Aluminum bearing alloy

Details Aluminum bearing alloy Aluminum bearing alloy

2001-07-25

2003-10-28

Wyszomierski, George (Department: 1742)

Metal treatment

Stock

Aluminum base

C420S548000, C420S550000

Reexamination Certificate

active

06638375

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an aluminum bearing alloy generally used in bearings for high-power engines of automobiles and industrial machines.
2. Description of Related Art
An aluminum bearing alloy of the above-described type usually contains Sn giving conformability thereto. Pb also gives conformability to the aluminum bearing alloy. However, Pb cannot easily be distributed uniformly in the alloy and is one of injurious metals. Pb is not used for these reasons.
A plate-shaped cast aluminum bearing alloy containing Sn is cladded to a back steel plate to thereby be used for bearing. In manufacturing bearings using the aforesaid aluminum bearing alloy, annealing is indispensable after cladding to improve the toughness of the bearing alloy and the adhesive strength between the bearing alloy and the back steel plate. When annealing places the aluminum bearing alloy containing Sn under the condition of a high temperature, Al grains and Sn phases in the alloy structure are coarsened such that a high-temperature hardness and a fatigue strength of the aluminum bearing alloy are reduced.
In view of the aforesaid problem, it has been suggested that minute hard particles, for example, Si particles having a diameter less than 5 &mgr;m should be contained in the aluminum alloy so that Sn phases and Al grains are prevented from being coarsened and so that an Al matrix is strengthened, whereupon the aluminum bearing alloy provides a high bearing performance under the conditions of high load and high temperature.
Furthermore, each of JP-A-58-64332 and JP-A-58-67841 proposed containment of hard particles from a point of view different from strengthening the Al matrix for the same purpose as described above. The former, JP-A-58-64332, discloses that Si particles are used as hard particles and that the size and distribution of the Si particles are controlled so that the bearing characteristics, particularly conformability and anti-seizure property are rapidly improved under the conditions of high load and high temperature. Conventional Si particles mainly have a diameter of less than 5 &mgr;m. However, coarsened Si particles having a diameter ranging between 5 and 40 &mgr;m can be obtained as the result of improvements in the conditions of the thermal treatment etc. The coarsened Si particles scrape off protrusions on the surface of the shaft and an edge such as burrs around nodular graphite on the surface of the shaft at an initial stage of sliding, resulting in smooth sliding of the bearing (lapping). Consequently, seizure is prevented even under the condition of high load, whereupon the anti-seizure property can rapidly be improved.
On the other hand, the latter publication, JP-A-58-67841, discloses that particles consisting of or including at least one of Mn, Fe, Mo, Ni, Zr, Co, Ti, Sb, Cr, and Nb are crystallized as a separate metal or deposited or yielded as an intermetallic compound containing Mn or the like with Al. It is further disclosed that the crystallized separate metal or deposited intermetallic compound having a diameter ranging between 5 and 40 &mgr;m has the same effect as the Si particles in the above-described JP-A-58-46332. For example, when added to an Al alloy, Mn or the like is crystallized as a separate metal, or hard particles containing Mn or the like certainly exist although no crystalline can be specified. Thus, JP-A-58-46332 suggests Mn, Fe, etc. as an element accelerating generation of hard particles in an alloy excluding Si.
Regarding an alloy containing Si, only Si particles are conventionally hard particles crystallized in the aluminum bearing alloy. Regarding an alloy excluding Si, an added metal is crystallized in its original condition or crystallization of a binary intermetallic compound is suggested without crystallized substance being specified. Additionally, coarsened hard particles cause the lapping of the shaft, whereupon anti-seizure property is improved.
Hard particles contained in Al are generally distributed uniformly for the strengthening purpose. A large effect is achieved as the size of the particles becomes smaller. Accordingly, when the hard particles such as Si are coarsened as in the aforesaid publications, the strength of the Al matrix is reduced such that the fatigue resistance is reduced. In other words, regarding the size of crystallized particles, when the diameter of the crystallized particles is reduced in order that the fatigue resistance may be improved, the anti-seizure property cannot be improved. On the contrary, when the diameter of the crystallized particles is increased in order that the anti-seizure property may be improved, the fatigue resistance cannot be improved.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an aluminum bearing alloy in which the anti-seizure property thereof can be improved by hard particles without reduction in the fatigue resistance thereof.
The above-described object can be achieved by crystallizing a ternary-element intermetallic compound of Al—Si—Fe or a multi-element intermetallic compound with the base of Al—Si—Fe in an aluminum bearing alloy. More specifically, the present invention provides an aluminum bearing alloy comprising, by mass, 3 to 40% Sn, 0.5 to 7% Si, 0.05 to 2% Fe, balance of Al, and unavoidable impurities, wherein a ternary-element intermetallic compound of Al—Si—Fe and Si particles are contained as hard particles.
In a first preferred form, the aluminum bearing alloy further comprises at least one or more of Mn, V, Mo, Cr, Co, Ni and W in an amount or a total amount of 0.01 to 3%. In the alloy, said one or more of Mn, V, Mo, Cr, Co, Ni and W are added to the Al—Si—Fe such that a multi-element intermetallic compound is contained as hard particles.
In a second preferred form, the hard particles have a maximum diameter ranging between 1 and 20 &mgr;m on a bearing surface and a number of the hard particles for every 1 mm
2
ranges between 6 and 100.
In a third preferred form, the alloy contains by mass, 0.01 to 2% of at least one or more of B, Ti and Zr.
In a fourth preferred form, the alloy contains by mass, 0.1 to 5% of at least one or more of Cu, Mg and Zn.
Crystallization of the intermetallic compound of Al—Si—Fe will now be described. Firstly, in a well-konwn ternary-element state of Al—Si—Fe, a ternary-element eutectic compound is in the phase of Fe
2
Al
9
Si
2
and has a crystallizing temperature of 573° C. A eutectic reaction is shown as L→Sn+Si+Fe
2
Al
9
Si
2
.
FIG. 1
shows the structure of an alloy of Al—Sn—Si—Fe in the invention claimed in claim
1
. As obvious from
FIG. 1
, a ternary-element intermetallic compound of Al—Si—Fe is crystallized as a eutectic compound in the shape of a needle, bar or plate.
FIG. 2
shows the structure of an alloy in the invention claimed in claim
2
, for example, an alloy of Al—Sn—Si—Fe—Mn. A multi-element intermetallic compound of Al—Si—Fe—Mn is seen in FIG.
2
.
FIG. 3
shows the structure of an alloy of Al—Sn—Si—Fe—Cr. A multi-element intermetallic compound of Al—Si—Fe—Cr is seen in FIG.
3
.
A multi-element intermetallic compound such as Al—Si—Fe—Mn or Al—Si—Fe—Cr has various forms and is crystallized as a eutectic compound in which compounds including those having shapes of a needle, bar and plate each with three-dimensionally unspecified thickness are combined together in a complicated form. The ternary-element intermetallic compound of Al—Si—Fe and the multi-element intermetallic compound containing Al—Si—Fe as a base are exceedingly stable, and its basic shape is not changed even by the heat treatment after cladding with a back metal. These intermetallic compounds differ from an alloy containing only Si. More specifically, Si crystallizes as a eutectic in the form like a three-dimensionally connected coral. The crystallized Si is crushed to pieces by rolling after casting or rolling in the cladding with the back metal. Further, Si also changes its form by a subsequent heat treatment. This is a characteristic of Si and partic

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