Thixotropic molding material, method for producing thixotropic molding material, and thixotropic molded body

Abstract

To provide a thixomolded body with high mechanical strength and high rigidity, and to provide a material for thixomolding capable of manufacturing such a thixomolded body and a manufacturing method thereof.SOLUTION: A material for thixomolding includes: a metal body mainly composed of Mg; and a coating part comprising SiC particles adhering on the surface of the metal body via a binder, and mainly composed of SiC. A mass fraction of the SiC particles with respect to the total mass of the metal body and the SiC particles is 2.0 mass% or more and 40.0 mass% or less. Further, the binder preferably contains waxes. Furthermore, the content of the binder is preferably 0.001 mass% or more and 0.200 mass% or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a thixoforming material, a method for manufacturing the thixoforming material, and a thixoformed body.

Background Art

[0002] Magnesium has properties such as a low specific gravity, good electromagnetic wave shielding properties, vibration attenuation ability, machinability, and biocompatibility. Against this background, magnesium alloy parts have begun to be used in products such as automobiles, airplanes, mobile phones, and notebook computers.

[0003] For example, Patent Document 1 discloses a magnesium-based composite material in which SiC is dispersed in a base material made of magnesium or a magnesium alloy. Further, as a method for manufacturing such a composite material, a method is mentioned in which SiC is placed in a mold and then impregnated with a molten metal of magnesium, and then the obtained solidified product is pressurized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the method described in Patent Document 1, SiC is placed in a mold in advance, and then a molten metal of magnesium is introduced and compounded. In this method, it is necessary to bring SiC and magnesium into contact with each other and mix them in the mold, but depending on the shape of the mold, it is difficult to mix them uniformly. For this reason, there is a problem that the homogeneity of the manufactured molded body decreases, and the mechanical strength and rigidity of the molded body decrease.

Means for Solving the Problems

[0006] The thixoforming material according to the application example of the present invention is a metal body mainly composed of Mg and 、 Front a coating part attached to the surface of the metal body and provided with SiC particles mainly composed of SiC, An adhesive part that adheres the metal body and the coating part and contains a binder containing waxes; and has the mass fraction of the SiC particles in the total mass of the metal body and the SiC particles is 2.0 mass% or more and 40.0 mass% or less and the content of the binder is 0.001% by mass or more and 0.200% by mass or less; in the form of pellets or chips; the average particle size is 0.5 mm or more and 10 mm or less.

[0007] The manufacturing method of the thixoforming material according to the application example of the present invention is preparing a mixture containing a metal body mainly composed of Mg, SiC particles mainly composed of SiC, Containing waxes a binder, and a solvent, a preparation step; a stirring step of stirring the mixture; heating the stirred mixture to remove at least a part of the binder contained in the mixture to obtain a thixotropic molding material; a degreasing step; and has the mass fraction of the SiC particles in the total mass of the metal body and the SiC particles is 2.0 mass% or more and 40.0 mass% or less, the content of the binder is 0.001 mass% or more and 0.200 mass% or less and the thixotropic molding material has the metal body, a coating part that adheres to the surface of the metal body and contains the SiC particles, and an adhesive part that adheres the metal body and the coating part and contains the binder; the thixotropic molding material is in the form of pellets or chips, and the average particle size is 0.5 mm or more and 10 mm or less; .

[0008] The thixoformed body according to the application example of the present invention is a matrix part mainly composed of Mg, a particle part dispersed in the matrix part and mainly composed of SiC, and has the SiC content is 2.0 mass% or more and 40.0 mass% or lessand when the range of 500 μm square starting from the surface is defined as A1, the range of 500 μm square centered at a point 1 mm deep from the surface is defined as A2, the area fraction of the particle part in the range A1 is defined as As [%], and the area fraction of the particle part in the range A2 is defined as Ac [%], |As - Ac| / Ac is 30.0% or less; It is.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, the thixoforming material, the method for manufacturing the thixoforming material, and the thixoformed body of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0011] 1. Thixoforming Method First, the thixoforming method in which the thixoforming material according to the embodiment is used will be described. The thixoforming method is a molding method in which a pellet-shaped or chip-shaped material is heated in a cylinder to a solid-liquid coexisting state in which a liquid phase and a solid phase coexist, and then thixotropy is expressed by the rotation of a screw, and the obtained semi-solidified material is injected into a mold. According to such a thixoforming method, since the fluidity of the semi-solidified material is enhanced by heating and shearing, thin-walled parts and parts with complex shapes can be molded as compared with the die-casting method. FIG. 1 is a cross-sectional view showing an example of an injection molding machine used in the thixoforming method.

[0012] As shown in FIG. 1, the injection molding machine 1 includes a mold 2, a hopper 5, a heating cylinder 7, a screw 8, and a nozzle 9. The mold 2 forms a cavity Cv. When the thixotropic molding material 10 is put into the hopper 5, the thixotropic molding material 10 is supplied to the heating cylinder 7. The thixotropic molding material 10 supplied to the heating cylinder 7 is transferred while being sheared by the screw 8 while being heated by the heater 6. As a result, the thixotropic molding material 10 is semi-molten and slurried. The obtained slurry is injected into the cavity Cv in the mold 2 through the nozzle 9 without being exposed to the atmosphere. Then, by cooling the slurry injected into the cavity Cv, a thixotropic molded body is obtained.

[0013] In addition, other materials may be put into the hopper 5 together with the thixotropic molding material 10.

[0014] 2. Thixotropic molding material Next, the thixotropic molding material according to the embodiment will be described. FIG. 2 is a cross-sectional view schematically showing the thixotropic molding material according to the embodiment.

[0015] The thixotropic molding material 10 shown in FIG. 2 is a raw material used in the thixotropic molding method, and includes a chip-shaped metal body 11, a coating portion 12 attached to the surface of the metal body 11, and an adhesive portion 13 including a binder that bonds the metal body 11 and the coating portion 12.

[0016] 2.1. Metal body The metal body 11 is, for example, a slice obtained by cutting or cutting a Mg-based alloy cast in a mold or the like. Note that the manufacturing method of the metal body 11 is not limited to this.

[0017] The metal body 11 has Mg as the main component and contains various additive components. Examples of the additive components include lithium, beryllium, calcium, aluminum, silicon, manganese, iron, nickel, copper, zinc, strontium, yttrium, zirconium, silver, tin, gold, rare earth elements, etc. One or a mixture of two or more of these is used. Examples of the rare earth element include cerium.

[0018] The main component refers to the element with the highest content rate in the metal body 11. The content rate of the main component is preferably more than 50% by mass, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0019] The additive components preferably include aluminum and zinc. Thereby, the melting point of the metal body 11 is lowered and the fluidity of the slurry is improved. As a result, the moldability of the thixoforming material 10 can be enhanced.

[0020] Also, the additive components preferably include at least one selected from the group consisting of manganese, yttrium, strontium, and rare earth elements in addition to aluminum and zinc. Thereby, the mechanical properties, corrosion resistance, wear resistance, and thermal conductivity of the thixoformed body can be enhanced.

[0021] The additive components can exist in the metal body 11 in the form of a single substance, alloy, oxide, intermetallic compound, etc. Also, the additive components may be segregated at the grain boundaries of the metal structure such as Mg or Mg alloy in the metal body 11, or may be uniformly dispersed.

[0022] The average particle size of the thixoforming material 10 is not particularly limited, but is preferably 0.5 mm or more, and more preferably 1.5 mm or more and 10 mm or less. By setting the average particle size within the above range, the generation of bridges, etc. in the heating cylinder 7 of the injection molding machine 1 can be suppressed.

[0023] The average particle size of the thixotropic molding material 10 is the average value of the diameters of circles having the same area as the projected area of the thixotropic molding material 10. The average value is calculated from 100 or more randomly selected thixotropic molding materials 10.

[0024] The average aspect ratio of the thixotropic molding material 10 is preferably 5.0 or less, more preferably 4.0 or less. The thixotropic molding material 10 having such an average aspect ratio enhances the fillability in the heating cylinder 7 and improves the temperature uniformity during heating. As a result, a thixotropic molded body having high mechanical properties and high dimensional accuracy can be obtained.

[0025] The average aspect ratio of the thixotropic molding material 10 is the average value of the aspect ratios calculated by major axis / minor axis in the projected image of the thixotropic molding material 10. The average value is calculated from 100 or more randomly selected thixotropic molding materials 10. Further, the major axis is the maximum length that can be taken in the projected image, and the minor axis is the maximum length in the direction orthogonal to the major axis.

[0026] 2.2. Coated portion The coated portion 12 contains SiC particles 14 mainly composed of SiC. Specifically, for example, the coated portion 12 is formed by a plurality of SiC particles 14 adhering to the surface of the metal body 11.

[0027] The coated portion 12 preferably covers the entire surface of the metal body 11, but may cover a part of the surface.

[0028] The SiC particles 14 are not particularly limited as long as they are particles mainly composed of silicon carbide, and may be particles mainly composed of amorphous SiC or particles mainly composed of crystalline SiC.

[0029] The average particle size of the SiC particles 14 is set to be 0.3 μm or more and 20 μm or less, preferably 1 μm or more and 15 μm or less, and more preferably 2 μm or more and 10 μm or less. By setting the average particle size of the SiC particles 14 within the above range, the balance between the coating rate of the coating portion 12 and the SiC content in the thixotropic molding material 10 can be optimized. Further, when the SiC particles 14 are adhered to the surface of the metal body 11, the SiC particles 14 can be uniformly distributed, and the SiC particles 14 are less likely to fall off.

[0030] In addition, when the average particle size of the SiC particles 14 is less than the lower limit value, the SiC particles 14 are less likely to be dispersed, so the above-mentioned balance may deteriorate. On the other hand, when the average particle size of the SiC particles 14 exceeds the upper limit value, the SiC particles 14 may easily fall off.

[0031] Among the thixotropic molding materials 10, the mass fraction of the SiC particles 14 in the total mass of the metal body 11 and the SiC particles 14 is set to be 2.0 mass% or more and 40.0 mass% or less, preferably 3.0 mass% or more and 35.0 mass% or less, and more preferably 5.0 mass% or more and 20.0 mass% or less. By setting the mass fraction of the SiC particles 14 within the above range, the mechanical strength and rigidity of the produced thixotropic molded body can be increased. Further, by setting the mass fraction of the SiC particles 14 within the above range, it is possible to suppress a decrease in the moldability of the thixotropic molding material 10.

[0032] In addition, when the mass fraction of the SiC particles 14 is less than the lower limit value, there is a possibility that the mechanical strength and rigidity of the thixotropic molded body cannot be sufficiently increased. On the other hand, when the mass fraction of the SiC particles 14 exceeds the upper limit value, the moldability of the thixotropic molding material 10 may decrease.

[0033] The coating portion 12 may contain substances other than the SiC particles 14. In that case, the content of the substances other than the SiC particles 14 may be less than the content of the SiC particles 14 in terms of mass ratio.

[0034] Further, the SiC particles 14 may contain elements other than Si and C. In that case, the content of elements other than Si and C may be less than the content of Si and less than the content of C in terms of mass ratio.

[0035] 2.3. Adhesive part The adhesive part 13 is interposed between the metal body 11 and the SiC particles 14 or between the SiC particles 14.

[0036] The adhesive part 13 contains a binder. As the binder, an organic material for binding the metal body 11 and the coating part 12 is used. For example, polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, styrene resins such as polystyrene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, polyethers, polyvinyl alcohol, polyvinyl pyrrolidone, or copolymers thereof, various resins, waxes, alcohols, higher fatty acids, fatty acid metals, higher fatty acid esters, higher fatty acid amides, nonionic surfactants, silicone-based lubricants, etc. are used. Further, the binder may be a mixture containing at least one of these components and other components, or may be a mixture containing two or more of these components.

[0037] Among these, the binder preferably contains waxes, and more preferably contains paraffin wax or its derivatives. Waxes have good binding properties and can strongly bond between the metal body 11 and the SiC particles 14 or between the SiC particles 14. Further, in combination with the degreasing conditions, a thixotropic molding material capable of suppressing gas generation during molding can be realized.

[0038] Examples of waxes include natural waxes such as candelilla wax, carnauba wax, rice wax, wood rosin, plant waxes such as jojoba oil, beeswax, animal waxes such as lanolin and spermaceti wax, mineral waxes such as montan wax, ozokerite, and ceresin, paraffin wax, microcrystalline wax, petroleum waxes such as petrolatum, synthetic hydrocarbons such as polyethylene wax, modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives, hydrogenated waxes such as hydrogenated castor oil and hydrogenated castor oil derivatives, fatty acids such as 12-hydroxy stearic acid, acid amides such as stearic acid amide, and synthetic waxes such as imide phthalate anhydride esters.

[0039] As described above, the thixotropic molding material 10 according to the embodiment includes a metal body 11 and a coating portion 12. The metal body 11 is mainly composed of Mg. The coating portion 12 adheres to the surface of the metal body 11 via a binder and contains SiC particles 14 mainly composed of SiC. In the thixotropic molding material 10, the mass fraction of the SiC particles 14 in the total mass of the metal body 11 and the SiC particles 14 is 2.0% by mass or more and 40.0% by mass or less.

[0040] By performing thixotropic molding using such a thixotropic molding material 10, a thixotropic molded body in which SiC is uniformly dispersed can be manufactured. In such a thixotropic molded body, since SiC having a higher Young's modulus than Mg is uniformly dispersed, the rigidity can be increased. Further, since SiC is uniformly dispersed, it is possible to inhibit the coarsening of Mg crystals precipitated during the solidification process in thixotropic molding. As a result, the Mg crystals can be made finer and the slip at the grain boundaries can be suppressed. As a result, the mechanical strength of the obtained thixotropic molded body can be increased.

[0041] Further, the thixotropic molding material 10 may contain additives other than the above-described metal body 11, coating portion 12, and adhesive portion 13. Examples of the additives include coupling agents, surfactants, dispersants, lubricants, antioxidants, ultraviolet absorbers, thickeners, rust preventives, antiseptics, fungicides, and the like.

[0042] 3. Manufacturing Method of Thixotropic Molding Material Next, a method for manufacturing the above-described thixotropic molding material 10 will be described. FIG. 3 is a process diagram for explaining the manufacturing method of the thixotropic molding material according to the embodiment.

[0043] The manufacturing method of the thixotropic molding material 10 shown in FIG. 3 includes a preparation step S102, a drying step S104, a stirring step S106, and a degreasing step S108.

[0044] 3.1. Preparation Step In the preparation step S102, a mixture containing the metal body 11, SiC particles 14, a binder, and a solvent is prepared. The metal body 11 is the same as the above-described metal body 11. Also, the SiC particles 14 are the same as the above-described SiC particles 14.

[0045] The solvent is not particularly limited as long as it is a liquid that disperses the binder. Examples of the solvent include water, isopropanol, acetone, and the like. For mixing, a mixer, a kneader, or the like is used. Note that this step may be a step of preparing a previously prepared mixture.

[0046] The content of the binder in the mixture is not particularly limited, but is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less. By setting the content of the binder within the above range, the SiC particles 14 can be uniformly dispersed based on the dispersing action of the binder.

[0047] Note that if the binder content is below the lower limit value, the amount of the binder is insufficient, making it difficult to uniformly adhere the SiC particles 14 to the metal body 11 and also making it difficult to uniformly disperse the SiC particles 14. On the other hand, if the binder content exceeds the upper limit value, the amount of the binder becomes excessive, and the SiC particles 14 that are not adhered to the metal body 11 are likely to aggregate. Therefore, in the debinding process S108 described later, the amount of binder residue increases, and internal defects are likely to occur in the thixoformed body.

[0048] The temperature of the solvent is preferably set to be equal to or higher than the melting point of the binder as needed. Thereby, the binder is likely to dissolve in the solvent. As a result, the binder can be dispersed more uniformly. The temperature of the solvent is preferably set to be 10°C or more higher than the melting point of the binder, and more preferably set to be 20°C or more and 50°C or less higher.

[0049] In this case, the above-described mixture may be put into a container and the entire container may be heated from the outside using a hot bath or the like.

[0050] The melting point of the binder used is not particularly limited, but is preferably 40°C or more and 80°C or less, more preferably 43°C or more and 65°C or less, and even more preferably 45°C or more and 60°C or less. If the melting point of the binder is within the above range, the binder can be efficiently melted in a short time. Further, if the melting point of the binder is within the above range, the thixoforming material 10 to be manufactured has good lubricity in thixoforming and can enhance the fluidity of the slurry.

[0051] 3.2. Drying Process In the drying process S104, the mixture is dried. Thereby, the SiC particles 14 are adhered to the surface of the metal body 11 via the binder and the solvent is volatilized to obtain a dried body. Further, in the present embodiment, since the SiC particles 14 are dispersed using the binder, the SiC particles 14 can be adhered to the surface of the metal body 11 with a uniform thickness.

[0052] For drying, methods such as heating the mixture and exposing the mixture to gas can be used. Among these, when heating the mixture, for example, the entire container containing the mixture can be heated using a hot bath or the like. In the drying step S104, all the solvents in the mixture may be removed, or some solvents may remain without being removed.

[0053] The temperature when heating the mixture may be equal to or higher than the temperature at which the solvent volatilizes and the binder softens. Specifically, it is set according to the composition of the solvent, preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 80°C or lower. Thereby, while suppressing the detachment of the SiC particles 14 attached to the surface of the metal body 11, the solvent can be volatilized and removed.

[0054] Also, the heating time of the mixture is appropriately set according to the heating temperature. As an example, it is preferably 10 minutes or more and 300 minutes or less, and more preferably 20 minutes or more and 200 minutes or less.

[0055] Note that the drying step S104 may be performed as necessary, may be omitted, or the drying step S104 and the stirring step S106 may be performed simultaneously.

[0056] 3.3. Stirring Step In the stirring step S106, the mixture is stirred. When the drying step is performed, the dried mixture is stirred. Stirring methods such as using a stirring rod or a stir bar, and shaking the container containing the mixture with a lid can be used. By such stirring, the SiC particles 14 can be attached to the surface of the metal body 11 via the binder. Note that a part of the SiC particles 14 may be directly attached to the surface of the metal body 11 without passing through the binder. Also, stirring can suppress the aggregation of the metal bodies 11 into lumps.

[0057] Note that after the stirring step S106, the drying step S104 and the stirring step S106 may be repeated as necessary. As a result, the adhesion of the SiC particles 14 is repeated, so that the SiC particles 14 can be adhered to the surface of the metal body 11 in multiple layers. Consequently, more SiC particles 14 can be adhered to the surface of the metal body 11. The number of repetitions is not particularly limited, but is, for example, 2 or more and 10 or less. Also in this case, the drying step S104 and the stirring step S106 may be performed simultaneously.

[0058] 3.4. Degreasing Step In the degreasing step S108, the stirred mixture is subjected to a degreasing treatment. Thereby, the thixotropic molding material 10 is obtained. Examples of the degreasing treatment include a method of heating the mixture and a method of exposing the mixture to a gas that decomposes the binder. As a result, at least a part of the binder contained in the mixture can be removed. Consequently, it is possible to prevent a large amount of the binder from being transferred into the heating cylinder 7 and suppress the generation of a large amount of gas in the heating cylinder 7.

[0059] The heating temperature of the mixture in the degreasing treatment is not particularly limited as long as it is a temperature at which the binder is thermally decomposed, but is preferably 200°C or higher and 500°C or lower, and more preferably 250°C or higher and 450°C or lower. By setting the heating temperature within the above range, it is possible to appropriately remove the binder while suppressing the adverse effect on the metal body 11 due to the degreasing treatment.

[0060] Note that if the heating temperature is lower than the lower limit value, a large amount of the binder that is not removed remains, and there is a risk of generating a large amount of gas in the heating cylinder 7. On the other hand, if the heating temperature exceeds the upper limit value, there is a risk of causing an adverse thermal effect on the metal body 11, or all of the binder being removed, resulting in the SiC particles 14 falling off the metal body 11.

[0061] The heating time of the mixture in the degreasing treatment is not particularly limited, and for example, it may be 5 minutes or more, preferably 1 hour or more and 100 hours or less, and more preferably 10 hours or more and 50 hours or less. Thereby, while suppressing the adverse effects on the metal body 11 associated with the degreasing treatment, the binder can be appropriately removed.

[0062] The amount of the binder after degreasing, that is, the content of the binder in the thixoforming material 10 is not particularly limited, but is preferably 0.001% by mass or more and 0.200% by mass or less, more preferably 0.010% by mass or more and 0.100% by mass or less, and still more preferably 0.015% by mass or more and 0.040% by mass or less. By setting the content of the binder in the thixoforming material 10 within the above range, while ensuring the adhesiveness of the coating portion 12 by the adhesive portion 13, it is possible to prevent the amount of the binder that thermally decomposes in the heating cylinder 7 from becoming more than necessary.

[0063] In addition, when the content rate of the binder is less than the lower limit value, the amount of the binder is insufficient, and the coating portion 12 may easily fall off. On the other hand, when the content rate of the binder exceeds the upper limit value, the amount of the binder becomes excessive, a large amount of gas is generated in the heating cylinder 7, and voids are likely to occur in the thixoformed body.

[0064] As described above, the method for manufacturing the thixoforming material 10 according to the present embodiment includes a preparation step S102, a stirring step S106, and a degreasing step S108. In the preparation step S102, a mixture containing a metal body 11 mainly composed of Mg, SiC particles 14 mainly composed of SiC, a binder, and a solvent is prepared. In the stirring step S106, the mixture is stirred. In the degreasing step S108, the stirred mixture is heated to remove at least a part of the binder contained in the mixture, and the thixoforming material 10 is obtained. And the mass fraction of the SiC particles 14 in the total mass of the metal body 11 and the SiC particles 14 is 2.0% by mass or more and 40.0% by mass or less. Further, the content of the binder in the thixoforming material 10 is 0.001% by mass or more and 0.200% by mass or less.

[0065] According to such a configuration, even if the amount of SiC particles 14 is large, the SiC particles 14 can be attached to the surface of the metal body 11 via the binder, so that the SiC particles 14 can be uniformly dispersed in the heating cylinder 7. As a result, the SiC particles 14 can function as a filler and can reduce the size of Mg crystals precipitated during the solidification process. As a result, a thixoformed body having high mechanical strength and high rigidity can be obtained.

[0066] Note that the thixoforming material 10 does not necessarily have to be manufactured by this manufacturing method. That is, the thixoforming material 10 may be manufactured, for example, without undergoing the degreasing step S108.

[0067] 4. Thixoformed body Next, a thixoformed body according to an embodiment will be described. FIG. 4 is a partial cross-sectional view schematically showing a thixoformed body according to an embodiment.

[0068] The thixoformed body 100 shown in FIG. 4 is a formed body obtained by a thixoforming method, and has a matrix portion 200 and a particle portion 300. The matrix portion 200 is a portion mainly derived from the metal body 11 of the thixoforming material 10 and contains Mg as a main component. The particle portion 300 is a portion mainly derived from the coating portion 12 of the thixoforming material 10 and contains SiC as a main component.

[0069] As shown in FIG. 4, when the cross section of the thixoformed body 100 is viewed, the area occupied by the matrix portion 200 is larger than the area occupied by the particle portion 300. Therefore, the particle portion 300 is in a state of being dispersed in the matrix portion 200.

[0070] In the thixoformed body 100, the SiC content is 2.0% by mass or more and 40.0% by mass or less, preferably 3.0% by mass or more and 35.0% by mass or less, and more preferably 5.0% by mass or more and 30.0% by mass or less.

[0071] In such a thixoformed body 100, since SiC is dispersed, the coarsening of Mg crystals contained in the matrix part 200 is suppressed by SiC, and the crystallization grain size is made finer. Further, the particle part 300 mainly composed of SiC functions as a filler. Thereby, the thixoformed body 100 has high mechanical strength and high rigidity.

[0072] Note that the content rate of SiC is calculated from the area fraction occupied by the particle part 300, the specific gravity of the matrix part 200, and the specific gravity of the particle part 300 in the cross section of the thixoformed body 100. As the specific gravity of the matrix part 200, for example, the specific gravity of the material constituting the metal body 11 can be used, and as the specific gravity of the particle part 300, the specific gravity of the material constituting the SiC particles 14 can be used.

[0073] Further, the content rate of Si and the content rate of C may be obtained by elemental analysis, and the content rate of SiC may be calculated from them.

[0074] Examples of the elemental analysis method include the atomic absorption spectrometry for iron and steel specified in JIS G 1257:2000, the ICP emission spectrometry for iron and steel specified in JIS G 1258:2007, the spark discharge emission spectrometry for iron and steel specified in JIS G 1253:2002, the fluorescent X-ray analysis method for iron and steel specified in JIS G 1256:1997, the gravimetric, titrimetric, and absorptiometric methods specified in JIS G 1211 to G 1237, and the like.

[0075] In particular, for the measurement of the content rate of C, for example, the oxygen flow combustion (high-frequency induction heating furnace combustion)-infrared absorption method specified in JIS G 1211:2011 is used. Examples of the analyzer corresponding to this measurement method include carbon and sulfur analyzers manufactured by LECO Japan Co., Ltd.

[0076] In FIG. 4, a range A1 of 500 μm square starting from the surface 101 of the thixoformed body 100 and a range A2 of 500 μm square centered at a point 1 mm deep from the surface 101 are illustrated. When the area fraction of the particle portion 300 in the range A1 is As [%] and the area fraction of the particle portion 300 in the range A2 is Ac [%], in the thixoformed body 100 according to the present embodiment, |As - Ac| / Ac is preferably 30.0% or less, more preferably 25.0% or less, and even more preferably 20.0% or less.

[0077] In such a thixoformed body 100, the difference in the occupied area of the particle portion 300 is suppressed to be small between the range A1 located near the surface 101 and the range A2 located deeper than that. That is, in the thixoformed body 100, the uneven distribution of the particle portion 300 is suppressed. Thereby, the mechanical strength and rigidity of the thixoformed body 100 can be further increased.

[0078] The area fraction As of the particle portion 300 in the range A1 is calculated as follows. First, in the observation image of the range A1, the area of the particle portion 300 is calculated by image processing. For the image processing, for example, image analysis software such as OLYMPUS Stream can be used. Also, the magnification of the observation image is preferably 300 times or more. Next, the ratio of the area of the particle portion 300 to the total area of the range A1 is calculated. This ratio becomes the area fraction As. Note that the range A1 is a range forming a square with a side length of 500 μm, and at least a part thereof may be in contact with the surface 101.

[0079] The area fraction Ac of the particle portion 300 in the range A2 is also calculated in the same manner as the area fraction As. Note that the range A2 is a range forming a square with a side length of 500 μm, and its center point O is a point 1 mm deep from the surface 101. Also, in the cross section of the thixoformed body 100, when the length in the depth direction is less than 2 mm, the midpoint in the depth direction can be regarded as the center point O.

[0080] The area fraction As and the area fraction Ac are each determined by the SiC content in the thixoformed body 100, but are preferably 0.5% or more and 30.0% or less, more preferably 1.5% or more and 20.0% or less, and even more preferably 2.5% or more and 15.0% or less. Thereby, the thixoformed body 100 has particularly high mechanical strength and high rigidity.

[0081] The average particle size of the particle portion 300 is preferably 0.3 μm or more and 10.0 μm or less, and more preferably 1.0 μm or more and 5.0 μm or less. If the average particle size of the particle portion 300 is within the above range, since the particle portion 300 has a small diameter as a whole, it is less likely to become a starting point for cracks or the like. In addition, the particle portion 300 can be distributed more uniformly, and the function of suppressing the coarsening of Mg crystals can be exerted in a wider region. Thereby, the mechanical strength and rigidity of the thixoformed body 100 can be further increased.

[0082] The average particle size of the particle portion 300 is calculated as follows. First, in the ranges A1 and A2, all the particle sizes of the included particle portions 300 are measured. The particle size of the particle portion 300 is the intermediate value between the length of the major axis and the length of the minor axis in the image of the particle portion 300 included in the observation image. The average value of the particle sizes calculated in this way becomes the average particle size of the particle portion 300.

[0083] Further, the average aspect ratio of the particle portion 300 is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. If the average aspect ratio of the particle portion 300 is within the above range, the anisotropy of the structure of the particle portion 300 becomes small. Therefore, the mechanical strength and rigidity of the thixoformed body 100 can be increased isotropically.

[0084] The average aspect ratio of the particle portion 300 is calculated as follows. First, in the ranges A1 and A2, the lengths of the major axis and the minor axis of the included particle portion 300 are determined respectively. Next, the ratio of the length of the major axis to the length of the minor axis is defined as the "aspect ratio". The average value of the aspect ratios calculated in this way is the average aspect ratio of the particle portion 300.

[0085] In the thixoformed body 100, due to the action of the particle portion 300, as described above, the growth of Mg crystals deposited on the matrix portion 200 is suppressed.

[0086] The average grain size of Mg crystals in the thixoformed body 100 is preferably 1.0 μm or more and 8.0 μm or less, more preferably 2.0 μm or more and 7.0 μm or less, and even more preferably 3.0 μm or more and 6.0 μm or less.

[0087] If the average grain size of Mg crystals is within the above range, slippage is particularly unlikely to occur at the grain boundaries of Mg crystals. Therefore, the mechanical strength of the thixoformed body 100 can be particularly enhanced.

[0088] In addition, Mg crystals can be identified on an image by performing crystal orientation analysis (EBSD analysis) on the cross-sectional surface of the matrix portion 200. Thereby, the median value of the length of the major axis and the length of the minor axis of the Mg crystals identified on the image can be defined as the grain size of the Mg crystals. By averaging this grain size with 100 or more measurement values, the average grain size of the Mg crystals can be obtained.

[0089] Also, the tensile strength of the thixoformed body 100 is preferably 170 MPa or more and 350 MPa or less, more preferably 200 MPa or more and 300 MPa or less. Further, the Young's modulus of the thixoformed body 100 is preferably 40 GPa or more and 80 GPa or less, more preferably 44 GPa or more and 70 GPa or less.

[0090] The thixoformed body 100 having a tensile strength and a Young's modulus within the above ranges has particularly high specific strength and specific rigidity. Since such a thixoformed body 100 is lightweight and has high strength, it is suitable for, for example, parts used in transportation equipment such as automobiles and aircraft, and parts used in mobile devices such as mobile phones and notebook computers.

[0091] The tensile strength of the thixoformed body 100 is measured as follows. First, a test piece is cut out from the thixoformed body 100. Examples of the test piece include No. 13 test pieces specified in JIS. Next, the test piece is attached to a tensile testing machine, and the stress corresponding to the maximum force applied to the test piece at 25°C is calculated. The obtained stress is taken as the tensile strength of the thixoformed body 100.

[0092] Also, the Young's modulus of the thixoformed body 100 is measured as follows. First, a test piece is cut out from the thixoformed body 100. Next, the test piece is attached to a tensile testing machine, and a tensile load is applied to the test piece at 25°C. Next, the change amount of the tensile strain when the tensile load is varied and the change amount of the tensile stress when the tensile load is varied are calculated respectively. Then, the ratio of the latter change amount to the former change amount is calculated, and this is taken as the Young's modulus of the thixoformed body 100. Note that the Young's modulus of the thixoformed body 100 may be a value measured by a method other than the above measurement method, for example, the resonance method or the ultrasonic pulse method.

[0093] Also, the Vickers hardness of the surface 101 of the thixoformed body 100 is preferably 80 or more and 350 or less, more preferably 90 or more and 300 or less, and even more preferably 100 or more and 250 or less.

[0094] If the Vickers hardness is within the above range, a thixoformed body 100 with high surface hardness and less likely to be scratched can be realized.

[0095] The Vickers hardness of the surface 101 of the thixoformed body 100 is measured in accordance with the method of the Vickers hardness test specified in JIS Z 2244:2009. The measurement load shall be 200 gf.

[0096] Also, the thermal conductivity of the thixoformed body 100 is preferably 52 W / (m·K) or more, more preferably 54 W / (m·K) or more, and even more preferably 57 W / (m·K) or more. The thixoformed body 100 having such a thermal conductivity can be applied, for example, to a site where heat dissipation is required.

[0097] The thermal conductivity of the thixoformed body 100 is measured, for example, by the laser flash method or the like.

[0098] As described above, the thixoforming material, the method for manufacturing the thixoforming material, and the thixoformed body of the present invention have been described based on the illustrated embodiments. However, the thixoforming material and the thixoformed body of the present invention are not limited to the above embodiments. For example, arbitrary components may be added to the above embodiments. Further, the method for manufacturing the thixoforming material of the present invention may have arbitrary purpose steps added to the above embodiments.

Examples

[0099] Next, specific examples of the present invention will be described. 5. Manufacture of Thixoforming Material

[0100] 5.1. Sample No. 1 First, a magnesium alloy chip, which is a metal body, SiC particles, a binder, and a solvent were mixed to obtain a mixture. For the magnesium alloy chip, a 4 mm × 2 mm × 1 mm chip made of AZ91D alloy manufactured by STU Co., Ltd. was used. The AZ91D alloy is a Mg-based alloy containing 9% by mass of Al and 1% by mass of Zn. Also, as the binder, "Paraffin Wax 115" manufactured by Nippon Seisen Co., Ltd. was used. The melting point of Paraffin Wax 115 was 48°C. Further, for the solvent, 35 mL of isopropanol was used per 4.5 g of the binder.

[0101] Next, the obtained mixture was heated to obtain a dried body. Subsequently, the obtained dried body was stirred. Then, after further heating the stirred dried body, the operation of stirring was repeated three times. For stirring, a method of shaking the container containing the dried body was used.

[0102] Next, the stirred dried body was subjected to a degreasing treatment. As a result, at least a part of the binder was removed to obtain a thixoforming material. In the obtained thixoforming material, almost the entire surface of the magnesium alloy chip was covered with SiC particles. The manufacturing conditions in the above manufacturing method are shown in Table 1. In Table 1, the input amount of SiC particles is the ratio of the mass of the input SiC particles to the total mass of the magnesium alloy chip and SiC particles. Also, the input amount of the binder is the ratio of the mass of the input binder to the total mass of the thixoforming material.

[0103] 5.2. Sample Nos. 2 to 5 A thixoforming material was obtained in the same manner as in Sample No. 1, except that the manufacturing conditions were changed as shown in Table 1.

[0104] 5.3. Sample No. 6 A thixoforming material was obtained in the same manner as in Sample No. 1, except that SiC particles and the binder were not used.

[0105] 5.4. Sample Nos. 7 to 14 The thixoforming material was obtained in the same manner as Sample No. 1, except that the manufacturing conditions were changed as shown in Table 1. When manufacturing the thixoforming material of Sample No. 13, the degreasing treatment was omitted.

[0106] 5.5. Sample No. 15 The thixoforming material was obtained in the same manner as Sample No. 1, except that SiC particles were used while no binder was used.

[0107] In Table 1, for the thixoforming materials of each sample number, those corresponding to the present invention were designated as "Examples", and those not corresponding to the present invention were designated as "Comparative Examples".

[0108] 6. Evaluation of Thixoforming Materials 6.1. Amount of SiC Particles after Degreasing For the thixoforming materials of each sample number, the amount of SiC particles after degreasing was calculated by the following method.

[0109] First, the mass M1 of the thixoforming material was measured. Since the thixoforming material has undergone degreasing treatment, the remaining binder is considered to be almost zero and is not taken into account in the calculation. Next, the thixoforming material was immersed in acetone and washed with an ultrasonic cleaner for 10 minutes. As a result, the attached SiC particles can be removed, and only the magnesium alloy chips can be taken out. Next, the magnesium alloy chips after washing were taken out of the acetone, dried, and then the mass M2 was measured.

[0110] Then, the mass fraction of SiC particles with respect to the magnesium alloy chips calculated by (M1 - M2) / M1 × 100 was taken as the amount of SiC particles after degreasing [%]. The calculation results are shown in Table 1.

[0111] 6.2. Adhesion Rate of SiC The adhesion rate of SiC particles was calculated by dividing the amount of SiC particles after degreasing by the input amount of SiC particles. The calculation results are shown in Table 1.

[0112] 6.3. Amount of Binder after Degreasing For the thixotropic molding materials of each sample No., the amount of the binder after degreasing was calculated by the following method.

[0113] First, for one grain of the thixotropic molding material, the thermogravimetric change in the temperature range of 50 to 450 °C was measured using a differential thermal thermogravimetric simultaneous measurement device (TGA / DSC 1LF) manufactured by Mettler Toledo. The temperature increase was carried out at a rate of 10 °C / min while flowing air at a flow rate of 30 mL / min under the atmosphere. Then, in order to eliminate the influence of the solvent, based on 200 °C, the weight change at 450 °C was calculated as the amount of the binder after degreasing. The calculation results are shown in Table 1.

[0114] [Table 1]

[0115] As shown in Table 1, in the thixotropic molding materials corresponding to the examples, although the amount of the binder was minimized by degreasing, it was confirmed that SiC particles adhered with a sufficient adhesion rate.

[0116] 7. Manufacture of Thixotropic Molded Body 7.1. Sample No. 16 The thixotropic molding material of Sample No. 1 was put into an injection molding machine to obtain a thixotropic molded body of Sample No. 16. As the injection molding machine, a magnesium injection molding machine JLM75MG manufactured by Japan Steel Works, Ltd. was used.

[0117] 7.2. Sample Nos. 17 to 30 Thixotropic molded bodies were obtained in the same manner as Sample No. 16 except that the manufacturing conditions were changed as shown in Table 2.

[0118] 8. Analysis of Thixotropic Molded Body 8.1. Cross-Section Observation The thixotropic molded bodies of each sample No. were cut, and the cut surfaces were observed with an optical microscope. Next, image processing was performed on the observed images to identify the particle portions and measure the average aspect ratio and average particle size of the particle portions. The measurement results are shown in Table 2.

[0119] Also, ranges A1 and A2 as shown in FIG. 4 were specified, and the area fractions As and Ac of the particle portions were calculated. Then, |As - Ac| / Ac was calculated as a percentage. The calculation results are shown in Table 2.

[0120] 8.2. Content of SiC For the thixoformed bodies of each sample No., the content of SiC was calculated from the area fraction of the particle portion and the specific gravities of Mg and SiC. The calculation results are shown in Table 2.

[0121] 8.3. Average grain size of Mg crystals For the thixoformed bodies of each sample No., the average grain size of Mg crystals was calculated by EBSD analysis. The calculation results are shown in Table 2.

[0122] 9. Evaluation of thixoformed bodies 9.1. Formability The thixoformed bodies of each sample No. were observed, and the forming state of the thixoformed bodies was evaluated based on the fluidity of the molten metal, the presence or absence of internal defects such as shrinkage cavities and entrained air, etc. Specifically, those with poor fluidity of the molten metal and many internal defects were rated as "NG", and those with relatively few such defects were rated as "OK". The evaluation results are shown in Table 2.

[0123] 9.2. Tensile strength For the thixoformed bodies of each sample No., the tensile strength was measured. Specifically, test pieces conforming to JIS standards were formed from the thixoformed bodies, and the tensile strength was measured using a tensile testing machine. The measurement results are shown in Table 2.

[0124] 9.3. Young's modulus For the thixoformed bodies of each sample No., the Young's modulus was measured. The measurement results are shown in Table 2.

[0125] 9.4. Thermal conductivity For the thixoformed bodies of each sample No., the thermal conductivity was measured. The measurement results are shown in Table 2.

[0126]

Table 2

[0127] As is clear from Table 2, it was found that the thixoformed body corresponding to the example had higher mechanical strength and higher rigidity than the thixoformed body corresponding to the comparative example. Also, when the SiC content was too low, the mechanical strength and rigidity could not be sufficiently increased. On the other hand, when the SiC content was too high, it was found that the formability became poor.

[0128] Furthermore, in the comparative example where no binder was added in the production of the thixoforming material, the mechanical strength and rigidity of the thixoformed body could not be increased. The reason for this is that SiC particles fell off from the magnesium alloy chips and the SiC particles could not be sufficiently dispersed.

Explanation of Signs

[0129] 1... Injection molding machine, 2... Mold, 5... Hopper, 6... Heater, 7... Heating cylinder, 8... Screw, 9... Nozzle, 10... Thixoforming material, 11... Metal body, 12... Coated part, 13... Adhesive part, 14... SiC particles, 100... Thixoformed body, 101... Surface, 200... Matrix part, 300... Particle part, A1... Range, A2... Range, Cv... Cavity, O... Center point, S102... Preparation process, S104... Drying process, S106... Stirring process, S108... Debinding process

Claims

1. A metal body mainly composed of Mg, a coating portion adhering to the surface of the metal body and comprising SiC particles mainly composed of SiC, an adhesive portion that adheres the metal body and the coating portion and contains a binder containing waxes, having, wherein the mass fraction of the SiC particles in the total mass of the metal body and the SiC particles is 2.0% by mass or more and 40.0% by mass or less, the content rate of the binder is 0.001% by mass or more and 0.200% by mass or less, being in the form of pellets or chips, a thixoforming material characterized in that the average particle size is 0.5 mm or more and 10 mm or less.

2. The thixoforming material according to Claim 1, wherein the average particle size of the SiC particles is 0.3 μm or more and 20 μm or less.

3. The thixoforming material according to Claim 1 or 2, wherein the coating portion contains the SiC particles adhering in multiple layers.

4. a preparation step of preparing a mixture containing a metal body mainly composed of Mg, SiC particles mainly composed of SiC, a binder containing waxes, and a solvent; a stirring step of stirring the mixture; a degreasing step of heating the stirred mixture to remove at least a part of the binder contained in the mixture to obtain a thixoforming material; having, wherein the mass fraction of the SiC particles in the total mass of the metal body and the SiC particles is 2.0% by mass or more and 40.0% by mass or less, the content rate of the binder is 0.001% by mass or more and 0.200% by mass or less, the thixoforming material has the metal body, a coating portion adhering to the surface of the metal body and containing the SiC particles, and an adhesive portion that adheres the metal body and the coating portion and contains the binder a method for manufacturing a thixoforming material, characterized in that the thixoforming material is in the form of pellets or chips and the average particle size is 0.5 mm or more and 10 mm or less.

5. The method for manufacturing a thixoforming material according to Claim 4, further having a drying step provided between the preparation step and the stirring step for drying the mixture.

6. The method for manufacturing a thixoforming material according to Claim 5, wherein the drying step and the stirring step are repeated.

7. a matrix portion mainly composed of Mg, a particle portion dispersed in the matrix portion and mainly composed of SiC, having, wherein the SiC content is 2.0% by mass or more and 40.0% by mass or less, Let the range of 500 μm square starting from the surface be A1, the range of 500 μm square centered at a point 1 mm deep from the surface be A2, the area fraction of the particle part in the range A1 be As [%], and the area fraction of the particle part in the range A2 be Ac [%]. A thixotropic molded body, wherein |As - Ac| / Ac is 30.0% or less.

8. The thixotropic molded body according to claim 7, wherein the average particle size of the particle part is 0.3 μm or more and 10.0 μm or less.

9. The thixotropic molded body according to claim 7 or 8, wherein the average aspect ratio of the particle part is 3.0 or less.

10. The matrix part contains Mg crystals, The thixotropic molded body according to any one of claims 7 to 9, wherein the average particle size of the Mg crystals is 1.0 μm or more and 8.0 μm or less.

11. The tensile strength is 170 MPa or more and 350 MPa or less, The thixotropic molded body according to any one of claims 7 to 10, wherein the Young's modulus is 40 GPa or more and 80 GPa or less.

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