JP2024121140A - Flux, its manufacturing method and molten metal treatment method - Google Patents

Abstract

To provide a novel flux capable of efficiently removing Mg from an aluminum matrix molten metal.SOLUTION: The flux includes a molten salt containing metallic copper and a copper oxide or a solid salt thereof, and is capable of removing Mg from an aluminum matrix molten metal. The metallic copper is precipitated during a treatment of the aluminum matrix molten metal, and reacts with oxygen above the molten salt to form a copper oxide. The copper oxide reacts with the Mg taken from the aluminum matrix molten metal to the molten salt to be metallic copper. Thickness of the flux (molten salt) on the aluminum matrix molten metal is preferably 0.05 to 5 mm, for instance. While suppressing the amount of flux use, a waste substance generated in a molten metal treatment is reduced, and Mg can be continuously and efficiently removed from the aluminum matrix molten metal.SELECTED DRAWING: Figure 6

Description

The present invention relates to fluxes and other materials for use in aluminum-based molten metals.

As environmental awareness grows, lightweight aluminum-based components are being used in a variety of fields. Reusing scrap aluminum rather than using newly refined aluminum can promote the use of aluminum-based components while saving energy, reducing environmental impact, and achieving decarbonization.

When scrap is used, various elements other than Al may be present in the molten metal. Unnecessary or excess elements must be removed from the raw molten metal (Al-based molten metal) produced by melting scrap. As an example, the following document describes the removal of Mg.

US4097270A JP2007-154268A Patent Publication 2008-50637 Patent Publication 2011-168830 Patent Publication No. 2021-110025 Patent Publication No. 2021-110026

Light Metals 33 (1983) 243-248 Light Metals 54 (2004) 75-81

Patent Document 1 describes a method in which an Al-based molten metal containing Mg is reacted with silica (SiO ₂ ) (2Mg+SiO ₂ →2MgO+Si) to remove Mg as MgO (a type of metal oxide treatment method).

Patent Document 2 proposes a method in which pellets containing aluminum borate (9Al ₂ O ₃ .2B ₂ O ₃ ) are added to an Al-based molten metal containing Mg, Mg is deposited on the pellets, and then removed as a reaction product (MgAl ₂ O ₄ ).

Patent Documents 3 and 4 propose a method of removing Mg by adding powdered battery slag obtained by roasting used dry batteries to an Al-based molten metal containing Mg. The main components of battery slag are ZnO and _MnO2 , and Mg is removed as a reaction product with these oxides (MgO _{, MgMn2O4} or _MgMnO3 ). The chlorides contained in the battery slag increase the wettability of these oxides with the Al-based molten metal and promote the generation of reaction products. When using battery slag from an alkaline dry battery, which has a smaller amount of chloride than a manganese dry battery, chlorides (a mixed salt of KCl and NaCl) are replenished.

In Patent Documents 5 and 6, CuO is added to a molten salt formed to a sufficient thickness on the aluminum-based molten metal, and the Mg contained in the aluminum-based molten metal is removed by being absorbed into the thick molten salt. In this case, the amount of Mg removed depends on the amount of CuO added to the molten salt, so continuous replenishment of CuO is required to continuously remove Mg.

Non-Patent Documents 1 and 2 describe the chlorine gas treatment method and the flux treatment method. In the chlorine gas treatment method, Mg reacted with gases such as chlorine, hexachloroethane, and carbon tetrachloride injected into the Al-based molten metal is removed as _MgCl2 (Mg+ _Cl2 → _MgCl2 ). In the flux treatment method, Mg reacted with fluorides ( _AlF3 , _{NaAlF4 , K3AlF6} , etc.) added to the Al-based molten metal is removed as _MgF2 (for example, 3Mg+ _2AlF3 → _3MgF2 +2Al). In such treatment methods, much of the Al is trapped in dross and lost, and the working environment is deteriorated and hazardous waste is generated.

The present invention was made in consideration of these circumstances, and aims to provide a new flux for use in aluminum-based molten metal.

As a result of intensive research into solving this problem, the inventor came up with the idea of oxidizing metallic copper in the molten salt formed on the aluminum-based molten metal, and continuously removing magnesium from the aluminum-based molten metal, and realized this idea. By expanding on this result, the inventor has completed the present invention, which will be described below.

Flux
The present invention is a flux that contains metallic copper, copper oxide, and chloride and is disposed on an aluminum-based molten metal that contains Mg.

The flux of the present invention can be used to perform molten metal treatment (refining, etc.) to remove magnesium (Mg) from aluminum-based molten metal (Al-based molten metal).

Furthermore, by using the flux of the present invention, it is possible to, for example, reduce the amount of flux used, reduce waste (dross, etc.) generated after using the flux, and prevent the generation of hazardous waste and deterioration of the working environment. In other words, it is possible to reduce the costs required for flux and disposal, reduce the environmental load, and ultimately reduce the processing costs of Al-based molten metal. The mechanism by which such excellent effects are obtained is thought to be as follows.

When the flux of the present invention is added to an Al-based molten metal, a molten salt (molten chloride) is formed on the Al-based molten metal. The copper oxide (CuO and/or Cu ₂ O) in the molten salt reduces itself (CuO.Cu ₂ O→Cu) to become metallic copper, and in exchange, oxidizes Mg taken into the molten salt from the Al-based molten metal (Mg→MgO). The metallic copper (Cu) precipitated in the molten salt (including the interface of the Al-based molten metal) easily produces copper oxide under conditions where oxygen can be supplied (e.g., in the air). This copper oxide is consumed in the oxidation of Mg (production of MgO) described above, and precipitates as metallic copper.

In this way, the change from copper oxide to copper metal (reduction of copper oxide) and the change from copper metal to copper oxide (oxidation of copper metal) can be repeated in the molten salt. In this case, Mg contained in the Al-based molten metal can be continuously removed without continuously replenishing copper oxide from the outside to the molten salt formed on the Al-based molten metal, and the above-mentioned effects can be obtained. As is clear from the above explanation, molten metal treatment using the flux of the present invention also avoids the large-scale generation of harmful gases and waste, and the deterioration of the working environment.

<Production method of flux>
The present invention can also be understood as a method for producing a flux. The flux can be obtained, for example, by mixing metallic copper and/or copper oxide with a chloride (mixing raw materials (e.g., powders), melt mixing, etc.). The chloride can be a molten salt or a solid salt (lump, particulate, powder, etc.).

The flux may contain both metallic copper and copper oxide from the beginning, or one (part of) metallic copper or copper oxide may change to the other, resulting in the flux containing both. For example, a molten salt containing either metallic copper or copper oxide formed on an Al-based molten metal may later become a molten salt (flux) containing both metallic copper and copper oxide.

When magnesium (Mg) is contained in the chloride (solid salt or molten salt), the redox reaction between metallic copper and copper oxide is promoted. Mg may be mixed in as a chloride ( _MgCl2 ) from the beginning, or may be supplied from the Al-based molten metal to the molten salt during molten metal treatment (flux preparation).

<Method of treating molten metal>
The present invention can also be understood as a molten metal treatment method for removing Mg from an Al-based molten metal using the above-mentioned flux. The molten metal treatment is preferably performed under conditions in which oxygen can be supplied to the metallic copper in the flux. By forming the flux or molten salt into a layer of a predetermined thickness, contact between the metallic copper and oxygen can be promoted. As an example, the molten metal treatment is preferably performed in an oxygen-containing atmosphere (e.g., air atmosphere). The oxygen-containing atmosphere may be actively pumped or circulated.

Because metallic copper and copper oxide are produced in a reciprocal cycle, the flux of the present invention can be used continuously or repeatedly even if the Al-based molten metal being treated is replenished or replaced. When the chloride (molten salt) decreases during molten metal treatment due to evaporation or seepage into the crucible, chloride (which may be in either liquid or solid phase) can be replenished. This maintains the appropriate amount of molten salt or flux, allowing for stable continuation of molten metal treatment.

<<Aluminum-based alloy>>
The present invention may be understood as an Al-based alloy made of an Al-based molten metal (including a semi-molten state) after melt treatment (after purification) or a solidified product thereof (ingot, etc.).

"others"
(1) The "flux" referred to in this specification may be either a liquid phase (molten salt containing copper oxide and/or metallic copper) or a solid phase (solid salt containing copper oxide and/or metallic copper). As appropriate, a liquid phase flux is referred to as a "molten flux" and a solid phase flux is referred to as a "solid flux". A solid flux may be a mixture (e.g., a mixed powder) of flux raw materials (solid phase) or a solidified product of molten flux. The "flux" referred to in this specification may be regenerated (reused) any number of times as long as Mg contained in the Al-based molten metal can be removed (concentration reduced).

"Metallic copper" is a metal whose main component is Cu, and its shape and size can vary. For example, metallic copper may be dendritic, needle-like, rod-like, plate-like, etc. Metallic copper is not limited to pure copper (high purity copper, copper alone), and may contain impurities, alloy elements, compounds, etc. Strictly speaking, metallic copper should contain 90% or more, 95% or more, or even 98% or more of Cu relative to the whole. In this specification, the concentration and composition are the mass percentage (mass%) of the whole of the target object (molten metal, composition, etc.) unless otherwise specified, and are simply indicated as "%".

"Copper oxide" is cuprous oxide (Cu ₂ O) and/or cupric oxide (CuO). Usually, CuO predominates.

When an element is indicated only by its name (e.g., magnesium) or symbol (e.g., Mg), it can be in any state (element, compound, ion, etc.) unless otherwise specified.

(2) In this specification, "x to y" includes a lower limit of x and an upper limit of y, unless otherwise specified. Any numerical value included in the various numerical values or numerical ranges described in this specification may be used as a new lower limit or upper limit to create a new range such as "a to b." In this specification, "x to y μm" means x μm to y μm. The same applies to other units.

1 is a graph showing the relationship between the amount of Mg removed or the amount of Cu increased and the molten metal treatment time. 13 is a photograph showing the change over time of the upper surface of the flux. Photographs showing the appearance of flux raw materials, molten flux, and solid flux. 1 is a photograph showing the front and back sides of a solid flux. The images show an SEM image and an EDX image of the black area seen on the front side. These are SEM and EDX images of the brown area seen on the front side. The SEM and EDX images show the white area seen on the front side. 4 shows an SEM image and an EDX image of the back side. 1 shows an SEM image and an EDX image of the vicinity of the front side of a predetermined cross section of the solid flux. The SEM and EDX images are of the rear side of the cross section. The solid flux is washed with water and the residue is then subjected to SEM and EDX images. 1 is a graph showing the relationship between molten salt thickness and Mg removal efficiency. FIG. 2 is a schematic diagram showing a state where a molten metal treatment is performed in an air atmosphere or an Ar atmosphere. 6 is a photograph showing the surface of each flux after a predetermined time has elapsed. 1 is a bar graph showing the amount of Mg removed when molten metal was treated in each atmosphere. FIG. 1 is a schematic diagram showing a state in which a molten metal treatment is repeated while reusing flux. 1 is a bar graph showing the relationship between the number of times of reuse and the Mg concentration in the Al-based molten metal. FIG. 2 is a schematic diagram for explaining the mechanism by which Mg is removed from an Al-based molten metal by a flux. FIG. 1 is a standard free energy diagram of formation of metal oxides and metal chlorides.

One or more components selected arbitrarily from the present specification may be added to the components of the present invention described above. These may be method-related components or components related to substances (e.g., flux (Mg removal agent), Al alloy (molten metal), etc.).

<Magnesium removal principle>
The principle by which Mg is removed from the Al-based molten metal is believed to be as follows.

(1) Basic reaction Mg in an Al-based molten metal can be oxidized as follows:
Anode reaction: Mg → ^Mg + 2e ⁽ 1)

Cu ²⁺ and Cu ⁺ in the molten salt can be reduced as follows and precipitated as metallic copper.
Cathodic reaction: Cu ⁺ 2e ^→ Cu (2a)
Cu ⁺ + e ^- → Cu (2b)

Therefore, the oxidation-reduction reaction between Mg and CuO, and Cu ₂ O is as follows.
CuO + Mg → Cu + MgO (3a)
Cu ₂ O + Mg → 2Cu + MgO (3b)

Based on the standard free energy of formation (also simply called "free energy") of metal element chlorides and oxides, these reactions are thought to proceed in a stable direction where the free energy change ΔG is negative (ΔG<0), that is, from the left side to the right side. Incidentally, the relationship in magnitude of the free energies (660°C) is shown, for example, in Knacke O., Kubaschwski O., Hesselmann K., "Thermochemical Properties of Inorganic Substances" (1991), SPRINGER-VERLAG (see Figure 7). The tendency shown in Figure 7 is the same at least from 660 to 800°C.

(2) Reactions in chlorides Copper oxide itself is difficult to wet with Al-based molten metal, and the reaction in the molten salt is slow. However, the following reaction is likely to proceed in copper chlorides (CuCl ₂ , CuCl):
CuCl ₂ +Mg → Cu+MgCl ₂ (4a)
2CuCl + Mg → 2Cu + MgCl ₂ (4b)

Furthermore, in a chloride (molten salt) containing Mg, the following reaction is likely to occur even with copper oxide.
CuO + MgCl ₂ → CuCl ₂ + MgO (5a)
Cu ₂ O + MgCl ₂ → 2CuCl + MgO (5b)

In the end, if the chloride (molten salt) contains Mg, Mg in the Al-based molten metal can be efficiently removed as MgO even if inexpensive copper oxide is used instead of expensive copper chloride. It can be seen from reaction formulas (4a) and (4b) and reaction formulas (5a) and (5b) that _MgCl2 , which promotes reaction formulas (3a) and (3b), only acts as a catalyst.

Incidentally, in both reactions (5a) and (5b), when the reaction proceeds from the left side to the right side, the free energy change ΔG becomes negative (ΔG<0), which is a stable direction. Therefore, Mg trapped in the flux from the Al-based molten metal changes unilaterally from _MgCl2 to MgO, and almost no MgO returns to _MgCl2 . In this way, Mg in the Al-based molten metal becomes MgO in the flux (removal agent) and is removed.

(3) Oxidation of Metallic Copper Metallic copper produces copper oxide when it comes into contact with oxygen as follows.
2Cu+O ₂ → 2CuO (6a)
4Cu+O ₂ → 2Cu ₂ O (6b)

According to reaction formulas (3a) and (3b), the amount of MgO removed depends on the amount of CuO supplied (replenished). However, when reaction formulas (6a) and (6b) are also considered, it can be seen that even if CuO itself is not replenished, as long as oxygen (O, _O2 ) is supplied, Mg in the Al-based molten metal is taken up as MgO in the molten salt and is continuously removed. This state is shown diagrammatically in Figure 6.

Chloride
(1) The chloride is a metal chloride consisting of a metal element and Cl. Typical examples of the metal element are K, Na, and Ca. In addition, the metal element may include, for example, an alkali metal (Li, etc.) or an alkaline earth metal (Ba, etc.). The molten salt or flux may also include a halide other than the chloride (e.g., a bromide).

The chloride may be a simple salt (e.g., KCl, NaCl, CaCl ₂ ) or a complex salt thereof. The use of a complex salt makes it possible to adjust the melting point, density (specific gravity), wettability, vapor pressure, hygroscopicity, etc., and to reduce costs. For example, KCl, which lowers the melting point of the chloride, may be contained in an amount of 30 to 70 mass % (simply referred to as "%") or 40 to 65% of the entire chloride. NaCl may be contained in an amount of 30 to 60% or 35 to 47% of the entire chloride. MgCl ₂ , which acts as a catalyst, may be contained in an amount of, for example, 1 to 20% or 3 to 10% of the entire chloride.

The chloride may be a mixture (mixed salt) of multiple types of raw salts, a molten salt obtained by melting and solidifying (coagulating) the entire raw salt, or a mineral-derived chloride obtained from a mineral (e.g., carnallite anhydrous: KMgCl ₃ ), etc.

(2) The chloride content of the entire flux is, for example, 30-80%, 40-70%, or 45-65%. Too little or too much chloride can reduce the efficiency of magnesium removal.

《Copper metal/copper oxide》
The copper metal and copper oxide may be in any form that can be retained in a chloride (particularly a molten salt). In the case of copper metal, for example, dendritic particles, needle-like particles, rod-like particles, or plate-like particles may be used. There is no restriction on the size of these particles, and the maximum length may be, for example, 5 to 500 μm, 10 to 100 μm, or 15 to 65 μm. The size in this specification may be specified, for example, by the arithmetic average value of the maximum length of each particle that appears in a visual field (horizontal: 50 to 500 μm x vertical: 50 to 500 μm).

The copper oxide may have, for example, the same form (shape, size) as metallic copper. At least a portion of the copper oxide may be formed by oxidizing a portion of metallic copper (film-like, layer-like, shell-like, etc. copper oxide).

The flux (raw material) before being placed (put into) the Al-based molten metal does not need to contain metallic copper. In other words, metallic copper may be precipitated during the treatment of the Al-based molten metal to remove Mg.

Flux
As long as the flux melts on the Al-based molten metal, it may be in a liquid state or a solid state. The flux before being poured into the Al-based molten metal may be a mixture of raw materials (mixed powder, etc.) or a solid (melted product) obtained by dissolving and solidifying the mixture. The solid may be, for example, in a lump or granular form (crushed powder, granules, powder, etc.).

The flux may contain magnesium oxide. The magnesium oxide may be formed during the molten metal treatment. Porous magnesium oxide can contribute to reducing the density (specific gravity) of the flux and preventing the precipitated Cu (metallic copper) from being mixed into the molten Al.

Molten metal treatment
The thickness of the flux (or molten salt) above the Al-based molten metal from which Mg is removed may be, for example, 0.05 to 5 mm, 0.1 to 4 mm, 0.5 to 3 mm, or 1 to 2.5 mm. At this time, metallic copper in the molten salt reacts with oxygen above the flux to easily generate copper oxide. Therefore, the molten metal treatment may be performed, for example, in an oxygen-containing atmosphere at least above the flux. The oxygen-containing atmosphere may be an air atmosphere or an atmosphere in which the oxygen concentration (oxygen partial pressure) is controlled.

The flux can be continuously used or reused even when replenishing or replacing the Al-based molten metal. When the chloride (molten salt) in the flux decreases, it should be replenished as appropriate. Such replenishment may be controlled, for example, based on the thickness of the flux (molten salt) on the Al-based molten metal.

The flux may cover only a portion of the surface of the Al-based molten metal. Covering the entire surface of the Al-based molten metal improves the efficiency of Mg removal and inhibits oxidation of Al.

The longer the treatment time, the more the Mg concentration in the Al-based molten metal can be reduced. However, when recycling scrap, etc., it is often sufficient if the Mg concentration is within the desired range. The treatment time per session is, for example, 0.1 to 3 hours, 0.3 to 2 hours, or 0.5 to 1 hour. The Mg concentration in the Al-based molten metal may be gradually reduced by repeating the molten metal treatment to remove Mg.

The present invention will be explained in more detail while showing a specific example of the removal of Mg from Al-based molten metal using flux.

［Overall Overview］
Unless otherwise stated, the various experiments were carried out under the conditions shown below.

(1) Raw Materials Commercially available pure Al (purity 99.7%) and Al-20%Mg (purity 99.7%) were melted in a graphite crucible to prepare an Al-(0.75% to 0.76%)Mg molten metal (710°C ± 20°C). Concentrations (%) are mass percentages (mass%) unless otherwise specified.

The chloride used was a mixed chloride (KCl-41% NaCl-5% MgCl ₂ ) prepared by blending commercially available reagents. The mixed chloride was prepared by crushing melted and solidified solid salts into particles of about 3 mm. The density (specific gravity) of the mixed chloride was 2.4 g/cm ³ or less, and the molten salt separated into two phases from the Al-based molten metal and formed on the Al-based molten metal. Instead of a solid salt (particulate, etc.), a mixture of raw salts (powder, etc.) may be used as the chloride as it is.

Cupric oxide (CuO) powder (a commercially available reagent) was used as the copper source for metallic copper or copper oxide.

(2) Molten metal treatment The molten metal treatment was carried out in an open atmosphere unless otherwise specified. During the molten metal treatment, the Al-based molten metal was kept at 710° C.±20° C., and no stirring or other operations were performed.

(3) Concentration Analysis The chemical components (Mg concentration, etc.) of the Al-based molten metal were analyzed as follows. First, the Al-based molten metal sampled from approximately the center of the crucible was poured into a mold (stainless steel analytical mold) and allowed to solidify naturally in the air. The chemical components (Mg concentration, Cu concentration) of the resulting Al alloy casting (sample) were measured using an X-ray fluorescence analyzer (XRF: ZSX Primus II manufactured by Rigaku Corporation).

(4) Observation and elemental analysis The fluxes and other materials were observed visually and also with a scanning electron microscope (SEM/SU3500, Hitachi High-Technologies Corporation). Elemental analysis was also performed with an energy dispersive X-ray spectrometer (EDX) attached to the microscope.

[Example 1] (Amount of Mg removed)
Molten metal treatment
Molten salt (9 g) was added onto the Al-based molten metal (1,800 g). At this time, the height from the surface of the Al-based molten metal to the top surface of the molten salt (molten salt thickness) was 0.6 mm. CuO (9 g) was further added onto the molten salt. In this way, a flux was formed on the Al-based molten metal. The thickness of the flux was approximately 3 mm. The molten salt thickness was converted from the volume. The flux thickness was measured using a scale (stainless steel ruler). The molten salt thickness: flux thickness = 1:2-8.

"measurement"
The components of the Al-based molten metal were analyzed every time a predetermined treatment time elapsed after the addition of CuO. The amount of Mg removed and the amount of Cu increased relative to the entire Al-based molten metal were calculated from the amount of change in concentration in the Al-based molten metal (the difference between the concentration at each predetermined time and the initial concentration). Each amount of change was shown in moles to compare with the theoretical value (stoichiometric value) obtained from the chemical reaction formula. The relationship between the treatment time and the amount of change in Mg and Cu is shown in Figure 1A.

"observation"
The change over time of the flux surface after the addition of CuO was observed. The changes are summarized in Figure 1B. The time (min) shown in Figure 1B is the time elapsed after the addition of CuO.

"evaluation"
(1) Amount of Mg According to reaction formula (3a), the theoretical amount (maximum amount) of Mg removed should be the same mole as the added CuO (9 g: 0.113 mol). However, as is clear from Fig. 1A, the amount of Mg removed exceeded the theoretical amount after 30 minutes had elapsed, and further increased monotonically with the passage of treatment time.

It has been confirmed that Mg is not substantially removed from the Al-based molten metal unless CuO is added. It has also been confirmed that the amount of Mg removed remains within the theoretical value if the molten salt layer on the Al-based molten metal is made considerably thick. These findings reveal the involvement of another chemical reaction (i.e., reaction (6a)) in addition to reactions (3a), (4a), and (5a).

(2) Cu content As is clear from the Cu increase shown in Figure 1A, no mixing (dissolution, penetration, etc.) of Cu into the Al-based molten metal was observed. This also makes it clear that Cu remains in the flux, regardless of its shape, structure, etc.

(3) Flux As is clear from Figure 1B, brown areas (precipitation of metallic copper) were observed immediately after adding CuO to the molten salt. However, after 30 minutes, the brown areas decreased significantly, and black and white areas increased. Furthermore, the black areas (mainly CuO) and white areas (mainly MgO) increased with time.

[Example 2] (Flux)
Based on the results of Example 1, the flux formed on the Al-based molten alloy was observed and analyzed as follows.

Flux Preparation
A mixed chloride (5 g) was added onto the Al-based molten metal to form a molten salt layer (0.3 mm thick). CuO (5 g) was further added onto the molten salt layer. After 30 minutes, the flux on the Al-based molten metal was removed and allowed to cool naturally and solidify. The observation sample thus obtained is shown in Figure 2A. A photograph showing the mixed chloride and CuO used in the preparation and the flux on the Al-based molten metal is also shown in Figure 2A.

"exterior"
The front and back sides of the observation sample (solid flux) are shown in Figure 2B. On the front side, a black area was observed near the top center, and brown and white areas were observed one level below that near the periphery. On the back side, a deposit (Al-based alloy) formed by solidification of the Al-based molten metal and a brown area were observed.

"analysis"
(1) Front side The black, brown and white parts of the front side were scraped off with a spatula, and the collected powders were observed with a SEM and analyzed by EDX. The results are shown in Figures 2C to 2E.

As is clear from FIG. 2C, the black portion was composed of CuO and/or Cu ₂ O (sometimes referred to as "copper oxide"), and contained a mixture of coarse grains with a maximum length of about 20 μm and fine grains with a maximum length of about several μm.

As is clear from Figure 2D, the brown area was metallic copper (containing some MgO and copper oxide). The metallic copper was plate-shaped, needle-shaped, or dendritic (dendrite-shaped) with a maximum length of 50 μm or less.

As is clear from Figure 2E, the white part is MgO and is porous. Thus, it was found that metallic copper (brown part) and MgO (white part) are dispersed near the periphery of copper oxide (black part) on the front side of the observation sample.

(2) Back side The back side was observed and analyzed by EDX. The results are shown in Figure 2F. As is clear from Figure 2F, MgO and chlorides (K, Na, Cl) were observed around the fine metallic copper (brown area).

Fine metallic copper particles were trapped in the porous MgO. MgO does not dissolve in the Al-based molten metal, and because porous MgO has a low bulk density, it is difficult for the particles to migrate into the Al-based molten metal and tends to remain in the flux (molten salt).

(3) Cross-Section The cross-section of the dashed line portion shown in Fig. 2B was observed and analyzed by EDX. The front side of the cross-section is shown in Fig. 2G, and the back side of the cross-section is shown in Fig. 2H. As is clear from Fig. 2G, fine copper oxide particles were observed adhering to plate-shaped, needle-shaped, and chunky copper oxide particles with a thickness of 20 μm or less on the front side. As is clear from Fig. 2H, a large amount of plate-shaped, needle-shaped, and chunky metallic copper particles with a thickness of 20 μm or less were observed on the back side.

From this, it is believed that the metallic copper precipitated in the flux reacted with oxygen in the air near the outermost surface of the flux, partially turning into copper oxide. In other words, it is believed that the precipitation of metallic copper and the formation of copper oxide were repeated on the back side (the Al-based molten metal side) and front side of the flux, causing Mg to be removed from the Al-based molten metal in excess of the theoretical value.

(4) Water washing The observation sample was washed with water to remove chlorides, and the sample was observed and analyzed by EDX. The results are shown in Figure 2I. As is clear from Figure 2I, a large amount of fine dendritic or rod-like metallic copper with a thickness of 10 μm or less was observed.

[Example 3] (Molten salt thickness/Mg removal efficiency)
(1) Molten metal treatment The same molten metal treatment as in Example 1 was performed while changing the thickness of the molten salt. The amount of Al-based molten metal was 80 to 1000 g, and the treatment time was 30 minutes (constant). The components of the Al-based molten metal after treatment were analyzed, and the amount of Mg removed was calculated. The relationship between the molar ratio of the amount of Mg removed to the theoretical value (referred to as Mg removal efficiency (%)) and the thickness of the molten salt is summarized in Figure 3.

(2) Evaluation As is clear from FIG. 3, it was found that when the thickness of the molten salt was 0.05 to 5 mm (more than 0.05 mm and less than 5 mm) or further 0.06 mm to 4 mm, Mg could be removed in excess of the theoretical value calculated from the amount of CuO added (Mg removal efficiency: 100%).

If the molten salt is too thin, the dissolution of the added CuO is delayed, and it is believed that the Mg removal efficiency within the above treatment time is less than 100%. Conversely, if the molten salt layer is too thick, it is believed that the molten salt prevents the precipitated metallic copper from coming into contact with oxygen, and the Mg removal efficiency within the above treatment time is less than 100%.

[Example 4] (Treatment atmosphere)
(1) Molten metal treatment The same molten metal treatment as in Example 1 was carried out, except that the atmosphere above the molten salt was changed. The Al-based molten metal: 1000 g, the molten salt thickness: 0.3 mm, the amount of CuO added: 5 g, and the treatment time (time elapsed after the addition of CuO): 120 minutes were set.

As shown in FIG. 4A, the atmosphere above the molten salt was air or Ar. After adding CuO, Ar was introduced to partially replace the atmosphere above the molten salt with Ar. At this time, the molten salt was shielded from the outside air by a lid placed above the molten salt.

(2) Observation and Analysis The surfaces of the fluxes after the treatment time are shown in Fig. 4B. In addition, the concentration of the Al-based molten metal after the treatment was analyzed, and the amount of Mg removed was calculated. The results are shown in Fig. 4C.

(3) Evaluation As is clear from Fig. 4B, the flux when the molten metal was treated in the air atmosphere had the same structure (black part, brown part, white part) as in Example 1 and Example 2. On the other hand, the flux when the molten metal was treated in the Ar atmosphere had almost no black parts, and only white and brown parts were observed. When the lid was removed and the Ar atmosphere was opened to the air atmosphere, part of the brown part emitted red heat and changed to black. This is thought to be because the metallic copper precipitated near the surface of the molten salt was rapidly oxidized by oxygen in the air.

As is clear from Figure 4C, the amount of Mg removed when the molten metal was treated in an Ar atmosphere was approximately the theoretical value. On the other hand, the amount of Mg removed when the molten metal was treated in an air atmosphere was more than three times the theoretical value. The reason why the amount of Mg removed when the molten metal was treated in an Ar atmosphere slightly exceeded the theoretical value is thought to be because oxygen remained above the molten salt.

It was found that by creating an oxygen-containing atmosphere above the molten salt (and even copper oxide), even small amounts of molten salt and CuO can continuously and efficiently remove Mg from the Al-based molten metal.

[Example 5] (Flux Reuse)
(1) Molten metal treatment The same molten metal treatment as in Example 1 was carried out. At this time, the Al-based molten metal: 500 g, the molten salt thickness: 0.15 mm (molten salt: 2.5 g), and the CuO added amount: 2.5 g were used. Thirty minutes after the CuO addition, the flux (dross) on the Al-based molten metal was entirely collected. Using the flux thus obtained (referred to as "initial flux"), the molten metal treatment was repeated seven times in total under the following two conditions (condition A and condition B). This state is shown diagrammatically in FIG. 5A.
Condition A: The removed flux was reused as it was each time.
Condition B: The flux was reused by adding 2 g of chloride each time it was removed.
(2 g of chloride is equivalent to a thickness of 0.12 mm of molten salt)

The Al-based molten metal was renewed every time flux was added. In other words, the initial Mg concentration of the Al-based molten metal was kept constant every time. The Mg concentration of the Al-based molten metal was measured after each treatment. The results are summarized in Figure 5B. The Mg concentration of the Al-based molten metal when the initial flux was generated was 0.76%.

(2) Evaluation As is clear from FIG. 5B, even when the flux was reused about four times, the Mg concentration in the Al-based molten metal was reduced to the same level as when the initial flux was prepared.

As in condition B, the addition of chlorides (replenishment of molten salt) made it easier to reduce the Mg concentration in the Al-based molten metal. In other words, a tendency for the Mg removal rate to increase was observed. The molten salt decreases due to evaporation and penetration into the crucible. It is believed that the addition of chlorides maintained the flux at a thickness suitable for Mg removal.

From the above, it has been confirmed that the present invention can efficiently remove Mg from Al-based molten metal while reducing the amount of flux used and waste generated during molten metal treatment.

Claims (14)

A flux containing metallic copper, copper oxide, and chlorides, which is placed on an aluminum-based molten alloy containing Mg. The flux according to claim 1, which contains magnesium. The flux according to claim 1, wherein the metallic copper and the copper oxide are contained in the molten chloride salt. The flux according to claim 1, wherein the metallic copper and the copper oxide are contained in the chloride solid salt. The flux according to claim 1, wherein the metallic copper is in the form of dendritic particles, needle-like particles, rod-like particles, or plate-like particles. The flux according to claim 1, wherein at least a portion of the copper oxide is formed by oxidizing a portion of the metallic copper. The flux according to claim 1, which contains magnesium oxide. The flux according to claim 7, wherein the magnesium oxide is porous. A method for producing flux obtained by mixing metallic copper and/or copper oxide with chlorides. The method for producing a flux according to claim 9, wherein the chloride contains magnesium. A molten metal treatment method for removing Mg from the aluminum-based molten metal using the flux according to any one of claims 1 to 8. The molten metal treatment method according to claim 11, wherein the flux is applied to a thickness of 0.05 to 5 mm on the aluminum-based molten metal in an atmosphere where it can come into contact with oxygen. The molten metal treatment method according to claim 12, wherein the flux is reused after refilling or replacing the aluminum-based molten metal. The molten metal treatment method according to claim 13, in which the chloride is replenished.

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