JP2019077895A - REGENERATION METHOD OF Al ALLOY - Google Patents

Abstract

To provide a regeneration method of an Al alloy capable of a regenerated Al alloy (molten metal) of which Fe concentration are effectively reduced, while using a scrap consisting of an Al alloy cast or the like as a raw material.SOLUTION: There is provided a regeneration method of an Al alloy having a preparation process for melting an Al alloy raw material and preparing a first molten metal having a composition of the molten metal of Mg+Zn≥13 mass% (Mg≥0 mass%, Zn≥0 mass%), a holding process for holding the first molten metal at a separation temperature at which an Fe compound is crystallized, an extraction process for extracting a second molten metal by removing at least a part of non-dissolved solid such as the Fe compound crystallized from the first molten metal, iron rubbish or the like. By the regeneration method, the crystallized Fe compound is easily separated, and a regenerated Al alloy molten metal with low concentration of Fe can be effectively obtained. By the regeneration method, reduction of Mn concentration is also achieved, and it is preferable that initial Mg concentration of the first molten metal is set at 0.5 mass% or more.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method of obtaining recycled Al alloy from scrap and the like.

  With the recent rise in environmental awareness and the like, weight reduction of various members and devices has been promoted, and the use amount of aluminum alloy (simply referred to as "Al alloy") is increasing. A large amount of energy is required for the production (refining) of new Al. In comparison, less energy is required to remelt Al alloy scrap. Therefore, it is desirable to recycle scraps of Al alloy for use.

  When the Al alloy scrap is remelted, in general, elements such as Fe, Si, Cu, Mg and Zn are mixed in the molten metal. In order to obtain a reclaimed Al alloy from scrap, it is necessary to remove unnecessary elements (impurity elements) or excess elements. Related descriptions are given in the following documents as methods for removing such elements.

U.S. Pat. No. 2,464,610 U.S. Pat. No. 5,741,348 JP 2002-155322 A U.S. Pat. No. 4,734,127 WO 2013/168213 WO 2013/168214

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

(1) Method of Removing Intermetallic Compound Patent Documents 1 and 2 and non-patent documents relate to a method of removing a transition metal element such as Fe as an intermetallic compound (also simply referred to as “IMC”) 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 Fe-based intermetallic compounds. , 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) % Is added to reduce the amount of Fe. However, when Si is 8% or less, 0.5% or more of Fe remains in the molten metal even after removal of the intermetallic compound, and the removal efficiency is low. Non-Patent Document 1 is a molten Al alloy (Fe <1.5%, Mn <1.5%, Si <10%, Cr <0.2%, Mg <1%, Cu <1%, Ti <0.1%, Ni <1%) , Zn <1%), it has been reported that Fe and Mn can not be simultaneously reduced to 0.3% or less. In addition, unless otherwise indicated, "%" as used in this specification means mass%.

(2) Segregation solidification method, crystal fractionation method Patent documents 3-6, non-patent documents 1 and 2 separate the Al crystallized material from the residual liquid phase from the molten metal in the semi-solidified state where the Al phase crystallized out Segregation solidification method or crystal fractionation method to reduce Incidentally, in Non-Patent Document 1, the semi-solidified molten metal is squeezed to remove the remaining liquid phase. Further, in Non-Patent Document 2, the semi-solidified molten metal is stirred to make the Al crystallized product into a sphere and separated from the residual liquid phase. In such a method, it is necessary to cool the molten metal until Al phase crystallizes out, and energy loss is large.

(3) Semi-melting purification method Non-Patent Document 3 heats an Al alloy (solid) to a semi-molten state, separates it into a liquid phase and residual Al crystals, and removes impurities exceeding the solid solubility limit of the Al phase. It relates to a melt refining method. Specifically, in Non-Patent Document 3, Al-8.39% Si-0.06% Mn-0.05% Mg alloy in a semi-molten state is pressurized to separate a liquid phase, and Al-0.96% Si-1.14% from the residual component An Mn-1.56% Mg alloy is obtained. In this method, it is difficult to remove Fe and Mn by intermetallic compounds. In addition, since the amount of residual Al crystals in the semi-molten state depends on temperature, the alloy composition that can use this method is limited.

(4) Zone melting method Besides the method described above, as a method of removing impurities from the Al alloy, the ingot is partially heated and melted from one end side, the impurities are collected at the end side, and heating is started There is also a zone melting method to increase the purity at one end side.

  The present invention has been made in view of such circumstances, and provides a method of regenerating an Al alloy which can obtain an Al alloy (molten metal) from which Fe is efficiently removed by a method different from the prior art. With the goal.

  The inventors of the present invention conducted intensive studies to solve this problem, and as a result, the total concentration of Mg and Zn contained in the Al alloy melt in which scraps and the like are dissolved is at least a predetermined concentration, thereby removing Fe contained in the melt ( Concentration reduction). The development of this result has led to the completion of the invention described hereinafter.

<< Regeneration method of Al alloy >>
(1) The present invention is a preparation step of preparing a first molten metal in which at least a part of an Al alloy raw material is melted to make a molten metal composition Mg + Zn ≧ 13 mass% (Mg ≧ 0 mass%, Zn ≧ 0 mass%) A holding step of holding the first molten metal at a separation temperature at which the Fe compound crystallizes out, and an extraction of extracting the second molten metal from which at least a portion of undissolved solid such as Fe compound or iron scrap is removed from the first molten metal A method of regenerating an Al alloy comprising the steps of:

(2) According to the method for regenerating the Al alloy of the present invention (simply referred to as "regeneration method"), an iron compound (simply referred to as "Fe compound") crystallized from the first molten metal in which the Al alloy raw material is dissolved Undissolved iron scraps can be easily removed, and a regenerated Al alloy with a sufficiently reduced Fe concentration can be obtained efficiently. Since this regenerated Al alloy is obtained not in a solid state but in a liquid state (that is, in a molten metal state), it is possible to ship it as a reclaimed metal as it is or to reuse it without remelting or the like.

  The reason why Fe concentration can be reduced by the regeneration method of the present invention is considered as follows. By setting the concentration of Mg and / or Zn of the first molten metal to a predetermined value or more, a high melting point Fe compound is formed in the molten metal, and the crystallization temperature of the Al phase (particularly α-Al) is It will decrease. These acted synergistically to expand the crystallization temperature range of the Fe compound and increase the amount of crystallization of the Fe compound so that more Fe compound could be efficiently removed from the first molten metal . As a result, it is considered that a second molten metal having a sufficiently reduced Fe concentration can be obtained.

<< Others >>
Unless otherwise stated, “x to y” as used herein includes the lower limit x and the upper limit y. Ranges such as “a to b” may be newly established as new lower limit values or upper limit values for arbitrary numerical values included in various numerical values or numerical ranges described in the present specification.

It is a graph which shows the relationship between the molten metal temperature or Fe concentration in a liquid phase, and a solid phase rate. It is a table which shows the influence which Mg concentration and Zn concentration have on the Fe concentration which can be reduced. It is a graph which shows the relationship between initial stage Mn concentration, and Fe concentration which can be reduced, or Mn concentration. It is a SEM image of metal structure concerning each sample.

  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 also be components relating to things (eg, recycled Al alloy, recycled Al alloy member, etc.) even if they are method components.

<< Principle of Fe Removal >>
The principle by which Fe is removed by the regeneration method of the present invention will be described with reference to FIGS. FIGS. 1 to 3 show the results calculated based on the Scheil formula using analysis software (Thermo-Calc manufactured by Thermo-Calc Software AB).

(1) Fe removal Al-2% Si-1% Fe-0.5% Mn-0.5% Cu alloy molten metal (simply referred to as "base molten metal") and Al-2% Si-1% Fe-0. Regarding the 5% Mn-0.5% Cu-10% Mg-10% Zn alloy molten metal (simply referred to as "10% Mg-10% Zn molten metal"), the molten metal temperature or the Fe concentration and solid phase ratio in the liquid phase And their relationship are shown in FIG.

  As apparent from FIG. 1, in the case of the base molten metal, the melting point of the Fe compound (intermetallic compound) is low, and the Fe compound (solid phase) hardly crystallizes, so Fe can not be effectively removed from the molten metal. In the case of a 10% Mg-10% Zn melt, the melting point of the Fe compound (intermetallic compound) rises and the crystallization temperature of the Al phase (α-Al) also decreases. For this reason, it turns out that Fe content after removal of undissolved solid, such as Fe compound and iron scraps, falls sharply to 0.263%, when crystallization amount of Fe compound also increases and it keeps at 573 ° C.

  Since the Fe compound usually has a specific gravity larger than that of the molten metal, the Fe compound settles to the lower layer area of the molten metal, and both can be easily separated. Therefore, according to the present invention, Fe, which is an impurity, can be efficiently removed as an Fe compound. In addition, even when unmelted solids such as iron scraps come in contact with the molten metal, Fe can not be dissolved in the molten metal. For this reason, a molten Al alloy (second molten metal) having a sufficiently reduced Fe concentration can be obtained.

By the way, as long as the Fe compound mentioned in the present specification is a compound containing Fe (for example, an intermetallic compound containing Fe), its composition or form does not matter. As typical Fe compounds, for example, Al ₁₃ Fe ₄ , Al ₁₅ Si ₂ (Fe, Mn) ₄ containing Mn, etc. are given.

(2) Relationship between Mg concentration and Zn concentration and Fe concentration Al-2% Si-1% Fe-0.5% Mn-0.5% Cu- (0-30)% Mg- (0-30)% The relationship between the Mg concentration and the Zn concentration, and the Fe concentration that can be reduced is shown as a list in FIG. 2 for the molten Zn alloy.

  As apparent from FIG. 2, the Fe concentration is 0.65% or less by adjusting the composition (concentration) of the first molten metal so that Mg + Zn ≧ 13%, Mg + Zn ≧ 15%, and further Mg + Zn ≧ 18%. It can be seen that it can be reduced to 0.5% or less, or even 0.4% or less. The concentration of one of Mg and Zn may be 0%, but is preferably 1% or more, 4% or more, 7% or more, and further 9% or more.

(3) Mn concentration Al-2% Si-1% Fe- (0-10)% Mn-0.5% Cu-8% Mg-8% Zn alloy molten metal (first molten metal) having different initial Mn concentrations The relationship between the initial Mn concentration and the limit concentrations of Fe and Mn which can be dissolved in the molten metal (in the liquid phase) (so-called dissolution limit / simply referred to as "Fe concentration", "Mn concentration") is shown in FIG. . As apparent from FIG. 3, it can be seen that the Fe concentration in the molten metal can be reduced as the initial Mn concentration increases. In this case, it can be seen that the Fe concentration can be reduced to 0.35% or less, 0.3% or less, or even 0.25% or less.

  It was also found that the Mn concentration in the liquid phase (in the second melt) was stable at around 0.2% even if the initial Mn concentration in the first melt was increased. Thereby, for example, even if a large amount of Mn is added to the first molten metal in order to reduce the Fe concentration, the Mn concentration in the second molten metal can be maintained within the predetermined range. Such a second molten metal is suitable for producing an Al alloy (such as a wrought material) having a low Mn concentration. Based on the above, for example, it is preferable to set the initial Mn concentration in the first molten metal to 0.5% or more, 1% or more, 3% or more, and further 5% or more. From the tendency of FIG. 3, it is considered that Mn (initial Mn) contained in the first molten metal mainly crystallizes out and precipitates as a Fe compound containing Mn.

<< Preparation process >>
(1) A first molten metal is prepared in which the concentration of Mg and Zn in the molten metal in which at least a part of the Al alloy raw material is melted is in a desired range. Under the present circumstances, after analyzing the molten metal component after melt | dissolution of Al alloy raw material, a suitable quantity Mg source raw material (for example, pure Mg, Mg alloy, Mg compound) and / or Zn source raw material (for example pure Zn, Zn alloy) to the molten metal The Zn compound may be added to adjust the composition of the first molten metal. Moreover, in order to suppress oxidation and evaporation of Mg and Zn, the molten metal temperature at the time of addition of the Mg source material and the Zn source material is preferably 800 ° C. or less, and more preferably 660 ° C. or less. Of course, as long as the oxidation and evaporation of Mg and Zn can be suppressed, the first molten metal may be prepared by simultaneously melting the Al alloy raw material and the Mg source raw material and / or the Zn source raw material. The melting temperature (the first molten metal temperature) may be a temperature at which at least a part of the Al alloy raw material melts, but in the case of using an Al alloy scrap, it may be a temperature at which iron scraps remain molten, for example, 570 to 760 ° C. Furthermore, what is necessary is just to be about 590-730 degreeC.

(2) It is preferable to mainly use scraps of Al alloy as the Al alloy raw material. The Al alloy raw material may be a wrought material or a casting. However, in the regeneration method of the present invention, the second molten metal is extracted from the first molten metal having a relatively high concentration of Mg, Zn and further Mn. Therefore, it is preferable that the scrap of an Al alloy wrought material containing a large amount of these elements is generally included in the Al alloy raw material.

  For example, the Al alloy wrought material (scrap), which is a raw material, is an Al-Mn alloy No. 3000 Al alloy, an Al-Mg alloy No. 5000 Al alloy, and an Al-Mg-Si alloy. It is preferable that it is any one or more of 6000-series Al alloy and 7000-series Al alloy which is an Al-Zn-Mg (-Cu) -based alloy. In particular, it is preferable that a 5000-series Al alloy or a 7000-series Al alloy containing a relatively large amount of Mg or Zn be included in the Al alloy raw material. Incidentally, the Al alloy name (number) is based on the international aluminum alloy name or the Japanese Industrial Standard (JIS H4140). The Al alloy raw material may be a member including a metal (for example, a steel material) other than the Al alloy.

  Incidentally, even if the first molten metal contains a large amount of Si (for example, 5% or more), Fe can be sufficiently removed by the above-described removal principle (mechanism). However, in consideration of the case where the second molten metal is used for regeneration of the wrought material, the second molten metal is preferably Si: 5% or less, 4% or less, or 3% or less with respect to the whole.

<< holding process >>
The first molten metal obtained in the preparation step is maintained at a temperature at which Fe compounds crystallize and separation of the solid phase and the remaining liquid phase is possible. At this time, if the first molten metal is cooled to a temperature at which α-Al crystallizes, efficient separation of the crystallized Fe compound becomes difficult. Therefore, it is preferable to hold the first molten metal at a temperature (separation temperature) in a range where the Al compound does not crystallize out and the Fe compound crystallizes out. The separation temperature may be adjusted according to the alloy composition of the first molten metal, but is preferably, for example, (α-Al crystallization start temperature) + (5 to 30 ° C., further 10 to 20 ° C.). More specifically, for example, the temperature may be adjusted within the range of 540 to 620 ° C., and more preferably 550 to 600 ° C.

  The holding step is preferably a slow cooling step in order to promote the crystallization of the Fe compound and the grain growth thereof. For example, it is preferable that the cooling rate is gradually cooled in the range of 0.5 to 10 ° C./minute, and more preferably 2 to 7 ° C./minute. The cooling rate referred to herein is an average value obtained by dividing the temperature difference by the required time from the start of the holding step to the start of the next extraction step. In addition, a holding time may be provided in a temperature range from the initial temperature of the first molten metal to the separation temperature to promote crystallization of the Fe compound or to achieve coarsening thereof. The holding step at this time is a slow cooling step in which the cooling rate is reduced according to the holding time.

Extraction process
By removing at least a part of the undissolved solid such as the Fe compound or iron scraps crystallized from the first molten metal, it is possible to obtain the second molten metal in which the concentration of Fe is reduced. The extraction of the second molten metal can also be carried out by removing the Fe compound, which is a solid phase, from the crucible containing the molten metal with a filter or the like. However, an Fe compound having a specific gravity larger than that of the molten metal tends to settle in the lower layer of the molten metal. Therefore, extraction of the second molten metal may be performed by taking out only the (supernatant) molten metal having a reduced concentration of Fe from the middle (middle to upper layer) of the crucible containing the molten metal. In any case, the present step of extracting the second molten metal in the liquid phase may be performed in the same temperature range as the separation temperature. In addition, it is preferable that residual solids not dissolved in the preparation step (for example, iron scraps and the like contained in part of the Al alloy raw material) are also removed in the extraction step.

  It is preferable that the extracted second molten metal is used as it is for producing a wrought material or the like without being solidified once. The second molten metal may be further refined or pure Al (new block) or an alloy source may be added to adjust it to a desired component before using it (component adjustment step). Of course, after the second molten metal is solidified once, it may be supplied as a recycled ingot (ingot) which is a raw material for a wrought material or the like.

  Assuming the first molten metal in the present invention, an Al alloy molten metal containing Fe, Mg, Zn and Mn was prepared. The metal structure observation and the component measurement of each were performed using the sample which solidified the molten metal extracted from the each layer area | region. The present invention will be described in more detail based on such specific examples.

<< Production of samples >>
(1) Preparation process The raw material was put into a graphite crucible (height 130 mm × diameter 105 mm × bottom diameter 70 mm, mouth thickness 10 mm) and heated to 860 ° C. to melt. The raw materials were blended such that the alloy composition of the molten metal was Al-1% Si-1% Fe-1% Mn-0.5% Cu-10% Mg-20% Zn. However, the Mg source material (pure Mg) and the Zn source material (pure Zn) were added to the molten metal whose temperature was lowered to 760 ° C. by previously dissolving the other materials. This suppressed the oxidation and evaporation of Mg and Zn. Thus, about 700 g of an initial molten metal (first molten metal) was prepared.

  A portion of the initial molten metal was poured into a mold for analysis (φ 40 mm × 30 mm), allowed to cool indoors, and allowed to spontaneously solidify. Thus, Sample 0 for initial melt analysis was obtained.

(2) Holding Step The initial molten metal was furnace-cooled to 565 ° C. (α-Al crystallization start temperature + 5 ° C.) for 30 minutes. The molten metal in each region of the upper layer part, the middle layer part and the lower layer part was extracted and solidified from the molten metal after the cooling as follows.

  The upper layer portion of the molten metal (the surface layer portion with a thickness of about 10 mm) was collected with a spoon and allowed to spontaneously solidify in an analysis die (φ 40 mm × 30 mm). Thus, sample 1 for upper layer analysis was obtained.

  The molten metal after removal of the upper layer portion was poured into a mold (about 30 mm × 40 mm × 200 mm) for producing a test material for collecting a mold specimen according to JIS H 5202: 2010, and was naturally solidified. Thus, a sample 2 for middle layer analysis was obtained.

  The solidified portion remaining at the bottom of the crucible after pouring of the middle layer was allowed to cool together with the crucible and allowed to solidify in the room. Thus, a sample 3 for lower layer analysis was obtained.

<< Analysis of sample >>
The cross section of each sample was observed with a scanning electron microscope (SEM) and the Fe concentration and the Mn concentration were analyzed by fluorescent X-ray analysis. The results are summarized in FIG. The observation and analysis of Samples 0 to 2 were performed on the central portion (φ 20 mm) of the horizontal cross section at a height of 10 mm from the bottom of the sample. The observation and analysis of sample 3 were performed on the central portion (φ 20 mm) of the horizontal cross section at a position 5 mm high from the bottom of the sample.

"Evaluation"
As apparent from FIG. 4, in the sample 1 of the upper layer portion, the Fe concentration (composition) is slightly lower than that of the sample 0 in the initial state. In the sample 3 of the lower layer portion, a large amount of Fe compound was crystallized, and the Fe concentration and the Mn concentration were significantly increased as compared with the sample 0 in the initial state. In sample 2 which is in the middle of them, it is found that the crystallization of the Fe compound is small and the Fe concentration and the Mn concentration are significantly reduced. Specifically, in the middle layer, the Fe concentration was reduced to 0.587% (initial) → 0.137%, and the Mn concentration was reduced to 0.786% (initial) → 0.291%.

  From the above, according to the regeneration method of the present invention, it was confirmed that a regenerated Al alloy (molten metal) having a sufficiently reduced Fe concentration (further, a Mn concentration) can be obtained from an Al alloy raw material such as scrap. .

Claims (6)

Preparing the first molten metal by melting at least a part of the Al alloy raw material and setting the molten metal composition to Mg + Zn ≧ 13 mass% (Mg ≧ 0 mass%, Zn ≧ 0 mass%);
A holding step of holding the first molten metal at a separation temperature at which the Fe compound crystallizes out;
Extracting the second molten metal from which at least a portion of the Fe compound crystallized out of the first molten metal is removed;
A method of regenerating Al alloy provided with   The method according to claim 1, wherein the first molten metal is 0.5 mass% or more of Mn based on the whole.   The method for regenerating an Al alloy according to any one of claims 1 to 3, wherein the second molten metal is Si: 5% by mass or less based on the whole.   The method for regenerating an Al alloy according to any one of claims 1 to 3, wherein the Al alloy raw material includes scraps of an Al alloy wrought material.   The method for regenerating an Al alloy according to claim 4, wherein the Al alloy wrought material includes any of No. 3000 series Al alloy, No. 5000 series Al alloy, No. 6000 series Al alloy and No. 7000 series Al alloy.   The said holding | maintenance process is a cooling rate of 0.5-10 degrees C / min, The reproduction | regeneration method of Al alloy in any one of Claims 1-5.