WO2001034330A1

WO2001034330A1 - Aluminium alloy and method for the production thereof

Info

Publication number: WO2001034330A1
Application number: PCT/GB2000/004303
Authority: WO
Inventors: Carl Perrin; Paul Aidan Shenton; Ian Matthew Laing; Trevor Anthony Wright
Original assignee: Dana Corporation
Priority date: 1999-11-12
Filing date: 2000-11-10
Publication date: 2001-05-17
Also published as: GB9926675D0; AU1401301A

Abstract

An aluminium-based bearing alloy and a method for the production thereof are described, the method comprising the steps of providing a first aluminium-based material in particulate form; providing a second aluminium-based material in particulate form; compacting said first and second aluminium-based materials together to form a body under conditions to cause said body to be cohesive; and, working said body to produce a required form of said bearing material.

Description

ALUMINIUM ALLOY AND METHOD FOR THE PRODUCTION THEREOF

The present invention relates to aluminium alloys for use particularly, though not exclusively, as materials for plain sliding bearings and to a method for their production.

Bearing materials comprising a relatively soft matrix such as an aluminium alloy and having a dispersion of hard particles such as silicon for example therein are well known. Conversely, bearing materials comprising a relatively hard matrix, again such as an aluminium alloy and a soft phase such as tin for example dispersed therein are also well known. However, most of the known aluminium alloy materials are produced by the casting of a molten alloy wherein the constituents of the alloy are generally held in solution in a single phase liquid at the pouring temperature. The hard particles or the soft phase are generally formed during cooling and solidification by precipitation from the liquid. Thus, the only influence that can be made upon the size, morphology and distribution of the second phase is that which is possible by the steps of mechanical working and heat treatment subsequent to casting.

It is not possible by the metal casting route alone to produce, for example, a matrix comprising a first aluminium material dispersed with or within a second, distinct aluminium alloy material.

In many current aluminium-based plain bearing materials, a low melting point soft-phase such as tin or lead is employed to enhance the tribological properties of the alloy. However, many high performance modern engines operate at such a high temperature that the strength of the bearing material is compromised by the presence of such a soft phase. Again, such soft phases are introduced into the alloy mainly by being taken into solution during the melting of the aluminium matrix material and are precipitated out during the casting and solidification process .

Generally, it is not possible to introduce other materials such as so-called solid lubricant materials such as graphite or molybdenum disulphide, for example, and which are capable of operating at higher temperatures into the material by a casting route due to either segregation due to density differences and/or chemical reaction problems plus poor wettability.

Furthermore, certain aluminium alloys such as those containing zinc for example are useful as bearing alloys. However, they are very difficult to produce by conventional bearing alloy production techniques of casting a thick billet, followed by rolling down and subsequently roll-pressure bonding a thin strip to a steel backing for example. Such zinc containing alloys are very prone to cracking during cold rolling.

It is an objective of the present invention to be able to produce an aluminium alloy bearing material wherein the matrix and further phases are "tailored" to particular bearing requirements in an engine with respect to at least one of scuff resistance, seizure resistance, wear resistance, fatigue strength and temperature capability for example.

According to a first aspect of the present invention, there is provided a method of making an aluminium-based bearing material, the method comprising the steps of: providing a first aluminium-based material m particulate form; providing a second aluminium-based material m particulate form; compacting sa d first and second aluminium-based materials together to form a body under conditions to cause said body to be cohesive; and working said body to form said alummium-based bearing material.

The alummium-based material produced by the method of the present invention comprises a matrix having regions of the first alummium-based material and regions of the second alummium-based material, said regions of said first and said second alummium-based materials having distinct and different compositions from each other in the as-compacted material.

Depending upon the heating regime employed during production and the alloying constituents of the alummium-based materials, there may be diffusion zones at the junctions of said regions of said first and second materials. However, m some alloy systems diffusion may cause the final resulting material to be virtually homogeneous composition. For example, bearing material made by a preferred embodiment of the method of the present invention and described below, the method comprising compacting 50 weight % of commercially pure aluminium particles and 50 weιght% of particles of an AlZn5Sιl .5CulMg0.5 alloy resulted in a virtually homogeneous bearing alloy in the final material after compaction, extrusion, rolling down and annealing with virtually no discernible variation the zinc content of the final bearing alloy. Different alummium-based material combinations on the other hand may retain a relatively mhomogeneous structure after processing. For example, commercially pure aluminium compacted with an aluminium-silicon-copper alloy results m a structure wherein the silicon has an inhomogeneous distribution in the matrix, the distribution stemming from the positions of the aluminium-silicon alloy particles in the compacted material whereas, the copper may be relatively homogeneously distributed throughout the matrix.

The aluminium-based bearing material defined above may also include regions of additional aluminium-based materials, ie the material may be constituted by three or more separate and distinct aluminium-based materials.

The first aluminium-based material may be relatively pure aluminium such as so-called commercially pure aluminium for example and the second aluminium-based material may be another aluminium alloy.

The aluminium-based bearing material of the present invention is in effect a composite material wherein at least two separate and distinct aluminium-based materials may coexist in the matrix. There may be a distribution of discrete "islands" of the second material in a matrix of the first material or vice versa. Because of heating effects during production of the bearing material, there will be diffusion zones between the constituent aluminium-based materials. As described above, the diffusion zones may effectively result in a relatively homogeneous bearing alloy material being formed.

In one embodiment of the present invention the aluminium- based alloy, for example, may be commercially pure aluminium. The composition of the second aluminium material may be an aluminium-zinc alloy may be based, for example, upon the known 7XXX range of aluminium alloys containing from 0 to 10 wt% zinc; 0 to 4 wt% magnesium; 0 to 0.5 wt% manganese; 0 to 3 wt% copper; 0 to 0.5 wt% silicon; 0 to 0.3 wr% chromium; 0 to 0.2 wt% titanium; 0 to 1 wt% iron; balance aluminium apart from unavoidable impurities .

Other alloys which may be used as the second aluminium- based material may include aluminium-silicon-copper containing up to 20 wt% silicon and up to 8 wt% copper, e.g. Al-4Si-lCu or Al-llSi-lCu.

Further aluminium alloys which may be used for the second aluminium alloy may be based upon the known 6XXX range of alloys containing from 0 to 2 wt% silicon; 0 to 1 wt% copper; 0 to 1 wt% manganese; 0 to 1.5 wt% magnesium; 0 to 0.3 wt% zinc; 0 to 0.5wt% chromium; 0 to 0.2 wt% titanium; 0 to 1 wt% iron; balance aluminium apart from unavoidable impurities.

Advantages accruing from the use of the 6XXX and/or 7XXX ranges of alloys include strength, ductility, good machinability and the ability to age harden to further "tailor" properties to specific applications.

Although specific examples have been given above, the first aluminium-based material may not necessarily be a relatively pure aluminium material but may be another aluminium alloy.

In essence, any aluminium-based alloy which has shown itself to be suitable for use in plain bearing applications may be useful in the composite material of the present invention.

In effect, the first aluminium-based material may constitute a relatively soft phase within the composite material of the present invention whilst the second aluminium-based material may constitute a relatively hard phase within the composite material.

In a preferred embodiment of the present invention, the maximum hardness of the first aluminium-based material may be 40 Hv whereas the minimum hardness of the second aluminium-based material may be 45 Hv.

The relative proportions of the first aluminium-based material to the second aluminium-based material may range from 2 to 95 wt% of the first aluminium-based material with the balance being substantially made up of the second aluminium-based material except where further additions are made to the material. Preferably, the relative proportions may lie in the range from 10 wt% to 50 wt% of the first aluminium-based material.

In a preferred embodiment of the present invention, the material may further include one or more so-called solid lubricant materials. Suitable materials may include graphite, molybdenum disulphide and tungsten disulphide for example.

Where employed, additions of molybdenum and tungsten disulphide may be in the range from 0.1 to 10wt% with a preferred range from 1 to 3wt% .

Where employed, graphite additions may be in the range from 0.1 to 30wt% with a preferred range from 2 to 5wt%.

In a preferred embodiment of the method of the present invention said first and second aluminium-based materials are fed into an extrusion apparatus, the extrusion apparatus comprising fixed and moveable members defining an elongate passageway therebetween, an abutment extending into the passageway and die means associated with the abutment, the die means having at least one orifice leading from the passageway and means for feeding said first and second particulate materials into said passageway; compacting said particulate mixture in said apparatus; and, extruding said compacted mixture through said die orifice of said apparatus to form an elongate body of the bearing material.

The first and second aluminium-based materials may be mixed together prior to feeding into the extrusion apparatus .

The extrusion apparatus may be of the continuous rotary type described in GB-A-1 370 894 or GB-A-1 434 201 for example and known to those people skilled in the extrusion art as a "CONFORM" (trade name) machine.

An advantage of the preferred embodiment of the method of the present invention is that it provides a continuous process such that unlimited lengths of bearing alloy may be produced subject only to the ability to keep feeding material into the extrusion apparatus. Other compaction and extrusion processes are not continuous in nature. Furthermore, the bearing material so formed may be in any desired corss sectional shape such as round, tubular, rectangular, flat strip or any shape required.

The die means may also be provided with heating means to raise the temperature of the material being extruded to a desired level. The apparatus works on the principle of a movable die member which forms for example three sides of the elongate passageway and is in the form of a continuous groove in the periphery of a wheel driven about an axis, and a fixed stationary shoe member which forms a fourth side of the passageway. Since the driven wheel possesses more surface area of the passageway, the particulate material is drawn into the passageway by friction and dragged along the passageway whilst being heated (by friction) and simultaneously consolidated before reaching the abutment which is positioned along the passageway remote from the material feed entry point. On reaching the abutment the consolidated material is forced to change direction by plastically deforming and is extruded through the orifice of the die means.

The orifice of the die means can be any desired shape such as round or of rectangular cross section, for example, or the die may form a tube if desired so that round bush bearings may be formed directly from extruded tubular material. The die may alternatively be of a design which permits the "canning" of an extrusion of the desired composition by a third aluminium alloy or by substantially pure aluminium.

Because no actual melting of the material occurs and the consolidation steps are all in the solid phase, no segregation occurs due to density differences when solid lubricant materials are employed in the mixture and because the temperatures are relatively low, no chemical reactions occur such as the decomposition of molybdenum disulphide or a reaction between molten aluminium and graphite, for example. However, although the temperatures employed are below the melting points of the materials involved, the temperatures are sufficiently high due to the cumulative die heating and friction heating effects to cause simultaneous sintering, annealing and recrystallisation of the consolidated material during extrusion thereof. Thus, the extruded material may be directly cold pressure welded, such as by roll-pressure bonding for example, to a strong backing material such as steel for example immediately following extrusion for the subsequent production of bimetal bearings (i.e. bearings comprising a lining of a bearing alloy bonded to a strong backing material such as steel for example) . Alternatively, the extruded material may be subjected to a rolling step following extrusion and prior to bonding to a backing material. Consequently, in addition to the alloy of the present invention being able to be more closely suited in compositional and property terms to particular engine applications, much of the tedious, wasteful and expensive processing steps associated with prior art casting, working and heat treatment processes may be avoided.

Due to the temperatures at which the preferred embodiment of the method of the present invention operates, it is preferred that low melting point phases such as tin, lead and the like are not present since they are either molten or have such low strength that the extrusion process causes them to be exuded from the structure. Thus, the aluminium-based bearing materials according to the present invention may be essentially free of tin and lead and alloys thereof and also of any other low melting point phases.

The form of the particulate material of the first and second aluminium-based materials may be extremely diverse and may range from powders having relatively small particle sizes from less than lOμm to lOrnm diameter pellets for example. The method according to the present invention will process swarf and shaving type particles as well as more regular shaped particles. Such wide ranges of particulate size which may be accommodated by the preferred embodiment of the method of the present invention gives great control over the material which is formed. For example, control over the size of the particulate input material gives control, to a large extent, over the sizes of the regions of the first and second aluminium-based materials. Particulate size control also gives control over the distribution of additional phases such as solid lubricants within the matrix.

An advantage of the method of the present invention compared with, for example, the prior art technique of powder-rolling is that material with much lower porosity levels is produced giving higher strength and greater ductility. Whilst it is possible to cast aluminium-zinc alloys for example by the known twin-roll casting technique, it is not possible by this technique to produce a matrix structure comprising at least two distinct aluminium-based materials coexisting together.

Materials made according to the method of the present invention have exhibited improved scuff resistance and seizure resistance compared with prior art cast and wrought materials which utilise low melting point soft phases such as tin and lead.

According to a second aspect of the present invention, there is provided an aluminium-based bearing material as defined in the claims appended hereto.

In order that the present invention may be more fully understood, examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a schematic cross section of a first embodiment of a matrix of an alloy according to the present invention;

Figure 2 shows a similar view to Figure 1 but of a second embodiment;

Figure 3 shows a schematic section of extrusion apparatus;

Figure 4 shows a graph of tensile data at 25°C of a bearing material according to the present invention and comparative cast alloys;

Figure 5 shows similar data to that of Figure 4 but tested at 190°C;

Figure β shows a histogram of data relating to scuff resistance and seizure resistance for an alloy according to the present invention and comparative alloys;

Figure 7 shows a section through a "Sapphire" bearing test apparatus;

Figure 8 shows a graph of bearing specific load vs test duration for a seizure test carried out on the apparatus of Figure 7; and

Figure 9 which shows a graph of a typical test bearing temperature trace as a function of applied load during a test procedure to determine the conformability and compatibility of a bearing material. Figure 1 shows a schematic representation of the matrix structure of a first embodiment of an alloy according to the present invention. The alloy indicated generally at 10 has a matrix 12 comprising a relatively hard phase of an aluminium-zinc alloy and inclusions 14 of a relatively soft phase comprising commercially pure aluminium for example. The alloy comprises 70 wt% of the aluminium-zinc alloy 12 and 30 wt% of commercially pure aluminium 14.

Figure 2, on the other hand shows an alloy 20 having a matrix 22 comprising a soft commercially pure aluminium phase and inclusions of a relatively hard, aluminium-zinc alloy 24. The proportions of inclusions of alloy 24 are from 10 to 50 wt%.

Figure 3 shows a schematic representation of the main parts of a so-called "CONFORM" (trade name) extrusion machine 30 and which is essentially similar to the apparatus described in GB-A-1 370 894 for example. The apparatus comprises a rotatable wheel 32 which is rotated about a central axis 34. The wheel 32 has an endless groove 36 in the periphery thereof, the groove 36 forming the major surface area of a closed passageway 40 which is formed between the groove 36 and the curved surface 42 of a shoe member 44 which fits closely against the edge 46 of the wheel 32. The shoe member 44 also includes an abutment block 48 which has a projection 50 which projects into and effectively blocks the passageway 40. The shoe member 44 and abutment block 48 also house and retain a die 52 with heater means (not shown) which has a chamber 54 and die orifice 56 of predetermined shape, e.g. a flat rectangular slot for example, corresponding to the shape of the extruded product desired to be produced. Particulate material 60 to be compacted and extruded is fed into a hopper portion 62 in the shoe member 44. The wheel 32 is rotated by drive means (not shown) causing particulate material to be dragged into the passageway 40 due to the greater surface area of the groove 34 compared with the surface 42 which forms a stationary closure wall of the passageway 40. As the particulate material 60 is dragged into the passageway 40, it is compacted and heated by friction effects until it meets the projection 50 which blocks the passageway 40 against any further progress by the compacted material 60 which is forced to change direction by plastically deforming into the chamber 54 of the die 52 before being extruded through the die orifice 56 to form an extruded strip 66 for example.

Example 1

An alloy consisting of a 70/30 mixture of powders in the ratio 70 wt% of an alloy of composition

AlZn5Sil .5CulMg0.5 and 30 wt% of commercially pure aluminium where powder particle sizes lie in the range from 40 to 450μm. This represents the schematic example described in Fig 1 with the matrix (12) consisting of the AlZn alloy and the inclusions (14) consisting of the commercially pure aluminium.

The powders were vacuum dried at 400 C for 1 hr . Die temperature of the machine described in Fig. 3 was set to 250°C but working temperatures increased to 400-450°C due to mechanical work of the process. The strip was annealed post extrusion typically at temperatures between 350-390°C for 8 hrs, this being performed prior to rolling from a thickness of 3mm down to 0.9mm. Subsequent roll-pressure bonding of the extruded and rolled alloy to a steel backing strip decreased thickness further from 0.9mm to 0.51mm.

Example 2

An alloy consisting of a 50/50 mixture of powders, one of commercially pure aluminium and the other of an alloy of composition AlZn5Sil .5CulMg0.5 where powder particle size lies in the range from 40-450μm. This represents the upper end of the range of compositions described for the schematic example of Fig. 2 with the matrix (22) consisting of aluminium and the inclusions (24) consisting of the AlZn alloy.

Processing conditions were as described with reference to Example 1.

Table of Compositions of Alloys

The above table shows the compositions of alloys shown in Figs 4-6. The composition of the 50/50 alloy according to the present invention represents the overall composition of the powder mix. AS15 and AS124A are known commercial bearing alloys for comparison.

Figures 4 to 6 give results of tests performed on the materials of Example 2 and on the comparative alloys AS15 and AS124A. Results of Mechanical Tests

Results in Figs 4 and 5 show the tensile properties

(Ultimate Tensile Strength and % Elongation to fracture or Strain) for the selected materials at room temperature and 190°C. they show that the 50/50 mix is considerably stronger than AS124A at both temperatures and retains a higher percentage of its room temp strength at 190°C.

However, there is no increase in ductility with temperature (as shown by the strain' figures) for the 50/50 mix whereas the AS124A alloy undergoes a significant increase in ductility with temperature.

Fig 6 shows the scuff/seizure properties for the two comparative alloys and the alloy according to the invention. As can be seen, both the scuff and seizure figures are a considerable improvement over the conventional alloys. The improvements obtained are due both to the composition of the alloy which can be made by the method the present invention but not by a conventional casting route and the unique microstructures which are obtained by using the inventive method.

A Sapphire test machine, which is known in the bearing art and is shown in Figure 7, can be used to measure scuff and seizure performance of bearings. In the test, the bearing temperature is measured as the dynamic load on the bearing is steadily increased until seizure occurs when running against a nodular cast iron shaft. Figure 8 shows a graph of increasing load with time until scuffing or seizure occurs. The bearings were tested to determine the fatigue strength thereof, the load at which scuffing occurred and the ultimate load at which seizure occurred. The Sapphire apparatus 80 comprises a test shaft 82 having a central eccentric portion 84 supported by the test bearings 86, 88, the outer ends of the shaft are supported in slave bearings 90, 92. The shaft is rotated by a drive motor 96 and load is applied to the test bearings 86, 88 by a connecting rod 100 to which is applied a force by a piston 102 which is actuated by hydraulic means 106, 108. Strain gauges 110 measure the applied load. The fatigue load capacity is that load which causes fatigue at 200 hours running. In operation, the apparatus 80 applies a load to the test bearings 86, 88 by means of the eccentric portion 84 and the hydraulically loaded piston 102 thus imposing a sinusoidal dynamic load on the bearings. Via a computer control system (not shown) , a programmed progressive load increase becomes the basis of the measurement of surface properties. In this mode of increasing load, the minimum oil film thickness steadily reduces and the test measures, via the temperature increase (see Figure 9), the load at which the material is wiped or scuffed as it comes into contact with the geometrical inaccuracies or asperities in the shaft and/or the load at which the material welds itself to the shaft. Scuff resistance is a measure of material conformability whilst seizure resistance is a measure of compatibility.

A typical bearing temperature trace is shown in Figure 9 as a function of the applied load. This temperature trace shows the occurrence of temperature excursions that then self-correct as the load increases, ie as the oil film thickness decreases. These temperature excursions are indicative that the bearing system accommodates geometrically, ie possesses conformability . The load at which the first temperature excursion occurs has been used as a measure of conformability of the materials.

Under the most extreme operating conditions, when the material can no longer conform or condition the shaft journal sufficiently o avoid thermal runaway, seizure takes place. The components of the bearing alloy are chosen so as to avoid thermal welding of the bearing to the shaft, so building security into the alloy system whenever asperity contact between the bearing and the shaft journal occurs thus producing frictional heating. The load at which this takes place has been used as a measure of the compatibility of the material.

Claims

1. A method of making an aluminium-based bearing material, the method comprising the steps of: providing a first aluminium-based material in particulate form; providing a second aluminium-based material in particulate form; compacting said first and second aluminium-based materials together to form a body under conditions to cause said body to be cohesive; and, working said body to produce a required form of said bearing material.

2. A method according to claim 1 further including the step of mixing said first and second materials together prior to compaction.

3. A method according to either claim 1 or claim 2 wherein said compaction and working steps are effected by the steps of: feeding said first and second aluminium-based materials into an extrusion apparatus .

4. A method according to claim 3 further comprising the steps of providing the extrusion apparatus with fixed and moveable members defining an elongate passageway therebetween, an abutment extending into the passageway and die means associated with the abutment, the die means having at least one orifice leading from the passageway, feeding said first and second aluminium-based materials into said passageway, compacting said particulate materials in said apparatus; and, extruding said compacted materials through said die orifice of said apparatus to form an elongate body of the bearing material.

5. A method according to claim 4 further comprising the step of providing means for feeding said first and second particulate materials into said passageway.

6. A method according to any one of preceding claims 3 to 5 wherein the extrusion apparatus is of the continuous rotary type.

7. A method according to claim 6 wherein the apparatus is of the "CONFORM" type, as hereinbefore defined.

8. A method according to any one of preceding claims 4 to 7 wherein the die means are provided with heating means to raise the temperature of the material being extruded to a desired level.

9. A method according to any one of preceding claims 4 to 8 wherein the shape of the orifice of the die means is selected from: round or rectangular cross section or the die may form a tubular extrudate.

10. A method according to any one of preceding claims 4 to 9 wherein the die may permit the "canning" of the extrudate by a third aluminium alloy or by substantially pure aluminium.

11. A method according to any one of preceding claims 3 to 10 wherein the extrudate is further reduced in cross section.

12. A method according to claim 11 wherein the reduction in cross section is by rolling.

13. A method according to any one preceding claim wherein the bearing material is bonded to a strong backing material.

14. A method according to any one preceding claim wherein a hardness of said first alummium-based material is a maximum of 40Hv and a hardness of said second alummium-based material is a minimum of 45Hv.

15. A method according to any one preceding claim wherein the relative proportions of the first alummium-based material to the second alummium- based material range from 2 to 95 wt% of the first alummium-based material with the balance being substantially made up of the second alummium-based material except where further additions are made to the material.

16. A method according to claim 15 wherein the relative proportions lie in the range from 10 wt% to 50 wt% of the first alummium-based material.

17. An alummium-based bearing material, the material comprising a matrix having regions of a first alummium-based material and regions of a second alum ium-based material, a substantial part of said regions of said first and said second alummium- based materials having different compositions from each other, there being diffusion zones at the junctions of said regions of said first and second materials.

18. An alummium-based bearing alloy according to claim 17 wherein the first alummium-based material may be relatively pure aluminium.

19. An alummium-based bearing alloy according to either claim 17 or claim 18 wherein the first alummium- based material is commercially pure aluminium.

20. An alummium-based bearing alloy according to any one preceding claim from 17 to 19 wherein the second alummium-based material is an aluminium alloy.

21. An alummium-based bearing alloy according to claim 20 wherein the second alummium-based material is selected from the group comprising: alum ium-zmc alloys; 7XXX series range of aluminium alloys containing from 0 to 10 wt% zmc, 0 to 4 wt% magnesium, 0 to 0.5 wt% manganese, 0 to 3 wt% copper, 0 to 0.5 wt% silicon, 0 to 0.3 wt% chromium, 0 to 0.2 wt% titanium, 0 to 1 wt% iron, balance aluminium apart from unavoidable impurities; alummium-silicon-copper alloys containing up to 20 wt% silicon and up to 8 wt% copper; and 6XXX series range of alloys containing from 0 to 2 wt% silicon, 0 to 1 wt% copper, 0 to 1 wt% manganese, 0 to 1.5 wt% magnesium, 0 to 0.3 wt% zinc, 0 to 0.5wt% chromium, 0 to 0.2 wt% titanium, 0 to 1 wt% iron, balance aluminium apart from unavoidable impurities.

22. An aluminium-based bearing alloy according to any one preceding claim from 17 to 21 wherein the maximum hardness of the first aluminium-based material is 40 Hv.

23. An aluminium-based bearing alloy according to any one preceding claim from 17 to 22 wherein the minimum hardness of the second aluminium-based material is 45 Hv.

24. An aluminium-based bearing alloy according to any one preceding claim from 17 to 23 wherein the relative proportions of the first aluminium-based material to the second aluminium-based material may range from 2 to 95 wt% of the first aluminium-based material with the balance being substantially made up of the second aluminium-based material except where further additions are made to the material.

25. An aluminium-based bearing alloy according to claim 24 wherein the relative proportions lie in the range from 10 wt% to 50 wt% of the first aluminium-based material.

26. An aluminium-based bearing alloy according to any one preceding claim from 17 to 25 wherein the bearing material further includes one or more solid lubricant materials.

27. An aluminium-based bearing alloy according to claim

26 wherein the solid lubricant materials are selected from the group comprising: graphite; molybdenum disulphide; and, tungsten disulphide.

28. An aluminium-based bearing alloy according to either claim 26 or claim 27 wherein the content of molybdenum or tungsten disulphide lies in the range from 0.1 to 10wt%.

29. An aluminium-based bearing alloy according to claim 28 wherein the solid lubricant content lies in the range from 1 to 3wt%.

30. An aluminium-based bearing alloy according to claim 27 wherein the content of graphite lies in the range from 0.1 to 30wt%.

31. An aluminium-based bearing alloy according to claim 30 wherein the graphite content lies in the range from 2 to 5wt% .

32. An aluminium-based bearing alloy according to any one preceding claim from 17 to 31 further including at least a third aluminium based material in the matrix thereof.

33. A bearing when made by the method of any one of preceding claims 1 to 16.

34. A bearing having a lining of the aluminium-based bearing material as claimed in any one of preceding claims 17 to 32.