Impurity removal method, and production method for aluminum alloy material

Abstract

To provide an impurity removal method enabling reduction of environmental load and furthermore enabling efficient removal of impurities mixed in aluminum or aluminum alloy, and to provide aluminum alloy casting material.SOLUTION: An impurity removal method is provided, comprising: a mixing step of mixing magnesium or magnesium alloy into molten metal including aluminum or aluminum alloy and impurities, in such a manner that the content of Mg in the molten metal is 5 mass% or more and 18 mass% or less; a holding step of maintaining the molten state after the mixing step at a temperature range of 550°C or higher and 660°C or lower; and a separation step of separating the generated intermetallic compounds from the molten metal.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for removing impurities and a method for producing an aluminum-based alloy material. [Background technology]

[0002] Currently, in light of resource depletion, recycling of various items is progressing, and recycling of metals, which are consumed in large quantities, has been carried out for some time. For example, aluminum has excellent recyclability, and many aluminum products made from aluminum wrought materials, including aluminum cans and die-cast products, are remelted after disposal and recycled into new products. Aluminum generates large amounts of carbon dioxide (CO2) during the production of ingots, but recycling aluminum products can reduce the amount of ingots used and promote the reduction of carbon dioxide emissions.

[0003] After disposal, aluminum products contain impurities, and the concentration of these elements gradually increases with repeated recycling. For this reason, aluminum products are generally recycled in a cascade process into products with looser component standards.

[0004] On the other hand, for discarded aluminum products, it may be desirable to remove impurities and then recycle them horizontally, or to remove some elements and recycle them into products with different compositions.

[0005] Many techniques for removing impurities from molten aluminum or aluminum alloy have been reported, and in particular, there are many known techniques for crystallizing impurity elements as intermetallic compounds, and then separating and removing the intermetallic compounds by centrifugation, suction, etc. For example, techniques for reducing the impurity concentration from molten aluminum or aluminum alloy include a three-layer electrolytic refining method and a segregation method in the process of producing aluminum ingot, but these methods may be excessively costly as methods for refining scrap containing a large amount of impurity elements. Furthermore, a technique has been investigated in which a predetermined amount of Mg or an Mg alloy is added to a molten metal containing impurities, and intermetallic compounds formed from the molten metal are removed (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-77895 A [Patent Document 2] JP 2019-183265 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the techniques described in the prior art, in order to sufficiently reduce the impurity concentration, it is necessary to add a high concentration of Mg or to lower the molten metal temperature excessively, which increases the load of the subsequent Mg concentration reduction process and reduces productivity due to solidification of the molten metal during the process, making it inefficient. In addition, Mg itself emits a large amount of carbon dioxide gas during the production of ingots. In other words, the prior art involves the addition of excessive Mg, which creates a problem in that the carbon dioxide gas reduction effect of recycling cannot be fully achieved.

[0008] Therefore, in order to realize horizontal recycling of aluminum from wrought material to wrought material, it is desirable to have technology that can remove impurities that have a negative impact on quality from molten aluminum or aluminum alloy, and reduce them to an acceptable concentration in the wrought material or below, or to a level that can be diluted using aluminum bullion within an industrially feasible range, as well as technology that can practically carry out these processes efficiently.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide an impurity removal method and a manufacturing method for aluminum-based alloy material that can efficiently remove impurities mixed in aluminum or aluminum alloys while reducing the environmental burden. [Means for solving the problem]

[0010] As a result of extensive investigations, the inventors have found that the above problems can be solved by the following configuration, and have completed the present invention. That is, the present invention has the following configuration. [1] A mixing step of mixing magnesium or a magnesium alloy into a molten metal containing aluminum or an aluminum alloy and impurities such that the Mg content in the molten metal is 5% by mass or more and 18% by mass or less; A holding step of holding the molten metal after the mixing step at a temperature in the range of 550°C to 660°C; a separation step of separating the generated intermetallic compound from the molten metal; The impurity removal method includes the steps of: [2] The impurity removal method according to [1], further comprising a cooling step of cooling the molten metal after the mixing step. [3] The impurity removal method according to [1] or [2], further comprising a heating step of heating the molten metal after the intermetallic compound is separated in the separation step. [4] The method for removing impurities according to [1] or [2], wherein the holding time in the holding step is 3 minutes or longer. [5] The method for removing impurities according to [1] or [2], wherein the impurities include at least one selected from the group consisting of Cr, Ti, V and Zr. [6] The impurity removal method according to [3], and a casting step of casting the molten metal heated in the heating step, wherein the temperature of the molten metal heated in the heating step is maintained until the casting step. [7] A method for producing a wrought material, comprising the method for producing an aluminum-based alloy material according to [6] and a plastic working step. Effect of the Invention

[0011] An impurity removal method according to one aspect of the present invention can efficiently remove impurities contained in aluminum or an aluminum alloy while reducing the environmental load. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a flow diagram showing a method for removing impurities according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a flow diagram showing a method for removing impurities according to another embodiment of the present invention. [Diagram 3] FIG. 3 is a flow diagram showing a method for producing an aluminum alloy material according to one embodiment of the present invention. [Figure 4] FIG. 4 is a flow diagram showing a method for producing an aluminum alloy material according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An impurity removal method according to an embodiment of the present invention includes a mixing step of mixing magnesium or a magnesium alloy with a molten metal containing aluminum or an aluminum alloy and impurities so that the Mg content in the molten metal is 5% by mass or more and 18% by mass or less, a holding step of holding the molten metal after the mixing step at a temperature in the range of 550°C or more and 660°C or less, and a separation step of separating the generated intermetallic compounds from the molten metal. The impurity removal method according to the embodiment of the present invention may further include a cooling step of cooling the molten metal after the mixing step. Moreover, the impurity removal method according to the embodiment of the present invention may further include a heating step of heating the molten metal after the intermetallic compound has been separated in the separating step.

[0014] In the impurity removal method according to the embodiment of the present invention, the liquidus temperature of the molten metal can be appropriately lowered by controlling the Mg content in the molten metal within the above range in the mixing step, and the molten metal after the mixing step can be cooled in the cooling step as necessary, and the molten metal can be held at a temperature within the above range in the holding step, thereby producing an intermetallic compound containing the impurities in the molten metal containing aluminum and magnesium (Al-Mg-based molten metal). The impurity removal method according to the embodiment of the present invention can reduce the amount of aluminum ingot used by recycling aluminum, and can reduce the amount of carbon dioxide gas generated due to the production of ingots. As a result, the impurity removal method according to the embodiment of the present invention can reduce the environmental load.

[0015] The holding time in the holding step is preferably 3 minutes or more. By setting the holding time of the molten metal in the holding step to be equal to or longer than the lower limit, the impurities can be easily and reliably removed.

[0016] The impurities may include at least one selected from the group consisting of Cr, Ti, V, and Zr. Even when the impurities include at least one selected from the group consisting of Cr, Ti, V, and Zr, the impurities can be easily removed from the molten metal while suppressing the amount of magnesium added in the mixing step by the impurity removal method according to the embodiment of the present invention.

[0017] A manufacturing method of an aluminum-based alloy material according to another embodiment of the present invention includes the above-mentioned impurity removal method and a casting step of casting the molten metal heated in the heating step, and maintains the temperature of the molten metal heated in the heating step until the casting step.

[0018] The method for producing an aluminum-based alloy material according to the embodiment of the present invention uses the impurity removal method according to the embodiment of the present invention, and therefore makes it possible to recycle aluminum.

[0019] The method for producing an aluminum-based alloy material according to an embodiment of the present invention may include a composition adjustment step of adjusting the composition of the molten metal after the intermetallic compounds are separated by the separation step, before the casting step. By including a composition adjustment step of adjusting the composition of the molten metal after the intermetallic compounds are separated by the separation step, before the casting step, recycling of aluminum can be performed more easily.

[0020] A method for producing an aluminum-based alloy material according to yet another aspect of the present invention includes an impurity removing method, and a casting step of casting the molten metal into an ingot, and maintains the temperature of the molten metal heated in the heating step until the casting step.

[0021] The method for producing an aluminum-based alloy material according to the embodiment of the present invention uses the impurity removal method according to the embodiment of the present invention, and therefore makes it possible to recycle aluminum.

[0022] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that, with respect to the numerical values ​​described in this specification, it is possible to adopt only one of the upper limit value and the lower limit value described, or to arbitrarily combine the upper limit value and the lower limit value.

[0023] [Impurity removal method] In another embodiment of the impurity removal method of the present invention, impurities that are difficult to remove when mixed into aluminum or an aluminum alloy are removed from an Al-Mg molten metal. In the impurity removal method of the present invention, Mg, an essential element of the JIS-A5000 system, is contained in the molten metal, and the molten metal is maintained at a temperature in the range of 550°C to 660°C to promote eutectic formation of impurities, and the generated intermetallic compounds are separated from the molten metal to remove the impurities. In the impurity removal method of the present invention, a step of intentionally mixing unnecessary impurities to generate the intermetallic compounds is not required, and the yield can be improved. By using the impurity removal method of the present invention, the concentration of impurities in the molten metal can be efficiently reduced to, for example, the allowable value of the JIS-A5000 system or less while suppressing the concentration of Mg in the molten metal.

[0024] In order to realize horizontal recycling of aluminum from wrought material to wrought material, it is necessary to reduce impurities to the allowable concentration or less of the wrought material. From this perspective, according to the impurity removal method according to the embodiment of the present invention, the concentration of impurities that are mixed into aluminum or aluminum alloys and are difficult to remove can be reduced to, for example, 0.2 mass % or less.

[0025] The impurity removal method according to the embodiment of the present invention includes the mixing step S1, the holding step S3, and the separation step S4 as described above. When the impurity removal method according to the embodiment of the present invention further includes the cooling step S2, as shown in Fig. 1, the method includes the mixing step S1 of mixing magnesium or a magnesium alloy with a molten metal containing aluminum or an aluminum alloy and impurities so that the Mg content in the molten metal is 5 mass% or more and 18 mass% or less, the cooling step S2 of cooling the molten metal after the mixing step, the holding step S3 of holding the molten metal after the cooling step S2 in the range of 550°C or more and 660°C or less, and the separation step S4 of separating the generated intermetallic compound from the molten metal. Furthermore, the impurity removal method according to the embodiment of the present invention may include a heating step S5 of heating the molten metal after the intermetallic compound is separated in the separation step S4, as shown in FIG. In the impurity removal method according to the embodiment of the present invention, the molten metal may be held under an inert atmosphere in order to prevent oxidation of Mg, etc. Also, in order to prevent oxidation of Mg, etc., a small amount (e.g., about 30 ppm by mass) of Be (beryllium) may be added to the molten metal, or a flux may be sprayed thereon.

[0026] 〔impurities〕 Impurities to be removed by the impurity removal method according to the embodiment of the present invention are not particularly limited, but include, for example, transition metal elements. Transition metal elements may adhere to aluminum products as impurities, and the concentration of impurities tends to increase with repeated recycling. In addition, as the uses of aluminum products expand, it is considered that transition metal elements are added to aluminum products to impart strength, rigidity, heat resistance, and the like. On the other hand, transition metal elements are generally difficult to remove by refining.

[0027] The present inventors have mainly studied methods for removing such transition metal elements, and have searched for elements that can be efficiently removed from the molten metal while suppressing the Mg content in the molten metal. As a result, the present inventors have found that, among the above transition metal elements, at least one selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium) and Zr (zirconium) is suitable as the impurity.

[0028] Cr, Ti, V, and Zr are easily mixed in as additive elements of aluminum alloys, or as elements contained in grain refiners, base metals, etc. These elements combine with aluminum to form stable compounds whose crystallization temperatures are higher than the liquidus temperature of aluminum, making them easy to remove from the liquid phase, and the activity of these elements increases when Mg is mixed into the molten metal, making it possible to form compounds at higher temperatures. That is, Cr, Ti, V, and Zr have higher compound formation temperatures than Fe and Mn, and by mixing Mg into the molten metal, the liquidus temperature of aluminum is lowered, whereas the compound formation temperatures of Cr, Ti, V, and Zr are higher. Therefore, in the impurity removal method according to the embodiment of the present invention, the impurity is at least one selected from the group consisting of Cr, Ti, V, and Zr, so that the amount of Mg added in the mixing step S1 can be reduced while an intermetallic compound can be easily formed in the holding step S3, and therefore the impurities can be easily removed from the molten metal.

[0029] (Mixing process) The mixing step according to an embodiment of the present invention is a step of mixing magnesium or a magnesium alloy into a molten metal containing aluminum or an aluminum alloy and impurities so that the Mg content in the molten metal is 5% by mass or more and 18% by mass or less.

[0030] In the mixing step S1, magnesium or a magnesium alloy is mixed into the molten metal containing aluminum or an aluminum alloy and the above-mentioned impurities, and Mg, which is an essential element in JIS-A5000-based aluminum alloys, is contained. The inclusion of Mg in the molten metal promotes the generation of intermetallic compounds containing the above-mentioned impurities in the Al-Mg-based molten metal. The impurity removal method according to the embodiment of the present invention does not require excessive dissolution of unnecessary impurities in the molten metal in order to generate the intermetallic compounds. In addition, since Mg is not an impurity, the impurity removal method according to the embodiment of the present invention does not require a step for removing Mg. Therefore, in the impurity removal method according to the embodiment of the present invention, for example, the molten metal after the impurities are removed can be diluted as necessary and used for aluminum recycling. The dilution procedure (Mg concentration reduction step) of the molten metal after the impurities are removed will be described later. Examples of magnesium alloys mixed in the mixing step S1 include JIS-MC5 and JIS-MDC2A.

[0031] Effects of mixing magnesium or a magnesium alloy in the mixing step S1 include, for example, the following (a) and (b). (a) The liquidus temperature is lowered, so that the molten metal can be kept at a low temperature, promoting the formation of the intermetallic compounds. (b) Mg increases the activity of impurity elements, promoting the formation of the above intermetallic compounds.

[0032] The impurity removal method according to the embodiment of the present invention can convert the impurities into intermetallic compounds in the molten metal by one or both of the effects (a) and (b) described above.

[0033] As described above, in the mixing step S1, magnesium or a magnesium alloy is mixed so that the Mg content in the molten metal is 5% by mass or more and 18% by mass or less. The lower limit of the Mg content in the molten metal after the mixing step S1 is preferably 7.5% by mass. On the other hand, the upper limit of the content is preferably 15% by mass, more preferably 12% by mass. Moreover, the upper limit of the content is further preferably less than 11% by mass. If the content is less than the lower limit, the liquidus temperature of the molten metal may not be sufficiently low. On the other hand, if the content exceeds the upper limit, the Mg concentration in the molten metal after the impurities are removed by the separation step S4 becomes high, which may increase the cost required for diluting Mg and may increase the environmental load.

[0034] The lower limit of the temperature of the molten metal in the mixing step according to the embodiment of the present invention is preferably 660° C., more preferably 680° C., and even more preferably 700° C. Meanwhile, the upper limit of the temperature of the molten metal in the mixing step is preferably 850° C., more preferably 800° C., even more preferably 780° C., and even more preferably 750° C. Furthermore, although the temperature of the molten metal decreases when the raw materials are mixed at room temperature, there is no problem if the temperature temporarily deviates from the above temperature range, and the molten metal may be heated as necessary.

[0035] (cooling process) The impurity removal method according to the embodiment of the present invention may further include a cooling step S2 of the molten metal after the mixing step S1. The cooling step S2 is a step of adjusting the temperature of the molten metal after the mixing step to the temperature in the holding step S3. Since cooling is often performed in this adjustment, this is referred to as a cooling step in this specification. In the cooling step S2, the molten metal is cooled after the mixing step S1, thereby promoting the generation of intermetallic compounds in the molten metal. The cooling method in the cooling step S2 is not particularly limited, and may be, for example, cooling in the atmosphere under temperature control, or cooling by turning off the heater. Aluminum or an aluminum alloy may be added to the molten metal to perform quenching. From the viewpoint of shortening the processing time, a part of the raw materials used may not be used in the mixing step, but may be added for the purpose of cooling the molten metal. In other words, it is preferable to cool the molten metal by adding, for example, aluminum or an aluminum alloy, magnesium, or a magnesium alloy to the molten metal. The aluminum or aluminum alloy, magnesium, or magnesium alloy to be added may be, for example, aluminum bullion, aluminum scrap, magnesium bullion, magnesium scrap, or the like. When using this cooling method, the Mg concentration after adding and melting all the raw materials may be the same as the Mg concentration specified in the mixing step S1. In addition, if the temperature after the mixing step S1 is within the temperature range of the holding step S3, the cooling step S2 may not be provided.

[0036] In the impurity removing method according to the embodiment of the present invention, the molten metal after the mixing step S1 may be cooled in a cooling step S2. The cooling may be performed so as to have a temperature in a holding step S3 described below. In order to efficiently generate the intermetallic compounds from the molten metal, it is desirable to cool the molten metal to a low-temperature liquid phase in the cooling step S2. If the cooling is insufficient, the efficiency of generating the intermetallic compounds may be insufficient. Conversely, if the cooling is excessive, the aluminum in the molten metal may solidify, or the rate of generation of the intermetallic compounds may slow down.

[0037] In the cooling step S2 according to the embodiment of the present invention, the cooling rate of the molten metal is not particularly limited, but has a large effect on productivity. The cooling rate of the molten metal in the cooling step S2 is, for example, preferably -5°C / min or more, more preferably -10°C / min or more, and even more preferably -15°C / min or more.

[0038] In the impurity removal method according to the embodiment of the present invention, the impurities can be converted into intermetallic compounds in the molten metal by the cooling effect of the cooling step S2 in addition to the mixing step S1.

[0039] (holding process) In the holding step S3 according to the embodiment of the present invention, the molten metal mixed in the mixing step S1 is held in a temperature range of 550° C. or more and 660° C. or less. When the impurity removal method according to the embodiment of the present invention further includes a cooling step S2, the molten metal cooled in the cooling step S2 is held in a temperature range of 550° C. or more and 660° C. or less. In the holding step S3, it is preferable to hold the temperature of the molten metal cooled in the cooling step S2. By maintaining the molten metal at a specific temperature in the holding step S3, in addition to the mixing step S1 (and, if necessary, the cooling step S2), the effect of maintaining the molten metal temperature in the holding step S3 produces the intermetallic compound in the molten metal.

[0040] The lower limit of the holding temperature of the molten metal in the holding step S3 is 550°C as described above, preferably 560°C, more preferably 570°C, and even more preferably 580°C. On the other hand, the upper limit of the holding temperature is 660°C as described above, preferably 650°C, more preferably 640°C, and even more preferably 625°C. In order to efficiently generate the intermetallic compounds from the molten metal, it is desirable to hold the molten metal in a low-temperature liquid phase in the holding step S3. If the holding temperature exceeds the upper limit, the efficiency of generating the intermetallic compounds may be insufficient. Conversely, if the holding temperature is below the lower limit, the aluminum in the molten metal may solidify, or the rate of generation of the intermetallic compounds may be slow.

[0041] In the impurity removing method according to the embodiment of the present invention, the holding time in the holding step is preferably 3 minutes or longer. The lower limit of the holding time of the molten metal in the holding step S3 is preferably 3 minutes, more preferably 5 minutes, and even more preferably 10 minutes. If the holding time is less than the lower limit, it may be difficult to sufficiently generate the intermetallic compound. On the other hand, the upper limit of the holding time is preferably 180 minutes, more preferably 120 minutes, and even more preferably 60 minutes. In the impurity removal method according to the embodiment of the present invention, by setting the holding time to the upper limit or less, it is possible to suppress excessive fuel costs required for temperature control of the molten metal. In addition, the impurity removal method according to the embodiment of the present invention can sufficiently generate the intermetallic compound even if the holding time is less than the upper limit. Therefore, by subjecting the molten metal after the intermetallic compound is separated by the separation step S4 described later to aluminum recycling, it is possible to reduce the emission of carbon dioxide gas.

[0042] In the impurity removal method according to the embodiment of the present invention, the temperature change of the molten metal in the holding step S3 is, for example, preferably within -20°C, more preferably within -15°C, and even more preferably within -10°C of the desired holding temperature selected within the above-mentioned holding temperature range. If the temperature becomes higher than the held temperature, the impurity concentration in the molten metal may not be sufficiently reduced. Also, if the temperature drops too much below the held temperature, the molten metal may solidify.

[0043] (separation process) In the separation step S4, for example, the intermetallic compound generated in the holding step S3 is separated from the molten metal. In the separation step S4, the intermetallic compound is separated from the molten metal after the holding step S3, thereby removing the impurities from the molten metal. As a method for separating the intermetallic compounds in the separation step S4, for example, there is a method of recovering only the supernatant by tilting the crucible in a state where the intermetallic compounds are precipitated in the holding step S3. There is also a method of filtering the entire molten metal containing the intermetallic compounds with a refractory filter. There are also other methods, such as a method of adhering the intermetallic compounds to a flux and floating them up, and a method of solidifying the intermetallic compounds in a precipitated state and cutting and removing the precipitate layer of the intermetallic compounds. These methods can be appropriately selected according to the equipment available, and can also be combined. By the above separation methods, the intermetallic compounds can be separated from the molten metal, and the molten metal with a reduced impurity concentration can be recovered. The impurity concentration in the molten metal in which the impurity concentration has been reduced by separation of the intermetallic compounds is, for example, preferably 0.2 mass % or less, and more preferably 0.15 mass % or less.

[0044] (Heating process) The impurity removal method according to the embodiment of the present invention may further include a heating step of heating the molten metal after the intermetallic compound has been separated in the separation step. The heating step S5 according to the embodiment of the present invention is a step of heating the molten metal after the separation step S4. In the heating step S5, the molten metal separated after the separating step S4 is heated, so that the tapped molten metal can be moved safely and efficiently. For example, when the molten metal separated in the separation step S4 is moved through a trough, the temperature of the molten metal may drop and solidify on the trough. If the molten metal solidifies, it may become difficult to recover the molten metal after refining, and the flow path of the trough may become narrow, causing the molten metal to scatter, which may injure workers. In the heating step S5, in order to prevent the molten metal from solidifying, it is preferable to heat the molten metal tapped after the holding step S3, for example, by using a trough.

[0045] The molten metal can be heated by any method as long as the temperature of the molten metal can be maintained, for example, by heating the refractory part constituting the trough and the molten metal on the trough with a burner, by inserting a heating element into the molten metal on the trough, or by embedding a heating element inside the refractory trough.

[0046] Since the temperature of the molten metal can be maintained by heating in the launder, the temperature drop immediately after the molten metal is tapped and immediately before casting can be reduced. The temperature drop immediately after the molten metal is tapped and immediately before casting is preferably, for example, 50° C. or less, and more preferably 30° C. or less. If the molten metal on the launder does not contain intermetallic compounds, the molten metal temperature may be increased by heating to a temperature higher than the holding temperature. On the other hand, when a method is adopted in which the entire molten metal containing intermetallic compounds is filtered with a refractory filter in the separation step S4, if the molten metal temperature rises before filtration, the intermetallic compounds will re-dissolve in the molten metal, decreasing the purity of the molten metal, and therefore excessive heating is not preferable. Furthermore, when the molten metal is collected by directly pouring it into a container without using a gutter or the like, the heating step is not necessarily required.

[0047] In the impurity removal method according to the embodiment of the present invention, the heating step S5 is provided, so that the holding step S3 and the separation step S4 can be performed at a lower temperature than in the past, and the generation and separation of intermetallic compounds in the molten metal are promoted. In addition, the effect of improving productivity can be obtained by avoiding equipment trouble caused by solidification of the molten metal during tapping and transportation.

[0048] (Mg concentration reduction process) The impurity removal method according to the embodiment of the present invention may further include a Mg concentration reduction step, in which the Mg concentration of the molten metal containing Mg added in the mixing step S1 may be diluted to a level equal to or lower than the standard concentration according to the JIS-A5000 series. The molten metal (Al-Mg alloy molten metal) from which the intermetallic compounds have been removed by the separation step can be used as an Al-Mg intermediate alloy for molten aluminum having a low impurity concentration. When using the alloy as an Al-Mg intermediate alloy, if the Mg concentration of the molten metal is high, the Mg concentration of the molten metal can be reduced to an arbitrary level by adding, for example, aluminum ingot or aluminum scrap with a low impurity concentration to the molten metal after the intermetallic compounds have been removed.

[0049] In the Mg concentration reduction step, the molten metal can be held under vacuum to evaporate Mg, which has a high vapor pressure, and reduce the Mg concentration in the molten metal. Furthermore, by using a flux for removing Mg, it is possible to obtain an Al-Mg molten metal with a low Mg concentration.

[0050] The aluminum recycling method in which the Mg concentration reducing step is added to the above-mentioned mixing step S1, cooling step S2, holding step S3, separating step S4, and heating step S5 is one embodiment of the present invention.

[0051] <Advantages> In the impurity removal method according to the embodiment of the present invention, the liquidus temperature of the molten metal can be appropriately lowered by controlling the Mg content in the molten metal within the above range in the mixing step S1, and therefore, by holding the molten metal at a temperature within the above range in the holding step S3, it is possible to generate intermetallic compounds containing the impurities in the molten metal containing aluminum and Mg (Al-Mg molten metal). In addition, since the molten metal discharged in the separation step S4 has a low temperature due to the formation of intermetallic compounds, it can be transferred while preventing the solidification from progressing by heating it in the molten metal heating step S5 as necessary after it is poured out. The impurity removal method according to the embodiment of the present invention can reduce the amount of aluminum bullion used by recycling aluminum, and therefore can reduce the amount of carbon dioxide gas generated due to the production of aluminum bullion. As a result, the impurity removal method according to the embodiment of the present invention can reduce the environmental load.

[0052] In the impurity removal method according to the embodiment of the present invention, Mg, an essential element in aluminum alloys such as JIS-A5000 series, is contained in the molten metal to promote compounding of the impurity elements, and the intermetallic compounds thus generated are separated from the molten metal, thereby removing the impurity elements. In the impurity removal method according to the embodiment of the present invention, impurity elements that have been difficult to remove in the past can be efficiently removed by coexisting with Mg, thereby reducing the concentration of the impurity elements to a concentration that can be incorporated into the aluminum plate. In this case, the amount of metal used to manufacture the aluminum plate can be reduced by keeping the Mg content in the molten metal low. Therefore, according to the impurity removal method according to the embodiment of the present invention, it is possible to use scrap that is difficult to recycle as a substitute for aluminum metal, and to reduce the amount of carbon dioxide gas emissions.

[0053] [Method of manufacturing aluminum alloys] Next, a method for producing an aluminum-based alloy using the impurity removal method according to an embodiment of the present invention will be described with reference to Figures 3 and 4. The method for producing an aluminum-based alloy according to an embodiment of the present invention includes the impurity removal method according to an embodiment of the present invention and a casting step of casting the molten metal to form an ingot (Figure 3). The method for producing an aluminum-based alloy according to an embodiment of the present invention also includes the impurity removal method according to an embodiment of the present invention and a casting step of casting the molten metal to form an ingot, and the impurity removal method includes a heating step, and the temperature of the molten metal heated in the heating step is maintained until the casting step (Figure 4). The method for producing an aluminum alloy according to an embodiment of the present invention produces, for example, an Al-Mg alloy. The method for producing an aluminum alloy according to an embodiment of the present invention includes a casting step S6 in which the molten metal after the intermetallic compounds are separated in the heating step S5 is heated and the transferred molten metal is cast while preventing the solidification from proceeding.

[0054] Furthermore, the method for producing an aluminum-based alloy according to an embodiment of the present invention may include, prior to the casting step, a component adjusting step of adjusting components of the molten metal after the intermetallic compounds have been separated by the separation step.

[0055] In the manufacturing method of the aluminum-based alloy according to the embodiment of the present invention, the casting step may be performed only once or multiple times after the heating step S5 as shown in Fig. 4. In addition, when the casting step is performed multiple times, the composition adjustment step can be performed before any of the casting steps. Furthermore, the composition adjustment step can be performed multiple times.

[0056] For example, after the heating step S5, the composition adjusting step and the casting step S6 may each be performed once in this order. Also, after the heating step S5, the casting step (first casting step), the composition adjusting step, and the casting step (second casting step) may be performed in this order. However, the number and order of the casting steps and the composition adjusting steps are not limited to these. Each step of the composition adjusting step and the casting step will be described in detail below.

[0057] (Component adjustment process) In the component adjustment step, the components of the molten metal from which the impurities have been removed through the separation step S4 are adjusted. In the component adjustment step, aluminum ingot, alloy elements, etc. are added to the molten metal. By adding aluminum ingot and alloy elements in the component adjustment step, it becomes easier to manufacture JIS-A5000 series aluminum alloy materials by the manufacturing method for aluminum-based alloy materials described below. In addition, in the component adjustment step, the components of the molten metal can also be adjusted by diluting the molten metal. Furthermore, when the component adjustment step is performed multiple times, it is also possible to change the components added each time.

[0058] (Casting process) In the casting step, the molten metal from which the impurities have been removed through the separation step S4 is cast. In the manufacturing method of the aluminum-based alloy according to the embodiment of the present invention, the molten metal from the separation step S4 contains Mg, and impurities have been removed from the molten metal. Therefore, the casting step is suitable for casting an Al-Mg-based alloy.

[0059] <Advantages> The method for producing an aluminum-based alloy according to an embodiment of the present invention uses the impurity removal method according to an embodiment of the present invention, so that aluminum can be recycled. Also, the method for producing an aluminum-based alloy according to an embodiment of the present invention includes the component adjustment step, so that aluminum can be recycled more easily.

[0060] [Method of manufacturing aluminum alloy material] The manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention includes the impurity removing method according to the embodiment of the present invention, and a casting step of casting the molten metal to form an ingot, and the temperature of the molten metal heated in the heating step is maintained until the casting step. The manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention may also include a plastic processing step of plastically processing the aluminum-based alloy obtained through the casting step S6.

[0061] The manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention may include a component adjustment step of adjusting the composition of the molten metal after the intermetallic compounds are separated by the separation step S4. When the manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention includes the component adjustment step, the manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention may further include a casting step after the component adjustment step, and the above-mentioned plastic processing step may be performed on the aluminum-based alloy obtained in the casting step. This component adjustment step may be performed in the same procedure as the component adjustment step in the manufacturing method of the aluminum-based alloy according to the embodiment of the present invention described above. By including the component adjustment step, the manufacturing method of the aluminum-based alloy material according to the embodiment of the present invention may easily control the composition of the aluminum-based alloy material obtained. As a result, aluminum recycling may be more easily performed.

[0062] (Plastic working process) In the plastic working step, the aluminum-based alloy is subjected to plastic working to produce an aluminum-based alloy material. Examples of the plastic working include hot working and cold working. Specific examples of the processing include rolling, extrusion, and forging. In the plastic working step, the aluminum-based alloy may be subjected to heat treatment as necessary. Examples of the heat treatment include homogenization heat treatment, solution heat treatment, and aging treatment.

[0063] In the above-mentioned plastic processing step, for example, an Al-Mg alloy material is produced. Among them, in the above-mentioned plastic processing step, it is preferable to produce a JIS-A5000-series aluminum alloy material. That is, the manufacturing method of the aluminum alloy material according to the embodiment of the present invention is suitably used as a manufacturing method of the JIS-A5000-series aluminum alloy material. In the manufacturing method of the aluminum alloy material according to the embodiment of the present invention, the molten metal after the above-mentioned separation step S4 contains Mg, which is an essential element of the JIS-A5000-series, and impurities are removed from the molten metal. Therefore, the manufacturing method of the aluminum alloy material according to the embodiment of the present invention is easy to use as a manufacturing method of the JIS-A5000-series aluminum alloy material. The aluminum alloy material obtained through the above-mentioned plastic processing step is generally called a wrought material. That is, the present invention also relates to a method for producing an aluminum-based alloy material according to an embodiment of the present invention, and a method for producing a wrought material including a plastic working step.

[0064] <Advantages> The method for producing an aluminum-based alloy material according to the embodiment of the present invention uses the impurity removal method according to the embodiment of the present invention, and therefore makes it possible to recycle aluminum.

[0065] [Other embodiments] The above-mentioned embodiment does not limit the configuration of the present invention. Therefore, the above-mentioned embodiment may omit, replace or add components of each part of the above-mentioned embodiment based on the description in this specification and common general technical knowledge, and it should be understood that all of these are within the scope of the present invention.

[0066] For example, in the impurity removal method according to the embodiment of the present invention, the molten metal may be stirred when generating the intermetallic compound in the holding step S3. However, in the impurity removal method according to the embodiment of the present invention, the intermetallic compound can be easily generated without stirring the molten metal. When stirring the molten metal, it is preferable to leave the molten metal after stirring to allow the intermetallic compound suspended in the molten metal by stirring to settle or precipitate.

[0067] The method for producing an aluminum-based alloy according to the embodiment of the present invention is not limited to the configuration including the above-mentioned component adjustment step. For example, when the method for producing an aluminum-based alloy according to the embodiment of the present invention does not include the above-mentioned component adjustment step, it is also possible to use the aluminum-based alloy obtained by the method for producing an aluminum-based alloy according to the embodiment of the present invention as an intermediate alloy, and to separately adjust the components of this intermediate alloy. EXAMPLES

[0068] The present invention will be described in detail below based on examples. However, the present invention should not be construed as being limited to the descriptions of these examples.

[0069] Example 1 Aluminum ingot, Al-Cr intermediate alloy, Al-Mg intermediate alloy, and Al-Be intermediate alloy were blended so that Cr, Mg, and the impurity elements shown in Table 1 were contained in the amounts shown in Table 1, and about 2.3 t was melted in a rotary furnace to prepare a molten metal at about 660 ° C. Note that Ti was contained in the raw materials used, so no Ti-containing alloy was added. Next, the temperature of this molten metal was lowered to 635 ° C, and the molten metal was kept stationary for 7 minutes. Thereafter, the supernatant was poured out from the rotary furnace while adjusting the molten metal temperature, and about 400 kg was collected in six separate containers while the trough was heated with a burner. Samples for analysis were taken from the trough during collection in each container. After the molten metal was collected, the weight of the container containing the molten metal was measured, and the weight of the empty container was subtracted to obtain the amount of molten metal collected. The impurity concentrations (Cr concentration and Ti concentration in the ingot) of the collected molten metal were analyzed by solid-state emission spectroscopy. The recovery yield was defined as the amount of molten metal recovered relative to the initial charges of aluminum ingot, Al-Cr intermediate alloy, Al-Mg intermediate alloy, and Al-Be intermediate alloy, and the amount of molten metal recovered from each vessel was added up in the order of tapping, and is shown in Table 1. Table 1 also shows the temperature of the molten metal immediately after tapping (tap temperature) (°C) and the temperature of the molten metal just before it passes through the trough and enters the receiving vessel (temperature after passing through the trough) (°C). "Δ" in Table 1 indicates the difference (°C) between the tapping temperature and the temperature after passing through the trough.

[0070] Comparative Example 1 Aluminum ingot, Al-Cr intermediate alloy, Al-Mg intermediate alloy, and Al-Be intermediate alloy were mixed so that Cr, Mg, and the impurity elements shown in Table 1 were contained in the amounts shown in Table 1, and about 2.3 t was melted in a rotary furnace to prepare a molten metal at 681°C, which was then left to stand for 15 minutes. After that, the supernatant was poured out from the rotary furnace while adjusting the molten metal temperature, and collected in containers in six batches of about 400 kg each. Samples for analysis were taken from the trough during collection in each container. After the molten metal was collected, the weight of the container containing the molten metal was measured, and the weight of the empty container was subtracted to obtain the amount of molten metal collected. The impurity concentrations (Cr concentration and Ti concentration in the ingot) of the collected molten metal were analyzed by solid-state emission spectroscopy. The recovery yield is defined as the amount of molten metal recovered relative to the initial charging amount, and the amount of molten metal recovered from each vessel was added up in the order of tapping, and is shown in Table 1. Table 1 also shows the temperature of the molten metal immediately after tapping (tap temperature) (°C) and the temperature of the molten metal just before it passes through the trough and enters the receiving vessel (temperature after passing through the trough) (°C). "Δ" in Table 1 indicates the difference (°C) between the tapping temperature and the temperature after passing through the trough.

[0071] [Cr removal judgment] Based on the results of the analysis of the impurity concentrations in Example 1 and Comparative Example 1, the Cr removal was judged according to the following evaluation criteria, and the results are shown in Table 1. ○: Cr concentration is less than 0.2 mass% ×: Cr concentration is 0.2 mass% or more

[0072] [Table 1]

[0073] From the above results, it was confirmed that for molten aluminum containing impurities, especially Cr and Ti, by heating the trough with a burner in the heating process after pouring, the molten metal can be transferred without solidifying even if the pouring temperature is lowered, intermetallic compounds containing impurities are sufficiently generated, and molten metal with reduced impurity concentration can be recovered with a yield of approximately 80%. This method can also be applied to the removal of V and Zr. [Industrial Applicability]

[0074] As described above, the impurity removal method according to one aspect of the present invention is suitable for removing impurities that have become mixed into aluminum or an aluminum alloy.

Claims

1. a mixing step of mixing magnesium or a magnesium alloy into a molten metal containing aluminum or an aluminum alloy and impurities such that the Mg content in the molten metal is 5% by mass or more and 18% by mass or less; A holding step of holding the molten metal after the mixing step at a temperature in the range of 550° C. or more and 660° C. or less; a separation step of separating the generated intermetallic compound from the molten metal; The impurity removal method includes the steps of:

2. The impurity removal method according to claim 1 , further comprising a cooling step of cooling the molten metal after the mixing step.

3. The impurity removing method according to claim 1 or 2, further comprising a heating step of heating the molten metal after the intermetallic compound is separated in the separating step.

4. The method for removing impurities according to claim 1 or 2, wherein the holding time in the holding step is 3 minutes or more.

5. 3. The method for removing impurities according to claim 1, wherein the impurities include at least one selected from the group consisting of Cr, Ti, V, and Zr.

6. The method for removing impurities according to claim 3, and a casting step of casting the molten metal heated in the heating step, wherein the temperature of the molten metal heated in the heating step is maintained until the casting step.

7. A method for producing a wrought material, comprising the method for producing an aluminum-based alloy material according to claim 6 and a plastic working step.

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