JP7414592B2 - Al alloy regeneration method - Google Patents

Description

The present invention relates to a method of regenerating (recycling) Al alloy scrap.

BACKGROUND ART With the recent rise in environmental awareness, efforts are being made to reduce the weight of various members and devices, and the amount of aluminum alloy (simply referred to as "Al alloy") used is increasing. Although a large amount of energy is required to produce new Al (refining), only a small amount of energy is required to remelt Al alloy scrap (also simply referred to as "scrap"). For this reason, recycling or reuse (simply referred to as "recycling") of scrap is desired.

When scrap is remelted, Fe is usually mixed in the molten metal. In order to obtain recycled Al alloy from scrap, it is necessary to remove unnecessary elements (impurity elements). Related descriptions of methods for removing such elements can be found in the following documents.

U.S. Patent No. 2,464,610 US Patent No. 5,741,348 JP 2002-155322 U.S. Patent No. 4,734,127 WO2013/168213 WO2013/168214

Furukawa Electric Times No. 104 (July 1999) 25-30 Metallurgical Transactions 5(1974)785-787 Material Transactions, JIM.38(1997)622-699

(1) Intermetallic Compound Removal Method Patent Documents 1 and 2 and Non-Patent Documents relate to a method of removing Fe from a molten metal as an intermetallic compound. Specifically, in Patent Document 1, Cr, Mn, and Co are added to an Al-(11.6-13.5)%Si-(0.8-9)%Fe alloy to crystallize Fe-based intermetallic compounds. , the amount of Fe in the molten metal is reduced.

Patent Document 2 describes an Al-(0-12)%Si-(0.49-2.1)%Fe-(0.37-1.91)%Mn alloy (Cr<0.4%, Ti<0.41%, Zr<0.26%, Mo<0.01 %) by adding Mn to reduce the amount of Fe. However, the Fe removal efficiency relative to the amount of Mn used is low.

(2) Segregation solidification method, crystal fractionation method Patent Documents 3 to 6 and Non-Patent Documents 1 and 2 disclose impurities by separating Al crystallized substances from the residual liquid phase from a semi-solid molten metal in which an Al phase has crystallized. This invention relates to a segregation solidification method or a crystal fractionation method that reduces the Incidentally, in Non-Patent Document 1, the residual liquid phase is removed by squeezing the semi-solidified molten metal. Furthermore, in Non-Patent Document 2, a semi-solid molten metal is stirred to spheroidize Al crystallized material and separated from the residual liquid phase. Such a method requires cooling the molten metal until the Al phase crystallizes, resulting in large energy loss.

(3) Semi-melt refining method Non-patent document 3 discloses a semi-molten refining method in which an Al alloy (solid) is heated to a semi-molten state, separated into a liquid phase and residual Al crystals, and impurities exceeding the solid solubility limit of the Al phase are removed. Concerning melt purification method. Specifically, in Non-Patent Document 3, a semi-molten Al-8.39%Si-0.06%Mn-0.05%Mg alloy is pressurized to separate the liquid phase, and the remaining portion is separated from the Al-0.96%Si-1.14% A Mn-1.56%Mg alloy was obtained. With this method, it is difficult to remove Fe as an intermetallic compound. Furthermore, since the amount of residual Al crystals in a semi-molten state depends on temperature, the alloy compositions to which this method can be applied are limited.

(4) Zone melting method In addition to the above-mentioned method, as a method to remove impurities from an Al alloy, an ingot is partially heated and melted from one end, the impurities are collected at the end, and the end where heating is started is used. There is also a zone melting method that increases the purity of the side.

The present invention has been made in view of the above circumstances, and provides a new method for recycling Al alloy, etc., which can increase the ratio of the amount of Fe removed to the amount of Mn used (removal efficiency) and recycle Al alloy scrap. The purpose is to

As a result of intensive research to solve this problem, the inventors of the present invention succeeded in increasing the removal efficiency more than before by mixing multiple molten metals with different Mn concentrations and hot water temperatures. By developing this result, we have completed the present invention described below.

《Recycling method of Al alloy》
(1) The present invention includes a mixing step of obtaining a third molten metal by mixing a first molten metal and a second molten metal prepared by melting a raw material at least one of which contains Al alloy scrap, and a mixing step of obtaining a third molten metal, and a step of crystallizing from the third molten metal. an extraction step of extracting a fourth molten metal from which at least a part of the Fe compound has been removed, the first molten metal has a higher Mn concentration than the second molten metal and a hot water temperature. This is a method for regenerating an Al alloy in which the temperature of the second molten metal is within the crystallization temperature range of the Fe compound.

(2) According to the Al alloy regeneration method (simply referred to as "regeneration method" or "recycling method") of the present invention, while reducing the overall Mn usage amount or Mn concentration, from molten metal using scrap, It becomes possible to remove Fe or reduce the Fe concentration. In other words, the removal efficiency (Fe/Mn), which is the ratio of the amount of Fe removed to the amount of Mn, can be increased, and efficient recycling of Al alloy scrap (regeneration of Al alloy) is possible.

The reason why the removal efficiency was improved by the present invention is surmised as follows. The second molten metal has a lower Mn concentration than the first molten metal, and its temperature is within the crystallization temperature range of the Fe compound. In such a second molten metal, an Fe compound (with or without Mn) with a high Fe concentration is crystallized.

When the first molten metal with a high Mn concentration is added to such a second molten metal, the Fe compound in the second molten metal becomes a nucleus, and the growth of the Fe compound containing Mn is promoted. As a result, instead of an Fe compound having a general stoichiometric ratio (ratio of Mn and Fe), a Fe compound in which Fe is concentrated or unevenly distributed with respect to Mn may be newly generated. As a result, it is thought that scrap can now be recycled with high removal efficiency (yield).

"others"
(1) The recycled Al alloy from which Fe has been removed (reduced Fe concentration) may be used in a solid state or in a liquid state (for example, as the fourth molten metal). For example, the recycled Al alloy in the liquid phase can be used as a recycled metal as it is without remelting or the like.

(2) The composition of the Fe compound may change as the regeneration process progresses. The specific composition and form of the Fe compound does not matter as long as it can be separated and removed from the third molten metal (as long as the fourth molten metal can be extracted). For example, the Fe compound may be an intermetallic compound containing Fe, an alloy containing Fe, or a mixture thereof. Examples of intermetallic compounds that can form part of the Fe compound include Al ₁₃ Fe ₄ and Al ₁₅ Si ₂ (Fe, Mn) ₄ .

(3) Unless otherwise specified, the concentrations, compositions, etc. referred to in this specification are mass proportions (mass %) to the entire target object (molten metal, alloy, compound, etc.), and when appropriate, mass % is simply expressed as "%". It is written as

(4) Unless otherwise specified, "x to y" as used herein includes a lower limit x and an upper limit y. A new range such as "a to b" can be established by setting any numerical value included in the various numerical values or numerical ranges described herein as a new lower limit or upper limit.

It is a graph showing the relationship between the crystallization temperature of an Fe compound and the Mn concentration or Fe concentration. FIG. 2 is an explanatory diagram showing the regeneration method for each sample and the Fe/Mn concentration of the regenerated molten metal. It is an analysis result by EPMA of the residue (Fe compound) based on sample 1. It is an analysis result by EPMA of the residue (Fe compound) based on sample C1.

One or more components arbitrarily selected from the present specification may be added to the components of the present invention described above. The content described in this specification can be a component related to a product (for example, recycled Al alloy (molten metal)) even if it is a method component.

《Mixing process》
In the mixing step, at least the first molten metal and the second molten metal, which have different Mn concentrations and different hot water temperatures, are mixed. For convenience, we will mainly explain the case where the first molten metal and the second molten metal are mixed. However, the mixing process involves mixing three or more types of molten metals (first molten metal, second molten metal, and other molten metals) with different Mn concentrations and/or temperatures. ) may be mixed.

(1) First molten metal and second molten metal It is sufficient that at least one of the first molten metal and the second molten metal is prepared from scrap raw materials (preparation step). The scrap raw materials include one or more types of raw materials including Al alloy scrap (simply referred to as "scrap"), recycled Al alloy ingots (Al alloy ingots produced using Al alloy scrap as raw materials), and the like. It is more preferable that each molten metal is prepared based on scrap raw materials because scrap recycling is promoted. When preparing each molten metal, it does not matter whether the scrap raw materials are the same or the preparation times are different or the same.

The scrap raw material may include dissimilar metal materials (Fe base material, Mg base material, etc.) in addition to Al alloys made of castings, wrought materials, etc. Further, in addition to the scrap itself, the scrap raw material may also include adjusting raw materials (additives made of alloys, compounds, pure metals, etc.) for making each molten metal have a desired composition.

Preparation of the first molten metal is preferably carried out at a temperature at which raw materials such as Al alloy scrap and additives are sufficiently melted (for example, about 650 to 930°C, or more preferably about 680 to 880°C). However, the temperature of the water may be such that iron scraps and the like remain undissolved. The second molten metal is prepared by, for example, bringing the temperature to a temperature at which raw materials such as Al alloy scrap are sufficiently melted (above the upper limit temperature for crystallization of Fe compounds), and then adjusting (lowering) the temperature to the crystallization temperature range of Fe compounds. may be done. In any case, it is preferable that the second molten metal is in a state in which the core Fe compound is crystallized before mixing with the first molten metal.

The second molten metal preferably has a Mn concentration of less than 1% by mass, 0.7% by mass or less, and further 0.4% by mass or less based on the entire second molten metal. Although the lower limit of the Mn concentration is not limited, it may be, for example, 0.05% by mass or more, or even 0.1% by mass or more.

In order to grow an Al-Fe-Mn-Si based compound around the core of the first molten metal, for example, the Mn concentration is 1% by mass or more, 1.4% by mass or more, and even 1. It is preferable that the content is 7% by mass or more. The Mn concentration does not have an upper limit, but may be, for example, 5% by mass or less, 4% by mass or less, or even 3% by mass or less. In order to increase removal efficiency, the difference in Mn concentration between the first molten metal and the second molten metal may be set to, for example, 1% by mass or more, 1.5% by mass or more, or even 1.8% by mass or more.

The crystallization temperature range of the Fe compound may vary depending on the component composition of the molten metal. An example of the upper limit crystallization temperature (crystallization start temperature) of Fe compounds and the upper limit crystallization temperature of α-Al is shown in FIG. FIG. 1 shows the results of calculations based on the Scheil equation using analysis software (Thermo-Calc, manufactured by Thermo-Calc Software AB). The Al alloy molten metal composition (one example) at that time is Al-11%Si-2%Cu-(0.5-1.5)%Fe-(0.2-2)%Mn-0.3%Mg- It was set to 0.8% Zn.

As can be seen from FIG. 1, the higher the Mn concentration and Fe concentration, the more Fe compounds are generated and the crystallization temperature range becomes wider.

Therefore, the temperature of the first molten metal is preferably higher than the temperature of the second molten metal and, depending on the Mn concentration and Fe concentration, higher than the upper limit temperature for crystallization of the Fe compound. Specifically, the temperature of the first molten metal may be, for example, 700 to 900°C, or more preferably 750 to 850°C.

The temperature of the second molten metal is preferably within the crystallization temperature range of the core Fe compound, for example. Other compounds, metals, etc. may crystallize within the temperature range. However, in order to increase recycling efficiency (Al yield), the temperature of the second molten metal is preferably in a temperature range where α-Al does not crystallize. In other words, the temperature of the second molten metal is preferably higher than the upper limit temperature for crystallization of α-Al (approximately 577° C.). Specifically, the temperature of the second molten metal may be, for example, 620 to 570°C, or more preferably 600 to 575°C.

(2) Third molten metal The third molten metal is obtained by mixing the first molten metal and the second molten metal. The mixing may be done, for example, by pouring the first molten metal into the second molten metal, by pouring the second molten metal into the first molten metal, or by placing the first molten metal and the second molten metal in separate containers. It may also be poured into a crucible (such as a crucible). When pouring the second molten metal into the first molten metal side or into another container, it may be done while suppressing the mixing of the precipitated Fe compound. Specifically, except for the lower layer region, the upper to middle layer regions (supernatant portion) of the second molten metal may be poured elsewhere.

The Fe compound crystallizes and grows in the third molten metal due to the passage of time and temperature change (temperature fall) after mixing (crystallization step). In order to promote crystallization, the third molten metal may be heated, stirred, etc. For example, the temperature of the third molten metal is (upper limit temperature for crystallization of α-Al) + (3 to 53 degrees Celsius, furthermore, 13 to 33 degrees Celsius), specifically, 580 to 630 degrees Celsius, furthermore, 590 to 610 degrees Celsius. Good. Note that the time for the crystallization step is not limited, but may be, for example, 5 to 120 minutes, or more preferably 15 to 60 minutes.

《Extraction process》
By removing at least a portion of the Fe compound crystallized in the third molten metal, a fourth molten metal with a reduced Fe concentration is extracted. Since Fe compounds with high specific gravity tend to settle in the lower layer of the third molten metal, the fourth molten metal can only be extracted from the molten metal in the middle to upper layer of the third molten metal (supernatant molten metal with reduced Fe concentration). It is done by taking out the Alternatively, the fourth molten metal may be extracted from the third molten metal by filtering the solid phase Fe compound using a filter or the like.

Removal of undissolved substances other than Fe compounds (for example, iron scraps, etc.) may be performed in the third molten metal preparation stage (mixing process) or in the fourth molten metal extraction stage.

The extracted fourth molten metal may be directly used for producing wrought materials, castings, etc., without being solidified. Before reuse (before recycling), the fourth molten metal may be further refined, or pure Al (new lump) or an alloy source may be added to adjust the composition to a desired composition (component adjustment step). Of course, the fourth molten metal may be provided as a solidified recycled ingot.

The composition of each molten metal does not matter as long as the Fe removal principle (mechanism) according to the present invention can be realized. To give just one example, each molten metal may satisfy one or more of the composition ranges shown below depending on the desired characteristics of the Al alloy member.
Si: 1-13% further 3-12%, Cu: 0.5-5% further 1.5-4%,
Mg: 0.1-6% further 0.2-4%, Zn: 0.3-7% further 0.6-5%,
Mn: 0.1-5%, further 0.3-3%, Fe: 0.5% or less, further 0.4% or less

For each Al alloy molten metal (sample) prepared by changing the Fe removal method (regeneration method), the components were measured and the separated Fe compounds were observed. The present invention will be explained in more detail based on these specific examples.

《Sample 1》
(1) Original molten metal As shown in FIG. 2, a die-casting material (JIS ADC12) with a relatively high Fe content (concentration) was used as a raw material instead of Al alloy scrap. Its chemical composition (initial composition) was Al-11%Si-2%Cu-1%Fe-0.2%Mn-0.3%Mg-0.8%Zn. Note that the composition (concentration) in this example is a mass ratio (mass %) to the entire molten metal or alloy, and is simply expressed as "%".

In sample 1, 1 kg of the raw material was placed in each of two graphite crucibles (#10: height 182 mm x diameter 147 mm x bottom diameter 94 mm, mouth thickness 12 mm) and heated to 800°C. In this way, 1 kg of molten metal having the same composition (referred to as "original molten metal") was prepared in each graphite crucible (simply referred to as "crucible"). Incidentally, the upper limit temperature for crystallization of the Fe compound in the original molten metal is 591°C. Note that all the crystallization temperatures shown in this example were obtained from the analysis software (thermodynamic calculation software) described above.

(2) Preparation process 16.2g of granular pure Mn was added to one raw molten metal, and stirring and standing were repeated to completely dissolve the entire raw material (scrap raw material) containing Mn. In this way, a molten metal (800° C.) with a Mn concentration of 2% was prepared. This molten metal is called "first molten metal." Incidentally, the upper limit temperature for crystallization of the Fe compound in the first molten metal is 676°C.

The other raw molten metal was taken out of the furnace together with the crucible without adding Mn, and left to cool in the atmosphere to 578°C (upper limit temperature for crystallization of α-Al (577°C) + 1°C) ( cooling process). The molten metal thus obtained is called "second molten metal." It is presumed that the second molten metal was in a state where the Fe compound was finely crystallized or a part of it was precipitated due to the temperature lowering treatment. Since the second molten metal has the same composition as the original molten metal, the upper limit temperature for crystallization of the Fe compound in the second molten metal is also 591°C.

(3) Mixing process The first molten metal crucible taken out of the furnace was tilted, and the first molten metal was poured into the second molten metal crucible. In this way, the first molten metal and the second molten metal were mixed. The temperature of the mixed molten metal (referred to as "mixed molten metal") was approximately 640°C.

(4) Crystallization Step The mixed molten metal was left to cool to 600°C (α-Al crystallization upper limit temperature (577°C) + 23°C) while stirring in the atmosphere. The molten metal thus obtained is called the "third molten metal." It is presumed that in the third molten metal, which was cooled while being stirred, crystallization and growth of Fe compounds progressed, and most of the Fe compounds were in a precipitated state. Incidentally, the upper limit temperature for crystallization of the Fe compound in the third molten metal is 636°C.

(5) Extraction process The third molten metal was tilted together with the crucible, and only the molten metal (supernatant) in the upper layer region was poured into the empty crucible. In this way, a recycled molten metal (fourth molten metal) of Al alloy was obtained.

《Sample C1/Sample C2》
As comparative examples, samples C1 and C2 were also produced as shown in FIG. For each sample, raw molten metal was prepared by heating 2 kg of raw material to 800° C. in one crucible. In sample C1, 16.2 g of the aforementioned Mn was added to the original molten metal to prepare a molten metal with a Mn concentration of 1%. In sample C2, 36.7 g of the same Mn was added to the original molten metal to prepare a molten metal with a Mn concentration of 2%. In addition, in each sample, as in the case of sample 1, stirring and standing were repeated to completely dissolve the raw material containing Mn.

Each of the Mn-added molten metals was subjected to the same crystallization process and extraction process as in the case of Sample 1 to obtain recycled molten metals.

《Measurement/Observation》
(1) Component measurement The recycled molten metal (supernatant molten metal) of each sample was reheated to 750°C and thoroughly stirred, then a part of it was poured into an analytical mold (φ40 mm x 30 mm) and left to cool indoors. and allowed to solidify naturally. Using each of the sample alloys thus obtained, the concentration in a horizontal section at a height of approximately 5 mm from the bottom surface was determined by X-ray fluorescence analysis. The obtained Fe concentration and Mn concentration are also shown in FIG. 2.

(2) Observation of Fe compounds For sample 1 and sample C1, the residue (solidified material) at the bottom of the supernatant molten metal after extraction (for sample 1, the bottom of the third molten metal) was observed using an electronic probe microanalyzer (EPMA). ·analyzed. The obtained results (concentration distributions of Fe, Mn, Si, and Al) are shown in FIGS. 3A and 3B (both simply referred to as "FIG. 3"), respectively. Note that the EPMA observation sample was manufactured by mirror polishing a part of the solidified material embedded in the thermosetting resin.

"evaluation"
(1) Fe concentration As is clear from comparing the Fe concentrations of samples 1 to C2 shown in Figure 2, the Fe concentration of sample 1 is about 2 times higher than that of sample C1, which has the same amount of Mn added. The Fe concentration was approximately halfway between that of sample C2, which was twice as high. From these results, it was found that by mixing two molten metals with different Mn concentrations and hot water temperatures, the amount of Fe removed (removal efficiency) relative to the amount of Mn used could be significantly improved. Specifically, it was found that the mixing process improved the removal efficiency by about 25 to 75%.

(2) Fe compound As is clear from comparing the Al-Fe-Mn-Si compounds (Fe compounds) shown in Figure 3, the Fe compound of sample 1 has a high Fe concentration near the center and a high Mn concentration. A low part was being generated. On the other hand, the Fe compound of sample C1 had substantially uniform Fe concentration and Mn concentration.

In the Fe compound of Sample 1, a first Fe compound (a compound with a high Fe concentration and a low Mn concentration) serving as a nucleus is crystallized before the mixing process, and then a second Fe compound (a compound with a Fe concentration and a low Mn concentration) is formed around the nucleus after the mixing process. It is thought that it was formed by the growth of a compound (with a substantially uniform concentration). It is presumed that the generation of the first Fe compound contributed to the improvement in the removal efficiency described above.

From the above, it has become clear that according to the recycling method of the present invention, Fe can be removed while suppressing the amount of Mn, and Al alloy scrap can be recycled efficiently.

Claims (4)

a mixing step of obtaining a third molten metal by mixing a first molten metal and a second molten metal prepared by melting raw materials at least one of which includes Al alloy scrap or recycled Al alloy ingot;
an extraction step of extracting a fourth molten metal from which at least a portion of the Fe compound crystallized from the third molten metal has been removed;
A method for regenerating an Al alloy, comprising:
The first molten metal has a higher Mn concentration and a higher temperature than the second molten metal,
A method for regenerating an Al alloy in which the temperature of the second molten metal is within the crystallization temperature range of an Fe compound. The first molten metal has a Mn concentration of 1% by mass or more based on the whole,
2. The method for regenerating an Al alloy according to claim 1, wherein the second molten metal has a Mn concentration of less than 1% by mass based on the entire second molten metal. 3. The method for regenerating an Al alloy according to claim 1, wherein the temperature of the first molten metal is higher than the upper limit temperature for crystallization of the Fe compound. The method for regenerating an Al alloy according to claim 1, wherein the temperature of the second molten metal is higher than the upper limit temperature for crystallization of α-Al.

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