Production method for aluminum alloy ingot, continuously cast aluminum alloy rod, and forged aluminum alloy product

Abstract

A method including a primary melting step in which raw materials containing aluminum alloy scraps with a Si content of 0.60 mass % to 0.90 mass % or less and the contents of the other additive elements within the same formulation ranges as those of the aluminum alloy ingot are melted to obtain a first molten metal, a primary casting step in which the first molten metal is solidified into an ingot, and a secondary melting step in which the Si content is adjusted to 0.90 mass % to 1.9% mass %.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for producing an aluminum alloy ingot, a continuously cast aluminum alloy rod, and a forged aluminum alloy product.

[0002] Priority is claimed on Japanese Patent Application No. 2023-084135, filed May 22, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] In recent years, amid global carbon neutrality, reducing the amount of CO2 emissions in producing steps has become a critical issue.

[0004] In order to minimize the amount of CO2 emissions during aluminum production, utilizing aluminum alloy scraps with a lower melting point than pure aluminum (a purity of 99.0% or more) is important for improving the energy consumption rate during melting.

[0005] Methods for producing aluminum alloys and aluminum alloy products using aluminum alloy scraps as raw materials are known (for example, Patent Documents 1 to 3). Aluminum alloy scraps are recovered from used aluminum products, produced as recycled raw materials through melting and component adjustment, and used as raw materials for aluminum alloys.CITATION LISTPatent DocumentPatent Document 1: Published Japanese Translation No. 2020-514556 of the PCT International Publication

[0007] Patent Document 2: Published Japanese Translation No. 2020-527653 of the PCT International Publication

[0008] Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2022-137762SUMMARY OF INVENTIONTechnical Problem

[0009] In utilizing aluminum alloy scraps as aluminum alloy raw materials derived from such recycled raw materials, for example, when scraps for 6000 series alloys are used, it is preferable to use scraps with high purity such as 6063 sash fragments generated from building materials. However, impurities such as Si, Fe, and Mn are mixed in from the scraps. In melting and casting steps, when these compounds (for example, Al—Fe—Mn—Si) grow coarsely and are present in the cast rod, the mechanical properties of the product deteriorate.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a 6000 series aluminum alloy ingot through which it is possible to utilize commercially available aluminum alloy scraps in the aluminum alloy production and minimize coarsening of Al—Fe—Mn—Si compounds generated from elements mixed in from the aluminum alloy scraps, a continuously cast aluminum alloy rod, and a forged aluminum alloy product.Solution to Problem

[0011] In order to achieve the above objects, the present invention provides the following aspects.

[0012] Aspect 1 of the present invention is a method for producing an aluminum alloy ingot containing additive elements of Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Si in a range of 0.90 mass % or more and 1.9 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, with the remainder being made up of Al and unavoidable impurities, the method including a primary melting step in which raw materials containing aluminum alloy scraps with a Si content of 0.60 mass % or more and 0.90 mass % or less and the contents of the other additive elements within the same formulation ranges as those of the aluminum alloy ingot are melted to obtain a first molten metal, a primary casting step in which the first molten metal obtained in the primary melting step is solidified into an ingot, and a cooling rate from a liquid-phase temperature to a solid-phase temperature at the final solidification part of the ingot is 10° C. / sec or more, and a secondary melting step in which metallic Si or a Si-containing alloy is added to a molten metal obtained by melting the ingot obtained in the primary casting step, and the Si content is adjusted to be within a range of 0.90 mass % or more and 1.9% mass % or less.

[0013] Aspect 2 of the present invention is the method for producing an aluminum alloy ingot according to Aspect 1, wherein the aluminum alloy scraps are at least one of scraps containing 3000 series alloys, scraps containing 4000 series alloys, scraps containing 5000 series alloys, and scraps containing 6000 series alloys.

[0014] Aspect 3 of the present invention is a continuously cast aluminum alloy rod obtained using an aluminum alloy ingot produced by the method for producing an aluminum alloy ingot according to Aspect 1 or 2 and having a 0.2% yield strength of 350 MPa or more.

[0015] Aspect 4 of the present invention is a forged aluminum alloy product obtained using the continuously cast aluminum alloy rod according to Aspect 3 and having a 0.2% yield strength of 370 MPa or more.Advantageous Effects of Invention

[0016] According to the method for producing an aluminum alloy ingot of the present invention, it is possible to provide a method for producing a 6000 series aluminum alloy ingot through which it is possible to utilize commercially available aluminum alloy scraps and minimize coarsening of Al—Fe—Mn—Si compounds generated from elements mixed in from the aluminum alloy scraps.BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 A conceptual view when a first molten metal obtained in a primary melting step is once solidified into an ingot and the ingot is introduced into a secondary melting step.

[0018] FIG. 2 A cross-sectional schematic view of a continuous casting mold of a vertical continuous casting device.

[0019] FIG. 3 A cross-sectional schematic view of a horizontal continuous casting device.

[0020] FIG. 4A A schematic view illustrating a structure observation part of a continuously cast aluminum alloy rod of the present embodiment.

[0021] FIG. 4B A schematic view illustrating a part of the continuously cast aluminum alloy rod of the present embodiment where tensile properties are evaluated.

[0022] FIG. 5 A schematic view illustrating preparation of a forged product for evaluating the tensile properties of a forged aluminum alloy product of the present embodiment.DESCRIPTION OF EMBODIMENTS

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0024] Here, in the drawings used in the following description, in order to facilitate understanding of features, featured parts are enlarged for convenience of illustration in some cases, and dimensional ratios of components are not necessarily the same as actual ones. In addition, materials, sizes and the like exemplified in the following description are only examples, and the present invention is not necessarily limited thereto and can be appropriately changed and implemented within a range not changing the effects.[Method for Producing Aluminum Alloy Ingot]

[0025] An aluminum alloy ingot produced by a method for producing an aluminum alloy ingot according to the present embodiment will be described.

[0026] The aluminum alloy ingot of the present embodiment contains additive elements of Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Si in a range of 0.90 mass % or more and 1.9 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, with the remainder being made up of Al and unavoidable impurities.

[0027] The aluminum alloy ingot of the present embodiment corresponds to a forged product of a 6000 series aluminum alloy in that it contains Mg and Si.(Cu: 0.30 Mass % or More and 1.0 Mass % or Less)

[0028] Cu has a function of finely dispersing a Mg—Si-based compound in the aluminum alloy and has a function of improving the tensile strength of the aluminum alloy by precipitating as an Al—Cu—Mg—Si-based compound including a Q phase. When the Cu content is within the above range, it is possible to improve mechanical properties of the aluminum alloy ingot at room temperature.(Mg: 0.80 Mass % or More and 1.8 Mass % or Less)

[0029] Mg has a function of improving the tensile strength of the aluminum alloy. When Mg is solid-solutionized in an aluminum base phase or precipitates as a Mg—Si-based compound (Mg2Si) such as a β″ phase or an Al—Cu—Mg—Si-based compound (AlCuMgSi) including a Q phase, it contributes to strengthening of the aluminum alloy. In addition, Mg2Si has a function of minimizing formation of a CuAl2 phase in the aluminum alloy. When formation of a CuAl2 phase is minimized, the corrosion resistance of the aluminum alloy ingot is improved. When the Mg content is within the above range, it is possible to improve the mechanical properties and corrosion resistance of the aluminum alloy ingot at room temperature.(Si: 0.90 Mass % or More and 1.9 Mass % or Less)

[0030] Like Mg, Si has a function of improving the mechanical properties and corrosion resistance of the aluminum alloy ingot at room temperature. However, when excessive Si is added to the aluminum alloy, there is a risk of coarse primary crystal Si grains crystallizing and the tensile strength of the aluminum alloy decreasing. When the Si content is within the above range, it is possible to improve the mechanical properties and corrosion resistance of the aluminum alloy ingot at room temperature while minimizing crystallization of primary crystal Si.(Mn: 0.30 Mass % or More and 1.2 Mass % or Less)

[0031] Mn has a function of improving the tensile strength of the aluminum alloy by forming fine granular crystals containing intermetallic compounds such as Al—Mn—Fe—Si and Al—Mn—Cr—Fe—Si in the aluminum alloy. When the Mn content is within the above range, it is possible to improve mechanical properties of the aluminum alloy ingot at room temperature.(Fe: 0.20 Mass % or More and 0.65 Mass % or Less)

[0032] Fe has a function of improving the tensile strength of the aluminum alloy by crystallizing intermetallic compounds such as Al—Mn—Fe—Si, Al—Mn—Cr—Fe—Si, Al—Fe—Si, Al—Cu—Fe, and Al—Mn—Fe in the aluminum alloy as fine crystals. When the Fe content is within the above range, it is possible to improve mechanical properties of the aluminum alloy ingot at room temperature.

[0033] Here, the relationship of Fe / Mn is less than 1.4. When the relationship of Fe / Mn is less than 1.4, it is possible to minimize crystallization of AlFeSi-based compounds with a size of 2.0 μm or more, and it is possible to improve mechanical properties.(Cr: 0.050 Mass % or More and 0.30 Mass % or Less)

[0034] Cr has a function of improving the tensile strength of the aluminum alloy by forming fine granular crystals containing intermetallic compounds such as Al—Mn—Cr—Fe—Si and Al—Fe—Cr in the aluminum alloy. When the Cr content is within the above range, it is possible to improve mechanical properties of the aluminum alloy ingot at room temperature.(Ti: 0.010 Mass % or More and 0.10 Mass % or Less)

[0035] Ti has a function of refining aluminum alloy crystal grains and improving stretching processability. When the Ti content is less than 0.010 mass %, there is a risk of a sufficient crystal grain refinement effect not being obtained. On the other hand, when the Ti content is more than 0.10 mass %, there is a risk of coarse crystals being formed and stretching processability deteriorating. In addition, when a large amount of coarse crystals containing Ti are mixed into the aluminum alloy ingot, the toughness may decrease. Therefore, the Ti content is 0.010 mass % or more and 0.10 mass % or less. The Ti content is preferably 0.015 mass % or more and 0.050 mass % or less.(B: 0.0010 Mass % or More and 0.030 Mass % or Less)

[0036] B has a function of refining aluminum alloy crystal grains and improving stretching processability.

[0037] When B is added to the aluminum alloy together with the above Ti, the crystal grain refinement effect is improved. When the B content is less than 0.0010 mass %, there is a risk of a sufficient crystal grain refinement effect not being obtained. On the other hand, when the B content is more than 0.030 mass %, there is a risk of coarse crystals being formed and mixed into the aluminum alloy ingot as inclusions. In addition, when a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content is 0.0010 mass % or more and 0.030 mass %. The B content is preferably 0.0050 mass % or more and 0.025 mass %.(Zr: 0.0010 Mass % or More and 0.050 Mass % or Less)

[0038] When the Zr content is 0.050 mass % or less, it precipitates in the forms of Al3Zr and Al—(Ti, Zr), and thus contributes to improving the strength of the aluminum alloy ingot according to the recrystallization minimization effect and precipitation strengthening. However, when the Zr content is more than 0.050 mass %, it crystallizes as a coarse Zr compound, and thus there is a risk of the corrosion resistance of the aluminum alloy ingot decreasing. Therefore, the Zr content is 0.050 mass % or less. In addition, in order to obtain the above recrystallization minimization effect and the effect of improving the strength of the forged product according to precipitation strengthening, the Zr content is preferably 0.0010 mass % or more.(Zn: 0.250 Mass % or Less)

[0039] The Zn content may be 0.250 mass % or less. When the Zn content is more than 0.250 mass %, MgZn2 is formed and precipitates from an Al base phase to the grain boundaries, causing intergranular corrosion, and leading to a decrease in the corrosion resistance of the aluminum alloy ingot. Therefore, it is preferable that the Zn content be 0.250 mass % or less or that it not be included at all.(Unavoidable Impurities)

[0040] Unavoidable impurities are impurities that are unavoidably mixed into the aluminum alloy from raw materials of the aluminum alloy ingot or in the producing step. Examples of unavoidable impurities include Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities be not more than 0.1 mass %.[Method for Producing Aluminum Alloy Ingot]

[0041] Next, a method for producing an aluminum alloy ingot of the present embodiment will be described.

[0042] The aluminum alloy ingot of the present embodiment can be produced, for example, by a method including a melting (molten metal formation) step and a casting step. Here, in the aluminum alloy ingot of the present embodiment, the melting step includes two sub-steps (a primary melting step and a secondary melting step), and the casting step also includes two sub-steps (a primary casting step and a secondary casting step (main casting step)). These sub-steps are performed in the order of primary melting step→primary casting step→secondary melting step→secondary casting step.

[0043] Both the primary casting step and the secondary melting step are common in that they are steps of forming a molten aluminum alloy.

[0044] Both the primary casting step and the secondary casting step are common in that they are steps of preparing an aluminum alloy ingot (rod).<Primary Melting Step>

[0045] In the primary melting step, a first molten metal is obtained by melting raw materials containing aluminum alloy scraps with a Si content of 0.60 mass % or more and 0.90 mass % or less and the contents of the above additive elements (Cu, Mg, Mn, Fe, Zn, Cr, Ti, B, Zr) within the same formulation ranges as those of the aluminum alloy ingot to be produced.

[0046] FIG. 1 is a diagram conceptually showing a part of the method for producing an aluminum alloy ingot of the present embodiment.

[0047] Specifically, the diagram conceptually shows the flow in which raw materials containing mixed aluminum alloy scraps are prepared (raw material preparation step), next, the raw materials are put into a primary melting furnace, and a primary melting step is performed to obtain a first molten metal (primary melting step), the first molten metal is once solidified into an ingot (first molten metal solidifying (casting) step), and a secondary melting step is then performed in a secondary melting furnace using the ingot as a raw material to obtain a secondary molten metal (secondary melting step).

[0048] The primary melting step is performed under conditions such that added raw materials (materials) are completely melted. Examples of raw materials include aluminum alloy scraps, aluminum base metals, Cu fragments, and base alloys, and for example, melting is performed at 780 to 850° C.

[0049] Examples of aluminum alloy scraps include scraps of Al—Mn-based (3000 series) alloys such as aluminum cans and recycled aluminum can ingots, scraps of Al—Si-based (4000 series) alloys such as ADC12 and A356, scraps of Al—Mg-based (5000 series) alloys such as 5052 and 5083, and scraps of Al—Mg—Si-based (6000 series) alloys such as 6063 and 6061.

[0050] Aluminum base metals (pure aluminum) are classified into regular-purity base metals, high-purity base metals, and alloy base metals based on the purity and components, and can be divided into ingots (general raw material ingots), slabs (ingots adjusted for rolling), billets (ingots adjusted for extrusion) and the like based on the shape and application.

[0051] When the Si content is less than 0.60 mass %, for example, metallic Si or a Si-containing alloy is added and the Si content is adjusted to be within a range of 0.60 mass % or more and 0.90 mass %. Metallic Si is preferable as the additive material due to ease of adjustment.

[0052] In addition, when the Si content exceeds 0.90 mass %, aluminum base metals or aluminum alloy scraps with a low Si content are added and the Si content is adjusted to be within a range of 0.60 mass % or more and 0.90 mass %. Examples of aluminum alloy scraps with a low Si content include 3000 series alloy scraps, scraps containing 5000 series alloys, and scraps containing 6000 series alloys.

[0053] The Si content (component analysis) can be performed, for example, by emission spectroscopic analysis.

[0054] When Si, Fe, and Mn are mixed in from the scraps and melted, Al—Fe—Mn—Si compounds are generated in a predetermined temperature range during melting. The amount of these compounds generated is particularly greatly affected by the amount of Si. When the generation amount increases, it is necessary to set the melting temperature to 850° C. or higher in order to melt the compounds. However, this is not preferable because this increases energy used during melting.

[0055] In addition, when the Si content is below 0.6 mass %, the amount of Si added in the secondary melting step becomes excessive, and some time is taken for the added Si to completely melt, leading to energy loss. Therefore, it is necessary for the Si content of the alloy composition obtained in the primary melting step to be 0.60 mass % or more and 0.90 mass % or less.

[0056] When the usage proportion (mixing proportion) of the aluminum alloy scraps in the raw material is higher, this is preferable because the energy consumption rate during melting is improved.

[0057] The mixing proportion of the aluminum alloy scraps may be, for example, 50% or more. For example, it may be 60% or more, 70% or more, 80% or more, 90% or more, or 100%. On the other hand, although the effect of improving the energy consumption rate during melting is reduced, the mixing proportion of the aluminum alloy scraps may be less than 50%, for example, 40%, 30%, 20%, or 10%.

[0058] The melting point of the pure aluminum base metal is about 660° C. On the other hand, for example, ADC12 has a melting point of 570° C., and other materials also have a melting point of 650° C. or lower, which is at least 10° C. lower, and this makes them easier to melt, and when this property is utilized, the energy consumption rate during melting is improved.

[0059] As the aluminum alloy scraps, Al—Si-based (4000 series) alloys containing 4 mass % to 12 mass % of Si and 0.01 mass % or more and 3.0 mass % or less of Cu such as ADC12 and A356, Al—Mn-based (3000 series) alloys containing 0.7 mass % to 1.4 mass % of Mn and 0.5 mass % or more and 1.4 mass % or less of Mg such as other aluminum cans and recycled aluminum can ingots, Al—Mg-based (5000 series) alloys containing 2.0 mass % to 5.0 mass % of Mg such as 5052 and 5083, and Al—Mg—Si-based (6000 series) alloys containing 0.2 mass % or more and 0.8 mass % or less of Si and 0.45 mass % or more and 1.2 mass % or less of Mg such as 6063 and 6061 can be used within the range not exceeding the formulation range.

[0060] The aluminum can scraps are generally used after the heat treatment step at 400 to 500° C. in order to remove the paint from the surface of the can before melting.

[0061] When an Al—Si-based alloy is added, the amount of Si added in the secondary melting step can be reduced. Therefore, it is preferable to use this in combination with scraps of other types of alloys.<Primary Casting Step>

[0062] The primary casting step is a primary casting step in which the first molten metal obtained in the primary melting step is solidified into an ingot. In this case, a cooling rate from a liquid-phase temperature to a solid-phase temperature at the final solidification part of the ingot is 10° C. / sec or more.

[0063] Regarding the cooling rate at the final solidification part, the temperature of the ingot center, which is the final solidification part, is measured using a thermocouple, and a cooling rate from a liquid-phase temperature to a solid-phase temperature is calculated. For example, a K type (positive electrode: chromel, negative electrode: alumel) thermocouple can be used.

[0064] Here, as is well known, the “final solidification part” of the ingot is a part of the molten metal where solidification is completed. When the molten metal is poured into a mold, the molten metal cools and solidifies from the vicinity of the wall surface of the mold, finally, the part of the molten metal at the opening of the mold solidifies last, and this part that solidifies last is the final solidification part. In this specification, the “final solidification part” refers to the part where the remaining molten metal finally solidifies after 95% volume of the molten metal in the mold has solidified.

[0065] The approximate position of the “final solidification part” is shown using the vertical continuous casting device shown in FIG. 2 and the lateral (horizontal) continuous casting device shown in FIG. 3.

[0066] A continuous casting mold 200 in a vertical continuous casting device shown in FIG. 2 has a cylindrical shape with both ends of a molding hole 11 having a circular cross section being open, and is composed of a cylindrical mold main body 200A and a cylindrical carbon ring 200B on an inner circumferential surface 200Aa of the mold main body 200A that is fitted into the molding hole 11. One end of the molding hole 11 is an inlet 12 of a molten metal M, and the other end is a casting outlet 13 of an ingot S. In addition, the mold main body 200A has, in its interior, a cavity 21 through which cooling water C flows, an inlet 22 to the cavity 21 is provided at the upper part, and a discharge port 23 surrounding the casting outlet 13 is provided. The cooling water C introduced from the inlet 22 is primarily cooled and solidifies through the carbon ring 200B, and is then sprayed onto the ingot S that is discharged and cast from the discharge port 23, and thereby the ingot S is secondarily cooled. In addition, a recess 26, corresponding to the thickness of the carbon ring 200B, is formed in an area of the inner circumferential surface 200Aa of the mold main body 200A, excluding a part on the side of the casting outlet 13.

[0067] In FIG. 2, the symbol Sf indicates the final solidification part, and the symbol Th indicates a part where the temperature is measured by a thermocouple to measure the cooling rate at the final solidification part.

[0068] A horizontal continuous casting device 2000 shown in FIG. 3 includes a molten metal receiving part (not shown) having a tapping hole on the side wall, a pouring nozzle 20 having a pouring path with a circular cross section, and a continuous casting mold 400 having a cylindrical mold main body 400A having a molding hole 41 with a circular cross section. The continuous casting mold 400 shown in FIG. 3 includes the cylindrical mold main body 400A having a molten metal inlet 12 at one end and an ingot casting outlet 13 at the other end, and a carbon ring 400B that is arranged on an inner circumferential surface 400Aa of the mold main body 400A that is fitted into the molding hole 41. A lubricating oil supply pipe 43 that opens to the molding hole 41 is provided on the side of the inlet of the molding hole 41.

[0069] The mold main body 400A has, in its interior, a cavity 42 through which the cooling water C flows, and a discharge port 44 surrounding the casting outlet 13 is provided. The cooling water C introduced from an inlet (not shown) flows through the cavity 42, primarily cools and solidifies the molten metal M in the molding hole 41 through the mold main body 400A and the carbon ring 400B, and it then sprayed onto the ingot (ingot) S that is discharged and cast from the discharge port 44, and thereby the ingot S is secondarily cooled. In addition, a recess, corresponding to the thickness of the carbon ring 400B, is formed in an area of the inner circumferential surface 400Aa of the mold main body 400A, excluding a part of the side of the casting outlet 13.

[0070] In FIG. 3, the symbol Sf indicates the final solidification part, and the symbol Th indicates a part where the temperature is measured by a thermocouple to measure the cooling rate at the final solidification part.

[0071] Specifically, in the primary casting step, when the molten metal obtained in the primary melting step is solidified into an ingot, the molten metal is poured into a mold made of cast iron or the like, to cast the ingot. In this case, the temperature of the mold is controlled so that the cooling rate at the final solidification part of the ingot is 10° C. / sec or more. The casting may be performed by pouring the molten metal into a stationary mold and solidifying it or by performing vertical continuous casting. When the molten metal is poured into a stationary mold, the temperature of the mold may be 200° C. or lower, and is preferably 100° C. or lower. If the cooling rate exceeds 10° C. / sec, an Al—Fe—Mn—Si-based compound grows coarsely in the final solidification part, and this compound will not decompose unless it melts at a temperature exceeding 800° C. in the secondary melting step.

[0072] When the secondary melting step and casting are performed without decomposition, the unmelted Al—Fe—Mn—Si-based compound may mix into and remain in the product, and mechanical properties deteriorate.

[0073] When melting is performed at a temperature exceeding 800° C., oxidation loss during melting is accelerated, and thus the material loss increases.<Secondary Melting Step>

[0074] The secondary melting step is a step of adding metallic Si or a Si-containing alloy to a molten metal obtained by melting the ingot obtained in the primary casting step, and adjusting the Si content to 0.90 mass % or more and 1.9% mass %. Metallic Si is preferable as the additive material due to ease of adjustment.

[0075] The component adjustment here is performed at 700° C. or higher and 800° C. or lower.

[0076] If the temperature is below 700° C., the Al—Fe—Mn—Si-based compound grow coarsely due to the temperature drop in the molten metal path when this molten metal is cast, and the mechanical properties of the product deteriorate. In addition, when the temperature exceeds 800° C., the amount of hydrogen from the atmosphere dissolved in the aluminum molten metal increases, the amount of hydrogen gas in the molten metal increases, the porosity occurs in the resulting cast product, and thus the mechanical properties deteriorate. Therefore, a range of 700° C. or higher and 800° C. or lower is preferable.<Secondary Casting Step (Main Casting Step)>

[0077] The molten metal obtained in the secondary melting step is subjected to a flux treatment, then subjected to a gas bubbling filtration (GBF) treatment, and then poured into a casting mold.

[0078] The poured molten metal is continuously cast by either a vertical (longitudinal) continuous casting method or a horizontal (lateral) continuous casting method to obtain a continuously cast aluminum alloy rod.[Continuously Cast Aluminum Alloy Rod]

[0079] The continuously cast aluminum alloy rod according to the present embodiment is produced by performing continuous casting by either a vertical (longitudinal) continuous casting method or a horizontal (lateral) continuous casting method using the aluminum alloy ingot obtained by the method for producing an aluminum alloy ingot according to the present embodiment, and has a 0.2% yield strength of 350 MPa or more.[Forged Aluminum Alloy Product]

[0080] The forged aluminum alloy product according to the present embodiment is produced using the continuously cast aluminum alloy rod according to the present embodiment, and has a 0.2% yield strength of 370 MPa or more.

[0081] For example, the continuously cast aluminum alloy rod according to the present embodiment can be subjected to a homogenization heat treatment step, a forging step, a solution treatment step, a quenching treatment step, and an aging treatment step to produce the forged aluminum alloy product according to the present embodiment.EXAMPLES

[0082] Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.(Example of Aluminum Alloy Scraps)

[0083] Table 1 shows the component analysis values (mass %) of the scraps obtained by performing emission spectroscopic analysis of aluminum alloy scraps obtained from secondary alloy manufacturers and scrap manufacturers. The component analysis was performed according to emission spectroscopic analysis of aluminum and aluminum alloys specified in JIS H 1305 2005.TABLE 1AlloyclassificationSiFeCuMnMgADC124000 series10.60.523.10.020.25A3564000 series6.430.140.010.000.25Recycled3000 series0.270.450.150.731.15aluminumcan ingot60636000 series0.430.230.030.020.25(buildingmaterialsash)6061 scrap6000 series0.710.220.340.030.9150525000 series0.120.250.000.002.52fragmentExamples 1 to 6 and Comparative Examples 1 to 6

[0084] The compositions of samples of Examples 1 to 6 and Comparative Examples 1 to 6 are as follows.

[0085] In Examples 1 to 6, combinations (mixtures) of aluminum alloy scraps and aluminum base metals shown in Table 1 or only aluminum alloy scraps were used as raw materials.

[0086] In all the examples and comparative examples, regarding the contents of elements other than Si, mixing was performed so that the sample contained additive elements of Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, with the remainder being made up of Al and unavoidable impurities.

[0087] In addition, in the examples, mixing was performed so that the Si content was within a range of 0.60 mass % or more and 0.90 mass % or less. On the other hand, in the comparative examples, mixing was performed so that the Si content was outside a range of 0.60 mass % or more and 0.90 mass % or less.

[0088] In all the examples and comparative examples, the melting step and the casting step were performed using a vertical continuous casting device.

[0089] In the examples, the molten metal obtained in the primary melting step was once poured into a mold made of cast iron, and pouring cast was performed to obtain an ingot. When casting into an ingot, casting was performed so that the cooling rate at the final solidification part was 10° C. / sec or more. Specifically, a 5 kg ingot was cast at a mold temperature of 200° C. or lower. On the other hand, in the comparative examples, when the molten metal obtained in the primary melting step was once cast into an ingot, casting was performed so that the cooling rate at the final solidification part exceeded 10° C. / sec. Specifically, a 5 kg ingot was cast when the mold temperature exceeded 200° C.

[0090] Regarding the cooling rate at the final solidification part, the temperature of the ingot center, which is the final solidification part, was measured using a K type thermocouple as shown in FIG. 2, and the cooling rate from a liquid-phase temperature to a solid-phase temperature was calculated.

[0091] For each of the examples and comparative examples, melting and component adjustment in the secondary melting step were performed using the ingot obtained in the primary casting step. The secondary melting was performed at 780° C. After raw materials melted, a jig was used to check the presence of precipitates on the bottom of the furnace (residues on the bottom of the furnace). In addition, using the obtained molten metal, in the main casting step, casting was performed to obtain a continuous cast rod.

[0092] The casting conditions in the main casting step are as follows.

[0093] Casting diameter: diameter φ82 mm

[0094] Casting speed: 230 mm / min

[0095] Amount of cooling water: 30 L / min

[0096] Casting temperature: 720° C.<Evaluation after Secondary Melting Step>

[0097] As described above, after the secondary melting at 780° C., the presence of precipitates (Al—Fe—Mn—Si compound) on the bottom of the furnace was checked, and those without precipitates on the bottom of the furnace were determined as O, and those with precipitates were determined as x. To check the precipitates on the bottom of the furnace, an iron stirring tool was used. When the stirring tool came into contact with the precipitates on the bottom of the furnace, a feeling similar to hitting a pebble was perceived.<Evaluation of Continuous Cast Rod (Tensile Properties)>

[0098] The tensile properties of the obtained continuously cast aluminum alloy rod 10 were measured by the following method.

[0099] The tensile properties were evaluated according to the ASTM-E8 standard. That is, with reference to FIG. 4(a) and FIG. 4(b), a tension test piece with an inter-mark distance of 25.4 mm and a parallel part diameter of 6.4 mm was collected from a center part 10b that extends in the casting direction of the aluminum alloy continuous casting rod 10. A tensile test was performed on the obtained test piece at room temperature (25° C.) at a rate of 2 mm / min, and the 0.2% yield strength was measured. The results are shown in Table 2.<Evaluation of Forged Product (Tensile Properties)>

[0100] As shown in FIG. 5, a 50% upset product obtained by upsetting the continuously cast aluminum alloy rod 10 with a diameter of 82 mm from its side direction to a thickness of 41 mm was subjected to a T6 treatment under the following conditions and then underwent the tensile test;

[0101] Forging conditions: forging temperature 520° C.

[0102] T6 treatment conditions: at 540° C. for 3 hr (solution treatment)→quenching step (water temperature 40° C.)→at 180° C. for 6 hr (aging treatment step).

[0103] The tensile test was performed on the tension test piece at room temperature (25° C.) at a rate of 2 mm / min, and the 0.2% yield strength was measured. The results are shown in Table 2.TABLE 2Secondary0.2% yieldMixing ratiomelting stepstrength afterRecy-Precipi-T6 treatmentcledPrimary meltingtates onCastingUpsetAlumi-alumi-step-forging stepbottom ofrodproductnumnum5052Cast-Coolingfurnace(350(370basecan60636061frag-SiingrateSiwhenMPaMPametalADC12A356ingotsashscrapment(masstemper-(° C. / (massmelting atororDetermi-(%)(%)(%)(%)(%)(%)(%)%)aturesec)%)780° C.more)more)nationExample 150.050151010100.7015014.501.25no353375∘Example 240.001025101050.8315015.101.35no355380∘Example 330.001040100100.8115014.801.22no352374∘Example 420.00753101000.7119011.301.33no358382∘Example 510.00565101000.6119010.501.33no357383∘Example 60.005651010100.6219010.601.35no360381∘Comparative50.050151010100.702108.001.25yes343364xExample 1Comparative40.001025101050.832107.601.35yes339360xExample 2Comparative30.001040100100.812107.801.22yes347366xExample 3Comparative20.00753101000.712504.301.33yes332355xExample 4Comparative10.00565101000.612504.501.33yes330358xExample 5Comparative0.005651010100.622503.901.35yes335354xExample 6

[0104] As can be understood from Table 2, after the secondary melting step, in all of the examples, there were no precipitates (Al—Fe—Mn—Si compound) on the bottom of the furnace, but in all of the comparative examples, there were no precipitates (Al—Fe—Mn—Si compound) on the bottom of the furnace.

[0105] In addition, all of the continuously cast aluminum alloy rods of the examples had a 0.2% yield strength of 350 MPa or more, but all of the continuously cast aluminum alloy rods of the comparative examples had a 0.2% yield strength of less than 350 MPa. In addition, all of the forged aluminum alloy products of the examples had a 0.2% yield strength of 370 MPa or more, but all of the aluminum alloy continuous forged products of the comparative examples had a 0.2% yield strength of less than 350 MPa.REFERENCE SIGNS LIST10 Continuously cast aluminum alloy rod

Claims

1: A method for producing an aluminum alloy ingot containing additive elements of Cu in a range of 0.30 mass % or more and 1.0 mass % or less, Mg in a range of 0.80 mass % or more and 1.8 mass % or less, Si in a range of 0.90 mass % or more and 1.9 mass % or less, Mn in a range of 0.30 mass % or more and 1.2 mass % or less, Fe in a range of 0.20 mass % or more and 0.65 mass % or less, Zn in a range of 0.25 mass % or less, Cr in a range of 0.050 mass % or more and 0.30 mass % or less, Ti in a range of 0.01 mass % or more and 0.1 mass % or less, B in a range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in a range of 0.0010 mass % or more and 0.050 mass % or less, with the remainder being made up of Al and unavoidable impurities, the method comprising:a primary melting step in which raw materials containing aluminum alloy scraps with a Si content of 0.60 mass % or more and 0.90 mass % or less and the contents of the other additive elements within the same formulation ranges as those of the aluminum alloy ingot are melted to obtain a first molten metal;a primary casting step in which the first molten metal obtained in the primary melting step is solidified into an ingot, and a cooling rate from a liquid-phase temperature to a solid-phase temperature at the final solidification part of the ingot is 10° C. / sec or more; anda secondary melting step in which metallic Si or a Si-containing alloy is added to a molten metal obtained by melting the ingot obtained in the primary casting step, and the Si content is adjusted to be within a range of 0.90 mass % or more and 1.9% mass % or less.2: The method for producing an aluminum alloy ingot according to claim 1, wherein the aluminum alloy scraps are at least one of scraps containing 3000 series alloys, scraps containing 4000 series alloys, scraps containing 5000 series alloys, and scraps containing 6000 series alloys.3: A continuously cast aluminum alloy rod obtained using an aluminum alloy ingot produced by the method for producing an aluminum alloy ingot according to claim 1 and having a 0.2% yield strength of 350 MPa or more.4: A forged aluminum alloy product obtained using the continuously cast aluminum alloy rod according to claim 3 and having a 0.2% yield strength of 370 MPa or more.5: A continuously cast aluminum alloy rod obtained using an aluminum alloy ingot produced by the method for producing an aluminum alloy ingot according to claim 2 and having a 0.2% yield strength of 350 MPa or more.6: A forged aluminum alloy product obtained using the continuously cast aluminum alloy rod according to claim 5 and having a 0.2% yield strength of 370 MPa or more.

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