JPH0636983B2 - Method for manufacturing partial composite member - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a partial composite member in which a predetermined portion of an Al alloy is reinforced with SiC whiskers.

[Conventional technology]

As a means to locally strengthen the parts of the internal combustion engine, such as pistons, rocker arms, connecting rods, etc., that are made of a lightweight Al alloy and are subjected to severe thermal shock or sliding with SiC whiskers, the preforms of SiC whiskers are used as molds. A method is known in which the molten metal of Al alloy is set under pressure and cast under pressure (for example, JP-A-55-24763 and JP-A-55-24945).
Issue). However, since the SiC whisker preform is an extremely fragile aggregate, it often suffers from deformation and breakage during the pressure casting stage. For this reason, researches on methods for strengthening preforms have been actively conducted, but none have been sufficiently satisfied.

Further, some O ₂ or SiO ₂ intervenes in the surface layer portion of the SiC whiskers during the process of heat treatment during manufacturing, but the presence of these oxidizing components causes the presence of S in the SiC whiskers.
promote selective reaction with the Mg contained in the Al alloy serving as i and the matrix, causing complex defects Mg ₂
A segregated portion such as Si is deposited. This phenomenon is usually caused by casting of AC8A, AC4C, AC4D, etc. as a matrix or 2618, 2024, 5052, 6061.
This is a serious obstacle because Al alloys containing Mg such as wrought materials are frequently used.

In order to prevent the above-mentioned segregation, Si intervening in the surface layer in advance is used.
A method of press-casting a molten aluminum alloy using a SiC whisker preform from which the C ₂ component has been removed (Japanese Patent Publication No. 62-404).
No. 09 gazette) is an effective means, but there is a drawback that the preform itself cannot be strengthened by this method.

Alternatively, a partial composite method may be considered in which a pre-composite body having a predetermined shape is preliminarily formed of SiC whiskers and an Al alloy, set at a predetermined location of a mold, and then cast in a molten metal of the Al alloy. However, in this case, Al ₂ O ₃ is generated on the surface due to oxidation during the process of forming the pre-composite or during the preheating step during casting, and this oxide film significantly impedes the wettability with the matrix Al alloy. This results in a decrease in the bonding strength at the interface.

[Problems to be Solved by the Invention]

The inventors of the present invention have conducted extensive studies for the purpose of solving the above-mentioned problems that become obstacles when a predetermined portion of an Al alloy is partially strengthened by SiC whiskers, and as a result, SiC whiskers and Al alloy powder have been used in advance. It was confirmed that it is effective to apply a noble metal-based metal thin film on the surface of the formed sintered composite, set this on the strengthened portion, and cast in the molten aluminum to confirm the effect of the present invention. Led to development.

In the case of forming a fiber-reinforced composite material, a method of improving wear resistance and self-lubricating property of the composite by pressure casting using a fiber molded body in which a metal substance is vapor-deposited on the surface of the reinforcing fiber (JP-A-58) -93843) is known, it is not easy to form a homogeneous thin film metal coating on minute short fibers such as SiC whiskers, and the coating metal is Pb, Zn, Sn having anti-friction properties. , Cu, etc., are different from the present invention.

[Means for Solving the Problems]

That is, the method for manufacturing a partial composite member according to the present invention is
A mixture of SiC whiskers and Al alloy powder is sintered into a predetermined shape to prepare a composite base material, a thin film of a noble metal-based material is formed on the surface of the composite base material, and the composite base material is set at a predetermined location of a mold and then the Al alloy is formed. The characteristic feature of the structure is that it is cast and wrapped with the molten metal.

The diameter of SiC whiskers used as reinforcement is 0.1 to 5μ.
An acicular single crystal having an aspect property of m and a length of 30 to 100 μm is used.

In the present invention, the composite base material for constituting the reinforced portion,
Wet-mixing SiC whiskers and Al alloy powder, hot pressing this mixture in a vacuum or an inert atmosphere,
It is manufactured by sintering into a predetermined shape using HIP or the like. The Al alloy powder used is the same as the matrix Al alloy cast in the subsequent step, and the mixing ratio of the SiC whiskers and the Al alloy powder is Si in the composite base material.
The Vf of the C whiskers is set to a desired value within the range of 10 to 50%.

Then, a thin film of a noble metal-based material is formed on the surface of the composite base material. The noble metal-based substance is Au, Ag, Pt or Pt-
It is preferable to select from Pd, and the film is preferably formed by a coating means such as ion plating, vacuum deposition, and thermal spraying so as to have a thickness of 6 μm or less. When the thickness of the coating exceeds 6 μm, noble metal components remain on the surface of the composite base material in the casting process in the subsequent step, which causes a decrease in bonding with the Al alloy to be cast.

The composite base material on which the surface thin film of the noble metal-based material is formed is set at a predetermined position corresponding to the strengthened part of the mold, and the molten Al alloy is cast by the pressure casting method. At this time, it is preferable to preheat the composite base material in the range of −20 to −100 ° C. from the solidus and set the molten metal temperature of the Al alloy to be higher than the liquidus temperature by 50 ° C. or more. Preheating temperature of composite base material is solidus-2
Material deformation occurs at temperatures above 0 ° C, and this is the solidus -1
When the temperature is lower than 00 ° C or the temperature of the molten aluminum is lower than the liquidus temperature + 50 ° C, the cooling of the molten metal progresses rapidly, causing a phenomenon of defective bonding. Pressure during casting is 250-3000
It is desirable to set in the range of kg / cm ² . The reason for this is
If the applied pressure is less than 250 kg / cm ^2, the interfacial bonding force between the composite base material and the matrix Al alloy becomes insufficient, and 3000 kg / cm ²
This is because the material will be deformed if the value exceeds.

In this manner, the Al alloy-based partial composite member having the SiC whisker reinforced portion at the specified portion is manufactured.

[Work]

According to the present invention, since the surface of the composite base material obtained by previously sintering the SiC whiskers and the Al alloy powder is coated with the thin film of the noble metal-based material to form the strengthened portion, the strengthened portion portion is formed at the stage of molten metal casting. Is not deformed or destroyed, and an oxide layer of Al ₂ O ₃ or the like is not formed on the surface. Therefore, the molten metal of the matrix Al alloy always contacts through the noble metal thin film having good wettability, and this noble metal component is finally dispersed in the structure of the matrix Al alloy due to the pressure applied at the time of casting. Does not remain at the interface.

Due to the above action, a partial composite form of an integral structure in which the interface between the composite base material and the matrix Al alloy is strongly bonded is developed.

〔Example〕

 The present invention will be described below based on examples.

Example 1 A SiC whisker having an average diameter of 0.5 μm and an average length of 20 μm and Al alloy powder (AC8A) were stirred and dispersed in water, filtered, and dried to obtain a uniform mixture of SiC whiskers having a Vf of 10%. 280 g of this mixture was hot pressed to a temperature of 6
00 ° C, vacuum degree 5 × 10 ^-5 Torr, pressure 1000 kg / cm ² ,
Sintered under the condition of 20 minutes pressing time, thickness 20mm, diameter 80
A disc-shaped composite base material of mm was prepared.

The above composite base material was cut from the central portion into a half-moon shape, and Au was vacuum-deposited on the cut surface in a thin film state of 0.23 μm (vacuum degree 7 × 10 ⁻⁵ Torr).

The composite base material on which the Au thin film was formed was set in a mold having a diameter of 80.0 mm in a half-moon shape, preheated to 500 ° C. in Ar and set in a pressure casting machine. Next, a molten matrix Al alloy (AC8A) maintained at a temperature of 700 ° C was poured into the mold, and the temperature was changed to 500
Pressure casting was performed while applying a pressure of kg / cm ² .

The obtained partial composite material had a shape in which a crescent-shaped matrix Al alloy was joined through the cut surface of the composite base material, but the results were observed by the results of SEM observation and line analysis by EPMA. No residual Au was observed on the joint surface.

The tensile strength of this partial composite in the direction perpendicular to the joint surface was measured and found to be 32 kgf / mm ² .

Example 2 A partial composite material was produced in the same manner as in Example 1 except that Pt was used instead of Au in the same manner as in Example 1 to perform cut surface coating.

When the tensile strength of this material was measured according to Example 1, it was 30 kgf / mm ² .

Comparative Example 1 Using the same composite base material as in Example 1, a matrix Al alloy was pressure-cast under the same conditions as in Example 1 without coating the cut surface.

When the tensile strength of this material was measured according to Example 1, it was 4 kgf / mm ² , which was a remarkably low value as compared with Examples 1 and 2.

Comparative Example 2 Using the same SiC whiskers as in Example 1, the diameter was 80 m.
m, height 30mm, Vf10% preform,
This was cut in two from the center.

A partial composite material was manufactured under the same conditions as in Example 1 using the above half-moon shaped preform.

When the tensile strength of this material was measured according to Example 1, it was 16 kgf / mm ² , which was extremely inferior to Examples 1 and 2.

〔The invention's effect〕

As described above, according to the present invention, since the reinforced portion is composed of the composite base material made of a strong sintered body, it deforms by receiving an external force at the process stage like a preform molded body,
There is no destruction. For this reason, it becomes possible to easily mold even a strengthened portion having a thin wall and a complicated shape. Further, since the surface of the composite base material is coated with a noble metal-based substance, troubles caused by inclusion of oxides such as Al ₂ O ₃ are effectively eliminated, and good interface bonding with the matrix Al alloy is always obtained. .

Therefore, since it is possible to manufacture a tough one-piece partial composite member by a relatively simple manufacturing process, for example, a SiC whisker reinforced structure local to a portion such as a piston bed which is subjected to severe thermal shock, friction, etc. Is extremely useful in the case of forming

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Claims (2)

[Claims] 1. A composite base material is produced by sintering a mixture of SiC whiskers and Al alloy powder into a predetermined shape, and a thin film of a noble metal-based material is formed on the surface of the composite base material to form a predetermined location on a mold. A method for producing a partial composite member, which comprises setting and then casting with a molten aluminum alloy. 2. The method for producing a partial composite member according to claim 1, wherein the noble metal-based material is selected from Au, Ag, Pt or Pt-Pd, and the thin film is formed to a thickness of 6 μm or less.