JP7592186B2 - Method for manufacturing semi-solidified slurry, method for manufacturing compact, and compact - Google Patents

Description

The present invention relates to a method for producing a semi-solidified slurry, a method for producing a molded body, and the molded body.

In a method for producing a semi-solidified slurry of metal consisting of a solid phase and a liquid phase, Patent Document 1 discloses a technology in which multiple rods are swirled and rotated (spinned) within molten metal to produce a semi-solidified slurry.

JP 2018-15771 A

In the prior art, the molten metal is stirred by rotating and swiveling a rod (spinning), but the solid and liquid phases do not mix sufficiently, resulting in variations in the solid phase ratio at different parts of the resulting semi-solidified slurry.

The present invention has been made to solve this problem, and aims to provide a method for manufacturing a semi-solidified slurry that can reduce the variation in solid phase ratio from one part of the semi-solidified slurry to another, a method for manufacturing a molded body that can reduce the variation in crystal grain size, and a molded body.

To achieve this objective, the method for producing a semi-solidified slurry of the present invention includes a preparation step of putting molten metal into a bottomed vessel, and a stirring step of stirring the molten metal by reciprocating a rod immersed in the molten metal in the longitudinal direction of the rod until the solid fraction in the lowest solid fraction part of the molten metal in the vessel reaches 80% or more.

The method for producing a molded body of the present invention includes a molding step in which a semi-solidified slurry is obtained by the above-mentioned method for producing a semi-solidified slurry, and then the semi-solidified slurry is pressurized, deformed, and molded.

In the molded product of the present invention, when the longest line segment among the line segments connecting two points of the outline projected onto a plane perpendicular to the pressure direction is drawn, and the cross section of the sample is obtained by cutting each portion along a plurality of cut planes that intersect the longest line segment perpendicularly to the line segment and divide the line segment into six equal parts, the eutectic area ratio, which is the ratio of the area of the eutectic appearing in a predetermined cross-sectional field to the area of the field, is measured for each field. The coefficient of variation, obtained by dividing the standard deviation of the eutectic area ratio by the average value of the eutectic area ratio, is 0.15 or less.

According to the method for producing a semi-solidified slurry of claim 1, in the stirring step, a rod inserted in the molten metal is reciprocated in the length direction of the rod to stir the molten metal, so that the solid and liquid phases can be homogeneously stirred when the molten metal solidifies, even if the solid fraction is high. Furthermore, the molten metal is stirred until the solid fraction in the part with the lowest solid fraction reaches 80% or more, so that the liquid phase portion that solidifies and grows into a solid phase is reduced, while the variation in the distribution of the liquid phase around the solid phase is reduced. This reduces the variation in the solid fraction for each part of the obtained semi-solidified slurry, and further reduces the variation in the size of the crystal grains.

According to the method for producing a semi-solidified slurry described in claim 2, in the method for producing a semi-solidified slurry described in claim 1, the position perpendicular to the length direction of the rod when the rod reciprocates is different from the previous position, so that the solid phase and liquid phase when the molten metal solidifies can be easily mixed homogeneously at multiple positions perpendicular to the length direction of the molten metal rod. This makes it possible to further reduce the variation in the solid phase ratio at each part of the obtained semi-solidified slurry.

According to the method for producing a semi-solidified slurry described in claim 3, in the method for producing a semi-solidified slurry described in claim 1 or 2, in a cross section perpendicular to the longitudinal direction of the rods, the rods are present at intervals from each other, and the center of one of the two adjacent rods is located within a circle whose radius is 7 times the thickness of the other rod and whose center is the center of the other rod. Therefore, the reciprocating motion of the rods affects the molten metal between the rods, making it easy to homogeneously mix the solid and liquid phases as the molten metal solidifies. This further reduces the variation in the solid phase ratio for each part of the obtained semi-solidified slurry.

According to the method for producing a semi-solidified slurry described in claim 4, in the method for producing a semi-solidified slurry described in any one of claims 1 to 3, an electromagnetic stirring step is provided prior to or simultaneously with the stirring step, so that the crystal grain size of the resulting semi-solidified slurry can be further reduced by the electromagnetic stirring step.

According to the method for producing a molded body described in claim 5, a semi-solidified slurry having small variations in solid fraction and small variations in crystal grain size from one part to another can be obtained by the method for producing a semi-solidified slurry described in any one of claims 1 to 4. This semi-solidified slurry is pressurized, deformed, and molded, so that a molded body having stable yield strength can be obtained in every part.

According to the molded body of claim 6, when the longest line segment among the lines connecting two points of the outline projected onto a plane perpendicular to the pressure direction is drawn, and the cross section of the sample is obtained by cutting each portion along a plurality of cut planes that intersect perpendicularly to the line segment and divide the line segment into six equal parts, and the eutectic area ratio, which is the ratio of the area of the eutectic appearing in a visual field on a predetermined cross section to the area of the visual field, is measured for each visual field, the coefficient of variation of the eutectic area ratio of the molded body is 0.15 or less, so that the variation in the yield strength, which is correlated with the eutectic area ratio, for each portion can be reduced. Thus, a molded body having stable yield strength can be obtained in every portion.

(a) is a cross-sectional view of the vessel when the rod is out of the molten metal, and (b) is a cross-sectional view of the vessel when the rod is immersed in the molten metal. 1(a) is a cross-sectional view of the vessel when the rod is out of the molten metal at a horizontal position different from that in FIG. 1(a), and FIG. 1(b) is a cross-sectional view of the vessel when the rod is immersed in the molten metal at a horizontal position different from that in FIG. 1(b). 2(a) is a cross-sectional view of the vessel taken along line IIIa-IIIa in FIG. 1(b), and FIG. 2(b) is a cross-sectional view of the vessel taken along line IIIb-IIIb in FIG. 2(b). FIG. 4A is a perspective view of a semi-solidified slurry, and FIG. 4B is a cross-sectional view of the semi-solidified slurry as viewed from the arrow IVb in FIG. FIG. 2 is a schematic diagram showing the movement of a solid phase and a liquid phase in a molten metal during a stirring process. 1A is a perspective view of a molded body, and FIG. 1B is a projection of the molded body drawn on a plane perpendicular to line A in FIG. FIG. 13 is a diagram showing the relationship between the stirring method and the solid fraction. FIG. 1 is a diagram showing the relationship between the stirring method and the eutectic area ratio.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. A method for producing a semi-solidified slurry 40 and a method for producing a molded body 100 in one embodiment will be described with reference to Figs. 1(a) to 4. Fig. 1(a) is a cross-sectional view of the vessel 20 when the rod 30 is sticking out of the molten metal 10. Fig. 1(b) is a cross-sectional view of the vessel 20 when the rod 30 is in the molten metal 10. In Figs. 1(a) and 1(b), the up-down direction, the left-right direction, and the direction perpendicular to the plane of the paper are respectively referred to as the up-down direction, the left-right direction, and the front-rear direction of the vessel 20 (the same applies to Figs. 2(a), 2(b), and 5(a) to 5(d)).

As shown in Fig. 1(a), molten metal 10 is placed in a vessel 20 with a bottom. The molten metal 10 is a molten metal, such as an aluminum alloy, a magnesium alloy, a copper alloy, or an iron alloy. The molten metal 10 may be a mixture of molten metal and powder or _fiber . Examples of the powder or fiber material include ceramics such as SiC and _Al2O3 , and carbon. In a preparation process, the molten metal 10 is poured from a spout of a high-temperature furnace (not shown) capable of maintaining a molten state, or a container is placed in the furnace and poured from the container into the vessel 20, so that the molten metal 10 is placed in the vessel 20.

The metal is preferably a heat-treatable alloy whose mechanical properties (particularly yield strength) are improved by solution treatment and aging treatment. Examples of the metal include heat-treatable alloys of the A6000 series of aluminum alloys, A6051 and A6061, and the A2000 series of A2011, A2017, A2618, and A7000. The metal may be based on a system such as magnesium alloy Mg-Zn(-Zr) (ZK series), Mg-Zn-Cu (ZC series), Mg-Zn-RE (ZE and EZ series; RE here means rare earth element), Mg-Zn-Mn(-Al) (ZM series), Mg-Al-Zn(Mn) (AZ and AM series), Mg-Y-RE(-Zr) (WE series), Mg-Ag-RE(-Zr) (QE and EQ series), Mg-Sn(-Zn,Al,Si)-based alloy, etc. In addition, the metal may be a copper alloy or an iron alloy. In this embodiment, the metal is a heat-treated alloy of aluminum.

The vessel 20 may be made of either metal or nonmetal, so long as it has high-temperature strength against the temperature of the molten metal 10 and does not react with the molten metal 10. The vessel 20 is open at the top, has a bottom 21 at the bottom, and has a rectangular cross section perpendicular to the up-down direction. In the left-right and front-to-back directions (hereinafter referred to as the "horizontal direction") of the vessel 20, planar walls 22 are arranged to the right, left, front, and rear, and are connected to each other. The lower end of each wall 22 is connected to the respective horizontal end of the bottom 21.

A plurality of rods 30 are connected to one surface of the base 32 at intervals. The tip of the rod 30 opposite to the tip connected to the base 32 has a pointed cone-shaped tip 31. The cross-sectional shape of the rod 30 may be a circle, ellipse, square, triangle, polygon, or star. A circular shape with few protruding parts on the outside is preferable for the cross-sectional shape of the rod 30.

The rods 30 are arranged parallel to one another. The length of the rods 30 is set to be longer than the distance from the liquid surface 11 of the molten metal 10 in the vessel 20 to the bottom 21 of the vessel 20. In the preparation process, the rods 30 are outside the liquid surface 11 of the molten metal 10.

The rod 30 is made of a metal or nonmetallic material that can withstand the temperature of the molten metal 10. At least the surface of the rod 30 is coated with a coating such as DLC (diamond-like carbon). The coating prevents the rod 30 from being worn down due to friction with the molten metal 10 and prevents the molten metal 10 from adhering to it.

1(b), in the stirring process, the molten metal 10 is inserted into the vessel 20 immediately after it is placed therein, or after the vessel 20 is held (exposed) to the atmosphere, vacuum, or inert gas such as argon gas or nitrogen gas for a predetermined time after it is placed therein, and then the rod 30 is inserted from the liquid surface 11 of the molten metal 10 toward the bottom 21 (downward) of the vessel 20. The rod 30 is then moved back and forth in the length direction of the rod 30 to stir the molten metal 10. The predetermined time for holding the molten metal 10 in the atmosphere, vacuum, or inert gas is appropriately set depending on the amount of molten metal 10, the type of metal in the molten metal 10, the shape and size of the vessel 20, the atmospheric temperature of the atmosphere, vacuum, or inert gas, etc.

Figure 2(a) is a cross-sectional view of the vessel 20 when the rod 30 is out of the molten metal 10 at a horizontal position different from that in Figure 1(a), and Figure 2(b) is a cross-sectional view of the vessel 20 when the rod 30 is in the molten metal 10 at a horizontal position different from that in Figure 1(b).

The horizontal position of rod 30 in Figure 2(a) is a position moved to the right by a distance a from the horizontal position of rod 30 in Figure 1(a). As shown in Figure 1(b), rod 30 is once inserted toward the bottom 21 of vessel 20, and then rises from the bottom 21 of vessel 20 toward the liquid surface 11 of molten metal 10, returning to the position of rod 30 in Figure 1(a). Then, as shown in Figure 2(a), rod 30 moves to the right by a distance a.

Next, as shown in Figure 2(b), the rod 30 is moved a distance a to the right and then inserted from the horizontal position from the surface 11 of the molten metal 10 toward the bottom 21 of the vessel 20. After that, the rod 30 rises further from the bottom 21 of the vessel 20 toward the surface 11 of the molten metal 10, returning to the position of the rod 30 in Figure 2(a).

Figure 3(a) is a cross-sectional view of vessel 20 taken along line IIIa-IIIa in Figure 1(b), and Figure 3(b) is a cross-sectional view of vessel 20 taken along line IIIb-IIIb in Figure 2(b). In Figures 3(a) and 3(b), the up-down direction, left-right direction, and perpendicular direction to the paper correspond to the front-rear, left-right, and up-down directions of vessel 20, respectively. In Figure 3(b), the dotted lines show four representative cross sections of the multiple rods 30 in Figure 3(a), and indicate the position before moving horizontally a distance a.

As shown in Figure 3(a), in a cross section perpendicular to the longitudinal direction of the rods 30, multiple rods 30 are present with a gap between them. The center of one of the two adjacent rods 30 is located within a circle whose radius is a length L2 that is 7 times the thickness L1 of the other rod 30 and whose center is the center of the other rod 30. The thicknesses of the adjacent rods 30 may be different or the same.

Distance a is a variable value (a value including the same magnitude) whose magnitude changes with each reciprocating motion of rod 30. The direction in which distance a operates also changes with each reciprocating motion of rod 30, either left and right, front and back, or both. Therefore, in the stirring process, rod 30 can perform reciprocating motion at a horizontal position different from the previous reciprocating motion, making it easier to homogeneously stir solid phase 50 (described later) and liquid phase 60 (described later) when molten metal 10 solidifies at multiple horizontal positions of molten metal 10.

The rod 30 repeats the reciprocating motion shown in Figures 1(a) to 3(b) until the solid fraction of any part of the molten metal 10 becomes 80% or more. Note that "until the solid fraction of any part of the molten metal 10 becomes 80% or more" means that the solid fraction of the part of the molten metal 10 with the lowest solid fraction becomes 80% or more.

Figure 4(a) is a perspective view of the semi-solidified slurry 40, and Figure 4(b) is a cross-sectional view of the semi-solidified slurry 40 shown in the arrow IVb of Figure 4(a). The semi-solidified slurry 40 in Figure 4(a) is the semi-solidified slurry 40 that is taken out of the vessel 20 by stirring the molten metal 10 in the stirring process and then reversing the up-down direction. In the semi-solidified slurry 40, a solid phase 50 and a liquid phase 60 coexist.

4(a) and 4(b), the solid fraction of the molten metal 10 after the stirring process, i.e., the semi-solidified slurry 40, can be obtained by taking out the semi-solidified slurry 40 from the vessel 20 immediately after the stirring process, quenching it in water, and observing 15 cross sections with a metallurgical microscope (200x). The 15 cross sections of the semi-solidified slurry 40 are 15 cross sections in total, including the upper part 41, the central part 42, and the lower part 43 of the semi-solidified slurry 40, which are in contact with the wall 22 of the vessel 20 at three points from the top to the bottom, namely, the wall side parts 44, 44, the middle part 45, 45, and the central part 46. The part that has been quenched and solidified is the liquid phase 60 of the semi-solidified slurry 40. The solid fraction (%) can be obtained by dividing the area of the solid phase 50 that appears in the field of view on the cross section by the area of the field of view and multiplying it by 100 in each of the 15 cross sections. The field of view is a rectangular area 450 μm long and 600 μm wide.

The solid fraction of the molten metal 10 in the stirring process can be determined, for example, by creating a graph in advance showing the correlation between the kinetic viscosity of the molten metal 10 and the solid fraction, providing a viscosity meter on the rod 30, and measuring the kinetic viscosity of the molten metal 10 during stirring, thereby obtaining a semi-solidified slurry 40 with a desired solid fraction. Also, a graph showing the correlation between stirring time and the solid fraction can be created in advance, and stirring can be performed until the time at which the desired solid fraction is obtained from the graph, thereby obtaining a semi-solidified slurry 40 with a desired solid fraction.

The tip 31 is positioned with its pointed end facing away from the liquid surface 11 of the molten metal 10 toward the bottom 21 of the vessel 20. Because the tip 31 is pointed, it is easy to insert the rod 30 into the molten metal 10 even when the molten metal 10 has a high solid fraction of 80% or more.

In the stirring process, the center of one of the two adjacent rods 30 is located within a circle whose radius is a length L2 that is 7 times the thickness L1 of the other rod 30 and whose center is the center of the other rod 30, and the two rods are stirred until the solid fraction reaches a high solid fraction of 80% or more. Therefore, even if the distance from the center to the center of the adjacent rods 30 is long, the molten metal 10 between them can be sufficiently stirred.

Next, the movement of the solid phase 50 and liquid phase 60 in the molten metal 10 during the stirring process will be described with reference to Figures 5(a) to 5(d). Figure 5(a) is a schematic diagram of the molten metal 10 entering the vessel 20 during the preparation process. Figure 5(b) is a schematic diagram showing the state of the molten metal 10 when the rod 30 is inserted into the molten metal 10 during the stirring process. Figure 5(c) is a schematic diagram showing the state of the molten metal 10 a predetermined time after Figure 5(b). Figure 5(d) is a schematic diagram showing the state of the molten metal 10 a further predetermined time after Figure 5(c).

In Figures 5(a) to 5(d), the solid phase 50 represented by a square and the liquid phase 60 represented by a triangle are schematic representations of the distribution of the solid phase 50 and the liquid phase 60 in the molten metal 10. In Figures 5(a) to 5(d), the portion of the liquid surface 11 of the molten metal 10 where there is a large amount of solid phase 50 is omitted. In Figures 5(b) to 5(d), in order to simplify the drawings, all but one of the rods 30 are omitted.

As shown in FIG. 5(a), the molten metal 10 poured from the furnace into the vessel 20 is cooled from the portion closer to the wall 22 and bottom 21 of the vessel 20 than the horizontal center portion of the vessel 20, and a first layer 70 containing more solid phase 50 is formed from the portion closer to the wall 22 and bottom 21 of the vessel 20. A second layer 80 containing more liquid phase 60 than the first layer 70 is formed inside the first layer 70. A third layer 90 containing more liquid phase 60 than the second layer 80 is formed further inside the second layer 80, including the horizontal center portion of the vessel 20. All of the first layer 70 to the third layer 90 include the vicinity of the liquid surface 11 of the molten metal 10 (excluding the portion of the liquid surface 11 of the molten metal 10 where the solid phase 50 is abundant). Note that the boundary between the first layer 70 and the second layer 80 and the boundary between the second layer 80 and the third layer 90 are not clearly defined, but a boundary line is provided for the purpose of explanation.

As shown in FIG. 5B, the rod 30 is inserted from the liquid surface 11 toward the bottom 21 while displacing the solid phase 50 and liquid phase 60 in the molten metal 10 to the outside of the rod 30. The displaced solid phase 50 and liquid phase 60 are present around the rod 30.

Next, as shown in Figure 5(c), when the rod 30 is raised from the bottom 21 of the molten metal 10 toward the liquid surface 11, the liquid phase 60, which has higher fluidity and is easier to move than the solid phase 50, flows into the part of the molten metal 10 where the rod 30 was before the solid phase 50. The liquid phase 60 flows in greater quantity and faster than the solid phase 50 into the part closer to the bottom 21 where the rod 30 was, so the molten metal 10 with more liquid phase 60 moves to the part closer to the bottom 21.

After that, as shown in Fig. 5(d), the molten metal 10 containing a large amount of liquid phase 60 flows into the area where the rod 30 was present, followed by the molten metal 10 containing a large amount of solid phase 50. The solid phase 50 of the first layer 70, where a large amount of solid phase 50 was present, is pushed aside, and the molten metal 10 containing a large amount of liquid phase 60 can be poured into that area, so that the solid phase 50 and the liquid phase 60 can be easily mixed.

The molten metal 10 with a large amount of liquid phase 60 that has moved to the first layer 70 is located in the first layer 70 closer to the wall 22 and bottom 21 than the second layer 80 and third layer 90, and is therefore more likely to cool and become a solid phase 50. The molten metal 10 with a large amount of liquid phase 60 that was present in the second layer 80 and third layer 90, which are less likely to become a solid phase 50, moves to the first layer 70, which is more likely to become a solid phase 50, and can be homogeneously turned into a solid phase 50 without leaving any part with a large amount of liquid phase 60. Thus, a semi-solidified slurry 40 with little variation in the solid phase ratio from part to part can be obtained.

In the stirring process, the molten metal 10 is stirred by reciprocating movement of the rod 30 until the solid phase ratio becomes 80% or more, so that the amount of liquid phase 60 present around the solid phase 50 is reduced while the variation in the distribution of the liquid phase 60 around the solid phase 50 is reduced. The liquid phase 60 with small distribution variation uses the nearby solid phase 50 as a nucleus to further grow the solid phase 50, so the variation in the size of the particles (crystal grains) of the solid phase 50 can be reduced.

In an embodiment, the speed of the reciprocating motion of the rod 30 depends on the magnitude of the reciprocating motion, but is preferably, for example, 200 mm/sec-300 mm/sec, with two or more reciprocating motions per second. Because two or more reciprocating motions are performed per second, the negative pressure generated in the area where the rod 30 was present when the rod 30 rises from the bottom 21 of the molten metal 10 toward the liquid surface 11 is increased compared to when the speed is slower, promoting the flow of the solid phase 50 and liquid phase 60. This shortens the stirring time.

The horizontal position at which the rod 30 reciprocates is different from the horizontal position of the previous reciprocating motion, so the effect of the reciprocating motion can be obtained at multiple different horizontal positions within the molten metal 10. At any horizontal position of the molten metal 10, the solid phase 50 and the liquid phase 60 tend to mix, and the distribution of the solid phase 50 and the liquid phase 60 within the semi-solidified slurry 40 tends to be homogenous. This makes it possible to reduce the variation in the solid phase ratio for each part of the semi-solidified slurry 40.

The surface temperature of the rod 30 before it comes into contact with the molten metal 10 is lower than that of the molten metal 10. Therefore, the molten metal 10 that comes into contact with the surface of the rod 30 tends to solidify quickly. Since there is almost no difference in the surface temperatures of multiple rods 30, the molten metal 10 near the horizontal center of the vessel 20 and the molten metal 10 near the wall 22 of the vessel 20 are cooled regardless of the distance to the wall 22 of the molten metal 10. This reduces the variation in the solid phase ratio from one part to another.

During the stirring process, when the rod 30 is raised from the bottom 21 of the vessel 20 toward the liquid surface 11 of the molten metal 10 during the reciprocating motion of the rod 30, at least a portion of the rod 30 is exposed to the atmosphere, etc., and the rod 30 is cooled. When the part of the rod 30 exposed to the atmosphere, etc. and the cooled part come into contact with the molten metal 10, it promotes the generation of a solid phase 50. Therefore, the time required for the molten metal 10 to solidify can be shortened.

In the stirring process, when the rod 30 is raised from the bottom 21 of the vessel 20 toward the liquid surface 11 of the molten metal 10 during the reciprocating motion of the rod 30, the rod 30 has a small portion protruding from its outer shape, so the molten metal 10 is less likely to adhere to the rod 30. Therefore, a semi-solidified slurry 40 with a stable volume can be repeatedly obtained. In the stirring process, the rod 30 may be vibrated while reciprocating. In this case, when the rod 30 is raised from the bottom 21 of the vessel 20 toward the liquid surface 11 of the molten metal 10, the vibration makes it even more difficult for the molten metal 10 to adhere to the rod 30. The direction of vibration is preferably the length direction of the rod 30. Even if the molten metal 10 adheres to the rod 30, the adhering molten metal 10 can be easily blown off with air or the like. After the preparation process, an electromagnetic stirring process for electromagnetically stirring the molten metal 10 may be performed before the stirring process or simultaneously with the stirring process. When electromagnetic stirring is performed prior to the stirring step, it is preferable to perform the stirring step immediately after the electromagnetic stirring step.

Electromagnetic stirring reduces the size of the particles (crystal grains) of the solid phase 50 in the resulting semi-solidified slurry 40. Reducing the size of the particles of the solid phase 50 increases the area of contact between the solid phase 50 and the liquid phase 60, allowing more eutectic to crystallize between the solid phases 50.

The resulting semi-solidified slurry 40 is then placed in a mold from the vessel 20. The mold is closed and pressure is applied to the semi-solidified slurry 40 to deform the semi-solidified slurry 40 and form a green body 100 (described below). The mold is opened and the green body 100 is removed. The green body 100 is then subjected to solution treatment and artificial aging treatment (collectively referred to as "T6 treatment").

During molding, the liquid phase 60 of the semi-solidified slurry 40 is divided into a portion that exists around the primary crystal (solid phase 50) and grows the primary crystal, and a portion that becomes a eutectic containing the components of the primary crystal (solid phase 50) and other elements. The eutectic portion contains elements of the primary crystal and elements different from the primary crystal. Since a certain amount of elements other than the primary crystal are present around the primary crystal in the eutectic, when the molded body 100 is molded and the obtained molded body 100 is subjected to solution treatment and aging treatment, a precipitation phase, which is a strengthening mechanism, precipitates (generates) around the primary crystal. When the precipitation phase is generated, the movement of the primary crystal due to slip between particles is suppressed by the precipitation phase, improving the mechanical properties (especially the yield strength) of the molded body 100.

The obtained molded body 100 was molded using a semi-solidified slurry 40 with a high solid phase ratio and little variation in the solid phase ratio from part to part, so there is little variation in the distribution of eutectic crystallized between the solid phases 50 (primary crystals). Therefore, the molded body 100 that has been subjected to the T6 treatment can have little variation in the distribution of the precipitated phase, and can have little variation in the distribution of mechanical properties (especially yield strength).

The molded body 100 is a press-molded product used, for example, for a housing. Press molding employs processes such as drawing and forging using a mold. The molded body 100 has continuous fiber flows (grain flows), which are the flows of the metal's crystal structure.

Next, with reference to Figures 6(a) and 6(b), a method for determining the eutectic area ratio and the coefficient of variation of the eutectic area ratio of the molded body 100 will be described. Figure 6(a) is a perspective view of the molded body 100 that has been pressurized in a mold, removed, and subjected to T6 treatment. Line A in Figure 6(a) is a line along the direction in which the molded body 100 is pressurized in the mold. The direction in which the molded body 100 is pressurized may be from the upper surface 101 toward the lower surface 102, from the lower surface 102 toward the upper surface 101, or from both the upper surface 101 and the lower surface 102. In addition, the upper surface 101 and the lower surface 102 may be uneven, and the shape of the upper surface 101 and the shape of the lower surface 102 may be different.

6(b) is a projection of the molded body 100 drawn on a plane perpendicular to line A in FIG. 6(a). As shown in FIG. 6(b), first, the longest line segment 112 is drawn among the lines connecting two points 110, 111 on the outline 103 of the projection of the molded body 100. Next, the molded body 100 is cut along five cut surfaces 113 that intersect perpendicularly with the line segment 112 and divide the line segment 112 into six equal parts. The eutectic area ratio of each part can be obtained from the cross section of the sample obtained from each of the six equal parts. In this embodiment, the eutectic area ratio is obtained from the cross section of the sample of each part obtained by dividing the molded body 100 into six equal parts by the cut surface 113, but the eutectic area ratio may be obtained from the cross section of the sample of each part obtained by dividing the molded body 100 into seven or more equal parts by six or more cut surfaces 113.

The eutectic area ratio is the ratio of the area of the eutectic appearing in a field of view on a cross section to the area of the field of view. When the eutectic area ratio of the molded body 100 is measured multiple times for each field of view, the coefficient of variation obtained by dividing the standard deviation of the eutectic area ratio by the average value of the eutectic area ratio is 0.15 or less. When a longitudinal direction exists in the orthogonal direction of the molded body 100, the cross section of the molded body 100 is a cross section obtained from six or more parts obtained by equally dividing the distance of the molded body 100 in the longitudinal direction. The field of view on the cross section is a rectangular region 450 μm long and 600 μm wide.

Since the coefficient of variation of the eutectic area ratio of the molded body 100 is 0.15 or less, it is possible to obtain a molded body 100 with little variation in the eutectic area ratio relative to the average value of the eutectic area ratio, and it is possible to reduce the variation in the yield strength, which is correlated with the eutectic area ratio, from one part to another. Therefore, it is possible to obtain a molded body 100 with stable yield strength in each part.

The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

Samples 1-3 of semi-solidified slurries were produced by stirring the molten metal 10 using different stirring methods. The metal used was A6061, a heat-treated aluminum alloy. The vessel 20 to hold the molten metal 10 was a stainless steel rectangular vessel with a bottom, measuring 60 mm wide, 60 mm long, 50 mm high and 0.8 mm thick. In samples 2 and 3, the speed at which the rod 30 was moved was approximately the same, between 200 mm/sec and 300 mm/sec. All other conditions were the same.

Sample 1 is a semi-solidified slurry obtained by performing only electromagnetic stirring for 10 seconds without any time gap after the preparation process. Sample 2 is a semi-solidified slurry obtained by performing electromagnetic stirring for 10 seconds without any time gap after the preparation process, and then stirring by rotating the rod 30 for 30 seconds without any further time gap. Sample 3 is a semi-solidified slurry obtained by performing electromagnetic stirring for 10 seconds without any time gap after the preparation process, and then stirring by reciprocating the rod 30 for 30 seconds without any further time gap.

The obtained samples 1-3 were quenched in water, and the cross sections of 15 locations were observed with a metal microscope (200x) to determine the solid fraction. The quenched and solidified portions were the liquid phase 60 of each sample. The solid fraction (%) was calculated by dividing the area of the solid phase 50 that appeared in the field of view on each cross section by the area of the field of view and multiplying by 100. The field of view was a rectangular area of 450 μm in length and 600 μm in width for each of the 15 locations. Figure 7 shows the relationship between the solid fraction and each sample with different stirring methods.

As shown in Figure 7, the solid fraction of sample 1 ranged from 55% to 100%, with a standard deviation of 13.51%. The solid fraction of sample 2 ranged from 36% to 100%, with a standard deviation of 19.40%. The solid fraction of sample 3 ranged from 85.2% to 100%, with a standard deviation of 4.10%. Even in the area with the lowest solid fraction, sample 3 had a solid fraction of 80% or more.

Next, Sample 1 and Sample 3 were molded in a mold by applying a pressure of about 70 MPa to 140 MPa using a press machine equipped with a mold to obtain molded bodies. The obtained molded bodies were subjected to solution treatment and artificial aging treatment, and six tensile test pieces were made from each molded body, and the 0.2% yield strength was measured. The six tensile test pieces were made from each part obtained by dividing the molded body into six equal parts in the longitudinal direction perpendicular to the direction in which the sample was pressed. The measurement of the 0.2% yield strength was in accordance with JIS Z2241:2011. The tensile test pieces were No. 14B test pieces in accordance with JIS Z2241:2011. The 0.2% yield strength of Sample 1 was in the range of 78 MPa to 271 MPa, with a standard deviation of 81.58 MPa. The 0.2% yield strength of Sample 3 was in the range of 220 MPa to 255 MPa, with a standard deviation of 8.54 MPa.

Next, the fracture surfaces of each of the six tensile test pieces in the tensile test were polished and observed under a metallurgical microscope (200x magnification), and the eutectic area ratio was measured. Specifically, a rectangular area of 450 μm in length and 600 μm in width was arbitrarily set on the fracture surface of each of the six tensile test pieces, and the eutectic area ratio within that area was measured. Figure 8 shows the relationship between each sample with different stirring methods and the eutectic area ratio.

As shown in Figure 8, the eutectic area ratio of sample 1 was in the range of 0.4%-1.5%, with a standard deviation of 0.41% and an average value of 1.09%. The coefficient of variation of the eutectic area ratio of sample 1 was 0.38. The eutectic area ratio of sample 3 was in the range of 1.1%-1.6%, with a standard deviation of 0.20% and an average value of 1.41%. The coefficient of variation of the eutectic area ratio of sample 3 was 0.15.

Compared to Samples 1 and 2, Sample 3 is presumably characterized in that the up-and-down reciprocating motion of the rod 30 allows the solid phase 50 and liquid phase 60 in the molten metal 10 to be stirred homogeneously, thereby reducing the variation in solid phase ratio from one location to another.

In sample 3, the variation in the eutectic area ratio from one region to another is small, so the variation in the distribution of eutectic between primary crystals is also small. It is presumed that the small variation in the distribution of eutectic between primary crystals results in small variation in the distribution of precipitated phases obtained by solution treatment and artificial aging treatment, and therefore small variation in the 0.2% yield strength from one region to another.

The present invention has been described above based on embodiments and examples, but the present invention is in no way limited to the above embodiments and examples, and it can be easily inferred that various improvements and modifications are possible within the scope of the invention without departing from its spirit.

In the embodiment, the molten metal 10 put into the vessel 20 is a molten metal 10 of heat-treated aluminum alloy A6061, but this is not necessarily limited to this. As long as the metal can produce a semi-solidified slurry 40, other heat-treated alloys and non-heat-treated alloys can be used. In this case, even if the metal is a non-heat-treated alloy, the molded body 100 molded by pressurizing the semi-solidified slurry 40 obtained by the stirring process does not produce a precipitation phase, which is a strengthening mechanism between primary crystals, but the variation in crystal grain size is small and the variation in the distribution of primary crystals and eutectic is small, so that a molded body 100 with stable strength can be obtained in all parts.

In the embodiment, the vessel 20 has been described as having a rectangular cross section perpendicular to the vertical direction, but this is not necessarily limited to this. It is of course possible to adopt a vessel 20 having a circular, elliptical, or polygonal cross section perpendicular to the vertical direction.

In the embodiment, the rods 30 are described as being arranged in parallel to one another, but this is not necessarily limited to this. The rods 30 may not be parallel to one another. It is of course possible to set the arrangement of each rod 30 appropriately in accordance with the shape of the vessel 20. It is also of course possible to set the arrangement regardless of the shape of the vessel 20. The rods 30 may be arranged to spread apart from one another, for example, toward the bottom 21 and wall 22 of the vessel 20.

In the embodiment, a case where there are multiple rods 30 has been described, but this is not necessarily limited to this. There may also be a single rod 30.

In the embodiment, the case where the rod 30 moves upward in a reciprocating motion until the tip 31 emerges from the liquid surface 11 of the molten metal 10 during the stirring process has been described, but this is not necessarily limited to this. Of course, the rod 30 can repeat the reciprocating motion in the up and down direction while the tip 31 remains within the molten metal 10.

In the embodiment, a method for producing a semi-solidified slurry 40 in which the electromagnetic stirring process is performed before or simultaneously with the stirring process has been described, but this is not necessarily limited to this. It is of course possible to combine a stirring process with a stirring method other than electromagnetic stirring. Examples of stirring methods other than electromagnetic stirring include a method of stirring by ultrasonic vibration, a method of stirring by injecting gas into the molten metal 10, a method of stirring by high-frequency induction, a method of stirring by rotating, revolving, or vibrating the rod 30, and a method of stirring by combining these.

In the embodiment, the semi-solidified slurry 40 is set from the vessel 20 into the mold of the forming die and pressurized to form in the forming process, but this is not necessarily limited to the above. The molten metal 10 may be directly placed in the mold in the preparation process, and the semi-solidified slurry 40 may be obtained in the mold by the stirring process, after which it is pressurized and formed as is. In this case, the vessel 20 is the mold into which the molten metal 10 is placed.

Reference Signs List 10 Molten metal 20 Container 21 Bottom 30 Rod 40 Semi-solidified slurry 50 Solid phase 60 Liquid phase 100 Molded body

Claims (6)

A method for producing a semi-solidified slurry consisting of a solid phase and a liquid phase, comprising the steps of:
The preparation process involves pouring molten metal into a vessel with a bottom;
and a stirring step of stirring the molten metal by reciprocating a rod immersed in the molten metal in a longitudinal direction of the rod until a solid fraction in a portion of the molten metal in the vessel with a lowest solid fraction reaches 80% or more. The method for producing a semi-solidified slurry according to claim 1, wherein the reciprocating motion in the stirring step is different from the position perpendicular to the longitudinal direction of the rod in the immediately preceding reciprocating motion. In a cross section perpendicular to the longitudinal direction of the rod,
The rods are present in a plurality of locations spaced apart from one another,
3. The method for producing a semi-solidified slurry according to claim 1 or 2, wherein the center of one of the two adjacent rods is located within a circle whose radius is 7 times the thickness of the other rod and whose center is the center of the other rod. The method for producing a semi-solidified slurry according to any one of claims 1 to 3, further comprising an electromagnetic stirring step of stirring the molten metal in the vessel by electromagnetic stirring after the preparation step and before the stirring step or simultaneously with the stirring step. A method for producing a molded body, comprising a molding step of pressurizing and deforming the semi-solidified slurry after obtaining the semi-solidified slurry by the method for producing a semi-solidified slurry according to any one of claims 1 to 4. A press-molded product is a metal molded body that is made of primary crystals and eutectic crystals and has continuous fiber flow,
A molded body in which, when the longest line segment among the line segments connecting two points of the outline projected onto a plane perpendicular to the pressure direction is drawn, and the cross section of the sample is obtained by cutting each portion along a plurality of cut planes that intersect perpendicularly to the longest line segment and divide the line segment into six equal parts, a eutectic area ratio, which is the ratio of the area of the eutectic appearing in a visual field on a predetermined cross section to the area of the visual field, is measured for each of the visual fields, and the coefficient of variation, which is the standard deviation of the eutectic area ratio divided by the average value of the eutectic area ratio, is 0.15 or less.

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