JPS5959855A - High strength powder moldings of aluminum alloy having excellent lubricity resistance to heat and wear and its production - Google Patents

Abstract

PURPOSE:To provide an A alloy molding which has high strength at high temp. and resistance to wear and seizure and has also self-lubricity by incorporating essentially Si, Ni and a solid lubricant selected from graphite, MoS2, BN. CONSTITUTION:A titled Al alloy powder molding contg., by weight %, 10.0- 30.0% Si, 5.0-15.0% Ni, and 0.2-5.0% a solid lubricant selected from graphite, MoS2, BN, contg. further 0.5-5.0% Cu and according to need 0.2-3.0% Mg, and the balance Al contg. unavoidable impurities. The size of the Si crystal grains of such Al alloy powder molding is dispersed finely to <=15mum and the size of the intermetallic compd. to <=20mum. The molding is adapted to the production of parts such as cylinder liners, wear rings of pistons of an internal- combustion engine.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid lubricant-dispersed heat-resistant high-Si aluminum alloy suitable for parts such as cylinder liners of internal combustion engines and wear rings of pistons, and a method for producing the same.

Replacing the cylinder block of an automobile engine from cast iron to aluminum alloy casting has a great effect on weight reduction, but even in this case, aluminum alloy casting has insufficient wear resistance for the inner circumferential side that slides on the piston rings and pistons. A cylinder liner made of flake graphite cast iron is used in the cylinder liner. Making this cylinder liner from aluminum alloy not only has the effect of further weight reduction, but also has better thermal conductivity than cast iron, and has a larger coefficient of thermal expansion than cast iron, which is close to the coefficient of thermal expansion of the aluminum alloy casting of the cylinder block. Even when the temperature rises during operation, the adhesion between the liner and the block is good, resulting in an engine with good heat dissipation, and the inner wall temperature of the liner is lowered, making it possible to extend the life of the lubricating oil, and to reduce the viscosity of the lubricating oil. It is expected that this will enable the use of lubricating oil and improve fuel efficiency.

Also, since high-Si aluminum alloy has a larger coefficient of thermal expansion than cast iron, it is possible to set the clearance between the aluminum alloy piston and the piston smaller. The consumption of lubricating oil can be reduced. Furthermore, since the high-Si aluminum alloy has a low coefficient of friction, friction loss between the piston ring and the piston ring is reduced, which is also expected to improve fuel efficiency.

In addition, the wear-resistant 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, in order to prevent wear in the part where the compression ring is set near the head of the aluminum alloy piston. It is used. It is expected that fuel efficiency will further improve if the weight of the piston's wear ring can be reduced.

Although there are many advantages to using aluminum alloys for cylinder liners and wear-resistant rings, conventionally known aluminum alloys do not have sufficient strength at high temperatures and are not suitable for use as casting members.

That is, 20. OSi-4, OCu-0, 8Mg-0
,5Ni-At! Extruded aluminum alloy powder with the remaining composition cylinder liner (outer diameter 73 gate inner diameter 6
The molten metal temperature was 675 cm in a cylinder block (weight 3.4 Kr) of AD (12 alloy) as 5 mm height 105 cm).
As a result of the die-casting test at ℃, the hardness was I11 + R80 by T6 treatment before casting.
) has softened to about IR840.

Therefore, it is determined that this aluminum alloy powder compact cannot be used as a cylinder liner for castings.

Casting is done by die casting or low pressure casting, but it is desirable to make the liner as thin as possible from a cost standpoint. However, as the thickness becomes thinner, it becomes more easily deformed due to the mechanical stress applied during the liner conveyance process during casting and during positioning, so it is necessary to have high rigidity (high hardness) even at high temperatures.

! ! However, when using sliding parts such as cylinder liners and wear-resistant rings, be careful not to damage the sliding surfaces.

It is also important not to wear out the mating surface. In order to achieve our goals, Al! - A method of mixing Si-based alloy powder and carbon powder and hot extrusion molding (Japanese Patent Publication No. 48-968
6), AQ-Si alloy powder, graphite, and SiC.

A method of obtaining a hot extruded hollow object by adding Sn or the like has been proposed (Japanese Unexamined Patent Publication No. 52-109415), and aluminum alloy Hamura having self-lubricating properties is known. However, none of these conventionally known materials have excellent high-temperature properties, and cannot be used as cylinder liner materials for castings.

The present invention was made in order to solve these difficulties, and an object of the present invention is to provide an aluminum alloy molded body that has excellent strength, wear resistance, and seizure resistance at high temperatures, and also has self-lubricating properties at high temperatures. It is said that

The present inventors have already developed an aluminum alloy that does not soften under the heat load during casting, does not soften under the temperature applied during use, and has excellent 1lti4 wear resistance and seizure resistance. As a body, a molded body of an alloy powder made by adding a large amount of Ni to a high-Si aluminum alloy has been proposed (Japanese Patent Application No. 119901/1983).

The present invention is an improvement on the previous application, and further improves the sliding properties by incorporating a solid lubricant of 0.2 to 5.0%, which is stable even at high temperatures.

The aluminum alloy powder compact of the present invention has a weight ratio of Si
10.0-30.0% and %N! 5.0 to 15.0%, solid lubricant 0.2 to 5.0%, and optionally Cu Q, 5 to 5.0% and λ momme 0.2 to 3.0%, It has a composition in which the remainder is AQ, and the size of Si crystal grains is 15μ? n or less, the size of the intermetallic compound is 20
It is characterized by being finely dispersed to micrometers or less.

Furthermore, the second invention is Si 10.0-30.0%%N'
5, o~15.0%, Cu Q as necessary, 5~5
．． The gist of this method is to disperse and rapidly solidify a molten aluminum alloy containing 0% MgO and 2 to 3.0% MgO, add and mix a homogeneous lubricant to the resulting alloy powder, and then hot extrude. An alloy powder compact having a structure in which s-plate crystal grains and intermetallic compounds are finely dispersed is obtained.

The present invention will be explained in more detail below.

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

When the SI is less than 10%, the amount of dispersion is small, and the heat resistance i1j, l
The abrasion resistance is not good and the effect is insufficient. JSi l Q
In the hypoeutectic region around %, primary Si cannot be crystallized and has a fine eutectic structure. As the amount of Ss added increases, Si begins to crystallize as primary crystals, and heat resistance and wear resistance also improve. However, if the Si content exceeds 30, the coarse primary crystal Si will not disappear even if it is made into powder by the dispersion and rapid solidification method which is the essence of the production method of the present invention, which will be described later.

When aluminum alloy powder with a coarse primary Si structure is used in extrusion processing, it significantly deteriorates the compressibility of the powder, making it difficult to form a green compact, and also has high deformation resistance during hot extrusion. Therefore, it requires a large extrusion force, which causes wear on the extrusion die and significantly shortens its life. In addition to these manufacturing problems, the Toga property has the same difficulties as the casting property, making it unsuitable for use as a 0% cylinder liner property, so crystallization of coarse primary Si is not possible. You have to be strong to avoid it. In addition, when using cast iron i7- as a cylinder liner in an aluminum alloy cylinder block, the coefficient of thermal expansion decreases with the addition amount of Sl, and if the SI exceeds 30φ, the adhesion with the cylinder block material may deteriorate. It became necessary to increase the clearance between the screws and the screws.

Therefore, the amount of Si added is preferably 10.0 to 30.0 parts, preferably 15.0 to 25.0 parts.

Ni is an important component in the alloy powder compact of the present invention. The effect of Ni addition is to improve high temperature strength and wear resistance. When Ni is added to the hypereutectic alloy, the Sushi 2AA intermetallic compound precipitates, and in the alloy powder produced by the dispersion rapid solidification method, which is the mainstay of the production method of the present invention, it exists as a rod-shaped structure, and during subsequent hot processing. The extrusion process divides the particles into fine pieces and disperses them into the matrix.

This compound is stable and difficult to grow even at high temperatures, and does not lose strength even when kept at high temperatures for a long time. Therefore, even after being exposed to high temperatures like a cylinder liner for a casting, there is little decrease in hardness and it is possible to maintain wear resistance.

No significant effect was observed when the amount of Ni added was less than 5%;
When the number is 5 or more, the solubility of Si in the matrix decreases, and excess Si becomes primary crystals and crystallizes in large amounts. Furthermore, since the melting temperature of the alloy is high, the oxidation of the molten metal progresses, requiring special oxidation prevention measures, which is not economical. If the intermetallic compound folded in the casing becomes coarse and becomes difficult to split even during subsequent hot extrusion processing, it will be difficult to separate (this will also impede extrudability.The amount of Ni added is 5.0 to 15%). It has been found that an effect that has never been seen before is achieved in the range of . This brings about the novel effect of improving wear resistance by dividing and refining this intermetallic compound.

Furthermore, the present invention is characterized in that a solid lubricant selected from graphite, molybdenum disulfide, and boron nitride is added in a proportion of 0.2 to 5.0%. The above-mentioned solid lubricants have the role of imparting self-lubricating properties, and are stable and maintain lubricity even at high temperatures, so they are suitable for members such as cylinder liners and wear-resistant rings of pistons. Because the stiff solid lubricant is dispersed in the base material of the aluminum alloy molded body, it not only functions as an oil reservoir, but also works under severe sliding conditions that cause oil film breakage.

It acts as a solid lubricant and has the effect of preventing seizure.

However, if the strength of the base material is weak, the base material on the sliding surface will undergo plastic flow due to the heat generated by sliding and the drop in strength due to warping, resulting in an open [-1] shape on the sliding surface. This will cover the existing solid lubricant. Therefore, it exhibits excellent effects when combined with a base material that has high high temperature strength and hardness.

If the amount of solid lubricant added is less than 0.296, the sliding properties will be affected.
On the other hand, if it exceeds 540, cracks will occur in the extruded phase during hot extrusion, making it impossible to obtain a sound particle. The effects of the above three types of solid lubricants are the same.
However, the type should be selected depending on the operating temperature of the cylinder/liner. 1. Of the three types of solid lubricants mentioned above, molybdenum disulfide has the lowest thermal stability, and boron nitride is the most stable up to high temperatures. .

According to the present invention, the alloy powder compact can be made from 05 to 50% as required.
% CLI and 0.2 to 3.0% Mg can be added. Cu or ~1 g is known as a component that imparts age hardenability to aluminum alloys and strengthens their grains. Also in the present invention, it is effective to strengthen the quality by adding (2) and 100% within the above-mentioned range within the solid solubility limit at the solution treatment temperature.

Furthermore, in the alloy powder compact of the present invention, F”e,
It is also possible to improve the high temperature strength by adding Mn, Ti, Cr, V, Zr, Mo, Co, etc. during the process of obtaining the alloy powder.

1l-i, where the size of Si crystal grains is 15 μm or less,
This is because it has better ductility than conventional molded products and has improved machinability, making machining easier and preventing chattering and cracking during machining. In addition, the fine crystals of Sr improve wear resistance and reduce the coefficient of friction, making it suitable for cylinder liners and the like.

High-temperature strength and wear resistance are significantly improved by finely and uniformly dispersing the size of intermetallic compounds containing Ni such as AQ and 3Ni to substantially less than 5 μn1, and even large ones to less than 20 μnt. Become something.

The aluminum alloy powder compact according to the present invention has significantly improved high-temperature strength compared to conventional products, and also has excellent wear resistance and seizure resistance1.Furthermore, the product of the present invention has a small coefficient of friction. It also has excellent self-lubricating properties, making it ideal for parts such as internal combustion engine cylinder liners, which are used at high temperatures and require wear resistance, seizure resistance, and self-lubricating properties. It is.

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

The second aspect of the present invention relates to a method for manufacturing the aluminum alloy powder compact of the first aspect, and the gist thereof is to disperse and rapidly solidify a high-Si aluminum alloy molten metal containing Ni, and to solidify the resulting alloy powder. Add lubricant and mix (~
Afterwards, it is hot extruded.

Si and Ni are used to disperse and rapidly solidify the molten alloy.

This is to dissolve alloying elements such as Cu, M, and g into a supersaturated solid solution, and to refine the primary S+ and intermetallic compound phases. As a method for dispersing and rapidly solidifying, known metal powder manufacturing methods such as an atomization method and a centrifugal pulverization method can be used. An alloy powder with a satisfactory structure can be obtained by reducing the particle size of the powder to 0.5 scale or less by Kowara's method and rapidly solidifying it.

Next, a solid lubricant selected from graphite, molybdenum disulfide, and boron nitride is added to the alloy powder at a weight ratio of 0.2 to 5.
Add 0% and mix. The solid lubricant has no solubility in the aluminum alloy and has poor wettability with the aluminum alloy, so 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 at the powder stage and then use the subsequent hot extrusion process to uniformly disperse it. Solid lubricant is 50 μn
It is best to add it in the form of a fine powder of 1 or less. The mixture is stirred in an inert atmosphere to prevent oxidation of the aluminum alloy powder.

Next, the mixed powder is processed into a molded body by hot extrusion. Hot extrusion not only finishes the aluminum alloy particles into a strong bond, but also presses and firmly bonds the aluminum alloy particles and solid lubricant particles, and further improves the primary crystal S1 crystallized in the alloy powder. Eutectic is an essential requirement for refining the grains of intermetallic compounds and improving the mechanical properties of materials.

It is better to prepare the green compact before hot extrusion and work in two parts. For the production of green compacts, alloy powder is heated to a temperature of 200 to 350°C.
Do this in a temperature range of about If the temperature exceeds 350°C, oxidation becomes significant, so it is preferable to carry out the process in a non-oxidizing atmosphere such as nitrogen gas or argon.

The compacting pressure is preferably about 0.5 to 3 ton/cni, and the green compact density is desirably a true density ratio of 70 or higher in terms of handling of the green compact.

Hot extrusion is carried out at a temperature of 350°C or higher, preferably 400°C to 40°C.
Perform in a temperature range of 70°C. The purpose of kneading is to facilitate processing of the green compact, and at the same time promote bonding between particles, break up the rod-like structures of crystals 8i and intermetallic compounds, and make them finer, thereby improving the strength and frictional properties of the green compact. In hot extrusion, the green compact is preheated in a non-oxidizing atmosphere by stirring in the air, and then inserted into a container at the same temperature. An extrusion ratio of 10 or more is preferable.

If the extrusion ratio is less than 10, voids will remain in the extrusion phase, and the diffusion bonding between sweet powders and the separation effect of rod-shaped intermetallic compounds will be insufficient, making it impossible to obtain splinters with high strength and toughness. It's for a reason.

According to the method of the present invention, Si primary crystals, eutectics, intermetallic compounds,
It becomes possible to disperse all solid lubricants extremely finely and uniformly, and it becomes possible to easily obtain a lubricant that has excellent heat resistance, wear resistance, and lubricating properties, especially compared to old materials. In addition, it is possible to further improve the yield characteristics by subjecting the molded alloy powder obtained according to the present invention to a stabilizing heat treatment.Next, the present invention will be explained with reference to examples.

EXAMPLES Molten high-Si aluminum alloys having various alloy compositions shown in Table 1 were gas atomized to obtain raw material alloy powders of -48 me s b.

Next, except for N112, solid water was used as shown in Table 1.
The agent powder was added and mixed uniformly in a V-type cone mixer under nitrogen gas. Regarding the solid lubricant powders used, for graphite, artificial graphite powder of 15 μm or less (LONZA ■G S~15) was used, for boron nitride, 441 (+++ powder or less (Showa Denko UIIi)) was used, and for molybdenum disulfide, L
Powder (Nippon Molybdenum) with a particle size of 1/11 t or less was used.

Next, these mixed powders were preheated to a temperature of 250°C and filled into a mold that was heated and maintained at the same temperature.
Compression molded at J pressure to a diameter of 90mm and a length of 200mm.
A green compact was obtained.

Next, these compacts were inserted into a 5051 alloy cylinder with an outer diameter of 100 mm, an inner diameter of 90 mm, and a length of 205 tnm, and a lid with a diameter of 90 mm and a thickness of 5 mm was placed, and the joints were closed to prevent movement. A billet as shown in Figure 1 was made by caulking.

Next, each billet was heated to a temperature of 450°C, then inserted into a container with an inner diameter of 104mm kept at the same temperature with the lid 3 facing the die side, and indirectly extruded with a die of 30mm inner diameter. An extrusion ratio of 12) was carried out to obtain a round bar molded body.

The obtained molded body was cut, and a tensile test piece with a gage distance of 50 mm and a parallel part diameter of 6 mm, consisting only of the powder extrusion part, was subjected to one force. After holding the test temperature at 1001 (r), a tensile test was conducted.Also, the hardness of the chucking part at the end of the test piece after the tensile test at room temperature was measured.The chucking part was also observed for wire assembly. The size of the crystal grains of the 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 held at high temperatures. In addition, the addition of solid lubricants also improves strength and
The decrease in hardness is small.

Microscopic structure photographs of test pieces Nα3 to Nα5 in Table 2 are shown in FIGS. 4 to 9. Structure observation was performed on a plane perpendicular to the extrusion direction and a plane parallel to the extrusion direction. In the figure, the strong black color is the solid lubricant phase V,
The part with high concentration is the intermetallic compound phase containing N1. Figures 4 and 5 show the samples in which 4 qb of boron nitride was added corresponding to Na3 in the example, Figures 6 and 7 show the samples in which 3 Qb of graphite was added corresponding to Na4, and Figures 8 and 7 Figure 9 is N
[5 g of molybdenum disulfide corresponding to L5 was added.

Figures 4, 6, and 8 are planes perpendicular to the extrusion direction;
FIG. 5, FIG. 7, and FIG. 9 are observations taken on a plane parallel to the extrusion direction.

As is clear from the microstructure photographs, 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. It can be seen that the particles are stretched and dispersed in a direction parallel to the extrusion direction.

Next, the hot extrusion molded body was cut and hot forged into a shape having a diameter of 70 mm and a thickness of 10 mm.
0) After holding for 1r, machining was performed to obtain a disk-shaped test piece with a sliding surface made only of powder extruded material, and then a fire resistance test was conducted.

The test device for the 0 seizure resistance column test is schematically shown in FIGS. The lubricating oil is supplied from the back side through the oil filling hole 6.

A pressing force P is applied to the stator 4 by a hydraulic device M (not shown) toward the right at a predetermined pressure. A rotor 7 is disposed opposite to the disk 5, and is configured to rotate at a constant speed of one inch by a drive device (not shown). Sample holder 7Vc attached to the end face of rotor 7 relative to sample disk 5! Four prismatic specimens 8 measuring 5 mm x 5 mm x 10 mm are removably mounted at equal intervals on a concentric circle, and the square end faces are slidably attached to the sample disk 5. In such a device, a predetermined pressing force P is applied to the stator 4 so that the sample disk 5 and the mating material test piece 8 come into contact with each other at a predetermined blood pressure, and a predetermined pressure is applied to the sliding surface from the oiling hole 6. The rotor 7 is rotated while being refueled at the refueling speed.

The pressure acting on the stator 4 is increased stepwise at regular intervals, and the rotation of the rotor 7 generates a torque (due to frictional force) on the stator 4 due to the friction between the specimen 8 and the sample disk 5. The resulting torque) T is the spindle'
9 is applied to the load cell 10, the change is read by the dynamic strain δ111, and recorded in the recording word 112. Assuming that seizure occurred when torque T suddenly increased y1,
The contact surface pressure at that time is the seizure surface pressure, and the magnitude is 1ffi,! Determine whether the seizing property is good or bad.

The sample disk 5 used for the test was %300℃×10011r
The mating material test piece 8 was one made of spheroidal graphite cast iron with hard chrome plating on the sliding surface, and SiC with an average grain size of 0.8μ was used for the surface liner. This study was also carried out on flake graphite cast iron, which is used in The test conditions were °% speed of 3 m/see, lubricating oil was base oil = #20, temperature was 90°C, oil amount was 300 m6/mn, contact pressure was 20 Kf/crti for 20 minutes of break-in, and then 30 Kq/cnt for 3 minutes. , and thereafter increases by 10 KyAni every 3 minutes. The results are shown in Table-3.

As is clear from the results, the present invention's Na3~N[ Those with LO show excellent seizure resistance.

In addition, as seen in the comparison cavity (A390 mold 5lIJ cavity creation), compared to SiC dispersed iron plating, when combined with rerr chrome metal plating, the "I" pressure at which seizure occurs is significantly lower [1]. It is noteworthy that for Nα3 to Nα6 according to the present invention, the difference due to the difference in mating surface treatment is reduced.

Furthermore, compared to the comparative profit (A390 mold casting) and Nα2, N
[The surface pressure at which seizure occurs in the compacts of 13 to Nα6 is high, but the stiffness is due to the large amount of hard phase consisting of Si grains and intermetallic compounds dispersed in the AA base, which forms minute irregularities and acts to retain the oil film. In addition to acting as a solid lubricant, there is a mutual effect of the lubrication effect due to the dispersion of the solid lubricant, the action as an oil reservoir, and the dispersion strengthening due to the profiteering intermetallic compound.

In other words, in materials in which solid lubricant is not dispersed in a base material with low high temperature strength or hardness, the surface temperature increases due to heat generation due to sliding.
The stress caused by sliding causes plastic flow in the surface area, which covers the solid lubricant area and causes it to lose its solid lubricant effect and function as an oil reservoir, leading to early seizures, but the high temperature strength and hardness of the base material Plastic flow occurs on the surface (solid side? 1", it is thought that this is because the agent part can maintain a high surface pressure.

Table 3 As shown above, the alloy of the present invention has Ai! Vj around the alloy,
In addition, it is suitable for applications such as cylinder liners and piston wear rings that are used in relatively high temperature ranges, and has solid lubricant dispersion and high temperature strength.

Due to the mutual effect of high hardness and dispersion strengthening, it exhibits excellent cotton seizing resistance. In addition, the dispersion of solid lubricants has the effect of retaining oil on the sliding surfaces, which has the effect of preventing seizures even during cold starts, as well as cutting and grinding to break the chips into fine pieces. It also has the effect of making it easier.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an intermediate billet, in which 1 is a powder compact, 2 is a circular mold, and 3 is a lid. Figures 2 and 3 are diagrams showing the outline of the seizure resistance test equipment, where 5 is a sample disk, 8 is a mating phase test piece, 9 is a spindle, 10-piece load cell, 1 is a dynamic strain meter, and 12 is a It is a recorder. FIGS. 4 to 9 are micrographs of the cross-sections of the alloy powder compacts according to the present invention. Patent Applicant Riken Showa Denko Co., Ltd. Agent Patent Attorney Sei Kikuchi - a 4 Shima No.

Claims (1)

[Claims] m, S i 10.0 to 30.0% by weight, and N
solid lubricant selected from graphite, molybdenum disulfide, and boron nitride. Q% is an essential component, and if necessary, Cu0.5~5.
0% and Mg0.2 to 3.0%, the remainder is /V containing unavoidable impurities, and the size of S1 crystal grain is 1
51Ltn or less, and the size of the intermetallic compound is 2
A heat-wear resistant, high-potassium aluminum alloy powder compact with excellent lubricity and characterized by being finely dispersed to a size of 0 μm or less. (2) 5ito, o~30.0chi and Ni' in weight ratio
5.0-15.0, and if necessary, Cu
Q, containing 5 to 50 chi and Mg 0.2 to 3.0%,
A molten aluminum alloy, the remainder of which consists of unavoidable impurities, is dispersed and rapidly solidified to form a powder, and a solid lubricant selected from graphite, molybdenum disulfide, and boron nitride is added to and mixed with the resulting alloy powder. , characterized by hot extrusion molding. A method for producing a heat-resistant, wear-resistant, high-strength aluminum alloy powder compact having excellent lubricity and having Si crystal grains of 15 μm or less and intermetallic compounds dispersed in fine particles of 20 μ7 or less.