JPS6111908B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to improve the heat resistance, heat insulation, wear resistance, etc. of the aluminum alloy casting member used in the piston of a diesel engine, and to improve the combustion, thermal efficiency, and startability of the engine. This article relates to a conjugate with and a method for producing the same. Combustion methods currently used in diesel engines include direct injection, pre-combustion chamber, and swirl chamber. Among these, the direct injection type has low fuel consumption and heat load, and has excellent durability, and is generally used for large and medium-sized cars, but recently, prototype research is also underway for use in small cars. be. However, the aluminum alloy used for these pistons rapidly loses strength and hardness as the temperature rises due to the heat load on the top surface, so it is prone to wear and cracking at high temperatures, and due to thermal expansion. There were drawbacks such as seizing and abrasion of the ring part, which made it impossible to seal the gas, resulting in a decrease in output and poor starting. For this reason, these countermeasures have been actively implemented in various fields, such as fitting cast iron to the top of the piston, tightening bolts,
Furthermore, casting fittings of ceramics and cermets are being considered. However, these improvement methods can cause cracks to occur due to rapid heating during aluminum casting, and "rattling" due to engine operation and high temperatures.
The current situation is that it has not yet been put into practical use due to reliability issues such as damage due to differences in thermal expansion. The present invention solves these problems, and has a relatively small difference in coefficient of thermal expansion from ceramics, which have excellent heat resistance, heat insulation, and wear resistance.
An aluminum alloy that has a high affinity with aluminum alloys and is made by interposing iron or an iron-based alloy with high toughness as an intermediate layer between the ceramic member and the aluminum alloy member, and bonding the ceramic member to the ceramic member by bonding them to each other. The purpose is to provide a cast body and a method for manufacturing the same. Next, the conjugate of the present invention and its manufacturing method will be explained. The figure is a sectional view showing an embodiment of an aluminum alloy cast body to which a ceramic member of the present invention is adhered and bonded. The ceramic member 1 shown in the figure has a relatively large coefficient of thermal expansion and is slightly water-absorbing. Preferably, the coefficient of linear expansion is 8 x 10 ^-6 /°C (RT~1000
℃) or more, and the apparent porosity is 10 to 18%. The reason why this apparent porosity is limited is that if it is less than 10%, it will be susceptible to thermal shock, and if it is more than 18%, the mechanical strength will deteriorate. The starting raw materials for such ceramics are Al ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , ZrO ₂ ,
Oxides such as TiO ₂ , SiO ₂ , MgAl ₂ O ₄ , CaZrO ₃ , MgZrO ₃ and MgTiO ₃ , and one or more of them.
Fine powder with a particle size of 44μ or less, which is larger than seeds, is produced in 1984.
Using the method described in No. 14833, a ceramic calcined body having a porosity of 15 to 40%, which is bonded and hardened with chromium oxide, or one or more of the above oxides, is produced as in the above patent. using the method of
The ceramic member is bond-strengthened with Cr ₂ O ₃ or a high-temperature sintered body made of one or more of the above-mentioned oxides and has an apparent porosity of 10 to 18%. Next, iron or an iron-based alloy is used for a metal member 2 which is an intermediate layer between the ceramic member 1 and an aluminum alloy cast member 3 to be described later. These metal members 2 include a nickel or chrome plating film 2a. The iron-based alloy is carbon steel, nickel steel, stainless steel, etc., and preferably a material whose coefficient of thermal expansion is relatively close to that of the ceramic member 1, such as an iron-nickel alloy with Fe64%,
The 36% Ni composition alloy has a linear expansion coefficient of 9×10 ^-6 /℃ (RT
~500℃), Kovar with a composition of 50% Fe, 29% Ni, and 17% Co is 9.3 × 10 ^-6 /℃ (30 ~ 700℃), Sylvania
No. 4 alloy shows a value of 9.6 to 10.2×10 ^-6 (25 to 400℃), with a composite gold composition of stabilized ZrO ₂ , Al ₂ O ₃ + Cr ₂ O ₃ + SiO ₂ , and expansion of zirconate and titanate ceramics. The coefficients are approximately the same, and an extremely good bonded body can be obtained in both members 1 and 2 by a reaction in which the slurry coating layer 4, which is mainly composed of a concentrated aqueous solution of chromic acid, is converted into Cr ₂ O ₃ by heat treatment. The aluminum alloy member 3 is an Al-Si-Cu (-Ni, -Mg) alloy having a melting point of 570°C or higher, and is preferably an aluminum alloy casting having a relatively small coefficient of thermal expansion, such as JISAC-4C, AC8A to C
(linear expansion coefficient α = 20 to ²⁵
%, Cu2%, Mg1%, Cr0.5%, remaining Al) is α≒17
×10 ^-6 /°C, making it a suitable material. Next, the manufacturing process for joining the aluminum alloy cast member 3 and the ceramic member 1 will be described. First, as a first step, the ceramic member 1 and the iron alloy member 2 are joined. That is, a concentrated aqueous solution of a soluble chromium compound, e.g.
ZnCrO ₄ , CaCrO ₄ , MgCrO ₄ , Cr ₂ O ₃ etc.
A solution with a specific gravity of 1.65 prepared by dissolving H ₂ CrO ₄ in an aqueous solution with a specific gravity of 1.6 or more, or Al ₂ O ₃ , Cr ₂ O ₃ ,
44μ or less of SiO ₂ , ZrO ₂ , TiO ₂ , preferably 20μ
One or more of the following fine powders are contained in a concentrated aqueous solution of H ₂ CrO ₄ with a specific gravity of 1.7 at 5 to 25% by weight, thoroughly ground and mixed using a ball mill for 24 hours to form a slurry, and this slurry is applied. After 10 to 15 minutes, both members 1 and 2 are fitted and bonded via the coated layer 4. Then, with this adhesive body fixed, the temperature is increased at a rate of 3.5°C/min using an electric furnace, and heat treatment is performed preferably at 460 to 660°C. The heating retention time at the maximum temperature varies depending on the size of these members, but a satisfactory joined body can usually be obtained within 30 minutes. Next, in the second step, a commercially available cleaning flux, for example FL-3, is coated on the exposed joint surfaces of the ceramic member 1 and the iron-based alloy member 2 of the iron alloy joined body that were joined in the first step. and set this joined body in an aluminum alloy mold,
While maintaining the temperature at approximately 250-300°C, aluminum alloy liquid is injected and cast. In this case, the ceramic member 1 does not wet the aluminum alloy at the casting temperature. Therefore, only the iron or iron alloy member 2 is joined, and a joined product of the aluminum alloy cast body 3 and the ceramic member 1 is manufactured. For the aluminum alloy casting/ceramics bonded body manufactured in this way, a specimen with an area of 2 x 2 cm ² was cut perpendicular to the bonding surface, and
Two metal rods were bonded to the ceramic surface and the aluminum alloy surface using epoxy adhesive, respectively, and a tensile test was conducted. As a result, although there were considerable differences depending on the selection of the combination of each member, in a good system combination, the joint strength showed a value of 450 Kg/cm ² or more. In addition, the thermal conductivity of ceramic members shows different values related to the number of combinations of oxides and porosity, but in ceramics prepared with an apparent porosity of 10 to 15%, it is 0.002 to 0.008 cal. /cm・sec・C. Furthermore, crack inspection using a dyed impregnating solution revealed that no cracks occurred during casting of the aluminum alloy. As explained above, it has become clear that according to the present invention, ceramics can be firmly bonded to the top of an aluminum alloy piston for a diesel engine, and the heat resistance, heat insulation, wear resistance, etc. of the piston can be significantly improved. The disadvantages of conventional methods such as cracks and damage caused by rattling during operation have been eliminated, and as a countermeasure to the heat load of diesel engines, the bonded product of aluminum alloy castings and ceramics has been adopted as an industrial manufacturing method for pistons for diesel engines. suitable. Next, the present invention will be explained in further detail with reference to Examples. Example 1 1.1 Adjustment of ceramic parts

[Table] was pulverized and mixed in a ball mill for 48 hours to create a casting slurry, and this was poured into a flat-bottom cup-shaped chamois mold with an inner diameter of 44 mm and a depth of 2.2 mm to form a cup-shaped cup with a wall thickness of 5 mm. Solid casting was performed, and after semi-drying, the medium mold was taken out and poured into a mold with a specific gravity of 1.65 obtained by dissolving Cr ₂ O ₃ in a concentrated aqueous solution of chromic acid.
After sufficiently moistening with a solution consisting of xCrO ₃ −yCr ₂ O ₃・zH ₂ O,
Raise the temperature at a rate of 3.5℃/min to a maximum of 660℃
℃ for 30 minutes to bond and harden the oxide particles with Cr ₂ O ₃ and then cooled. This heat treatment makes the ceramic body difficult to handle.
Since it has sufficient strength, it is released from the mold, immersed in a concentrated aqueous solution of H ₂ CrO ₄ with a specific gravity of 1.7, impregnated with the solution, wiped off the liquid adhering to the surface, and placed in a furnace.
Increase the temperature at a rate of 3.5℃/min until the maximum temperature
Heating was maintained at 660°C for 30 minutes. moreover,
Impregnation and heat treatment with this solution were repeated eight times to prepare a ceramic member. Since this processed material can be easily machined with ordinary machine tools in the second iteration, the ceramic body is finished so that it matches the joint surface of the separately machined iron alloy component, and then the third and subsequent iterations A ceramic member was prepared by impregnation and heat treatment. The physical properties of a test ceramic specimen prepared under the same conditions were an apparent porosity of 12% and a thermal conductivity of 12%.
0.003 to 0.004 cal/cm・sec・℃, linear thermal expansion coefficient
The value was 10.2×10 ^-6 /°C. 1.2 Iron-based alloy member used as the intermediate layer This member is made of stainless steel 430 {linear thermal expansion coefficient 10.8×10 ^-6 /℃ (20 to 500℃)}, with a wall thickness of 1.2 mm, an inner diameter of 43.2 mm, and a depth of The inner and outer surfaces of the 21.6 mm cup were roughened using aqua regia. 1.3 Preparation of binder (solution) The binder is a mixed fine powder of 1 part by weight of α-Al ₂ O ₃ , 1 part by weight of ZrO ₂ , and 1 part by weight of TiO ₂ , all of which are less than 10μ in size, and mixed with a concentrated amount of H ₂ CrO ₄ . A 20% by weight solution of ZnCrO ₄ +H ₂ CrO ₄ having a specific gravity of 1.7, which is obtained by dissolving ZnO in an aqueous solution, was added and mixed for 48 hours using a ball mill to prepare a slurry. 1.4 Joining the ceramic member and the iron alloy member The slurry described in Section 1.3 was thoroughly applied to both the joint surfaces of the ceramic member and the iron alloy member, and after 10 minutes, the two members were fitted and bonded. This was placed in an electric furnace in a fixed state, heated at a rate of 3.5°C/min, held at a maximum of 560°C for 30 minutes for heat treatment, and then allowed to cool to complete the bonding of the ceramic and iron alloy parts. 1.5 Joining with ceramic parts by casting aluminum alloy Silumin alloy (Si16%, Cu2%, MgO1.3%, Al remainder) (α≒
18×10 ^-6 ) was used. First, the inner diameter is 60mm and the depth is 70mm.
The joined body described in Section 1.4 was placed in the center of the upper part of the mold with the ceramic part facing up so as to be embedded in the casting in a casting mold of 1.5 mm in diameter, heated and held at approximately 300°C, and then heated to approximately 720°C. The aluminum alloy liquid was injected into the mold and cast. In this way, by interposing the ceramic member and the aluminum alloy casting member with a thin layer of iron alloy as an intermediate layer, an aluminum alloy material is cast that has a considerably large thermal expansion relative to the ceramics, and the two do not wet each other. It can be easily joined by the method. The aluminum casting of this joint has a cylindrical shape with a diameter of 60 mm and a length of 70 mm, with a ceramic cup embedded in the top. While the outer periphery of this cylinder was cooled by a water-cooled pipe, a combustion flame was blown onto the ceramic part using a propane gas burner, and the surface temperature inside the ceramic cup was maintained at approximately 500°C for 10 hours.
A heating test was conducted. As a result, no cracks were observed in the ceramic part. In addition, the bonding strength of the test piece was 360
Kg/cm ² or more (epoxy adhesive Armstrong
735 peeled off on the adhesive surface). Example 2 2.1 Adjustment of ceramic parts

After wet mixing the formulation in [Table] in a ball mill for 48 hours,
The mixture was dehydrated to a water content of about 20% and kneaded thoroughly. This was press-fitted into a cylindrical reinforced plaster mold with an inner diameter of 45 mm and a depth of 80 mm at a pressure of approximately 100 kg/cm ² . After semi-drying, the mold was released and roughly processed into a cylinder with a thickness of 10 mm. After drying, it was placed in an electric furnace. It was calcined at about 1050°C. Next, this calcined body was turned into a ceramic cylinder having an outer diameter of 39.8 mm, a length of 60 mm, and a wall thickness of 6 mm. This was immersed in a concentrated aqueous solution of H ₂ CrO ₄ with a specific gravity of 1.65, thoroughly impregnated with the solution, gently wiped off the liquid adhering to the surface, and heated at a maximum temperature of 760°C at a speed of 3.5°C/min.
and held for about 30 minutes for heat treatment. this
The H ₂ CrO ₄ solution impregnation and heat treatment were repeated 8 times to strengthen and condition the ceramic component.
The physical properties of a test piece prepared under the same conditions showed an apparent porosity of 12%, a thermal conductivity of 0.007 Cal/cm・sec.℃, and a linear thermal expansion coefficient of 8.5×10 ^-6 (RT to 1000℃). Ta. 2.2 Iron-based alloy members used as intermediate layer Nickel steel (Invar) is used as the iron-based alloy member.
Ni36%, thermal expansion coefficient 9×10 ^-6 /℃ (RT~500
A cylinder with a wall thickness of 1.2 mm, an inner diameter of 40 mm, and a length of 60 mm was immersed in aqua regia (HNO ₃ volume 1 + HCl volume 2.5) to roughen the surface. 2.3 Preparation of bonding agent (solution) Same as Section 1.3 of Example 1 2.4 Joining of ceramic members and iron-based alloy members Same as described in Section 1.4 of Example 1 2.5 Bonding of aluminum alloy cast parts to ceramic members As aluminum alloy is a silumin alloy,
Commercially available hypersilumin (Si18%, Cu1%,
Mg0.7%, Ni1.7%, remaining Al composition), coefficient of linear thermal expansion
Using 17×10 ^-6 (RT ~ 100℃), the joined body described in Section 2.4 was heated and held at 300℃ in an aluminum alloy mold, and 710℃ aluminum alloy liquid was poured into the mold to form a ceramic. An aluminum alloy outer cylinder with a wall thickness of 10 mm was formed around the outer periphery of the iron alloy, and an aluminum alloy casting/ceramics joint was manufactured. This product was cut in the axial direction of the cylinder, and the state of cracks in the inner ceramic part was examined.Also, while cooling the aluminum outer surface, a propane gas combustion flame was blown onto the ceramic surface to heat it to approximately 450℃, and after holding it for 1 hour, 1hr
The forced air cooling test was repeated 10 times. As a result, no abnormalities such as cracks or peeling were observed in the joints and ceramic parts. In addition, a tensile bonding strength test was conducted on a rectangular specimen cut from this sample in the same manner as in Example 1.
The bonding strength was cm ² or higher.

[Brief explanation of the drawing]

The figure is a sectional view showing an embodiment of an aluminum alloy cast body to which a ceramic member of the present invention is adhered and bonded. 1...Ceramics member, 2...Iron or iron-based alloy member, 3...Aluminum alloy casting member, 4...
...Slurry coating layer, 2a...Nickel or chrome plating film.

Claims (1)

[Claims] 1. ZrO ₂ , Al ₂ O ₃ ,
Cr ₂ O ₃ , SiO ₂ , Fe ₂ O ₃ , TiO ₂ , CaZrO ₃ or
In a calcined state consisting of one or more powders of metal oxides such as MgAl ₂ O ₄ or such oxides,
Ceramic components with bond strength strengthened by Cr oxide,
High-temperature sintered ceramic members with an apparent porosity of 10% to _{18 %} , which are made of oxides such as Al ₂ O ₃ , Cr ₂ O ₃ ,
It is strongly bonded through a coating layer of slurry containing one or more metal oxides such as SiO ₂ , ZrO _{2 or} TiO 2 , and this bond is further bonded to the iron or iron-based metal oxide. 1. An aluminum alloy cast body having a ceramic member adhesively bonded to the surface of the aluminum alloy cast body so that the alloy member side is interposed as an intermediate layer. 2 ZrO ₂ , Al ₂ O ₃ ,
Cr ₂ O ₃ , SiO ₂ , Fe ₂ O ₃ , TiO ₂ , CaZrO ₃ , or
In a calcined state consisting of one or more powders of metal oxides such as MgAl ₂ O ₄ or such oxides,
Ceramic components with bond strength strengthened by Cr oxide,
A soluble Cr compound that can be converted into Cr ₂ O ₃ by heat treatment on at least one of the mutual bonding surfaces of a high-temperature sintered ceramic member having an apparent porosity of 10% to 18% made of an oxide. A simple concentrated aqueous solution or a small amount of Al ₂ O ₃ , Cr ₂ O ₃ , SiO ₂ , ZrO ₂
Alternatively, both parts may be polymerized by applying a concentrated aqueous solution of a soluble Cr compound containing one or more metal oxides such as _TiO2 , and then heat-treated to form a strong bond. This bonded body is further set in an aluminum alloy mold, and an aluminum alloy liquid is injected and cast under heating conditions at an appropriate temperature to form an aluminum alloy so that the iron or iron-based alloy member side is interposed as an intermediate layer. A method for producing an aluminum alloy cast body in which a ceramic member is adhered and bonded to the surface of the cast body.