Patent Application
20110277889
The present invention relates to an Al (aluminum) based bearing alloy containing Si (silicon) and a production method thereof.
A slide bearing including an Al-based bearing alloy on a substrate has relatively satisfactory initial conformability, and high fatigue resistance under high specific load, and thus it is used in an internal combustion engine of an automobile.
An Al-based bearing alloy having higher fatigue resistance is disclosed in, for example, JP-A-3-6345. The Al-based bearing alloy in JP-A-3-6345 contains 1 to 15 mass % of Si and 0.005 to 0.5 mass % of Sr. JP-A-3-6345 discloses that the Al-based bearing alloy contains Sr in order to have a fine size of a Si particle, and that the Al-based bearing alloy can bear high loads and is prevented from being brittle due to the fine Si particle, thereby improving fatigue resistance of the Al-based bearing alloy.
In recent years, an Al-based bearing alloy having high seizure resistance besides fatigue resistance is desired. Specifically, in the field of a recent internal combustion engine, a connecting rod or the like has reduced thickness to reduce a weight of the internal combustion engine in order to improve fuel consumption. The reduction in thickness of the connecting rod reduces rigidity of the connecting rod, and the connecting rod is easily deformed. Thus, a slide bearing provided in the connecting rod is also easily deformed. Thereby, a sliding counterpart member easily comes into local contact with a slide side surface of the Al-based bearing alloy. If the counterpart member continues to slide while being in direct contact with the Al-based bearing alloy, seizure may occur.
The present invention is achieved in view of the above-described circumstances, and has an object to provide an Al-based bearing alloy having high seizure resistance and a production method thereof.
The inventors have noted a size of a Si particle in an Al-based bearing alloy containing 1 to 15 mass % of Si and diligently repeated experiments. As a result, the inventors have found that even if a content of Si particles is the same in the Al-based bearing alloy containing 1 to 15% by mass of Si, satisfactory seizure resistance of the Al-based bearing alloy can be obtained when a total length of circumferences of Si particles observed in a predetermined range of an observation field on a slide side surface is within a predetermined range.
The inventors have achieved the invention described below based on the above finding.
The present invention provides an Al-based bearing alloy containing 1 to 15 mass % of Si, wherein a total length of circumference of Si particles observed in an observation field of 37820 μm2 on a slide side surface is 4000 to 6000 μm.
As an Al-based bearing alloy of the present invention, an embodiment of an Al-based bearing alloy layer on a substrate of a slide bearing will be explained below. The Al-based bearing alloy may be used as a slide member (slide bearing) rather than formed on a back metal layer.
First, an embodiment of the Al-based bearing alloy is shown in
The substrate 2 is a member on which the Al-based bearing alloy 3 is formed, and it is, for example, a back metal layer made of steel, iron, or the like.
As shown in
The Al-based bearing alloy 3 contains inevitable impurities.
In the embodiment, a total circumferential lengths of Si (Si particles 5) observed in an observation field of 37820 μm2 on a surface 3a of the Al-based bearing alloy 3 is 4000 to 6000 μm. The surface 3a of the Al-based bearing alloy 3 is observed by an optical microscope. The observation field can be changed by adjusting an observation range of the optical microscope, and the observation field is determined to be 37820 μm2 in the embodiment.
A circumferential length of each Si particle 5 observed by the optical microscope is measured using image analysis software, for example, Image-Pro Plus (Version 4.5) (trade name) (produced by Planetron, Inc.).
In the embodiment, the total circumferential lengths of the Si particles 5 observed in the observation field of 37820 μm2 on the surface 3a of the Al-based bearing alloy 3 is a predetermined length or more, that is 4000 μm or more in the embodiment, to increase an interface area between the matrix 4 and the Si particles 5. This increases interface energy at interfaces between the matrix 4 and the Si particles 5, and the increase in the interface energy increases surface energy of the surface 3a of the Al-based bearing alloy 3, thereby increasing wettability of a lubricant on the surface 3a. Such increased wettability of the surface 3a prevents oil film break. Thus, according to the embodiment, wettability of the surface 3a can be increased to prevent direct contact between the Al-based bearing alloy 3 and a counterpart member. This provides satisfactory seizure resistance of the Al-based bearing alloy 3.
In the embodiment, the total circumferential lengths of the Si particles 5 observed in the observation field of 37820 μm2 on the surface 3a of the Al-based bearing alloy 3 is 6000 μm or less. When the total circumferential lengths of the Si particles 5 is 6000 μm or less, the matrix 4 does not include so many Si particles 5 that make the matrix 4 too hard. This provides satisfactory conformability of the Al-based bearing alloy 3 in the embodiment.
For the Al-based bearing alloy of the present invention, preferably, the observation field of 37820 μm2 on the slide side surface is divided into regions, each region including one Si particle by a region partitioning method. Preferably, an average aspect ratio of the regions is 1 to 2.
The region partitioning method is shown in
With the same content of Si (Si particle 5), the size of the Si particle 5 and the number of the Si particles 5 have a correlation. When the Si particle 5 is large, the number of the Si particles 5 is small, thereby increasing an area of each region obtained by the region partitioning method. On the other hand, when the Si particle 5 is small, the number of the Si particles is large, thereby reducing the area of each region.
The “aspect ratio of the region” refers to a ratio of length of a major axis to length of a minor axis of the region, that is, a value obtained by dividing the length of the major axis by the length of the minor axis. The major axis herein refers to a maximum length in a region obtained by the region partitioning method. The minor axis refers to a length in a direction passing through a center of the major axis and perpendicular to the major axis in the region.
The “average aspect ratio” in the embodiment is an average value of aspect ratios of the respective regions in the observation field obtained by the region partitioning method. The observation field in the embodiment is 37820 μm2.
In the embodiment, the average aspect ratio of the regions is 1 to 2. When the average aspect ratio of the regions is closer to 1, each region has a more circular or equilateral polygonal shape. The Si particles 5 are more uniformly dispersed in the matrix 4, and surface energy becomes more uniform on the entire surface 3a of the Al-based bearing alloy 3. Thus, uniform wettability can be obtained on the entire surface 3a of the Al-based bearing alloy 3 to prevent local oil film break. This also provides satisfactory seizure resistance of the Al-based bearing alloy 3.
The slide bearing 1 is produced by a casting step, a rolling step, a roll bonding step, a heat treatment (annealing) step, and a machining step.
A production method of an Al-based bearing alloy of the present invention preferably includes the steps of: melting Al or an Al alloy and Si to produce a molten alloy; cooling the molten alloy at a rate of 80° C./sec to 130° C./sec to form an Al-based cast plate; and rolling the Al-based cast plate at a reduction of 50% to 95% to produce the Al-based bearing alloy.
In the casting step, the molten metal is obtained by melting Si with Al or an Al alloy and is cast at a cooling rate of 80° C./sec to 130° C./sec to produce the Al-based cast plate. The Cooling rate of the molten metal causes molten. Si to be crystallized in a matrix 4. The Si (Si particles 5) is finer than conventional Si (Si particles).
In a rolling step, the Al-based cast plate is rolled by a roller or the like, to produce the Al-based bearing alloy 3. Rolling is performed until a reduction in the rolling step reaches 50% to 95%. While rolling pass may be conducted at any number of times, preferably it is once to five times.
The term “reduction” indicates a degree of rolling as compared with a state before rolled (before the rolling step). The reduction Z (%) is expressed by a formula:
Z={(X−Y)/X}×100(%)
Where X (mm) is a plate thickness before rolled (before the rolling step), and Y (mm) is a plate thickness after rolled (after rolling step).
According to the embodiment, the Al-based cast plate obtained by the casting step is rolled at a reduction of 50% or more, and thus the Al-based bearing alloy 3 can be obtained in which the total circumferential lengths of the Si particles 5 observed in an observation field of 37820 μm2 on the surface 3a is 4000 μm or more.
According to the embodiment, the Al-based cast plate obtained by the casting step is rolled at a reduction of 95% or less, and thus the Al-based bearing alloy 3 can be obtained in which the total circumferential lengths of the Si particles 5 observed in an observation field of 37820 μm2 on the surface 3a is 6000 μm or less.
In the roll bonding step, the Al-based bearing alloy 3 obtained in the rolling step is roll-bonded to a substrate (back metal layer) 2, to produce a bearing forming plate material.
Then, the bearing forming plate material obtained by the roll bonding step is annealed by a heat treatment (annealing) step, and machined by a machining step to produce a semicircular or circular slide bearing 1.
Although the slide bearing 1 having a two-layer structure including the substrate 2 and the Al-based bearing alloy 3 is described, it may have a three-layer structure including an adhesive layer, for example an intermediate layer of pure Al or the like between the Al-based bearing alloy 3 and the substrate 2. Also, an overlay layer of Bi, Sn, a Bi alloy, a Sn alloy, or the like may be formed on the Al-based bearing alloy 3. When the overlay layer is applied on the Al-based bearing alloy 3, seizure resistance of the Al-based bearing alloy 3 is exhibited after the overlay layer wears.
The Al-based bearing alloy 3 may be subjected to solution treatment to increase strength of the Al-based bearing alloy 3.
In order to confirm advantages of the embodiment, samples (Examples 1 to 5 and Comparative examples 11 to 13) of slide bearings including Al-based bearing alloys containing compositions shown in Table 1 were produced, and seizure tests of the samples were conducted.
Production methods of Examples 1 to 5 are as described below. First, Al and Si are melted at ratios shown in Table 1, and then cast with a casting device 11 shown in
The casting device 11 includes a melting furnace 12 that stores materials for casting. Materials to be melted having the compositions shown in Table 1 are charged in the melting furnace 12. The compositions in Table 1 contain inevitable impurities.
The casting device includes a bath 13 for storing molten metal poured from the melting furnace 12.
The bath 13 is provided with a molten metal supply nozzle 14 that discharges the molten metal stored in the bath 13. On a tip side of the molten metal supply nozzle 14, a pair of rollers 15, 15 with a minute gap therebetween are placed. The pair of rollers 15, 15 are placed so that axes thereof extend horizontally in a direction perpendicular to a flow of the molten metal. Thus, the molten metal in the melting furnace 12 passes through the bath 13 and the molten metal supply nozzle 14 and is supplied between the pair of rollers 15, 15.
The pair of rollers 15, 15 are cooled by cooling means such as a cooling pipe 16. A plurality of cooling pipes 16 extends axially in the pair of rollers 15, 15. A coolant such as water is supplied into the cooling pipes 16 to cool the pair of rollers 15, 15. An amount of the water supplied into the cooling pipes 16 and a flow rate thereof are adjusted depending on a degree of opening and closing of an unshown valve controlled by an unshown control device. In production of Examples 1 to 5, the degree of opening and closing of the valve is adjusted so as to cool the molten metal supplied between the pair of rollers 15, 15 from the molten metal supply nozzle 14 at a cooling rate of 80° C./sec to 130° C./sec (cooling rate shown in Table 1). Cooling at 80° C./sec to 130° C./sec is performed until the molten metal reaches 550° C.
The molten metal is cooled and solidified by the pair of rollers 15, 15 to produce an Al-based cast plate 17. The obtained Al-based cast plate 17 is cut to a predetermined length by a cutter 18 and wound by a toiler 19. Then, the Al-based cast plate 17 is rolled by a pair of rollers 20, 20 shown in
Then, the Al-based cast plate 17 having reached a predetermined reduction is roll-bonded to a steel plate forming the substrate (back metal layer). Thus, a bearing forming plate material is produced. The bearing forming plate material is heated for several hours to be annealed and then machined to produce a slide bearing. Thus, the slide bearing was produced for Examples 1 to 5.
On the other hand, a production method of Comparative examples 11 to 13 is different from the production method of Examples 1 to 5 in the following points.
Comparative example 11 was obtained by the same production method as Examples 1 to 5 except that the reduction in the rolling step was 40%.
Comparative example 12 was obtained by the same production method as Examples 1 to 5 except that the cooling rate in the casting step was 70° C./sec.
Comparative example 13 was obtained by the same production method as Examples 1 to 5 except that the cooling rate in the casting step is 70° C./sec, and the reduction in the rolling step is 40%.
For thus obtained Examples samples 1 to 5 and Comparative examples 11 to 13, a surface of each sample was observed, and a seizure test was conducted under a test condition shown in Table 2. The results thereof are shown in Table 1.
For “total circumferential lengths of Si particles” and “Average aspect ratios of regions” of Examples 1 to 5 and Comparative examples 11 to 13 in Table 1 were measured by photographing a microstructure with an optical microscope and analyzing an image in an observation field of 37820 μm2 using image analysis software, for example, Image-Pro Plus (Version 4.5) (trade name) (produced by Planetron, Inc.).
Next, the results of the seizure test are analyzed.
From comparison between Examples 1 to 5 and Comparative examples 11 and 13, it is understood that Examples 1 to 5 have high seizure resistance because the total circumferential lengths of the Si particles is 4000 μm or more.
From comparison between Examples 1 to 5 and Comparative example 12, it is understood that Examples 1 to 5 have high seizure resistance because the total circumferential lengths of the Si particles is 6000 μm or less.
From comparison between Examples 1 to 4 and Example 5, it is understood that Examples 1 to 4 have extremely high seizure resistance because an average aspect ratios of regions obtained by the region partitioning method is 2 or less.
The present invention may be changed and carried out without departing from the spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-109223 | May 2010 | JP | national |
