JP2024089869A - Sintered body and method for manufacturing the same - Google Patents

Abstract

To provide a method for manufacturing a sintered compact having improved boundary strength between the sintered compact and cast-in light metal alloy.SOLUTION: A method for manufacturing a sintered compact cast-in by light metal alloy comprises: a molding process of providing a green compact by molding metal powder, which has a composition that contains C: 0.5 to 2.5% and Cu: 5 to 40% in mass% and a main component in the balance of Fe, into a desired shape; a vacuum sintering process of providing the sintered compact by sintering the green compact under vacuum; and a blast treatment process of providing a rough surface region having a plurality of concavo-convex parts on the surface of the sintered compact by blast treatment of blasting particles including alumina particles onto at least a part of the surface of the sintered compact.SELECTED DRAWING: Figure 5

Description

The present invention relates to a sintered body and a method for manufacturing a sintered body.

To reduce the weight of automobile parts and improve their heat dissipation, automobile parts made of aluminum alloy, a type of light metal alloy, are becoming more common. However, aluminum alloys have problems in that their material properties as structural parts for automobiles are insufficient, such as lower mechanical properties such as strength, wear resistance, and rigidity compared to conventional cast iron, and a high thermal expansion coefficient. One method for improving the material properties of aluminum alloy parts is to cast different materials using gravity casting, die casting, etc., or to composite with different materials. As one such composite technology, for example, an engine block has been proposed in which an iron-based material is cast into the bearing part of an aluminum alloy housing cap attached to the lower part of an aluminum alloy cylinder block body (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 60-219436

However, during the process of encasing an iron-based material in an aluminum alloy, when the molten aluminum alloy solidifies while in contact with the iron-based material, tensile forces are generated in the aluminum alloy due to temperature differences at different locations. At this time, there is a risk that the aluminum alloy will peel off from the iron-based material.

In view of the above circumstances, the present invention aims to provide a sintered body with improved boundary strength between the light metal alloy being cast in place, and a method for manufacturing the sintered body.

The present invention is a method for producing a sintered body to be cast-in with a light metal alloy, comprising: a molding step of forming a powder compact into a desired shape using a metal powder containing, by mass, 0.5-2.5% C, 5-40% Cu, with the remainder being mainly Fe; a vacuum sintering step of sintering the powder compact under vacuum to produce the sintered body; and a blasting step of blasting at least a portion of the surface of the sintered body with particles containing alumina particles to provide a rough surface region having a plurality of irregularities on the surface of the sintered body.

The method for producing a sintered body of the present invention is also characterized in that the metal powder contains reduced iron powder produced by a reduction method or a mechanical crushing method.

In addition, in the method for producing a sintered body of the present invention, when the average of the arithmetic mean slope RΔa of the protrusions constituting the convex portion of the unevenness calculated in each of the four regions in the rough surface region is defined as the four-point average arithmetic mean slope, and the average of the average spacing S of the apexes of the adjacent protrusions calculated in each of the four regions in the rough surface region is defined as the four-point average spacing, the blasting process is characterized in that the blasting process is performed so that the four-point average arithmetic mean slope is 0.34 or more and the four-point average spacing is 116.9 μm or less.

The method for producing a sintered body of the present invention is also characterized in that the blasting process is performed so that the four-point average spacing is 90 μm or more.

The method for producing a sintered body of the present invention is also characterized in that the alumina particles having a particle size distribution in the range of 300 to 1700 μm are used in the blasting process.

The method for producing a sintered body of the present invention is also characterized in that, in the blasting process, an alumina region made of alumina is provided so as to be exposed on the surface of the roughened region.

In addition, in the manufacturing method of the sintered body of the present invention, the alumina region is characterized in that it extends from the deepest part of the depression that constitutes the concave portion of the uneven portion to the inside of the sintered body in the depth direction of the depression.

In addition, in the method for producing a sintered body of the present invention, at least a portion of the alumina region is in contact with the light metal alloy when the sintered body is cast-in with the light metal alloy.

In addition, in the manufacturing method of the sintered body of the present invention, in the vacuum sintering process, the pressure of the pores of the sintered body near the surface of the rough surface region is made vacuum, and in the blasting process, the free Cu phase that fills the pores is exposed to the surface of the rough surface region, and when the sintered body is cast in the light metal alloy, the molten light metal alloy comes into contact with the free Cu phase that fills the pores, and the molten light metal alloy moves into the pores due to the pressure difference between the inside and outside of the pores.

The sintered body of the present invention is a sintered body that is cast in a light metal alloy, and the sintered body has a composition that contains, by mass, 0.5 to 2.5% C, 5 to 40% Cu, and the remainder being mainly Fe, and has a rough surface region with multiple irregularities on its outer circumferential surface, and is characterized in that when the average of the arithmetic mean slope RΔa of the protrusions that make up the convex parts of the irregularities calculated in each of the four regions in the rough surface region is defined as the four-point average arithmetic mean slope, and the average of the average spacing S of the apexes of the adjacent protrusions calculated in each of the four regions in the rough surface region is defined as the four-point average spacing, the four-point average arithmetic mean slope is 0.34 or more and the four-point average spacing is 116.9 μm or less.

The sintered body of the present invention is also characterized in that the four-point average spacing is 90 μm or more.

The sintered body of the present invention is also characterized in that the rough surface region is made of alumina and has an alumina region exposed on the surface of the rough surface region.

The sintered body of the present invention is also characterized in that the alumina region extends from the deepest part of the depression that constitutes the concave portion of the uneven portion toward the inside of the sintered body in the depth direction of the depression.

The sintered body of the present invention is a sintered body that is cast in a light metal alloy, and the sintered body has a composition that contains, by mass, 0.5 to 2.5% C, 5 to 40% Cu, and the remainder being mainly Fe, and has a rough surface region with multiple irregularities on its outer circumferential surface, and the rough surface region has an alumina region that is exposed on at least a portion of the surface of the rough surface region and is made of alumina.

The sintered body of the present invention is characterized in that when the sintered body is cast in the light metal alloy, at least a portion of the surface of the alumina region forms a contact region with which the light metal alloy comes into contact.

The sintered body of the present invention is a sintered body that is cast in a light metal alloy, and the sintered body has a composition that contains, by mass, 0.5 to 2.5% C, 5 to 40% Cu, and the remainder being mainly Fe, and has holes that are filled with free Cu phases exposed on the surface of the sintered body and have vacuum holes inside, and when the sintered body is cast in the light metal alloy, the molten light metal alloy comes into contact with the free Cu phase that fills the holes, and the molten light metal alloy moves into the holes due to the pressure difference between the inside and outside of the holes.

The sintered body of the present invention and the manufacturing method for the sintered body have the excellent effect that the light metal alloy is unlikely to peel off even when it is cast-in with the light metal alloy.

1A is a schematic front view of an auxiliary member as a sintered body according to an embodiment of the present invention, and FIG. 1B is a schematic bottom view of the auxiliary member as a sintered body according to an embodiment of the present invention. 1A is a cross-sectional view of a rough surface region of a sintered body according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of a rough surface region of a sintered body according to an embodiment of the present invention, which is cast-in with an aluminum alloy. FIG. 2 is a schematic cross-sectional view showing an auxiliary member as a sintered body in an embodiment of the present invention, which is cast-in with an aluminum alloy. FIG. 2 is a diagram illustrating a concept (local gradient K) of a parameter (arithmetic mean gradient RΔa) in an embodiment of the present invention. 1 is a flowchart showing a method for producing a sintered body according to an embodiment of the present invention. 1A is a SEM image photograph of the rough surface region of the reinforcing member of the present invention in Example 1, observed by an EPMA (Electron Probe Micro Analyzer) at a magnification of 400 times. 1B is a SEM image photograph of the rough surface region of the reinforcing member of the comparative example in Example 1, observed by an EPMA at a magnification of 400 times. (A) is a photograph of an SEM image (upper left region) of the rough surface region of the reinforcement member of the present invention in Example 1 observed at a magnification of 40 times by EPMA, and photographs of characteristic X-ray images by Kα ray of Fe (lower left region), Al (upper right region), and Cu (lower right region). (B) is a photograph of an SEM image (upper left region) of the rough surface region of the reinforcement member of the comparative example in Example 1 observed at a magnification of 40 times by EPMA, and photographs of characteristic X-ray images by Kα ray of Fe (lower left region), Al (upper right region), and Cu (lower right region).

The following describes an embodiment of the present invention with reference to the accompanying drawings. Figures 1 to 7 show an example of an embodiment of the invention, and parts with the same reference numerals in the figures represent the same items.

<Sintered body>
A sintered body 1 according to an embodiment of the present invention will be described below with reference to Figures 1 to 3. The sintered body 1 according to this embodiment is a structure that has been subjected to a sintering process and is cast-in with a light metal alloy. The light metal alloy may be, for example, an aluminum alloy, but is not limited thereto, and may be other types of light metal alloys. Note that, although the light metal alloy will be described below by taking an example in which the light metal alloy is an aluminum alloy, the following description is also applicable to light metal alloys other than aluminum alloys. The sintered body 1 may be, for example, a reinforcing member 100 (see Figures 1(A) and (B)) that is attached to a position corresponding to a bearing part of an internal combustion engine, or may be another structure.

As shown in FIG. 1A, the reinforcing member 100 has a main body 110 and two extensions 120. The main body 110 is formed in an arch shape. The extensions 120 extend from the both lower ends of the main body 110 to the side away from the main body 110 along a straight line A connecting both lower ends of the main body 110. The main body 110 and the extensions 120 are assumed to be integrally formed, but may be configured as separate members and connected by a connecting means. A pair of reinforcing members 100 are arranged at positions corresponding to the bearing portion. The pair of reinforcing members 100 are arranged in the bearing portion in such a manner that their inner circumferential surfaces 130 face each other.

In addition, as shown in FIG. 1(A), the sintered body 1 in this embodiment preferably has a plurality of through holes 150 penetrating the sintered body 1 in the height direction H of the sintered body 1 perpendicular to the linear direction A. When the sintered body 1 is cast-in with an aluminum alloy, the molten aluminum alloy passes through the through holes 150 (see FIG. 3), improving the flow of the molten aluminum alloy around the sintered body 1 and supplying the molten aluminum alloy uniformly to the inner peripheral surface 130 and the outer peripheral surface 140 of the sintered body 1. As a result, the boundary strength between the sintered body 1 and the aluminum alloy is improved.

<Rough surface area>
As shown in FIG. 2A, the sintered body 1 has a rough surface region 4 having a plurality of uneven portions 5. The uneven portion 5 is an uneven portion formed on the surface 1B of the sintered body 1. The uneven portion 5 is composed of a recessed portion 6 and a protruding portion 7 adjacent to the recessed portion 6. The recessed portion 6 constitutes a concave portion of the uneven portion 5, and is a portion recessed toward the inside of the sintered body 1 with respect to the top of the adjacent protruding portion 7. The protruding portion 7 constitutes a convex portion of the uneven portion 5, and is a portion protruding toward the outside of the sintered body 1 with respect to the base surface of the adjacent recessed portion 6. A plurality of recessed portions 6 and protruding portions 7 are arranged alternately to provide a plurality of uneven portions 5. As shown in FIG. 2(B) , if the molten aluminum alloy 11 enters the multiple uneven portions 5 (recesses 6) of the rough surface region 4 during the process of casting the sintered body 1 with the aluminum alloy 11, the bonding area between the aluminum alloy 11 and the sintered body 1 increases, thereby improving the boundary strength between the aluminum alloy 11 and the sintered body 1.

In each of the four arbitrary regions in the rough surface region 4, the average of the ten-point average roughness Rz derived based on the cross-sectional curve in the range of the reference measurement length serving as the measurement standard in accordance with the provisions of JIS B 0601-1982 is defined as the four-point ten-point average roughness. It is preferable that the four-point ten-point average roughness in the rough surface region 4 of the sintered body 1 is in the range of 10 to 100 μm. If the four-point ten-point average roughness is less than 10 μm, sufficient increase in surface area is not obtained, and adhesion and boundary strength with the aluminum alloy 11 are insufficient. On the other hand, if the four-point ten-point average roughness exceeds 100 μm and becomes rough, the dimensions and precision are insufficient, and surface cracks are likely to occur on the outermost surface, resulting in reduced adhesion and boundary strength. Incidentally, considering the adhesion and boundary strength due to the increase in surface area, and the surface cracks, the reduction in adhesion and boundary strength, it is more preferable that the surface roughness is in the range of 20 to 60 μm in the four-point ten-point average roughness. The ten-point average roughness Rz is one of the surface roughness parameters.

By the way, the positions of the four arbitrary regions in the rough surface region 4 are not limited, and may be any region in the rough surface region 4. For example, in the case of the reinforcing member 100 shown in FIG. 1(A) and (B), the four regions in the rough surface region 4 may be four regions selected from one of the inner circumferential surface 130, the outer circumferential surface 140, the front surface 160, and the back surface 170 of the reinforcing member 100 (the same surface), or may be four regions selected from multiple surfaces (multiple surfaces) of the inner circumferential surface 130, the outer circumferential surface 140, the front surface 160, and the back surface 170. The four regions selected from the same surface may be selected, for example, at equal intervals (for example, 1 (mm) or 2 (mm)) or at unequal intervals. The intervals between the four regions are determined taking into consideration the variation in the ten-point average roughness Rz. In addition, each of the four arbitrary regions may have a width that allows a cross-sectional curve within the range of the reference measurement length corresponding to the above ten-point average roughness Rz to be obtained. Furthermore, each of the four regions may have a width that allows a roughness curve to be obtained within the range of the reference measurement length corresponding to the average spacing S of the local peaks below. Also, each of the four regions may have a width that allows a roughness curve to be obtained within the range of the reference measurement length corresponding to the arithmetic mean slope RΔa below.

In each of any four regions in the rough surface region 4, in accordance with the provisions of JIS B 0601-1994, if the average of the average spacing S of the local peaks (average spacing of the peaks of adjacent protrusions 7) derived based on the roughness curve in the range of the reference measurement length that is the measurement standard is defined as the four-point average spacing, the four-point average spacing in the rough surface region 4 of the sintered body 1 is preferably 116.9 μm or less, more preferably 115.0 μm or less, and even more preferably 112.0 μm or less. If the four-point average spacing is 116.9 μm or more, the number of uneven parts 5 formed in the rough surface region 4 will be small, and a sufficient increase in surface area will not be obtained. In addition, in the rough surface region 4 of the sintered body 1, the four-point average spacing is preferably 90 μm or more, more preferably 95 μm or more, and even more preferably 97 μm or more. This is because the processing to make the four-point average spacing 90 μm or less is time-consuming, and the width of the recess 6 becomes too narrow, making it difficult for the molten aluminum alloy 11 to enter the recess 6. The average spacing S of the local peaks is one of the surface roughness parameters.

When the average of the arithmetic mean slope RΔa of the protrusions 7 of the uneven portion 5 in each of any four regions in the rough surface region 4 is defined as the four-point average of the arithmetic mean slope, the four-point average of the arithmetic mean slope is preferably 0.34 or more, more preferably 0.35 or more, and even more preferably 0.36 or more. If the four-point average of the arithmetic mean slope is 0.34 or less, the protrusions 7 do not have a sufficient slope and become smooth, which makes it difficult to make the four-point average of the average interval 116.9 μm or less. The arithmetic mean slope RΔa represents the arithmetic mean of the local slope K (= dZ/dX) (see Figure 4) in the roughness curve in the range of the reference measurement length that is the measurement standard.

When the sintered body 1 is composed of the reinforcing member 100 described above, as shown in FIG. 3, the thickness of the inner peripheral surface side cast-in insert portion 20 of the internal combustion engine 2 covering the inner peripheral surface 130 side of the reinforcing member 100 is thin. Therefore, when the sintered body 1 is set in a corresponding mold (not shown) and the molten aluminum alloy 11 is poured into the mold to cast-in the sintered body 1, as the molten aluminum alloy 11 cools and solidifies, a force pulling the inner peripheral surface side cast-in insert portion 20 outward (in the direction of the arrow F) acts on the inner peripheral surface side cast-in insert portion 20 as shown in FIG. 3 due to the difference in the solidification speed depending on the location. As a result, there is a risk that the inner peripheral surface side cast-in insert portion 20 will peel off from the inner peripheral surface 130 of the reinforcing member 100. For this reason, it is preferable to improve the boundary strength between the inner peripheral surface 130 of the reinforcing member 100 and the inner peripheral surface side cast-in insert portion 20 by providing a rough surface region 4 on the inner peripheral surface 130 of the reinforcing member 100.

On the other hand, in the portion where the outer circumferential surface 140 of the reinforcing member 100 is cast-in, there is little risk of the aluminum alloy 11 peeling off. For this reason, the outer circumferential surface 140 of the reinforcing member 100 may or may not have a roughened surface region 4.

Therefore, the rough surface region 4 may be provided on at least a portion of the surface of the sintered body 1 (the inner peripheral surface 130 in the case of the reinforcing member 100). However, this is not limited thereto, and the rough surface region 4 may be provided on the entire surface area of the sintered body 1.

When the sintered body 1 having the rough surface region 4 as described above is cast-in with the aluminum alloy 11, a sufficient bonding area is obtained between the two, improving the boundary strength between the sintered body 1 and the aluminum alloy 11.

<Alumina region>
As shown in FIG. 2A, the sintered body 1 in this embodiment has a plurality of alumina regions 8 exposed on the surface of the uneven portion 5 of the rough surface region 4. The alumina region 8 is made of alumina (aluminum oxide: Al ₂ O ₃ ). As shown in FIG. 2A, the alumina region 8 starts from the deepest part of the recessed portion 6 and spreads toward the inside of the sintered body 1 in the depth direction of the recessed portion 6. The alumina region 8 is in contact (continuous) with the surrounding constituent parts (matrix 1A) of the sintered body 1, except for the exposed surface exposed on the surface of the sintered body 1. As a result, that is, the exposed surface of the alumina region 8 forms the bottom surface of the recessed portion 6. The matrix 1A of the sintered body 1 refers to the part that becomes the base of the sintered body 1 other than the alumina region 8.

In this embodiment, the alumina region 8 is preferably provided only in some of the multiple recesses 6, but this is not limited thereto and may be provided in all of the multiple recesses 6. The alumina region 8 may be provided by separately attaching alumina after the rough surface region 4 is provided. The alumina region 8 may also be made of the remains of an alumina grid used in the blasting process of the manufacturing method for the sintered body described later. In this case, the alumina in the alumina region 8 is considered to be mechanically embedded in the product (the sintered precursor described later) that has undergone the sintering process of the manufacturing method described later.

During the process of casting the sintered body 1 into the aluminum alloy 11, the molten aluminum alloy 11 enters the recessed portion 6 as shown in FIG. 2(B). When the surface 1B of the sintered body 1 where the rough surface region 4 is not formed is extended to the rough surface region 4, or the surface of the sintered body 1 that existed in the region corresponding to the rough surface region 4 before the rough surface region 4 is formed is defined as a virtual surface 1C, the molten aluminum alloy 11 eventually enters the deepest portion of the recessed portion 6 that is shallow based on the virtual surface 1C, but the molten aluminum alloy 11 may enter only partway into the recessed portion 6 that is deep based on the virtual surface 1C without reaching the deepest portion.

As shown in FIG. 2B, if the molten aluminum alloy 11 does not reach the deepest part of the recess 6, an air layer 12 is formed between the sintered body 1 and the aluminum alloy 11. The smaller the volume of the air layer 12, the better in terms of improving the boundary strength between the aluminum alloy 11 and the sintered body 1. If an alumina region is formed by arranging alumina particles in the lower region starting from the deepest part of the recess 6, the bottom of the deepest part of the recess 6 can be raised and the apparent depth of the recess 6 based on the virtual surface 1C of the recess 6 can be made shallower, thereby reducing the volume of the air layer 12.

When the molten aluminum alloy 11 flows into the alumina region 8 until it comes into contact with the alumina region 8, a contact region 13 is formed where the surface (exposed surface) of the alumina region 8 and the aluminum alloy 11 come into contact. If the contact region 13 extends to the entire surface (exposed surface) of the alumina region 8, the air layer 12 is not formed. Even if the contact region 13 is only a partial region of the surface (exposed surface) of the alumina region 8, the air layer 12 can be made small. Therefore, in either case, when the contact region 13 is provided, the boundary strength between the aluminum alloy 11 and the sintered body 1 is increased. Furthermore, since the aluminum alloy 11 and alumina contain the same type of metal, no problems arise when they come into contact.

<Vacancies and free Cu phase>
2(A), the sintered body 1 in this embodiment has a free Cu phase 9. The free Cu phase 9 includes a plurality of first free Cu phases 9A exposed on the surface of the uneven portion 5 of the rough surface region 4, and a plurality of second free Cu phases 9B located inside the sintered body 1 near the surface of the uneven portion 5. The free Cu phase 9, the first free Cu phase 9A, and the second free Cu phase 9B are regions composed of copper (Cu).

When the sintered body 1 is cast-in with the aluminum alloy 11, the molten aluminum alloy 11 comes into contact with the first free Cu phase 9A. Since copper has better wettability with light metal alloys such as the aluminum alloy 11 than iron, the contact area between the molten aluminum alloy 11 and the first free Cu phase 9A becomes larger. Then, when the molten aluminum alloy 11 comes into contact with the first free Cu phase 9A, the first free Cu phase 9A reacts with the molten aluminum alloy 11, forming a strong bond between the two.

Some of the first free Cu phases 9A block voids 10 located inside the sintered body 1 near the surface of the uneven portion 5 of the rough surface region 4. When the molten aluminum alloy 11 comes into contact with the first free Cu phases 9A, the first free Cu phases 9A react with the molten aluminum alloy 11, and the voids 10 are opened to the outside. At this time, the molten aluminum alloy 11 is sucked into the voids 10 due to the pressure difference between the inside and outside of the voids 10. When the molten aluminum alloy 11 solidifies in the voids 10, it exerts an anchor effect, further improving the boundary strength between the aluminum alloy 11 and the sintered body 1.

The larger the pressure difference, the easier it is for the molten aluminum alloy 11 to be guided into the void 10. In this embodiment, the internal pressure of the void 10 is a vacuum, so the pressure difference between the inside and outside of the void 10 is large. Therefore, in this embodiment, the molten aluminum alloy 11 can be reliably guided into the void 10. Incidentally, a vacuum refers to a pressure lower than atmospheric pressure (pressure outside the sintered body 1), and the vacuum state includes low vacuum, medium vacuum, high vacuum, and ultra-high vacuum according to JIS (Japanese Industrial Standards). In this embodiment, any vacuum state may be used, but in order to increase the pressure difference, a pressure equal to or lower than a medium vacuum, including a high vacuum and an ultra-high vacuum, is preferable. In FIG. 2(A), a plurality of voids 10 configured as described above are provided, but this is not limited thereto, and only one may be provided.

<Materials constituting the sintered body>
The sintered body 1 in this embodiment has a matrix composition containing, in mass%, 0.5 to 2.5% C (carbon), 5 to 40% Cu (copper), and Fe (iron) and unavoidable impurities. In the sintered body 1 in this embodiment, the main component of the remainder is Fe, but this is not limited to this. In addition, in the sintered body 1, not only the main component of the remainder but also the entire main component may be Fe, in which case the sintered body 1 may be called an iron-based sintered body. In addition, the above-mentioned remainder may contain, for example, in mass%, one or more selected from 30% or less Cr (chromium), 10% or less Mo (molybdenum), 3% or less Si (silicon), 2.5% or less Mn (manganese), and 5% or less W (tungsten), in total 40% or less. In this specification, mass% in the composition is simply written as %.

<C (Carbon)>
C is an element that increases the strength and hardness of the sintered body 1, and in this embodiment, in order to ensure strength or to make the matrix into a pearlite structure with excellent machinability, a content of 0.5% or more is required. On the other hand, if the content exceeds 2.5%, cementite precipitates in a mesh-like shape in the matrix of the sintered body 1, and the machinability and strength of the sintered body 1 decrease. Also, if the content exceeds 2.5%, C remains as graphite, which may cause a decrease in adhesion between the sintered body 1 and the aluminum alloy when the sintered body 1 is cast-in with the aluminum alloy. For this reason, the C content is limited to 0.5 to 2.5%. The C content is preferably 0.5 to 2.0%, and more preferably 0.8 to 1.5%.

<Cu (Copper)>
Cu dissolves in the matrix to increase the strength of the sintered body 1, and precipitates as a free Cu phase 9 in the matrix to react with the aluminum alloy 11 when the sintered body 1 is cast-in with the aluminum alloy 11, thereby increasing the boundary strength between the sintered body 1 and the aluminum alloy 11. If the Cu content is less than 5%, the precipitation of the free Cu phase 9 is hardly observed, and the desired boundary strength cannot be ensured. On the other hand, if the Cu content exceeds 40%, mechanical properties such as strength are reduced. For this reason, the Cu content is limited to the range of 5 to 40%. The Cu content is preferably 5 to 30%, and more preferably 5 to 25%.

<Cr (chromium), Mo (molybdenum), Si (silicon), Mn (manganese), W (tungsten)>
Cr, Mo, Si, Mn, and W are all elements that have the effect of increasing the strength of the sintered body 1, and one or more of them can be contained as necessary. However, if the content exceeds 30% Cr, 10% Mo, 3% Si, 2.5% Mn, and 5% W, sintering becomes difficult and the strength decreases. In particular, if the content of Cr and W exceeds the above values, the carbides become coarse and the machinability decreases. If the content of Si exceeds the above values, the amount of silicon oxide increases, the melting point decreases, and the machinability deteriorates. If the content of these elements exceeds 40% in total, uniform distribution of the alloy elements becomes difficult and the strength decreases. Cr, Mo, Si, and W have a smaller thermal expansion coefficient than Fe, and are suitable for adjusting the thermal expansion coefficient of the sintered body 1.

<Remainder>
In the matrix composition of the sintered body 1 of this embodiment, the main component of the remainder is Fe. In addition, the sintered body 1 of this embodiment has the above-mentioned matrix composition, and further has a structure having voids 10, a matrix structure, and a free Cu phase 9 (first free Cu phase 9A and second free Cu phase 9B) dispersed in the matrix. In addition, a free graphite phase of 2% or less by volume may be dispersed in the matrix. Incidentally, the matrix composition of the sintered body 1 of this embodiment may have Fe as the main component not only of the remainder but also of the entire composition. In addition, the above-mentioned balance contains inevitable impurities other than Fe, but other components may or may not be contained.

<Base Organization>
In the sintered body 1 of this embodiment, the base structure is preferably a pearlite structure. By making the base structure a pearlite structure, machinability is improved. Note that, from the viewpoint of machinability, the base structure may be sorbite or troostite instead of pearlite. Note that there is no problem with bainite, martensite, or a mixture thereof.

<Free Cu Phase>
The free Cu phase 9 (first free Cu phase 9A and second free Cu phase 9B) dispersed in the matrix of the sintered body 1 is preferably 5 to 30% by volume. If the free Cu phase 9 is less than 5%, the formation of intermetallic compounds between Cu and the aluminum alloy 11 is small, and the boundary strength is reduced. On the other hand, if the free Cu phase 9 is more than 30%, the strength of the sintered body 1 becomes equal to or lower than that of the aluminum alloy 11, and the boundary strength is also reduced. Since a large number of free Cu phases 9 are dispersed in the matrix, when the molten aluminum alloy 11 is cast, the free Cu phase 9 reacts with the molten aluminum alloy 11 to form an intermetallic compound, and therefore the molten aluminum alloy 11 does not penetrate deep into the sintered body 1, and a large number of joining points can be secured, resulting in high boundary strength.

<Hole>
The sintered body 1 includes pores 10 (see FIG. 2A), but in this embodiment, the pores 10 exist independently or discontinuously. Here, "discontinuous pores" means pores in which a plurality of pores 10 are continuous, but do not have continuity with a larger number of pores 10 (not shown). In the present invention, "pores exist independently or discontinuously" refers to a case where a value defined by (amount of continuous pores)/(total amount of pores)×100% is 50 or less. When the value exceeds 50, the pores 10 are considered to be continuous. The total amount of pores is calculated from the density measured by the Archimedes method. The amount of continuous pores is calculated by immersing the sintered body 1 in liquid wax or the like for 60 minutes to allow the wax to penetrate, and calculating the amount from the weight change before and after penetration.

The presence of independent or intermittent pores 10 reduces the penetration of the molten aluminum alloy 11 into the interior of the sintered body 1 during casting, reduces deterioration of the properties due to the penetration of the aluminum alloy 11, and enables the original strength and thermal expansion coefficient of the sintered body 1 to be maintained. The porosity of the sintered body 1 of this embodiment is preferably 5 to 35% by volume. If the porosity is less than 5% by volume, a large molding pressure is required during pressure molding, large molding equipment is required, and productivity is reduced, which is economically disadvantageous. On the other hand, if the porosity exceeds 35% by volume, the aluminum alloy 11 to be cast-in penetrates deep into the sintered body 1, and the properties of the sintered body 1 are deteriorated. The porosity is calculated by measuring the density of the sintered body 1 by the Archimedes method and converting it to volume %.

<Fine particles for improving machinability>
In addition, in the sintered body 1 of this embodiment, it is preferable to disperse fine particles for improving machinability in the matrix having the above-mentioned composition in order to improve machinability. The fine particles for improving machinability to be dispersed are preferably one or more types selected from MnS, CaF ₂ , BN, and enstatite. MnS, CaF ₂ , BN, and enstatite are all particles that improve machinability, and can be selected and contained as necessary.

By uniformly dispersing these fine particles for improving machinability in the matrix, the chips produced during cutting are broken down into sizes determined by the distance between these fine particles, so cutting resistance is kept low. Furthermore, it is preferable that the fine particles for improving machinability dispersed in the matrix have a particle size of 150 μm or less. If the particle size of the fine particles exceeds 150 μm, the boundary strength decreases. The particle size is preferably 5 to 100 μm.

The content of the fine particles for improving machinability dispersed in the matrix of the sintered body 1 is preferably 0.1 to 5 mass% of the mixed powder (total amount of iron-based powder, copper powder, graphite powder, and fine particle powder for improving machinability). If the content of the fine particles for improving machinability is less than 0.1 mass%, the effect of improving machinability is not observed. On the other hand, if it is contained in an amount exceeding 5 mass%, the adhesive strength with the matrix and the adhesive strength at the interface decrease. For this reason, it is preferable to contain fine particles for improving machinability with a particle size of 150 μm or less in the range of 0.1 to 5 mass%.

<Thermal expansion coefficient>
The sintered body 1 of this embodiment having the above-mentioned matrix composition and structure has an average thermal expansion coefficient of 13.5×10 ⁻⁶ /°C or less from room temperature to 200°C. If the average thermal expansion coefficient from room temperature to 200°C is 13.5×10 ⁻⁶ /°C or less, the average thermal expansion coefficient can be 15.0×10 ⁻⁶ /°C or less even when the aluminum alloy 11 is infiltrated into the intermittently existing voids 10, and can be set to a value close to the thermal expansion coefficient (about 9×10 ⁻⁶ to 12×10 ⁻⁶ /K) of an iron-based crankshaft of an internal combustion engine. For example, as shown in FIG. 3, when the sintered body 1 is cast into the bearing portion 3 of the internal combustion engine 2, the thermal expansion of the bearing portion 3 during operation of the internal combustion engine 2 can be suppressed, and the difference in the thermal expansion coefficient between the bearing portion 3 and the crankshaft can be used to appropriately maintain the amount of clearance change.

<Method of manufacturing sintered body>
An example of a method for producing the sintered body 1 in this embodiment will be described below with reference to Fig. 5. As shown in Fig. 5, the method for producing the sintered body 1 in this embodiment includes a powder mixing step S100, a molding step S110, a vacuum sintering step S120, a processing step S130, and a blasting step S140.

<Powder mixing process>
In the powder mixing step S100, a plurality of types of powder are mixed to prepare a metal powder that is the raw material of the sintered body 1. The metal powder is prepared by mixing an iron-based powder, a copper powder, a graphite powder, a lubricant powder, and/or fine particles for improving machinability. The mixing method is not particularly limited, but it is preferable to use a V mill from an economical viewpoint.

The iron-based powder is preferably pure iron powder. The pure iron powder of the sintered body 1 of this embodiment is preferably a type different from atomized iron powder (non-atomized iron powder), and reduced iron powder is particularly preferable. The reduced iron powder may be provided by a reduction method or a mechanical crushing method. The reduction method is a method of subjecting an object to a reduction action (for example, rough reduction (first reduction) before finish reduction (second reduction)). The reduced iron powder provided by the reduction method is provided by subjecting the mill scale, which is the raw material, to rough reduction (first reduction), followed by crushing and finish reduction (second reduction). The mechanical crushing method refers to a method in which a compression action, bending action, shear action, impact action, friction action, etc. are applied alone to crush the object to be crushed, or a combination of multiple actions is used to crush the object to be crushed. In the mechanical crushing method, when the object to be crushed is a relatively large lump, the object to be crushed is crushed by a g-crusher, hammer mill, or stamp mill, and when the object to be crushed to a certain extent, the object to be crushed is refined by a ball mill or vibration mill. Reduced iron powder prepared by mechanical crushing is prepared by mechanically crushing the raw material and then performing finish reduction.

On the other hand, atomized iron powder is prepared by the atomization method. Specifically, atomized iron powder is prepared by atomizing molten steel with high-pressure water, followed by finish reduction. Atomized iron powder generally has good compressibility, and the density tends to increase when compressed. However, sintered bodies using atomized iron powder tend to form fine pores, and tend to have smaller surface roughness than those using reduced iron powder, even if the density is the same. As a result, the surface roughness of sintered bodies using reduced iron powder is greater and intermittent pores are more likely to be obtained than those using atomized iron powder. Therefore, when a sintered body using reduced iron powder is cast-encased with an aluminum alloy, the boundary strength between the reduced iron powder and the aluminum alloy is increased. In addition, when a sintered body using atomized iron powder is cast-encased with aluminum, the grain boundaries tend to be largely oxidized due to the heat of the molten aluminum, and the strength is deteriorated, but a sintered body using reduced iron powder has a low degree of oxidation of the grain boundaries and does not deteriorate in strength. For the above reasons, it is preferable to use reduced iron powder as the iron-based powder.

It is preferable to use pure copper powder as the copper powder. Copper powder is added so that the Cu content in the metal powder (total amount of iron-based powder, alloy element powder, copper powder, graphite powder, and fine particle powder for improving machinability) is 5 to 40 mass%. If the Cu content in the metal powder is less than 5 mass%, precipitation of free Cu phase 9 is not observed. On the other hand, if it exceeds 40 mass%, mechanical properties such as strength decrease. For this reason, it is preferable to use copper powder so that the Cu content in the metal powder is 5 to 40 mass%, more preferably 5 to 30 mass%, and even more preferably 5 to 25 mass%.

Graphite powder is added as an alloying element that increases the strength of the sintered body, makes the matrix structure pearlite, and improves machinability. For this purpose, it is necessary to add the metal powder with an adjusted C content of 0.5 to 2.5 mass%. Lubricant powder is added in the metal powder to improve moldability during powder compaction and increase the green density. Zinc stearate and the like are preferable as lubricant powder. The amount of lubricant powder mixed in the metal powder is preferably 0.5 to 5 parts by weight per 100 parts by weight of the total amount of metal powder (total amount of iron-based powder, copper powder, alloying element powder, graphite powder, and fine particle powder for improving machinability).

In the present invention, in addition to the above-mentioned iron-based powder, copper powder, graphite powder, and lubricant powder, the metal powder can further contain a fine particle powder for improving machinability in order to improve machinability. The fine particle powder for improving machinability is preferably one or more selected from MnS, CaF ₂ , BN, and enstatite. MnS, CaF ₂ , BN, and enstatite are all particles that improve machinability, and can be selected and contained as necessary. In addition, the fine particle powder for improving machinability added to the metal powder is preferably a fine particle powder with a particle size of 150 μm or less. If the particle size of the fine particle powder exceeds 150 μm, the boundary strength decreases. The particle size is preferably 5 to 100 μm. When the metal powder contains a fine particle powder for improving machinability, the content of the fine particle powder for improving machinability is preferably 0.1 to 5 mass% based on the total amount of the metal powder (the total amount of the iron-based powder, copper powder, alloying element powder, graphite powder, and fine particle powder for improving machinability). If it is less than 0.1 mass%, the effect of improving machinability is small, while if it exceeds 5 mass%, the boundary strength decreases.

In addition, in this embodiment, it is preferable to further add alloy element powders such as Cr powder, Mo powder, W powder, Fe-Cr powder, Fe-Mo powder, and Fe-W powder, either alone or in combination, to the above-mentioned metal powder, so that the total amount of the metal powder (total amount of iron-based powder, alloy element powder, copper powder, graphite powder, and fine particle powder for improving machinability) contains 40% or less by mass of one or more selected from Cr: 30% or less, Mo: 10% or less, Si: 3% or less, Mn: 2.5% or less, and W: 5% or less.

Cr powder, Mo powder, W powder, Fe-Cr powder, Fe-Mo powder, and Fe-W powder are all blended to improve the strength of the sintered body and reduce the thermal expansion coefficient, and it is preferable to blend them in a total amount of 40 mass% or less. If the blending amount exceeds 40 mass%, the uniformity of the alloy elements decreases and the strength deteriorates. There is no need to limit the blending method, but it is economically preferable to use a V mill.

<Molding process>
In the molding step S110, the metal powder prepared in the powder mixing step S100 is molded into a desired shape to prepare a green compact. There is no particular limitation on the molding method in the molding step S110, but examples include molding methods such as metal mold molding in which the metal powder is placed in a mold and compressed by a press, and metal powder injection molding (MIM). When performing mold molding, it is preferable to adjust the pressure molding conditions of the green compact so that the sintered body 1 has an average thermal expansion coefficient of 13.5×10 ⁻⁶ /° C. or less from room temperature to 200° C.

<Vacuum sintering process>
In the vacuum sintering step S120, the powder compact is put into a vacuum sintering furnace and sintered under vacuum (vacuum sintering process) to provide a sintered precursor. In this embodiment, the one that has undergone the blasting process S140 is called the sintered body 1, and the one that has not undergone the blasting process S140 is called the sintered precursor to distinguish it from the sintered body 1. The sintering temperature is preferably 1100 to 1180°C. In addition, vacuum refers to a state of pressure lower than atmospheric pressure, and the pressure in the sintering furnace is preferably 1 (torr) or less. By sintering the powder compact under vacuum, it is possible to restrict the formation of an oxide film on the surface of the sintered precursor. As a result, the surface of the sintered precursor is in a cleaned state. In addition, in the vacuum sintering step S120, the pressure in the pores 10 inside the sintered precursor can be made vacuum. In addition, in the vacuum sintering step S120, the pressure in the pores 10 can be made lower than when the sintering process is performed under an atmosphere. As a result, when the molten aluminum alloy 11 comes into contact with the first free Cu phase 9A filling the voids 10 and the voids 10 are opened to the outside, the molten aluminum alloy 11 can be reliably drawn into the inside of the voids 10, thereby strengthening the boundary strength between the aluminum alloy 11 and the sintered body 1.

As for the sintering conditions, it is preferable to adjust the temperature and time so that the sintered precursor has an average thermal expansion coefficient of 13.5×10 ⁻⁶ /° C. or less from room temperature to 200° C. Also, in order to make the pores 10 exist singly or intermittently, it is preferable to adjust the sintering conditions and perform partial liquid phase sintering. As a result, the pores 10 are filled with the free Cu phase 9, and the pores 10 exist singly and intermittently.

<Blast treatment process>
In the blasting process S140, a blasting process is performed by spraying alumina particles (hereinafter, appropriately, referred to as alumina grid) against at least a part of the surface of the sintered precursor. The blasting process completes the sintered body 1. The alumina grid (alumina particles) has an acute shape. The media used in the blasting process in this process is composed of alumina grids, but may also contain other materials as long as it mainly includes alumina grids. When the alumina grid is collided with the surface of the sintered precursor by the blasting process, the alumina grid penetrates the surface of the sintered precursor, and the surface of the sintered precursor is scraped. As a result, a rough surface region 4 having a plurality of uneven portions 5 is provided on the surface of the sintered precursor, and the sintered body 1 is completed.

During the blasting process, many alumina grids are broken into various shapes and sizes due to collisions between alumina grids and between alumina grids and the surface of the sintered precursor. The broken alumina grids can then collide with the surface of the sintered precursor and become embedded in it. As a result, the number of alumina grids that collide with the sintered precursor per unit area is large. On the other hand, when a general steel grid (polygonal particles with sharp edges made of special steel) is used as the blasting media, the number of steel grids that are broken is small. As a result, the number of steel grids that collide with the sintered precursor per unit area is smaller than that of the alumina grid. Comparing the two, the pitch (average distance S between the apexes of the protrusions 7) of adjacent protrusions 7 is shorter when the alumina grid is used as the blasting media. Also, compared to the case of using a steel grid, the case of using an alumina grid contains many protrusions 7 with a large inclination, and many of the protrusions 7 are sharply pointed.

Compared to when a steel grid is used as the blasting medium, when an alumina grid is used as the blasting medium, the roughened region 4 of the sintered body 1 has a larger surface area, which increases the bonding strength between the aluminum alloy 11 and the sintered body 1, and more reliably prevents the aluminum alloy 11 from peeling off from the sintered body 1. From the perspective of improving the bonding strength between the aluminum alloy 11 and the sintered body 1, the blasting process may be performed on a portion of the sintered body 1 where the aluminum alloy 11 is likely to peel off (the inner peripheral surface 130 in the case of the reinforcing member 100).

When an alumina grid is used as the blasting medium, the 4-point average of the ten-point mean roughness of the rough surface region 4 of the sintered body 1, which has already been described, is preferably in the range of 10 to 100 μm, and more preferably 30 to 60 μm. Also, the blasting is preferably performed so that the 4-point average of the arithmetic mean slope of the rough surface region 4 of the sintered body 1, which has already been described, is 0.34 or more, more preferably 0.35 or more, and even more preferably 0.36 or more. Also, the blasting is preferably performed so that the 4-point average of the average spacing of the rough surface region 4 of the sintered body 1, which has already been described, is 116.9 μm or less, more preferably 115.0 μm or less, and even more preferably 112.0 μm or less. In addition, the blasting process is preferably performed so that the four-point average of the average spacing of the rough surface region 4 of the sintered body 1 is 90 μm or more, more preferably 95 μm or more, and even more preferably 97 μm or more. The four-point average of the ten-point average roughness, the four-point average of the arithmetic mean slope, and the four-point average of the average spacing are adjusted by adjusting the shot particle size, air pressure, etc. The aggregate of alumina grid (alumina particles) used in the blasting process preferably has a particle size distribution in the range of 300 to 1700 μm, and more preferably has a particle size distribution in the range of 600 to 1700 μm. However, in the above particle size distribution, a small amount of fine particles that could not be removed by classification will be ignored.

Note that an oxide film is formed on the surface of the sintered precursor after a typical sintering process, and the oxide film is removed in the next blasting process, so the blasting process takes a certain amount of time. However, in this embodiment, almost no oxide film is formed on the surface of the sintered precursor after the vacuum sintering process S120, and the surface is clean. Therefore, in the blasting process in the blasting process S140, it is only necessary to consider providing the rough surface region 4 on the surface of the sintered precursor. In addition, since the surface of the sintered precursor is clean, it is easy to provide the rough surface region 4 on the surface of the sintered body 1. As a result, the blasting process in the blasting process S140 of this embodiment can be completed in a shorter time than usual.

In addition, by carrying out the blasting treatment, the free Cu phase 9 dispersed in the matrix of the sintered precursor is exposed to a large extent on the surface. This improves the wettability of the aluminum alloy 11 with the molten metal, promotes the reaction with the aluminum alloy 11, reduces gaps at the interface, and improves adhesion. In addition, the molten aluminum alloy 11 can be easily guided into the voids 10 blocked by the first free Cu phase 9A, which adds an anchor effect and improves the bonding strength after adhesion.

<Processing steps>
In the processing step S130, a processing device (not shown) is used to perform dry processing on the sintered body 1. One example of the processing performed on the sintered body 1 is drilling, but this is not limited to this, and other processing such as cutting may also be used. In any case, any processing may be performed depending on the desired shape. Note that the processing step S130 is performed if necessary, but is not necessarily required.

The sintered body 1 produced by the above-mentioned manufacturing method is attached to a corresponding part in a mold, and molten aluminum alloy 11 is poured into the mold and high-pressure die-cast to produce an aluminum alloy part (e.g., an internal combustion engine 2). In this case, the sintered body 1 of this embodiment does not require preheating at a high temperature of 500 to 600°C, which was essential for conventional sintered bodies, and preheating at room temperature or up to about 200°C is sufficient. Even without such preheating or with preheating at a low temperature, the sintered body 1 of the present invention has good molten flow when the molten aluminum alloy 11 is poured, and adhesion and boundary strength with the molten aluminum alloy 11 can be ensured, so that the manufacturing process of the aluminum alloy part that casts the sintered body 1 can be simplified and the manufacturing cost of the part can be reduced.

The present invention will now be described in more detail with reference to examples.

In order to verify the characteristics of the sintered body of the present invention, the inventors of the present invention created multiple reinforcing members (see reinforcing member 100 shown in FIG. 1(A)) having a composition containing, by mass%, 1.00% C, 10% Cu, and the remainder being Fe and unavoidable impurities. Specifically, first, metal powder was filled into a die modeled after the reinforcing member, and a green compact was made by pressure molding using a molding press (molding step S110). Then, the green compact was sintered at a furnace pressure of 1 (torr) and a sintering temperature in the furnace in the range of 1000 to 1180°C to obtain a sintered precursor (vacuum sintering step S120). The metal powder included iron-based powder, copper powder, graphite powder, and lubricant powder. Next, the sintered precursor was processed to make a predetermined hole (processing step S130).

Finally, to compare the characteristics of the rough surface area created by blasting using an alumina grid with the characteristics of the rough surface area created by blasting using a steel grid, three reinforcing members with rough surface areas created by blasting using an alumina grid (hereinafter referred to as the reinforcing members of the present invention) were created, and three reinforcing members with rough surface areas created by blasting using a steel grid (hereinafter referred to as the reinforcing members of the comparative example) were created (blasting process S140).

The blasting process was performed using a shot blasting device (not shown) that fires media from a nozzle under a specified air pressure. The nozzle diameter was set to 7 (mm), the air pressure to 5 (kg/cm ² ), and the alumina grid and steel grid used were 20 mesh (#20). The 20 mesh alumina grid contains alumina particles with a particle size distribution in the range of 600 to 1700 (μm). The 20 mesh alumina grid and steel grid were each sprayed onto the surface of the reinforcing member for 4 (s) using the shot blasting device.

Comparison of surface roughness using SEM images of rough surface areas
6(A) and (B) show SEM images of the rough surface area of the reinforcing member of the present invention and the comparative example, observed by EPMA (Electron Probe Micro Analyzer: the same below) at a magnification of 400 times. FIG. 6(A) is an SEM image of the rough surface area of the reinforcing member of the present invention. FIG. 6(B) is an SEM image of the rough surface area of the reinforcing member of the comparative example. Comparing the two, as is clear from the photographs, the rough surface area of the reinforcing member of the comparative example has a gentle slope of the protrusions and a large gap between adjacent protrusions, whereas the rough surface area of the reinforcing member of the present invention has a steep slope of the protrusions and a small gap between adjacent protrusions. In other words, even when confirmed by the photograph, it can be confirmed that the rough surface area of the reinforcing member of the present invention is rougher than the rough surface area of the reinforcing member of the comparative example, and the surface area is increased.

<Comparison of 4-point average of ten-point average roughness, 4-point average of average spacing, and 4-point average of arithmetic mean slope>
In this embodiment, four areas in the rough surface area that are the basis of the four-point average of the ten-point average roughness, four-point average of the average interval, and four-point average of the arithmetic mean slope of the rough surface area are arbitrarily selected from each of the rough surface areas of the three present invention side reinforcing members and the three comparative example side reinforcing members, and are referred to as the first to fourth areas here. The ten-point average roughness Rz, the average interval S of the local peaks, and the arithmetic mean slope RΔa of the first to fourth areas of the three present invention side reinforcing members and the three comparative example side reinforcing members are shown in Tables 1 and 2. The ten-point average roughness Rz is in accordance with the JIS B 0601-1982 standard, the average interval S of the local peaks is in accordance with the JIS B 0601-1994 standard, and the arithmetic mean slope RΔa is the same as that already described with reference to FIG. 4. Tables 1 and 2 also show the ten-point average roughness Rz, the average interval S between local peaks, and the four-point average arithmetic mean slope RΔa of the first to fourth areas of the rough surface region. In Tables 1 and 2, the reference measurement length used as the basis for measuring the ten-point average roughness Rz, the average interval S between local peaks, and the arithmetic mean slope RΔa of the rough surface region 4 is 5 mm. Even if the reference measurement length is 5 mm, by combining all or any of the first to fourth areas, the reference measurement length can be substantially extended to at least 12.5 mm, so that substantially the same evaluation values (ten-point average roughness Rz, average interval S between local peaks, and arithmetic mean slope RΔa) as those obtained when the reference measurement length is 12.5 mm can be obtained. In addition, the indication of "average" in each of Tables 1, 2, and 5 to 8 represents the corresponding four-point average of ten-point mean roughness, four-point average of average interval, and four-point average of arithmetic mean slope.

Comparing the 4-point average ten-point roughness of both with reference to Tables 1 and 2, the rough surface area of the reinforcing member of the present invention has a minimum ten-point average four-point roughness of 48.94 (μm) (see reinforcing member No. 1 in Table 1) and a maximum ten-point average four-point roughness of 52.08 (μm) (see reinforcing member No. 3 in Table 1), whereas the rough surface area of the reinforcing member of the comparative example has a minimum ten-point average four-point roughness of 46.64 (μm) (see reinforcing member No. 1 in Table 2) and a maximum ten-point average four-point roughness of 44.07 (μm) (see reinforcing member No. 3 in Table 2).

Comparing the four-point average spacing of both with reference to Tables 1 and 2, in the rough surface area of the reinforcing member of the present invention, the minimum value of the four-point average spacing is 1103.29 (μm) (see reinforcing member No. 3 in Table 1), and the maximum value of the four-point average spacing is 111.30 (μm) (see reinforcing member No. 2 in Table 1), whereas in the rough surface area of the reinforcing member of the comparative example, the minimum value of the four-point average spacing is 116.96 (μm) (see reinforcing member No. 1 in Table 2), and the maximum value of the four-point average spacing is 119.48 (μm) (see reinforcing member No. 2 in Table 2). It was confirmed that there is a large difference between the four-point average spacing of both. In other words, it was confirmed that there are more uneven parts in the rough surface area of the reinforcing member of the present invention than in the rough surface area of the reinforcing member of the comparative example. Also, referring to Table 1, in the rough surface region of the side reinforcing member of the present invention, the average distance S between local peaks on each surface is 90.00 (μm) or more and 116.9 (μm) or less.

Comparing the arithmetic mean slope four-point averages of both with reference to Tables 1 and 2, in the rough surface area of the reinforcement member of the present invention, the minimum value of the arithmetic mean slope four-point average is 0.36 (see reinforcement member No. 1 in Table 1) and the maximum value of the arithmetic mean slope four-point average is 0.38 (see reinforcement member No. 3 in Table 1), whereas in the rough surface area of the reinforcement member of the comparative example, the minimum value of the arithmetic mean slope four-point average is 0.31 (see reinforcement member No. 3 in Table 2) and the maximum value of the arithmetic mean slope four-point average is 0.32 (see reinforcement members No. 1 and 2 in Table 1). It was confirmed that there is a large difference between the arithmetic mean slope four-point averages of both. In other words, it was confirmed that the protrusions of the rough surface area of the reinforcement member of the present invention are sharper than the protrusions of the rough surface area of the reinforcement member of the comparative example. Also, with reference to Table 1, in the rough surface area of the reinforcement member of the present invention, the average of the arithmetic mean slope four-point average on each surface is 0.34 or more.

<Comparison of 2-point average of ten-point average roughness, 2-point average of average spacing, and 2-point average of arithmetic mean slope>
In this embodiment, two areas in the rough surface area that are the basis of the two-point average of the ten-point average roughness, two-point average of the average interval, and two-point average of the arithmetic mean slope of the rough surface area are arbitrarily selected from the rough surface areas of the three present invention side reinforcing members and the three comparative example side reinforcing members, and are referred to as the first and second areas here. The reference measurement length that is the basis of the measurement is 12.5 (mm), and the ten-point average roughness Rz, the average interval S of the local peaks, and the arithmetic mean slope RΔa of the first and second areas of the three present invention side reinforcing members and the three comparative example side reinforcing members are shown in Tables 3 and 4. The ten-point average roughness Rz is in accordance with the JIS B 0601-1982 standard, the average interval S of the local peaks is in accordance with the JIS B 0601-1994 standard, and the arithmetic mean slope RΔa is the same as that already described with reference to FIG. 4. Tables 3 and 4 also show the ten-point average roughness Rz, the average interval S of the local peaks, and the two-point average ten-point average roughness, two-point average average interval, and two-point average arithmetic mean slope derived based on the arithmetic mean slope RΔa of the first and second areas. The two-point average ten-point average roughness represents the average of the ten-point average roughness Rz derived based on the cross-sectional curve in the range of the reference measurement length in accordance with the provisions of JIS B 0601-1982 in each of the two regions in the rough surface region. The two-point average average interval represents the average of the average interval S of the local peaks (the average interval between the peaks of adjacent protrusions) derived based on the roughness curve in the range of the reference measurement length in accordance with the provisions of JIS B 0601-1994 in each of the four regions in the rough surface region. The two-point average arithmetic mean slope represents the average of the arithmetic mean slope RΔa of the protrusions 7 of the uneven portion 5 derived based on the roughness curve in the range of the reference measurement length. In addition, the term "average" in each of Tables 3 and 4 represents the corresponding two-point average of ten-point mean roughness, two-point average of average interval, and two-point average of arithmetic mean slope.

Comparing the two-point average ten-point roughness values of both reinforcing members with reference to Tables 3 and 4, the minimum two-point average ten-point roughness value in the rough surface area of the reinforcing member of the present invention is 63.96 (μm) (see reinforcing member No. 3 in Table 3) and the maximum two-point average ten-point roughness value is 68.80 (μm) (see reinforcing member No. 1 in Table 3), whereas the minimum two-point average ten-point roughness value in the rough surface area of the reinforcing member of the comparative example is 57.01 (μm) (see reinforcing member No. 2 in Table 4) and the maximum two-point average ten-point roughness value is 66.30 (μm) (see reinforcing member No. 1 in Table 4). In other words, it was confirmed that the rough surface area of the reinforcing member of the present invention has a higher two-point average ten-point roughness value than the rough surface area of the reinforcing member of the comparative example.

Comparing the two-point average spacing of both with reference to Tables 3 and 4, in the rough surface area of the reinforcing member of the present invention, the minimum value of the two-point average spacing is 106.46 (μm) (see reinforcing member No. 2 in Table 3) and the maximum value of the two-point average spacing is 118.86 (μm) (see reinforcing member No. 1 in Table 3), whereas in the rough surface area of the reinforcing member of the comparative example, the minimum value of the two-point average spacing is 121.54 (μm) (see reinforcing member No. 2 in Table 4) and the maximum value of the two-point average spacing is 129.68 (μm) (see reinforcing member No. 1 in Table 4). It was confirmed that there is a large difference between the two-point average spacing of both. In other words, it was confirmed that there are more uneven parts in the rough surface area of the reinforcing member of the present invention than in the rough surface area of the reinforcing member of the comparative example.

Comparing the two-point average arithmetic mean slopes of both with reference to Tables 3 and 4, in the rough surface area of the reinforcing member of the present invention, the minimum value of the two-point average arithmetic mean slope is 0.46 (see reinforcing member No. 3 in Table 3) and the maximum value of the two-point average arithmetic mean slope is 0.50 (see reinforcing member No. 2 in Table 3), whereas in the rough surface area of the reinforcing member of the comparative example, the minimum value of the two-point average arithmetic mean slope is 0.30 (see reinforcing member No. 3 in Table 4) and the maximum value of the two-point average arithmetic mean slope is 0.33 (see reinforcing member No. 1 in Table 4). It was confirmed that there was a large difference in the two-point average average intervals of both. In other words, it was confirmed that the protrusions of the rough surface area of the reinforcing member of the present invention were more sharply pointed than the protrusions of the rough surface area of the reinforcing member of the comparative example. Also, with reference to Table 3, in the rough surface area of the reinforcing member of the present invention, the two-point average arithmetic mean slope on each surface is 0.34 or more.

<Comparison of elemental analysis of rough surface area>
The inventors conducted SEM image observations (upper left regions of each of Figures 7(A) and (B)) of the rough surface regions of the reinforcing member of the present invention and the comparative example using an EPMA at a magnification of 40x, as well as characteristic X-ray image observations using Fe-Kα radiation (lower left regions of each of Figures 7(A) and (B)), Al-Kα radiation (upper right regions of each of Figures 7(A) and (B)), and Cu-Kα radiation (lower right regions of each of Figures 7(A) and (B)).

As is clear from the SEM image in the upper right region of Figure 7 (A), numerous Al regions (white (light gray) regions) containing Al are distributed in the rough surface region of the reinforcing member of the present invention. The Al regions indicate the presence of Al elements, and the closer to white the region is in relative terms, the stronger the detection intensity, indicating the presence of a large amount of Al elements.

Also, as is clear from the SEM image photograph in the lower right region of FIG. 7(A), many white (light gray) regions are distributed in the rough surface region of the reinforcing member of the present invention. The white (light gray) regions are Cu regions composed of Cu. Compared with the SEM image photograph in the lower right region of FIG. 7(B), the total area of the Cu regions exposed on the surface is clearly larger in the photograph of FIG. 7(A). When an alumina grid is used in the blasting process, not only does the alumina grid being sprayed collide with the reinforcing member, but the alumina grid itself is also crushed and further fined to collide with the reinforcing member. As a result, since some of the alumina grid is crushed and further fined, the number of alumina grids colliding with the reinforcing member per unit area increases, and it is presumed that the surface of the reinforcing member is largely scraped off, so that the surface area of the Cu region exposed on the surface in the rough surface region of the reinforcing member of the present invention is presumed to be large. On the other hand, when a steel grid is used in the blasting process, the steel grid itself is not often crushed into smaller pieces and collides with the reinforcing member 100, so it is assumed that the amount of steel grid that collides with the reinforcing member per unit area is less than that of an alumina grid. Therefore, the surface area of the Cu region exposed to the rough surface area of the comparative example reinforcing member is smaller than the surface area of the Cu region exposed to the rough surface area of the present invention reinforcing member.

In order to verify the characteristics of the sintered body in this embodiment, the inventors of the present application created multiple reinforcing members (see reinforcing member 100 shown in Figure 1 (A)) containing, by mass%, 1.00% C, 10% Cu, with the remainder being Fe and unavoidable impurities. Then, using the shot blasting device used in the first embodiment, blasting treatment was performed on each reinforcing member under different setting conditions, and 12 reinforcing members of the present invention were created.

Specifically, as the first set conditions for the blasting treatment, the air pressure was set to 5 (kg/ ^cm2 ), the shot time (spray time: the same below) was set to 8 (s), and the two reinforcing members were each blasted with a shot blasting device using a 20 mesh (#20) alumina grid to provide two reinforcing members on the present invention side. Note that, for the 20 mesh (#20) alumina grid, the particle size distribution is in the range of 600 to 1700 (μm).

As a second set condition for the blasting treatment, the air pressure was set to 5 (kg/ ^cm2 ) and the shot time was set to 8 (s), and a 16 mesh (#16) alumina grid was used to blast the two reinforcing members with a shot blasting device, thereby providing two reinforcing members on the present invention side.

As a third set condition for the blasting treatment, the air pressure was set to 5 (kg/ ^cm2 ) and the shot time was set to 4 (s), half the above. Using an alumina grid of 16 mesh (#16), the two reinforcing members were blasted using a shot blasting device to provide two reinforcing members on the present invention side.

As a fourth setting condition for the blasting treatment, the air pressure was set to 5.5 (kg/ ^cm2 ), which was higher than the above, and the shot time was set to 8 (s). Using an alumina grid of 16 mesh (#16), the two reinforcing members were blasted with a shot blasting device to provide two reinforcing members on the present invention side.

As a fifth setting condition for the blasting treatment, the air pressure was set to 5.5 (kg/ ^cm2 ), which was higher than the above, and the shot time was set to 4 (s), which was half the above. Using a 16 mesh (#16) alumina grid, the two reinforcing members were blasted using a shot blasting device, thereby providing two reinforcing members on the present invention side.

The ten-point average roughness Rz, average spacing S between local peaks, and arithmetic mean slope RΔa of the first to fourth areas in the rough surface regions formed on the twelve side reinforcement members of the present invention thus prepared are shown in Tables 5 to 8. In Tables 5 to 8, the reference measurement length used to measure the ten-point average roughness Rz, average spacing S between local peaks, and arithmetic mean slope RΔa of rough surface region 4 is 5 (mm).

From Table 5, it can be seen that the ten-point average roughness (four-point average) of the roughened surface area formed on each surface of the side reinforcing member of the present invention is greater when a 16-mesh (#16) alumina grid is used than when a 20-mesh (#20) alumina grid is used.

Table 6 confirms that the four-point average spacing of the rough surface area formed on each side of the side reinforcing member of the present invention is smaller when a 20-mesh (#20) alumina grid is used than when a 16-mesh (#16) alumina grid is used. Table 6 also confirms that the four-point average spacing of the rough surface area formed on each side of the side reinforcing member of the present invention is smaller when the air pressure of the shot blasting device is reduced.

From Table 7, it can be seen that the arithmetic mean slope four-point average of the rough surface area formed on each surface of the side reinforcing member of the present invention is slightly larger when a 16 mesh (#16) alumina grid is used than when a 20 mesh (#20) alumina grid is used. In addition, the air pressure and shot time of the shot blasting device have little effect on the arithmetic mean slope four-point average.

The inventors then cast the reinforcing member of the present invention into an aluminum alloy to produce an aluminum alloy member of the specified shape shown in Figure 3. Specifically, the reinforcing member of the present invention was attached to a specified position in a mold for forming the aluminum alloy member, and molten aluminum alloy (ADC12) was injected into the mold at high pressure by die casting to produce the aluminum alloy member. As a comparative example, an aluminum alloy member of the same shape was also produced in which the reinforcing member of the present invention was replaced with a reinforcing member of the comparative example. Four reinforcing members of the present invention and four reinforcing members of the comparative example were produced under the same conditions as in Example 1.

From one of the obtained aluminum alloy members, a portion including both the reinforcing member of the present invention and the aluminum alloy portion was cut, and two tensile test pieces (size: 5 mm x 10 mm x length 30 mm) of the present invention were taken at arbitrary positions a and b (see FIG. 3). Similarly, two tensile test pieces (size: 5 mm x 10 mm x length 30 mm) of the comparative example were taken by cutting at the same positions a and b from the aluminum alloy member as the comparative example. The tensile test piece of the present invention includes the boundary between the reinforcing member of the present invention and the aluminum alloy portion. The tensile test piece of the comparative example includes the boundary between the reinforcing member of the comparative example and the aluminum alloy portion. The direction of taking the tensile test piece of the present invention and the tensile test piece of the comparative example was a direction including the boundary surface perpendicular to the axis of the test piece. Using the tensile test piece of the present invention and the tensile test piece of the comparative example, a tensile test conforming to the provisions of JIS Z 2241 was performed, and the tensile strength (boundary strength) was measured.

The results are shown in Table 8. The boundary strength ratio in Table 8 represents the ratio (N2/N1) of the boundary strength N2 of the tensile test piece on the present invention side to the boundary strength N1 of the reinforcement member on the comparative example side. In addition, in Table 8, the four sets of the reinforcement member on the comparative example side and the tensile test piece on the present invention side that are compared in boundary strength are represented as No. 1 to No. 4. The average boundary strength ratio of the four tensile test pieces on the present invention side at position a was 1.72, and the average boundary strength ratio of the four tensile test pieces on the present invention side at position b was 2.66. In addition, looking at each boundary strength ratio, the minimum value was 1.33, the maximum value reached 3.55, and half of them exceeded 2. From the above results, it was confirmed that the boundary strength N2 of the tensile test piece on the present invention side was greater than the boundary strength N1 of the reinforcement member on the comparative example side.

As is clear from the results of the tensile tests above, it has been confirmed that the sintered body of the present invention has a greater boundary strength than conventional bodies when cast-in with a light metal alloy such as an aluminum alloy.

Next, in order to confirm the effect of the vacuum sintering process in the vacuum sintering step S102, the inventors prepared a sintered precursor (hereinafter referred to as the sintered precursor of the present invention) made under the same conditions as in Example 1, and a sintered precursor (hereinafter referred to as the sintered precursor of the comparative example) that had been sintered under a nitrogen atmosphere. The sintered precursor of the present invention is a reinforcing member that has been subjected to a vacuum sintering process (vacuum sintering step S102) but not a blasting process. The sintered precursor of the comparative example is a reinforcing member that has been provided by replacing the vacuum sintering process with a sintering process under a nitrogen gas atmosphere (atmospheric sintering process) and has not been blasted.

Then, the sintered precursor of the present invention and the sintered precursor of the comparative example were cast in an aluminum alloy to produce 10 aluminum alloy members, five of each, similar to those in Example 3. Five test pieces, a total of 10, similar to those in Example 3 were taken from each aluminum alloy member. In the five test pieces containing the sintered precursor of the present invention, no peeling was observed at the boundary between the sintered precursor of the present invention and the aluminum alloy part in any of the five test pieces. However, in the five test pieces containing the sintered precursor of the comparative example, peeling was observed at the boundary between the sintered precursor of the comparative example and the aluminum alloy part in three of the five test pieces. As a result, it was confirmed that the sintered precursor of the present invention had superior boundary strength to the sintered precursor of the comparative example, even without measuring the boundary strength in a tensile test. This confirmed that vacuum sintering is superior to atmospheric sintering in terms of boundary strength.

The sintered body and the method for manufacturing the sintered body of the present invention are not limited to the above-mentioned embodiment, and various modifications can be made without departing from the gist of the present invention.

REFERENCE SIGNS LIST 1 sintered body 2 internal combustion engine 3 bearing portion 4 rough surface region 5 uneven portion 6 recessed portion 7 protrusion portion 8 alumina region 9 free Cu phase 9A first free Cu phase 9B second free Cu phase 10 void 11 aluminum alloy 12 air space 20 inner peripheral surface side cast-in insert portion 100 reinforcing member 110 main body portion 120 extension portion 130 inner peripheral surface 140 outer peripheral surface 150 through hole 160 front surface 170 rear surface S100 powder mixing process S110 molding process S120 machining process S130 vacuum sintering process S140 blasting process

Claims (16)

A method for producing a sintered body that is cast-in with a light metal alloy, comprising the steps of:
A molding process of forming a metal powder having a composition, in mass%, containing 0.5 to 2.5% C, 5 to 40% Cu, and the remainder being mainly composed of Fe, into a desired shape to obtain a green compact;
a vacuum sintering step of sintering the green compact under vacuum to provide a sintered body;
a blasting process for providing a rough surface region having a plurality of projections and recesses on the surface of the sintered body by blasting particles containing alumina particles against at least a part of the surface of the sintered body;
The present invention is characterized in that it comprises
A method for manufacturing a sintered body. The metal powder includes reduced iron powder produced by a reduction method or a mechanical pulverization method.
A method for producing the sintered body according to claim 1. The average of the arithmetic mean slope RΔa of the protrusions constituting the convex portion of the unevenness portion derived in each of the four regions in the rough surface region is defined as the arithmetic mean slope four-point average, and the average of the average spacing S of the apexes of the adjacent protrusions derived in each of the four regions in the rough surface region is defined as the average spacing four-point average,
In the blasting process, the blasting is performed so that the arithmetic mean slope four-point average is 0.34 or more and the average interval four-point average is 116.9 μm or less.
A method for producing the sintered body according to claim 1. In the blasting process, the blasting is performed so that the four-point average interval is 90 μm or more.
A method for producing the sintered body according to claim 3. The blasting process is characterized in that the alumina particles having a particle size distribution in the range of 300 to 1700 μm are used.
A method for producing the sintered body according to claim 3. In the blasting process, an alumina region made of alumina is provided so as to be exposed on the surface of the roughened surface region.
A method for producing the sintered body according to claim 1. the alumina region extends from a deepest portion of a depression portion constituting a concave portion of the uneven portion to an inner side of the sintered body in a depth direction of the depression portion.
A method for producing the sintered body according to claim 6. At least a part of the alumina region is in contact with the light metal alloy when the sintered body is cast-in with the light metal alloy.
A method for producing the sintered body according to claim 6. In the vacuum sintering step, the pressure in the pores of the sintered body near the surface of the rough surface region is made vacuum,
In the blasting process, a free Cu phase that fills the pores is exposed on the surface of the roughened surface region,
When the sintered body is cast-in with the light metal alloy, the molten metal of the light metal alloy comes into contact with the free Cu phase that blocks the voids, and the molten metal of the light metal alloy moves into the voids due to a pressure difference between the inside and outside of the voids.
A method for producing the sintered body according to claim 1. A sintered body cast in a light metal alloy,
The sintered body has a composition, in mass%, containing C: 0.5 to 2.5%, Cu: 5 to 40%, and the remainder being mainly composed of Fe;
A rough surface area having a plurality of projections and recesses on an outer circumferential surface of the rough surface area;
The average of the arithmetic mean slopes RΔa of the protrusions constituting the convex portions of the unevenness, which are derived in each of the four regions in the rough surface region, is defined as the arithmetic mean slope four-point average, and the average of the average spacing S of the apexes of the adjacent protrusions, which are derived in each of the four regions in the rough surface region, is defined as the average spacing four-point average,
The four-point average of the arithmetic mean slope is 0.34 or more, and the four-point average of the average spacing is 116.9 μm or less.
Sintered body. The four-point average interval is 90 μm or more.
The sintered body according to claim 10. The rough surface region is made of alumina and has an alumina region exposed on a surface of the rough surface region.
The sintered body according to claim 10. the alumina region extends from a deepest portion of a depression portion constituting a concave portion of the uneven portion to an inner side of the sintered body in a depth direction of the depression portion.
The sintered body according to claim 12. A sintered body cast in a light metal alloy,
The sintered body has a composition, in mass%, containing C: 0.5 to 2.5%, Cu: 5 to 40%, and the remainder being mainly composed of Fe;
A rough surface area having a plurality of projections and recesses on an outer circumferential surface of the rough surface area;
The rough surface region is characterized in that it has an alumina region exposed on at least a portion of the surface of the rough surface region and made of alumina.
Sintered body. When the sintered body is cast-in with the light metal alloy, at least a part of the surface of the alumina region forms a contact region with which the light metal alloy comes into contact.
The sintered body according to claim 14. A sintered body cast in a light metal alloy,
The sintered body has a composition, in mass%, containing C: 0.5 to 2.5%, Cu: 5 to 40%, and the remainder being mainly composed of Fe;
The sintered body has a surface filled with a free Cu phase and a vacuum void inside,
When the sintered body is cast-in with the light metal alloy, the molten metal of the light metal alloy comes into contact with the free Cu phase that blocks the voids, and the molten metal of the light metal alloy moves into the voids due to a pressure difference between the inside and outside of the voids.
Sintered body.