JP2021143351A - REGENERATION METHOD OF Al ALLOY - Google Patents

Abstract

To provide a novel recycling method of Al alloy scrap capable of heightening a ratio (removal efficiency) of an Fe amount to be removed relative to a Mn amount.SOLUTION: A regeneration method of an Al alloy of the present invention comprises: a mixing step of obtaining a third molten metal by mixing a first molten metal and a second molten metal prepared by dissolving a raw material at least one of which contains an Al alloy scrap or a regenerated Al alloy ingot; and an extraction step for extracting a fourth molten metal from which at least a part of an Fe compound precipitated from the third molten metal is removed. Here, the first molten metal has a larger Mn concentration and a higher temperature of the molten metal than the second molten metal, and the second molten metal has the temperature of the molten metal within the crystallization temperature range of the Fe compound. The first molten metal has a Mn concentration relative to a total of, for example, 1 mass% or more. The second molten metal has a Mn concentration relative to a total of, for example, smaller than 1 mass%. According to the regeneration method of the Al alloy of the present invention, for example, the removal efficiency can be increased by about 25 to 75%.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for recycling Al alloy scrap and the like.

With the recent rise in environmental awareness, the weight of various members and devices has been reduced, and the amount of aluminum alloys (simply referred to as "Al alloys") used is increasing. A large amount of energy is required to produce (refining) new Al, but a small amount of energy is required to redissolve Al alloy scrap (also simply referred to as “scrap”). For this reason, it is desirable to recycle or reuse scrap (simply referred to as "recycling").

When scrap is redissolved, Fe is usually mixed in the molten metal. In order to obtain a recycled Al alloy from scrap, it is necessary to remove unnecessary elements (impurity elements). As a method for removing such an element, a related description is found in the following documents.

U.S. Pat. No. 2464610 U.S. Pat. No. 5,741348 Japanese Patent Application Laid-Open No. 2002-155322 U.S. Pat. No. 4,734,127 WO2013 / 168213 WO2013 / 168214

Furukawa Electric Time Signal 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 for removing Fe as an intermetallic compound from a molten metal. Specifically, in Patent Document 1, Cr, Mn, and Co are added to an Al- (11.6 to 13.5)% Si- (0.8 to 9)% Fe alloy to crystallize an Fe-based intermetallic compound. , The amount of Fe in the molten metal is reduced.

In Patent Document 2, Al- (0 to 12)% Si- (0.49 to 2.1)% Fe- (0.37 to 1.91)% Mn alloy (Cr <0.4%, Ti <0.41%, Zr <0.26%, Mo <0.01 %) To reduce the amount of Fe. However, the efficiency of removing Fe with respect to the amount of Mn used is low.

(2) Segregation solidification method, crystal fractionation method In Patent Documents 3 to 6 and Non-Patent Documents 1 and 2, Al crystals are separated from the residual liquid phase from the molten metal in a semi-solidified state in which the Al phase is crystallized, and impurities are present. The present invention relates to a segregation solidification method or a crystal fractionation method for reducing the amount of water. Incidentally, in Non-Patent Document 1, the semi-solidified molten metal is squeezed to remove the residual liquid phase. Further, in Non-Patent Document 2, the semi-solidified molten metal is stirred to spheroidize the Al crystallized product and separate it from the residual liquid phase. In such a method, it is necessary to cool the molten metal until the Al phase crystallizes, and the energy loss is large.

(3) Semi-melt purification method In Non-Patent Document 3, the Al alloy (solid) is heated to a semi-melted state to separate it into a liquid phase and a residual Al crystal, and impurities exceeding the solid solubility limit of the Al phase are removed. Regarding the melt purification method. Specifically, in Non-Patent Document 3, Al-8.39% Si-0.06% Mn-0.05% Mg alloy in a semi-molten state is pressed to separate the liquid phase, and Al-0.96% Si-1.14% is separated from the residue. Mn-1.56% Mg alloy is obtained. With this method, it is difficult to remove Fe as an intermetallic compound. Further, since the amount of residual Al crystals in the semi-molten state depends on the temperature, the alloy composition that can use this method is limited.

(4) Band melting method In addition to the method described above, as a method for removing impurities from the Al alloy, the ingot is partially heated and melted from one end side, impurities are collected on the end side, and heating is started at one end. There is also a band melting method that increases the purity of the side.

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

As a result of diligent research to solve this problem, the present inventor has succeeded in improving the removal efficiency as compared with the conventional case by mixing a plurality of molten metal having different Mn concentration and hot water temperature. By developing this result, the present invention described below has been completed.

<< How to regenerate Al alloy >>
(1) The present invention comprises a mixing step of mixing a first molten metal and a second molten metal prepared by melting a raw material containing Al alloy scrap at least one of them to obtain a third molten metal, and crystallization from the third molten metal. A method for regenerating an Al alloy, comprising 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 and a hot water temperature than the second molten metal. The second molten metal is a method for regenerating an Al alloy in which the temperature of the molten metal is within the crystallization temperature range of the Fe compound.

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

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

When the first molten metal having 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, an Fe compound in which Fe is concentrated or unevenly distributed with respect to Mn can be newly produced instead of the Fe compound in line with the general stoichiometric ratio (ratio of Mn and Fe). As a result, it is considered that scrap can be recycled with high removal efficiency (yield).

"others"
(1) The regenerated Al alloy from which Fe has been removed (reduction of Fe concentration) may be used in a solid phase state or in a liquid phase state (for example, as a fourth molten metal). The regenerated Al alloy in the liquid phase state can be used as it is as a regenerated bullion without being redissolved, for example.

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

(3) Unless otherwise specified, the concentration, composition, etc. referred to in the present specification are the mass ratio (mass%) to the whole of the object (molten metal, alloy, compound, etc.), and the mass% is simply "%" as appropriate. Write.

(4) Unless otherwise specified, "x to y" in the present specification includes a lower limit value x and an upper limit value y. A range such as "ab" may be newly established with any numerical value included in the various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

It is a graph which shows the relationship between the crystallization temperature of Fe compound, Mn concentration or Fe concentration. It is explanatory drawing which shows the regeneration method which concerns on each sample, and the Fe · Mn concentration of the regenerated molten metal. It is the analysis result by EPMA of the residue (Fe compound) which concerns on Sample 1. It is the analysis result by EPMA of the residue (Fe compound) which concerns on sample C1.

One or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. The contents described in the present specification can be components related to a product (for example, a regenerated 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 having different Mn concentration and hot water temperature are mixed. For convenience, the case where the first molten metal and the second molten metal are mixed will be mainly described, but in the mixing step, three or more kinds of molten metal having different Mn concentration and / or hot water temperature (first molten metal, second molten metal and other molten metal) are described. ) 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 material comprises one or more kinds of raw materials including Al alloy scrap (simply referred to as "scrap"), recycled Al alloy ingots (Al alloy ingots produced from Al alloy scrap as raw materials), and the like. It is more preferable that each molten metal is prepared based on the scrap raw material because the recycling of scrap is promoted. When preparing each molten metal, it does not matter whether the scrap raw materials are different or the preparation time is different.

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, and the like. Further, the scrap raw material may include, in addition to the scrap itself, an adjusting raw material (additive composed of an alloy, a compound, a pure metal, etc.) for adjusting each molten metal to a desired component composition.

The first molten metal may be prepared at a temperature at which raw materials such as Al alloy scrap and additives are sufficiently melted (for example, about 650 to 930 ° C. and further about 680 to 880 ° C.). However, the hot water temperature may be a temperature at which iron scraps and the like remain undissolved. The second molten metal is prepared, for example, by adjusting (lowering the temperature) to a temperature in which the raw materials such as Al alloy scrap are sufficiently melted (exceeding the upper limit temperature for crystallization of the Fe compound) and then adjusting to the crystallization temperature range of the Fe compound. 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 may have, for example, a Mn concentration of less than 1% by mass, 0.7% by mass or less, and further 0.4% by mass or less with respect to the whole. The Mn concentration is not limited to the lower limit value, but may be, for example, 0.05% by mass or more, further 0.1% by mass or more.

Since the first molten metal grows an Al-Fe-Mn-Si compound around its nucleus, for example, the Mn concentration is 1% by mass or more, 1.4% by mass or more, and further 1. It is preferably 7% by mass or more. The Mn concentration is not limited to the upper limit value, but may be, for example, 5% by mass or less, 4% by mass or less, and further 3% by mass or less. In order to increase the removal efficiency, the difference in Mn concentration between the first molten metal and the second molten metal may be, for example, 1% by mass or more, 1.5% by mass or more, and further 1.8% by mass or more.

The crystallization temperature range of the Fe compound can change depending on the composition of the molten metal. An example of the upper limit temperature for crystallization of the Fe compound (the upper limit temperature for crystallization) and the upper limit temperature for crystallization of α-Al is shown in FIG. FIG. 1 shows the result of calculation based on the Scheil equation using analysis software (Thermo-Calc Software AB Thermo-Calc). The composition of the molten Al alloy at that time (example) was Al-11% Si-2% Cu- (0.5 to 1.5)% Fe- (0.2 to 2)% Mn-0.3% Mg-. It was set to 0.8% Zn.

As can be seen from FIG. 1, it can be seen that the higher the Mn concentration and the Fe concentration, the wider the crystallization temperature range due to the formation of Fe compounds.

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

The temperature of the second molten metal may be, for example, within the crystallization temperature range of the core Fe compound. Other compounds, metals, etc. may crystallize within the temperature range. However, in order to increase the recycling efficiency (Al yield), the temperature of the second molten metal is preferably in a temperature range in which α-Al does not crystallize. That is, the temperature of the second molten metal is preferably higher than the upper limit temperature for crystallization of α-Al (about 577 ° C.). Specifically, the temperature of the second molten metal may be, for example, 620 to 570 ° C., 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 performed, for example, by pouring the first melt into the second melt side, pouring the second melt into the first melt side, or pouring the first melt and the second melt into different bodies. It may be poured into (crucible, etc.). When the second molten metal is poured into the first molten metal side or another body, the mixing of the precipitated Fe compound may be suppressed. Specifically, except for the lower layer region, the upper layer region to the middle layer region (supernatant portion) of the second molten metal may be poured into other layers.

The Fe compound crystallizes and grows in the third molten metal due to the passage of time after mixing and the temperature change (temperature drop) (crystallization step). In order to promote the crystallization, the temperature of the third molten metal may be lowered, stirred or the like. For example, the third molten metal is (α-Al upper limit temperature for crystallization) + (3 to 53 ° C., further 13 to 33 ° C.), specifically, 580 to 630 ° C., further 590 to 610 ° C. It is good. The time of the crystallization step is not limited, but is preferably 5 to 120 minutes, more preferably 15 to 60 minutes, for example.

<< Extraction process >>
By removing at least a part of the Fe compound crystallized in the third molten metal, the fourth molten metal having a reduced Fe concentration is extracted. Since the Fe compound having a large specific density tends to settle in the lower layer region of the third molten metal, the extraction of the fourth molten metal is limited to, for example, the molten metal in the middle to upper layer regions of the third molten metal (supernatant molten metal having a reduced Fe concentration). Is taken out and made. In addition, the fourth molten metal may be extracted from the third molten metal by filtering the Fe compound which is a solid phase with a filter or the like.

Undissolved substances other than the Fe compound (for example, iron scraps and the like) may be removed in the preparation step (mixing step) of the third molten metal or in the extraction step of the fourth molten metal.

The extracted fourth molten metal may be directly used for producing a wrought material, a casting, or the like without solidifying. The fourth molten metal may be further refined before reuse (before recycling), or may be adjusted to a desired component by adding pure Al (new ingot) or an alloy source (component adjusting step). Of course, the fourth molten metal may be provided as a solidified regenerated ingot.

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

For each molten Al alloy (sample) prepared by changing the method for removing Fe (regeneration method), the components thereof were measured and the separated Fe compound was observed. The present invention will be described in more detail based on these specific examples.

<< Sample 1 >>
(1) Raw molten metal As shown in FIG. 2, a die casting material (JIS ADC12) having a relatively high Fe content (concentration) was used as a raw material as a substitute for Al alloy scrap. The chemical composition (initial composition) was Al-11% Si-2% Cu-1% Fe-0.2% Mn-0.3% Mg-0.8% Zn. The composition (concentration) referred to in this example is the mass ratio (mass%) of the target molten metal or alloy to the whole, and is simply indicated by "%".

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

(2) Preparation Step 16.2 g of granular pure Mn was added to one of the 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.) having 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 allowed to stand in the atmosphere to cool to 578 ° C (upper limit temperature for crystallization of α-Al (577 ° C) + 1 ° C) ( Temperature lowering process). The molten metal thus obtained is called "second molten metal". It is presumed that the second molten metal was in a state in which the Fe compound was finely crystallized or a part thereof was precipitated by 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 step The crucible of the first molten metal taken out of the furnace was tilted, and the first molten metal was poured into the crucible of the second molten metal. 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 about 640 ° C.

(4) Crystallization Step The mixed molten metal was allowed to cool to 600 ° C. (upper temperature of α-Al crystallization (577 ° C.) + 23 ° C.) while stirring in the air. The molten metal thus obtained is called "third molten metal". It is presumed that in the third molten metal whose temperature was lowered while being stirred, the crystallization and growth of the Fe compound proceeded, and most of the Fe compound was 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 step The third molten metal was tilted together with the crucible, and only the molten metal (supernatant) in the upper layer was poured into the empty crucible. In this way, a recycled molten metal of Al alloy (fourth molten metal) was obtained.

<< Sample C1 and Sample C2 >>
As a comparative example, as shown in FIG. 2, sample C1 and sample C2 were also produced. For each sample, 2 kg of the raw material was heated to 800 ° C. in one crucible to prepare a raw molten metal. In sample C1, 16.2 g of the above-mentioned Mn was added to the raw molten metal to prepare a molten metal having an Mn concentration of 1%. In sample C2, 36.7 g of the same Mn was added to the raw molten metal to prepare a molten metal having an Mn concentration of 2%. In each sample, as in the case of sample 1, stirring and standing were repeated to completely dissolve the raw material containing Mn.

Each molten metal to which Mn was added was also subjected to the same crystallization step and extraction step as in the case of Sample 1 to obtain a regenerated molten metal.

《Measurement / Observation》
(1) Component measurement The regenerated molten metal (supernatant molten metal) of each sample is reheated to 750 ° C., and after sufficient stirring, a part of the molten metal is poured into an analysis mold (φ40 mm × 30 mm) and allowed to cool indoors. And naturally solidified. Using the alloy of each sample thus obtained, the concentration in a horizontal cross section having a height of about 5 mm from the bottom surface was measured by fluorescent X-ray analysis. The obtained Fe concentration and Mn concentration are also shown in FIG.

(2) Observation of Fe compound For Sample 1 and Sample C1, the residue (coagulated product) on the bottom of the supernatant molten metal after extraction (in the case of Sample 1, the bottom of the third molten metal) was observed with an electron probe microanalyzer (EPMA). ·analyzed. The obtained results (concentration distribution of Fe, Mn, Si and Al) are shown in FIGS. 3A and 3B (both are simply referred to as "FIG. 3"), respectively. The EPMA observation sample was produced by mirror-polishing a part of the coagulated product embedded in the thermosetting resin.

"evaluation"
(1) Fe Concentration As is clear from comparing the Fe concentrations of Samples 1 to C2 shown in FIG. 2, the Fe concentration of Sample 1 is such that the Fe concentration of Sample C1 having the same Mn addition amount and the Mn addition amount are about 2. It was substantially in the middle of the Fe concentration of sample C2, which was double. From these facts, it was found that by mixing two molten metal having different Mn concentration and hot water temperature, the amount of Fe removed (removal efficiency) with respect to the amount of Mn used can be significantly improved. Specifically, it was found that the removal efficiency was improved by about 25 to 75% by the mixing step.

(2) Fe Compound As is clear from a comparison of the Al-Fe-Mn-Si based compounds (Fe compounds) shown in FIG. 3, the Fe compound of Sample 1 has a high Fe concentration and a Mn concentration near the center. The low part was 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, after the core first Fe compound (compound having a high Fe concentration and a low Mn concentration) crystallizes before the mixing step, the second Fe compound (Fe concentration and Mn) surrounds the nucleus after the mixing step. It is considered that a compound having a substantially uniform concentration) was grown. Then, it is presumed that the formation of the first Fe compound contributed to the improvement of the removal efficiency described above.

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

Claims (4)

A mixing step of mixing a first molten metal and a second molten metal prepared by melting a raw material containing at least one of Al alloy scrap or recycled Al alloy ingot to obtain a third molten metal.
An extraction step of extracting the fourth molten metal from which at least a part of the Fe compound crystallized from the third molten metal has been removed, and
It is a method of regenerating an Al alloy equipped with
The first molten metal has a higher Mn concentration and a higher hot water temperature than the second molten metal.
The second molten metal is a method for regenerating an Al alloy whose temperature is within the crystallization temperature range of the Fe compound. The first molten metal has a Mn concentration of 1% by mass or more with respect to the whole.
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 with respect to the whole. The method for regenerating an Al alloy according to claim 1 or 2, 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 any one of claims 1 to 3, wherein the temperature of the second molten metal is higher than the upper limit temperature for crystallization of α-Al.

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