Patent Document 5). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 08-029398 [Patent Document 2] Patent No. 4648968 [Patent Document 3] Patent No. 5295205 [Patent Document 4] Patent No. 5366063 [Patent Document 5] Patent No. 4643388 [Non-patent literature]

[0008] [Non-Patent Document 1] Toshio Haga: Casting Engineering, 86 (2014), 1 48-53. Summary of the Invention [Problem to be solved by the invention]

[0009] However, when the aluminum alloy ingots cast by the methods of Patent Documents 1 to 5 and Non-Patent Document 1 have a large cross section, there is a problem in that the metal structure is not sufficiently refined and uniform, and uneven portions remain in part of the metal structure.

[0010] An object of the present invention is to provide an aluminum alloy ingot in which the metal structure is made fine and uniform by applying a high cooling rate and the metal structure inside the ingot is prevented from becoming non-uniform, and a method for producing the same. [Means for solving the problem]

[0011] To solve the above problems, the present inventors focused on dendrite arm spacing (hereinafter referred to as DAS) among the metallographic properties. Specifically, during the solidification process of an aluminum alloy ingot during casting, the α-Al primary crystals formed by solidification assume a dendritic crystal (dendrite) morphology, and the formation and growth of α-Al dendrites forms the metallographic structure. Since DAS is proportional to the cooling rate during solidification of the ingot and can be easily measured by methods such as optical microscopy, it can be used as an indicator of the metallographic properties immediately after casting. In the present invention, the inventors discovered that by controlling DAS within an appropriate range, an aluminum alloy ingot with good mechanical properties and reliability can be obtained.

[0012] The present invention has been made based on the above-mentioned findings, and provides an aluminum alloy ingot comprising 0.15 mass% to 1.0 mass% Cu, 0.6 mass% to 1.2 mass% Mg, 0.95 mass% to 1.35 mass% Si, 0.4 mass% to 0.6 mass% Mn, 0.15 mass% to 0.70 mass% Fe, 0.09 mass% to 0.25 mass% Cr, 0.012 mass% to 0.035 mass% Ti, and the balance being Al and unavoidable impurities, characterized in that a difference between the maximum and minimum values ​​of secondary dendrite arm spacing in a cross section orthogonal to the casting direction of the aluminum alloy ingot is in the range of 5 μm to 20 μm.

[0013] According to the present invention, by keeping the difference between the maximum and minimum values ​​of DAS in the range of 5 μm to 20 μm, it is possible to obtain an aluminum alloy bar having good mechanical properties and a large cross section perpendicular to the casting direction (for example, a diameter in the range of 10 mm to 100 mm).

[0014] In the present invention, B: 0.0001% by mass to 0.03% by mass may further be contained.

[0015] In the present invention, the standard deviation of the secondary dendrite arm spacing may be 5 μm or less.

[0016] The method for producing an aluminum alloy ingot of the present invention is a method for producing an aluminum alloy ingot as described in each of the above paragraphs, and comprises using a horizontal continuous casting apparatus for producing an aluminum alloy ingot by supplying molten aluminum alloy in a molten metal receptacle from one end side of a hollow mold arranged so that the central axis of the hollow portion is horizontally aligned to a hollow portion of the mold, the molten metal being continuously supplied from one end side of the mold to the hollow portion, and supplying cooling water to a cooling water cavity formed outside an inner peripheral surface of the hollow portion and containing cooling water for cooling the inner peripheral surface, and a heat flux value per unit area in a cooling wall portion of the mold between the inner peripheral surface and an inner bottom surface of the cooling water cavity forming a plane parallel to the inner peripheral surface is 10×10 5 W / m 2 The molten metal is cooled and solidified under the above conditions to produce an aluminum alloy ingot.

[0017] In the present invention, the cooling wall portion of the mold may be formed to have a thickness in the range of 0.5 mm or more and 3.0 mm or less. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an aluminum alloy ingot in which a high cooling rate is applied to make the metal structure fine and uniform, and in which non-uniformity of the metal structure within the ingot is suppressed, and a method for producing the same. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the distance between the centers of the secondary arms (DAS) of dendrites. [Figure 2] 1 is a cross-sectional view showing an example of the vicinity of a mold of a horizontal continuous casting apparatus for producing an aluminum alloy ingot of the present invention. [Figure 3] FIG. 3 is an enlarged cross-sectional view showing the cooling water cavity and its vicinity in FIG. 2. [Figure 4] FIG. 2 is an explanatory diagram illustrating the heat flux of a cooling wall portion of the horizontal continuous casting device. [Figure 5] FIG. 1 is an explanatory diagram showing an aluminum alloy rod used in an example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An aluminum alloy ingot according to one embodiment of the present invention and a method for manufacturing the same will be described below with reference to the drawings. The following embodiment is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for the sake of clarity, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0021] (aluminum alloy ingot) The aluminum alloy ingot of this embodiment is an aluminum alloy bar having a circular cross section, cast by the aluminum alloy ingot manufacturing method described below, and has a composition consisting of 0.15 to 1.0 mass% Cu, 0.6 to 1.2 mass% Mg, 0.95 to 1.35 mass% Si, 0.4 to 0.6 mass% Mn, 0.15 to 0.70 mass% Fe, 0.09 to 0.25 mass% Cr, 0.012 to 0.035 mass% Ti, and the balance being Al and unavoidable impurities. In addition to the above-mentioned components, the aluminum alloy ingot may further contain 0.0001 to 0.03 mass% B.

[0022] In such an aluminum alloy bar, the difference between the maximum and minimum DAS values ​​in a cross section perpendicular to the casting direction is in the range of 5 μm to 20 μm, and the standard deviation of this DAS is preferably 5 μm or less.

[0023] Here, the DAS can be measured by the method for measuring the secondary branch spacing of dendrites described in Non-Patent Document 2, for example. Non-patent document 2: Japan Institute of Light Metals, Casting and Solidification Division: Light Metals, 38 (1998), 54-60. As shown in Figure 1, DAS is the distance between the centers of the secondary arms of adjacent dendrites. This type of DAS measurement can be applied to metal structures where the secondary arms of dendrites are well developed, there are a relatively large number of dendrites with aligned arms, and measurement of the arm spacing is not hindered. To measure, select a portion of an observation surface where secondary arms of dendrites or arms that are judged to be secondary arms are aligned and measure.

[0024] The aluminum alloy rod of this embodiment has a difference between the maximum and minimum values ​​of DAS in the range of 5 μm to 20 μm, and therefore has good mechanical properties and can be an aluminum alloy rod with a large cross section perpendicular to the casting direction (for example, a diameter in the range of 10 mm to 100 mm).

[0025] If the difference between the maximum and minimum DAS values ​​is less than 5 μm, the ingot must be thin-walled, limiting its applicable applications. On the other hand, if the difference between the maximum and minimum DAS values ​​exceeds 20 μm, the degree of non-uniformity of the metal structure within the ingot becomes too large, resulting in deterioration of the mechanical properties of the ingot.

[0026] Furthermore, since the aluminum alloy bar of this embodiment has a standard deviation of DAS of 5 μm or less, it can have good mechanical properties and can be an aluminum alloy bar with a large cross section perpendicular to the casting direction (for example, a diameter in the range of 10 mm to 100 mm).If the standard deviation of DAS exceeds 5 μm, the degree of non-uniformity of the metal structure inside the ingot becomes too large, and the mechanical properties of the ingot deteriorate.

[0027] (Method of manufacturing aluminum alloy ingots) Next, a method for producing an aluminum alloy rod (aluminum alloy ingot) having the above-mentioned secondary dendrite arm spacing will be described. The aluminum alloy rod described above can be produced, for example, by a horizontal continuous casting method using a hollow cylindrical mold equipped with a cooling means, whose central axis is held so as to be approximately horizontal (approximately horizontal means horizontal), and can have a diameter in the range of, for example, 10 mm to 100 mm.

[0028] Although aluminum alloy rods can be manufactured with diameters outside this range, it is preferable to set the diameter within the range of 10 mm to 100 mm in order to industrially reduce the scale and cost of equipment for subsequent plastic processing steps, such as forging, roll forging, drawing, rolling, and impact processing. Casting with a different diameter can be achieved by replacing the mold with a removable cylindrical mold having an inner diameter corresponding to the diameter, and adjusting the molten metal temperature and casting speed accordingly. The amounts of cooling water and lubricating oil can also be adjusted as needed.

[0029] Such an aluminum alloy rod can be used, for example, as a material for subsequent plastic processing such as forging, roll forging, drawing, rolling, impact processing, etc. Alternatively, it can also be used as a material for machining such as burr machining and drilling.

[0030] FIG. 2 is a cross-sectional view showing an example of the vicinity of a mold of a horizontal continuous casting apparatus for producing an aluminum alloy ingot of the present invention. The horizontal continuous casting apparatus 10 of this embodiment has a molten metal receiving portion (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (insulating member) 13 arranged between one end side 12a of the mold 12 and the molten metal receiving portion 11.

[0031] The molten metal receiving section 11 is composed of a molten metal inlet section 11a that receives molten aluminum alloy (hereinafter referred to as molten alloy) M that has been adjusted to a specified alloy composition in an external melting furnace or the like, a molten metal holding section 11b, and an outlet section 11c that flows into the hollow section 21 of the mold 12. The molten metal receiving section 11 maintains the upper liquid level of the molten alloy M at a position higher than the upper surface of the hollow section 21 of the mold 12, and in the case of multiple casting, stably distributes the molten alloy M to each mold 12.

[0032] The molten alloy M held in the molten metal holding portion 11b in the molten metal receiving portion 11 is poured into the hollow portion 21 of the mold 12 through a pouring passage 13a provided in the refractory plate 13. The molten alloy M supplied into the hollow portion 21 is then cooled and solidified by a cooling device 23 (described later) and drawn out from the other end 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

[0033] A drawing drive device (not shown) that draws out the cast aluminum alloy rod B at a constant speed may be installed at the other end 12b of the mold 12. It is also preferable that a synchronous cutter (not shown) that cuts the continuously drawn aluminum alloy rod B to a desired length be installed.

[0034] The refractory plate 13 is a member that blocks heat transfer between the molten metal receiver 11 and the mold 12, and may be made of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, graphite, etc. Such a refractory plate 13 may also be made up of multiple layers made of different materials.

[0035] In this embodiment, the mold 12 is a hollow cylindrical member made of, for example, one or a combination of two or more materials selected from aluminum, copper, or alloys thereof. The materials for the mold 12 may be selected from the optimal combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0036] The hollow portion 21 of the mold 12 is formed to have a circular cross section in order to cast the aluminum alloy rod B into a cylindrical rod shape, and the mold 12 is held so that the mold central axis (central axis) C passing through the center of this hollow portion 21 is aligned approximately horizontally.

[0037] The inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0 to 3 degrees (more preferably 0 to 1 degree) with respect to the mold central axis C toward the casting direction of the aluminum alloy bar B (see FIG. 5). That is, the inner peripheral surface 21a is tapered so as to open in a cone shape toward the casting direction. The angle of this taper is the elevation angle.

[0038] If the elevation angle is less than 0 degrees, the aluminum alloy rod B encounters resistance at the other end 12b, which is the mold outlet, when it is pulled out of the mold 12, making casting difficult. On the other hand, if the elevation angle exceeds 3 degrees, the inner peripheral surface 21a will not make sufficient contact with the molten alloy M, which may reduce the heat transfer effect from the molten alloy M and its solidified shell to the mold 12, resulting in insufficient solidification. This is undesirable because it increases the likelihood of casting problems, such as the formation of a remelted skin on the surface of the aluminum alloy rod B or the ejection of unsolidified molten alloy M from the end of the aluminum alloy rod B.

[0039] The cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when the hollow portion 21 of the mold 12 is viewed from the other end side 21b) may be selected to match the shape of the aluminum alloy rod to be cast, such as a triangular or rectangular cross-sectional shape, a polygon, a semicircle, an ellipse, or an irregular cross-sectional shape that does not have an axis or plane of symmetry, in addition to the circular shape of this embodiment.

[0040] A fluid supply pipe 22 is disposed at one end 12a of the mold 12 to supply a lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied from the fluid supply pipe 22 can be one or more lubricating fluids selected from a gas lubricant and a liquid lubricant. When supplying both a gas lubricant and a liquid lubricant, it is preferable to provide separate fluid supply pipes for each. The lubricating fluid supplied under pressure from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricant supply port 22a.

[0041] In this embodiment, the lubricating fluid is supplied under pressure from the lubricant supply port 22a to the inner circumferential surface 21a of the mold 12. The liquid lubricant may be heated to decompose into a gas and then supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be disposed in the lubricant supply port 22a, and the lubricating fluid may be allowed to seep out onto the inner circumferential surface 21a of the mold 12 through the porous material.

[0042] A cooling device 23, which is a cooling means for cooling and solidifying the molten alloy M, is formed inside the mold 12. The cooling device 23 of this embodiment has a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21 a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 and the hollow portion 21 of the mold 12.

[0043] The cooling water cavity 24 is formed in the mold 12 outside the inner peripheral surface 21a of the hollow portion 21 and has an annular shape so as to surround the hollow portion 21, and cooling water W is supplied to the cavity 24 via a cooling water supply pipe . The inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, which removes heat from the molten alloy M filling the hollow portion 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, forming a solidified shell on the surface of the molten alloy M.

[0044] The cooling water jetting passages 25 spray cooling water directly from shower openings 25a facing the hollow portion 21 toward the aluminum alloy rods B at the other end 12b of the mold 12 to cool the aluminum alloy rods B. The vertical cross-sectional shape of the cooling water jetting passages 25 may be, for example, semicircular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

[0045] In this embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first stored in the cooling water cavity 24 to cool the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and then the cooling water W in the cooling water cavity 24 is sprayed toward the aluminum alloy bar B from the cooling water spray passage 25. However, these may also be configured to be supplied by separate cooling water supply pipes.

[0046] The length from the position where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 hits the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13 is called the effective mold length L, and this effective mold length L is preferably 10 mm to 40 mm, for example. If this effective mold length L is less than 10 mm, a good coating cannot be formed, making casting impossible. If it exceeds 40 mm, forced cooling is ineffective, solidification by the mold wall becomes dominant, and contact resistance between the mold 12 and the molten alloy M or aluminum alloy rod B increases, resulting in cracks on the casting surface, tearing inside the mold, and other unstable casting, which is undesirable.

[0047] It is preferable that the supply of cooling water to the cooling water cavity 24 and the spray of cooling water from the shower opening 25a of the cooling water spray passage 25 can be controlled by control signals from a control device (not shown).

[0048] The cooling water cavity 24 is formed so that the inner bottom surface 24a closer to the hollow portion 21 of the mold 12 is parallel to the inner peripheral surface 21a of the hollow portion 21 of the mold 12. Note that "parallel" here also includes the case where the inner bottom surface 24a of the cooling water cavity 24 is formed at an elevation angle of 0 to 3 degrees with respect to the inner peripheral surface 21a of the hollow portion 21 of the mold 12, that is, the case where the inner bottom surface 24a is inclined at an angle of more than 0 degrees up to 3 degrees with respect to the inner peripheral surface 21a.

[0049] As shown in FIG. 3, the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24a of the cooling water cavity 24 faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, has a heat flux value per unit area of ​​10×10 5 W / m 2 That's it, 50 x 10 5 W / m 2 It is formed so as to fall within the following ranges.

[0050] The mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12, i.e., the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is, for example, 0.5 mm to 3.0 mm, and preferably 0.5 mm to 2.5 mm. The material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is in the range of 100 W / m K to 400 W / m K.

[0051] In Fig. 3, molten alloy M in molten metal receptacle 11 is supplied through refractory plate 13 to one end 12a of mold 12, which is held so that its central axis C is substantially horizontal, and is forcedly cooled at the other end 12b of mold 12 to form aluminum alloy rod B. Aluminum alloy rod B is withdrawn at a constant speed by a withdrawal drive device (not shown) installed near the other end 12b of mold 12, and is thus continuously cast to form long aluminum alloy rod B. The withdrawn aluminum alloy rod B is then cut to a desired length, for example, by a synchronized cutting machine (not shown).

[0052] The composition of the molten alloy M of the aluminum alloy stored in the molten metal receiver 11 may be the same as that of the aluminum alloy bar described above, namely, 0.15 to 1.0 mass% Cu, 0.6 to 1.2 mass% Mg, 0.95 to 1.35 mass% Si, 0.4 to 0.6 mass% Mn, 0.15 to 0.70 mass% Fe, 0.09 to 0.25 mass% Cr, 0.012 to 0.035 mass% Ti, with the balance being Al and unavoidable impurities. It may further contain 0.0001 to 0.03 mass% B.

[0053] The composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using a photoelectric photometric emission spectrophotometer as described in JIS H 1305 (eg, PDA-5500 manufactured by Shimadzu Corporation, Japan).

[0054] The difference in height between the liquid level of the molten alloy M stored in the molten metal receiver 11 and the upper inner circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting the difference in height within this range, the pressure of the molten alloy M supplied into the mold 12 and the lubricating oil and the gas produced by vaporizing the lubricating oil are suitably balanced, resulting in stable castability.

[0055] The liquid lubricant can be a vegetable oil, such as rapeseed oil, castor oil, or salad oil, which are preferred because they have little adverse effect on the environment.

[0056] The lubricating oil supply rate is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min to 1 mL / min). If the supply rate is too low, the molten alloy of the aluminum alloy rod B may not solidify due to insufficient lubrication, and may leak from the mold. If the supply rate is too high, the excess may get mixed into the aluminum alloy rod B, causing internal defects.

[0057] The casting speed, which is the speed at which the aluminum alloy rod B is withdrawn from the mold 12, is preferably 200 mm / min to 1500 mm / min (more preferably 400 mm / min to 1000 mm / min), because a casting speed within this range results in a uniform and fine network structure of crystals formed by casting, which increases the resistance of the aluminum matrix to deformation at high temperatures and improves its high-temperature mechanical strength.

[0058] The amount of cooling water sprayed from the shower openings 25a of the cooling water spray passages 25 is preferably 10 L / min to 50 L / min (more preferably 25 L / min to 40 L / min) per mold. If the amount of cooling water is less than this, the molten alloy may not solidify and leak from the mold. Also, the surface of the cast aluminum alloy bar B may remelt, forming a non-uniform structure that may remain as internal defects. On the other hand, if the amount of cooling water is greater than this range, the mold 12 may lose too much heat, causing it to solidify prematurely.

[0059] The average temperature of the molten alloy M flowing from the molten metal receiver 11 into the mold 12 is preferably, for example, 650°C to 750°C (more preferably 680°C to 720°C). If the temperature of the molten alloy M is too low, coarse crystallized matter will form in the mold 12 or before that, and will be incorporated as internal defects inside the aluminum alloy bar B. On the other hand, if the temperature of the molten alloy M is too high, a large amount of hydrogen gas will be easily incorporated into the molten alloy 255, which will be incorporated as porosity in the aluminum alloy bar B, potentially causing internal cavities.

[0060] In the present embodiment, in the cooling wall portion 27 of the mold 12, the heat flux value per unit area from the molten alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24 is 10×10 5 W / m 2 That's it, 50 x 10 5 W / m 2 By setting the temperature within the following range, it is possible to prevent the aluminum alloy rod B from seizing.

[0061] The cooling wall portion 27 of the mold 12 receives heat by extracting heat from the molten alloy M, and performs heat exchange by cooling this heat with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, we focused on the heat flux per unit area, as shown in the explanatory diagram in Figure 4. The heat flux per unit area is expressed by Fourier's law as follows: Q = -k × ((T1-T2 / L) (1) Q: Heat flux k: Thermal conductivity (W / m K) of the portion through which heat passes (in this embodiment, the cooling wall portion 27 of the mold 12) T1: low temperature of the location where heat passes (in this embodiment, the inner bottom surface 24a of the cooling water cavity 24) T2: High temperature side temperature of the portion through which heat passes (in this embodiment, the inner peripheral surface 21a of the hollow portion 21 of the mold 12) L: Length (mm) of the section where heat passes through (in this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

[0062] Good results were obtained even when the amount of lubricant was reduced during casting. Based on the mold material, thickness, and temperature measurement data, the heat flux value per unit area was 10 × 10 5 W / m 2 By configuring the cooling wall portion 27 of the mold 12 so that the heat flux value per unit area is 50×10 or more, it is possible to prevent the cast aluminum alloy rod B from seizing. 5 W / m 2 It is preferable to do the following:

[0063] To achieve this heat flux range for the cooling wall 27 of the mold 12, the mold 12 should be formed so that the thickness t of the cooling wall 27 of the mold 12 is, for example, in the range of 0.5 mm to 3.0 mm. Also, the thermal conductivity of at least the cooling wall 27 of the mold 12 should be in the range of 100 W / m K to 400 W / m K.

[0064] When producing an aluminum alloy bar according to one embodiment of the present invention, the horizontal continuous casting apparatus described above is used to continuously supply the molten alloy M stored in the molten metal receptacle 11 from one end 12a of the mold 12 into the hollow portion 21. Cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0065] The molten alloy M supplied into the hollow portion 21 is cooled to a temperature at which the heat flux per unit area of ​​the cooling wall portion 27 is 10×10 5 W / m 2 The aluminum alloy rod B is cooled and solidified under the above conditions to be cast. During casting of the aluminum alloy rod B, it is preferable to set the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, to 100°C or less.

[0066] The aluminum alloy rod B thus obtained has a heat flux value per unit area in the cooling wall portion 27 of 10×10 5 W / m 2 Cooling and solidification under the above conditions suppresses the adhesion of reaction products, such as carbides, that occur due to contact between the lubricating oil gas and the molten alloy M. This eliminates the need to remove carbides and the like from the surface of the aluminum alloy rod B by cutting, and allows the aluminum alloy rod B to be produced with a high yield.

[0067] As described above, according to the manufacturing method for an aluminum alloy ingot of this embodiment, the heat flux value per unit area of ​​the cooling wall portion 27 of the mold 12, where the inner bottom surface 24a of the cooling water cavity 24 faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is 10×10 5 W / m 2 By achieving the above, it is possible to realize an aluminum alloy ingot having excellent mechanical properties, in which the difference between the maximum and minimum DAS values ​​in a cross section perpendicular to the casting direction is in the range of 5 μm to 20 μm and the standard deviation of this DAS is 5 μm or less, and in which the degree of non-uniformity of the metal structure inside the ingot is small.

[0068] The method for producing an aluminum alloy ingot according to the present invention, in which the difference between the maximum and minimum values ​​of secondary dendrite arm spacing in a cross section perpendicular to the casting direction of the aluminum alloy ingot is in the range of 5 μm to 20 μm, is not limited to the horizontal continuous casting method described above, and known continuous casting methods such as vertical continuous casting can also be used. Furthermore, in order to improve the reliability of the final product, it is also preferable to subject the molten metal to a degassing treatment or a filtering treatment as appropriate.

[0069] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0070] The effects of the present invention were verified. For the verification, aluminum alloy ingots (aluminum alloy rods) having a circular cross section and a diameter of 49 mm were cast from molten metal having the composition shown in Table 1 using a horizontal continuous casting apparatus 10 having the structure shown in Fig. 2. Note that the example in which the mold of the horizontal continuous casting apparatus 10 was made of pure aluminum served as the material for forming the mold, and the comparative example in which the mold was made of porous graphite served as the material for forming the mold.

[0071] [Table 1]

[0072] As shown in FIG. 5, the aluminum alloy rods of the examples and comparative examples were each vertically removed from a range of 5 mm from the top end to a range of 5 mm from the bottom end, and the DAS was measured in three fields for each of the three regions, the top, center, and bottom, and the standard deviation was calculated.

[0073] The DAS was measured in accordance with the secondary branch method defined in the aforementioned Non-Patent Document 2. This secondary branch method is applied to a structure in which secondary dendrite arms are developed and aligned dendrites are relatively common, and the measurement of arm spacing is not hindered. The DAS was measured on a circular cross section obtained by cutting the aluminum alloy bar obtained by the above-mentioned method in a direction perpendicular to the casting direction.

[0074] As a pretreatment for these measurement surfaces, they were polished with emery paper, then with diamond paste, and then with a buff using a colloidal silica suspension to create a mirror finish, and then Barker etching was performed to expose the grain boundaries.Observation under an optical microscope was performed at 100x magnification, and the areas where dendrites could be clearly observed were selected as the measurement targets.

[0075] Here, a region about 10 mm from the surface of an aluminum alloy bar obtained by the horizontal continuous casting apparatus 10 forms a solidified shell due to rapid cooling of the molten metal flowing into the mold, and a solidification structure different from the central equiaxed crystal region is formed. Generally, a structure suitable for DAS measurement using the above-mentioned secondary branch method is not obtained from a position 5 mm from the outermost surface of the ingot. Therefore, as shown in Figure 5, the regions 5 mm from the top and bottom ends were excluded, and the ingot was divided into three regions: an upper region from 5 mm to 10 mm from the top end, a central region, and a lower region from 5 mm to 10 mm from the bottom end, and DAS measurements were performed in each region.

[0076] The field of view for DAS measurement was set to a field containing three crystal grains in which three or more secondary arms were clearly observed. As shown in Figure 1, a line segment was drawn connecting the centers of each aligned arm, and the number of intersections between the line segment and the center of each arm, n, was calculated as shown in Equation 2. i The length of the line segment is l i The DAS was calculated by dividing the DAS=Σ i l i / Σ i n i ···(2)

[0077] The DAS was measured in three randomly selected fields per region, for a total of nine DAS measurements per sample. From these measurement results, the difference between the maximum and minimum values ​​and the standard deviation were calculated. These results are shown in Table 2.

[0078] [Table 2]

[0079] Next, the mechanical properties of each of the cast aluminum alloy rods of the Examples and Comparative Examples were evaluated. To evaluate the mechanical properties, each aluminum alloy bar was subjected to homogenization treatment, solution treatment, and artificial aging treatment under the conditions shown in Table 3.

[0080] [Table 3]

[0081] The mechanical properties after this artificial aging were evaluated according to the following procedure. Specifically, test pieces with a gauge length of 25.4 mm and a parallel part diameter of 6.4 mm were taken from the aluminum alloy bars after the artificial aging treatment, and tensile tests were carried out at room temperature (25°C) at a rate of 2 mm / min to measure the tensile strength, 0.2% proof stress, and broken line elongation. The results are shown in Table 4.

[0082] [Table 4]

[0083] According to the results shown in Table 4, it was confirmed that the aluminum alloy rods of the examples, which were cast so that the difference between the maximum and minimum values ​​of the secondary dendrite arm spacing in a cross section perpendicular to the casting direction of the aluminum alloy ingot, was in the range of 5 μm to 20 μm, had better mechanical properties at room temperature than the comparative examples. In other words, the manufacturing method of the present invention makes it possible to obtain aluminum alloy ingots with excellent mechanical properties. [Explanation of symbols]

[0084] 10...Horizontal continuous casting equipment 11...Tundish 12...Mold 13... Refractory plate (heat insulating member) 21...Hollow part 21a...Inner peripheral surface 23…Cooling device 24...Cooling water cavity 24a…Inner bottom surface 25…Cooling water injection passage 26…Cooling water supply pipe 27...Cooling wall B: Aluminum alloy rod M...molten alloy W...cooling water

Claims

1. An aluminum alloy ingot comprising 0.15% by mass to 1.0% by mass of Cu, 0.6% by mass to 1.2% by mass of Mg, 0.95% by mass to 1.35% by mass of Si, 0.4% by mass to 0.6% by mass of Mn, 0.15% by mass to 0.70% by mass of Fe, 0.09% by mass to 0.25% by mass of Cr, 0.012% by mass to 0.035% by mass of Ti, and the balance being Al and unavoidable impurities, An aluminum alloy ingot, wherein the difference between the maximum and minimum values ​​of secondary dendrite arm spacing in a cross section perpendicular to the casting direction of the aluminum alloy ingot is in the range of 5 μm to 20 μm.

2. 2. The aluminum alloy ingot according to claim 1, further comprising: B: 0.0001% by mass to 0.03% by mass.

3. 3. The aluminum alloy ingot according to claim 1, wherein the standard deviation of the secondary dendrite arm spacing is 5 μm or less.

4. A method for producing an aluminum alloy ingot according to any one of claims 1 to 3, comprising: A horizontal continuous casting apparatus is used to produce an aluminum alloy ingot by supplying molten aluminum alloy in a molten metal receiver from one end side of a hollow mold arranged so that the central axis of the hollow portion is aligned horizontally into the hollow portion of the mold, The molten metal is continuously supplied from one end side of the mold to the hollow portion, and cooling water is supplied to a cooling water cavity formed outside an inner peripheral surface of the hollow portion and containing cooling water for cooling the inner peripheral surface, The heat flux value per unit area in the cooling wall portion of the mold between the inner circumferential surface and the inner bottom surface of the cooling water cavity, which is parallel to the inner circumferential surface, is 10×10 ５ W / m ２ The method for producing an aluminum alloy ingot comprises cooling and solidifying the molten metal under the above conditions to produce an aluminum alloy ingot.

5. 5. The method for producing an aluminum alloy ingot according to claim 4, wherein the thickness of the cooling wall of the mold is formed to be in the range of 0.5 mm to 3.0 mm.

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