JPH0471971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a reinforcing fiber preform that can be suitably used for manufacturing metal matrix composite materials.

(Prior Art and its Problems) Metal matrix composite materials are manufactured by a method in which a molten metal serving as a matrix is poured into a reinforcing fiber preform and solidified under pressure.

The above-mentioned reinforcing fiber preforms are generally prepared by dispersing short fibers, whiskers, etc. in water or an organic solvent in which a binder is dissolved, and filtering and molding this dispersion, and compression molding this dispersion.

The reinforced fiber preforms obtained by these methods have low density and bending strength, and deform or shrink when molten metal is injected at high pressure, making it impossible to obtain a metal matrix composite material with a desired shape, or making it impossible to obtain a metal matrix composite material with a desired shape. There is a problem in that the reinforcing fibers are not uniformly dispersed in the material, resulting in a material with uneven strength.

As mentioned above, reinforcing fiber preforms prepared by known methods cannot provide a metal matrix composite material with a desired shape, so it is necessary to cut the metal matrix composite material into a predetermined shape after manufacturing it. be. However, it is difficult to cut fiber-reinforced metal matrix composite materials, and as a result, the productivity of metal composite materials is extremely low, which is a problem that cannot be ignored from an industrial perspective.

(Technical means for solving the problems) An object of the present invention is to solve the above-mentioned problems.
That is, the object of the present invention is to provide a reinforcing fiber preform for a metal matrix composite material that has high density and bending strength and does not deform or shrink during injection of molten metal, and a method for manufacturing the same.

According to the present invention, there is provided a method for producing a reinforcing fiber preform for a metal matrix composite material, which comprises directly arranging reinforcing fibers selected from short fibers and whiskers in a mold, and heating and pressurizing the reinforcing fibers.

Specific examples of reinforcing fibers include alumina, silica-alumina, silicon carbide, fired products of polymetallocarbosilane (manufactured by Ube Industries, Ltd., Tyrano: registered trademark),
Examples include short fibers such as silicon nitride; whiskers such as silicon carbide and silicon nitride. The length of the reinforcing fibers is usually 10 mm or less, preferably 1 to 5 mm.

If necessary, a small amount of a preform strength improver can be added to these reinforcing fibers. Specific examples of the strength improver include oxide particles such as silica and alumina, nitride particles such as aluminum nitride and boron nitride, and carbide particles such as boron carbide and titanium carbide. The amount of strength improver added is usually less than % by weight based on the reinforcing fiber.

After the reinforcing fibers are placed in a mold having a desired shape, they are heated and pressurized.

The heating temperature is also related to the pressing force, but it is usually 500~
The temperature is 1500°C, preferably 700-1000°C. The heating temperature is preferably set as low as possible so long as a predetermined preform strength can be obtained.

The pressing force is related to the desired preform density, but is generally between 5 and 200 kg/cm ² .

In the present invention, it is necessary to heat and pressurize the reinforcing fibers in the mold at the same time, and it is not possible to obtain a preform that does not deform or shrink during injection of molten metal by using only one of the treatments.

As the heating and pressurizing device, a device known per se can be used, and examples of such devices include a hot press device, an atmosphere pressurizing device, a hydrostatic pressurizing device (HIP), and the like.

According to the manufacturing method of the present invention, the density is 0.5 g/cm ³ or more,
A reinforced fiber preform with a bending strength of 10 kg/cm ² or more can be easily obtained.

The reinforcing fiber preform for metal matrix composite materials of the present invention is placed in a mold, the molten metal that will become the matrix is poured into it, and the two are integrated and solidified under pressure to form the metal matrix composite material. can be manufactured. At this time, since the preform of the present invention does not substantially deform or shrink during injection of molten metal, there is no need for difficult and costly machining of the metal matrix composite material to be manufactured, or there is only a slight amount of machining. It can be made into a final product with only some processing.

(Effects of the Invention) The reinforced fiber preform of the present invention has excellent characteristics in that it has high strength and does not deform or shrink when molten metal is poured into it. Furthermore, the preform of the present invention can provide a metal matrix composite material with higher strength at high temperatures than preforms prepared by known methods. Further, although it is not necessarily clear why the reinforcing fiber preform obtained by the present invention has high strength, it is thought that at least some of the reinforcing fibers become entangled during heating and pressurization, and furthermore, some of them become fixed.

(Example) Examples and comparative examples of the present invention are shown below.

Example 1 α-type silicon nitride whiskers with a diameter of 0.1 to 0.5 μm and a length of 10 to 20 μm were placed in a graphite jig with a diameter of 50 mm, and hot pressed at 800° C. and a pressure of 100 Kg/cm ² in a nitrogen gas atmosphere. A whisker preform with a diameter of 50 mm and a thickness of 10 mm was obtained. This preform had a density of about 0.53 g/cm ³ and a bending strength of 36.5 Kg/cm ² .
When this preform was observed with a scanning electron microscope, it was found that the whiskers were entangled with each other and some of the whiskers were fixed.

After preheating the above preform to 600℃, it is placed in a mold, and aluminum (A1070) heated and molten to 770℃ is injected into it and solidified while pressurized at 1000Kg/cm ² to produce an aluminum composite material. did. The whisker volume content of the composite material was 16%.

As can be seen from FIG. 1, which shows the center cut section of the composite material obtained, no deformation or shrinkage of the preform was observed. From this composite material 3×4×40
Cut out a mm test piece, and for this test piece, the span is 30 mm, and the crosshead speed is 0.5.
Three-point bending tests at mm/min were measured at temperatures from room temperature to 400°C. The results are shown in Table 1.

Table 1 Temperature (°C) Bending strength (Kg/mm ² ) 25 57 100 53 200 47 300 38 400 21 Example 2 Silica/alumina short fibers (manufactured by Isolite Kogyo Co., Ltd., khao wool)
A preform was manufactured by repeating Example 1 except that . The obtained preform had a density of about 0.73 g/cm ³ and a bending strength of 47.3 Kg/cm ² .
When this preform was observed with a scanning electron microscope, it was found that the whiskers were entangled with each other and some of the whiskers were fixed.

An aluminum composite material was produced from the above preform in the same manner as in Example 1. The preform in the obtained composite material had the same size as before casting, and no deformation or shrinkage was observed.

Example 3 Preform preparation and aluminum composite material were prepared by repeating the same method as in Example 1 except that silicon carbide whiskers were used instead of α-type silicon nitride whiskers and the heating temperature during preform molding was changed to 1000°C. was manufactured.

The preform had a density of about 0.68 g/cm ³ and a bending strength of 40.2 Kg/cm ² . Also, no deformation or shrinkage of the preform in the composite material was observed.

Comparative Example 1 Example 1 was repeated except that instead of hot pressing the α-type silicon nitride whiskers, uniaxial molding was performed at room temperature and at a pressure of 100 kg/cm ² . Pressure was applied so that the preform had a density of approximately 0.53 g/cm ³ , but the resulting preform exhibited a so-called springback phenomenon in which the volume increased when the mold was released, resulting in a density of approximately 0.33 g/cm ^{3 .} All I could get was that. This preform had very low strength and was prone to chipping and falling off, especially at the periphery. In an attempt to obtain a preform with a density of 0.5 g/cm ³ or more, the pressure was increased, but springback and even cracking of the preform occurred, making it impossible to produce a preform with the above density.

An aluminum composite material was produced in the same manner as in Example 1 using the above preform having a density of about 0.33 g/cm ³ . As can be seen from FIG. 2, which shows the center cut section of the composite material obtained, deformation and shrinkage were observed in the preform, and cracks were also observed in the preform. The room temperature bending strength of this composite material was 23 Kg/mm ² .

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing central cut sections of the aluminum composite materials obtained in Example 1 and Comparative Example 1, respectively. 1... Whiskers constituting the preform, 2...
Aluminum that makes up the matrix.

Claims (1)

[Claims] 1. A method for producing a reinforcing fiber preform for a metal matrix composite material, which comprises directly arranging reinforcing fibers selected from short fibers and whiskers in a mold, and heating and pressurizing the reinforcing fibers.