JPH0637682B2 - Heat resistant and abrasion resistant high strength aluminum alloy powder compact having excellent lubricity and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid lubricant-dispersed heat-resistant type suitable for parts such as a cylinder liner of an internal combustion engine and a wear ring of a piston.
The present invention relates to a Si aluminum alloy powder compact and a method for producing the same.

Replacing the cylinder block of an automobile engine with cast iron from aluminum alloy casting has a great effect on weight reduction, but even in that case, the wear resistance is insufficient with aluminum alloy casting on the inner circumference side that slides with the piston ring and piston. In addition, a cylinder liner made of flake graphite cast iron material is used around the casting. If this cylinder liner is made of aluminum alloy, the effect of weight reduction will be further improved, and the coefficient of thermal conductivity will be better than that of cast iron, and the coefficient of thermal expansion will be greater than that of cast iron, which is close to the coefficient of thermal expansion of the aluminum alloy casting of the cylinder block. Therefore, even if the temperature is high during operation, the adhesion between the liner and block is good, resulting in an engine with good heat dissipation, and the temperature of the inner wall of the liner decreases, so that the life of the lubricating oil can be extended and the viscosity is low. It is expected that the above lubricating oil can be used and fuel efficiency can be improved.

Also, since the high Si aluminum alloy has a larger coefficient of thermal expansion than cast iron, it is possible that the clearance between the aluminum alloy piston and the piston can be set to a small value. The consumption of lubricating oil can be suppressed. Further, since the high Si aluminum alloy has a low friction coefficient, the friction loss between the high Si aluminum alloy and the piston ring is reduced, so that it is expected that the fuel efficiency is improved.

The wear ring of the piston is made of Niresist cast iron whose coefficient of thermal expansion is close to that of the aluminum alloy of the piston as a measure against wear of the part where the low compression ring is set on the head of the aluminum alloy piston. ing. If the piston wear ring can also be made lighter, fuel economy is expected to improve further.

Thus, although there are many advantages in using an aluminum alloy for the cylinder liner and the wear-resistant ring, the conventionally known aluminum alloy is not sufficient in strength at high temperature and is insufficient as such a member for cast metal.

That is, an aluminum alloy powder extruded material having a composition of 20.0Si-4.0Cu-0.8Mg-0.5Ni-Al was used as a cylinder liner (outer diameter 73 mm, inner diameter 65 mm, height 105 mm).
A DC-12 alloy cylinder block (weight: 3.4 kg) was subjected to a casting test by a die-cast method at a molten metal temperature of 675 ° C. As a result, the hardness was H _RB 80 by T ₆ treatment before casting.
Was softened to about H _RB 40. Therefore, it is judged that this aluminum alloy powder compact cannot be used as a caster cylinder liner.

The casting is made by die casting or low pressure casting, but it is desirable that the liner be as thin as possible in terms of cost. However, as the wall thickness decreases, the liner transfer process during casting and the mechanical stress applied during positioning tend to change. Therefore, high rigidity (high hardness) is required even at high temperatures.

In addition, it is important that a sliding member such as a cylinder liner or a wear ring does not damage the sliding mating surface or wear the mating surface. In order to achieve these objects, a method of mixing Al-Si alloy powder and carbon powder and hot extrusion molding (Japanese Patent Publication No. Sho 48-9686), Al-Si alloy powder graphite, SiC, Sn, etc. A method of adding a hot-extruded hollow body to obtain a hollow body (Japanese Patent Laid-Open No. 52-109415) has been proposed.
Aluminum alloy materials having self-lubricating property are known. However, none of these conventionally known materials have excellent high-temperature characteristics, and cannot be used as a caster cylinder liner material.

The present invention has been made in order to solve these problems, strength at high temperature, wear resistance, excellent seizure resistance, and also to provide an aluminum alloy powder compact having a self-lubricating property at high temperature. Has an aim.

The present inventors have not already softened against the heat load during casting, and have not been softened even at the temperature applied during use, and have excellent wear resistance and seizure resistance. As a compact, we have proposed an alloy powder compact formed by adding a large amount of Ni to a high Si aluminum alloy.
57-119901). The present invention is an improvement of the present invention, in which the sliding property is further enhanced by adding 0.2 to 5.0% of a solid lubricant which is stable even at high temperature to the prior application.

The aluminum alloy powder compact of the present invention has a weight ratio of Si10.0
~ 30.0%, Ni 5.0 ~ 15.0% and solid lubricant 0.2 ~ 5.0%
It is characterized in that it has a composition containing Al as the balance, and the size of Si crystal grains is 15 μm or less and the size of intermetallic compounds is 20 μm or less.

The second invention is Si 10.0 to 30.0% and Ni 5.0 to 15.0%.
The gist of the present invention is to hot-extrude an aluminum alloy melt containing the alloy, which is dispersed and rapidly solidified, and a solid lubricant is added and mixed to the obtained alloy powder. An alloy powder compact having a structure in which Si crystal grains and intermetallic compounds are finely dispersed is obtained.

The present invention will be described in more detail below.

First, the reasons for limiting each component of the alloy compact according to the present invention will be described.

If Si is less than 10%, the amount of dispersion is small and the effect on heat and wear resistance is insufficient. Primary crystals in the hypoeutectic region near Si 10%
Si does not crystallize and has a fine eutectic structure. Si
As the amount of addition of Si increases, Si begins to crystallize as a primary crystal, and heat resistance and wear resistance also improve. However
If the Si content exceeds 30%, a coarse primary crystal will be formed even if powdered by the dispersion rapid solidification method, which is the essence of the production method of the present invention described later.
Si will not disappear.

When an aluminum alloy powder with a coarse primary crystal Si structure is used by extrusion molding, the compressibility of the powder is significantly deteriorated, making it difficult to form a green compact, and the deformation resistance also increases during hot extrusion. However, there is a problem that a large pushing force is required and the extrusion die is worn to shorten the life remarkably. In addition to such manufacturing problems, the material properties also have the same drawbacks as in the case of cast materials, which makes them unsuitable as cylinder liner materials, so crystallization of coarse primary crystal Si must be avoided. I have to. When used as a cylinder liner after being cast in an aluminum alloy cylinder liner, the coefficient of thermal expansion decreases with the amount of Si added, and if Si exceeds 30%, the adhesion with the cylinder block material will deteriorate and the piston It becomes necessary to increase the clearance between and.

Therefore, the addition amount of Si is 10.0 to 30.0%, preferably 15.0 to 2
5.0% is good.

Ni is an important component in the alloy powder compact of the present invention. The effect of adding Ni is to improve high temperature strength and wear resistance.
When Ni is added to the hypereutectic alloy, a Ni-Al intermetallic compound precipitates, which exists as a rod-like structure in the alloy powder by the dispersion rapid solidification method, which is the essence of the production method of the present invention, and the hot It is divided by the extrusion process and finely dispersed in the matrix. This compound is stable and does not easily grow even at high temperatures, and does not lose its strength even if kept at high temperatures for a long time. Therefore, even after being exposed to a high temperature like a cast liner cylinder liner, the hardness does not decrease so much and it becomes possible to maintain wear resistance.

When the amount of Ni added is 5% or less, no remarkable effect is observed, and 15%
If the above, the solubility of Si in the matrix becomes low,
Excess Si forms primary crystals and crystallizes in large amounts. Further, the melting temperature of the alloy becomes high and the oxidation of the molten metal proceeds, so that a special antioxidation measure is required and it is not economical. Further, the precipitated intermetallic compound becomes coarse, and not only is it difficult to be separated by the subsequent hot extrusion process, but also the extrudability is hindered. It has been confirmed that a Ni addition amount of 5.0 to 15.0% exerts an unprecedented effect. It is said that the strength of the alloy is improved by utilizing the intermetallic compound containing Ni that precipitates by adding a large amount of Ni in this way, especially the strength at high temperature, and the intermetallic compound is fragmented and refined to improve wear resistance. It has a new effect.

Further, the present invention is characterized by adding 0.2 to 5.0% of a solid lubricant selected from graphite, molybdenum disulfide and boron nitride. The above-mentioned solid lubricant has a role of imparting self-lubricating property, and is stable and maintains lubricity even at high temperature, and therefore is suitable for a member such as a cylinder liner or a wear ring of a piston. Since these solid lubricants are dispersed and present in the base material of the aluminum alloy compact, they act as solid lubricants in addition to the effect of acting as an oil sump, under severe sliding conditions that cause oil film breakage. It has the effect of preventing seizure.

However, when the strength of the base material is weak, the base material on the sliding surface causes plastic flow due to heat generation due to sliding and the accompanying decrease in material strength, and the base material on the sliding surface exists in an open state. Cover the solid lubricant part. Therefore, when used in combination with a base material having high-temperature strength and high hardness, excellent effects are exhibited.

If the addition amount of the solid lubricant is 0.2% or less, no effect on the sliding property is recognized, while if it exceeds 5.0%, cracks occur in the extruded material during hot extrusion, and a sound material cannot be obtained. The effects of the above three types of solid lubricants are almost the same, but the type is selected according to the operating temperature of the cylinder liner. That is, regarding the thermal stability of the above three types of solid lubricants, molybdenum disulfide has the lowest thermal stability, and boron nitride has the highest thermal stability.

The alloy powder compact according to the present invention is 0.5 to 5.0 as required.
Cu and 0.2-3.0% Mg can be added.
Cu and Mg are known as components that impart age hardening to an aluminum alloy and strengthen the material. In the present invention also Cu and Cu within the above range within the solid solution limit at the solution treatment temperature.
Adding Mg is effective for strengthening the material.

Further, in the alloy powder compact of the present invention, Fe, Mn,
It is also possible to add Ti, Cr, V, Zr, Mo, Co and the like in the process of obtaining the alloy powder to improve the high temperature strength.

If the size of the Si crystal grains is 15 μm or less, the ductility is better than that of the conventional molded product and the machinability is also improved, so machining becomes easier and chattering and shavings are less likely to occur during processing. This is because. Further, it is because the fine crystals of Si improve the wear resistance and reduce the coefficient of friction, which makes it suitable for cylinder liners and the like.

Substantially the size of intermetallic compounds containing Ni such as Al ₃ Ni
By finely and uniformly dispersing 5 μm or less and even 20 μm or less, high temperature strength and abrasion resistance are remarkably improved.

The aluminum alloy powder compact according to the present invention is significantly improved in high temperature strength as compared with the conventional product, and is also excellent in wear resistance and seizure resistance. Furthermore, since the product of the present invention has a small coefficient of friction and is excellent in self-lubricating property, it is particularly required to be used at a high temperature like a cylinder liner of an internal combustion engine and to have wear resistance, seizure resistance and self-lubricating property. It is the most suitable member.

The aluminum alloy powder compact according to the present invention is obtained by the method described below.

The second of the present invention relates to a method for producing an aluminum alloy powder compact of the first invention, the gist of which is to solidify the alloy powder obtained by dispersing and quenching a high Si aluminum alloy melt containing Ni. The purpose is to perform hot extrusion molding after adding and mixing a lubricant.

The purpose of dispersion quenching and solidification of the molten alloy is to super-saturate solid solution of alloying elements such as Si, Ni, Cu, and Mg, and to refine the primary crystal Si and intermetallic compound phases. As the method of dispersion rapid solidification, known methods for producing metal powder such as atomization method and centrifugal pulverization method can be used. An alloy powder having a satisfactory structure can be obtained by refining the powder grain size to 0.5 mm or less by these methods and rapidly solidifying.

Next, a solid lubricant selected from graphite, molybdenum disulfide, and boron nitride is added to the alloy powder in an amount of 0.2 to 5.0% by weight.
Add and mix. Since the solid lubricant has no solubility in an aluminum alloy and has poor wettability with the aluminum alloy, it is extremely difficult to uniformly distribute it in the molten metal stage. Therefore, it is extremely effective to add and mix the solid lubricant in the powder stage and further uniformly disperse it by using the subsequent hot extrusion process. The solid lubricant is preferably added in the form of fine powder of 50 μm or less. Mixing is performed by stirring and mixing in an inert atmosphere to prevent oxidation of the aluminum alloy powder.

Next, the mixed powder is processed into a molding pair by hot extrusion. The hot extrusion not only finishes the aluminum alloy particles into a strong bonded body, but also press-bonds the aluminum alloy particles and the solid lubricant particles to firmly bond them, and further the primary crystal Si crystallized in the alloy powder, This is an essential requirement for refining the crystal grains of eutectic and intermetallic compounds and improving the mechanical properties of the material.

It is convenient for the work to prepare the green compact before hot extrusion. Manufacture of green compacts is carried out by alloy powder in the temperature range of about 200-350 ℃. If the temperature exceeds 350 ° C, the oxidation becomes remarkable, so it is desirable to carry out in a non-oxidizing atmosphere such as nitrogen gas or argon. Molding pressure is 0.5 to 3 ton / cm ²
It is desirable that the density of the green compact is 70% or more in terms of the true density ratio for handling the green compact.

Hot extrusion is at temperatures above 350 ° C, preferably 400-470 ° C
Temperature range. This is for facilitating the processing of the green compact and at the same time for promoting the bonding between the particles to form a strong compact. Further, it is intended to finely disperse the elements of the supersaturated solid solution and to divide the rod-like structure of the primary crystal Si and the intermetallic compound into fine particles to improve the strength and frictional characteristics of the compact. Hot extrusion is performed by preheating the green compact in air or in a non-oxidizing atmosphere and inserting it into a container at approximately the same temperature. The extrusion ratio is preferably 10 or more. If the extrusion ratio is less than 10, voids will remain in the extruded material, and because the diffusion bonding between powders and the effect of separating the rod-shaped intermetallic compound are insufficient, a material with high strength and toughness cannot be obtained. is there.

According to the method of the present invention, it is possible to disperse all of Si primary crystal, eutectic crystal, intermetallic compound, and solid lubricant extremely finely, and particularly excellent in heat resistance, wear resistance and lubrication characteristics of the material. It is possible to easily obtain the member. Also,
The alloy powder compact obtained by the present invention may be subjected to a stabilizing heat treatment to further improve the material properties.

Next, the present invention will be described with reference to examples.

Example A high Si aluminum alloy melt having various alloy compositions shown in Table 1 was gas atomized to obtain -48 mesh raw material alloy powder.

Next, except for No. 2, solid lubricant powder was added as shown in Table 1 and mixed uniformly with a V-type cone mixer under nitrogen gas filling. For the solid lubricant powder used,
Graphite is an artificial graphite powder of 15 μm or less (KS-LONZA KS-
15), boron nitride is a powder of 44 μm or less (Showa Denko UH
As P), molybdenum disulfide used was powder (Nippon Molybdenum) having a particle size of 44 μm or less.

Next, these mixed powders are preheated to a temperature of 250 ° C., filled in a mold heated and maintained at the same temperature, and compression molded at a pressure of 1.5 ton / cm ² to obtain a powder compact with a diameter of 90 mm and a length of 200 mm. Got

Next, apply these green compacts to an outer diameter of 100 mm, an inner diameter of 90 mm, and a length of 205
Insert it into a 5051 alloy cylinder with a diameter of 90 mm and cover with a diameter of 90 mm and a thickness of 5 mm.
I made a billet as shown in the figure.

Next, each billet is heated to a temperature of 450 ° C, and the lid 3 is inserted into a container with an inner diameter of 104 mm that is maintained at about the same temperature so that the lid 3 is on the die side. Indirect extrusion with a die with an inner diameter of 30 mm (extrusion ratio 12 ) Was performed to obtain a round bar molded body.

The obtained molded body was cut, and processed into a pulling needle test piece with a gauge length of 50 mm and a parallel portion diameter of 6 mm, which was only from the powder extruded material part, and was held at 300 ° C for 100 hours, and then at each tensile test temperature for 100 hours.
After holding, a tensile test was performed. Further, the hardness of the chucking portion at the end of the test piece after the tensile test was measured at room temperature. Further, the structure of the chucked portion was observed and the size of the crystal grains of the obtained molded body was measured.

The results are shown in Table-2.

As is clear from the results, the alloy of the present invention has high strength and hardness after being kept at high temperature. Also, the strength can be improved by adding a solid lubricant.
Little decrease in hardness.

The microscopic structures of the test pieces No. 3 to No. 5 in Table 2 were observed. The structure was observed on a plane perpendicular to the extrusion direction and a plane parallel to the extrusion direction. In the microstructure observation, the solid lubricant showed a strong black color, and the intermetallic compound phase containing Ni showed a part with a high concentration.

In the alloy powder compact of the present invention, the eutectic phase and the intermetallic compound are extremely finely and uniformly distributed, and the solid lubricant is uniformly dispersed in the plane perpendicular to the extrusion direction,
Moreover, it can be seen that the particles are stretched and dispersed in the direction parallel to the extrusion direction.

Next, the hot extruded body was cut, and a material with a diameter of 70 mm and a thickness of 10 mm was made by hot casting. After holding at 300 ° C for 100 hours, the sliding surface was machined to make a circle made of only powder extruded material. A seizure resistance test was conducted after forming a plate-shaped test piece.

-Seizure resistance test The test apparatus is schematically shown in Fig. 2 and Fig. 3, and the back side is provided at the center of the sample disk 5 with a diameter of 70 mm that is detachably attached to the stator 4. The lubricating oil is injected from the oil through the oil injection hole 6. A pressing force P is applied to the stator 4 by a hydraulic device (not shown) toward the right at a predetermined pressure. A rotor 7 is disposed opposite to the disk 5 and is rotated at a predetermined speed by a driving device (not shown). In the sample holder 7 attached to the end face of the rotor 7 with respect to the sample disc 5, four 5 mm × 5 mm × 10 mm prismatic mating material test pieces 8 are concentrically arranged at regular intervals and can be removed. It is slidably attached to the sample disk 5. In such an apparatus, a predetermined pressing force P is applied to the stator 4 so that the sample disk 5 and the mating material test piece 8 are brought into contact with each other with a predetermined surface pressure, and the lubrication hole 6 moves to the sliding surface. The rotor 7 is rotated while refueling at a predetermined refueling speed.

The pressure acting on the stator 4 is gradually increased at regular intervals, and the rotor 7 rotates to rotate the test piece 8 of the mating material.
Then, a torque (torque generated by a frictional force) T generated in the stator 4 by the friction with the sample disk 5 is applied to the load cell 10 through the spindle 9, and the change is read by the dynamic strain gauge 11 and recorded in the recorder 12. Record. It is assumed that seizure occurs when the torque T rapidly rises, and the contact surface pressure at that time is taken as the seizure surface pressure.

The sample disk 5 used for the test was used after being heat-treated at 300 ° C. × 100 Hr and then polished, and the mating material test piece 8 was made of spheroidal graphite cast iron and had its sliding surface plated with hard chrome.
Polishing was performed as two types of iron plating in which 15 to 20% by area ratio of SiC having an average particle diameter of 0.8 μm was dispersed in the base material.
Further, A390.0 die cast material as a comparative material (T ₆ treated product) was also carried out for the flake graphite cast iron is used for the cylinder Lana. Test conditions are speed 8m / sec
, Lubricating oil is Pace oil # 20, temperature 90 ℃, oil amount 300m
1 / min, contact pressure was 20 kg / cm ² for 20 minutes, and 30 kg / cm ² for 3 minutes after running-in for 3 minutes, then 10 k every 3 minutes.
Increase in steps of g / cm ² . The results are shown in Table-3.

As is clear from the results, according to the present invention, No. 3 to No. 6 can be used rather than the combination of flake graphite cast iron (cylinder liner material) and chrome plating (piston ring surface) currently found in many gasoline engine combinations. The ones have excellent seizure resistance. Further, as seen in the comparative material (A390.0 die casting material), in the case of combination with the hard chrome plating, the seizure occurrence surface pressure is significantly lower than that of the SiC dispersed iron plating. It is noteworthy that the results of No. 3 to No. 6 according to No. 3 are different due to the difference in the surface treatment of the mating member.

Furthermore, N compared to the comparative material (A390.0 die casting material) and No.2.
The surface pressure of seizure of the molded products of o.3 to No.6 is high, but this is due to the large amount of hard phase consisting of Si particles and intermetallic compounds dispersed in the Al base material, resulting in minute irregularities and an oil film. In addition to the effect of retaining the solid lubricant, it has a lubricating effect due to the dispersion of the solid lubricant, an effect as an oil sump, and a synergistic effect of strengthening the dispersion by the intermetallic compound of the base material.

That is, in a material in which a solid lubricant is dispersed in a base material having a high temperature strength and a low hardness, the surface temperature rises due to heat generated by sliding,
Due to the stress caused by sliding, the surface part causes plastic flow, covering the solid lubricant part and losing the solid lubrication action and the action as an oil sump, and seizure occurs early, but when the high temperature strength and hardness of the base material are high It is considered that plastic flow on the surface portion is unlikely to occur and the solid lubricant portion can be maintained at a higher surface pressure.

As described above, the alloy of the present invention is suitable for applications such as a cylinder liner or piston wear ring that is cast in an Al alloy and used in a relatively high temperature range during use. Excellent seizure resistance with synergistic effect with base material with high strength and high dispersion strength. In addition, the dispersion of the solid lubricant has the effect of retaining oil on the sliding surface, so it has the effect of preventing seizure even during cold starting, and also has the effect of cutting and grinding to cut chips into fine pieces. Also has the effect of facilitating.

[Brief description of drawings]

FIG. 1 is a view showing the structure of an intermediate billet, in which 1 is a green compact, 2 is a cylinder, and 3 is a lid. 2 and 3 are diagrams showing an outline of the seizure resistance test apparatus, 5 is a sample disk, 8 is a mating material test piece, 9 is a spindle, 10 is a load cell, 11 is a dynamic strain gauge, and 12 is recording. It is total.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B22F 9/10 (56) References JP-A-57-63603 (JP, A) JP-A-55- 97447 (JP, A)

Claims (2)

[Claims] 1. Si 10.0 to 30.0% by weight and Ni 5.0 to 15.0 by weight.
%, Solid lubricant 0.2-5.0% selected from graphite, molybdenum disulfide and boron nitride as essential components, the balance consisting of Al containing unavoidable impurities, and Si crystal grain size of 15 μm or less. And the size of the intermetallic compound is 20
A heat-resistant, wear-resistant and high-strength aluminum alloy powder compact excellent in lubricity, characterized by being finely dispersed to a size of μm or less. 2. Si 10.0 to 30.0% and Ni 5.0 to 15.0% by weight
A molten aluminum alloy containing the unavoidable impurities and the remainder being dispersed and rapidly solidified to form a powder, and a solid lubricant selected from graphite, molybdenum disulfide and boron nitride is added to the resulting alloy powder and mixed. After that, hot extrusion molding is performed, and the size of the Si crystal grains is 15 μm or less and the size of the intermetallic compound is 20 μm or less. Method for producing compact aluminum alloy powder compact.