GB2491268A

GB2491268A - A bearing with a tin-aluminium bearing layer

Info

Publication number: GB2491268A
Application number: GB1209314.2A
Authority: GB
Inventors: Shigeru Inami; Naohisa Kawakami; Satoru Kurimoto; Kazuaki Toda
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 2011-05-25
Filing date: 2012-05-23
Publication date: 2012-11-28
Anticipated expiration: 2032-05-23
Also published as: KR101302041B1; DE102012208528A1; KR20120132369A; DE102012208528B4; GB201209314D0; JP5981097B2; GB2491268B; JP2012246945A

Abstract

A bearing which comprises a base and a bearing layer on the base. The bearing alloy layer includes a surface layer comprising aluminium and 30-70 % by mass of tin which forms a microstructure of aluminium-phase grains 12 and elongate tin-phase grains 13 which have an average aspect ratio at least four, with the centres of adjacent tin-phase grains 13 being separated by 10 microns or less. The surface layer can be formed on an exposed surface of a bearing layer comprising and aluminium-tin alloy by applying a laser to melt the aluminium and tin and then cooling to a temperature in the range 350-500 0C where the aluminium is a solid-liquid state and the tin molten, and then cooling to a lower temperature where the tin and remaining aluminium solidify. Alternatively tin powder or Al-Sn powder can be supplied to the surface of a bearing layer comprising aluminium, with the powder and surface being irradiated with a laser to melt them. After laser treatment the bearing can be annealed.

Description

ALUMINUM ALLOY BEARING

Field of the invention

The present invention relates to an aluminum alloy bearing including an aluminum-based bearing alloy layer containing tin.

Background of the invention

Soft metals such as a white metal or an Al-Sn alloy have been used in bearings for internal combustion engines or the like.

In order to improve fatigue strength of a soft metal, JP-A-09-109l 8, for example, discloses that the soft metal is remelted by irradiating a laser to eliminate casting defects in the metal, and the remelted soft metal is quickly cooled to prevent growth of coarse structure so that a fine uniform microstructure is formed.

Brief Summary of the invention

For example, an aluminum alloy bearing including an aluminum-based bearing alloy layer containing tin is exposed to a harder situation, when a performance of the engine is further enhanced. The above method for improving the fatigue strength is insufficient for improving seizure resistance of the aluminum alloy bearing in the cases.

The present invention is made in view of the above circumstances. An object of the invention is to provide an aluminum alloy bearing including an aluminum-based bearing alloy layer containing tin and having improved seizure resistance.

According to an embodiment of the invention, an aluminum alloy bearing includes a base and an aluminum-based bearing alloy layer on the base. The aluminum-based bearing alloy layer includes a surface layer containing aluminum and 30 to 70 mass% of tin on a slide surface side, The surface layer includes aluminum-phase grains comprising aluminum, arid tin-phase grains comprising tin. An average distance between adjacent tin-phase grains is not greater than 10 sm, and an average aspect ratio of the tin-phase grains is not less than four.

The base is a structure on which the aluminum-based bearing alloy layer is formed. For example, when an intermediate layer is provided between a back metal layer and the aluminum-based bearing alloy layer, the base includes the back metal layer and the intermediate layer. Furthermore, when the aluminum-based bearing alloy layer is formed on the back metal layer, the back metal layer corresponds to the base.

When the intermediate layer is provided, the intermediate layer may be made of pure aluminum or an aluminum alloy. As the aluminum alloy, those of itS No. 1000 to No. 3000 may be used.

The aluminum-based bearing alloy layer is composed of stacked layers containing aluminum and tin, which includes a surface layer on a slide surface side, and an inverted layer on a base side. A base side of the inverted layer is in contact with the intermediate layer when the base is provided with the intermediate layer, or is in contact with the back metal layer when the base is not provided with the intermediate layer. The aluminum-based bearing alloy layer may include one or more layers containing aluminum as a main component between the surface layer and the inverted layer.

The surface layer contains aluminum and 30 to 70% by mass of tin, and comprises aluminum-phase grains comprising aluminum, and tin-phase grains comprising tin.

While An aluminum-phase grain is an aggregate of aluminum atoms, and a tin-phase grain is an aggregate of tin atoms, other atoms may be dissolved in these phase grains. Furthermore, the surface layer may include other phase grains composed of other atoms besides these phase grains.

The surface layer is adjusted so that the tin-phase grains have an average aspect ratio of at least four, more preferably at least six. The aspect ratio of the tin-phase grains is measured as follows. A minimum ellipse is drawn in contact with an outer perimeter of a tin-phase grain 1 as shown in Fig. 2 and a length L1 of a major axis and a length L2 of a minor axis of the ellipse are measured. The aspect ratio is a ratio of the length L1 to a length L2. Fig. 2 shows a matrix 2, and center of gravity of the tin-phase grains 1 as 0, which are explained later.

The average aspect ratio of the tin-phase grains is obtained as follows. First, from images of the tin-phase grains in an observed field of view, a total area and aspect ratios of the respective tin-phase grains in the field are obtained.

Next, the areas of the tin-phase grains are accumulated in a sequence from a tin-phase grain having a larger aspect ratio. Tin-phase grains until the accumulated area reaches 50% of the total area of the tin-phase grains are used for calculating the average aspect ratio.

The average aspect ratio of the tin-phase grains is obtained as an average of aspect ratios of the target tin-phase grains.

A relation of the aspect ratios of the tin-phase grains distributed in the surface layer will be described referring to Figs. 3A and 3B. Figs. 3A and 3B schematically show tin- phase grains 3 and 4 having different aspect ratios, and matrixes 5 and 6 composed of aluminum-phase grains. Pig. 3A shows an example of sectional shape of the tin-phase grain 3 with a large aspect ratio and the matrix 5, and an area of the tin-phase grain 3 in the slide surface 28 is shown as 51. Furthermore, Fig. 3B shows an example of sectional shape of the tin-phase grain 4 with a smaller aspect ratio than the tin-phase grain 3, and the matrix 6. An area of the tin-phase grain 4 in the slide surface 28 is shown as 52.

As shown in Figs. 3A and 3B, as an average aspect ratio of the tin-phase grains is larger, a greater number of the tin-phase grains 3 in elongated shapes are distributed.

Furthermore, if a sectional area S of the tin-phase grain 3 and a sectional area S12 of the tin-phase grain 4 are assumed to be same, the areas of the tin-phase grains 3 and 4 on the slide surface 28 satisfy S1<S2.

According to the above constitution, it is configured that a load from a counterpart member is received by the aluminum-phase grains, the tin-phase grains and the like which form the surface layer. In Figs. 3A and 3B, the load of the counterpart member is shown by F1.

Since a melting point of tin is lower than that of aluminum, the tin-phase grains become more softened than the aluminum-phase grains by a friction heat generated when the counterpart member slides on the slide surface of the surface layer, so that the tin-phase grains can more plastically flow. Accordingly, the aluminum-phase grains bear the load from the counterpart member and press the softened tin-phase grains so that tin-phase grains rise onto the slide surface. The pressure which pushes out the tin-phase grain 3 is conceptually shown by P1 in Fig. 3A, and the pressure which pushes out the tin-phase grain 4 is conceptually shown by P2 in Fig. 313.

As an average aspect ratio of the tin-phase grains distributed in the surface layer is larger, in particular when the average aspect ratio is not less than four, it is facilitated that the tin-phase grains are pushed out onto the slide surface from an inside of the surface layer by the pressure from the aluminum-phase grains since an area of the tin-phase grains on the slide surface are small. In the case of Figs. 3A and 3B, the pressures with which the aluminum-phase grains push out the tin-phase grains satisfy P1>P2.

Furthermore, the tin-phase grains pushed out on the slide surface are softened and can plastically flow. Therefore, they can be spread on the slide surface. ln other words, the aluminum-phase grains distributed on the slide surface are covered with the tin-phase grains pushed out on the slide surface. As a result, the counterpart member hardly hits directly the aluminum-phase grains which are harder than the tin-phase grains. Thereby, seizure resistance of the surface layer can be improved, and thus seizure resistance of the aluminum alloy bearing can be improved.

Furthermore, when the average aspect ratio of the tin-phase grains is not less than six in the surface layer, the aluminum-phase grains distributed on the slide surface are more easily covered with the tin-phase grains pushed out onto the slide surface. Therefore, the effect of improving the seizure resistance can be greater.

The surface layer is configured so that an average distance between adjacent tin-phase grains is not greater than 10 pm, more preferably not greater than 7 pm. The distance between adjacent tin-phase grains is defined as a distance between a center of gravity of a certain tin-phase grain and a center of gravity of other tin-phase grain which is adjacent to the certain tin-phase grain, or a so-called a distance between centers of gravity. Fig. 2 shows an example of the distance of adjacent tin-phase grains, as L3.

When the average distances between adjacent tin-phase grains distributed in the surface layer is not greater than 10 pm, the aluminum-phase grains which distributed among the tin-phase grains are more easily covered with the tin-phase grains which are pushed out onto the slide surface. Thereby, the seizure resistance of the surface layer can be more improved, and thus the seizure resistance of the aluminum alloy bearing can be more improved.

Furthermore, when the average between adjacent tin-phase grains is not greater than 7 pm, the aluminum-phase grains distributed on the slide surface are more easily covered with the tin-phase grains, and the effect of more improving seizure resistance can be obtained.

Accordingly, the surface layer can have the effect of improving seizure resistance by containing 30 to 70 mss% of tin, having the average distance between adjacent tin-phase grains being not greater than 10 pm and the average aspect ratio of the tin-phase grains being not less than four.

An average thickness of the surface layer is preferably not less than 50 pm.

When the average thickness of the surface layer is not less than 50 pm, the number of tin-phase grains extending in a thickness direction of the surface layer may be increased. Accordingly, the tin-phase grains in the surface layer can be more easily pushed out onto the slide surface by the pressure from the aluminum-phase grains, and the aluminum-phase grains on the slide surface are more easily covered with the tin-phase grains. Thereby, the seizure resistance of the surface layer can be more improved, and thus the seizure resistance of the aluminum alloy bearing can be more improved.

An inverted layer, opposite to the surface layer, contains aluminum and 30 to 50 mass% of tin. The inverted layer comprises aluminum-phase grains comprising aluminum and tin-phase grains comprising tin, and an average distance between adjacent tin-phase grains is preferably not less than 10 tm. The average distance in the inverted layer is also obtained based on a distance between centers of gravity similarly to the case of the surface layer.

A relation of the distances between adjacent tin-phase grains in the inverted layer is described referring to Figs. 4A and 4B. Figs. 4A and 4B schematically show distributions and shapes of tin-phase grains 7 and 8 which have the same area rate of the tin-phase grains in an observed field of view, but have different average distances between adjacent tin-phase grains in the inverted layer, as well as shapes of matrixes 9 and 10. Fig. 4A shows an example of a plurality of tin-phase grains 7 having a larger average distance and a matrix 9, where all the tin-phase grains 7 are assumed to be in the same shape and disposed equidistantly. In this case, an area of each of the tin-phase grains 7 in the field of view is shown as S3. Fig. 4B shows an example of a plurality of tin-phase grains 8 having a smaller average distance than the case of the tin-phase grains 7 and a matrix 10, where all tin-phase grains 8 are assumed to be in the same shape and disposed equidistantly. In this case, an area of each of the tin-phase grains 8 in the

field of view is shown as S4.

As shown in Figs. 4A and 4B, as the average distance between adjacent tin-phase grains in the inverted layer is larger, the number of tin-phase grains distributed in the field of view becomes smaller, and the area per tin-phase grain becomes larger. As a result, a total length of the boundaries where the aluminum-phase grains and the tin-phase grains are in contact with each other in the field of view becomes shorter.

As the total length is shorter, that is, as a total area of an interface at which the aluminum-phase grains and the tin-phase grains are in contact with each other is smaller, a total area of starting points of a bonding failure between the aluminum-phase grains and the tin-phase grains becomes smaller. As the total area of the starting points becomes smaller, a possibility of presence of the starting points between the inverted layer and the base becomes low, and the inverted layer is surely bonded to the base. Therefore, the distance between adjacent tin-phase grains is made larger in the inverted layer, for example the average distances is made 10 jim or more, whereby the aluminum-based bearing alloy layer having excellent seizure resistance can be surely bonded on the base.

Accordingly, when the inverted layer contains 30 to 50 mass% of tin and has the average distance between adjacent tin-phase grains being not less than 10 jim, the aluminum-phase grains having higher strength than the tin-phase grains are properly distributed in the inverted layer, and favorable cushion properties can be given while strengthening entire inverted layer. in addition, bonding strength between the base and the aluminum-based bearing alloy layer can be ensured. Therefore, the aluminum alloy bearing becomes to have extremely excellent seizure resistance.

Furthermore2 it is preferable, in view of improving the seizure resistance and fatigue strength of the aluminum alloy bearing, to make the average distance between adjacent tin-phase grains in the inverted layer larger than that in the surface layer.

When the average distance between adjacent tin-phase grains in the surface layer is indicated as A1, and that in the inverted layer is indicated as A2, a ratio of A2 to A1 is preferably not less than three. As the value ofA1 is smaller, the seizure resistance of the surface layer is more improved, whereas as the value of A2 is larger, the bonding strength between the base and the aluminum-based bearing alloy layer is more enhanced so that the aluminum-based bearing alloy layer can be firmly bonded to the base. When the ratio A2/A is three or more, the seizure resistance of the entire aluminum alloy bearing can be more improved.

Annealing may be applied to the aluminum alloy bearing of the embodiment of the invention. Even when the annealing treatment is performed, the effect of seizure resistance is kept as e uivalent to or better than that of the aluminum alloy bearing before the annealing.

The annealing may be conducted at 250 to 350°C for four to six hours.

Through annealing the aluminum alloy bearing, many tin-phase grains 11 in the surface layer are connected to each other, and an annular tin-phase grain 13 enclosing the aluminum-phase grain 12 is formed, as schematically shown in Figs. 5A and 5W Fig. 5A is a view showing a surface layer before annealing, and Fig. SB is a view showing the surface layer after annealing.

When an average circumferential lengths I of the annular tin-phase grains is indicated as L, and an average width d of the annular tin-phase grains is indicated as D, a ratio of L to D is preferably not less than 10.

The circumferential length 1 of the annular tin-phase grains 13 is determined as follows, as schematically shown in Figs. 5A and 5B. An aluminum-phase grain 12 in an observed field of view is regarded as a circle with the same area having a diameter "h", and a tin-phase grain enclosing the aluminum-phase grain 12 is regarded as an annular shape having a width "d". A circle is assumed which has a diameter of "h + d", and the circumferential length of the circle is determined as the circumferential length I of the annular tin-phase grains 13.

* 30 Next, an average diameter H of the aluminum-phase grains and the average width D of the annular tin-phase grains after annealing are obtained as follows.

When lines (dotted lines in Fig.6) Lp are drawn, for example in a vertical direction, in a composition image in the observed field of view as shown in Fig. 6, the average diameter H of the aluminum-phase grains is determined to be an average of lengths of portions where the lines Lp overlap the alumirn.im-phase grains 12.

The average width D of the annular tin-phase grains is obtained as follows.

First, the lines Lp are drawn in the composition image of the field of view as above, and an average length of portions where the lines Lp overlap the annular tin-phase grains is obtained.

The length per the one portion can be assumed to be the shortest distance between the outer circumferences of adjacent aluminum-phase grains, that is, a length of two widths of the two annular tin-phase grains adjacent to each other, Therefore, by dividing the average lengths by two, the average width 0 of one annular tin-phase grain is obtained.

When the ratio L/D is not less than 10, the annular tin-phase grain has an elongated shape as in the case in which the average aspect ratio of the tin-phase grains is not less than four. Thus, the area of the annular tin-phase grains on the slide surface is small.

Accordingly, the annular tin-phase grains are easily pushed out onto the slide surface from an inside of the surface layer by the pressure from the aluminum-phase grains. As a result, the aluminum-phase grains distributed in the slide surface are easily covered with the annular tin-phase grains which are pushed out onto the slide surface, and the counterpart member hardly directly contact the aluminum-phase grains which are harder than the annular tin-phase grains.

Thereby, according to the configuration of the embodiment of the invention, the seizure resistance of the surface layer can be more improved, and thus the seizure resistance of the aluminum alloy bearing can be more improved.

Furthermore, an average diameter of the aluminum-phase grains enclosed by the annular tin-phase grains which are distributed in the surface layer is preferably not greater than.

tim. In this case, the aluminum-phase grains enclosed by the annular tin-phase grains are easily covered with the annular tin-phase grains which are pushed out onto the slide surface.

Thereby, the seizure resistance of the surface layer can be more improved, and thus the seizure resistance of the aluminum alloy bearing can be more improved.

As a method for forming the surface layer on the slide surface side of the aluminum bearing alloy layer, following methods are raised for example. The layer containing aluminum as a main component before formation of the surface layer in the aluminum-based bearing alloy layer is referred to as an "aluminum-based layer".

In a first method for forming the surface layer, the surface layer on the slide surface side of the aluminum-based layer is formed by applying laser treatment and cooling treatment to the surface of the aluminum-based layer containing predetermined amounts of aluminum and tin. In this case, the base side of the aluminum-based layer becomes the inverted layer.

in the laser treatment, a laser beam is irradiated on the surface of the aluminum-based layer to heat the surface until both aluminum and tin are melted.

in the cooling treatment, two-stage treatment composed of first and second cooling treatments is performed. In the first cooling treatment, the surface of the aluminum-based layer which is melted by the laser treatment is cooled to a temperature 350°C to 50 0°C at which tin is in a liquid state and aluminum is in a solid and liquid state, and then kept at the temperature for a predetermined time to crystallize a necessary amount of aluminum phase.

The amount (in volume ratio) of the crystallized aluminum phase in a solid phase is adjusted by changing, for example, the temperature and the time. In the subsequent second cooling treatment, the surface of the aluminum-based layer is cooled after, the first cooling treatment and the tin phase is crystallized. At this time, the tin phase is crystallized between the aluminum phases crystallized in the first cooling. Aluminum phase which remains as a liquid phase after the first cooling treatment is also crystallized in the second cooling treatment.

As the above, an aspect ratio of the tin-phase grains can be made larger since a distance between the aluminum-phase grains can be controlled by performing the first and second cooling treatments after the laser treatment.

A second method for forming the surface layer on the slide surface side of the aluminum-based layer includes supplying a tin powder on the aluminum-based layer and applying the laser treatment and the cooling treatment as described above to the tin powder as well as the surface of the aluminum-based layer. More specifically, the tin powder is supplied on the surface of the aluminum-based layer, and laser is irradiated on the tin powder and the surface of the aluminum-based layer to heat the tin powder and the surface until they are melted.

At this time, the surface of the aluminum-based layer is also melted by the irradiation of the laser, and therefore, part of the aluminum of the melted aluminum-based layer forms the aluminum-phase grains in the surface layer.

In the cooling treatment, a necessary amount of the aluminum phases is crystallized in the surface layer through the first cooling treatment, and the tin phase is crystallized between the aluminum phase grains through the second cooling treatment. In place of the tin powder, Al-Sn alloy powder may be used.

Mass ratio of aluminum to tin in the surface layer is adjusted by changing an amount of e.g. tin powder and a mass ratio of aluminum to tin contained in the aluminum-based layer.

Conditions of the laser treatment and the cooling treatment may be changed depending on an amount of aluminum and tin contained in the surface layer of the aluminum-based bearing alloy layer or the like.

The method for forming the surface layer is not limited to the above methods.

Brief Description of the Drawings

Fig. 1 is a sectional view schematically showing an aluminum alloy bearing according to an embodiment of the invention; Fig. 2 is a conceptual view for explaining an aspect ratio; Figs. 3A and 38 are sectional views of surface layers schematically showing.

shapes of tin-phase grains with different aspect ratios; Figs. 4A and 48 are views schematically showing relations of a distance between adjacent tin-phase grains and sizes of the tin-phase grains in an inverted layer; Figs. 5A is a view schematically showing the surface layer before annealing; Figs. 58 is a view schematically showing the surface layer after the annealing; and Fig. 6 is a view showing the surface layer after the annealing treatment is performed.

Detailed Description of the invention

A sectional view of an embodiment of the aluminum alloy bearing is shown in Fig. 1. The aluminum alloy bearing 21 shown in Fig. I is for an internal combustion engine in an industrial machine for example. The aluminum alloy bearing 21 includes a base 22 and an aluminum-based bearing alloy layer 23 on the base 22. The base 22 includes a back metal layer 24 and an intermediate layer 25 on the back metal layer 24. The aluminum-based bearing alloy layer 23 is of a two-layer structure having an inverted layer 26 which is in contact with the intermediate layer 25, and a surface layer 27 which is provided on the inverted layer 26.

A surface layer of the aluminum alloy bearing 21 after annealing treatment is shown in Fig. 6.

Next, a test for confirming effects of the aluminum alloy bearing 21 of the embodiment will be explained.

Examples 1 to 10 having the structure of the aluminum alloy bearing 21 of the present embodiment were obtained as follows. First, plate materials of the aluminum-based bearing alloys having compositions shown in Table 1 were casted. Thereafter, thin plates materials for the intermediate layers made of aluminum were clad onto the casted aluminum-based bearing alloys to produce multiple-layer aluminum alloy plates. The multiple-layer -10 -aluminum alloy plates were clad to steel plates for the back metal layers, and annealed to produce plate materials for bearing, so-called bimetals.

Examples l and 3 to 6 were subjected to laser treatment. Surfaces of the aluminum-based layers of the bimetals were irradiated by a laser beam to melt the surfaces.

Then, first cooling treatment was performed in which the surfaces of the melted aluminum-based bearing alloys were cooled to 350 to 500°C and kept at the temperature for a predetermined time.

Second cooling treatment was performed after the first cooling treatment, in which the surfaces of the aluminum-based bearing alloys were cooled to crystallize a tin phase. Thereby, examples I and 3 to 6 having the surface layers 27 on a slide surface side of the aluminum-based bearing alloy layers 23 were obtained.

In examples 2 and 7, laser treatment was performed after tin powder is spread onto the surfaces of the aluminum-based layers of the bimetals, and the surfaces and the tin powder were melted. Then, the first cooling treatment and the second cooling treatment similar to the above description were performed, and the tin phase was crystallized after the aluminum phase was crystallized. Thereby, example products 2 and 7 having the surface layers 27 on the slide surfaces of the aluminum-based bearing alloy layers 23 were obtained.

Example products 8 to 10 were obtained by annealing example 6 at 250 to 350°C for four to six hours.

A surface of a bimetal of comparative example Ii is made of an aluminum-based bearing alloy, but was not subjected to laser treatment and the cooling treatment.

Comparative examples 12 and 13 were made by the production method, cooling process of which is different from those of the examples. The first and second cooling treatments, which were performed for examples 1 to 7, were not performed after the laser treatment, but continuous cooling of the surface layers from the molten state to a solidified state was performed to crystallize aluminum phase and tin phase.

Table 1 shows measured values of examples 1 to 10 and comparative examples 11 to 13, The "distance between adjacent tin-phase grains", the "aspect ratio of tin-phase grains", the "average diameter of aluminum-phase grains", the "ratio LiD" and the "thickness" of the "surface layer" in Table I were adjusted by properly changing the compositions of the aluminum-based bearing alloy of the bimetal, an amount of spread tin powder, an intensity of irradiation and the irradiating time of the laser, or the like. In examples I to 10 and comparative examples 12 and 13, they were also adjusted by properly changing a temperature and a time of crystallization of the tin phase or the like in the first cooling treatment.

The samples of examples 1 to 10 and comparative examples 11 to 13 were -11 -subjected to seizure test under conditions shown in Table 2. Test results are shown in Table I. Oil for use in the seizure test was applied to the slide surfaces before the test.

[Table 1]

_________ SURFACE LAYER

DISTANCE BETWEEN L AFTER ANNEALING

SAMPLE No. Al Sn ADJACENT Sn-PHASE A ECT RAT! AVERAGE DIAMETER THICKNESS (MASS%) (MASS%) GRAINS OF Sn-PHASE OF Al-PHASE GRAIN RATIO (pm) ________ ________ At (pm) ____________ (pm) _______ ___________ EXAMPLE! balance 60 80 5.0 -________ -30 EXAMPLE2 -balance 70 7.5 5.5 --200 EXAMPLE 3 balance 40 8.5 4.5 --200 EXAMPLE 4 balance 40 7.5 -5.5 --200 EXAMPLES balance 40 2M SM --300 --EXAMPLE 6 balance -30 6.0 7.5 --300 EXAMPL.E7 balance 70 5.0 10 --300 EXAMPLES balance 30 -______________ iS 8.0 300 EXAMPLE9 -balance 30 --15 15 300 --EXAMPLE 10 balance 30 -6.0 20 300

COMPARATIVE

EXAMPLE balance 40 16 3.0 --500 COMPARATIvE EXAMPLE 12 balance 40 15 8.0 --200 COMPARATIvE LEXAMPL?13 balance 40 4.0 3.0 --200 -Continued.

_______ ANTi-SURFACE LAYER

-_______ _______ MAXIMUM

DiSTANCE BETWEEN RATIO SPECIFIC LOAD Al Sn ADJACENT Sn-PHASE A21A1 WITHOUT SEIZURE (MASS%) (MASS%) GRAINS (MPa) Al (pm) balance -60 9.0 LI 22 - -balance 60 9.0 1.2 24 balance 40 15 1.8 25 -balance 40 26 3.5 26 -balance 40 15 7.5 29 balance 30 21 3.5 27 - -balance 40 ---20 4.0 --28 balance 30 21 IA 27 -balance 30 --21 L4 -28 balance -30 213.5 29 -balance 40 16 EM 14 balance 40 16 1.1 16 balance 40 16 4.0 17

[Table 2]

ITEMS ---CONDITIONS

LOAD PATTERN CONTINUOUS LOAD (9.2MPalmin) SPEED 0.2m/sec LUBRICATING OIL VGO5 - -SHAFT MATERiAL S5SC SHAFT HARDNESS HV600800 SHAFTROUGHNESS ---Rylpm EVALUATION Maximum specific load is determined when a METHOD temperature at a back surface exceeds 150°C or _______________________ -__a_frictional_force_exceed_50N The contents of "Al" and "Sn" in Table 1 are show with mass percent in the surface layer and the inverted layer. The concentrations were obtained with use of a fluorescent X-ray apparatus.

The "distance between adjacent tin-phase grains" of the "surface layer" in Table I represents the average distances between adjacent tin-phase grains of the surface layer, and the "aspect ratio of tin-phase grains" of the "surface layer" represents an average aspect ratio of the tin-phase grains of the surface layer. These values as well as the "average diameter of Al-phase grains" and "ratio LID" of "after annealing" in Table I were obtained as follows. The aluminum-based bearing alloy layer was grinded from the slide surface of the surface layer toward the base side, and measurement was performed at a depth of 20 sm from the most recessed portion of the slide surface in the surface layer. The values were obtained in an observed field of view of 150 p.m x 150 p.m in the plane parallel with the slide surface.

The average distance between adjacent tin-phase grains in the surface layer was obtained by analyzing, with use of analysis software ("Image-ProPlus (Version 4.5)" produced by Planetron, inc.), a composition image of the observed field of view obtained with an electron microscope. The average distance in the surface layer is indicated by "A11'.

In determining the average distance of the surface layer, tin-phase grains having an area equal to or greater than a detectable lower limit (0.07 jim2) for the analysis software were used.

The average aspect ratio of the tin-phase grains in the surface layer was obtained as follows with use of the analysis software. First, a total area of the tin-phase grains within the field of view was obtained by adding areas of all the tin-phase grains having an area of 0.07 jim2 or greater within the field of view, and an aspect ratio of each tin-phase grain was obtained.

Next, areas of the tin-phase grains were accumulated in a sequence from the grain having larger aspect ratio until the accumulated area reaches 50% of the total area of the tin-phase grains.

-15 -i nese tin-phase grains with larger aspect ratios were used for calculating the average value of the aspect ratios. Thus, the average aspect ratio is obtained by averaging the aspect ratios of the targeted tin-phase grains.

The "average diameter of Al-phase grains" of "after annealing" of Table 1 was obtained as follows. Lines Lp were drawn in a vertical direction, for example at a space of 10 im as shown in Fig. 6 in a composition image of the field of view, and lines Lq were also drawn in a lateral direction at a space of 10 tm in the same composition image. Lengths of each portion where the lines overlap the aluminum-phase grain 12 enclosed by the annular tin-phase grain 13 are averaged (quasi-diameter of the aluminum-phase grain). in the measurement, aluminum-phase grains which are not enclosed by the annular tin-phase grains 13 were not measured. When tin-phase grains ii were interspersed in the aluminum-phase grain 12 enclosed by the annular tin-phase grain 13, the interspersed tin-phase grains 11 were disregarded to obtain the average diameter even if the tin-phase grains II overlapped the lines.

The "D" of "ratio LID" of "after annealing" of Table 1 represents an average width D in a width direction of the annular tin-phase grains. The value D was obtained as follows. Each length of portions where the lines in Fig. 6 overlap the annular tin phase grains 13 is obtained and the lengths are averaged. The resulting value was divided by two. in the measurement of D, tin-phase grains 11 which were not annular were not measured.

The "L" of "ratio L/D" of "after annealing" of Table 1 represents an average circumferential length L of the annular tin-phase grains. The quasi-diameter of the aluminum-phase grain and the width of the annular tin-phase grain are added. A virtual circle having a diameter corresponding to the sum of the quasi-diameter and the width is assumed. The value L was obtained by averaging the circumferential lengths of the virtual circles.

The "ratio L/D" of Table I represents a ration L/D obtained by dividing L by D. The value of "thickness" of "surface layer" of Table I was obtained by measuring thicknesses at a plurality of portions in the surface layer from a sectional photograph of the surface layer, and then averaging the thicknesses.

The "distance between adjacent Sn-phase grains" of the "inverted layer" of Table I represents the average distance between adjacent tin-phase grains in the inverted layer. The value was obtained by grinding the aluminum-based bearing alloy layer from the slide surface in the surface layer toward the base side until a position which is of 20 gm height from a part of the base located closest to the aluminum-based bearing alloy layer. Measurement was performed in an observation field of view of 150 im x 150 1.Lm on a surface parallel to the slide surface at the height of 20 pm from the base.

in this case, the average distance is an average value of the distances between centers of gravity of the tin-phase grains adjacent to each another in the inverted layer. it was obtained with use of the analysis software as in the method for obtaining the average distances of the tin-phase grains in the surface layer The average distance between adjacent tin-phase grains in the inverted layer is referred to as "A2".

The "ratio A2/A1" in Table 1 is a ratio ofA2/A1 obtained by dividing A2 by A1.

Next, the results of the seizure test will be analyzed.

Comparing examples 1 to 7 with comparative examples I to 3, it is understood that examples 1 to 7 have more excellent seizure resistance than comparative examples 11 to 13, since examples I to 7 have the average distance between adjacent tin-phase grains in the surface layers being not greater than 10 pm, and the average aspect ratio of the tin-phase grains being not less than four.

Comparing example 1 with examples 2 to 7, it can be understood that examples 2 to 7 have much more excellent seizure resistance than example 1 since examples 2 to 7 have the average thickness of the surface layers being not less than 50 pm.

Comparing examples 1 and 2 with examples 3 to 7, it can be understood that examples 3 to 7 have much more excellent seizure resistance than examples 1 and 2 since examples 3 to 7 have the average distances between adjacent tin-phase grains in the inverted layers being not less than 10 pm.

Comparing examples I to 3 with examples 4 to 7, it can be understood that examples 1 to 3 have much more excellent seizure resistance than examples I to 3 since examples 4 to 7 have the ratio A2/A1 being not less than three.

Comparing examples I to 4 with examples 5 to 7, it can be understood that examples 5 to 7 have much more excellent seizure resistance than examples 1 to 4 since examples 5 to 7 have the average distance between adjacent tin-phase grains being not greater than 7 pm in the surface layers and the average aspect ratio of the tin-phase grains being not less than six.

Comparing example 6 with examples 8 to 10, it can be understood that examples 8 to TO can obtain seizure resistance equivalent to or more than that of example 6 before annealing.

Comparing example 8 with examples 9 and 10, it can be understood that examples 9 and 10 have far more excellent seizure resistance than example 8 since examples 9 and 10 have the ratio LID being not less than 10.

Comparing examples 8 and 9 with example 10, it can be understood that example has far more excellent seizure resistance than examples 8 and 9 since example 10 has the average diameter of the aluminum-phase grains enclosed by the annular tin-phase grains in the surface layers being not greater than 10 pm.

The present embodiment can be modified within the range of claims.

Although inevitable impurities are not described, each composition may contain inevitable impurities.

The aluminum-based bearing alloy layer, the surface layer, the inverted layer, and the intermediate layer may contain elements other than aluminum and tin, such as copper, silicon, manganese, zirconium, iron, or additives such as hard grains or a solid lubricant within a range with which the effects of the invention are not affected.

Claims

-18 -Claims: 1. An aluminum alloy bearing (21), comprising: a base (22), and an aluminum-based bearing alloy layer (23) on the base (22), wherein the aluminum-based bearing alloy layer (23) has a surface layer (27) containing aluminum and 30 to mass% of tin on a slide surface (28) side, wherein the surface layer (27) includes an aluminum-phase grains (2) comprising aluminum, and tin-phase grains (1) comprising tin, and wherein an average distance between adjacent tin-phase grains is not greater than 10 jim and an average aspect ratio of the tin-phase grains is not less than four.
2. The aluminum alloy bearing according to claim 1, wherein an average thickness of the surface layer (27) is not less than 50 jim.
3. The aluminum alloy bearing according to claim 1 or claim 2, wherein the base (22) includes a back metal layer (24), and an intermediate layer (25) provided between the back metal layer (24) and the aluminum-based bearing alloy layer (23), wherein the aluminum-based bearing alloy layer (23) Rirther includes an inverted layer (26) in contact with the intermediate layer (25), the inverted layer (26) containing aluminum and 30 mass% to 50 mass% of tin and including aluminum-phase grains comprising aluminum and tin-phase grains comprising tin, and an average distance between adjacent tin-phase grains being not smaller than 10 jim.
4. The aluminum alloy bearing according to claim 3, wherein a ratio of A2 to A1 is not less than three, where A1 indicates the average distance between adjacent tin-phase grains in the surface layer and A2 indicates the average distance between adjacent tin-phase grains in the inverted layer.
5. The aluminum alloy bearing according to any one of the preceding claims, wherein the average distance between adjacent tin-phase grains in the surface layer is not greater than 7 jim, and the average aspect ratios of the tin-phase grains in the surface layer is not less than six.
6. An aluminum alloy bearing produced by annealing the aluminum alloy bearing according to any one of the preceding claims.
7. The aluminum alloy bearing according to claim 6 wherein the annealing is conducted at 250 to 350°C for four to six hours.
8. The aluminum alloy bearing according to claim 6 or 7, wherein the surface layer includes annular tin-phase grains (13) enclosing the aluminum-phase grains (12), and a ratio L to D is not less than 10 where L indicates an average circumferential length of the annular tin-phase -19 -grains (13) and D indicates an average width of the annular tin-phase grains (13).
9. The aluminum alloy bearing according to any of claims 6 to 8, wherein the surface layer includes annular tin-phase grains (13) enclosing the aluminum-phase grains (12), and an average diameter of the aluminum-phase grains (12) enclosed by the annular tin-phase grains (13) is not greater than 10 Mm.
10. An aluminum alloy bearing as hereinbefore described with reference to any oneof examples I to 10.