JP5715678B2 - Magnesium matrix composite - Google Patents

Description

  The present invention relates to a magnesium-based composite material in which SiC (so-called pure magnesium) or a magnesium alloy is used as a base material, and SiC is dispersed in the base material, and a manufacturing method thereof. In particular, the present invention relates to a magnesium-based composite material having a low porosity and excellent thermal characteristics.

  Conventionally, a composite material in which ceramic particles are dispersed in a base material (matrix) made of metal has been used as a constituent material of a heat dissipation member such as a heat spreader of a semiconductor element, and Al-SiC is representative. Further, for the main purpose of reducing the weight of the heat dissipating member, a composite material using magnesium or an alloy thereof, which is lighter than aluminum, as a base material has been studied (see Patent Document 1).

  Patent Document 1 is excellent in thermal properties by impregnating molten metal (magnesium) as a base material with SiC as a raw material placed in a mold (high thermal conductivity, thermal expansion coefficient with heat generation target) It is disclosed that a composite material can be manufactured with good workability.

JP 2006-299304 A

  In the conventional composite material, pores may exist (see Patent Document 1, paragraph 0003). It is expected that thermal characteristics can be improved by reducing the porosity, that is, by reducing the porosity in the composite material. However, Patent Document 1 does not fully examine how much the porosity should be reduced. In addition, methods for reducing the porosity have not been sufficiently studied.

  The porosity can be reduced by increasing the impregnation temperature (the temperature of the molten metal at the time of impregnation). However, in order to make the porosity very small (for example, less than 3%), the impregnation temperature needs to be higher than 1000 ° C. At such a high temperature, defects such as shrinkage nests and gas holes occur during solidification. It becomes easy to cause deterioration of the casting surface and deterioration of thermal characteristics. Therefore, it is difficult to improve the thermal characteristics by reducing the porosity by this method. In addition, this method requires a large apparatus for heating at the time of impregnation and shortens the life of the mold (mold), resulting in an increase in cost.

Alternatively, the porosity can be reduced by mixing an infiltrant such as SiO _{2 with} the raw material. However, in order to make the porosity very small (for example, less than 3%), it is necessary to increase the infiltrant. When SiO ₂ is used as the infiltrant, reaction products such as Mg—Si compounds and Mg oxides are generated. Since these products have a low thermal conductivity, if a large amount of SiO ₂ is used as the infiltrant, the above products cause a decrease in thermal characteristics. Therefore, it is difficult for this method to improve the thermal characteristics by reducing the porosity.

  Accordingly, one of the objects of the present invention is to provide a magnesium-based composite material having a low porosity. Another object of the present invention is to provide a method for producing a magnesium-based composite material suitable for producing a magnesium-based composite material having a low porosity.

The present inventors have found that a magnesium-based composite material having good thermal characteristics can be obtained by setting the porosity to less than 3%. In addition, the present inventors have used the raw material SiC after performing a specific treatment, or by performing a specific treatment on the composite coagulated product, so that the impregnation temperature is not excessively increased, and the infiltrant contains SiO _2. It was found that a magnesium-based composite material having a low porosity can be obtained without using the material. The present invention is based on these findings.

  The magnesium-based composite material of the present invention is a composite material in which SiC is dispersed in a base material made of magnesium or a magnesium alloy, and the porosity in the composite material is less than 3%.

  The composite material of the present invention can be produced by the following production method (I) or (II) of the magnesium-based composite material of the present invention.

[Production Method (I)]
The production method (I) is a method for producing a composite material in which SiC is dispersed in a base material made of magnesium or a magnesium alloy, and includes the following oxidation treatment step and impregnation step.
Oxidation treatment step: The raw material SiC is heated to form an oxide film on the surface thereof.
In this oxidation treatment step, the oxide film is formed so that the heating temperature is 700 ° C. or higher and the mass ratio of the raw material to SiC satisfies 0.4% or more and 1.5% or less.
Impregnation step: The coated SiC on which the oxide film is formed is placed in a mold, and the aggregate of the coated SiC in the mold is impregnated with a molten metal as a base material at a temperature of 675 ° C. or higher and 1000 ° C. or lower.

[Production Method (II)]
The production method (II) is a method for producing a composite material in which SiC is dispersed in a base material made of magnesium or a magnesium alloy, and includes the following preparation process and pressurization process.
Preparation step: A composite solidified product of SiC and magnesium or a magnesium alloy is prepared.
Pressurizing step: Pressurizing the composite coagulated product to crush pores present in the composite coagulated product.
In this pressurization step, the composite solidified product is pressurized at a temperature of normal temperature or higher, lower than the melting point (liquidus temperature) of the base material magnesium or magnesium alloy, and a pressure of 1 ton / cm ² or higher.

According to the production method (I) of the present invention, since an oxide film mainly composed of SiO ₂ having high wettability with magnesium is present on the surface of the raw material SiC, a molten metal (a molten metal of magnesium or magnesium alloy) is formed on the SiC aggregate. ), The oxide film and the molten metal are sufficiently in contact with each other, so that the molten metal easily wraps around the SiC. Therefore, according to the production method (I) of the present invention, pores generated due to insufficient circulation of the molten metal can be effectively reduced, and a composite material having a porosity of less than 3% can be obtained. Further, according to the production method (I) of the present invention, by using the coated SiC, SiO ₂ having high wettability with respect to magnesium can be concentrated on the surface of the raw material SiC. SiO ₂ does not exist excessively, and the presence ratio of the reaction product in the obtained composite material can be reduced. Therefore, according to the production method (I) of the present invention, a composite material having excellent thermal characteristics can be obtained by suppressing the deterioration of thermal characteristics due to the presence of the reaction product.

According to the production method (II) of the present invention, by pressing the composite solidified product under specific conditions, the pores can be actively eliminated and a composite material having a low porosity can be obtained. In particular, according to the production method (II) of the present invention, a composite material having a porosity of 5% or less, particularly less than 3%, can be obtained regardless of the presence or absence of an infiltrant (SiO ₂ ). When the infiltrant (SiO ₂ ) is not used in the production method (II) of the present invention, the amount of reaction product that contributes to the deterioration of thermal characteristics can be effectively reduced.

  In addition, according to the production methods (I) and (II) of the present invention, it is not necessary to heat the molten metal excessively, so defects such as shrinkage and gas holes are unlikely to occur in the composite material, resulting in deterioration of thermal characteristics. hard.

  According to the composite material of the present invention, the porosity is very small and the thermal characteristics are excellent. In particular, by being produced by the above-described production method (I) or (II) of the present invention, as described above, there is little deterioration in thermal characteristics due to the presence of reaction products, shrinkage nests, and gas holes, and the thermal characteristics are excellent. Hereinafter, the present invention will be described in more detail.

[Composite material]
<Base material composition>
The base material may be either so-called pure magnesium composed of 99.8% by mass or more of Mg and impurities, or a magnesium alloy composed of additive elements and the balance Mg and impurities. A composite material in which pure magnesium is a base material has high thermal conductivity. A composite material whose base material is a magnesium alloy is excellent in corrosion resistance and mechanical properties (strength). Moreover, since a magnesium alloy generally has a lower liquidus temperature than pure magnesium, the temperature during impregnation can be further lowered. Examples of the additive element include at least one of Li, Ag, Ni, Ca, Al, Zn, Mn, Si, Cu, and Zr. When the content of the additive element is increased, the thermal conductivity is lowered, and therefore the total content is preferably 20% by mass or less (the base material is 100% by mass. The same applies to the content of the additive element). In particular, Al is more preferably 3% by mass or less, Zn is 5% by mass or less, and other elements are each preferably 10% by mass or less. Addition of Li has the effect of reducing the weight of the composite material and improving the workability. Known magnesium alloys, for example, AZ, AS, AM, ZK, ZC, LA, etc. in the ASTM symbol may be used. A raw material for the base material is prepared so as to have a desired composition.

<Dispersant>
"shape"
As a raw material of the dispersion material, particulate or fibrous SiC powder, a sintered body obtained by sintering SiC powder, or a product obtained by molding SiC powder can be used. The SiC dispersed in the composite material exists while maintaining the shape of the SiC used as a raw material. In particular, when powder is used as a raw material, since it is excellent in fluidity, (1) it is easy to increase the filling rate in the mold, and it is easy to form a composite material having a high SiC content, (2) it is easy to fill the mold, There is an effect that the productivity of the composite material is good, and (3) a complex-shaped mold can be filled, and a complex-shaped composite material can be easily produced. In addition, when a plurality of types of SiC powders having different average particle diameters are used in combination, the filling rate can be increased more easily, and this technique can be suitably used for increasing the content of SiC in the composite material. The size of SiC used as a raw material is preferably about 1 μm or more and 3000 μm or less in average particle diameter (in the case of a fiber, average short diameter), which is preferable because it is easily dispersed uniformly in the base material. When using SiC powders of different sizes, the large powder has an average particle size of 50 μm or more and 1/10 or less of the shortest inner dimension of the mold, and the small powder has an average particle size of 1 of the average particle size of the large powder. When it is / 20 or more and 1/2 or less, it is easy to increase the filling rate as described above. The size and shape of SiC in the composite material can be confirmed, for example, by observing the cross section of the composite material with an SEM, an optical microscope, or the like. The use of SiC powders having different sizes can be confirmed, for example, as follows. In a cross-sectional micrograph of a composite material (e.g., 100 times), the field of view includes about 50 SiC particles having a particle size of 3 μm or more, and the particle size of each SiC particle having a particle size of 3 μm or more present in this field of view is shown. For example, it is measured by a cutting method. Obtain the average and standard deviation of the particle size of about 50 SiC. When the value obtained by dividing the standard deviation by the average is 0.5 or more, it can be determined that SiC having a different size is used. In addition, the magnification at the time of the above observation may be adjusted as appropriate so that about 50 SiC grains appear in one field of view according to the grain size of SiC.

"Content"
The content of SiC in the composite material is substantially equal to the amount of the raw material because the raw material SiC is generally present in the composite material as it is. When the content of SiC in the composite material is large, the thermal conductivity increases and the thermal expansion coefficient tends to decrease. The amount of the raw material may be adjusted according to a desired thermal expansion coefficient. For example, when the SiC content is 50% or more and 80% or less by volume, a composite material having a thermal expansion coefficient of 4 × 10 ⁻⁶ to 10 × 10 ⁻⁶ / K (4 to 10 ppm / K) is obtained. . A more preferable content of SiC is 55% or more and 80% or less by volume ratio.

"purity"
If the high-purity SiC is used as the raw material and the purity of the SiC present in the composite material is 95% or higher, particularly 99% or higher, the characteristics of SiC can be fully utilized. Moreover, when SiC with high crystallinity is used, the thermal conductivity of the composite material tends to be high.

<Organization>
《Porosity》
Invention composite material obtained by the present invention production method (II) obtained by crushing and eliminating pores of the present invention composite material obtained by the present invention production method (I) with improved wettability between the molten metal and the dispersion material The material has a low porosity. The specific porosity is less than 3%, preferably less than 1%, more preferably less than 0.5%. It is desirable that no pores exist, and ultimately a porosity of 0% is desired. A method for measuring the porosity will be described later.

<Oxygen concentration>
When an oxide film was actively formed on the raw material SiC and the thickness of the oxide film effective for reducing the porosity was examined, it was over 60 nm and about 320 nm. In the composite material of the present invention manufactured using such a coated SiC, the Mg oxide (for example, MgO) generated by the reaction between the molten metal and the oxide film is in the vicinity of SiC, specifically from the outline of SiC. Many are considered to exist in the region of 100 to 300 nm. Therefore, in the base material existing around each SiC, when the region of similar shape from the SiC contour line to 150 nm or less is the outer peripheral region of SiC, and the region of 1 μm or more from the SiC contour line is the main region, SiC One having a higher oxygen concentration in the outer peripheral region than that in the main region is an example of the composite material of the present invention. Since the composite material of the present invention has a structure in which SiC is uniformly dispersed in the base material, when the above-described coated SiC is used as a raw material, the outer peripheral region of any SiC in the cross-section at any location of the composite material is: Oxygen concentration is higher than the main region. Therefore, the oxygen concentration can be examined for the outer peripheral region of any SiC in any part of the composite material. However, when the composite material is used as a heat dissipation member, the central portion of the composite material is involved in the heat dissipation performance. It is preferable to examine the oxygen concentration in the outer peripheral region of SiC present in the substrate. That is, a region inside the region from the outer peripheral edge in the cross section of the composite material to 1/10 of the minimum length of the composite material is taken as a central region, and the oxygen concentration is examined for this central region.

  For example, when the composite material of the present invention is a plate-like material having a width of about 50 mm and a thickness of about 5 mm, the minimum length corresponds to the thickness. Therefore, the area inside 5 mm × 1/10 = 500 μm from the outer peripheral edge of the composite material becomes the central area. Specifically, a plane passing through a half of the thickness is a center plane, and a center line in the width direction of this center plane is taken, and from this center line to the width direction up to 24.5 mm, respectively, and from the center plane The area up to 2 mm in the thickness direction is the center area. In addition, for example, when the composite material of the present invention is a plate-like material having a thickness of 1 mm or less, the thickness corresponds to the minimum length, and similarly, the inner side of the region up to 1/10 of the thickness. The area may be the central area. In particular, when the thickness is small, the plane passing through the half of the thickness is the central plane, and the area from the central plane to the thickness direction is about 100 μm, that is, the area is about 200 μm thick. It may be an area.

  One or more SiCs are selected from the central region, an outer peripheral region and a main region are selected for the selected SiC, and oxygen concentrations are measured and compared. More specifically, for example, SiC is selected using the EDX analyzer attached to the TEM apparatus, and the outer peripheral region and the main region are taken for each selected SiC, and the measurement point is selected from each outer peripheral region and the main region. . The measurement point of the outer peripheral region is a point 150 nm from the SiC contour line (any point on the periphery of the outer peripheral region), the measurement point of the main region is a point on the base material 3 μm from the SiC contour line, Locations that do not include other SiC peripheral regions can be selected. For one SiC, select five or more measurement points in the outer peripheral region and measurement points in the main region, and observe them. It is preferable to select three or more (preferably five) SiC and select one or more (preferably five or more) measurement points in the outer peripheral region and main region of each SiC for observation. .

  For example, the oxygen concentration in the outer peripheral region and main region of SiC can be measured by using the EDX analyzer attached to the SEM device, the characteristic X-ray spectroscopy using the EDX analyzer attached to the TEM device, Auger electron spectroscopy, etc. This can be confirmed.

<Thermal characteristics>
One embodiment of the composite material of the present invention is one having a thermal conductivity κ of 180 W / m · K or more. In addition, one embodiment of the composite material of the present invention includes a material having a thermal expansion coefficient α of 4 × 10 ⁻⁶ / K (4 ppm / K) or more and 10 × 10 ⁻⁶ / K (10 ppm / K) or less.

Composite materials that satisfy the above thermal characteristics have high thermal conductivity, semiconductor elements (about 4 to 7 ppm / K (e.g., Si: 4.2 ppm / K, GaAs: 6.5 ppm / K)) and peripheral components (e.g., metal (Package made of ceramics such as stainless steel (around 20 ppm / K), steel (11-12 ppm / K)) and Al ₂ O ₃ (6.5 ppm / K)) and excellent thermal expansion coefficient. That is, this composite material has thermal characteristics suitable for a heat radiating member disposed in the vicinity of the semiconductor element. Since the thermal conductivity and the coefficient of thermal expansion change depending on the composition of the base material and the content of SiC, it is preferable to appropriately adjust the raw materials so as to obtain desired thermal characteristics. Since the heat conductivity is preferably higher, there is no particular upper limit. 200 W / m · K or more is more preferable.

[Production Method (I)]
In this method, a dispersion material as a dispersion material is placed in a molding die. → A dispersion metal material assembly is impregnated with a molten metal as a base material, and the molten metal and the dispersion material are combined. → The composite is cooled. Then, the composite material is manufactured by a process of solidifying the molten metal. In particular, a material in which an oxide film is formed on SiC is used as a dispersion material.

  If the ratio of the oxide film to the raw material SiC is small (the amount of oxide film is small), the effect of improving the wettability with the molten metal by the oxide film cannot be obtained sufficiently, and the ratio is large (the amount of oxide film is large). The amount of Mg oxide, which is a reaction product, increases, resulting in deterioration of thermal characteristics. The oxide film is formed so that the mass ratio of the oxide film to the raw material SiC is 0.4% to 1.5%. Preferably, the oxide film is formed so that the mass ratio is 0.4% or more and 1% or less. However, the more (thick) the oxide film is, the more the molten metal can be impregnated at a low temperature and in a short time. Therefore, for example, when the effect of simplifying the heating device of the mold during impregnation, shortening of the impregnation time (cycle time), and extending the life of the mold is desired rather than improving the thermal characteristics, the mass ratio exceeds 1.5%. SiC with an oxide film can be used.

  When forming the oxide film, if the temperature of heating the raw material SiC is less than 700 ° C., the oxide film cannot be sufficiently formed on the surface of the SiC, and the porosity is increased by not being sufficiently wet with the molten metal. The heating temperature for forming the oxide film is 700 ° C. or higher. The oxidation reaction on the surface of SiC becomes active at 800 ° C., and the higher the heating temperature, the faster the formation rate of the oxide film. Therefore, 800 ° C. or higher, particularly 850 ° C. or higher, and more preferably 875 ° C. or higher is preferable. However, if the heating temperature is too high, the formation rate of the oxide film becomes too fast, and it becomes difficult to control the amount (thickness) and uniformity of the oxide film. If the oxide film increases or the oxide film thickness becomes nonuniform, the thermal conductivity may decrease due to a large amount of reaction products and partial wetting of the molten metal may occur. Is preferred. The amount of oxide film is also affected by the heating time, and tends to increase as the heating time increases. A preferable heating time is about 2 hours. The amount of oxide film is also affected by the size of the raw material SiC, and tends to increase as the raw material SiC becomes finer. Therefore, the heating temperature, the heating time, and the size of the raw material SiC may be appropriately adjusted so that the oxide film amount becomes a desired amount (mass ratio). Also, if you want to change the SiC size of the raw material while maintaining the total amount of oxide film at a predetermined amount, adjust the heating temperature and heating time when forming the oxide film according to the changed SiC size. Good.

  For example, when the dispersion material is powder, the dispersal material is placed in the mold by tapping the powder as it is, filling the mold, or casting the slurry into the mold. Is mentioned. Casting molding can easily disperse the raw material of the dispersion material not only in a simple shape but also in a complicated shape. Moreover, when performing casting molding, the gap between SiC can be reduced and the filling rate of SiC can be raised by tapping or compressing suitably. Furthermore, a molded body made of a dispersion material material may be prepared in advance and placed in a mold. The molded body is, for example, a slurry formed and dried, a dispersion material raw material and a binder mixed and pressure-molded, a sintered body of these molded bodies, or a commercially available sintered body. Material is available. In a sintered body sintered after forming, when SiC is directly bonded by sintering, a composite material having a small thermal expansion coefficient tends to be obtained. When sintering, the oxidation treatment may be performed after sintering. When using a commercially available sintered material, the sintered material is oxidized.

  When contact between the dispersion material and the molten metal is performed in an inert atmosphere such as Ar, the reaction between the molten metal (especially Mg) and the atmospheric gas can be prevented, and the deterioration of the thermal characteristics due to the presence of the reaction product is suppressed. it can. When the atmospheric pressure is set to atmospheric pressure or lower, it is preferable that pores due to gas uptake hardly occur.

  The preferable impregnation temperature of the molten metal depends on the amount of oxide film (thickness) .If the amount of oxide film is small in the above range, the impregnation temperature is preferably high.If the amount of oxide film is large in the above range, the impregnation temperature is It may be low. Specifically, in the case of 0.4 mass% or more and 0.65 mass% or less, the impregnation temperature is preferably 800 ° C or more and 1000 ° C or less, and in the case of more than 0.65 mass% and less than 1.5%, the impregnation temperature is 675 ° C or more and 875 ° C or less. Of course, it may be over 875 ° C. More specifically, for example, when the base material is pure magnesium and the oxide film amount is about 0.4% by mass with respect to the total amount of raw material SiC, the impregnation temperature of the molten metal is more than 750 ° C. As a result, the wettability between the molten metal and the dispersion material becomes high, and impregnation is possible. The higher the impregnation temperature, the higher the wettability and the lower the porosity. Therefore, the impregnation temperature is preferably 800 ° C. or higher, particularly 850 ° C. or higher. For example, when the base material is pure magnesium and the oxide film amount is about 0.8% by mass with respect to the total amount of raw material SiC, and the impregnation temperature of the molten metal is 675 ° C. or higher, the molten metal and the dispersion material The wettability with a raw material becomes high and can be impregnated. At this time, as in the case where the amount of the oxide film is about 0.4 mass%, the higher the impregnation temperature, the higher the wettability and the lower the porosity. Therefore, the impregnation temperature is preferably 700 ° C. or higher, particularly 725 ° C. or higher. When the amount of oxide film is larger (however, 1.5% by mass or less), it is considered that good impregnation can be achieved even when the impregnation temperature of the molten metal is less than 700 ° C. However, when the base material is pure magnesium, if the impregnation temperature exceeds 1000 ° C., defects such as shrinkage cavities and gas holes may occur in the composite material, and Mg may boil.

  On the other hand, when the base material is a magnesium alloy, the liquidus temperature is lower than the melting point of pure magnesium, so that the impregnation is possible at a lower temperature. For example, when the base material is AZ31 or AZ91, impregnation is possible even when the amount of oxide film is small even if the impregnation temperature is 800 ° C. or less. When the base material is AZ91, the impregnation temperature is 650 ° C. or more. Also in this case, the impregnation temperature is preferably 700 ° C. or higher because the wettability increases and the porosity decreases as the temperature increases, as in the case where the pure magnesium is used as the base material. When the base material is a magnesium alloy, the vapor pressure decreases and the boiling point increases, so that the impregnation temperature can be raised slightly and can be set to 1000 ° C. or higher, but it is still preferably less than 1100 ° C.

  Solidification of the molten metal in the composite is also preferably performed in an inert atmosphere, and the atmospheric pressure may be atmospheric pressure, but may be higher than atmospheric pressure in order to suppress generation of defects during solidification. It is preferable that the cooling of the composite is carried out quickly throughout the entire body in order to suppress the growth of the crystallized product. Cooling speed can be increased by using a mold made of carbon, graphite, stainless steel, etc., which has excellent thermal conductivity, or by forced cooling such as air cooling or water cooling using a fan as well as natural cooling. .

  Furthermore, in the production method (I), the porosity can be further reduced by providing a pressurizing step of pressurizing the solidified solidified solid and crushing pores existing in the solidified solidified.

In the pressurizing step, pressurization may be performed at room temperature, but if the composite solidified product is heated, the plastic workability of the base material can be improved and the pores can be crushed with a lower pressure. Or when making the pressure at the time of pressurization constant, if it pressurizes in the state which heated the composite solidified substance, a pore can be crushed more effectively than the case of normal temperature. Applied pressure is preferably 1 ton / cm ² or more, liable crush larger pores, 3 ton / cm ² or more, further 5 ton / cm ² or more, is to 9ton / cm ² or less so as not to damage the SiC by pressurization preferable. The pressurizing pressure may be changed according to the heating temperature. For example, when the heating temperature is increased to over 240 ° C., the pores can be effectively crushed by setting the pressurizing pressure to 1 ton / cm ² or more. When the heating temperature is set to a relatively low temperature of 150 ° C. or higher and 240 ° C. or lower, the pores can be effectively crushed by setting the pressure to 3 ton / cm ² or higher. When the temperature is normal temperature or higher and lower than 150 ° C., the pores can be effectively crushed by setting the pressure to 5 ton / cm ² or higher. As described above, the higher the temperature, the more easily the pores are crushed. However, the upper limit of the heating temperature is the melting point (liquidus temperature) of magnesium or a magnesium alloy as the base material so that the solidified base material does not melt. A more preferable heating temperature is 400 ° C. or more and 600 ° C. or less. The pressurization temperature and pressurization pressure may be appropriately selected within a range in which the composite solidified product is not damaged or excessive strain is not introduced. If the pressurization time is too long, distortion or the like is added to the base material, and therefore the pressurization time is preferably about 10 minutes. In addition, when several percent of Li by mass is added to magnesium, the crystal structure of magnesium becomes a bcc structure that is easily plastically deformed, and even at room temperature to less than 150 ° C, pores can be formed at a relatively low pressure of 5 ton / cm ² or less. Can be effectively crushed.

  After the pressurizing step, annealing may be performed to remove distortion generated in the base material. The upper limit of the annealing temperature is the melting point (liquidus temperature) of the base material magnesium or magnesium alloy.

[Production Method (II)]
By pressurizing the composite solidified product in a heated state as described above, the pores can be crushed and disappeared, so that the porosity can be effectively reduced. Specifically, a composite coagulated product having a porosity of 5% or less, particularly less than 3% is obtained. There is no particular limitation on the method for producing the composite coagulated product to be pressurized. As described above, the composite coagulated product manufactured by the manufacturing method (I) of the present invention is manufactured by the same infiltration method as the manufacturing method (I) of the present invention using SiC without forming an oxide film as a raw material. However, even those manufactured by the powder metallurgy method (a method in which the base material powder and the dispersion material raw material powder are mixed and molded and fired) generally have a large number of pores, the melting method (the dispersion material on the molten metal of the base material) It may be produced by a method of solidifying a mixed molten metal mixed with raw materials. The pressurizing conditions (temperature, pressure, time) are the same as those described above.

  According to the production method of the present invention, a composite material having a low porosity can be produced without increasing the impregnation temperature or using an infiltrant. According to the composite material of the present invention, since the content and porosity of the phase having low thermal conductivity derived from the use of the infiltrant are low, the thermal characteristics are excellent.

It is a micrograph of the composite material produced in Test Example 1, (I) is sample No. 1-1, (II) is sample No. 1-2, (III) is sample No. 1-3, (IV) Indicates Sample No. 1-4. Of the samples prepared in Test Example 1, for the sample using SiC powder of # 120: # 600 = 8: 2 as the raw material, the heating temperature when oxidizing the raw material SiC and the obtained composite material It is a graph which shows the relationship with a porosity. 4 is a micrograph of the composite material produced in Test Example 2, wherein (I) shows sample No. 2-9 and (II) shows sample No. 2-16.

(Test Example 1)
A magnesium-based composite material in which the base metal was pure magnesium or a magnesium alloy and the dispersion material was SiC was produced, and the porosity and thermal characteristics were examined.

  The composite material was produced as follows. As raw materials, the base material shown in Table 1 (Mg: pure magnesium composed of 99.8% by mass or more of Mg and impurities (described as `` Mg '' in Table 1), AZ31 and AZ91: magnesium alloy containing Al, Zn), and SiC powders having different average particle sizes (average particle size: # 120 (about 150 μm), # 600 (about 25 μm), # 1000 (about 15 μm)) and a SiC sintered body were prepared. All the raw materials used were commercially available.

  The raw SiC powder and the SiC sintered body were subjected to oxidation treatment at the temperature (° C.) shown in Table 1. The heating time was 2 hours for all samples. After the oxidation treatment, the amount of oxide film was measured. The results are shown in Table 1. The amount of oxide film was measured with an ICP-AES (Inductively Coupled Plasma Emission Spectroscopy) apparatus. In addition, those not subjected to oxidation treatment are described as “no oxidation” in Table 1.

  A mixture of oxidized SiC powder, coated SiC sintered body, and untreated SiC powder mixed at the mixing ratio (volume ratio) shown in Table 1 is poured into a rectangular parallelepiped mold (50 mm x 30 mm x 6 mm) After that, it was leveled by applying appropriate vibrations (tap filling). Then, the molten metal as a base material is introduced into the mold, and the mold is held at the impregnation temperature (° C.) and the impregnation time (hour) shown in Table 1, and the molten metal is added to the SiC aggregate in the mold. Was impregnated. After the impregnation time elapsed, the mold was cooled to solidify the molten metal to obtain a composite material (composite solidified product). The process from introduction of the molten metal to cooling was performed in an Ar atmosphere (atmospheric pressure).

  Each composite material obtained was examined for porosity (%), thermal conductivity (W / K · m), thermal expansion coefficient (ppm / K), and SiC content (volume ratio,%). The results are shown in Table 1.

  The porosity (%) in the composite material was determined as follows. First, the obtained composite material was embedded in a resin and fixed so that SiC existing in a region not impregnated with the base metal was not released. An arbitrary cross section of the composite material embedded in the resin was polished with a rotating polishing plate using a commercially available non-corrosive diamond paste and a lubricating liquid, and then this cross section was observed with an optical microscope (magnification: 50 times). In the image, an area of 2 mm × 3 mm or more is image-processed with a commercially available image processing apparatus, and the total area of all pores existing in the area is obtained, and {(total area) / (area of area)} × 100 Table 1 shows the average value of the porosity of the cross section with n = 3 as the porosity in this cross section.

  The thermal conductivity and the thermal expansion coefficient of the composite material were measured using a commercially available measuring instrument after cutting out a test piece from the obtained composite material. In addition, the thermal expansion coefficient was measured about the range of 30-150 degreeC. In addition, Table 1 describes that “not measurable” when the test piece could not be obtained due to the reason that the impregnation was not sufficiently performed after the impregnation time and the thermal characteristics could not be measured.

  The content of SiC in the composite material was determined as follows. An arbitrary cross section of the composite material is observed with an optical microscope (magnification: 50 times), and this observation image is subjected to image processing with a commercially available image processing apparatus to obtain a total area of all SiC present in the cross section, and this total The area converted into the volume ratio is defined as the volume ratio based on this cross section, and the average value of the volume ratio of the cross section of n = 3 is shown in Table 1.

  As shown in Table 1, it can be seen that a composite material having a porosity of less than 3% has a high thermal conductivity when compared with a base material having the same composition. In addition, such a composite material is subjected to an oxidation treatment at a heating temperature of 700 ° C. or more, and uses a coated SiC powder in which an oxide film of 0.4% by mass or more is formed on SiC, and an impregnation temperature according to the composition of the base material. It turns out that it can manufacture by adjusting suitably. Furthermore, it can be seen that the oxide film amount can be increased to more than 0.65 mass% by reducing the average particle size of the raw SiC powder and increasing the amount of small SiC powder used or by increasing the oxidation treatment temperature. When the amount of oxide film exceeds 0.65% by mass, it can be seen that a composite material having low porosity and high thermal conductivity can be produced even when the impregnation temperature is lower than when the amount of oxide film is 0.45% by mass.

  FIG. 1 is an optical micrograph (50 ×) of a cross-section of the produced composite material, (I) is sample No. 1-1, (II) is sample No. 1-2, (III) is sample No. 1-3 and (IV) show Sample No. 1-4. FIG. 2 is a graph showing the relationship between the heating temperature and the porosity during the oxidation treatment for a sample using SiC powder of # 120: # 600 = 8: 2 as a raw material. In FIG. 1, the portions that appear black are pores, and the plurality of particles that appear rectangular are SiC (the same applies to FIG. 3 described later). As shown in FIG. 1, sample Nos. 1-3 and 1-4 manufactured using the coated SiC powder have pores as compared to sample No. 1-1 manufactured using the untreated SiC powder. It can be seen that the number is significantly reduced. In particular, sample No. 1-1 has many large pores, whereas sample No. 1-3 (oxide film amount: 0.45 mass%) has few large pores. It can be seen that Sample No. 1-2 (amount of oxide film: 0.21 mass%) having a heating temperature of less than 700 ° C. has many pores. In sample No. 1-4 (the amount of oxide film: 0.86% by mass) in which the heating temperature during the oxidation treatment was higher, pores could not be substantially confirmed. From these photographs and the graph of FIG. 2, it can be seen that the pores can be remarkably reduced if the heating temperature during the oxidation treatment is 700 ° C. or higher, particularly 800 ° C. or higher, and the amount of oxide film is 0.4 mass% or higher. It can also be seen that the pores can be sufficiently reduced even when the oxide film amount is 1% by mass or less.

  Furthermore, among the composite materials manufactured using the coated SiC powder on which an oxide film was formed with a heating temperature of 700 ° C. or higher, the cross section of each sample having a porosity of less than 3% was analyzed with an Auger electron spectrometer. As a result, oxygen was recognized in the outer peripheral region of SiC in the center region of each sample, and this oxygen concentration was higher than that in the main region for this SiC. This confirms that the oxide film formed on the raw material SiC reacts with the molten metal and promotes the contact between the SiC and the molten metal. In addition, the comparison of the oxygen concentration is performed by selecting SiC from the central region and arbitrarily selecting five measurement points from the outer peripheral region (a point 150 nm from the outline of the SiC) and the main region for this SiC, In all five points, the oxygen concentration in the outer peripheral region of SiC was higher than that in the main region.

  Furthermore, among the composite materials manufactured using coated SiC powder with an oxide film formed at a heating temperature of 700 ° C. or higher, those having a high thermal conductivity of 180 W / K · m or higher are obtained, and the porosity is low. As the result, the thermal conductivity tends to be improved. In addition, a composite material having a thermal conductivity of 180 W / K · m or more and a thermal expansion coefficient of 4 to 10 ppm / K is expected to be suitably used for a heat radiating member because it has the thermal characteristics required for the heat radiating member. The

  In addition, it can be seen that when the composite material is manufactured using the coated SiC powder, the porosity can be reduced when the impregnation temperature is 675 ° C. or higher. When the base material is pure magnesium and the impregnation temperature is 1000 ° C., the porosity may exceed 3%. This is thought to be due to the formation of shrinkage cavities and gas holes, and measures such as maintaining the molten state at a temperature of 875 ° C. or lower for a sufficient amount of time or performing dehydrogenation treatment before the solidification process. It is thought that improvement is possible.

(Test Example 2)
A magnesium-based composite material was prepared by applying pressure treatment to a composite solidified material in which the base metal was pure magnesium and the dispersion material was SiC, and the porosity was examined.

  In this test, multiple composite solidified products were prepared under the same conditions as the sample No. 1-1 composite solidified product prepared in Test Example 1 (prepared using untreated SiC powder). The solidified product was subjected to the following pressure treatment.

The composite solidified material thus prepared was subjected to pressure treatment at 1 to 5 ton / cm ² for 10 minutes while being maintained at room temperature (30 ° C.) to 600 ° C. to prepare a composite material. Table 2 shows the production conditions and porosity of each sample.

  With respect to the obtained composite material, the porosity (%) was measured in the same manner as in Test Example 1. The results are shown in Table 2. Further, FIG. 3 (I) shows an optical microscope photograph (50 times) of a cross section of sample No. 2-9 and FIG. 3 (II) of sample No. 2-16. When the content of SiC in the composite material was determined in the same manner as in Test Example 1, all the samples were 58 to 60% by volume.

As shown in FIG. 3, it can be seen that large pores can be eliminated by performing pressure treatment under specific conditions. Specifically, the applied pressure at normal temperature as shown in Table 2 5 ton / cm ² or more, when the heating temperature is 0.99 ° C., the applied pressure 3t / cm ² or more, when the heating temperature is above 240 ° C. It can be seen that the porosity of the composite material is greatly reduced when the pressure applied is 1 t / cm ² or more. Moreover, it turns out that a porosity can be reduced effectively, so that the heating temperature at the time of pressurization is high, and a pressurization pressure is high. The composite material having a low porosity produced in this way is considered to exhibit high heat conduction characteristics as in Test Example 1. From this test, it can be seen that a composite material having a low porosity can be obtained by applying a specific pressure treatment after the impregnation treatment of the molten metal without performing a specific treatment on the raw material SiC. Moreover, when the said specific pressurization process is performed to the composite solidified material which performed specific process to raw material SiC, it is anticipated that a porosity can be reduced effectively.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention. For example, the content, size, shape, and composition of the base material of SiC in the composite material can be changed as appropriate.

  The composite material of the present invention is excellent in heat dissipation, and is excellent in matching of the thermal expansion coefficient with the semiconductor element and its peripheral components. Therefore, it can be suitably used as a constituent material of a heat radiating member such as a heat spreader. Moreover, the manufacturing method of this invention composite material can be utilized suitably for manufacture of the said composite material.

Claims (2)

A magnesium-based composite material in which SiC is dispersed in a base material made of magnesium or a magnesium alloy,
The content of SiC in the magnesium-based composite material is 50% or more and 80% or less by volume ratio,
The porosity in the magnesium-based composite material is less than 3%;
The thermal conductivity is 180 W / m · K or more,
Thermal expansion coefficient of Ri der 4 × ^{10 -6} / K or ¹⁰ × 10 ^-6 / K or less,
In the magnesium-based composite material, SiC powders having different sizes are dispersed,
The large SiC powder has an average particle size of 50 μm or more and 150 μm or less,
The small SiC powder has an average particle size of 1/20 or more of the average particle size of the large SiC powder and 1/2 or less of the average particle size of the large SiC powder,
A magnesium-based composite material in which the volume ratio of the large SiC powder is larger than that of the small SiC powder . The magnesium-based composite material according to claim 1, wherein the thermal conductivity is 223 W / m · K or more.