Serially cast aluminum alloy rod and method for producing serially cast aluminum alloy rod

Abstract

A serially cast aluminum alloy rod which, at a radial midpoint in a cross section thereof perpendicular to the casting direction, has an average crystal grain diameter in the range of 50-120 μm and in which, in an area extending to the center from a position located 3 mm inward from the peripheral surface toward the center, the difference between the maximum value and the minimum value of the average crystal grain diameter is 50 μm or less; and a method for producing the serially cast aluminum alloy rod.

Description

Continuously cast aluminum alloy rod, and method for manufacturing continuously cast aluminum alloy rod

[0001] This application claims priority to Japanese Patent Application No. 2024-010516, filed on January 26, 2024, the contents of which are incorporated herein by reference.

[0002] Aluminum alloy forgings are finding increasing applications as structural components for various products, taking advantage of their light weight and high strength. However, in areas where the processing rate is low, these aluminum alloy forgings tend to be affected by the mechanical properties and structure of the aluminum alloy continuously cast rod (hereinafter, sometimes simply referred to as "continuously cast rod") that is the raw material for production, and the extent to which properties can be improved by plastic processing is also limited. Therefore, if the properties of the continuously cast rod itself are poor, the forgings may not satisfy the required properties (see, for example, Patent Document 1).

[0003] Furthermore, there is a strong correlation between the properties of continuously cast rods and the cooling rate and grain size. At the stage of continuously cast rods where no plastic working is performed, the grain size becomes smaller, which improves the properties of tensile strength, 0.2% yield strength, and elongation. This grain size is also correlated with the cooling rate, but is particularly strongly correlated with the amount of heterogeneous nuclei. Generally, an Al-Ti-B mother alloy is used, and TiB ２ However, the grain size can be reduced by the action of heterogeneous nuclei such as TiB. ２ Since is a hard particle, if added in excess, there is a concern that it may shorten the life of cutting tools and the like used in machining.

[0004] Japanese Patent No. 4774630 (B)

[0005] The present invention has been made in view of the above technical background, and has as its object to provide a continuously cast aluminum alloy rod having uniform mechanical properties with little change in crystal characteristics from the peripheral portion to the center by reducing the variation in average crystal grain size in the radial direction, and a method for producing a continuously cast aluminum alloy rod.

[0006] In order to solve the above problems, the present invention provides the following means.

[0007] (1) Si is in the range of 0.40 mass% or more and 0.8 mass% or less, Fe is in the range of 0.15 mass% or more and 0.5 mass% or less, Cu is in the range of 0.15 mass% or more and 0.40 mass% or less, Mn is in the range of 0.15 mass% or less, Mg is in the range of 0.8 mass% or more and 1.5 mass% or less, Cr is in the range of 0.04 mass% or more and 0.35 mass% or less, Zn is in the range of 0.25 mass% or less, Ti is in the range of 0.005 mass% or more and 0.03 mass% or less, B is in the range of 0.00015 mass% or more and 0. 1. A continuously cast rod of an aluminum alloy having a cylindrical shape, the aluminum alloy having an alloy composition containing 0.006% by mass or less of each of Al and Zn in a range of 0.006% by mass or less, with the balance consisting of Al and inevitable impurities, wherein the average crystal grain size at the midpoint of the radius in a cross section perpendicular to the casting direction is in a range of 50 μm or more and 120 μm or less, and the difference between the maximum and minimum values ​​of the average crystal grain size in the range from a position 3 mm from the outer peripheral surface toward the center to the center is 50 μm or less.

[0008] (2) A method for producing a continuously cast rod of an aluminum alloy as set forth in (1), comprising: a molten metal pouring step of pouring a molten alloy having the alloy composition into a mold body for continuous casting; a primary cooling step of circulating a cooling medium through a cavity formed around the mold body to solidify the molten alloy and form the continuously cast rod; and a secondary cooling step of directly spraying the cooling medium toward the continuously cast rod that has undergone the primary cooling step, wherein the cooling rate at the center of the continuously cast rod from the molten metal pouring step to the completion of the primary cooling step is controlled to be 3°C / sec or more.

[0009] According to the present invention, it is possible to provide a continuously cast aluminum alloy rod having uniform mechanical properties with little change in crystal properties from the peripheral portion to the center portion by reducing the variation in average crystal grain size in the radial direction, and a method for manufacturing a continuously cast aluminum alloy rod.

[0010] 1 is a schematic diagram showing an example of a position where a crystal grain size sample is collected. 2 is a schematic cross-sectional view showing an example of a vertical casting apparatus used in a method for producing a continuously cast aluminum alloy rod according to an embodiment of the present invention. 3 is a schematic diagram showing an example of an observation portion in measuring the life of a cutting tool.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto. Appropriate changes can be made within the scope that does not change the effects of the present invention.

[0012] [Continuously Cast Aluminum Alloy Rod] A continuously cast aluminum alloy rod (hereinafter simply referred to as a continuously cast rod) according to one embodiment of the present invention contains Si in the range of 0.40% by mass to 0.8% by mass, Fe in the range of 0.15% by mass to 0.5% by mass, Cu in the range of 0.15% by mass to 0.40% by mass, Mn in the range of 0.15% by mass or less, Mg in the range of 0.8% by mass to 1.5% by mass, Cr in the range of 0.04% by mass to 0.35% by mass, Zn in the range of 0.25% by mass or less, Ti in the range of 0.005% by mass to 0.03% by mass, and Fe in the range of 0.15% by mass to 0.5% by mass. % or less by mass, B in the range of 0.00015% by mass or more and 0.006% by mass or less, and the balance being Al and unavoidable impurities, wherein the average crystal grain size at the midpoint of the radius in a cross section perpendicular to the casting direction is in the range of 50 μm or more and 120 μm or less, and the difference between the maximum and minimum values ​​of the average crystal grain size in the range from a position 3 mm from the outer peripheral surface toward the center to the center is 50 μm or less.

[0013] The continuously cast rod of this embodiment is cylindrical and is continuously cast with minute irregularities on the outer circumferential surface. The resulting continuously cast rod has a casting diameter perpendicular to the casting direction (longitudinal direction) of, for example, 40 mm to 130 mm.

[0014] (Si: 0.40 mass % or more and 0.8 mass % or less) Si coexists with Mg to form Mg ２ It forms Si-based precipitates and contributes to improving the strength of forged products. If the Si content is 0.40% by mass or more, the strength of forged products can be improved. On the other hand, if the Si content exceeds 0.80% by mass, grain boundary precipitation of Si increases, which may reduce the toughness of the forged material. Therefore, the Si content is set to 0.40% by mass or more and 0.80% by mass or less. Although not particularly limited, the Si content may be 0.60% by mass or more and 0.80% by mass or less.

[0015] (Fe: 0.15% by mass or more and 0.5% by mass or less) Fe crystallizes in aluminum alloys as fine crystals containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Fe-Si, and Al-Mn-Fe, thereby preventing grain coarsening. If the Fe content is lower than 0.15% by mass, there is a concern that the effect of preventing grain coarsening may not be sufficiently achieved. On the other hand, if the Fe content exceeds 0.5% by mass, there is a concern that coarse intermetallic compounds may be generated, reducing the toughness of the forged product. Therefore, the Fe content is set to 0.15% by mass or more and 0.5% by mass or less. Although not particularly limited, the Fe content may be 0.15% by mass or more and 0.25% by mass or less.

[0016] (Cu: 0.15% by mass or more and 0.40% by mass or less) Cu has the effect of finely dispersing Mg—Si compounds in the aluminum alloy and improving the tensile strength of the aluminum alloy by precipitating as Al—Cu compounds. If the Cu content is lower than 0.15% by mass, there is a concern that age hardening may not be sufficient. On the other hand, if the Cu content exceeds 0.4% by mass, there is a concern that the toughness of the forged product may be reduced. Furthermore, if the Cu content is excessively increased, there is a concern that the corrosion resistance of the forged product may be reduced, the susceptibility to intergranular corrosion may be increased, and stress corrosion cracking may occur. Therefore, the Cu content is set to 0.15% by mass or more and 0.40% by mass or less. Although not particularly limited, the Cu content may be 0.25% by mass or more and 0.38% by mass or less.

[0017] (Mn: 0.15% by mass or less) Mn forms fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Fe, Al-Mn, and Al-Mn-Si in the aluminum alloy, thereby improving the tensile strength of the aluminum alloy. On the other hand, if the Mn content exceeds 0.15% by mass, coarse intermetallic compounds may be generated, which may reduce the toughness of the forged product. Therefore, the Mn content is set to 0.15% by mass or less. Although not particularly limited, the Mn content may be 0.05% by mass or more and 0.13% by mass or less.

[0018] (Mg: 0.8 mass % or more, 1.5 mass % or less) Mg coexists with Si to form Mg ２ It forms Si-based precipitates and contributes to improving the strength of forged products. If the Mg content is lower than 0.80 mass%, the effect of precipitation strengthening is not sufficiently obtained, and there is a concern that high strength cannot be ensured. On the other hand, if the Mg content exceeds 1.5 mass%, Mg ２ There is a concern that an excessive increase in Si-based precipitates may reduce the toughness of the forged product. Therefore, the Mg content is set to 0.8 mass% or more and 1.5 mass% or less. Although not particularly limited, the Mg content may be 0.95 mass% or more and 1.25 mass% or less.

[0019] (Cr: 0.04% by mass or more, 0.35% by mass or less) Cr crystallizes as an AlCrSi phase, while Cr that does not crystallize precipitates and has the effect of suppressing recrystallization. If the Cr content is lower than 0.04% by mass, the above-mentioned recrystallization suppression effect is reduced, and the recrystallized structure coarsens and grows, reducing strength. In addition, structural control becomes difficult, resulting in a coarse recrystallized structure and a decrease in toughness. On the other hand, if the Cr content exceeds 0.35% by mass, coarse intermetallic compounds are generated, which may reduce the toughness of the forged product. Therefore, the Cr content is set to 0.04% by mass or more, and 0.35% by mass or less. Although not particularly limited, the Cr content may be 0.15% by mass or more and 0.28% by mass or less.

[0020] (Zn: 0.25% by mass or less) Zn is basically contained in the aluminum and is unavoidable, but to improve the strength of the forged product, Zn may be contained in a range of 0.25% by mass or less. Although not particularly limited, the Zn content may be 0.001% by mass or more.

[0021] (Ti: 0.005% by mass or more, 0.03% by mass or less) Ti has the effect of refining the crystal grains of an aluminum alloy and improving the wrought workability, thereby contributing to preventing the occurrence of ingot cracking in a continuously cast rod. If the Ti content is less than 0.005% by mass, there is a concern that this effect of improving the wrought workability will be reduced. On the other hand, if the Ti content exceeds 0.03% by mass, coarse Ti compounds will crystallize, reducing the toughness of the forged product. Therefore, the Ti content is set to 0.005% by mass or more, 0.03% by mass or less.

[0022] (B: 0.00015% by mass or more, 0.006% by mass or less) B has the effect of refining the crystal grains of an aluminum alloy and improving the wrought workability. By adding B to an aluminum alloy together with the above-mentioned Ti, the effect of refining the crystal grains is improved. If the B content is less than 0.00015% by mass, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the B content exceeds 0.006% by mass, TiB ２ Therefore, the B content is set to 0.00015 mass % or more and 0.006 mass % or less.

[0023] (Inevitable Impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from raw materials or the manufacturing process. Examples of inevitable impurities include Ni, Sn, and Be. The total content of these inevitable impurities preferably does not exceed 0.1% by mass.

[0024] (Average grain size at the midpoint of the radius in a cross section perpendicular to the casting direction is 50 μm or more and 120 μm or less) As shown in the schematic diagram of the sampling positions of grain size samples in FIG. 1 , the average grain size in a small rectangular region at 1 / 2r including the midpoint of radius r in a substantially circular cross section perpendicular to the casting direction of the continuously cast rod is set to 50 μm or more and 120 μm or less. In FIG. 1 , (1) indicates a portion 3 mm below the casting surface, (2) indicates the 1 / 2r portion, and (3) indicates the center. The range of the 1 / 2r portion is, for example, an area of ​​100 mm including the midpoint of radius r in a substantially circular cross section perpendicular to the casting direction of the continuously cast rod. ２ If the average grain size at the 1 / 2r portion (midpoint) exceeds 120 μm, the grain size becomes coarse, which may result in a deterioration in the mechanical properties of the forged product.

[0025] (The difference between the maximum and minimum average grain size in the range from a position 3 mm from the outer periphery toward the center to the center is 50 μm or less) As shown in the schematic diagram of the sampling positions of grain size samples shown in FIG. 1 , in the substantially circular cross section of the continuously cast rod perpendicular to the casting direction, the difference between the maximum and minimum average grain size is set to 50 μm or less between a small rectangular region 3 mm below the casting surface, which is located 3 mm from the outer periphery toward the center, and a small rectangular region in the central part including the center. The range 3 mm below the casting surface is, for example, an area of ​​100 mm 2 including a position 3 mm from the outer periphery toward the center in the substantially circular cross section of the continuously cast rod perpendicular to the casting direction. ２ The central area is a rectangular area of ​​100 mm2 including the center in a substantially circular cross section perpendicular to the casting direction of the continuously cast rod. ２ It is a rectangular area.

[0026] Since the grain size tends to change unilaterally from the outer periphery (cast surface) toward the center, by measuring the average grain size at a position 3 mm below the cast surface and at the center, the maximum and minimum values ​​of the average grain size in the range from a position 3 mm from the outer periphery toward the center to the center can be obtained without taking continuous samples in the radial direction. By keeping the difference between the maximum and minimum values ​​at 50 μm or less, the radial variation of the grain size is reduced, thereby suppressing variations in the mechanical properties depending on the location of the continuously cast rod and achieving a continuously cast rod with uniform properties.

[0027] As described above, the continuously cast rod of the aluminum alloy of this embodiment can suppress the deterioration of mechanical properties due to coarse crystal grains, and can realize a continuously cast rod with uniform crystal grain size and excellent workability, in which areas with coarse crystal grains do not coincide with areas with low forging processing rates.

[0028] [Method for Manufacturing Continuously Cast Aluminum Alloy Rod] Next, an example of a method for manufacturing a continuously cast aluminum alloy rod according to this embodiment will be described. First, an example of a vertical casting apparatus used in the method for manufacturing a continuously cast aluminum alloy rod according to this embodiment will be described. FIG. 2 is a cross-sectional schematic diagram showing an example of a vertical casting apparatus used in the method for manufacturing a continuously cast aluminum alloy rod according to this embodiment. A vertical continuous casting apparatus 10 for continuous casting has a continuous casting mold 100. The continuous casting mold 100 has a cylindrical mold body 100A having an inlet 12 for molten alloy at one end and an outlet 13 for casting ingots at the other end. The mold body 100A is made of an aluminum alloy containing a large amount of Mg. Alternatively, a Cu alloy can also be suitably used.

[0029] The mold body 100A has a cavity 21 through which cooling water C flows, an inlet 22 to the cavity 21 provided at the top, and a jetting port 23 surrounding the casting outlet 13. The cooling water C introduced from the inlet 22 flows through the cavity 21 and cools the molten metal M in the forming hole 11 via the mold body 100A, solidifying the molten alloy (primary cooling). The cooling water C is then jetted from the jetting port 23 onto the ingot (continuously cast bar) S being cast, thereby cooling the ingot S (secondary cooling).

[0030] The method for producing a continuously cast aluminum alloy rod of this embodiment includes at least the following steps: a molten metal pouring step in which a molten alloy having the above-described alloy composition is poured using, for example, the above-described vertical continuous casting apparatus 10; a primary cooling step in which a cooling medium is circulated into the cavity to solidify the molten alloy and form a continuously cast rod; and a secondary cooling step in which a cooling medium is directly sprayed toward the continuously cast rod that has undergone the primary cooling step. The method is characterized by controlling the cooling rate at the center of the continuously cast rod from the molten metal pouring step to the completion of the primary cooling step to be 3°C / sec or higher.

[0031] The molten alloy poured in the molten metal pouring step is prepared by melting an aluminum alloy material having the alloy composition of the embodiment of the continuously cast rod described above. The Ti and B contained in this alloy composition are preferably added simultaneously to the molten metal using an Al-Ti-B master alloy. A preferred addition method is to add rod material using a rod feeder. Using a rod feeder allows for accurate setting of the addition rate, enabling the addition of the refiner at the desired mass ratio.

[0032] The most preferable place to simultaneously add Ti and B is a GBF furnace, which blows inert gas into the molten aluminum alloy to degas it. Adding Ti and B to a GBF furnace has the effect of removing inclusions contained in the rod material, and the rotation of the GBF rotor also allows the molten metal to be stirred, so that the fine metal compounds present in the rod material are uniformly dispersed. The advantage of adding Ti and B in the rod is that Al is easily removed by rapid solidification during the production of the rod. ３ Ti and TiB ２ Since the size of the refined intermetallic compounds such as those mentioned above is smaller than that of the base metal, refinement performance can be further improved.

[0033] The temperature at which Al-Ti-B is added is preferably the alloy molten temperature of 750°C. If it is added when the molten alloy temperature exceeds 770°C, the intended effect of the addition cannot be obtained. Also, if it is added when the molten alloy temperature is below 710°C, the intended effect of the addition cannot be obtained.

[0034] The casting speed and other conditions are set so that the cooling rate at the center of the continuously cast rod is 3°C / sec or higher from the molten metal pouring step to the completion of the primary cooling step, which is before the start of the secondary cooling step. By setting such a cooling rate, it is possible to cast a continuously cast rod having the characteristics described in the above-mentioned embodiment of the continuously cast rod, namely, an average grain size at the midpoint of the radius in a cross section perpendicular to the casting direction of 50 µm to 120 µm, and a difference between the maximum and minimum average grain size in the range from 3 mm from the outer peripheral surface toward the center to the center of 50 µm or lower.

[0035] 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.

[0036] Next, verification examples of the effects of the present invention will be described, but the present invention is not particularly limited to these verification examples.

[0037] [Examples 1-9 and Comparative Examples 1-4] (Production of Continuously Cast Products) First, an aluminum alloy material having the alloy composition shown in Table 1 below (the remainder being aluminum) was prepared. The molten alloy was formed by melting raw materials containing the main elements Si, Cu, and Mg. The molten alloy was then transferred to a holding furnace, where it was held for a certain period of time before being tapped. An Al-Ti-B master alloy, serving as a grain refiner, was simultaneously added to the molten alloy in the GBF furnace using a rod feeder. GBF treatment was then performed within the same GBF furnace. The GBF-treated molten alloy was then transferred to a trough and cast using a gas-pressurized hot-top casting method. This molten alloy treatment device was designed to remove aluminum oxide and hydrogen gas present in the molten alloy. The molten alloy tapped from the holding furnace underwent GBF treatment, and the purified molten alloy was transferred from the bottom to the top of the GBF furnace and poured into the mold body of a continuous casting device.

[0038]

[0039] [Evaluation] The following evaluations were carried out on the continuously cast aluminum alloy rods obtained as described above in Examples 1 to 9 and Comparative Examples 1 to 4. The evaluation results are shown in Table 1 above.

[0040] <Grain size> Samples were taken from the continuously cast rods based on the locations where the grain size samples were taken in Figure 1 and observed at 85x magnification using an optical microscope to measure the grain size. Five fields were measured for each sample location. <Grain size difference> This was calculated from the average grain size at the center and a portion 3 mm below the casting surface. <Tool life> Using the obtained continuously cast rods, cutting trials were performed using a carbide-tipped saw as a cutting tool, and the condition was observed using a digital microscope. Cutting tool life measurement method: 1,000 ingots with a diameter of 80 cm were cut, and the wear amount of the cutting edge was measured before and after cutting. Figure 3 shows a photograph of an example of an observed portion used in cutting tool life measurement. (Evaluation criteria) "satisfied": Wear amount less than 150 μm. "not satisfied": Wear amount 150 μm or more.

[0041] From the results shown in Table 1, it was confirmed that the method for producing a continuously cast aluminum alloy rod of this embodiment reduces the variation in average crystal grain size in the radial direction and produces a continuously cast aluminum alloy rod having uniform mechanical properties with little change in crystal properties from the peripheral portion to the center portion.

[0042] According to the present invention, it is possible to provide a continuously cast aluminum alloy rod having uniform mechanical properties with little change in crystal properties from the peripheral portion to the center portion by reducing the variation in average crystal grain size in the radial direction, and a method for manufacturing a continuously cast aluminum alloy rod.

[0043] 10 Vertical continuous casting device 12 Inlet 13 Casting outlet 100 Continuous casting mold

Claims

1. A continuous casting rod of a cylindrical aluminum alloy having an alloy composition containing Si in the range of 0.40% by mass or more and 0.8% by mass or less, Fe in the range of 0.15% by mass or more and 0.5% by mass or less, Cu in the range of 0.15% by mass or more and 0.40% by mass or less, Mn in the range of 0.15% by mass or less, Mg in the range of 0.8% by mass or more and 1.5% by mass or less, Cr in the range of 0.04% by mass or more and 0.35% by mass or less, Zn in the range of 0.25% by mass or less, Ti in the range of 0.005% by mass or more and 0.03% by mass or less, and B in the range of 0.00015% by mass or more and 0.006% by mass or less, with the balance being Al and inevitable impurities, wherein the average crystal grain size at the midpoint of the radius in a cross section perpendicular to the casting direction is in the range of 50 μm or more and 120 μm or less, and the difference between the maximum value and the minimum value of the average crystal grain size in the range from the position 3 mm inward from the outer peripheral surface to the center is 50 μm or less. A continuous casting rod of an aluminum alloy characterized by the above.

2. A method for manufacturing a continuous casting rod of the aluminum alloy according to claim 1, comprising: a molten metal injection step of injecting a molten metal having the alloy composition into the inside of a mold body of a continuous casting mold; a primary cooling step of circulating a cooling medium in a cavity formed around the mold body to solidify the molten metal to form the continuous casting rod; and a secondary cooling step of directly injecting the cooling medium toward the continuous casting rod that has undergone the primary cooling step, and controlling the cooling rate at the center of the continuous casting rod from the molten metal injection step to the completion of the primary cooling step to be 3°C / second or more. A method for manufacturing a continuous casting rod of an aluminum alloy characterized by the above.

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