JP4686690B2 - Magnesium-based composite powder, magnesium-based alloy material, and production method thereof - Google Patents

Description

The present invention relates to a magnesium-based composite powder and magnesium-based alloy material containing Mg ₂ Si having high rigidity, and methods for producing them.

  Magnesium alloys are characterized by a light weight reduction effect due to their low specific gravity, and are widely commercialized and put into practical use mainly in the case of mobile phones and portable audio equipment. In the design of products and members, rigidity is an important material factor in addition to mechanical properties such as strength and hardness of the material.

  For example, when a magnesium alloy is applied to a housing (case) for an automatic transmission (AT), even if it has a tensile strength and a creep strength equivalent to those of an aluminum alloy currently used (for example, ADC12), Since the rigidity (Young's modulus) of the magnesium alloy is about 60% of that of the aluminum alloy, the same size and thickness cause bending and deformation when a load is applied. Therefore, until now, in the practical use of magnesium alloys, there has been a problem that a thickening design is required depending on the products and members to be applied, and a weight reduction effect cannot be obtained.

In order to improve the rigidity of a metal material such as a magnesium alloy, it is generally effective to use a so-called composite material by dispersing compound particles having rigidity higher than that of the metal material. For example, magnesium silicide (Mg ₂ Si) has a Young's modulus of 120 GPa and is significantly larger than that of a general magnesium alloy (43 to 44 GPa). Therefore, in a composite material in which the particles are dispersed in the alloy. Increased rigidity can be expected.

However, when producing an Mg-Si based alloy by the melting / casting method, since the eutectic point exists in the vicinity of about 1% by weight based on the Si content, when adding Si far exceeding 1% by weight, Mg ₂ Si produced by reaction with Mg grows coarsely. In such a magnesium alloy containing coarse Mg ₂ Si particles, the strength and toughness are reduced due to stress concentration in the particles, and the explosion in the melting process is accompanied by heat generation due to the reaction between Mg and Si. There is a danger of. In addition, the presence of coarse Mg ₂ Si particles deteriorates the casting performance (castability) into the mold and causes a problem that a large number of defects and voids exist in the cast alloy material. Therefore, an AS21 alloy (Mg-2% Al-1% Si), an AS41 alloy (Mg-4% Al-1% Si), and the like are Mg ₂ Si-containing magnesium alloys that can be manufactured by a melting and casting method. However, when about 1% by weight of Si is added, the volume fraction of the generated Mg ₂ Si particles is less than about 1% of the whole, so that it is difficult to remarkably improve the rigidity of the magnesium alloy.

On the other hand, S.M. K. THAKUR et al. (Source: Metallurgical and Materials Transactions A, Vol. 35A, March 2004, p.1167-1176) formed a preform that was solidified from three types of mixed powder containing Si powder, and dissolved it here. A method for producing a magnesium alloy containing Mg ₂ Si particles by an infiltration method in which the magnesium alloy is infiltrated while being pressurized is proposed. However, in this method, Mg ₂ Si synthesized by the reaction between the dissolved Mg alloy and Si is accompanied by grain growth in the reaction process, and as a result, coarse Mg ₂ Si particles of about 70 to 100 μm are contained in the magnesium alloy. Exists. As a result, various performance problems as described above occur.
Metallurgical and Materials Transactions A, Vol. 35A, March 2004, p.1167-1176

Inventor of the present application disclosed, in Japanese Patent Application No. 2003-2602 (filed on Jan. 8, 2003), a technique for producing a magnesium-based composite material in which Mg ₂ Si particles are dispersed using powder metallurgy. Here, a magnesium composite powder in which a fine Si powder or SiO ₂ powder is adhered to the surface of a magnesium-based alloy powder by a mechanical bonding method or a bonding method using a binder and a method for manufacturing the same are proposed. Further, the composite powder is subjected to warm plastic working, and in the process, Mg ₂ Si particles are generated using a solid phase reaction between Mg and Si or SiO _2. It has been proposed to obtain a magnesium-based composite material in which Mg ₂ Si particles are uniformly dispersed.

The magnesium-based composite material obtained by the technique disclosed in Japanese Patent Application No. 2003-2602 exhibits high tensile strength, but high-temperature heating (for example, 400 to 550 ° C.) necessary for the reaction between Mg and Si or SiO _2. Degree) is required. In that case, it accompanies the coarsening of a magnesium crystal grain. In other words, it is effective to lower the heating temperature to achieve higher strength, but it is difficult to lower the temperature to about 300 ° C., for example, because of the solid-phase reaction.

An object of the present invention is to obtain a magnesium alloy having high rigidity and high strength containing a large amount of fine Mg ₂ Si particles without performing high-temperature heating.

In order to produce a magnesium-based composite material in which Mg ₂ Si particles are dispersed, the inventor of the present application uses a magnesium-based composite powder in which Mg ₂ Si particles are present on the surface of the Mg-based powder and / or inside the substrate. I found it effective. Using Si particles as disclosed in Japanese Patent Application No. 2003-2602, rather than the method of synthesizing the _Mg 2 Si particles by solid-phase reaction with Mg powder, the use of _Mg 2 Si particles, the following advantages It was found that can be obtained.

  (1) The high-temperature heating up to about 400 to 550 ° C. required to promote the Si—Mg reaction is not necessary, and as a result, the strength of the Mg-based alloy is suppressed by suppressing the coarseness and growth of Mg crystal grains in the base. Reduction can be suppressed.

(2) By avoiding the exothermic phenomenon in the Si-Mg reaction process, the coarsening of Mg ₂ Si particles and Mg crystal grains can be suppressed.

In short, a magnesium-based alloy can be produced by warm extrusion at about 200 to 400 ° C. without performing the high-temperature heating necessary for the solid-state reaction between Mg and Si as described above. As a result, a highly rigid and high strength magnesium-based alloy containing a large amount of fine Mg ₂ Si particles can be obtained.

The magnesium-based composite powder according to the present invention includes a magnesium-based powder and magnesium silicide (Mg ₂ Si) particles attached to the surface of the magnesium-based powder via a binder .

In the magnesium-based composite powder, the maximum particle size of Mg ₂ Si is 50 μm or less, preferably 20 μm or less, more preferably 5 μm or less. The content of Mg ₂ Si in the magnesium-based composite powder is preferably 5 to 60% on a volume basis.

The magnesium-based alloy material according to the present invention is obtained by compacting and sintering the above-mentioned magnesium-based composite powder, and Mg ₂ Si particles are dispersed in the substrate.

In one embodiment, the manufacturing method of the magnesium group composite powder according to the present invention includes the following steps.
a) A step of preparing magnesium (Mg) based powder and magnesium silicide (Mg ₂ Si) particles.
b) A step of applying a binder to the surface of the Mg-based powder.
mixing the c) Mg based powder coated with binder and _Mg 2 Si particles and stirring to, the step of coupling the _Mg 2 Si particles to the surface of the Mg based powder.

  The method for producing a magnesium-based alloy material according to the present invention includes a step of compacting the above-mentioned magnesium-based composite powder, and the compacted body in an inert gas atmosphere or a non-oxidizing gas atmosphere at 200 to 400 ° C. A step of heating, and a step of extruding and densifying the green compact immediately after the heating.

  Features and effects of the present invention will be described in the following section.

(1) Magnesium-based composite powder (A) Content of Mg ₂ Si When the entire magnesium-based composite powder is taken as 100%, it contains 5 to 60% Mg ₂ Si on a volume basis. Further, from the viewpoint of machinability (cutting property) of the magnesium-based alloy obtained by solidifying the composite powder, a more preferable content of Mg ₂ Si is 20 to 40% on a volume basis. When the content of Mg ₂ Si particles is less than 5%, a magnesium alloy having sufficient rigidity cannot be obtained. On the other hand, if the content of Mg 2 _Si particles exceeds 60%, Mg 2 in the magnesium based composite powder containing _Si particles occur segregation and aggregation of the Mg 2 _Si particles, magnesium group obtained by solidifying such powder In alloys, strength and toughness are reduced. A more preferable content of Mg ₂ Si particles having a rigidity equivalent to that of an aluminum alloy and ensuring excellent strength and machinability is 20 to 40% on a volume basis.

(B) a maximum particle size of _Mg 2 Si which is contained in a maximum particle size of the magnesium based composite powder of _Mg 2 Si is 50μm or less, preferably 20μm or less, more preferably 5μm or less. When the maximum particle diameter of the Mg ₂ Si particles exceeds 50 μm, there arises a problem that mechanical properties and machinability of the obtained magnesium-based alloy are deteriorated. When the value is 20 μm or less, good machinability can be maintained even when Mg ₂ Si particles exceeding 40% by volume are included. Furthermore, when the maximum particle diameter of Mg ₂ Si particles is 5 μm or less, the machinability of the magnesium-based alloy is improved, and at the same time, the tensile strength of the alloy is improved by the dispersion of fine Mg ₂ Si particles.

(C) Rigidity (Young's modulus)
The Young's modulus of the magnesium-based alloy is 48 to 90 GPa. If the Young's modulus is less than 48 GPa, the rate of increase of the existing magnesium alloy with respect to the Young's modulus is 10% or less, and it is difficult to apply it to automobile cover / case-related parts and housing parts such as personal computers and portable devices. is there. On the other hand, as described above, when the Young's modulus exceeds 90 GPa, the Mg ₂ Si content exceeds 60% on a volume basis, so that the toughness and machinability of the alloy material are lowered.

(2) Manufacturing method of magnesium-based composite powder (A) Magnesium-based composite powder using adhesion by binder FIGS. 1 and 2 show a manufacturing method of Mg-based composite powder using a binder solution, and FIG. The cross-sectional structure of the Mg-based composite powder obtained by the method is schematically shown.

In this method, a composite powder is produced using a wet granulator or a spray dryer. In the method shown in FIG. 1, a mixture _{2 of} Mg-based powder and Mg ₂ Si particles is put into a container 1, and hot air 3 is supplied from the lower part of the container 1 to float this mixture 2. In this state, the binder solution 4 is sprayed onto the mixture 2 from above to apply the binder to the surface of each particle and simultaneously dry at a high temperature. As a result, as shown in FIG. 3, Mg ₂ Si particles 8 adhere to and bind to the surface of the Mg-based powder 7 via the binder 9.

In the method shown in FIG. 2, the binder solution 4 is sprayed from the lower part perpendicular to the air flow direction in a state where the mixture ₂ of Mg-based powder and Mg ₂ Si particles is suspended in the container 1 with a relatively low air volume. ing.

Although not shown in the figure, Mg ₂ Si particles are mixed and stirred in the binder solution, and this binder solution is sprayed onto the Mg-based powder suspended by hot air and applied in the same manner. Mg ₂ Si particles can be adhered and bonded to the powder surface via a binder.

As another method, a predetermined amount of Mg-based powder is put into a container, and oleic acid serving as a binder is added in an amount of 0.2 to 0.5% by weight with respect to the Mg-based powder. Is oscillated or rotated to apply oleic acid to the Mg-based powder surface in the container. Thereafter, Mg ₂ Si particles are added to the container, and the container is vibrated or rotated again to adhere the Mg ₂ Si particles to the surface of the Mg-based powder coated with oleic acid. In this way, an Mg-based composite powder as shown in FIG. 3 is obtained.

(B) Magnesium-based composite powder by mechanical bonding (reference example which is not an example of the present invention)
On the other hand, as a mechanical bonding method, Mg-based powder and Mg ₂ Si particles are mixed and put into a ball mill, mixed grinding mill, roller compactor, rolling mill, etc., and mixed powder is subjected to compression / shear processing, etc. To give an Mg-based granulated product in which Mg ₂ Si particles are mechanically bonded and adhered to the surface of the Mg-based powder. If necessary, an Mg-based composite powder having a predetermined size and shape having a cross-sectional structure as shown in FIG. 4 can be obtained from this granulated product by a pulverizing / sieving machine. In the Mg-based composite powder 15 shown in FIG. 4, Mg ₂ Si particles 8 are mechanically bonded and attached to the surface of the Mg-based powder 7.

(C) Magnesium-based composite powder using Mg ₂ Si particle-dispersed Mg-based sintered alloy (reference example that is not an example of the present invention)
(A) Method shown in FIG. 5 By preparing Mg-based powder and Mg ₂ Si particles as starting materials, mixing and stirring both at a predetermined blending ratio, filling in a mold and solidifying under pressure An Mg-based green compact in which Mg ₂ Si particles are dispersed is prepared.

By heating the above compacted body in an inert gas or non-oxidizing gas or in a vacuum at a temperature lower than the melting point of the Mg-based powder, Mg ₂ Si particle-dispersed Mg-based sintering is performed by solid-phase diffusion between the Mg-based powders. Bonds are obtained.

The above-mentioned Mg ₂ Si particle-dispersed Mg-based sintered alloy is pulverized by a pulverizer such as a ball mill or a crusher mill or by machining such as cutting to obtain a predetermined size and shape with a sectional structure as shown in FIG. Mg-based composite powder 16 having the following is obtained. In the Mg-based composite powder 16 shown in FIG. 6, Mg ₂ Si particles are mainly dispersed inside the base of the Mg-based powder 7.

In the above Mg ₂ Si particle-dispersed Mg-based sintered alloy, when the content of Mg ₂ Si particles exceeds 60% on a volume basis, segregation / aggregation of Mg ₂ Si particles occurs, and a tool in cutting work There is a problem of machinability such as a reduction in life. From this viewpoint, the content of Mg ₂ Si particles is desirably 60% or less.

(B) Method shown in FIG. 7 Mg base powder and Si particles are prepared as starting materials, mixed and stirred at a predetermined blending ratio, filled into a mold, and solidified under pressure to form Si particles. An Mg-based green compact with dispersed therein is prepared.

By heating the above compacted body in an inert gas or non-oxidizing gas or in a vacuum below the melting point of the Mg-based powder, simultaneously with the synthesis of Mg ₂ Si by solid-phase reaction between Si and Mg, Mg-based An Mg ₂ Si particle-dispersed Mg-based sintered alloy is obtained by solid phase diffusion between powders.

The above-mentioned Mg ₂ Si particle-dispersed Mg-based sintered alloy is pulverized by a pulverizer such as a ball mill or a crusher mill or by machining such as cutting, so that a predetermined size and shape can be obtained with the structure shown in FIG. An Mg-based composite powder containing Mg ₂ Si particles having is obtained.

(D) Magnesium-based composite powder using Mg ₂ Si particle-dispersed Mg-based cast alloy (reference example which is not an example of the present invention)
(A) Method shown in FIG. 8 Mg ₂ Si particles prepared as a starting material are put into a molten Mg-based alloy and stirred, and then cast into a mold. The added Mg ₂ Si particles are uniformly dispersed in the Mg-based cast alloy taken out from the mold.

The above cast alloy is pulverized by a pulverizer such as a ball mill or a crusher mill or by machining such as cutting, whereby Mg containing Si ₂ Si particles having a predetermined size and shape as shown in FIG. A matrix composite powder is obtained. Note that the melting temperature of the molten Mg-based alloy after the Mg ₂ Si particles are added is lower than the solidus temperature of Mg and Mg ₂ Si in the Mg-Si equilibrium diagram. Conversely, when heated to a temperature higher than the solidus temperature, Mg ₂ Si is dissolved in the molten Mg-based alloy, and the problem arises that Mg ₂ Si is coarsened and grows in the solidification process after casting.

(B) Method shown in FIG. 9 Mg-based powder and Mg ₂ Si particles are prepared as starting materials, and both are mixed and stirred at a predetermined blending ratio, then filled in a mold, and solidified under pressure to form Mg. ₂ An Mg-based green compact with Si particles dispersed therein is prepared. This green compact is put into a crucible and heated to produce a molten Mg-based alloy in which Mg ₂ Si particles are dispersed. After the molten metal is sufficiently stirred, it is cast into a mold.

In the Mg-based casting alloy taken out from the mold, the added Mg ₂ Si particles are uniformly dispersed, and this alloy is pulverized by a grinding machine such as a ball mill or a crusher mill or by machining such as cutting. A Mg-based composite powder containing Mg ₂ Si particles having a predetermined size and shape with a cross-sectional structure as shown in FIG. 6 is obtained.

(C) Method shown in FIG. 10 Mg-based powder and Si particles are prepared as starting materials, mixed and stirred at a predetermined blending ratio, filled in a mold, and solidified under pressure to obtain Si. An Mg-based green compact with dispersed particles is prepared.

By heating the above compacted body in an inert gas or non-oxidizing gas or in a vacuum below the melting point of the Mg-based powder, simultaneously with the synthesis of Mg ₂ Si by solid-phase reaction between Si and Mg, Mg-based A Mg ₂ Si particle-dispersed Mg-based sintered alloy is obtained by solid phase diffusion between powders.

The above sintered alloy is put into a crucible and heated to produce a molten Mg-based alloy in which Mg ₂ Si particles are dispersed. After the molten metal is sufficiently stirred, it is cast into a mold. In the Mg-based casting alloy taken out from the mold, the added Mg ₂ Si particles are uniformly dispersed, and this alloy is pulverized by a grinding machine such as a ball mill or a crusher mill or by machining such as cutting. A Mg-based composite powder containing Mg ₂ Si particles having a predetermined size and shape with a cross-sectional structure as shown in FIG. 6 is obtained.

  In addition, since the cutting oil used in the cutting process adheres to the Mg-based composite powder, it is used as a raw material after the cutting oil component is removed by a cleaning process.

(3) Magnesium-based alloy material An Mg-based alloy in which Mg ₂ Si particles are dispersed can be obtained by using the Mg-based composite powder containing the above Mg ₂ Si particles as a starting material and molding and solidifying this.

  After compacting the Mg-based composite powder, it is heated and subjected to extrusion, forging, or rolling. The heating temperature of the molded body at that time is preferably about 200 to 400 ° C. When the temperature is lower than 200 ° C., extrusion may become difficult. On the other hand, when the temperature exceeds 400 ° C., the temperature of the material after extrusion increases with an increase in the extrusion speed, which may cause a decrease in strength due to coarsening of crystal grains.

Fine Mg ₂ Si particles are uniformly dispersed in the base of the Mg-based alloy obtained as described above. Since the particle diameter of the Mg ₂ Si particles dispersed in the alloy is the same as the particle diameter in the Mg-based composite powder, the maximum particle diameter of the Mg ₂ Si particles in the Mg-based alloy is 50 μm or less, preferably 20 μm or less. More preferably, it is 5 μm or less. The content of Mg ₂ Si in the Mg-based alloy is 5 to 60% on a volume basis. As a result, it is possible to produce an Mg-based alloy having high rigidity and high strength.

Prepare pure Mg powder (purity 99.9%, average particle diameter 350 μm) and Si powder (purity 99.9%, average particle diameter 22 μm), and blend both powders with Mg: Si = 2: 1 (molar ratio) Then, a mixing process was performed for 30 minutes using a ball mill. The mixed powder is set in a discharge plasma sintering apparatus filled in a carbon mold (inner diameter: 35 mmφ), adjusted to a pressure of 100 MPa and a sample temperature of 600 ° C. in a vacuum, and sintered for 15 minutes. did. As a result, a disk-shaped sample made of Mg ₂ Si and having an outer diameter of 35 mmφ and a thickness of 12 mm was obtained.

The above disk-shaped sample was pulverized with a jet mill and finely pulverized and sieved so that the maximum particle size was 15 μm or less, thereby preparing Mg ₂ Si particles as a starting material. On the other hand, an AZ31 (nominal composition Mg-3Al-1Zn / mass%) alloy powder having a diameter of about 2 mm was prepared as a Mg-based powder as a starting material.

Based on the method shown in FIG. 5, AZ31 powder and Mg ₂ Si particles were first mixed at a predetermined ratio, filled in a metal mold having a diameter of 60 mmφ, and a pressure of 400 MPa was applied to produce a compacted body. By sintering this compacted body in a nitrogen gas atmosphere at 550 ° C. for 1 hour, an AZ31 sintered alloy in which Mg ₂ Si particles were dispersed was obtained. Then, an Mg based composite powder having a diameter of about 0.5 to 3 mm was produced from this sintered alloy by cutting.

FIG. 11 shows a cross-sectional organization observation result of the composite powder when the content of Mg ₂ Si particles is 16% on a volume basis with respect to the entire Mg-based composite powder. Mg ₂ Si particles having a particle size of 15 μm or less were uniformly dispersed in the AZ31 substrate without segregation or aggregation, and the Mg-based composite powder according to the present invention was obtained.

  First, pure Mg powder (purity 99.9%, average particle size 350 μm) and Si powder (purity 99.9%, average particle size 22 μm) are prepared based on the method shown in FIG. After blending, the mixture was mixed for 30 minutes using a ball mill. The mixed powder was filled in a mold having a diameter of 60 mmφ, and a pressure of 400 MPa was applied to produce a green compact.

By heat-treating the above green compact in a vacuum at 590 ° C for 1 hour, Mg ₂ Si particles are synthesized by solid-phase reaction between Si and Mg, and at the same time, sintering between Mg powders is promoted. Thus, an Mg ₂ Si particle-dispersed Mg sintered material was obtained. The sintered material was pulverized by a ball mill to produce a Mg-based composite powder having a diameter of about 0.3 to 1 mm.

FIG. 12 shows the X-ray diffraction result of the Mg-based composite powder when the content of Mg ₂ Si particles is 7% on the volume basis with respect to the entire Mg-based composite powder. Since only the peaks of Mg and Mg ₂ Si were detected and there was no Si peak used as a starting material, it completely reacted with Mg and consumed for the synthesis of Mg ₂ Si. Further, since there is no MgO peak, no oxidation occurs during the sintering process.

As a result of the organization observation with an optical microscope, the average particle diameter of Mg ₂ Si dispersed in the powder base is about 24 μm, which is equivalent to the particle diameter of the Si powder as the starting material. No noticeable coarse grain growth occurred in the reaction process. As a result, an Mg-based composite powder in which Mg ₂ Si particles defined by the present invention were uniformly dispersed in the substrate was obtained.

Prepare pure Mg powder (purity 99.9%, average particle diameter 350 μm) and Si powder (purity 99.9%, average particle diameter 22 μm), and blend both powders with Mg: Si = 2: 1 (molar ratio) Then, a mixing process was performed for 30 minutes using a ball mill. The mixed powder is filled in a carbon mold (inner diameter: 35 mmφ) and set in a discharge plasma sintering apparatus, adjusted to a pressure of 100 MPa and a sample temperature of 600 ° C. in a vacuum, and sintered for 30 minutes. did. As a result, a disk-shaped sample made of Mg ₂ Si and having an outer diameter of 35 mmφ and a thickness of 18 mm was obtained.

The above disk-shaped sample was pulverized with a jet mill processing machine, and pulverized and sieved so that the maximum particle size was 10 μm or less, thereby producing Mg ₂ Si particles as a starting material.

Based on the method shown in FIG. 8, first, AZ61 (nominal composition Mg-6Al-1Zn / mass%) alloy melt was prepared in a carbon crucible. In a state where the molten metal temperature is controlled at 720 to 740 ° C., the above-mentioned Mg ₂ Si particles are added at a predetermined ratio and sufficiently stirred, and then cast into a mold to produce an AZ61 cast alloy material in which the Mg ₂ Si particles are dispersed. did.

From the above cast alloy, an Mg-based composite powder made of an AZ61 alloy having a diameter of about 0.5 to 3 mm was produced by cutting. Table 1 shows the content (volume basis) of Mg ₂ Si particles with respect to the entire cast alloy material. Moreover, the result of the cross-sectional organization observation of the obtained composite powder and the damage situation of the cemented carbide tool in the cutting work when producing the powder are shown in the same table.

Sample No. which is an example of the present invention. In Nos. 1 to 5, Mg ₂ Si particles are uniformly dispersed in the substrate without containing segregation or aggregation of Mg ₂ Si particles in the Mg-based composite powder by containing an appropriate amount of Mg ₂ Si. In addition, although slight slight rubbing traces are confirmed with respect to tool wear (damage condition) when producing the Mg-based composite powder by cutting, there is no problem.

On the other hand, sample No. In No. 6, since the Mg ₂ Si content is as high as 65%, aggregation of Mg ₂ Si particles occurs in the powder base, and the casting alloy produces a large amount of hard Mg ₂ Si when producing powder by cutting. Therefore, there is a problem that deep damage occurs in the tool and Mg is adhered to the damaged portion.

  Prepare pure Mg powder (purity 99.9%, average particle diameter 350 μm) and Si powder (purity 99.9%, average particle diameter 22 μm), and blend both powders with Mg: Si = 2: 1 (molar ratio) Then, a mixing process was performed for 30 minutes using a ball mill.

The above mixed powder is set in a discharge plasma sintering apparatus filled in a carbon mold (inner diameter: 35 mmφ), adjusted to a pressure of 100 MPa and a sample temperature of 600 ° C. in a vacuum, and sintered for 15 minutes. gave. As a result, a disk-shaped sample made of Mg ₂ Si and having an outer diameter of 35 mmφ and a thickness of 12 mm was obtained.

The above disk-shaped sample was pulverized by a jet mill processing machine. At that time, Mg ₂ Si particles having different maximum particle diameters were produced by changing the pulverization conditions.

Based on the method shown in FIG. 9, an AM60 (nominal composition Mg-6Al-0.5Mn / mass%) alloy powder having a diameter of 3 mm is prepared as a Mg-based powder as a starting material, and Mg ₂ Si particles are mixed at a predetermined ratio. The mixture was mixed, filled in a mold having a diameter of 60 mmφ, and a pressure of 400 MPa was applied to produce a green compact.

Next, after the powder compact is put into the AM60 alloy melt (melt temperature: 720 to 740 ° C.) in the carbon crucible and stirred sufficiently, it is cast into a mold and the AM60 cast alloy in which Mg ₂ Si particles are dispersed. The material was made. Then, an Mg-based composite powder (diameter: 0.5 to 3 mm) having an AM60 alloy as a base material was produced from the cast alloy by cutting. The content of _Mg 2 Si in the Mg based casting alloy obtained is 22% by volume.

In order to calculate the maximum particle size of the Mg ₂ Si particles dispersed in the Mg-based composite powder matrix, the cross-sectional structure of the composite powder is observed with an optical microscope, and from the results, the maximum particle size of the Mg ₂ Si particles is analyzed by image analysis. Asked. The results are shown in Table 2. Moreover, the damage state of the cemented carbide tool in the cutting process at the time of producing Mg-based composite powder from a cast alloy is shown in the same table.

Sample No. which is an example of the present invention. In Nos. 7 to 10, by containing Mg ₂ Si having an appropriate particle size in the cast alloy, tool wear and damage when producing powder by cutting are not caused, and the surface properties are good.

On the other hand, sample No. In Nos. 11 to 12, since the maximum particle diameter of Mg ₂ Si contained in the cast alloy is larger than 50 μm, deep damage occurs in the tool during cutting, and Mg adheres to the damaged portion at the same time. Problems arise.

  Using the Mg-based composite powder described in Example 3 and Example 4 as a starting material, green compacts of each powder were produced by molding. Each green compact was heated and held in a nitrogen gas atmosphere controlled at 350 ° C. for 5 minutes, and then immediately subjected to extrusion (extrusion ratio 37) to produce an extruded material. Tensile test pieces were prepared from each extruded material, the tensile properties (tensile strength and elongation at break) at room temperature were evaluated, and Young's modulus was measured. The results are shown in Table 3.

Sample No. which is an example of the present invention. In 1-5 and 7-10, magnesium-based alloys having excellent strength and toughness are obtained. 4 and 5 have high rigidity comparable to aluminum alloys. Sample No. As shown in 7 and 8, when the maximum particle size of Mg ₂ Si particles dispersed in the alloy is as fine as less than 5 μm or 20 μm, the elongation increases remarkably in addition to the strength.

On the other hand, sample No. In No. 6, since the Mg ₂ Si content was large, the Mg-based alloy became brittle, making it difficult to produce a tensile test piece by machining. Sample No. which is a comparative example. In Nos. 11 to 12, since the maximum particle diameter of Mg ₂ Si was larger than 50 μm, the toughness of the Mg-based alloy was lowered, and the tensile strength was also lowered.

Prepare pure Mg powder (purity 99.9%, average particle diameter 350 μm) and Si powder (purity 99.9%, average particle diameter 22 μm), and blend both powders with Mg: Si = 2: 1 (molar ratio) Then, a mixing process was performed for 30 minutes using a ball mill. The mixed powder is set in a discharge plasma sintering apparatus filled in a carbon mold (inner diameter: 35 mmφ), adjusted to a pressure of 100 MPa and a sample temperature of 600 ° C. in a vacuum, and sintered for 30 minutes. did. As a result, a disk-shaped sample made of Mg ₂ Si and having an outer diameter of 35 mmφ and a thickness of 18 mm was obtained.

The above disk-shaped sample was pulverized with a jet mill processing machine, and pulverized and sieved so that the maximum particle size was 10 μm or less, thereby producing Mg ₂ Si particles as a starting material.

Next, 200 g of pure Mg powder (purity 99%) with a particle diameter of 0.5 to 2 mm is put into a 350 ml capacity vinyl container, and a vibration mill is added with 0.6 g of oleic acid added to the container. The container was vibrated for 15 minutes to uniformly apply oleic acid to the surface of the pure Mg powder in the container. Furthermore, by adding the above Mg ₂ Si particles into this container (13% on a volume basis with respect to the whole mixed powder) and further applying vibration for 15 minutes to adhere the Mg ₂ Si particles to the surface of the pure Mg powder. The Mg-based composite powder defined by the present invention was produced.

The X-ray diffraction results of the Mg-based composite powder obtained as described above are shown in FIG. Only the peaks of Mg and Mg ₂ Si, which are input materials, are detected, and in the result of observation with a scanning electron microscope, fine Mg ₂ Si particles are uniformly attached to the surface of coarse pure Mg powder. confirmed. From the above, it is recognized that Mg-based composite powder can be produced even when oleic acid is used as a binder.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and changes can be made to the illustrated embodiment within the same range as the present invention or within an equivalent range.

  The magnesium-based alloy obtained by the present invention can greatly improve the low rigidity, which is a performance problem of conventional magnesium alloys, and requires high rigidity such as automotive parts and structural members such as engine parts and mission parts. Can be advantageously used in certain applications.

Using binder on the surface of the Mg based powder is an illustrative view showing one example of a method of attaching the Mg 2 _Si particles. Using binder on the surface of the Mg based powder is an illustrative view showing another example of a method of attaching the Mg 2 _Si particles. On the surface of the Mg based powder is an illustrative view showing one example of the magnesium based composite powder attached the Mg 2 _Si particles. On the surface of the Mg based powder is an illustrative view showing another example of the magnesium based composite powder attached the Mg 2 _Si particles. It is a figure which shows an example of the method of manufacturing a magnesium group composite powder. The material mixture of the Mg based powder is an illustrative view showing one example of the magnesium based composite powder is dispersed Mg 2 _Si particles. It is a figure which shows the other example of the method of manufacturing a magnesium group composite powder. It is a figure which shows the further another example of the method of manufacturing a magnesium group composite powder. It is a figure which shows the further another example of the method of manufacturing a magnesium group composite powder. It is a figure which shows the further another example of the method of manufacturing a magnesium group composite powder. The Mg-based alloy in the matrix is a microphotograph showing an example of a cross section structure of a magnesium based composite powder that is dispersed Mg 2 _Si particles. It is a figure which shows an example of the X-ray-diffraction result of magnesium group composite powder. It is a figure which shows the other example of the X-ray-diffraction result of magnesium group composite powder.

Explanation of symbols

1 container, 2 mixture, 3 warm air, 4 binder solution, 7 Mg-based powder, 8 Mg ₂ Si particles, 9 binder, 15 magnesium-based composite powder, 16 magnesium-based composite powder.

Claims (8)

A magnesium-based composite powder comprising a magnesium-based powder and magnesium silicide (Mg ₂ Si) particles attached to the surface of the magnesium-based powder via a binder . The magnesium-based composite powder according to claim 1, wherein the maximum particle diameter of the Mg ₂ Si is 50 µm or less. The magnesium-based composite powder according to claim 1, wherein the maximum particle diameter of the Mg ₂ Si is 20 μm or less. The magnesium-based composite powder according to claim 1, wherein the maximum particle diameter of the Mg ₂ Si is 5 µm or less. 2. The magnesium-based composite powder according to claim 1, wherein a content of the Mg ₂ Si with respect to the magnesium-based composite powder is 5 to 60% on a volume basis. A magnesium-based alloy material in which the magnesium-based composite powder according to any one of claims 1 to 5 is compacted and sintered, and Mg ₂ Si particles are dispersed in the substrate. Preparing a magnesium (Mg) based powder and magnesium silicide (Mg ₂ Si) particles;
Applying a binder to the surface of the Mg-based powder;
The binder of the coated Mg based powder the Mg 2 _Si particles and mixed and stirred to the a, and a step of bonding the Mg 2 _Si particles to the surface of the Mg based powder, a manufacturing method of magnesium based composite powder. A step of compacting the magnesium-based composite powder according to claim 1;
Heating the green compact in an inert gas atmosphere or non-oxidizing gas atmosphere at 200 to 400 ° C .;
A method for producing a magnesium-based alloy material, comprising a step of extruding and densifying the green compact immediately after the heating.