JPH0151529B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved method for producing fiber reinforced metal composites by pressure casting.

[Conventional technology]

Whiskers composed of acicular single crystals such as SiC, Si ₃ N ₄ or graphite have excellent physical properties in terms of specific strength, specific modulus, heat resistance and chemical stability, so they are particularly popular among Al. It is useful as a composite reinforcing material for light metals.

Pressure casting is known as an effective means for producing fiber-reinforced metal composites using this type of whiskers. In the pressure casting method, as shown in FIG. 1, a preformed whisker aggregate preform 1 is placed in a mold 2 as a fiber skeleton,
After injecting the molten matrix metal 3 into the preform, it is impregnated and solidified inside the preform structure while being pressurized by the plunger 4.The most important operational condition when using this method is that the matrix metal is It is to maintain the molten metal state normally. When the molten metal cools during the impregnation process and the matrix metal solidifies, smooth penetration into the preform structure is inhibited, resulting in cracks in the composite part,
This results in property defects such as extreme shrinkage deformation of the composite and heterogeneity of the composite structure.

Furthermore, in order to ensure smooth impregnation, conventional methods have been used to infiltrate the molten metal from the top and all sides of the whisker preform in the direction of the arrows, as shown in Figure 1. This leads to a phenomenon in which gas components occluded within the structure or component segregation due to certain reactions occurring during impregnation with molten metal are trapped in the composite central portion, causing tissue defects.

[Problem that the invention seeks to solve]

Among the above-mentioned phenomena, means for preheating the mold and preform are commonly used to prevent solidification of the matrix metal. However, the temperature of the mold cannot be raised sufficiently due to equipment constraints, and is insufficient to maintain a normal molten metal state throughout the impregnation process.

On the other hand, no effective countermeasures have been taken so far regarding the structural segregation caused by the entire surface penetration of the molten metal into the preform.

The present invention has been made to solve these problems at the same time.

[Means for solving problems]

The method for manufacturing a fiber-reinforced metal composite provided by the present invention includes placing a whisker preform as a fiber skeleton in a mold, injecting molten matrix metal into the mold, and forming the composite by pressure casting. The main structural feature is that the whisker preform is set in a preheated inner mold with upper and lower openings and inserted into the mold.

Hereinafter, the present invention will be explained in detail with reference to the explanatory diagram of FIG.

First, a whisker preform 1 serving as a fiber skeleton is set in a preheated insert mold 5. The whisker preform is an aggregate of short fibers formed by a dry or wet method after dissolving generated whiskers such as SiC, Si ₃ N ₄ or graphite, and is formed into an outer shape that matches the inner shape of the insert mold 5. be done. The inner mold 5 is made of a hard metal with excellent thermal conductivity, such as tool steel, and has an upper and lower opening shape, and the inner surface is formed to conform to the final shape such as a cylinder, an inverted cone, or a concave and convex groove. The outer surface is designed and processed so that it comes into close contact with the inner wall of the mold 2 when inserted. In addition to the integral structure, this can also be a separate structure.

Before inserting into the mold 2, the insert mold 5 is heated using an electric furnace or the like, preferably to a temperature higher than the melting point of the matrix metal. It is effective to preheat the whisker preform 1 to be set therein, and for this purpose, it is operationally convenient to preheat the whisker preform while it is set in the inserting mold.

At this time, it is possible to control the degree of vertical shrinkage of the composite material by adjusting the preheating temperature of the insert mold and preform, so by pre-calibration, the fiber volume fraction (Vf) can be controlled. can be adjusted appropriately.

The inner mold 5 with the whisker preform 1 set therein is then inserted into the mold 2 and placed above the lower punch 6. Preferably, the mold is heated throughout the impregnation process via an attached heating device. Subsequently, a molten matrix metal 3 is poured into the mold and pressurized with a plunger 4 from above. Due to the pressurization, the molten metal 3 penetrates only from the upper surface of the whisker preform 1 in the direction of the arrow. After the molten matrix metal 3 is sufficiently impregnated into the entire preform structure, it is solidified while maintaining the pressure.

[Effect]

According to the above manufacturing method, the whisker preform is set in a preheated inner mold and impregnated with molten metal, so that the system is maintained at a sufficient temperature to maintain a normal molten state of the matrix metal throughout the impregnation process. Realize. Furthermore, since the molten matrix metal permeates unidirectionally from the top surface of the whisker preform, the occluded gas component present inside the preform structure is discharged from the bottom of the system, and especially when using a matrix metal containing Mg, It functions to effectively eliminate the segregation of reaction parts that tends to occur.

〔Example〕

Diameter 0.5-1.5μm, length 60-100μm, density 3.18
g/cm ³ , the SiC whiskers, which have β-type crystal properties, are well dissolved and dispersed in pure water, and a wet whisker cake is formed by the pressurization method, and then heated and dried to form a cake with a diameter of 80 mm and a height of 130 mm. A cylindrical preform with a fiber volume fraction of 15% was created.

The above SiC whisker preform has an inner diameter of 80 mm.
The mold was inserted into an inner mold made of tool steel (SK material) with a diameter of 120 mm, an outer diameter of 120 mm, and a height of 140 mm, and then placed in an electric furnace and preheated to 700°C. Next, the preheated inner mold was inserted into a mold (inner diameter 120°C) maintained at a temperature of 300°C.
mm), and the Al alloy (JIS standard
2014) was injected. Subsequently, pressure was applied from above using a plunger at a pressure of 1000 Kg/cm ² , and the pressurized state was maintained until the molten metal was completely solidified.

SiC whisker-reinforced Al obtained in this way
Although the height of the composite material shrank to 116 mm, no defects such as cracks or cracks were observed in the structure.
The photograph in Figure 3 shows the metallographic structure of a cross-section of a composite cast body vertically divided, solution-treated, and treated with T6.The leader line 7 is the composite part, and the leader line 8 is the composite part in which the components are unevenly distributed. From this situation, the structure of the composite part had homogeneous properties with no component segregation.

Further, when the amount of gas contained in this composite material was measured by the Lansley method, it was found to be an average of 5.1 cc/100 g, with slight local deviations.

For comparison, SiC whisker reinforcement was performed using the same method as in the above example except that no interpolation mold was used.
An Al composite material was created. In this case, the whisker preform is placed in the center of the mold, and the molten metal is placed in the first
Penetration was made in the direction of the arrow in the figure.

The composite material obtained in this comparative example was shrunk and deformed to a height of 125 mm and a diameter of 75 mm at the composite portion. FIG. 4 is a photograph of the metallographic structure of a cross section after solution treatment and T6 treatment. An abnormal tissue portion 9 due to component segregation appeared in the center of the composite portion 7, and heterogeneity of the structure was observed. In addition, when the amount of gas contained in the composite material was measured, it was found that the center part was 21.1 cc/
100g, and 8.3cc/100g at the outer periphery, which is significantly higher than the example of the present invention, and shows a significant increase at the center compared to the outer periphery.

〔Effect of the invention〕

According to the present invention, the maintenance of a normal molten metal state during the impregnation process during pressure casting and the effect of unidirectional infiltration from the upper surface work synergistically, and a composite structure with homogeneous properties without any segregation abnormalities is always obtained. Therefore, it is of great value as a mass production technology for producing high-performance fiber-reinforced metal composites using whiskers as reinforcing materials.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an apparatus for explaining a conventional pressure casting method, and FIG. 2 is a sectional view of an apparatus for explaining a method of the present invention. FIG. 3 is a photograph of the metallographic structure of a processed cross section of a composite obtained by the method of the present invention, and FIG. 4 is a photograph of the metallographic structure of a processed cross section of the composite obtained by the conventional method. 1... Whisker preform, 2... Mold, 3... Molten matrix metal, 4... Plunger, 5... Insertion mold, 6... Lower punch, 7
...Composite part, 8...Composite part in which components are unevenly distributed,
9...Abnormal tissue part.

Claims (1)

[Claims] 1 A whisker preform is placed in a mold as a fiber skeleton, and when molten matrix metal is injected into the mold to form a composite by pressure casting, the whisker preform is placed in a preheated inner mold with upper and lower openings. 1. A method for producing a fiber-reinforced metal composite material, which comprises setting and inserting the fiber-reinforced metal composite material into a mold.