JP2003231927A - Method for smelting molten aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for smelting a molten Al alloy, which inhibits slag generation on the surface of the molten Al metal to the utmost, while keeping an excellent property of an alum flux of removing hydrogen and inclusions into the low levels, and improves the yield of the Al molten metal. <P>SOLUTION: This smelting method is characterized by making an average particle diameter of an alum powder to 1 mm or less, and controlling an amount of the generated slag in smelting the above molten metal, not to exceed 3 mass% to the amount of the molten aluminum alloy, in smelting the molten aluminum alloy for wrought materials with the use of an alum powder as a smelting flux, to reduce hydrogen in the molten metal, and removing the slag which has moved up to the surface of the molten metal, from the molten metal. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining pure aluminum or aluminum alloy (hereinafter, simply referred to as aluminum alloy, and aluminum is also referred to as Al) molten metal.

[0002]

2. Description of the Related Art As is well known, in the process of melting and casting an ingot for an Al alloy wrought material such as rolled plate, extruded shape, and forging, normally, in a melting furnace, an Al raw material (Al ingot, Al After melting (alloy product scrap, etc.), adjust the composition and
Refining molten alloy.

Refining of the molten Al alloy (hereinafter, simply referred to as molten Al) is to blow chlorine gas, chloride flux or non-halogen flux into the melt.
This is a process for cleaning the molten metal, such as degassing gas components such as hydrogen in the molten metal and slag inclusions and removing slag from the surface of the Al molten metal.

[0004] The molten Al after the refining is transferred from the melting furnace to the mold through a holding furnace or without passing through a holding furnace. At this time, the molten metal being transferred is supplied to the mold by further removing oxide-based inclusions such as alumina by a transfer gutter immediately before the mold or a filter provided in a filter box, and the Al Cast into ingots for wrought alloys.

In recent years, due to problems such as harmfulness of chlorine gas or chloride-based flux, instead of these, a non-halogen-based refining flux is blown into an Al melt by using an inert gas as a carrier gas to melt the melt. It has been used to accelerate degassing and slag.

As the non-halogen-based refining flux, for example, a mixed system mainly composed of potassium sulfate (K ₂ SO ₄ ) and further added thereto are lithium sulfate for lowering the melting point of sulfate and magnesium sulfate. Has been proposed (see Patent Document 1). Further, as a refining flux for degassing and removing slag of Al molten metal, a flux consisting of potassium sulfate alone has been proposed (see Patent Document 2).

[0007]

[Patent Document 1] Japanese Patent Application Laid-Open No. 07-207358 (pages 1 and 2)

[Patent Document 1] Japanese Patent Laid-Open No. 11-323449 (pages 1 and 2)

However, although these non-halogen-based refining fluxes certainly prevent the above-mentioned adverse effects caused by using chlorine or chloride, they are essential for H _{2 in} the molten metal.
There is a problem that the refining efficiency of degassing such as gas and deinclusions is inferior to that of chlorine or chloride.

In the field of Al alloy wrought materials, the demands on the surface properties (surface smoothness, surface roughness) and the like of the Al alloy wrought materials in the applications of electronic and electric parts are becoming more and more severe. In addition, demands for higher quality Al alloy wrought materials such as higher strength, higher formability, and higher corrosion resistance for packaging containers such as cans, transportation equipment such as automobiles, and structural material applications are becoming increasingly severe. ing. Therefore, along with this, there is an increasing need to further reduce impurities such as H ₂ and inclusions in the Al alloy ingot.

Further, the Al melting raw material is changed from the conventional Al-based ingot mainly to the Al-alloy wrought scrap mainly based on the social demand for establishing the recycling system of the Al-alloy wrought material scrap. It's starting. As a result, 100% scrap of Al-melting raw material is also being used. However, when Al alloy wrought material scrap is used as an Al melting raw material, it is difficult to avoid an increase in the amount of impurity elements or gas components such as H ₂ mixed in from the scrap even if the scrap is pretreated.

However, in the field of refining Al alloys, in response to these requirements and needs, a halogen-free refining flux having a refining efficiency similar to that of chlorine or chloride has not yet been put into practical use. In the actual situation, in order to carry out refining at a high reduction level of the above-mentioned degassing and deinclusions, it was the actual situation that chlorine or chloride flux had to be used in combination.

On the other hand, it has been proposed to use alum as a non-halogen type Al alloy refining flux (see Patent Document 3). This alum flux enables refining capable of achieving a high reduction level of degassing and deinclusions in response to the above requirements and needs.

[0013]

[Patent Document 3] Japanese Patent Laid-Open No. 2000-239757 (pages 1 and 2)

That is, alum flux decomposes at the temperature of refining (melting) an Al alloy and releases sulfurous acid gas and sulfate. The released sulfate or sulfur dioxide gas has a function of dehydrogenating by reacting with hydrogen in the molten metal.

More specifically, in this alum flux, sulfate fumes (fine particles) and SO _X gas react with hydrogen in the molten metal in a solid-gas reaction or a gas-gas reaction to generate a hydrogen compound. Degas the molten metal by vaporizing it or separating it from the molten metal as slag. It also has the effect of cleaning the molten metal, such as promoting the slag formation of inclusions and slag removing the slag from the surface of the Al melt.

[0016]

However, when the alum flux is blown into the molten aluminum, unreacted flux is likely to be produced. The unreacted flux floats on the surface of the Al melt without contributing to the refining action in the Al melt, reacts with the slag already present on the surface of the Al melt, and easily promotes the slag formation of the Al melt. Have an effect.

The formation of the unreacted flux and the slag formation of the molten aluminum are characteristic of all the above-mentioned powder fluxes which are solid refining agents, as compared with the gas refining agents such as chlorine gas, which has good reactivity, without being alum flux. Is also a problem.

However, this alum flux, when unreacted flux is generated and floats on the surface of the molten Al by the action or reactivity of the excellent dehydrogenation and deintercalation,
Unlike the other non-halogen-based fluxes for refining Al alloys up to now, there is a peculiar problem that the above-mentioned slag formation on the surface of the Al melt is promoted. And, as the slag formation on the surface of the molten aluminum is promoted, the amount of slag generated increases,
It is said that the yield of cast aluminum melt is relatively lowered.
It has practical problems.

The present invention has been made by paying attention to such a situation, and an object thereof is to maintain excellent dehydrogenation of alum flux and a high reduction level of de-inclusions while maintaining the surface of the molten aluminum. The present invention aims to provide a refining method of an Al alloy molten metal, which can suppress the formation of the molten Al alloy as much as possible and improve the yield of the Al molten metal.

[0020]

To achieve this object, the gist of the method for refining an Al alloy molten metal according to the present invention is to use an alum powder as a refining flux for an aluminum alloy molten metal for a wrought material. When refining the molten metal to reduce the hydrogen in the molten metal and removing the slag floating on the surface of the molten metal from the molten metal, the average particle size of the alum powder
The amount is 1 mm or less, and the amount of slag generated during the refining of the molten metal is suppressed to 3% by mass or less of the amount of the molten aluminum alloy.

The inventors of the present invention have a correlation between the average particle size of the alum powder and the amount of slag generated during the smelt refining when the alum powder is used as the refining flux for the wrought aluminum alloy melt. I found out that. That is, it has been found that the smaller or finer the average particle size of the alum powder is, the smaller the amount of slag generated during the refining of the molten metal is, and the higher the yield of the Al alloy molten metal is. It was also found that the average particle size of the alum powder that can suppress the amount of slag generated during the refining of the molten metal to 3% by mass or less of the molten amount of the Al alloy is 1 mm or less.

It should be noted that the above-mentioned Patent Document 3 also discloses that the particle size or particle size of the alum powder is appropriately selected according to the mode of blowing or adding to the molten metal. However, the recognition of the particle size or particle size of alum in Patent Document 3 is, as disclosed, within the range in which the blowing work such as clogging of the flux blowing lance due to the hygroscopicity of the alum is obstructed. Stay

In other words, in the present invention, the above-mentioned correlation between the average particle size of the alum powder blown into or added to the molten metal and the amount of slag generated, and the smaller the average particle size of the alum powder, the smaller the amount of slag generated. There is no recognition or suggestion that the alum powder has an average particle size of 1 mm or less that can suppress the amount of slag generated to 3% by mass or less of the amount of molten Al alloy.

Further, in the above-mentioned Patent Document 3, there is no disclosure of the average particle diameter of the alum powder used, but as the above-mentioned problem of the invention, the amount of slag produced increases and relatively cast.
It had a problem that the yield of the molten aluminum decreased, and the average particle size of the alum powder used was inevitably over 1 mm.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The significance of each requirement in the present invention will be described below. First, the alum powder as the flux in the present invention will be described. The definition of alum referred to in the present invention is the same as the definition disclosed in Patent Document 3.

That is, alum has the general formula R ³ R ¹ (SO ₄ ) ₂
nH ₂ O (n = 12, 10, 6, 4, 3, 2, or 0) or R ¹ [R ³ (H ₂ O)
₆ ] (SO ₄ ) ₂・ nH ₂ O (n = 12, 10, 6, 4, 3, 2, or 0) and other trivalent metals (R ³ ) represented by composition formulas and monovalent metals ( It is a generic term for double salts of sulfate of R ¹ ). The trivalent metal (R ³ ) includes Al, Fe, Cr, and the monovalent metal (R ¹ ) includes K, NH ₄ , and Na. Among them, the representative one is Al
K (SO ₄ ) ₂・ nH ₂ O (n = 12, 10, 6, 3, 2, or 0) potassium alum or baked potassium alum and AlNH
₄ (SO ₄ ) ₂ · nH ₂ O (n = 12, 10, 6, 4, 3, 2, or 0) ammonium alum or baked ammonium alum.

Next, the function and effect of the alum powder as the flux in the present invention will be described. Although each alum varies depending on the type, when heated, SO _X gas such as sulfur dioxide (SO) and SO ₂ begins to decompose and release at about 650 ° C below the molten metal temperature of the Al alloy, and about 950
It has the characteristic that thermal decomposition is completed at around ℃ and Al oxide is produced at the same time. Of these, the heating temperature is 400-550
For example, ammonium sulfate releases ammonium sulfate, and potassium alum releases potassium sulfate or the like at a temperature between ° C.

That is, the released sulfate and the decomposition released sulfurous acid gas have a function of reacting with hydrogen in the molten metal to perform dehydrogenation. The molten metal temperature of the Al alloy is about 700 ° C, and alum as a flux added or blown into the molten metal decomposes and releases SO _X gas such as SO ₂ and SO ₂ at this molten metal temperature, and these sulfates Fume and SO
_{The X} gas undergoes a solid-gas reaction or a gas-gas reaction with hydrogen in the molten metal. Then, it is possible to dehydrogenate the molten metal by vaporizing the generated hydrogen compound or separating and removing it from the molten metal as a slag. It also has the effect of cleaning the molten metal, such as promoting the slag formation of inclusions and slag removing the slag from the surface of the Al melt.

As a more specific action, the generated SO _X
The gas rapidly diffuses into the Al melt due to the stirring effect of the inert gas, so that the H ₂ gas in the melt is taken into the gas bubbles by diffusion and partial pressure equilibrium. Then, the fine SO _X gas bubbles float on the surface of the molten metal and volatilize, so that the H ₂ gas is removed from the molten metal. Further, the inclusions in the molten metal are floated from the molten metal to the surface of the molten metal due to the stirring effect or the floating effect of the generated SO _X gas or the inert gas, and the slag is promoted to be removed from the molten metal.

Further, the produced fumes also diffuse rapidly in the molten Al to generate hydrogen and a hydrogen compound by a gas-solid reaction, or they are melted and decomposed to form SO.
_It produces _X gas and exerts the same degassing and deinclusion effects as the produced SO _X gas. Therefore, the combined or synergistic action of these increases the effect of removing gas components such as H ₂ gas in the molten metal and, in particular, oxide-based inclusions.

On the other hand, among the above-mentioned characteristics of alum, the production temperature of aluminum oxide (Al), which is a harmful impurity or inclusion in the molten metal, is around 950 ° C. Therefore, since the generation temperature is sufficiently higher than the molten metal temperature of the Al alloy, Al oxide is rarely generated during the actual refining of the molten metal.

Alum as flux added or blown into the molten metal hardly remains in the molten metal as Al oxide or sulfate. Further, even if the Al oxide is produced, this Al oxide is produced in the molten metal, and the oxidation produced when the Al molten metal comes into contact with the atmosphere.
Very fine particles compared to Al. As a result, the generation
Due to the stirring effect or floating effect of SO _X gas or inert gas, it is easier to float on the surface of the molten metal than in the molten metal, slag formation is promoted, and the generated oxidized Al hardly remains in the molten metal.

Therefore, alum as the flux has an excellent effect that it is possible to dehydrogenate and deintercalate the molten metal without remaining in the molten metal.
However, depending on the refining conditions, ammonium alum may decompose into NH ₄ and produce hydrogen, and because this hydrogen remains in the molten metal, it takes a long time to stir with an inert gas to remove hydrogen. There is also the possibility of.

Therefore, it is most preferable to use potassium alum or baked potassium alum which has no possibility of such side effects. In the present invention, in addition to the specific examples described above, among the compounds classified as alum, a refining action of releasing a sulfate or sulfurous acid gas for dehydrogenation and not producing a residual impurity harmful to the molten metal is obtained. All the compounds possessed are included in the scope of the invention.

Based on the above alum flux, the relationship between the average particle size of the alum powder to be added and the amount of slag generated during the smelt refining, which is a feature of the present invention, will be described below. On the other hand, due to the action of the above excellent dehydrogenation and deinclusions, unreacted flux when blown into the molten aluminum is
When it floats on the surface of the Al melt, it reacts with the slag already present on the surface of the Al melt and has the effect of facilitating the slag formation of the Al melt. If the slag formation on the surface of the Al melt is promoted, the amount of slag (dross) produced increases, and the yield of the Al melt decreases.

In order to suppress the slag formation on the surface of the Al melt while maintaining the excellent dehydrogenation and the action of deintercalation against the slag formation promoting effect of the alum flux on the Al melt, in the present invention, Reduce the average particle size of the alum powder blown into the molten aluminum. The smaller the average particle size of the added alum powder, the larger the surface area of the alum powder and the faster the reaction rate. When the reaction speed increases, alum flux blown into molten Al is before flying on molten Al surface, a majority thereof, it is degraded released sulphate and SO _X gas. As a result, unreacted alum flux floating on the surface of the Al melt is reduced, so that the reaction with the slag existing on the surface of the Al melt is suppressed, and the slag formation on the surface of the Al melt is suppressed.

Further, since the finely-divided alum reduces unreacted alum floating on the surface of the molten Al, it does not inhibit the action of the above excellent dehydrogenation and deintercalation, but rather promotes or maintains it. While suppressing the slag formation on the surface of the molten aluminum.

FIG. 1 shows the average particle size of potassium alum powder.
The relationship between (mm) and the amount of slag (mass%) is shown. Fig. 1 shows the results of Example Table 1 described below (Invention Examples 1 to 3 and Comparative Examples 11 and 1).
2) is rearranged.

From this FIG. 1, the amount of slag generated is determined by the amount of molten Al alloy.
It can be seen that the average particle size of the alum powder that can be suppressed to 3% by mass or less is a small particle size of 1 mm or less. It is also found that when the average particle size of the alum powder increases beyond 1 mm, the amount of slag generated exceeds 3% by mass of the amount of molten Al alloy. Therefore, in the present invention, the average particle diameter of the alum powder as the refining flux is set to a small particle diameter of 1 mm or less.

The average particle size of alum powder which is actually widely used varies from a unit of several microns (μm) level to several tens of mm depending on the use. However, due to the industrial manufacturing process of alum powder, the average particle size of alum powder manufactured by a conventional method is usually larger than 1 mm. Therefore, the alum powder used as the smelting flux in the present invention should have an average particle size of 1 mm or less obtained by crushing, sieving, etc. of these industrially obtained large alum powders having an average particle size of more than 1 mm. There is a need to. Alternatively, it is necessary to directly obtain the alum powder by adding conditions and steps for selectively producing the alum powder having an average particle diameter of 1 mm or less.

However, even from the above-mentioned FIG. 1, in order to suppress the amount of slag, the average particle size of the alum powder should be several microns.
It is not necessary to make the unit of (μm) fine. Also, if too fine, due to the hygroscopicity of alum,
Mixing of hygroscopic water into the molten metal and obstruction of the flux blowing operation can be a serious problem. Therefore, the preferable lower limit of the average particle diameter of alum is about 0.1 mm. Due to the hygroscopicity of the alum, it is also preferable to use means such as heating and drying the alum immediately before use in order to use the alum as a flux in a dry state.

Next, the flux composition of the present invention will be described. In the present invention, the flux composition as the non-halogen refining flux is alum powder alone (1
Not only the composition of (00%) but also the combination or mixing with other flux is allowed. Therefore, the meaning of the present invention that the alum powder is used as the refining flux also permits the use in combination or mixing with other flux.

As described above, the alum flux of the present invention has the action and effect of dehydrogenating and deintercalating the molten metal and removing slag. Moreover, alum itself is cheaper than the conventional flux. Therefore,
From these characteristics, alum alone may be used, but various fluxes in refining have a role other than dehydrogenation and de-inclusions and slag of the molten metal, and in order to satisfy these other characteristics, or In order to improve the effects of dehydrogenation, deinclusions, slag, etc., they may be used in combination or mixed with other flux.

As other fluxes, potassium sulfate (K ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ), and sodium sulfate (Na ₂ SO ₄ ), which are used as a burner for dehydrogenation and inclusions of the molten metal, or for heat generation
Sulfates such as calcium sulphate (CaSO ₄ ) or ammonium sulphate, carbonates such as potassium carbonate (K ₂ CO ₃ ), or nitrates, as well as potassium silicofluoride (K ₂ SiF ₆ ), potassium aluminum fluoride (KAlF _4). , K ₃ AlF ₆ ). Furthermore,
Chlorides such as KCl and fluorides such as AlF ₃ are used for dehydrogenation and deintercalation of molten metal.

Further, Al atomized powder as an exothermic combustor, metal oxides such as iron oxide, nitrates such as potassium nitrate, lithium (Li) or magnesium (Mg) such as lithium borate for lowering the melting point of sulfates. ) Compounds. And, as the flux composition, these can be preferably used as a flux of 40 to 60 mass% in the case of the above-mentioned flux, 10 to 30 mass% in the case of the above-mentioned flux, and a mixed system flux added to alum. However, the use of chlorides such as KCl should be suppressed as much as possible in order to prevent the formation of chlorine.

Al of the flux containing alum of the present invention
The amount to be blown into or added to the molten metal is determined from the degassing amount and deintercalation amount of the Al molten metal and the required refining amount such as the amount of slag. In this regard, in the product field of the Al alloy, in order to meet the characteristic requirements of the fields of electronic and electrical parts, the field of transportation equipment such as automobiles, and the field of structural materials, H ₂ in the Al alloy ingot is
0.2ml / 100gAl or less, magnesia (MgO), alumina (Al
It is preferable that the total amount of oxides such as ₂ O ₃ ) and spinel (a complex oxide of Al and Mg) is 0.02 mass% (200 mass ppm) or less. The total amount of oxides referred to in the present invention is the total amount of the three main oxides that are large in amount and can be measured.

To carry out this level of refining, the amount of the flux containing alum to be blown into or added to the molten aluminum is preferably 1 to 0.01 mass% with respect to the molten aluminum. The amount of flux blown or added
If it is less than 0.01% by mass, degassing and deinclusions may not be possible at the above level. On the other hand, even if the amount of blown-in or added amount of flux exceeds 1% by mass, the refining effect is not improved, refining cost is increased, and the molten metal may be contaminated.

The addition of the flux containing alum to the molten metal is performed by blowing it into the molten metal or adding it to the surface of the molten metal.
(Spraying) etc. The blowing method in this is the same as the blowing method of the normal refining flux. That is, it is preferable for the efficiency of refining to blow a flux powder containing alum into the Al melt from a nozzle or a lance having one end charged in the Al melt and using an inert gas such as N ₂ or Ar gas as a carrier. The inert gas such as N ₂ or Ar gas serves as a carrier for the flux and also plays an important role in stirring (bubbling) the molten metal to promote the refining action of the flux including alum and the floating of the slag into the molten metal. Fulfill

Of course, in order to increase the effect of bubbling the molten metal, an inert gas is blown during or after the flux is blown by a lance different from the carrier gas or the same lance to stir the molten metal. May be. Of course, in addition to this blowing, a mode in which it is added to the surface of the molten metal is possible, and the point is that a preferable method for enhancing the refining effect can be appropriately selected.

The refining of the molten metal having alum as the flux in the present invention is preferably performed at least in a melting furnace. The reason for this is that from the past, refining of molten metal such as flux blowing has mainly been carried out in a melting furnace, and the melting furnace is a refining and equipment specification that is easy to carry out slag treatment after refining as a part of refining and This is because it has a structure. Further, there is also an effect that inclusions and the like can be roughly removed. Therefore, when the present invention is applied to a melting furnace, there is an advantage that existing equipment can be used as it is.

Of course, it is also possible to perform refining using alum as flux in the holding furnace after the melting furnace or in each transfer trough together with refining in the melting furnace or omitting refining in the melting furnace. However, in many cases, the refining equipment and the slag treatment equipment are not originally installed in the holding furnace and each transfer gutter. Therefore, it is advantageous to carry out refining in a melting furnace in that it is not necessary to newly install these facilities and existing facilities can be used as they are.

Further, in the present invention, H ₂ in the Al alloy ingot is set to 0.
2 ml / 100 g Al (H ₂ amount in 100 g of Al, unit ml) or less, and to ensure that the total amount of oxides (oxide-based inclusions) such as alumina is 0.02 mass% or less, molten metal It is preferable to carry out the degassing refining. Al molten metal after refining with flux in these melting furnaces, etc. is transferred from the melting furnace to a transfer gutter, and when the molten metal is supplied to the mold through the transfer gutter, an inert gas is blown into the melt flowing down the transfer gutter,
It is preferable to perform degassing refining of the molten metal. At this time, for the SNIF (sniff) method in which the drainage gutter is provided in the transfer gutter, or to use the transfer gutter as it is for the molten metal flowing down the transfer gutter (in the molten metal flow during transfer) And blow an inert gas into the bottom of the transfer gutter.

Further, in the present invention, in order to reliably ensure that the total amount of oxide inclusions in the Al alloy ingot is 200 mass ppm or less, the molten metal during the transfer from refining to casting is changed. It is preferable to filter with an external filtration filter or an internal filtration filter made of a ceramic porous body having an appropriate shape such as a plate, noodle, honeycomb, or tube. When the molten metal is supplied to the mold through the transfer trough, the molten metal is filtered by each of the filters to remove inclusions in the molten metal.

The Al alloy to be refined in the present invention is not particularly limited as long as it is an Al alloy for wrought material such as rolled plate, extruded material and forged material. For example, AA to JIS 1000
2000 series, 3000 series, 4000 series, 5000 series, 60 from pure Al of the series
It can be widely applied to Al alloys such as 00 series and 7000 series. The method of the present invention can also be used in combination with other refining methods for the purpose of removing metal impurity elements such as Pb, Ti, Sn, and Fe.

Further, the Al raw material to be refined in the present invention is mainly composed of scraps of Al alloy wrought product products containing a large amount of impurities, which exerts the refining effect of the present invention more (100% of scraps (Including use) is preferred. Of course, depending on the required quality of the cast Al alloy material, it is possible to use Al ingot as a melting raw material, and it is also possible to use together with the scrap, but scrap cheaper than Al ingot is used as a melting raw material. By doing so, the cost can be reduced, and the social significance of recycling scrap is great.

As described above, the alum flux according to the present invention has the effect of promoting the slag formation of inclusions, while
It has the effect of easily reacting with the slag already present on the surface of the molten metal and promoting the slag formation of the Al molten metal. But this
Depending on the refining conditions, due to the slag formation promoting action of the molten aluminum,
Al molten metal (Al metal content) in the slag formed on the surface of the Al molten metal
There is a possibility that a large amount of particles will be taken in or involved.

When this phenomenon occurs remarkably, the viscosity of the slag floating on the surface of the molten metal increases significantly due to the inclusion of the Al metal component, and the slag removing property for separating and removing the slag from the molten metal surface also includes workability. It will be significantly reduced. As a result, the amount of slag generated increases, and the amount of Al metal discharged together with the slag also increases due to the slag removal work, and the yield of Al molten metal also decreases.

For this problem, while maintaining excellent dehydrogenation of alum flux and a high reduction (refining) level of deinclusions, Al molten metal content (Al metal content) taken into the slag is suppressed as much as possible. Therefore, it is necessary to improve the slag removal property and the yield of the molten Al. To do so, the molten aluminum alloy for wrought material is subjected to refining with alum powder containing refining flux to reduce hydrogen in the molten metal, and at the same time, the slag floating on the surface of the molten metal is removed from the molten metal. At the time of smelting, the molten metal temperature during smelting was 730-
A relatively high temperature of 780 ° C is preferable.

The initial molten metal temperature (melting temperature) at the time of melting the aluminum alloy melting raw material is, as described in Patent Document 3, usually at a relatively high temperature level of 750 ° C. ± 10 ° C. However, the temperature of the molten metal during the molten metal refining after melting is slightly lowered by the melting time in the normal atmosphere atmosphere, depending on the time elapsed until the refining work and the blowing amount of the refining agent, carrier gas, etc. It may be as low as ~ 720 ° C.

In the above-mentioned conventional molten metal refining, although the molten metal temperature may be relatively low, a phenomenon in which the Al molten metal (Al metal content) is taken into the slag generated on the surface of the Al molten metal by refining may occur. , The absolute amount is small. Therefore, the viscosity of the slag floating on the surface of the molten metal is significantly increased, and the slag removing property for separating and removing the slag from the surface of the molten metal does not deteriorate including workability. However, when the molten metal refining is carried out using alum flux, this decrease in the molten metal temperature or at this relatively low molten metal temperature, the alum flux promotes the slag formation of the molten aluminum, and
It promotes the uptake of Al melt (Al metal content) into the slag formed on the surface of the melt.

On the other hand, when the molten metal is smelted by using the alum flux, if the molten metal temperature is set to a relatively high temperature of 730 to 780 ° C., even if the alum flux promotes slag formation of the molten aluminum. , The amount of Al molten metal (Al metal content) taken into the slag formed on the surface of the Al molten metal is significantly suppressed. Therefore, the viscosity of the slag floating on the surface of the molten metal is reduced, and the slag removing property can be improved. Further, if the temperature of the molten metal is set to a relatively high temperature of 730 to 780 ° C., the decomposition and reaction temperatures of alum are increased, and the refining effect described above can be exhibited more efficiently.

If the temperature of the refined molten metal is less than 730 ° C.,
Al molten metal (Al metal content) in slag formed on the surface of Al molten metal
Is likely to accelerate the uptake of. On the other hand, it is not necessary to raise the temperature of the molten metal above 780 ° C. When the temperature of the molten metal is higher than 780 ° C, the molten metal tends to absorb hydrogen gas in the atmosphere in the air, and the refining effect may be adversely affected. In addition, the generation of spinel (MgO.Al ₂ O ₃ ) as an inclusion also increases.

Further, in addition to the control of the molten metal temperature, in order to separate the Al metal component taken into the slag generated once on the Al molten metal surface and return it to the Al molten metal, it is generated on the Al molten metal surface. The slag may be stirred. This agitation destroys the shell covering the slag, so the Al metal content taken into the slag touches the high temperature atmosphere and the molten aluminum,
It has the effect of being redissolved and easily separated from the slag. It is also possible to add the above-mentioned flux having an exothermic action so that the Al metal component taken into the slag by heat generation is redissolved and easily separated from the slag.

Next, examples of the method of the present invention will be described.

[0065]

[Example 1] Various types from 2000 to 7000 shown in Table 1
Al alloy was melted, refined and cast. The melting conditions are each Al
1000kg internal volume using alloy wrought material scrap as melting raw material
In a / ch high-frequency induction melting furnace, it was melted in the air at a temperature of 750 ± 10 ° C and adjusted to the JIS or AA standard component composition of each Al alloy.

At this time, the amount of impurities in the Al melt (before refining of the melting furnace) was determined to be 0.4 in each of the melts as a result of the analysis of the melt by the partial pressure equilibrium method and the analysis of the solidified Al after cooling the melt.
~ 0.45ml / 100gAl, magnesia (MgO), alumina (Al ₂ O
₃ ), the total amount of oxides of spinel (a complex oxide of Al and Mg) is
The level was 0.04 to 0.03% by mass. However, hydrogen is measured by the Landsley method, and the amount of each oxide is JI
It was measured by the Br-methanol method specified in S.

After that, the molten aluminum in the melting furnace was refined with each flux composition under the conditions shown in Table 1. Here, all of the alum fluxes of the invention examples shown in Table 1 were commercially available baked potassium alum. For comparison of refining performance, as Comparative Example 15, an Al molten metal was refined using chlorine gas.

The refining with the flux is common to all the examples, using an injection lance made of an iron pipe immersed in an Al melt, and the amount of N ₂ gas as a carrier gas blown is 50 l (standard state) / min. Flux is 0 for each molten aluminum.
1% by mass was blown into the Al melt, and then bubbling with this N ₂ gas was performed for 30 minutes to degas the hydrogen and refine the deinclusions. Chlorine gas was blown into the molten aluminum by the lance at 50 l (standard state) / min × 15 minutes, and then bubbling with N ₂ gas was performed for 30 minutes.

During this refining treatment, the slag on the surface of the Al melt was continuously removed in each of the examples in Table 1, and the total weight of the discharged slag was calculated as follows.
Amount of slag (dross) generated divided by the weight of Al melt at the initial stage of melting
It was measured as (mass%).

In order to evaluate only the refining effect of each flux, the refining of the Al melt after refining without refining in the transfer trough and the filtration of the melt by the filter was performed.
An Al melt was cast to produce an Al alloy ingot.

Then, the amount of H ₂ in the produced Al alloy ingot was measured by the above measuring method. In addition, as oxide-based inclusions in the Al alloy ingot, magnesia (MgO), alumina (Al ₂ O
₃ ) and the amount of spinel (a complex oxide of Al and Mg) were measured by the above-mentioned measuring method, and the respective amounts were summed to obtain the oxide amount (total amount).

Of these, the amount of H ₂ in the Al alloy ingot was 0.2 ml / 100
Those with gAl or more were evaluated as ×, less than 0.2 ml to 0.15 ml / 100 gAl as Δ, and less than 0.15 ml / 100 gAl as ○. Also, the total amount of the above oxides is 0.0 if it is 0.02 mass% or more, and if it is less than 0.02 mass% and more than 0.01 mass%, △, 0.
Those having a content of 01 mass% or less were evaluated as ◯. These results are also shown in Table 1.

Further, in the Al alloy ingot further subjected to flux refining, assuming that the decomposition product of the added flux is a sulfate salt, the sulfate salt in the ingot is analyzed and quantified as S content, and this S content in the molten metal is analyzed. The amount of residue was evaluated. The evaluation is x if the amount of decomposition products is 0.002 mass% or more, less than 0.002 mass% ~
A sample with more than 0.0005 mass% was evaluated as △, and a sample with less than 0.0005 mass% was evaluated as ○.

As is clear from Table 1, all of Invention Examples 1 to 10 using alum were 0.15 ml of hydrogen in the Al alloy ingot except for Invention Example 7 in which the amount of alum was as small as 20%.
/ 100gAl or less and total amount of oxides such as alumina is 0.01 mass
It is reduced to a low level, below%. Moreover, these effects, despite refining the transfer gutter and removing the inclusions of the molten metal by the filtration filter, regardless of the type of Al alloy, the amount of flux used is 0.1% of the weight of the molten aluminum. It has been achieved even with a relatively small amount such as mass% and also with a high amount of hydrogen and a high total amount of oxides in the molten Al.

These effects are at the same level as in Comparative Example 15 refined with chlorine (Cl ₂ ) gas.
In addition, the residue (flux residue, S content) in the molten metal is also 0.
0005% by mass or less, and it is acceptable or little. Therefore, including this point, the flux according to the present invention is proved to have a high refining effect comparable to the refining method using chlorine gas.

However, the invention example 1 based on the above-mentioned FIG.
, 2 and 3 and Comparative Examples 11 and 12, as in Comparative Examples 11 and 12, when the average particle diameter of the alum powder increased beyond 1 mm, the amount of slag generated was 3% of the molten amount of Al alloy.
It can be seen that the mass increases beyond the mass%. On the other hand, invention examples
From 1, 2, and 3, it can be seen that the average particle size of the alum powder capable of suppressing the amount of slag generated to 3% by mass or less of the molten amount of the Al alloy is 1 mm or less.

Further, as an example not using alum powder, Comparative Example 13 using 100% K ₂ SO _{4 is} more advantageous than the invention examples in terms of dehydrogenation of molten metal, refining effect of deinclusions, and molten metal residue. Inferior Further, Comparative Example 14 using a flux containing a halogen-based KCl chloride and AlF ₃ fluoride as the main component and K ₂ SO ₄ was mixed, the dehydrogenation of the melt and the refining effect of the inclusions and the point of the melt residue Inferior to the invention example. In each of the comparative examples, the amount of slag generated was 3% by mass or less of the amount of the molten Al alloy, and it was found that the problem of slag generation was a problem peculiar to the flux using alum.

[0078]

[Table 1]

[0079]

Example 2 Next, the influence of the molten metal refining temperature on the slag removal property was investigated. Specifically, 6063 Al alloy molten metal produced by melting only 6063 Al alloy wrought material scrap as a melting raw material was used as a commercially available baked potassium alum 40% by mass and K ₂ SO ₄
Add 30% KAlF ₄ to 60% by mass alum flux.
Mass% While refining the molten metal using the added flux, the temperature of the molten metal refining at this time was changed variously as shown in Table 2, and after the refining, the slag on the surface of the molten metal was discharged to the outside of the furnace and the slag removal equipment was used. The molten metal was scraped off by hand using a scraper. The average particle size of the alum used was 0 in each example.
It was set to 7 mm. The average particle size of K ₂ SO ₄ is 0.7 mm or less.

This slag was continuously removed in the same manner as in Example 1 during the refining process, and the total weight of the discharged slag was divided by the weight of the molten aluminum at the initial stage of melting. do it,
It was measured as the amount of produced dross (mass%).

At the time of this slag removal, the slag discharged to the outside of the furnace was visually observed and the workability was evaluated to determine the viscosity of the slag in each example.
(Hardness), the amount of Al metal in the slag, the ease of slag discharge, etc. were evaluated, and the slag discharge performance was evaluated. On this occasion,
As a reference, chlorine gas was used as Comparative Example 22 in Table 2.
The relative evaluation was made in comparison with the slag that had been removed after the Al molten metal was smelted. The results are shown in Table 2.

Regarding the melting conditions, the same high-frequency induction melting furnace as in Example 1 was used and the melting was carried out in the atmosphere at a temperature of 750 ± 10 ° C. In each example, the molten metal was heated or allowed to cool to adjust the molten metal refining temperature. The refining conditions using the flux were the same as in Example 1 in common with each example.

Further, in the same manner as in Example 1, the refining effect was analyzed and evaluated by the amount of H ₂ in the produced Al alloy ingot, the amount of oxide (total amount), and the amount of sulfate (S content) in the ingot. did. These results are also shown in Table 2. The amount of each impurity in the Al melt before refining the melting furnace was at the same level as in Example 1.

As is clear from Table 2, Invention Examples 16 to 19 in which the molten metal refining temperature by alum flux was set to a relatively high temperature of 740 to 780 ° C., were the slags after the Al molten metal refining using the chlorine gas of Comparative Example 22. Like the slag, the viscosity of the slag is low, it is in the form of a free-flowing powder, and the amount of Al metal in the slag is small,
Al molten metal (Al metal content) in slag formed on the surface of Al molten metal
The uptake amount of was significantly suppressed. Further, the discharge work of the slag was easy, and like the comparative example 22, the slag discharge property was excellent. As a result of these, the amount of slag generated is 3 times the amount of molten Al alloy.
Less than mass%

In the same manner as in the case of Al molten metal refining using chlorine gas in Comparative Example 22, 0.15 ml / 100 g of hydrogen in the Al alloy ingot was prepared.
Al or less, the total amount of oxides such as alumina is 0.01% by mass or less,
It was reduced to a low level, and the dehydrogenation of the molten metal and the high refining effect of deinclusions were also achieved. Further, the residue (flux residue, S content) in the molten metal is 0.0005 mass% or less, which is an acceptably small amount.

On the other hand, in Comparative Examples 20 and 21 in which the smelt refining temperature is lower than 730 ° C., although the dehydrogenation of the melt and the high refining effect of the inclusions are achieved, the viscosity (hardness) of the slag Is high and has a large amount of Al metal content in the slag,
l Al melt in the slag formed on the surface of the melt (Al metal content)
The amount of uptake was high. Further, it was difficult to discharge the slag, and the amount of slag generated exceeded 3% by mass of the molten aluminum alloy.

Moreover, in the case of Al molten metal refining using chlorine gas in Comparative Example 22, as in Comparative Examples 20 and 21, even if the molten metal refining temperature is lower than 730 ° C., the slag discharge performance and the amount of slag generated are excellent. There is no influence of the molten metal refining temperature on the slag removal property. Therefore, it is understood that the influence of the molten metal refining temperature on the slag removal property is a problem peculiar to the flux using alum.

[0088]

[Table 2]

[0089]

As described above, according to the refining method of the present invention, while suppressing the excellent dehydrogenation of alum flux and the high reduction level of deinclusions, the slag formation on the surface of the molten aluminum is suppressed as much as possible. It is possible to provide a refining method for molten Al alloy, which can improve the yield of molten Al. In addition, when the molten metal is refined using alum flux, the molten metal temperature is set to a relatively high temperature of 730 to 780 ℃, so that the molten aluminum (Al metal content) is taken into the slag formed on the surface of the molten aluminum. The amount can be remarkably suppressed, the viscosity of the slag floating on the surface of the molten metal can be reduced, and the slag removing property can be improved. Therefore,
It is possible to spread the practical application of Al alloy molten metal refining by alum flux or to increase the practical value. In this way, when the practical application of Al alloy molten metal refining with alum flux spreads, the Al produced based on this ingot is produced.
The quality of Al alloy products such as alloy wrought materials can be significantly improved, and the applications of Al alloy wrought agents can be greatly expanded. In addition, as a melting raw material for Al alloy wrought material,
It is possible to mainly use wrought aluminum alloy scraps, which has great social significance such as establishing a scrap recycling system.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the average particle size of alum powder according to the present invention and the amount of slag generated.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C22B 9/10 101 C22B 9/10 101 102 102 (72) Inventor Nakajima 14 14 1 K-Fast Steel Works, Ltd. Chofu Factory F-term (reference) 4E014 NA03 4K001 AA02 BA22 EA03 EA04 EA06 GA17 KA13

Claims (8)

[Claims] 1. A molten aluminum alloy for wrought material,
Using alum powder as a refining flux, performing molten metal refining to reduce hydrogen in the molten metal, and in removing the slag floating on the surface of the molten metal from the molten metal together, the average particle diameter of the alum powder is set to 1 mm or less, and A method for refining an aluminum alloy melt, characterized in that the amount of slag generated during the molten metal refining is suppressed to 3% by mass or less of the amount of the aluminum alloy melt. 2. The molten metal temperature during the molten metal refining is 730 to 78.
The method for refining a molten aluminum alloy according to claim 1, wherein the temperature is 0 ° C. 3. The method for refining a molten aluminum alloy according to claim 1, wherein the slag floating on the surface of the molten metal is stirred and then the slag is removed. 4. The refining flux as defined in claim 1, further comprising 40 to 60% by mass of a sulfate mixed therein.
The method for refining a molten aluminum alloy according to the item. 5. The method for refining a molten aluminum alloy according to any one of claims 1 to 4, wherein 10 to 30% by mass of at least one selected from Al atomized powder and nitrate is further mixed as the refining flux. 6. The method for refining an aluminum alloy melt according to claim 1, wherein the amount of the refining flux used is 0.01 to 1 mass% with respect to the aluminum alloy melt. 7. The H ₂ in the aluminum alloy ingot is 0.2 ml / 1
The method for refining a molten aluminum alloy according to any one of claims 1 to 6, wherein the amount is 00 gAl or less. 8. The method for refining an aluminum alloy melt according to claim 1, wherein a part or all of the aluminum raw material is scrap of an aluminum alloy wrought material.