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

Abstract

To provide a thixomolded body with 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 containing Si particles adhering on the surface of the metal body via a binder, and mainly composed of Si. An average particle diameter of the Si particles is 1 μm or more and 100 μm or less, and a mass fraction of the Si particles with respect to the total mass of the metal body and the Si particles is 1.0 mass% or more and 30.0 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 thixomolded article.

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, aircraft, mobile phones, and notebook computers.

[0003] As a method for manufacturing magnesium parts, the thixoforming method is known. In the thixoforming method, a pellet-shaped or chip-shaped material is heated in a cylinder to a solid-liquid coexistence state in which a liquid phase and a solid phase coexist, and then thixotropy is developed 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 increased by heating and shearing, thin-walled parts and parts having a complex shape can be formed as compared with the die-casting method.

[0004] For example, Patent Document 1 discloses a metal base material composite material in which at least 2% by volume of Mg 2 Si phase is incorporated into a metal base material containing magnesium or a magnesium alloy, and a material for manufacturing a casting by thixoforming is disclosed. Specifically, magnesium or magnesium alloy particles and silicon or silicon alloy particles are introduced into a thixoforming process and solidified under shear. Thereby, the high-temperature characteristics of the casting can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1, when manufacturing a casting, particles such as magnesium and particles such as silicon are directly introduced into the thixoforming process. For this reason, when applying a shearing force by a screw in a heated cylinder, it is necessary to uniformly mix the particles. However, with only mixing by a screw, due to the separation caused by the difference in specific gravity of the particles and insufficient mixing time, they do not mix uniformly, and segregation of silicon or a silicon alloy is likely to occur in the mixture. When such segregation occurs, the properties of the casting cannot be sufficiently improved.

Means for Solving the Problems

[0007] The thixoforming material according to an application example of the present invention comprises a metal body mainly composed of Mg, a covering portion containing Si particles mainly composed of Si and adhering to the surface of the metal body via a binder, and has wherein the average particle diameter of the Si particles is 1 μm or more and 100 μm or less, and the mass fraction of the Si particles in the total mass of the metal body and the Si particles is 1.0 mass % or more and 30.0 mass% or less. % or less. and The content rate of the binder in the thixotropic molding material obtained after degreasing is 0.00 1 mass% or more and 0.200 mass% or less It is characterized by this.

[0008] The method for manufacturing a thixoforming material according to an application example of the present invention comprises a preparation step of preparing a mixture containing a metal body mainly composed of Mg, Si particles mainly composed of Si, a binder, and a solvent, a stirring step of stirring the mixture, heating the stirred mixture to at least one of the binders contained in the mixture and A degreasing process of removing parts to obtain a thixoforming material, having, the mass fraction of the Si particles in the total mass of the metal body and the Si particles is 1.0 mass % or more and 30.0 mass% or less, obtained after the degreasing process the content rate of the binder in the thixoforming material is 0 .001 mass% or more and 0.200 mass% or less, which is characterized in that.

[0009] The thixoformed body according to the application example of the present invention is, a matrix part mainly composed of Mg, particles dispersed in the matrix part and mainly composed of Mg2Si, having, the maximum particle size of the particle part is 1.0 μm or more 20.0 μm or less and, The content rate of Si is 5.0 mass% or more and 20.0 mass% or less, and observing the cross section, when the area fraction of the particle part in the range of 500 μm square starting from the surface is designated as As [%], and the area fraction of the particle part in the range of 500 μm square centered on the point at a depth of 1 mm from the surface is designated as Ac [%], |As - Ac| / Ac is and, which is characterized in that. 20.0% below

Brief Description of Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the thixoforming material of the present invention, the method for manufacturing the thixoforming material, and the thixoformed body will be described in detail based on the embodiments shown in the accompanying drawings.

[0012] 1. Thixoforming Method First, the thixoforming method in which the thixoforming material according to the embodiment is used will be described.

[0013] 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 coexistence 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, for example, compared with the die-casting method, thin-walled parts and parts with complex shapes can be molded.

[0014] FIG. 1 is a cross-sectional view showing an example of an injection molding machine used in the thixoforming method. 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 thixoforming material 10 is charged into the hopper 5, the thixoforming material 10 is supplied to the heating cylinder 7. The thixoforming 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 thixoforming material 10 is semi-melted and slurried. The obtained slurry is injected into the cavity Cv in the mold 2 through the nozzle 9 without coming into contact with the atmosphere. Then, by cooling the slurry injected into the cavity Cv, a thixoformed body is obtained.

[0015] Note that other materials may be introduced into the hopper 5 together with the thixotropic molding material 10.

[0016] 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.

[0017] 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 adheres the metal body 11 and the coating portion 12.

[0018] 2.1. Metal body The metal body 11 is, for example, a chip obtained by cutting or slicing a Mg-based alloy cast in a mold or the like. Note that the manufacturing method of the metal body 11 is not limited thereto.

[0019] The metal body 11 has Mg as a 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. A mixture of one or more of these is used. Examples of the rare earth element include cerium.

[0020] The main component refers to the element having 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 still more preferably 80% by mass or more.

[0021] 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 thixotropic molding material 10 can be enhanced.

[0022] In addition to aluminum and zinc, the additive component preferably contains at least one selected from the group consisting of manganese, yttrium, strontium, and rare earth elements. Thereby, the mechanical properties, corrosion resistance, wear resistance, and thermal conductivity of the thixoformed body can be enhanced.

[0023] The additive component can exist in the metal body 11 in the form of a single substance, an alloy, an oxide, an intermetallic compound, or the like. Further, the additive component may be segregated at the grain boundaries of the metal structure such as Mg or an Mg alloy in the metal body 11, or may be uniformly dispersed.

[0024] 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 or the like in the heating cylinder 7 of the injection molding machine 1 can be suppressed.

[0025] The average particle size of the thixoforming material 10 is the average value of the diameters of circles having the same area as the projected area of the thixoforming material 10. The average value is calculated from 100 or more randomly selected thixoforming materials 10.

[0026] The average aspect ratio of the thixoforming material 10 is preferably 5.0 or less, and more preferably 4.0 or less. The thixoforming material 10 having such an average aspect ratio enhances the filling property in the heating cylinder 7 and improves the temperature uniformity during heating. As a result, a thixoformed body having high mechanical properties and high dimensional accuracy can be obtained.

[0027] Note that the average aspect ratio of the thixoforming material 10 is the average value of the aspect ratios calculated by the major axis / minor axis in the projected image of the thixoforming material 10. The average value is calculated from 100 or more randomly selected thixoforming 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 maximum length.

[0028] 2.2. Coating part The coating part 12 contains Si particles 14 mainly composed of Si. Specifically, for example, a plurality of Si particles 14 adhere to the surface of the metal body 11 to form the coating part 12.

[0029] The coating part 12 preferably covers the entire surface of the metal body 11, but it may also cover a part of the surface.

[0030] The Si particles 14 are not particularly limited as long as they are particles mainly composed of silicon, and may be particles mainly composed of amorphous Si or particles mainly composed of crystalline Si.

[0031] The average particle size of the Si particles 14 is set to be 1 μm or more and 100 μm or less, preferably 1 μm or more and 25 μm or less, and more preferably 2 μm or more and 15 μm or less. By setting the average particle size of the Si particles 14 within the above range, the balance between the coating rate of the coating part 12 and the Si content rate in the thixoforming material 10 can be optimized. In addition, when the Si particles 14 are adhered to the surface of the metal body 11, the Si particles 14 are less likely to fall off.

[0032] Note that when the average particle size of the Si particles 14 is less than the lower limit value, the Si particles 14 are difficult to disperse, so the above-mentioned balance may deteriorate. On the other hand, when the average particle size of the Si particles 14 exceeds the upper limit value, the Si particles 14 may be likely to fall off.

[0033] Among the thixoforming materials 10, the mass fraction of the Si particles 14 in the total mass of the metal body 11 and the Si particles 14 is set to be 1.0 mass% or more and 30.0 mass% or less, preferably 1.5 mass% or more and 25.0 mass% or less, and more preferably 5.0 mass% or more and 20.0 mass% or less. By setting the mass fraction of the Si particles 14 within the above range, it is possible to suppress a significant decrease in the mechanical strength of the produced thixoformed body while suppressing a decrease in the formability of the thixoforming material 10.

[0034] In addition, if the mass fraction of the Si particles 14 is less than the lower limit value, the mechanical strength of the thixoformed body may not be sufficiently increased. On the other hand, if the mass fraction of the Si particles 14 exceeds the upper limit value, the moldability of the thixoforming material 10 may decrease.

[0035] The coating portion 12 may contain substances other than the Si particles 14. In that case, the content of substances other than the Si particles 14 may be less than the content of the Si particles 14 in terms of mass ratio.

[0036] Further, the Si particles 14 may contain elements other than Si. In that case, the content of elements other than Si may be less than the content of Si in terms of mass ratio.

[0037] 2.3. Adhesive portion The adhesive portion 13 is interposed between the metal body 11 and the Si particles 14 or between the Si particles 14.

[0038] The adhesive portion 13 contains a binder. As the binder, an organic material for binding the metal body 11 and the coating portion 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 such as 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 a mixture containing two or more of these components.

[0039] Among these, the binder preferably contains waxes, and more preferably contains paraffin wax or its derivatives. Waxes have good binding properties, can strongly bond between the metal body 11 and the Si particles 14 or between the Si particles 14 themselves, and can, in combination with the degreasing conditions, realize a thixotropic molding material that can suppress the generation of gas during molding to a low level.

[0040] Examples of waxes include natural waxes such as candelilla wax, carnauba wax, rice wax, wood wax, plant-based waxes such as jojoba oil, beeswax, lanolin, animal-based waxes such as whale wax, montan wax, ozokerite, mineral-based waxes such as ceresin, paraffin wax, microcrystalline wax, petroleum-based waxes such as petrolatum, synthetic hydrocarbons such as polyethylene wax, modified waxes such as montan wax derivatives, paraffin wax derivatives, microcrystalline wax derivatives, hydrogenated waxes such as hydrogenated castor oil, hydrogenated castor oil derivatives, fatty acids such as 12-hydroxy stearic acid, acid amides such as stearic acid amide, and synthetic waxes such as esters such as phthalimide anhydride.

[0041] As described above, the thixotropic molding material 10 according to the embodiment has a metal body 11 and a coating portion 12. The metal body 11 has Mg as a main component. The coating portion 12 adheres to the surface of the metal body 11 via a binder and contains Si particles 14 having Si as a main component. The average particle diameter of these Si particles 14 is 1 μm or more and 100 μm or less. Also, the mass fraction of the Si particles 14 in the total mass of the metal body 11 and the Si particles 14 is 1.0 mass% or more and 30.0 mass% or less.

[0042] By performing thixotropic molding using such a thixotropic molding material 10, when it becomes in a semi-molten state, Si can be uniformly dispersed. As a result, in thixotropic molding, primary crystal Mg 2 precipitates while Si is uniformly dispersed. As a result, a thixotropic molded body having high rigidity can be obtained.

[0043] In addition, the thixoforming 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.

[0044] 3. Method for manufacturing thixoforming material Next, a method for manufacturing the above-described thixoforming material 10 will be described. FIG. 3 is a process diagram for explaining a method for manufacturing a thixoforming material according to an embodiment.

[0045] The manufacturing method of the thixoforming material 10 shown in FIG. 3 includes a preparation step S102, a drying step S104, a stirring step S106, and a degreasing step S108.

[0046] 3.1. Preparation step In the preparation step S102, a mixture containing the metal body 11, Si particles 14, a binder, and a solvent is prepared. The metal body 11 is the same as the metal body 11 described above. Also, the Si particles 14 are the same as the Si particles 14 described above.

[0047] 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.

[0048] The content of the binder in the mixture is not particularly limited, but is preferably 1.0% by mass or more and 30.0% by mass or less, more preferably 2.0% by mass or more and 15.0% by mass or less, and even more preferably 3.0% by mass or more and 10.0% by mass or less. By setting the content of the binder within the above range, the Si particles 14 can be uniformly dispersed based on the dispersing action of the binder.

[0049] Note that if the content of the binder is below the lower limit value, the amount of the binder is insufficient, making it difficult to uniformly adhere the Si particles 14 to the metal body 11 and also making it difficult to uniformly disperse the Si particles 14. On the other hand, if the content of the binder exceeds the upper limit value, the amount of the binder becomes excessive, making it easier for the Si particles 14 that are not adhered to the metal body 11 to aggregate, and in the degreasing step S108 described later, the amount of binder residue increases, and a large amount of gas is generated in the heating cylinder, which may easily cause internal defects in the thixoformed body.

[0050] 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 more 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.

[0051] In this case, the above-described mixture may be put into a container and the whole container may be heated from the outside using a hot bath or the like.

[0052] 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. Also, if the melting point of the binder is within the above range, the thixoforming material 10 to be manufactured will have good lubricity in thixoforming and can enhance the flowability of the slurry.

[0053] 3.2. Drying Step In the drying step S104, the mixture is dried. Thereby, the Si 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. Also, in the present embodiment, since the Si particles 14 are dispersed using the binder, the Si particles 14 can be adhered to the surface of the metal body 11 with a uniform thickness.

[0054] For drying, methods such as heating the mixture or exposing the mixture to a 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. Note that in the drying step S104, all the solvents in the mixture may be removed, or some solvents may remain without being removed.

[0055] 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 Si particles 14 attached to the surface of the metal body 11, the solvent can be volatilized and removed.

[0056] 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.

[0057] 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.

[0058] 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 stirrer, or shaking the container containing the mixture with a lid can be used. By such stirring, the Si particles 14 can be attached to the surface of the metal body 11 via the binder. Note that a part of the Si particles 14 may be directly attached to the surface of the metal body 11 without passing through the binder. Also, by stirring, aggregation of the metal bodies 11 into lumps can be suppressed.

[0059] Note that after the stirring step S106, if necessary, the drying step S104 and the stirring step S106 may be repeated. As a result, the adhesion of the Si particles 14 is repeated, so that the Si particles 14 can be multi-layered on the surface of the metal body 11. As a result, more Si 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.

[0060] 3.4. Degreasing Step In the degreasing step S108, the stirred mixture is degreased. 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. As a result, it is possible to prevent a large amount of binder from being transferred into the heating cylinder 7 and suppress the generation of a large amount of gas in the heating cylinder 7.

[0061] 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.

[0062] Note that if the heating temperature is lower than the lower limit value, a large amount of 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 effect on the metal body 11 due to heat, or all of the binder being removed, and the Si particles 14 falling off from the metal body 11.

[0063] 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.

[0064] The amount of the binder after degreasing, that is, the content rate of the binder in the thixoforming material 10 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 even more preferably 0.015% by mass or more and 0.040% by mass or less. By setting the content rate 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.

[0065] 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 decomposition gas is generated in the heating cylinder 7, and voids are likely to occur in the thixoformed body.

[0066] As described above, the manufacturing method of 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, Si particles 14 mainly composed of Si, 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 to obtain the thixoforming material 10. And the mass fraction of the Si particles 14 in the total mass of the metal body 11 and the Si particles 14 is 1.0% by mass or more and 30.0% by mass or less. Also, the content rate of the binder in the thixoforming material 10 is 0.001% by mass or more and 0.200% by mass or less.

[0067] According to such a configuration, even if the amount of Si particles 14 is large, the Si particles 14 can be attached to the surface of the metal body 11 via the binder, so that the Si particles 14 can be uniformly dispersed in the heating cylinder 7. As a result, the reaction opportunities between Mg and Si are ensured equally, and primary crystal Mg 2 A thixoformed body in which Si is precipitated while being uniformly dispersed can be manufactured. As a result, a thixoformed body having high rigidity can be obtained.

[0068] 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.

[0069] 4. Thixoformed body Next, the thixoformed body according to the embodiment will be described. FIG. 4 is a partial cross-sectional view schematically showing the thixoformed body according to the embodiment.

[0070] The thixoformed body 100 shown in FIG. 4 is a formed body obtained by the thixoforming method, and has a matrix part 200 and a particle part 300. The matrix part 200 is a part mainly derived from the metal body 11 of the thixoforming material 10, and has Mg as a main component. The particle part 300 is a part mainly derived from the reaction product of the coating part 12 of the thixoforming material 10 and Mg, and has Mg 2 Si as a main component.

[0071] As shown in FIG. 4, when the cross-section of the thixoformed body 100 is viewed, the area occupied by the matrix part 200 is larger than the area occupied by the particle part 300. Therefore, the particle part 300 is in a state of being dispersed in the matrix part 200. Further, the maximum particle size of the particle part 300 is 1.0 μm or more and 50.0 μm or less.

[0072] Further, 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 30.0% or less.

[0073] 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. The particle portion 300 2 has Mg 2 Si as a main component and is a site with high rigidity. Therefore, such a thixoformed body 100 has high rigidity. Further, the maximum particle size of the particle portion 300 is within the above range. For this reason, a decrease in mechanical strength due to the particle portion 300 being too large is also suppressed.

[0074] Note that the maximum particle size of the particle portion 300 is 1.0 μm or more and 50.0 μm or less, preferably 3.0 μm or more and 30.0 μm or less, and more preferably 5.0 μm or more and 20.0 μm or less.

[0075] Also, |As - Ac| / Ac is 30.0% or less, preferably 25.0% or less, and more preferably 20.0% or less.

[0076] 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.

[0077] 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 at a depth of 1 mm from the surface 101. Also, in the cross section of the thixotropic molded body 100, when the length in the depth direction is less than 2 mm, the midpoint of the length in the depth direction can be regarded as the center point O.

[0078] The area fraction As and the area fraction Ac are each determined by the Si content in the thixotropic molded body 100, but are preferably 5% or more and 55% or less, more preferably 20% or more and 50% or less, and even more preferably 30% or more and 45% or less. Thereby, the thixotropic molded body 100 has particularly high rigidity.

[0079] Also, the maximum particle size of the particle portion 300 is calculated as follows. First, in the range A1 and the range 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 observation image of the particle portion 300. The maximum value among the particle sizes calculated in this way becomes the maximum particle size of the particle portion 300.

[0080] Furthermore, the average particle size of the particle portion 300 is preferably 0.5 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 as a whole has a small diameter, it is less likely for the particle portion 300 to become a starting point for cracks or the like. As a result, in addition to the rigidity of the thixotropic molded body 100, mechanical strengths such as bending strength and tensile strength can be increased.

[0081] The average particle size of the particle portion 300 is the average value of the particle sizes of all the particle portions 300 included when the particle sizes of all the particle portions 300 included in the range A1 and the range A2 are measured.

[0082] The Si content in the thixotropic molded body 100 is preferably 1.0% by mass or more and 30.0% by mass or less, more preferably 1.5% by mass or more and 25.0% by mass or less, and even more preferably 5.0% by mass or more and 20.0% by mass or less. As a result, the thixotropic molded body 100 has particularly high rigidity.

[0083] For the measurement of the Si content, for example, 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, etc. can be mentioned.

[0084] Also, 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. For this reason, the rigidity of the thixotropic molded body 100 can be increased isotropically.

[0085] 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.

[0086] Moreover, the tensile strength of the thixotropic molded body 100 is preferably 100 MPa or more and 350 MPa or less, and more preferably 150 MPa or more and 300 MPa or less. Further, the Young's modulus of the thixotropic molded body 100 is preferably 44 GPa or more and 80 GPa or less, and more preferably 50 GPa or more and 80 GPa or less.

[0087] The thixotropic molded body 100 having the tensile strength and Young's modulus within the above ranges has particularly high specific strength and specific rigidity. Such a thixotropic molded body 100 is lightweight and high-strength, and thus is suitable for, for example, parts used in transportation equipment such as automobiles and aircraft, and parts used in mobile devices such as mobile terminals and notebook personal computers.

[0088] The tensile strength of the thixotropic molded body 100 is measured as follows. First, a test piece is cut out from the thixotropic molded 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 thixotropic molded body 100.

[0089] 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 amount of change in tensile strain when the tensile load is varied and the amount of change in 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.

[0090] 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.

[0091] 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.

[0092] The Vickers hardness of the surface 101 of the thixoformed body 100 is measured according to the method of the Vickers hardness test specified in JIS Z 2244:2009. Note that the measurement load is 5 kgf.

[0093] FIG. 5 is an example of an X-ray diffraction pattern obtained for the thixoformed body according to the embodiment.

[0094] As shown in FIG. 5, when crystal structure analysis of the thixoformed body 100 is performed by X-ray diffraction method, peaks derived from α-Mg, β-Mg 17 Al 12 peaks derived from, and Mg 2 peaks derived from Si are included in the obtained X-ray diffraction pattern. α-Mg is the matrix phase of the matrix part 200 and is a solid solution mainly containing Mg.

[0095] When using CuKα rays as X-rays, the main peak derived from α-Mg is observed at 2θ = 36.5 to 37.5°, and Mg 2 The main peak derived from Mg 2 Si is observed at 2θ = 39.5 to 40.5°. The main peak derived from α-Mg refers to the peak with the maximum peak intensity among the peaks derived from α-Mg. Mg 2 The main peak derived from Mg 2 Si refers to the peak with the maximum peak intensity among the peaks derived from Mg

[0096] Mg 2 When the peak intensity of the main peak derived from Mg 2 Si is set to 100 for the main peak derived from α-Mg, it is preferably 20 or more and 250 or less, and more preferably 50 or more and 200 or less. In the thixoformed body 100 having such a peak intensity ratio, α-Mg and Mg

[0097] Si exist in a well-balanced manner, so high rigidity and high strength are achieved simultaneously. Therefore, a thixoformed body 100 with particularly excellent mechanical properties can be realized.

Examples

[0098] Next, specific examples of the present invention will be described. 5. Manufacture of Thixoforming Material 5.1. Sample No. 1 First, a magnesium alloy chip which is a metal body, Si 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. Note that 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.

[0099] 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 3 times. Note that for stirring, a method of shaking the container containing the dried body was used.

[0100] 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 Si particles. Note that the manufacturing conditions in the above manufacturing method are shown in Table 1. In Table 1, the input amount of Si particles is the ratio of the mass of the input Si particles to the total mass of the magnesium alloy chip and Si 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.

[0101] 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.

[0102] 5.3. Sample No. 6 A thixoforming material was obtained in the same manner as in Sample No. 1 except that Si particles and the binder were omitted and the manufacturing conditions were changed accordingly.

[0103] 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.

[0104] 5.5. Sample No. 15 The thixoforming material was obtained in the same manner as Sample No. 1, except that Si particles were used while omitting the binder and the manufacturing conditions were changed accordingly.

[0105] In Table 1, for the thixoforming materials of each Sample No., those corresponding to the present invention were designated as "Examples", and those not corresponding to the present invention were designated as "Comparative Examples".

[0106] 6. Evaluation of Thixoforming Materials 6.1. Amount of Si Particles after Degreasing For the thixoforming materials of each Sample No., the amount of Si particles after degreasing was calculated by the following method.

[0107] First, the mass M1 of the thixoforming material was measured. Since the thixoforming material has undergone a degreasing process, it is considered that the remaining binder is 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. This allows the attached Si particles to fall off, and only the magnesium alloy chips can be taken out. Next, the washed magnesium alloy chips were taken out of the acetone, dried, and then the mass M2 was measured.

[0108] Then, the mass fraction of Si particles with respect to the magnesium alloy chips, calculated by (M1 - M2) / M1 × 100, was taken as the amount of Si particles after degreasing [%]. The calculation results are shown in Table 1.

[0109] 6.2. Adhesion Rate of Si Particles The adhesion rate of Si particles was calculated by dividing the amount of Si particles after degreasing by the amount of Si particles charged. The calculation results are shown in Table 1. Note that the amount of Si particles after degreasing shown in Table 1 is an approximate value, while the adhesion rate shown in Table 1 is a value obtained by calculation based on the value before approximation. Therefore, the adhesion rate shown in Table 1 may deviate slightly from the value calculated from the amount of Si particles charged and the amount after degreasing shown in Table 1.

[0110] 6.3. Amount of Binder after Degreasing For the thixotropic molding materials of each sample No., the amount of binder after degreasing was calculated by the following method.

[0111] First, for one 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 in the atmosphere while flowing air at a flow rate of 30 mL / min and at a heating rate of 10 °C / min. Then, to eliminate the influence of the solvent, based on 200 °C, the weight change at the 450 °C point was calculated as the amount of binder after degreasing. The calculation results are shown in Table 1.

[0112]

Table 1

[0113] As shown in Table 1, in the thixotropic molding materials corresponding to the examples, although the amount of binder was minimized by degreasing, it was confirmed that Si particles adhered with a sufficient adhesion rate.

[0114] 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.

[0115] 7.2. Sample Nos. 17 to 27 A thixoformed body was obtained in the same manner as Sample No. 16, except that the manufacturing conditions were changed as shown in Table 2.

[0116] 8. Analysis of Thixoformed Body 8.1. Cross-Section Observation The thixoformed bodies of each sample No. were cut, and the cut surfaces were observed with an optical microscope. Fig. 6 is an observation image when the cut surface of the thixoformed body corresponding to the example was observed with an optical microscope. In Fig. 6, a particle part showing a dark color and a matrix part showing a light color are recognized. And many particle parts have a relatively small aspect ratio and an isotropic shape. The average aspect ratio and the maximum particle size of the obtained particle parts are shown in Table 2.

[0117] Also, ranges A1 and A2 as shown in Fig. 4 were specified, and the area fractions As and Ac of the particle parts were calculated. And |As - Ac| / Ac was calculated as a percentage. The calculation results are shown in Table 2.

[0118] 8.2. Si Content For the thixoformed bodies of each sample No., the Si content was measured by elemental analysis. The measurement results are shown in Table 2.

[0119] 9. Evaluation of Thixoformed Body 9.1. Formability The thixoformed bodies of each sample No. were observed, and the forming state of the thixoformed body was evaluated based on the fluidity of the molten metal, and the presence or absence of internal defects such as shrinkage cavities and entrained air. 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.

[0120] 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 with a tensile testing machine. The measurement results are shown in Table 2.

[0121] 9.3. Young's Modulus The Young's modulus of the thixoformed bodies of each sample No. was measured. The measurement results are shown in Table 2.

[0122] 9.4. Vickers hardness The Vickers hardness of the surface of the thixoformed bodies of each sample No. was measured. The measurement results are shown in Table 2.

[0123]

Table 2

[0124] As is clear from Table 2, it was confirmed that the thixoformed bodies corresponding to the examples had higher rigidity than the thixoformed bodies corresponding to the comparative examples. Also, when the Si content was too low, the rigidity could not be sufficiently increased, while when the Si content was too high, it was found that the formability deteriorated.

[0125] Furthermore, in the comparative example where no binder was added in the production of the thixoforming material, the rigidity of the thixoformed body could not be increased. The reason for this is that Si particles fell off from the magnesium alloy chips and the Si particles could not be sufficiently dispersed.

Explanation of symbols

[0126] 1... Injection molding machine, 2... Mold, 5... Hopper, 6... Heater, 7... Heating cylinder, 8... Screw, 9... Nozzle, 10... Thixoforming material, 11... Metal body, 12... Coating part, 13... Adhesive part, 14... Si 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... Degreasing process

Claims

1. A metallic body mainly composed of Mg, a covering portion containing Si particles mainly composed of Si and adhering to the surface of the metallic body via a binder, and having wherein the average particle diameter of the Si particles is 1 μm or more and 100 μm or less, the mass fraction of the Si particles in the total mass of the metallic body and the Si particles is 1.0 mass % or more and 30.0 mass % or less, and the content of the binder in the thixoforming material obtained after degreasing is 0.00 1 mass % or more and 0.200 mass % or less, a thixoforming material characterized by this.

2. The thixoforming material according to claim 1, wherein the binder contains waxes.

3. A preparation step of preparing a mixture containing a metallic body mainly composed of Mg, Si particles mainly composed of Si, a binder, 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, and having wherein the mass fraction of the Si particles in the total mass of the metallic body and the Si particles is 1.0 mass % or more and 30.0 mass % or less, and the content of the binder in the thixoforming material obtained after the degreasing step is 0 .001 mass % or more and 0.200 mass % or less, a manufacturing method of a thixoforming material characterized by this.

4. A matrix part mainly composed of Mg, and a particle part dispersed in the matrix part and mainly composed of Mg2Si, and having wherein the maximum particle diameter of the particle part is 1.0 μm or more and 20.0 μm or less, the Si content is 5.0 mass % or more and 20.0 mass % or less, observing the cross section, taking the area fraction of the particle part in the range of 500 μm square starting from the surface as As [%], and taking the area fraction of the particle part in the range of 500 μm square centered on the point at a depth of 1 mm from the surface as Ac [%], when |As - Ac| / Ac is 20.0% or less, a thixomolded body characterized by this.

5. The thixomolded body according to claim 4, wherein the average aspect ratio of the particle part is 3.0 or less.

6. The thixomolded body according to claim 4 or 5, wherein the tensile strength is 100 MPa or more and 350 MPa or less, and the Young's modulus is 44 GPa or more and 8 0 GPa or less. ​ ​ ​

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