JP2003171703A - Porous sintered compact and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous sintered compact having excellent molten-metal impregnation property. <P>SOLUTION: The following are used: raw-material powder composed essentially of metal powder; wires capable of being melted away, which have a melting point not higher than the sintering temperature of the metal powder and are disposed in the raw-material powder. The porous sintered compact can be manufactured by heating the raw-material powder together with the wires capable of being melted away to sinter the metal powder and has voids resultant from the melting of the wires capable of being melted away at the sintering. The voids can be easily formed by melting the wires capable of being melted away. These voids act as a runner for molten metal, by which molten- metal impregnation property can be improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a porous sintered body impregnated with molten metal and a method for producing the same.

[0002]

2. Description of the Related Art From the viewpoints of weight reduction, high performance, recycling, etc., the materials of various members are being changed from iron-based materials to light metals such as aluminum alloys and magnesium alloys. However, instead of replacing the whole with these materials, composite materials are used for various reasons such as strength, rigidity, slidability, and durability. For example, in the case of an engine cylinder block, a cast iron liner is often cast into the cylinder bore while the exterior part is made of aluminum alloy. However, the cast iron liner is not always preferable in terms of weight, thermal conductivity and the like. Therefore, it is considered that a preform of ceramic fiber or a porous sintered body made of metal is cast in place of it. However, the ceramic fiber preform is not always preferable in use in a cylinder liner to which a large load or surface pressure acts, in terms of rigidity and strength.

[0003]

[Patent Document 1] Japanese Patent Laid-Open No. 11-
Japanese Patent Publication No. 47913 discloses that the shape of the mold is devised so that the molten metal is impregnated from both sides of the ceramic fiber preform to improve the impregnation property. But,
In this method, the mold is complicated and expensive. In addition, the machining allowance after casting may become large, and unimpregnated portions may accumulate in the central portion of the ceramic fiber preform, causing porosity. It should be noted that this is not limited to ceramic fiber preforms for cylinder liners. The present invention has been made in view of such circumstances. That is, it is an object of the present invention to provide a porous sintered body that can be impregnated with molten metal quickly and reliably. Moreover, it aims at providing the manufacturing method which can produce such a porous sintered compact easily and efficiently.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve this problem, and as a result of repeated trial and error, as a result, a wire rod having a relatively low melting point is used to form a cavity inside a porous sintered body. The present invention has been completed, and has led to the completion of the present invention. (Porous Sintered Body) That is, the porous sintered body of the present invention is
A raw material powder composed mainly of metal powder and a fusible wire rod having a melting point equal to or lower than the sintering temperature of the metal powder and provided in the raw material powder are heated together to sinter the metal powder. It is characterized by having a cavity formed by melting the fusible wire at the time of binding.

The porous sintered body of the present invention is
The molten metal is not impregnated only through the pores formed when the metal powder is sintered. In addition to the pores, a cavity for positively guiding or impregnating the molten metal is provided. Due to the presence of this cavity, the impregnation property of the molten metal could be significantly improved. This "cavity"
May also replace conventional porosity, but is not so limited. Rather, by devising the shape of the cavity, it can be used as a runner for positively guiding the molten metal into the inside of the porous sintered body. By the way, this cavity is formed by a fusible wire that melts at a temperature lower than the sintering temperature of the metal powder. Therefore, by adjusting the disposition condition of the fusible wire rod, the runner reaching the inside of the porous sintered body can be easily formed. Further, by the method of arranging the fusible wire, it is possible to easily form a cavity that opens at the inflow side of the melt that can be impregnated and forms a runner.

The "porous sintered body" referred to in the present invention is
The number of pores formed by sintering the metal powder may be large or small. However, the pores may include the cavity. Therefore, in addition to the above porosity, a large number of “cavities” according to the present invention are sufficiently “porous”. Then, it is possible to calculate the porosity of the porous sintered body including the hollow portion.

(Manufacturing Method of Porous Sintered Body) Further, the present invention can be understood as the following manufacturing method of the porous sintered body in view of the above contents. (1) That is, the present invention relates to a filling step of filling a raw material powder mainly composed of a metal powder into a molding die in which a fusible wire having a melting point equal to or lower than the sintering temperature of the metal powder is filled, and the molding step. The sintered body comprises at least a forming step of pressing the raw material powder filled in the cavity of the mold into a powder molded body, and a sintering step of heating the powder molded body into a sintered body. Is
A method for producing a porous sintered body may include a cavity formed by melting the fusible wire in the sintering step. In this manufacturing method, a fusible wire is arranged in advance in a cavity of a mold, raw material powder is filled therein, and molding and sintering are performed. In this case, the shape of the cavity formed is easy to adjust because the degree of freedom of disposing the fusible wire is large. For example, when the cavity is a runner, it becomes easy to direct the opening of the runner toward the inflow side of the molten metal.

(2) Further, in the present invention, a filling powder for filling a molding die with a mixed powder obtained by mixing a raw material powder mainly containing a metal powder and a fusible wire having a melting point equal to or lower than the sintering temperature of the metal powder. And a sintering step of pressing the mixed powder filled in the molding die into a powder compact and a sintering step of heating the powder compact into a sintered body. The bonded body may have a cavity formed by melting the fusible wire rod in the sintering step, and may be a method for manufacturing a porous sintered body. This manufacturing method fills a mold with a mixed powder in which a fusible wire having an appropriate length and a metal powder are mixed in advance, and molds the powder.
Sintering is performed. In this case, almost uniform cavities can be formed in the entire porous sintered body. Therefore, the molten metal can be more surely impregnated into the entire porous sintered body.

(3) Further, in the present invention, a filling step of filling a raw material powder mainly containing a metal powder into a molding die, and the raw material powder filled in the molding die is pressure-molded at a low pressure to obtain a powder. A molding step of forming a molded body; a piercing step of piercing the powder molded body with a fusible wire having a melting point not higher than the sintering temperature of the metal powder; and heating the powder molded body after the piercing step. And a sinter step of forming a sinter, the sinter having a cavity formed by melting the fusible wire in the sinter step. It may be a manufacturing method. In this manufacturing method, a powder compact is first molded, and a fusible wire rod is stabbed into the powder compact and sintered. Since the fusible wire rod impinges on the existing powder compact, the degree of freedom in disposing the fusible wire rod is further increased. For example, it is easy to form the runner from all sides of the powder compact. Note that “piercing” also includes embedding. In this forming step, the reason why the pressure is low at the time of forming the raw material powder is to facilitate impingement of the fusible wire. Therefore, as long as the fusible wire rod can be stabbed into the powder compact, its specific pressing force does not matter.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to embodiments. The contents described below are applicable to both the porous sintered body according to the present invention and the manufacturing method thereof. (1) Dissolvable wire rod The meltable wire rod may be any wire that melts at the sintering temperature of the metal powder or lower. Therefore, the material such as metal or resin does not matter, and the length, the wire diameter (thickness), the cross-sectional shape, etc. do not matter. However, the melting point of the fusible wire is preferably close to the sintering temperature. If the difference between the sintering temperature of the metal powder and the melting point of the fusible wire is too large, the fusible wire will vaporize,
This is because the furnace body is contaminated during the sintering process. For example, when the metal powder is iron-based powder and the sintering temperature is 1100 ° C., copper (melting point: 1083 ° C.) may be used as the material of the fusible wire.

Further, it is preferable that the material of the fusible wire contains an alloy component element that forms an alloy with the main component element of the porous sintered body (metal powder). The proper combination can improve the strength, thermal conductivity, slidability, etc. of the porous sintered body. For example, when the main component element is iron (Fe) and the alloy component element is copper (Cu), Cu is F
The solid solution of e may improve the strength of the porous sintered body. In addition to this, various combinations of the main component element and the alloy component element can be considered. When the main component element is Fe, in addition to Cu as the alloy component element, carbon (C),
Chromium (Cr), molybdenum (Mo), nickel (N
i), vanadium (V), etc. can be considered.

The length of the fusible wire may be appropriately selected depending on the purpose. For example, the length of the fusible wire may be set according to the length or thickness of the porous sintered body. Specifically, when the cavity formed by melting the fusible wire is used as the runner of the molten metal, it is preferable that the length is such that the cavity penetrates from one of the porous sintered bodies to the other and is in a state close thereto. On the other hand, in the case where the powder compact is integrally molded with the mixed powder obtained by mixing the raw material powder with the fusible wire, the length thereof may be a short piece or a fiber. The wire diameter of the fusible wire may be appropriately selected depending on the purpose. For example,
When forming the above-mentioned runner, the thicker the better. For example, the wire diameter may be 0.5 mm or more, more preferably 1 mm or more. The present inventor confirmed by die casting that even a cavity having a wire diameter of about 1 mm could sufficiently function as a runner. The cross-sectional shape of the fusible wire is cost, availability,
From the viewpoint of handleability, it is preferable that the cross section is circular.

(2) Raw Material Powder The raw material powder is mainly composed of metal powder. Metal powder is F
Pure metal powder consisting of simple metals such as e, Al, and Mg,
It may be an alloy powder or a mixed powder thereof. However,
If the metal powder is an iron-based powder containing Fe as a main component, it is easily available and low in cost. The metal powder is atomized powder,
Any material such as reduced powder may be used, and the shape of the particles does not matter. However, when producing a porous sintered body having a high porosity, fine powder having a too small particle size is not preferable. For example, if the particle size is 5
It is preferable to use one having a thickness of about 0 to 150 μm. The raw material powder is not limited to such a metal powder alone, and may be a mixed powder (mixed raw material powder) containing a lubricant, an additive, or the like. In addition, various alloy element powders other than metals such as carbon (C) and boron (B) or powders containing them,
Further, it may contain various compound powders such as ceramic powder.

(3) Powder compact The volume ratio occupied by the metal powder in the powder compact (metal powder occupied volume ratio) is preferably 40 to 70% by volume.
If it is less than 40% by volume, the handleability is poor, while 70%
When the content exceeds the volume%, the porosity of the porous sintered body decreases, which is not preferable. The metal powder occupied volume ratio is 45 to 65% by volume,
45-60% by volume, and further targeting 50% by volume 45-
It may be about 55% by volume. The volume% in the present specification is the ratio of the bulk density of the powder compact to the true density of the metal powder. By the way, the present inventor has developed a new method suitable for forming such a powder compact having a low occupied volume ratio of metal powder.

That is, on the premise of the above-described manufacturing method of the present invention, a mixed raw material powder containing 2.5 mass% or more of a low temperature softening binder is used as a raw material powder, based on 100 mass%. Is filled in the mold (filling step),
The binder in the filled mixed raw material powder is softened or melted, and the mixed raw material powder is pressure-molded to form a powder compact (molding step). A powder compact of 40 to 70% by volume is heated to remove the binder and sinter the metal powder to form a porous sintered body (sintering step).

The low-temperature softening binder heated in the molding step softens or melts to cover the constituent particles of the metal powder and facilitate the adhesion of the constituent particles to each other. Therefore, even a powder compact having a small metal powder occupied volume ratio has good handleability and can be normally handled. Moreover, this binder is easily removed in the sintering process, and the contamination of the furnace body can be suppressed or prevented. The content of the powder compact is 10
When it is 0% by mass, it is 2.5% by mass or more, preferably 3% by mass or more. As the low temperature softening binder, for example, a lubricant for powder metallurgy such as stearic acid or amide wax can be used. These are cheap and easy to use. The "low temperature" of the binder here
Means a temperature at which the binder softens or melts in the molding process. Therefore, the specific temperature range varies depending on the type of binder, but it is sufficient that the binder is softened or melted in the preheated or heated mold. Thus, by using the low-temperature softening binder, a powder compact having a low metal powder occupying volume ratio, which is excellent in handleability, can be obtained, and a porous sintered body having a high porosity can be efficiently mass-produced. It has become possible.

(4) Porous sintered body The entire porous sintered body obtained after sintering is 100% by volume.
It is preferable that the porosity is 30 to 60% by volume.
Yes. This is because it is excellent in the impregnation property of the molten metal. Before this porosity
Considering the cavity formed by the fusible wire,
Easy to manufacture porous sintered body with high porosity, which was difficult to manufacture in the past
Will be obtained. Here, the porosity is porous sintered
The bulk density of the body (ρ) and the true density of its constituent materials (ρ ₀) And
Use {1- (ρ / ρ₀)} × 100 (%)
To be done.

By the way, even if the fusible wire is melted in the sintering step, it may be solidified thereafter, and eventually the cavity may be closed. However, when the fusible wire melts, the molten material spreads over the surface of the sintered metal powder through the pores formed in the periphery. Further, depending on the material of the fusible wire, it may evaporate and disappear. In any case, after melting the fusible wire, it will not solidify again and block the cavity. The present inventor has confirmed this, for example, in the case where a copper wire (fusible wire) is arranged in Fe powder (metal powder).
This will be described later.

Since the porous sintered body of the present invention is excellent in the impregnation property of the molten metal, it is suitable as a cast member. For example, an iron-based porous sintered body that is cast into a cylinder block to form a cylinder liner is preferable. At this time, since the porous sintered body is excellent in the impregnation property of the molten metal, the cylinder block can be manufactured with high productivity by die casting without using molten metal forging.

However, other than the case where the porous sintered body is used as the casting member, the porous sintered body may be used as the base material of the composite material. For example, a sliding member such as a bearing can be obtained by impregnating or embedding a soft material, which is a different material, or a lubricating material (solid lubricant) having excellent slidability into the pores of the porous sintered body. Further, in addition to the case where it is used as such a base material, the porous sintered body can be used for a filter or the like by utilizing the innumerable pores.

[0021]

EXAMPLES Next, the present invention will be specifically described with reference to examples. (Production of Porous Sintered Body) A porous sintered body for a cylinder liner to be cast into a cylinder portion of an aluminum alloy engine block was produced as follows. First, as a raw material
Reduced iron powder that is a metal powder (Pure iron: KIP24 made by Kawasaki Steel)
0M), graphite (C), and a lubricant for powder metallurgy (die wax W-02) made of stearic acid (melting point: 60 ° C.) were prepared. These were mixed at a ratio of Fe: 96.3 mass%, C: 0.7 mass% and stearic acid: 3 mass% (mixing step). This mixing was performed for 1 hour using a milling device.

Next, this mixed raw material powder was filled in a forming die (die) having a cylindrical cavity (filling step). At this time, a copper wire having a diameter of 1 mm, which is a fusible wire as shown in FIG. 1, was previously arranged in the cavity of the molding die in the axial direction. Although only one copper wire is shown in FIG. 1, 16 copper wires are evenly arranged circumferentially in the vicinity of the inner peripheral side of the cylinder. Moreover, the end of the copper wire was made to slightly project from the end of the powder compact. The mold provided with the copper wire was preheated to 80 ° C. before being filled with the mixed raw material powder so that the lubricant could be melted.

Next, the mixed raw material powder filled in the molding die is
Pressure was applied from above and below with a hydraulic press (pressing process). The pressure applied at this time was 100 MPa. The powder compact thus obtained was taken out of the molding die. The obtained powder compact had an outer diameter of 77 mm, a height of 130 mm, and a plate thickness of 3 mm, and was in a state of holding the copper wire. This powder compact had a strength that could be handled with bare hands and did not collapse due to some vibration or the like. When the metal powder occupying volume ratio of this powder compact was examined, it was about 50% by volume. Next, the powder compact was placed in an electric furnace and heated and sintered in an inert or vacuum atmosphere at 1250 ° C. for 30 hours (sintering step). Thus, a porous sintered body having the same shape as the above-mentioned powder compact and a porosity of about 50% by volume was obtained.

(Evaluation) FIG. 2 shows a state in which the obtained porous sintered body was observed by enlarging it with a microscope. As is clear from FIG. 10A, a cavity having substantially the same shape as the copper wire was formed in the portion where the copper wire was present. In this example, since the fusible wire rod was provided from one end to the other end in the axial direction of the porous sintered body, the formed cavity was a linear cylindrical cavity extending in the axial direction. In addition, the following is clear from FIG. 2B, which is an enlarged view of the portion A of FIG. That is, the copper wire was spread thinly (about 1 μm thick) on the inner peripheral surface of the formed cavity or on the surface of the iron powder that had penetrated through the pores and was sintered.
In any case, the copper wire after melting did not block the cavity again.

Next, this porous sintered body was cast into an aluminum alloy (JIS ADC12) to manufacture an engine block. This engine block was manufactured by die casting. The conditions for die casting are the molten metal temperature of 680 ° C.,
The mold temperature was 250 ° C. and the preheating of the molded body was 500 ° C. The die casting mold and the pouring method were designed so that the molten aluminum alloy would flow from the end opening of the porous sintered body.

Next, the cylinder bore portion of the engine block was cut, and the impregnation property of the aluminum alloy into the porous sintered body was examined. The sample collected was such that it contained a hollow portion formed by melting the copper wire (height 60
mm x outer diameter φ100 mm x inner diameter φ94 mm). A photograph of this sample observed with a microscope is shown in FIG. Further, as a comparative example, FIG. 3B shows a micrograph of a porous sintered body obtained by sintering a powder compact without a copper wire, in which the impregnating property was similarly examined. From these photographs, it can be seen that the aluminum alloy is sufficiently impregnated into the porous sintered body by using the cavity as a runner. Then, as shown in FIG. 3B, it can be seen that the unimpregnated portion (black spots) scattered when the cavity is not provided is almost absent in the case of FIG. 3A. In the photograph, a striped pattern (silicon deposits)
The white part with is the aluminum alloy part.

[0027]

According to the porous sintered body of the present invention, it is possible to easily improve the impregnation property of the molten metal due to the cavity formed inside. Further, according to the manufacturing method of the present invention, such a porous sintered body can be easily obtained.

[Brief description of drawings]

FIG. 1 is a view showing a state in which a copper wire is arranged in a powder compact according to an embodiment of the present invention, FIG. 1 (a) is a front view and FIG. 1 (b) is a side view.

FIG. 2 is a photomicrograph observing a cavity (runner) formed in a porous sintered body according to the present example, FIG. 2A is a photomicrograph, and FIG. It is a microscope picture which expanded the A section of (a).

FIG. 3 is a microstructure photograph showing a state in which a porous sintered body is impregnated with an aluminum alloy. FIG. 3 (a) shows an example, and FIG. 3 (b) shows a comparative example. .

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 38/00 304 C22C 38/00 304 38/16 38/16 (72) Inventor Keimei Baba Kariya city, Aichi prefecture 2-chome, Toyota-cho F-term inside Toyota Industries Corporation (reference) 4K018 AA24 BA13 CA00 CA11 DA01 DA19 FA32 HA01 JA32 KA08

Claims (9)

[Claims] 1. A raw material powder mainly composed of a metal powder and a fusible wire having a melting point equal to or lower than the sintering temperature of the metal powder and provided in the raw material powder are heated together to sinter the metal powder. A porous sintered body comprising a cavity formed by melting the fusible wire during the sintering. 2. The porous sintered body according to claim 1, wherein the cavity forms a runner by opening on the inflow side of the melt that can be impregnated. 3. The porous sintered body according to claim 1, wherein the fusible wire contains an alloy component element that forms an alloy with the main component element of the metal powder. 4. The porous sintered body according to claim 3, wherein the main component element is iron (Fe) and the alloy component element is copper (Cu). 5. The porous sintered body according to claim 1, which has a porosity of 30 to 60% by volume when the whole is 100% by volume. 6. The method for producing a porous sintered body according to claim 5, which is an iron-based porous sintered body which is cast into a cylinder block to form a cylinder liner. 7. A filling step of filling a raw material powder mainly composed of metal powder into a forming die in which a fusible wire having a melting point equal to or lower than the sintering temperature of the metal powder is filled, and a cavity of the forming die. The method comprises a molding step of at least pressing the filled raw material powder into a powder compact, and a sintering step of heating the powder compact into a sintered body. A method for producing a porous sintered body, comprising a cavity formed by melting the fusible wire rod in a binding step. 8. A filling step of filling a molding die with a mixed powder obtained by mixing a raw material powder mainly containing a metal powder and a fusible wire having a melting point of the metal powder or less, and a step of filling the molding die with the mixed powder. The method comprises a molding step of press-molding the filled mixed powder into a powder compact, and a sintering step of heating the powder compact into a sintered body. A method for producing a porous sintered body, comprising a cavity formed by melting the fusible wire rod in a step. 9. A filling step of filling a raw material powder mainly containing metal powder into a forming die, and a forming step of press-forming the raw material powder filled in the forming die at a low pressure to obtain a powder compact. A piercing step of piercing the powder molded body with a fusible wire rod having a melting point equal to or lower than the sintering temperature of the metal powder, and heating the powder molded body after the piercing step to form a sintered body. A method for producing a porous sintered body, comprising: a binding step, wherein the sintered body has a cavity formed by melting the fusible wire rod in the sintering step.