JPH01210166A - Manufacture of composite cast article - Google Patents

Abstract

PURPOSE: To improve the article quality by arranging a preheated preform of a divided solid filler on molten material of metal matrix, pressing from the preform side and also, penetrating the molten metal into the preform. CONSTITUTION: The molten matrix metal 16 and the refractory disc-shaped preform 18 impregnated with the matrix metal 16 are arranged into a die cavity formed with a die 10 and a die plate 11. A spacer strip 30 is arranged on the upper surface of the preform 18 and the die 10 is induction-heated. Successively, the preform 18 is pressed by descended a ram 26. At this time, the temp. difference is formed between the upper and the lower ends of the contents in the cavity, and the molten metal 16 is penetrated into the preform according to progressing of the pressurization and the matrix metal is cooled and solidified. By this method, the impregnation of molten iron into the composite article is sufficiently executed and the porous region is eliminated. Therefore, the article quality is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to metal matrix composite materials, more specifically,
The present invention relates to a method for manufacturing cast metal matrix composite articles and articles obtained by the method.

[Prior Art] Metal matrix composite materials are composed of segmented solid fillings, i.e.
An article consisting of a metal matrix, for example aluminum or an alloy thereof, in which fibrous or particulate material is distributed. Such solid fillers can be incorporated and distributed into such metal matrices and are incorporated into the metal such that they do not lose their form or identity due to dissolution in the metal or chemical bonding with the metal; at least substantially retains its integrity.

Japanese Patent Publication No. 58-204139 describes a method for manufacturing a composite material in which alternating layers of reinforcing fibers and aluminum foil are placed between a male mold and a female mold. The foil is heated to "melt" and subjected to relatively low pressure to produce a unitary composite material. However, this method is unsuitable for producing ingots with substantial bulk or thickness, at least when using discontinuous reinforcing fibers. In such cases, a large number of separate foil layers, each with a surface oxide film, are required, and the presence of oxides makes it impossible to achieve the desired properties of the product. Additionally, when producing bulky composite ingots, it is difficult to determine the appropriate amount of metal to provide; too much or too little metal will result in an unacceptable non-uniform product.

Also, for example, U.S. Patent No. 3,970°136
The material consists of a stack of alternating sheets of fibrous reinforcement and (in solid state) matrix metal, which is then heated to melt the metal, applying pressure as the metal melts. Infiltration of the metal into the fiber layer is avoided. However, the problem with this type of method known so far is that the resulting composite material tends to have porous regions with poor mechanical properties (especially if the fiber layer has some thickness). occurs. Additionally, these methods have limitations in the structure of the fiber-reinforced region that can be obtained.

SUMMARY OF THE INVENTION The present invention provides a new and improved method of manufacturing composite cast articles comprising a metal matrix and a segmented solid filler. A metal matrix melt is placed in a die cavity and a preheated preform of segmented solid filler is placed over the melt in the die cavity. Pressure is applied to the preform in a direction parallel to the axis of the cavity, forcing the preform into the molten metal and driving the molten metal to completely penetrate the preform filling, after which the resulting injection Allow the molded article to solidify. As used herein, the term "preform" means an effectively integrated porous compact of segmented solid-filled fibers or granules that has a green strength, i.e. The compressed body is subjected to sufficient compressive force such that its shape and dimensions when handled exhibit such strength that it is self-retaining.

In the new method, a metal matrix melt is fed into a die cavity. The preheated preform is then placed on the surface of the melt and the ram applies pressure onto it, forcing the preform downward into the melt to completely impregnate the preform with molten metal. do. Preferably, a spacer is provided between the top of the preform and the ram to aid penetration of the preform.

This method of forcing the preform into the melt has important advantages. That is, the melt is stationary and when a preheated preform is pushed into the melt, hot metal does not hit cold surfaces, thus avoiding metal spattering. Also,
Since convection can be eliminated, the heat flow is more uniform.

The metal in front of this tip surface remains molten within the preform layer and at least immediately after crossing the preform layer, so that the solidified tip surface completely passes through the metal-infiltrated preform layer along the axis of the cavity. The solidification process is carried out by adjusting the heat flow within the die cavity in such a way that it proceeds in one direction. The metal layer located beyond the preform layer (with respect to the direction of travel of the solidified tip surface) contains an excess of metal that penetrates from that metal layer into the preform during the pressing step.

It has been found that by combining features in this way it is possible to produce useful composite articles which are characterized by the absence of porous regions and therefore by having sufficiently suitable mechanical properties.

In the previously proposed method for producing fiber-reinforced or similar metal matrix composites by heating and pressing the metal and fiber layers, an astringent solidified front surface is encountered within the metal-impregnated fiber layer. easy. A porous region is formed at the junction of the tip surfaces due to the concentration of solidified metal. Also, since this region is bonded to the solidified tip surface on both sides, a continuous supply of molten metal to fill the holes is not possible. As a result, the porous regions remain unfilled and the resulting composite becomes weak.

However, in the method of the present invention, since there is only a single solidified front surface traveling in one direction through the entire preform layer, the pores formed by shrinkage are located between the convergent solidified front surfaces of the filler layer. cannot be included in

In addition, there is a continuous supply of molten metal in front of this tip surface.
Fills the voids formed by contraction under continuously applied osmotic pressure.

For example, by selectively heating or cooling one end of the die such that heat is preferentially transferred from one end of the die to one end of the die. By creating a temperature difference between opposite ends of the die cavity by insulating or by any suitable combination of these methods,
Preferably, the necessary heat flow adjustments within the die cavity are made during the pressurization step. Such a temperature difference may also result in two opposing solidified front surfaces advancing toward each other from opposite ends of the cavity along the axis of the cavity, but with different initiation times and/or advancement rates. The solidified leading edge is encountered in a region or layer of excess metal beyond the preform rather than within the preform layer, and only a single solidified leading edge passes through the preform.

The die is cooled by sequentially moving an external heat source in one direction along the die from one end of the die to the other and parallel to the axis of the die while applying forward osmotic pressure to the metal-preform within the cavity. The cavity may be heated. In this case, the unidirectional solidifying tip follows the heat source along the axis of the cavity.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

For purposes of illustration, the present invention will be described as an embodiment in a method of manufacturing a cast composite billet consisting of aluminum (matrix metal) and discontinuous reinforcing fibers of a refractory material such as SiC or AQ 203. Such composite materials are useful for structural and other purposes and are characterized by low weight and high strength.

In FIG. 1, a die plate 11 of metal or other suitable thermally conductive material (e.g. steel) defines an axially perpendicular and upwardly open cylindrical die cavity with a closed lower end. The created die IO is shown. The Goui plate is supported on a steel base plate 12,
Compressible insulation materials, such as fiber flux (F 1b
It is separated from the playback layer 12 by a layer 14 of refrax™.

Disposed within the die cavity is a matrix metal 16 and a disc-shaped preform 18 of refractory fibrous material that is impregnated with the matrix metal to produce a composite metal-fiber article. Examples of suitable fibrous materials for preforms include alumina, zirconium oxide, silica, silicon carbide,
Includes silicon nitride or titanium diboride, especially alumina in the form of chopped fibers and silicon carbide or silicon nitride in the form of whiskers or chopped fibers.

Preferably, a spacer strip 30 is provided transversely on the upper surface of the preform 18. These spacers 3
0 may be attached to the preform by, for example, sodium silicate tabs 31 around the lower peripheral edge of each spacer. The spacer is approximately lO of the area of the top of the preform.
Preferably, the sodium silicate does not migrate to the horizontal interface between the spacer and the preform.

In carrying out the method of the present invention, the goo is heated by, for example, a conventional induction or resistance heater 24, which surrounds the gou and is positioned to minimize heating of the base plate 12. Add molten metal to the heated goo, goui plate 11
The heat insulating material layer 20 is placed on top of the heat insulating material layer 20. The insulation layer is made of fibrous or such materials (eg "fiber flux", aluminum silicate fibers). A vertically movable ram 26, positioned in alignment with the die cavity, is advanced downwardly to force the preform I8. When the metal is completely molten, the ram can be operated to apply vertical downward pressure.

FIG. 1 shows the implementation of the method of the invention when the matrix metal is completely melted, the heating is stopped and the ram is just in contact with the preform 18. after that,
The pressure from the ram drives the preform downwardly into the condition shown in FIG. 4, driving molten matrix metal into the insulation layer 20 and preform 18, and compressing the insulation layer 14. do. Preferably, the insulation layer 20 is a more open woven fabric than the preform 18, so that this layer penetrates before the preform. Also, preferably,
The preform has sufficient compressive strength to withstand the pressure exerted by the ram and thus substantially retains its original shape and dimensions.

When pouring molten metal into a preheated gouer, the amount of heating of the metal changes depending on the goued temperature. For example, T(melt)−'r(
liquidus) + 120 °C, the Gouy temperature may be 500 °C, and T(melt) = T(liquidus) + 20
In the case of 0°C, the Gui temperature may be 300°C. When using a cooled gouer, a larger offset is required between the preform and the gouer wall to prevent modified metal from adhering to the gouer wall and the preform. This offset is typically about 2 for a 75ai gou diameter.
5 to about 12.5 im. Preferably, the preform is preheated to an elevated temperature, for example on the order of 700°C.

The spacer attached to the preform serves two functions. First, it provides space for liquid metal infiltration, commonly referred to as hydraulic infiltration. Second, spacers are used to collect residual gas from the preform. Therefore, if the spacer contains more fibers than the preform,
Its metal breakthrough pressure and pressure gradient are greater than within the preform and are not easily penetrated. For example, if the preform typically has a fiber Xt volume fraction (vr) of about 0.15, the spacer may have a Vr of about 0.25.

Preferably, the spacer penetrates last.

Since heat is no longer being applied to the system, as pressure is continuously applied, the matrix metal cools and solidifies as the preform impregnates. Finally, the ram can be pulled upwards and the formed composite product can be removed from the gou.

When pressurization begins, a temperature difference is created between the upper and lower ends of the contents of the die cavity.

Cooling and resulting solidification proceeds vertically inward from the top and bottom of the die cavity, but due to temperature differences, the amount of metal below the preform, and the vertical dimensions of the preform itself, The incoming upper and lower solidified tip surfaces are encountered in the metal below the preform, but not within the preform itself. For this to occur, the ram must continue to apply sufficient pressure to complete infiltration of the preform by the matrix metal before solidification of the metal is complete.

As a result of the above-mentioned characteristics, the impregnated matrix metal solidifies within the preform, but there is a single solidified front surface through which it passes in one direction, and therefore the preform The molten metal is constantly fed to fill the voids created by the contraction of the metal solidifying within the object, ie until the impregnation and solidification of the metal within the preform is complete. In this way, undesirable porosity of the resulting composite material can be avoided and satisfactory mechanical properties can be achieved throughout the composite material, even with a substantial thickness of the composite material.

To create an initial temperature differential, in the embodiment of FIG. "Cold" when placed in the cavity
, that is, not heated. The ram may be internally cooled if it is desired to promote solidification of the matrix metal, but such active cooling may not be necessary in all cases. Furthermore, before positioning the ram, the die plate l! is heated by a resistive or inductive heater 24, the peripheral part of this plate is in direct contact with the heating die, and in order to minimize heat loss, the plate is initially heated from the base plate 12, which is less heated by the layer 14. It should be noted that it is well insulated. Therefore, when the ram begins to press against the upper end of the contents of the die cavity, the relative low temperature of the ram and the relative high temperature of the Goo plate 11 at the lower end of the cavity contents will cause the lower end of the cavity to press against the upper end. It will make it hotter.

Initially, the cold ram absorbs heat from the upper end of the die cavity, creating a first solidified tip surface that moves down the cavity. The pressure exerted by the ram compresses the insulation layer 14 between the Gouy plate 11 and the base plate 12, reducing the insulation effectiveness of the layer 14 and reducing the gap between the initially heated Gouy plate and the initially cold base plate. heat is absorbed from the lower end of the die cavity. Solidification of the contained metal then begins at that location, sealing the escape route for molten metal at the bottom of the die and creating a second solidifying front surface that moves upward.

However, due to the effect of the initial temperature difference between the top and bottom of the die cavity, the upward advancement of the second tip surface is slower than the downward advancement of the first tip surface. Thus, ultimately the tip surfaces will be encountered at a location within the cavity substantially below the midpoint of their respective starting locations.

The relative thicknesses of the preform itself and of the metal below the preform are such that the two solidifying front surfaces advancing from the upper and lower ends of the cavity, respectively, are located below the preform. Choose to encounter. To ensure rapid heating of the fibers, the thickness of the preform is preferably 25 mm or less.

As shown in Fig. 4, when the thickness of the lower metal layer is sufficient and the impregnation of the preform is completed, an excess metal layer exists below the preform, and the solidified tip surface encounters that part. It is now possible to do so. The presence of excess molten metal in the puddle below the preform means that as the first solidified leading edge advances downwardly through the preform, the molten metal is constantly being used to penetrate the preform. It is important to ensure a continuous supply of metal.

In the example of the apparatus shown in FIG. 1, the wall thickness of the die 10 is, for example, 25111 mm, and the internal diameter is about 75 mm. Also, although this is the approximate diameter of the ram 26, the ram can enter the die cavity with some clearance. The vertical thickness of the central part of the Gui plate 11 is approximately 6 mm, and the vertical thickness of its thinner end portions is 3 mm.
IIj! , and the vertical thickness of the base plate 12 is 25+m. Both the base plate and the ram are
It's made from goo steel. The insulation layer is made from "Fiberflux" refractory fibers and the uncompressed vertical thickness of layer 14 is 3ii. The vertical thickness of layer 20 is 1
, 5 +u. Heater 24 is a resistance heater.

A typical method using the above device is to use a 70 mm diameter
, 30 mm vertical thickness, is impregnated with molten metal. The vertical thickness of the matrix metal below the preform after impregnation is 30 mm. 20-2
Apply a ram pressure of 00 mPa for 240 seconds.

For preforms with the dimensions and conditions described above and a fiber volume fraction (Vf) of 0.15, A12-2% Si
Using the alloy as the matrix metal and heating to 660°C and preheating the preform to 700°C, a satisfactory composite material was obtained. At these temperatures, the base plate temperature is approximately 200°C.

It will be understood that the invention is not limited to the methods and embodiments particularly described above, but can be implemented in other ways without departing from the inventive concept.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the location of a goo for carrying out the method of the present invention, FIG. 2 is a cross-sectional view of a partial chamber of the preform, FIG. 3 is a plan view of the top of the preform, and FIG. 2 is a cross-sectional view similar to FIG. 1 showing the preform in an impregnated state; FIG. 10... Gui, 11... Gui plate, 12...
Base plate, 14... Insulating material layer, 16... Matrix metal, 18... Preform, 20... Insulating material layer, 22... Insulating material layer, 24... Heater, 26
...Rum, 30...Spacer, 31...Beads. Patent Applicant: Alcan International Limited

Claims (1)

[Claims] 1. A method for producing a composite cast article comprising a metal matrix and a segmented solid filler incorporated into and dispersed within the matrix, the method comprising: depositing a melt of the metal matrix into a die cavity; Place the preheated preform of the split solid filler on top of the melt and apply pressure to the preform in a direction parallel to the axis of the cavity to inject the preform into the molten metal. driving, thereby completely impregnating the preform filler with the molten metal so that the solidified tip surface passes completely through the metal infiltrated preform layer along the axis of the cavity in one direction, while the preform solidifying the resulting cast article by adjusting the heat flow within the die cavity such that the metal in front of this tip surface remains molten within the material layer and at least immediately after crossing the preform layer; A method characterized by: 2. adjusting the heat flow comprises creating a temperature difference between opposite ends of the die cavity such that one end region of the die cavity is hotter than the other, and the excess metal-containing layer The method of claim 1, wherein the molding layer is located between the hot end of the die cavity. 3. The method of claim 2, wherein the step of creating a temperature differential includes selectively heating one end of the die. 4. The method of claim 2, wherein the step of creating a temperature differential includes selectively cooling one end of the die. 5. The method of claim 2, wherein the step of creating a temperature differential comprises selectively insulating one end of the die to preferentially remove heat from the die cavity at the other end of the die. Method. 6. A patent claim in which the pressurizing step is performed by a ram inserted into the die cavity at the other end of the die, and the ram is made of a material having a lower temperature and greater thermal conductivity than the other end of the die. The method described in item 5. 7. The method of claim 2, wherein the preform is disc-shaped and has a spacer attached to the top surface of the preform to separate the top surface of the preform from the ram. 8. Claim 1, wherein the matrix metal is aluminum and the filler comprises reinforced refractory fibers.
The method described in section.