Method for reducing or removing additive elements and / or impurities in aluminum alloys

Abstract

The purpose of this study is to provide a new method using molten Sn to reduce or remove additive elements and impurities in aluminum alloys. The method is characterized by a three-layer electrolysis method having a bottom Sn-Al alloy layer as an anode, a top refined Al layer as a cathode, and an intermediate layer as a molten electrolytic bath.

Description

[Technical Field]

[0001] The present invention relates to a method for reducing or eliminating alloying elements in an aluminum alloy material. [Background technology]

[0002] Aluminum alloys can be broadly divided into two types: wrought materials such as extruded materials and rolled materials, and cast materials such as die-cast materials. Among these, a relatively large amount of Si is added to the casting material in order to improve the fluidity during casting, reduce the thermal expansion coefficient, and improve wear resistance. Furthermore, Cu may be added to improve strength. When die-casting a product, gate overflow and runner parts are generated in addition to the product part, and since these parts other than the product are remelted and reused, Fe components are likely to be mixed in. Therefore, for example, the JIS ADC12 alloy contains, in mass %, Si: 9.6 to 12.0%, Cu: 1.05 to 3.05%, and Fe: 1.3% or less. The amounts and tolerances of components such as Si, Cu, and Fe are relatively wide, and the recycling rate of scrap material is also high. In contrast, JIS A6063, a representative example of wrought materials, contains small amounts of additives, such as Si: 0.20 to 0.6%, Fe: 0.35% or less, Cu: 0.10% or less, and Mg: 0.45 to 0.9%, in mass%, and the tolerance range is relatively narrow. These circumstances are one of the reasons why the recycling rate of wrought materials has not improved. Therefore, if the content of Si, Fe, and Cu can be reduced or removed from aluminum alloys, it is expected that not only will the recycling of wrought materials be improved, but also the added value of the aluminum as a high-purity raw material will be increased.

[0003] A method proposed so far for reducing or removing impurities in aluminum alloys is to add Mn to the molten aluminum alloy in order to form an intermetallic compound with the Fe component and separate it by crystallization (Patent Document 1). A method has been proposed in which Mg is added to form an intermetallic compound with Fe and Si components and then crystallize and separate the compound (Patent Document 2). However, this method of crystallizing and separating intermetallic compounds consumes a large amount of added Mn and Mg, making it difficult to reuse them. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 8-35021 [Patent Document 2] Japanese Patent Publication No. 2022-83833 [Patent Document 3] Japanese Patent Application Publication No. 10-371844 [Patent Document 4] Japan Patent Application No. 2023-077600 [Non-patent literature]

[0005] [Non-Patent Document 1] AJ McAlister and DJ Kahan: Bulletin of Alloy Phase Diagram, 4(1983), 410. [Non-patent document 2] RW Olesinski and GJ Abbaschian: Bulletin of Alloy Phase Diagram, 5(1984), 273 [Non-patent document 3] KC Hari Kumar, P. Wollants, and L. Delaey: Calphad, 20 (1996), pp. 139-149. [Non-patent document 4] S. Furtauer, D. Li, D. Cupid, H. Flandorfer: Intermetallics, 34 (2013), 142-147. [Non-Patent Document 5] Kosuke Hoshikawa, Ichiro Tanaka, and Tomohiro Megumi: Sumitomo Chemical (2013), 10-19. [Non-patent document 6] W. J Coy and RS Mateer: Trans. ASM, 58(1965), 99. [Non-Patent Document 7] AE Schwaneke, WL Falke and VR miller: J. Chem. Eng. Data, 23 (1978), 298-301. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a novel method for reducing or removing additive elements and impurities in aluminum alloys using molten Sn. [Means for solving the problem]

[0007] The method for reducing or removing additive elements and / or impurities in an aluminum alloy according to the present invention is characterized by a three-layer electrolysis method having a bottom Sn-Al alloy layer as an anode, a top refined Al layer as a cathode, and an intermediate layer as a molten electrolytic bath.

[0008] The principle of the three-layer electrolysis process is also called the three-layer electrorefining process, as disclosed in Non-Patent Document 5, and is a method that was originally established to further increase the purity of electrolytic aluminum produced by the Hall-L process. The bottom anode alloy layer is made of an Al-Cu alloy containing 30 to 40% Cu, and its specific gravity is approximately 3.0. This method involves electrolyzing the Al in this Al-Cu alloy, transferring it through the intermediate electrolytic bath to the topmost refined Al cathode layer. Since the specific gravity of the refined Al in the top layer is approximately 2.3, the molten electrolytic bath in the middle layer must be lighter than the specific gravity of the bottom anode alloy layer, but heavier than the specific gravity of the refined Al on the cathode side of the top layer; a specific gravity of approximately 2.7 is used. Also, salts of metals that are more active and have higher conductivity than aluminum are used.

[0009] The present invention is characterized in that, instead of the Al—Cu alloy used in the three-layer electrolysis method described in Non-Patent Document 5, a Sn—Al alloy containing 0 to about 50% Al is used. The specific gravity of this molten Sn—Al alloy is about 3.5 (according to Non-Patent Documents 6 and 7).

[0010] In the present invention, the aluminum alloy material supplied to the bottom layer may be a molten alloy in which solid Si and / or solid Fe are crystallized and separated from the molten Sn—Al alloy.

[0011] If the bottom Sn-Al alloy layer contains a large amount of Si, the density of the anode alloy will decrease, and electrolysis may become difficult, since the specific gravity of Si is approximately 2.3. However, from the phase diagram of Al and Sn disclosed in Non-Patent Document 1, the phase diagram of Si and Sn disclosed in Non-Patent Document 2, the phase diagram of Fe and Sn disclosed in Non-Patent Document 3, and the phase diagram of Cu and Sn disclosed in Non-Patent Document 4, the temperature of molten Sn and the melting curves of Al, Cu, Fe, and Si can be obtained as shown in Figure 1.

[0012] The dissolution curve in Figure 1 reveals the following: When the temperature of molten Sn is raised to 1000K or higher, Al, Cu, Si, and Fe are dissolved. When the temperature of the molten Sn is lowered to approximately 873K, it is found that approximately 50% of Al dissolves, approximately 30% of Cu dissolves, but Si and Fe do not dissolve and solid Si and Fe crystallize and separate. Since Si has a relatively light specific gravity of 2.3, it can be separated by flotation, while since Fe has a relatively heavy specific gravity of 7.9, it can be separated by sedimentation. This has been demonstrated in Patent Document 4, which was previously filed by the present inventors.

[0013] Therefore, in the present invention, the lowest Sn-Al alloy layer may be one in which molten Sn-Al has been used in advance and Si and Fe have been removed. However, if the melting temperature of the molten Sn-Al alloy is set to a temperature at which solid Si and solid Fe are crystallized, the solid Si and solid Fe can be separated in the supply section that supplies the aluminum raw material corresponding to Al that moves from the Sn-Al alloy of the anode to the cathode side, and therefore the aluminum raw material can be supplied continuously.

[0014] In the present invention, since Cu contained in the aluminum raw material is dissolved in the molten Sn—Al alloy layer, the Sn—Al alloy layer may be a Sn—Al—Cu alloy layer. [Effects of the Invention]

[0015] In the present invention, a Sn-Al alloy layer or a Sn-Al-Cu alloy layer is used as the bottom anode in the three-layer electrolysis method. Therefore, by setting the melting temperature within a predetermined range, it is possible to reduce or remove the Si and Fe components in the recycled aluminum raw material, while recovering even higher purity aluminum. This improves the horizontal recycling of wrought materials and also allows for the production of even higher purity aluminum. [Brief explanation of the drawings]

[0016] [Figure 1] The dissolution curves of Al, Cu, Si, and Fe in molten Sn are shown. [Figure 2] 1 shows a schematic diagram of an electrolysis device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] FIG. 2 shows a schematic diagram of an electrolysis apparatus for the method of reducing or removing additive elements or impurities in an aluminum alloy by the three-layer electrolysis method according to the present invention. The principle is to apply a voltage between the cathode and anode to perform molten salt electrolysis. The electrolytic cell 1 is made of firebricks or the like, and a charging furnace 2 supplies molten alloy to the anode alloy tank at the bottom of the electrolytic cell 1.

[0018] The electrolytic cell 1 has, as an anode alloy layer on the anode side, a Sn-Al alloy layer in which Al is dissolved in Sn, or a Sn-Al-Cu alloy layer in which Cu is further dissolved, and the specific gravity of these is approximately 3.5 to 6.1. A refined Al layer is formed by electrolysis on the top layer, which is the cathode side. The specific gravity of the refined Al layer is about 2.3. The intermediate layer contains a molten electrolytic bath made of molten salt. As the dissolving electrolytic bath, a known electrolytic bath as described in Patent Document 3 and Non-Patent Document 5 is used. For example, fluorides or chlorides of Na, Ba, Al, Ca, Mg, or mixed salts thereof are used, and those with a specific gravity of about 2.7, which are more active than aluminum and have good conductivity are selected. By the three-layer electrolysis method, Al dissolved in molten Sn is 3+ The ions move to the refined Al (cathode) side through electrolysis with molten salt, yielding high-purity aluminum.

[0019] Since Al is reduced from the anode alloy layer by melt electrolysis, aluminum raw material M containing Al and other components (impurities) such as Si, Fe, and Cu is charged from a charging furnace 2 . The charging furnace 2 stores molten Sn-Al alloy that has been kept at a temperature of about 873K in advance. At this temperature of around 873K, around 50% by mass of Al is dissolved in the molten Sn, and as electrolysis progresses, the amount of dissolved Al decreases. When aluminum raw material containing impurities such as Si, Fe, and Cu is added to the Al from the top of the charging furnace 2, the Al dissolves, but the Si does not dissolve and floats up and separates as solid Si with a specific gravity of 2.3 to the top of the charging furnace 2. This solid Si can be used as a Si raw material. Furthermore, Fe does not dissolve and settles out due to its specific gravity of 7.9. This prevents Si and Fe from being mixed into the anode alloy layer, making three-layer electrolytic refining possible. [Industrial Applicability]

[0020] The present invention makes it possible to reduce or remove components in aluminum alloys recovered from the market, etc., and therefore makes it possible to recycle them as high-purity aluminum materials. [Explanation of symbols]

[0021] 1 electrolytic cell 2 Feeding furnace

Claims

1. a bottom Sn—Al alloy layer as an anode; a top refined Al layer as a cathode; A method for reducing or removing additive elements and / or impurities in an aluminum alloy by a three-layer electrolysis method having an intermediate layer as a molten electrolytic bath, An aluminum alloy containing Si and / or Fe is poured into a molten Sn—Al alloy at a melting temperature at which solid Si and / or solid Fe are crystallized and separated, A method for reducing or removing additive components and / or impurities in an aluminum alloy, characterized in that the molten Sn-Al alloy is supplied to the lowermost Sn-Al alloy layer.

2. A method for reducing or removing additive components and / or impurities in an aluminum alloy according to claim 1, characterized in that a Sn-Al-Cu alloy layer is used instead of the Sn-Al alloy layer.

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