JP6867255B2 - Complex with low coefficient of thermal expansion and high adhesion - Google Patents

Description

The present invention relates to a composite obtained by impregnating an iron-based sintered body with an aluminum alloy, which is used as a reinforcing material in an aluminum alloy member used in an internal combustion engine of an automobile or the like, and particularly has a bonding strength. And a decrease in the coefficient of thermal expansion.

In recent years, from the viewpoint of preserving the global environment, there has been a strong demand for improving the fuel efficiency of automobiles and the like. In response to such demands, the weight of engines has been reduced, and aluminum alloy engines are becoming popular. However, the strength of the aluminum alloy is lower than that of the conventional cast iron, and there arises a problem that the strength is insufficient especially for a member to which a high load is applied at a high temperature. In addition, aluminum alloys have a problem that they lack material properties as structural parts for automobiles, such as having a higher coefficient of thermal expansion than conventional cast iron.

As a method for improving the material properties of an aluminum alloy member, for example, there is a technique of casting and wrapping different materials by gravity casting, die casting, etc., and a technique of compounding with different materials.

For example, in Patent Document 1, a metal porous body is held in a mold, a molten aluminum alloy is injected into the mold, and then the metal porous body is subjected to a high-pressure solidification casting method with ^{a pressing force of 400 kg / cm 2 or more.} The aluminum alloy casting material is molded and then the aluminum alloy casting material is heated and held at a temperature of 450 to 550 ° C. for 1 to 10 hours to hold the metal porous body and the metal porous material at the boundary between the metal porous body and the aluminum alloy. A method for producing an aluminum alloy casting, which is subjected to an intermetal compound formation treatment for forming a compound layer with a body metal, is described. According to the technique described in Patent Document 1, the bonding strength between the metal porous body and the aluminum alloy is high, and the durability is improved.

Further, Patent Document 2 includes an iron-based porous metal sintered body having a three-dimensional lattice structure having pores and a light metal impregnated into the pores of the porous metal sintered body and solidified, and is porous. A metal sintered composite material in which the metal constituting the metal sintered body is set to HV200 to 800 in microvickers hardness is described. In the technique described in Patent Document 2, at least one of Cr, Mo, V, W, Mn, and Si is 2 to 70%, carbon is 0.07 to 8.2%, unavoidable impurities, and residual iron by weight. A powder molded body formed by using an iron-based raw material powder having a composition is sintered, and an iron-based porous body having a gas-burnable composition having pores and a three-dimensional lattice structure having a volume ratio of 30 to 88% is obtained. A quality metal sintered body is prepared, and after gas quenching is performed to cool the porous metal sintered body in a gas, the pores of the porous metal sintered body are impregnated with a molten metal of a light metal and solidified to form a composite. It is supposed to be.

Further, Patent Document 3 describes a metal porous preformed body which is based on iron or an iron-based metal and contains 10 to 40% by weight of Cr, and is predetermined from the completion of pouring to the impregnation of molten metal. A technique is described in which a metal porous premold is impregnated with molten metal under pressure to form a metal composite member by a casting method in which a time lag exists.

Further, Patent Document 4 describes a porous metal sintered body for reinforcing a light alloy and a light alloy composite member using the same. The porous metal sintered body for reinforcing a light alloy described in Patent Document 4 is a porous metal sintered body obtained by pressing and sintering a mixed powder containing an alloy powder, and is a porous metal sintered body. However, a light alloy having a pore ratio of 15 to 50%, having pores having a diameter of more than 5 μm among the pores of 80% or more with respect to the total pore ratio, and having a ring strength of 200 MPa or more. A porous metal sintered body for reinforcing light alloys with excellent impregnation properties. Such a porous metal sintered body can be impregnated with a light alloy to form a composite member. According to the technique described in Patent Document 4, it is said that a porous metal sintered body for reinforcing a light alloy having excellent ring strength and excellent bondability after casting can be stably produced.

Further, Patent Document 5 describes an iron-based sintered body having excellent wrapability in a light metal alloy. The iron-based sintered body described in Patent Document 5 contains C: 0.5 to 2.5% and Cu: 5 to 40% in mass%, and has a composition consisting of the balance Fe and unavoidable impurities, vacancies, and substrates. An iron-based sintered body having a structure in which a free Cu phase is dispersed, an average coefficient of thermal expansion from room temperature to 200 ° C of 13.5 × 10 ^-6 / ° C or less, and a surface roughness of 10 to 100 μm in Rz. Is. In the iron-based sintered body described in Patent Document 5, the surface of the iron-based sintered body is shot-blasted and has the above-mentioned surface roughness Rz. Further, the iron-based sintered body described in Patent Document 5 contains pores, but can prevent deterioration of the characteristics of the iron-based sintered body due to permeation of the light metal alloy as pores that exist independently or intermittently from each other. It is supposed to be.

Special Fair 02-30790 Japanese Unexamined Patent Publication No. 08-319504 Japanese Unexamined Patent Publication No. 2001-276961 Japanese Unexamined Patent Publication No. 2003-7355 Japanese Unexamined Patent Publication No. 2004-204298

However, the technique described in Patent Document 1 has a problem that it is necessary to perform an intermetallic compound formation treatment, the manufacturing process becomes complicated, and the manufacturing cost rises. Further, in the technique described in Patent Document 2, it is necessary to contain a large amount of alloying elements such as Cr, Mo, and V so that gas quenching is possible, which is expensive and economical as a metal sintered composite material. There was a problem that it was disadvantageous. Further, in the techniques described in Patent Documents 3 and 4, it is necessary to preheat the metal porous premold to a high temperature in order to sufficiently impregnate the inside of the metal porous premold. There was a problem of becoming.

Further, in the techniques described in Patent Documents 4 and 5, there is a problem that the joint strength varies depending on the shape factor of the composite and the wall thickness of the aluminum alloy member, especially in the thin part, and the desired adhesion cannot be secured. , There was a problem that it was inferior in recyclability. Further, in the technique described in Patent Document 5, shot blasting is performed, which causes a problem that the manufacturing cost rises.

Further, recently, from the viewpoint of reducing the weight of an automobile body and improving fuel efficiency, there is a demand for compactification of each automobile member, and further improvement of functions of each member is required. In particular, in order to reduce the clearance between the miniaturized engine block and the crankshaft, it is strongly requested to compactly arrange it in a narrower space inside the engine block and to have both a low coefficient of thermal expansion and high interface (joint) strength. Has been done.

The present invention solves the problems of the prior art and is used by arranging and using a reinforcing material in the member in order to improve the strength of the aluminum alloy member. A composite obtained by impregnating an iron-based sintered body with an aluminum alloy. The average coefficient of thermal expansion from room temperature to 200 ° ^{C is as low as 14.0 × 10 -6} / ° C or less, and the boundary strength between the composite and the aluminum alloy constituting the member is 10 MPa or more. It is an object of the present invention to provide a composite having both a high coefficient of thermal expansion and a high coefficient of thermal expansion and a high bonding strength.

In order to achieve the above object, the present inventors first diligently examined various factors affecting the boundary (interface) strength between the composite and the aluminum alloy in the aluminum alloy member. As a result, first, the iron-based sintered body used for the composite was made into an iron-based sintered body containing Cu, having a matrix as pearlite, and having a structure in which the free Cu phase was dispersed in the matrix. The pores of the iron-based sintered body are made continuous pores, and the surface of the iron-based sintered body is 10 to 60 μm in surface roughness Rz in accordance with JIS B 0601 (1982) without further shot blasting. We came up with the idea of using a porous iron-based sintered body with a relatively rough surface texture in the range of. By using such a porous iron-based sintered body as the iron-based sintered body to be used, when it is placed in an aluminum alloy member and impregnated with the aluminum alloy, it can be combined with a composite having high bonding strength. Moreover, it was found that such a composite has a ^{low coefficient of thermal expansion of 14.0 × 10 -6} / ° C or less from room temperature to 200 ° C.

The reason for this has not been clarified at this time, but the present inventors consider it as follows. Cu and Al react with each other to easily form a compound. Therefore, in a porous iron-based sintered body containing Cu and having a structure in which free Cu is dispersed in the matrix phase, free Cu is also dispersed on the inner surface of the pores, and the pores of the porous iron-based sintered body are formed. When the aluminum alloy is impregnated, the free Cu and Al dispersed on the inner surface of the opened pores react with each other to improve the impregnation property of the aluminum alloy into the pores of the sintered body and bond as a composite. It is thought that the strength will increase. Furthermore, by making the pores continuous and not performing the shot blasting treatment, there is no blockage of the continuous pores, the aluminum alloy can be easily impregnated deeply, and the surface roughness is made relatively rough. We believe that this is the result of complicated actions such as the ease of impregnation of aluminum alloy. In addition, such a complex can be a complex having both the above-mentioned high bonding strength and the above-mentioned low coefficient of thermal expansion at a relatively low cost without containing an alloying element other than C and Cu. , Has the advantage.

The present invention has been completed with further studies based on such findings. That is, the gist of the present invention is as follows.
(1) A composite obtained by impregnating an iron-based sintered body with an aluminum alloy, wherein the iron-based sintered body is C: 0.4 to 1.5% and Cu: 10% or more and less than 20% in mass%. Containing, composition consisting of balance Fe and unavoidable impurities, vacancy ratio: 15 to 30% by volume, and vacancy is continuously present, the base is pearlite, and the free Cu phase is dispersed in the base. It is a porous iron-based sintered body having a texture of 10 to 60 μm and having a surface roughness Rz of 10 to 60 μm in accordance with the provisions of JIS B 0601 (1982) without being subjected to shot blasting treatment. The composite has an average thermal expansion coefficient of 14.0 × 10 ^-6 / ° C or less from room temperature to 200 ° C., and the boundary strength between the impregnated composite and the aluminum alloy in a state of being cast and wrapped in an aluminum alloy is 10 MPa. A complex characterized by the above.
(2) Iron-based powder, copper powder, graphite powder, and lubricant powder are mixed to form a mixed powder, and then the mixed powder is filled in a mold and pressure-molded to obtain a green compact. The green compact is sintered to form an iron-based sintered body having a predetermined shape, then the iron-based sintered body is cast and wrapped in an aluminum alloy, and the pores of the iron-based sintered body are impregnated with the aluminum alloy. In the method for producing a composite to be a composite, the iron-based powder is adjusted to a particle size distribution that passes through a 60-mesh sieve (-60 mesh) and does not pass through a 350-mesh sieve (+350 mesh). , The copper powder is blended so as to be 10% or more and less than 20% in mass% with respect to the total amount of the iron-based powder, the copper powder and the graphite powder, and the graphite powder is mixed with the iron-based powder, the copper powder and the graphite. The iron-based sintered body is mass-produced by blending so that the mass% with respect to the total amount with the powder is 0.4 to 1.5%, and adjusting the pressure molding conditions and / or the sintering conditions of the green compact. %, C: 0.4 to 1.5%, Cu: 10% or more and less than 20%, composition consisting of balance Fe and unavoidable impurities, vacancy rate: 15 to 30% by volume, and continuous vacancy It has a structure in which the free Cu phase is dispersed in the matrix, and has a surface roughness Rz of 10 in accordance with JIS B 0601 (1982) without performing shot blasting. A porous iron-based sintered body of ~ 60 μm is used, and the impregnated composite is cast and wrapped in an aluminum alloy with ^{an average thermal expansion coefficient of 14.0 × 10 -6 / ° C or less from room temperature to 200 ° C.} A method for producing a composite, which comprises a composite having a boundary strength between the impregnated composite and the aluminum alloy in a state of 10 MPa or more.
(3) The present invention is characterized in that the lubricant powder is blended so as to be 0.3 to 3.0 parts by mass with respect to 100 parts by mass of the total amount of the iron-based powder, the copper powder and the graphite powder. Method of manufacturing the complex to be used.
(4) In (1), the porous iron-based sintered body has one or a plurality of through holes in the wall thickness direction of the porous iron-based sintered body, and the through holes are shot blasted. A composite characterized by having a surface-like inner surface having a surface roughness Rz of 10 to 60 μm in accordance with JIS B 0601 (1982).
(5) In (2) or (3), the porous iron-based sintered body has one or more through holes in the wall thickness direction of the porous iron-based sintered body, and the through holes are formed. , A method for producing a composite, which is a sintered body having a surface-like inner surface having a surface roughness Rz of 10 to 60 μm in accordance with JIS B 0601 (1982) without subjecting to shot blasting. ..

According to the present invention, the composite ^{has a low coefficient of thermal expansion of 14.0 × 10 -6} / ° C or less from room temperature to 200 ° C., and is further cast and wrapped in an aluminum alloy in an aluminum alloy member. The boundary (interfacial) strength between the composite material impregnated with the aluminum alloy and the aluminum alloy constituting the member is as high as 10 MPa or more, and the adhesion is excellent. The combined composite can be manufactured relatively inexpensively and stably, which is extremely effective in the industry. Further, according to the present invention, even if the member is made compact, it can be easily formed into a complex having a desired bonding strength, and there is also an effect that weight reduction of automobiles and the like and improvement of fuel efficiency can be further promoted. Further, according to the present invention, iron-based materials can be removed by magnetic sorting after crushing at the time of disposal, and moreover, they do not contain alloying elements other than Fe, C and Cu, and are not contaminated with other elements. It also has the effect of being highly recyclable. In addition, Fe and Cu are one of the elements contained in the aluminum alloy, and even if they are mixed in the aluminum alloy, they do not cause a big problem, and the aluminum alloy-based material can be recycled, and the recyclability is also excellent. is there. Further, according to the present invention, it is effective in reducing the clearance between the journal portion of the internal combustion engine and the iron-based shaft.

It is a schematic explanatory drawing which shows typically the shape of the aluminum alloy member used in an Example, and the iron-based sintered body (complex) which was cast and wrapped. It is schematic explanatory drawing which shows another example of the shape of the aluminum alloy member used in the Example and the cast-wrapped iron-based sintered body (complex) schematically.

The composite of the present invention is a composite obtained by impregnating an iron-based sintered body with an aluminum alloy, and in the composite of the present invention, the iron-based sintered body is a porous iron-based sintered body.

The "porous iron-based sintered body" referred to here has a basic composition of C: 0.4 to 1.5%, Cu: 10% or more and less than 20%, and the balance Fe and unavoidable impurities in mass%. Pore ratio by volume: 15 to 30%, pores are continuously present, the matrix is pearlite, and the structure has a structure in which the free Cu phase is dispersed in the matrix, and shot blasting is performed. A porous iron-based sintered body with a surface roughness Rz of 10 to 60 μm that complies with JIS B 0601 (1982).

First, the reason for limiting the composition of the iron-based sintered body will be described. In the following, the mass% in the composition is simply expressed as%.
C: 0.4-1.5%
C is an element that increases the strength and hardness of the sintered body, and in the present invention, it is required to contain 0.4% or more in order to secure the desired strength and to make the matrix a pearlite structure having abundant machinability. On the other hand, if the content exceeds 1.5%, the carbide becomes coarse and the machinability is rather lowered. Therefore, C was limited to the range of 0.4 to 1.5%. It is preferably 0.6 to 1.0%.

Cu: 10% or more and less than 20%
Cu dissolves to increase the strength of the sintered body, and at the same time, it is dispersed in the matrix phase as a free Cu phase and also dispersed in the opening surface of the pores, and when the pores are impregnated with the aluminum alloy, It has the effect of reacting with the aluminum alloy to increase the bonding strength between the iron-based sintered body and the aluminum alloy. If the Cu content is less than 10%, even if the aluminum alloy is impregnated by die casting, the free Cu phase content is too small to achieve the desired composite. On the other hand, when it is contained in a large amount of 20% or more, the mechanical properties such as the strength of the complex are significantly lowered, and the coefficient of thermal expansion of the complex becomes larger than a desired value. Therefore, Cu was limited to the range of 10% or more and less than 20%.

The rest of the components other than those mentioned above consist of Fe and unavoidable impurities.
Further, in the porous iron-based sintered body used in the present invention, in addition to the above composition, the volume fraction has a pore ratio of 15 to 30%, and pores are continuously present, and the base is pearlite. It has a structure in which the free Cu phase is dispersed in the matrix.
The base of the porous iron-based sintered body used in the present invention is pearlite. Among the base structures, the pearlite base has good machinability and high thermal conductivity, which is advantageous for compounding. Therefore, the base of the iron-based sintered body used in the present invention is limited to pearlite.

Further, the porous iron-based sintered body used in the present invention has a structure in which the free Cu phase is dispersed in the above-mentioned matrix. The free Cu phase has the effect of reacting with the aluminum alloy impregnated in the pores during the production of the composite to firmly bond the aluminum alloy and the iron-based sintered body, and increases the bonding strength as the composite. .. The amount of dispersion of the free Cu phase is determined according to the Cu content of the iron-based sintered body or the amount of alloying elements contained therein, and is not particularly limited. In the composition range of the porous iron-based sintered body used in the present invention, Cu is contained above the solid solution limit, and a large amount of Cu is dispersed as a free Cu phase.

Further, the porous iron-based sintered body used in the present invention is a sintered body having a volume fraction of 15 to 30%.
Pore rate: 15 to 30%
If the pore ratio is less than 15%, the molten aluminum alloy will not impregnate the pores when the iron-based sintered body is cast and wrapped with the aluminum alloy, or when the aluminum alloy is impregnated, and the bonding strength will decrease. .. On the other hand, if it exceeds 30%, there are too many pores and the strength is lowered too much, which causes a decrease in the strength of the member. In addition, the coefficient of thermal expansion exceeds a desired value and becomes large. Therefore, the porosity of the iron-based sintered body used was limited to the range of 15 to 30% in terms of volume fraction. It is preferably 17 to 28%.
The "vacancy rate" referred to here is the total hole rate, and is calculated by converting from the density measured by the Archimedes method.

Further, in the porous iron-based sintered body used in the composite of the present invention, the pores need to be continuously present in order to impregnate the pores with the aluminum alloy. Here, "there are continuous vacancies" means the ratio of the continuous vacancies to the total vacancies (= {(continuous vacancies) / (total vacancies)} x 100%). Is more than 50%. The "total pore amount" shall be calculated by converting from the density measured by Archimedes' method. The "continuous pore amount" is obtained by immersing the sintered body in a liquid wax or the like for 60 minutes, permeating the wax or the like, converting the weight change amount before and after the permeation to obtain the amount, and determining the continuous pore amount. And.

Further, the porous iron-based sintered body used in the present invention is an iron group having a surface texture having a surface roughness Rz of 10 to 60 μm in accordance with JIS B 0601 (1982) without being subjected to shot blasting treatment. It is a sintered body. Rz specified in JIS B 0601 (1982) represents the surface texture including swell and roughness according to the cross-sectional curve, and is desirable as an index of adhesion (adhesion area). When the shot blasting treatment is performed, the vacancies near the surface are closed, the amount of continuous vacancies decreases, and the desired ratio of the amount of continuous vacancies cannot be secured. Therefore, the above-mentioned surface roughness Rz is set to the value in the state of being sintered without the shot blasting treatment.

If the surface roughness Rz of the surface of the iron-based sintered body is less than 10 μm, a sufficient surface area cannot be obtained when the iron-based sintered body is cast and wrapped, and the adhesion to the aluminum alloy is insufficient. On the other hand, if the surface roughness Rz exceeds 60 μm, the dimensional accuracy is insufficient and cracks are likely to occur on the outermost surface. Therefore, the porous iron-based sintered body to be used is an iron-based sintered body having a surface texture having a surface roughness Rz of 10 to 60 μm.

The composite obtained by impregnating the above-mentioned porous iron-based sintered body with an aluminum alloy is a composite in which the pores are impregnated with an aluminum alloy, and is a composite in which the porous iron-based sintered body is impregnated with the aluminum alloy. It is a composite having a boundary strength of 10 MPa or more with an aluminum alloy. Moreover, even if this complex is impregnated with an aluminum alloy, the average coefficient of thermal expansion from room temperature to 200 ° C is 14.0 × 10 ^-6 / ° C or less. The average coefficient of thermal expansion from room temperature to 200 ° C is preferably 13.5 × 10 ^-6 / ° C or less.

Next, a preferable method for producing the complex of the present invention will be described.
The iron-based powder, Cu powder, graphite powder, or alloy powder are mixed to obtain a mixed powder, and then the mixed powder is formed into a green compact having a predetermined shape. Then, the obtained green compact is sintered to obtain an iron-based sintered body. In addition, instead of iron-based powder (iron powder) and Cu powder, Fe—Cu alloy powder may be used. The Fe—Cu alloy powder may contain a powder obtained by partially alloying Cu around the iron powder. Needless to say, the blending amount of Cu powder or Fe—Cu alloy powder is adjusted so as to be the Cu content of the iron-based sintered body.

The iron-based powder passes through a 60-mesh sieve (hereinafter, also referred to as 60-mesh under or -60 mesh) and does not pass through a 350-mesh sieve (hereinafter, also referred to as 350-mesh over or +350-mesh). The powder is adjusted to the distribution.

The presence of +60 mesh particles reduces the compaction property of the mixed powder. On the other hand, the presence of -350 mesh particles makes it difficult for continuous pores to form, and the impregnation property of the aluminum alloy decreases. If the particles of -60 to +100 mesh are less than 40% of the total powder, it is advantageous to obtain a green compact having a desired porosity.

The iron-based powder having the above-mentioned particle size distribution is mixed with Cu powder, graphite powder, and lubricant powder together to obtain a mixed powder.

Graphite powder is blended to adjust the C content of the iron-based sintered body. The blending ratio is preferably 0.4 to 1.5% in mass% with respect to the total amount of the mixed powder. If the blending ratio is less than 0.4%, it becomes difficult to secure the desired strength. On the other hand, if the compounding ratio exceeds 1.5%, the carbides become coarse and the strength decreases. The particle size of the graphite powder is preferably 0.1 to 10 μm. If the particle size is less than 0.1 μm, handling becomes difficult, while if it exceeds 10 μm, uniform dispersion becomes difficult.

Further, the lubricant powder is blended in the mixed powder in order to improve the moldability at the time of powder compaction and increase the powder compact density. The blending amount in the mixed powder is preferably 0.3 to 3.0 parts by mass with respect to 100 parts by mass of the total amount of the mixed powder (total amount of iron-based powder, Cu powder, and graphite powder). The lubricant powder is preferably a commonly used lubricant powder such as zinc stearate.

Such a mixed powder is charged into a mold and pressure-molded to obtain a green compact having a shape substantially equal to a predetermined shape. The method for forming the green compact is not particularly limited, but it is preferable to use a forming press or the like. In the case of pressure molding, it is preferable to adjust the pressure molding conditions in relation to the sintering conditions so as to obtain the desired sintered body structure described above.

The pressure-molded green compact is then sintered to form an iron-based sintered body having a predetermined shape. Needless to say, the sintering conditions are adjusted so as to obtain the desired sintered body structure described above.

Here, the sintering is preferably performed at a sintering temperature of 1000 to 1200 ° C. in an inert gas atmosphere, a non-oxidizing atmosphere, or the like.

The sintered body thus obtained had a volume fraction of pore ratio of 15 to 30%, pores were continuously present, the matrix was pearlite, and the free Cu phase was dispersed in the matrix. A porous iron-based sintered body having a structure and having a surface roughness Rz of 10 to 60 μm in accordance with JIS B 0601 (1982) without being subjected to shot blasting treatment.

Further, the porous iron-based sintered body thus obtained is mounted on the corresponding portion of the mold forming the aluminum alloy member, the molten aluminum alloy is injected into the mold, and high-pressure die casting or molten metal forging is performed. Therefore, it is preferable to use an aluminum alloy member in which a porous iron-based sintered body is cast and wrapped. In the aluminum alloy member thus obtained, the porous iron-based sintered body is a composite in which the pores are impregnated with the aluminum alloy. Alternatively, the porous iron-based sintered body thus obtained may be impregnated with a molten aluminum alloy by high-pressure die casting, molten metal forging, or the like to form a complex.

As the aluminum alloy injected into the mold by high-pressure die casting or the like, any ordinary aluminum alloy such as ADC12 can be applied.

In the composite thus obtained, the pores are impregnated with an aluminum alloy, and the coefficient of thermal expansion of the composite is 14.0 × ^10-6 / K or less on average from room temperature to 200 ° C., and the aluminum alloy It is a composite in which the boundary (interfacial) strength between the composite impregnated with the aluminum alloy and the aluminum alloy constituting the member is 10 MPa or more in the state of being cast and wrapped in.

The porous iron-based sintered body used in the present invention is preferably a sintered body that has been processed into a predetermined shape and has one or more through holes in the wall thickness direction.

The porous iron-based sintered body used in the present invention is, for example, an aluminum alloy such as a cylinder block of an aluminum alloy engine as a reinforcing material for reinforcing a journal portion (bearing portion) that pivotally supports a crankshaft of an iron-based material. It is cast and wrapped in a manufacturing member and used as a composite.

As a general shape of the reinforcing material for reinforcing the bearing portion of the cylinder block, the shape schematically shown by the dotted line in FIG. 1 can be exemplified. That is, the reinforcing material corresponds to a concave bearing surface having a semicircular arc-shaped cross section of the journal portion (bearing portion) and continuously formed along the extending direction of the central axis, and has a semicircular to U-shaped cross section and a center. It has a shape composed of an inner peripheral surface having a shape continuous along the axial extension direction and an outer peripheral surface other than the inner peripheral surface.

In this case, depending on the shape of the porous iron-based sintered body to be cast and wrapped, the boundary (interfacial) strength between the composite impregnated with the aluminum alloy in the state of being cast and wrapped in the aluminum alloy and the aluminum alloy constituting the member may be high. There may be concerns about instability. For example, when the porous iron-based sintered body as a reinforcing material is thick and large, the circumference of the molten aluminum alloy molten metal poured during casting and packaging depends on the position of the sintered body. There is concern that it will be heterogeneous. When the circumference of the molten metal becomes inhomogeneous, the strength of the boundary (interface) between the composite impregnated with the aluminum alloy and the aluminum alloy constituting the member becomes inhomogeneous, and there may be a place where the boundary (interface) strength decreases. There is.

In such a case, the porous iron-based sintered body to be cast and wrapped has one or more through holes communicating the inner peripheral surface and the outer peripheral surface as schematically shown by a dotted line in FIG. It is preferable to use a porous iron-based sintered body having a bored shape. By providing a through hole that connects the inner peripheral surface and the outer peripheral surface, the circulation of the molten aluminum alloy molten metal poured during casting is improved, and the molten metal is uniformly supplied to the outer peripheral surface and the inner peripheral surface. The boundary strength is improved and the inhomogeneity of the boundary strength is easily eliminated.

In the case of a reinforcing material having a general shape in which the inner peripheral surface and the outer peripheral surface cannot be specified, which is different from the reinforcing material for reinforcing the bearing portion of the cylinder block described above, the through hole communicating with the inner peripheral surface and the outer peripheral surface is replaced with a porous material. It is preferable to provide through holes in the wall thickness direction of the quality iron-based sintered body. As a result, the circulation of the molten aluminum alloy molten metal poured during casting and packaging is improved, the molten metal is uniformly supplied regardless of the position, the boundary strength is improved, and the composite and members impregnated with the aluminum alloy are formed. The inhomogeneity of the strength of the boundary (intersection) with the constituent aluminum alloy can be easily eliminated.

As described above, the porous iron-based sintered body used in the present invention has a desired surface roughness without being subjected to shot blasting treatment, which is a surface roughness conforming to JIS B 0601 (1982). It can retain the surface texture of 10 to 60 μm at Rz. This also applies to the inner surface of the through hole, and there is an advantage that an inner surface exhibiting a desired surface roughness can be secured without performing shot blasting treatment, and it is not necessary to perform shot blasting treatment on the inner surface of the through hole. is there.

Hereinafter, the present invention will be further described based on Examples.

(Example 1)
As the iron-based powder, Cu powder and graphite powder are blended in the pure iron powder (iron-based powder) adjusted to have a particle size distribution that passes through a 60-mesh sieve and does not pass through a 350-mesh sieve (mass%). ), Further, the lubricating powder (lubricating particle powder) was blended in the blending amount (part by mass) shown in Table 1, and mixed and kneaded with a mixer to obtain a mixed powder. The average particle size of the mixed powder was 150 μm. As the average particle size, a diameter D50 was used in which the cumulative particle size distribution measured by the laser diffraction / scattering method was 50%.

The obtained mixed powder was filled in a mold and pressure-molded by a molding press to obtain a green compact having the shape shown by the dotted line in FIG. Then, these green compacts were subjected to a sintering treatment to obtain an iron-based sintered body. The sintering treatment was performed at a temperature in the range of 1000 to 1200 ° C. in a nitrogen gas atmosphere. The porosity was adjusted by the molding pressure.

First, the composition and porosity of the obtained iron-based sintered body were measured, and the structure was observed.
The porosity (volume fraction) was converted from the density measured by Archimedes' method. It was confirmed whether the vacancies existing in the sintered body were "continuous vacancies". The sintered body is immersed in liquid wax or the like for 60 minutes, the wax or the like is permeated into the pores, and the amount is calculated by converting from the amount of weight change before and after the permeation. Ratio of the amount of vacancies (= {(amount of continuous vacancies) / (total amount of vacancies)} x 100%)
The ratio of the amount of continuous vacancies defined in is calculated, and when the value exceeds 50, it is evaluated as "continuous vacancies". Here, as the "total pore amount", a value converted from the density measured by the Archimedes method was used.

For the structure, a test piece for structure observation was collected from the iron-based sintered body, the cross section in the press direction was polished, and the structure was exposed by corrosion with a nital solution. The presence or absence of the phase was measured. The amount of dispersion of the free Cu phase was determined by calculating the area ratio by surface analysis using EPMA in the state of being polished.

Moreover, the surface roughness of the obtained iron-based sintered body was measured. Using the outer surface of the obtained iron-based sintered body as the measurement surface, the surface roughness Rz was measured using a stylus type surface roughness meter in accordance with the provisions of JIS B 0601 (1982).

The results obtained are shown in Table 3.

All of the porous iron-based sintered bodies (examples of the present invention) that can be used in the present invention have a composition within a predetermined range, a volume fraction of 15 to 30%, and continuous pores. , The matrix is pearlite, has a structure in which the free Cu phase is dispersed in the matrix, and has a surface roughness Rz of 10 to 60 μm in accordance with JIS B 0601 (1982) without performing shot blasting. It is a porous iron-based sintered body. On the other hand, in the comparative example of the iron-based sintered body outside the scope of the present invention, the composition is out of the range of the present invention, the porosity is out of the desired range, and the pores are not continuous or the surface. Roughness is outside the scope of the present invention.

The obtained iron-based sintered body is mounted at a predetermined position on a mold for forming an aluminum alloy member, and a molten aluminum alloy (ADC12) is injected into the mold at high pressure by die casting to form aluminum having a predetermined shape as shown in FIG. It was made of alloy. First, the obtained aluminum alloy member was cut, and the vicinity of the center of the cross section was observed with an optical microscope to investigate the presence or absence of "non-impregnated" as an internal defect. Those with defects were evaluated as "x", and those without defects were evaluated as "○".

From the obtained aluminum alloy member, a tensile test piece (size: 5 mm × 10 mm × length) including a boundary between a composite formed by impregnating an iron-based sintered body with an aluminum alloy and an aluminum alloy constituting the member. 30 mm) was collected. The sampling positions of the tensile test pieces were set at the five boundary portions a to e shown in FIG. 1, and the collecting direction of the tensile test pieces was set to the direction including the boundary surface perpendicular to the axis of the test piece. Using these tensile test pieces, a tensile test was carried out in accordance with JIS Z 2241, and the tensile strength (boundary strength) was measured. When the tensile strength (boundary strength) was 10 MPa or more, it was evaluated as “◯”, and in other cases, it was evaluated as “x”.

Further, from the obtained member, a composite obtained by impregnating an iron-based sintered body with an aluminum alloy was sampled as a test piece (size: 2 mm × 2 mm × length 20 mm), and was 200 from room temperature by a thermal expansion measuring device. The average coefficient of thermal expansion up to ° C was measured. When the average coefficient of thermal expansion was 14.0 × 10 ^-6 / ° C or less, it was evaluated as “◯”, and in other cases, it was evaluated as “×”.

The results obtained are shown in Table 4.

All of the composites of the examples of the present invention have no internal defects, the boundary strength with the aluminum alloy is 10 MPa or more regardless of the measurement position, the bonding strength as a composite is high, and the coefficient of thermal expansion as a composite is 14.0. It shows a value of × 10 ^-6 / ° C or less, which is equivalent to the coefficient of thermal expansion of iron-based materials. On the other hand, the composite (comparative example) outside the scope of the present invention has an internal defect, the boundary strength with the aluminum alloy varies depending on the measurement position, or the boundary strength with the aluminum alloy is all less than 10 MPa. Or, the coefficient of thermal expansion is large, and the risk of generating noise and vibration due to thermal expansion during operation of the internal combustion engine is increasing.
(Example 2)
The mixed powder No. f shown in Table 1 is filled in a mold, pressure-molded with a molding press under the same conditions as the sintered body No. 7 shown in Table 3, and the powder having the shape shown by the dotted line in FIG. It was a body. Further, the mixed powder No. j shown in Table 1 was filled in a mold, pressure-molded with a molding press under the same conditions as the sintered body No. 14 shown in Table 3, and the shape shown by the dotted line in FIG. 2 was formed. It was made into a green compact. Then, these green compacts were subjected to a sintering heat treatment under the same conditions as the sintered body No. 7 and the sintered body No. 14 to obtain iron-based sintered bodies No. N7 and No. N14.

Regarding the obtained sintered bodies No. N7 and No. N14, the composition and the porosity were measured and the structures were observed in the same manner as in Example 1. Further, the surface roughness of the obtained iron-based sintered body was measured in the same manner as in Example 1. The results obtained are shown in Table 5.

As described above, the sintered body No. N7 is the same mixed powder as the sintered body No. 7 of Example 1, and the sintered body No. N14 is the same mixed powder as the sintered body No. 14 of Example 1. All of the obtained iron-based sintered bodies No. N7 and No. N14 (examples of the present invention) were sintered in Example 1 under the same pressure forming conditions and the same sintering heat treatment conditions. Same as body No.7 and sintered body No.14, with a predetermined range of composition and a predetermined range of porosity, and there are continuous vacancies, the base is pearlite, and the free Cu phase is contained in the base. It is a porous iron-based sintered body that has a dispersed structure and has a surface roughness Rz within a predetermined range in accordance with the provisions of JIS B 0601 (1982) without being subjected to shot blasting treatment.

Furthermore, using the obtained iron-based sintered bodies No. N7 and No. N14, they are mounted at a predetermined position on a mold for forming an aluminum alloy member, and a molten aluminum alloy (ADC12) is die-cast into the mold at high pressure. It was injected into a member made of an aluminum alloy having a predetermined shape shown in FIG. The aluminum alloy member having the predetermined shape shown in FIG. 2 has one more through hole for communicating the inner peripheral surface and the outer peripheral surface than the aluminum alloy member having the predetermined shape shown in FIG. A quality iron-based sintered body was used.

From the obtained aluminum alloy member, a tensile test piece (size) including a boundary portion between the composite formed by impregnating the iron-based sintered body with the aluminum alloy and the aluminum alloy constituting the member, as in Example 1. : 5 mm x 10 mm x length 30 mm) was collected. The sampling positions of the tensile test pieces were set at the five boundary portions a to e shown in FIG. 2, and the collecting direction of the tensile test pieces was set to the direction including the boundary surface perpendicular to the axis of the test piece. Using these tensile test pieces, a tensile test was carried out in accordance with JIS Z 2241, and the tensile strength (boundary strength) was measured. The case where the tensile strength (boundary strength) was 10 MPa or more was evaluated as “◯”. Further, when the tensile strength (boundary strength) is 10 MPa or more and the complex No. N7, the tensile strength (boundary strength) at the same position of the complex No. 7 in Example 1 and the complex No. N14 In the case of, the tensile strength (boundary strength) at the same position of the complex No. 14 of Example 1 was evaluated as “⊚” when it was higher than the tensile strength (boundary strength).

The results obtained are shown in Table 6.

The aluminum alloy member having the predetermined shape shown in FIG. 2 has one more through hole penetrating in the wall thickness direction connecting the inner peripheral surface and the outer peripheral surface than the aluminum alloy member having the predetermined shape shown in FIG. The effect of drilling through holes was confirmed using the drilled porous iron-based sintered body. From Table 6, the obtained composite materials No. N7 and No. N14 have no internal defects, the boundary strength with the aluminum alloy is 10 MPa or more, the bonding strength as a composite is high, and the composite is as a composite. The coefficient of thermal expansion is 14.0 × 10 ^-6 / ° C or less, which is equivalent to the coefficient of thermal expansion of iron-based materials. Moreover, both of the obtained composite materials No. N7 and No. N14 have a joint strength of "◎" in the vicinity where the through holes are formed, and the composite materials No. 7 and No. N14 having no through holes are formed. It is higher than the joint strength of No. 14 at the same position, and it can be confirmed that the joint strength is improved by forming a through hole that communicates the inner peripheral surface and the outer peripheral surface.

Claims (3)

A composite obtained by impregnating an iron-based sintered body with an aluminum alloy.
The iron-based sintered body contains, in mass%, C: 0.4 to 1.5%, Cu: 10% or more and less than 20%, and has a composition consisting of the balance Fe and unavoidable impurities.
Pore ratio by volume fraction: 16 to 29 %, with continuous vacancies, pearlite matrix, and a structure in which the free Cu phase is dispersed.
It is a porous iron-based sintered body with a surface roughness Rz of 20.1 to 49.5 μm that complies with JIS B 0601 (1982) without shot blasting.
The impregnated complex is
The average coefficient of thermal expansion from room temperature to 200 ° C is 14.0 × 10 ^-6 / ° C or less, and the boundary strength between the impregnated composite and the aluminum alloy in the state of being cast and wrapped in an aluminum alloy is 10 MPa or more. A complex characterized by. Iron-based powder, copper powder, graphite powder, and lubricant powder are mixed to form a mixed powder, and then the mixed powder is filled in a mold and pressure-molded to obtain a green compact, and then the green compact. The body is sintered to form an iron-based sintered body having a predetermined shape, and then the iron-based sintered body is cast and wrapped in an aluminum alloy, and the pores of the iron-based sintered body are impregnated with the aluminum alloy. In the method of manufacturing the complex
The iron-based powder was made into an iron-based powder adjusted to a particle size distribution that passed through a 60-mesh sieve (-60 mesh) and did not pass through a 350-mesh sieve (+350 mesh), and the copper powder was the iron-based powder and copper. The mixture was blended so as to be 10% or more and less than 20% in mass% with respect to the total amount of the powder and the graphite powder, and the graphite powder was mixed in 0.4% by mass with respect to the total amount of the iron-based powder, the copper powder and the graphite powder. Mix to ~ 1.5%,
By adjusting the pressure forming conditions and / or the sintering conditions of the green compact, the iron-based sintered body contains C: 0.4 to 1.5% and Cu: 10% or more and less than 20% in mass%. A structure consisting of the balance Fe and unavoidable impurities, a vacancy ratio of 16 to 29 % by volume, continuous vacancy, a pearlite matrix, and a structure in which the free Cu phase is dispersed in the matrix. A porous iron-based sintered body with a surface roughness Rz of 20.1 to 49.5 μm in accordance with JIS ZB 0601 (1982) without shot blasting.
The impregnated complex has an average coefficient of thermal expansion from room temperature to 200 ° C. of 14.0 × 10 ^-6 / ° C or less, and the impregnated complex and the aluminum alloy are cast in an aluminum alloy. A method for producing a complex, which comprises forming a complex having a boundary strength of 10 MPa or more. The composite according to claim 2, wherein the lubricant powder is blended so that the total amount of the iron-based powder, the copper powder, and the graphite powder is 0.3 to 3.0 parts by mass with respect to 100 parts by mass. How to make a body.

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