JPH05271827A - Production of al matrix composite - Google Patents

Abstract

PURPOSE:To efficiently produce an Al matrix composite reinforced with ceramic whisker and having high composite property via superior wettability and dispersibility by a gravity casting method. CONSTITUTION:A composite precursor (whisker Vf, <=40%) consisting of SiC whisker and Al alloy is extruded into a fine wire, and this fine wire is cut into short pieces, by which granular bodies are formed. These granular bodies are dispersed, with stirring, into a molten Al alloy, which is formed into composite state by a gravity casting method. It is preferable to form the granular bodies so that the diameter (D) of the fine wire is 0.5-5.0mm and length is 1D to 2D.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for compositely strengthening a ceramics-based whisker to an Al-based matrix metal composed of Al or an Al alloy, and more specifically, to the wettability between the ceramics-based whisker and the Al-based matrix metal. The present invention relates to a method for producing an Al-based composite material by a gravity casting method with improved uniform dispersibility.

[0002]

_2. Description of the Related Art Al-based composite materials obtained by compounding ceramic whiskers, which are acicular crystals such as SiC, Si ₃ N ₄ and Al ₂ O ₃ , with an Al-based metal are lightweight and have excellent material strength. In the field of automobiles, it has attracted attention as a wide-ranging member for sports and leisure, and has already entered the stage of practical application. As a means for industrially producing the Al-based composite material, a pressure casting method in which whiskers are dispersed in a molten matrix and solidified while being pressurized in a mold is suitable, but it is always stable by applying this method. There are many problems to be solved in order to obtain high and homogeneous composite performance. Further, whiskers have poor wettability with Al or an Al alloy, and therefore cannot be uniformly dispersed even by simply adding and mixing them in the molten matrix. Therefore, it is extremely difficult to form a composite by the gravity casting method.

It is generally known that the composite performance of MMC for compositely reinforcing a metal structure with a fibrous material largely depends on the wettability and dispersibility of the composite material of the fiber reinforcement with respect to the matrix metal. Many improved technologies have already been developed for the purpose of improving. For example, as a method for improving the wettability, a method of forming a metal film on the surface of the reinforcing fiber, and as an effective method for improving the dispersibility, a preform infiltration method is considered to be a typical technique. However, although these methods give good results when using long fibers having a well-defined morphology, when they are applied to whiskers, which are fine needle-shaped single crystals, the expected results are accompanied by remarkable complexity of processing. It is difficult to obtain.

Therefore, there has been proposed a method of strictly controlling the mixing conditions with the molten matrix in order to improve the wettability. Japanese Patent Publication No. 1-501489 discloses a method for producing a cast reinforced composite material in which reinforcing particles and molten metal are mixed so as to apply shear under a certain condition to promote wettability. In Kaihei 3-68728, there is Al or A
l Improving wettability by adding ceramic particles while positively convection the molten alloy and applying shearing force to the molten metal A
A method and apparatus for making a 1 or Al alloy composite is disclosed. However, these measures have the disadvantage of requiring complicated and expensive equipment.

FR by SiC whiskers having improved interfacial wettability and uniform dispersibility by a technique different from the above technique.
As a method for producing M, SiC whiskers are mutually contacted with a matrix metal composed of Al, Mg or an alloy thereof at a temperature of 800 ° C. or higher to form a precursor,
The present applicant has developed a method (Japanese Patent Laid-Open No. 59-43835) of stirring and dispersing in a melt of 1-alloy to form an ingot. Further, as a technique for producing a whisker-reinforced metal composite material which is an improvement of the present invention, a composite body in which whiskers are dispersed and complexed in a matrix metal in advance and subjected to plastic working is used to produce a composite material having a freezing point of the matrix metal of −50 ° C. to a freezing point (where the matrix metal is an alloy. In this case, it is preheated to a temperature range of liquidus temperature −50 ° C. to liquidus temperature), and then the same metal as the matrix metal is crossed over its freezing point to a freezing point of + 50 ° C. (when the metal is an alloy, A method in which a molten metal heated above the liquidus temperature and maintained in a temperature range of the liquidus temperature + 50 ° C.) is brought into contact with the composite to melt and disperse it, followed by pressurization and solidification (JP-A 1-222029). Are developing.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to the method described in Japanese Patent No. 2029, the wettability and uniform dispersibility of the whiskers and the matrix metal are improved, and it becomes possible to form a composite under the condition that these components do not react. However, in this technique, it is necessary to contact and agitate the molten metal at a high speed because a molded body that has been plastically processed is used as a precursor in which whiskers are dispersed and compounded in a matrix metal in advance. Further, the upper limit of the whisker content in the composite precursor has to be suppressed to a relatively low value of 35 vol%, and there is a drawback that a composite material having a high Vf cannot be obtained.

According to the present invention, when the composite precursor to be plastically worked is formed into a fine granular form, the wettability and dispersibility with the matrix metal are further improved, and it is not necessary to perform stirring and dispersion in the molten metal at a high speed. It was developed after confirming that a complex structure was obtained, and the purpose was to efficiently produce a ceramic-based whisker-reinforced Al-based composite material with high composite performance by gravity casting through its excellent wettability and dispersibility. It is to provide a method of manufacturing well.

[0008]

A method for producing an Al-based composite material according to the present invention for achieving the above object is a composite precursor composed of a ceramics-based whisker and an Al-based matrix metal (Vf 40% or less of whisker). ) Is extruded into a fine wire and then cut into short to form a granular body, and the granular body is stirred and dispersed in a molten metal of Al-based matrix metal,
The structural feature is that it is compounded by gravity casting.

The composite precursor as the base material of the present invention is SiC
Alternatively, use a ceramic type whisker such as Si ₃ N ₄ for Al.
Alternatively, it is a billet-like material dispersed by a preform infiltration method, powder metallurgy method or other means in a matrix metal made of the alloy, and does not necessarily have a normal composite structure. Therefore, it may be an incomplete pre-sintered body or a residual waste material to be discarded as a defective material having complex defects. However, it is necessary to set Vf (volume content) of the ceramic whiskers in the composite precursor to 40% or less. If this Vf exceeds 40%, it becomes difficult to perform the plastic working, and the thin wire extrusion processing does not proceed smoothly. Further, if Vf is less than 5%, sufficient composite reinforcing performance cannot be imparted. Therefore, the range of Vf is 5 to
It is desirable to set it in the range of 40%.

Next, the composite precursor is extruded into a fine wire and then cut into short particles to form a granular material. The hot extrusion method is used for extrusion, and the diameter (D) of the fine wire is 0.5.
It is preferable to carry out the nozzle conditions such that the thickness is up to 5.0 mm. If the diameter (D) of the fine wire is less than 0.5 mm, it becomes difficult to extrude the nozzle, and if it exceeds 5.0 mm, the dispersibility in the molten matrix metal is reduced, and it takes time to stir and disperse. In addition, the cutting of the thin wire has a length of 1D to 2D (D
Is preferably within the range of (fine wire diameter) in order to improve dispersibility.

The formed granular material is added to a molten metal of Al-based matrix metal, melted, and mixed by stirring. At this time, when the matrix metal is Al, the mixing is carried out by keeping the temperature at which the liquid phase is generated at the freezing point + 150 ° C, and when the matrix metal is the Al alloy, at the solidus temperature + 150 ° C. The stirring method is performed by vacuum or mechanical stirring in an Ar atmosphere, but it is not necessary to apply a high-speed or abrupt stirring operation, and a simple stirring operation enables sufficient homogeneous dispersion.

The Al-based molten metal in which the granular particles of the composite precursor are thus melt-dispersed is poured into a mold of a gravity casting apparatus and solidified while being pressurized to obtain an intended Al-based composite material.

[0013]

According to the present invention, the interfacial wettability is effectively improved by the shearing force applied during the process of extruding the composite precursor. In addition, since the composite precursor is formed into a granular material in which thin wires are cut into short pieces, melting and dispersion in the Al-based matrix metal melt proceeds extremely smoothly, and it is possible to obtain a homogeneous dispersion state by a simple stirring operation. Become. Through such an effect of improving wettability and dispersibility, an Al-based composite material having high composite performance is always efficiently produced by the gravity casting method.

[0014]

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

Example 1 SiC whiskers having an average diameter of 0.5 μm and an average length of 20 μm (“Tokai Carbon TWS-100, manufactured by Tokai Carbon Co., Ltd.”)
”] Al with a grain size of 44 μm or less so that Vf is 30%
The alloy (6061) powder was blended and homogeneously wet mixed in ethanol. After drying this mixed powder, it was sintered with a hot press at a temperature of 500 ° C and a pressure of 1 t / cm ² to obtain a diameter of 49
A billet-shaped composite precursor having a length of 100 mm and a length of 100 mm was prepared. This composite precursor was set in an extrusion container with an inner diameter of 50 mm, extruded into a fine wire with a diameter of 1.5 mm under the conditions of a temperature of 480 ° C and a surface pressure of 4.5 t / cm ² , and immediately after extrusion, it was cut to a length of 2 mm for granulation. Formed.

Then, a predetermined amount of the granular material is preheated to a temperature of 650 ° C., then added to the molten aluminum alloy (6061) held at 700 ° C., and mechanically maintained in vacuum for 5 minutes while maintaining the temperature of 700 ° C. Stirring was performed. Subsequently, the molten and melted molten metal was poured into a mold with a diameter of 120 mm, and solidified as it was to produce Si.
A C whisker Vf 15% SiC whisker reinforced Al alloy material was produced.

4 from the radial direction of the obtained Al alloy composite material
Sample of a book (diameter 10 mm, length 100 mm, parallel part 6 mm in diameter,
(Length 40 mm) was sampled and the tensile strength and proof stress were measured.The tensile strength was 27 kg / mm ^{2 on} average and the proof stress was 16 k on average.
A high value of g / mm ² was obtained, and the result was that the wettability and dispersibility of the SiC whiskers were extremely good.

Comparative Example 1 SiC whiskers having the same properties as in Example 1 were directly added to the molten Al alloy (6061) so that Vf was 15%, stirred and then solidified in a mold to have a diameter of 20 mm and a length of 20 mm. A composite precursor having a length of 201 mm was prepared. In this case, the wetness of the whisker and the molten Al alloy was poor, and the whisker and the Al alloy were separated after mixing, and a uniform composite state could not be obtained. This composite precursor was subjected to the same process as in Example 1 without extruding Al.
Although the mixture was added to the molten metal and mixed by stirring, the composite precursor floated on the molten metal and a homogeneous composite material was not obtained.

Examples 2 to 4, Comparative Examples 2 to 3 Using the same SiC whiskers and Al alloy (AC8A) as in Example 1, composite materials formed by powder sintering method, pressure casting method (preform impregnation method) The composite material formed in 1) and the extruded scraps (residual material) of the composite material were used as a composite precursor, and were formed into granules having a diameter of 1.0 mm and a length of 1.0 mm under the same hot-pressing conditions as in Example 1. A predetermined amount of these granules is added to a molten Al alloy (AC8A), stirred in an Ar atmosphere, and then Vf by gravity casting.
A 15% SiC whisker reinforced Al alloy material was produced. The properties of each composite material obtained are shown in Table 1 in comparison with the Vf of the composite precursor. The tensile strength in Table 1 is T ₆ treatment (52
Measured values after 0 ° C., 4 hours water cooling, 170 ° C., 10 hours).

[0020]

[Table 1]

From the results shown in Table 1, it is recognized that when the present invention is applied, a high-performance Al-based composite material can be produced regardless of the type of the composite precursor, but the composite precursor has a Vf of 40.
In the comparative examples exceeding%, it was not possible to extrude into fine wires.

[0022]

As described above, according to the present invention, it is possible to efficiently obtain a high-performance Al-based composite material having a homogeneous structure by whisker and Al-based matrix metal by gravity casting through excellent wettability and dispersibility. Can be manufactured well. Therefore, the obtained composite material is useful as a member for various applications in which lightweight and high strength properties are required.

Claims (2)

[Claims] 1. A composite precursor comprising a ceramic whisker and an Al matrix metal (whisker Vf
(40% or less) is extruded into fine wires and cut into short pieces to form granules, and the granules are stirred and dispersed in a molten metal of an Al-based matrix metal to form a composite by gravity casting. Method of manufacturing base composite material. 2. A fine wire having a diameter (D) of 0.5 to 5.0 mm.
2. The A according to claim 1, wherein the length is formed in the range of 1D to 2D.
Method for producing l-based composite material.