CN118103157A

CN118103157A - Method for producing semi-solidified slurry, method for producing molded article, and molded article

Info

Publication number: CN118103157A
Application number: CN202180103266.7A
Authority: CN
Inventors: 栗田大渡
Original assignee: Ahresty Corp
Current assignee: Ahresty Corp
Priority date: 2021-10-12
Filing date: 2021-10-12
Publication date: 2024-05-28
Also published as: WO2023062727A1; JPWO2023062727A1

Abstract

Provided are a method for producing a semi-solidified slurry, which can produce a semi-solidified slurry having small variations in solid phase ratios at each site, a method for producing a molded article, which can reduce variations in the size of crystal grains, and a molded article. The method for producing a semi-setting slurry comprises: a preparation step of loading a molten metal (10) into a bottomed vessel (20); and a stirring step of stirring the melt by reciprocating the rod (30) placed in the melt in the longitudinal direction of the rod until the solid phase ratio of any part of the melt in the vessel becomes 80% or more.

Description

Method for producing semi-solidified slurry, method for producing molded article, and molded article

Technical Field

The present invention relates to a method for producing a semi-setting slurry, a method for producing a molded article, and a molded article.

Background

In a method for producing a semi-solidified slurry of a metal composed of a solid phase and a liquid phase, patent document 1 discloses a technique of generating a semi-solidified slurry by rotating (spinning) a plurality of rods in a molten metal.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2018-15771

Disclosure of Invention

Technical problem to be solved by the invention

In the prior art, the rod is rotated and spun (rotated) to stir the molten metal, but there is a problem that the solid phase and the liquid phase are not sufficiently mixed, and the solid phase ratio of each part of the obtained semi-solidified slurry is deviated.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing a semi-solidified slurry, which can reduce variations in solid phase ratio at each portion of the semi-solidified slurry, a method for producing a molded article, which can reduce variations in crystal grain size, and a molded article.

Technical scheme for solving problems

In order to achieve the object, the method for producing a semi-setting slurry of the present invention comprises: a preparation step of filling a molten metal into a bottomed vessel; and a stirring step of stirring the melt by reciprocating the rod placed in the melt in the longitudinal direction of the rod until the solid phase ratio of any part of the melt in the vessel becomes 80% or more.

The method for producing a molded article according to the present invention includes a molding step of molding a semi-solidified slurry by pressurizing the semi-solidified slurry after the semi-solidified slurry is obtained by the method for producing a semi-solidified slurry.

When a plurality of eutectic area ratios are measured 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 ratios, which is the ratio of the area of the eutectic appearing in the field of view to the area of the field of view on a predetermined cross section, is 0.15 or less.

Effects of the invention

The method for producing a semi-solidified slurry according to claim 1, wherein in the stirring step, the rod placed in the melt is reciprocated in the longitudinal direction of the rod to stir the melt, whereby the solid phase and the liquid phase at the solidification of the melt are easily and uniformly stirred even if the solid phase ratio is high. Further, since the stirring is performed until the solid phase ratio of the melt becomes 80% or more, the liquid phase portion that solidifies and grows into a solid phase is reduced, and the dispersion deviation of the liquid phase around the solid phase is reduced. Therefore, the variation in solid phase ratio of each portion of the obtained semi-solidified slurry can be reduced, and the variation in crystal grain size can be reduced.

The method for producing a semi-solidified slurry according to claim 2, wherein the position orthogonal to the longitudinal direction of the rod when the rod reciprocates is different from that immediately before, and therefore, the solid phase and the liquid phase at the time of solidification of the melt are easily uniformly stirred at a plurality of positions orthogonal to the longitudinal direction of the rod. Therefore, the variation in solid phase ratio at each portion of the obtained semi-solidified slurry can be further reduced.

A method for producing a semi-solidified slurry according to claim 3, wherein in the method for producing a semi-solidified slurry according to claim 1 or 2, a plurality of rods are provided at intervals in a cross section orthogonal to the longitudinal direction of the rods, and the centers of one of the two adjacent rods are located in a circle having a radius of 7 times the thickness of the other rod and the center of the other rod, so that the influence of the reciprocation of the rods is easily exerted on the melt between the rods, and the solid phase and the liquid phase at the time of solidification of the melt are stirred uniformly. Therefore, the variation in solid phase ratio at each portion of the obtained semi-solidified slurry can be further reduced.

The method for producing a semi-solidified slurry according to claim 4, wherein the method for producing a semi-solidified slurry according to any one of claims 1 to 3 further comprises an electromagnetic stirring step performed before or simultaneously with the stirring step, whereby the size of crystal grains of the obtained semi-solidified slurry can be further reduced by the electromagnetic stirring step.

The method for producing a molded article according to claim 5, wherein the method for producing a semi-solidified slurry according to any one of claims 1 to 4 produces a semi-solidified slurry having small variations in solid phase ratio and small variations in grain size at each site. Since the semi-solidified slurry is pressed and deformed to be molded, a molded article having a stable yield strength at any position can be obtained.

The molded article according to claim 6, wherein the coefficient of variation of the eutectic area ratio of the molded article is 0.15 or less, whereby variation in the yield strength of each part related to the eutectic area ratio can be reduced. Therefore, a molded article having a stable yield strength at any position can be obtained.

Drawings

Fig. 1 (a) is a cross-sectional view of the vessel when the rod is out of the melt, and fig. 1 (b) is a cross-sectional view of the vessel when the rod is into the melt.

Fig. 2 (a) is a cross-sectional view of the vessel when the rod is pulled out of the melt at a position in the horizontal direction different from fig. 1 (a), and fig. 2 (b) is a cross-sectional view of the vessel when the rod is pulled into the melt at a position in the horizontal direction different from fig. 1 (b).

Fig. 3 (a) is a cross-sectional view of the vessel at line IIIa-IIIa of fig. 1 (b), and fig. 3 (b) is a cross-sectional view of the vessel at line IIIb-IIIb of fig. 2 (b).

Fig. 4 (a) is a perspective view of the semi-solidified slurry, and fig. 4 (b) is a cross-sectional view of the semi-solidified slurry shown by arrow IVb of fig. 4 (a).

Fig. 5 is a schematic diagram showing movement of a solid phase and a liquid phase in a melt in a stirring step.

Fig. 6 (a) is a perspective view of the molded body, and fig. 6 (b) is a projection view of the molded body drawn on a plane perpendicular to the line a of fig. 6 (a).

FIG. 7 is a graph showing a relationship between a stirring method and a solid phase ratio.

Fig. 8 is a graph showing a relationship between a stirring method and a eutectic area ratio.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. A method for producing the semi-solidified slurry 40 and a method for producing the molded body 100 according to one embodiment will be described with reference to fig. 1 (a) to 4. Fig. 1 (a) is a cross-sectional view of the vessel 20 as the rod 30 exits the melt 10. Fig. 1 (b) is a cross-sectional view of the vessel 20 as the rod 30 enters the melt 10. In fig. 1 (a) and 1 (b), the up-down direction of the paper surface, the left-right direction of the paper surface, and the vertical direction of the paper surface are referred to as the up-down direction, the left-right direction, and the front-back direction of the dish 20, respectively (the same applies to fig. 2 (a), 2 (b), and 5 (a) to 5 (d)).

As shown in fig. 1 (a), the melt 10 is filled into a bottomed vessel 20. The melt 10 is obtained by melting a metal, for example, an aluminum alloy, a magnesium alloy, a copper alloy, or an iron alloy. The melt 10 may be a mixture of powder and fiber in molten metal. Examples of the material of the powder or fiber include ceramics such as SiC and Al ₂O₃, and carbon. In the preparation step, the molten metal 10 is poured from a pouring port of a furnace (not shown) capable of maintaining a molten state, or a container is placed in the furnace and is drawn up, and the container is poured into the vessel 20, whereby the vessel 20 is filled with the molten metal 10.

The metal is preferably a heat treated alloy having improved mechanical properties (particularly yield strength) by performing solution treatment and aging treatment. The metal is, for example, a6000 series a6051, a6061, a2000 series a2011, a2017, a2618, or a7000 series heat-treated alloy of aluminum alloy. The metal may be, for example, mg-Zn (-Zr) (ZK series), mg-Zn-Cu (ZC series), mg-Zn-RE (ZE and EZ series) based on magnesium alloy; here, RE means rare earth elements), 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 alloys, and the like. In addition, copper alloy and iron alloy are used as metals. In this embodiment, the metal is a heat treated alloy of aluminum.

The vessel 20 may be a metal vessel or a nonmetal vessel as long as it has high temperature strength against the temperature of the melt 10 and does not react with the melt 10. The vessel 20 has a bottom 21 at the bottom and an upper opening, and a rectangular cross section orthogonal to the vertical direction. The planar walls 22 are disposed and connected in the right direction, the left direction, the front direction, and the rear direction in the left-right direction and the front-rear direction (hereinafter referred to as "horizontal direction") of the vessel 20. The lower end of each wall 22 is connected to each end of the bottom 21 in the horizontal direction.

The rods 30 are connected to one surface of the base 32 at a distance from each other. The rod 30 has a tapered distal end 31 with a sharp distal end at the distal end on the opposite side to the connection with the base 32. The cross-section of the rod 30 is circular, elliptical, quadrilateral, triangular, polygonal, and star-shaped. The cross-sectional shape of the rod 30 is preferably a circular shape with few protruding portions in the outer shape.

The plurality of rods 30 are arranged parallel to each other. The length of the rod 30 is set longer than the distance from the liquid surface 11 of the molten metal 10 charged into the vessel 20 to the bottom 21 of the vessel 20. In the preparation step, the rod 30 is extended beyond the liquid surface 11 of the melt 10.

The rod 30 is made of a metallic or non-metallic material capable of withstanding the temperature of the melt 10. A coating layer of DLC (diamond like carbon) or the like is applied to at least the surface of the rod 30. The rod 30 suppresses loss due to friction between the rod 30 and the melt 10 and adhesion of the melt 10 by the coating.

As shown in fig. 1 (b), in the stirring step, immediately after the molten metal 10 is charged into the vessel 20, or after the vessel 20 is held (exposed) in the atmosphere, in a vacuum, or in an inert gas such as argon or nitrogen for a predetermined time after the molten metal 10 is charged into the vessel 20, the rod 30 is inserted from the liquid surface 11 of the molten metal 10 toward the bottom 21 (downward direction) of the vessel 20. Then, the rod 30 is reciprocated along the length of the rod 30 to stir the melt 10. The predetermined time when the molten metal 10 is held in the atmosphere, in the vacuum, or in the inert gas is appropriately set according to the amount of the molten metal 10, the type of metal of the molten metal 10, the shape and size of the vessel 20, the ambient temperature of the atmosphere, the vacuum, or the inert gas, and the like.

Fig. 2 (a) is a cross-sectional view of the vessel 20 when the rod 30 comes out of the melt 10 at a position in the horizontal direction different from fig. 1 (a), and fig. 2 (b) is a cross-sectional view of the vessel 20 when the rod 30 enters the melt 10 at a position in the horizontal direction different from fig. 1 (b).

The horizontal position of the rod 30 in fig. 2 (a) is a position shifted rightward by a distance a from the horizontal position of the rod 30 in fig. 1 (a). As shown in fig. 1 (b), after being inserted toward the bottom 21 of the vessel 20 briefly, the rod 30 is lifted from the bottom 21 of the vessel 20 toward the liquid surface 11 of the melt 10, and returns to the position of the rod 30 in fig. 1 (a). Then, as shown in fig. 2 (a), the rod 30 is moved rightward by a distance a.

Next, as shown in fig. 2 (b), the rod 30 is inserted from the liquid surface 11 of the melt 10 toward the bottom 21 of the vessel 20 at a position in the horizontal direction where the rod 30 is moved rightward by the distance a. Then, the vessel is further raised from the bottom 21 of the vessel 20 toward the liquid surface 11 of the melt 10, and the position of the rod 30 in fig. 2 (a) is returned.

Fig. 3 (a) is a cross-sectional view of the vessel 20 at line IIIa-IIIa of fig. 1 (b), and fig. 3 (b) is a cross-sectional view of the vessel 20 at line IIIb-IIIb of fig. 2 (b). In fig. 3 (a) and 3 (b), the up-down direction of the paper surface, the left-right direction of the paper surface, and the vertical direction of the paper surface are respectively directed to the front-back direction, the left-right direction, and the up-down direction of the dish 20. In fig. 3 (b), the portions shown by the broken lines are representative four cross-sections among the cross-sections of the plurality of bars 30 in fig. 3 (a), and indicate positions before the horizontal movement by the distance a.

As shown in fig. 3 (a), in a cross section orthogonal to the longitudinal direction of the rod 30, a plurality of rods 30 are provided at intervals. The center of one bar 30 of the two adjacent bars 30 is located in a circle having a radius of 7 times the length L2 of the thickness L1 of the other bar 30 and the center of the other bar 30. The thicknesses of the adjacent rods 30 may be different from each other or the same.

The distance a is a variable value (including the same magnitude value) whose magnitude changes in each reciprocation of the rod 30. The direction of the distance a also varies in the left-right direction, the front-rear direction, or any one of the two directions according to the reciprocation of the rod 30. Therefore, in the stirring step, the rod 30 can reciprocate at a position in the horizontal direction different from the immediately preceding reciprocation, and therefore the solid phase 50 (described later) and the liquid phase 60 (described later) when the melt 10 is solidified can be easily uniformly stirred at a plurality of positions in the horizontal direction of the melt 10.

The rod 30 repeatedly reciprocates as shown in fig. 1 (a) to 3 (b) until the solid phase ratio of any part of the melt 10 becomes 80% or more. The solid phase ratio of any portion of the melt 10 being 80% or more means that the solid phase ratio is 80% or more in the portion where the solid phase ratio of the melt 10 is the lowest.

Fig. 4 (a) is a perspective view of the semi-solidified slurry 40, and fig. 4 (b) is a cross-sectional view of the semi-solidified slurry 40 shown by an arrow IVb of fig. 4 (a). The semi-solidified slurry 40 in fig. 4 (a) is the semi-solidified slurry 40 extracted from the vessel 20 by stirring the melt 10 in the stirring step to reverse the vertical direction. In semi-solidified slurry 40, solid phase 50 and liquid phase 60 coexist.

As shown in fig. 4 (a) and 4 (b), the solid phase ratio of the semi-solidified slurry 40, which is the melt 10 after the stirring step, can be obtained by taking the semi-solidified slurry 40 immediately after the stirring step out of the vessel 20, putting it into water, cooling it rapidly, and observing the cross sections of 15 sites with a metal microscope (200 times). Each of the sections of 15 parts of the semi-solidified slurry 40 is a section of five parts of 15 parts in total of three parts of the upper part 41, the central part 42, and the lower part 43 of the semi-solidified slurry 40 from above toward below, from the parts contacting the wall 22 of the vessel 20 toward inside, the wall side parts 44, the intermediate parts 45, and the central part 46. The rapidly cooled and solidified portion is the portion of the liquid phase 60 of the semi-solidified slurry 40. The solid phase ratio (%) can be obtained by dividing the area of the solid phase 50 appearing in the visual field on the cross section of each of the 15 sites by the area of the visual field and amplifying by 100 times. The field of view is a rectangular area with a longitudinal direction of 450 μm and a transverse direction of 600 μm.

Regarding the solid phase ratio of the melt 10 in the stirring step, for example, a graph of the correlation between the kinematic viscosity of the melt 10 and the solid phase ratio may be prepared in advance, and a viscosity meter may be provided to the rod 30 to measure the kinematic viscosity of the melt 10 during stirring, thereby obtaining the semi-solidified slurry 40 having a desired solid phase ratio. Further, a graph of the relationship between the stirring time and the solid phase ratio may be prepared in advance, and the semi-solidified slurry 40 having a desired solid phase ratio may be obtained by stirring the slurry to a desired solid phase ratio based on the graph.

The tip 31 is disposed so that the sharp tip portion faces the bottom 21 of the vessel 20 from the liquid surface 11 of the melt 10. Since the tip of the tip 31 is sharp, the rod 30 can be easily inserted into the melt 10 even when the solid phase ratio of the melt 10 is 80% or more.

In the stirring step, the center of one rod 30 of the adjacent two rods 30 is located in a circle having a radius equal to 7 times the length L2 of the thickness L1 of the other rod 30 and the center of the other rod 30, and is stirred to a high solid phase ratio of 80% or more, so that even if the distance from the centers of the adjacent rods 30 to each other is long, the melt 10 therebetween can be sufficiently stirred.

Next, the movement of the solid phase 50 and the liquid phase 60 in the melt 10 in the stirring step will be described with reference to fig. 5 (a) to 5 (d). Fig. 5 (a) is a schematic view of the case where the molten metal 10 is charged into the vessel 20 in the preparation step. Fig. 5 (b) is a schematic diagram showing the state of the melt 10 when the rod 30 is inserted into the melt 10 in the stirring step. Fig. 5 (c) is a schematic diagram showing the state of the melt 10 after a predetermined time from fig. 5 (b). Fig. 5 (d) is a schematic diagram showing the state of the melt 10 after a predetermined time has elapsed from fig. 5 (c).

In the diagrams of fig. 5 (a) to 5 (d), the solid phase 50 represented by a quadrangle and the liquid phase 60 represented by a triangle schematically represent the distribution of the solid phase 50 and the liquid phase 60 within the melt 10. In fig. 5 (a) to 5 (d), a portion of the liquid surface 11 of the melt 10 where the solid phase 50 is large is omitted. In fig. 5 (b) to 5 (d), the drawings are omitted except for one bar 30 for simplicity.

As shown in fig. 5 (a), the molten metal 10 charged into the vessel 20 from the furnace cools from the portion near the wall 22 and the bottom 21 of the vessel 20 compared to the central portion in the horizontal direction of the vessel 20, and a first layer 70 having a large amount of solid phase 50 is formed from the portion near the wall 22 and the bottom 21 of the vessel 20. A second layer 80 comprising more liquid phase 60 than the first layer 70 is formed inside the first layer 70. A third layer 90 is formed further inward than the second layer 80, the third layer 90 including a horizontally central portion of the vessel 20 and including more liquid phase 60 than the second layer 80. The first layer 70 to the third layer 90 each include the vicinity of the liquid surface 11 of the melt 10 (except for a portion where the solid phase 50 of the liquid surface 11 of the melt 10 is large). 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 do not have clear boundaries, but are provided for illustration.

As shown in fig. 5 (b), the rod 30 is inserted from the liquid surface 11 toward the bottom 21 while pushing the solid phase 50 and the liquid phase 60 in the melt 10 outward of the rod 30. The pushed-apart solid 50 and liquid 60 phases are present around the rod 30.

Next, as shown in fig. 5 (c), when the rod 30 is raised from the bottom 21 of the melt 10 toward the liquid surface 11, the liquid phase 60, which has higher fluidity than the solid phase 50 and is easily moved, flows into the portion of the rod 30 existing in the melt 10 before the solid phase 50. The liquid phase 60 flows into the portion of the rod 30 near the bottom 21 more rapidly than the solid phase 50, and therefore, the molten metal 10 in the liquid phase 60 moves more toward the portion near the bottom 21.

Then, as shown in fig. 5 (d), after the molten metal 10 having a large amount of the liquid phase 60 flows into the portion where the rod 30 exists, the molten metal 10 having a large amount of the solid phase 50 flows into the portion. Since the solid phase 50 of the first layer 70 having a large number of solid phases 50 can be pushed away, the melt 10 having a large number of liquid phases 60 flows into the portion, and thus the solid phase 50 and the liquid phase 60 can be easily mixed.

The melt 10 having moved to the liquid phase 60 of the first layer 70 is located in the first layer 70 closer to the wall 22 and the bottom 21 than the second layer 80 and the third layer 90, and is therefore easily cooled to become the solid phase 50. Since the melt 10 having a large amount of the liquid phase 60 existing in the second layer 80 and the third layer 90 which are difficult to be the solid phase 50 is moved to the first layer 70 which is easy to be the solid phase 50, a portion having a large amount of the liquid phase 60 does not remain, and the solid phase 50 can be uniformly formed. Thus, the semi-solidified slurry 40 with small variation in solid phase ratio at each portion can be obtained.

In the stirring step, the rod 30 is reciprocated to stir the melt 10 to a solid fraction of 80% or more, so that the dispersion of the liquid phase 60 around the solid phase 50 is reduced while the liquid phase 60 around the solid phase 50 is reduced. Since the liquid phase 60 having small dispersion is grown with the solid phase 50 in the vicinity as a core, the size variation of particles (crystal grains) of the solid phase 50 can be reduced.

In the embodiment, the speed of the reciprocation of the rod 30 also depends on the magnitude of the reciprocation, but is preferably, for example, 200 mm/sec to 300 mm/sec and is performed twice or more in 1 second. Since the reciprocation is performed twice or more for 1 second, the negative pressure generated in the portion of the rod 30 where the rod 30 is located when the rod 30 is raised from the bottom 21 of the melt 10 toward the liquid surface 11 is increased as compared with the case where the speed is slower, and the inflow of the solid phase 50 and the liquid phase 60 is promoted. Therefore, the stirring time can be shortened.

Since the horizontal position of the reciprocation of the rod 30 is different from the horizontal position of the immediately preceding reciprocation, the reciprocation effect can be obtained at a plurality of different positions in the horizontal direction in the melt 10. The solid phase 50 and the liquid phase 60 are easily mixed at any horizontal position of the melt 10, and the distribution of the solid phase 50 and the liquid phase 60 in the semi-solidified slurry 40 is easily uniform. Therefore, the variation in the solid phase ratio of each portion of the semi-solidified slurry 40 can be reduced.

The surface temperature of the rod 30 before contact with the melt 10 is lower than that of the melt 10. Therefore, the melt 10 in contact with the surface of the rod 30 is easily solidified rapidly. Since there is little difference in the surface temperatures of the plurality of rods 30, the melt 10 located near the center of the vessel 20 in the horizontal direction and the melt 10 located near the wall 22 of the vessel 20 are cooled regardless of the distance to the wall 22 of the melt 10. Therefore, the variation in the solid phase ratio of each site can be reduced.

In the stirring step, when the rod 30 is lifted from the bottom 21 of the vessel 20 toward the liquid surface 11 of the melt 10 during the reciprocation of the rod 30, at least a part of the rod 30 is exposed to the atmosphere or the like, and thus the rod 30 is cooled. When the portion of the rod 30 exposed to the atmosphere or the like and the cooled portion are brought into contact with the melt 10, the generation of the solid phase 50 is promoted. Therefore, the time for solidifying the melt 10 can be shortened.

In the stirring step, when the rod 30 is lifted from the bottom 21 of the vessel 20 toward the liquid surface 11 of the melt 10 during the reciprocation of the rod 30, the melt 10 is less likely to adhere to the rod 30 because the rod 30 has a small portion protruding from the outer shape. Thus, the volume-stable semi-solidified slurry 40 can be repeatedly obtained. In the stirring step, the rod 30 may vibrate while reciprocating. In this case, when the rod 30 is lifted from the bottom 21 of the vessel 20 toward the liquid surface 11 of the melt 10, the melt 10 is made more difficult to adhere to the rod 30 by vibration. The direction of vibration is particularly preferably the length direction of the rod 30. In addition, even if the melt 10 adheres to the rod 30, the adhering melt 10 can be easily blown off by blowing or the like. An electromagnetic stirring step of electromagnetic stirring the melt 10 after the preparation step and before the stirring step or simultaneously with the stirring step may be performed. In the case of electromagnetic stirring before the stirring step, it is preferable to perform the stirring step after the electromagnetic stirring step without time separation.

When electromagnetic stirring is performed, the size of particles (crystal grains) of the solid phase 50 of the obtained semi-solidified slurry 40 becomes small. If the particle size of the solid phase 50 becomes smaller, the area of contact between the solid phase 50 and the liquid phase 60 increases, and the eutectic crystal crystallized between the solid phases 50 can be increased.

Next, the resulting semi-solidified slurry 40 is placed from the vessel 20 into a molding die. The molding die is closed, and the semi-solidified slurry 40 is pressurized to deform the semi-solidified slurry 40, thereby molding the molded article 100 (described later). The molding die is opened, and the molded article 100 is taken out. Then, the molded body 100 is subjected to solution treatment and artificial aging treatment (collectively referred to as "T6 treatment").

The liquid phase 60 of the semi-solidified slurry 40 is formed to be present around the primary crystal (solid phase 50) and to be a portion where the primary crystal grows and a portion where the primary crystal is formed to be eutectic including a component of the primary crystal (solid phase 50) and other elements. The portion that becomes eutectic includes an element of primary crystal and an element different from the primary crystal. Since the eutectic crystal contains elements other than primary crystals to some extent around the primary crystals, when the obtained molded body 100 is subjected to solution treatment and aging treatment after the molded body 100 is molded, a precipitated phase is precipitated (formed) around the primary crystals as a strengthening mechanism. When the precipitated phase is generated, the primary crystal suppresses movement due to sliding between particles by the precipitated phase, and mechanical properties (particularly yield strength) of the molded body 100 are improved.

The obtained molded article 100 is molded using the semi-solidified slurry 40 having a high solid phase ratio and little variation in solid phase ratio at each site, and therefore, the variation in distribution of the eutectic crystals between the solid phases 50 (primary crystals) is also small. Therefore, the molded article 100 subjected to the T6 treatment can obtain the molded article 100 having less variation in distribution of the precipitated phase and less variation in distribution of mechanical properties (particularly, yield strength).

The molded article 100 is, for example, a press-molded article used for a case. The press molding is performed by drawing using a molding die, forging, or the like. The molded article 100 has a continuous flow fiber streamline (forging streamline) as a metal crystal structure.

Next, a method of determining the eutectic area ratio and the coefficient of variation of the eutectic area ratio of the molded body 100 will be described with reference to fig. 6 (a) and 6 (b). Fig. 6 (a) is a perspective view of the molded article 100 taken out after being pressurized in the molding die and subjected to T6 treatment. The line a in fig. 6 (a) is a line along the direction in which the molded body 100 is pressed in the molding die. The direction in which the molded body 100 is pressurized may be a direction from the upper surface 101 toward the lower surface 102, a direction from the lower surface 102 toward the upper surface 101, or both the upper surface 101 and the lower surface 102. The upper surface 101 and the lower surface 102 may have irregularities, and the shape of the upper surface 101 may be different from the shape of the lower surface 102.

Fig. 6 (b) is a projection view of the molded body 100 drawn on a plane perpendicular to the line a in fig. 6 (a). As shown in fig. 6 (b), first, a longest line segment 112 among the line segments connecting the two points 110 and 111 on the outline 103 of the projection view of the molded body 100 is drawn. Next, the molded body 100 is cut by six cut surfaces 113 intersecting the line segment 112 perpendicularly and dividing the line segment 112 into six equal parts. The eutectic area ratio of each portion can be obtained from the cross section of the sample obtained from each portion of the six aliquots. In the present embodiment, the eutectic area ratio is obtained from the cross section of the sample at each of the six equal parts of the molded body 100 by the cut surface 113, but the eutectic area ratio may be obtained from the cross section of the sample at each of the six equal parts of the molded body 100 by the six or more cut surfaces 113.

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

Since the coefficient of variation of the eutectic area ratio of the molded article 100 is 0.15 or less, the molded article 100 having little variation in the magnitude of the eutectic area ratio with respect to the average value of the eutectic area ratio can be obtained, and variation in each portion of the yield strength related to the eutectic area ratio can be reduced. Accordingly, the molded article 100 having a stable yield strength at any portion can be obtained.

Examples

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

Samples 1-3 of semi-solidified slurries were produced in which the molten metal 10 was stirred by different stirring methods. The metal used was a6061 as a heat-treated alloy of aluminum. The vessel 20 for containing the molten metal 10 was a stainless steel vessel having a rectangular cross section with a bottom and having a width of 60mm, a length of 60mm, a height of 50mm, and a thickness of 0.8 mm. In sample 2 and sample 3, the speed of the rod 30 was made to act at 200 mm/sec to 300 mm/sec, and to the same extent. The other conditions were all the same.

Sample 1 was a semi-coagulated slurry which was subjected to electromagnetic stirring for only 10 seconds without an interval after the preparation process. Sample 2 was a semi-solidified slurry obtained by stirring the mixture by rotating the rod 30 for 30 seconds without leaving time after electromagnetic stirring for 10 seconds without time interval after the preparation step. Sample 3 was a semi-solidified slurry obtained by performing electromagnetic stirring for 10 seconds at an interval after the preparation step, and then performing stirring by reciprocating the rod 30 for 30 seconds at an interval.

The obtained samples 1 to 3 were rapidly cooled in water, and the solid phase ratio was obtained by observing the cross section of each of the upper, central, and lower portions of the samples, and five or 15 portions of the upper, central, and lower portions of the samples, which are located inward from the portion in contact with the wall 22 of the vessel 20, and the central portion thereof, with a metal microscope (200 times). The rapidly cooled and solidified portion is the portion of the liquid phase 60 of each sample. The solid phase ratio (%) was obtained by dividing the area of the solid phase 50 appearing in the visual field on each section by the area of the visual field and multiplying the divided area by 100 times. For 15 sites, the field of view was a rectangular region with a longitudinal direction of 450 μm and a transverse direction of 600 μm, respectively. FIG. 7 is a graph showing the relationship between each sample and the solid phase ratio according to the stirring method.

As shown in fig. 7, the solid phase ratio of sample 1 was in the range of 55% -100% and the standard deviation was 13.51%. Sample 2 had a solids fraction in the range of 36% to 100% with a standard deviation of 19.40%. Sample 3 had a solids fraction in the range of 85.2% to 100% with a standard deviation of 4.10%. Sample 3 also had a solid fraction of 80% or more in the portion having the lowest solid fraction.

Next, molded articles were obtained, which were molded by applying a pressure of about 70MPa to 140MPa to sample 1 and sample 3 in a molding die using a press equipped with a molding die. After the solid solution treatment and the artificial aging treatment were performed on the obtained molded article, six tensile test pieces were produced from the molded article, and 0.2% yield strength was measured. Each of the six tensile test pieces was produced from each portion of the molded body that was hexagonally divided in the longitudinal direction in the orthogonal direction to the direction in which each sample was pressurized. The 0.2% yield strength was measured in accordance with JIS Z2241:2011. the tensile test piece was a test piece according to JIS Z2241:2011 test piece No. 14B. Sample 1 had a 0.2% yield strength in the range of 78MPa to 271MPa and a standard deviation of 81.58MPa. Sample 3 had a 0.2% yield strength in the range of 220MPa to 255MPa with a standard deviation of 8.54MPa.

Then, fracture surfaces of each of the six tensile test pieces were polished, and observed with a metal microscope (200 times), and the eutectic area ratios were measured. Specifically, rectangular regions each having a length of 450 μm and a width of 600 μm were arbitrarily set for the fracture surfaces of the 6 tensile test pieces, and the eutectic area ratio in the regions was measured. Fig. 8 is a graph showing the relationship between each sample and the eutectic area ratio according to the stirring method.

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

Sample 3 was compared with samples 1 and 2, and it was estimated that by reciprocating rod 30 in the up-down direction, solid phase 50 and liquid phase 60 in melt 10 could be stirred uniformly, and the variation in the solid phase ratio was reduced in each part.

Since the variation of the eutectic area ratio of sample 3 is small in each part, the variation of the eutectic distribution between primary crystals is small. It is presumed that since the distribution deviation of the eutectic between primary crystals is small, the distribution deviation of the precipitated phases obtained by the solution treatment and the artificial aging treatment is small, and the deviation of each portion of the 0.2% yield strength is small.

The present invention has been described above with reference to the embodiments and examples, but the present invention is not limited to the embodiments and examples, and it can be easily estimated that various modifications and variations can be made without departing from the gist of the present invention.

In the embodiment, the case where the molten metal 10 of the metal placed in the vessel 20 is the molten metal 10 of the heat-treated alloy a6061 of aluminum was described, but the present invention is not limited thereto. As the metal, other heat-treated alloys or non-heat-treated alloys may be used as long as the semi-solidified slurry 40 can be produced. In this case, even when the metal is a non-heat-treated alloy, the molded article 100 molded by pressurizing the semi-solidified slurry 40 obtained by the stirring step does not generate a precipitated phase as a strengthening mechanism between primary crystals, but since the variation in the size of crystal grains is small and the variation in the distribution of primary crystals and eutectic crystals is small, the molded article 100 having stable yield strength at any portion can be obtained.

In the embodiment, the description has been made of the case where the cross section of the vessel 20 orthogonal to the vertical direction is rectangular, but the present invention is not necessarily limited thereto. The vessel 20 may be a circular, elliptical, or polygonal cross section orthogonal to the vertical direction.

In the embodiment, the case where the rods 30 are arranged in parallel with each other has been described, but the present invention is not necessarily limited to this. The bars 30 may also be non-parallel to each other. The arrangement of the bars 30 may be appropriately set according to the shape of the vessel 20. It is needless to say that the setting may be performed regardless of the shape of the vessel 20. The bars 30 may be disposed so as to extend toward the bottom 21 and the wall 22 of the vessel 20, for example.

In the embodiment, the case where a plurality of bars 30 are provided is described, but this is not necessarily the case. The rod 30 may also be a single rod.

In the embodiment, the case where the rod 30 reciprocates upward until the tip 31 comes out of the liquid surface 11 of the melt 10 in the stirring step is described, but the invention is not limited thereto. The rod 30 can of course repeatedly reciprocate in the up-down direction with the tip 31 positioned in the melt 10.

In the embodiment, the method of producing the semi-solidified slurry 40 in which the electromagnetic stirring step is performed before or simultaneously with the stirring step is described, but the method is not necessarily limited thereto. Of course, the stirring may be performed by a combination of a stirring method other than electromagnetic stirring and a stirring step. Examples of the stirring method other than electromagnetic stirring include a method of stirring by ultrasonic vibration, a method of stirring by injecting a gas into the melt 10, a method of stirring by high-frequency induction, a method of stirring by rotating, revolving, vibrating the rod 30, and a method of stirring a combination thereof.

In the embodiment, the case where the semi-solidified slurry 40 is molded by being placed from the vessel 20 into the mold of the molding mold and pressurized in the molding step has been described, but the present invention is not necessarily limited thereto. In the preparation step, the molten metal 10 may be directly charged into a mold, and the semi-solidified slurry 40 may be obtained in the mold by the stirring step, and then the mold may be directly pressurized and molded. In this case, the vessel 20 is a mold in which the molten metal 10 is filled.

Description of the reference numerals

10: Melt, 20: vessel, 21: bottom, 30: rod, 40: semi-setting slurry, 50: solid phase, 60: liquid phase, 100: molded body.

Claims

1. A method for producing a semi-solidified slurry comprising a solid phase and a liquid phase, said method comprising:

A preparation step of filling a molten metal into a bottomed vessel; and

And a stirring step of stirring the melt by reciprocating a rod placed in the melt in a longitudinal direction of the rod until a solid phase ratio of any part of the melt in the vessel becomes 80% or more.

2. The method for producing a semi-solidified slurry according to claim 1, wherein,

The position of the reciprocation orthogonal to the longitudinal direction of the rod in the stirring step is different from the position of the reciprocation orthogonal to the longitudinal direction of the rod immediately before.

3. The method for producing a semi-solidified slurry according to claim 1 or 2, wherein,

In a cross section orthogonal to the length direction of the rod,

A plurality of the rods are spaced apart from each other,

The center of one of the two adjacent bars is located in a circle having a radius of 7 times the length of the other bar and a center of the other bar.

4. The method for producing a semi-solidified slurry according to any one of claims 1 to 3, wherein the method for producing a semi-solidified slurry includes an electromagnetic stirring step of stirring the melt in the vessel by electromagnetic stirring after the preparation step and before the stirring step or simultaneously with the stirring step.

5. A method for producing a molded article comprising a molding step,

The molding step is a step of molding the semi-solidified slurry by pressurizing the semi-solidified slurry after the semi-solidified slurry is obtained by the method for producing a semi-solidified slurry according to any one of claims 1 to 4.

6. A molded article made of a metal, which is composed of primary crystals and eutectic crystals and has fiber streamlines continuously present therein,

When a plurality of eutectic area ratios are measured for each field of view, a coefficient of variation obtained by dividing a standard deviation of the eutectic area ratio, which is a ratio of an area of the eutectic appearing in the field of view to an area of the field of view on a predetermined cross section, by an average value of the eutectic area ratios is 0.15 or less.