Method for producing hypereutectic material

Abstract

To provide a method for producing a hypereutectic material having a novel metal structure that has not been conventionally available.SOLUTION: A method according to the present invention for producing a hypereutectic material includes: a heating step of heating a hypereutectic Al-Fe alloy or a hypereutectic Al-Si alloy to a temperature equal to higher than the eutectic point and to a temperature equal to or higher than a liquidus temperature; and a cooling step of segregating primary crystals of the hypereutectic Al-Fe alloy or the hypereutectic Al-Si alloy to a surface layer portion of the hypereutectic material by applying an electromagnetic force to a molten metal generated by the heating step while cooling the molten metal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for producing a hypereutectic material. This application claims priority to U.S. Provisional Application No. 63 / 253,131, filed October 7, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Hard intermetallic compounds (hereinafter referred to as solid phase particles) that crystallize during the solidification process of molten metal have various effects on the properties of the metallic material produced by the solidification process. In some cases, they are essential for achieving the desired material properties, while in other cases, their removal is necessary. In the former case, the distribution and morphology of the particles are generally important, while in the latter case, it is necessary to establish a process technology to separate and remove the solid phase particles.

[0003] It has been reported that solid particles free in molten metal can be separated by applying electromagnetic force (Non-Patent Document 1). This method utilizes the reaction of the electromagnetic force acting on the molten metal. According to electromagnetic separation theory, solid particles with low electrical conductivity move in the opposite direction to the electromagnetic force. Since the solid particles then move to the surface of the molten metal, they can be removed. Alternatively, to obtain desired material properties, it is conceivable to retain the solid particles that have migrated to the surface within the molten metal. Therefore, the use of electromagnetic separation theory is of interest in solidification structure control and molten metal purification. However, there are many unknowns as to whether the effects as predicted by the theory can actually be achieved. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] J. Park, J. Sasa, K., and S. Asai: Journal of the Japan Institute of Metals, 59(1995), 312-318, 10.2320 / jinstmet1952.59.3_312 [Non-patent document 2] PDDesai, HMJames and CYHo:CINDAS Report 65 March 1983,9-38. [Non-patent document 3] A.Kofler: Z.Metallkde, 41 (1950), 221-226. [Non-patent document 4] E. Scheil: Z. Metalkde, 45 (1954), 298-309. [Non-Patent Document 5] LM Hogan: J. Aust. Inst. Met., 9 (1964), 228-239. [Non-patent document 6] E. Talaat and F. Hasse: Mater. Trans., JIM, 41 (2000), 507-515, 10.2320 / matertrans1989.41.507. [Non-Patent Document 7] Tetsuichi Mogi and Atsumi Ohno: Light Metals 38 (1988), 96-101, 10.2464 / jilm.38.96. Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, hypereutectic materials, which are a type of metallic material, include hypereutectic Al-Fe alloys and hypereutectic Al-Si alloys. These hypereutectic materials are required to have various material properties. One of the factors that determine the material properties of hypereutectic materials is the metal structure of the hypereutectic material. Examples of metal structures include the surface layer structure and the internal structure. One method for controlling the surface layer structure is to use the electromagnetic separation theory described above, but hypereutectic materials do not necessarily behave in accordance with the electromagnetic separation theory.

[0006] Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a hypereutectic material having a new metal structure that has not been seen before. [Means for solving the problem]

[0007] "1" In order to solve the above-mentioned problems, according to one aspect of the present invention, there is provided a method for producing a hypereutectic material, comprising: a heating step of heating a hypereutectic Al-Fe alloy or a hypereutectic Al-Si alloy to a temperature equal to or higher than the eutectic point and equal to or higher than the liquidus; and a cooling step of applying an electromagnetic force to the molten metal produced by the heating step while cooling the molten metal, thereby segregating primary crystals of the hypereutectic Al-Fe alloy or the hypereutectic Al-Si alloy in a surface layer of the hypereutectic material.

[0008] [2] According to another aspect of the present invention, in the method for producing a hypereutectic material according to [1], in the cooling step, 3 More than 260kN / m 3 It is preferable to apply an electromagnetic force having the following electromagnetic force density to the molten metal.

[0009] "3" According to one aspect of the present invention, there can be provided a method for producing a hypereutectic material, comprising: a heating step of heating a hypereutectic Al-Si alloy to a temperature equal to or higher than the eutectic point and equal to or higher than the liquidus; and a cooling step of applying an electric current to the molten metal produced by the heating step while cooling the molten metal, thereby segregating primary crystals of the hypereutectic Al-Si alloy in the surface layer of the hypereutectic material. [4] In the method for producing a hypereutectic material according to [3], in the cooling step, 2 More than 637kA / m 2 It is preferable to apply a current having the following current density to the molten metal:

[0010] [5] In the method for producing a hypereutectic material according to [1] or [2] above, by applying an electromagnetic force to the molten metal produced by the heating step while cooling the molten metal, primary Al is formed only in the surface layer of the hypereutectic material. 13 Fe4 is segregated, and the primary Al is added to the inside and surface of the hypereutectic material. 13 Eutectic Al finer than Fe4 13 It is preferable to crystallize Fe4.

[0011] [6] In the method for producing a hypereutectic material according to [3] or [4], it is preferable that primary crystal Si is segregated only in the surface layer portion of the hypereutectic material, and that eutectic crystals finer than the primary crystal Si are crystallized inside and in the surface layer portion of the hypereutectic material. [7] In the method for producing a hypereutectic material according to [1] above, in the cooling step, 3 More than 223kN / m 3 It is preferable to apply an electromagnetic force having the following electromagnetic force density to the molten metal. [Effects of the Invention]

[0012] According to the above-described aspects of the present invention, it is possible to provide a method for producing a hypereutectic material having a novel metal structure that has not been seen before. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram showing the relationship between the equilibrium diagram of each alloy and the test temperature. [Figure 2] FIG. 1 is an explanatory diagram showing the arrangement of samples. [Figure 3] (a) is a perspective view showing the state in which the sample is placed between the poles of a permanent magnet (Nd-Fe-B). The left figure in (b) is a graph showing the distribution of the magnitude of the magnetic flux density B when a magnetic field is applied to the sample. The right figure in (b) is a graph showing the magnitude of the magnetic flux density B. [Figure 4] 1 is an image showing the macrostructure of longitudinal cross sections of samples F950-[1], F950-[2], and F950-[3]. [Figure 5] 1 is an image showing the macrostructure of longitudinal cross sections of samples F750-[2], F850-[2], and F950-[2]. [Figure 6A] This is an X-ray CT image of sample F950-[1]. [Figure 6B] This is an X-ray CT image of sample F950-[1]. [Figure 7A] This is an X-ray CT image of sample F950-[2]. [Figure 7B] This is an X-ray CT image of sample F950-[2]. [Figure 8A] This is an X-ray CT image of sample F950-[3]. [Figure 8B] This is an X-ray CT image of sample F950-[3]. [Figure 9] This is a conceptual diagram showing the structure formation process observed in samples F950-[1], F950-[2], and F950-[3]. [Figure 10] These are images showing the macrostructures of samples S950-[1], S950-[2], and S950-[3] in longitudinal sections and arbitrary cross sections. [Figure 11] These are images showing the macrostructures of samples S650-[2], S750-[2], and S850-[2] in longitudinal sections and arbitrary cross sections. [Figure 12] Optical microscope photographs of samples S950-[1], S950-[2] and S950-[3]. [Figure 13] This is an image showing Si mapping by fluorescent X-rays for samples S950-[2] and S950-[3]. [Figure 14] FIG. 1 is an explanatory diagram showing a coupled zone. [Figure 15] These are images showing the macrostructure of samples obtained by conducting experiments with no current, with a current of 80 A applied, and with a current of 100 A applied. [Figure 16] 10 is an image showing the microstructure of a sample obtained by performing an experiment without current. [Figure 17] This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 80 A was applied. [Figure 18] This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 100 A was applied. [Figure 19] The images show the macrostructure of samples obtained by carrying out experiments in which a current of 150 A was applied, a current of 200 A was applied, a current of 250 A was applied, and a current of 300 A was applied. [Figure 20] This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 150 A was applied. [Figure 21]This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 200 A was applied. [Figure 22] This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 250 A was applied. [Figure 23] This is an image showing the microstructure of a sample obtained by conducting an experiment in which a current of 300 A was applied. [Figure 24] (a) is a conceptual diagram showing the appearance of a hypereutectic material, and (b) is a conceptual diagram showing a cross section of the hypereutectic material perpendicular to the longitudinal direction. DETAILED DESCRIPTION OF THE INVENTION

[0014] <1. Investigation by the Inventor> (A. Effect of electromagnetic force on primary crystal segregation phenomenon and solidification structure in Al-10Fe and Al-25Si alloys) First, we will explain the experiments conducted by the inventors and the considerations based on the results. The inventors selected Al-10Fe alloy and Al-25Si alloy as the samples for the experiments. The Al-10Fe alloy is a type of hypereutectic Al-Fe alloy, and the Al-25Si alloy is a type of hypereutectic Al-Si alloy. Here, the values ​​x and y in Al-xFe alloy and Al-ySi alloy indicate the mass percentage of Fe or Si relative to the total mass of the alloy. Practical hypereutectic Al-Si alloys are standardized over a wide composition range. Therefore, depending on the experimental results, hypereutectic Al-Si alloys may lead to new technological developments.

[0015] (1-1. Experimental conditions) The experiments used Al-10Fe alloy and Al-25Si alloy with the compositions shown in Table 1. The values ​​in Table 1 indicate the mass % of each element relative to the total mass of the alloy. The remainder in Table 1 is Al.

[0016] [Table 1]

[0017] Experimental samples were prepared by cutting each alloy ingot into a cylindrical shape with a diameter of 18 mm and a length of 90 mm. The sample was then inserted into a mullite tube with an inner diameter of 20 mm and a length of 120 mm, and both ends of the mullite tube were sealed with graphite electrodes. The mullite tube was oriented vertically with the positive graphite electrode at the bottom (vertical orientation). The positive graphite electrode was fixed to the mullite tube with ceramic adhesive, and the negative graphite electrode was allowed to move up and down to ensure sufficient contact with the molten alloy. A copper clamp was used to fasten the copper plate to each graphite electrode, and the sample was then placed in an electric furnace. The copper plate was connected to a cabtyre cable outside the electric furnace, and the copper plate was connected to a DC stabilized power supply (PR10-300 Matsusada Precision) via the cabtyre cable.

[0018] After the sample in the electric furnace was heated to a predetermined temperature (hereinafter, the predetermined temperature is also referred to as the "test temperature"), the sample was removed from the furnace, and the molten sample was immediately allowed to solidify naturally under the following cooling conditions.

[0019] [1] Cool the sample "as is" (i.e., without applying electromagnetic force) [2] Cool the sample while applying a current of 100A and a magnetic field to it. [3] Cool the sample while applying a current of 130A and a magnetic field to it.

[0020] The test temperatures for the Al-10Fe alloy were 750°C, 850°C, 950°C, or 1050°C. The test temperatures for the Al-25Si alloy were 650°C, 750°C, 850°C, or 950°C. Figure 1 shows the relationship between the equilibrium phase diagram and the test temperature for each alloy. Figure 1(a) shows the relationship between the equilibrium phase diagram and the test temperature for the hypereutectic Al-Fe alloy, and Figure 1(b) shows the relationship between the equilibrium phase diagram and the test temperature for the hypereutectic Al-Si alloy.

[0021] In Figure 1(a), the line L1 indicates the mass percentage of Fe contained in the Al-10Fe alloy (i.e., 10 mass%), and the point P1 indicates the test temperature. L indicates the liquid phase, and L + Al 13 Fe4 is in the liquid phase and primary Al 13 It shows a solid-liquid two-phase state of Fe4, and αAl+Al 13Fe4 is αAl and primary Al 13 This shows the solid phase of Fe4. Curves L2 and L3 show the liquidus line, and point P2 shows the eutectic point.

[0022] In Figure 1(b), the line L4 indicates the mass % of Si contained in the Al-25Si alloy (i.e., 25 mass%), and the point P3 indicates the test temperature. L indicates the liquid phase, L+Si indicates a solid-liquid two-phase state of the liquid phase and primary crystal Si, and αAl+Si indicates a solid phase of αAl and primary crystal Si. The lines L5 and L6 indicate the liquidus line, and the point P4 indicates the eutectic point. In Figure 1(a) and Figure 1(b), the solid-liquid two-phase state refers to the solid-liquid two-phase state of the primary crystal Al. 13 This means that Fe4 or primary crystal Si remains undissolved and is free in the liquid phase (L).

[0023] As shown in Figure 1(a) and Figure 1(b), at each test temperature, the Al-10Fe alloy and the Al-25Si alloy were either completely in the liquid phase (L) or in a solid-liquid two-phase state.

[0024] Under cooling conditions [2] and [3], an electromagnetic force was applied to each sample as follows. A DC current was passed through the sample, and a magnetic field was applied to each sample by placing the sample between the poles of a permanent magnet (Nd-Fe-B) (see Figure 3(a)). The direction of the magnetic field (the direction of magnetic flux density B (bold characters indicate vectors; the same applies below)) was perpendicular to the longitudinal direction of the sample (see Figure 2(a)). The magnitude of the magnetic field was constant (approximately 0.54 T). After cooling to room temperature, the samples were removed from the mullite tubes and subjected to macroscopic observation (visual observation; specifically, the cross-sections of the samples were scanned and the resulting images were visually observed), optical microscopy, and X-ray computed tomography (X-ray CT). Hereafter, Al-10Fe alloy will be referred to as "F" and Al-25Si alloy as "S", and the specimens after cooling treatment will be designated by the symbol "F" or "S" followed by the test temperature and cooling conditions. For example, a specimen obtained using Al-10Fe alloy at a test temperature of 950°C under the cooling conditions [1] will be designated as "F". 950-[1] " is written as follows.

[0025] (1-2. Sample arrangement and direction of electromagnetic force) In this experiment, as mentioned above, the sample was arranged vertically (the sample was arranged so that its longitudinal direction coincided with the vertical direction). Figure 2(a) shows the sample arrangement. In Figure 2(a), B indicates magnetic flux density, J indicates current density, and F indicates electromagnetic force density. Figure 2(b) shows the sample arranged horizontally (the sample was arranged so that its longitudinal direction coincided with the horizontal direction and was perpendicular to the direction of magnetic flux density B). The experimental results will be described later, but similar results were obtained whether the sample was arranged vertically or horizontally.

[0026] Figure 3(a) is a perspective view showing a sample placed between the magnetic poles of a permanent magnet (Nd-Fe-B). The left diagram of Figure 3(b) is a graph showing the distribution of the magnitude of magnetic flux density B when a magnetic field is applied to the sample. The horizontal axis w represents the distance from one end of the magnetic pole in the horizontal direction (the left end in Figure 3(a)), and the vertical axis H represents the distance from the bottom end of the magnetic pole in the vertical direction. The right diagram of Figure 3(b) is a graph showing the magnitude of magnetic flux density B. As shown in Figure 3(b), the magnetic field is applied uniformly to the entire sample.

[0027] The relationship between magnetic flux density B, current density J, and electromagnetic force density F is F = J × B, where "×" indicates the cross product. Under the above-mentioned cooling conditions [2] and [3], an electromagnetic force is applied to the molten metal of the sample. As shown in Figure 2(a), in this experiment, the current density J and magnetic flux density B are perpendicular to each other. Furthermore, the magnitude of the electromagnetic force density F under cooling conditions [2] and [3] is 172 kN / m 3 and 223 kN / m 3 This becomes:

[0028] If the sample in this experiment follows the electromagnetic separation theory, the force F acting on a spherical particle of volume V due to the electromagnetic force density F is P The magnitude of is expressed by the following formula (1).

number

[0029] where σL is the electrical conductivity of the molten metal (molten alloy), and σ P is the electrical conductivity of the solid particles, V is the volume of the solid particles, and F is the magnitude of the electromagnetic force density. 13 Fe4 is an intermetallic compound, and primary crystal Si is a semiconductor, and the electrical conductivity of either at high temperatures is unknown. However, Al in the molten metal is a good conductor, and its electrical conductivity just above the melting point is 4.0 x 10 6 Ω -1 m -1 Therefore, in both the Al-10Fe alloy and the Al-25Si alloy, σ P / σ L Assuming that ≒ 0, primary Al 13 Both Fe4 and primary Si crystals are expected to segregate on the opposite side to the direction of the electromagnetic force density F. For example, if the electromagnetic force density F acts from the right to the left of the sample as seen by the observer, each primary crystal free in the molten metal will be affected by the force F P It is estimated that the electromagnetic force density F is distributed in the opposite direction, i.e., biased towards the right half.

[0030] (1-3. Evaluation of Al-10Fe alloy by X-ray CT) Primary Al in Al-10Fe alloy 13 Fe4 was large enough to be observed macroscopically. 13 Fe4 can be easily observed by X-ray CT because of the density difference between it and αAl. 13 The morphology and distribution of Fe4 were observed using a three-dimensional measurement X-ray CT device (Yamato Scientific Co., Ltd. TDM1000H-II (2K)). The observation conditions were a tube voltage of 100 kV, a tube current of 35 μA, and a helical scan type.

[0031] On the other hand, eutectic Al 13 Fe4 was very fine and difficult to observe. Furthermore, the Si phase in the Al-25Si alloy has a density similar to that of αAl, and the difference in X-ray absorption coefficient is small, so it was not possible to obtain the contrast necessary for X-ray observation for either primary Si or eutectic Si. For this reason, both macroscopic and microscopic observations were performed on the Al-25Si alloy.

[0032] (1-4. Experimental Results and Discussion) (1-4-1. Macrostructure of Al-10Fe alloy) To observe the sample, the sample was first cut along a longitudinal cross section (a cross section parallel to the longitudinal direction of the sample and passing through the central axis in the longitudinal direction (an axis that passes through the center of the cross section perpendicular to the longitudinal direction and is parallel to the longitudinal direction)). The cut surface was then observed. Figure 4 shows the cross section of sample F. 950-[1] , F 950-[2] and F 950-[3] The macrostructure of the longitudinal cross section of sample F is shown. 950-[1] Then, the coarse needle-like primary Al 13 Fe4 was distributed throughout the entire cross section. 950-[2] , F 950-[3] So, primary Al 13 Fe4 was segregated on both edges of the cross section. This tendency was also observed in specimen F, where a larger electromagnetic force was acting. 950-[3] was more pronounced.

[0033] Figure 5 shows sample F 750-[2] , F 850-[2] , and F 950-[2] The macrostructure of the longitudinal cross section of sample F is shown. 750-[2] , F 850-[2] In this study, cooling and application of electromagnetic force were performed from a solid-liquid two-phase state. As is clear from Figure 5, when electromagnetic force was applied to a sample in a solid-liquid two-phase state, the segregation of primary crystals as shown in Figure 4 did not occur.

[0034] From the above, primary Al 13 The segregation of Fe4 occurs due to the force F expressed by equation (1). P The primary crystal Al was isolated in the molten metal. 13 Acting on Fe4, primary Al 13 It is thought that this was not formed by the movement of Fe4.

[0035] (1-4-2. X-ray CT observation of Al-10Fe alloy) X-ray CT was used to measure primary Al 13 The distribution and morphology of Fe4 were investigated. Figures 6A and 6B show the distribution and morphology of Fe4 in sample F. 950-[1]The X-ray CT image of the specimen is shown in Fig. 6A. The scanning directions are the X, Y, and Z axes shown in the figure. The Z axis is perpendicular to the longitudinal cross section of the specimen, the Y axis is parallel to the longitudinal direction of the specimen, and the X axis is perpendicular to both the Y and Z axes (parallel to the radial direction of the specimen). Figure 6A shows the cross-sectional image with the largest area in each direction.

[0036] Macroscopic observation (see Figure 4) shows that primary Al 13 However, the scanned images from each direction showed that the primary Al 13 It was revealed that Fe4 grows from the surface in contact with the inner wall of the mullite tube and graphite electrode (hereinafter also referred to as the "sample surface") toward the center of the sample. Numerous coarse crystals were also observed that crossed the sample. Figure 6B shows the results of a three-dimensional observation of the sample. As is clear from this figure, the three-dimensional observation revealed that primary Al 13 It was confirmed that Fe4 was in the form of plates.

[0037] Figures 7 and 8 show the F 950-[2] and F 950-[3] 7A and 8A, and 7B and 8B are the same as those in FIG. 6. As is clear from these figures, primary Al crystals were observed in all samples. 13 Fe4 grew from the entire surface of the sample toward the center. 950-[1] Compared to primary crystal Al 13 The number of Fe4 crystals was high, the width and length of the crystals were reduced, and the crystal shape changed from plate-like to sword-edge-like. 13 Fe4 was segregated in the surface layer of the sample. This tendency was particularly evident in sample F. 950-[3] This was particularly evident in

[0038] Based on the above observation results, sample F 950-[1] , F 950-[2] and F 950-[3]The process of microstructure formation observed in the experiment is summarized in a conceptual diagram as shown in Figure 9. Figure 9 is a conceptual diagram showing an enlarged portion of a cross section perpendicular to the Z axis (see Figure 6, etc.). In Figure 9, reference numeral 100 indicates the mullite tube, and reference numeral 200 indicates the primary crystals. As shown in Figure 9, in all samples, primary crystal Al was initially formed over the entire surface of the sample. 13 The crystal nuclei of Fe4 are formed, and then the primary crystal Al 13 Fe4 grows toward the center of the sample without being liberated from the surface. 950-[1] So, primary Al 13 The Fe4 crystals are wide and grow over a long distance toward the center of the sample. 950-[2] and F 950-[3] In the case of sample F, a larger number of narrow crystals emerge from the sample surface and grow densely in a narrow area near the sample surface. 950-[3] If the primary volume fraction of each sample is considered to be equal, sample F 950-[2] and F 950-[3] In this case, primary Al was observed in the surface layer of the specimen. 13 Segregation of Fe4 is formed. In this embodiment, unless otherwise specified, the "surface layer" of a sample or the like means the region where the primary crystals exist when the primary crystals segregate (the sample surface and its vicinity). Furthermore, the "interior" of a sample or the like means a portion other than the "surface layer".

[0039] Electromagnetic force is primary Al 13 It is thought that this affects the nucleation and growth of Fe4. The increase in the nucleation frequency due to electromagnetic force causes the primary Al 13 Fe4 may be refined. It is generally known that physical stimulation promotes nucleation. Also, considering the change in crystal width, it is likely that primary Al nucleated on the sample surface. 13 It is possible that the electromagnetic force made it difficult for Fe4 to grow toward the center of the sample. However, in any case, under the experimental conditions, electromagnetic force acts in one direction according to electromagnetic separation theory. Therefore, the reason why the influence of the electromagnetic force was observed across the entire sample surface needs to be investigated.

[0040] (1-4-3. Macroscopic observation of Al-25Si alloy) To observe the macrostructure, the sample was first cut in a longitudinal cross section. Then, the cut surface and an arbitrary cross section (a cross section perpendicular to the longitudinal direction of the sample) were observed. Figure 10 shows the macrostructure of sample S. 950-[1] , S 950-[2] , S 950-[3] The macrostructure of sample S is shown in longitudinal section and arbitrary cross section. 950-[1] In the case of sample S, primary crystal Si is irregularly dispersed in the sample. 950-[2] and S 950-[3] In the case of sample S, segregation was clearly observed at the edge of the cross section. 650-[2] , S 750-[2] , S 850-[2] The figure shows the macrostructure of the specimen S in a longitudinal section and an arbitrary cross section. In other words, the figure shows the relationship between the distribution of primary Si and the test temperature. 650-[2] In the case of sample S, the electromagnetic force was applied from the solid-liquid two-phase state, while in the other samples, the electromagnetic force was applied from the liquid phase state. Comparing the structures of each sample, the segregation of primary Si was found to be 650-[2] It was revealed that this phenomenon is observed only when electromagnetic force is applied from the liquid phase.

[0041] Because it is difficult to observe the Al-25Si alloy using X-ray CT, it was not possible to grasp the three-dimensional morphology of the primary Si crystal in detail. However, from the results described above, it can be concluded that the influence of electromagnetic force is basically limited to the primary Al crystal. 13 This is considered to be the same as in the case of Fe4. In other words, the electromagnetic force is generated by the free primary Al 13 It is speculated that the electromagnetic force does not affect Fe4 or primary Si, but affects their nucleation and crystal growth. Specifically, when electromagnetic force is applied to an Al-10Fe alloy or Al-25Si alloy in a completely liquid state (in other words, heated to a temperature above the eutectic point and above the liquidus), primary Al is formed over the entire surface (or its vicinity). 13 The crystal nuclei of Fe4 or primary Si crystals are formed, and then primary Al crystals are formed. 13 Fe4 or primary Si grows toward the center of the sample without being liberated from the surface, but segregates in the surface layer of the sample. This phenomenon is not observed when electromagnetic force is applied to Al-10Fe alloy or Al-25Si alloy in a solid-liquid two-phase state.

[0042] (1-4-4. Microstructure of Al-25Si alloy) Figure 12 shows the sample S 950-[1] , S 950-[2] and S 950-[3] As shown in the upper right inset of Figure 12, the observation areas were the surface layer A, intermediate region B, and central region C of the cross section of the center of the sample in the longitudinal direction (cross section perpendicular to the longitudinal direction). In this observation, the central region C was defined as a circular region that included the center of the observation area and had a radius of (1 / 3) × r (r is the radius of the observation area), the region of the circular region with a radius of (2 / 3) × r excluding the central region C was defined as the intermediate region B, and the region of the circular region with a radius of r excluding the intermediate region B and central region C was defined as the surface layer A.

[0043] Sample S 950-[1] In sample S, primary crystal Si was observed in all areas: surface area A, middle area B, and center area C. 950-[2] , S 950-[3] In the specimen, primary Si crystals were observed microscopically only in surface layer A. Furthermore, primary Si crystals were densely distributed on the surface of the specimen. This is thought to be the result of primary Si crystals not being liberated from the surface of the specimen, but growing in a narrow area that included the surface. The cross-sectional shapes of the primary Si crystals were rod-like, needle-like, or polygonal, and their sizes varied. In surface layer A, coarse clumps of Si with sides exceeding 1 mm were also observed. This suggests the possibility that adjacent crystals coalesced and grew during solidification.

[0044] Sample S 950-[2] and S 950-[3] In the middle part B and the center part C of sample S, fine eutectic crystals were observed throughout the structure. The eutectic crystals in the center part C near the center were particularly fine, and dendrites that were clearly primary α-Al were also observed. 950-[1] is a typical hypereutectic structure consisting of primary Si and eutectic, while sample S 950-[2] and S 950-[3] In the specimen, eutectic or hypoeutectic structures were observed in a wide range of regions, such as the middle region B and the center region C. These structures are very similar to those improved by rapid solidification or the addition of strontium (Sr).

[0045] Sample S is shown in Fig. 13.950-[2] and S 950-[3] The figure shows the Si mapping by fluorescent X-ray of both samples. In both samples, almost no difference in Si concentration was observed except for the surface layer A, which showed a high concentration of Si, and the middle part B and the center part C were homogeneous in composition. Furthermore, the Si contained within a φ3 mm diameter from the center of the center part C was quantified, and it was found that the Si content of sample S was 950-[2] 15.4 mass% Si, sample S 950-[3] Thus, in the middle part B and the center part C, the Si concentration was higher than the eutectic composition (12.6 mass% Si) shown in the equilibrium diagram, despite the absence of primary Si.

[0046] Kofler has clarified that in organic eutectic systems, a complete eutectic structure is formed from a supercooled liquid over a fairly wide composition range (Non-Patent Document 3). Scheil has also demonstrated this in metallic eutectic systems, calling such a composition range (a composition range in which a complete eutectic structure is formed from a supercooled liquid) the coupled zone (Non-Patent Documents 4 and 5). It has been reported that in the coupled zone, each phase constituting the eutectic has an equal growth rate, and the eutectic forms an ordered layer. For hypereutectic Al-Si alloy systems, a coupled zone such as that shown in Figure 14 has been shown (Non-Patent Document 6). Sample S 950-[2] and S 950-[3] The widespread eutectic and hypoeutectic structures observed in the above are thought to be solidification structures that have undergone a coupled zone (hereinafter also referred to as "undercooled solidification structures").

[0047] In hypereutectic Al-Si alloys, primary Si crystals are the precursor to the eutectic phase (Non-Patent Document 7). Therefore, if primary Si crystals are dispersed in the molten metal, eutectic Si crystals grow from the primary Si crystals without the supercooling required for eutectic nucleation during solidification. On the other hand, if a region without primary Si crystals is formed in the molten metal, supercooling is required for the crystallization of the eutectic crystals in that region. Sample S 950-[2] and S 950-[3]In this experiment, primary Si crystals were segregated in the surface layer A, but were not observed in the middle part B or the center part C. Therefore, it is thought that supercooling occurred in the middle part B and the center part C during the solidification process, resulting in the formation of a supercooled solidification structure. From the results of this experiment, it is difficult to consider the growth process of each phase. However, from the above, for example, in sample S, 950-[2] In this case, it is thought that solidification accompanied by eutectic nucleation newly began when the molten metal composition in the middle part B and the center part C reached 16.5 mass% Si during the solidification process.

[0048] All samples were melted in a mullite tube and then naturally solidified in the atmosphere. The cooling rate from when the sample was removed from the furnace until it reached the eutectic temperature was approximately 1.0°C / s, which is slower than the cooling rate in processes such as mold casting. Furthermore, this experiment used a practical alloy, and as shown in Table 1, the sample also contained a certain amount of impurity elements. Therefore, it is generally unlikely that significant supercooling would occur. From the above, it can be said that the phenomenon of a fine eutectic structure forming in the center and intermediate parts of the sample, where the cooling rate is slower than in the surface layer, is an interesting one.

[0049] (1-4-5. Summary) Through the structural observation of Al-10Fe alloy and Al-25Si alloy solidified under the application of electromagnetic force, primary Al was confirmed in Al-10Fe alloy and Al-25Si alloy. 13 The electromagnetic separation phenomenon of Fe4 and primary Si was verified, and the effect of electromagnetic force on the solidification structure of each alloy was investigated. As a result, the following conclusions were obtained.

[0050] [1] Primary Al in Al-10Fe alloy 13 Not only Fe4 but also primary crystal Si in the Al-25Si alloy segregates over the entire surface area of ​​the sample due to the electromagnetic force. The effect remains the same even if the sample orientation is changed from vertical to horizontal.

[0051] [2] Primary Al 13 The segregation of Fe4 and primary Si is thought to be the result of them growing densely in a narrow area near the surface of the sample without being liberated from the surface.

[0052] [3] The electromagnetic force acts on the primary Al crystals already in the molten metal. 13 It does not affect Fe4 or primary Si, nor does it affect their distribution. The segregation of primary crystals confirmed in this experiment is not due to existing electromagnetic separation theories, but is thought to be a new phenomenon.

[0053] [4] When primary Si crystals segregate to the surface of the molten alloy during solidification due to the application of electromagnetic force, the internal regions (middle and central regions) of the sample that do not contain primary Si crystals exhibit the appearance of a supercooled solidification structure, and fine eutectic crystals with dendritic primary Al crystals are observed. The internal structure of the Al-10Fe alloy has not been investigated in detail. However, since the Al-10Fe alloy and the Al-25Si alloy exhibit similar behavior when subjected to electromagnetic force during cooling, it is inferred that the Al-10Fe alloy has an internal structure similar to that of the Al-25Si alloy.

[0054] (B. Effect of electric current on solidification structure of Al-25Si alloy) The present inventor further investigated the effect of electric current on the solidification structure of Al-25Si alloy. That is, the present inventor suspected that the same behavior as described above would be observed when only electric current, not electromagnetic force, was applied to Al-25Si alloy, and conducted the following investigation.

[0055] (1-5. Experimental conditions) An Al-25Si alloy with the composition shown in Table 1 above was used in the experiment. An Al-25Si alloy ingot was cut into a square bar approximately 20 mm square using a cutting machine. The square bar-shaped ingot was then machined into a round bar with a diameter of 18 mm using a lathe. The cutting feed rate was 580 mm / min. The ingot round bar was then cut into a length of 90 mm using a fine cutter. To remove cutting oil and water that had adhered to the ingot during machining, the resulting round bar was immersed in an acetone solution (concentration 90.0% by mass) for 24 hours and then heated in an electric furnace heated to 400°C for 2 hours. Following these steps, an Al-25Si alloy sample was prepared.

[0056] Next, a graphite electrode was prepared. A graphite rod 100 mm long and 20 mm in diameter was prepared and cut into two 50 mm long rods. The 30 mm long section of each rod was used as a threaded portion for connecting to a heating device.

[0057] Next, a sample fixing device was prepared. A mullite tube (600 mm long, 25 mm outer diameter, 20 mm inner diameter) was cut to a length of 120 mm, and the sample prepared above was inserted into this mullite tube. A diamond cutter was used to cut the mullite tube. Then, both ends of the mullite tube were sealed with graphite electrodes. The unthreaded portion of the graphite electrode was inserted into the mullite tube. The mullite tube was then oriented vertically, and the lower graphite electrode was bonded to the mullite tube with Arlon ceramic. The upper graphite electrode was made movable up and down. After drying the mullite tube at room temperature, it was heated in an electric furnace at 90°C and 150°C for one hour each to harden it. Each graphite electrode was then connected to a stainless steel long nut, completing the sample fixing device. A clearance was provided above and below the upper graphite electrode to ensure that it could contact the sample even if the liquid level dropped as the sample melted.

[0058] The sample fixture was then connected to a DC power supply. Specifically, the graphite electrodes were connected to the stainless steel rods via upper and lower long nuts. These stainless steel rods were then connected to the DC power supply.

[0059] The sample holder was then placed in an electric furnace and heated to a temperature of 950°C, thereby melting the sample. The sample temperature was measured with a radiation thermometer.

[0060] After the sample temperature reached 950°C, the sample holder was removed from the electric furnace, and a current was passed through the sample using a DC power supply. The lower graphite electrode was the positive electrode, and the upper graphite electrode was the negative electrode. In other words, the current was passed upward. The magnitude of the current was as shown in Table 2. 10 minutes after the current began to pass through the sample, the DC power supply was turned off, and the sample was allowed to solidify naturally.

[0061] [Table 2]

[0062] Next, a sample for macrostructure observation was prepared. Specifically, after the experiment, the sample was removed from the sample holder and cut into two pieces along a longitudinal cross section (a cross section parallel to the longitudinal direction of the sample and passing through the longitudinal central axis (an axis parallel to the longitudinal direction and passing through the center of the cross section perpendicular to the longitudinal direction)). A fine cutter was used for cutting. One of the cut samples was used as the sample for macrostructure observation.

[0063] Next, samples for microstructure observation were prepared. The other end of the cut sample was cut into four equal parts in the longitudinal direction using a fine cutter. The cut samples were numbered (1 to 4) in order from the negative electrode side. The cross sections of the positive electrode side of these samples were used for observation.

[0064] Next, the samples for macrostructure observation and the samples for microstructure observation were embedded in resin. Each sample was then roughly polished with emery paper (#120 to #2000). Polishing was performed in order from the lowest grit size to the highest. Polishing with each abrasive paper was performed perpendicular to the polishing marks of the previous grit size, and continued until the previous polishing marks disappeared. A bench polisher (Marumoto Struers S-5629) was used to polish the samples. Next, the samples for microstructure observation were buffed and mirror-finished.

[0065] Next, macrostructure observation and microstructure observation were performed. Specifically, macrostructure observation was performed as follows. Specifically, the sample that had been roughly polished was scanned with a scanner and the structure was observed visually. Specifically, microstructure observation was performed as follows. Specifically, observation was performed at 100x and 1000x magnification using an optical microscope. Specifically, the observation surface was divided into a surface region A, a middle region B, and a center region C in the same manner as in Figure 12, and one region of each region was observed at 100x magnification. Furthermore, the center of the 100x observation region was observed at 1000x magnification.

[0066] (1-6. Experimental Results and Discussion) (1-6-1. Macro organization) Figure 15 shows the macrostructure of the samples obtained in experiments with no current, 80 A current application, and 100 A current application. Under the no-current condition, primary Si was observed uniformly throughout the sample. At 80 A, primary Si segregation to the surface layer was observed, and at 100 A, primary Si segregation to the surface layer was even more pronounced. Comparing these three samples confirmed that primary Si segregation to the surface layer can occur even with the application of DC current alone.

[0067] (1-6-2. Microstructure) Figures 16 to 18 show the microstructures of samples obtained by conducting experiments with no current (Figure 16), with an 80 A current applied (Figure 17), and with a 100 A current applied (Figure 18). The symbols A, B, and C in the figures represent the surface layer A, middle layer B, and center layer C, respectively. The numbers 1 to 4 represent the numbers assigned to the four equal-sized pieces of the sample.

[0068] Both the primary silicon and eutectic silicon had finer structures in the sample cooled with a 100 A DC current applied, compared to the sample cooled without a current (normal solidification) and the sample cooled with an 80 A DC current applied. A 1000x magnification photo of the eutectic portion, which shows the difference in eutectic morphology, clearly shows significant refinement of the eutectic in the sample cooled with a 100 A DC current applied. From the above, it is inferred that there is a correlation between the segregation of primary silicon and refinement of the eutectic.

[0069] (1-6-3. Macrostructure under each current condition) FIG. 19 shows the macrostructures of the samples obtained by carrying out experiments in which a current of 150 A was applied, a current of 200 A was applied, a current of 250 A was applied, and a current of 300 A was applied.

[0070] Comparing 150A and 200A, it was confirmed that the segregation of primary crystals was more pronounced at higher currents. Furthermore, when observing the three samples at 200A or higher, it was confirmed that primary crystals did not segregate at the bottom of the sample, but in the two samples at 250A or higher, primary crystals segregated in the center. Joule heat is thought to be the reason for the segregation in the center. This is thought to be because solidification progressed from the center rather than the top or bottom, as the graphite electrode maintained a high temperature due to Joule heat caused by the high current flow.

[0071] (1-6-4. Microstructure under each current condition) 20 to 23 show the microstructures of the samples obtained by applying a current of 150 A (FIG. 20), 200 A (FIG. 21), 250 A (FIG. 22), and 300 A (FIG. 23) respectively.

[0072] When observing the microstructure under each current condition, it was confirmed that there was a large amount of primary Si in the surface layer A, and that the primary Si was distributed over the entire surface of the sample, covering it. Furthermore, there was no primary Si in the middle part B or the center part C, and the eutectic structure was also refined from the surface part A to the center part C. However, this tendency was more pronounced when electromagnetic force was applied to the Al-25Si alloy.

[0073] (1-7. Summary) Even when only electric current is applied to the Al-25Si alloy, the segregation of primary Si crystals in the surface layer and the crystallization of fine eutectic crystals in the interior are observed. However, this tendency is more pronounced when electromagnetic force is applied to the Al-25Si alloy.

[0074] Although Al-10Fe alloy and Al-25Si alloy were used in the above experiments, it is presumed that other types of hypereutectic Al-Fe alloys and hypereutectic Al-Si alloys will exhibit similar behavior.

[0075] Based on the above findings, the present inventors have come up with the following hypereutectic material and method for producing the same.

[0076] <2.Hypereutectic material> Next, the hypereutectic material according to this embodiment will be described with reference to Fig. 24. Fig. 24(a) is a conceptual diagram showing the appearance of the hypereutectic material, and Fig. 24(b) is a conceptual diagram showing a cross section perpendicular to the longitudinal direction of the hypereutectic material.

[0077] The hypereutectic material 1 includes a hypereutectic Al—Fe alloy or a hypereutectic Al—Si alloy, and preferably is composed of a hypereutectic Al—Fe alloy or a hypereutectic Al—Si alloy.

[0078] A hypereutectic Al-Fe alloy contains 1.8 to 36.5 mass % Fe relative to the total mass of the alloy, for example, an Al-10Fe alloy.

[0079] A hypereutectic Al—Si alloy contains 12 mass % or more and less than 100 mass % of Si relative to the total mass of the alloy. For example, a hypereutectic Al—Si alloy is an Al-25Si alloy.

[0080] There is no particular limitation on the shape of the hypereutectic material 1. Although it is cylindrical in FIG. 1, it may have any shape, such as a square rod.

[0081] Primary crystals of a hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy are segregated in the surface layer portion 10 of the hypereutectic material 1. More specifically, primary crystals of a hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy are segregated throughout the entire surface layer portion 10. As described above, primary crystals of a hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy can be segregated in the surface layer portion 10 by applying an electromagnetic force to a molten hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy (applying only a current is also possible in the case of a hypereutectic Al-Si alloy). This allows the surface layer portion 10 of the hypereutectic material 1 to have the properties of the primary crystals. Furthermore, if the primary crystals are not required, they can be easily removed. For example, primary crystal Si has excellent sliding resistance and wear resistance, so the hypereutectic material 1 made of a hypereutectic Al-Si alloy may be used in devices (e.g., pistons) that require these properties.

[0082] The primary crystals of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy grow from the surface of the hypereutectic material 1 toward the center of the hypereutectic material 1. The primary crystals of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy have a shape, for example, sword-shaped, rod-shaped, needle-shaped, or polygonal, and are distributed finer and more densely in the surface layer portion 10 (than in the case where no electromagnetic force is applied to the molten metal).

[0083] On the other hand, a eutectic of a hypereutectic Al-Fe alloy or a hypereutectic Al-Si alloy is distributed in the interior 20 of the hypereutectic material 1. As described above, by applying an electromagnetic force to the molten hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy (in the case of a hypereutectic Al-Si alloy, application of only a current is also possible), the eutectic of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy can be distributed in the interior 20.

[0084] It is preferable that the eutectic be as fine as possible. For example, it is preferable that the eutectic be smaller than that of a hypereutectic material produced by a manufacturing method similar to that of the hypereutectic material according to this embodiment, except that no electromagnetic force is applied to the molten hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy. This allows the hypereutectic material 1 to be endowed with ductility and plastic deformability.

[0085] As described above, the metal structure of the hypereutectic material 1 can be identified by macrostructure observation, microstructure observation, and X-ray CT observation.

[0086] According to this embodiment, it is possible to provide a hypereutectic material having a new metal structure that has not been seen before.

[0087] <3. Method for manufacturing hypereutectic materials> Next, an example of a method for producing a hypereutectic material will be described. In the method for producing a hypereutectic material according to this embodiment, first, an ingot of a hypereutectic Al-Fe alloy or a hypereutectic Al-Si alloy is prepared. Next, this ingot is cut into a desired shape (for example, the cylindrical shape described above). Next, the cut ingot is placed in a manufacturing vessel. This manufacturing vessel has a hollow structure with open top and bottom. It is preferable that the manufacturing vessel does not react with the hypereutectic Al-Fe alloy or the hypereutectic Al-Si alloy in the manufacturing process described below. An example of a manufacturing vessel is the mullite tube described above.

[0088] Next, the opening of the manufacturing vessel is sealed with electrodes, and each electrode is connected to a DC power supply. Next, the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy is heated to a temperature above the eutectic point and above the liquidus. In other words, the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy is heated until it reaches the liquid phase (L) in the equilibrium diagram (heating step).

[0089] Next, the molten metal produced in the heating step is cooled while an electromagnetic force is applied to the molten metal, causing primary crystals of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy to segregate at the surface layer of the hypereutectic material (cooling step). In the case of a hypereutectic Al-Si alloy, only current may be applied. Through the above steps, the hypereutectic material 1 according to this embodiment can be produced.

[0090] The specific magnitude of the electromagnetic force or current applied to a hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy is thought to vary depending on the composition of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy. Therefore, a test piece of a hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy may be prepared, and the method for manufacturing a hypereutectic material according to this embodiment may be applied to this test piece to determine the specific magnitude of the electromagnetic force (or current) at which the primary crystals segregate to the surface layer. The greater the electromagnetic force or current, the more pronounced the segregation of the primary crystals and the refinement of the eutectic crystals tend to occur.

[0091] An example of the specific magnitude of electromagnetic force is 51.5 kN / m 3 More than 260kN / m3 The electromagnetic force densities are as follows: Note that the electromagnetic force density refers to the electromagnetic force acting per unit volume of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy. 3 If it is smaller, segregation of primary crystals may not occur. 3 If the current density is larger than this, the electrode will heat up, which may have a negative effect on the metal structure of the hypereutectic material. When applying only current to a hypereutectic Al-Si alloy, the current density must be 255 kA / m 2 More than 637kA / m 2 The current density means the current flowing per unit area of ​​a cross section perpendicular to the direction in which the current flows.

[0092] According to the method for producing a hypereutectic material according to this embodiment, the hypereutectic material 1 can be produced simply by applying an electromagnetic force (or current) to a molten metal of a hypereutectic Al-Fe alloy or a hypereutectic Al-Si alloy, and therefore the hypereutectic material 1 can be easily produced. In particular, in the case of a hypereutectic Al-Si alloy, the hypereutectic material 1 can be produced by applying only a current, which allows for simplification of the production equipment. [Example]

[0093] Next, an example of this embodiment will be described. In this example, the effects of this embodiment were confirmed by conducting the following experiment. First, ingots of Al-10Fe alloy and Al-25Si alloy having the compositions shown in Table 1 were prepared.

[0094] Experimental samples were then prepared by cutting each alloy ingot into a cylindrical shape with a diameter of 18 mm and a length of 90 mm. The sample was then inserted into a mullite tube with an inner diameter of 20 mm and a length of 120 mm, and both ends of the mullite tube were sealed with graphite electrodes. The mullite tube was oriented vertically with the positive graphite electrode at the bottom (vertical orientation). The positive graphite electrode was fixed to the mullite tube with ceramic adhesive, and the negative graphite electrode was allowed to move up and down to ensure sufficient contact with the molten alloy. The copper plate and each graphite electrode were fastened together using copper clamps, and the sample was then placed in an electric furnace. The copper plate was connected to a cabtyre cable outside the electric furnace, and the copper plate was connected to a DC stabilized power supply (PR10-300 Matsusada Precision) via the cabtyre cable.

[0095] Next, the sample in the electric furnace was heated to 950°C (test temperature), then removed from the furnace, and the molten sample was immediately cooled. During cooling, a current of 100A and a magnetic field of 0.54T were applied to the sample.

[0096] Next, after cooling the sample to room temperature, the sample was removed from the mullite tube and subjected to macroscopic structural observation (visual observation; specifically, the cross section of the sample was scanned and the resulting image was visually observed), optical microscopic structural observation, and X-ray computed tomography (X-ray CT). As a result, the metal structures shown in Figures 4, 7, 10, and 12 were observed. For the Al-25Si alloy, similar results were obtained when only current was applied. Details are as described above in <1. Investigation by the Inventor>.

[0097] Furthermore, when no electromagnetic force was applied to the molten Al-10Fe alloy, when the test temperature for the Al-Fe alloy was set to 850°C, and when the test temperature for the Al-25Si alloy was set to 650°C, no segregation of primary crystals was observed.

[0098] From the above results, it has become clear that by applying an electromagnetic force (or current) to a molten hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy, primary crystals of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy can be segregated in the surface layer of the hypereutectic material, and the eutectic can be distributed inside the hypereutectic material. In other words, it has become clear that the hypereutectic material 1 according to this embodiment can be produced. [Explanation of symbols]

[0099] 1 Hypereutectic material 10 Surface layer 20 internal

Claims

1. 1. A method for producing a hypereutectic material, comprising: a heating step of heating the hypereutectic Al—Fe alloy or hypereutectic Al—Si alloy to a temperature equal to or higher than the eutectic point and equal to or higher than the liquidus; a cooling step of applying an electromagnetic force to the molten metal produced by the heating step while cooling the molten metal, thereby segregating primary crystals of the hypereutectic Al-Fe alloy or hypereutectic Al-Si alloy in a surface layer portion of the hypereutectic material.

2. In the cooling step, 51.5 kN / m ３ More than 260kN / m ３ 2. The method for producing a hypereutectic material according to claim 1, wherein an electromagnetic force having an electromagnetic force density of the following is applied to the molten metal:

3. 1. A method for producing a hypereutectic material, comprising: a heating step of heating the hypereutectic Al-Si alloy to a temperature equal to or higher than the eutectic point and equal to or higher than the liquidus; and a cooling step of applying an electric current to the molten metal produced by the heating step while cooling the molten metal, thereby segregating primary crystals of the hypereutectic Al-Si alloy in a surface layer of the hypereutectic material.

4. In the cooling step, 255 kA / m ２ More than 637kA / m ２ 4. The method for producing a hypereutectic material according to claim 3, wherein a current having a current density of:

5. By applying an electromagnetic force to the molten metal generated by the heating step while cooling the molten metal, primary Al is formed only in the surface layer of the hypereutectic material. １３ Fe ４ and the primary crystal Al is segregated in the interior and surface layer of the hypereutectic material. １３ Fe ４ Eutectic Al finer than １３ Fe ４ 3. The method for producing a hypereutectic material according to claim 1, wherein the following is crystallized:

6. 5. The method for producing a hypereutectic material according to claim 3, wherein primary crystal Si is segregated only in the surface layer of the hypereutectic material, and eutectic crystals finer than the primary crystal Si are crystallized inside and in the surface layer of the hypereutectic material.

7. In the cooling step, 172 kN / m ３ More than 223kN / m ３ 2. The method for producing a hypereutectic material according to claim 1, wherein an electromagnetic force having an electromagnetic force density of the following is applied to the molten metal:

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