JPH0533079A - Production of partial composite member - Google Patents

Abstract

PURPOSE:To eliminate trouble due to alumina or other oxide present on the surface of a composite base material to be joined and to produce a tough partial composite member having integrated structure in a relatively simple process. CONSTITUTION:Short fibers such as SiC whiskers as a reinforcing material are dispersed in an Al-based matrix metal and the surface of the resulting composite base material to be joined is mechanically polished so as to remove an oxidized component and to roughen the exposed surface. A thin Al film of 0.5-20mum thickness is formed on the polished surface, the base material is set at a prescribed position of a casting mold and a molten Al-based metal is cast so as to coat the base material. This method is useful to locally reinforce a piston head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a partial composite member for composite-reinforcing a predetermined portion of an Al-based metal part with a short fiber reinforcing material.

[0002]

_2. Description of the Related Art Whiskers and short fibers composed of ceramic materials such as SiC, Si ₃ N ₄ , Al ₂ O ₃ are thermally and chemically stable and have excellent strength characteristics. Therefore, it is useful as a composite reinforcing material of metal materials, especially light metal materials such as Al and Mg.

As an example of the partially reinforced FRM, a piston, a rocker arm, a connecting rod, etc. of an internal combustion engine are made of a lightweight Al alloy, and only a portion which is subjected to severe thermal shock or sliding is locally made of SiC whiskers. A composite system for strengthening is known, and as a compounding means thereof, a SiC whisker preform is set at a predetermined position of a mold to form an Al.
A method of casting a molten alloy while pressurizing it has been developed (for example, JP-A-55-24763 and JP-A-55-24945). However, since the SiC whisker preform is an aggregate of extremely fragile short fibers, it often has a drawback of causing deformation, breakage and the like at the stage of pressure casting. From such a background, researches for strengthening preforms have been actively conducted, but none of them is sufficiently satisfactory.

With respect to the above points, a composite base material of a predetermined shape made of a short fiber reinforced material and a matrix metal is formed in advance by means such as forging, and this is set at a predetermined position of a mold, and then the cast metal Partially strengthened FR that injects molten metal
The M method is an effective countermeasure. However, in this case, the surface is oxidized in the process of forming the composite base material or in the preheating step at the time of casting, and this oxide film remarkably impedes the wettability of the casting metal with the molten metal to improve the bonding strength of the interface. Result in diminishing results.

As a partly strengthening composite means for solving these problems, a noble metal-based substance or an Al thin film is adhered and formed on the surface of a sintered composite base material formed in advance with SiC whiskers and Al alloy powder, and this is used as a strengthening part of the mold. After setting in a suitable place, it is cast in the molten aluminum alloy (Japanese Patent Application No. 1-29)
No. 3367, No. 2-114871), a method of plasma-treating the surface of the composite base material to remove the oxide film, and then partially strengthening the composite by casting aluminum melt (Japanese Patent Application No. 2-29899), the composite base. The joint surface of the material is mechanically polished to a state where the oxidized component is removed and the exposed surface is roughened, and then partially composite strengthened by casting of molten aluminum, or a composite in which a thin film of matrix metal alone is previously formed on the joint surface. Partial composite strengthening method (Japanese Patent Application No. 2-211867) in which the base material is set in the mold and the molten aluminum is cast in.
Etc. have been proposed by the applicant.

[0006]

Among the above-mentioned prior arts, the method of Japanese Patent Application No. 2-29899 is to cast in a state where the oxide film formed and adhered to the surface of the composite base material is positively removed. To obtain a normal partial composite tissue.
Therefore, if it can be efficiently processed, it will be advantageous in terms of cost, but in the case of this method, the plasma processing of the composite base material is performed under a reduced pressure condition of 200 Torr or less in the reducing or rare gas or gas mixture thereof. However, there is a problem in terms of efficiency as an industrial treatment process. Similarly, the method of Japanese Patent Application No. 2-146532 removes the oxide film on the surface of the composite base material by using a mechanical polishing means. However, since the composite base material itself is extremely easy to oxidize, Also in the method, unless the material from which the oxide film has been removed is immediately moved to the next casting step, an oxide film is formed again and the bonding strength is impaired.

Further, when the method of Japanese Patent Application No. 2-114871 is carried out, the Al coating effect does not appear when a thick oxide film layer is already formed on the composite base material before Al coating.

The present invention solves each problem by combining the oxide film removing means and the Al coating means according to the prior art, thereby efficiently manufacturing a tough and integral partial composite member. It is intended to provide a method.

[0009]

In order to achieve the above object, a method of manufacturing a partial composite member according to the present invention is to bond a composite base material in which a short fiber reinforcing material is dispersed and composited in an Al matrix metal. The surface was mechanically polished so that the oxidized component was removed and the exposed surface was roughened, and the composite base material with an Al thin film of 0.2 to 20 μm thickness formed on the treated surface was set at a predetermined location on the mold. Then, it is characterized in that it is subsequently cast in molten metal of Al-based metal.

Suitable short fiber reinforcing materials used in the present invention include, for example, Si ₃ N ₄ , SiC, Al ₂ O ₃ and K.
Ceramic whiskers such as ₂ O · nTiO ₂ and TiB ₂ or chopped short fibers can be mentioned.
Generally, any reinforcing material of a short fiber material used for FRM can be used without particular limitation. Further, Al or an Al-based light metal such as an Al-based alloy is used for the matrix metal serving as the composite base material and the casting material.

In the present invention, the composite base material for constituting the reinforced portion is prepared by setting a preform of a short fiber reinforced material formed in advance in a mold, and impregnating this with a molten matrix metal under high pressure. Pressure casting method (molten metal forging method) for solidifying into a solid state, or wet mixing of a reinforcing material and a matrix metal powder, and sintering this mixture into a predetermined shape using a hot press, HIP or the like in a vacuum or an inert atmosphere. It is produced by the powder metallurgy method.

The mixing ratio of the short fiber reinforcing material and the matrix metal is such that Vf of the short fiber reinforcing material in the composite base material is 1 to 50.
It is preferable to set a desired value in the range of%.
When Vf of the reinforcing material is less than 1%, the composite effect becomes insufficient, and when it exceeds 50%, a composite base material having a good structure cannot be obtained and the cost becomes high.

The formed composite base material may be subjected to a secondary treatment such as forging in order to form a more complicated shape.

The joint surface of the produced composite base material is mechanically polished before casting. As a method of mechanical polishing treatment,
Appropriate means such as shot blasting, barrel polishing, file polishing, and wire brush polishing can be applied. However, the most practical polishing means are carborundum, steel,
It is a shot blasting method using sand or the like as shot particles.

The mechanical polishing treatment is carried out until the oxides formed and adhered to the joint surface of the composite base material are removed and the exposed surface is appropriately roughened. A suitable degree of roughening is in the range of 10 to 500 μm Rz as the surface roughness, and a strong interfacial bonding with the molten metal is obtained in this surface state.

Then, a thin film of Al metal is formed on the surface of the composite base material. The Al material that forms the thin film has an Al content of 99.
% Pure Al, for example, ion plating,
The coating is formed using a coating means such as vacuum deposition or thermal spraying.
It is important to adjust the thickness of the coating within the range of 0.5 to 20 μm, and if it is less than 0.5 μm, the antioxidant function is insufficient.
If it exceeds μm, the Al layer remains on the surface of the composite base material in the casting process of the subsequent step, which causes a decrease in bonding with the Al-based matrix metal to be cast.

The composite base material on which the surface thin film of Al is formed is set at a predetermined position corresponding to the strengthened part of the mold, and the molten metal of the Al-based matrix metal is cast-in by the pressure casting method. The conditions for this are as follows:
It is preferable to preheat to a range of 100 ° C and set the temperature of the molten matrix to be 50 ° C or more higher than its liquidus temperature. Material deformation occurs when the preheating temperature of the composite base material exceeds the solidus -20 ° C, and if this is less than the solidus -100 ° C or the molten metal temperature of the matrix metal is below the liquidus temperature + 50 ° C, the molten metal Cooling progresses rapidly and a joint failure is likely to occur.
If the pressure during casting is too low, the interfacial bonding force between the composite base material and the matrix will be insufficient, and if it is too high, it will cause material deformation. Suitable pressure range is 10 to 3000
It is kg / cm ² .

By the above process, the partial composite member made of the Al-based matrix for the purpose of providing the reinforced portion of the short fiber reinforcement at the specified portion is manufactured.

[0019]

In the process of the present invention, the step of subjecting the joint surface of the composite base material to mechanical polishing treatment in advance to remove intervening oxidizing components and appropriately roughening the exposed surface is the matrix to be cast. It effectively functions to improve the wettability with the molten metal and increase the bonding strength at the interface. The Al thin film formed in the next coating step prevents a phenomenon in which an oxide layer is formed by a reinforcing material component existing on the surface of the composite base material or a matrix metal component containing Mg, Cu, etc. in the process of molten metal casting. The Al thin film mostly functions as a barrier to protect the Al thin film from being dispersed into the molten matrix at the casting stage, and a trace amount of the remaining Al component is converted into a component of the same quality as the matrix due to the diffusion of the alloying elements by the heat treatment.

In combination with the above-mentioned actions, a partial composite member having a composite reinforced structure at a predetermined portion and having an interface between the composite base material and the plain matrix portion strongly joined together can be efficiently produced. It becomes possible.

[0021]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Example 1 Dispersed water in which SiC whiskers having an average diameter of 0.5 μm and an average length of 20 μm were uniformly dispersed was pressure-filtered to form a preform. The preform was set in a preheated mold, transferred to a pressure casting machine, and a molten aluminum alloy (AC8A) heated to 720 ° C was poured into the preform to 1000 ° C by a plunger.
Pressure-cast under a pressure of kg / cm ² to obtain SiC whisker V
A disk-shaped composite base material having f18%, a diameter of 80 mm and a thickness of 20 mm was produced.

The composite base material thus produced is cut from the central portion into a half-moon shape, and the cut surface is subjected to shot blasting for 10 seconds using carborundum powder having a grain size of 80 mesh to remove the oxide film. , Exposed surface about 50μm R
The surface was roughened to z. Subsequently, pure Al having a purity of 99.5% was coated and formed on the polished surface by a vacuum deposition method so as to have an arbitrary film thickness.

Each composite base material on which an Al thin film is formed has a diameter of 80 mm.
The mold is set in a half-moon shape, preheated to 500 ° C in argon gas, and the matrix Al alloy (AC8A) melt maintained at 700 ° C is poured into the mold, and a pressure of 500 kg / cm ² is applied. While casting. The obtained partial composite member is
It had a form in which a half-moon shaped matrix material was joined through the cut surface of the composite base material.

With respect to these partial composite members, test pieces were cut out in a direction perpendicular to the joint surface, and the tensile strength was measured after T ₆ treatment. The result is shown in FIG. 1 as a graph showing the relationship between the Al film thickness formed on the composite base material and the tensile strength.

[0026]

[Figure 1]

From FIG. 1, the Al thin film shows a high tensile strength exceeding 25 kgf / mm ² in the range of 0.5 to 20 μm.
The tensile strength was 30 kgf /
In the composite structures of mm ² or more, the matrix part was found in all, but in the other composite structures, fracture was observed at the joint part.

Example 2 The same silicon carbide whiskers as in Example 1 and an Al alloy (AC8A) powder having a particle size of 325 mesh or less were stirred and dispersed in ethanol and dried to obtain a uniform mixture of SiC whiskers with Vf of 20%. It was The mixture is hot pressed to a temperature of 520
℃, pressure 2000kg / cm ² condition for 10 minutes, diameter 80mm,
A disk-shaped composite base material having a height of 80 mm was produced. The obtained disc-shaped composite base material was heated in air to a temperature of 450 ° C. to form an oxide film on the surface, and then hot forged into a half-moon shape having a diameter of 160 mm and a thickness of 40 mm.

Then, the half-moon shaped composite base material was sandblasted with 30 mesh carborundum powder for 10 seconds to remove the oxide film, and the exposed surface was roughened to a surface roughness of about 50 μm Rz. After the polishing treatment, a thin film of pure Al having a purity of 99.5% was formed by ion plating. 50 kg of the composite base material on which an Al thin film is formed in the same manner as in the example.
A partial composite member was manufactured by casting in a matrix melt of an Al alloy (AC8A) at a pressure of / cm ² . For comparison,
Partial composite members were manufactured according to an example in which mechanical polishing was not performed and an Al thin film was not covered. The tensile strength of each partial composite member was measured, and the results are shown in Table 1 in comparison with the manufacturing conditions.

[0030]

[Table 1]

From the results in Table 1, the partial composite member according to the process of the present invention, which was subjected to the mechanical polishing and the Al coating at the same time, showed a bonded high tensile strength structure morphology integrated with the matrix metal, but with the oxide film. In the case where the Al coating was applied in a certain state, the interface was completely peeled off at the joint, and in the case where the Al coating treatment was not performed after the mechanical polishing, the casting was insufficient and the tensile strength was not increased. ..

[0032]

As described above, according to the present invention, troubles due to oxides such as alumina existing on the joint surface of the composite base material are completely eliminated, and good interfacial joint with the matrix material can always be obtained. .. Therefore, it is possible to obtain a tough and monolithic partial composite member by a relatively simple manufacturing process. For example, a portion such as a piston head, which is subjected to severe thermal shock, friction, etc., is locally short fiber reinforced material. It is extremely useful for the purpose of compound strengthening.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the Al film thickness formed on a composite base material according to Example 1 and the tensile strength of a partial composite member.

Claims (1)

Claims: 1. A state in which an oxidizing component is removed and an exposed surface is roughened on a joint surface of a composite base material in which a short fibrous reinforcing material is dispersed and complexed in an Al matrix metal. Was mechanically polished, and the composite base material having an Al thin film with a thickness of 0.5 to 20 μm formed on the treated surface was set at a predetermined position of the mold, and then Al
A method for manufacturing a partial composite member, which comprises casting with a molten base metal.