JP7638717B2 - Method for removing impurities and method for manufacturing ingot - Google Patents

Description

The present invention relates to a method for removing impurities and a method for manufacturing ingots.

In recent years, due to the social demand for reducing carbon dioxide emissions, weight reduction of automobiles and other vehicles has been promoted around the world, and the demand for aluminum is expected to increase in the future. Therefore, it is expected that the amount of aluminum scrap generated will increase in line with the increase in demand in the future. Aluminum is generally considered to be a metal material with excellent recyclability. Many aluminum products made of drawn aluminum, such as aluminum cans, are remelted after disposal and recycled into new products. However, impurities adhere to discarded aluminum products, and the concentration of impurity elements gradually increases with repeated recycling. For this reason, discarded aluminum products are generally cascade recycled into products with looser component standards.

In order to prevent impurities from being mixed into aluminum, efforts are being made to improve sorting techniques after shredding. However, since it is difficult to completely remove attached materials, ultimately a technology will be required to remove impurities from molten aluminum or aluminum alloys.

Many techniques for removing impurities from molten aluminum or aluminum alloys have been reported, and one technique proposed for removing Fe, which is particularly difficult to remove, is to add Mn, an impurity, to crystallize an Al-Fe-Mn intermetallic compound, and then remove the intermetallic compound by centrifugation, suction, etc. (see JP-A-8-35021 and JP-A-7-70666).

In addition, as a technique for reducing the impurity concentration in molten aluminum or aluminum alloy, a technique using a three-layer electrolytic refining method or a segregation method in the process of manufacturing aluminum ingot has been disclosed (see Materia, Vol. 33 (1994), No. 1).

In addition, a method has been proposed in which Mg or an Mg alloy is added to molten aluminum or an aluminum alloy containing impurities, the molten metal is then cooled to a temperature at which only intermetallic compounds crystallize, and the intermetallic compounds containing impurities are crystallized in the molten metal, and the intermetallic compounds are separated from the molten metal (see JP 2019-183265 A).

Japanese Patent Application Publication No. 8-35021 Japanese Patent Application Publication No. 7-70666 JP 2019-183265 A

Kondo et al., Materia, 1994, Vol. 33, No. 1, 62-68

However, the techniques described in Patent Documents 1 and 2 have the risk of the added Mn increasing as an impurity. Also, while the technique described in Non-Patent Document 1 is theoretically capable of removing Fe, there is a risk of a low yield when used as a method for refining scrap containing a large amount of impurity elements. Furthermore, the three-layer electrolytic refining method is not profitable in areas with high electricity costs, and the segregation method has the risk of a lower yield the higher the impurity concentration of the raw material. Thus, the above conventional techniques are not sufficient as a method for recycling aluminum scrap containing a large amount of impurities collected from the market.

The technology described in Patent Document 3 makes it possible to a certain extent to achieve horizontal recycling of aluminum from wrought material to wrought material. However, after extensive research by the inventors, it was found that there is room for further improvement in the technology described in Patent Document 3 in terms of impurity removal efficiency, etc.

The present invention was made in consideration of these circumstances, and aims to provide an impurity removal method that can efficiently remove impurities that are mixed into aluminum or aluminum alloys and are difficult to remove.

The inventors discovered that impurities can be efficiently removed by mixing Mg, an essential element in JIS-A5000 series aluminum alloys, into molten aluminum or aluminum alloy containing impurities, and then separating solid-phase aluminum and intermetallic compounds containing impurities in or from the molten aluminum, thereby completing the present invention.

The impurity removal method according to one aspect of the present invention includes the steps of mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities, maintaining the temperature of the molten metal after the mixing step within a solid-liquid coexistence temperature range, and separating the solid-phase aluminum and the intermetallic compound containing the impurities produced in the maintaining step in the molten metal or from the molten metal in the solid-liquid coexistence temperature range, and stirring or squeezing the molten metal in the separating step.

The impurity removal method according to one aspect of the present invention can efficiently remove impurities that are mixed into aluminum or aluminum alloys and are difficult to remove from the molten metal.

FIG. 1 is a flow diagram showing a method for removing impurities according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a stirring procedure in the separation step of the impurity removal method of FIG. FIG. 3 is a schematic cross-sectional view showing an example of a squeezing procedure in the separation step of the impurity removal method of FIG. FIG. 4 is a flow diagram showing a method for producing an ingot according to one embodiment of the present invention.

[Description of the embodiments of the present invention]
First, the embodiments of the present invention will be listed and described.

The impurity removal method according to one aspect of the present invention includes the steps of mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities, maintaining the temperature of the molten metal after the mixing step within a solid-liquid coexistence temperature range, and separating the solid-phase aluminum and the intermetallic compound containing the impurities produced in the maintaining step in the molten metal or from the molten metal in the solid-liquid coexistence temperature range, and stirring or squeezing the molten metal in the separating step.

In the separation step, the impurity removal method can efficiently separate solid-phase aluminum and intermetallic compounds containing impurities from the molten metal or from the molten metal by stirring or squeezing the molten metal within the solid-liquid coexistence temperature range. Therefore, the impurity removal method can efficiently remove impurities that are mixed into aluminum or aluminum alloys and are difficult to remove.

The Mg content in the molten metal after the mixing process is preferably 5 mass% or more. In this way, by having the Mg content in the molten metal after the mixing process be equal to or greater than the lower limit, the intermetallic compounds can be easily and efficiently produced in the molten metal.

In the separation process, the solid-phase aluminum and the intermetallic compound may be unevenly distributed in the molten metal. In this way, the solid-phase aluminum and the intermetallic compound may be unevenly distributed in the molten metal in the separation process, whereby the impurities can be easily removed.

The solid-phase aluminum may contain α-aluminum dendrites, and the α-aluminum dendrites may be destroyed in the separation process. In this way, the solid-phase aluminum may contain α-aluminum dendrites, and the α-aluminum dendrites may be destroyed in the separation process, so that the intermetallic compound can be easily separated in the molten metal.

A method for producing an ingot according to another embodiment of the present invention includes a step of mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities, a step of maintaining the temperature of the molten metal after the mixing step within a solid-liquid coexistence temperature range, a step of separating the solid-phase aluminum and the intermetallic compound containing the impurities produced in the maintaining step in the solid-liquid coexistence temperature range in the molten metal or from the molten metal, and a step of solidifying the molten metal after the separation step, in which the molten metal is stirred or squeezed.

The ingot manufacturing method can easily remove impurities from the resulting ingot by efficiently separating solid-phase aluminum and intermetallic compounds containing impurities from the molten metal in the separation process. In addition, the ingot manufacturing method can produce an ingot with a reduced impurity content by efficiently separating solid-phase aluminum and intermetallic compounds containing impurities from the molten metal in the separation process.

In the present invention, the "solid-liquid coexistence temperature" means a temperature that is lower than the liquidus temperature and equal to or higher than the solidus temperature. In other words, in the present invention, the "solid-liquid coexistence temperature" is the temperature at which solid phase aluminum (α-aluminum) and liquid phase aluminum coexist.

The following describes in detail an embodiment of the present invention with reference to the drawings.

[Impurity removal method]
The impurity removal method can remove impurities that are mixed into aluminum or aluminum alloys and are difficult to remove by using Mg (magnesium), which is an essential element of the JIS-A5000 series. The impurity removal method can remove impurities such as metal elements that are difficult to remove during the aluminum recycling process. The impurity removal method can remove impurities by promoting the formation of intermetallic compounds of impurities by including Mg, which is an essential element in JIS-A5000 series aluminum alloys, in the molten metal, and separating the generated intermetallic compounds. The impurity removal method does not require the addition of additional impurities to generate the intermetallic compounds. In addition, since the impurity removal method includes a separation step S3 described later, the amount of Mg added can be kept relatively low.

As shown in FIG. 1, the impurity removal method includes a step of mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities (mixing step S1), a step of maintaining the temperature of the molten metal after the mixing step S1 within a solid-liquid coexistence temperature range (maintenance step S2), and a step of separating the solid-phase aluminum and the intermetallic compound containing the impurities produced in the maintenance step S2 in the solid-liquid coexistence temperature range or from the molten metal (separation step S3). In the impurity removal method, the molten metal is stirred or squeezed in the separation step S3.

〔impurities〕
The impurities include (1) Fe (iron) and (2) one or both of Mn (manganese), Co (cobalt), Ti (titanium), V (vanadium), Zr (zirconium), and Cr (chromium). The impurities may include one or more of the elements included in (1) and (2). When the impurity includes Fe, the intermetallic compound separated in the separation step S3 contains aluminum and Fe. When the impurity includes Mn, Co, Ti, V, Zr, Cr, or a combination thereof, the intermetallic compound separated in the separation step S3 is considered to contain aluminum and Mn, Co, Ti, V, Zr, Cr, or a combination thereof.

[Fe]
Fe is the most likely impurity element to be mixed into molten metal containing aluminum or an aluminum alloy, and is difficult to remove. Fe is easily mixed in from fasteners, shredders, etc. On the other hand, aluminum is an element that oxidizes easily, and since oxidation refining such as in converters in the steel industry is not possible, it is considered difficult to remove Fe. This impurity removal method can efficiently remove Fe from molten metal containing aluminum and Mg (Al-Mg molten metal), and therefore can easily realize horizontal recycling of aluminum from wrought material to wrought material.

[Mn, Co, Ti, V, Zr, Cr or a combination thereof]
Mn, Ti, V, Zr, and Cr are mixed in as additive elements of aluminum alloys, elements contained in grain refiners, ingots, etc. Co is an element contained in batteries and can be mixed in from scrap. According to the impurity removal method, when the impurities include Mn, Co, Ti, V, Zr, Cr, or a combination thereof, it is considered that an intermetallic compound containing aluminum and Mn, Co, Ti, V, Zr, Cr, or a combination thereof can be easily generated by the holding step S2. Furthermore, according to the impurity removal method, it is considered that impurities including Mn, Co, Ti, V, Zr, Cr, or a combination thereof can be efficiently removed from the Al-Mg molten metal in the separation step S3.

(Mixing process)
In the mixing step S1, for example, Mg or an Mg alloy is added to a molten metal containing aluminum or an aluminum alloy and the above-mentioned impurities. More specifically, in the mixing step S1, Mg or an Mg alloy is added to a molten metal obtained by melting aluminum scrap.

Mg is an essential element in JIS-A5000 series aluminum alloys. The moderate content of Mg in molten metal containing aluminum or an aluminum alloy promotes the formation of intermetallic compounds containing the above-mentioned impurities in the Al-Mg molten metal. According to the impurity removal method, it is not necessary to intentionally mix unnecessary impurities in order to generate intermetallic compounds, as has been done in the past. That is, in the mixing step S1, it is not necessary to mix components other than Mg or Mg alloys into the molten metal. In addition, since Mg is not an impurity, the impurity removal method does not require a step for removing Mg. Therefore, in the impurity removal method, for example, the molten metal after the above-mentioned impurities have been removed can be diluted as necessary and used for aluminum recycling. The procedure for diluting the molten metal after the above-mentioned impurities have been removed (dilution step) will be described later. Examples of Mg alloys mixed in the mixing step S1 include JIS-MC5 and JIS-MDC2A.

The effects of mixing Mg or an Mg alloy in the mixing step S1 include, for example, the following (a) to (c).
(a) The liquidus temperature is lowered, allowing the molten metal to be kept at a lower temperature, facilitating the formation of intermetallic compounds.
(b) Mg increases the activity of impurity elements, promoting the formation of intermetallic compounds.
(c) Mg reacts directly with impurity elements to form intermetallic compounds.

For example, when Fe is included as an impurity, it is presumed that the removal of Fe is promoted by the above effects (a) and (b). For impurities other than Fe, it is presumed that any of the above effects (a) to (c) or a combination of the effects (a) to (c) promotes the formation of intermetallic compounds, and that these intermetallic compounds can be efficiently removed from the molten metal.

The lower limit of the Mg content in the molten metal after the mixing step S1 is preferably 5% by mass, more preferably 8% by mass, and even more preferably 10% by mass. If the Mg content is less than the lower limit, the liquidus temperature may not be sufficiently lowered. On the other hand, the upper limit of the Mg content in the molten metal after the mixing step S1 is not particularly limited, but is preferably 30% by mass, more preferably 20% by mass, and even more preferably 15% by mass, from the viewpoint of preventing an increase in the dilution amount in the dilution step described below and an increase in the cost required for recycling aluminum.

(Holding process)
In the holding step S2, the molten metal after the mixing step S1 is held in a solid-liquid coexistence state. In the impurity removal method, by holding the molten metal in a solid-liquid coexistence state in the holding step S2, the intermetallic compounds containing the impurities can be sufficiently separated in the separation step S3 described below. Since the impurity removal method only requires holding the molten metal in a solid-liquid coexistence state, the Mg content in the molten metal can be made relatively small, and the amount of aluminum ingot (industrially pure aluminum, aluminum scrap with a low Mg concentration, etc.) added when diluting the molten metal after the impurities have been removed can be reduced.

In the holding step S2, the temperature of the molten metal after the mixing step S1 is held within the solid-liquid coexistence temperature range, so that the impurities contained in the molten metal are generated as intermetallic compounds. On the other hand, when the temperature of the molten metal after the mixing step S1 is held within the solid-liquid coexistence temperature range, solid-phase aluminum is generated along with the intermetallic compounds. The primary crystals of this solid-phase aluminum have a dendritic form. The solidification of the solid-phase aluminum proceeds as the generation of α-aluminum dendrites. These α-aluminum dendrites are of high purity. These α-aluminum dendrites grow in a granular form. In other words, the solid-phase aluminum contains α-aluminum dendrites and granular bodies in which the α-aluminum dendrites have grown. The total content ratio of the α-aluminum dendrites and the granular bodies in the solid-phase aluminum is very large. The intermetallic compounds are generated near the solid-liquid interface and are captured in the gaps between the α-aluminum dendrites (between the α-aluminum dendrites). In addition, the intermetallic compounds are incorporated into the granular material during the growth of the α-aluminum dendrites.

In the holding step S2, the molten metal after the mixing step S1 is cooled to a temperature range below the liquidus temperature and above the solidus temperature. If the Mg content [mass %] in the molten metal is C, the lower limit of the holding temperature T [°C] of the molten metal in the holding step S2 can be, for example, T≧-10.8C+660 when C≦19, and T≧450 when C>19. On the other hand, the upper limit of the holding temperature T [°C] of the molten metal in the holding step S2 can be T<-5.9C+660 (however, when C≦35).

In the holding step S2, it is preferable to hold the molten metal after the mixing step S1 in a solid-liquid coexistence temperature range where the liquid phase ratio is 60% or more. Specifically, the holding temperature T [°C] of the molten metal in the holding step S2 is preferably T≧-7.3C+660 (when C≦35). If the liquid phase ratio is less than the lower limit, the solid phase ratio may become too large, making it difficult to stir or squeeze the molten metal in the separation step S3.

(Separation process)
In the separation step S3, the intermetallic compound is separated together with the solid-phase aluminum in the molten metal or from the molten metal.

In the separation step S3, the molten metal held in the solid-liquid coexistence temperature range in the holding step S2 is stirred or squeezed. In the separation step S3, the molten metal may be stirred or squeezed after it is held in the solid-liquid coexistence temperature range, or the stirring or squeezing operation may be started before the molten metal reaches the solid-liquid coexistence temperature.

In the separation step S3, it is preferable to unevenly distribute the solid-phase aluminum and the intermetallic compounds containing the impurities generated in the holding step S2 in the molten metal. The impurity removal method can unevenly distribute the solid-phase aluminum and the intermetallic compounds in the molten metal, for example, by stirring or squeezing the molten metal stored in a furnace. With this configuration, the impurities can be easily removed.

In the separation step S3, it is preferable to destroy the α-aluminum dendrites contained in the solid-phase aluminum. As described above, the intermetallic compounds containing the impurities are trapped in the gaps between the α-aluminum dendrites in the solid-liquid coexistence temperature range. Therefore, by destroying the α-aluminum dendrites in the separation step S3, the intermetallic compounds can be released from between the α-aluminum dendrites. Since these intermetallic compounds usually have a higher specific gravity than the molten aluminum (liquid-phase aluminum), by destroying the α-aluminum dendrites, the intermetallic compounds can be easily separated to the bottom side of the molten aluminum.

In addition, in the separation step S3, it is preferable to destroy the granular bodies contained in the solid-phase aluminum together with the α-aluminum dendrites. As described above, the intermetallic compounds are incorporated into the granular bodies during the growth of the α-aluminum dendrites. Therefore, by destroying the granular bodies in the separation step S3, the intermetallic compounds incorporated into the granular bodies can be easily and reliably released from the granular bodies.

The steps of stirring and squeezing the molten metal in the separation step S3 are described below. Note that in the separation step S3, only one of the stirring and squeezing steps may be performed, but both stirring and squeezing may be performed.

[Mixing procedure]
When stirring the molten metal in the separation step S3, for example, as shown in Fig. 2, the molten metal X held in a furnace Y in a solid-liquid coexistence temperature range is stirred by a stirrer 10. The stirring means is not particularly limited as long as it can provide a stirring force sufficient to destroy the α-aluminum dendrites D, and examples of the stirring means include mechanical stirring using a rod or stirring blade, electromagnetic stirring using a stirrer, and stirring by blowing in an inert gas (Fig. 2 illustrates mechanical stirring using a stirring blade).

By stirring the molten metal X in the separation step S3, the α-aluminum dendrites D and the above-mentioned granular bodies are destroyed, and the intermetallic compound I containing the impurities captured in the gaps of the α-aluminum dendrites D or taken inside the above-mentioned granular bodies can be released. Examples of the intermetallic compound I include Al ₃ Fe when the impurity is Fe, Al ₆ Mn when the impurity is Mn, Al 3 Co when the impurity is Co, Al ₃ Ti when the impurity is Ti, Al ₃ V when the impurity is V, Al ₃ Zr when the impurity is Zr, and Al ₇ Cr when the impurity is Cr. These _{intermetallic} compounds have a larger specific gravity than liquid phase aluminum, so that by leaving the molten metal X still after stirring, they settle to the bottom of the molten metal X together with the α-aluminum dendrites D and the above-mentioned granular bodies. This allows the intermetallic compound I to be unevenly distributed at the bottom of the molten metal X together with the α-aluminum dendrites D and the above-mentioned granular bodies. The above-mentioned leaving after stirring is preferably performed in a state where the temperature of the molten metal X is maintained within the solid-liquid coexistence temperature range. Moreover, the above-mentioned leaving after stirring is more preferably performed so that the temperature of the molten metal X is maintained within the solid-liquid coexistence temperature range and at or below the temperature during the above-mentioned stirring.

[Compression procedure]
When squeezing the molten metal in the separation step S3, for example, as shown in Fig. 3, the molten metal X held in a furnace Y in a solid-liquid coexistence temperature range is pressed from the liquid surface side by a squeezing plate 20. As the squeezing plate 20, for example, one having a plurality of holes (not shown) through which the molten metal X can pass in the plate thickness direction can be used.

By squeezing the molten metal X in the separation step S3, the α-aluminum dendrites D and the above-mentioned granular bodies are destroyed, and the intermetallic compound I containing impurities that is trapped in the gaps between the α-aluminum dendrites D or incorporated inside the above-mentioned granular bodies is released, while the intermetallic compound I can be unevenly distributed at the bottom of the molten metal X together with the α-aluminum dendrites D and the above-mentioned granular bodies. As a result, the intermetallic compound I can be compacted at the bottom side of the furnace Y together with the α-aluminum dendrites D and the above-mentioned granular bodies.

It should be noted that methods other than those shown in FIG. 3 can also be used to squeeze the molten metal in the separation step S3. For example, in the separation step S3, it is possible to adopt a configuration in which the molten metal is squeezed from the liquid surface side, thereby discharging the liquid aluminum from the furnace while leaving the intermetallic compounds and α-aluminum dendrites in the furnace.

(Dilution process)
The impurities are separated by the separation step S3, and the molten metal from which the impurities have been removed can be diluted and used for aluminum recycling. More specifically, the liquid phase aluminum recovered after the impurities have been separated by the separation step S3 can be diluted and used for aluminum recycling. The aluminum recycling method in which a dilution step is added to the above-mentioned mixing step S1, holding step S2, and separation step S3 is one embodiment of the present invention. In the dilution step, the molten metal from which the impurities have been removed by the separation step S3 is mixed with industrial pure aluminum or aluminum scrap with a low Mg concentration (e.g., JIS-A1000 series) and diluted to the Mg standard concentration of A5000 series (Al-Mg alloy) specified by JIS.

In the dilution process, the Mg concentration of the molten metal containing the Mg added in the mixing process S1 is diluted to below the standard concentration of the JIS-A5000 series. Since Mg is not an impurity, it does not need to be removed from the molten metal. This aluminum recycling method reduces the Mg concentration in the dilution process, allowing the diluted molten metal to be used for aluminum products. In the dilution process, the molten metal containing a relatively high concentration of Mg can be held under vacuum to evaporate Mg, which has a high vapor pressure, thereby reducing the Mg concentration in the molten metal. In addition, in the dilution process, Mg can also be removed by blowing chlorine into the molten metal or by using a flux.

The molten metal after the separation step S3 can be reused without going through the dilution step. For example, the molten metal can be solidified after removing impurities and used as recycled ingot, or the molten metal can be solidified with the intermetallic compound I unevenly distributed, and the parts with high impurity concentrations can be selectively cut off and used as recycled ingot. The molten metal can also be diluted as necessary in the process of using the recycled ingot. Furthermore, the molten metal after the separation step S3 can be separated and collected by suction, etc., or solidified in a mold, etc., and used as an Mg intermediate alloy.

In addition, after separating the portion with a high impurity concentration from the ingot obtained after the separation step S3, the impurity removal method may be carried out again on this portion with a high impurity concentration. With this configuration, this portion with a high impurity concentration can be refined by the impurity removal method. In this case, new aluminum scrap or the like may be added when carrying out the impurity removal method. These configurations can also improve the yield.

<Advantages>
In the impurity removal method, the molten metal X is stirred or squeezed in a solid-liquid coexistence temperature range in the separation step S3, so that the solid-phase aluminum such as α-aluminum dendrites D and the intermetallic compound I can be efficiently separated in or from the molten metal X. To explain in more detail, in the solid-liquid coexistence temperature range, solid-phase aluminum (α-aluminum), liquid-phase aluminum, and the intermetallic compound I are substantially uniformly dispersed in the molten metal X. In this state, the intermetallic compound I is captured in the gaps between the α-aluminum dendrites or taken into the inside of the above-mentioned granular body, and is difficult to remove. In contrast, the impurity removal method breaks the α-aluminum dendrites D and the above-mentioned granular body in the separation step S3, so that the intermetallic compound I can be efficiently separated in or from the molten metal X together with the α-aluminum dendrites D and the above-mentioned granular body. Therefore, according to the impurity removal method, impurities that are mixed in aluminum or an aluminum alloy and are difficult to remove can be efficiently removed.

In this impurity removal method, Mg, an essential element in JIS-A5000 series aluminum alloys, is added to the molten metal X to promote the formation of an intermetallic compound of the impurities, and the impurities are removed by separating the intermetallic compound I that is formed. This impurity removal method does not require the deliberate mixing of unnecessary impurities to form intermetallic compound I, as has been done in the past, and can also improve yields.

This impurity removal method can efficiently remove metal elements that are difficult to remove during the aluminum recycling process, making it possible to realize horizontal recycling from aluminum wrought material to aluminum wrought material.

In this impurity removal method, in the mixing step S1, Mg or an Mg alloy is mixed into the molten metal containing aluminum or an aluminum alloy and impurities. On the other hand, by mixing Cu, which is an essential element of JIS-A2000 series alloys, or Zn, which is an essential element of JIS-A7000 series alloys, into the molten metal containing aluminum or an aluminum alloy and impurities in the mixing step S1, it is believed that solid-phase aluminum and intermetallic compounds containing impurities can be separated in the molten metal or from the molten metal in the separation step S3 in the same manner as described above. Also, in the mixing step S1, Mg or an Mg alloy, Cu or a Cu alloy, or Zn or a Zn alloy may be mixed alone or in any combination.

[Method of manufacturing ingot]
Next, a method for manufacturing an ingot using the impurity removal method will be described. As shown in FIG. 4, the method for manufacturing an ingot includes a step of mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities (mixing step S1), a step of maintaining the temperature of the molten metal after the mixing step S1 within a solid-liquid coexistence temperature range (holding step S2), a step of separating the solid-phase aluminum and the intermetallic compound containing the impurities generated in the holding step S2 in the solid-liquid coexistence temperature range or from the molten metal (separation step S3), and a step of solidifying the molten metal after the separation step S3 (solidification step S4). In the method for manufacturing an ingot, the molten metal is stirred or squeezed in the separation step S3. The mixing step S1, the holding step S2, and the separation step S3 in the method for manufacturing an ingot can be performed in the same procedure as the mixing step S1, the holding step S2, and the separation step S3 in the impurity removal method of FIG. 1. Therefore, the description of the mixing step S1, the holding step S2, and the separation step S3 will be omitted.

(Solidification process)
In the solidification step S4, the molten metal from which the impurities have been removed through the separation step S3 may be solidified, or the molten metal in which impurities are unevenly distributed through the separation step S3 may be solidified. In addition, in the solidification step S4, the molten metal diluted after the separation step S3 may be solidified. When the diluted molten metal is solidified in the solidification step S4, the manufacturing method of the ingot may include the above-mentioned dilution step between the separation step S3 and the solidification step S4.

<Advantages>
In the ingot manufacturing method, the solid-phase aluminum and the intermetallic compound containing the impurities are efficiently separated from the molten metal in the separation step S3, so that the impurities can be easily removed from the obtained ingot. Also, in the ingot manufacturing method, the solid-phase aluminum and the intermetallic compound containing the impurities are efficiently separated from the molten metal in the separation step S3, so that an ingot with a reduced impurity content can be manufactured.

[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 technical knowledge, and it should be understood that all of these are within the scope of the present invention.

In the above embodiment, a configuration has been described in which the separation step separates α-aluminum dendrites and intermetallic compounds containing impurities in or from the molten metal. However, in the separation step, as long as the solid-phase aluminum and the intermetallic compounds are separated, the solid-phase aluminum does not need to contain α-aluminum dendrites. Furthermore, even if the solid-phase aluminum contains α-aluminum dendrites, the separation step does not need to destroy the α-aluminum dendrites.

The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to the descriptions in these examples.

[Example]
[No. 1]
An aluminum alloy containing impurities and pure Mg were dissolved in a graphite crucible to prepare a molten metal containing Fe as an impurity and Si as another element (mixing step). The contents of various elements in the molten metal are shown in Table 1. The molten metal was then furnace-cooled to 641°C, and a silicon nitride stirring rod was inserted into the molten metal to start stirring the molten metal. While stirring, the molten metal was furnace-cooled to 602°C or less, and then held within the solid-liquid coexistence temperature range (holding step). The stirring was continued while the molten metal was held within the solid-liquid coexistence temperature range, and when the molten metal reached 591°C, the stirring rod was removed, and the molten metal was left to stand at the solid-liquid coexistence temperature of 590°C for 15 minutes (separation step). By this separation step, α-aluminum dendrites and intermetallic compounds containing Fe were separated on the bottom side of the molten metal. After this separation step, the power to the furnace was turned off and the molten metal was solidified to obtain an ingot. A portion was taken from the top of the ingot and the Fe concentration was analyzed by ICP atomic emission spectrometry. The analysis results are shown in Table 1.

[No. 2]
An aluminum alloy containing impurities and pure Mg were dissolved in a graphite crucible to prepare a molten metal containing Fe as an impurity and Si as another element (mixing step). The contents of various elements in the molten metal are shown in Table 1. The molten metal was then cooled to 594°C, which is the solid-liquid coexistence temperature (holding step), and the crucible was removed from the furnace. The molten metal was quickly squeezed from the liquid surface side using an iron jig (separation step). By this separation step, α-aluminum dendrites and intermetallic compounds containing Fe were separated on the bottom side of the molten metal. After this separation step, the molten metal was air-cooled and solidified to obtain an ingot. The jig used in the separation step was cast-in while inserted into the molten metal. A part of the upper side of the jig of the ingot was collected, and the Fe concentration was analyzed by ICP emission spectroscopy. The analysis results are shown in Table 1.

[No. 3]
An aluminum alloy containing impurities and pure Mg were dissolved in a graphite crucible to prepare a molten metal containing Mn as an impurity and Si, Cu and Zn as other elements (mixing step). The contents of various elements in this molten metal are shown in Table 1. Thereafter, this molten metal was furnace-cooled to 593°C, which is the solid-liquid coexistence temperature (holding step), and the crucible was removed from the furnace, and the molten metal was quickly squeezed from the liquid surface side using an iron jig (separation step). By this separation step, α-aluminum dendrites and intermetallic compounds containing Mn were separated on the bottom side of the molten metal. After this separation step, the molten metal was air-cooled and solidified to obtain an ingot. The jig used in the separation step was cast-in while inserted in the molten metal. A part of the upper side of the jig of this ingot was collected, and the Mn concentration was analyzed by ICP emission spectroscopy. The analysis results are shown in Table 1.

[Comparative Example]
[No. 4]
An aluminum alloy containing impurities and pure Mg were dissolved in a graphite crucible to prepare a molten metal containing Fe as an impurity and Si as another element (mixing process). The contents of various elements in the molten metal are shown in Table 1. The molten metal was then air-cooled to 600°C, which is the solid-liquid coexistence temperature, and allowed to stand for 15 minutes. The furnace was then turned off to solidify the molten metal, thereby obtaining an ingot. A portion was taken from the top of the ingot, and the Fe concentration was analyzed by ICP emission spectroscopy. The analysis results are shown in Table 1.

[No. 5]
An aluminum alloy containing impurities and pure Mg were dissolved in a graphite crucible to prepare a molten metal containing Fe as an impurity and Si as another element (mixing process). The contents of various elements in this molten metal are shown in Table 1. The molten metal was then furnace-cooled to 651°C, which is higher than the solid-liquid coexistence temperature, and a silicon nitride stirring rod was inserted into the molten metal while maintaining this temperature to stir the molten metal. After this stirring, the molten metal was held at 651°C for 15 minutes. The furnace was then turned off to solidify the molten metal, thereby obtaining an ingot. A portion was taken from the top of the ingot, and the Fe concentration was analyzed by ICP emission spectroscopy. The analysis results are shown in Table 1.

As shown in Table 1, in No. 1 to No. 3, the temperature of the molten metal is maintained within the solid-liquid coexistence temperature range in the holding step, while the molten metal is stirred or squeezed in the separation step, which allows for sufficient impurity removal. In contrast, in No. 4, the molten metal is not stirred or squeezed in the separation step, so the impurity removal rate is insufficient. In addition, in No. 5, the molten metal is not maintained in the solid-liquid coexistence temperature range when it is stirred, so the impurity removal rate is insufficient.

[No. 6]
From the Al-X binary equilibrium phase diagram (where X=Mn), the solubility [mass%] of X in liquid phase aluminum at 700°C was read. Next, using the calculation software "FactSage 8.0", the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

[No. 7]
The solubility [mass%] of X in liquid phase aluminum at 700°C was read from the Al-X binary equilibrium phase diagram in the same manner as in No. 6, except that X = Co, and the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

[No. 8]
The solubility [mass%] of X in liquid phase aluminum at 700°C was read from the Al-X binary equilibrium phase diagram in the same manner as in No. 6, except that X = Ti, and the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

[No. 9]
The solubility [mass%] of X in liquid phase aluminum at 700°C was read from the Al-X binary equilibrium phase diagram in the same manner as in No. 6, except that X = V. Furthermore, the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

[No. 10]
The solubility [mass%] of X in liquid phase aluminum at 700°C was read from the Al-X binary equilibrium phase diagram in the same manner as in No. 6, except that X = Zr, and the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

[No. 11]
The solubility [mass%] of X in liquid phase aluminum at 700°C was read from the Al-X binary equilibrium phase diagram in the same manner as in No. 6, except that X = Cr, and the concentration [mass%] of X in liquid phase aluminum in an equilibrium state at 590°C, which is the solid-liquid coexistence temperature, was calculated for Al-10 mass% Mg-1 mass% X. The results are shown in Table 2.

As shown in Table 2, even when X is any of Mn, Co, Ti, V, Zr, and Cr, the concentration of X in liquid phase aluminum at 590°C is sufficiently smaller than the solubility of X in liquid phase aluminum at 700°C, specifically, sufficiently smaller than 1 mass%. From this, it is believed that the impurity removal method can efficiently remove impurities even when X (impurity) is any of Mn, Co, Ti, V, Zr, and Cr.

As described above, the impurity removal method according to one embodiment of the present invention can efficiently remove metal elements that are difficult to remove during the aluminum recycling process, and is therefore suitable for achieving horizontal recycling of aluminum from wrought material to wrought material.

10 Stirrer 20 Compression plate D α-aluminum dendrite I Intermetallic compound X Molten metal Y Furnace

Claims (4)

mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities;
a step of maintaining the temperature of the molten metal after the mixing step within a solid-liquid coexistence temperature range;
a separation step of distributing the solid-phase aluminum and the intermetallic compound containing the impurities produced in the holding step unevenly in the molten metal in the solid-liquid coexistence temperature range or removing them from the molten metal,
The method for removing impurities, in the separation step, comprises stirring and leaving the molten metal to stand, or squeezing the molten metal . The method for removing impurities according to claim 1, wherein the Mg content in the molten metal after the mixing step is 5% by mass or more. the solid phase aluminum comprises α-aluminum dendrites;
3. The method for removing impurities according to claim 1 , wherein the α-aluminum dendrites are destroyed in the separating step. mixing Mg or an Mg alloy with a molten metal containing aluminum or an aluminum alloy and impurities;
a step of maintaining the temperature of the molten metal after the mixing step within a solid-liquid coexistence temperature range;
a separation step of distributing the solid-phase aluminum and the intermetallic compound containing the impurities produced in the holding step unevenly in the molten metal in the solid-liquid coexistence temperature range or removing them from the molten metal;
and a step of solidifying the molten metal after the separation step,
The method for producing an ingot, wherein the separation step comprises stirring and leaving the molten metal to stand, or squeezing the molten metal .

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